1 /*
2 * Copyright (c) 2008, 2023, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package java.lang.invoke;
27
28 import jdk.internal.access.SharedSecrets;
29 import jdk.internal.value.PrimitiveClass;
30 import jdk.internal.foreign.Utils;
31 import jdk.internal.javac.PreviewFeature;
32 import jdk.internal.misc.Unsafe;
33 import jdk.internal.misc.VM;
34 import jdk.internal.org.objectweb.asm.ClassReader;
35 import jdk.internal.org.objectweb.asm.Opcodes;
36 import jdk.internal.org.objectweb.asm.Type;
37 import jdk.internal.reflect.CallerSensitive;
38 import jdk.internal.reflect.CallerSensitiveAdapter;
39 import jdk.internal.reflect.Reflection;
40 import jdk.internal.util.ClassFileDumper;
41 import jdk.internal.vm.annotation.ForceInline;
42 import sun.invoke.util.ValueConversions;
43 import sun.invoke.util.VerifyAccess;
44 import sun.invoke.util.Wrapper;
45 import sun.reflect.misc.ReflectUtil;
46 import sun.security.util.SecurityConstants;
47
48 import java.lang.constant.ConstantDescs;
49 import java.lang.foreign.GroupLayout;
50 import java.lang.foreign.MemoryLayout;
51 import java.lang.foreign.MemorySegment;
52 import java.lang.foreign.ValueLayout;
53 import java.lang.invoke.LambdaForm.BasicType;
54 import java.lang.reflect.Constructor;
55 import java.lang.reflect.Field;
56 import java.lang.reflect.Member;
57 import java.lang.reflect.Method;
58 import java.lang.reflect.Modifier;
59 import java.nio.ByteOrder;
60 import java.security.ProtectionDomain;
61 import java.util.ArrayList;
62 import java.util.Arrays;
63 import java.util.BitSet;
64 import java.util.Comparator;
65 import java.util.Iterator;
66 import java.util.List;
67 import java.util.Objects;
68 import java.util.Set;
69 import java.util.concurrent.ConcurrentHashMap;
70 import java.util.stream.Stream;
71
72 import static java.lang.invoke.LambdaForm.BasicType.V_TYPE;
73 import static java.lang.invoke.MethodHandleImpl.Intrinsic;
74 import static java.lang.invoke.MethodHandleNatives.Constants.*;
75 import static java.lang.invoke.MethodHandleStatics.UNSAFE;
76 import static java.lang.invoke.MethodHandleStatics.newIllegalArgumentException;
77 import static java.lang.invoke.MethodHandleStatics.newInternalError;
78 import static java.lang.invoke.MethodType.methodType;
79
80 /**
81 * This class consists exclusively of static methods that operate on or return
82 * method handles. They fall into several categories:
83 * <ul>
84 * <li>Lookup methods which help create method handles for methods and fields.
85 * <li>Combinator methods, which combine or transform pre-existing method handles into new ones.
86 * <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns.
87 * </ul>
88 * A lookup, combinator, or factory method will fail and throw an
89 * {@code IllegalArgumentException} if the created method handle's type
90 * would have <a href="MethodHandle.html#maxarity">too many parameters</a>.
91 *
92 * @author John Rose, JSR 292 EG
93 * @since 1.7
94 */
95 public class MethodHandles {
96
97 private MethodHandles() { } // do not instantiate
98
99 static final MemberName.Factory IMPL_NAMES = MemberName.getFactory();
100
101 // See IMPL_LOOKUP below.
102
103 //// Method handle creation from ordinary methods.
104
105 /**
106 * Returns a {@link Lookup lookup object} with
107 * full capabilities to emulate all supported bytecode behaviors of the caller.
108 * These capabilities include {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access} to the caller.
109 * Factory methods on the lookup object can create
110 * <a href="MethodHandleInfo.html#directmh">direct method handles</a>
111 * for any member that the caller has access to via bytecodes,
112 * including protected and private fields and methods.
113 * This lookup object is created by the original lookup class
114 * and has the {@link Lookup#ORIGINAL ORIGINAL} bit set.
115 * This lookup object is a <em>capability</em> which may be delegated to trusted agents.
116 * Do not store it in place where untrusted code can access it.
117 * <p>
118 * This method is caller sensitive, which means that it may return different
119 * values to different callers.
120 * In cases where {@code MethodHandles.lookup} is called from a context where
121 * there is no caller frame on the stack (e.g. when called directly
122 * from a JNI attached thread), {@code IllegalCallerException} is thrown.
123 * To obtain a {@link Lookup lookup object} in such a context, use an auxiliary class that will
124 * implicitly be identified as the caller, or use {@link MethodHandles#publicLookup()}
125 * to obtain a low-privileged lookup instead.
126 * @return a lookup object for the caller of this method, with
127 * {@linkplain Lookup#ORIGINAL original} and
128 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access}.
129 * @throws IllegalCallerException if there is no caller frame on the stack.
130 */
131 @CallerSensitive
132 @ForceInline // to ensure Reflection.getCallerClass optimization
133 public static Lookup lookup() {
134 final Class<?> c = Reflection.getCallerClass();
135 if (c == null) {
136 throw new IllegalCallerException("no caller frame");
137 }
138 return new Lookup(c);
139 }
140
141 /**
142 * This lookup method is the alternate implementation of
143 * the lookup method with a leading caller class argument which is
144 * non-caller-sensitive. This method is only invoked by reflection
145 * and method handle.
146 */
147 @CallerSensitiveAdapter
148 private static Lookup lookup(Class<?> caller) {
149 if (caller.getClassLoader() == null) {
150 throw newInternalError("calling lookup() reflectively is not supported: "+caller);
151 }
152 return new Lookup(caller);
153 }
154
155 /**
156 * Returns a {@link Lookup lookup object} which is trusted minimally.
157 * The lookup has the {@code UNCONDITIONAL} mode.
158 * It can only be used to create method handles to public members of
159 * public classes in packages that are exported unconditionally.
160 * <p>
161 * As a matter of pure convention, the {@linkplain Lookup#lookupClass() lookup class}
162 * of this lookup object will be {@link java.lang.Object}.
163 *
164 * @apiNote The use of Object is conventional, and because the lookup modes are
165 * limited, there is no special access provided to the internals of Object, its package
166 * or its module. This public lookup object or other lookup object with
167 * {@code UNCONDITIONAL} mode assumes readability. Consequently, the lookup class
168 * is not used to determine the lookup context.
169 *
170 * <p style="font-size:smaller;">
171 * <em>Discussion:</em>
172 * The lookup class can be changed to any other class {@code C} using an expression of the form
173 * {@link Lookup#in publicLookup().in(C.class)}.
174 * A public lookup object is always subject to
175 * <a href="MethodHandles.Lookup.html#secmgr">security manager checks</a>.
176 * Also, it cannot access
177 * <a href="MethodHandles.Lookup.html#callsens">caller sensitive methods</a>.
178 * @return a lookup object which is trusted minimally
179 *
180 * @revised 9
181 */
182 public static Lookup publicLookup() {
183 return Lookup.PUBLIC_LOOKUP;
184 }
185
186 /**
187 * Returns a {@link Lookup lookup} object on a target class to emulate all supported
188 * bytecode behaviors, including <a href="MethodHandles.Lookup.html#privacc">private access</a>.
189 * The returned lookup object can provide access to classes in modules and packages,
190 * and members of those classes, outside the normal rules of Java access control,
191 * instead conforming to the more permissive rules for modular <em>deep reflection</em>.
192 * <p>
193 * A caller, specified as a {@code Lookup} object, in module {@code M1} is
194 * allowed to do deep reflection on module {@code M2} and package of the target class
195 * if and only if all of the following conditions are {@code true}:
196 * <ul>
197 * <li>If there is a security manager, its {@code checkPermission} method is
198 * called to check {@code ReflectPermission("suppressAccessChecks")} and
199 * that must return normally.
200 * <li>The caller lookup object must have {@linkplain Lookup#hasFullPrivilegeAccess()
201 * full privilege access}. Specifically:
202 * <ul>
203 * <li>The caller lookup object must have the {@link Lookup#MODULE MODULE} lookup mode.
204 * (This is because otherwise there would be no way to ensure the original lookup
205 * creator was a member of any particular module, and so any subsequent checks
206 * for readability and qualified exports would become ineffective.)
207 * <li>The caller lookup object must have {@link Lookup#PRIVATE PRIVATE} access.
208 * (This is because an application intending to share intra-module access
209 * using {@link Lookup#MODULE MODULE} alone will inadvertently also share
210 * deep reflection to its own module.)
211 * </ul>
212 * <li>The target class must be a proper class, not a primitive or array class.
213 * (Thus, {@code M2} is well-defined.)
214 * <li>If the caller module {@code M1} differs from
215 * the target module {@code M2} then both of the following must be true:
216 * <ul>
217 * <li>{@code M1} {@link Module#canRead reads} {@code M2}.</li>
218 * <li>{@code M2} {@link Module#isOpen(String,Module) opens} the package
219 * containing the target class to at least {@code M1}.</li>
220 * </ul>
221 * </ul>
222 * <p>
223 * If any of the above checks is violated, this method fails with an
224 * exception.
225 * <p>
226 * Otherwise, if {@code M1} and {@code M2} are the same module, this method
227 * returns a {@code Lookup} on {@code targetClass} with
228 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access}
229 * with {@code null} previous lookup class.
230 * <p>
231 * Otherwise, {@code M1} and {@code M2} are two different modules. This method
232 * returns a {@code Lookup} on {@code targetClass} that records
233 * the lookup class of the caller as the new previous lookup class with
234 * {@code PRIVATE} access but no {@code MODULE} access.
235 * <p>
236 * The resulting {@code Lookup} object has no {@code ORIGINAL} access.
237 *
238 * @apiNote The {@code Lookup} object returned by this method is allowed to
239 * {@linkplain Lookup#defineClass(byte[]) define classes} in the runtime package
240 * of {@code targetClass}. Extreme caution should be taken when opening a package
241 * to another module as such defined classes have the same full privilege
242 * access as other members in {@code targetClass}'s module.
243 *
244 * @param targetClass the target class
245 * @param caller the caller lookup object
246 * @return a lookup object for the target class, with private access
247 * @throws IllegalArgumentException if {@code targetClass} is a primitive type or void or array class
248 * @throws NullPointerException if {@code targetClass} or {@code caller} is {@code null}
249 * @throws SecurityException if denied by the security manager
250 * @throws IllegalAccessException if any of the other access checks specified above fails
251 * @since 9
252 * @see Lookup#dropLookupMode
253 * @see <a href="MethodHandles.Lookup.html#cross-module-lookup">Cross-module lookups</a>
254 */
255 public static Lookup privateLookupIn(Class<?> targetClass, Lookup caller) throws IllegalAccessException {
256 if (caller.allowedModes == Lookup.TRUSTED) {
257 return new Lookup(targetClass);
258 }
259
260 @SuppressWarnings("removal")
261 SecurityManager sm = System.getSecurityManager();
262 if (sm != null) sm.checkPermission(SecurityConstants.ACCESS_PERMISSION);
263 if (targetClass.isPrimitive())
264 throw new IllegalArgumentException(targetClass + " is a primitive class");
265 if (targetClass.isArray())
266 throw new IllegalArgumentException(targetClass + " is an array class");
267 // Ensure that we can reason accurately about private and module access.
268 int requireAccess = Lookup.PRIVATE|Lookup.MODULE;
269 if ((caller.lookupModes() & requireAccess) != requireAccess)
270 throw new IllegalAccessException("caller does not have PRIVATE and MODULE lookup mode");
271
272 // previous lookup class is never set if it has MODULE access
273 assert caller.previousLookupClass() == null;
274
275 Class<?> callerClass = caller.lookupClass();
276 Module callerModule = callerClass.getModule(); // M1
277 Module targetModule = targetClass.getModule(); // M2
278 Class<?> newPreviousClass = null;
279 int newModes = Lookup.FULL_POWER_MODES & ~Lookup.ORIGINAL;
280
281 if (targetModule != callerModule) {
282 if (!callerModule.canRead(targetModule))
283 throw new IllegalAccessException(callerModule + " does not read " + targetModule);
284 if (targetModule.isNamed()) {
285 String pn = targetClass.getPackageName();
286 assert !pn.isEmpty() : "unnamed package cannot be in named module";
287 if (!targetModule.isOpen(pn, callerModule))
288 throw new IllegalAccessException(targetModule + " does not open " + pn + " to " + callerModule);
289 }
290
291 // M2 != M1, set previous lookup class to M1 and drop MODULE access
292 newPreviousClass = callerClass;
293 newModes &= ~Lookup.MODULE;
294 }
295 return Lookup.newLookup(targetClass, newPreviousClass, newModes);
296 }
297
298 /**
299 * Returns the <em>class data</em> associated with the lookup class
300 * of the given {@code caller} lookup object, or {@code null}.
301 *
302 * <p> A hidden class with class data can be created by calling
303 * {@link Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...)
304 * Lookup::defineHiddenClassWithClassData}.
305 * This method will cause the static class initializer of the lookup
306 * class of the given {@code caller} lookup object be executed if
307 * it has not been initialized.
308 *
309 * <p> A hidden class created by {@link Lookup#defineHiddenClass(byte[], boolean, Lookup.ClassOption...)
310 * Lookup::defineHiddenClass} and non-hidden classes have no class data.
311 * {@code null} is returned if this method is called on the lookup object
312 * on these classes.
313 *
314 * <p> The {@linkplain Lookup#lookupModes() lookup modes} for this lookup
315 * must have {@linkplain Lookup#ORIGINAL original access}
316 * in order to retrieve the class data.
317 *
318 * @apiNote
319 * This method can be called as a bootstrap method for a dynamically computed
320 * constant. A framework can create a hidden class with class data, for
321 * example that can be {@code Class} or {@code MethodHandle} object.
322 * The class data is accessible only to the lookup object
323 * created by the original caller but inaccessible to other members
324 * in the same nest. If a framework passes security sensitive objects
325 * to a hidden class via class data, it is recommended to load the value
326 * of class data as a dynamically computed constant instead of storing
327 * the class data in private static field(s) which are accessible to
328 * other nestmates.
329 *
330 * @param <T> the type to cast the class data object to
331 * @param caller the lookup context describing the class performing the
332 * operation (normally stacked by the JVM)
333 * @param name must be {@link ConstantDescs#DEFAULT_NAME}
334 * ({@code "_"})
335 * @param type the type of the class data
336 * @return the value of the class data if present in the lookup class;
337 * otherwise {@code null}
338 * @throws IllegalArgumentException if name is not {@code "_"}
339 * @throws IllegalAccessException if the lookup context does not have
340 * {@linkplain Lookup#ORIGINAL original} access
341 * @throws ClassCastException if the class data cannot be converted to
342 * the given {@code type}
343 * @throws NullPointerException if {@code caller} or {@code type} argument
344 * is {@code null}
345 * @see Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...)
346 * @see MethodHandles#classDataAt(Lookup, String, Class, int)
347 * @since 16
348 * @jvms 5.5 Initialization
349 */
350 public static <T> T classData(Lookup caller, String name, Class<T> type) throws IllegalAccessException {
351 Objects.requireNonNull(caller);
352 Objects.requireNonNull(type);
353 if (!ConstantDescs.DEFAULT_NAME.equals(name)) {
354 throw new IllegalArgumentException("name must be \"_\": " + name);
355 }
356
357 if ((caller.lookupModes() & Lookup.ORIGINAL) != Lookup.ORIGINAL) {
358 throw new IllegalAccessException(caller + " does not have ORIGINAL access");
359 }
360
361 Object classdata = classData(caller.lookupClass());
362 if (classdata == null) return null;
363
364 try {
365 return BootstrapMethodInvoker.widenAndCast(classdata, type);
366 } catch (RuntimeException|Error e) {
367 throw e; // let CCE and other runtime exceptions through
368 } catch (Throwable e) {
369 throw new InternalError(e);
370 }
371 }
372
373 /*
374 * Returns the class data set by the VM in the Class::classData field.
375 *
376 * This is also invoked by LambdaForms as it cannot use condy via
377 * MethodHandles::classData due to bootstrapping issue.
378 */
379 static Object classData(Class<?> c) {
380 UNSAFE.ensureClassInitialized(c);
381 return SharedSecrets.getJavaLangAccess().classData(c);
382 }
383
384 /**
385 * Returns the element at the specified index in the
386 * {@linkplain #classData(Lookup, String, Class) class data},
387 * if the class data associated with the lookup class
388 * of the given {@code caller} lookup object is a {@code List}.
389 * If the class data is not present in this lookup class, this method
390 * returns {@code null}.
391 *
392 * <p> A hidden class with class data can be created by calling
393 * {@link Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...)
394 * Lookup::defineHiddenClassWithClassData}.
395 * This method will cause the static class initializer of the lookup
396 * class of the given {@code caller} lookup object be executed if
397 * it has not been initialized.
398 *
399 * <p> A hidden class created by {@link Lookup#defineHiddenClass(byte[], boolean, Lookup.ClassOption...)
400 * Lookup::defineHiddenClass} and non-hidden classes have no class data.
401 * {@code null} is returned if this method is called on the lookup object
402 * on these classes.
403 *
404 * <p> The {@linkplain Lookup#lookupModes() lookup modes} for this lookup
405 * must have {@linkplain Lookup#ORIGINAL original access}
406 * in order to retrieve the class data.
407 *
408 * @apiNote
409 * This method can be called as a bootstrap method for a dynamically computed
410 * constant. A framework can create a hidden class with class data, for
411 * example that can be {@code List.of(o1, o2, o3....)} containing more than
412 * one object and use this method to load one element at a specific index.
413 * The class data is accessible only to the lookup object
414 * created by the original caller but inaccessible to other members
415 * in the same nest. If a framework passes security sensitive objects
416 * to a hidden class via class data, it is recommended to load the value
417 * of class data as a dynamically computed constant instead of storing
418 * the class data in private static field(s) which are accessible to other
419 * nestmates.
420 *
421 * @param <T> the type to cast the result object to
422 * @param caller the lookup context describing the class performing the
423 * operation (normally stacked by the JVM)
424 * @param name must be {@link java.lang.constant.ConstantDescs#DEFAULT_NAME}
425 * ({@code "_"})
426 * @param type the type of the element at the given index in the class data
427 * @param index index of the element in the class data
428 * @return the element at the given index in the class data
429 * if the class data is present; otherwise {@code null}
430 * @throws IllegalArgumentException if name is not {@code "_"}
431 * @throws IllegalAccessException if the lookup context does not have
432 * {@linkplain Lookup#ORIGINAL original} access
433 * @throws ClassCastException if the class data cannot be converted to {@code List}
434 * or the element at the specified index cannot be converted to the given type
435 * @throws IndexOutOfBoundsException if the index is out of range
436 * @throws NullPointerException if {@code caller} or {@code type} argument is
437 * {@code null}; or if unboxing operation fails because
438 * the element at the given index is {@code null}
439 *
440 * @since 16
441 * @see #classData(Lookup, String, Class)
442 * @see Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...)
443 */
444 public static <T> T classDataAt(Lookup caller, String name, Class<T> type, int index)
445 throws IllegalAccessException
446 {
447 @SuppressWarnings("unchecked")
448 List<Object> classdata = (List<Object>)classData(caller, name, List.class);
449 if (classdata == null) return null;
450
451 try {
452 Object element = classdata.get(index);
453 return BootstrapMethodInvoker.widenAndCast(element, type);
454 } catch (RuntimeException|Error e) {
455 throw e; // let specified exceptions and other runtime exceptions/errors through
456 } catch (Throwable e) {
457 throw new InternalError(e);
458 }
459 }
460
461 /**
462 * Performs an unchecked "crack" of a
463 * <a href="MethodHandleInfo.html#directmh">direct method handle</a>.
464 * The result is as if the user had obtained a lookup object capable enough
465 * to crack the target method handle, called
466 * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect}
467 * on the target to obtain its symbolic reference, and then called
468 * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs}
469 * to resolve the symbolic reference to a member.
470 * <p>
471 * If there is a security manager, its {@code checkPermission} method
472 * is called with a {@code ReflectPermission("suppressAccessChecks")} permission.
473 * @param <T> the desired type of the result, either {@link Member} or a subtype
474 * @param target a direct method handle to crack into symbolic reference components
475 * @param expected a class object representing the desired result type {@code T}
476 * @return a reference to the method, constructor, or field object
477 * @throws SecurityException if the caller is not privileged to call {@code setAccessible}
478 * @throws NullPointerException if either argument is {@code null}
479 * @throws IllegalArgumentException if the target is not a direct method handle
480 * @throws ClassCastException if the member is not of the expected type
481 * @since 1.8
482 */
483 public static <T extends Member> T reflectAs(Class<T> expected, MethodHandle target) {
484 @SuppressWarnings("removal")
485 SecurityManager smgr = System.getSecurityManager();
486 if (smgr != null) smgr.checkPermission(SecurityConstants.ACCESS_PERMISSION);
487 Lookup lookup = Lookup.IMPL_LOOKUP; // use maximally privileged lookup
488 return lookup.revealDirect(target).reflectAs(expected, lookup);
489 }
490
491 /**
492 * A <em>lookup object</em> is a factory for creating method handles,
493 * when the creation requires access checking.
494 * Method handles do not perform
495 * access checks when they are called, but rather when they are created.
496 * Therefore, method handle access
497 * restrictions must be enforced when a method handle is created.
498 * The caller class against which those restrictions are enforced
499 * is known as the {@linkplain #lookupClass() lookup class}.
500 * <p>
501 * A lookup class which needs to create method handles will call
502 * {@link MethodHandles#lookup() MethodHandles.lookup} to create a factory for itself.
503 * When the {@code Lookup} factory object is created, the identity of the lookup class is
504 * determined, and securely stored in the {@code Lookup} object.
505 * The lookup class (or its delegates) may then use factory methods
506 * on the {@code Lookup} object to create method handles for access-checked members.
507 * This includes all methods, constructors, and fields which are allowed to the lookup class,
508 * even private ones.
509 *
510 * <h2><a id="lookups"></a>Lookup Factory Methods</h2>
511 * The factory methods on a {@code Lookup} object correspond to all major
512 * use cases for methods, constructors, and fields.
513 * Each method handle created by a factory method is the functional
514 * equivalent of a particular <em>bytecode behavior</em>.
515 * (Bytecode behaviors are described in section {@jvms 5.4.3.5} of
516 * the Java Virtual Machine Specification.)
517 * Here is a summary of the correspondence between these factory methods and
518 * the behavior of the resulting method handles:
519 * <table class="striped">
520 * <caption style="display:none">lookup method behaviors</caption>
521 * <thead>
522 * <tr>
523 * <th scope="col"><a id="equiv"></a>lookup expression</th>
524 * <th scope="col">member</th>
525 * <th scope="col">bytecode behavior</th>
526 * </tr>
527 * </thead>
528 * <tbody>
529 * <tr>
530 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</th>
531 * <td>{@code FT f;}</td><td>{@code (T) this.f;}</td>
532 * </tr>
533 * <tr>
534 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</th>
535 * <td>{@code static}<br>{@code FT f;}</td><td>{@code (FT) C.f;}</td>
536 * </tr>
537 * <tr>
538 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</th>
539 * <td>{@code FT f;}</td><td>{@code this.f = x;}</td>
540 * </tr>
541 * <tr>
542 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</th>
543 * <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td>
544 * </tr>
545 * <tr>
546 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</th>
547 * <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>
548 * </tr>
549 * <tr>
550 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</th>
551 * <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td>
552 * </tr>
553 * <tr>
554 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</th>
555 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
556 * </tr>
557 * <tr>
558 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</th>
559 * <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td>
560 * </tr>
561 * <tr>
562 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</th>
563 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td>
564 * </tr>
565 * <tr>
566 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</th>
567 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, arg);}</td>
568 * </tr>
569 * <tr>
570 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</th>
571 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
572 * </tr>
573 * <tr>
574 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</th>
575 * <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td>
576 * </tr>
577 * <tr>
578 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSpecial lookup.unreflectSpecial(aMethod,this.class)}</th>
579 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
580 * </tr>
581 * <tr>
582 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findClass lookup.findClass("C")}</th>
583 * <td>{@code class C { ... }}</td><td>{@code C.class;}</td>
584 * </tr>
585 * </tbody>
586 * </table>
587 *
588 * Here, the type {@code C} is the class or interface being searched for a member,
589 * documented as a parameter named {@code refc} in the lookup methods.
590 * The method type {@code MT} is composed from the return type {@code T}
591 * and the sequence of argument types {@code A*}.
592 * The constructor also has a sequence of argument types {@code A*} and
593 * is deemed to return the newly-created object of type {@code C}.
594 * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}.
595 * The formal parameter {@code this} stands for the self-reference of type {@code C};
596 * if it is present, it is always the leading argument to the method handle invocation.
597 * (In the case of some {@code protected} members, {@code this} may be
598 * restricted in type to the lookup class; see below.)
599 * The name {@code arg} stands for all the other method handle arguments.
600 * In the code examples for the Core Reflection API, the name {@code thisOrNull}
601 * stands for a null reference if the accessed method or field is static,
602 * and {@code this} otherwise.
603 * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand
604 * for reflective objects corresponding to the given members declared in type {@code C}.
605 * <p>
606 * The bytecode behavior for a {@code findClass} operation is a load of a constant class,
607 * as if by {@code ldc CONSTANT_Class}.
608 * The behavior is represented, not as a method handle, but directly as a {@code Class} constant.
609 * <p>
610 * In cases where the given member is of variable arity (i.e., a method or constructor)
611 * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}.
612 * In all other cases, the returned method handle will be of fixed arity.
613 * <p style="font-size:smaller;">
614 * <em>Discussion:</em>
615 * The equivalence between looked-up method handles and underlying
616 * class members and bytecode behaviors
617 * can break down in a few ways:
618 * <ul style="font-size:smaller;">
619 * <li>If {@code C} is not symbolically accessible from the lookup class's loader,
620 * the lookup can still succeed, even when there is no equivalent
621 * Java expression or bytecoded constant.
622 * <li>Likewise, if {@code T} or {@code MT}
623 * is not symbolically accessible from the lookup class's loader,
624 * the lookup can still succeed.
625 * For example, lookups for {@code MethodHandle.invokeExact} and
626 * {@code MethodHandle.invoke} will always succeed, regardless of requested type.
627 * <li>If there is a security manager installed, it can forbid the lookup
628 * on various grounds (<a href="MethodHandles.Lookup.html#secmgr">see below</a>).
629 * By contrast, the {@code ldc} instruction on a {@code CONSTANT_MethodHandle}
630 * constant is not subject to security manager checks.
631 * <li>If the looked-up method has a
632 * <a href="MethodHandle.html#maxarity">very large arity</a>,
633 * the method handle creation may fail with an
634 * {@code IllegalArgumentException}, due to the method handle type having
635 * <a href="MethodHandle.html#maxarity">too many parameters.</a>
636 * </ul>
637 *
638 * <h2><a id="access"></a>Access checking</h2>
639 * Access checks are applied in the factory methods of {@code Lookup},
640 * when a method handle is created.
641 * This is a key difference from the Core Reflection API, since
642 * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
643 * performs access checking against every caller, on every call.
644 * <p>
645 * All access checks start from a {@code Lookup} object, which
646 * compares its recorded lookup class against all requests to
647 * create method handles.
648 * A single {@code Lookup} object can be used to create any number
649 * of access-checked method handles, all checked against a single
650 * lookup class.
651 * <p>
652 * A {@code Lookup} object can be shared with other trusted code,
653 * such as a metaobject protocol.
654 * A shared {@code Lookup} object delegates the capability
655 * to create method handles on private members of the lookup class.
656 * Even if privileged code uses the {@code Lookup} object,
657 * the access checking is confined to the privileges of the
658 * original lookup class.
659 * <p>
660 * A lookup can fail, because
661 * the containing class is not accessible to the lookup class, or
662 * because the desired class member is missing, or because the
663 * desired class member is not accessible to the lookup class, or
664 * because the lookup object is not trusted enough to access the member.
665 * In the case of a field setter function on a {@code final} field,
666 * finality enforcement is treated as a kind of access control,
667 * and the lookup will fail, except in special cases of
668 * {@link Lookup#unreflectSetter Lookup.unreflectSetter}.
669 * In any of these cases, a {@code ReflectiveOperationException} will be
670 * thrown from the attempted lookup. The exact class will be one of
671 * the following:
672 * <ul>
673 * <li>NoSuchMethodException — if a method is requested but does not exist
674 * <li>NoSuchFieldException — if a field is requested but does not exist
675 * <li>IllegalAccessException — if the member exists but an access check fails
676 * </ul>
677 * <p>
678 * In general, the conditions under which a method handle may be
679 * looked up for a method {@code M} are no more restrictive than the conditions
680 * under which the lookup class could have compiled, verified, and resolved a call to {@code M}.
681 * Where the JVM would raise exceptions like {@code NoSuchMethodError},
682 * a method handle lookup will generally raise a corresponding
683 * checked exception, such as {@code NoSuchMethodException}.
684 * And the effect of invoking the method handle resulting from the lookup
685 * is <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a>
686 * to executing the compiled, verified, and resolved call to {@code M}.
687 * The same point is true of fields and constructors.
688 * <p style="font-size:smaller;">
689 * <em>Discussion:</em>
690 * Access checks only apply to named and reflected methods,
691 * constructors, and fields.
692 * Other method handle creation methods, such as
693 * {@link MethodHandle#asType MethodHandle.asType},
694 * do not require any access checks, and are used
695 * independently of any {@code Lookup} object.
696 * <p>
697 * If the desired member is {@code protected}, the usual JVM rules apply,
698 * including the requirement that the lookup class must either be in the
699 * same package as the desired member, or must inherit that member.
700 * (See the Java Virtual Machine Specification, sections {@jvms
701 * 4.9.2}, {@jvms 5.4.3.5}, and {@jvms 6.4}.)
702 * In addition, if the desired member is a non-static field or method
703 * in a different package, the resulting method handle may only be applied
704 * to objects of the lookup class or one of its subclasses.
705 * This requirement is enforced by narrowing the type of the leading
706 * {@code this} parameter from {@code C}
707 * (which will necessarily be a superclass of the lookup class)
708 * to the lookup class itself.
709 * <p>
710 * The JVM imposes a similar requirement on {@code invokespecial} instruction,
711 * that the receiver argument must match both the resolved method <em>and</em>
712 * the current class. Again, this requirement is enforced by narrowing the
713 * type of the leading parameter to the resulting method handle.
714 * (See the Java Virtual Machine Specification, section {@jvms 4.10.1.9}.)
715 * <p>
716 * The JVM represents constructors and static initializer blocks as internal methods
717 * with special names ({@value ConstantDescs#INIT_NAME},
718 * {@value ConstantDescs#VNEW_NAME} and {@value ConstantDescs#CLASS_INIT_NAME}).
719 * The internal syntax of invocation instructions allows them to refer to such internal
720 * methods as if they were normal methods, but the JVM bytecode verifier rejects them.
721 * A lookup of such an internal method will produce a {@code NoSuchMethodException}.
722 * <p>
723 * If the relationship between nested types is expressed directly through the
724 * {@code NestHost} and {@code NestMembers} attributes
725 * (see the Java Virtual Machine Specification, sections {@jvms
726 * 4.7.28} and {@jvms 4.7.29}),
727 * then the associated {@code Lookup} object provides direct access to
728 * the lookup class and all of its nestmates
729 * (see {@link java.lang.Class#getNestHost Class.getNestHost}).
730 * Otherwise, access between nested classes is obtained by the Java compiler creating
731 * a wrapper method to access a private method of another class in the same nest.
732 * For example, a nested class {@code C.D}
733 * can access private members within other related classes such as
734 * {@code C}, {@code C.D.E}, or {@code C.B},
735 * but the Java compiler may need to generate wrapper methods in
736 * those related classes. In such cases, a {@code Lookup} object on
737 * {@code C.E} would be unable to access those private members.
738 * A workaround for this limitation is the {@link Lookup#in Lookup.in} method,
739 * which can transform a lookup on {@code C.E} into one on any of those other
740 * classes, without special elevation of privilege.
741 * <p>
742 * The accesses permitted to a given lookup object may be limited,
743 * according to its set of {@link #lookupModes lookupModes},
744 * to a subset of members normally accessible to the lookup class.
745 * For example, the {@link MethodHandles#publicLookup publicLookup}
746 * method produces a lookup object which is only allowed to access
747 * public members in public classes of exported packages.
748 * The caller sensitive method {@link MethodHandles#lookup lookup}
749 * produces a lookup object with full capabilities relative to
750 * its caller class, to emulate all supported bytecode behaviors.
751 * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object
752 * with fewer access modes than the original lookup object.
753 *
754 * <p style="font-size:smaller;">
755 * <a id="privacc"></a>
756 * <em>Discussion of private and module access:</em>
757 * We say that a lookup has <em>private access</em>
758 * if its {@linkplain #lookupModes lookup modes}
759 * include the possibility of accessing {@code private} members
760 * (which includes the private members of nestmates).
761 * As documented in the relevant methods elsewhere,
762 * only lookups with private access possess the following capabilities:
763 * <ul style="font-size:smaller;">
764 * <li>access private fields, methods, and constructors of the lookup class and its nestmates
765 * <li>create method handles which {@link Lookup#findSpecial emulate invokespecial} instructions
766 * <li>avoid <a href="MethodHandles.Lookup.html#secmgr">package access checks</a>
767 * for classes accessible to the lookup class
768 * <li>create {@link Lookup#in delegated lookup objects} which have private access to other classes
769 * within the same package member
770 * </ul>
771 * <p style="font-size:smaller;">
772 * Similarly, a lookup with module access ensures that the original lookup creator was
773 * a member in the same module as the lookup class.
774 * <p style="font-size:smaller;">
775 * Private and module access are independently determined modes; a lookup may have
776 * either or both or neither. A lookup which possesses both access modes is said to
777 * possess {@linkplain #hasFullPrivilegeAccess() full privilege access}.
778 * <p style="font-size:smaller;">
779 * A lookup with <em>original access</em> ensures that this lookup is created by
780 * the original lookup class and the bootstrap method invoked by the VM.
781 * Such a lookup with original access also has private and module access
782 * which has the following additional capability:
783 * <ul style="font-size:smaller;">
784 * <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> methods,
785 * such as {@code Class.forName}
786 * <li>obtain the {@linkplain MethodHandles#classData(Lookup, String, Class)
787 * class data} associated with the lookup class</li>
788 * </ul>
789 * <p style="font-size:smaller;">
790 * Each of these permissions is a consequence of the fact that a lookup object
791 * with private access can be securely traced back to an originating class,
792 * whose <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> and Java language access permissions
793 * can be reliably determined and emulated by method handles.
794 *
795 * <h2><a id="cross-module-lookup"></a>Cross-module lookups</h2>
796 * When a lookup class in one module {@code M1} accesses a class in another module
797 * {@code M2}, extra access checking is performed beyond the access mode bits.
798 * A {@code Lookup} with {@link #PUBLIC} mode and a lookup class in {@code M1}
799 * can access public types in {@code M2} when {@code M2} is readable to {@code M1}
800 * and when the type is in a package of {@code M2} that is exported to
801 * at least {@code M1}.
802 * <p>
803 * A {@code Lookup} on {@code C} can also <em>teleport</em> to a target class
804 * via {@link #in(Class) Lookup.in} and {@link MethodHandles#privateLookupIn(Class, Lookup)
805 * MethodHandles.privateLookupIn} methods.
806 * Teleporting across modules will always record the original lookup class as
807 * the <em>{@linkplain #previousLookupClass() previous lookup class}</em>
808 * and drops {@link Lookup#MODULE MODULE} access.
809 * If the target class is in the same module as the lookup class {@code C},
810 * then the target class becomes the new lookup class
811 * and there is no change to the previous lookup class.
812 * If the target class is in a different module from {@code M1} ({@code C}'s module),
813 * {@code C} becomes the new previous lookup class
814 * and the target class becomes the new lookup class.
815 * In that case, if there was already a previous lookup class in {@code M0},
816 * and it differs from {@code M1} and {@code M2}, then the resulting lookup
817 * drops all privileges.
818 * For example,
819 * {@snippet lang="java" :
820 * Lookup lookup = MethodHandles.lookup(); // in class C
821 * Lookup lookup2 = lookup.in(D.class);
822 * MethodHandle mh = lookup2.findStatic(E.class, "m", MT);
823 * }
824 * <p>
825 * The {@link #lookup()} factory method produces a {@code Lookup} object
826 * with {@code null} previous lookup class.
827 * {@link Lookup#in lookup.in(D.class)} transforms the {@code lookup} on class {@code C}
828 * to class {@code D} without elevation of privileges.
829 * If {@code C} and {@code D} are in the same module,
830 * {@code lookup2} records {@code D} as the new lookup class and keeps the
831 * same previous lookup class as the original {@code lookup}, or
832 * {@code null} if not present.
833 * <p>
834 * When a {@code Lookup} teleports from a class
835 * in one nest to another nest, {@code PRIVATE} access is dropped.
836 * When a {@code Lookup} teleports from a class in one package to
837 * another package, {@code PACKAGE} access is dropped.
838 * When a {@code Lookup} teleports from a class in one module to another module,
839 * {@code MODULE} access is dropped.
840 * Teleporting across modules drops the ability to access non-exported classes
841 * in both the module of the new lookup class and the module of the old lookup class
842 * and the resulting {@code Lookup} remains only {@code PUBLIC} access.
843 * A {@code Lookup} can teleport back and forth to a class in the module of
844 * the lookup class and the module of the previous class lookup.
845 * Teleporting across modules can only decrease access but cannot increase it.
846 * Teleporting to some third module drops all accesses.
847 * <p>
848 * In the above example, if {@code C} and {@code D} are in different modules,
849 * {@code lookup2} records {@code D} as its lookup class and
850 * {@code C} as its previous lookup class and {@code lookup2} has only
851 * {@code PUBLIC} access. {@code lookup2} can teleport to other class in
852 * {@code C}'s module and {@code D}'s module.
853 * If class {@code E} is in a third module, {@code lookup2.in(E.class)} creates
854 * a {@code Lookup} on {@code E} with no access and {@code lookup2}'s lookup
855 * class {@code D} is recorded as its previous lookup class.
856 * <p>
857 * Teleporting across modules restricts access to the public types that
858 * both the lookup class and the previous lookup class can equally access
859 * (see below).
860 * <p>
861 * {@link MethodHandles#privateLookupIn(Class, Lookup) MethodHandles.privateLookupIn(T.class, lookup)}
862 * can be used to teleport a {@code lookup} from class {@code C} to class {@code T}
863 * and produce a new {@code Lookup} with <a href="#privacc">private access</a>
864 * if the lookup class is allowed to do <em>deep reflection</em> on {@code T}.
865 * The {@code lookup} must have {@link #MODULE} and {@link #PRIVATE} access
866 * to call {@code privateLookupIn}.
867 * A {@code lookup} on {@code C} in module {@code M1} is allowed to do deep reflection
868 * on all classes in {@code M1}. If {@code T} is in {@code M1}, {@code privateLookupIn}
869 * produces a new {@code Lookup} on {@code T} with full capabilities.
870 * A {@code lookup} on {@code C} is also allowed
871 * to do deep reflection on {@code T} in another module {@code M2} if
872 * {@code M1} reads {@code M2} and {@code M2} {@link Module#isOpen(String,Module) opens}
873 * the package containing {@code T} to at least {@code M1}.
874 * {@code T} becomes the new lookup class and {@code C} becomes the new previous
875 * lookup class and {@code MODULE} access is dropped from the resulting {@code Lookup}.
876 * The resulting {@code Lookup} can be used to do member lookup or teleport
877 * to another lookup class by calling {@link #in Lookup::in}. But
878 * it cannot be used to obtain another private {@code Lookup} by calling
879 * {@link MethodHandles#privateLookupIn(Class, Lookup) privateLookupIn}
880 * because it has no {@code MODULE} access.
881 * <p>
882 * The {@code Lookup} object returned by {@code privateLookupIn} is allowed to
883 * {@linkplain Lookup#defineClass(byte[]) define classes} in the runtime package
884 * of {@code T}. Extreme caution should be taken when opening a package
885 * to another module as such defined classes have the same full privilege
886 * access as other members in {@code M2}.
887 *
888 * <h2><a id="module-access-check"></a>Cross-module access checks</h2>
889 *
890 * A {@code Lookup} with {@link #PUBLIC} or with {@link #UNCONDITIONAL} mode
891 * allows cross-module access. The access checking is performed with respect
892 * to both the lookup class and the previous lookup class if present.
893 * <p>
894 * A {@code Lookup} with {@link #UNCONDITIONAL} mode can access public type
895 * in all modules when the type is in a package that is {@linkplain Module#isExported(String)
896 * exported unconditionally}.
897 * <p>
898 * If a {@code Lookup} on {@code LC} in {@code M1} has no previous lookup class,
899 * the lookup with {@link #PUBLIC} mode can access all public types in modules
900 * that are readable to {@code M1} and the type is in a package that is exported
901 * at least to {@code M1}.
902 * <p>
903 * If a {@code Lookup} on {@code LC} in {@code M1} has a previous lookup class
904 * {@code PLC} on {@code M0}, the lookup with {@link #PUBLIC} mode can access
905 * the intersection of all public types that are accessible to {@code M1}
906 * with all public types that are accessible to {@code M0}. {@code M0}
907 * reads {@code M1} and hence the set of accessible types includes:
908 *
909 * <ul>
910 * <li>unconditional-exported packages from {@code M1}</li>
911 * <li>unconditional-exported packages from {@code M0} if {@code M1} reads {@code M0}</li>
912 * <li>
913 * unconditional-exported packages from a third module {@code M2}if both {@code M0}
914 * and {@code M1} read {@code M2}
915 * </li>
916 * <li>qualified-exported packages from {@code M1} to {@code M0}</li>
917 * <li>qualified-exported packages from {@code M0} to {@code M1} if {@code M1} reads {@code M0}</li>
918 * <li>
919 * qualified-exported packages from a third module {@code M2} to both {@code M0} and
920 * {@code M1} if both {@code M0} and {@code M1} read {@code M2}
921 * </li>
922 * </ul>
923 *
924 * <h2><a id="access-modes"></a>Access modes</h2>
925 *
926 * The table below shows the access modes of a {@code Lookup} produced by
927 * any of the following factory or transformation methods:
928 * <ul>
929 * <li>{@link #lookup() MethodHandles::lookup}</li>
930 * <li>{@link #publicLookup() MethodHandles::publicLookup}</li>
931 * <li>{@link #privateLookupIn(Class, Lookup) MethodHandles::privateLookupIn}</li>
932 * <li>{@link Lookup#in Lookup::in}</li>
933 * <li>{@link Lookup#dropLookupMode(int) Lookup::dropLookupMode}</li>
934 * </ul>
935 *
936 * <table class="striped">
937 * <caption style="display:none">
938 * Access mode summary
939 * </caption>
940 * <thead>
941 * <tr>
942 * <th scope="col">Lookup object</th>
943 * <th style="text-align:center">original</th>
944 * <th style="text-align:center">protected</th>
945 * <th style="text-align:center">private</th>
946 * <th style="text-align:center">package</th>
947 * <th style="text-align:center">module</th>
948 * <th style="text-align:center">public</th>
949 * </tr>
950 * </thead>
951 * <tbody>
952 * <tr>
953 * <th scope="row" style="text-align:left">{@code CL = MethodHandles.lookup()} in {@code C}</th>
954 * <td style="text-align:center">ORI</td>
955 * <td style="text-align:center">PRO</td>
956 * <td style="text-align:center">PRI</td>
957 * <td style="text-align:center">PAC</td>
958 * <td style="text-align:center">MOD</td>
959 * <td style="text-align:center">1R</td>
960 * </tr>
961 * <tr>
962 * <th scope="row" style="text-align:left">{@code CL.in(C1)} same package</th>
963 * <td></td>
964 * <td></td>
965 * <td></td>
966 * <td style="text-align:center">PAC</td>
967 * <td style="text-align:center">MOD</td>
968 * <td style="text-align:center">1R</td>
969 * </tr>
970 * <tr>
971 * <th scope="row" style="text-align:left">{@code CL.in(C1)} same module</th>
972 * <td></td>
973 * <td></td>
974 * <td></td>
975 * <td></td>
976 * <td style="text-align:center">MOD</td>
977 * <td style="text-align:center">1R</td>
978 * </tr>
979 * <tr>
980 * <th scope="row" style="text-align:left">{@code CL.in(D)} different module</th>
981 * <td></td>
982 * <td></td>
983 * <td></td>
984 * <td></td>
985 * <td></td>
986 * <td style="text-align:center">2R</td>
987 * </tr>
988 * <tr>
989 * <th scope="row" style="text-align:left">{@code CL.in(D).in(C)} hop back to module</th>
990 * <td></td>
991 * <td></td>
992 * <td></td>
993 * <td></td>
994 * <td></td>
995 * <td style="text-align:center">2R</td>
996 * </tr>
997 * <tr>
998 * <th scope="row" style="text-align:left">{@code PRI1 = privateLookupIn(C1,CL)}</th>
999 * <td></td>
1000 * <td style="text-align:center">PRO</td>
1001 * <td style="text-align:center">PRI</td>
1002 * <td style="text-align:center">PAC</td>
1003 * <td style="text-align:center">MOD</td>
1004 * <td style="text-align:center">1R</td>
1005 * </tr>
1006 * <tr>
1007 * <th scope="row" style="text-align:left">{@code PRI1a = privateLookupIn(C,PRI1)}</th>
1008 * <td></td>
1009 * <td style="text-align:center">PRO</td>
1010 * <td style="text-align:center">PRI</td>
1011 * <td style="text-align:center">PAC</td>
1012 * <td style="text-align:center">MOD</td>
1013 * <td style="text-align:center">1R</td>
1014 * </tr>
1015 * <tr>
1016 * <th scope="row" style="text-align:left">{@code PRI1.in(C1)} same package</th>
1017 * <td></td>
1018 * <td></td>
1019 * <td></td>
1020 * <td style="text-align:center">PAC</td>
1021 * <td style="text-align:center">MOD</td>
1022 * <td style="text-align:center">1R</td>
1023 * </tr>
1024 * <tr>
1025 * <th scope="row" style="text-align:left">{@code PRI1.in(C1)} different package</th>
1026 * <td></td>
1027 * <td></td>
1028 * <td></td>
1029 * <td></td>
1030 * <td style="text-align:center">MOD</td>
1031 * <td style="text-align:center">1R</td>
1032 * </tr>
1033 * <tr>
1034 * <th scope="row" style="text-align:left">{@code PRI1.in(D)} different module</th>
1035 * <td></td>
1036 * <td></td>
1037 * <td></td>
1038 * <td></td>
1039 * <td></td>
1040 * <td style="text-align:center">2R</td>
1041 * </tr>
1042 * <tr>
1043 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PROTECTED)}</th>
1044 * <td></td>
1045 * <td></td>
1046 * <td style="text-align:center">PRI</td>
1047 * <td style="text-align:center">PAC</td>
1048 * <td style="text-align:center">MOD</td>
1049 * <td style="text-align:center">1R</td>
1050 * </tr>
1051 * <tr>
1052 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PRIVATE)}</th>
1053 * <td></td>
1054 * <td></td>
1055 * <td></td>
1056 * <td style="text-align:center">PAC</td>
1057 * <td style="text-align:center">MOD</td>
1058 * <td style="text-align:center">1R</td>
1059 * </tr>
1060 * <tr>
1061 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PACKAGE)}</th>
1062 * <td></td>
1063 * <td></td>
1064 * <td></td>
1065 * <td></td>
1066 * <td style="text-align:center">MOD</td>
1067 * <td style="text-align:center">1R</td>
1068 * </tr>
1069 * <tr>
1070 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(MODULE)}</th>
1071 * <td></td>
1072 * <td></td>
1073 * <td></td>
1074 * <td></td>
1075 * <td></td>
1076 * <td style="text-align:center">1R</td>
1077 * </tr>
1078 * <tr>
1079 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PUBLIC)}</th>
1080 * <td></td>
1081 * <td></td>
1082 * <td></td>
1083 * <td></td>
1084 * <td></td>
1085 * <td style="text-align:center">none</td>
1086 * <tr>
1087 * <th scope="row" style="text-align:left">{@code PRI2 = privateLookupIn(D,CL)}</th>
1088 * <td></td>
1089 * <td style="text-align:center">PRO</td>
1090 * <td style="text-align:center">PRI</td>
1091 * <td style="text-align:center">PAC</td>
1092 * <td></td>
1093 * <td style="text-align:center">2R</td>
1094 * </tr>
1095 * <tr>
1096 * <th scope="row" style="text-align:left">{@code privateLookupIn(D,PRI1)}</th>
1097 * <td></td>
1098 * <td style="text-align:center">PRO</td>
1099 * <td style="text-align:center">PRI</td>
1100 * <td style="text-align:center">PAC</td>
1101 * <td></td>
1102 * <td style="text-align:center">2R</td>
1103 * </tr>
1104 * <tr>
1105 * <th scope="row" style="text-align:left">{@code privateLookupIn(C,PRI2)} fails</th>
1106 * <td></td>
1107 * <td></td>
1108 * <td></td>
1109 * <td></td>
1110 * <td></td>
1111 * <td style="text-align:center">IAE</td>
1112 * </tr>
1113 * <tr>
1114 * <th scope="row" style="text-align:left">{@code PRI2.in(D2)} same package</th>
1115 * <td></td>
1116 * <td></td>
1117 * <td></td>
1118 * <td style="text-align:center">PAC</td>
1119 * <td></td>
1120 * <td style="text-align:center">2R</td>
1121 * </tr>
1122 * <tr>
1123 * <th scope="row" style="text-align:left">{@code PRI2.in(D2)} different package</th>
1124 * <td></td>
1125 * <td></td>
1126 * <td></td>
1127 * <td></td>
1128 * <td></td>
1129 * <td style="text-align:center">2R</td>
1130 * </tr>
1131 * <tr>
1132 * <th scope="row" style="text-align:left">{@code PRI2.in(C1)} hop back to module</th>
1133 * <td></td>
1134 * <td></td>
1135 * <td></td>
1136 * <td></td>
1137 * <td></td>
1138 * <td style="text-align:center">2R</td>
1139 * </tr>
1140 * <tr>
1141 * <th scope="row" style="text-align:left">{@code PRI2.in(E)} hop to third module</th>
1142 * <td></td>
1143 * <td></td>
1144 * <td></td>
1145 * <td></td>
1146 * <td></td>
1147 * <td style="text-align:center">none</td>
1148 * </tr>
1149 * <tr>
1150 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PROTECTED)}</th>
1151 * <td></td>
1152 * <td></td>
1153 * <td style="text-align:center">PRI</td>
1154 * <td style="text-align:center">PAC</td>
1155 * <td></td>
1156 * <td style="text-align:center">2R</td>
1157 * </tr>
1158 * <tr>
1159 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PRIVATE)}</th>
1160 * <td></td>
1161 * <td></td>
1162 * <td></td>
1163 * <td style="text-align:center">PAC</td>
1164 * <td></td>
1165 * <td style="text-align:center">2R</td>
1166 * </tr>
1167 * <tr>
1168 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PACKAGE)}</th>
1169 * <td></td>
1170 * <td></td>
1171 * <td></td>
1172 * <td></td>
1173 * <td></td>
1174 * <td style="text-align:center">2R</td>
1175 * </tr>
1176 * <tr>
1177 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(MODULE)}</th>
1178 * <td></td>
1179 * <td></td>
1180 * <td></td>
1181 * <td></td>
1182 * <td></td>
1183 * <td style="text-align:center">2R</td>
1184 * </tr>
1185 * <tr>
1186 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PUBLIC)}</th>
1187 * <td></td>
1188 * <td></td>
1189 * <td></td>
1190 * <td></td>
1191 * <td></td>
1192 * <td style="text-align:center">none</td>
1193 * </tr>
1194 * <tr>
1195 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PROTECTED)}</th>
1196 * <td></td>
1197 * <td></td>
1198 * <td style="text-align:center">PRI</td>
1199 * <td style="text-align:center">PAC</td>
1200 * <td style="text-align:center">MOD</td>
1201 * <td style="text-align:center">1R</td>
1202 * </tr>
1203 * <tr>
1204 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PRIVATE)}</th>
1205 * <td></td>
1206 * <td></td>
1207 * <td></td>
1208 * <td style="text-align:center">PAC</td>
1209 * <td style="text-align:center">MOD</td>
1210 * <td style="text-align:center">1R</td>
1211 * </tr>
1212 * <tr>
1213 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PACKAGE)}</th>
1214 * <td></td>
1215 * <td></td>
1216 * <td></td>
1217 * <td></td>
1218 * <td style="text-align:center">MOD</td>
1219 * <td style="text-align:center">1R</td>
1220 * </tr>
1221 * <tr>
1222 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(MODULE)}</th>
1223 * <td></td>
1224 * <td></td>
1225 * <td></td>
1226 * <td></td>
1227 * <td></td>
1228 * <td style="text-align:center">1R</td>
1229 * </tr>
1230 * <tr>
1231 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PUBLIC)}</th>
1232 * <td></td>
1233 * <td></td>
1234 * <td></td>
1235 * <td></td>
1236 * <td></td>
1237 * <td style="text-align:center">none</td>
1238 * </tr>
1239 * <tr>
1240 * <th scope="row" style="text-align:left">{@code PUB = publicLookup()}</th>
1241 * <td></td>
1242 * <td></td>
1243 * <td></td>
1244 * <td></td>
1245 * <td></td>
1246 * <td style="text-align:center">U</td>
1247 * </tr>
1248 * <tr>
1249 * <th scope="row" style="text-align:left">{@code PUB.in(D)} different module</th>
1250 * <td></td>
1251 * <td></td>
1252 * <td></td>
1253 * <td></td>
1254 * <td></td>
1255 * <td style="text-align:center">U</td>
1256 * </tr>
1257 * <tr>
1258 * <th scope="row" style="text-align:left">{@code PUB.in(D).in(E)} third module</th>
1259 * <td></td>
1260 * <td></td>
1261 * <td></td>
1262 * <td></td>
1263 * <td></td>
1264 * <td style="text-align:center">U</td>
1265 * </tr>
1266 * <tr>
1267 * <th scope="row" style="text-align:left">{@code PUB.dropLookupMode(UNCONDITIONAL)}</th>
1268 * <td></td>
1269 * <td></td>
1270 * <td></td>
1271 * <td></td>
1272 * <td></td>
1273 * <td style="text-align:center">none</td>
1274 * </tr>
1275 * <tr>
1276 * <th scope="row" style="text-align:left">{@code privateLookupIn(C1,PUB)} fails</th>
1277 * <td></td>
1278 * <td></td>
1279 * <td></td>
1280 * <td></td>
1281 * <td></td>
1282 * <td style="text-align:center">IAE</td>
1283 * </tr>
1284 * <tr>
1285 * <th scope="row" style="text-align:left">{@code ANY.in(X)}, for inaccessible {@code X}</th>
1286 * <td></td>
1287 * <td></td>
1288 * <td></td>
1289 * <td></td>
1290 * <td></td>
1291 * <td style="text-align:center">none</td>
1292 * </tr>
1293 * </tbody>
1294 * </table>
1295 *
1296 * <p>
1297 * Notes:
1298 * <ul>
1299 * <li>Class {@code C} and class {@code C1} are in module {@code M1},
1300 * but {@code D} and {@code D2} are in module {@code M2}, and {@code E}
1301 * is in module {@code M3}. {@code X} stands for class which is inaccessible
1302 * to the lookup. {@code ANY} stands for any of the example lookups.</li>
1303 * <li>{@code ORI} indicates {@link #ORIGINAL} bit set,
1304 * {@code PRO} indicates {@link #PROTECTED} bit set,
1305 * {@code PRI} indicates {@link #PRIVATE} bit set,
1306 * {@code PAC} indicates {@link #PACKAGE} bit set,
1307 * {@code MOD} indicates {@link #MODULE} bit set,
1308 * {@code 1R} and {@code 2R} indicate {@link #PUBLIC} bit set,
1309 * {@code U} indicates {@link #UNCONDITIONAL} bit set,
1310 * {@code IAE} indicates {@code IllegalAccessException} thrown.</li>
1311 * <li>Public access comes in three kinds:
1312 * <ul>
1313 * <li>unconditional ({@code U}): the lookup assumes readability.
1314 * The lookup has {@code null} previous lookup class.
1315 * <li>one-module-reads ({@code 1R}): the module access checking is
1316 * performed with respect to the lookup class. The lookup has {@code null}
1317 * previous lookup class.
1318 * <li>two-module-reads ({@code 2R}): the module access checking is
1319 * performed with respect to the lookup class and the previous lookup class.
1320 * The lookup has a non-null previous lookup class which is in a
1321 * different module from the current lookup class.
1322 * </ul>
1323 * <li>Any attempt to reach a third module loses all access.</li>
1324 * <li>If a target class {@code X} is not accessible to {@code Lookup::in}
1325 * all access modes are dropped.</li>
1326 * </ul>
1327 *
1328 * <h2><a id="secmgr"></a>Security manager interactions</h2>
1329 * Although bytecode instructions can only refer to classes in
1330 * a related class loader, this API can search for methods in any
1331 * class, as long as a reference to its {@code Class} object is
1332 * available. Such cross-loader references are also possible with the
1333 * Core Reflection API, and are impossible to bytecode instructions
1334 * such as {@code invokestatic} or {@code getfield}.
1335 * There is a {@linkplain java.lang.SecurityManager security manager API}
1336 * to allow applications to check such cross-loader references.
1337 * These checks apply to both the {@code MethodHandles.Lookup} API
1338 * and the Core Reflection API
1339 * (as found on {@link java.lang.Class Class}).
1340 * <p>
1341 * If a security manager is present, member and class lookups are subject to
1342 * additional checks.
1343 * From one to three calls are made to the security manager.
1344 * Any of these calls can refuse access by throwing a
1345 * {@link java.lang.SecurityException SecurityException}.
1346 * Define {@code smgr} as the security manager,
1347 * {@code lookc} as the lookup class of the current lookup object,
1348 * {@code refc} as the containing class in which the member
1349 * is being sought, and {@code defc} as the class in which the
1350 * member is actually defined.
1351 * (If a class or other type is being accessed,
1352 * the {@code refc} and {@code defc} values are the class itself.)
1353 * The value {@code lookc} is defined as <em>not present</em>
1354 * if the current lookup object does not have
1355 * {@linkplain #hasFullPrivilegeAccess() full privilege access}.
1356 * The calls are made according to the following rules:
1357 * <ul>
1358 * <li><b>Step 1:</b>
1359 * If {@code lookc} is not present, or if its class loader is not
1360 * the same as or an ancestor of the class loader of {@code refc},
1361 * then {@link SecurityManager#checkPackageAccess
1362 * smgr.checkPackageAccess(refcPkg)} is called,
1363 * where {@code refcPkg} is the package of {@code refc}.
1364 * <li><b>Step 2a:</b>
1365 * If the retrieved member is not public and
1366 * {@code lookc} is not present, then
1367 * {@link SecurityManager#checkPermission smgr.checkPermission}
1368 * with {@code RuntimePermission("accessDeclaredMembers")} is called.
1369 * <li><b>Step 2b:</b>
1370 * If the retrieved class has a {@code null} class loader,
1371 * and {@code lookc} is not present, then
1372 * {@link SecurityManager#checkPermission smgr.checkPermission}
1373 * with {@code RuntimePermission("getClassLoader")} is called.
1374 * <li><b>Step 3:</b>
1375 * If the retrieved member is not public,
1376 * and if {@code lookc} is not present,
1377 * and if {@code defc} and {@code refc} are different,
1378 * then {@link SecurityManager#checkPackageAccess
1379 * smgr.checkPackageAccess(defcPkg)} is called,
1380 * where {@code defcPkg} is the package of {@code defc}.
1381 * </ul>
1382 * Security checks are performed after other access checks have passed.
1383 * Therefore, the above rules presuppose a member or class that is public,
1384 * or else that is being accessed from a lookup class that has
1385 * rights to access the member or class.
1386 * <p>
1387 * If a security manager is present and the current lookup object does not have
1388 * {@linkplain #hasFullPrivilegeAccess() full privilege access}, then
1389 * {@link #defineClass(byte[]) defineClass},
1390 * {@link #defineHiddenClass(byte[], boolean, ClassOption...) defineHiddenClass},
1391 * {@link #defineHiddenClassWithClassData(byte[], Object, boolean, ClassOption...)
1392 * defineHiddenClassWithClassData}
1393 * calls {@link SecurityManager#checkPermission smgr.checkPermission}
1394 * with {@code RuntimePermission("defineClass")}.
1395 *
1396 * <h2><a id="callsens"></a>Caller sensitive methods</h2>
1397 * A small number of Java methods have a special property called caller sensitivity.
1398 * A <em>caller-sensitive</em> method can behave differently depending on the
1399 * identity of its immediate caller.
1400 * <p>
1401 * If a method handle for a caller-sensitive method is requested,
1402 * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> apply,
1403 * but they take account of the lookup class in a special way.
1404 * The resulting method handle behaves as if it were called
1405 * from an instruction contained in the lookup class,
1406 * so that the caller-sensitive method detects the lookup class.
1407 * (By contrast, the invoker of the method handle is disregarded.)
1408 * Thus, in the case of caller-sensitive methods,
1409 * different lookup classes may give rise to
1410 * differently behaving method handles.
1411 * <p>
1412 * In cases where the lookup object is
1413 * {@link MethodHandles#publicLookup() publicLookup()},
1414 * or some other lookup object without the
1415 * {@linkplain #ORIGINAL original access},
1416 * the lookup class is disregarded.
1417 * In such cases, no caller-sensitive method handle can be created,
1418 * access is forbidden, and the lookup fails with an
1419 * {@code IllegalAccessException}.
1420 * <p style="font-size:smaller;">
1421 * <em>Discussion:</em>
1422 * For example, the caller-sensitive method
1423 * {@link java.lang.Class#forName(String) Class.forName(x)}
1424 * can return varying classes or throw varying exceptions,
1425 * depending on the class loader of the class that calls it.
1426 * A public lookup of {@code Class.forName} will fail, because
1427 * there is no reasonable way to determine its bytecode behavior.
1428 * <p style="font-size:smaller;">
1429 * If an application caches method handles for broad sharing,
1430 * it should use {@code publicLookup()} to create them.
1431 * If there is a lookup of {@code Class.forName}, it will fail,
1432 * and the application must take appropriate action in that case.
1433 * It may be that a later lookup, perhaps during the invocation of a
1434 * bootstrap method, can incorporate the specific identity
1435 * of the caller, making the method accessible.
1436 * <p style="font-size:smaller;">
1437 * The function {@code MethodHandles.lookup} is caller sensitive
1438 * so that there can be a secure foundation for lookups.
1439 * Nearly all other methods in the JSR 292 API rely on lookup
1440 * objects to check access requests.
1441 *
1442 * @revised 9
1443 */
1444 public static final
1445 class Lookup {
1446 /** The class on behalf of whom the lookup is being performed. */
1447 private final Class<?> lookupClass;
1448
1449 /** previous lookup class */
1450 private final Class<?> prevLookupClass;
1451
1452 /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */
1453 private final int allowedModes;
1454
1455 static {
1456 Reflection.registerFieldsToFilter(Lookup.class, Set.of("lookupClass", "allowedModes"));
1457 }
1458
1459 /** A single-bit mask representing {@code public} access,
1460 * which may contribute to the result of {@link #lookupModes lookupModes}.
1461 * The value, {@code 0x01}, happens to be the same as the value of the
1462 * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.
1463 * <p>
1464 * A {@code Lookup} with this lookup mode performs cross-module access check
1465 * with respect to the {@linkplain #lookupClass() lookup class} and
1466 * {@linkplain #previousLookupClass() previous lookup class} if present.
1467 */
1468 public static final int PUBLIC = Modifier.PUBLIC;
1469
1470 /** A single-bit mask representing {@code private} access,
1471 * which may contribute to the result of {@link #lookupModes lookupModes}.
1472 * The value, {@code 0x02}, happens to be the same as the value of the
1473 * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.
1474 */
1475 public static final int PRIVATE = Modifier.PRIVATE;
1476
1477 /** A single-bit mask representing {@code protected} access,
1478 * which may contribute to the result of {@link #lookupModes lookupModes}.
1479 * The value, {@code 0x04}, happens to be the same as the value of the
1480 * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.
1481 */
1482 public static final int PROTECTED = Modifier.PROTECTED;
1483
1484 /** A single-bit mask representing {@code package} access (default access),
1485 * which may contribute to the result of {@link #lookupModes lookupModes}.
1486 * The value is {@code 0x08}, which does not correspond meaningfully to
1487 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1488 */
1489 public static final int PACKAGE = Modifier.STATIC;
1490
1491 /** A single-bit mask representing {@code module} access,
1492 * which may contribute to the result of {@link #lookupModes lookupModes}.
1493 * The value is {@code 0x10}, which does not correspond meaningfully to
1494 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1495 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup}
1496 * with this lookup mode can access all public types in the module of the
1497 * lookup class and public types in packages exported by other modules
1498 * to the module of the lookup class.
1499 * <p>
1500 * If this lookup mode is set, the {@linkplain #previousLookupClass()
1501 * previous lookup class} is always {@code null}.
1502 *
1503 * @since 9
1504 */
1505 public static final int MODULE = PACKAGE << 1;
1506
1507 /** A single-bit mask representing {@code unconditional} access
1508 * which may contribute to the result of {@link #lookupModes lookupModes}.
1509 * The value is {@code 0x20}, which does not correspond meaningfully to
1510 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1511 * A {@code Lookup} with this lookup mode assumes {@linkplain
1512 * java.lang.Module#canRead(java.lang.Module) readability}.
1513 * This lookup mode can access all public members of public types
1514 * of all modules when the type is in a package that is {@link
1515 * java.lang.Module#isExported(String) exported unconditionally}.
1516 *
1517 * <p>
1518 * If this lookup mode is set, the {@linkplain #previousLookupClass()
1519 * previous lookup class} is always {@code null}.
1520 *
1521 * @since 9
1522 * @see #publicLookup()
1523 */
1524 public static final int UNCONDITIONAL = PACKAGE << 2;
1525
1526 /** A single-bit mask representing {@code original} access
1527 * which may contribute to the result of {@link #lookupModes lookupModes}.
1528 * The value is {@code 0x40}, which does not correspond meaningfully to
1529 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1530 *
1531 * <p>
1532 * If this lookup mode is set, the {@code Lookup} object must be
1533 * created by the original lookup class by calling
1534 * {@link MethodHandles#lookup()} method or by a bootstrap method
1535 * invoked by the VM. The {@code Lookup} object with this lookup
1536 * mode has {@linkplain #hasFullPrivilegeAccess() full privilege access}.
1537 *
1538 * @since 16
1539 */
1540 public static final int ORIGINAL = PACKAGE << 3;
1541
1542 private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE | MODULE | UNCONDITIONAL | ORIGINAL);
1543 private static final int FULL_POWER_MODES = (ALL_MODES & ~UNCONDITIONAL); // with original access
1544 private static final int TRUSTED = -1;
1545
1546 /*
1547 * Adjust PUBLIC => PUBLIC|MODULE|ORIGINAL|UNCONDITIONAL
1548 * Adjust 0 => PACKAGE
1549 */
1550 private static int fixmods(int mods) {
1551 mods &= (ALL_MODES - PACKAGE - MODULE - ORIGINAL - UNCONDITIONAL);
1552 if (Modifier.isPublic(mods))
1553 mods |= UNCONDITIONAL;
1554 return (mods != 0) ? mods : PACKAGE;
1555 }
1556
1557 /** Tells which class is performing the lookup. It is this class against
1558 * which checks are performed for visibility and access permissions.
1559 * <p>
1560 * If this lookup object has a {@linkplain #previousLookupClass() previous lookup class},
1561 * access checks are performed against both the lookup class and the previous lookup class.
1562 * <p>
1563 * The class implies a maximum level of access permission,
1564 * but the permissions may be additionally limited by the bitmask
1565 * {@link #lookupModes lookupModes}, which controls whether non-public members
1566 * can be accessed.
1567 * @return the lookup class, on behalf of which this lookup object finds members
1568 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1569 */
1570 public Class<?> lookupClass() {
1571 return lookupClass;
1572 }
1573
1574 /** Reports a lookup class in another module that this lookup object
1575 * was previously teleported from, or {@code null}.
1576 * <p>
1577 * A {@code Lookup} object produced by the factory methods, such as the
1578 * {@link #lookup() lookup()} and {@link #publicLookup() publicLookup()} method,
1579 * has {@code null} previous lookup class.
1580 * A {@code Lookup} object has a non-null previous lookup class
1581 * when this lookup was teleported from an old lookup class
1582 * in one module to a new lookup class in another module.
1583 *
1584 * @return the lookup class in another module that this lookup object was
1585 * previously teleported from, or {@code null}
1586 * @since 14
1587 * @see #in(Class)
1588 * @see MethodHandles#privateLookupIn(Class, Lookup)
1589 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1590 */
1591 public Class<?> previousLookupClass() {
1592 return prevLookupClass;
1593 }
1594
1595 // This is just for calling out to MethodHandleImpl.
1596 private Class<?> lookupClassOrNull() {
1597 return (allowedModes == TRUSTED) ? null : lookupClass;
1598 }
1599
1600 /** Tells which access-protection classes of members this lookup object can produce.
1601 * The result is a bit-mask of the bits
1602 * {@linkplain #PUBLIC PUBLIC (0x01)},
1603 * {@linkplain #PRIVATE PRIVATE (0x02)},
1604 * {@linkplain #PROTECTED PROTECTED (0x04)},
1605 * {@linkplain #PACKAGE PACKAGE (0x08)},
1606 * {@linkplain #MODULE MODULE (0x10)},
1607 * {@linkplain #UNCONDITIONAL UNCONDITIONAL (0x20)},
1608 * and {@linkplain #ORIGINAL ORIGINAL (0x40)}.
1609 * <p>
1610 * A freshly-created lookup object
1611 * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class} has
1612 * all possible bits set, except {@code UNCONDITIONAL}.
1613 * A lookup object on a new lookup class
1614 * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object}
1615 * may have some mode bits set to zero.
1616 * Mode bits can also be
1617 * {@linkplain java.lang.invoke.MethodHandles.Lookup#dropLookupMode directly cleared}.
1618 * Once cleared, mode bits cannot be restored from the downgraded lookup object.
1619 * The purpose of this is to restrict access via the new lookup object,
1620 * so that it can access only names which can be reached by the original
1621 * lookup object, and also by the new lookup class.
1622 * @return the lookup modes, which limit the kinds of access performed by this lookup object
1623 * @see #in
1624 * @see #dropLookupMode
1625 *
1626 * @revised 9
1627 */
1628 public int lookupModes() {
1629 return allowedModes & ALL_MODES;
1630 }
1631
1632 /** Embody the current class (the lookupClass) as a lookup class
1633 * for method handle creation.
1634 * Must be called by from a method in this package,
1635 * which in turn is called by a method not in this package.
1636 */
1637 Lookup(Class<?> lookupClass) {
1638 this(lookupClass, null, FULL_POWER_MODES);
1639 }
1640
1641 private Lookup(Class<?> lookupClass, Class<?> prevLookupClass, int allowedModes) {
1642 assert PrimitiveClass.isPrimaryType(lookupClass);
1643 assert prevLookupClass == null || ((allowedModes & MODULE) == 0
1644 && prevLookupClass.getModule() != lookupClass.getModule());
1645 assert !lookupClass.isArray() && !lookupClass.isPrimitive();
1646 this.lookupClass = lookupClass;
1647 this.prevLookupClass = prevLookupClass;
1648 this.allowedModes = allowedModes;
1649 }
1650
1651 private static Lookup newLookup(Class<?> lookupClass, Class<?> prevLookupClass, int allowedModes) {
1652 // make sure we haven't accidentally picked up a privileged class:
1653 checkUnprivilegedlookupClass(lookupClass);
1654 return new Lookup(lookupClass, prevLookupClass, allowedModes);
1655 }
1656
1657 /**
1658 * Creates a lookup on the specified new lookup class.
1659 * The resulting object will report the specified
1660 * class as its own {@link #lookupClass() lookupClass}.
1661 *
1662 * <p>
1663 * However, the resulting {@code Lookup} object is guaranteed
1664 * to have no more access capabilities than the original.
1665 * In particular, access capabilities can be lost as follows:<ul>
1666 * <li>If the new lookup class is different from the old lookup class,
1667 * i.e. {@link #ORIGINAL ORIGINAL} access is lost.
1668 * <li>If the new lookup class is in a different module from the old one,
1669 * i.e. {@link #MODULE MODULE} access is lost.
1670 * <li>If the new lookup class is in a different package
1671 * than the old one, protected and default (package) members will not be accessible,
1672 * i.e. {@link #PROTECTED PROTECTED} and {@link #PACKAGE PACKAGE} access are lost.
1673 * <li>If the new lookup class is not within the same package member
1674 * as the old one, private members will not be accessible, and protected members
1675 * will not be accessible by virtue of inheritance,
1676 * i.e. {@link #PRIVATE PRIVATE} access is lost.
1677 * (Protected members may continue to be accessible because of package sharing.)
1678 * <li>If the new lookup class is not
1679 * {@linkplain #accessClass(Class) accessible} to this lookup,
1680 * then no members, not even public members, will be accessible
1681 * i.e. all access modes are lost.
1682 * <li>If the new lookup class, the old lookup class and the previous lookup class
1683 * are all in different modules i.e. teleporting to a third module,
1684 * all access modes are lost.
1685 * </ul>
1686 * <p>
1687 * The new previous lookup class is chosen as follows:
1688 * <ul>
1689 * <li>If the new lookup object has {@link #UNCONDITIONAL UNCONDITIONAL} bit,
1690 * the new previous lookup class is {@code null}.
1691 * <li>If the new lookup class is in the same module as the old lookup class,
1692 * the new previous lookup class is the old previous lookup class.
1693 * <li>If the new lookup class is in a different module from the old lookup class,
1694 * the new previous lookup class is the old lookup class.
1695 *</ul>
1696 * <p>
1697 * The resulting lookup's capabilities for loading classes
1698 * (used during {@link #findClass} invocations)
1699 * are determined by the lookup class' loader,
1700 * which may change due to this operation.
1701 *
1702 * @param requestedLookupClass the desired lookup class for the new lookup object
1703 * @return a lookup object which reports the desired lookup class, or the same object
1704 * if there is no change
1705 * @throws IllegalArgumentException if {@code requestedLookupClass} is a primitive type or void or array class
1706 * @throws NullPointerException if the argument is null
1707 *
1708 * @revised 9
1709 * @see #accessClass(Class)
1710 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1711 */
1712 public Lookup in(Class<?> requestedLookupClass) {
1713 Objects.requireNonNull(requestedLookupClass);
1714 if (requestedLookupClass.isPrimitive())
1715 throw new IllegalArgumentException(requestedLookupClass + " is a primitive class");
1716 if (requestedLookupClass.isArray())
1717 throw new IllegalArgumentException(requestedLookupClass + " is an array class");
1718
1719 if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all
1720 return new Lookup(requestedLookupClass, null, FULL_POWER_MODES);
1721 if (requestedLookupClass == this.lookupClass)
1722 return this; // keep same capabilities
1723 int newModes = (allowedModes & FULL_POWER_MODES) & ~ORIGINAL;
1724 Module fromModule = this.lookupClass.getModule();
1725 Module targetModule = requestedLookupClass.getModule();
1726 Class<?> plc = this.previousLookupClass();
1727 if ((this.allowedModes & UNCONDITIONAL) != 0) {
1728 assert plc == null;
1729 newModes = UNCONDITIONAL;
1730 } else if (fromModule != targetModule) {
1731 if (plc != null && !VerifyAccess.isSameModule(plc, requestedLookupClass)) {
1732 // allow hopping back and forth between fromModule and plc's module
1733 // but not the third module
1734 newModes = 0;
1735 }
1736 // drop MODULE access
1737 newModes &= ~(MODULE|PACKAGE|PRIVATE|PROTECTED);
1738 // teleport from this lookup class
1739 plc = this.lookupClass;
1740 }
1741 if ((newModes & PACKAGE) != 0
1742 && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {
1743 newModes &= ~(PACKAGE|PRIVATE|PROTECTED);
1744 }
1745 // Allow nestmate lookups to be created without special privilege:
1746 if ((newModes & PRIVATE) != 0
1747 && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {
1748 newModes &= ~(PRIVATE|PROTECTED);
1749 }
1750 if ((newModes & (PUBLIC|UNCONDITIONAL)) != 0
1751 && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, this.prevLookupClass, allowedModes)) {
1752 // The requested class it not accessible from the lookup class.
1753 // No permissions.
1754 newModes = 0;
1755 }
1756 return newLookup(requestedLookupClass, plc, newModes);
1757 }
1758
1759 /**
1760 * Creates a lookup on the same lookup class which this lookup object
1761 * finds members, but with a lookup mode that has lost the given lookup mode.
1762 * The lookup mode to drop is one of {@link #PUBLIC PUBLIC}, {@link #MODULE
1763 * MODULE}, {@link #PACKAGE PACKAGE}, {@link #PROTECTED PROTECTED},
1764 * {@link #PRIVATE PRIVATE}, {@link #ORIGINAL ORIGINAL}, or
1765 * {@link #UNCONDITIONAL UNCONDITIONAL}.
1766 *
1767 * <p> If this lookup is a {@linkplain MethodHandles#publicLookup() public lookup},
1768 * this lookup has {@code UNCONDITIONAL} mode set and it has no other mode set.
1769 * When dropping {@code UNCONDITIONAL} on a public lookup then the resulting
1770 * lookup has no access.
1771 *
1772 * <p> If this lookup is not a public lookup, then the following applies
1773 * regardless of its {@linkplain #lookupModes() lookup modes}.
1774 * {@link #PROTECTED PROTECTED} and {@link #ORIGINAL ORIGINAL} are always
1775 * dropped and so the resulting lookup mode will never have these access
1776 * capabilities. When dropping {@code PACKAGE}
1777 * then the resulting lookup will not have {@code PACKAGE} or {@code PRIVATE}
1778 * access. When dropping {@code MODULE} then the resulting lookup will not
1779 * have {@code MODULE}, {@code PACKAGE}, or {@code PRIVATE} access.
1780 * When dropping {@code PUBLIC} then the resulting lookup has no access.
1781 *
1782 * @apiNote
1783 * A lookup with {@code PACKAGE} but not {@code PRIVATE} mode can safely
1784 * delegate non-public access within the package of the lookup class without
1785 * conferring <a href="MethodHandles.Lookup.html#privacc">private access</a>.
1786 * A lookup with {@code MODULE} but not
1787 * {@code PACKAGE} mode can safely delegate {@code PUBLIC} access within
1788 * the module of the lookup class without conferring package access.
1789 * A lookup with a {@linkplain #previousLookupClass() previous lookup class}
1790 * (and {@code PUBLIC} but not {@code MODULE} mode) can safely delegate access
1791 * to public classes accessible to both the module of the lookup class
1792 * and the module of the previous lookup class.
1793 *
1794 * @param modeToDrop the lookup mode to drop
1795 * @return a lookup object which lacks the indicated mode, or the same object if there is no change
1796 * @throws IllegalArgumentException if {@code modeToDrop} is not one of {@code PUBLIC},
1797 * {@code MODULE}, {@code PACKAGE}, {@code PROTECTED}, {@code PRIVATE}, {@code ORIGINAL}
1798 * or {@code UNCONDITIONAL}
1799 * @see MethodHandles#privateLookupIn
1800 * @since 9
1801 */
1802 public Lookup dropLookupMode(int modeToDrop) {
1803 int oldModes = lookupModes();
1804 int newModes = oldModes & ~(modeToDrop | PROTECTED | ORIGINAL);
1805 switch (modeToDrop) {
1806 case PUBLIC: newModes &= ~(FULL_POWER_MODES); break;
1807 case MODULE: newModes &= ~(PACKAGE | PRIVATE); break;
1808 case PACKAGE: newModes &= ~(PRIVATE); break;
1809 case PROTECTED:
1810 case PRIVATE:
1811 case ORIGINAL:
1812 case UNCONDITIONAL: break;
1813 default: throw new IllegalArgumentException(modeToDrop + " is not a valid mode to drop");
1814 }
1815 if (newModes == oldModes) return this; // return self if no change
1816 return newLookup(lookupClass(), previousLookupClass(), newModes);
1817 }
1818
1819 /**
1820 * Creates and links a class or interface from {@code bytes}
1821 * with the same class loader and in the same runtime package and
1822 * {@linkplain java.security.ProtectionDomain protection domain} as this lookup's
1823 * {@linkplain #lookupClass() lookup class} as if calling
1824 * {@link ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain)
1825 * ClassLoader::defineClass}.
1826 *
1827 * <p> The {@linkplain #lookupModes() lookup modes} for this lookup must include
1828 * {@link #PACKAGE PACKAGE} access as default (package) members will be
1829 * accessible to the class. The {@code PACKAGE} lookup mode serves to authenticate
1830 * that the lookup object was created by a caller in the runtime package (or derived
1831 * from a lookup originally created by suitably privileged code to a target class in
1832 * the runtime package). </p>
1833 *
1834 * <p> The {@code bytes} parameter is the class bytes of a valid class file (as defined
1835 * by the <em>The Java Virtual Machine Specification</em>) with a class name in the
1836 * same package as the lookup class. </p>
1837 *
1838 * <p> This method does not run the class initializer. The class initializer may
1839 * run at a later time, as detailed in section 12.4 of the <em>The Java Language
1840 * Specification</em>. </p>
1841 *
1842 * <p> If there is a security manager and this lookup does not have {@linkplain
1843 * #hasFullPrivilegeAccess() full privilege access}, its {@code checkPermission} method
1844 * is first called to check {@code RuntimePermission("defineClass")}. </p>
1845 *
1846 * @param bytes the class bytes
1847 * @return the {@code Class} object for the class
1848 * @throws IllegalAccessException if this lookup does not have {@code PACKAGE} access
1849 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure
1850 * @throws IllegalArgumentException if {@code bytes} denotes a class in a different package
1851 * than the lookup class or {@code bytes} is not a class or interface
1852 * ({@code ACC_MODULE} flag is set in the value of the {@code access_flags} item)
1853 * @throws VerifyError if the newly created class cannot be verified
1854 * @throws LinkageError if the newly created class cannot be linked for any other reason
1855 * @throws SecurityException if a security manager is present and it
1856 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1857 * @throws NullPointerException if {@code bytes} is {@code null}
1858 * @since 9
1859 * @see Lookup#privateLookupIn
1860 * @see Lookup#dropLookupMode
1861 * @see ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain)
1862 */
1863 public Class<?> defineClass(byte[] bytes) throws IllegalAccessException {
1864 ensureDefineClassPermission();
1865 if ((lookupModes() & PACKAGE) == 0)
1866 throw new IllegalAccessException("Lookup does not have PACKAGE access");
1867 return makeClassDefiner(bytes.clone()).defineClass(false);
1868 }
1869
1870 private void ensureDefineClassPermission() {
1871 if (allowedModes == TRUSTED) return;
1872
1873 if (!hasFullPrivilegeAccess()) {
1874 @SuppressWarnings("removal")
1875 SecurityManager sm = System.getSecurityManager();
1876 if (sm != null)
1877 sm.checkPermission(new RuntimePermission("defineClass"));
1878 }
1879 }
1880
1881 /**
1882 * The set of class options that specify whether a hidden class created by
1883 * {@link Lookup#defineHiddenClass(byte[], boolean, ClassOption...)
1884 * Lookup::defineHiddenClass} method is dynamically added as a new member
1885 * to the nest of a lookup class and/or whether a hidden class has
1886 * a strong relationship with the class loader marked as its defining loader.
1887 *
1888 * @since 15
1889 */
1890 public enum ClassOption {
1891 /**
1892 * Specifies that a hidden class be added to {@linkplain Class#getNestHost nest}
1893 * of a lookup class as a nestmate.
1894 *
1895 * <p> A hidden nestmate class has access to the private members of all
1896 * classes and interfaces in the same nest.
1897 *
1898 * @see Class#getNestHost()
1899 */
1900 NESTMATE(NESTMATE_CLASS),
1901
1902 /**
1903 * Specifies that a hidden class has a <em>strong</em>
1904 * relationship with the class loader marked as its defining loader,
1905 * as a normal class or interface has with its own defining loader.
1906 * This means that the hidden class may be unloaded if and only if
1907 * its defining loader is not reachable and thus may be reclaimed
1908 * by a garbage collector (JLS {@jls 12.7}).
1909 *
1910 * <p> By default, a hidden class or interface may be unloaded
1911 * even if the class loader that is marked as its defining loader is
1912 * <a href="../ref/package-summary.html#reachability">reachable</a>.
1913
1914 *
1915 * @jls 12.7 Unloading of Classes and Interfaces
1916 */
1917 STRONG(STRONG_LOADER_LINK);
1918
1919 /* the flag value is used by VM at define class time */
1920 private final int flag;
1921 ClassOption(int flag) {
1922 this.flag = flag;
1923 }
1924
1925 static int optionsToFlag(Set<ClassOption> options) {
1926 int flags = 0;
1927 for (ClassOption cp : options) {
1928 flags |= cp.flag;
1929 }
1930 return flags;
1931 }
1932 }
1933
1934 /**
1935 * Creates a <em>hidden</em> class or interface from {@code bytes},
1936 * returning a {@code Lookup} on the newly created class or interface.
1937 *
1938 * <p> Ordinarily, a class or interface {@code C} is created by a class loader,
1939 * which either defines {@code C} directly or delegates to another class loader.
1940 * A class loader defines {@code C} directly by invoking
1941 * {@link ClassLoader#defineClass(String, byte[], int, int, ProtectionDomain)
1942 * ClassLoader::defineClass}, which causes the Java Virtual Machine
1943 * to derive {@code C} from a purported representation in {@code class} file format.
1944 * In situations where use of a class loader is undesirable, a class or interface
1945 * {@code C} can be created by this method instead. This method is capable of
1946 * defining {@code C}, and thereby creating it, without invoking
1947 * {@code ClassLoader::defineClass}.
1948 * Instead, this method defines {@code C} as if by arranging for
1949 * the Java Virtual Machine to derive a nonarray class or interface {@code C}
1950 * from a purported representation in {@code class} file format
1951 * using the following rules:
1952 *
1953 * <ol>
1954 * <li> The {@linkplain #lookupModes() lookup modes} for this {@code Lookup}
1955 * must include {@linkplain #hasFullPrivilegeAccess() full privilege} access.
1956 * This level of access is needed to create {@code C} in the module
1957 * of the lookup class of this {@code Lookup}.</li>
1958 *
1959 * <li> The purported representation in {@code bytes} must be a {@code ClassFile}
1960 * structure (JVMS {@jvms 4.1}) of a supported major and minor version.
1961 * The major and minor version may differ from the {@code class} file version
1962 * of the lookup class of this {@code Lookup}.</li>
1963 *
1964 * <li> The value of {@code this_class} must be a valid index in the
1965 * {@code constant_pool} table, and the entry at that index must be a valid
1966 * {@code CONSTANT_Class_info} structure. Let {@code N} be the binary name
1967 * encoded in internal form that is specified by this structure. {@code N} must
1968 * denote a class or interface in the same package as the lookup class.</li>
1969 *
1970 * <li> Let {@code CN} be the string {@code N + "." + <suffix>},
1971 * where {@code <suffix>} is an unqualified name.
1972 *
1973 * <p> Let {@code newBytes} be the {@code ClassFile} structure given by
1974 * {@code bytes} with an additional entry in the {@code constant_pool} table,
1975 * indicating a {@code CONSTANT_Utf8_info} structure for {@code CN}, and
1976 * where the {@code CONSTANT_Class_info} structure indicated by {@code this_class}
1977 * refers to the new {@code CONSTANT_Utf8_info} structure.
1978 *
1979 * <p> Let {@code L} be the defining class loader of the lookup class of this {@code Lookup}.
1980 *
1981 * <p> {@code C} is derived with name {@code CN}, class loader {@code L}, and
1982 * purported representation {@code newBytes} as if by the rules of JVMS {@jvms 5.3.5},
1983 * with the following adjustments:
1984 * <ul>
1985 * <li> The constant indicated by {@code this_class} is permitted to specify a name
1986 * that includes a single {@code "."} character, even though this is not a valid
1987 * binary class or interface name in internal form.</li>
1988 *
1989 * <li> The Java Virtual Machine marks {@code L} as the defining class loader of {@code C},
1990 * but no class loader is recorded as an initiating class loader of {@code C}.</li>
1991 *
1992 * <li> {@code C} is considered to have the same runtime
1993 * {@linkplain Class#getPackage() package}, {@linkplain Class#getModule() module}
1994 * and {@linkplain java.security.ProtectionDomain protection domain}
1995 * as the lookup class of this {@code Lookup}.
1996 * <li> Let {@code GN} be the binary name obtained by taking {@code N}
1997 * (a binary name encoded in internal form) and replacing ASCII forward slashes with
1998 * ASCII periods. For the instance of {@link java.lang.Class} representing {@code C}:
1999 * <ul>
2000 * <li> {@link Class#getName()} returns the string {@code GN + "/" + <suffix>},
2001 * even though this is not a valid binary class or interface name.</li>
2002 * <li> {@link Class#descriptorString()} returns the string
2003 * {@code "L" + N + "." + <suffix> + ";"},
2004 * even though this is not a valid type descriptor name.</li>
2005 * <li> {@link Class#describeConstable()} returns an empty optional as {@code C}
2006 * cannot be described in {@linkplain java.lang.constant.ClassDesc nominal form}.</li>
2007 * </ul>
2008 * </ul>
2009 * </li>
2010 * </ol>
2011 *
2012 * <p> After {@code C} is derived, it is linked by the Java Virtual Machine.
2013 * Linkage occurs as specified in JVMS {@jvms 5.4.3}, with the following adjustments:
2014 * <ul>
2015 * <li> During verification, whenever it is necessary to load the class named
2016 * {@code CN}, the attempt succeeds, producing class {@code C}. No request is
2017 * made of any class loader.</li>
2018 *
2019 * <li> On any attempt to resolve the entry in the run-time constant pool indicated
2020 * by {@code this_class}, the symbolic reference is considered to be resolved to
2021 * {@code C} and resolution always succeeds immediately.</li>
2022 * </ul>
2023 *
2024 * <p> If the {@code initialize} parameter is {@code true},
2025 * then {@code C} is initialized by the Java Virtual Machine.
2026 *
2027 * <p> The newly created class or interface {@code C} serves as the
2028 * {@linkplain #lookupClass() lookup class} of the {@code Lookup} object
2029 * returned by this method. {@code C} is <em>hidden</em> in the sense that
2030 * no other class or interface can refer to {@code C} via a constant pool entry.
2031 * That is, a hidden class or interface cannot be named as a supertype, a field type,
2032 * a method parameter type, or a method return type by any other class.
2033 * This is because a hidden class or interface does not have a binary name, so
2034 * there is no internal form available to record in any class's constant pool.
2035 * A hidden class or interface is not discoverable by {@link Class#forName(String, boolean, ClassLoader)},
2036 * {@link ClassLoader#loadClass(String, boolean)}, or {@link #findClass(String)}, and
2037 * is not {@linkplain java.instrument/java.lang.instrument.Instrumentation#isModifiableClass(Class)
2038 * modifiable} by Java agents or tool agents using the <a href="{@docRoot}/../specs/jvmti.html">
2039 * JVM Tool Interface</a>.
2040 *
2041 * <p> A class or interface created by
2042 * {@linkplain ClassLoader#defineClass(String, byte[], int, int, ProtectionDomain)
2043 * a class loader} has a strong relationship with that class loader.
2044 * That is, every {@code Class} object contains a reference to the {@code ClassLoader}
2045 * that {@linkplain Class#getClassLoader() defined it}.
2046 * This means that a class created by a class loader may be unloaded if and
2047 * only if its defining loader is not reachable and thus may be reclaimed
2048 * by a garbage collector (JLS {@jls 12.7}).
2049 *
2050 * By default, however, a hidden class or interface may be unloaded even if
2051 * the class loader that is marked as its defining loader is
2052 * <a href="../ref/package-summary.html#reachability">reachable</a>.
2053 * This behavior is useful when a hidden class or interface serves multiple
2054 * classes defined by arbitrary class loaders. In other cases, a hidden
2055 * class or interface may be linked to a single class (or a small number of classes)
2056 * with the same defining loader as the hidden class or interface.
2057 * In such cases, where the hidden class or interface must be coterminous
2058 * with a normal class or interface, the {@link ClassOption#STRONG STRONG}
2059 * option may be passed in {@code options}.
2060 * This arranges for a hidden class to have the same strong relationship
2061 * with the class loader marked as its defining loader,
2062 * as a normal class or interface has with its own defining loader.
2063 *
2064 * If {@code STRONG} is not used, then the invoker of {@code defineHiddenClass}
2065 * may still prevent a hidden class or interface from being
2066 * unloaded by ensuring that the {@code Class} object is reachable.
2067 *
2068 * <p> The unloading characteristics are set for each hidden class when it is
2069 * defined, and cannot be changed later. An advantage of allowing hidden classes
2070 * to be unloaded independently of the class loader marked as their defining loader
2071 * is that a very large number of hidden classes may be created by an application.
2072 * In contrast, if {@code STRONG} is used, then the JVM may run out of memory,
2073 * just as if normal classes were created by class loaders.
2074 *
2075 * <p> Classes and interfaces in a nest are allowed to have mutual access to
2076 * their private members. The nest relationship is determined by
2077 * the {@code NestHost} attribute (JVMS {@jvms 4.7.28}) and
2078 * the {@code NestMembers} attribute (JVMS {@jvms 4.7.29}) in a {@code class} file.
2079 * By default, a hidden class belongs to a nest consisting only of itself
2080 * because a hidden class has no binary name.
2081 * The {@link ClassOption#NESTMATE NESTMATE} option can be passed in {@code options}
2082 * to create a hidden class or interface {@code C} as a member of a nest.
2083 * The nest to which {@code C} belongs is not based on any {@code NestHost} attribute
2084 * in the {@code ClassFile} structure from which {@code C} was derived.
2085 * Instead, the following rules determine the nest host of {@code C}:
2086 * <ul>
2087 * <li>If the nest host of the lookup class of this {@code Lookup} has previously
2088 * been determined, then let {@code H} be the nest host of the lookup class.
2089 * Otherwise, the nest host of the lookup class is determined using the
2090 * algorithm in JVMS {@jvms 5.4.4}, yielding {@code H}.</li>
2091 * <li>The nest host of {@code C} is determined to be {@code H},
2092 * the nest host of the lookup class.</li>
2093 * </ul>
2094 *
2095 * <p> A hidden class or interface may be serializable, but this requires a custom
2096 * serialization mechanism in order to ensure that instances are properly serialized
2097 * and deserialized. The default serialization mechanism supports only classes and
2098 * interfaces that are discoverable by their class name.
2099 *
2100 * @param bytes the bytes that make up the class data,
2101 * in the format of a valid {@code class} file as defined by
2102 * <cite>The Java Virtual Machine Specification</cite>.
2103 * @param initialize if {@code true} the class will be initialized.
2104 * @param options {@linkplain ClassOption class options}
2105 * @return the {@code Lookup} object on the hidden class,
2106 * with {@linkplain #ORIGINAL original} and
2107 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege} access
2108 *
2109 * @throws IllegalAccessException if this {@code Lookup} does not have
2110 * {@linkplain #hasFullPrivilegeAccess() full privilege} access
2111 * @throws SecurityException if a security manager is present and it
2112 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2113 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure
2114 * @throws UnsupportedClassVersionError if {@code bytes} is not of a supported major or minor version
2115 * @throws IllegalArgumentException if {@code bytes} denotes a class in a different package
2116 * than the lookup class or {@code bytes} is not a class or interface
2117 * ({@code ACC_MODULE} flag is set in the value of the {@code access_flags} item)
2118 * @throws IncompatibleClassChangeError if the class or interface named as
2119 * the direct superclass of {@code C} is in fact an interface, or if any of the classes
2120 * or interfaces named as direct superinterfaces of {@code C} are not in fact interfaces
2121 * @throws ClassCircularityError if any of the superclasses or superinterfaces of
2122 * {@code C} is {@code C} itself
2123 * @throws VerifyError if the newly created class cannot be verified
2124 * @throws LinkageError if the newly created class cannot be linked for any other reason
2125 * @throws NullPointerException if any parameter is {@code null}
2126 *
2127 * @since 15
2128 * @see Class#isHidden()
2129 * @jvms 4.2.1 Binary Class and Interface Names
2130 * @jvms 4.2.2 Unqualified Names
2131 * @jvms 4.7.28 The {@code NestHost} Attribute
2132 * @jvms 4.7.29 The {@code NestMembers} Attribute
2133 * @jvms 5.4.3.1 Class and Interface Resolution
2134 * @jvms 5.4.4 Access Control
2135 * @jvms 5.3.5 Deriving a {@code Class} from a {@code class} File Representation
2136 * @jvms 5.4 Linking
2137 * @jvms 5.5 Initialization
2138 * @jls 12.7 Unloading of Classes and Interfaces
2139 */
2140 @SuppressWarnings("doclint:reference") // cross-module links
2141 public Lookup defineHiddenClass(byte[] bytes, boolean initialize, ClassOption... options)
2142 throws IllegalAccessException
2143 {
2144 Objects.requireNonNull(bytes);
2145 Objects.requireNonNull(options);
2146
2147 ensureDefineClassPermission();
2148 if (!hasFullPrivilegeAccess()) {
2149 throw new IllegalAccessException(this + " does not have full privilege access");
2150 }
2151
2152 return makeHiddenClassDefiner(bytes.clone(), Set.of(options), false).defineClassAsLookup(initialize);
2153 }
2154
2155 /**
2156 * Creates a <em>hidden</em> class or interface from {@code bytes} with associated
2157 * {@linkplain MethodHandles#classData(Lookup, String, Class) class data},
2158 * returning a {@code Lookup} on the newly created class or interface.
2159 *
2160 * <p> This method is equivalent to calling
2161 * {@link #defineHiddenClass(byte[], boolean, ClassOption...) defineHiddenClass(bytes, initialize, options)}
2162 * as if the hidden class is injected with a private static final <i>unnamed</i>
2163 * field which is initialized with the given {@code classData} at
2164 * the first instruction of the class initializer.
2165 * The newly created class is linked by the Java Virtual Machine.
2166 *
2167 * <p> The {@link MethodHandles#classData(Lookup, String, Class) MethodHandles::classData}
2168 * and {@link MethodHandles#classDataAt(Lookup, String, Class, int) MethodHandles::classDataAt}
2169 * methods can be used to retrieve the {@code classData}.
2170 *
2171 * @apiNote
2172 * A framework can create a hidden class with class data with one or more
2173 * objects and load the class data as dynamically-computed constant(s)
2174 * via a bootstrap method. {@link MethodHandles#classData(Lookup, String, Class)
2175 * Class data} is accessible only to the lookup object created by the newly
2176 * defined hidden class but inaccessible to other members in the same nest
2177 * (unlike private static fields that are accessible to nestmates).
2178 * Care should be taken w.r.t. mutability for example when passing
2179 * an array or other mutable structure through the class data.
2180 * Changing any value stored in the class data at runtime may lead to
2181 * unpredictable behavior.
2182 * If the class data is a {@code List}, it is good practice to make it
2183 * unmodifiable for example via {@link List#of List::of}.
2184 *
2185 * @param bytes the class bytes
2186 * @param classData pre-initialized class data
2187 * @param initialize if {@code true} the class will be initialized.
2188 * @param options {@linkplain ClassOption class options}
2189 * @return the {@code Lookup} object on the hidden class,
2190 * with {@linkplain #ORIGINAL original} and
2191 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege} access
2192 *
2193 * @throws IllegalAccessException if this {@code Lookup} does not have
2194 * {@linkplain #hasFullPrivilegeAccess() full privilege} access
2195 * @throws SecurityException if a security manager is present and it
2196 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2197 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure
2198 * @throws UnsupportedClassVersionError if {@code bytes} is not of a supported major or minor version
2199 * @throws IllegalArgumentException if {@code bytes} denotes a class in a different package
2200 * than the lookup class or {@code bytes} is not a class or interface
2201 * ({@code ACC_MODULE} flag is set in the value of the {@code access_flags} item)
2202 * @throws IncompatibleClassChangeError if the class or interface named as
2203 * the direct superclass of {@code C} is in fact an interface, or if any of the classes
2204 * or interfaces named as direct superinterfaces of {@code C} are not in fact interfaces
2205 * @throws ClassCircularityError if any of the superclasses or superinterfaces of
2206 * {@code C} is {@code C} itself
2207 * @throws VerifyError if the newly created class cannot be verified
2208 * @throws LinkageError if the newly created class cannot be linked for any other reason
2209 * @throws NullPointerException if any parameter is {@code null}
2210 *
2211 * @since 16
2212 * @see Lookup#defineHiddenClass(byte[], boolean, ClassOption...)
2213 * @see Class#isHidden()
2214 * @see MethodHandles#classData(Lookup, String, Class)
2215 * @see MethodHandles#classDataAt(Lookup, String, Class, int)
2216 * @jvms 4.2.1 Binary Class and Interface Names
2217 * @jvms 4.2.2 Unqualified Names
2218 * @jvms 4.7.28 The {@code NestHost} Attribute
2219 * @jvms 4.7.29 The {@code NestMembers} Attribute
2220 * @jvms 5.4.3.1 Class and Interface Resolution
2221 * @jvms 5.4.4 Access Control
2222 * @jvms 5.3.5 Deriving a {@code Class} from a {@code class} File Representation
2223 * @jvms 5.4 Linking
2224 * @jvms 5.5 Initialization
2225 * @jls 12.7 Unloading of Classes and Interface
2226 */
2227 public Lookup defineHiddenClassWithClassData(byte[] bytes, Object classData, boolean initialize, ClassOption... options)
2228 throws IllegalAccessException
2229 {
2230 Objects.requireNonNull(bytes);
2231 Objects.requireNonNull(classData);
2232 Objects.requireNonNull(options);
2233
2234 ensureDefineClassPermission();
2235 if (!hasFullPrivilegeAccess()) {
2236 throw new IllegalAccessException(this + " does not have full privilege access");
2237 }
2238
2239 return makeHiddenClassDefiner(bytes.clone(), Set.of(options), false)
2240 .defineClassAsLookup(initialize, classData);
2241 }
2242
2243 // A default dumper for writing class files passed to Lookup::defineClass
2244 // and Lookup::defineHiddenClass to disk for debugging purposes. To enable,
2245 // set -Djdk.invoke.MethodHandle.dumpHiddenClassFiles or
2246 // -Djdk.invoke.MethodHandle.dumpHiddenClassFiles=true
2247 //
2248 // This default dumper does not dump hidden classes defined by LambdaMetafactory
2249 // and LambdaForms and method handle internals. They are dumped via
2250 // different ClassFileDumpers.
2251 private static ClassFileDumper defaultDumper() {
2252 return DEFAULT_DUMPER;
2253 }
2254
2255 private static final ClassFileDumper DEFAULT_DUMPER = ClassFileDumper.getInstance(
2256 "jdk.invoke.MethodHandle.dumpClassFiles", "DUMP_CLASS_FILES");
2257
2258 static class ClassFile {
2259 final String name; // internal name
2260 final int accessFlags;
2261 final byte[] bytes;
2262 ClassFile(String name, int accessFlags, byte[] bytes) {
2263 this.name = name;
2264 this.accessFlags = accessFlags;
2265 this.bytes = bytes;
2266 }
2267
2268 static ClassFile newInstanceNoCheck(String name, byte[] bytes) {
2269 return new ClassFile(name, 0, bytes);
2270 }
2271
2272 /**
2273 * This method checks the class file version and the structure of `this_class`.
2274 * and checks if the bytes is a class or interface (ACC_MODULE flag not set)
2275 * that is in the named package.
2276 *
2277 * @throws IllegalArgumentException if ACC_MODULE flag is set in access flags
2278 * or the class is not in the given package name.
2279 */
2280 static ClassFile newInstance(byte[] bytes, String pkgName) {
2281 var cf = readClassFile(bytes);
2282
2283 // check if it's in the named package
2284 int index = cf.name.lastIndexOf('/');
2285 String pn = (index == -1) ? "" : cf.name.substring(0, index).replace('/', '.');
2286 if (!pn.equals(pkgName)) {
2287 throw newIllegalArgumentException(cf.name + " not in same package as lookup class");
2288 }
2289 return cf;
2290 }
2291
2292 private static ClassFile readClassFile(byte[] bytes) {
2293 int magic = readInt(bytes, 0);
2294 if (magic != 0xCAFEBABE) {
2295 throw new ClassFormatError("Incompatible magic value: " + magic);
2296 }
2297 int minor = readUnsignedShort(bytes, 4);
2298 int major = readUnsignedShort(bytes, 6);
2299 if (!VM.isSupportedClassFileVersion(major, minor)) {
2300 throw new UnsupportedClassVersionError("Unsupported class file version " + major + "." + minor);
2301 }
2302
2303 String name;
2304 int accessFlags;
2305 try {
2306 ClassReader reader = new ClassReader(bytes);
2307 // ClassReader does not check if `this_class` is CONSTANT_Class_info
2308 // workaround to read `this_class` using readConst and validate the value
2309 int thisClass = reader.readUnsignedShort(reader.header + 2);
2310 Object constant = reader.readConst(thisClass, new char[reader.getMaxStringLength()]);
2311 if (!(constant instanceof Type type)) {
2312 throw new ClassFormatError("this_class item: #" + thisClass + " not a CONSTANT_Class_info");
2313 }
2314 if (!type.getDescriptor().startsWith("L")) {
2315 throw new ClassFormatError("this_class item: #" + thisClass + " not a CONSTANT_Class_info");
2316 }
2317 name = type.getInternalName();
2318 accessFlags = reader.readUnsignedShort(reader.header);
2319 } catch (RuntimeException e) {
2320 // ASM exceptions are poorly specified
2321 ClassFormatError cfe = new ClassFormatError();
2322 cfe.initCause(e);
2323 throw cfe;
2324 }
2325 // must be a class or interface
2326 if ((accessFlags & Opcodes.ACC_MODULE) != 0) {
2327 throw newIllegalArgumentException("Not a class or interface: ACC_MODULE flag is set");
2328 }
2329 return new ClassFile(name, accessFlags, bytes);
2330 }
2331
2332 private static int readInt(byte[] bytes, int offset) {
2333 if ((offset+4) > bytes.length) {
2334 throw new ClassFormatError("Invalid ClassFile structure");
2335 }
2336 return ((bytes[offset] & 0xFF) << 24)
2337 | ((bytes[offset + 1] & 0xFF) << 16)
2338 | ((bytes[offset + 2] & 0xFF) << 8)
2339 | (bytes[offset + 3] & 0xFF);
2340 }
2341
2342 private static int readUnsignedShort(byte[] bytes, int offset) {
2343 if ((offset+2) > bytes.length) {
2344 throw new ClassFormatError("Invalid ClassFile structure");
2345 }
2346 return ((bytes[offset] & 0xFF) << 8) | (bytes[offset + 1] & 0xFF);
2347 }
2348 }
2349
2350 /*
2351 * Returns a ClassDefiner that creates a {@code Class} object of a normal class
2352 * from the given bytes.
2353 *
2354 * Caller should make a defensive copy of the arguments if needed
2355 * before calling this factory method.
2356 *
2357 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or
2358 * {@code bytes} denotes a class in a different package than the lookup class
2359 */
2360 private ClassDefiner makeClassDefiner(byte[] bytes) {
2361 ClassFile cf = ClassFile.newInstance(bytes, lookupClass().getPackageName());
2362 return new ClassDefiner(this, cf, STRONG_LOADER_LINK, defaultDumper());
2363 }
2364
2365 /**
2366 * Returns a ClassDefiner that creates a {@code Class} object of a normal class
2367 * from the given bytes. No package name check on the given bytes.
2368 *
2369 * @param name internal name
2370 * @param bytes class bytes
2371 * @param dumper dumper to write the given bytes to the dumper's output directory
2372 * @return ClassDefiner that defines a normal class of the given bytes.
2373 */
2374 ClassDefiner makeClassDefiner(String name, byte[] bytes, ClassFileDumper dumper) {
2375 // skip package name validation
2376 ClassFile cf = ClassFile.newInstanceNoCheck(name, bytes);
2377 return new ClassDefiner(this, cf, STRONG_LOADER_LINK, dumper);
2378 }
2379
2380 /**
2381 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2382 * from the given bytes. The name must be in the same package as the lookup class.
2383 *
2384 * Caller should make a defensive copy of the arguments if needed
2385 * before calling this factory method.
2386 *
2387 * @param bytes class bytes
2388 * @param dumper dumper to write the given bytes to the dumper's output directory
2389 * @return ClassDefiner that defines a hidden class of the given bytes.
2390 *
2391 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or
2392 * {@code bytes} denotes a class in a different package than the lookup class
2393 */
2394 ClassDefiner makeHiddenClassDefiner(byte[] bytes, ClassFileDumper dumper) {
2395 ClassFile cf = ClassFile.newInstance(bytes, lookupClass().getPackageName());
2396 return makeHiddenClassDefiner(cf, Set.of(), false, dumper);
2397 }
2398
2399 /**
2400 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2401 * from the given bytes and options.
2402 * The name must be in the same package as the lookup class.
2403 *
2404 * Caller should make a defensive copy of the arguments if needed
2405 * before calling this factory method.
2406 *
2407 * @param bytes class bytes
2408 * @param options class options
2409 * @param accessVmAnnotations true to give the hidden class access to VM annotations
2410 * @return ClassDefiner that defines a hidden class of the given bytes and options
2411 *
2412 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or
2413 * {@code bytes} denotes a class in a different package than the lookup class
2414 */
2415 private ClassDefiner makeHiddenClassDefiner(byte[] bytes,
2416 Set<ClassOption> options,
2417 boolean accessVmAnnotations) {
2418 ClassFile cf = ClassFile.newInstance(bytes, lookupClass().getPackageName());
2419 return makeHiddenClassDefiner(cf, options, accessVmAnnotations, defaultDumper());
2420 }
2421
2422 /**
2423 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2424 * from the given bytes and the given options. No package name check on the given bytes.
2425 *
2426 * @param name internal name that specifies the prefix of the hidden class
2427 * @param bytes class bytes
2428 * @param options class options
2429 * @param dumper dumper to write the given bytes to the dumper's output directory
2430 * @return ClassDefiner that defines a hidden class of the given bytes and options.
2431 */
2432 ClassDefiner makeHiddenClassDefiner(String name, byte[] bytes, Set<ClassOption> options, ClassFileDumper dumper) {
2433 Objects.requireNonNull(dumper);
2434 // skip name and access flags validation
2435 return makeHiddenClassDefiner(ClassFile.newInstanceNoCheck(name, bytes), options, false, dumper);
2436 }
2437
2438 /**
2439 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2440 * from the given class file and options.
2441 *
2442 * @param cf ClassFile
2443 * @param options class options
2444 * @param accessVmAnnotations true to give the hidden class access to VM annotations
2445 * @param dumper dumper to write the given bytes to the dumper's output directory
2446 */
2447 private ClassDefiner makeHiddenClassDefiner(ClassFile cf,
2448 Set<ClassOption> options,
2449 boolean accessVmAnnotations,
2450 ClassFileDumper dumper) {
2451 int flags = HIDDEN_CLASS | ClassOption.optionsToFlag(options);
2452 if (accessVmAnnotations | VM.isSystemDomainLoader(lookupClass.getClassLoader())) {
2453 // jdk.internal.vm.annotations are permitted for classes
2454 // defined to boot loader and platform loader
2455 flags |= ACCESS_VM_ANNOTATIONS;
2456 }
2457
2458 return new ClassDefiner(this, cf, flags, dumper);
2459 }
2460
2461 static class ClassDefiner {
2462 private final Lookup lookup;
2463 private final String name; // internal name
2464 private final byte[] bytes;
2465 private final int classFlags;
2466 private final ClassFileDumper dumper;
2467
2468 private ClassDefiner(Lookup lookup, ClassFile cf, int flags, ClassFileDumper dumper) {
2469 assert ((flags & HIDDEN_CLASS) != 0 || (flags & STRONG_LOADER_LINK) == STRONG_LOADER_LINK);
2470 this.lookup = lookup;
2471 this.bytes = cf.bytes;
2472 this.name = cf.name;
2473 this.classFlags = flags;
2474 this.dumper = dumper;
2475 }
2476
2477 String internalName() {
2478 return name;
2479 }
2480
2481 Class<?> defineClass(boolean initialize) {
2482 return defineClass(initialize, null);
2483 }
2484
2485 Lookup defineClassAsLookup(boolean initialize) {
2486 Class<?> c = defineClass(initialize, null);
2487 return new Lookup(c, null, FULL_POWER_MODES);
2488 }
2489
2490 /**
2491 * Defines the class of the given bytes and the given classData.
2492 * If {@code initialize} parameter is true, then the class will be initialized.
2493 *
2494 * @param initialize true if the class to be initialized
2495 * @param classData classData or null
2496 * @return the class
2497 *
2498 * @throws LinkageError linkage error
2499 */
2500 Class<?> defineClass(boolean initialize, Object classData) {
2501 Class<?> lookupClass = lookup.lookupClass();
2502 ClassLoader loader = lookupClass.getClassLoader();
2503 ProtectionDomain pd = (loader != null) ? lookup.lookupClassProtectionDomain() : null;
2504 Class<?> c = null;
2505 try {
2506 c = SharedSecrets.getJavaLangAccess()
2507 .defineClass(loader, lookupClass, name, bytes, pd, initialize, classFlags, classData);
2508 assert !isNestmate() || c.getNestHost() == lookupClass.getNestHost();
2509 return c;
2510 } finally {
2511 // dump the classfile for debugging
2512 if (dumper.isEnabled()) {
2513 String name = internalName();
2514 if (c != null) {
2515 dumper.dumpClass(name, c, bytes);
2516 } else {
2517 dumper.dumpFailedClass(name, bytes);
2518 }
2519 }
2520 }
2521 }
2522
2523 /**
2524 * Defines the class of the given bytes and the given classData.
2525 * If {@code initialize} parameter is true, then the class will be initialized.
2526 *
2527 * @param initialize true if the class to be initialized
2528 * @param classData classData or null
2529 * @return a Lookup for the defined class
2530 *
2531 * @throws LinkageError linkage error
2532 */
2533 Lookup defineClassAsLookup(boolean initialize, Object classData) {
2534 Class<?> c = defineClass(initialize, classData);
2535 return new Lookup(c, null, FULL_POWER_MODES);
2536 }
2537
2538 private boolean isNestmate() {
2539 return (classFlags & NESTMATE_CLASS) != 0;
2540 }
2541 }
2542
2543 private ProtectionDomain lookupClassProtectionDomain() {
2544 ProtectionDomain pd = cachedProtectionDomain;
2545 if (pd == null) {
2546 cachedProtectionDomain = pd = SharedSecrets.getJavaLangAccess().protectionDomain(lookupClass);
2547 }
2548 return pd;
2549 }
2550
2551 // cached protection domain
2552 private volatile ProtectionDomain cachedProtectionDomain;
2553
2554 // Make sure outer class is initialized first.
2555 static { IMPL_NAMES.getClass(); }
2556
2557 /** Package-private version of lookup which is trusted. */
2558 static final Lookup IMPL_LOOKUP = new Lookup(Object.class, null, TRUSTED);
2559
2560 /** Version of lookup which is trusted minimally.
2561 * It can only be used to create method handles to publicly accessible
2562 * members in packages that are exported unconditionally.
2563 */
2564 static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, null, UNCONDITIONAL);
2565
2566 private static void checkUnprivilegedlookupClass(Class<?> lookupClass) {
2567 String name = lookupClass.getName();
2568 if (name.startsWith("java.lang.invoke."))
2569 throw newIllegalArgumentException("illegal lookupClass: "+lookupClass);
2570 }
2571
2572 /**
2573 * Displays the name of the class from which lookups are to be made,
2574 * followed by "/" and the name of the {@linkplain #previousLookupClass()
2575 * previous lookup class} if present.
2576 * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)
2577 * If there are restrictions on the access permitted to this lookup,
2578 * this is indicated by adding a suffix to the class name, consisting
2579 * of a slash and a keyword. The keyword represents the strongest
2580 * allowed access, and is chosen as follows:
2581 * <ul>
2582 * <li>If no access is allowed, the suffix is "/noaccess".
2583 * <li>If only unconditional access is allowed, the suffix is "/publicLookup".
2584 * <li>If only public access to types in exported packages is allowed, the suffix is "/public".
2585 * <li>If only public and module access are allowed, the suffix is "/module".
2586 * <li>If public and package access are allowed, the suffix is "/package".
2587 * <li>If public, package, and private access are allowed, the suffix is "/private".
2588 * </ul>
2589 * If none of the above cases apply, it is the case that
2590 * {@linkplain #hasFullPrivilegeAccess() full privilege access}
2591 * (public, module, package, private, and protected) is allowed.
2592 * In this case, no suffix is added.
2593 * This is true only of an object obtained originally from
2594 * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
2595 * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
2596 * always have restricted access, and will display a suffix.
2597 * <p>
2598 * (It may seem strange that protected access should be
2599 * stronger than private access. Viewed independently from
2600 * package access, protected access is the first to be lost,
2601 * because it requires a direct subclass relationship between
2602 * caller and callee.)
2603 * @see #in
2604 *
2605 * @revised 9
2606 */
2607 @Override
2608 public String toString() {
2609 String cname = lookupClass.getName();
2610 if (prevLookupClass != null)
2611 cname += "/" + prevLookupClass.getName();
2612 switch (allowedModes) {
2613 case 0: // no privileges
2614 return cname + "/noaccess";
2615 case UNCONDITIONAL:
2616 return cname + "/publicLookup";
2617 case PUBLIC:
2618 return cname + "/public";
2619 case PUBLIC|MODULE:
2620 return cname + "/module";
2621 case PUBLIC|PACKAGE:
2622 case PUBLIC|MODULE|PACKAGE:
2623 return cname + "/package";
2624 case PUBLIC|PACKAGE|PRIVATE:
2625 case PUBLIC|MODULE|PACKAGE|PRIVATE:
2626 return cname + "/private";
2627 case PUBLIC|PACKAGE|PRIVATE|PROTECTED:
2628 case PUBLIC|MODULE|PACKAGE|PRIVATE|PROTECTED:
2629 case FULL_POWER_MODES:
2630 return cname;
2631 case TRUSTED:
2632 return "/trusted"; // internal only; not exported
2633 default: // Should not happen, but it's a bitfield...
2634 cname = cname + "/" + Integer.toHexString(allowedModes);
2635 assert(false) : cname;
2636 return cname;
2637 }
2638 }
2639
2640 /**
2641 * Produces a method handle for a static method.
2642 * The type of the method handle will be that of the method.
2643 * (Since static methods do not take receivers, there is no
2644 * additional receiver argument inserted into the method handle type,
2645 * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)
2646 * The method and all its argument types must be accessible to the lookup object.
2647 * <p>
2648 * The returned method handle will have
2649 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2650 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2651 * <p>
2652 * If the returned method handle is invoked, the method's class will
2653 * be initialized, if it has not already been initialized.
2654 * <p><b>Example:</b>
2655 * {@snippet lang="java" :
2656 import static java.lang.invoke.MethodHandles.*;
2657 import static java.lang.invoke.MethodType.*;
2658 ...
2659 MethodHandle MH_asList = publicLookup().findStatic(Arrays.class,
2660 "asList", methodType(List.class, Object[].class));
2661 assertEquals("[x, y]", MH_asList.invoke("x", "y").toString());
2662 * }
2663 * @param refc the class from which the method is accessed
2664 * @param name the name of the method
2665 * @param type the type of the method
2666 * @return the desired method handle
2667 * @throws NoSuchMethodException if the method does not exist
2668 * @throws IllegalAccessException if access checking fails,
2669 * or if the method is not {@code static},
2670 * or if the method's variable arity modifier bit
2671 * is set and {@code asVarargsCollector} fails
2672 * @throws SecurityException if a security manager is present and it
2673 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2674 * @throws NullPointerException if any argument is null
2675 */
2676 public MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2677 MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type);
2678 return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerLookup(method));
2679 }
2680
2681 /**
2682 * Produces a method handle for a virtual method.
2683 * The type of the method handle will be that of the method,
2684 * with the receiver type (usually {@code refc}) prepended.
2685 * The method and all its argument types must be accessible to the lookup object.
2686 * <p>
2687 * When called, the handle will treat the first argument as a receiver
2688 * and, for non-private methods, dispatch on the receiver's type to determine which method
2689 * implementation to enter.
2690 * For private methods the named method in {@code refc} will be invoked on the receiver.
2691 * (The dispatching action is identical with that performed by an
2692 * {@code invokevirtual} or {@code invokeinterface} instruction.)
2693 * <p>
2694 * The first argument will be of type {@code refc} if the lookup
2695 * class has full privileges to access the member. Otherwise
2696 * the member must be {@code protected} and the first argument
2697 * will be restricted in type to the lookup class.
2698 * <p>
2699 * The returned method handle will have
2700 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2701 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2702 * <p>
2703 * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual}
2704 * instructions and method handles produced by {@code findVirtual},
2705 * if the class is {@code MethodHandle} and the name string is
2706 * {@code invokeExact} or {@code invoke}, the resulting
2707 * method handle is equivalent to one produced by
2708 * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or
2709 * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}
2710 * with the same {@code type} argument.
2711 * <p>
2712 * If the class is {@code VarHandle} and the name string corresponds to
2713 * the name of a signature-polymorphic access mode method, the resulting
2714 * method handle is equivalent to one produced by
2715 * {@link java.lang.invoke.MethodHandles#varHandleInvoker} with
2716 * the access mode corresponding to the name string and with the same
2717 * {@code type} arguments.
2718 * <p>
2719 * <b>Example:</b>
2720 * {@snippet lang="java" :
2721 import static java.lang.invoke.MethodHandles.*;
2722 import static java.lang.invoke.MethodType.*;
2723 ...
2724 MethodHandle MH_concat = publicLookup().findVirtual(String.class,
2725 "concat", methodType(String.class, String.class));
2726 MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class,
2727 "hashCode", methodType(int.class));
2728 MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class,
2729 "hashCode", methodType(int.class));
2730 assertEquals("xy", (String) MH_concat.invokeExact("x", "y"));
2731 assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy"));
2732 assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy"));
2733 // interface method:
2734 MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class,
2735 "subSequence", methodType(CharSequence.class, int.class, int.class));
2736 assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString());
2737 // constructor "internal method" must be accessed differently:
2738 MethodType MT_newString = methodType(void.class); //()V for new String()
2739 try { assertEquals("impossible", lookup()
2740 .findVirtual(String.class, "<init>", MT_newString));
2741 } catch (NoSuchMethodException ex) { } // OK
2742 MethodHandle MH_newString = publicLookup()
2743 .findConstructor(String.class, MT_newString);
2744 assertEquals("", (String) MH_newString.invokeExact());
2745 * }
2746 *
2747 * @param refc the class or interface from which the method is accessed
2748 * @param name the name of the method
2749 * @param type the type of the method, with the receiver argument omitted
2750 * @return the desired method handle
2751 * @throws NoSuchMethodException if the method does not exist
2752 * @throws IllegalAccessException if access checking fails,
2753 * or if the method is {@code static},
2754 * or if the method's variable arity modifier bit
2755 * is set and {@code asVarargsCollector} fails
2756 * @throws SecurityException if a security manager is present and it
2757 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2758 * @throws NullPointerException if any argument is null
2759 */
2760 public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2761 if (refc == MethodHandle.class) {
2762 MethodHandle mh = findVirtualForMH(name, type);
2763 if (mh != null) return mh;
2764 } else if (refc == VarHandle.class) {
2765 MethodHandle mh = findVirtualForVH(name, type);
2766 if (mh != null) return mh;
2767 }
2768 byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual);
2769 MemberName method = resolveOrFail(refKind, refc, name, type);
2770 return getDirectMethod(refKind, refc, method, findBoundCallerLookup(method));
2771 }
2772 private MethodHandle findVirtualForMH(String name, MethodType type) {
2773 // these names require special lookups because of the implicit MethodType argument
2774 if ("invoke".equals(name))
2775 return invoker(type);
2776 if ("invokeExact".equals(name))
2777 return exactInvoker(type);
2778 assert(!MemberName.isMethodHandleInvokeName(name));
2779 return null;
2780 }
2781 private MethodHandle findVirtualForVH(String name, MethodType type) {
2782 try {
2783 return varHandleInvoker(VarHandle.AccessMode.valueFromMethodName(name), type);
2784 } catch (IllegalArgumentException e) {
2785 return null;
2786 }
2787 }
2788
2789 /**
2790 * Produces a method handle which creates an object and initializes it, using
2791 * the constructor of the specified type.
2792 * The parameter types of the method handle will be those of the constructor,
2793 * while the return type will be a reference to the constructor's class.
2794 * The constructor and all its argument types must be accessible to the lookup object.
2795 * <p>
2796 * The requested type must have a return type of {@code void}.
2797 * (This is consistent with the JVM's treatment of constructor type descriptors.)
2798 * <p>
2799 * The returned method handle will have
2800 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2801 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
2802 * <p>
2803 * If the returned method handle is invoked, the constructor's class will
2804 * be initialized, if it has not already been initialized.
2805 * <p><b>Example:</b>
2806 * {@snippet lang="java" :
2807 import static java.lang.invoke.MethodHandles.*;
2808 import static java.lang.invoke.MethodType.*;
2809 ...
2810 MethodHandle MH_newArrayList = publicLookup().findConstructor(
2811 ArrayList.class, methodType(void.class, Collection.class));
2812 Collection orig = Arrays.asList("x", "y");
2813 Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig);
2814 assert(orig != copy);
2815 assertEquals(orig, copy);
2816 // a variable-arity constructor:
2817 MethodHandle MH_newProcessBuilder = publicLookup().findConstructor(
2818 ProcessBuilder.class, methodType(void.class, String[].class));
2819 ProcessBuilder pb = (ProcessBuilder)
2820 MH_newProcessBuilder.invoke("x", "y", "z");
2821 assertEquals("[x, y, z]", pb.command().toString());
2822 * }
2823 *
2824 *
2825 * @param refc the class or interface from which the method is accessed
2826 * @param type the type of the method, with the receiver argument omitted, and a void return type
2827 * @return the desired method handle
2828 * @throws NoSuchMethodException if the constructor does not exist
2829 * @throws IllegalAccessException if access checking fails
2830 * or if the method's variable arity modifier bit
2831 * is set and {@code asVarargsCollector} fails
2832 * @throws SecurityException if a security manager is present and it
2833 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2834 * @throws NullPointerException if any argument is null
2835 */
2836 public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2837 if (refc.isArray()) {
2838 throw new NoSuchMethodException("no constructor for array class: " + refc.getName());
2839 }
2840 if (type.returnType() != void.class) {
2841 throw new NoSuchMethodException("Constructors must have void return type: " + refc.getName());
2842 }
2843 String name = ConstantDescs.INIT_NAME;
2844 MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type);
2845 return getDirectConstructor(refc, ctor);
2846 }
2847
2848 /**
2849 * Looks up a class by name from the lookup context defined by this {@code Lookup} object,
2850 * <a href="MethodHandles.Lookup.html#equiv">as if resolved</a> by an {@code ldc} instruction.
2851 * Such a resolution, as specified in JVMS {@jvms 5.4.3.1}, attempts to locate and load the class,
2852 * and then determines whether the class is accessible to this lookup object.
2853 * <p>
2854 * For a class or an interface, the name is the {@linkplain ClassLoader##binary-name binary name}.
2855 * For an array class of {@code n} dimensions, the name begins with {@code n} occurrences
2856 * of {@code '['} and followed by the element type as encoded in the
2857 * {@linkplain Class##nameFormat table} specified in {@link Class#getName}.
2858 * <p>
2859 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class},
2860 * its class loader, and the {@linkplain #lookupModes() lookup modes}.
2861 *
2862 * @param targetName the {@linkplain ClassLoader##binary-name binary name} of the class
2863 * or the string representing an array class
2864 * @return the requested class.
2865 * @throws SecurityException if a security manager is present and it
2866 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2867 * @throws LinkageError if the linkage fails
2868 * @throws ClassNotFoundException if the class cannot be loaded by the lookup class' loader.
2869 * @throws IllegalAccessException if the class is not accessible, using the allowed access
2870 * modes.
2871 * @throws NullPointerException if {@code targetName} is null
2872 * @since 9
2873 * @jvms 5.4.3.1 Class and Interface Resolution
2874 */
2875 public Class<?> findClass(String targetName) throws ClassNotFoundException, IllegalAccessException {
2876 Class<?> targetClass = Class.forName(targetName, false, lookupClass.getClassLoader());
2877 return accessClass(targetClass);
2878 }
2879
2880 /**
2881 * Ensures that {@code targetClass} has been initialized. The class
2882 * to be initialized must be {@linkplain #accessClass accessible}
2883 * to this {@code Lookup} object. This method causes {@code targetClass}
2884 * to be initialized if it has not been already initialized,
2885 * as specified in JVMS {@jvms 5.5}.
2886 *
2887 * <p>
2888 * This method returns when {@code targetClass} is fully initialized, or
2889 * when {@code targetClass} is being initialized by the current thread.
2890 *
2891 * @param <T> the type of the class to be initialized
2892 * @param targetClass the class to be initialized
2893 * @return {@code targetClass} that has been initialized, or that is being
2894 * initialized by the current thread.
2895 *
2896 * @throws IllegalArgumentException if {@code targetClass} is a primitive type or {@code void}
2897 * or array class
2898 * @throws IllegalAccessException if {@code targetClass} is not
2899 * {@linkplain #accessClass accessible} to this lookup
2900 * @throws ExceptionInInitializerError if the class initialization provoked
2901 * by this method fails
2902 * @throws SecurityException if a security manager is present and it
2903 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2904 * @since 15
2905 * @jvms 5.5 Initialization
2906 */
2907 public <T> Class<T> ensureInitialized(Class<T> targetClass) throws IllegalAccessException {
2908 if (targetClass.isPrimitive())
2909 throw new IllegalArgumentException(targetClass + " is a primitive class");
2910 if (targetClass.isArray())
2911 throw new IllegalArgumentException(targetClass + " is an array class");
2912
2913 if (!VerifyAccess.isClassAccessible(targetClass, lookupClass, prevLookupClass, allowedModes)) {
2914 throw makeAccessException(targetClass);
2915 }
2916 checkSecurityManager(targetClass);
2917
2918 // ensure class initialization
2919 Unsafe.getUnsafe().ensureClassInitialized(targetClass);
2920 return targetClass;
2921 }
2922
2923 /*
2924 * Returns IllegalAccessException due to access violation to the given targetClass.
2925 *
2926 * This method is called by {@link Lookup#accessClass} and {@link Lookup#ensureInitialized}
2927 * which verifies access to a class rather a member.
2928 */
2929 private IllegalAccessException makeAccessException(Class<?> targetClass) {
2930 String message = "access violation: "+ targetClass;
2931 if (this == MethodHandles.publicLookup()) {
2932 message += ", from public Lookup";
2933 } else {
2934 Module m = lookupClass().getModule();
2935 message += ", from " + lookupClass() + " (" + m + ")";
2936 if (prevLookupClass != null) {
2937 message += ", previous lookup " +
2938 prevLookupClass.getName() + " (" + prevLookupClass.getModule() + ")";
2939 }
2940 }
2941 return new IllegalAccessException(message);
2942 }
2943
2944 /**
2945 * Determines if a class can be accessed from the lookup context defined by
2946 * this {@code Lookup} object. The static initializer of the class is not run.
2947 * If {@code targetClass} is an array class, {@code targetClass} is accessible
2948 * if the element type of the array class is accessible. Otherwise,
2949 * {@code targetClass} is determined as accessible as follows.
2950 *
2951 * <p>
2952 * If {@code targetClass} is in the same module as the lookup class,
2953 * the lookup class is {@code LC} in module {@code M1} and
2954 * the previous lookup class is in module {@code M0} or
2955 * {@code null} if not present,
2956 * {@code targetClass} is accessible if and only if one of the following is true:
2957 * <ul>
2958 * <li>If this lookup has {@link #PRIVATE} access, {@code targetClass} is
2959 * {@code LC} or other class in the same nest of {@code LC}.</li>
2960 * <li>If this lookup has {@link #PACKAGE} access, {@code targetClass} is
2961 * in the same runtime package of {@code LC}.</li>
2962 * <li>If this lookup has {@link #MODULE} access, {@code targetClass} is
2963 * a public type in {@code M1}.</li>
2964 * <li>If this lookup has {@link #PUBLIC} access, {@code targetClass} is
2965 * a public type in a package exported by {@code M1} to at least {@code M0}
2966 * if the previous lookup class is present; otherwise, {@code targetClass}
2967 * is a public type in a package exported by {@code M1} unconditionally.</li>
2968 * </ul>
2969 *
2970 * <p>
2971 * Otherwise, if this lookup has {@link #UNCONDITIONAL} access, this lookup
2972 * can access public types in all modules when the type is in a package
2973 * that is exported unconditionally.
2974 * <p>
2975 * Otherwise, {@code targetClass} is in a different module from {@code lookupClass},
2976 * and if this lookup does not have {@code PUBLIC} access, {@code lookupClass}
2977 * is inaccessible.
2978 * <p>
2979 * Otherwise, if this lookup has no {@linkplain #previousLookupClass() previous lookup class},
2980 * {@code M1} is the module containing {@code lookupClass} and
2981 * {@code M2} is the module containing {@code targetClass},
2982 * then {@code targetClass} is accessible if and only if
2983 * <ul>
2984 * <li>{@code M1} reads {@code M2}, and
2985 * <li>{@code targetClass} is public and in a package exported by
2986 * {@code M2} at least to {@code M1}.
2987 * </ul>
2988 * <p>
2989 * Otherwise, if this lookup has a {@linkplain #previousLookupClass() previous lookup class},
2990 * {@code M1} and {@code M2} are as before, and {@code M0} is the module
2991 * containing the previous lookup class, then {@code targetClass} is accessible
2992 * if and only if one of the following is true:
2993 * <ul>
2994 * <li>{@code targetClass} is in {@code M0} and {@code M1}
2995 * {@linkplain Module#reads reads} {@code M0} and the type is
2996 * in a package that is exported to at least {@code M1}.
2997 * <li>{@code targetClass} is in {@code M1} and {@code M0}
2998 * {@linkplain Module#reads reads} {@code M1} and the type is
2999 * in a package that is exported to at least {@code M0}.
3000 * <li>{@code targetClass} is in a third module {@code M2} and both {@code M0}
3001 * and {@code M1} reads {@code M2} and the type is in a package
3002 * that is exported to at least both {@code M0} and {@code M2}.
3003 * </ul>
3004 * <p>
3005 * Otherwise, {@code targetClass} is not accessible.
3006 *
3007 * @param <T> the type of the class to be access-checked
3008 * @param targetClass the class to be access-checked
3009 * @return {@code targetClass} that has been access-checked
3010 * @throws IllegalAccessException if the class is not accessible from the lookup class
3011 * and previous lookup class, if present, using the allowed access modes.
3012 * @throws SecurityException if a security manager is present and it
3013 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3014 * @throws NullPointerException if {@code targetClass} is {@code null}
3015 * @since 9
3016 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
3017 */
3018 public <T> Class<T> accessClass(Class<T> targetClass) throws IllegalAccessException {
3019 if (!isClassAccessible(targetClass)) {
3020 throw makeAccessException(targetClass);
3021 }
3022 checkSecurityManager(targetClass);
3023 return targetClass;
3024 }
3025
3026 /**
3027 * Produces an early-bound method handle for a virtual method.
3028 * It will bypass checks for overriding methods on the receiver,
3029 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
3030 * instruction from within the explicitly specified {@code specialCaller}.
3031 * The type of the method handle will be that of the method,
3032 * with a suitably restricted receiver type prepended.
3033 * (The receiver type will be {@code specialCaller} or a subtype.)
3034 * The method and all its argument types must be accessible
3035 * to the lookup object.
3036 * <p>
3037 * Before method resolution,
3038 * if the explicitly specified caller class is not identical with the
3039 * lookup class, or if this lookup object does not have
3040 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
3041 * privileges, the access fails.
3042 * <p>
3043 * The returned method handle will have
3044 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3045 * the method's variable arity modifier bit ({@code 0x0080}) is set.
3046 * <p style="font-size:smaller;">
3047 * <em>(Note: JVM internal methods named {@value ConstantDescs#INIT_NAME}
3048 * are not visible to this API,
3049 * even though the {@code invokespecial} instruction can refer to them
3050 * in special circumstances. Use {@link #findConstructor findConstructor}
3051 * to access instance initialization methods in a safe manner.)</em>
3052 * <p><b>Example:</b>
3053 * {@snippet lang="java" :
3054 import static java.lang.invoke.MethodHandles.*;
3055 import static java.lang.invoke.MethodType.*;
3056 ...
3057 static class Listie extends ArrayList {
3058 public String toString() { return "[wee Listie]"; }
3059 static Lookup lookup() { return MethodHandles.lookup(); }
3060 }
3061 ...
3062 // no access to constructor via invokeSpecial:
3063 MethodHandle MH_newListie = Listie.lookup()
3064 .findConstructor(Listie.class, methodType(void.class));
3065 Listie l = (Listie) MH_newListie.invokeExact();
3066 try { assertEquals("impossible", Listie.lookup().findSpecial(
3067 Listie.class, "<init>", methodType(void.class), Listie.class));
3068 } catch (NoSuchMethodException ex) { } // OK
3069 // access to super and self methods via invokeSpecial:
3070 MethodHandle MH_super = Listie.lookup().findSpecial(
3071 ArrayList.class, "toString" , methodType(String.class), Listie.class);
3072 MethodHandle MH_this = Listie.lookup().findSpecial(
3073 Listie.class, "toString" , methodType(String.class), Listie.class);
3074 MethodHandle MH_duper = Listie.lookup().findSpecial(
3075 Object.class, "toString" , methodType(String.class), Listie.class);
3076 assertEquals("[]", (String) MH_super.invokeExact(l));
3077 assertEquals(""+l, (String) MH_this.invokeExact(l));
3078 assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method
3079 try { assertEquals("inaccessible", Listie.lookup().findSpecial(
3080 String.class, "toString", methodType(String.class), Listie.class));
3081 } catch (IllegalAccessException ex) { } // OK
3082 Listie subl = new Listie() { public String toString() { return "[subclass]"; } };
3083 assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method
3084 * }
3085 *
3086 * @param refc the class or interface from which the method is accessed
3087 * @param name the name of the method (which must not be "<init>")
3088 * @param type the type of the method, with the receiver argument omitted
3089 * @param specialCaller the proposed calling class to perform the {@code invokespecial}
3090 * @return the desired method handle
3091 * @throws NoSuchMethodException if the method does not exist
3092 * @throws IllegalAccessException if access checking fails,
3093 * or if the method is {@code static},
3094 * or if the method's variable arity modifier bit
3095 * is set and {@code asVarargsCollector} fails
3096 * @throws SecurityException if a security manager is present and it
3097 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3098 * @throws NullPointerException if any argument is null
3099 */
3100 public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,
3101 Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
3102 checkSpecialCaller(specialCaller, refc);
3103 Lookup specialLookup = this.in(specialCaller);
3104 MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type);
3105 return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerLookup(method));
3106 }
3107
3108 /**
3109 * Produces a method handle giving read access to a non-static field.
3110 * The type of the method handle will have a return type of the field's
3111 * value type.
3112 * The method handle's single argument will be the instance containing
3113 * the field.
3114 * Access checking is performed immediately on behalf of the lookup class.
3115 * @param refc the class or interface from which the method is accessed
3116 * @param name the field's name
3117 * @param type the field's type
3118 * @return a method handle which can load values from the field
3119 * @throws NoSuchFieldException if the field does not exist
3120 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
3121 * @throws SecurityException if a security manager is present and it
3122 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3123 * @throws NullPointerException if any argument is null
3124 * @see #findVarHandle(Class, String, Class)
3125 */
3126 public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3127 MemberName field = resolveOrFail(REF_getField, refc, name, type);
3128 return getDirectField(REF_getField, refc, field);
3129 }
3130
3131 /**
3132 * Produces a method handle giving write access to a non-static field.
3133 * The type of the method handle will have a void return type.
3134 * The method handle will take two arguments, the instance containing
3135 * the field, and the value to be stored.
3136 * The second argument will be of the field's value type.
3137 * Access checking is performed immediately on behalf of the lookup class.
3138 * @param refc the class or interface from which the method is accessed
3139 * @param name the field's name
3140 * @param type the field's type
3141 * @return a method handle which can store values into the field
3142 * @throws NoSuchFieldException if the field does not exist
3143 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
3144 * or {@code final}
3145 * @throws SecurityException if a security manager is present and it
3146 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3147 * @throws NullPointerException if any argument is null
3148 * @see #findVarHandle(Class, String, Class)
3149 */
3150 public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3151 MemberName field = resolveOrFail(REF_putField, refc, name, type);
3152 return getDirectField(REF_putField, refc, field);
3153 }
3154
3155 /**
3156 * Produces a VarHandle giving access to a non-static field {@code name}
3157 * of type {@code type} declared in a class of type {@code recv}.
3158 * The VarHandle's variable type is {@code type} and it has one
3159 * coordinate type, {@code recv}.
3160 * <p>
3161 * Access checking is performed immediately on behalf of the lookup
3162 * class.
3163 * <p>
3164 * Certain access modes of the returned VarHandle are unsupported under
3165 * the following conditions:
3166 * <ul>
3167 * <li>if the field is declared {@code final}, then the write, atomic
3168 * update, numeric atomic update, and bitwise atomic update access
3169 * modes are unsupported.
3170 * <li>if the field type is anything other than {@code byte},
3171 * {@code short}, {@code char}, {@code int}, {@code long},
3172 * {@code float}, or {@code double} then numeric atomic update
3173 * access modes are unsupported.
3174 * <li>if the field type is anything other than {@code boolean},
3175 * {@code byte}, {@code short}, {@code char}, {@code int} or
3176 * {@code long} then bitwise atomic update access modes are
3177 * unsupported.
3178 * </ul>
3179 * <p>
3180 * If the field is declared {@code volatile} then the returned VarHandle
3181 * will override access to the field (effectively ignore the
3182 * {@code volatile} declaration) in accordance to its specified
3183 * access modes.
3184 * <p>
3185 * If the field type is {@code float} or {@code double} then numeric
3186 * and atomic update access modes compare values using their bitwise
3187 * representation (see {@link Float#floatToRawIntBits} and
3188 * {@link Double#doubleToRawLongBits}, respectively).
3189 * @apiNote
3190 * Bitwise comparison of {@code float} values or {@code double} values,
3191 * as performed by the numeric and atomic update access modes, differ
3192 * from the primitive {@code ==} operator and the {@link Float#equals}
3193 * and {@link Double#equals} methods, specifically with respect to
3194 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
3195 * Care should be taken when performing a compare and set or a compare
3196 * and exchange operation with such values since the operation may
3197 * unexpectedly fail.
3198 * There are many possible NaN values that are considered to be
3199 * {@code NaN} in Java, although no IEEE 754 floating-point operation
3200 * provided by Java can distinguish between them. Operation failure can
3201 * occur if the expected or witness value is a NaN value and it is
3202 * transformed (perhaps in a platform specific manner) into another NaN
3203 * value, and thus has a different bitwise representation (see
3204 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
3205 * details).
3206 * The values {@code -0.0} and {@code +0.0} have different bitwise
3207 * representations but are considered equal when using the primitive
3208 * {@code ==} operator. Operation failure can occur if, for example, a
3209 * numeric algorithm computes an expected value to be say {@code -0.0}
3210 * and previously computed the witness value to be say {@code +0.0}.
3211 * @param recv the receiver class, of type {@code R}, that declares the
3212 * non-static field
3213 * @param name the field's name
3214 * @param type the field's type, of type {@code T}
3215 * @return a VarHandle giving access to non-static fields.
3216 * @throws NoSuchFieldException if the field does not exist
3217 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
3218 * @throws SecurityException if a security manager is present and it
3219 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3220 * @throws NullPointerException if any argument is null
3221 * @since 9
3222 */
3223 public VarHandle findVarHandle(Class<?> recv, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3224 MemberName getField = resolveOrFail(REF_getField, recv, name, type);
3225 MemberName putField = resolveOrFail(REF_putField, recv, name, type);
3226 return getFieldVarHandle(REF_getField, REF_putField, recv, getField, putField);
3227 }
3228
3229 /**
3230 * Produces a method handle giving read access to a static field.
3231 * The type of the method handle will have a return type of the field's
3232 * value type.
3233 * The method handle will take no arguments.
3234 * Access checking is performed immediately on behalf of the lookup class.
3235 * <p>
3236 * If the returned method handle is invoked, the field's class will
3237 * be initialized, if it has not already been initialized.
3238 * @param refc the class or interface from which the method is accessed
3239 * @param name the field's name
3240 * @param type the field's type
3241 * @return a method handle which can load values from the field
3242 * @throws NoSuchFieldException if the field does not exist
3243 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
3244 * @throws SecurityException if a security manager is present and it
3245 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3246 * @throws NullPointerException if any argument is null
3247 */
3248 public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3249 MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
3250 return getDirectField(REF_getStatic, refc, field);
3251 }
3252
3253 /**
3254 * Produces a method handle giving write access to a static field.
3255 * The type of the method handle will have a void return type.
3256 * The method handle will take a single
3257 * argument, of the field's value type, the value to be stored.
3258 * Access checking is performed immediately on behalf of the lookup class.
3259 * <p>
3260 * If the returned method handle is invoked, the field's class will
3261 * be initialized, if it has not already been initialized.
3262 * @param refc the class or interface from which the method is accessed
3263 * @param name the field's name
3264 * @param type the field's type
3265 * @return a method handle which can store values into the field
3266 * @throws NoSuchFieldException if the field does not exist
3267 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
3268 * or is {@code final}
3269 * @throws SecurityException if a security manager is present and it
3270 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3271 * @throws NullPointerException if any argument is null
3272 */
3273 public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3274 MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
3275 return getDirectField(REF_putStatic, refc, field);
3276 }
3277
3278 /**
3279 * Produces a VarHandle giving access to a static field {@code name} of
3280 * type {@code type} declared in a class of type {@code decl}.
3281 * The VarHandle's variable type is {@code type} and it has no
3282 * coordinate types.
3283 * <p>
3284 * Access checking is performed immediately on behalf of the lookup
3285 * class.
3286 * <p>
3287 * If the returned VarHandle is operated on, the declaring class will be
3288 * initialized, if it has not already been initialized.
3289 * <p>
3290 * Certain access modes of the returned VarHandle are unsupported under
3291 * the following conditions:
3292 * <ul>
3293 * <li>if the field is declared {@code final}, then the write, atomic
3294 * update, numeric atomic update, and bitwise atomic update access
3295 * modes are unsupported.
3296 * <li>if the field type is anything other than {@code byte},
3297 * {@code short}, {@code char}, {@code int}, {@code long},
3298 * {@code float}, or {@code double}, then numeric atomic update
3299 * access modes are unsupported.
3300 * <li>if the field type is anything other than {@code boolean},
3301 * {@code byte}, {@code short}, {@code char}, {@code int} or
3302 * {@code long} then bitwise atomic update access modes are
3303 * unsupported.
3304 * </ul>
3305 * <p>
3306 * If the field is declared {@code volatile} then the returned VarHandle
3307 * will override access to the field (effectively ignore the
3308 * {@code volatile} declaration) in accordance to its specified
3309 * access modes.
3310 * <p>
3311 * If the field type is {@code float} or {@code double} then numeric
3312 * and atomic update access modes compare values using their bitwise
3313 * representation (see {@link Float#floatToRawIntBits} and
3314 * {@link Double#doubleToRawLongBits}, respectively).
3315 * @apiNote
3316 * Bitwise comparison of {@code float} values or {@code double} values,
3317 * as performed by the numeric and atomic update access modes, differ
3318 * from the primitive {@code ==} operator and the {@link Float#equals}
3319 * and {@link Double#equals} methods, specifically with respect to
3320 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
3321 * Care should be taken when performing a compare and set or a compare
3322 * and exchange operation with such values since the operation may
3323 * unexpectedly fail.
3324 * There are many possible NaN values that are considered to be
3325 * {@code NaN} in Java, although no IEEE 754 floating-point operation
3326 * provided by Java can distinguish between them. Operation failure can
3327 * occur if the expected or witness value is a NaN value and it is
3328 * transformed (perhaps in a platform specific manner) into another NaN
3329 * value, and thus has a different bitwise representation (see
3330 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
3331 * details).
3332 * The values {@code -0.0} and {@code +0.0} have different bitwise
3333 * representations but are considered equal when using the primitive
3334 * {@code ==} operator. Operation failure can occur if, for example, a
3335 * numeric algorithm computes an expected value to be say {@code -0.0}
3336 * and previously computed the witness value to be say {@code +0.0}.
3337 * @param decl the class that declares the static field
3338 * @param name the field's name
3339 * @param type the field's type, of type {@code T}
3340 * @return a VarHandle giving access to a static field
3341 * @throws NoSuchFieldException if the field does not exist
3342 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
3343 * @throws SecurityException if a security manager is present and it
3344 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3345 * @throws NullPointerException if any argument is null
3346 * @since 9
3347 */
3348 public VarHandle findStaticVarHandle(Class<?> decl, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3349 MemberName getField = resolveOrFail(REF_getStatic, decl, name, type);
3350 MemberName putField = resolveOrFail(REF_putStatic, decl, name, type);
3351 return getFieldVarHandle(REF_getStatic, REF_putStatic, decl, getField, putField);
3352 }
3353
3354 /**
3355 * Produces an early-bound method handle for a non-static method.
3356 * The receiver must have a supertype {@code defc} in which a method
3357 * of the given name and type is accessible to the lookup class.
3358 * The method and all its argument types must be accessible to the lookup object.
3359 * The type of the method handle will be that of the method,
3360 * without any insertion of an additional receiver parameter.
3361 * The given receiver will be bound into the method handle,
3362 * so that every call to the method handle will invoke the
3363 * requested method on the given receiver.
3364 * <p>
3365 * The returned method handle will have
3366 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3367 * the method's variable arity modifier bit ({@code 0x0080}) is set
3368 * <em>and</em> the trailing array argument is not the only argument.
3369 * (If the trailing array argument is the only argument,
3370 * the given receiver value will be bound to it.)
3371 * <p>
3372 * This is almost equivalent to the following code, with some differences noted below:
3373 * {@snippet lang="java" :
3374 import static java.lang.invoke.MethodHandles.*;
3375 import static java.lang.invoke.MethodType.*;
3376 ...
3377 MethodHandle mh0 = lookup().findVirtual(defc, name, type);
3378 MethodHandle mh1 = mh0.bindTo(receiver);
3379 mh1 = mh1.withVarargs(mh0.isVarargsCollector());
3380 return mh1;
3381 * }
3382 * where {@code defc} is either {@code receiver.getClass()} or a super
3383 * type of that class, in which the requested method is accessible
3384 * to the lookup class.
3385 * (Unlike {@code bind}, {@code bindTo} does not preserve variable arity.
3386 * Also, {@code bindTo} may throw a {@code ClassCastException} in instances where {@code bind} would
3387 * throw an {@code IllegalAccessException}, as in the case where the member is {@code protected} and
3388 * the receiver is restricted by {@code findVirtual} to the lookup class.)
3389 * @param receiver the object from which the method is accessed
3390 * @param name the name of the method
3391 * @param type the type of the method, with the receiver argument omitted
3392 * @return the desired method handle
3393 * @throws NoSuchMethodException if the method does not exist
3394 * @throws IllegalAccessException if access checking fails
3395 * or if the method's variable arity modifier bit
3396 * is set and {@code asVarargsCollector} fails
3397 * @throws SecurityException if a security manager is present and it
3398 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3399 * @throws NullPointerException if any argument is null
3400 * @see MethodHandle#bindTo
3401 * @see #findVirtual
3402 */
3403 public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
3404 Class<? extends Object> refc = receiver.getClass(); // may get NPE
3405 MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
3406 MethodHandle mh = getDirectMethodNoRestrictInvokeSpecial(refc, method, findBoundCallerLookup(method));
3407 if (!mh.type().leadingReferenceParameter().isAssignableFrom(receiver.getClass())) {
3408 throw new IllegalAccessException("The restricted defining class " +
3409 mh.type().leadingReferenceParameter().getName() +
3410 " is not assignable from receiver class " +
3411 receiver.getClass().getName());
3412 }
3413 return mh.bindArgumentL(0, receiver).setVarargs(method);
3414 }
3415
3416 /**
3417 * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
3418 * to <i>m</i>, if the lookup class has permission.
3419 * If <i>m</i> is non-static, the receiver argument is treated as an initial argument.
3420 * If <i>m</i> is virtual, overriding is respected on every call.
3421 * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped.
3422 * The type of the method handle will be that of the method,
3423 * with the receiver type prepended (but only if it is non-static).
3424 * If the method's {@code accessible} flag is not set,
3425 * access checking is performed immediately on behalf of the lookup class.
3426 * If <i>m</i> is not public, do not share the resulting handle with untrusted parties.
3427 * <p>
3428 * The returned method handle will have
3429 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3430 * the method's variable arity modifier bit ({@code 0x0080}) is set.
3431 * <p>
3432 * If <i>m</i> is static, and
3433 * if the returned method handle is invoked, the method's class will
3434 * be initialized, if it has not already been initialized.
3435 * @param m the reflected method
3436 * @return a method handle which can invoke the reflected method
3437 * @throws IllegalAccessException if access checking fails
3438 * or if the method's variable arity modifier bit
3439 * is set and {@code asVarargsCollector} fails
3440 * @throws NullPointerException if the argument is null
3441 */
3442 public MethodHandle unreflect(Method m) throws IllegalAccessException {
3443 if (m.getDeclaringClass() == MethodHandle.class) {
3444 MethodHandle mh = unreflectForMH(m);
3445 if (mh != null) return mh;
3446 }
3447 if (m.getDeclaringClass() == VarHandle.class) {
3448 MethodHandle mh = unreflectForVH(m);
3449 if (mh != null) return mh;
3450 }
3451 MemberName method = new MemberName(m);
3452 byte refKind = method.getReferenceKind();
3453 if (refKind == REF_invokeSpecial)
3454 refKind = REF_invokeVirtual;
3455 assert(method.isMethod());
3456 @SuppressWarnings("deprecation")
3457 Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
3458 return lookup.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method, findBoundCallerLookup(method));
3459 }
3460 private MethodHandle unreflectForMH(Method m) {
3461 // these names require special lookups because they throw UnsupportedOperationException
3462 if (MemberName.isMethodHandleInvokeName(m.getName()))
3463 return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m));
3464 return null;
3465 }
3466 private MethodHandle unreflectForVH(Method m) {
3467 // these names require special lookups because they throw UnsupportedOperationException
3468 if (MemberName.isVarHandleMethodInvokeName(m.getName()))
3469 return MethodHandleImpl.fakeVarHandleInvoke(new MemberName(m));
3470 return null;
3471 }
3472
3473 /**
3474 * Produces a method handle for a reflected method.
3475 * It will bypass checks for overriding methods on the receiver,
3476 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
3477 * instruction from within the explicitly specified {@code specialCaller}.
3478 * The type of the method handle will be that of the method,
3479 * with a suitably restricted receiver type prepended.
3480 * (The receiver type will be {@code specialCaller} or a subtype.)
3481 * If the method's {@code accessible} flag is not set,
3482 * access checking is performed immediately on behalf of the lookup class,
3483 * as if {@code invokespecial} instruction were being linked.
3484 * <p>
3485 * Before method resolution,
3486 * if the explicitly specified caller class is not identical with the
3487 * lookup class, or if this lookup object does not have
3488 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
3489 * privileges, the access fails.
3490 * <p>
3491 * The returned method handle will have
3492 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3493 * the method's variable arity modifier bit ({@code 0x0080}) is set.
3494 * @param m the reflected method
3495 * @param specialCaller the class nominally calling the method
3496 * @return a method handle which can invoke the reflected method
3497 * @throws IllegalAccessException if access checking fails,
3498 * or if the method is {@code static},
3499 * or if the method's variable arity modifier bit
3500 * is set and {@code asVarargsCollector} fails
3501 * @throws NullPointerException if any argument is null
3502 */
3503 public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException {
3504 checkSpecialCaller(specialCaller, m.getDeclaringClass());
3505 Lookup specialLookup = this.in(specialCaller);
3506 MemberName method = new MemberName(m, true);
3507 assert(method.isMethod());
3508 // ignore m.isAccessible: this is a new kind of access
3509 return specialLookup.getDirectMethodNoSecurityManager(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerLookup(method));
3510 }
3511
3512 /**
3513 * Produces a method handle for a reflected constructor.
3514 * The type of the method handle will be that of the constructor,
3515 * with the return type changed to the declaring class.
3516 * The method handle will perform a {@code newInstance} operation,
3517 * creating a new instance of the constructor's class on the
3518 * arguments passed to the method handle.
3519 * <p>
3520 * If the constructor's {@code accessible} flag is not set,
3521 * access checking is performed immediately on behalf of the lookup class.
3522 * <p>
3523 * The returned method handle will have
3524 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3525 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
3526 * <p>
3527 * If the returned method handle is invoked, the constructor's class will
3528 * be initialized, if it has not already been initialized.
3529 * @param c the reflected constructor
3530 * @return a method handle which can invoke the reflected constructor
3531 * @throws IllegalAccessException if access checking fails
3532 * or if the method's variable arity modifier bit
3533 * is set and {@code asVarargsCollector} fails
3534 * @throws NullPointerException if the argument is null
3535 */
3536 public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException {
3537 MemberName ctor = new MemberName(c);
3538 assert(ctor.isObjectConstructor() || ctor.isStaticValueFactoryMethod());
3539 @SuppressWarnings("deprecation")
3540 Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
3541 Class<?> defc = c.getDeclaringClass();
3542 if (ctor.isObjectConstructor()) {
3543 assert(ctor.getMethodType().returnType() == void.class);
3544 return lookup.getDirectConstructorNoSecurityManager(defc, ctor);
3545 } else {
3546 // static init factory is a static method
3547 assert(ctor.isMethod() && ctor.getMethodType().returnType() == defc && ctor.getReferenceKind() == REF_invokeStatic) : ctor.toString();
3548 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // must not be caller-sensitive
3549 return lookup.getDirectMethodNoSecurityManager(ctor.getReferenceKind(), defc, ctor, lookup);
3550 }
3551 }
3552
3553 /**
3554 * Produces a method handle giving read access to a reflected field.
3555 * The type of the method handle will have a return type of the field's
3556 * value type.
3557 * If the field is {@code static}, the method handle will take no arguments.
3558 * Otherwise, its single argument will be the instance containing
3559 * the field.
3560 * If the {@code Field} object's {@code accessible} flag is not set,
3561 * access checking is performed immediately on behalf of the lookup class.
3562 * <p>
3563 * If the field is static, and
3564 * if the returned method handle is invoked, the field's class will
3565 * be initialized, if it has not already been initialized.
3566 * @param f the reflected field
3567 * @return a method handle which can load values from the reflected field
3568 * @throws IllegalAccessException if access checking fails
3569 * @throws NullPointerException if the argument is null
3570 */
3571 public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
3572 return unreflectField(f, false);
3573 }
3574
3575 /**
3576 * Produces a method handle giving write access to a reflected field.
3577 * The type of the method handle will have a void return type.
3578 * If the field is {@code static}, the method handle will take a single
3579 * argument, of the field's value type, the value to be stored.
3580 * Otherwise, the two arguments will be the instance containing
3581 * the field, and the value to be stored.
3582 * If the {@code Field} object's {@code accessible} flag is not set,
3583 * access checking is performed immediately on behalf of the lookup class.
3584 * <p>
3585 * If the field is {@code final}, write access will not be
3586 * allowed and access checking will fail, except under certain
3587 * narrow circumstances documented for {@link Field#set Field.set}.
3588 * A method handle is returned only if a corresponding call to
3589 * the {@code Field} object's {@code set} method could return
3590 * normally. In particular, fields which are both {@code static}
3591 * and {@code final} may never be set.
3592 * <p>
3593 * If the field is {@code static}, and
3594 * if the returned method handle is invoked, the field's class will
3595 * be initialized, if it has not already been initialized.
3596 * @param f the reflected field
3597 * @return a method handle which can store values into the reflected field
3598 * @throws IllegalAccessException if access checking fails,
3599 * or if the field is {@code final} and write access
3600 * is not enabled on the {@code Field} object
3601 * @throws NullPointerException if the argument is null
3602 */
3603 public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
3604 return unreflectField(f, true);
3605 }
3606
3607 private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
3608 MemberName field = new MemberName(f, isSetter);
3609 if (isSetter && field.isFinal()) {
3610 if (field.isTrustedFinalField()) {
3611 String msg = field.isStatic() ? "static final field has no write access"
3612 : "final field has no write access";
3613 throw field.makeAccessException(msg, this);
3614 }
3615 }
3616 assert(isSetter
3617 ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
3618 : MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
3619 @SuppressWarnings("deprecation")
3620 Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
3621 return lookup.getDirectFieldNoSecurityManager(field.getReferenceKind(), f.getDeclaringClass(), field);
3622 }
3623
3624 /**
3625 * Produces a VarHandle giving access to a reflected field {@code f}
3626 * of type {@code T} declared in a class of type {@code R}.
3627 * The VarHandle's variable type is {@code T}.
3628 * If the field is non-static the VarHandle has one coordinate type,
3629 * {@code R}. Otherwise, the field is static, and the VarHandle has no
3630 * coordinate types.
3631 * <p>
3632 * Access checking is performed immediately on behalf of the lookup
3633 * class, regardless of the value of the field's {@code accessible}
3634 * flag.
3635 * <p>
3636 * If the field is static, and if the returned VarHandle is operated
3637 * on, the field's declaring class will be initialized, if it has not
3638 * already been initialized.
3639 * <p>
3640 * Certain access modes of the returned VarHandle are unsupported under
3641 * the following conditions:
3642 * <ul>
3643 * <li>if the field is declared {@code final}, then the write, atomic
3644 * update, numeric atomic update, and bitwise atomic update access
3645 * modes are unsupported.
3646 * <li>if the field type is anything other than {@code byte},
3647 * {@code short}, {@code char}, {@code int}, {@code long},
3648 * {@code float}, or {@code double} then numeric atomic update
3649 * access modes are unsupported.
3650 * <li>if the field type is anything other than {@code boolean},
3651 * {@code byte}, {@code short}, {@code char}, {@code int} or
3652 * {@code long} then bitwise atomic update access modes are
3653 * unsupported.
3654 * </ul>
3655 * <p>
3656 * If the field is declared {@code volatile} then the returned VarHandle
3657 * will override access to the field (effectively ignore the
3658 * {@code volatile} declaration) in accordance to its specified
3659 * access modes.
3660 * <p>
3661 * If the field type is {@code float} or {@code double} then numeric
3662 * and atomic update access modes compare values using their bitwise
3663 * representation (see {@link Float#floatToRawIntBits} and
3664 * {@link Double#doubleToRawLongBits}, respectively).
3665 * @apiNote
3666 * Bitwise comparison of {@code float} values or {@code double} values,
3667 * as performed by the numeric and atomic update access modes, differ
3668 * from the primitive {@code ==} operator and the {@link Float#equals}
3669 * and {@link Double#equals} methods, specifically with respect to
3670 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
3671 * Care should be taken when performing a compare and set or a compare
3672 * and exchange operation with such values since the operation may
3673 * unexpectedly fail.
3674 * There are many possible NaN values that are considered to be
3675 * {@code NaN} in Java, although no IEEE 754 floating-point operation
3676 * provided by Java can distinguish between them. Operation failure can
3677 * occur if the expected or witness value is a NaN value and it is
3678 * transformed (perhaps in a platform specific manner) into another NaN
3679 * value, and thus has a different bitwise representation (see
3680 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
3681 * details).
3682 * The values {@code -0.0} and {@code +0.0} have different bitwise
3683 * representations but are considered equal when using the primitive
3684 * {@code ==} operator. Operation failure can occur if, for example, a
3685 * numeric algorithm computes an expected value to be say {@code -0.0}
3686 * and previously computed the witness value to be say {@code +0.0}.
3687 * @param f the reflected field, with a field of type {@code T}, and
3688 * a declaring class of type {@code R}
3689 * @return a VarHandle giving access to non-static fields or a static
3690 * field
3691 * @throws IllegalAccessException if access checking fails
3692 * @throws NullPointerException if the argument is null
3693 * @since 9
3694 */
3695 public VarHandle unreflectVarHandle(Field f) throws IllegalAccessException {
3696 MemberName getField = new MemberName(f, false);
3697 MemberName putField = new MemberName(f, true);
3698 return getFieldVarHandleNoSecurityManager(getField.getReferenceKind(), putField.getReferenceKind(),
3699 f.getDeclaringClass(), getField, putField);
3700 }
3701
3702 /**
3703 * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
3704 * created by this lookup object or a similar one.
3705 * Security and access checks are performed to ensure that this lookup object
3706 * is capable of reproducing the target method handle.
3707 * This means that the cracking may fail if target is a direct method handle
3708 * but was created by an unrelated lookup object.
3709 * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a>
3710 * and was created by a lookup object for a different class.
3711 * @param target a direct method handle to crack into symbolic reference components
3712 * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object
3713 * @throws SecurityException if a security manager is present and it
3714 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3715 * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails
3716 * @throws NullPointerException if the target is {@code null}
3717 * @see MethodHandleInfo
3718 * @since 1.8
3719 */
3720 public MethodHandleInfo revealDirect(MethodHandle target) {
3721 if (!target.isCrackable()) {
3722 throw newIllegalArgumentException("not a direct method handle");
3723 }
3724 MemberName member = target.internalMemberName();
3725 Class<?> defc = member.getDeclaringClass();
3726 byte refKind = member.getReferenceKind();
3727 assert(MethodHandleNatives.refKindIsValid(refKind));
3728 if (refKind == REF_invokeSpecial && !target.isInvokeSpecial())
3729 // Devirtualized method invocation is usually formally virtual.
3730 // To avoid creating extra MemberName objects for this common case,
3731 // we encode this extra degree of freedom using MH.isInvokeSpecial.
3732 refKind = REF_invokeVirtual;
3733 if (refKind == REF_invokeVirtual && defc.isInterface())
3734 // Symbolic reference is through interface but resolves to Object method (toString, etc.)
3735 refKind = REF_invokeInterface;
3736 // Check SM permissions and member access before cracking.
3737 try {
3738 checkAccess(refKind, defc, member);
3739 checkSecurityManager(defc, member);
3740 } catch (IllegalAccessException ex) {
3741 throw new IllegalArgumentException(ex);
3742 }
3743 if (allowedModes != TRUSTED && member.isCallerSensitive()) {
3744 Class<?> callerClass = target.internalCallerClass();
3745 if ((lookupModes() & ORIGINAL) == 0 || callerClass != lookupClass())
3746 throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass);
3747 }
3748 // Produce the handle to the results.
3749 return new InfoFromMemberName(this, member, refKind);
3750 }
3751
3752 /// Helper methods, all package-private.
3753
3754 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3755 checkSymbolicClass(refc); // do this before attempting to resolve
3756 Objects.requireNonNull(name);
3757 Objects.requireNonNull(type);
3758 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), allowedModes,
3759 NoSuchFieldException.class);
3760 }
3761
3762 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
3763 checkSymbolicClass(refc); // do this before attempting to resolve
3764 Objects.requireNonNull(type);
3765 checkMethodName(refKind, name); // implicit null-check of name
3766 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), allowedModes,
3767 NoSuchMethodException.class);
3768 }
3769
3770 MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException {
3771 checkSymbolicClass(member.getDeclaringClass()); // do this before attempting to resolve
3772 Objects.requireNonNull(member.getName());
3773 Objects.requireNonNull(member.getType());
3774 return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(), allowedModes,
3775 ReflectiveOperationException.class);
3776 }
3777
3778 MemberName resolveOrNull(byte refKind, MemberName member) {
3779 // do this before attempting to resolve
3780 if (!isClassAccessible(member.getDeclaringClass())) {
3781 return null;
3782 }
3783 Objects.requireNonNull(member.getName());
3784 Objects.requireNonNull(member.getType());
3785 return IMPL_NAMES.resolveOrNull(refKind, member, lookupClassOrNull(), allowedModes);
3786 }
3787
3788 MemberName resolveOrNull(byte refKind, Class<?> refc, String name, MethodType type) {
3789 // do this before attempting to resolve
3790 if (!isClassAccessible(refc)) {
3791 return null;
3792 }
3793 Objects.requireNonNull(type);
3794 // implicit null-check of name
3795 if (isIllegalMethodName(refKind, name)) {
3796 return null;
3797 }
3798
3799 return IMPL_NAMES.resolveOrNull(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), allowedModes);
3800 }
3801
3802 void checkSymbolicClass(Class<?> refc) throws IllegalAccessException {
3803 if (!isClassAccessible(refc)) {
3804 throw new MemberName(refc).makeAccessException("symbolic reference class is not accessible", this);
3805 }
3806 }
3807
3808 boolean isClassAccessible(Class<?> refc) {
3809 Objects.requireNonNull(refc);
3810 Class<?> caller = lookupClassOrNull();
3811 Class<?> type = refc;
3812 while (type.isArray()) {
3813 type = type.getComponentType();
3814 }
3815 return caller == null || VerifyAccess.isClassAccessible(type, caller, prevLookupClass, allowedModes);
3816 }
3817
3818 /*
3819 * "<init>" can only be invoked via invokespecial
3820 * "<vnew>" factory can only invoked via invokestatic
3821 */
3822 boolean isIllegalMethodName(byte refKind, String name) {
3823 if (name.startsWith("<")) {
3824 return MemberName.VALUE_FACTORY_NAME.equals(name) ? refKind != REF_invokeStatic
3825 : refKind != REF_newInvokeSpecial;
3826 }
3827 return false;
3828 }
3829
3830 /** Check name for an illegal leading "<" character. */
3831 void checkMethodName(byte refKind, String name) throws NoSuchMethodException {
3832 if (isIllegalMethodName(refKind, name)) {
3833 throw new NoSuchMethodException("illegal method name: " + name + " " + refKind);
3834 }
3835 }
3836
3837 /**
3838 * Find my trustable caller class if m is a caller sensitive method.
3839 * If this lookup object has original full privilege access, then the caller class is the lookupClass.
3840 * Otherwise, if m is caller-sensitive, throw IllegalAccessException.
3841 */
3842 Lookup findBoundCallerLookup(MemberName m) throws IllegalAccessException {
3843 if (MethodHandleNatives.isCallerSensitive(m) && (lookupModes() & ORIGINAL) == 0) {
3844 // Only lookups with full privilege access are allowed to resolve caller-sensitive methods
3845 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
3846 }
3847 return this;
3848 }
3849
3850 /**
3851 * Returns {@code true} if this lookup has {@code PRIVATE} and {@code MODULE} access.
3852 * @return {@code true} if this lookup has {@code PRIVATE} and {@code MODULE} access.
3853 *
3854 * @deprecated This method was originally designed to test {@code PRIVATE} access
3855 * that implies full privilege access but {@code MODULE} access has since become
3856 * independent of {@code PRIVATE} access. It is recommended to call
3857 * {@link #hasFullPrivilegeAccess()} instead.
3858 * @since 9
3859 */
3860 @Deprecated(since="14")
3861 public boolean hasPrivateAccess() {
3862 return hasFullPrivilegeAccess();
3863 }
3864
3865 /**
3866 * Returns {@code true} if this lookup has <em>full privilege access</em>,
3867 * i.e. {@code PRIVATE} and {@code MODULE} access.
3868 * A {@code Lookup} object must have full privilege access in order to
3869 * access all members that are allowed to the
3870 * {@linkplain #lookupClass() lookup class}.
3871 *
3872 * @return {@code true} if this lookup has full privilege access.
3873 * @since 14
3874 * @see <a href="MethodHandles.Lookup.html#privacc">private and module access</a>
3875 */
3876 public boolean hasFullPrivilegeAccess() {
3877 return (allowedModes & (PRIVATE|MODULE)) == (PRIVATE|MODULE);
3878 }
3879
3880 /**
3881 * Perform steps 1 and 2b <a href="MethodHandles.Lookup.html#secmgr">access checks</a>
3882 * for ensureInitialized, findClass or accessClass.
3883 */
3884 void checkSecurityManager(Class<?> refc) {
3885 if (allowedModes == TRUSTED) return;
3886
3887 @SuppressWarnings("removal")
3888 SecurityManager smgr = System.getSecurityManager();
3889 if (smgr == null) return;
3890
3891 // Step 1:
3892 boolean fullPrivilegeLookup = hasFullPrivilegeAccess();
3893 if (!fullPrivilegeLookup ||
3894 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
3895 ReflectUtil.checkPackageAccess(refc);
3896 }
3897
3898 // Step 2b:
3899 if (!fullPrivilegeLookup) {
3900 smgr.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
3901 }
3902 }
3903
3904 /**
3905 * Perform steps 1, 2a and 3 <a href="MethodHandles.Lookup.html#secmgr">access checks</a>.
3906 * Determines a trustable caller class to compare with refc, the symbolic reference class.
3907 * If this lookup object has full privilege access except original access,
3908 * then the caller class is the lookupClass.
3909 *
3910 * Lookup object created by {@link MethodHandles#privateLookupIn(Class, Lookup)}
3911 * from the same module skips the security permission check.
3912 */
3913 void checkSecurityManager(Class<?> refc, MemberName m) {
3914 Objects.requireNonNull(refc);
3915 Objects.requireNonNull(m);
3916
3917 if (allowedModes == TRUSTED) return;
3918
3919 @SuppressWarnings("removal")
3920 SecurityManager smgr = System.getSecurityManager();
3921 if (smgr == null) return;
3922
3923 // Step 1:
3924 boolean fullPrivilegeLookup = hasFullPrivilegeAccess();
3925 if (!fullPrivilegeLookup ||
3926 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
3927 ReflectUtil.checkPackageAccess(refc);
3928 }
3929
3930 // Step 2a:
3931 if (m.isPublic()) return;
3932 if (!fullPrivilegeLookup) {
3933 smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION);
3934 }
3935
3936 // Step 3:
3937 Class<?> defc = m.getDeclaringClass();
3938 if (!fullPrivilegeLookup && PrimitiveClass.asPrimaryType(defc) != PrimitiveClass.asPrimaryType(refc)) {
3939 ReflectUtil.checkPackageAccess(defc);
3940 }
3941 }
3942
3943 void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
3944 boolean wantStatic = (refKind == REF_invokeStatic);
3945 String message;
3946 if (m.isObjectConstructor())
3947 message = "expected a method, not a constructor";
3948 else if (!m.isMethod())
3949 message = "expected a method";
3950 else if (wantStatic != m.isStatic())
3951 message = wantStatic ? "expected a static method" : "expected a non-static method";
3952 else
3953 { checkAccess(refKind, refc, m); return; }
3954 throw m.makeAccessException(message, this);
3955 }
3956
3957 void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
3958 boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
3959 String message;
3960 if (wantStatic != m.isStatic())
3961 message = wantStatic ? "expected a static field" : "expected a non-static field";
3962 else
3963 { checkAccess(refKind, refc, m); return; }
3964 throw m.makeAccessException(message, this);
3965 }
3966
3967 private boolean isArrayClone(byte refKind, Class<?> refc, MemberName m) {
3968 return Modifier.isProtected(m.getModifiers()) &&
3969 refKind == REF_invokeVirtual &&
3970 m.getDeclaringClass() == Object.class &&
3971 m.getName().equals("clone") &&
3972 refc.isArray();
3973 }
3974
3975 /** Check public/protected/private bits on the symbolic reference class and its member. */
3976 void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
3977 assert(m.referenceKindIsConsistentWith(refKind) &&
3978 MethodHandleNatives.refKindIsValid(refKind) &&
3979 (MethodHandleNatives.refKindIsField(refKind) == m.isField()));
3980 int allowedModes = this.allowedModes;
3981 if (allowedModes == TRUSTED) return;
3982 int mods = m.getModifiers();
3983 if (isArrayClone(refKind, refc, m)) {
3984 // The JVM does this hack also.
3985 // (See ClassVerifier::verify_invoke_instructions
3986 // and LinkResolver::check_method_accessability.)
3987 // Because the JVM does not allow separate methods on array types,
3988 // there is no separate method for int[].clone.
3989 // All arrays simply inherit Object.clone.
3990 // But for access checking logic, we make Object.clone
3991 // (normally protected) appear to be public.
3992 // Later on, when the DirectMethodHandle is created,
3993 // its leading argument will be restricted to the
3994 // requested array type.
3995 // N.B. The return type is not adjusted, because
3996 // that is *not* the bytecode behavior.
3997 mods ^= Modifier.PROTECTED | Modifier.PUBLIC;
3998 }
3999 if (Modifier.isProtected(mods) && refKind == REF_newInvokeSpecial) {
4000 // cannot "new" a protected ctor in a different package
4001 mods ^= Modifier.PROTECTED;
4002 }
4003 if (Modifier.isFinal(mods) &&
4004 MethodHandleNatives.refKindIsSetter(refKind))
4005 throw m.makeAccessException("unexpected set of a final field", this);
4006 int requestedModes = fixmods(mods); // adjust 0 => PACKAGE
4007 if ((requestedModes & allowedModes) != 0) {
4008 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
4009 mods, lookupClass(), previousLookupClass(), allowedModes))
4010 return;
4011 } else {
4012 // Protected members can also be checked as if they were package-private.
4013 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
4014 && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
4015 return;
4016 }
4017 throw m.makeAccessException(accessFailedMessage(refc, m), this);
4018 }
4019
4020 String accessFailedMessage(Class<?> refc, MemberName m) {
4021 Class<?> defc = m.getDeclaringClass();
4022 int mods = m.getModifiers();
4023 // check the class first:
4024 boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
4025 (PrimitiveClass.asPrimaryType(defc) == PrimitiveClass.asPrimaryType(refc) ||
4026 Modifier.isPublic(refc.getModifiers())));
4027 if (!classOK && (allowedModes & PACKAGE) != 0) {
4028 // ignore previous lookup class to check if default package access
4029 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), null, FULL_POWER_MODES) &&
4030 (PrimitiveClass.asPrimaryType(defc) == PrimitiveClass.asPrimaryType(refc) ||
4031 VerifyAccess.isClassAccessible(refc, lookupClass(), null, FULL_POWER_MODES)));
4032 }
4033 if (!classOK)
4034 return "class is not public";
4035 if (Modifier.isPublic(mods))
4036 return "access to public member failed"; // (how?, module not readable?)
4037 if (Modifier.isPrivate(mods))
4038 return "member is private";
4039 if (Modifier.isProtected(mods))
4040 return "member is protected";
4041 return "member is private to package";
4042 }
4043
4044 private void checkSpecialCaller(Class<?> specialCaller, Class<?> refc) throws IllegalAccessException {
4045 int allowedModes = this.allowedModes;
4046 if (allowedModes == TRUSTED) return;
4047 if ((lookupModes() & PRIVATE) == 0
4048 || (specialCaller != lookupClass()
4049 // ensure non-abstract methods in superinterfaces can be special-invoked
4050 && !(refc != null && refc.isInterface() && refc.isAssignableFrom(specialCaller))))
4051 throw new MemberName(specialCaller).
4052 makeAccessException("no private access for invokespecial", this);
4053 }
4054
4055 private boolean restrictProtectedReceiver(MemberName method) {
4056 // The accessing class only has the right to use a protected member
4057 // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc.
4058 if (!method.isProtected() || method.isStatic()
4059 || allowedModes == TRUSTED
4060 || method.getDeclaringClass() == lookupClass()
4061 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass()))
4062 return false;
4063 return true;
4064 }
4065 private MethodHandle restrictReceiver(MemberName method, DirectMethodHandle mh, Class<?> caller) throws IllegalAccessException {
4066 assert(!method.isStatic());
4067 // receiver type of mh is too wide; narrow to caller
4068 if (!method.getDeclaringClass().isAssignableFrom(caller)) {
4069 throw method.makeAccessException("caller class must be a subclass below the method", caller);
4070 }
4071 MethodType rawType = mh.type();
4072 if (caller.isAssignableFrom(rawType.parameterType(0))) return mh; // no need to restrict; already narrow
4073 MethodType narrowType = rawType.changeParameterType(0, caller);
4074 assert(!mh.isVarargsCollector()); // viewAsType will lose varargs-ness
4075 assert(mh.viewAsTypeChecks(narrowType, true));
4076 return mh.copyWith(narrowType, mh.form);
4077 }
4078
4079 /** Check access and get the requested method. */
4080 private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException {
4081 final boolean doRestrict = true;
4082 final boolean checkSecurity = true;
4083 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerLookup);
4084 }
4085 /** Check access and get the requested method, for invokespecial with no restriction on the application of narrowing rules. */
4086 private MethodHandle getDirectMethodNoRestrictInvokeSpecial(Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException {
4087 final boolean doRestrict = false;
4088 final boolean checkSecurity = true;
4089 return getDirectMethodCommon(REF_invokeSpecial, refc, method, checkSecurity, doRestrict, callerLookup);
4090 }
4091 /** Check access and get the requested method, eliding security manager checks. */
4092 private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException {
4093 final boolean doRestrict = true;
4094 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
4095 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerLookup);
4096 }
4097 /** Common code for all methods; do not call directly except from immediately above. */
4098 private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method,
4099 boolean checkSecurity,
4100 boolean doRestrict,
4101 Lookup boundCaller) throws IllegalAccessException {
4102 checkMethod(refKind, refc, method);
4103 // Optionally check with the security manager; this isn't needed for unreflect* calls.
4104 if (checkSecurity)
4105 checkSecurityManager(refc, method);
4106 assert(!method.isMethodHandleInvoke());
4107 if (refKind == REF_invokeSpecial &&
4108 refc != lookupClass() &&
4109 !refc.isInterface() && !lookupClass().isInterface() &&
4110 refc != lookupClass().getSuperclass() &&
4111 refc.isAssignableFrom(lookupClass())) {
4112 assert(!method.getName().equals(ConstantDescs.INIT_NAME)); // not this code path
4113
4114 // Per JVMS 6.5, desc. of invokespecial instruction:
4115 // If the method is in a superclass of the LC,
4116 // and if our original search was above LC.super,
4117 // repeat the search (symbolic lookup) from LC.super
4118 // and continue with the direct superclass of that class,
4119 // and so forth, until a match is found or no further superclasses exist.
4120 // FIXME: MemberName.resolve should handle this instead.
4121 Class<?> refcAsSuper = lookupClass();
4122 MemberName m2;
4123 do {
4124 refcAsSuper = refcAsSuper.getSuperclass();
4125 m2 = new MemberName(refcAsSuper,
4126 method.getName(),
4127 method.getMethodType(),
4128 REF_invokeSpecial);
4129 m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull(), allowedModes);
4130 } while (m2 == null && // no method is found yet
4131 refc != refcAsSuper); // search up to refc
4132 if (m2 == null) throw new InternalError(method.toString());
4133 method = m2;
4134 refc = refcAsSuper;
4135 // redo basic checks
4136 checkMethod(refKind, refc, method);
4137 }
4138 DirectMethodHandle dmh = DirectMethodHandle.make(refKind, refc, method, lookupClass());
4139 MethodHandle mh = dmh;
4140 // Optionally narrow the receiver argument to lookupClass using restrictReceiver.
4141 if ((doRestrict && refKind == REF_invokeSpecial) ||
4142 (MethodHandleNatives.refKindHasReceiver(refKind) &&
4143 restrictProtectedReceiver(method) &&
4144 // All arrays simply inherit the protected Object.clone method.
4145 // The leading argument is already restricted to the requested
4146 // array type (not the lookup class).
4147 !isArrayClone(refKind, refc, method))) {
4148 mh = restrictReceiver(method, dmh, lookupClass());
4149 }
4150 mh = maybeBindCaller(method, mh, boundCaller);
4151 mh = mh.setVarargs(method);
4152 return mh;
4153 }
4154 private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh, Lookup boundCaller)
4155 throws IllegalAccessException {
4156 if (boundCaller.allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method))
4157 return mh;
4158
4159 // boundCaller must have full privilege access.
4160 // It should have been checked by findBoundCallerLookup. Safe to check this again.
4161 if ((boundCaller.lookupModes() & ORIGINAL) == 0)
4162 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
4163
4164 assert boundCaller.hasFullPrivilegeAccess();
4165
4166 MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, boundCaller.lookupClass);
4167 // Note: caller will apply varargs after this step happens.
4168 return cbmh;
4169 }
4170
4171 /** Check access and get the requested field. */
4172 private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
4173 final boolean checkSecurity = true;
4174 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
4175 }
4176 /** Check access and get the requested field, eliding security manager checks. */
4177 private MethodHandle getDirectFieldNoSecurityManager(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
4178 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
4179 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
4180 }
4181 /** Common code for all fields; do not call directly except from immediately above. */
4182 private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field,
4183 boolean checkSecurity) throws IllegalAccessException {
4184 checkField(refKind, refc, field);
4185 // Optionally check with the security manager; this isn't needed for unreflect* calls.
4186 if (checkSecurity)
4187 checkSecurityManager(refc, field);
4188 DirectMethodHandle dmh = DirectMethodHandle.make(refc, field);
4189 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) &&
4190 restrictProtectedReceiver(field));
4191 if (doRestrict)
4192 return restrictReceiver(field, dmh, lookupClass());
4193 return dmh;
4194 }
4195 private VarHandle getFieldVarHandle(byte getRefKind, byte putRefKind,
4196 Class<?> refc, MemberName getField, MemberName putField)
4197 throws IllegalAccessException {
4198 final boolean checkSecurity = true;
4199 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
4200 }
4201 private VarHandle getFieldVarHandleNoSecurityManager(byte getRefKind, byte putRefKind,
4202 Class<?> refc, MemberName getField, MemberName putField)
4203 throws IllegalAccessException {
4204 final boolean checkSecurity = false;
4205 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
4206 }
4207 private VarHandle getFieldVarHandleCommon(byte getRefKind, byte putRefKind,
4208 Class<?> refc, MemberName getField, MemberName putField,
4209 boolean checkSecurity) throws IllegalAccessException {
4210 assert getField.isStatic() == putField.isStatic();
4211 assert getField.isGetter() && putField.isSetter();
4212 assert MethodHandleNatives.refKindIsStatic(getRefKind) == MethodHandleNatives.refKindIsStatic(putRefKind);
4213 assert MethodHandleNatives.refKindIsGetter(getRefKind) && MethodHandleNatives.refKindIsSetter(putRefKind);
4214
4215 checkField(getRefKind, refc, getField);
4216 if (checkSecurity)
4217 checkSecurityManager(refc, getField);
4218
4219 if (!putField.isFinal()) {
4220 // A VarHandle does not support updates to final fields, any
4221 // such VarHandle to a final field will be read-only and
4222 // therefore the following write-based accessibility checks are
4223 // only required for non-final fields
4224 checkField(putRefKind, refc, putField);
4225 if (checkSecurity)
4226 checkSecurityManager(refc, putField);
4227 }
4228
4229 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(getRefKind) &&
4230 restrictProtectedReceiver(getField));
4231 if (doRestrict) {
4232 assert !getField.isStatic();
4233 // receiver type of VarHandle is too wide; narrow to caller
4234 if (!getField.getDeclaringClass().isAssignableFrom(lookupClass())) {
4235 throw getField.makeAccessException("caller class must be a subclass below the method", lookupClass());
4236 }
4237 refc = lookupClass();
4238 }
4239 return VarHandles.makeFieldHandle(getField, refc,
4240 this.allowedModes == TRUSTED && !getField.isTrustedFinalField());
4241 }
4242 /** Check access and get the requested constructor. */
4243 private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException {
4244 final boolean checkSecurity = true;
4245 return getDirectConstructorCommon(refc, ctor, checkSecurity);
4246 }
4247 /** Check access and get the requested constructor, eliding security manager checks. */
4248 private MethodHandle getDirectConstructorNoSecurityManager(Class<?> refc, MemberName ctor) throws IllegalAccessException {
4249 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
4250 return getDirectConstructorCommon(refc, ctor, checkSecurity);
4251 }
4252 /** Common code for all constructors; do not call directly except from immediately above. */
4253 private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor,
4254 boolean checkSecurity) throws IllegalAccessException {
4255 assert(ctor.isObjectConstructor());
4256 checkAccess(REF_newInvokeSpecial, refc, ctor);
4257 // Optionally check with the security manager; this isn't needed for unreflect* calls.
4258 if (checkSecurity)
4259 checkSecurityManager(refc, ctor);
4260 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
4261 return DirectMethodHandle.make(ctor).setVarargs(ctor);
4262 }
4263
4264 /** Hook called from the JVM (via MethodHandleNatives) to link MH constants:
4265 */
4266 /*non-public*/
4267 MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type)
4268 throws ReflectiveOperationException {
4269 if (!(type instanceof Class || type instanceof MethodType))
4270 throw new InternalError("unresolved MemberName");
4271 MemberName member = new MemberName(refKind, defc, name, type);
4272 MethodHandle mh = LOOKASIDE_TABLE.get(member);
4273 if (mh != null) {
4274 checkSymbolicClass(defc);
4275 return mh;
4276 }
4277 if (defc == MethodHandle.class && refKind == REF_invokeVirtual) {
4278 // Treat MethodHandle.invoke and invokeExact specially.
4279 mh = findVirtualForMH(member.getName(), member.getMethodType());
4280 if (mh != null) {
4281 return mh;
4282 }
4283 } else if (defc == VarHandle.class && refKind == REF_invokeVirtual) {
4284 // Treat signature-polymorphic methods on VarHandle specially.
4285 mh = findVirtualForVH(member.getName(), member.getMethodType());
4286 if (mh != null) {
4287 return mh;
4288 }
4289 }
4290 MemberName resolved = resolveOrFail(refKind, member);
4291 mh = getDirectMethodForConstant(refKind, defc, resolved);
4292 if (mh instanceof DirectMethodHandle dmh
4293 && canBeCached(refKind, defc, resolved)) {
4294 MemberName key = mh.internalMemberName();
4295 if (key != null) {
4296 key = key.asNormalOriginal();
4297 }
4298 if (member.equals(key)) { // better safe than sorry
4299 LOOKASIDE_TABLE.put(key, dmh);
4300 }
4301 }
4302 return mh;
4303 }
4304 private boolean canBeCached(byte refKind, Class<?> defc, MemberName member) {
4305 if (refKind == REF_invokeSpecial) {
4306 return false;
4307 }
4308 if (!Modifier.isPublic(defc.getModifiers()) ||
4309 !Modifier.isPublic(member.getDeclaringClass().getModifiers()) ||
4310 !member.isPublic() ||
4311 member.isCallerSensitive()) {
4312 return false;
4313 }
4314 ClassLoader loader = defc.getClassLoader();
4315 if (loader != null) {
4316 ClassLoader sysl = ClassLoader.getSystemClassLoader();
4317 boolean found = false;
4318 while (sysl != null) {
4319 if (loader == sysl) { found = true; break; }
4320 sysl = sysl.getParent();
4321 }
4322 if (!found) {
4323 return false;
4324 }
4325 }
4326 try {
4327 MemberName resolved2 = publicLookup().resolveOrNull(refKind,
4328 new MemberName(refKind, defc, member.getName(), member.getType()));
4329 if (resolved2 == null) {
4330 return false;
4331 }
4332 checkSecurityManager(defc, resolved2);
4333 } catch (SecurityException ex) {
4334 return false;
4335 }
4336 return true;
4337 }
4338 private MethodHandle getDirectMethodForConstant(byte refKind, Class<?> defc, MemberName member)
4339 throws ReflectiveOperationException {
4340 if (MethodHandleNatives.refKindIsField(refKind)) {
4341 return getDirectFieldNoSecurityManager(refKind, defc, member);
4342 } else if (MethodHandleNatives.refKindIsMethod(refKind)) {
4343 return getDirectMethodNoSecurityManager(refKind, defc, member, findBoundCallerLookup(member));
4344 } else if (refKind == REF_newInvokeSpecial) {
4345 return getDirectConstructorNoSecurityManager(defc, member);
4346 }
4347 // oops
4348 throw newIllegalArgumentException("bad MethodHandle constant #"+member);
4349 }
4350
4351 static ConcurrentHashMap<MemberName, DirectMethodHandle> LOOKASIDE_TABLE = new ConcurrentHashMap<>();
4352 }
4353
4354 /**
4355 * Produces a method handle constructing arrays of a desired type,
4356 * as if by the {@code anewarray} bytecode.
4357 * The return type of the method handle will be the array type.
4358 * The type of its sole argument will be {@code int}, which specifies the size of the array.
4359 *
4360 * <p> If the returned method handle is invoked with a negative
4361 * array size, a {@code NegativeArraySizeException} will be thrown.
4362 *
4363 * @param arrayClass an array type
4364 * @return a method handle which can create arrays of the given type
4365 * @throws NullPointerException if the argument is {@code null}
4366 * @throws IllegalArgumentException if {@code arrayClass} is not an array type
4367 * @see java.lang.reflect.Array#newInstance(Class, int)
4368 * @jvms 6.5 {@code anewarray} Instruction
4369 * @since 9
4370 */
4371 public static MethodHandle arrayConstructor(Class<?> arrayClass) throws IllegalArgumentException {
4372 if (!arrayClass.isArray()) {
4373 throw newIllegalArgumentException("not an array class: " + arrayClass.getName());
4374 }
4375 MethodHandle ani = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_Array_newInstance).
4376 bindTo(arrayClass.getComponentType());
4377 return ani.asType(ani.type().changeReturnType(arrayClass));
4378 }
4379
4380 /**
4381 * Produces a method handle returning the length of an array,
4382 * as if by the {@code arraylength} bytecode.
4383 * The type of the method handle will have {@code int} as return type,
4384 * and its sole argument will be the array type.
4385 *
4386 * <p> If the returned method handle is invoked with a {@code null}
4387 * array reference, a {@code NullPointerException} will be thrown.
4388 *
4389 * @param arrayClass an array type
4390 * @return a method handle which can retrieve the length of an array of the given array type
4391 * @throws NullPointerException if the argument is {@code null}
4392 * @throws IllegalArgumentException if arrayClass is not an array type
4393 * @jvms 6.5 {@code arraylength} Instruction
4394 * @since 9
4395 */
4396 public static MethodHandle arrayLength(Class<?> arrayClass) throws IllegalArgumentException {
4397 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.LENGTH);
4398 }
4399
4400 /**
4401 * Produces a method handle giving read access to elements of an array,
4402 * as if by the {@code aaload} bytecode.
4403 * The type of the method handle will have a return type of the array's
4404 * element type. Its first argument will be the array type,
4405 * and the second will be {@code int}.
4406 *
4407 * <p> When the returned method handle is invoked,
4408 * the array reference and array index are checked.
4409 * A {@code NullPointerException} will be thrown if the array reference
4410 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
4411 * thrown if the index is negative or if it is greater than or equal to
4412 * the length of the array.
4413 *
4414 * @param arrayClass an array type
4415 * @return a method handle which can load values from the given array type
4416 * @throws NullPointerException if the argument is null
4417 * @throws IllegalArgumentException if arrayClass is not an array type
4418 * @jvms 6.5 {@code aaload} Instruction
4419 */
4420 public static MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException {
4421 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.GET);
4422 }
4423
4424 /**
4425 * Produces a method handle giving write access to elements of an array,
4426 * as if by the {@code astore} bytecode.
4427 * The type of the method handle will have a void return type.
4428 * Its last argument will be the array's element type.
4429 * The first and second arguments will be the array type and int.
4430 *
4431 * <p> When the returned method handle is invoked,
4432 * the array reference and array index are checked.
4433 * A {@code NullPointerException} will be thrown if the array reference
4434 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
4435 * thrown if the index is negative or if it is greater than or equal to
4436 * the length of the array.
4437 *
4438 * @param arrayClass the class of an array
4439 * @return a method handle which can store values into the array type
4440 * @throws NullPointerException if the argument is null
4441 * @throws IllegalArgumentException if arrayClass is not an array type
4442 * @jvms 6.5 {@code aastore} Instruction
4443 */
4444 public static MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException {
4445 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.SET);
4446 }
4447
4448 /**
4449 * Produces a VarHandle giving access to elements of an array of type
4450 * {@code arrayClass}. The VarHandle's variable type is the component type
4451 * of {@code arrayClass} and the list of coordinate types is
4452 * {@code (arrayClass, int)}, where the {@code int} coordinate type
4453 * corresponds to an argument that is an index into an array.
4454 * <p>
4455 * Certain access modes of the returned VarHandle are unsupported under
4456 * the following conditions:
4457 * <ul>
4458 * <li>if the component type is anything other than {@code byte},
4459 * {@code short}, {@code char}, {@code int}, {@code long},
4460 * {@code float}, or {@code double} then numeric atomic update access
4461 * modes are unsupported.
4462 * <li>if the component type is anything other than {@code boolean},
4463 * {@code byte}, {@code short}, {@code char}, {@code int} or
4464 * {@code long} then bitwise atomic update access modes are
4465 * unsupported.
4466 * </ul>
4467 * <p>
4468 * If the component type is {@code float} or {@code double} then numeric
4469 * and atomic update access modes compare values using their bitwise
4470 * representation (see {@link Float#floatToRawIntBits} and
4471 * {@link Double#doubleToRawLongBits}, respectively).
4472 *
4473 * <p> When the returned {@code VarHandle} is invoked,
4474 * the array reference and array index are checked.
4475 * A {@code NullPointerException} will be thrown if the array reference
4476 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
4477 * thrown if the index is negative or if it is greater than or equal to
4478 * the length of the array.
4479 *
4480 * @apiNote
4481 * Bitwise comparison of {@code float} values or {@code double} values,
4482 * as performed by the numeric and atomic update access modes, differ
4483 * from the primitive {@code ==} operator and the {@link Float#equals}
4484 * and {@link Double#equals} methods, specifically with respect to
4485 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
4486 * Care should be taken when performing a compare and set or a compare
4487 * and exchange operation with such values since the operation may
4488 * unexpectedly fail.
4489 * There are many possible NaN values that are considered to be
4490 * {@code NaN} in Java, although no IEEE 754 floating-point operation
4491 * provided by Java can distinguish between them. Operation failure can
4492 * occur if the expected or witness value is a NaN value and it is
4493 * transformed (perhaps in a platform specific manner) into another NaN
4494 * value, and thus has a different bitwise representation (see
4495 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
4496 * details).
4497 * The values {@code -0.0} and {@code +0.0} have different bitwise
4498 * representations but are considered equal when using the primitive
4499 * {@code ==} operator. Operation failure can occur if, for example, a
4500 * numeric algorithm computes an expected value to be say {@code -0.0}
4501 * and previously computed the witness value to be say {@code +0.0}.
4502 * @param arrayClass the class of an array, of type {@code T[]}
4503 * @return a VarHandle giving access to elements of an array
4504 * @throws NullPointerException if the arrayClass is null
4505 * @throws IllegalArgumentException if arrayClass is not an array type
4506 * @since 9
4507 */
4508 public static VarHandle arrayElementVarHandle(Class<?> arrayClass) throws IllegalArgumentException {
4509 return VarHandles.makeArrayElementHandle(arrayClass);
4510 }
4511
4512 /**
4513 * Produces a VarHandle giving access to elements of a {@code byte[]} array
4514 * viewed as if it were a different primitive array type, such as
4515 * {@code int[]} or {@code long[]}.
4516 * The VarHandle's variable type is the component type of
4517 * {@code viewArrayClass} and the list of coordinate types is
4518 * {@code (byte[], int)}, where the {@code int} coordinate type
4519 * corresponds to an argument that is an index into a {@code byte[]} array.
4520 * The returned VarHandle accesses bytes at an index in a {@code byte[]}
4521 * array, composing bytes to or from a value of the component type of
4522 * {@code viewArrayClass} according to the given endianness.
4523 * <p>
4524 * The supported component types (variables types) are {@code short},
4525 * {@code char}, {@code int}, {@code long}, {@code float} and
4526 * {@code double}.
4527 * <p>
4528 * Access of bytes at a given index will result in an
4529 * {@code ArrayIndexOutOfBoundsException} if the index is less than {@code 0}
4530 * or greater than the {@code byte[]} array length minus the size (in bytes)
4531 * of {@code T}.
4532 * <p>
4533 * Access of bytes at an index may be aligned or misaligned for {@code T},
4534 * with respect to the underlying memory address, {@code A} say, associated
4535 * with the array and index.
4536 * If access is misaligned then access for anything other than the
4537 * {@code get} and {@code set} access modes will result in an
4538 * {@code IllegalStateException}. In such cases atomic access is only
4539 * guaranteed with respect to the largest power of two that divides the GCD
4540 * of {@code A} and the size (in bytes) of {@code T}.
4541 * If access is aligned then following access modes are supported and are
4542 * guaranteed to support atomic access:
4543 * <ul>
4544 * <li>read write access modes for all {@code T}, with the exception of
4545 * access modes {@code get} and {@code set} for {@code long} and
4546 * {@code double} on 32-bit platforms.
4547 * <li>atomic update access modes for {@code int}, {@code long},
4548 * {@code float} or {@code double}.
4549 * (Future major platform releases of the JDK may support additional
4550 * types for certain currently unsupported access modes.)
4551 * <li>numeric atomic update access modes for {@code int} and {@code long}.
4552 * (Future major platform releases of the JDK may support additional
4553 * numeric types for certain currently unsupported access modes.)
4554 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
4555 * (Future major platform releases of the JDK may support additional
4556 * numeric types for certain currently unsupported access modes.)
4557 * </ul>
4558 * <p>
4559 * Misaligned access, and therefore atomicity guarantees, may be determined
4560 * for {@code byte[]} arrays without operating on a specific array. Given
4561 * an {@code index}, {@code T} and its corresponding boxed type,
4562 * {@code T_BOX}, misalignment may be determined as follows:
4563 * <pre>{@code
4564 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
4565 * int misalignedAtZeroIndex = ByteBuffer.wrap(new byte[0]).
4566 * alignmentOffset(0, sizeOfT);
4567 * int misalignedAtIndex = (misalignedAtZeroIndex + index) % sizeOfT;
4568 * boolean isMisaligned = misalignedAtIndex != 0;
4569 * }</pre>
4570 * <p>
4571 * If the variable type is {@code float} or {@code double} then atomic
4572 * update access modes compare values using their bitwise representation
4573 * (see {@link Float#floatToRawIntBits} and
4574 * {@link Double#doubleToRawLongBits}, respectively).
4575 * @param viewArrayClass the view array class, with a component type of
4576 * type {@code T}
4577 * @param byteOrder the endianness of the view array elements, as
4578 * stored in the underlying {@code byte} array
4579 * @return a VarHandle giving access to elements of a {@code byte[]} array
4580 * viewed as if elements corresponding to the components type of the view
4581 * array class
4582 * @throws NullPointerException if viewArrayClass or byteOrder is null
4583 * @throws IllegalArgumentException if viewArrayClass is not an array type
4584 * @throws UnsupportedOperationException if the component type of
4585 * viewArrayClass is not supported as a variable type
4586 * @since 9
4587 */
4588 public static VarHandle byteArrayViewVarHandle(Class<?> viewArrayClass,
4589 ByteOrder byteOrder) throws IllegalArgumentException {
4590 Objects.requireNonNull(byteOrder);
4591 return VarHandles.byteArrayViewHandle(viewArrayClass,
4592 byteOrder == ByteOrder.BIG_ENDIAN);
4593 }
4594
4595 /**
4596 * Produces a VarHandle giving access to elements of a {@code ByteBuffer}
4597 * viewed as if it were an array of elements of a different primitive
4598 * component type to that of {@code byte}, such as {@code int[]} or
4599 * {@code long[]}.
4600 * The VarHandle's variable type is the component type of
4601 * {@code viewArrayClass} and the list of coordinate types is
4602 * {@code (ByteBuffer, int)}, where the {@code int} coordinate type
4603 * corresponds to an argument that is an index into a {@code byte[]} array.
4604 * The returned VarHandle accesses bytes at an index in a
4605 * {@code ByteBuffer}, composing bytes to or from a value of the component
4606 * type of {@code viewArrayClass} according to the given endianness.
4607 * <p>
4608 * The supported component types (variables types) are {@code short},
4609 * {@code char}, {@code int}, {@code long}, {@code float} and
4610 * {@code double}.
4611 * <p>
4612 * Access will result in a {@code ReadOnlyBufferException} for anything
4613 * other than the read access modes if the {@code ByteBuffer} is read-only.
4614 * <p>
4615 * Access of bytes at a given index will result in an
4616 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
4617 * or greater than the {@code ByteBuffer} limit minus the size (in bytes) of
4618 * {@code T}.
4619 * <p>
4620 * Access of bytes at an index may be aligned or misaligned for {@code T},
4621 * with respect to the underlying memory address, {@code A} say, associated
4622 * with the {@code ByteBuffer} and index.
4623 * If access is misaligned then access for anything other than the
4624 * {@code get} and {@code set} access modes will result in an
4625 * {@code IllegalStateException}. In such cases atomic access is only
4626 * guaranteed with respect to the largest power of two that divides the GCD
4627 * of {@code A} and the size (in bytes) of {@code T}.
4628 * If access is aligned then following access modes are supported and are
4629 * guaranteed to support atomic access:
4630 * <ul>
4631 * <li>read write access modes for all {@code T}, with the exception of
4632 * access modes {@code get} and {@code set} for {@code long} and
4633 * {@code double} on 32-bit platforms.
4634 * <li>atomic update access modes for {@code int}, {@code long},
4635 * {@code float} or {@code double}.
4636 * (Future major platform releases of the JDK may support additional
4637 * types for certain currently unsupported access modes.)
4638 * <li>numeric atomic update access modes for {@code int} and {@code long}.
4639 * (Future major platform releases of the JDK may support additional
4640 * numeric types for certain currently unsupported access modes.)
4641 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
4642 * (Future major platform releases of the JDK may support additional
4643 * numeric types for certain currently unsupported access modes.)
4644 * </ul>
4645 * <p>
4646 * Misaligned access, and therefore atomicity guarantees, may be determined
4647 * for a {@code ByteBuffer}, {@code bb} (direct or otherwise), an
4648 * {@code index}, {@code T} and its corresponding boxed type,
4649 * {@code T_BOX}, as follows:
4650 * <pre>{@code
4651 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
4652 * ByteBuffer bb = ...
4653 * int misalignedAtIndex = bb.alignmentOffset(index, sizeOfT);
4654 * boolean isMisaligned = misalignedAtIndex != 0;
4655 * }</pre>
4656 * <p>
4657 * If the variable type is {@code float} or {@code double} then atomic
4658 * update access modes compare values using their bitwise representation
4659 * (see {@link Float#floatToRawIntBits} and
4660 * {@link Double#doubleToRawLongBits}, respectively).
4661 * @param viewArrayClass the view array class, with a component type of
4662 * type {@code T}
4663 * @param byteOrder the endianness of the view array elements, as
4664 * stored in the underlying {@code ByteBuffer} (Note this overrides the
4665 * endianness of a {@code ByteBuffer})
4666 * @return a VarHandle giving access to elements of a {@code ByteBuffer}
4667 * viewed as if elements corresponding to the components type of the view
4668 * array class
4669 * @throws NullPointerException if viewArrayClass or byteOrder is null
4670 * @throws IllegalArgumentException if viewArrayClass is not an array type
4671 * @throws UnsupportedOperationException if the component type of
4672 * viewArrayClass is not supported as a variable type
4673 * @since 9
4674 */
4675 public static VarHandle byteBufferViewVarHandle(Class<?> viewArrayClass,
4676 ByteOrder byteOrder) throws IllegalArgumentException {
4677 Objects.requireNonNull(byteOrder);
4678 return VarHandles.makeByteBufferViewHandle(viewArrayClass,
4679 byteOrder == ByteOrder.BIG_ENDIAN);
4680 }
4681
4682
4683 /// method handle invocation (reflective style)
4684
4685 /**
4686 * Produces a method handle which will invoke any method handle of the
4687 * given {@code type}, with a given number of trailing arguments replaced by
4688 * a single trailing {@code Object[]} array.
4689 * The resulting invoker will be a method handle with the following
4690 * arguments:
4691 * <ul>
4692 * <li>a single {@code MethodHandle} target
4693 * <li>zero or more leading values (counted by {@code leadingArgCount})
4694 * <li>an {@code Object[]} array containing trailing arguments
4695 * </ul>
4696 * <p>
4697 * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
4698 * the indicated {@code type}.
4699 * That is, if the target is exactly of the given {@code type}, it will behave
4700 * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
4701 * is used to convert the target to the required {@code type}.
4702 * <p>
4703 * The type of the returned invoker will not be the given {@code type}, but rather
4704 * will have all parameters except the first {@code leadingArgCount}
4705 * replaced by a single array of type {@code Object[]}, which will be
4706 * the final parameter.
4707 * <p>
4708 * Before invoking its target, the invoker will spread the final array, apply
4709 * reference casts as necessary, and unbox and widen primitive arguments.
4710 * If, when the invoker is called, the supplied array argument does
4711 * not have the correct number of elements, the invoker will throw
4712 * an {@link IllegalArgumentException} instead of invoking the target.
4713 * <p>
4714 * This method is equivalent to the following code (though it may be more efficient):
4715 * {@snippet lang="java" :
4716 MethodHandle invoker = MethodHandles.invoker(type);
4717 int spreadArgCount = type.parameterCount() - leadingArgCount;
4718 invoker = invoker.asSpreader(Object[].class, spreadArgCount);
4719 return invoker;
4720 * }
4721 * This method throws no reflective or security exceptions.
4722 * @param type the desired target type
4723 * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
4724 * @return a method handle suitable for invoking any method handle of the given type
4725 * @throws NullPointerException if {@code type} is null
4726 * @throws IllegalArgumentException if {@code leadingArgCount} is not in
4727 * the range from 0 to {@code type.parameterCount()} inclusive,
4728 * or if the resulting method handle's type would have
4729 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4730 */
4731 public static MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
4732 if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
4733 throw newIllegalArgumentException("bad argument count", leadingArgCount);
4734 type = type.asSpreaderType(Object[].class, leadingArgCount, type.parameterCount() - leadingArgCount);
4735 return type.invokers().spreadInvoker(leadingArgCount);
4736 }
4737
4738 /**
4739 * Produces a special <em>invoker method handle</em> which can be used to
4740 * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
4741 * The resulting invoker will have a type which is
4742 * exactly equal to the desired type, except that it will accept
4743 * an additional leading argument of type {@code MethodHandle}.
4744 * <p>
4745 * This method is equivalent to the following code (though it may be more efficient):
4746 * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)}
4747 *
4748 * <p style="font-size:smaller;">
4749 * <em>Discussion:</em>
4750 * Invoker method handles can be useful when working with variable method handles
4751 * of unknown types.
4752 * For example, to emulate an {@code invokeExact} call to a variable method
4753 * handle {@code M}, extract its type {@code T},
4754 * look up the invoker method {@code X} for {@code T},
4755 * and call the invoker method, as {@code X.invoke(T, A...)}.
4756 * (It would not work to call {@code X.invokeExact}, since the type {@code T}
4757 * is unknown.)
4758 * If spreading, collecting, or other argument transformations are required,
4759 * they can be applied once to the invoker {@code X} and reused on many {@code M}
4760 * method handle values, as long as they are compatible with the type of {@code X}.
4761 * <p style="font-size:smaller;">
4762 * <em>(Note: The invoker method is not available via the Core Reflection API.
4763 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
4764 * on the declared {@code invokeExact} or {@code invoke} method will raise an
4765 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
4766 * <p>
4767 * This method throws no reflective or security exceptions.
4768 * @param type the desired target type
4769 * @return a method handle suitable for invoking any method handle of the given type
4770 * @throws IllegalArgumentException if the resulting method handle's type would have
4771 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4772 */
4773 public static MethodHandle exactInvoker(MethodType type) {
4774 return type.invokers().exactInvoker();
4775 }
4776
4777 /**
4778 * Produces a special <em>invoker method handle</em> which can be used to
4779 * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
4780 * The resulting invoker will have a type which is
4781 * exactly equal to the desired type, except that it will accept
4782 * an additional leading argument of type {@code MethodHandle}.
4783 * <p>
4784 * Before invoking its target, if the target differs from the expected type,
4785 * the invoker will apply reference casts as
4786 * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
4787 * Similarly, the return value will be converted as necessary.
4788 * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
4789 * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
4790 * <p>
4791 * This method is equivalent to the following code (though it may be more efficient):
4792 * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)}
4793 * <p style="font-size:smaller;">
4794 * <em>Discussion:</em>
4795 * A {@linkplain MethodType#genericMethodType general method type} is one which
4796 * mentions only {@code Object} arguments and return values.
4797 * An invoker for such a type is capable of calling any method handle
4798 * of the same arity as the general type.
4799 * <p style="font-size:smaller;">
4800 * <em>(Note: The invoker method is not available via the Core Reflection API.
4801 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
4802 * on the declared {@code invokeExact} or {@code invoke} method will raise an
4803 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
4804 * <p>
4805 * This method throws no reflective or security exceptions.
4806 * @param type the desired target type
4807 * @return a method handle suitable for invoking any method handle convertible to the given type
4808 * @throws IllegalArgumentException if the resulting method handle's type would have
4809 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4810 */
4811 public static MethodHandle invoker(MethodType type) {
4812 return type.invokers().genericInvoker();
4813 }
4814
4815 /**
4816 * Produces a special <em>invoker method handle</em> which can be used to
4817 * invoke a signature-polymorphic access mode method on any VarHandle whose
4818 * associated access mode type is compatible with the given type.
4819 * The resulting invoker will have a type which is exactly equal to the
4820 * desired given type, except that it will accept an additional leading
4821 * argument of type {@code VarHandle}.
4822 *
4823 * @param accessMode the VarHandle access mode
4824 * @param type the desired target type
4825 * @return a method handle suitable for invoking an access mode method of
4826 * any VarHandle whose access mode type is of the given type.
4827 * @since 9
4828 */
4829 public static MethodHandle varHandleExactInvoker(VarHandle.AccessMode accessMode, MethodType type) {
4830 return type.invokers().varHandleMethodExactInvoker(accessMode);
4831 }
4832
4833 /**
4834 * Produces a special <em>invoker method handle</em> which can be used to
4835 * invoke a signature-polymorphic access mode method on any VarHandle whose
4836 * associated access mode type is compatible with the given type.
4837 * The resulting invoker will have a type which is exactly equal to the
4838 * desired given type, except that it will accept an additional leading
4839 * argument of type {@code VarHandle}.
4840 * <p>
4841 * Before invoking its target, if the access mode type differs from the
4842 * desired given type, the invoker will apply reference casts as necessary
4843 * and box, unbox, or widen primitive values, as if by
4844 * {@link MethodHandle#asType asType}. Similarly, the return value will be
4845 * converted as necessary.
4846 * <p>
4847 * This method is equivalent to the following code (though it may be more
4848 * efficient): {@code publicLookup().findVirtual(VarHandle.class, accessMode.name(), type)}
4849 *
4850 * @param accessMode the VarHandle access mode
4851 * @param type the desired target type
4852 * @return a method handle suitable for invoking an access mode method of
4853 * any VarHandle whose access mode type is convertible to the given
4854 * type.
4855 * @since 9
4856 */
4857 public static MethodHandle varHandleInvoker(VarHandle.AccessMode accessMode, MethodType type) {
4858 return type.invokers().varHandleMethodInvoker(accessMode);
4859 }
4860
4861 /*non-public*/
4862 static MethodHandle basicInvoker(MethodType type) {
4863 return type.invokers().basicInvoker();
4864 }
4865
4866 /// method handle modification (creation from other method handles)
4867
4868 /**
4869 * Produces a method handle which adapts the type of the
4870 * given method handle to a new type by pairwise argument and return type conversion.
4871 * The original type and new type must have the same number of arguments.
4872 * The resulting method handle is guaranteed to report a type
4873 * which is equal to the desired new type.
4874 * <p>
4875 * If the original type and new type are equal, returns target.
4876 * <p>
4877 * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
4878 * and some additional conversions are also applied if those conversions fail.
4879 * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied
4880 * if possible, before or instead of any conversions done by {@code asType}:
4881 * <ul>
4882 * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type,
4883 * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast.
4884 * (This treatment of interfaces follows the usage of the bytecode verifier.)
4885 * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive,
4886 * the boolean is converted to a byte value, 1 for true, 0 for false.
4887 * (This treatment follows the usage of the bytecode verifier.)
4888 * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive,
4889 * <em>T0</em> is converted to byte via Java casting conversion (JLS {@jls 5.5}),
4890 * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}.
4891 * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean,
4892 * then a Java casting conversion (JLS {@jls 5.5}) is applied.
4893 * (Specifically, <em>T0</em> will convert to <em>T1</em> by
4894 * widening and/or narrowing.)
4895 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
4896 * conversion will be applied at runtime, possibly followed
4897 * by a Java casting conversion (JLS {@jls 5.5}) on the primitive value,
4898 * possibly followed by a conversion from byte to boolean by testing
4899 * the low-order bit.
4900 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive,
4901 * and if the reference is null at runtime, a zero value is introduced.
4902 * </ul>
4903 * @param target the method handle to invoke after arguments are retyped
4904 * @param newType the expected type of the new method handle
4905 * @return a method handle which delegates to the target after performing
4906 * any necessary argument conversions, and arranges for any
4907 * necessary return value conversions
4908 * @throws NullPointerException if either argument is null
4909 * @throws WrongMethodTypeException if the conversion cannot be made
4910 * @see MethodHandle#asType
4911 */
4912 public static MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
4913 explicitCastArgumentsChecks(target, newType);
4914 // use the asTypeCache when possible:
4915 MethodType oldType = target.type();
4916 if (oldType == newType) return target;
4917 if (oldType.explicitCastEquivalentToAsType(newType)) {
4918 return target.asFixedArity().asType(newType);
4919 }
4920 return MethodHandleImpl.makePairwiseConvert(target, newType, false);
4921 }
4922
4923 private static void explicitCastArgumentsChecks(MethodHandle target, MethodType newType) {
4924 if (target.type().parameterCount() != newType.parameterCount()) {
4925 throw new WrongMethodTypeException("cannot explicitly cast " + target + " to " + newType);
4926 }
4927 }
4928
4929 /**
4930 * Produces a method handle which adapts the calling sequence of the
4931 * given method handle to a new type, by reordering the arguments.
4932 * The resulting method handle is guaranteed to report a type
4933 * which is equal to the desired new type.
4934 * <p>
4935 * The given array controls the reordering.
4936 * Call {@code #I} the number of incoming parameters (the value
4937 * {@code newType.parameterCount()}, and call {@code #O} the number
4938 * of outgoing parameters (the value {@code target.type().parameterCount()}).
4939 * Then the length of the reordering array must be {@code #O},
4940 * and each element must be a non-negative number less than {@code #I}.
4941 * For every {@code N} less than {@code #O}, the {@code N}-th
4942 * outgoing argument will be taken from the {@code I}-th incoming
4943 * argument, where {@code I} is {@code reorder[N]}.
4944 * <p>
4945 * No argument or return value conversions are applied.
4946 * The type of each incoming argument, as determined by {@code newType},
4947 * must be identical to the type of the corresponding outgoing parameter
4948 * or parameters in the target method handle.
4949 * The return type of {@code newType} must be identical to the return
4950 * type of the original target.
4951 * <p>
4952 * The reordering array need not specify an actual permutation.
4953 * An incoming argument will be duplicated if its index appears
4954 * more than once in the array, and an incoming argument will be dropped
4955 * if its index does not appear in the array.
4956 * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
4957 * incoming arguments which are not mentioned in the reordering array
4958 * may be of any type, as determined only by {@code newType}.
4959 * {@snippet lang="java" :
4960 import static java.lang.invoke.MethodHandles.*;
4961 import static java.lang.invoke.MethodType.*;
4962 ...
4963 MethodType intfn1 = methodType(int.class, int.class);
4964 MethodType intfn2 = methodType(int.class, int.class, int.class);
4965 MethodHandle sub = ... (int x, int y) -> (x-y) ...;
4966 assert(sub.type().equals(intfn2));
4967 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
4968 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
4969 assert((int)rsub.invokeExact(1, 100) == 99);
4970 MethodHandle add = ... (int x, int y) -> (x+y) ...;
4971 assert(add.type().equals(intfn2));
4972 MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
4973 assert(twice.type().equals(intfn1));
4974 assert((int)twice.invokeExact(21) == 42);
4975 * }
4976 * <p>
4977 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4978 * variable-arity method handle}, even if the original target method handle was.
4979 * @param target the method handle to invoke after arguments are reordered
4980 * @param newType the expected type of the new method handle
4981 * @param reorder an index array which controls the reordering
4982 * @return a method handle which delegates to the target after it
4983 * drops unused arguments and moves and/or duplicates the other arguments
4984 * @throws NullPointerException if any argument is null
4985 * @throws IllegalArgumentException if the index array length is not equal to
4986 * the arity of the target, or if any index array element
4987 * not a valid index for a parameter of {@code newType},
4988 * or if two corresponding parameter types in
4989 * {@code target.type()} and {@code newType} are not identical,
4990 */
4991 public static MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
4992 reorder = reorder.clone(); // get a private copy
4993 MethodType oldType = target.type();
4994 permuteArgumentChecks(reorder, newType, oldType);
4995 // first detect dropped arguments and handle them separately
4996 int[] originalReorder = reorder;
4997 BoundMethodHandle result = target.rebind();
4998 LambdaForm form = result.form;
4999 int newArity = newType.parameterCount();
5000 // Normalize the reordering into a real permutation,
5001 // by removing duplicates and adding dropped elements.
5002 // This somewhat improves lambda form caching, as well
5003 // as simplifying the transform by breaking it up into steps.
5004 for (int ddIdx; (ddIdx = findFirstDupOrDrop(reorder, newArity)) != 0; ) {
5005 if (ddIdx > 0) {
5006 // We found a duplicated entry at reorder[ddIdx].
5007 // Example: (x,y,z)->asList(x,y,z)
5008 // permuted by [1*,0,1] => (a0,a1)=>asList(a1,a0,a1)
5009 // permuted by [0,1,0*] => (a0,a1)=>asList(a0,a1,a0)
5010 // The starred element corresponds to the argument
5011 // deleted by the dupArgumentForm transform.
5012 int srcPos = ddIdx, dstPos = srcPos, dupVal = reorder[srcPos];
5013 boolean killFirst = false;
5014 for (int val; (val = reorder[--dstPos]) != dupVal; ) {
5015 // Set killFirst if the dup is larger than an intervening position.
5016 // This will remove at least one inversion from the permutation.
5017 if (dupVal > val) killFirst = true;
5018 }
5019 if (!killFirst) {
5020 srcPos = dstPos;
5021 dstPos = ddIdx;
5022 }
5023 form = form.editor().dupArgumentForm(1 + srcPos, 1 + dstPos);
5024 assert (reorder[srcPos] == reorder[dstPos]);
5025 oldType = oldType.dropParameterTypes(dstPos, dstPos + 1);
5026 // contract the reordering by removing the element at dstPos
5027 int tailPos = dstPos + 1;
5028 System.arraycopy(reorder, tailPos, reorder, dstPos, reorder.length - tailPos);
5029 reorder = Arrays.copyOf(reorder, reorder.length - 1);
5030 } else {
5031 int dropVal = ~ddIdx, insPos = 0;
5032 while (insPos < reorder.length && reorder[insPos] < dropVal) {
5033 // Find first element of reorder larger than dropVal.
5034 // This is where we will insert the dropVal.
5035 insPos += 1;
5036 }
5037 Class<?> ptype = newType.parameterType(dropVal);
5038 form = form.editor().addArgumentForm(1 + insPos, BasicType.basicType(ptype));
5039 oldType = oldType.insertParameterTypes(insPos, ptype);
5040 // expand the reordering by inserting an element at insPos
5041 int tailPos = insPos + 1;
5042 reorder = Arrays.copyOf(reorder, reorder.length + 1);
5043 System.arraycopy(reorder, insPos, reorder, tailPos, reorder.length - tailPos);
5044 reorder[insPos] = dropVal;
5045 }
5046 assert (permuteArgumentChecks(reorder, newType, oldType));
5047 }
5048 assert (reorder.length == newArity); // a perfect permutation
5049 // Note: This may cache too many distinct LFs. Consider backing off to varargs code.
5050 form = form.editor().permuteArgumentsForm(1, reorder);
5051 if (newType == result.type() && form == result.internalForm())
5052 return result;
5053 return result.copyWith(newType, form);
5054 }
5055
5056 /**
5057 * Return an indication of any duplicate or omission in reorder.
5058 * If the reorder contains a duplicate entry, return the index of the second occurrence.
5059 * Otherwise, return ~(n), for the first n in [0..newArity-1] that is not present in reorder.
5060 * Otherwise, return zero.
5061 * If an element not in [0..newArity-1] is encountered, return reorder.length.
5062 */
5063 private static int findFirstDupOrDrop(int[] reorder, int newArity) {
5064 final int BIT_LIMIT = 63; // max number of bits in bit mask
5065 if (newArity < BIT_LIMIT) {
5066 long mask = 0;
5067 for (int i = 0; i < reorder.length; i++) {
5068 int arg = reorder[i];
5069 if (arg >= newArity) {
5070 return reorder.length;
5071 }
5072 long bit = 1L << arg;
5073 if ((mask & bit) != 0) {
5074 return i; // >0 indicates a dup
5075 }
5076 mask |= bit;
5077 }
5078 if (mask == (1L << newArity) - 1) {
5079 assert(Long.numberOfTrailingZeros(Long.lowestOneBit(~mask)) == newArity);
5080 return 0;
5081 }
5082 // find first zero
5083 long zeroBit = Long.lowestOneBit(~mask);
5084 int zeroPos = Long.numberOfTrailingZeros(zeroBit);
5085 assert(zeroPos <= newArity);
5086 if (zeroPos == newArity) {
5087 return 0;
5088 }
5089 return ~zeroPos;
5090 } else {
5091 // same algorithm, different bit set
5092 BitSet mask = new BitSet(newArity);
5093 for (int i = 0; i < reorder.length; i++) {
5094 int arg = reorder[i];
5095 if (arg >= newArity) {
5096 return reorder.length;
5097 }
5098 if (mask.get(arg)) {
5099 return i; // >0 indicates a dup
5100 }
5101 mask.set(arg);
5102 }
5103 int zeroPos = mask.nextClearBit(0);
5104 assert(zeroPos <= newArity);
5105 if (zeroPos == newArity) {
5106 return 0;
5107 }
5108 return ~zeroPos;
5109 }
5110 }
5111
5112 static boolean permuteArgumentChecks(int[] reorder, MethodType newType, MethodType oldType) {
5113 if (newType.returnType() != oldType.returnType())
5114 throw newIllegalArgumentException("return types do not match",
5115 oldType, newType);
5116 if (reorder.length != oldType.parameterCount())
5117 throw newIllegalArgumentException("old type parameter count and reorder array length do not match",
5118 oldType, Arrays.toString(reorder));
5119
5120 int limit = newType.parameterCount();
5121 for (int j = 0; j < reorder.length; j++) {
5122 int i = reorder[j];
5123 if (i < 0 || i >= limit) {
5124 throw newIllegalArgumentException("index is out of bounds for new type",
5125 i, newType);
5126 }
5127 Class<?> src = newType.parameterType(i);
5128 Class<?> dst = oldType.parameterType(j);
5129 if (src != dst)
5130 throw newIllegalArgumentException("parameter types do not match after reorder",
5131 oldType, newType);
5132 }
5133 return true;
5134 }
5135
5136 /**
5137 * Produces a method handle of the requested return type which returns the given
5138 * constant value every time it is invoked.
5139 * <p>
5140 * Before the method handle is returned, the passed-in value is converted to the requested type.
5141 * If the requested type is primitive, widening primitive conversions are attempted,
5142 * else reference conversions are attempted.
5143 * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
5144 * @param type the return type of the desired method handle
5145 * @param value the value to return
5146 * @return a method handle of the given return type and no arguments, which always returns the given value
5147 * @throws NullPointerException if the {@code type} argument is null
5148 * @throws ClassCastException if the value cannot be converted to the required return type
5149 * @throws IllegalArgumentException if the given type is {@code void.class}
5150 */
5151 public static MethodHandle constant(Class<?> type, Object value) {
5152 if (type.isPrimitive()) {
5153 if (type == void.class)
5154 throw newIllegalArgumentException("void type");
5155 Wrapper w = Wrapper.forPrimitiveType(type);
5156 value = w.convert(value, type);
5157 if (w.zero().equals(value))
5158 return zero(w, type);
5159 return insertArguments(identity(type), 0, value);
5160 } else {
5161 if (!PrimitiveClass.isPrimitiveValueType(type) && value == null)
5162 return zero(Wrapper.OBJECT, type);
5163 return identity(type).bindTo(value);
5164 }
5165 }
5166
5167 /**
5168 * Produces a method handle which returns its sole argument when invoked.
5169 * @param type the type of the sole parameter and return value of the desired method handle
5170 * @return a unary method handle which accepts and returns the given type
5171 * @throws NullPointerException if the argument is null
5172 * @throws IllegalArgumentException if the given type is {@code void.class}
5173 */
5174 public static MethodHandle identity(Class<?> type) {
5175 Wrapper btw = (type.isPrimitive() ? Wrapper.forPrimitiveType(type) : Wrapper.OBJECT);
5176 int pos = btw.ordinal();
5177 MethodHandle ident = IDENTITY_MHS[pos];
5178 if (ident == null) {
5179 ident = setCachedMethodHandle(IDENTITY_MHS, pos, makeIdentity(btw.primitiveType()));
5180 }
5181 if (ident.type().returnType() == type)
5182 return ident;
5183 // something like identity(Foo.class); do not bother to intern these
5184 assert (btw == Wrapper.OBJECT);
5185 return makeIdentity(type);
5186 }
5187
5188 /**
5189 * Produces a constant method handle of the requested return type which
5190 * returns the default value for that type every time it is invoked.
5191 * The resulting constant method handle will have no side effects.
5192 * <p>The returned method handle is equivalent to {@code empty(methodType(type))}.
5193 * It is also equivalent to {@code explicitCastArguments(constant(Object.class, null), methodType(type))},
5194 * since {@code explicitCastArguments} converts {@code null} to default values.
5195 * @param type the expected return type of the desired method handle
5196 * @return a constant method handle that takes no arguments
5197 * and returns the default value of the given type (or void, if the type is void)
5198 * @throws NullPointerException if the argument is null
5199 * @see MethodHandles#constant
5200 * @see MethodHandles#empty
5201 * @see MethodHandles#explicitCastArguments
5202 * @since 9
5203 */
5204 public static MethodHandle zero(Class<?> type) {
5205 Objects.requireNonNull(type);
5206 if (type.isPrimitive()) {
5207 return zero(Wrapper.forPrimitiveType(type), type);
5208 } else if (PrimitiveClass.isPrimitiveValueType(type)) {
5209 // singleton default value
5210 Object value = UNSAFE.uninitializedDefaultValue(type);
5211 return identity(type).bindTo(value);
5212 } else {
5213 return zero(Wrapper.OBJECT, type);
5214 }
5215 }
5216
5217 private static MethodHandle identityOrVoid(Class<?> type) {
5218 return type == void.class ? zero(type) : identity(type);
5219 }
5220
5221 /**
5222 * Produces a method handle of the requested type which ignores any arguments, does nothing,
5223 * and returns a suitable default depending on the return type.
5224 * That is, it returns a zero primitive value, a {@code null}, or {@code void}.
5225 * <p>The returned method handle is equivalent to
5226 * {@code dropArguments(zero(type.returnType()), 0, type.parameterList())}.
5227 *
5228 * @apiNote Given a predicate and target, a useful "if-then" construct can be produced as
5229 * {@code guardWithTest(pred, target, empty(target.type())}.
5230 * @param type the type of the desired method handle
5231 * @return a constant method handle of the given type, which returns a default value of the given return type
5232 * @throws NullPointerException if the argument is null
5233 * @see MethodHandles#zero
5234 * @see MethodHandles#constant
5235 * @since 9
5236 */
5237 public static MethodHandle empty(MethodType type) {
5238 Objects.requireNonNull(type);
5239 return dropArgumentsTrusted(zero(type.returnType()), 0, type.ptypes());
5240 }
5241
5242 private static final MethodHandle[] IDENTITY_MHS = new MethodHandle[Wrapper.COUNT];
5243 private static MethodHandle makeIdentity(Class<?> ptype) {
5244 MethodType mtype = MethodType.methodType(ptype, ptype);
5245 LambdaForm lform = LambdaForm.identityForm(BasicType.basicType(ptype));
5246 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.IDENTITY);
5247 }
5248
5249 private static MethodHandle zero(Wrapper btw, Class<?> rtype) {
5250 int pos = btw.ordinal();
5251 MethodHandle zero = ZERO_MHS[pos];
5252 if (zero == null) {
5253 zero = setCachedMethodHandle(ZERO_MHS, pos, makeZero(btw.primitiveType()));
5254 }
5255 if (zero.type().returnType() == rtype)
5256 return zero;
5257 assert(btw == Wrapper.OBJECT);
5258 return makeZero(rtype);
5259 }
5260 private static final MethodHandle[] ZERO_MHS = new MethodHandle[Wrapper.COUNT];
5261 private static MethodHandle makeZero(Class<?> rtype) {
5262 MethodType mtype = methodType(rtype);
5263 LambdaForm lform = LambdaForm.zeroForm(BasicType.basicType(rtype));
5264 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.ZERO);
5265 }
5266
5267 private static synchronized MethodHandle setCachedMethodHandle(MethodHandle[] cache, int pos, MethodHandle value) {
5268 // Simulate a CAS, to avoid racy duplication of results.
5269 MethodHandle prev = cache[pos];
5270 if (prev != null) return prev;
5271 return cache[pos] = value;
5272 }
5273
5274 /**
5275 * Provides a target method handle with one or more <em>bound arguments</em>
5276 * in advance of the method handle's invocation.
5277 * The formal parameters to the target corresponding to the bound
5278 * arguments are called <em>bound parameters</em>.
5279 * Returns a new method handle which saves away the bound arguments.
5280 * When it is invoked, it receives arguments for any non-bound parameters,
5281 * binds the saved arguments to their corresponding parameters,
5282 * and calls the original target.
5283 * <p>
5284 * The type of the new method handle will drop the types for the bound
5285 * parameters from the original target type, since the new method handle
5286 * will no longer require those arguments to be supplied by its callers.
5287 * <p>
5288 * Each given argument object must match the corresponding bound parameter type.
5289 * If a bound parameter type is a primitive, the argument object
5290 * must be a wrapper, and will be unboxed to produce the primitive value.
5291 * <p>
5292 * The {@code pos} argument selects which parameters are to be bound.
5293 * It may range between zero and <i>N-L</i> (inclusively),
5294 * where <i>N</i> is the arity of the target method handle
5295 * and <i>L</i> is the length of the values array.
5296 * <p>
5297 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5298 * variable-arity method handle}, even if the original target method handle was.
5299 * @param target the method handle to invoke after the argument is inserted
5300 * @param pos where to insert the argument (zero for the first)
5301 * @param values the series of arguments to insert
5302 * @return a method handle which inserts an additional argument,
5303 * before calling the original method handle
5304 * @throws NullPointerException if the target or the {@code values} array is null
5305 * @throws IllegalArgumentException if {@code pos} is less than {@code 0} or greater than
5306 * {@code N - L} where {@code N} is the arity of the target method handle and {@code L}
5307 * is the length of the values array.
5308 * @throws ClassCastException if an argument does not match the corresponding bound parameter
5309 * type.
5310 * @see MethodHandle#bindTo
5311 */
5312 public static MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
5313 int insCount = values.length;
5314 Class<?>[] ptypes = insertArgumentsChecks(target, insCount, pos);
5315 if (insCount == 0) return target;
5316 BoundMethodHandle result = target.rebind();
5317 for (int i = 0; i < insCount; i++) {
5318 Object value = values[i];
5319 Class<?> ptype = ptypes[pos+i];
5320 if (ptype.isPrimitive()) {
5321 result = insertArgumentPrimitive(result, pos, ptype, value);
5322 } else {
5323 value = ptype.cast(value); // throw CCE if needed
5324 result = result.bindArgumentL(pos, value);
5325 }
5326 }
5327 return result;
5328 }
5329
5330 private static BoundMethodHandle insertArgumentPrimitive(BoundMethodHandle result, int pos,
5331 Class<?> ptype, Object value) {
5332 Wrapper w = Wrapper.forPrimitiveType(ptype);
5333 // perform unboxing and/or primitive conversion
5334 value = w.convert(value, ptype);
5335 return switch (w) {
5336 case INT -> result.bindArgumentI(pos, (int) value);
5337 case LONG -> result.bindArgumentJ(pos, (long) value);
5338 case FLOAT -> result.bindArgumentF(pos, (float) value);
5339 case DOUBLE -> result.bindArgumentD(pos, (double) value);
5340 default -> result.bindArgumentI(pos, ValueConversions.widenSubword(value));
5341 };
5342 }
5343
5344 private static Class<?>[] insertArgumentsChecks(MethodHandle target, int insCount, int pos) throws RuntimeException {
5345 MethodType oldType = target.type();
5346 int outargs = oldType.parameterCount();
5347 int inargs = outargs - insCount;
5348 if (inargs < 0)
5349 throw newIllegalArgumentException("too many values to insert");
5350 if (pos < 0 || pos > inargs)
5351 throw newIllegalArgumentException("no argument type to append");
5352 return oldType.ptypes();
5353 }
5354
5355 /**
5356 * Produces a method handle which will discard some dummy arguments
5357 * before calling some other specified <i>target</i> method handle.
5358 * The type of the new method handle will be the same as the target's type,
5359 * except it will also include the dummy argument types,
5360 * at some given position.
5361 * <p>
5362 * The {@code pos} argument may range between zero and <i>N</i>,
5363 * where <i>N</i> is the arity of the target.
5364 * If {@code pos} is zero, the dummy arguments will precede
5365 * the target's real arguments; if {@code pos} is <i>N</i>
5366 * they will come after.
5367 * <p>
5368 * <b>Example:</b>
5369 * {@snippet lang="java" :
5370 import static java.lang.invoke.MethodHandles.*;
5371 import static java.lang.invoke.MethodType.*;
5372 ...
5373 MethodHandle cat = lookup().findVirtual(String.class,
5374 "concat", methodType(String.class, String.class));
5375 assertEquals("xy", (String) cat.invokeExact("x", "y"));
5376 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
5377 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
5378 assertEquals(bigType, d0.type());
5379 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
5380 * }
5381 * <p>
5382 * This method is also equivalent to the following code:
5383 * <blockquote><pre>
5384 * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))}
5385 * </pre></blockquote>
5386 * @param target the method handle to invoke after the arguments are dropped
5387 * @param pos position of first argument to drop (zero for the leftmost)
5388 * @param valueTypes the type(s) of the argument(s) to drop
5389 * @return a method handle which drops arguments of the given types,
5390 * before calling the original method handle
5391 * @throws NullPointerException if the target is null,
5392 * or if the {@code valueTypes} list or any of its elements is null
5393 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
5394 * or if {@code pos} is negative or greater than the arity of the target,
5395 * or if the new method handle's type would have too many parameters
5396 */
5397 public static MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) {
5398 return dropArgumentsTrusted(target, pos, valueTypes.toArray(new Class<?>[0]).clone());
5399 }
5400
5401 static MethodHandle dropArgumentsTrusted(MethodHandle target, int pos, Class<?>[] valueTypes) {
5402 MethodType oldType = target.type(); // get NPE
5403 int dropped = dropArgumentChecks(oldType, pos, valueTypes);
5404 MethodType newType = oldType.insertParameterTypes(pos, valueTypes);
5405 if (dropped == 0) return target;
5406 BoundMethodHandle result = target.rebind();
5407 LambdaForm lform = result.form;
5408 int insertFormArg = 1 + pos;
5409 for (Class<?> ptype : valueTypes) {
5410 lform = lform.editor().addArgumentForm(insertFormArg++, BasicType.basicType(ptype));
5411 }
5412 result = result.copyWith(newType, lform);
5413 return result;
5414 }
5415
5416 private static int dropArgumentChecks(MethodType oldType, int pos, Class<?>[] valueTypes) {
5417 int dropped = valueTypes.length;
5418 MethodType.checkSlotCount(dropped);
5419 int outargs = oldType.parameterCount();
5420 int inargs = outargs + dropped;
5421 if (pos < 0 || pos > outargs)
5422 throw newIllegalArgumentException("no argument type to remove"
5423 + Arrays.asList(oldType, pos, valueTypes, inargs, outargs)
5424 );
5425 return dropped;
5426 }
5427
5428 /**
5429 * Produces a method handle which will discard some dummy arguments
5430 * before calling some other specified <i>target</i> method handle.
5431 * The type of the new method handle will be the same as the target's type,
5432 * except it will also include the dummy argument types,
5433 * at some given position.
5434 * <p>
5435 * The {@code pos} argument may range between zero and <i>N</i>,
5436 * where <i>N</i> is the arity of the target.
5437 * If {@code pos} is zero, the dummy arguments will precede
5438 * the target's real arguments; if {@code pos} is <i>N</i>
5439 * they will come after.
5440 * @apiNote
5441 * {@snippet lang="java" :
5442 import static java.lang.invoke.MethodHandles.*;
5443 import static java.lang.invoke.MethodType.*;
5444 ...
5445 MethodHandle cat = lookup().findVirtual(String.class,
5446 "concat", methodType(String.class, String.class));
5447 assertEquals("xy", (String) cat.invokeExact("x", "y"));
5448 MethodHandle d0 = dropArguments(cat, 0, String.class);
5449 assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
5450 MethodHandle d1 = dropArguments(cat, 1, String.class);
5451 assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
5452 MethodHandle d2 = dropArguments(cat, 2, String.class);
5453 assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
5454 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
5455 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
5456 * }
5457 * <p>
5458 * This method is also equivalent to the following code:
5459 * <blockquote><pre>
5460 * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))}
5461 * </pre></blockquote>
5462 * @param target the method handle to invoke after the arguments are dropped
5463 * @param pos position of first argument to drop (zero for the leftmost)
5464 * @param valueTypes the type(s) of the argument(s) to drop
5465 * @return a method handle which drops arguments of the given types,
5466 * before calling the original method handle
5467 * @throws NullPointerException if the target is null,
5468 * or if the {@code valueTypes} array or any of its elements is null
5469 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
5470 * or if {@code pos} is negative or greater than the arity of the target,
5471 * or if the new method handle's type would have
5472 * <a href="MethodHandle.html#maxarity">too many parameters</a>
5473 */
5474 public static MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
5475 return dropArgumentsTrusted(target, pos, valueTypes.clone());
5476 }
5477
5478 /* Convenience overloads for trusting internal low-arity call-sites */
5479 static MethodHandle dropArguments(MethodHandle target, int pos, Class<?> valueType1) {
5480 return dropArgumentsTrusted(target, pos, new Class<?>[] { valueType1 });
5481 }
5482 static MethodHandle dropArguments(MethodHandle target, int pos, Class<?> valueType1, Class<?> valueType2) {
5483 return dropArgumentsTrusted(target, pos, new Class<?>[] { valueType1, valueType2 });
5484 }
5485
5486 // private version which allows caller some freedom with error handling
5487 private static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, Class<?>[] newTypes, int pos,
5488 boolean nullOnFailure) {
5489 Class<?>[] oldTypes = target.type().ptypes();
5490 int match = oldTypes.length;
5491 if (skip != 0) {
5492 if (skip < 0 || skip > match) {
5493 throw newIllegalArgumentException("illegal skip", skip, target);
5494 }
5495 oldTypes = Arrays.copyOfRange(oldTypes, skip, match);
5496 match -= skip;
5497 }
5498 Class<?>[] addTypes = newTypes;
5499 int add = addTypes.length;
5500 if (pos != 0) {
5501 if (pos < 0 || pos > add) {
5502 throw newIllegalArgumentException("illegal pos", pos, Arrays.toString(newTypes));
5503 }
5504 addTypes = Arrays.copyOfRange(addTypes, pos, add);
5505 add -= pos;
5506 assert(addTypes.length == add);
5507 }
5508 // Do not add types which already match the existing arguments.
5509 if (match > add || !Arrays.equals(oldTypes, 0, oldTypes.length, addTypes, 0, match)) {
5510 if (nullOnFailure) {
5511 return null;
5512 }
5513 throw newIllegalArgumentException("argument lists do not match",
5514 Arrays.toString(oldTypes), Arrays.toString(newTypes));
5515 }
5516 addTypes = Arrays.copyOfRange(addTypes, match, add);
5517 add -= match;
5518 assert(addTypes.length == add);
5519 // newTypes: ( P*[pos], M*[match], A*[add] )
5520 // target: ( S*[skip], M*[match] )
5521 MethodHandle adapter = target;
5522 if (add > 0) {
5523 adapter = dropArgumentsTrusted(adapter, skip+ match, addTypes);
5524 }
5525 // adapter: (S*[skip], M*[match], A*[add] )
5526 if (pos > 0) {
5527 adapter = dropArgumentsTrusted(adapter, skip, Arrays.copyOfRange(newTypes, 0, pos));
5528 }
5529 // adapter: (S*[skip], P*[pos], M*[match], A*[add] )
5530 return adapter;
5531 }
5532
5533 /**
5534 * Adapts a target method handle to match the given parameter type list. If necessary, adds dummy arguments. Some
5535 * leading parameters can be skipped before matching begins. The remaining types in the {@code target}'s parameter
5536 * type list must be a sub-list of the {@code newTypes} type list at the starting position {@code pos}. The
5537 * resulting handle will have the target handle's parameter type list, with any non-matching parameter types (before
5538 * or after the matching sub-list) inserted in corresponding positions of the target's original parameters, as if by
5539 * {@link #dropArguments(MethodHandle, int, Class[])}.
5540 * <p>
5541 * The resulting handle will have the same return type as the target handle.
5542 * <p>
5543 * In more formal terms, assume these two type lists:<ul>
5544 * <li>The target handle has the parameter type list {@code S..., M...}, with as many types in {@code S} as
5545 * indicated by {@code skip}. The {@code M} types are those that are supposed to match part of the given type list,
5546 * {@code newTypes}.
5547 * <li>The {@code newTypes} list contains types {@code P..., M..., A...}, with as many types in {@code P} as
5548 * indicated by {@code pos}. The {@code M} types are precisely those that the {@code M} types in the target handle's
5549 * parameter type list are supposed to match. The types in {@code A} are additional types found after the matching
5550 * sub-list.
5551 * </ul>
5552 * Given these assumptions, the result of an invocation of {@code dropArgumentsToMatch} will have the parameter type
5553 * list {@code S..., P..., M..., A...}, with the {@code P} and {@code A} types inserted as if by
5554 * {@link #dropArguments(MethodHandle, int, Class[])}.
5555 *
5556 * @apiNote
5557 * Two method handles whose argument lists are "effectively identical" (i.e., identical in a common prefix) may be
5558 * mutually converted to a common type by two calls to {@code dropArgumentsToMatch}, as follows:
5559 * {@snippet lang="java" :
5560 import static java.lang.invoke.MethodHandles.*;
5561 import static java.lang.invoke.MethodType.*;
5562 ...
5563 ...
5564 MethodHandle h0 = constant(boolean.class, true);
5565 MethodHandle h1 = lookup().findVirtual(String.class, "concat", methodType(String.class, String.class));
5566 MethodType bigType = h1.type().insertParameterTypes(1, String.class, int.class);
5567 MethodHandle h2 = dropArguments(h1, 0, bigType.parameterList());
5568 if (h1.type().parameterCount() < h2.type().parameterCount())
5569 h1 = dropArgumentsToMatch(h1, 0, h2.type().parameterList(), 0); // lengthen h1
5570 else
5571 h2 = dropArgumentsToMatch(h2, 0, h1.type().parameterList(), 0); // lengthen h2
5572 MethodHandle h3 = guardWithTest(h0, h1, h2);
5573 assertEquals("xy", h3.invoke("x", "y", 1, "a", "b", "c"));
5574 * }
5575 * @param target the method handle to adapt
5576 * @param skip number of targets parameters to disregard (they will be unchanged)
5577 * @param newTypes the list of types to match {@code target}'s parameter type list to
5578 * @param pos place in {@code newTypes} where the non-skipped target parameters must occur
5579 * @return a possibly adapted method handle
5580 * @throws NullPointerException if either argument is null
5581 * @throws IllegalArgumentException if any element of {@code newTypes} is {@code void.class},
5582 * or if {@code skip} is negative or greater than the arity of the target,
5583 * or if {@code pos} is negative or greater than the newTypes list size,
5584 * or if {@code newTypes} does not contain the {@code target}'s non-skipped parameter types at position
5585 * {@code pos}.
5586 * @since 9
5587 */
5588 public static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos) {
5589 Objects.requireNonNull(target);
5590 Objects.requireNonNull(newTypes);
5591 return dropArgumentsToMatch(target, skip, newTypes.toArray(new Class<?>[0]).clone(), pos, false);
5592 }
5593
5594 /**
5595 * Drop the return value of the target handle (if any).
5596 * The returned method handle will have a {@code void} return type.
5597 *
5598 * @param target the method handle to adapt
5599 * @return a possibly adapted method handle
5600 * @throws NullPointerException if {@code target} is null
5601 * @since 16
5602 */
5603 public static MethodHandle dropReturn(MethodHandle target) {
5604 Objects.requireNonNull(target);
5605 MethodType oldType = target.type();
5606 Class<?> oldReturnType = oldType.returnType();
5607 if (oldReturnType == void.class)
5608 return target;
5609 MethodType newType = oldType.changeReturnType(void.class);
5610 BoundMethodHandle result = target.rebind();
5611 LambdaForm lform = result.editor().filterReturnForm(V_TYPE, true);
5612 result = result.copyWith(newType, lform);
5613 return result;
5614 }
5615
5616 /**
5617 * Adapts a target method handle by pre-processing
5618 * one or more of its arguments, each with its own unary filter function,
5619 * and then calling the target with each pre-processed argument
5620 * replaced by the result of its corresponding filter function.
5621 * <p>
5622 * The pre-processing is performed by one or more method handles,
5623 * specified in the elements of the {@code filters} array.
5624 * The first element of the filter array corresponds to the {@code pos}
5625 * argument of the target, and so on in sequence.
5626 * The filter functions are invoked in left to right order.
5627 * <p>
5628 * Null arguments in the array are treated as identity functions,
5629 * and the corresponding arguments left unchanged.
5630 * (If there are no non-null elements in the array, the original target is returned.)
5631 * Each filter is applied to the corresponding argument of the adapter.
5632 * <p>
5633 * If a filter {@code F} applies to the {@code N}th argument of
5634 * the target, then {@code F} must be a method handle which
5635 * takes exactly one argument. The type of {@code F}'s sole argument
5636 * replaces the corresponding argument type of the target
5637 * in the resulting adapted method handle.
5638 * The return type of {@code F} must be identical to the corresponding
5639 * parameter type of the target.
5640 * <p>
5641 * It is an error if there are elements of {@code filters}
5642 * (null or not)
5643 * which do not correspond to argument positions in the target.
5644 * <p><b>Example:</b>
5645 * {@snippet lang="java" :
5646 import static java.lang.invoke.MethodHandles.*;
5647 import static java.lang.invoke.MethodType.*;
5648 ...
5649 MethodHandle cat = lookup().findVirtual(String.class,
5650 "concat", methodType(String.class, String.class));
5651 MethodHandle upcase = lookup().findVirtual(String.class,
5652 "toUpperCase", methodType(String.class));
5653 assertEquals("xy", (String) cat.invokeExact("x", "y"));
5654 MethodHandle f0 = filterArguments(cat, 0, upcase);
5655 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
5656 MethodHandle f1 = filterArguments(cat, 1, upcase);
5657 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
5658 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
5659 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
5660 * }
5661 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
5662 * denotes the return type of both the {@code target} and resulting adapter.
5663 * {@code P}/{@code p} and {@code B}/{@code b} represent the types and values
5664 * of the parameters and arguments that precede and follow the filter position
5665 * {@code pos}, respectively. {@code A[i]}/{@code a[i]} stand for the types and
5666 * values of the filtered parameters and arguments; they also represent the
5667 * return types of the {@code filter[i]} handles. The latter accept arguments
5668 * {@code v[i]} of type {@code V[i]}, which also appear in the signature of
5669 * the resulting adapter.
5670 * {@snippet lang="java" :
5671 * T target(P... p, A[i]... a[i], B... b);
5672 * A[i] filter[i](V[i]);
5673 * T adapter(P... p, V[i]... v[i], B... b) {
5674 * return target(p..., filter[i](v[i])..., b...);
5675 * }
5676 * }
5677 * <p>
5678 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5679 * variable-arity method handle}, even if the original target method handle was.
5680 *
5681 * @param target the method handle to invoke after arguments are filtered
5682 * @param pos the position of the first argument to filter
5683 * @param filters method handles to call initially on filtered arguments
5684 * @return method handle which incorporates the specified argument filtering logic
5685 * @throws NullPointerException if the target is null
5686 * or if the {@code filters} array is null
5687 * @throws IllegalArgumentException if a non-null element of {@code filters}
5688 * does not match a corresponding argument type of target as described above,
5689 * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()},
5690 * or if the resulting method handle's type would have
5691 * <a href="MethodHandle.html#maxarity">too many parameters</a>
5692 */
5693 public static MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
5694 // In method types arguments start at index 0, while the LF
5695 // editor have the MH receiver at position 0 - adjust appropriately.
5696 final int MH_RECEIVER_OFFSET = 1;
5697 filterArgumentsCheckArity(target, pos, filters);
5698 MethodHandle adapter = target;
5699
5700 // keep track of currently matched filters, as to optimize repeated filters
5701 int index = 0;
5702 int[] positions = new int[filters.length];
5703 MethodHandle filter = null;
5704
5705 // process filters in reverse order so that the invocation of
5706 // the resulting adapter will invoke the filters in left-to-right order
5707 for (int i = filters.length - 1; i >= 0; --i) {
5708 MethodHandle newFilter = filters[i];
5709 if (newFilter == null) continue; // ignore null elements of filters
5710
5711 // flush changes on update
5712 if (filter != newFilter) {
5713 if (filter != null) {
5714 if (index > 1) {
5715 adapter = filterRepeatedArgument(adapter, filter, Arrays.copyOf(positions, index));
5716 } else {
5717 adapter = filterArgument(adapter, positions[0] - 1, filter);
5718 }
5719 }
5720 filter = newFilter;
5721 index = 0;
5722 }
5723
5724 filterArgumentChecks(target, pos + i, newFilter);
5725 positions[index++] = pos + i + MH_RECEIVER_OFFSET;
5726 }
5727 if (index > 1) {
5728 adapter = filterRepeatedArgument(adapter, filter, Arrays.copyOf(positions, index));
5729 } else if (index == 1) {
5730 adapter = filterArgument(adapter, positions[0] - 1, filter);
5731 }
5732 return adapter;
5733 }
5734
5735 private static MethodHandle filterRepeatedArgument(MethodHandle adapter, MethodHandle filter, int[] positions) {
5736 MethodType targetType = adapter.type();
5737 MethodType filterType = filter.type();
5738 BoundMethodHandle result = adapter.rebind();
5739 Class<?> newParamType = filterType.parameterType(0);
5740
5741 Class<?>[] ptypes = targetType.ptypes().clone();
5742 for (int pos : positions) {
5743 ptypes[pos - 1] = newParamType;
5744 }
5745 MethodType newType = MethodType.methodType(targetType.rtype(), ptypes, true);
5746
5747 LambdaForm lform = result.editor().filterRepeatedArgumentForm(BasicType.basicType(newParamType), positions);
5748 return result.copyWithExtendL(newType, lform, filter);
5749 }
5750
5751 /*non-public*/
5752 static MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
5753 filterArgumentChecks(target, pos, filter);
5754 MethodType targetType = target.type();
5755 MethodType filterType = filter.type();
5756 BoundMethodHandle result = target.rebind();
5757 Class<?> newParamType = filterType.parameterType(0);
5758 LambdaForm lform = result.editor().filterArgumentForm(1 + pos, BasicType.basicType(newParamType));
5759 MethodType newType = targetType.changeParameterType(pos, newParamType);
5760 result = result.copyWithExtendL(newType, lform, filter);
5761 return result;
5762 }
5763
5764 private static void filterArgumentsCheckArity(MethodHandle target, int pos, MethodHandle[] filters) {
5765 MethodType targetType = target.type();
5766 int maxPos = targetType.parameterCount();
5767 if (pos + filters.length > maxPos)
5768 throw newIllegalArgumentException("too many filters");
5769 }
5770
5771 private static void filterArgumentChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
5772 MethodType targetType = target.type();
5773 MethodType filterType = filter.type();
5774 if (filterType.parameterCount() != 1
5775 || filterType.returnType() != targetType.parameterType(pos))
5776 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
5777 }
5778
5779 /**
5780 * Adapts a target method handle by pre-processing
5781 * a sub-sequence of its arguments with a filter (another method handle).
5782 * The pre-processed arguments are replaced by the result (if any) of the
5783 * filter function.
5784 * The target is then called on the modified (usually shortened) argument list.
5785 * <p>
5786 * If the filter returns a value, the target must accept that value as
5787 * its argument in position {@code pos}, preceded and/or followed by
5788 * any arguments not passed to the filter.
5789 * If the filter returns void, the target must accept all arguments
5790 * not passed to the filter.
5791 * No arguments are reordered, and a result returned from the filter
5792 * replaces (in order) the whole subsequence of arguments originally
5793 * passed to the adapter.
5794 * <p>
5795 * The argument types (if any) of the filter
5796 * replace zero or one argument types of the target, at position {@code pos},
5797 * in the resulting adapted method handle.
5798 * The return type of the filter (if any) must be identical to the
5799 * argument type of the target at position {@code pos}, and that target argument
5800 * is supplied by the return value of the filter.
5801 * <p>
5802 * In all cases, {@code pos} must be greater than or equal to zero, and
5803 * {@code pos} must also be less than or equal to the target's arity.
5804 * <p><b>Example:</b>
5805 * {@snippet lang="java" :
5806 import static java.lang.invoke.MethodHandles.*;
5807 import static java.lang.invoke.MethodType.*;
5808 ...
5809 MethodHandle deepToString = publicLookup()
5810 .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
5811
5812 MethodHandle ts1 = deepToString.asCollector(String[].class, 1);
5813 assertEquals("[strange]", (String) ts1.invokeExact("strange"));
5814
5815 MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
5816 assertEquals("[up, down]", (String) ts2.invokeExact("up", "down"));
5817
5818 MethodHandle ts3 = deepToString.asCollector(String[].class, 3);
5819 MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2);
5820 assertEquals("[top, [up, down], strange]",
5821 (String) ts3_ts2.invokeExact("top", "up", "down", "strange"));
5822
5823 MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1);
5824 assertEquals("[top, [up, down], [strange]]",
5825 (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange"));
5826
5827 MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3);
5828 assertEquals("[top, [[up, down, strange], charm], bottom]",
5829 (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom"));
5830 * }
5831 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
5832 * represents the return type of the {@code target} and resulting adapter.
5833 * {@code V}/{@code v} stand for the return type and value of the
5834 * {@code filter}, which are also found in the signature and arguments of
5835 * the {@code target}, respectively, unless {@code V} is {@code void}.
5836 * {@code A}/{@code a} and {@code C}/{@code c} represent the parameter types
5837 * and values preceding and following the collection position, {@code pos},
5838 * in the {@code target}'s signature. They also turn up in the resulting
5839 * adapter's signature and arguments, where they surround
5840 * {@code B}/{@code b}, which represent the parameter types and arguments
5841 * to the {@code filter} (if any).
5842 * {@snippet lang="java" :
5843 * T target(A...,V,C...);
5844 * V filter(B...);
5845 * T adapter(A... a,B... b,C... c) {
5846 * V v = filter(b...);
5847 * return target(a...,v,c...);
5848 * }
5849 * // and if the filter has no arguments:
5850 * T target2(A...,V,C...);
5851 * V filter2();
5852 * T adapter2(A... a,C... c) {
5853 * V v = filter2();
5854 * return target2(a...,v,c...);
5855 * }
5856 * // and if the filter has a void return:
5857 * T target3(A...,C...);
5858 * void filter3(B...);
5859 * T adapter3(A... a,B... b,C... c) {
5860 * filter3(b...);
5861 * return target3(a...,c...);
5862 * }
5863 * }
5864 * <p>
5865 * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to
5866 * one which first "folds" the affected arguments, and then drops them, in separate
5867 * steps as follows:
5868 * {@snippet lang="java" :
5869 * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2
5870 * mh = MethodHandles.foldArguments(mh, coll); //step 1
5871 * }
5872 * If the target method handle consumes no arguments besides than the result
5873 * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)}
5874 * is equivalent to {@code filterReturnValue(coll, mh)}.
5875 * If the filter method handle {@code coll} consumes one argument and produces
5876 * a non-void result, then {@code collectArguments(mh, N, coll)}
5877 * is equivalent to {@code filterArguments(mh, N, coll)}.
5878 * Other equivalences are possible but would require argument permutation.
5879 * <p>
5880 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5881 * variable-arity method handle}, even if the original target method handle was.
5882 *
5883 * @param target the method handle to invoke after filtering the subsequence of arguments
5884 * @param pos the position of the first adapter argument to pass to the filter,
5885 * and/or the target argument which receives the result of the filter
5886 * @param filter method handle to call on the subsequence of arguments
5887 * @return method handle which incorporates the specified argument subsequence filtering logic
5888 * @throws NullPointerException if either argument is null
5889 * @throws IllegalArgumentException if the return type of {@code filter}
5890 * is non-void and is not the same as the {@code pos} argument of the target,
5891 * or if {@code pos} is not between 0 and the target's arity, inclusive,
5892 * or if the resulting method handle's type would have
5893 * <a href="MethodHandle.html#maxarity">too many parameters</a>
5894 * @see MethodHandles#foldArguments
5895 * @see MethodHandles#filterArguments
5896 * @see MethodHandles#filterReturnValue
5897 */
5898 public static MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) {
5899 MethodType newType = collectArgumentsChecks(target, pos, filter);
5900 MethodType collectorType = filter.type();
5901 BoundMethodHandle result = target.rebind();
5902 LambdaForm lform = result.editor().collectArgumentsForm(1 + pos, collectorType.basicType());
5903 return result.copyWithExtendL(newType, lform, filter);
5904 }
5905
5906 private static MethodType collectArgumentsChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
5907 MethodType targetType = target.type();
5908 MethodType filterType = filter.type();
5909 Class<?> rtype = filterType.returnType();
5910 Class<?>[] filterArgs = filterType.ptypes();
5911 if (pos < 0 || (rtype == void.class && pos > targetType.parameterCount()) ||
5912 (rtype != void.class && pos >= targetType.parameterCount())) {
5913 throw newIllegalArgumentException("position is out of range for target", target, pos);
5914 }
5915 if (rtype == void.class) {
5916 return targetType.insertParameterTypes(pos, filterArgs);
5917 }
5918 if (rtype != targetType.parameterType(pos)) {
5919 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
5920 }
5921 return targetType.dropParameterTypes(pos, pos + 1).insertParameterTypes(pos, filterArgs);
5922 }
5923
5924 /**
5925 * Adapts a target method handle by post-processing
5926 * its return value (if any) with a filter (another method handle).
5927 * The result of the filter is returned from the adapter.
5928 * <p>
5929 * If the target returns a value, the filter must accept that value as
5930 * its only argument.
5931 * If the target returns void, the filter must accept no arguments.
5932 * <p>
5933 * The return type of the filter
5934 * replaces the return type of the target
5935 * in the resulting adapted method handle.
5936 * The argument type of the filter (if any) must be identical to the
5937 * return type of the target.
5938 * <p><b>Example:</b>
5939 * {@snippet lang="java" :
5940 import static java.lang.invoke.MethodHandles.*;
5941 import static java.lang.invoke.MethodType.*;
5942 ...
5943 MethodHandle cat = lookup().findVirtual(String.class,
5944 "concat", methodType(String.class, String.class));
5945 MethodHandle length = lookup().findVirtual(String.class,
5946 "length", methodType(int.class));
5947 System.out.println((String) cat.invokeExact("x", "y")); // xy
5948 MethodHandle f0 = filterReturnValue(cat, length);
5949 System.out.println((int) f0.invokeExact("x", "y")); // 2
5950 * }
5951 * <p>Here is pseudocode for the resulting adapter. In the code,
5952 * {@code T}/{@code t} represent the result type and value of the
5953 * {@code target}; {@code V}, the result type of the {@code filter}; and
5954 * {@code A}/{@code a}, the types and values of the parameters and arguments
5955 * of the {@code target} as well as the resulting adapter.
5956 * {@snippet lang="java" :
5957 * T target(A...);
5958 * V filter(T);
5959 * V adapter(A... a) {
5960 * T t = target(a...);
5961 * return filter(t);
5962 * }
5963 * // and if the target has a void return:
5964 * void target2(A...);
5965 * V filter2();
5966 * V adapter2(A... a) {
5967 * target2(a...);
5968 * return filter2();
5969 * }
5970 * // and if the filter has a void return:
5971 * T target3(A...);
5972 * void filter3(V);
5973 * void adapter3(A... a) {
5974 * T t = target3(a...);
5975 * filter3(t);
5976 * }
5977 * }
5978 * <p>
5979 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5980 * variable-arity method handle}, even if the original target method handle was.
5981 * @param target the method handle to invoke before filtering the return value
5982 * @param filter method handle to call on the return value
5983 * @return method handle which incorporates the specified return value filtering logic
5984 * @throws NullPointerException if either argument is null
5985 * @throws IllegalArgumentException if the argument list of {@code filter}
5986 * does not match the return type of target as described above
5987 */
5988 public static MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
5989 MethodType targetType = target.type();
5990 MethodType filterType = filter.type();
5991 filterReturnValueChecks(targetType, filterType);
5992 BoundMethodHandle result = target.rebind();
5993 BasicType rtype = BasicType.basicType(filterType.returnType());
5994 LambdaForm lform = result.editor().filterReturnForm(rtype, false);
5995 MethodType newType = targetType.changeReturnType(filterType.returnType());
5996 result = result.copyWithExtendL(newType, lform, filter);
5997 return result;
5998 }
5999
6000 private static void filterReturnValueChecks(MethodType targetType, MethodType filterType) throws RuntimeException {
6001 Class<?> rtype = targetType.returnType();
6002 int filterValues = filterType.parameterCount();
6003 if (filterValues == 0
6004 ? (rtype != void.class)
6005 : (rtype != filterType.parameterType(0) || filterValues != 1))
6006 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
6007 }
6008
6009 /**
6010 * Filter the return value of a target method handle with a filter function. The filter function is
6011 * applied to the return value of the original handle; if the filter specifies more than one parameters,
6012 * then any remaining parameter is appended to the adapter handle. In other words, the adaptation works
6013 * as follows:
6014 * {@snippet lang="java" :
6015 * T target(A...)
6016 * V filter(B... , T)
6017 * V adapter(A... a, B... b) {
6018 * T t = target(a...);
6019 * return filter(b..., t);
6020 * }
6021 * }
6022 * <p>
6023 * If the filter handle is a unary function, then this method behaves like {@link #filterReturnValue(MethodHandle, MethodHandle)}.
6024 *
6025 * @param target the target method handle
6026 * @param filter the filter method handle
6027 * @return the adapter method handle
6028 */
6029 /* package */ static MethodHandle collectReturnValue(MethodHandle target, MethodHandle filter) {
6030 MethodType targetType = target.type();
6031 MethodType filterType = filter.type();
6032 BoundMethodHandle result = target.rebind();
6033 LambdaForm lform = result.editor().collectReturnValueForm(filterType.basicType());
6034 MethodType newType = targetType.changeReturnType(filterType.returnType());
6035 if (filterType.parameterCount() > 1) {
6036 for (int i = 0 ; i < filterType.parameterCount() - 1 ; i++) {
6037 newType = newType.appendParameterTypes(filterType.parameterType(i));
6038 }
6039 }
6040 result = result.copyWithExtendL(newType, lform, filter);
6041 return result;
6042 }
6043
6044 /**
6045 * Adapts a target method handle by pre-processing
6046 * some of its arguments, and then calling the target with
6047 * the result of the pre-processing, inserted into the original
6048 * sequence of arguments.
6049 * <p>
6050 * The pre-processing is performed by {@code combiner}, a second method handle.
6051 * Of the arguments passed to the adapter, the first {@code N} arguments
6052 * are copied to the combiner, which is then called.
6053 * (Here, {@code N} is defined as the parameter count of the combiner.)
6054 * After this, control passes to the target, with any result
6055 * from the combiner inserted before the original {@code N} incoming
6056 * arguments.
6057 * <p>
6058 * If the combiner returns a value, the first parameter type of the target
6059 * must be identical with the return type of the combiner, and the next
6060 * {@code N} parameter types of the target must exactly match the parameters
6061 * of the combiner.
6062 * <p>
6063 * If the combiner has a void return, no result will be inserted,
6064 * and the first {@code N} parameter types of the target
6065 * must exactly match the parameters of the combiner.
6066 * <p>
6067 * The resulting adapter is the same type as the target, except that the
6068 * first parameter type is dropped,
6069 * if it corresponds to the result of the combiner.
6070 * <p>
6071 * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
6072 * that either the combiner or the target does not wish to receive.
6073 * If some of the incoming arguments are destined only for the combiner,
6074 * consider using {@link MethodHandle#asCollector asCollector} instead, since those
6075 * arguments will not need to be live on the stack on entry to the
6076 * target.)
6077 * <p><b>Example:</b>
6078 * {@snippet lang="java" :
6079 import static java.lang.invoke.MethodHandles.*;
6080 import static java.lang.invoke.MethodType.*;
6081 ...
6082 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
6083 "println", methodType(void.class, String.class))
6084 .bindTo(System.out);
6085 MethodHandle cat = lookup().findVirtual(String.class,
6086 "concat", methodType(String.class, String.class));
6087 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
6088 MethodHandle catTrace = foldArguments(cat, trace);
6089 // also prints "boo":
6090 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
6091 * }
6092 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
6093 * represents the result type of the {@code target} and resulting adapter.
6094 * {@code V}/{@code v} represent the type and value of the parameter and argument
6095 * of {@code target} that precedes the folding position; {@code V} also is
6096 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
6097 * types and values of the {@code N} parameters and arguments at the folding
6098 * position. {@code B}/{@code b} represent the types and values of the
6099 * {@code target} parameters and arguments that follow the folded parameters
6100 * and arguments.
6101 * {@snippet lang="java" :
6102 * // there are N arguments in A...
6103 * T target(V, A[N]..., B...);
6104 * V combiner(A...);
6105 * T adapter(A... a, B... b) {
6106 * V v = combiner(a...);
6107 * return target(v, a..., b...);
6108 * }
6109 * // and if the combiner has a void return:
6110 * T target2(A[N]..., B...);
6111 * void combiner2(A...);
6112 * T adapter2(A... a, B... b) {
6113 * combiner2(a...);
6114 * return target2(a..., b...);
6115 * }
6116 * }
6117 * <p>
6118 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
6119 * variable-arity method handle}, even if the original target method handle was.
6120 * @param target the method handle to invoke after arguments are combined
6121 * @param combiner method handle to call initially on the incoming arguments
6122 * @return method handle which incorporates the specified argument folding logic
6123 * @throws NullPointerException if either argument is null
6124 * @throws IllegalArgumentException if {@code combiner}'s return type
6125 * is non-void and not the same as the first argument type of
6126 * the target, or if the initial {@code N} argument types
6127 * of the target
6128 * (skipping one matching the {@code combiner}'s return type)
6129 * are not identical with the argument types of {@code combiner}
6130 */
6131 public static MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
6132 return foldArguments(target, 0, combiner);
6133 }
6134
6135 /**
6136 * Adapts a target method handle by pre-processing some of its arguments, starting at a given position, and then
6137 * calling the target with the result of the pre-processing, inserted into the original sequence of arguments just
6138 * before the folded arguments.
6139 * <p>
6140 * This method is closely related to {@link #foldArguments(MethodHandle, MethodHandle)}, but allows to control the
6141 * position in the parameter list at which folding takes place. The argument controlling this, {@code pos}, is a
6142 * zero-based index. The aforementioned method {@link #foldArguments(MethodHandle, MethodHandle)} assumes position
6143 * 0.
6144 *
6145 * @apiNote Example:
6146 * {@snippet lang="java" :
6147 import static java.lang.invoke.MethodHandles.*;
6148 import static java.lang.invoke.MethodType.*;
6149 ...
6150 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
6151 "println", methodType(void.class, String.class))
6152 .bindTo(System.out);
6153 MethodHandle cat = lookup().findVirtual(String.class,
6154 "concat", methodType(String.class, String.class));
6155 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
6156 MethodHandle catTrace = foldArguments(cat, 1, trace);
6157 // also prints "jum":
6158 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
6159 * }
6160 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
6161 * represents the result type of the {@code target} and resulting adapter.
6162 * {@code V}/{@code v} represent the type and value of the parameter and argument
6163 * of {@code target} that precedes the folding position; {@code V} also is
6164 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
6165 * types and values of the {@code N} parameters and arguments at the folding
6166 * position. {@code Z}/{@code z} and {@code B}/{@code b} represent the types
6167 * and values of the {@code target} parameters and arguments that precede and
6168 * follow the folded parameters and arguments starting at {@code pos},
6169 * respectively.
6170 * {@snippet lang="java" :
6171 * // there are N arguments in A...
6172 * T target(Z..., V, A[N]..., B...);
6173 * V combiner(A...);
6174 * T adapter(Z... z, A... a, B... b) {
6175 * V v = combiner(a...);
6176 * return target(z..., v, a..., b...);
6177 * }
6178 * // and if the combiner has a void return:
6179 * T target2(Z..., A[N]..., B...);
6180 * void combiner2(A...);
6181 * T adapter2(Z... z, A... a, B... b) {
6182 * combiner2(a...);
6183 * return target2(z..., a..., b...);
6184 * }
6185 * }
6186 * <p>
6187 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
6188 * variable-arity method handle}, even if the original target method handle was.
6189 *
6190 * @param target the method handle to invoke after arguments are combined
6191 * @param pos the position at which to start folding and at which to insert the folding result; if this is {@code
6192 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
6193 * @param combiner method handle to call initially on the incoming arguments
6194 * @return method handle which incorporates the specified argument folding logic
6195 * @throws NullPointerException if either argument is null
6196 * @throws IllegalArgumentException if either of the following two conditions holds:
6197 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
6198 * {@code pos} of the target signature;
6199 * (2) the {@code N} argument types at position {@code pos} of the target signature (skipping one matching
6200 * the {@code combiner}'s return type) are not identical with the argument types of {@code combiner}.
6201 *
6202 * @see #foldArguments(MethodHandle, MethodHandle)
6203 * @since 9
6204 */
6205 public static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner) {
6206 MethodType targetType = target.type();
6207 MethodType combinerType = combiner.type();
6208 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType);
6209 BoundMethodHandle result = target.rebind();
6210 boolean dropResult = rtype == void.class;
6211 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType());
6212 MethodType newType = targetType;
6213 if (!dropResult) {
6214 newType = newType.dropParameterTypes(pos, pos + 1);
6215 }
6216 result = result.copyWithExtendL(newType, lform, combiner);
6217 return result;
6218 }
6219
6220 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType) {
6221 int foldArgs = combinerType.parameterCount();
6222 Class<?> rtype = combinerType.returnType();
6223 int foldVals = rtype == void.class ? 0 : 1;
6224 int afterInsertPos = foldPos + foldVals;
6225 boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
6226 if (ok) {
6227 for (int i = 0; i < foldArgs; i++) {
6228 if (combinerType.parameterType(i) != targetType.parameterType(i + afterInsertPos)) {
6229 ok = false;
6230 break;
6231 }
6232 }
6233 }
6234 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos))
6235 ok = false;
6236 if (!ok)
6237 throw misMatchedTypes("target and combiner types", targetType, combinerType);
6238 return rtype;
6239 }
6240
6241 /**
6242 * Adapts a target method handle by pre-processing some of its arguments, then calling the target with the result
6243 * of the pre-processing replacing the argument at the given position.
6244 *
6245 * @param target the method handle to invoke after arguments are combined
6246 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code
6247 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
6248 * @param combiner method handle to call initially on the incoming arguments
6249 * @param argPositions indexes of the target to pick arguments sent to the combiner from
6250 * @return method handle which incorporates the specified argument folding logic
6251 * @throws NullPointerException if either argument is null
6252 * @throws IllegalArgumentException if either of the following two conditions holds:
6253 * (1) {@code combiner}'s return type is not the same as the argument type at position
6254 * {@code pos} of the target signature;
6255 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature are
6256 * not identical with the argument types of {@code combiner}.
6257 */
6258 /*non-public*/
6259 static MethodHandle filterArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
6260 return argumentsWithCombiner(true, target, position, combiner, argPositions);
6261 }
6262
6263 /**
6264 * Adapts a target method handle by pre-processing some of its arguments, calling the target with the result of
6265 * the pre-processing inserted into the original sequence of arguments at the given position.
6266 *
6267 * @param target the method handle to invoke after arguments are combined
6268 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code
6269 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
6270 * @param combiner method handle to call initially on the incoming arguments
6271 * @param argPositions indexes of the target to pick arguments sent to the combiner from
6272 * @return method handle which incorporates the specified argument folding logic
6273 * @throws NullPointerException if either argument is null
6274 * @throws IllegalArgumentException if either of the following two conditions holds:
6275 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
6276 * {@code pos} of the target signature;
6277 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature
6278 * (skipping {@code position} where the {@code combiner}'s return will be folded in) are not identical
6279 * with the argument types of {@code combiner}.
6280 */
6281 /*non-public*/
6282 static MethodHandle foldArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
6283 return argumentsWithCombiner(false, target, position, combiner, argPositions);
6284 }
6285
6286 private static MethodHandle argumentsWithCombiner(boolean filter, MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
6287 MethodType targetType = target.type();
6288 MethodType combinerType = combiner.type();
6289 Class<?> rtype = argumentsWithCombinerChecks(position, filter, targetType, combinerType, argPositions);
6290 BoundMethodHandle result = target.rebind();
6291
6292 MethodType newType = targetType;
6293 LambdaForm lform;
6294 if (filter) {
6295 lform = result.editor().filterArgumentsForm(1 + position, combinerType.basicType(), argPositions);
6296 } else {
6297 boolean dropResult = rtype == void.class;
6298 lform = result.editor().foldArgumentsForm(1 + position, dropResult, combinerType.basicType(), argPositions);
6299 if (!dropResult) {
6300 newType = newType.dropParameterTypes(position, position + 1);
6301 }
6302 }
6303 result = result.copyWithExtendL(newType, lform, combiner);
6304 return result;
6305 }
6306
6307 private static Class<?> argumentsWithCombinerChecks(int position, boolean filter, MethodType targetType, MethodType combinerType, int ... argPos) {
6308 int combinerArgs = combinerType.parameterCount();
6309 if (argPos.length != combinerArgs) {
6310 throw newIllegalArgumentException("combiner and argument map must be equal size", combinerType, argPos.length);
6311 }
6312 Class<?> rtype = combinerType.returnType();
6313
6314 for (int i = 0; i < combinerArgs; i++) {
6315 int arg = argPos[i];
6316 if (arg < 0 || arg > targetType.parameterCount()) {
6317 throw newIllegalArgumentException("arg outside of target parameterRange", targetType, arg);
6318 }
6319 if (combinerType.parameterType(i) != targetType.parameterType(arg)) {
6320 throw newIllegalArgumentException("target argument type at position " + arg
6321 + " must match combiner argument type at index " + i + ": " + targetType
6322 + " -> " + combinerType + ", map: " + Arrays.toString(argPos));
6323 }
6324 }
6325 if (filter && combinerType.returnType() != targetType.parameterType(position)) {
6326 throw misMatchedTypes("target and combiner types", targetType, combinerType);
6327 }
6328 return rtype;
6329 }
6330
6331 /**
6332 * Makes a method handle which adapts a target method handle,
6333 * by guarding it with a test, a boolean-valued method handle.
6334 * If the guard fails, a fallback handle is called instead.
6335 * All three method handles must have the same corresponding
6336 * argument and return types, except that the return type
6337 * of the test must be boolean, and the test is allowed
6338 * to have fewer arguments than the other two method handles.
6339 * <p>
6340 * Here is pseudocode for the resulting adapter. In the code, {@code T}
6341 * represents the uniform result type of the three involved handles;
6342 * {@code A}/{@code a}, the types and values of the {@code target}
6343 * parameters and arguments that are consumed by the {@code test}; and
6344 * {@code B}/{@code b}, those types and values of the {@code target}
6345 * parameters and arguments that are not consumed by the {@code test}.
6346 * {@snippet lang="java" :
6347 * boolean test(A...);
6348 * T target(A...,B...);
6349 * T fallback(A...,B...);
6350 * T adapter(A... a,B... b) {
6351 * if (test(a...))
6352 * return target(a..., b...);
6353 * else
6354 * return fallback(a..., b...);
6355 * }
6356 * }
6357 * Note that the test arguments ({@code a...} in the pseudocode) cannot
6358 * be modified by execution of the test, and so are passed unchanged
6359 * from the caller to the target or fallback as appropriate.
6360 * @param test method handle used for test, must return boolean
6361 * @param target method handle to call if test passes
6362 * @param fallback method handle to call if test fails
6363 * @return method handle which incorporates the specified if/then/else logic
6364 * @throws NullPointerException if any argument is null
6365 * @throws IllegalArgumentException if {@code test} does not return boolean,
6366 * or if all three method types do not match (with the return
6367 * type of {@code test} changed to match that of the target).
6368 */
6369 public static MethodHandle guardWithTest(MethodHandle test,
6370 MethodHandle target,
6371 MethodHandle fallback) {
6372 MethodType gtype = test.type();
6373 MethodType ttype = target.type();
6374 MethodType ftype = fallback.type();
6375 if (!ttype.equals(ftype))
6376 throw misMatchedTypes("target and fallback types", ttype, ftype);
6377 if (gtype.returnType() != boolean.class)
6378 throw newIllegalArgumentException("guard type is not a predicate "+gtype);
6379
6380 test = dropArgumentsToMatch(test, 0, ttype.ptypes(), 0, true);
6381 if (test == null) {
6382 throw misMatchedTypes("target and test types", ttype, gtype);
6383 }
6384 return MethodHandleImpl.makeGuardWithTest(test, target, fallback);
6385 }
6386
6387 static <T> RuntimeException misMatchedTypes(String what, T t1, T t2) {
6388 return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
6389 }
6390
6391 /**
6392 * Makes a method handle which adapts a target method handle,
6393 * by running it inside an exception handler.
6394 * If the target returns normally, the adapter returns that value.
6395 * If an exception matching the specified type is thrown, the fallback
6396 * handle is called instead on the exception, plus the original arguments.
6397 * <p>
6398 * The target and handler must have the same corresponding
6399 * argument and return types, except that handler may omit trailing arguments
6400 * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
6401 * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
6402 * <p>
6403 * Here is pseudocode for the resulting adapter. In the code, {@code T}
6404 * represents the return type of the {@code target} and {@code handler},
6405 * and correspondingly that of the resulting adapter; {@code A}/{@code a},
6406 * the types and values of arguments to the resulting handle consumed by
6407 * {@code handler}; and {@code B}/{@code b}, those of arguments to the
6408 * resulting handle discarded by {@code handler}.
6409 * {@snippet lang="java" :
6410 * T target(A..., B...);
6411 * T handler(ExType, A...);
6412 * T adapter(A... a, B... b) {
6413 * try {
6414 * return target(a..., b...);
6415 * } catch (ExType ex) {
6416 * return handler(ex, a...);
6417 * }
6418 * }
6419 * }
6420 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
6421 * be modified by execution of the target, and so are passed unchanged
6422 * from the caller to the handler, if the handler is invoked.
6423 * <p>
6424 * The target and handler must return the same type, even if the handler
6425 * always throws. (This might happen, for instance, because the handler
6426 * is simulating a {@code finally} clause).
6427 * To create such a throwing handler, compose the handler creation logic
6428 * with {@link #throwException throwException},
6429 * in order to create a method handle of the correct return type.
6430 * @param target method handle to call
6431 * @param exType the type of exception which the handler will catch
6432 * @param handler method handle to call if a matching exception is thrown
6433 * @return method handle which incorporates the specified try/catch logic
6434 * @throws NullPointerException if any argument is null
6435 * @throws IllegalArgumentException if {@code handler} does not accept
6436 * the given exception type, or if the method handle types do
6437 * not match in their return types and their
6438 * corresponding parameters
6439 * @see MethodHandles#tryFinally(MethodHandle, MethodHandle)
6440 */
6441 public static MethodHandle catchException(MethodHandle target,
6442 Class<? extends Throwable> exType,
6443 MethodHandle handler) {
6444 MethodType ttype = target.type();
6445 MethodType htype = handler.type();
6446 if (!Throwable.class.isAssignableFrom(exType))
6447 throw new ClassCastException(exType.getName());
6448 if (htype.parameterCount() < 1 ||
6449 !htype.parameterType(0).isAssignableFrom(exType))
6450 throw newIllegalArgumentException("handler does not accept exception type "+exType);
6451 if (htype.returnType() != ttype.returnType())
6452 throw misMatchedTypes("target and handler return types", ttype, htype);
6453 handler = dropArgumentsToMatch(handler, 1, ttype.ptypes(), 0, true);
6454 if (handler == null) {
6455 throw misMatchedTypes("target and handler types", ttype, htype);
6456 }
6457 return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
6458 }
6459
6460 /**
6461 * Produces a method handle which will throw exceptions of the given {@code exType}.
6462 * The method handle will accept a single argument of {@code exType},
6463 * and immediately throw it as an exception.
6464 * The method type will nominally specify a return of {@code returnType}.
6465 * The return type may be anything convenient: It doesn't matter to the
6466 * method handle's behavior, since it will never return normally.
6467 * @param returnType the return type of the desired method handle
6468 * @param exType the parameter type of the desired method handle
6469 * @return method handle which can throw the given exceptions
6470 * @throws NullPointerException if either argument is null
6471 */
6472 public static MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) {
6473 if (!Throwable.class.isAssignableFrom(exType))
6474 throw new ClassCastException(exType.getName());
6475 return MethodHandleImpl.throwException(methodType(returnType, exType));
6476 }
6477
6478 /**
6479 * Constructs a method handle representing a loop with several loop variables that are updated and checked upon each
6480 * iteration. Upon termination of the loop due to one of the predicates, a corresponding finalizer is run and
6481 * delivers the loop's result, which is the return value of the resulting handle.
6482 * <p>
6483 * Intuitively, every loop is formed by one or more "clauses", each specifying a local <em>iteration variable</em> and/or a loop
6484 * exit. Each iteration of the loop executes each clause in order. A clause can optionally update its iteration
6485 * variable; it can also optionally perform a test and conditional loop exit. In order to express this logic in
6486 * terms of method handles, each clause will specify up to four independent actions:<ul>
6487 * <li><em>init:</em> Before the loop executes, the initialization of an iteration variable {@code v} of type {@code V}.
6488 * <li><em>step:</em> When a clause executes, an update step for the iteration variable {@code v}.
6489 * <li><em>pred:</em> When a clause executes, a predicate execution to test for loop exit.
6490 * <li><em>fini:</em> If a clause causes a loop exit, a finalizer execution to compute the loop's return value.
6491 * </ul>
6492 * The full sequence of all iteration variable types, in clause order, will be notated as {@code (V...)}.
6493 * The values themselves will be {@code (v...)}. When we speak of "parameter lists", we will usually
6494 * be referring to types, but in some contexts (describing execution) the lists will be of actual values.
6495 * <p>
6496 * Some of these clause parts may be omitted according to certain rules, and useful default behavior is provided in
6497 * this case. See below for a detailed description.
6498 * <p>
6499 * <em>Parameters optional everywhere:</em>
6500 * Each clause function is allowed but not required to accept a parameter for each iteration variable {@code v}.
6501 * As an exception, the init functions cannot take any {@code v} parameters,
6502 * because those values are not yet computed when the init functions are executed.
6503 * Any clause function may neglect to take any trailing subsequence of parameters it is entitled to take.
6504 * In fact, any clause function may take no arguments at all.
6505 * <p>
6506 * <em>Loop parameters:</em>
6507 * A clause function may take all the iteration variable values it is entitled to, in which case
6508 * it may also take more trailing parameters. Such extra values are called <em>loop parameters</em>,
6509 * with their types and values notated as {@code (A...)} and {@code (a...)}.
6510 * These become the parameters of the resulting loop handle, to be supplied whenever the loop is executed.
6511 * (Since init functions do not accept iteration variables {@code v}, any parameter to an
6512 * init function is automatically a loop parameter {@code a}.)
6513 * As with iteration variables, clause functions are allowed but not required to accept loop parameters.
6514 * These loop parameters act as loop-invariant values visible across the whole loop.
6515 * <p>
6516 * <em>Parameters visible everywhere:</em>
6517 * Each non-init clause function is permitted to observe the entire loop state, because it can be passed the full
6518 * list {@code (v... a...)} of current iteration variable values and incoming loop parameters.
6519 * The init functions can observe initial pre-loop state, in the form {@code (a...)}.
6520 * Most clause functions will not need all of this information, but they will be formally connected to it
6521 * as if by {@link #dropArguments}.
6522 * <a id="astar"></a>
6523 * More specifically, we shall use the notation {@code (V*)} to express an arbitrary prefix of a full
6524 * sequence {@code (V...)} (and likewise for {@code (v*)}, {@code (A*)}, {@code (a*)}).
6525 * In that notation, the general form of an init function parameter list
6526 * is {@code (A*)}, and the general form of a non-init function parameter list is {@code (V*)} or {@code (V... A*)}.
6527 * <p>
6528 * <em>Checking clause structure:</em>
6529 * Given a set of clauses, there is a number of checks and adjustments performed to connect all the parts of the
6530 * loop. They are spelled out in detail in the steps below. In these steps, every occurrence of the word "must"
6531 * corresponds to a place where {@link IllegalArgumentException} will be thrown if the required constraint is not
6532 * met by the inputs to the loop combinator.
6533 * <p>
6534 * <em>Effectively identical sequences:</em>
6535 * <a id="effid"></a>
6536 * A parameter list {@code A} is defined to be <em>effectively identical</em> to another parameter list {@code B}
6537 * if {@code A} and {@code B} are identical, or if {@code A} is shorter and is identical with a proper prefix of {@code B}.
6538 * When speaking of an unordered set of parameter lists, we say they the set is "effectively identical"
6539 * as a whole if the set contains a longest list, and all members of the set are effectively identical to
6540 * that longest list.
6541 * For example, any set of type sequences of the form {@code (V*)} is effectively identical,
6542 * and the same is true if more sequences of the form {@code (V... A*)} are added.
6543 * <p>
6544 * <em>Step 0: Determine clause structure.</em><ol type="a">
6545 * <li>The clause array (of type {@code MethodHandle[][]}) must be non-{@code null} and contain at least one element.
6546 * <li>The clause array may not contain {@code null}s or sub-arrays longer than four elements.
6547 * <li>Clauses shorter than four elements are treated as if they were padded by {@code null} elements to length
6548 * four. Padding takes place by appending elements to the array.
6549 * <li>Clauses with all {@code null}s are disregarded.
6550 * <li>Each clause is treated as a four-tuple of functions, called "init", "step", "pred", and "fini".
6551 * </ol>
6552 * <p>
6553 * <em>Step 1A: Determine iteration variable types {@code (V...)}.</em><ol type="a">
6554 * <li>The iteration variable type for each clause is determined using the clause's init and step return types.
6555 * <li>If both functions are omitted, there is no iteration variable for the corresponding clause ({@code void} is
6556 * used as the type to indicate that). If one of them is omitted, the other's return type defines the clause's
6557 * iteration variable type. If both are given, the common return type (they must be identical) defines the clause's
6558 * iteration variable type.
6559 * <li>Form the list of return types (in clause order), omitting all occurrences of {@code void}.
6560 * <li>This list of types is called the "iteration variable types" ({@code (V...)}).
6561 * </ol>
6562 * <p>
6563 * <em>Step 1B: Determine loop parameters {@code (A...)}.</em><ul>
6564 * <li>Examine and collect init function parameter lists (which are of the form {@code (A*)}).
6565 * <li>Examine and collect the suffixes of the step, pred, and fini parameter lists, after removing the iteration variable types.
6566 * (They must have the form {@code (V... A*)}; collect the {@code (A*)} parts only.)
6567 * <li>Do not collect suffixes from step, pred, and fini parameter lists that do not begin with all the iteration variable types.
6568 * (These types will be checked in step 2, along with all the clause function types.)
6569 * <li>Omitted clause functions are ignored. (Equivalently, they are deemed to have empty parameter lists.)
6570 * <li>All of the collected parameter lists must be effectively identical.
6571 * <li>The longest parameter list (which is necessarily unique) is called the "external parameter list" ({@code (A...)}).
6572 * <li>If there is no such parameter list, the external parameter list is taken to be the empty sequence.
6573 * <li>The combined list consisting of iteration variable types followed by the external parameter types is called
6574 * the "internal parameter list".
6575 * </ul>
6576 * <p>
6577 * <em>Step 1C: Determine loop return type.</em><ol type="a">
6578 * <li>Examine fini function return types, disregarding omitted fini functions.
6579 * <li>If there are no fini functions, the loop return type is {@code void}.
6580 * <li>Otherwise, the common return type {@code R} of the fini functions (their return types must be identical) defines the loop return
6581 * type.
6582 * </ol>
6583 * <p>
6584 * <em>Step 1D: Check other types.</em><ol type="a">
6585 * <li>There must be at least one non-omitted pred function.
6586 * <li>Every non-omitted pred function must have a {@code boolean} return type.
6587 * </ol>
6588 * <p>
6589 * <em>Step 2: Determine parameter lists.</em><ol type="a">
6590 * <li>The parameter list for the resulting loop handle will be the external parameter list {@code (A...)}.
6591 * <li>The parameter list for init functions will be adjusted to the external parameter list.
6592 * (Note that their parameter lists are already effectively identical to this list.)
6593 * <li>The parameter list for every non-omitted, non-init (step, pred, and fini) function must be
6594 * effectively identical to the internal parameter list {@code (V... A...)}.
6595 * </ol>
6596 * <p>
6597 * <em>Step 3: Fill in omitted functions.</em><ol type="a">
6598 * <li>If an init function is omitted, use a {@linkplain #empty default value} for the clause's iteration variable
6599 * type.
6600 * <li>If a step function is omitted, use an {@linkplain #identity identity function} of the clause's iteration
6601 * variable type; insert dropped argument parameters before the identity function parameter for the non-{@code void}
6602 * iteration variables of preceding clauses. (This will turn the loop variable into a local loop invariant.)
6603 * <li>If a pred function is omitted, use a constant {@code true} function. (This will keep the loop going, as far
6604 * as this clause is concerned. Note that in such cases the corresponding fini function is unreachable.)
6605 * <li>If a fini function is omitted, use a {@linkplain #empty default value} for the
6606 * loop return type.
6607 * </ol>
6608 * <p>
6609 * <em>Step 4: Fill in missing parameter types.</em><ol type="a">
6610 * <li>At this point, every init function parameter list is effectively identical to the external parameter list {@code (A...)},
6611 * but some lists may be shorter. For every init function with a short parameter list, pad out the end of the list.
6612 * <li>At this point, every non-init function parameter list is effectively identical to the internal parameter
6613 * list {@code (V... A...)}, but some lists may be shorter. For every non-init function with a short parameter list,
6614 * pad out the end of the list.
6615 * <li>Argument lists are padded out by {@linkplain #dropArgumentsToMatch(MethodHandle, int, List, int) dropping unused trailing arguments}.
6616 * </ol>
6617 * <p>
6618 * <em>Final observations.</em><ol type="a">
6619 * <li>After these steps, all clauses have been adjusted by supplying omitted functions and arguments.
6620 * <li>All init functions have a common parameter type list {@code (A...)}, which the final loop handle will also have.
6621 * <li>All fini functions have a common return type {@code R}, which the final loop handle will also have.
6622 * <li>All non-init functions have a common parameter type list {@code (V... A...)}, of
6623 * (non-{@code void}) iteration variables {@code V} followed by loop parameters.
6624 * <li>Each pair of init and step functions agrees in their return type {@code V}.
6625 * <li>Each non-init function will be able to observe the current values {@code (v...)} of all iteration variables.
6626 * <li>Every function will be able to observe the incoming values {@code (a...)} of all loop parameters.
6627 * </ol>
6628 * <p>
6629 * <em>Example.</em> As a consequence of step 1A above, the {@code loop} combinator has the following property:
6630 * <ul>
6631 * <li>Given {@code N} clauses {@code Cn = {null, Sn, Pn}} with {@code n = 1..N}.
6632 * <li>Suppose predicate handles {@code Pn} are either {@code null} or have no parameters.
6633 * (Only one {@code Pn} has to be non-{@code null}.)
6634 * <li>Suppose step handles {@code Sn} have signatures {@code (B1..BX)Rn}, for some constant {@code X>=N}.
6635 * <li>Suppose {@code Q} is the count of non-void types {@code Rn}, and {@code (V1...VQ)} is the sequence of those types.
6636 * <li>It must be that {@code Vn == Bn} for {@code n = 1..min(X,Q)}.
6637 * <li>The parameter types {@code Vn} will be interpreted as loop-local state elements {@code (V...)}.
6638 * <li>Any remaining types {@code BQ+1..BX} (if {@code Q<X}) will determine
6639 * the resulting loop handle's parameter types {@code (A...)}.
6640 * </ul>
6641 * In this example, the loop handle parameters {@code (A...)} were derived from the step functions,
6642 * which is natural if most of the loop computation happens in the steps. For some loops,
6643 * the burden of computation might be heaviest in the pred functions, and so the pred functions
6644 * might need to accept the loop parameter values. For loops with complex exit logic, the fini
6645 * functions might need to accept loop parameters, and likewise for loops with complex entry logic,
6646 * where the init functions will need the extra parameters. For such reasons, the rules for
6647 * determining these parameters are as symmetric as possible, across all clause parts.
6648 * In general, the loop parameters function as common invariant values across the whole
6649 * loop, while the iteration variables function as common variant values, or (if there is
6650 * no step function) as internal loop invariant temporaries.
6651 * <p>
6652 * <em>Loop execution.</em><ol type="a">
6653 * <li>When the loop is called, the loop input values are saved in locals, to be passed to
6654 * every clause function. These locals are loop invariant.
6655 * <li>Each init function is executed in clause order (passing the external arguments {@code (a...)})
6656 * and the non-{@code void} values are saved (as the iteration variables {@code (v...)}) into locals.
6657 * These locals will be loop varying (unless their steps behave as identity functions, as noted above).
6658 * <li>All function executions (except init functions) will be passed the internal parameter list, consisting of
6659 * the non-{@code void} iteration values {@code (v...)} (in clause order) and then the loop inputs {@code (a...)}
6660 * (in argument order).
6661 * <li>The step and pred functions are then executed, in clause order (step before pred), until a pred function
6662 * returns {@code false}.
6663 * <li>The non-{@code void} result from a step function call is used to update the corresponding value in the
6664 * sequence {@code (v...)} of loop variables.
6665 * The updated value is immediately visible to all subsequent function calls.
6666 * <li>If a pred function returns {@code false}, the corresponding fini function is called, and the resulting value
6667 * (of type {@code R}) is returned from the loop as a whole.
6668 * <li>If all the pred functions always return true, no fini function is ever invoked, and the loop cannot exit
6669 * except by throwing an exception.
6670 * </ol>
6671 * <p>
6672 * <em>Usage tips.</em>
6673 * <ul>
6674 * <li>Although each step function will receive the current values of <em>all</em> the loop variables,
6675 * sometimes a step function only needs to observe the current value of its own variable.
6676 * In that case, the step function may need to explicitly {@linkplain #dropArguments drop all preceding loop variables}.
6677 * This will require mentioning their types, in an expression like {@code dropArguments(step, 0, V0.class, ...)}.
6678 * <li>Loop variables are not required to vary; they can be loop invariant. A clause can create
6679 * a loop invariant by a suitable init function with no step, pred, or fini function. This may be
6680 * useful to "wire" an incoming loop argument into the step or pred function of an adjacent loop variable.
6681 * <li>If some of the clause functions are virtual methods on an instance, the instance
6682 * itself can be conveniently placed in an initial invariant loop "variable", using an initial clause
6683 * like {@code new MethodHandle[]{identity(ObjType.class)}}. In that case, the instance reference
6684 * will be the first iteration variable value, and it will be easy to use virtual
6685 * methods as clause parts, since all of them will take a leading instance reference matching that value.
6686 * </ul>
6687 * <p>
6688 * Here is pseudocode for the resulting loop handle. As above, {@code V} and {@code v} represent the types
6689 * and values of loop variables; {@code A} and {@code a} represent arguments passed to the whole loop;
6690 * and {@code R} is the common result type of all finalizers as well as of the resulting loop.
6691 * {@snippet lang="java" :
6692 * V... init...(A...);
6693 * boolean pred...(V..., A...);
6694 * V... step...(V..., A...);
6695 * R fini...(V..., A...);
6696 * R loop(A... a) {
6697 * V... v... = init...(a...);
6698 * for (;;) {
6699 * for ((v, p, s, f) in (v..., pred..., step..., fini...)) {
6700 * v = s(v..., a...);
6701 * if (!p(v..., a...)) {
6702 * return f(v..., a...);
6703 * }
6704 * }
6705 * }
6706 * }
6707 * }
6708 * Note that the parameter type lists {@code (V...)} and {@code (A...)} have been expanded
6709 * to their full length, even though individual clause functions may neglect to take them all.
6710 * As noted above, missing parameters are filled in as if by {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}.
6711 *
6712 * @apiNote Example:
6713 * {@snippet lang="java" :
6714 * // iterative implementation of the factorial function as a loop handle
6715 * static int one(int k) { return 1; }
6716 * static int inc(int i, int acc, int k) { return i + 1; }
6717 * static int mult(int i, int acc, int k) { return i * acc; }
6718 * static boolean pred(int i, int acc, int k) { return i < k; }
6719 * static int fin(int i, int acc, int k) { return acc; }
6720 * // assume MH_one, MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
6721 * // null initializer for counter, should initialize to 0
6722 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
6723 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
6724 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
6725 * assertEquals(120, loop.invoke(5));
6726 * }
6727 * The same example, dropping arguments and using combinators:
6728 * {@snippet lang="java" :
6729 * // simplified implementation of the factorial function as a loop handle
6730 * static int inc(int i) { return i + 1; } // drop acc, k
6731 * static int mult(int i, int acc) { return i * acc; } //drop k
6732 * static boolean cmp(int i, int k) { return i < k; }
6733 * // assume MH_inc, MH_mult, and MH_cmp are handles to the above methods
6734 * // null initializer for counter, should initialize to 0
6735 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
6736 * MethodHandle MH_pred = MethodHandles.dropArguments(MH_cmp, 1, int.class); // drop acc
6737 * MethodHandle MH_fin = MethodHandles.dropArguments(MethodHandles.identity(int.class), 0, int.class); // drop i
6738 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
6739 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
6740 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
6741 * assertEquals(720, loop.invoke(6));
6742 * }
6743 * A similar example, using a helper object to hold a loop parameter:
6744 * {@snippet lang="java" :
6745 * // instance-based implementation of the factorial function as a loop handle
6746 * static class FacLoop {
6747 * final int k;
6748 * FacLoop(int k) { this.k = k; }
6749 * int inc(int i) { return i + 1; }
6750 * int mult(int i, int acc) { return i * acc; }
6751 * boolean pred(int i) { return i < k; }
6752 * int fin(int i, int acc) { return acc; }
6753 * }
6754 * // assume MH_FacLoop is a handle to the constructor
6755 * // assume MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
6756 * // null initializer for counter, should initialize to 0
6757 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
6758 * MethodHandle[] instanceClause = new MethodHandle[]{MH_FacLoop};
6759 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
6760 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
6761 * MethodHandle loop = MethodHandles.loop(instanceClause, counterClause, accumulatorClause);
6762 * assertEquals(5040, loop.invoke(7));
6763 * }
6764 *
6765 * @param clauses an array of arrays (4-tuples) of {@link MethodHandle}s adhering to the rules described above.
6766 *
6767 * @return a method handle embodying the looping behavior as defined by the arguments.
6768 *
6769 * @throws IllegalArgumentException in case any of the constraints described above is violated.
6770 *
6771 * @see MethodHandles#whileLoop(MethodHandle, MethodHandle, MethodHandle)
6772 * @see MethodHandles#doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
6773 * @see MethodHandles#countedLoop(MethodHandle, MethodHandle, MethodHandle)
6774 * @see MethodHandles#iteratedLoop(MethodHandle, MethodHandle, MethodHandle)
6775 * @since 9
6776 */
6777 public static MethodHandle loop(MethodHandle[]... clauses) {
6778 // Step 0: determine clause structure.
6779 loopChecks0(clauses);
6780
6781 List<MethodHandle> init = new ArrayList<>();
6782 List<MethodHandle> step = new ArrayList<>();
6783 List<MethodHandle> pred = new ArrayList<>();
6784 List<MethodHandle> fini = new ArrayList<>();
6785
6786 Stream.of(clauses).filter(c -> Stream.of(c).anyMatch(Objects::nonNull)).forEach(clause -> {
6787 init.add(clause[0]); // all clauses have at least length 1
6788 step.add(clause.length <= 1 ? null : clause[1]);
6789 pred.add(clause.length <= 2 ? null : clause[2]);
6790 fini.add(clause.length <= 3 ? null : clause[3]);
6791 });
6792
6793 assert Stream.of(init, step, pred, fini).map(List::size).distinct().count() == 1;
6794 final int nclauses = init.size();
6795
6796 // Step 1A: determine iteration variables (V...).
6797 final List<Class<?>> iterationVariableTypes = new ArrayList<>();
6798 for (int i = 0; i < nclauses; ++i) {
6799 MethodHandle in = init.get(i);
6800 MethodHandle st = step.get(i);
6801 if (in == null && st == null) {
6802 iterationVariableTypes.add(void.class);
6803 } else if (in != null && st != null) {
6804 loopChecks1a(i, in, st);
6805 iterationVariableTypes.add(in.type().returnType());
6806 } else {
6807 iterationVariableTypes.add(in == null ? st.type().returnType() : in.type().returnType());
6808 }
6809 }
6810 final List<Class<?>> commonPrefix = iterationVariableTypes.stream().filter(t -> t != void.class).toList();
6811
6812 // Step 1B: determine loop parameters (A...).
6813 final List<Class<?>> commonSuffix = buildCommonSuffix(init, step, pred, fini, commonPrefix.size());
6814 loopChecks1b(init, commonSuffix);
6815
6816 // Step 1C: determine loop return type.
6817 // Step 1D: check other types.
6818 // local variable required here; see JDK-8223553
6819 Stream<Class<?>> cstream = fini.stream().filter(Objects::nonNull).map(MethodHandle::type)
6820 .map(MethodType::returnType);
6821 final Class<?> loopReturnType = cstream.findFirst().orElse(void.class);
6822 loopChecks1cd(pred, fini, loopReturnType);
6823
6824 // Step 2: determine parameter lists.
6825 final List<Class<?>> commonParameterSequence = new ArrayList<>(commonPrefix);
6826 commonParameterSequence.addAll(commonSuffix);
6827 loopChecks2(step, pred, fini, commonParameterSequence);
6828 // Step 3: fill in omitted functions.
6829 for (int i = 0; i < nclauses; ++i) {
6830 Class<?> t = iterationVariableTypes.get(i);
6831 if (init.get(i) == null) {
6832 init.set(i, empty(methodType(t, commonSuffix)));
6833 }
6834 if (step.get(i) == null) {
6835 step.set(i, dropArgumentsToMatch(identityOrVoid(t), 0, commonParameterSequence, i));
6836 }
6837 if (pred.get(i) == null) {
6838 pred.set(i, dropArguments(constant(boolean.class, true), 0, commonParameterSequence));
6839 }
6840 if (fini.get(i) == null) {
6841 fini.set(i, empty(methodType(t, commonParameterSequence)));
6842 }
6843 }
6844
6845 // Step 4: fill in missing parameter types.
6846 // Also convert all handles to fixed-arity handles.
6847 List<MethodHandle> finit = fixArities(fillParameterTypes(init, commonSuffix));
6848 List<MethodHandle> fstep = fixArities(fillParameterTypes(step, commonParameterSequence));
6849 List<MethodHandle> fpred = fixArities(fillParameterTypes(pred, commonParameterSequence));
6850 List<MethodHandle> ffini = fixArities(fillParameterTypes(fini, commonParameterSequence));
6851
6852 assert finit.stream().map(MethodHandle::type).map(MethodType::parameterList).
6853 allMatch(pl -> pl.equals(commonSuffix));
6854 assert Stream.of(fstep, fpred, ffini).flatMap(List::stream).map(MethodHandle::type).map(MethodType::parameterList).
6855 allMatch(pl -> pl.equals(commonParameterSequence));
6856
6857 return MethodHandleImpl.makeLoop(loopReturnType, commonSuffix, finit, fstep, fpred, ffini);
6858 }
6859
6860 private static void loopChecks0(MethodHandle[][] clauses) {
6861 if (clauses == null || clauses.length == 0) {
6862 throw newIllegalArgumentException("null or no clauses passed");
6863 }
6864 if (Stream.of(clauses).anyMatch(Objects::isNull)) {
6865 throw newIllegalArgumentException("null clauses are not allowed");
6866 }
6867 if (Stream.of(clauses).anyMatch(c -> c.length > 4)) {
6868 throw newIllegalArgumentException("All loop clauses must be represented as MethodHandle arrays with at most 4 elements.");
6869 }
6870 }
6871
6872 private static void loopChecks1a(int i, MethodHandle in, MethodHandle st) {
6873 if (in.type().returnType() != st.type().returnType()) {
6874 throw misMatchedTypes("clause " + i + ": init and step return types", in.type().returnType(),
6875 st.type().returnType());
6876 }
6877 }
6878
6879 private static List<Class<?>> longestParameterList(Stream<MethodHandle> mhs, int skipSize) {
6880 return mhs.filter(Objects::nonNull)
6881 // take only those that can contribute to a common suffix because they are longer than the prefix
6882 .map(MethodHandle::type)
6883 .filter(t -> t.parameterCount() > skipSize)
6884 .max(Comparator.comparingInt(MethodType::parameterCount))
6885 .map(methodType -> List.of(Arrays.copyOfRange(methodType.ptypes(), skipSize, methodType.parameterCount())))
6886 .orElse(List.of());
6887 }
6888
6889 private static List<Class<?>> buildCommonSuffix(List<MethodHandle> init, List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, int cpSize) {
6890 final List<Class<?>> longest1 = longestParameterList(Stream.of(step, pred, fini).flatMap(List::stream), cpSize);
6891 final List<Class<?>> longest2 = longestParameterList(init.stream(), 0);
6892 return longest1.size() >= longest2.size() ? longest1 : longest2;
6893 }
6894
6895 private static void loopChecks1b(List<MethodHandle> init, List<Class<?>> commonSuffix) {
6896 if (init.stream().filter(Objects::nonNull).map(MethodHandle::type).
6897 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonSuffix))) {
6898 throw newIllegalArgumentException("found non-effectively identical init parameter type lists: " + init +
6899 " (common suffix: " + commonSuffix + ")");
6900 }
6901 }
6902
6903 private static void loopChecks1cd(List<MethodHandle> pred, List<MethodHandle> fini, Class<?> loopReturnType) {
6904 if (fini.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
6905 anyMatch(t -> t != loopReturnType)) {
6906 throw newIllegalArgumentException("found non-identical finalizer return types: " + fini + " (return type: " +
6907 loopReturnType + ")");
6908 }
6909
6910 if (pred.stream().noneMatch(Objects::nonNull)) {
6911 throw newIllegalArgumentException("no predicate found", pred);
6912 }
6913 if (pred.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
6914 anyMatch(t -> t != boolean.class)) {
6915 throw newIllegalArgumentException("predicates must have boolean return type", pred);
6916 }
6917 }
6918
6919 private static void loopChecks2(List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, List<Class<?>> commonParameterSequence) {
6920 if (Stream.of(step, pred, fini).flatMap(List::stream).filter(Objects::nonNull).map(MethodHandle::type).
6921 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonParameterSequence))) {
6922 throw newIllegalArgumentException("found non-effectively identical parameter type lists:\nstep: " + step +
6923 "\npred: " + pred + "\nfini: " + fini + " (common parameter sequence: " + commonParameterSequence + ")");
6924 }
6925 }
6926
6927 private static List<MethodHandle> fillParameterTypes(List<MethodHandle> hs, final List<Class<?>> targetParams) {
6928 return hs.stream().map(h -> {
6929 int pc = h.type().parameterCount();
6930 int tpsize = targetParams.size();
6931 return pc < tpsize ? dropArguments(h, pc, targetParams.subList(pc, tpsize)) : h;
6932 }).toList();
6933 }
6934
6935 private static List<MethodHandle> fixArities(List<MethodHandle> hs) {
6936 return hs.stream().map(MethodHandle::asFixedArity).toList();
6937 }
6938
6939 /**
6940 * Constructs a {@code while} loop from an initializer, a body, and a predicate.
6941 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
6942 * <p>
6943 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
6944 * method will, in each iteration, first evaluate the predicate and then execute its body (if the predicate
6945 * evaluates to {@code true}).
6946 * The loop will terminate once the predicate evaluates to {@code false} (the body will not be executed in this case).
6947 * <p>
6948 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
6949 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
6950 * and updated with the value returned from its invocation. The result of loop execution will be
6951 * the final value of the additional loop-local variable (if present).
6952 * <p>
6953 * The following rules hold for these argument handles:<ul>
6954 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
6955 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
6956 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
6957 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
6958 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
6959 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
6960 * It will constrain the parameter lists of the other loop parts.
6961 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
6962 * list {@code (A...)} is called the <em>external parameter list</em>.
6963 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
6964 * additional state variable of the loop.
6965 * The body must both accept and return a value of this type {@code V}.
6966 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
6967 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
6968 * <a href="MethodHandles.html#effid">effectively identical</a>
6969 * to the external parameter list {@code (A...)}.
6970 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
6971 * {@linkplain #empty default value}.
6972 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
6973 * Its parameter list (either empty or of the form {@code (V A*)}) must be
6974 * effectively identical to the internal parameter list.
6975 * </ul>
6976 * <p>
6977 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
6978 * <li>The loop handle's result type is the result type {@code V} of the body.
6979 * <li>The loop handle's parameter types are the types {@code (A...)},
6980 * from the external parameter list.
6981 * </ul>
6982 * <p>
6983 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
6984 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
6985 * passed to the loop.
6986 * {@snippet lang="java" :
6987 * V init(A...);
6988 * boolean pred(V, A...);
6989 * V body(V, A...);
6990 * V whileLoop(A... a...) {
6991 * V v = init(a...);
6992 * while (pred(v, a...)) {
6993 * v = body(v, a...);
6994 * }
6995 * return v;
6996 * }
6997 * }
6998 *
6999 * @apiNote Example:
7000 * {@snippet lang="java" :
7001 * // implement the zip function for lists as a loop handle
7002 * static List<String> initZip(Iterator<String> a, Iterator<String> b) { return new ArrayList<>(); }
7003 * static boolean zipPred(List<String> zip, Iterator<String> a, Iterator<String> b) { return a.hasNext() && b.hasNext(); }
7004 * static List<String> zipStep(List<String> zip, Iterator<String> a, Iterator<String> b) {
7005 * zip.add(a.next());
7006 * zip.add(b.next());
7007 * return zip;
7008 * }
7009 * // assume MH_initZip, MH_zipPred, and MH_zipStep are handles to the above methods
7010 * MethodHandle loop = MethodHandles.whileLoop(MH_initZip, MH_zipPred, MH_zipStep);
7011 * List<String> a = Arrays.asList("a", "b", "c", "d");
7012 * List<String> b = Arrays.asList("e", "f", "g", "h");
7013 * List<String> zipped = Arrays.asList("a", "e", "b", "f", "c", "g", "d", "h");
7014 * assertEquals(zipped, (List<String>) loop.invoke(a.iterator(), b.iterator()));
7015 * }
7016 *
7017 *
7018 * @apiNote The implementation of this method can be expressed as follows:
7019 * {@snippet lang="java" :
7020 * MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
7021 * MethodHandle fini = (body.type().returnType() == void.class
7022 * ? null : identity(body.type().returnType()));
7023 * MethodHandle[]
7024 * checkExit = { null, null, pred, fini },
7025 * varBody = { init, body };
7026 * return loop(checkExit, varBody);
7027 * }
7028 * }
7029 *
7030 * @param init optional initializer, providing the initial value of the loop variable.
7031 * May be {@code null}, implying a default initial value. See above for other constraints.
7032 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
7033 * above for other constraints.
7034 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
7035 * See above for other constraints.
7036 *
7037 * @return a method handle implementing the {@code while} loop as described by the arguments.
7038 * @throws IllegalArgumentException if the rules for the arguments are violated.
7039 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
7040 *
7041 * @see #loop(MethodHandle[][])
7042 * @see #doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
7043 * @since 9
7044 */
7045 public static MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
7046 whileLoopChecks(init, pred, body);
7047 MethodHandle fini = identityOrVoid(body.type().returnType());
7048 MethodHandle[] checkExit = { null, null, pred, fini };
7049 MethodHandle[] varBody = { init, body };
7050 return loop(checkExit, varBody);
7051 }
7052
7053 /**
7054 * Constructs a {@code do-while} loop from an initializer, a body, and a predicate.
7055 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
7056 * <p>
7057 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
7058 * method will, in each iteration, first execute its body and then evaluate the predicate.
7059 * The loop will terminate once the predicate evaluates to {@code false} after an execution of the body.
7060 * <p>
7061 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
7062 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
7063 * and updated with the value returned from its invocation. The result of loop execution will be
7064 * the final value of the additional loop-local variable (if present).
7065 * <p>
7066 * The following rules hold for these argument handles:<ul>
7067 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
7068 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
7069 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
7070 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
7071 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
7072 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
7073 * It will constrain the parameter lists of the other loop parts.
7074 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
7075 * list {@code (A...)} is called the <em>external parameter list</em>.
7076 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
7077 * additional state variable of the loop.
7078 * The body must both accept and return a value of this type {@code V}.
7079 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
7080 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
7081 * <a href="MethodHandles.html#effid">effectively identical</a>
7082 * to the external parameter list {@code (A...)}.
7083 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
7084 * {@linkplain #empty default value}.
7085 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
7086 * Its parameter list (either empty or of the form {@code (V A*)}) must be
7087 * effectively identical to the internal parameter list.
7088 * </ul>
7089 * <p>
7090 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
7091 * <li>The loop handle's result type is the result type {@code V} of the body.
7092 * <li>The loop handle's parameter types are the types {@code (A...)},
7093 * from the external parameter list.
7094 * </ul>
7095 * <p>
7096 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
7097 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
7098 * passed to the loop.
7099 * {@snippet lang="java" :
7100 * V init(A...);
7101 * boolean pred(V, A...);
7102 * V body(V, A...);
7103 * V doWhileLoop(A... a...) {
7104 * V v = init(a...);
7105 * do {
7106 * v = body(v, a...);
7107 * } while (pred(v, a...));
7108 * return v;
7109 * }
7110 * }
7111 *
7112 * @apiNote Example:
7113 * {@snippet lang="java" :
7114 * // int i = 0; while (i < limit) { ++i; } return i; => limit
7115 * static int zero(int limit) { return 0; }
7116 * static int step(int i, int limit) { return i + 1; }
7117 * static boolean pred(int i, int limit) { return i < limit; }
7118 * // assume MH_zero, MH_step, and MH_pred are handles to the above methods
7119 * MethodHandle loop = MethodHandles.doWhileLoop(MH_zero, MH_step, MH_pred);
7120 * assertEquals(23, loop.invoke(23));
7121 * }
7122 *
7123 *
7124 * @apiNote The implementation of this method can be expressed as follows:
7125 * {@snippet lang="java" :
7126 * MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
7127 * MethodHandle fini = (body.type().returnType() == void.class
7128 * ? null : identity(body.type().returnType()));
7129 * MethodHandle[] clause = { init, body, pred, fini };
7130 * return loop(clause);
7131 * }
7132 * }
7133 *
7134 * @param init optional initializer, providing the initial value of the loop variable.
7135 * May be {@code null}, implying a default initial value. See above for other constraints.
7136 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
7137 * See above for other constraints.
7138 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
7139 * above for other constraints.
7140 *
7141 * @return a method handle implementing the {@code while} loop as described by the arguments.
7142 * @throws IllegalArgumentException if the rules for the arguments are violated.
7143 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
7144 *
7145 * @see #loop(MethodHandle[][])
7146 * @see #whileLoop(MethodHandle, MethodHandle, MethodHandle)
7147 * @since 9
7148 */
7149 public static MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
7150 whileLoopChecks(init, pred, body);
7151 MethodHandle fini = identityOrVoid(body.type().returnType());
7152 MethodHandle[] clause = {init, body, pred, fini };
7153 return loop(clause);
7154 }
7155
7156 private static void whileLoopChecks(MethodHandle init, MethodHandle pred, MethodHandle body) {
7157 Objects.requireNonNull(pred);
7158 Objects.requireNonNull(body);
7159 MethodType bodyType = body.type();
7160 Class<?> returnType = bodyType.returnType();
7161 List<Class<?>> innerList = bodyType.parameterList();
7162 List<Class<?>> outerList = innerList;
7163 if (returnType == void.class) {
7164 // OK
7165 } else if (innerList.isEmpty() || innerList.get(0) != returnType) {
7166 // leading V argument missing => error
7167 MethodType expected = bodyType.insertParameterTypes(0, returnType);
7168 throw misMatchedTypes("body function", bodyType, expected);
7169 } else {
7170 outerList = innerList.subList(1, innerList.size());
7171 }
7172 MethodType predType = pred.type();
7173 if (predType.returnType() != boolean.class ||
7174 !predType.effectivelyIdenticalParameters(0, innerList)) {
7175 throw misMatchedTypes("loop predicate", predType, methodType(boolean.class, innerList));
7176 }
7177 if (init != null) {
7178 MethodType initType = init.type();
7179 if (initType.returnType() != returnType ||
7180 !initType.effectivelyIdenticalParameters(0, outerList)) {
7181 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
7182 }
7183 }
7184 }
7185
7186 /**
7187 * Constructs a loop that runs a given number of iterations.
7188 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
7189 * <p>
7190 * The number of iterations is determined by the {@code iterations} handle evaluation result.
7191 * The loop counter {@code i} is an extra loop iteration variable of type {@code int}.
7192 * It will be initialized to 0 and incremented by 1 in each iteration.
7193 * <p>
7194 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
7195 * of that type is also present. This variable is initialized using the optional {@code init} handle,
7196 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
7197 * <p>
7198 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
7199 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
7200 * iteration variable.
7201 * The result of the loop handle execution will be the final {@code V} value of that variable
7202 * (or {@code void} if there is no {@code V} variable).
7203 * <p>
7204 * The following rules hold for the argument handles:<ul>
7205 * <li>The {@code iterations} handle must not be {@code null}, and must return
7206 * the type {@code int}, referred to here as {@code I} in parameter type lists.
7207 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
7208 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
7209 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
7210 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
7211 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
7212 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
7213 * of types called the <em>internal parameter list</em>.
7214 * It will constrain the parameter lists of the other loop parts.
7215 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
7216 * with no additional {@code A} types, then the internal parameter list is extended by
7217 * the argument types {@code A...} of the {@code iterations} handle.
7218 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
7219 * list {@code (A...)} is called the <em>external parameter list</em>.
7220 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
7221 * additional state variable of the loop.
7222 * The body must both accept a leading parameter and return a value of this type {@code V}.
7223 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
7224 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
7225 * <a href="MethodHandles.html#effid">effectively identical</a>
7226 * to the external parameter list {@code (A...)}.
7227 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
7228 * {@linkplain #empty default value}.
7229 * <li>The parameter list of {@code iterations} (of some form {@code (A*)}) must be
7230 * effectively identical to the external parameter list {@code (A...)}.
7231 * </ul>
7232 * <p>
7233 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
7234 * <li>The loop handle's result type is the result type {@code V} of the body.
7235 * <li>The loop handle's parameter types are the types {@code (A...)},
7236 * from the external parameter list.
7237 * </ul>
7238 * <p>
7239 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
7240 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
7241 * arguments passed to the loop.
7242 * {@snippet lang="java" :
7243 * int iterations(A...);
7244 * V init(A...);
7245 * V body(V, int, A...);
7246 * V countedLoop(A... a...) {
7247 * int end = iterations(a...);
7248 * V v = init(a...);
7249 * for (int i = 0; i < end; ++i) {
7250 * v = body(v, i, a...);
7251 * }
7252 * return v;
7253 * }
7254 * }
7255 *
7256 * @apiNote Example with a fully conformant body method:
7257 * {@snippet lang="java" :
7258 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
7259 * // => a variation on a well known theme
7260 * static String step(String v, int counter, String init) { return "na " + v; }
7261 * // assume MH_step is a handle to the method above
7262 * MethodHandle fit13 = MethodHandles.constant(int.class, 13);
7263 * MethodHandle start = MethodHandles.identity(String.class);
7264 * MethodHandle loop = MethodHandles.countedLoop(fit13, start, MH_step);
7265 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("Lambdaman!"));
7266 * }
7267 *
7268 * @apiNote Example with the simplest possible body method type,
7269 * and passing the number of iterations to the loop invocation:
7270 * {@snippet lang="java" :
7271 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
7272 * // => a variation on a well known theme
7273 * static String step(String v, int counter ) { return "na " + v; }
7274 * // assume MH_step is a handle to the method above
7275 * MethodHandle count = MethodHandles.dropArguments(MethodHandles.identity(int.class), 1, String.class);
7276 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class);
7277 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i) -> "na " + v
7278 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "Lambdaman!"));
7279 * }
7280 *
7281 * @apiNote Example that treats the number of iterations, string to append to, and string to append
7282 * as loop parameters:
7283 * {@snippet lang="java" :
7284 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
7285 * // => a variation on a well known theme
7286 * static String step(String v, int counter, int iterations_, String pre, String start_) { return pre + " " + v; }
7287 * // assume MH_step is a handle to the method above
7288 * MethodHandle count = MethodHandles.identity(int.class);
7289 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class, String.class);
7290 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i, _, pre, _) -> pre + " " + v
7291 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "na", "Lambdaman!"));
7292 * }
7293 *
7294 * @apiNote Example that illustrates the usage of {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}
7295 * to enforce a loop type:
7296 * {@snippet lang="java" :
7297 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
7298 * // => a variation on a well known theme
7299 * static String step(String v, int counter, String pre) { return pre + " " + v; }
7300 * // assume MH_step is a handle to the method above
7301 * MethodType loopType = methodType(String.class, String.class, int.class, String.class);
7302 * MethodHandle count = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(int.class), 0, loopType.parameterList(), 1);
7303 * MethodHandle start = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(String.class), 0, loopType.parameterList(), 2);
7304 * MethodHandle body = MethodHandles.dropArgumentsToMatch(MH_step, 2, loopType.parameterList(), 0);
7305 * MethodHandle loop = MethodHandles.countedLoop(count, start, body); // (v, i, pre, _, _) -> pre + " " + v
7306 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("na", 13, "Lambdaman!"));
7307 * }
7308 *
7309 * @apiNote The implementation of this method can be expressed as follows:
7310 * {@snippet lang="java" :
7311 * MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
7312 * return countedLoop(empty(iterations.type()), iterations, init, body);
7313 * }
7314 * }
7315 *
7316 * @param iterations a non-{@code null} handle to return the number of iterations this loop should run. The handle's
7317 * result type must be {@code int}. See above for other constraints.
7318 * @param init optional initializer, providing the initial value of the loop variable.
7319 * May be {@code null}, implying a default initial value. See above for other constraints.
7320 * @param body body of the loop, which may not be {@code null}.
7321 * It controls the loop parameters and result type in the standard case (see above for details).
7322 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
7323 * and may accept any number of additional types.
7324 * See above for other constraints.
7325 *
7326 * @return a method handle representing the loop.
7327 * @throws NullPointerException if either of the {@code iterations} or {@code body} handles is {@code null}.
7328 * @throws IllegalArgumentException if any argument violates the rules formulated above.
7329 *
7330 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle, MethodHandle)
7331 * @since 9
7332 */
7333 public static MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
7334 return countedLoop(empty(iterations.type()), iterations, init, body);
7335 }
7336
7337 /**
7338 * Constructs a loop that counts over a range of numbers.
7339 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
7340 * <p>
7341 * The loop counter {@code i} is a loop iteration variable of type {@code int}.
7342 * The {@code start} and {@code end} handles determine the start (inclusive) and end (exclusive)
7343 * values of the loop counter.
7344 * The loop counter will be initialized to the {@code int} value returned from the evaluation of the
7345 * {@code start} handle and run to the value returned from {@code end} (exclusively) with a step width of 1.
7346 * <p>
7347 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
7348 * of that type is also present. This variable is initialized using the optional {@code init} handle,
7349 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
7350 * <p>
7351 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
7352 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
7353 * iteration variable.
7354 * The result of the loop handle execution will be the final {@code V} value of that variable
7355 * (or {@code void} if there is no {@code V} variable).
7356 * <p>
7357 * The following rules hold for the argument handles:<ul>
7358 * <li>The {@code start} and {@code end} handles must not be {@code null}, and must both return
7359 * the common type {@code int}, referred to here as {@code I} in parameter type lists.
7360 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
7361 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
7362 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
7363 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
7364 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
7365 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
7366 * of types called the <em>internal parameter list</em>.
7367 * It will constrain the parameter lists of the other loop parts.
7368 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
7369 * with no additional {@code A} types, then the internal parameter list is extended by
7370 * the argument types {@code A...} of the {@code end} handle.
7371 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
7372 * list {@code (A...)} is called the <em>external parameter list</em>.
7373 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
7374 * additional state variable of the loop.
7375 * The body must both accept a leading parameter and return a value of this type {@code V}.
7376 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
7377 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
7378 * <a href="MethodHandles.html#effid">effectively identical</a>
7379 * to the external parameter list {@code (A...)}.
7380 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
7381 * {@linkplain #empty default value}.
7382 * <li>The parameter list of {@code start} (of some form {@code (A*)}) must be
7383 * effectively identical to the external parameter list {@code (A...)}.
7384 * <li>Likewise, the parameter list of {@code end} must be effectively identical
7385 * to the external parameter list.
7386 * </ul>
7387 * <p>
7388 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
7389 * <li>The loop handle's result type is the result type {@code V} of the body.
7390 * <li>The loop handle's parameter types are the types {@code (A...)},
7391 * from the external parameter list.
7392 * </ul>
7393 * <p>
7394 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
7395 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
7396 * arguments passed to the loop.
7397 * {@snippet lang="java" :
7398 * int start(A...);
7399 * int end(A...);
7400 * V init(A...);
7401 * V body(V, int, A...);
7402 * V countedLoop(A... a...) {
7403 * int e = end(a...);
7404 * int s = start(a...);
7405 * V v = init(a...);
7406 * for (int i = s; i < e; ++i) {
7407 * v = body(v, i, a...);
7408 * }
7409 * return v;
7410 * }
7411 * }
7412 *
7413 * @apiNote The implementation of this method can be expressed as follows:
7414 * {@snippet lang="java" :
7415 * MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
7416 * MethodHandle returnVar = dropArguments(identity(init.type().returnType()), 0, int.class, int.class);
7417 * // assume MH_increment and MH_predicate are handles to implementation-internal methods with
7418 * // the following semantics:
7419 * // MH_increment: (int limit, int counter) -> counter + 1
7420 * // MH_predicate: (int limit, int counter) -> counter < limit
7421 * Class<?> counterType = start.type().returnType(); // int
7422 * Class<?> returnType = body.type().returnType();
7423 * MethodHandle incr = MH_increment, pred = MH_predicate, retv = null;
7424 * if (returnType != void.class) { // ignore the V variable
7425 * incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
7426 * pred = dropArguments(pred, 1, returnType); // ditto
7427 * retv = dropArguments(identity(returnType), 0, counterType); // ignore limit
7428 * }
7429 * body = dropArguments(body, 0, counterType); // ignore the limit variable
7430 * MethodHandle[]
7431 * loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
7432 * bodyClause = { init, body }, // v = init(); v = body(v, i)
7433 * indexVar = { start, incr }; // i = start(); i = i + 1
7434 * return loop(loopLimit, bodyClause, indexVar);
7435 * }
7436 * }
7437 *
7438 * @param start a non-{@code null} handle to return the start value of the loop counter, which must be {@code int}.
7439 * See above for other constraints.
7440 * @param end a non-{@code null} handle to return the end value of the loop counter (the loop will run to
7441 * {@code end-1}). The result type must be {@code int}. See above for other constraints.
7442 * @param init optional initializer, providing the initial value of the loop variable.
7443 * May be {@code null}, implying a default initial value. See above for other constraints.
7444 * @param body body of the loop, which may not be {@code null}.
7445 * It controls the loop parameters and result type in the standard case (see above for details).
7446 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
7447 * and may accept any number of additional types.
7448 * See above for other constraints.
7449 *
7450 * @return a method handle representing the loop.
7451 * @throws NullPointerException if any of the {@code start}, {@code end}, or {@code body} handles is {@code null}.
7452 * @throws IllegalArgumentException if any argument violates the rules formulated above.
7453 *
7454 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle)
7455 * @since 9
7456 */
7457 public static MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
7458 countedLoopChecks(start, end, init, body);
7459 Class<?> counterType = start.type().returnType(); // int, but who's counting?
7460 Class<?> limitType = end.type().returnType(); // yes, int again
7461 Class<?> returnType = body.type().returnType();
7462 MethodHandle incr = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopStep);
7463 MethodHandle pred = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopPred);
7464 MethodHandle retv = null;
7465 if (returnType != void.class) {
7466 incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
7467 pred = dropArguments(pred, 1, returnType); // ditto
7468 retv = dropArguments(identity(returnType), 0, counterType);
7469 }
7470 body = dropArguments(body, 0, counterType); // ignore the limit variable
7471 MethodHandle[]
7472 loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
7473 bodyClause = { init, body }, // v = init(); v = body(v, i)
7474 indexVar = { start, incr }; // i = start(); i = i + 1
7475 return loop(loopLimit, bodyClause, indexVar);
7476 }
7477
7478 private static void countedLoopChecks(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
7479 Objects.requireNonNull(start);
7480 Objects.requireNonNull(end);
7481 Objects.requireNonNull(body);
7482 Class<?> counterType = start.type().returnType();
7483 if (counterType != int.class) {
7484 MethodType expected = start.type().changeReturnType(int.class);
7485 throw misMatchedTypes("start function", start.type(), expected);
7486 } else if (end.type().returnType() != counterType) {
7487 MethodType expected = end.type().changeReturnType(counterType);
7488 throw misMatchedTypes("end function", end.type(), expected);
7489 }
7490 MethodType bodyType = body.type();
7491 Class<?> returnType = bodyType.returnType();
7492 List<Class<?>> innerList = bodyType.parameterList();
7493 // strip leading V value if present
7494 int vsize = (returnType == void.class ? 0 : 1);
7495 if (vsize != 0 && (innerList.isEmpty() || innerList.get(0) != returnType)) {
7496 // argument list has no "V" => error
7497 MethodType expected = bodyType.insertParameterTypes(0, returnType);
7498 throw misMatchedTypes("body function", bodyType, expected);
7499 } else if (innerList.size() <= vsize || innerList.get(vsize) != counterType) {
7500 // missing I type => error
7501 MethodType expected = bodyType.insertParameterTypes(vsize, counterType);
7502 throw misMatchedTypes("body function", bodyType, expected);
7503 }
7504 List<Class<?>> outerList = innerList.subList(vsize + 1, innerList.size());
7505 if (outerList.isEmpty()) {
7506 // special case; take lists from end handle
7507 outerList = end.type().parameterList();
7508 innerList = bodyType.insertParameterTypes(vsize + 1, outerList).parameterList();
7509 }
7510 MethodType expected = methodType(counterType, outerList);
7511 if (!start.type().effectivelyIdenticalParameters(0, outerList)) {
7512 throw misMatchedTypes("start parameter types", start.type(), expected);
7513 }
7514 if (end.type() != start.type() &&
7515 !end.type().effectivelyIdenticalParameters(0, outerList)) {
7516 throw misMatchedTypes("end parameter types", end.type(), expected);
7517 }
7518 if (init != null) {
7519 MethodType initType = init.type();
7520 if (initType.returnType() != returnType ||
7521 !initType.effectivelyIdenticalParameters(0, outerList)) {
7522 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
7523 }
7524 }
7525 }
7526
7527 /**
7528 * Constructs a loop that ranges over the values produced by an {@code Iterator<T>}.
7529 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
7530 * <p>
7531 * The iterator itself will be determined by the evaluation of the {@code iterator} handle.
7532 * Each value it produces will be stored in a loop iteration variable of type {@code T}.
7533 * <p>
7534 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
7535 * of that type is also present. This variable is initialized using the optional {@code init} handle,
7536 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
7537 * <p>
7538 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
7539 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
7540 * iteration variable.
7541 * The result of the loop handle execution will be the final {@code V} value of that variable
7542 * (or {@code void} if there is no {@code V} variable).
7543 * <p>
7544 * The following rules hold for the argument handles:<ul>
7545 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
7546 * {@code (V T A...)V}, where {@code V} is non-{@code void}, or else {@code (T A...)void}.
7547 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
7548 * and we will write {@code (V T A...)V} with the understanding that a {@code void} type {@code V}
7549 * is quietly dropped from the parameter list, leaving {@code (T A...)V}.)
7550 * <li>The parameter list {@code (V T A...)} of the body contributes to a list
7551 * of types called the <em>internal parameter list</em>.
7552 * It will constrain the parameter lists of the other loop parts.
7553 * <li>As a special case, if the body contributes only {@code V} and {@code T} types,
7554 * with no additional {@code A} types, then the internal parameter list is extended by
7555 * the argument types {@code A...} of the {@code iterator} handle; if it is {@code null} the
7556 * single type {@code Iterable} is added and constitutes the {@code A...} list.
7557 * <li>If the iteration variable types {@code (V T)} are dropped from the internal parameter list, the resulting shorter
7558 * list {@code (A...)} is called the <em>external parameter list</em>.
7559 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
7560 * additional state variable of the loop.
7561 * The body must both accept a leading parameter and return a value of this type {@code V}.
7562 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
7563 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
7564 * <a href="MethodHandles.html#effid">effectively identical</a>
7565 * to the external parameter list {@code (A...)}.
7566 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
7567 * {@linkplain #empty default value}.
7568 * <li>If the {@code iterator} handle is non-{@code null}, it must have the return
7569 * type {@code java.util.Iterator} or a subtype thereof.
7570 * The iterator it produces when the loop is executed will be assumed
7571 * to yield values which can be converted to type {@code T}.
7572 * <li>The parameter list of an {@code iterator} that is non-{@code null} (of some form {@code (A*)}) must be
7573 * effectively identical to the external parameter list {@code (A...)}.
7574 * <li>If {@code iterator} is {@code null} it defaults to a method handle which behaves
7575 * like {@link java.lang.Iterable#iterator()}. In that case, the internal parameter list
7576 * {@code (V T A...)} must have at least one {@code A} type, and the default iterator
7577 * handle parameter is adjusted to accept the leading {@code A} type, as if by
7578 * the {@link MethodHandle#asType asType} conversion method.
7579 * The leading {@code A} type must be {@code Iterable} or a subtype thereof.
7580 * This conversion step, done at loop construction time, must not throw a {@code WrongMethodTypeException}.
7581 * </ul>
7582 * <p>
7583 * The type {@code T} may be either a primitive or reference.
7584 * Since type {@code Iterator<T>} is erased in the method handle representation to the raw type {@code Iterator},
7585 * the {@code iteratedLoop} combinator adjusts the leading argument type for {@code body} to {@code Object}
7586 * as if by the {@link MethodHandle#asType asType} conversion method.
7587 * Therefore, if an iterator of the wrong type appears as the loop is executed, runtime exceptions may occur
7588 * as the result of dynamic conversions performed by {@link MethodHandle#asType(MethodType)}.
7589 * <p>
7590 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
7591 * <li>The loop handle's result type is the result type {@code V} of the body.
7592 * <li>The loop handle's parameter types are the types {@code (A...)},
7593 * from the external parameter list.
7594 * </ul>
7595 * <p>
7596 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
7597 * the loop variable as well as the result type of the loop; {@code T}/{@code t}, that of the elements of the
7598 * structure the loop iterates over, and {@code A...}/{@code a...} represent arguments passed to the loop.
7599 * {@snippet lang="java" :
7600 * Iterator<T> iterator(A...); // defaults to Iterable::iterator
7601 * V init(A...);
7602 * V body(V,T,A...);
7603 * V iteratedLoop(A... a...) {
7604 * Iterator<T> it = iterator(a...);
7605 * V v = init(a...);
7606 * while (it.hasNext()) {
7607 * T t = it.next();
7608 * v = body(v, t, a...);
7609 * }
7610 * return v;
7611 * }
7612 * }
7613 *
7614 * @apiNote Example:
7615 * {@snippet lang="java" :
7616 * // get an iterator from a list
7617 * static List<String> reverseStep(List<String> r, String e) {
7618 * r.add(0, e);
7619 * return r;
7620 * }
7621 * static List<String> newArrayList() { return new ArrayList<>(); }
7622 * // assume MH_reverseStep and MH_newArrayList are handles to the above methods
7623 * MethodHandle loop = MethodHandles.iteratedLoop(null, MH_newArrayList, MH_reverseStep);
7624 * List<String> list = Arrays.asList("a", "b", "c", "d", "e");
7625 * List<String> reversedList = Arrays.asList("e", "d", "c", "b", "a");
7626 * assertEquals(reversedList, (List<String>) loop.invoke(list));
7627 * }
7628 *
7629 * @apiNote The implementation of this method can be expressed approximately as follows:
7630 * {@snippet lang="java" :
7631 * MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
7632 * // assume MH_next, MH_hasNext, MH_startIter are handles to methods of Iterator/Iterable
7633 * Class<?> returnType = body.type().returnType();
7634 * Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
7635 * MethodHandle nextVal = MH_next.asType(MH_next.type().changeReturnType(ttype));
7636 * MethodHandle retv = null, step = body, startIter = iterator;
7637 * if (returnType != void.class) {
7638 * // the simple thing first: in (I V A...), drop the I to get V
7639 * retv = dropArguments(identity(returnType), 0, Iterator.class);
7640 * // body type signature (V T A...), internal loop types (I V A...)
7641 * step = swapArguments(body, 0, 1); // swap V <-> T
7642 * }
7643 * if (startIter == null) startIter = MH_getIter;
7644 * MethodHandle[]
7645 * iterVar = { startIter, null, MH_hasNext, retv }, // it = iterator; while (it.hasNext())
7646 * bodyClause = { init, filterArguments(step, 0, nextVal) }; // v = body(v, t, a)
7647 * return loop(iterVar, bodyClause);
7648 * }
7649 * }
7650 *
7651 * @param iterator an optional handle to return the iterator to start the loop.
7652 * If non-{@code null}, the handle must return {@link java.util.Iterator} or a subtype.
7653 * See above for other constraints.
7654 * @param init optional initializer, providing the initial value of the loop variable.
7655 * May be {@code null}, implying a default initial value. See above for other constraints.
7656 * @param body body of the loop, which may not be {@code null}.
7657 * It controls the loop parameters and result type in the standard case (see above for details).
7658 * It must accept its own return type (if non-void) plus a {@code T} parameter (for the iterated values),
7659 * and may accept any number of additional types.
7660 * See above for other constraints.
7661 *
7662 * @return a method handle embodying the iteration loop functionality.
7663 * @throws NullPointerException if the {@code body} handle is {@code null}.
7664 * @throws IllegalArgumentException if any argument violates the above requirements.
7665 *
7666 * @since 9
7667 */
7668 public static MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
7669 Class<?> iterableType = iteratedLoopChecks(iterator, init, body);
7670 Class<?> returnType = body.type().returnType();
7671 MethodHandle hasNext = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iteratePred);
7672 MethodHandle nextRaw = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iterateNext);
7673 MethodHandle startIter;
7674 MethodHandle nextVal;
7675 {
7676 MethodType iteratorType;
7677 if (iterator == null) {
7678 // derive argument type from body, if available, else use Iterable
7679 startIter = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_initIterator);
7680 iteratorType = startIter.type().changeParameterType(0, iterableType);
7681 } else {
7682 // force return type to the internal iterator class
7683 iteratorType = iterator.type().changeReturnType(Iterator.class);
7684 startIter = iterator;
7685 }
7686 Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
7687 MethodType nextValType = nextRaw.type().changeReturnType(ttype);
7688
7689 // perform the asType transforms under an exception transformer, as per spec.:
7690 try {
7691 startIter = startIter.asType(iteratorType);
7692 nextVal = nextRaw.asType(nextValType);
7693 } catch (WrongMethodTypeException ex) {
7694 throw new IllegalArgumentException(ex);
7695 }
7696 }
7697
7698 MethodHandle retv = null, step = body;
7699 if (returnType != void.class) {
7700 // the simple thing first: in (I V A...), drop the I to get V
7701 retv = dropArguments(identity(returnType), 0, Iterator.class);
7702 // body type signature (V T A...), internal loop types (I V A...)
7703 step = swapArguments(body, 0, 1); // swap V <-> T
7704 }
7705
7706 MethodHandle[]
7707 iterVar = { startIter, null, hasNext, retv },
7708 bodyClause = { init, filterArgument(step, 0, nextVal) };
7709 return loop(iterVar, bodyClause);
7710 }
7711
7712 private static Class<?> iteratedLoopChecks(MethodHandle iterator, MethodHandle init, MethodHandle body) {
7713 Objects.requireNonNull(body);
7714 MethodType bodyType = body.type();
7715 Class<?> returnType = bodyType.returnType();
7716 List<Class<?>> internalParamList = bodyType.parameterList();
7717 // strip leading V value if present
7718 int vsize = (returnType == void.class ? 0 : 1);
7719 if (vsize != 0 && (internalParamList.isEmpty() || internalParamList.get(0) != returnType)) {
7720 // argument list has no "V" => error
7721 MethodType expected = bodyType.insertParameterTypes(0, returnType);
7722 throw misMatchedTypes("body function", bodyType, expected);
7723 } else if (internalParamList.size() <= vsize) {
7724 // missing T type => error
7725 MethodType expected = bodyType.insertParameterTypes(vsize, Object.class);
7726 throw misMatchedTypes("body function", bodyType, expected);
7727 }
7728 List<Class<?>> externalParamList = internalParamList.subList(vsize + 1, internalParamList.size());
7729 Class<?> iterableType = null;
7730 if (iterator != null) {
7731 // special case; if the body handle only declares V and T then
7732 // the external parameter list is obtained from iterator handle
7733 if (externalParamList.isEmpty()) {
7734 externalParamList = iterator.type().parameterList();
7735 }
7736 MethodType itype = iterator.type();
7737 if (!Iterator.class.isAssignableFrom(itype.returnType())) {
7738 throw newIllegalArgumentException("iteratedLoop first argument must have Iterator return type");
7739 }
7740 if (!itype.effectivelyIdenticalParameters(0, externalParamList)) {
7741 MethodType expected = methodType(itype.returnType(), externalParamList);
7742 throw misMatchedTypes("iterator parameters", itype, expected);
7743 }
7744 } else {
7745 if (externalParamList.isEmpty()) {
7746 // special case; if the iterator handle is null and the body handle
7747 // only declares V and T then the external parameter list consists
7748 // of Iterable
7749 externalParamList = List.of(Iterable.class);
7750 iterableType = Iterable.class;
7751 } else {
7752 // special case; if the iterator handle is null and the external
7753 // parameter list is not empty then the first parameter must be
7754 // assignable to Iterable
7755 iterableType = externalParamList.get(0);
7756 if (!Iterable.class.isAssignableFrom(iterableType)) {
7757 throw newIllegalArgumentException(
7758 "inferred first loop argument must inherit from Iterable: " + iterableType);
7759 }
7760 }
7761 }
7762 if (init != null) {
7763 MethodType initType = init.type();
7764 if (initType.returnType() != returnType ||
7765 !initType.effectivelyIdenticalParameters(0, externalParamList)) {
7766 throw misMatchedTypes("loop initializer", initType, methodType(returnType, externalParamList));
7767 }
7768 }
7769 return iterableType; // help the caller a bit
7770 }
7771
7772 /*non-public*/
7773 static MethodHandle swapArguments(MethodHandle mh, int i, int j) {
7774 // there should be a better way to uncross my wires
7775 int arity = mh.type().parameterCount();
7776 int[] order = new int[arity];
7777 for (int k = 0; k < arity; k++) order[k] = k;
7778 order[i] = j; order[j] = i;
7779 Class<?>[] types = mh.type().parameterArray();
7780 Class<?> ti = types[i]; types[i] = types[j]; types[j] = ti;
7781 MethodType swapType = methodType(mh.type().returnType(), types);
7782 return permuteArguments(mh, swapType, order);
7783 }
7784
7785 /**
7786 * Makes a method handle that adapts a {@code target} method handle by wrapping it in a {@code try-finally} block.
7787 * Another method handle, {@code cleanup}, represents the functionality of the {@code finally} block. Any exception
7788 * thrown during the execution of the {@code target} handle will be passed to the {@code cleanup} handle. The
7789 * exception will be rethrown, unless {@code cleanup} handle throws an exception first. The
7790 * value returned from the {@code cleanup} handle's execution will be the result of the execution of the
7791 * {@code try-finally} handle.
7792 * <p>
7793 * The {@code cleanup} handle will be passed one or two additional leading arguments.
7794 * The first is the exception thrown during the
7795 * execution of the {@code target} handle, or {@code null} if no exception was thrown.
7796 * The second is the result of the execution of the {@code target} handle, or, if it throws an exception,
7797 * a {@code null}, zero, or {@code false} value of the required type is supplied as a placeholder.
7798 * The second argument is not present if the {@code target} handle has a {@code void} return type.
7799 * (Note that, except for argument type conversions, combinators represent {@code void} values in parameter lists
7800 * by omitting the corresponding paradoxical arguments, not by inserting {@code null} or zero values.)
7801 * <p>
7802 * The {@code target} and {@code cleanup} handles must have the same corresponding argument and return types, except
7803 * that the {@code cleanup} handle may omit trailing arguments. Also, the {@code cleanup} handle must have one or
7804 * two extra leading parameters:<ul>
7805 * <li>a {@code Throwable}, which will carry the exception thrown by the {@code target} handle (if any); and
7806 * <li>a parameter of the same type as the return type of both {@code target} and {@code cleanup}, which will carry
7807 * the result from the execution of the {@code target} handle.
7808 * This parameter is not present if the {@code target} returns {@code void}.
7809 * </ul>
7810 * <p>
7811 * The pseudocode for the resulting adapter looks as follows. In the code, {@code V} represents the result type of
7812 * the {@code try/finally} construct; {@code A}/{@code a}, the types and values of arguments to the resulting
7813 * handle consumed by the cleanup; and {@code B}/{@code b}, those of arguments to the resulting handle discarded by
7814 * the cleanup.
7815 * {@snippet lang="java" :
7816 * V target(A..., B...);
7817 * V cleanup(Throwable, V, A...);
7818 * V adapter(A... a, B... b) {
7819 * V result = (zero value for V);
7820 * Throwable throwable = null;
7821 * try {
7822 * result = target(a..., b...);
7823 * } catch (Throwable t) {
7824 * throwable = t;
7825 * throw t;
7826 * } finally {
7827 * result = cleanup(throwable, result, a...);
7828 * }
7829 * return result;
7830 * }
7831 * }
7832 * <p>
7833 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
7834 * be modified by execution of the target, and so are passed unchanged
7835 * from the caller to the cleanup, if it is invoked.
7836 * <p>
7837 * The target and cleanup must return the same type, even if the cleanup
7838 * always throws.
7839 * To create such a throwing cleanup, compose the cleanup logic
7840 * with {@link #throwException throwException},
7841 * in order to create a method handle of the correct return type.
7842 * <p>
7843 * Note that {@code tryFinally} never converts exceptions into normal returns.
7844 * In rare cases where exceptions must be converted in that way, first wrap
7845 * the target with {@link #catchException(MethodHandle, Class, MethodHandle)}
7846 * to capture an outgoing exception, and then wrap with {@code tryFinally}.
7847 * <p>
7848 * It is recommended that the first parameter type of {@code cleanup} be
7849 * declared {@code Throwable} rather than a narrower subtype. This ensures
7850 * {@code cleanup} will always be invoked with whatever exception that
7851 * {@code target} throws. Declaring a narrower type may result in a
7852 * {@code ClassCastException} being thrown by the {@code try-finally}
7853 * handle if the type of the exception thrown by {@code target} is not
7854 * assignable to the first parameter type of {@code cleanup}. Note that
7855 * various exception types of {@code VirtualMachineError},
7856 * {@code LinkageError}, and {@code RuntimeException} can in principle be
7857 * thrown by almost any kind of Java code, and a finally clause that
7858 * catches (say) only {@code IOException} would mask any of the others
7859 * behind a {@code ClassCastException}.
7860 *
7861 * @param target the handle whose execution is to be wrapped in a {@code try} block.
7862 * @param cleanup the handle that is invoked in the finally block.
7863 *
7864 * @return a method handle embodying the {@code try-finally} block composed of the two arguments.
7865 * @throws NullPointerException if any argument is null
7866 * @throws IllegalArgumentException if {@code cleanup} does not accept
7867 * the required leading arguments, or if the method handle types do
7868 * not match in their return types and their
7869 * corresponding trailing parameters
7870 *
7871 * @see MethodHandles#catchException(MethodHandle, Class, MethodHandle)
7872 * @since 9
7873 */
7874 public static MethodHandle tryFinally(MethodHandle target, MethodHandle cleanup) {
7875 Class<?>[] targetParamTypes = target.type().ptypes();
7876 Class<?> rtype = target.type().returnType();
7877
7878 tryFinallyChecks(target, cleanup);
7879
7880 // Match parameter lists: if the cleanup has a shorter parameter list than the target, add ignored arguments.
7881 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
7882 // target parameter list.
7883 cleanup = dropArgumentsToMatch(cleanup, (rtype == void.class ? 1 : 2), targetParamTypes, 0, false);
7884
7885 // Ensure that the intrinsic type checks the instance thrown by the
7886 // target against the first parameter of cleanup
7887 cleanup = cleanup.asType(cleanup.type().changeParameterType(0, Throwable.class));
7888
7889 // Use asFixedArity() to avoid unnecessary boxing of last argument for VarargsCollector case.
7890 return MethodHandleImpl.makeTryFinally(target.asFixedArity(), cleanup.asFixedArity(), rtype, targetParamTypes);
7891 }
7892
7893 private static void tryFinallyChecks(MethodHandle target, MethodHandle cleanup) {
7894 Class<?> rtype = target.type().returnType();
7895 if (rtype != cleanup.type().returnType()) {
7896 throw misMatchedTypes("target and return types", cleanup.type().returnType(), rtype);
7897 }
7898 MethodType cleanupType = cleanup.type();
7899 if (!Throwable.class.isAssignableFrom(cleanupType.parameterType(0))) {
7900 throw misMatchedTypes("cleanup first argument and Throwable", cleanup.type(), Throwable.class);
7901 }
7902 if (rtype != void.class && cleanupType.parameterType(1) != rtype) {
7903 throw misMatchedTypes("cleanup second argument and target return type", cleanup.type(), rtype);
7904 }
7905 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
7906 // target parameter list.
7907 int cleanupArgIndex = rtype == void.class ? 1 : 2;
7908 if (!cleanupType.effectivelyIdenticalParameters(cleanupArgIndex, target.type().parameterList())) {
7909 throw misMatchedTypes("cleanup parameters after (Throwable,result) and target parameter list prefix",
7910 cleanup.type(), target.type());
7911 }
7912 }
7913
7914 /**
7915 * Creates a table switch method handle, which can be used to switch over a set of target
7916 * method handles, based on a given target index, called selector.
7917 * <p>
7918 * For a selector value of {@code n}, where {@code n} falls in the range {@code [0, N)},
7919 * and where {@code N} is the number of target method handles, the table switch method
7920 * handle will invoke the n-th target method handle from the list of target method handles.
7921 * <p>
7922 * For a selector value that does not fall in the range {@code [0, N)}, the table switch
7923 * method handle will invoke the given fallback method handle.
7924 * <p>
7925 * All method handles passed to this method must have the same type, with the additional
7926 * requirement that the leading parameter be of type {@code int}. The leading parameter
7927 * represents the selector.
7928 * <p>
7929 * Any trailing parameters present in the type will appear on the returned table switch
7930 * method handle as well. Any arguments assigned to these parameters will be forwarded,
7931 * together with the selector value, to the selected method handle when invoking it.
7932 *
7933 * @apiNote Example:
7934 * The cases each drop the {@code selector} value they are given, and take an additional
7935 * {@code String} argument, which is concatenated (using {@link String#concat(String)})
7936 * to a specific constant label string for each case:
7937 * {@snippet lang="java" :
7938 * MethodHandles.Lookup lookup = MethodHandles.lookup();
7939 * MethodHandle caseMh = lookup.findVirtual(String.class, "concat",
7940 * MethodType.methodType(String.class, String.class));
7941 * caseMh = MethodHandles.dropArguments(caseMh, 0, int.class);
7942 *
7943 * MethodHandle caseDefault = MethodHandles.insertArguments(caseMh, 1, "default: ");
7944 * MethodHandle case0 = MethodHandles.insertArguments(caseMh, 1, "case 0: ");
7945 * MethodHandle case1 = MethodHandles.insertArguments(caseMh, 1, "case 1: ");
7946 *
7947 * MethodHandle mhSwitch = MethodHandles.tableSwitch(
7948 * caseDefault,
7949 * case0,
7950 * case1
7951 * );
7952 *
7953 * assertEquals("default: data", (String) mhSwitch.invokeExact(-1, "data"));
7954 * assertEquals("case 0: data", (String) mhSwitch.invokeExact(0, "data"));
7955 * assertEquals("case 1: data", (String) mhSwitch.invokeExact(1, "data"));
7956 * assertEquals("default: data", (String) mhSwitch.invokeExact(2, "data"));
7957 * }
7958 *
7959 * @param fallback the fallback method handle that is called when the selector is not
7960 * within the range {@code [0, N)}.
7961 * @param targets array of target method handles.
7962 * @return the table switch method handle.
7963 * @throws NullPointerException if {@code fallback}, the {@code targets} array, or any
7964 * any of the elements of the {@code targets} array are
7965 * {@code null}.
7966 * @throws IllegalArgumentException if the {@code targets} array is empty, if the leading
7967 * parameter of the fallback handle or any of the target
7968 * handles is not {@code int}, or if the types of
7969 * the fallback handle and all of target handles are
7970 * not the same.
7971 */
7972 public static MethodHandle tableSwitch(MethodHandle fallback, MethodHandle... targets) {
7973 Objects.requireNonNull(fallback);
7974 Objects.requireNonNull(targets);
7975 targets = targets.clone();
7976 MethodType type = tableSwitchChecks(fallback, targets);
7977 return MethodHandleImpl.makeTableSwitch(type, fallback, targets);
7978 }
7979
7980 private static MethodType tableSwitchChecks(MethodHandle defaultCase, MethodHandle[] caseActions) {
7981 if (caseActions.length == 0)
7982 throw new IllegalArgumentException("Not enough cases: " + Arrays.toString(caseActions));
7983
7984 MethodType expectedType = defaultCase.type();
7985
7986 if (!(expectedType.parameterCount() >= 1) || expectedType.parameterType(0) != int.class)
7987 throw new IllegalArgumentException(
7988 "Case actions must have int as leading parameter: " + Arrays.toString(caseActions));
7989
7990 for (MethodHandle mh : caseActions) {
7991 Objects.requireNonNull(mh);
7992 if (mh.type() != expectedType)
7993 throw new IllegalArgumentException(
7994 "Case actions must have the same type: " + Arrays.toString(caseActions));
7995 }
7996
7997 return expectedType;
7998 }
7999
8000 /**
8001 * Creates a var handle object, which can be used to dereference a {@linkplain java.lang.foreign.MemorySegment memory segment}
8002 * at a given byte offset, using the provided value layout.
8003 *
8004 * <p>The provided layout specifies the {@linkplain ValueLayout#carrier() carrier type},
8005 * the {@linkplain ValueLayout#byteSize() byte size},
8006 * the {@linkplain ValueLayout#byteAlignment() byte alignment} and the {@linkplain ValueLayout#order() byte order}
8007 * associated with the returned var handle.
8008 *
8009 * <p>The list of coordinate types associated with the returned var handle is {@code (MemorySegment, long)},
8010 * where the {@code long} coordinate type corresponds to byte offset into the given memory segment coordinate.
8011 * Thus, the returned var handle accesses bytes at an offset in a given memory segment, composing bytes to or from
8012 * a value of the var handle type. Moreover, the access operation will honor the endianness and the
8013 * alignment constraints expressed in the provided layout.
8014 *
8015 * <p>As an example, consider the memory layout expressed by a {@link GroupLayout} instance constructed as follows:
8016 * {@snippet lang="java" :
8017 * GroupLayout seq = java.lang.foreign.MemoryLayout.structLayout(
8018 * MemoryLayout.paddingLayout(4),
8019 * ValueLayout.JAVA_INT.withOrder(ByteOrder.BIG_ENDIAN).withName("value")
8020 * );
8021 * }
8022 * To access the member layout named {@code value}, we can construct a memory segment view var handle as follows:
8023 * {@snippet lang="java" :
8024 * VarHandle handle = MethodHandles.memorySegmentViewVarHandle(ValueLayout.JAVA_INT.withOrder(ByteOrder.BIG_ENDIAN)); //(MemorySegment, long) -> int
8025 * handle = MethodHandles.insertCoordinates(handle, 1, 4); //(MemorySegment) -> int
8026 * }
8027 *
8028 * @apiNote The resulting var handle features certain <i>access mode restrictions</i>,
8029 * which are common to all memory segment view var handles. A memory segment view var handle is associated
8030 * with an access size {@code S} and an alignment constraint {@code B}
8031 * (both expressed in bytes). We say that a memory access operation is <em>fully aligned</em> if it occurs
8032 * at a memory address {@code A} which is compatible with both alignment constraints {@code S} and {@code B}.
8033 * If access is fully aligned then following access modes are supported and are
8034 * guaranteed to support atomic access:
8035 * <ul>
8036 * <li>read write access modes for all {@code T}, with the exception of
8037 * access modes {@code get} and {@code set} for {@code long} and
8038 * {@code double} on 32-bit platforms.
8039 * <li>atomic update access modes for {@code int}, {@code long},
8040 * {@code float}, {@code double} or {@link MemorySegment}.
8041 * (Future major platform releases of the JDK may support additional
8042 * types for certain currently unsupported access modes.)
8043 * <li>numeric atomic update access modes for {@code int}, {@code long} and {@link MemorySegment}.
8044 * (Future major platform releases of the JDK may support additional
8045 * numeric types for certain currently unsupported access modes.)
8046 * <li>bitwise atomic update access modes for {@code int}, {@code long} and {@link MemorySegment}.
8047 * (Future major platform releases of the JDK may support additional
8048 * numeric types for certain currently unsupported access modes.)
8049 * </ul>
8050 *
8051 * If {@code T} is {@code float}, {@code double} or {@link MemorySegment} then atomic
8052 * update access modes compare values using their bitwise representation
8053 * (see {@link Float#floatToRawIntBits},
8054 * {@link Double#doubleToRawLongBits} and {@link MemorySegment#address()}, respectively).
8055 * <p>
8056 * Alternatively, a memory access operation is <em>partially aligned</em> if it occurs at a memory address {@code A}
8057 * which is only compatible with the alignment constraint {@code B}; in such cases, access for anything other than the
8058 * {@code get} and {@code set} access modes will result in an {@code IllegalStateException}. If access is partially aligned,
8059 * atomic access is only guaranteed with respect to the largest power of two that divides the GCD of {@code A} and {@code S}.
8060 * <p>
8061 * In all other cases, we say that a memory access operation is <em>misaligned</em>; in such cases an
8062 * {@code IllegalStateException} is thrown, irrespective of the access mode being used.
8063 * <p>
8064 * Finally, if {@code T} is {@code MemorySegment} all write access modes throw {@link IllegalArgumentException}
8065 * unless the value to be written is a {@linkplain MemorySegment#isNative() native} memory segment.
8066 *
8067 * @param layout the value layout for which a memory access handle is to be obtained.
8068 * @return the new memory segment view var handle.
8069 * @throws NullPointerException if {@code layout} is {@code null}.
8070 * @see MemoryLayout#varHandle(MemoryLayout.PathElement...)
8071 * @since 19
8072 */
8073 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN)
8074 public static VarHandle memorySegmentViewVarHandle(ValueLayout layout) {
8075 Objects.requireNonNull(layout);
8076 return Utils.makeSegmentViewVarHandle(layout);
8077 }
8078
8079 /**
8080 * Adapts a target var handle by pre-processing incoming and outgoing values using a pair of filter functions.
8081 * <p>
8082 * When calling e.g. {@link VarHandle#set(Object...)} on the resulting var handle, the incoming value (of type {@code T}, where
8083 * {@code T} is the <em>last</em> parameter type of the first filter function) is processed using the first filter and then passed
8084 * to the target var handle.
8085 * Conversely, when calling e.g. {@link VarHandle#get(Object...)} on the resulting var handle, the return value obtained from
8086 * the target var handle (of type {@code T}, where {@code T} is the <em>last</em> parameter type of the second filter function)
8087 * is processed using the second filter and returned to the caller. More advanced access mode types, such as
8088 * {@link VarHandle.AccessMode#COMPARE_AND_EXCHANGE} might apply both filters at the same time.
8089 * <p>
8090 * For the boxing and unboxing filters to be well-formed, their types must be of the form {@code (A... , S) -> T} and
8091 * {@code (A... , T) -> S}, respectively, where {@code T} is the type of the target var handle. If this is the case,
8092 * the resulting var handle will have type {@code S} and will feature the additional coordinates {@code A...} (which
8093 * will be appended to the coordinates of the target var handle).
8094 * <p>
8095 * If the boxing and unboxing filters throw any checked exceptions when invoked, the resulting var handle will
8096 * throw an {@link IllegalStateException}.
8097 * <p>
8098 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
8099 * atomic access guarantees as those featured by the target var handle.
8100 *
8101 * @param target the target var handle
8102 * @param filterToTarget a filter to convert some type {@code S} into the type of {@code target}
8103 * @param filterFromTarget a filter to convert the type of {@code target} to some type {@code S}
8104 * @return an adapter var handle which accepts a new type, performing the provided boxing/unboxing conversions.
8105 * @throws IllegalArgumentException if {@code filterFromTarget} and {@code filterToTarget} are not well-formed, that is, they have types
8106 * other than {@code (A... , S) -> T} and {@code (A... , T) -> S}, respectively, where {@code T} is the type of the target var handle,
8107 * or if it's determined that either {@code filterFromTarget} or {@code filterToTarget} throws any checked exceptions.
8108 * @throws NullPointerException if any of the arguments is {@code null}.
8109 * @since 19
8110 */
8111 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN)
8112 public static VarHandle filterValue(VarHandle target, MethodHandle filterToTarget, MethodHandle filterFromTarget) {
8113 return VarHandles.filterValue(target, filterToTarget, filterFromTarget);
8114 }
8115
8116 /**
8117 * Adapts a target var handle by pre-processing incoming coordinate values using unary filter functions.
8118 * <p>
8119 * When calling e.g. {@link VarHandle#get(Object...)} on the resulting var handle, the incoming coordinate values
8120 * starting at position {@code pos} (of type {@code C1, C2 ... Cn}, where {@code C1, C2 ... Cn} are the return types
8121 * of the unary filter functions) are transformed into new values (of type {@code S1, S2 ... Sn}, where {@code S1, S2 ... Sn} are the
8122 * parameter types of the unary filter functions), and then passed (along with any coordinate that was left unaltered
8123 * by the adaptation) to the target var handle.
8124 * <p>
8125 * For the coordinate filters to be well-formed, their types must be of the form {@code S1 -> T1, S2 -> T1 ... Sn -> Tn},
8126 * where {@code T1, T2 ... Tn} are the coordinate types starting at position {@code pos} of the target var handle.
8127 * <p>
8128 * If any of the filters throws a checked exception when invoked, the resulting var handle will
8129 * throw an {@link IllegalStateException}.
8130 * <p>
8131 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
8132 * atomic access guarantees as those featured by the target var handle.
8133 *
8134 * @param target the target var handle
8135 * @param pos the position of the first coordinate to be transformed
8136 * @param filters the unary functions which are used to transform coordinates starting at position {@code pos}
8137 * @return an adapter var handle which accepts new coordinate types, applying the provided transformation
8138 * to the new coordinate values.
8139 * @throws IllegalArgumentException if the handles in {@code filters} are not well-formed, that is, they have types
8140 * other than {@code S1 -> T1, S2 -> T2, ... Sn -> Tn} where {@code T1, T2 ... Tn} are the coordinate types starting
8141 * at position {@code pos} of the target var handle, if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive,
8142 * or if more filters are provided than the actual number of coordinate types available starting at {@code pos},
8143 * or if it's determined that any of the filters throws any checked exceptions.
8144 * @throws NullPointerException if any of the arguments is {@code null} or {@code filters} contains {@code null}.
8145 * @since 19
8146 */
8147 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN)
8148 public static VarHandle filterCoordinates(VarHandle target, int pos, MethodHandle... filters) {
8149 return VarHandles.filterCoordinates(target, pos, filters);
8150 }
8151
8152 /**
8153 * Provides a target var handle with one or more <em>bound coordinates</em>
8154 * in advance of the var handle's invocation. As a consequence, the resulting var handle will feature less
8155 * coordinate types than the target var handle.
8156 * <p>
8157 * When calling e.g. {@link VarHandle#get(Object...)} on the resulting var handle, incoming coordinate values
8158 * are joined with bound coordinate values, and then passed to the target var handle.
8159 * <p>
8160 * For the bound coordinates to be well-formed, their types must be {@code T1, T2 ... Tn },
8161 * where {@code T1, T2 ... Tn} are the coordinate types starting at position {@code pos} of the target var handle.
8162 * <p>
8163 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
8164 * atomic access guarantees as those featured by the target var handle.
8165 *
8166 * @param target the var handle to invoke after the bound coordinates are inserted
8167 * @param pos the position of the first coordinate to be inserted
8168 * @param values the series of bound coordinates to insert
8169 * @return an adapter var handle which inserts additional coordinates,
8170 * before calling the target var handle
8171 * @throws IllegalArgumentException if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive,
8172 * or if more values are provided than the actual number of coordinate types available starting at {@code pos}.
8173 * @throws ClassCastException if the bound coordinates in {@code values} are not well-formed, that is, they have types
8174 * other than {@code T1, T2 ... Tn }, where {@code T1, T2 ... Tn} are the coordinate types starting at position {@code pos}
8175 * of the target var handle.
8176 * @throws NullPointerException if any of the arguments is {@code null} or {@code values} contains {@code null}.
8177 * @since 19
8178 */
8179 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN)
8180 public static VarHandle insertCoordinates(VarHandle target, int pos, Object... values) {
8181 return VarHandles.insertCoordinates(target, pos, values);
8182 }
8183
8184 /**
8185 * Provides a var handle which adapts the coordinate values of the target var handle, by re-arranging them
8186 * so that the new coordinates match the provided ones.
8187 * <p>
8188 * The given array controls the reordering.
8189 * Call {@code #I} the number of incoming coordinates (the value
8190 * {@code newCoordinates.size()}), and call {@code #O} the number
8191 * of outgoing coordinates (the number of coordinates associated with the target var handle).
8192 * Then the length of the reordering array must be {@code #O},
8193 * and each element must be a non-negative number less than {@code #I}.
8194 * For every {@code N} less than {@code #O}, the {@code N}-th
8195 * outgoing coordinate will be taken from the {@code I}-th incoming
8196 * coordinate, where {@code I} is {@code reorder[N]}.
8197 * <p>
8198 * No coordinate value conversions are applied.
8199 * The type of each incoming coordinate, as determined by {@code newCoordinates},
8200 * must be identical to the type of the corresponding outgoing coordinate
8201 * in the target var handle.
8202 * <p>
8203 * The reordering array need not specify an actual permutation.
8204 * An incoming coordinate will be duplicated if its index appears
8205 * more than once in the array, and an incoming coordinate will be dropped
8206 * if its index does not appear in the array.
8207 * <p>
8208 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
8209 * atomic access guarantees as those featured by the target var handle.
8210 * @param target the var handle to invoke after the coordinates have been reordered
8211 * @param newCoordinates the new coordinate types
8212 * @param reorder an index array which controls the reordering
8213 * @return an adapter var handle which re-arranges the incoming coordinate values,
8214 * before calling the target var handle
8215 * @throws IllegalArgumentException if the index array length is not equal to
8216 * the number of coordinates of the target var handle, or if any index array element is not a valid index for
8217 * a coordinate of {@code newCoordinates}, or if two corresponding coordinate types in
8218 * the target var handle and in {@code newCoordinates} are not identical.
8219 * @throws NullPointerException if any of the arguments is {@code null} or {@code newCoordinates} contains {@code null}.
8220 * @since 19
8221 */
8222 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN)
8223 public static VarHandle permuteCoordinates(VarHandle target, List<Class<?>> newCoordinates, int... reorder) {
8224 return VarHandles.permuteCoordinates(target, newCoordinates, reorder);
8225 }
8226
8227 /**
8228 * Adapts a target var handle by pre-processing
8229 * a sub-sequence of its coordinate values with a filter (a method handle).
8230 * The pre-processed coordinates are replaced by the result (if any) of the
8231 * filter function and the target var handle is then called on the modified (usually shortened)
8232 * coordinate list.
8233 * <p>
8234 * If {@code R} is the return type of the filter, then:
8235 * <ul>
8236 * <li>if {@code R} <em>is not</em> {@code void}, the target var handle must have a coordinate of type {@code R} in
8237 * position {@code pos}. The parameter types of the filter will replace the coordinate type at position {@code pos}
8238 * of the target var handle. When the returned var handle is invoked, it will be as if the filter is invoked first,
8239 * and its result is passed in place of the coordinate at position {@code pos} in a downstream invocation of the
8240 * target var handle.</li>
8241 * <li> if {@code R} <em>is</em> {@code void}, the parameter types (if any) of the filter will be inserted in the
8242 * coordinate type list of the target var handle at position {@code pos}. In this case, when the returned var handle
8243 * is invoked, the filter essentially acts as a side effect, consuming some of the coordinate values, before a
8244 * downstream invocation of the target var handle.</li>
8245 * </ul>
8246 * <p>
8247 * If any of the filters throws a checked exception when invoked, the resulting var handle will
8248 * throw an {@link IllegalStateException}.
8249 * <p>
8250 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
8251 * atomic access guarantees as those featured by the target var handle.
8252 *
8253 * @param target the var handle to invoke after the coordinates have been filtered
8254 * @param pos the position in the coordinate list of the target var handle where the filter is to be inserted
8255 * @param filter the filter method handle
8256 * @return an adapter var handle which filters the incoming coordinate values,
8257 * before calling the target var handle
8258 * @throws IllegalArgumentException if the return type of {@code filter}
8259 * is not void, and it is not the same as the {@code pos} coordinate of the target var handle,
8260 * if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive,
8261 * if the resulting var handle's type would have <a href="MethodHandle.html#maxarity">too many coordinates</a>,
8262 * or if it's determined that {@code filter} throws any checked exceptions.
8263 * @throws NullPointerException if any of the arguments is {@code null}.
8264 * @since 19
8265 */
8266 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN)
8267 public static VarHandle collectCoordinates(VarHandle target, int pos, MethodHandle filter) {
8268 return VarHandles.collectCoordinates(target, pos, filter);
8269 }
8270
8271 /**
8272 * Returns a var handle which will discard some dummy coordinates before delegating to the
8273 * target var handle. As a consequence, the resulting var handle will feature more
8274 * coordinate types than the target var handle.
8275 * <p>
8276 * The {@code pos} argument may range between zero and <i>N</i>, where <i>N</i> is the arity of the
8277 * target var handle's coordinate types. If {@code pos} is zero, the dummy coordinates will precede
8278 * the target's real arguments; if {@code pos} is <i>N</i> they will come after.
8279 * <p>
8280 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
8281 * atomic access guarantees as those featured by the target var handle.
8282 *
8283 * @param target the var handle to invoke after the dummy coordinates are dropped
8284 * @param pos position of the first coordinate to drop (zero for the leftmost)
8285 * @param valueTypes the type(s) of the coordinate(s) to drop
8286 * @return an adapter var handle which drops some dummy coordinates,
8287 * before calling the target var handle
8288 * @throws IllegalArgumentException if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive.
8289 * @throws NullPointerException if any of the arguments is {@code null} or {@code valueTypes} contains {@code null}.
8290 * @since 19
8291 */
8292 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN)
8293 public static VarHandle dropCoordinates(VarHandle target, int pos, Class<?>... valueTypes) {
8294 return VarHandles.dropCoordinates(target, pos, valueTypes);
8295 }
8296 }