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.foreign.Utils;
30 import jdk.internal.javac.PreviewFeature;
31 import jdk.internal.misc.Unsafe;
32 import jdk.internal.misc.VM;
33 import jdk.internal.org.objectweb.asm.ClassReader;
34 import jdk.internal.org.objectweb.asm.Opcodes;
35 import jdk.internal.org.objectweb.asm.Type;
36 import jdk.internal.reflect.CallerSensitive;
37 import jdk.internal.reflect.CallerSensitiveAdapter;
38 import jdk.internal.reflect.Reflection;
39 import jdk.internal.util.ClassFileDumper;
40 import jdk.internal.vm.annotation.ForceInline;
41 import sun.invoke.util.ValueConversions;
42 import sun.invoke.util.VerifyAccess;
43 import sun.invoke.util.Wrapper;
44 import sun.reflect.misc.ReflectUtil;
45 import sun.security.util.SecurityConstants;
46
47 import java.lang.constant.ConstantDescs;
48 import java.lang.foreign.GroupLayout;
49 import java.lang.foreign.MemoryLayout;
50 import java.lang.foreign.MemorySegment;
51 import java.lang.foreign.ValueLayout;
52 import java.lang.invoke.LambdaForm.BasicType;
53 import java.lang.reflect.Constructor;
54 import java.lang.reflect.Field;
55 import java.lang.reflect.Member;
56 import java.lang.reflect.Method;
57 import java.lang.reflect.Modifier;
58 import java.nio.ByteOrder;
59 import java.security.ProtectionDomain;
60 import java.util.ArrayList;
61 import java.util.Arrays;
62 import java.util.BitSet;
63 import java.util.Comparator;
64 import java.util.Iterator;
65 import java.util.List;
66 import java.util.Objects;
67 import java.util.Set;
68 import java.util.concurrent.ConcurrentHashMap;
69 import java.util.stream.Stream;
70
71 import static java.lang.invoke.LambdaForm.BasicType.V_TYPE;
72 import static java.lang.invoke.MethodHandleImpl.Intrinsic;
73 import static java.lang.invoke.MethodHandleNatives.Constants.*;
74 import static java.lang.invoke.MethodHandleStatics.UNSAFE;
75 import static java.lang.invoke.MethodHandleStatics.newIllegalArgumentException;
76 import static java.lang.invoke.MethodHandleStatics.newInternalError;
77 import static java.lang.invoke.MethodType.methodType;
78
79 /**
80 * This class consists exclusively of static methods that operate on or return
81 * method handles. They fall into several categories:
82 * <ul>
83 * <li>Lookup methods which help create method handles for methods and fields.
84 * <li>Combinator methods, which combine or transform pre-existing method handles into new ones.
85 * <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns.
86 * </ul>
87 * A lookup, combinator, or factory method will fail and throw an
88 * {@code IllegalArgumentException} if the created method handle's type
89 * would have <a href="MethodHandle.html#maxarity">too many parameters</a>.
90 *
91 * @author John Rose, JSR 292 EG
92 * @since 1.7
93 */
94 public class MethodHandles {
95
96 private MethodHandles() { } // do not instantiate
97
98 static final MemberName.Factory IMPL_NAMES = MemberName.getFactory();
99
100 // See IMPL_LOOKUP below.
101
102 //// Method handle creation from ordinary methods.
103
104 /**
105 * Returns a {@link Lookup lookup object} with
106 * full capabilities to emulate all supported bytecode behaviors of the caller.
107 * These capabilities include {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access} to the caller.
108 * Factory methods on the lookup object can create
109 * <a href="MethodHandleInfo.html#directmh">direct method handles</a>
110 * for any member that the caller has access to via bytecodes,
111 * including protected and private fields and methods.
112 * This lookup object is created by the original lookup class
113 * and has the {@link Lookup#ORIGINAL ORIGINAL} bit set.
114 * This lookup object is a <em>capability</em> which may be delegated to trusted agents.
115 * Do not store it in place where untrusted code can access it.
116 * <p>
117 * This method is caller sensitive, which means that it may return different
118 * values to different callers.
119 * In cases where {@code MethodHandles.lookup} is called from a context where
120 * there is no caller frame on the stack (e.g. when called directly
121 * from a JNI attached thread), {@code IllegalCallerException} is thrown.
122 * To obtain a {@link Lookup lookup object} in such a context, use an auxiliary class that will
123 * implicitly be identified as the caller, or use {@link MethodHandles#publicLookup()}
124 * to obtain a low-privileged lookup instead.
125 * @return a lookup object for the caller of this method, with
126 * {@linkplain Lookup#ORIGINAL original} and
127 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access}.
128 * @throws IllegalCallerException if there is no caller frame on the stack.
129 */
130 @CallerSensitive
131 @ForceInline // to ensure Reflection.getCallerClass optimization
132 public static Lookup lookup() {
133 final Class<?> c = Reflection.getCallerClass();
134 if (c == null) {
135 throw new IllegalCallerException("no caller frame");
136 }
137 return new Lookup(c);
138 }
139
140 /**
141 * This lookup method is the alternate implementation of
142 * the lookup method with a leading caller class argument which is
143 * non-caller-sensitive. This method is only invoked by reflection
144 * and method handle.
145 */
146 @CallerSensitiveAdapter
147 private static Lookup lookup(Class<?> caller) {
148 if (caller.getClassLoader() == null) {
149 throw newInternalError("calling lookup() reflectively is not supported: "+caller);
150 }
151 return new Lookup(caller);
152 }
153
154 /**
155 * Returns a {@link Lookup lookup object} which is trusted minimally.
156 * The lookup has the {@code UNCONDITIONAL} mode.
157 * It can only be used to create method handles to public members of
158 * public classes in packages that are exported unconditionally.
159 * <p>
160 * As a matter of pure convention, the {@linkplain Lookup#lookupClass() lookup class}
161 * of this lookup object will be {@link java.lang.Object}.
162 *
163 * @apiNote The use of Object is conventional, and because the lookup modes are
164 * limited, there is no special access provided to the internals of Object, its package
165 * or its module. This public lookup object or other lookup object with
166 * {@code UNCONDITIONAL} mode assumes readability. Consequently, the lookup class
167 * is not used to determine the lookup context.
168 *
169 * <p style="font-size:smaller;">
170 * <em>Discussion:</em>
171 * The lookup class can be changed to any other class {@code C} using an expression of the form
172 * {@link Lookup#in publicLookup().in(C.class)}.
173 * A public lookup object is always subject to
174 * <a href="MethodHandles.Lookup.html#secmgr">security manager checks</a>.
175 * Also, it cannot access
176 * <a href="MethodHandles.Lookup.html#callsens">caller sensitive methods</a>.
177 * @return a lookup object which is trusted minimally
178 *
179 * @revised 9
180 */
181 public static Lookup publicLookup() {
182 return Lookup.PUBLIC_LOOKUP;
183 }
184
185 /**
186 * Returns a {@link Lookup lookup} object on a target class to emulate all supported
187 * bytecode behaviors, including <a href="MethodHandles.Lookup.html#privacc">private access</a>.
188 * The returned lookup object can provide access to classes in modules and packages,
189 * and members of those classes, outside the normal rules of Java access control,
190 * instead conforming to the more permissive rules for modular <em>deep reflection</em>.
191 * <p>
192 * A caller, specified as a {@code Lookup} object, in module {@code M1} is
193 * allowed to do deep reflection on module {@code M2} and package of the target class
194 * if and only if all of the following conditions are {@code true}:
195 * <ul>
196 * <li>If there is a security manager, its {@code checkPermission} method is
197 * called to check {@code ReflectPermission("suppressAccessChecks")} and
198 * that must return normally.
199 * <li>The caller lookup object must have {@linkplain Lookup#hasFullPrivilegeAccess()
200 * full privilege access}. Specifically:
201 * <ul>
202 * <li>The caller lookup object must have the {@link Lookup#MODULE MODULE} lookup mode.
203 * (This is because otherwise there would be no way to ensure the original lookup
204 * creator was a member of any particular module, and so any subsequent checks
205 * for readability and qualified exports would become ineffective.)
206 * <li>The caller lookup object must have {@link Lookup#PRIVATE PRIVATE} access.
207 * (This is because an application intending to share intra-module access
208 * using {@link Lookup#MODULE MODULE} alone will inadvertently also share
209 * deep reflection to its own module.)
210 * </ul>
211 * <li>The target class must be a proper class, not a primitive or array class.
212 * (Thus, {@code M2} is well-defined.)
213 * <li>If the caller module {@code M1} differs from
214 * the target module {@code M2} then both of the following must be true:
215 * <ul>
216 * <li>{@code M1} {@link Module#canRead reads} {@code M2}.</li>
217 * <li>{@code M2} {@link Module#isOpen(String,Module) opens} the package
218 * containing the target class to at least {@code M1}.</li>
219 * </ul>
220 * </ul>
221 * <p>
222 * If any of the above checks is violated, this method fails with an
223 * exception.
224 * <p>
225 * Otherwise, if {@code M1} and {@code M2} are the same module, this method
226 * returns a {@code Lookup} on {@code targetClass} with
227 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access}
228 * with {@code null} previous lookup class.
229 * <p>
230 * Otherwise, {@code M1} and {@code M2} are two different modules. This method
231 * returns a {@code Lookup} on {@code targetClass} that records
232 * the lookup class of the caller as the new previous lookup class with
233 * {@code PRIVATE} access but no {@code MODULE} access.
234 * <p>
235 * The resulting {@code Lookup} object has no {@code ORIGINAL} access.
236 *
237 * @apiNote The {@code Lookup} object returned by this method is allowed to
238 * {@linkplain Lookup#defineClass(byte[]) define classes} in the runtime package
239 * of {@code targetClass}. Extreme caution should be taken when opening a package
240 * to another module as such defined classes have the same full privilege
241 * access as other members in {@code targetClass}'s module.
242 *
243 * @param targetClass the target class
244 * @param caller the caller lookup object
245 * @return a lookup object for the target class, with private access
246 * @throws IllegalArgumentException if {@code targetClass} is a primitive type or void or array class
247 * @throws NullPointerException if {@code targetClass} or {@code caller} is {@code null}
248 * @throws SecurityException if denied by the security manager
249 * @throws IllegalAccessException if any of the other access checks specified above fails
250 * @since 9
251 * @see Lookup#dropLookupMode
252 * @see <a href="MethodHandles.Lookup.html#cross-module-lookup">Cross-module lookups</a>
253 */
254 public static Lookup privateLookupIn(Class<?> targetClass, Lookup caller) throws IllegalAccessException {
255 if (caller.allowedModes == Lookup.TRUSTED) {
256 return new Lookup(targetClass);
257 }
258
259 @SuppressWarnings("removal")
260 SecurityManager sm = System.getSecurityManager();
261 if (sm != null) sm.checkPermission(SecurityConstants.ACCESS_PERMISSION);
262 if (targetClass.isPrimitive())
263 throw new IllegalArgumentException(targetClass + " is a primitive class");
264 if (targetClass.isArray())
265 throw new IllegalArgumentException(targetClass + " is an array class");
266 // Ensure that we can reason accurately about private and module access.
267 int requireAccess = Lookup.PRIVATE|Lookup.MODULE;
268 if ((caller.lookupModes() & requireAccess) != requireAccess)
269 throw new IllegalAccessException("caller does not have PRIVATE and MODULE lookup mode");
270
271 // previous lookup class is never set if it has MODULE access
272 assert caller.previousLookupClass() == null;
273
274 Class<?> callerClass = caller.lookupClass();
275 Module callerModule = callerClass.getModule(); // M1
276 Module targetModule = targetClass.getModule(); // M2
277 Class<?> newPreviousClass = null;
278 int newModes = Lookup.FULL_POWER_MODES & ~Lookup.ORIGINAL;
279
280 if (targetModule != callerModule) {
281 if (!callerModule.canRead(targetModule))
282 throw new IllegalAccessException(callerModule + " does not read " + targetModule);
283 if (targetModule.isNamed()) {
284 String pn = targetClass.getPackageName();
285 assert !pn.isEmpty() : "unnamed package cannot be in named module";
286 if (!targetModule.isOpen(pn, callerModule))
287 throw new IllegalAccessException(targetModule + " does not open " + pn + " to " + callerModule);
288 }
289
290 // M2 != M1, set previous lookup class to M1 and drop MODULE access
291 newPreviousClass = callerClass;
292 newModes &= ~Lookup.MODULE;
293 }
294 return Lookup.newLookup(targetClass, newPreviousClass, newModes);
295 }
296
297 /**
298 * Returns the <em>class data</em> associated with the lookup class
299 * of the given {@code caller} lookup object, or {@code null}.
300 *
301 * <p> A hidden class with class data can be created by calling
302 * {@link Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...)
303 * Lookup::defineHiddenClassWithClassData}.
304 * This method will cause the static class initializer of the lookup
305 * class of the given {@code caller} lookup object be executed if
306 * it has not been initialized.
307 *
308 * <p> A hidden class created by {@link Lookup#defineHiddenClass(byte[], boolean, Lookup.ClassOption...)
309 * Lookup::defineHiddenClass} and non-hidden classes have no class data.
310 * {@code null} is returned if this method is called on the lookup object
311 * on these classes.
312 *
313 * <p> The {@linkplain Lookup#lookupModes() lookup modes} for this lookup
314 * must have {@linkplain Lookup#ORIGINAL original access}
315 * in order to retrieve the class data.
316 *
317 * @apiNote
318 * This method can be called as a bootstrap method for a dynamically computed
319 * constant. A framework can create a hidden class with class data, for
320 * example that can be {@code Class} or {@code MethodHandle} object.
321 * The class data is accessible only to the lookup object
322 * created by the original caller but inaccessible to other members
323 * in the same nest. If a framework passes security sensitive objects
324 * to a hidden class via class data, it is recommended to load the value
325 * of class data as a dynamically computed constant instead of storing
326 * the class data in private static field(s) which are accessible to
327 * other nestmates.
328 *
329 * @param <T> the type to cast the class data object to
330 * @param caller the lookup context describing the class performing the
331 * operation (normally stacked by the JVM)
332 * @param name must be {@link ConstantDescs#DEFAULT_NAME}
333 * ({@code "_"})
334 * @param type the type of the class data
335 * @return the value of the class data if present in the lookup class;
336 * otherwise {@code null}
337 * @throws IllegalArgumentException if name is not {@code "_"}
338 * @throws IllegalAccessException if the lookup context does not have
339 * {@linkplain Lookup#ORIGINAL original} access
340 * @throws ClassCastException if the class data cannot be converted to
341 * the given {@code type}
342 * @throws NullPointerException if {@code caller} or {@code type} argument
343 * is {@code null}
344 * @see Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...)
345 * @see MethodHandles#classDataAt(Lookup, String, Class, int)
346 * @since 16
347 * @jvms 5.5 Initialization
348 */
349 public static <T> T classData(Lookup caller, String name, Class<T> type) throws IllegalAccessException {
350 Objects.requireNonNull(caller);
351 Objects.requireNonNull(type);
352 if (!ConstantDescs.DEFAULT_NAME.equals(name)) {
353 throw new IllegalArgumentException("name must be \"_\": " + name);
354 }
355
356 if ((caller.lookupModes() & Lookup.ORIGINAL) != Lookup.ORIGINAL) {
357 throw new IllegalAccessException(caller + " does not have ORIGINAL access");
358 }
359
360 Object classdata = classData(caller.lookupClass());
361 if (classdata == null) return null;
362
363 try {
364 return BootstrapMethodInvoker.widenAndCast(classdata, type);
365 } catch (RuntimeException|Error e) {
366 throw e; // let CCE and other runtime exceptions through
367 } catch (Throwable e) {
368 throw new InternalError(e);
369 }
370 }
371
372 /*
373 * Returns the class data set by the VM in the Class::classData field.
374 *
375 * This is also invoked by LambdaForms as it cannot use condy via
376 * MethodHandles::classData due to bootstrapping issue.
377 */
378 static Object classData(Class<?> c) {
379 UNSAFE.ensureClassInitialized(c);
380 return SharedSecrets.getJavaLangAccess().classData(c);
381 }
382
383 /**
384 * Returns the element at the specified index in the
385 * {@linkplain #classData(Lookup, String, Class) class data},
386 * if the class data associated with the lookup class
387 * of the given {@code caller} lookup object is a {@code List}.
388 * If the class data is not present in this lookup class, this method
389 * returns {@code null}.
390 *
391 * <p> A hidden class with class data can be created by calling
392 * {@link Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...)
393 * Lookup::defineHiddenClassWithClassData}.
394 * This method will cause the static class initializer of the lookup
395 * class of the given {@code caller} lookup object be executed if
396 * it has not been initialized.
397 *
398 * <p> A hidden class created by {@link Lookup#defineHiddenClass(byte[], boolean, Lookup.ClassOption...)
399 * Lookup::defineHiddenClass} and non-hidden classes have no class data.
400 * {@code null} is returned if this method is called on the lookup object
401 * on these classes.
402 *
403 * <p> The {@linkplain Lookup#lookupModes() lookup modes} for this lookup
404 * must have {@linkplain Lookup#ORIGINAL original access}
405 * in order to retrieve the class data.
406 *
407 * @apiNote
408 * This method can be called as a bootstrap method for a dynamically computed
409 * constant. A framework can create a hidden class with class data, for
410 * example that can be {@code List.of(o1, o2, o3....)} containing more than
411 * one object and use this method to load one element at a specific index.
412 * The class data is accessible only to the lookup object
413 * created by the original caller but inaccessible to other members
414 * in the same nest. If a framework passes security sensitive objects
415 * to a hidden class via class data, it is recommended to load the value
416 * of class data as a dynamically computed constant instead of storing
417 * the class data in private static field(s) which are accessible to other
418 * nestmates.
419 *
420 * @param <T> the type to cast the result object to
421 * @param caller the lookup context describing the class performing the
422 * operation (normally stacked by the JVM)
423 * @param name must be {@link java.lang.constant.ConstantDescs#DEFAULT_NAME}
424 * ({@code "_"})
425 * @param type the type of the element at the given index in the class data
426 * @param index index of the element in the class data
427 * @return the element at the given index in the class data
428 * if the class data is present; otherwise {@code null}
429 * @throws IllegalArgumentException if name is not {@code "_"}
430 * @throws IllegalAccessException if the lookup context does not have
431 * {@linkplain Lookup#ORIGINAL original} access
432 * @throws ClassCastException if the class data cannot be converted to {@code List}
433 * or the element at the specified index cannot be converted to the given type
434 * @throws IndexOutOfBoundsException if the index is out of range
435 * @throws NullPointerException if {@code caller} or {@code type} argument is
436 * {@code null}; or if unboxing operation fails because
437 * the element at the given index is {@code null}
438 *
439 * @since 16
440 * @see #classData(Lookup, String, Class)
441 * @see Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...)
442 */
443 public static <T> T classDataAt(Lookup caller, String name, Class<T> type, int index)
444 throws IllegalAccessException
445 {
446 @SuppressWarnings("unchecked")
447 List<Object> classdata = (List<Object>)classData(caller, name, List.class);
448 if (classdata == null) return null;
449
450 try {
451 Object element = classdata.get(index);
452 return BootstrapMethodInvoker.widenAndCast(element, type);
453 } catch (RuntimeException|Error e) {
454 throw e; // let specified exceptions and other runtime exceptions/errors through
455 } catch (Throwable e) {
456 throw new InternalError(e);
457 }
458 }
459
460 /**
461 * Performs an unchecked "crack" of a
462 * <a href="MethodHandleInfo.html#directmh">direct method handle</a>.
463 * The result is as if the user had obtained a lookup object capable enough
464 * to crack the target method handle, called
465 * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect}
466 * on the target to obtain its symbolic reference, and then called
467 * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs}
468 * to resolve the symbolic reference to a member.
469 * <p>
470 * If there is a security manager, its {@code checkPermission} method
471 * is called with a {@code ReflectPermission("suppressAccessChecks")} permission.
472 * @param <T> the desired type of the result, either {@link Member} or a subtype
473 * @param target a direct method handle to crack into symbolic reference components
474 * @param expected a class object representing the desired result type {@code T}
475 * @return a reference to the method, constructor, or field object
476 * @throws SecurityException if the caller is not privileged to call {@code setAccessible}
477 * @throws NullPointerException if either argument is {@code null}
478 * @throws IllegalArgumentException if the target is not a direct method handle
479 * @throws ClassCastException if the member is not of the expected type
480 * @since 1.8
481 */
482 public static <T extends Member> T reflectAs(Class<T> expected, MethodHandle target) {
483 @SuppressWarnings("removal")
484 SecurityManager smgr = System.getSecurityManager();
485 if (smgr != null) smgr.checkPermission(SecurityConstants.ACCESS_PERMISSION);
486 Lookup lookup = Lookup.IMPL_LOOKUP; // use maximally privileged lookup
487 return lookup.revealDirect(target).reflectAs(expected, lookup);
488 }
489
490 /**
491 * A <em>lookup object</em> is a factory for creating method handles,
492 * when the creation requires access checking.
493 * Method handles do not perform
494 * access checks when they are called, but rather when they are created.
495 * Therefore, method handle access
496 * restrictions must be enforced when a method handle is created.
497 * The caller class against which those restrictions are enforced
498 * is known as the {@linkplain #lookupClass() lookup class}.
499 * <p>
500 * A lookup class which needs to create method handles will call
501 * {@link MethodHandles#lookup() MethodHandles.lookup} to create a factory for itself.
502 * When the {@code Lookup} factory object is created, the identity of the lookup class is
503 * determined, and securely stored in the {@code Lookup} object.
504 * The lookup class (or its delegates) may then use factory methods
505 * on the {@code Lookup} object to create method handles for access-checked members.
506 * This includes all methods, constructors, and fields which are allowed to the lookup class,
507 * even private ones.
508 *
509 * <h2><a id="lookups"></a>Lookup Factory Methods</h2>
510 * The factory methods on a {@code Lookup} object correspond to all major
511 * use cases for methods, constructors, and fields.
512 * Each method handle created by a factory method is the functional
513 * equivalent of a particular <em>bytecode behavior</em>.
514 * (Bytecode behaviors are described in section {@jvms 5.4.3.5} of
515 * the Java Virtual Machine Specification.)
516 * Here is a summary of the correspondence between these factory methods and
517 * the behavior of the resulting method handles:
518 * <table class="striped">
519 * <caption style="display:none">lookup method behaviors</caption>
520 * <thead>
521 * <tr>
522 * <th scope="col"><a id="equiv"></a>lookup expression</th>
523 * <th scope="col">member</th>
524 * <th scope="col">bytecode behavior</th>
525 * </tr>
526 * </thead>
527 * <tbody>
528 * <tr>
529 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</th>
530 * <td>{@code FT f;}</td><td>{@code (T) this.f;}</td>
531 * </tr>
532 * <tr>
533 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</th>
534 * <td>{@code static}<br>{@code FT f;}</td><td>{@code (FT) C.f;}</td>
535 * </tr>
536 * <tr>
537 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</th>
538 * <td>{@code FT f;}</td><td>{@code this.f = x;}</td>
539 * </tr>
540 * <tr>
541 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</th>
542 * <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td>
543 * </tr>
544 * <tr>
545 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</th>
546 * <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>
547 * </tr>
548 * <tr>
549 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</th>
550 * <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td>
551 * </tr>
552 * <tr>
553 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</th>
554 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
555 * </tr>
556 * <tr>
557 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</th>
558 * <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td>
559 * </tr>
560 * <tr>
561 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</th>
562 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td>
563 * </tr>
564 * <tr>
565 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</th>
566 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, arg);}</td>
567 * </tr>
568 * <tr>
569 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</th>
570 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
571 * </tr>
572 * <tr>
573 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</th>
574 * <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td>
575 * </tr>
576 * <tr>
577 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSpecial lookup.unreflectSpecial(aMethod,this.class)}</th>
578 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
579 * </tr>
580 * <tr>
581 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findClass lookup.findClass("C")}</th>
582 * <td>{@code class C { ... }}</td><td>{@code C.class;}</td>
583 * </tr>
584 * </tbody>
585 * </table>
586 *
587 * Here, the type {@code C} is the class or interface being searched for a member,
588 * documented as a parameter named {@code refc} in the lookup methods.
589 * The method type {@code MT} is composed from the return type {@code T}
590 * and the sequence of argument types {@code A*}.
591 * The constructor also has a sequence of argument types {@code A*} and
592 * is deemed to return the newly-created object of type {@code C}.
593 * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}.
594 * The formal parameter {@code this} stands for the self-reference of type {@code C};
595 * if it is present, it is always the leading argument to the method handle invocation.
596 * (In the case of some {@code protected} members, {@code this} may be
597 * restricted in type to the lookup class; see below.)
598 * The name {@code arg} stands for all the other method handle arguments.
599 * In the code examples for the Core Reflection API, the name {@code thisOrNull}
600 * stands for a null reference if the accessed method or field is static,
601 * and {@code this} otherwise.
602 * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand
603 * for reflective objects corresponding to the given members declared in type {@code C}.
604 * <p>
605 * The bytecode behavior for a {@code findClass} operation is a load of a constant class,
606 * as if by {@code ldc CONSTANT_Class}.
607 * The behavior is represented, not as a method handle, but directly as a {@code Class} constant.
608 * <p>
609 * In cases where the given member is of variable arity (i.e., a method or constructor)
610 * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}.
611 * In all other cases, the returned method handle will be of fixed arity.
612 * <p style="font-size:smaller;">
613 * <em>Discussion:</em>
614 * The equivalence between looked-up method handles and underlying
615 * class members and bytecode behaviors
616 * can break down in a few ways:
617 * <ul style="font-size:smaller;">
618 * <li>If {@code C} is not symbolically accessible from the lookup class's loader,
619 * the lookup can still succeed, even when there is no equivalent
620 * Java expression or bytecoded constant.
621 * <li>Likewise, if {@code T} or {@code MT}
622 * is not symbolically accessible from the lookup class's loader,
623 * the lookup can still succeed.
624 * For example, lookups for {@code MethodHandle.invokeExact} and
625 * {@code MethodHandle.invoke} will always succeed, regardless of requested type.
626 * <li>If there is a security manager installed, it can forbid the lookup
627 * on various grounds (<a href="MethodHandles.Lookup.html#secmgr">see below</a>).
628 * By contrast, the {@code ldc} instruction on a {@code CONSTANT_MethodHandle}
629 * constant is not subject to security manager checks.
630 * <li>If the looked-up method has a
631 * <a href="MethodHandle.html#maxarity">very large arity</a>,
632 * the method handle creation may fail with an
633 * {@code IllegalArgumentException}, due to the method handle type having
634 * <a href="MethodHandle.html#maxarity">too many parameters.</a>
635 * </ul>
636 *
637 * <h2><a id="access"></a>Access checking</h2>
638 * Access checks are applied in the factory methods of {@code Lookup},
639 * when a method handle is created.
640 * This is a key difference from the Core Reflection API, since
641 * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
642 * performs access checking against every caller, on every call.
643 * <p>
644 * All access checks start from a {@code Lookup} object, which
645 * compares its recorded lookup class against all requests to
646 * create method handles.
647 * A single {@code Lookup} object can be used to create any number
648 * of access-checked method handles, all checked against a single
649 * lookup class.
650 * <p>
651 * A {@code Lookup} object can be shared with other trusted code,
652 * such as a metaobject protocol.
653 * A shared {@code Lookup} object delegates the capability
654 * to create method handles on private members of the lookup class.
655 * Even if privileged code uses the {@code Lookup} object,
656 * the access checking is confined to the privileges of the
657 * original lookup class.
658 * <p>
659 * A lookup can fail, because
660 * the containing class is not accessible to the lookup class, or
661 * because the desired class member is missing, or because the
662 * desired class member is not accessible to the lookup class, or
663 * because the lookup object is not trusted enough to access the member.
664 * In the case of a field setter function on a {@code final} field,
665 * finality enforcement is treated as a kind of access control,
666 * and the lookup will fail, except in special cases of
667 * {@link Lookup#unreflectSetter Lookup.unreflectSetter}.
668 * In any of these cases, a {@code ReflectiveOperationException} will be
669 * thrown from the attempted lookup. The exact class will be one of
670 * the following:
671 * <ul>
672 * <li>NoSuchMethodException — if a method is requested but does not exist
673 * <li>NoSuchFieldException — if a field is requested but does not exist
674 * <li>IllegalAccessException — if the member exists but an access check fails
675 * </ul>
676 * <p>
677 * In general, the conditions under which a method handle may be
678 * looked up for a method {@code M} are no more restrictive than the conditions
679 * under which the lookup class could have compiled, verified, and resolved a call to {@code M}.
680 * Where the JVM would raise exceptions like {@code NoSuchMethodError},
681 * a method handle lookup will generally raise a corresponding
682 * checked exception, such as {@code NoSuchMethodException}.
683 * And the effect of invoking the method handle resulting from the lookup
684 * is <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a>
685 * to executing the compiled, verified, and resolved call to {@code M}.
686 * The same point is true of fields and constructors.
687 * <p style="font-size:smaller;">
688 * <em>Discussion:</em>
689 * Access checks only apply to named and reflected methods,
690 * constructors, and fields.
691 * Other method handle creation methods, such as
692 * {@link MethodHandle#asType MethodHandle.asType},
693 * do not require any access checks, and are used
694 * independently of any {@code Lookup} object.
695 * <p>
696 * If the desired member is {@code protected}, the usual JVM rules apply,
697 * including the requirement that the lookup class must either be in the
698 * same package as the desired member, or must inherit that member.
699 * (See the Java Virtual Machine Specification, sections {@jvms
700 * 4.9.2}, {@jvms 5.4.3.5}, and {@jvms 6.4}.)
701 * In addition, if the desired member is a non-static field or method
702 * in a different package, the resulting method handle may only be applied
703 * to objects of the lookup class or one of its subclasses.
704 * This requirement is enforced by narrowing the type of the leading
705 * {@code this} parameter from {@code C}
706 * (which will necessarily be a superclass of the lookup class)
707 * to the lookup class itself.
708 * <p>
709 * The JVM imposes a similar requirement on {@code invokespecial} instruction,
710 * that the receiver argument must match both the resolved method <em>and</em>
711 * the current class. Again, this requirement is enforced by narrowing the
712 * type of the leading parameter to the resulting method handle.
713 * (See the Java Virtual Machine Specification, section {@jvms 4.10.1.9}.)
714 * <p>
715 * The JVM represents constructors and static initializer blocks as internal methods
716 * with special names ({@value ConstantDescs#INIT_NAME} and {@value
717 * ConstantDescs#CLASS_INIT_NAME}).
718 * The internal syntax of invocation instructions allows them to refer to such internal
719 * methods as if they were normal methods, but the JVM bytecode verifier rejects them.
720 * A lookup of such an internal method will produce a {@code NoSuchMethodException}.
721 * <p>
722 * If the relationship between nested types is expressed directly through the
723 * {@code NestHost} and {@code NestMembers} attributes
724 * (see the Java Virtual Machine Specification, sections {@jvms
725 * 4.7.28} and {@jvms 4.7.29}),
726 * then the associated {@code Lookup} object provides direct access to
727 * the lookup class and all of its nestmates
728 * (see {@link java.lang.Class#getNestHost Class.getNestHost}).
729 * Otherwise, access between nested classes is obtained by the Java compiler creating
730 * a wrapper method to access a private method of another class in the same nest.
731 * For example, a nested class {@code C.D}
732 * can access private members within other related classes such as
733 * {@code C}, {@code C.D.E}, or {@code C.B},
734 * but the Java compiler may need to generate wrapper methods in
735 * those related classes. In such cases, a {@code Lookup} object on
736 * {@code C.E} would be unable to access those private members.
737 * A workaround for this limitation is the {@link Lookup#in Lookup.in} method,
738 * which can transform a lookup on {@code C.E} into one on any of those other
739 * classes, without special elevation of privilege.
740 * <p>
741 * The accesses permitted to a given lookup object may be limited,
742 * according to its set of {@link #lookupModes lookupModes},
743 * to a subset of members normally accessible to the lookup class.
744 * For example, the {@link MethodHandles#publicLookup publicLookup}
745 * method produces a lookup object which is only allowed to access
746 * public members in public classes of exported packages.
747 * The caller sensitive method {@link MethodHandles#lookup lookup}
748 * produces a lookup object with full capabilities relative to
749 * its caller class, to emulate all supported bytecode behaviors.
750 * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object
751 * with fewer access modes than the original lookup object.
752 *
753 * <p style="font-size:smaller;">
754 * <a id="privacc"></a>
755 * <em>Discussion of private and module access:</em>
756 * We say that a lookup has <em>private access</em>
757 * if its {@linkplain #lookupModes lookup modes}
758 * include the possibility of accessing {@code private} members
759 * (which includes the private members of nestmates).
760 * As documented in the relevant methods elsewhere,
761 * only lookups with private access possess the following capabilities:
762 * <ul style="font-size:smaller;">
763 * <li>access private fields, methods, and constructors of the lookup class and its nestmates
764 * <li>create method handles which {@link Lookup#findSpecial emulate invokespecial} instructions
765 * <li>avoid <a href="MethodHandles.Lookup.html#secmgr">package access checks</a>
766 * for classes accessible to the lookup class
767 * <li>create {@link Lookup#in delegated lookup objects} which have private access to other classes
768 * within the same package member
769 * </ul>
770 * <p style="font-size:smaller;">
771 * Similarly, a lookup with module access ensures that the original lookup creator was
772 * a member in the same module as the lookup class.
773 * <p style="font-size:smaller;">
774 * Private and module access are independently determined modes; a lookup may have
775 * either or both or neither. A lookup which possesses both access modes is said to
776 * possess {@linkplain #hasFullPrivilegeAccess() full privilege access}.
777 * <p style="font-size:smaller;">
778 * A lookup with <em>original access</em> ensures that this lookup is created by
779 * the original lookup class and the bootstrap method invoked by the VM.
780 * Such a lookup with original access also has private and module access
781 * which has the following additional capability:
782 * <ul style="font-size:smaller;">
783 * <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> methods,
784 * such as {@code Class.forName}
785 * <li>obtain the {@linkplain MethodHandles#classData(Lookup, String, Class)
786 * class data} associated with the lookup class</li>
787 * </ul>
788 * <p style="font-size:smaller;">
789 * Each of these permissions is a consequence of the fact that a lookup object
790 * with private access can be securely traced back to an originating class,
791 * whose <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> and Java language access permissions
792 * can be reliably determined and emulated by method handles.
793 *
794 * <h2><a id="cross-module-lookup"></a>Cross-module lookups</h2>
795 * When a lookup class in one module {@code M1} accesses a class in another module
796 * {@code M2}, extra access checking is performed beyond the access mode bits.
797 * A {@code Lookup} with {@link #PUBLIC} mode and a lookup class in {@code M1}
798 * can access public types in {@code M2} when {@code M2} is readable to {@code M1}
799 * and when the type is in a package of {@code M2} that is exported to
800 * at least {@code M1}.
801 * <p>
802 * A {@code Lookup} on {@code C} can also <em>teleport</em> to a target class
803 * via {@link #in(Class) Lookup.in} and {@link MethodHandles#privateLookupIn(Class, Lookup)
804 * MethodHandles.privateLookupIn} methods.
805 * Teleporting across modules will always record the original lookup class as
806 * the <em>{@linkplain #previousLookupClass() previous lookup class}</em>
807 * and drops {@link Lookup#MODULE MODULE} access.
808 * If the target class is in the same module as the lookup class {@code C},
809 * then the target class becomes the new lookup class
810 * and there is no change to the previous lookup class.
811 * If the target class is in a different module from {@code M1} ({@code C}'s module),
812 * {@code C} becomes the new previous lookup class
813 * and the target class becomes the new lookup class.
814 * In that case, if there was already a previous lookup class in {@code M0},
815 * and it differs from {@code M1} and {@code M2}, then the resulting lookup
816 * drops all privileges.
817 * For example,
818 * {@snippet lang="java" :
819 * Lookup lookup = MethodHandles.lookup(); // in class C
820 * Lookup lookup2 = lookup.in(D.class);
821 * MethodHandle mh = lookup2.findStatic(E.class, "m", MT);
822 * }
823 * <p>
824 * The {@link #lookup()} factory method produces a {@code Lookup} object
825 * with {@code null} previous lookup class.
826 * {@link Lookup#in lookup.in(D.class)} transforms the {@code lookup} on class {@code C}
827 * to class {@code D} without elevation of privileges.
828 * If {@code C} and {@code D} are in the same module,
829 * {@code lookup2} records {@code D} as the new lookup class and keeps the
830 * same previous lookup class as the original {@code lookup}, or
831 * {@code null} if not present.
832 * <p>
833 * When a {@code Lookup} teleports from a class
834 * in one nest to another nest, {@code PRIVATE} access is dropped.
835 * When a {@code Lookup} teleports from a class in one package to
836 * another package, {@code PACKAGE} access is dropped.
837 * When a {@code Lookup} teleports from a class in one module to another module,
838 * {@code MODULE} access is dropped.
839 * Teleporting across modules drops the ability to access non-exported classes
840 * in both the module of the new lookup class and the module of the old lookup class
841 * and the resulting {@code Lookup} remains only {@code PUBLIC} access.
842 * A {@code Lookup} can teleport back and forth to a class in the module of
843 * the lookup class and the module of the previous class lookup.
844 * Teleporting across modules can only decrease access but cannot increase it.
845 * Teleporting to some third module drops all accesses.
846 * <p>
847 * In the above example, if {@code C} and {@code D} are in different modules,
848 * {@code lookup2} records {@code D} as its lookup class and
849 * {@code C} as its previous lookup class and {@code lookup2} has only
850 * {@code PUBLIC} access. {@code lookup2} can teleport to other class in
851 * {@code C}'s module and {@code D}'s module.
852 * If class {@code E} is in a third module, {@code lookup2.in(E.class)} creates
853 * a {@code Lookup} on {@code E} with no access and {@code lookup2}'s lookup
854 * class {@code D} is recorded as its previous lookup class.
855 * <p>
856 * Teleporting across modules restricts access to the public types that
857 * both the lookup class and the previous lookup class can equally access
858 * (see below).
859 * <p>
860 * {@link MethodHandles#privateLookupIn(Class, Lookup) MethodHandles.privateLookupIn(T.class, lookup)}
861 * can be used to teleport a {@code lookup} from class {@code C} to class {@code T}
862 * and produce a new {@code Lookup} with <a href="#privacc">private access</a>
863 * if the lookup class is allowed to do <em>deep reflection</em> on {@code T}.
864 * The {@code lookup} must have {@link #MODULE} and {@link #PRIVATE} access
865 * to call {@code privateLookupIn}.
866 * A {@code lookup} on {@code C} in module {@code M1} is allowed to do deep reflection
867 * on all classes in {@code M1}. If {@code T} is in {@code M1}, {@code privateLookupIn}
868 * produces a new {@code Lookup} on {@code T} with full capabilities.
869 * A {@code lookup} on {@code C} is also allowed
870 * to do deep reflection on {@code T} in another module {@code M2} if
871 * {@code M1} reads {@code M2} and {@code M2} {@link Module#isOpen(String,Module) opens}
872 * the package containing {@code T} to at least {@code M1}.
873 * {@code T} becomes the new lookup class and {@code C} becomes the new previous
874 * lookup class and {@code MODULE} access is dropped from the resulting {@code Lookup}.
875 * The resulting {@code Lookup} can be used to do member lookup or teleport
876 * to another lookup class by calling {@link #in Lookup::in}. But
877 * it cannot be used to obtain another private {@code Lookup} by calling
878 * {@link MethodHandles#privateLookupIn(Class, Lookup) privateLookupIn}
879 * because it has no {@code MODULE} access.
880 * <p>
881 * The {@code Lookup} object returned by {@code privateLookupIn} is allowed to
882 * {@linkplain Lookup#defineClass(byte[]) define classes} in the runtime package
883 * of {@code T}. Extreme caution should be taken when opening a package
884 * to another module as such defined classes have the same full privilege
885 * access as other members in {@code M2}.
886 *
887 * <h2><a id="module-access-check"></a>Cross-module access checks</h2>
888 *
889 * A {@code Lookup} with {@link #PUBLIC} or with {@link #UNCONDITIONAL} mode
890 * allows cross-module access. The access checking is performed with respect
891 * to both the lookup class and the previous lookup class if present.
892 * <p>
893 * A {@code Lookup} with {@link #UNCONDITIONAL} mode can access public type
894 * in all modules when the type is in a package that is {@linkplain Module#isExported(String)
895 * exported unconditionally}.
896 * <p>
897 * If a {@code Lookup} on {@code LC} in {@code M1} has no previous lookup class,
898 * the lookup with {@link #PUBLIC} mode can access all public types in modules
899 * that are readable to {@code M1} and the type is in a package that is exported
900 * at least to {@code M1}.
901 * <p>
902 * If a {@code Lookup} on {@code LC} in {@code M1} has a previous lookup class
903 * {@code PLC} on {@code M0}, the lookup with {@link #PUBLIC} mode can access
904 * the intersection of all public types that are accessible to {@code M1}
905 * with all public types that are accessible to {@code M0}. {@code M0}
906 * reads {@code M1} and hence the set of accessible types includes:
907 *
908 * <ul>
909 * <li>unconditional-exported packages from {@code M1}</li>
910 * <li>unconditional-exported packages from {@code M0} if {@code M1} reads {@code M0}</li>
911 * <li>
912 * unconditional-exported packages from a third module {@code M2}if both {@code M0}
913 * and {@code M1} read {@code M2}
914 * </li>
915 * <li>qualified-exported packages from {@code M1} to {@code M0}</li>
916 * <li>qualified-exported packages from {@code M0} to {@code M1} if {@code M1} reads {@code M0}</li>
917 * <li>
918 * qualified-exported packages from a third module {@code M2} to both {@code M0} and
919 * {@code M1} if both {@code M0} and {@code M1} read {@code M2}
920 * </li>
921 * </ul>
922 *
923 * <h2><a id="access-modes"></a>Access modes</h2>
924 *
925 * The table below shows the access modes of a {@code Lookup} produced by
926 * any of the following factory or transformation methods:
927 * <ul>
928 * <li>{@link #lookup() MethodHandles::lookup}</li>
929 * <li>{@link #publicLookup() MethodHandles::publicLookup}</li>
930 * <li>{@link #privateLookupIn(Class, Lookup) MethodHandles::privateLookupIn}</li>
931 * <li>{@link Lookup#in Lookup::in}</li>
932 * <li>{@link Lookup#dropLookupMode(int) Lookup::dropLookupMode}</li>
933 * </ul>
934 *
935 * <table class="striped">
936 * <caption style="display:none">
937 * Access mode summary
938 * </caption>
939 * <thead>
940 * <tr>
941 * <th scope="col">Lookup object</th>
942 * <th style="text-align:center">original</th>
943 * <th style="text-align:center">protected</th>
944 * <th style="text-align:center">private</th>
945 * <th style="text-align:center">package</th>
946 * <th style="text-align:center">module</th>
947 * <th style="text-align:center">public</th>
948 * </tr>
949 * </thead>
950 * <tbody>
951 * <tr>
952 * <th scope="row" style="text-align:left">{@code CL = MethodHandles.lookup()} in {@code C}</th>
953 * <td style="text-align:center">ORI</td>
954 * <td style="text-align:center">PRO</td>
955 * <td style="text-align:center">PRI</td>
956 * <td style="text-align:center">PAC</td>
957 * <td style="text-align:center">MOD</td>
958 * <td style="text-align:center">1R</td>
959 * </tr>
960 * <tr>
961 * <th scope="row" style="text-align:left">{@code CL.in(C1)} same package</th>
962 * <td></td>
963 * <td></td>
964 * <td></td>
965 * <td style="text-align:center">PAC</td>
966 * <td style="text-align:center">MOD</td>
967 * <td style="text-align:center">1R</td>
968 * </tr>
969 * <tr>
970 * <th scope="row" style="text-align:left">{@code CL.in(C1)} same module</th>
971 * <td></td>
972 * <td></td>
973 * <td></td>
974 * <td></td>
975 * <td style="text-align:center">MOD</td>
976 * <td style="text-align:center">1R</td>
977 * </tr>
978 * <tr>
979 * <th scope="row" style="text-align:left">{@code CL.in(D)} different module</th>
980 * <td></td>
981 * <td></td>
982 * <td></td>
983 * <td></td>
984 * <td></td>
985 * <td style="text-align:center">2R</td>
986 * </tr>
987 * <tr>
988 * <th scope="row" style="text-align:left">{@code CL.in(D).in(C)} hop back to module</th>
989 * <td></td>
990 * <td></td>
991 * <td></td>
992 * <td></td>
993 * <td></td>
994 * <td style="text-align:center">2R</td>
995 * </tr>
996 * <tr>
997 * <th scope="row" style="text-align:left">{@code PRI1 = privateLookupIn(C1,CL)}</th>
998 * <td></td>
999 * <td style="text-align:center">PRO</td>
1000 * <td style="text-align:center">PRI</td>
1001 * <td style="text-align:center">PAC</td>
1002 * <td style="text-align:center">MOD</td>
1003 * <td style="text-align:center">1R</td>
1004 * </tr>
1005 * <tr>
1006 * <th scope="row" style="text-align:left">{@code PRI1a = privateLookupIn(C,PRI1)}</th>
1007 * <td></td>
1008 * <td style="text-align:center">PRO</td>
1009 * <td style="text-align:center">PRI</td>
1010 * <td style="text-align:center">PAC</td>
1011 * <td style="text-align:center">MOD</td>
1012 * <td style="text-align:center">1R</td>
1013 * </tr>
1014 * <tr>
1015 * <th scope="row" style="text-align:left">{@code PRI1.in(C1)} same package</th>
1016 * <td></td>
1017 * <td></td>
1018 * <td></td>
1019 * <td style="text-align:center">PAC</td>
1020 * <td style="text-align:center">MOD</td>
1021 * <td style="text-align:center">1R</td>
1022 * </tr>
1023 * <tr>
1024 * <th scope="row" style="text-align:left">{@code PRI1.in(C1)} different package</th>
1025 * <td></td>
1026 * <td></td>
1027 * <td></td>
1028 * <td></td>
1029 * <td style="text-align:center">MOD</td>
1030 * <td style="text-align:center">1R</td>
1031 * </tr>
1032 * <tr>
1033 * <th scope="row" style="text-align:left">{@code PRI1.in(D)} different module</th>
1034 * <td></td>
1035 * <td></td>
1036 * <td></td>
1037 * <td></td>
1038 * <td></td>
1039 * <td style="text-align:center">2R</td>
1040 * </tr>
1041 * <tr>
1042 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PROTECTED)}</th>
1043 * <td></td>
1044 * <td></td>
1045 * <td style="text-align:center">PRI</td>
1046 * <td style="text-align:center">PAC</td>
1047 * <td style="text-align:center">MOD</td>
1048 * <td style="text-align:center">1R</td>
1049 * </tr>
1050 * <tr>
1051 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PRIVATE)}</th>
1052 * <td></td>
1053 * <td></td>
1054 * <td></td>
1055 * <td style="text-align:center">PAC</td>
1056 * <td style="text-align:center">MOD</td>
1057 * <td style="text-align:center">1R</td>
1058 * </tr>
1059 * <tr>
1060 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PACKAGE)}</th>
1061 * <td></td>
1062 * <td></td>
1063 * <td></td>
1064 * <td></td>
1065 * <td style="text-align:center">MOD</td>
1066 * <td style="text-align:center">1R</td>
1067 * </tr>
1068 * <tr>
1069 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(MODULE)}</th>
1070 * <td></td>
1071 * <td></td>
1072 * <td></td>
1073 * <td></td>
1074 * <td></td>
1075 * <td style="text-align:center">1R</td>
1076 * </tr>
1077 * <tr>
1078 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PUBLIC)}</th>
1079 * <td></td>
1080 * <td></td>
1081 * <td></td>
1082 * <td></td>
1083 * <td></td>
1084 * <td style="text-align:center">none</td>
1085 * <tr>
1086 * <th scope="row" style="text-align:left">{@code PRI2 = privateLookupIn(D,CL)}</th>
1087 * <td></td>
1088 * <td style="text-align:center">PRO</td>
1089 * <td style="text-align:center">PRI</td>
1090 * <td style="text-align:center">PAC</td>
1091 * <td></td>
1092 * <td style="text-align:center">2R</td>
1093 * </tr>
1094 * <tr>
1095 * <th scope="row" style="text-align:left">{@code privateLookupIn(D,PRI1)}</th>
1096 * <td></td>
1097 * <td style="text-align:center">PRO</td>
1098 * <td style="text-align:center">PRI</td>
1099 * <td style="text-align:center">PAC</td>
1100 * <td></td>
1101 * <td style="text-align:center">2R</td>
1102 * </tr>
1103 * <tr>
1104 * <th scope="row" style="text-align:left">{@code privateLookupIn(C,PRI2)} fails</th>
1105 * <td></td>
1106 * <td></td>
1107 * <td></td>
1108 * <td></td>
1109 * <td></td>
1110 * <td style="text-align:center">IAE</td>
1111 * </tr>
1112 * <tr>
1113 * <th scope="row" style="text-align:left">{@code PRI2.in(D2)} same package</th>
1114 * <td></td>
1115 * <td></td>
1116 * <td></td>
1117 * <td style="text-align:center">PAC</td>
1118 * <td></td>
1119 * <td style="text-align:center">2R</td>
1120 * </tr>
1121 * <tr>
1122 * <th scope="row" style="text-align:left">{@code PRI2.in(D2)} different package</th>
1123 * <td></td>
1124 * <td></td>
1125 * <td></td>
1126 * <td></td>
1127 * <td></td>
1128 * <td style="text-align:center">2R</td>
1129 * </tr>
1130 * <tr>
1131 * <th scope="row" style="text-align:left">{@code PRI2.in(C1)} hop back to module</th>
1132 * <td></td>
1133 * <td></td>
1134 * <td></td>
1135 * <td></td>
1136 * <td></td>
1137 * <td style="text-align:center">2R</td>
1138 * </tr>
1139 * <tr>
1140 * <th scope="row" style="text-align:left">{@code PRI2.in(E)} hop to third module</th>
1141 * <td></td>
1142 * <td></td>
1143 * <td></td>
1144 * <td></td>
1145 * <td></td>
1146 * <td style="text-align:center">none</td>
1147 * </tr>
1148 * <tr>
1149 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PROTECTED)}</th>
1150 * <td></td>
1151 * <td></td>
1152 * <td style="text-align:center">PRI</td>
1153 * <td style="text-align:center">PAC</td>
1154 * <td></td>
1155 * <td style="text-align:center">2R</td>
1156 * </tr>
1157 * <tr>
1158 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PRIVATE)}</th>
1159 * <td></td>
1160 * <td></td>
1161 * <td></td>
1162 * <td style="text-align:center">PAC</td>
1163 * <td></td>
1164 * <td style="text-align:center">2R</td>
1165 * </tr>
1166 * <tr>
1167 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PACKAGE)}</th>
1168 * <td></td>
1169 * <td></td>
1170 * <td></td>
1171 * <td></td>
1172 * <td></td>
1173 * <td style="text-align:center">2R</td>
1174 * </tr>
1175 * <tr>
1176 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(MODULE)}</th>
1177 * <td></td>
1178 * <td></td>
1179 * <td></td>
1180 * <td></td>
1181 * <td></td>
1182 * <td style="text-align:center">2R</td>
1183 * </tr>
1184 * <tr>
1185 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PUBLIC)}</th>
1186 * <td></td>
1187 * <td></td>
1188 * <td></td>
1189 * <td></td>
1190 * <td></td>
1191 * <td style="text-align:center">none</td>
1192 * </tr>
1193 * <tr>
1194 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PROTECTED)}</th>
1195 * <td></td>
1196 * <td></td>
1197 * <td style="text-align:center">PRI</td>
1198 * <td style="text-align:center">PAC</td>
1199 * <td style="text-align:center">MOD</td>
1200 * <td style="text-align:center">1R</td>
1201 * </tr>
1202 * <tr>
1203 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PRIVATE)}</th>
1204 * <td></td>
1205 * <td></td>
1206 * <td></td>
1207 * <td style="text-align:center">PAC</td>
1208 * <td style="text-align:center">MOD</td>
1209 * <td style="text-align:center">1R</td>
1210 * </tr>
1211 * <tr>
1212 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PACKAGE)}</th>
1213 * <td></td>
1214 * <td></td>
1215 * <td></td>
1216 * <td></td>
1217 * <td style="text-align:center">MOD</td>
1218 * <td style="text-align:center">1R</td>
1219 * </tr>
1220 * <tr>
1221 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(MODULE)}</th>
1222 * <td></td>
1223 * <td></td>
1224 * <td></td>
1225 * <td></td>
1226 * <td></td>
1227 * <td style="text-align:center">1R</td>
1228 * </tr>
1229 * <tr>
1230 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PUBLIC)}</th>
1231 * <td></td>
1232 * <td></td>
1233 * <td></td>
1234 * <td></td>
1235 * <td></td>
1236 * <td style="text-align:center">none</td>
1237 * </tr>
1238 * <tr>
1239 * <th scope="row" style="text-align:left">{@code PUB = publicLookup()}</th>
1240 * <td></td>
1241 * <td></td>
1242 * <td></td>
1243 * <td></td>
1244 * <td></td>
1245 * <td style="text-align:center">U</td>
1246 * </tr>
1247 * <tr>
1248 * <th scope="row" style="text-align:left">{@code PUB.in(D)} different module</th>
1249 * <td></td>
1250 * <td></td>
1251 * <td></td>
1252 * <td></td>
1253 * <td></td>
1254 * <td style="text-align:center">U</td>
1255 * </tr>
1256 * <tr>
1257 * <th scope="row" style="text-align:left">{@code PUB.in(D).in(E)} third module</th>
1258 * <td></td>
1259 * <td></td>
1260 * <td></td>
1261 * <td></td>
1262 * <td></td>
1263 * <td style="text-align:center">U</td>
1264 * </tr>
1265 * <tr>
1266 * <th scope="row" style="text-align:left">{@code PUB.dropLookupMode(UNCONDITIONAL)}</th>
1267 * <td></td>
1268 * <td></td>
1269 * <td></td>
1270 * <td></td>
1271 * <td></td>
1272 * <td style="text-align:center">none</td>
1273 * </tr>
1274 * <tr>
1275 * <th scope="row" style="text-align:left">{@code privateLookupIn(C1,PUB)} fails</th>
1276 * <td></td>
1277 * <td></td>
1278 * <td></td>
1279 * <td></td>
1280 * <td></td>
1281 * <td style="text-align:center">IAE</td>
1282 * </tr>
1283 * <tr>
1284 * <th scope="row" style="text-align:left">{@code ANY.in(X)}, for inaccessible {@code X}</th>
1285 * <td></td>
1286 * <td></td>
1287 * <td></td>
1288 * <td></td>
1289 * <td></td>
1290 * <td style="text-align:center">none</td>
1291 * </tr>
1292 * </tbody>
1293 * </table>
1294 *
1295 * <p>
1296 * Notes:
1297 * <ul>
1298 * <li>Class {@code C} and class {@code C1} are in module {@code M1},
1299 * but {@code D} and {@code D2} are in module {@code M2}, and {@code E}
1300 * is in module {@code M3}. {@code X} stands for class which is inaccessible
1301 * to the lookup. {@code ANY} stands for any of the example lookups.</li>
1302 * <li>{@code ORI} indicates {@link #ORIGINAL} bit set,
1303 * {@code PRO} indicates {@link #PROTECTED} bit set,
1304 * {@code PRI} indicates {@link #PRIVATE} bit set,
1305 * {@code PAC} indicates {@link #PACKAGE} bit set,
1306 * {@code MOD} indicates {@link #MODULE} bit set,
1307 * {@code 1R} and {@code 2R} indicate {@link #PUBLIC} bit set,
1308 * {@code U} indicates {@link #UNCONDITIONAL} bit set,
1309 * {@code IAE} indicates {@code IllegalAccessException} thrown.</li>
1310 * <li>Public access comes in three kinds:
1311 * <ul>
1312 * <li>unconditional ({@code U}): the lookup assumes readability.
1313 * The lookup has {@code null} previous lookup class.
1314 * <li>one-module-reads ({@code 1R}): the module access checking is
1315 * performed with respect to the lookup class. The lookup has {@code null}
1316 * previous lookup class.
1317 * <li>two-module-reads ({@code 2R}): the module access checking is
1318 * performed with respect to the lookup class and the previous lookup class.
1319 * The lookup has a non-null previous lookup class which is in a
1320 * different module from the current lookup class.
1321 * </ul>
1322 * <li>Any attempt to reach a third module loses all access.</li>
1323 * <li>If a target class {@code X} is not accessible to {@code Lookup::in}
1324 * all access modes are dropped.</li>
1325 * </ul>
1326 *
1327 * <h2><a id="secmgr"></a>Security manager interactions</h2>
1328 * Although bytecode instructions can only refer to classes in
1329 * a related class loader, this API can search for methods in any
1330 * class, as long as a reference to its {@code Class} object is
1331 * available. Such cross-loader references are also possible with the
1332 * Core Reflection API, and are impossible to bytecode instructions
1333 * such as {@code invokestatic} or {@code getfield}.
1334 * There is a {@linkplain java.lang.SecurityManager security manager API}
1335 * to allow applications to check such cross-loader references.
1336 * These checks apply to both the {@code MethodHandles.Lookup} API
1337 * and the Core Reflection API
1338 * (as found on {@link java.lang.Class Class}).
1339 * <p>
1340 * If a security manager is present, member and class lookups are subject to
1341 * additional checks.
1342 * From one to three calls are made to the security manager.
1343 * Any of these calls can refuse access by throwing a
1344 * {@link java.lang.SecurityException SecurityException}.
1345 * Define {@code smgr} as the security manager,
1346 * {@code lookc} as the lookup class of the current lookup object,
1347 * {@code refc} as the containing class in which the member
1348 * is being sought, and {@code defc} as the class in which the
1349 * member is actually defined.
1350 * (If a class or other type is being accessed,
1351 * the {@code refc} and {@code defc} values are the class itself.)
1352 * The value {@code lookc} is defined as <em>not present</em>
1353 * if the current lookup object does not have
1354 * {@linkplain #hasFullPrivilegeAccess() full privilege access}.
1355 * The calls are made according to the following rules:
1356 * <ul>
1357 * <li><b>Step 1:</b>
1358 * If {@code lookc} is not present, or if its class loader is not
1359 * the same as or an ancestor of the class loader of {@code refc},
1360 * then {@link SecurityManager#checkPackageAccess
1361 * smgr.checkPackageAccess(refcPkg)} is called,
1362 * where {@code refcPkg} is the package of {@code refc}.
1363 * <li><b>Step 2a:</b>
1364 * If the retrieved member is not public and
1365 * {@code lookc} is not present, then
1366 * {@link SecurityManager#checkPermission smgr.checkPermission}
1367 * with {@code RuntimePermission("accessDeclaredMembers")} is called.
1368 * <li><b>Step 2b:</b>
1369 * If the retrieved class has a {@code null} class loader,
1370 * and {@code lookc} is not present, then
1371 * {@link SecurityManager#checkPermission smgr.checkPermission}
1372 * with {@code RuntimePermission("getClassLoader")} is called.
1373 * <li><b>Step 3:</b>
1374 * If the retrieved member is not public,
1375 * and if {@code lookc} is not present,
1376 * and if {@code defc} and {@code refc} are different,
1377 * then {@link SecurityManager#checkPackageAccess
1378 * smgr.checkPackageAccess(defcPkg)} is called,
1379 * where {@code defcPkg} is the package of {@code defc}.
1380 * </ul>
1381 * Security checks are performed after other access checks have passed.
1382 * Therefore, the above rules presuppose a member or class that is public,
1383 * or else that is being accessed from a lookup class that has
1384 * rights to access the member or class.
1385 * <p>
1386 * If a security manager is present and the current lookup object does not have
1387 * {@linkplain #hasFullPrivilegeAccess() full privilege access}, then
1388 * {@link #defineClass(byte[]) defineClass},
1389 * {@link #defineHiddenClass(byte[], boolean, ClassOption...) defineHiddenClass},
1390 * {@link #defineHiddenClassWithClassData(byte[], Object, boolean, ClassOption...)
1391 * defineHiddenClassWithClassData}
1392 * calls {@link SecurityManager#checkPermission smgr.checkPermission}
1393 * with {@code RuntimePermission("defineClass")}.
1394 *
1395 * <h2><a id="callsens"></a>Caller sensitive methods</h2>
1396 * A small number of Java methods have a special property called caller sensitivity.
1397 * A <em>caller-sensitive</em> method can behave differently depending on the
1398 * identity of its immediate caller.
1399 * <p>
1400 * If a method handle for a caller-sensitive method is requested,
1401 * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> apply,
1402 * but they take account of the lookup class in a special way.
1403 * The resulting method handle behaves as if it were called
1404 * from an instruction contained in the lookup class,
1405 * so that the caller-sensitive method detects the lookup class.
1406 * (By contrast, the invoker of the method handle is disregarded.)
1407 * Thus, in the case of caller-sensitive methods,
1408 * different lookup classes may give rise to
1409 * differently behaving method handles.
1410 * <p>
1411 * In cases where the lookup object is
1412 * {@link MethodHandles#publicLookup() publicLookup()},
1413 * or some other lookup object without the
1414 * {@linkplain #ORIGINAL original access},
1415 * the lookup class is disregarded.
1416 * In such cases, no caller-sensitive method handle can be created,
1417 * access is forbidden, and the lookup fails with an
1418 * {@code IllegalAccessException}.
1419 * <p style="font-size:smaller;">
1420 * <em>Discussion:</em>
1421 * For example, the caller-sensitive method
1422 * {@link java.lang.Class#forName(String) Class.forName(x)}
1423 * can return varying classes or throw varying exceptions,
1424 * depending on the class loader of the class that calls it.
1425 * A public lookup of {@code Class.forName} will fail, because
1426 * there is no reasonable way to determine its bytecode behavior.
1427 * <p style="font-size:smaller;">
1428 * If an application caches method handles for broad sharing,
1429 * it should use {@code publicLookup()} to create them.
1430 * If there is a lookup of {@code Class.forName}, it will fail,
1431 * and the application must take appropriate action in that case.
1432 * It may be that a later lookup, perhaps during the invocation of a
1433 * bootstrap method, can incorporate the specific identity
1434 * of the caller, making the method accessible.
1435 * <p style="font-size:smaller;">
1436 * The function {@code MethodHandles.lookup} is caller sensitive
1437 * so that there can be a secure foundation for lookups.
1438 * Nearly all other methods in the JSR 292 API rely on lookup
1439 * objects to check access requests.
1440 *
1441 * @revised 9
1442 */
1443 public static final
1444 class Lookup {
1445 /** The class on behalf of whom the lookup is being performed. */
1446 private final Class<?> lookupClass;
1447
1448 /** previous lookup class */
1449 private final Class<?> prevLookupClass;
1450
1451 /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */
1452 private final int allowedModes;
1453
1454 static {
1455 Reflection.registerFieldsToFilter(Lookup.class, Set.of("lookupClass", "allowedModes"));
1456 }
1457
1458 /** A single-bit mask representing {@code public} access,
1459 * which may contribute to the result of {@link #lookupModes lookupModes}.
1460 * The value, {@code 0x01}, happens to be the same as the value of the
1461 * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.
1462 * <p>
1463 * A {@code Lookup} with this lookup mode performs cross-module access check
1464 * with respect to the {@linkplain #lookupClass() lookup class} and
1465 * {@linkplain #previousLookupClass() previous lookup class} if present.
1466 */
1467 public static final int PUBLIC = Modifier.PUBLIC;
1468
1469 /** A single-bit mask representing {@code private} access,
1470 * which may contribute to the result of {@link #lookupModes lookupModes}.
1471 * The value, {@code 0x02}, happens to be the same as the value of the
1472 * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.
1473 */
1474 public static final int PRIVATE = Modifier.PRIVATE;
1475
1476 /** A single-bit mask representing {@code protected} access,
1477 * which may contribute to the result of {@link #lookupModes lookupModes}.
1478 * The value, {@code 0x04}, happens to be the same as the value of the
1479 * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.
1480 */
1481 public static final int PROTECTED = Modifier.PROTECTED;
1482
1483 /** A single-bit mask representing {@code package} access (default access),
1484 * which may contribute to the result of {@link #lookupModes lookupModes}.
1485 * The value is {@code 0x08}, which does not correspond meaningfully to
1486 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1487 */
1488 public static final int PACKAGE = Modifier.STATIC;
1489
1490 /** A single-bit mask representing {@code module} access,
1491 * which may contribute to the result of {@link #lookupModes lookupModes}.
1492 * The value is {@code 0x10}, which does not correspond meaningfully to
1493 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1494 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup}
1495 * with this lookup mode can access all public types in the module of the
1496 * lookup class and public types in packages exported by other modules
1497 * to the module of the lookup class.
1498 * <p>
1499 * If this lookup mode is set, the {@linkplain #previousLookupClass()
1500 * previous lookup class} is always {@code null}.
1501 *
1502 * @since 9
1503 */
1504 public static final int MODULE = PACKAGE << 1;
1505
1506 /** A single-bit mask representing {@code unconditional} access
1507 * which may contribute to the result of {@link #lookupModes lookupModes}.
1508 * The value is {@code 0x20}, which does not correspond meaningfully to
1509 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1510 * A {@code Lookup} with this lookup mode assumes {@linkplain
1511 * java.lang.Module#canRead(java.lang.Module) readability}.
1512 * This lookup mode can access all public members of public types
1513 * of all modules when the type is in a package that is {@link
1514 * java.lang.Module#isExported(String) exported unconditionally}.
1515 *
1516 * <p>
1517 * If this lookup mode is set, the {@linkplain #previousLookupClass()
1518 * previous lookup class} is always {@code null}.
1519 *
1520 * @since 9
1521 * @see #publicLookup()
1522 */
1523 public static final int UNCONDITIONAL = PACKAGE << 2;
1524
1525 /** A single-bit mask representing {@code original} access
1526 * which may contribute to the result of {@link #lookupModes lookupModes}.
1527 * The value is {@code 0x40}, which does not correspond meaningfully to
1528 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1529 *
1530 * <p>
1531 * If this lookup mode is set, the {@code Lookup} object must be
1532 * created by the original lookup class by calling
1533 * {@link MethodHandles#lookup()} method or by a bootstrap method
1534 * invoked by the VM. The {@code Lookup} object with this lookup
1535 * mode has {@linkplain #hasFullPrivilegeAccess() full privilege access}.
1536 *
1537 * @since 16
1538 */
1539 public static final int ORIGINAL = PACKAGE << 3;
1540
1541 private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE | MODULE | UNCONDITIONAL | ORIGINAL);
1542 private static final int FULL_POWER_MODES = (ALL_MODES & ~UNCONDITIONAL); // with original access
1543 private static final int TRUSTED = -1;
1544
1545 /*
1546 * Adjust PUBLIC => PUBLIC|MODULE|ORIGINAL|UNCONDITIONAL
1547 * Adjust 0 => PACKAGE
1548 */
1549 private static int fixmods(int mods) {
1550 mods &= (ALL_MODES - PACKAGE - MODULE - ORIGINAL - UNCONDITIONAL);
1551 if (Modifier.isPublic(mods))
1552 mods |= UNCONDITIONAL;
1553 return (mods != 0) ? mods : PACKAGE;
1554 }
1555
1556 /** Tells which class is performing the lookup. It is this class against
1557 * which checks are performed for visibility and access permissions.
1558 * <p>
1559 * If this lookup object has a {@linkplain #previousLookupClass() previous lookup class},
1560 * access checks are performed against both the lookup class and the previous lookup class.
1561 * <p>
1562 * The class implies a maximum level of access permission,
1563 * but the permissions may be additionally limited by the bitmask
1564 * {@link #lookupModes lookupModes}, which controls whether non-public members
1565 * can be accessed.
1566 * @return the lookup class, on behalf of which this lookup object finds members
1567 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1568 */
1569 public Class<?> lookupClass() {
1570 return lookupClass;
1571 }
1572
1573 /** Reports a lookup class in another module that this lookup object
1574 * was previously teleported from, or {@code null}.
1575 * <p>
1576 * A {@code Lookup} object produced by the factory methods, such as the
1577 * {@link #lookup() lookup()} and {@link #publicLookup() publicLookup()} method,
1578 * has {@code null} previous lookup class.
1579 * A {@code Lookup} object has a non-null previous lookup class
1580 * when this lookup was teleported from an old lookup class
1581 * in one module to a new lookup class in another module.
1582 *
1583 * @return the lookup class in another module that this lookup object was
1584 * previously teleported from, or {@code null}
1585 * @since 14
1586 * @see #in(Class)
1587 * @see MethodHandles#privateLookupIn(Class, Lookup)
1588 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1589 */
1590 public Class<?> previousLookupClass() {
1591 return prevLookupClass;
1592 }
1593
1594 // This is just for calling out to MethodHandleImpl.
1595 private Class<?> lookupClassOrNull() {
1596 return (allowedModes == TRUSTED) ? null : lookupClass;
1597 }
1598
1599 /** Tells which access-protection classes of members this lookup object can produce.
1600 * The result is a bit-mask of the bits
1601 * {@linkplain #PUBLIC PUBLIC (0x01)},
1602 * {@linkplain #PRIVATE PRIVATE (0x02)},
1603 * {@linkplain #PROTECTED PROTECTED (0x04)},
1604 * {@linkplain #PACKAGE PACKAGE (0x08)},
1605 * {@linkplain #MODULE MODULE (0x10)},
1606 * {@linkplain #UNCONDITIONAL UNCONDITIONAL (0x20)},
1607 * and {@linkplain #ORIGINAL ORIGINAL (0x40)}.
1608 * <p>
1609 * A freshly-created lookup object
1610 * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class} has
1611 * all possible bits set, except {@code UNCONDITIONAL}.
1612 * A lookup object on a new lookup class
1613 * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object}
1614 * may have some mode bits set to zero.
1615 * Mode bits can also be
1616 * {@linkplain java.lang.invoke.MethodHandles.Lookup#dropLookupMode directly cleared}.
1617 * Once cleared, mode bits cannot be restored from the downgraded lookup object.
1618 * The purpose of this is to restrict access via the new lookup object,
1619 * so that it can access only names which can be reached by the original
1620 * lookup object, and also by the new lookup class.
1621 * @return the lookup modes, which limit the kinds of access performed by this lookup object
1622 * @see #in
1623 * @see #dropLookupMode
1624 *
1625 * @revised 9
1626 */
1627 public int lookupModes() {
1628 return allowedModes & ALL_MODES;
1629 }
1630
1631 /** Embody the current class (the lookupClass) as a lookup class
1632 * for method handle creation.
1633 * Must be called by from a method in this package,
1634 * which in turn is called by a method not in this package.
1635 */
1636 Lookup(Class<?> lookupClass) {
1637 this(lookupClass, null, FULL_POWER_MODES);
1638 }
1639
1640 private Lookup(Class<?> lookupClass, Class<?> prevLookupClass, int allowedModes) {
1641 assert prevLookupClass == null || ((allowedModes & MODULE) == 0
1642 && prevLookupClass.getModule() != lookupClass.getModule());
1643 assert !lookupClass.isArray() && !lookupClass.isPrimitive();
1644 this.lookupClass = lookupClass;
1645 this.prevLookupClass = prevLookupClass;
1646 this.allowedModes = allowedModes;
1647 }
1648
1649 private static Lookup newLookup(Class<?> lookupClass, Class<?> prevLookupClass, int allowedModes) {
1650 // make sure we haven't accidentally picked up a privileged class:
1651 checkUnprivilegedlookupClass(lookupClass);
1652 return new Lookup(lookupClass, prevLookupClass, allowedModes);
1653 }
1654
1655 /**
1656 * Creates a lookup on the specified new lookup class.
1657 * The resulting object will report the specified
1658 * class as its own {@link #lookupClass() lookupClass}.
1659 *
1660 * <p>
1661 * However, the resulting {@code Lookup} object is guaranteed
1662 * to have no more access capabilities than the original.
1663 * In particular, access capabilities can be lost as follows:<ul>
1664 * <li>If the new lookup class is different from the old lookup class,
1665 * i.e. {@link #ORIGINAL ORIGINAL} access is lost.
1666 * <li>If the new lookup class is in a different module from the old one,
1667 * i.e. {@link #MODULE MODULE} access is lost.
1668 * <li>If the new lookup class is in a different package
1669 * than the old one, protected and default (package) members will not be accessible,
1670 * i.e. {@link #PROTECTED PROTECTED} and {@link #PACKAGE PACKAGE} access are lost.
1671 * <li>If the new lookup class is not within the same package member
1672 * as the old one, private members will not be accessible, and protected members
1673 * will not be accessible by virtue of inheritance,
1674 * i.e. {@link #PRIVATE PRIVATE} access is lost.
1675 * (Protected members may continue to be accessible because of package sharing.)
1676 * <li>If the new lookup class is not
1677 * {@linkplain #accessClass(Class) accessible} to this lookup,
1678 * then no members, not even public members, will be accessible
1679 * i.e. all access modes are lost.
1680 * <li>If the new lookup class, the old lookup class and the previous lookup class
1681 * are all in different modules i.e. teleporting to a third module,
1682 * all access modes are lost.
1683 * </ul>
1684 * <p>
1685 * The new previous lookup class is chosen as follows:
1686 * <ul>
1687 * <li>If the new lookup object has {@link #UNCONDITIONAL UNCONDITIONAL} bit,
1688 * the new previous lookup class is {@code null}.
1689 * <li>If the new lookup class is in the same module as the old lookup class,
1690 * the new previous lookup class is the old previous lookup class.
1691 * <li>If the new lookup class is in a different module from the old lookup class,
1692 * the new previous lookup class is the old lookup class.
1693 *</ul>
1694 * <p>
1695 * The resulting lookup's capabilities for loading classes
1696 * (used during {@link #findClass} invocations)
1697 * are determined by the lookup class' loader,
1698 * which may change due to this operation.
1699 *
1700 * @param requestedLookupClass the desired lookup class for the new lookup object
1701 * @return a lookup object which reports the desired lookup class, or the same object
1702 * if there is no change
1703 * @throws IllegalArgumentException if {@code requestedLookupClass} is a primitive type or void or array class
1704 * @throws NullPointerException if the argument is null
1705 *
1706 * @revised 9
1707 * @see #accessClass(Class)
1708 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1709 */
1710 public Lookup in(Class<?> requestedLookupClass) {
1711 Objects.requireNonNull(requestedLookupClass);
1712 if (requestedLookupClass.isPrimitive())
1713 throw new IllegalArgumentException(requestedLookupClass + " is a primitive class");
1714 if (requestedLookupClass.isArray())
1715 throw new IllegalArgumentException(requestedLookupClass + " is an array class");
1716
1717 if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all
1718 return new Lookup(requestedLookupClass, null, FULL_POWER_MODES);
1719 if (requestedLookupClass == this.lookupClass)
1720 return this; // keep same capabilities
1721 int newModes = (allowedModes & FULL_POWER_MODES) & ~ORIGINAL;
1722 Module fromModule = this.lookupClass.getModule();
1723 Module targetModule = requestedLookupClass.getModule();
1724 Class<?> plc = this.previousLookupClass();
1725 if ((this.allowedModes & UNCONDITIONAL) != 0) {
1726 assert plc == null;
1727 newModes = UNCONDITIONAL;
1728 } else if (fromModule != targetModule) {
1729 if (plc != null && !VerifyAccess.isSameModule(plc, requestedLookupClass)) {
1730 // allow hopping back and forth between fromModule and plc's module
1731 // but not the third module
1732 newModes = 0;
1733 }
1734 // drop MODULE access
1735 newModes &= ~(MODULE|PACKAGE|PRIVATE|PROTECTED);
1736 // teleport from this lookup class
1737 plc = this.lookupClass;
1738 }
1739 if ((newModes & PACKAGE) != 0
1740 && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {
1741 newModes &= ~(PACKAGE|PRIVATE|PROTECTED);
1742 }
1743 // Allow nestmate lookups to be created without special privilege:
1744 if ((newModes & PRIVATE) != 0
1745 && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {
1746 newModes &= ~(PRIVATE|PROTECTED);
1747 }
1748 if ((newModes & (PUBLIC|UNCONDITIONAL)) != 0
1749 && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, this.prevLookupClass, allowedModes)) {
1750 // The requested class it not accessible from the lookup class.
1751 // No permissions.
1752 newModes = 0;
1753 }
1754 return newLookup(requestedLookupClass, plc, newModes);
1755 }
1756
1757 /**
1758 * Creates a lookup on the same lookup class which this lookup object
1759 * finds members, but with a lookup mode that has lost the given lookup mode.
1760 * The lookup mode to drop is one of {@link #PUBLIC PUBLIC}, {@link #MODULE
1761 * MODULE}, {@link #PACKAGE PACKAGE}, {@link #PROTECTED PROTECTED},
1762 * {@link #PRIVATE PRIVATE}, {@link #ORIGINAL ORIGINAL}, or
1763 * {@link #UNCONDITIONAL UNCONDITIONAL}.
1764 *
1765 * <p> If this lookup is a {@linkplain MethodHandles#publicLookup() public lookup},
1766 * this lookup has {@code UNCONDITIONAL} mode set and it has no other mode set.
1767 * When dropping {@code UNCONDITIONAL} on a public lookup then the resulting
1768 * lookup has no access.
1769 *
1770 * <p> If this lookup is not a public lookup, then the following applies
1771 * regardless of its {@linkplain #lookupModes() lookup modes}.
1772 * {@link #PROTECTED PROTECTED} and {@link #ORIGINAL ORIGINAL} are always
1773 * dropped and so the resulting lookup mode will never have these access
1774 * capabilities. When dropping {@code PACKAGE}
1775 * then the resulting lookup will not have {@code PACKAGE} or {@code PRIVATE}
1776 * access. When dropping {@code MODULE} then the resulting lookup will not
1777 * have {@code MODULE}, {@code PACKAGE}, or {@code PRIVATE} access.
1778 * When dropping {@code PUBLIC} then the resulting lookup has no access.
1779 *
1780 * @apiNote
1781 * A lookup with {@code PACKAGE} but not {@code PRIVATE} mode can safely
1782 * delegate non-public access within the package of the lookup class without
1783 * conferring <a href="MethodHandles.Lookup.html#privacc">private access</a>.
1784 * A lookup with {@code MODULE} but not
1785 * {@code PACKAGE} mode can safely delegate {@code PUBLIC} access within
1786 * the module of the lookup class without conferring package access.
1787 * A lookup with a {@linkplain #previousLookupClass() previous lookup class}
1788 * (and {@code PUBLIC} but not {@code MODULE} mode) can safely delegate access
1789 * to public classes accessible to both the module of the lookup class
1790 * and the module of the previous lookup class.
1791 *
1792 * @param modeToDrop the lookup mode to drop
1793 * @return a lookup object which lacks the indicated mode, or the same object if there is no change
1794 * @throws IllegalArgumentException if {@code modeToDrop} is not one of {@code PUBLIC},
1795 * {@code MODULE}, {@code PACKAGE}, {@code PROTECTED}, {@code PRIVATE}, {@code ORIGINAL}
1796 * or {@code UNCONDITIONAL}
1797 * @see MethodHandles#privateLookupIn
1798 * @since 9
1799 */
1800 public Lookup dropLookupMode(int modeToDrop) {
1801 int oldModes = lookupModes();
1802 int newModes = oldModes & ~(modeToDrop | PROTECTED | ORIGINAL);
1803 switch (modeToDrop) {
1804 case PUBLIC: newModes &= ~(FULL_POWER_MODES); break;
1805 case MODULE: newModes &= ~(PACKAGE | PRIVATE); break;
1806 case PACKAGE: newModes &= ~(PRIVATE); break;
1807 case PROTECTED:
1808 case PRIVATE:
1809 case ORIGINAL:
1810 case UNCONDITIONAL: break;
1811 default: throw new IllegalArgumentException(modeToDrop + " is not a valid mode to drop");
1812 }
1813 if (newModes == oldModes) return this; // return self if no change
1814 return newLookup(lookupClass(), previousLookupClass(), newModes);
1815 }
1816
1817 /**
1818 * Creates and links a class or interface from {@code bytes}
1819 * with the same class loader and in the same runtime package and
1820 * {@linkplain java.security.ProtectionDomain protection domain} as this lookup's
1821 * {@linkplain #lookupClass() lookup class} as if calling
1822 * {@link ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain)
1823 * ClassLoader::defineClass}.
1824 *
1825 * <p> The {@linkplain #lookupModes() lookup modes} for this lookup must include
1826 * {@link #PACKAGE PACKAGE} access as default (package) members will be
1827 * accessible to the class. The {@code PACKAGE} lookup mode serves to authenticate
1828 * that the lookup object was created by a caller in the runtime package (or derived
1829 * from a lookup originally created by suitably privileged code to a target class in
1830 * the runtime package). </p>
1831 *
1832 * <p> The {@code bytes} parameter is the class bytes of a valid class file (as defined
1833 * by the <em>The Java Virtual Machine Specification</em>) with a class name in the
1834 * same package as the lookup class. </p>
1835 *
1836 * <p> This method does not run the class initializer. The class initializer may
1837 * run at a later time, as detailed in section 12.4 of the <em>The Java Language
1838 * Specification</em>. </p>
1839 *
1840 * <p> If there is a security manager and this lookup does not have {@linkplain
1841 * #hasFullPrivilegeAccess() full privilege access}, its {@code checkPermission} method
1842 * is first called to check {@code RuntimePermission("defineClass")}. </p>
1843 *
1844 * @param bytes the class bytes
1845 * @return the {@code Class} object for the class
1846 * @throws IllegalAccessException if this lookup does not have {@code PACKAGE} access
1847 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure
1848 * @throws IllegalArgumentException if {@code bytes} denotes a class in a different package
1849 * than the lookup class or {@code bytes} is not a class or interface
1850 * ({@code ACC_MODULE} flag is set in the value of the {@code access_flags} item)
1851 * @throws VerifyError if the newly created class cannot be verified
1852 * @throws LinkageError if the newly created class cannot be linked for any other reason
1853 * @throws SecurityException if a security manager is present and it
1854 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1855 * @throws NullPointerException if {@code bytes} is {@code null}
1856 * @since 9
1857 * @see Lookup#privateLookupIn
1858 * @see Lookup#dropLookupMode
1859 * @see ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain)
1860 */
1861 public Class<?> defineClass(byte[] bytes) throws IllegalAccessException {
1862 ensureDefineClassPermission();
1863 if ((lookupModes() & PACKAGE) == 0)
1864 throw new IllegalAccessException("Lookup does not have PACKAGE access");
1865 return makeClassDefiner(bytes.clone()).defineClass(false);
1866 }
1867
1868 private void ensureDefineClassPermission() {
1869 if (allowedModes == TRUSTED) return;
1870
1871 if (!hasFullPrivilegeAccess()) {
1872 @SuppressWarnings("removal")
1873 SecurityManager sm = System.getSecurityManager();
1874 if (sm != null)
1875 sm.checkPermission(new RuntimePermission("defineClass"));
1876 }
1877 }
1878
1879 /**
1880 * The set of class options that specify whether a hidden class created by
1881 * {@link Lookup#defineHiddenClass(byte[], boolean, ClassOption...)
1882 * Lookup::defineHiddenClass} method is dynamically added as a new member
1883 * to the nest of a lookup class and/or whether a hidden class has
1884 * a strong relationship with the class loader marked as its defining loader.
1885 *
1886 * @since 15
1887 */
1888 public enum ClassOption {
1889 /**
1890 * Specifies that a hidden class be added to {@linkplain Class#getNestHost nest}
1891 * of a lookup class as a nestmate.
1892 *
1893 * <p> A hidden nestmate class has access to the private members of all
1894 * classes and interfaces in the same nest.
1895 *
1896 * @see Class#getNestHost()
1897 */
1898 NESTMATE(NESTMATE_CLASS),
1899
1900 /**
1901 * Specifies that a hidden class has a <em>strong</em>
1902 * relationship with the class loader marked as its defining loader,
1903 * as a normal class or interface has with its own defining loader.
1904 * This means that the hidden class may be unloaded if and only if
1905 * its defining loader is not reachable and thus may be reclaimed
1906 * by a garbage collector (JLS {@jls 12.7}).
1907 *
1908 * <p> By default, a hidden class or interface may be unloaded
1909 * even if the class loader that is marked as its defining loader is
1910 * <a href="../ref/package-summary.html#reachability">reachable</a>.
1911
1912 *
1913 * @jls 12.7 Unloading of Classes and Interfaces
1914 */
1915 STRONG(STRONG_LOADER_LINK);
1916
1917 /* the flag value is used by VM at define class time */
1918 private final int flag;
1919 ClassOption(int flag) {
1920 this.flag = flag;
1921 }
1922
1923 static int optionsToFlag(Set<ClassOption> options) {
1924 int flags = 0;
1925 for (ClassOption cp : options) {
1926 flags |= cp.flag;
1927 }
1928 return flags;
1929 }
1930 }
1931
1932 /**
1933 * Creates a <em>hidden</em> class or interface from {@code bytes},
1934 * returning a {@code Lookup} on the newly created class or interface.
1935 *
1936 * <p> Ordinarily, a class or interface {@code C} is created by a class loader,
1937 * which either defines {@code C} directly or delegates to another class loader.
1938 * A class loader defines {@code C} directly by invoking
1939 * {@link ClassLoader#defineClass(String, byte[], int, int, ProtectionDomain)
1940 * ClassLoader::defineClass}, which causes the Java Virtual Machine
1941 * to derive {@code C} from a purported representation in {@code class} file format.
1942 * In situations where use of a class loader is undesirable, a class or interface
1943 * {@code C} can be created by this method instead. This method is capable of
1944 * defining {@code C}, and thereby creating it, without invoking
1945 * {@code ClassLoader::defineClass}.
1946 * Instead, this method defines {@code C} as if by arranging for
1947 * the Java Virtual Machine to derive a nonarray class or interface {@code C}
1948 * from a purported representation in {@code class} file format
1949 * using the following rules:
1950 *
1951 * <ol>
1952 * <li> The {@linkplain #lookupModes() lookup modes} for this {@code Lookup}
1953 * must include {@linkplain #hasFullPrivilegeAccess() full privilege} access.
1954 * This level of access is needed to create {@code C} in the module
1955 * of the lookup class of this {@code Lookup}.</li>
1956 *
1957 * <li> The purported representation in {@code bytes} must be a {@code ClassFile}
1958 * structure (JVMS {@jvms 4.1}) of a supported major and minor version.
1959 * The major and minor version may differ from the {@code class} file version
1960 * of the lookup class of this {@code Lookup}.</li>
1961 *
1962 * <li> The value of {@code this_class} must be a valid index in the
1963 * {@code constant_pool} table, and the entry at that index must be a valid
1964 * {@code CONSTANT_Class_info} structure. Let {@code N} be the binary name
1965 * encoded in internal form that is specified by this structure. {@code N} must
1966 * denote a class or interface in the same package as the lookup class.</li>
1967 *
1968 * <li> Let {@code CN} be the string {@code N + "." + <suffix>},
1969 * where {@code <suffix>} is an unqualified name.
1970 *
1971 * <p> Let {@code newBytes} be the {@code ClassFile} structure given by
1972 * {@code bytes} with an additional entry in the {@code constant_pool} table,
1973 * indicating a {@code CONSTANT_Utf8_info} structure for {@code CN}, and
1974 * where the {@code CONSTANT_Class_info} structure indicated by {@code this_class}
1975 * refers to the new {@code CONSTANT_Utf8_info} structure.
1976 *
1977 * <p> Let {@code L} be the defining class loader of the lookup class of this {@code Lookup}.
1978 *
1979 * <p> {@code C} is derived with name {@code CN}, class loader {@code L}, and
1980 * purported representation {@code newBytes} as if by the rules of JVMS {@jvms 5.3.5},
1981 * with the following adjustments:
1982 * <ul>
1983 * <li> The constant indicated by {@code this_class} is permitted to specify a name
1984 * that includes a single {@code "."} character, even though this is not a valid
1985 * binary class or interface name in internal form.</li>
1986 *
1987 * <li> The Java Virtual Machine marks {@code L} as the defining class loader of {@code C},
1988 * but no class loader is recorded as an initiating class loader of {@code C}.</li>
1989 *
1990 * <li> {@code C} is considered to have the same runtime
1991 * {@linkplain Class#getPackage() package}, {@linkplain Class#getModule() module}
1992 * and {@linkplain java.security.ProtectionDomain protection domain}
1993 * as the lookup class of this {@code Lookup}.
1994 * <li> Let {@code GN} be the binary name obtained by taking {@code N}
1995 * (a binary name encoded in internal form) and replacing ASCII forward slashes with
1996 * ASCII periods. For the instance of {@link java.lang.Class} representing {@code C}:
1997 * <ul>
1998 * <li> {@link Class#getName()} returns the string {@code GN + "/" + <suffix>},
1999 * even though this is not a valid binary class or interface name.</li>
2000 * <li> {@link Class#descriptorString()} returns the string
2001 * {@code "L" + N + "." + <suffix> + ";"},
2002 * even though this is not a valid type descriptor name.</li>
2003 * <li> {@link Class#describeConstable()} returns an empty optional as {@code C}
2004 * cannot be described in {@linkplain java.lang.constant.ClassDesc nominal form}.</li>
2005 * </ul>
2006 * </ul>
2007 * </li>
2008 * </ol>
2009 *
2010 * <p> After {@code C} is derived, it is linked by the Java Virtual Machine.
2011 * Linkage occurs as specified in JVMS {@jvms 5.4.3}, with the following adjustments:
2012 * <ul>
2013 * <li> During verification, whenever it is necessary to load the class named
2014 * {@code CN}, the attempt succeeds, producing class {@code C}. No request is
2015 * made of any class loader.</li>
2016 *
2017 * <li> On any attempt to resolve the entry in the run-time constant pool indicated
2018 * by {@code this_class}, the symbolic reference is considered to be resolved to
2019 * {@code C} and resolution always succeeds immediately.</li>
2020 * </ul>
2021 *
2022 * <p> If the {@code initialize} parameter is {@code true},
2023 * then {@code C} is initialized by the Java Virtual Machine.
2024 *
2025 * <p> The newly created class or interface {@code C} serves as the
2026 * {@linkplain #lookupClass() lookup class} of the {@code Lookup} object
2027 * returned by this method. {@code C} is <em>hidden</em> in the sense that
2028 * no other class or interface can refer to {@code C} via a constant pool entry.
2029 * That is, a hidden class or interface cannot be named as a supertype, a field type,
2030 * a method parameter type, or a method return type by any other class.
2031 * This is because a hidden class or interface does not have a binary name, so
2032 * there is no internal form available to record in any class's constant pool.
2033 * A hidden class or interface is not discoverable by {@link Class#forName(String, boolean, ClassLoader)},
2034 * {@link ClassLoader#loadClass(String, boolean)}, or {@link #findClass(String)}, and
2035 * is not {@linkplain java.instrument/java.lang.instrument.Instrumentation#isModifiableClass(Class)
2036 * modifiable} by Java agents or tool agents using the <a href="{@docRoot}/../specs/jvmti.html">
2037 * JVM Tool Interface</a>.
2038 *
2039 * <p> A class or interface created by
2040 * {@linkplain ClassLoader#defineClass(String, byte[], int, int, ProtectionDomain)
2041 * a class loader} has a strong relationship with that class loader.
2042 * That is, every {@code Class} object contains a reference to the {@code ClassLoader}
2043 * that {@linkplain Class#getClassLoader() defined it}.
2044 * This means that a class created by a class loader may be unloaded if and
2045 * only if its defining loader is not reachable and thus may be reclaimed
2046 * by a garbage collector (JLS {@jls 12.7}).
2047 *
2048 * By default, however, a hidden class or interface may be unloaded even if
2049 * the class loader that is marked as its defining loader is
2050 * <a href="../ref/package-summary.html#reachability">reachable</a>.
2051 * This behavior is useful when a hidden class or interface serves multiple
2052 * classes defined by arbitrary class loaders. In other cases, a hidden
2053 * class or interface may be linked to a single class (or a small number of classes)
2054 * with the same defining loader as the hidden class or interface.
2055 * In such cases, where the hidden class or interface must be coterminous
2056 * with a normal class or interface, the {@link ClassOption#STRONG STRONG}
2057 * option may be passed in {@code options}.
2058 * This arranges for a hidden class to have the same strong relationship
2059 * with the class loader marked as its defining loader,
2060 * as a normal class or interface has with its own defining loader.
2061 *
2062 * If {@code STRONG} is not used, then the invoker of {@code defineHiddenClass}
2063 * may still prevent a hidden class or interface from being
2064 * unloaded by ensuring that the {@code Class} object is reachable.
2065 *
2066 * <p> The unloading characteristics are set for each hidden class when it is
2067 * defined, and cannot be changed later. An advantage of allowing hidden classes
2068 * to be unloaded independently of the class loader marked as their defining loader
2069 * is that a very large number of hidden classes may be created by an application.
2070 * In contrast, if {@code STRONG} is used, then the JVM may run out of memory,
2071 * just as if normal classes were created by class loaders.
2072 *
2073 * <p> Classes and interfaces in a nest are allowed to have mutual access to
2074 * their private members. The nest relationship is determined by
2075 * the {@code NestHost} attribute (JVMS {@jvms 4.7.28}) and
2076 * the {@code NestMembers} attribute (JVMS {@jvms 4.7.29}) in a {@code class} file.
2077 * By default, a hidden class belongs to a nest consisting only of itself
2078 * because a hidden class has no binary name.
2079 * The {@link ClassOption#NESTMATE NESTMATE} option can be passed in {@code options}
2080 * to create a hidden class or interface {@code C} as a member of a nest.
2081 * The nest to which {@code C} belongs is not based on any {@code NestHost} attribute
2082 * in the {@code ClassFile} structure from which {@code C} was derived.
2083 * Instead, the following rules determine the nest host of {@code C}:
2084 * <ul>
2085 * <li>If the nest host of the lookup class of this {@code Lookup} has previously
2086 * been determined, then let {@code H} be the nest host of the lookup class.
2087 * Otherwise, the nest host of the lookup class is determined using the
2088 * algorithm in JVMS {@jvms 5.4.4}, yielding {@code H}.</li>
2089 * <li>The nest host of {@code C} is determined to be {@code H},
2090 * the nest host of the lookup class.</li>
2091 * </ul>
2092 *
2093 * <p> A hidden class or interface may be serializable, but this requires a custom
2094 * serialization mechanism in order to ensure that instances are properly serialized
2095 * and deserialized. The default serialization mechanism supports only classes and
2096 * interfaces that are discoverable by their class name.
2097 *
2098 * @param bytes the bytes that make up the class data,
2099 * in the format of a valid {@code class} file as defined by
2100 * <cite>The Java Virtual Machine Specification</cite>.
2101 * @param initialize if {@code true} the class will be initialized.
2102 * @param options {@linkplain ClassOption class options}
2103 * @return the {@code Lookup} object on the hidden class,
2104 * with {@linkplain #ORIGINAL original} and
2105 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege} access
2106 *
2107 * @throws IllegalAccessException if this {@code Lookup} does not have
2108 * {@linkplain #hasFullPrivilegeAccess() full privilege} access
2109 * @throws SecurityException if a security manager is present and it
2110 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2111 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure
2112 * @throws UnsupportedClassVersionError if {@code bytes} is not of a supported major or minor version
2113 * @throws IllegalArgumentException if {@code bytes} denotes a class in a different package
2114 * than the lookup class or {@code bytes} is not a class or interface
2115 * ({@code ACC_MODULE} flag is set in the value of the {@code access_flags} item)
2116 * @throws IncompatibleClassChangeError if the class or interface named as
2117 * the direct superclass of {@code C} is in fact an interface, or if any of the classes
2118 * or interfaces named as direct superinterfaces of {@code C} are not in fact interfaces
2119 * @throws ClassCircularityError if any of the superclasses or superinterfaces of
2120 * {@code C} is {@code C} itself
2121 * @throws VerifyError if the newly created class cannot be verified
2122 * @throws LinkageError if the newly created class cannot be linked for any other reason
2123 * @throws NullPointerException if any parameter is {@code null}
2124 *
2125 * @since 15
2126 * @see Class#isHidden()
2127 * @jvms 4.2.1 Binary Class and Interface Names
2128 * @jvms 4.2.2 Unqualified Names
2129 * @jvms 4.7.28 The {@code NestHost} Attribute
2130 * @jvms 4.7.29 The {@code NestMembers} Attribute
2131 * @jvms 5.4.3.1 Class and Interface Resolution
2132 * @jvms 5.4.4 Access Control
2133 * @jvms 5.3.5 Deriving a {@code Class} from a {@code class} File Representation
2134 * @jvms 5.4 Linking
2135 * @jvms 5.5 Initialization
2136 * @jls 12.7 Unloading of Classes and Interfaces
2137 */
2138 @SuppressWarnings("doclint:reference") // cross-module links
2139 public Lookup defineHiddenClass(byte[] bytes, boolean initialize, ClassOption... options)
2140 throws IllegalAccessException
2141 {
2142 Objects.requireNonNull(bytes);
2143 Objects.requireNonNull(options);
2144
2145 ensureDefineClassPermission();
2146 if (!hasFullPrivilegeAccess()) {
2147 throw new IllegalAccessException(this + " does not have full privilege access");
2148 }
2149
2150 return makeHiddenClassDefiner(bytes.clone(), Set.of(options), false).defineClassAsLookup(initialize);
2151 }
2152
2153 /**
2154 * Creates a <em>hidden</em> class or interface from {@code bytes} with associated
2155 * {@linkplain MethodHandles#classData(Lookup, String, Class) class data},
2156 * returning a {@code Lookup} on the newly created class or interface.
2157 *
2158 * <p> This method is equivalent to calling
2159 * {@link #defineHiddenClass(byte[], boolean, ClassOption...) defineHiddenClass(bytes, initialize, options)}
2160 * as if the hidden class is injected with a private static final <i>unnamed</i>
2161 * field which is initialized with the given {@code classData} at
2162 * the first instruction of the class initializer.
2163 * The newly created class is linked by the Java Virtual Machine.
2164 *
2165 * <p> The {@link MethodHandles#classData(Lookup, String, Class) MethodHandles::classData}
2166 * and {@link MethodHandles#classDataAt(Lookup, String, Class, int) MethodHandles::classDataAt}
2167 * methods can be used to retrieve the {@code classData}.
2168 *
2169 * @apiNote
2170 * A framework can create a hidden class with class data with one or more
2171 * objects and load the class data as dynamically-computed constant(s)
2172 * via a bootstrap method. {@link MethodHandles#classData(Lookup, String, Class)
2173 * Class data} is accessible only to the lookup object created by the newly
2174 * defined hidden class but inaccessible to other members in the same nest
2175 * (unlike private static fields that are accessible to nestmates).
2176 * Care should be taken w.r.t. mutability for example when passing
2177 * an array or other mutable structure through the class data.
2178 * Changing any value stored in the class data at runtime may lead to
2179 * unpredictable behavior.
2180 * If the class data is a {@code List}, it is good practice to make it
2181 * unmodifiable for example via {@link List#of List::of}.
2182 *
2183 * @param bytes the class bytes
2184 * @param classData pre-initialized class data
2185 * @param initialize if {@code true} the class will be initialized.
2186 * @param options {@linkplain ClassOption class options}
2187 * @return the {@code Lookup} object on the hidden class,
2188 * with {@linkplain #ORIGINAL original} and
2189 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege} access
2190 *
2191 * @throws IllegalAccessException if this {@code Lookup} does not have
2192 * {@linkplain #hasFullPrivilegeAccess() full privilege} access
2193 * @throws SecurityException if a security manager is present and it
2194 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2195 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure
2196 * @throws UnsupportedClassVersionError if {@code bytes} is not of a supported major or minor version
2197 * @throws IllegalArgumentException if {@code bytes} denotes a class in a different package
2198 * than the lookup class or {@code bytes} is not a class or interface
2199 * ({@code ACC_MODULE} flag is set in the value of the {@code access_flags} item)
2200 * @throws IncompatibleClassChangeError if the class or interface named as
2201 * the direct superclass of {@code C} is in fact an interface, or if any of the classes
2202 * or interfaces named as direct superinterfaces of {@code C} are not in fact interfaces
2203 * @throws ClassCircularityError if any of the superclasses or superinterfaces of
2204 * {@code C} is {@code C} itself
2205 * @throws VerifyError if the newly created class cannot be verified
2206 * @throws LinkageError if the newly created class cannot be linked for any other reason
2207 * @throws NullPointerException if any parameter is {@code null}
2208 *
2209 * @since 16
2210 * @see Lookup#defineHiddenClass(byte[], boolean, ClassOption...)
2211 * @see Class#isHidden()
2212 * @see MethodHandles#classData(Lookup, String, Class)
2213 * @see MethodHandles#classDataAt(Lookup, String, Class, int)
2214 * @jvms 4.2.1 Binary Class and Interface Names
2215 * @jvms 4.2.2 Unqualified Names
2216 * @jvms 4.7.28 The {@code NestHost} Attribute
2217 * @jvms 4.7.29 The {@code NestMembers} Attribute
2218 * @jvms 5.4.3.1 Class and Interface Resolution
2219 * @jvms 5.4.4 Access Control
2220 * @jvms 5.3.5 Deriving a {@code Class} from a {@code class} File Representation
2221 * @jvms 5.4 Linking
2222 * @jvms 5.5 Initialization
2223 * @jls 12.7 Unloading of Classes and Interface
2224 */
2225 public Lookup defineHiddenClassWithClassData(byte[] bytes, Object classData, boolean initialize, ClassOption... options)
2226 throws IllegalAccessException
2227 {
2228 Objects.requireNonNull(bytes);
2229 Objects.requireNonNull(classData);
2230 Objects.requireNonNull(options);
2231
2232 ensureDefineClassPermission();
2233 if (!hasFullPrivilegeAccess()) {
2234 throw new IllegalAccessException(this + " does not have full privilege access");
2235 }
2236
2237 return makeHiddenClassDefiner(bytes.clone(), Set.of(options), false)
2238 .defineClassAsLookup(initialize, classData);
2239 }
2240
2241 // A default dumper for writing class files passed to Lookup::defineClass
2242 // and Lookup::defineHiddenClass to disk for debugging purposes. To enable,
2243 // set -Djdk.invoke.MethodHandle.dumpHiddenClassFiles or
2244 // -Djdk.invoke.MethodHandle.dumpHiddenClassFiles=true
2245 //
2246 // This default dumper does not dump hidden classes defined by LambdaMetafactory
2247 // and LambdaForms and method handle internals. They are dumped via
2248 // different ClassFileDumpers.
2249 private static ClassFileDumper defaultDumper() {
2250 return DEFAULT_DUMPER;
2251 }
2252
2253 private static final ClassFileDumper DEFAULT_DUMPER = ClassFileDumper.getInstance(
2254 "jdk.invoke.MethodHandle.dumpClassFiles", "DUMP_CLASS_FILES");
2255
2256 static class ClassFile {
2257 final String name; // internal name
2258 final int accessFlags;
2259 final byte[] bytes;
2260 ClassFile(String name, int accessFlags, byte[] bytes) {
2261 this.name = name;
2262 this.accessFlags = accessFlags;
2263 this.bytes = bytes;
2264 }
2265
2266 static ClassFile newInstanceNoCheck(String name, byte[] bytes) {
2267 return new ClassFile(name, 0, bytes);
2268 }
2269
2270 /**
2271 * This method checks the class file version and the structure of `this_class`.
2272 * and checks if the bytes is a class or interface (ACC_MODULE flag not set)
2273 * that is in the named package.
2274 *
2275 * @throws IllegalArgumentException if ACC_MODULE flag is set in access flags
2276 * or the class is not in the given package name.
2277 */
2278 static ClassFile newInstance(byte[] bytes, String pkgName) {
2279 var cf = readClassFile(bytes);
2280
2281 // check if it's in the named package
2282 int index = cf.name.lastIndexOf('/');
2283 String pn = (index == -1) ? "" : cf.name.substring(0, index).replace('/', '.');
2284 if (!pn.equals(pkgName)) {
2285 throw newIllegalArgumentException(cf.name + " not in same package as lookup class");
2286 }
2287 return cf;
2288 }
2289
2290 private static ClassFile readClassFile(byte[] bytes) {
2291 int magic = readInt(bytes, 0);
2292 if (magic != 0xCAFEBABE) {
2293 throw new ClassFormatError("Incompatible magic value: " + magic);
2294 }
2295 int minor = readUnsignedShort(bytes, 4);
2296 int major = readUnsignedShort(bytes, 6);
2297 if (!VM.isSupportedClassFileVersion(major, minor)) {
2298 throw new UnsupportedClassVersionError("Unsupported class file version " + major + "." + minor);
2299 }
2300
2301 String name;
2302 int accessFlags;
2303 try {
2304 ClassReader reader = new ClassReader(bytes);
2305 // ClassReader does not check if `this_class` is CONSTANT_Class_info
2306 // workaround to read `this_class` using readConst and validate the value
2307 int thisClass = reader.readUnsignedShort(reader.header + 2);
2308 Object constant = reader.readConst(thisClass, new char[reader.getMaxStringLength()]);
2309 if (!(constant instanceof Type type)) {
2310 throw new ClassFormatError("this_class item: #" + thisClass + " not a CONSTANT_Class_info");
2311 }
2312 if (!type.getDescriptor().startsWith("L")) {
2313 throw new ClassFormatError("this_class item: #" + thisClass + " not a CONSTANT_Class_info");
2314 }
2315 name = type.getInternalName();
2316 accessFlags = reader.readUnsignedShort(reader.header);
2317 } catch (RuntimeException e) {
2318 // ASM exceptions are poorly specified
2319 ClassFormatError cfe = new ClassFormatError();
2320 cfe.initCause(e);
2321 throw cfe;
2322 }
2323 // must be a class or interface
2324 if ((accessFlags & Opcodes.ACC_MODULE) != 0) {
2325 throw newIllegalArgumentException("Not a class or interface: ACC_MODULE flag is set");
2326 }
2327 return new ClassFile(name, accessFlags, bytes);
2328 }
2329
2330 private static int readInt(byte[] bytes, int offset) {
2331 if ((offset+4) > bytes.length) {
2332 throw new ClassFormatError("Invalid ClassFile structure");
2333 }
2334 return ((bytes[offset] & 0xFF) << 24)
2335 | ((bytes[offset + 1] & 0xFF) << 16)
2336 | ((bytes[offset + 2] & 0xFF) << 8)
2337 | (bytes[offset + 3] & 0xFF);
2338 }
2339
2340 private static int readUnsignedShort(byte[] bytes, int offset) {
2341 if ((offset+2) > bytes.length) {
2342 throw new ClassFormatError("Invalid ClassFile structure");
2343 }
2344 return ((bytes[offset] & 0xFF) << 8) | (bytes[offset + 1] & 0xFF);
2345 }
2346 }
2347
2348 /*
2349 * Returns a ClassDefiner that creates a {@code Class} object of a normal class
2350 * from the given bytes.
2351 *
2352 * Caller should make a defensive copy of the arguments if needed
2353 * before calling this factory method.
2354 *
2355 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or
2356 * {@code bytes} denotes a class in a different package than the lookup class
2357 */
2358 private ClassDefiner makeClassDefiner(byte[] bytes) {
2359 ClassFile cf = ClassFile.newInstance(bytes, lookupClass().getPackageName());
2360 return new ClassDefiner(this, cf, STRONG_LOADER_LINK, defaultDumper());
2361 }
2362
2363 /**
2364 * Returns a ClassDefiner that creates a {@code Class} object of a normal class
2365 * from the given bytes. No package name check on the given bytes.
2366 *
2367 * @param name internal name
2368 * @param bytes class bytes
2369 * @param dumper dumper to write the given bytes to the dumper's output directory
2370 * @return ClassDefiner that defines a normal class of the given bytes.
2371 */
2372 ClassDefiner makeClassDefiner(String name, byte[] bytes, ClassFileDumper dumper) {
2373 // skip package name validation
2374 ClassFile cf = ClassFile.newInstanceNoCheck(name, bytes);
2375 return new ClassDefiner(this, cf, STRONG_LOADER_LINK, dumper);
2376 }
2377
2378 /**
2379 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2380 * from the given bytes. The name must be in the same package as the lookup class.
2381 *
2382 * Caller should make a defensive copy of the arguments if needed
2383 * before calling this factory method.
2384 *
2385 * @param bytes class bytes
2386 * @param dumper dumper to write the given bytes to the dumper's output directory
2387 * @return ClassDefiner that defines a hidden class of the given bytes.
2388 *
2389 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or
2390 * {@code bytes} denotes a class in a different package than the lookup class
2391 */
2392 ClassDefiner makeHiddenClassDefiner(byte[] bytes, ClassFileDumper dumper) {
2393 ClassFile cf = ClassFile.newInstance(bytes, lookupClass().getPackageName());
2394 return makeHiddenClassDefiner(cf, Set.of(), false, dumper);
2395 }
2396
2397 /**
2398 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2399 * from the given bytes and options.
2400 * The name must be in the same package as the lookup class.
2401 *
2402 * Caller should make a defensive copy of the arguments if needed
2403 * before calling this factory method.
2404 *
2405 * @param bytes class bytes
2406 * @param options class options
2407 * @param accessVmAnnotations true to give the hidden class access to VM annotations
2408 * @return ClassDefiner that defines a hidden class of the given bytes and options
2409 *
2410 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or
2411 * {@code bytes} denotes a class in a different package than the lookup class
2412 */
2413 private ClassDefiner makeHiddenClassDefiner(byte[] bytes,
2414 Set<ClassOption> options,
2415 boolean accessVmAnnotations) {
2416 ClassFile cf = ClassFile.newInstance(bytes, lookupClass().getPackageName());
2417 return makeHiddenClassDefiner(cf, options, accessVmAnnotations, defaultDumper());
2418 }
2419
2420 /**
2421 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2422 * from the given bytes and the given options. No package name check on the given bytes.
2423 *
2424 * @param name internal name that specifies the prefix of the hidden class
2425 * @param bytes class bytes
2426 * @param options class options
2427 * @param dumper dumper to write the given bytes to the dumper's output directory
2428 * @return ClassDefiner that defines a hidden class of the given bytes and options.
2429 */
2430 ClassDefiner makeHiddenClassDefiner(String name, byte[] bytes, Set<ClassOption> options, ClassFileDumper dumper) {
2431 Objects.requireNonNull(dumper);
2432 // skip name and access flags validation
2433 return makeHiddenClassDefiner(ClassFile.newInstanceNoCheck(name, bytes), options, false, dumper);
2434 }
2435
2436 /**
2437 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2438 * from the given class file and options.
2439 *
2440 * @param cf ClassFile
2441 * @param options class options
2442 * @param accessVmAnnotations true to give the hidden class access to VM annotations
2443 * @param dumper dumper to write the given bytes to the dumper's output directory
2444 */
2445 private ClassDefiner makeHiddenClassDefiner(ClassFile cf,
2446 Set<ClassOption> options,
2447 boolean accessVmAnnotations,
2448 ClassFileDumper dumper) {
2449 int flags = HIDDEN_CLASS | ClassOption.optionsToFlag(options);
2450 if (accessVmAnnotations | VM.isSystemDomainLoader(lookupClass.getClassLoader())) {
2451 // jdk.internal.vm.annotations are permitted for classes
2452 // defined to boot loader and platform loader
2453 flags |= ACCESS_VM_ANNOTATIONS;
2454 }
2455
2456 return new ClassDefiner(this, cf, flags, dumper);
2457 }
2458
2459 static class ClassDefiner {
2460 private final Lookup lookup;
2461 private final String name; // internal name
2462 private final byte[] bytes;
2463 private final int classFlags;
2464 private final ClassFileDumper dumper;
2465
2466 private ClassDefiner(Lookup lookup, ClassFile cf, int flags, ClassFileDumper dumper) {
2467 assert ((flags & HIDDEN_CLASS) != 0 || (flags & STRONG_LOADER_LINK) == STRONG_LOADER_LINK);
2468 this.lookup = lookup;
2469 this.bytes = cf.bytes;
2470 this.name = cf.name;
2471 this.classFlags = flags;
2472 this.dumper = dumper;
2473 }
2474
2475 String internalName() {
2476 return name;
2477 }
2478
2479 Class<?> defineClass(boolean initialize) {
2480 return defineClass(initialize, null);
2481 }
2482
2483 Lookup defineClassAsLookup(boolean initialize) {
2484 Class<?> c = defineClass(initialize, null);
2485 return new Lookup(c, null, FULL_POWER_MODES);
2486 }
2487
2488 /**
2489 * Defines the class of the given bytes and the given classData.
2490 * If {@code initialize} parameter is true, then the class will be initialized.
2491 *
2492 * @param initialize true if the class to be initialized
2493 * @param classData classData or null
2494 * @return the class
2495 *
2496 * @throws LinkageError linkage error
2497 */
2498 Class<?> defineClass(boolean initialize, Object classData) {
2499 Class<?> lookupClass = lookup.lookupClass();
2500 ClassLoader loader = lookupClass.getClassLoader();
2501 ProtectionDomain pd = (loader != null) ? lookup.lookupClassProtectionDomain() : null;
2502 Class<?> c = null;
2503 try {
2504 c = SharedSecrets.getJavaLangAccess()
2505 .defineClass(loader, lookupClass, name, bytes, pd, initialize, classFlags, classData);
2506 assert !isNestmate() || c.getNestHost() == lookupClass.getNestHost();
2507 return c;
2508 } finally {
2509 // dump the classfile for debugging
2510 if (dumper.isEnabled()) {
2511 String name = internalName();
2512 if (c != null) {
2513 dumper.dumpClass(name, c, bytes);
2514 } else {
2515 dumper.dumpFailedClass(name, bytes);
2516 }
2517 }
2518 }
2519 }
2520
2521 /**
2522 * Defines the class of the given bytes and the given classData.
2523 * If {@code initialize} parameter is true, then the class will be initialized.
2524 *
2525 * @param initialize true if the class to be initialized
2526 * @param classData classData or null
2527 * @return a Lookup for the defined class
2528 *
2529 * @throws LinkageError linkage error
2530 */
2531 Lookup defineClassAsLookup(boolean initialize, Object classData) {
2532 Class<?> c = defineClass(initialize, classData);
2533 return new Lookup(c, null, FULL_POWER_MODES);
2534 }
2535
2536 private boolean isNestmate() {
2537 return (classFlags & NESTMATE_CLASS) != 0;
2538 }
2539 }
2540
2541 private ProtectionDomain lookupClassProtectionDomain() {
2542 ProtectionDomain pd = cachedProtectionDomain;
2543 if (pd == null) {
2544 cachedProtectionDomain = pd = SharedSecrets.getJavaLangAccess().protectionDomain(lookupClass);
2545 }
2546 return pd;
2547 }
2548
2549 // cached protection domain
2550 private volatile ProtectionDomain cachedProtectionDomain;
2551
2552 // Make sure outer class is initialized first.
2553 static { IMPL_NAMES.getClass(); }
2554
2555 /** Package-private version of lookup which is trusted. */
2556 static final Lookup IMPL_LOOKUP = new Lookup(Object.class, null, TRUSTED);
2557
2558 /** Version of lookup which is trusted minimally.
2559 * It can only be used to create method handles to publicly accessible
2560 * members in packages that are exported unconditionally.
2561 */
2562 static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, null, UNCONDITIONAL);
2563
2564 private static void checkUnprivilegedlookupClass(Class<?> lookupClass) {
2565 String name = lookupClass.getName();
2566 if (name.startsWith("java.lang.invoke."))
2567 throw newIllegalArgumentException("illegal lookupClass: "+lookupClass);
2568 }
2569
2570 /**
2571 * Displays the name of the class from which lookups are to be made,
2572 * followed by "/" and the name of the {@linkplain #previousLookupClass()
2573 * previous lookup class} if present.
2574 * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)
2575 * If there are restrictions on the access permitted to this lookup,
2576 * this is indicated by adding a suffix to the class name, consisting
2577 * of a slash and a keyword. The keyword represents the strongest
2578 * allowed access, and is chosen as follows:
2579 * <ul>
2580 * <li>If no access is allowed, the suffix is "/noaccess".
2581 * <li>If only unconditional access is allowed, the suffix is "/publicLookup".
2582 * <li>If only public access to types in exported packages is allowed, the suffix is "/public".
2583 * <li>If only public and module access are allowed, the suffix is "/module".
2584 * <li>If public and package access are allowed, the suffix is "/package".
2585 * <li>If public, package, and private access are allowed, the suffix is "/private".
2586 * </ul>
2587 * If none of the above cases apply, it is the case that
2588 * {@linkplain #hasFullPrivilegeAccess() full privilege access}
2589 * (public, module, package, private, and protected) is allowed.
2590 * In this case, no suffix is added.
2591 * This is true only of an object obtained originally from
2592 * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
2593 * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
2594 * always have restricted access, and will display a suffix.
2595 * <p>
2596 * (It may seem strange that protected access should be
2597 * stronger than private access. Viewed independently from
2598 * package access, protected access is the first to be lost,
2599 * because it requires a direct subclass relationship between
2600 * caller and callee.)
2601 * @see #in
2602 *
2603 * @revised 9
2604 */
2605 @Override
2606 public String toString() {
2607 String cname = lookupClass.getName();
2608 if (prevLookupClass != null)
2609 cname += "/" + prevLookupClass.getName();
2610 switch (allowedModes) {
2611 case 0: // no privileges
2612 return cname + "/noaccess";
2613 case UNCONDITIONAL:
2614 return cname + "/publicLookup";
2615 case PUBLIC:
2616 return cname + "/public";
2617 case PUBLIC|MODULE:
2618 return cname + "/module";
2619 case PUBLIC|PACKAGE:
2620 case PUBLIC|MODULE|PACKAGE:
2621 return cname + "/package";
2622 case PUBLIC|PACKAGE|PRIVATE:
2623 case PUBLIC|MODULE|PACKAGE|PRIVATE:
2624 return cname + "/private";
2625 case PUBLIC|PACKAGE|PRIVATE|PROTECTED:
2626 case PUBLIC|MODULE|PACKAGE|PRIVATE|PROTECTED:
2627 case FULL_POWER_MODES:
2628 return cname;
2629 case TRUSTED:
2630 return "/trusted"; // internal only; not exported
2631 default: // Should not happen, but it's a bitfield...
2632 cname = cname + "/" + Integer.toHexString(allowedModes);
2633 assert(false) : cname;
2634 return cname;
2635 }
2636 }
2637
2638 /**
2639 * Produces a method handle for a static method.
2640 * The type of the method handle will be that of the method.
2641 * (Since static methods do not take receivers, there is no
2642 * additional receiver argument inserted into the method handle type,
2643 * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)
2644 * The method and all its argument types must be accessible to the lookup object.
2645 * <p>
2646 * The returned method handle will have
2647 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2648 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2649 * <p>
2650 * If the returned method handle is invoked, the method's class will
2651 * be initialized, if it has not already been initialized.
2652 * <p><b>Example:</b>
2653 * {@snippet lang="java" :
2654 import static java.lang.invoke.MethodHandles.*;
2655 import static java.lang.invoke.MethodType.*;
2656 ...
2657 MethodHandle MH_asList = publicLookup().findStatic(Arrays.class,
2658 "asList", methodType(List.class, Object[].class));
2659 assertEquals("[x, y]", MH_asList.invoke("x", "y").toString());
2660 * }
2661 * @param refc the class from which the method is accessed
2662 * @param name the name of the method
2663 * @param type the type of the method
2664 * @return the desired method handle
2665 * @throws NoSuchMethodException if the method does not exist
2666 * @throws IllegalAccessException if access checking fails,
2667 * or if the method is not {@code static},
2668 * or if the method's variable arity modifier bit
2669 * is set and {@code asVarargsCollector} fails
2670 * @throws SecurityException if a security manager is present and it
2671 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2672 * @throws NullPointerException if any argument is null
2673 */
2674 public MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2675 MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type);
2676 return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerLookup(method));
2677 }
2678
2679 /**
2680 * Produces a method handle for a virtual method.
2681 * The type of the method handle will be that of the method,
2682 * with the receiver type (usually {@code refc}) prepended.
2683 * The method and all its argument types must be accessible to the lookup object.
2684 * <p>
2685 * When called, the handle will treat the first argument as a receiver
2686 * and, for non-private methods, dispatch on the receiver's type to determine which method
2687 * implementation to enter.
2688 * For private methods the named method in {@code refc} will be invoked on the receiver.
2689 * (The dispatching action is identical with that performed by an
2690 * {@code invokevirtual} or {@code invokeinterface} instruction.)
2691 * <p>
2692 * The first argument will be of type {@code refc} if the lookup
2693 * class has full privileges to access the member. Otherwise
2694 * the member must be {@code protected} and the first argument
2695 * will be restricted in type to the lookup class.
2696 * <p>
2697 * The returned method handle will have
2698 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2699 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2700 * <p>
2701 * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual}
2702 * instructions and method handles produced by {@code findVirtual},
2703 * if the class is {@code MethodHandle} and the name string is
2704 * {@code invokeExact} or {@code invoke}, the resulting
2705 * method handle is equivalent to one produced by
2706 * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or
2707 * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}
2708 * with the same {@code type} argument.
2709 * <p>
2710 * If the class is {@code VarHandle} and the name string corresponds to
2711 * the name of a signature-polymorphic access mode method, the resulting
2712 * method handle is equivalent to one produced by
2713 * {@link java.lang.invoke.MethodHandles#varHandleInvoker} with
2714 * the access mode corresponding to the name string and with the same
2715 * {@code type} arguments.
2716 * <p>
2717 * <b>Example:</b>
2718 * {@snippet lang="java" :
2719 import static java.lang.invoke.MethodHandles.*;
2720 import static java.lang.invoke.MethodType.*;
2721 ...
2722 MethodHandle MH_concat = publicLookup().findVirtual(String.class,
2723 "concat", methodType(String.class, String.class));
2724 MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class,
2725 "hashCode", methodType(int.class));
2726 MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class,
2727 "hashCode", methodType(int.class));
2728 assertEquals("xy", (String) MH_concat.invokeExact("x", "y"));
2729 assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy"));
2730 assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy"));
2731 // interface method:
2732 MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class,
2733 "subSequence", methodType(CharSequence.class, int.class, int.class));
2734 assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString());
2735 // constructor "internal method" must be accessed differently:
2736 MethodType MT_newString = methodType(void.class); //()V for new String()
2737 try { assertEquals("impossible", lookup()
2738 .findVirtual(String.class, "<init>", MT_newString));
2739 } catch (NoSuchMethodException ex) { } // OK
2740 MethodHandle MH_newString = publicLookup()
2741 .findConstructor(String.class, MT_newString);
2742 assertEquals("", (String) MH_newString.invokeExact());
2743 * }
2744 *
2745 * @param refc the class or interface from which the method is accessed
2746 * @param name the name of the method
2747 * @param type the type of the method, with the receiver argument omitted
2748 * @return the desired method handle
2749 * @throws NoSuchMethodException if the method does not exist
2750 * @throws IllegalAccessException if access checking fails,
2751 * or if the method is {@code static},
2752 * or if the method's variable arity modifier bit
2753 * is set and {@code asVarargsCollector} fails
2754 * @throws SecurityException if a security manager is present and it
2755 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2756 * @throws NullPointerException if any argument is null
2757 */
2758 public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2759 if (refc == MethodHandle.class) {
2760 MethodHandle mh = findVirtualForMH(name, type);
2761 if (mh != null) return mh;
2762 } else if (refc == VarHandle.class) {
2763 MethodHandle mh = findVirtualForVH(name, type);
2764 if (mh != null) return mh;
2765 }
2766 byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual);
2767 MemberName method = resolveOrFail(refKind, refc, name, type);
2768 return getDirectMethod(refKind, refc, method, findBoundCallerLookup(method));
2769 }
2770 private MethodHandle findVirtualForMH(String name, MethodType type) {
2771 // these names require special lookups because of the implicit MethodType argument
2772 if ("invoke".equals(name))
2773 return invoker(type);
2774 if ("invokeExact".equals(name))
2775 return exactInvoker(type);
2776 assert(!MemberName.isMethodHandleInvokeName(name));
2777 return null;
2778 }
2779 private MethodHandle findVirtualForVH(String name, MethodType type) {
2780 try {
2781 return varHandleInvoker(VarHandle.AccessMode.valueFromMethodName(name), type);
2782 } catch (IllegalArgumentException e) {
2783 return null;
2784 }
2785 }
2786
2787 /**
2788 * Produces a method handle which creates an object and initializes it, using
2789 * the constructor of the specified type.
2790 * The parameter types of the method handle will be those of the constructor,
2791 * while the return type will be a reference to the constructor's class.
2792 * The constructor and all its argument types must be accessible to the lookup object.
2793 * <p>
2794 * The requested type must have a return type of {@code void}.
2795 * (This is consistent with the JVM's treatment of constructor type descriptors.)
2796 * <p>
2797 * The returned method handle will have
2798 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2799 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
2800 * <p>
2801 * If the returned method handle is invoked, the constructor's class will
2802 * be initialized, if it has not already been initialized.
2803 * <p><b>Example:</b>
2804 * {@snippet lang="java" :
2805 import static java.lang.invoke.MethodHandles.*;
2806 import static java.lang.invoke.MethodType.*;
2807 ...
2808 MethodHandle MH_newArrayList = publicLookup().findConstructor(
2809 ArrayList.class, methodType(void.class, Collection.class));
2810 Collection orig = Arrays.asList("x", "y");
2811 Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig);
2812 assert(orig != copy);
2813 assertEquals(orig, copy);
2814 // a variable-arity constructor:
2815 MethodHandle MH_newProcessBuilder = publicLookup().findConstructor(
2816 ProcessBuilder.class, methodType(void.class, String[].class));
2817 ProcessBuilder pb = (ProcessBuilder)
2818 MH_newProcessBuilder.invoke("x", "y", "z");
2819 assertEquals("[x, y, z]", pb.command().toString());
2820 * }
2821 * @param refc the class or interface from which the method is accessed
2822 * @param type the type of the method, with the receiver argument omitted, and a void return type
2823 * @return the desired method handle
2824 * @throws NoSuchMethodException if the constructor does not exist
2825 * @throws IllegalAccessException if access checking fails
2826 * or if the method's variable arity modifier bit
2827 * is set and {@code asVarargsCollector} fails
2828 * @throws SecurityException if a security manager is present and it
2829 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2830 * @throws NullPointerException if any argument is null
2831 */
2832 public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2833 if (refc.isArray()) {
2834 throw new NoSuchMethodException("no constructor for array class: " + refc.getName());
2835 }
2836 String name = ConstantDescs.INIT_NAME;
2837 MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type);
2838 return getDirectConstructor(refc, ctor);
2839 }
2840
2841 /**
2842 * Looks up a class by name from the lookup context defined by this {@code Lookup} object,
2843 * <a href="MethodHandles.Lookup.html#equiv">as if resolved</a> by an {@code ldc} instruction.
2844 * Such a resolution, as specified in JVMS {@jvms 5.4.3.1}, attempts to locate and load the class,
2845 * and then determines whether the class is accessible to this lookup object.
2846 * <p>
2847 * For a class or an interface, the name is the {@linkplain ClassLoader##binary-name binary name}.
2848 * For an array class of {@code n} dimensions, the name begins with {@code n} occurrences
2849 * of {@code '['} and followed by the element type as encoded in the
2850 * {@linkplain Class##nameFormat table} specified in {@link Class#getName}.
2851 * <p>
2852 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class},
2853 * its class loader, and the {@linkplain #lookupModes() lookup modes}.
2854 *
2855 * @param targetName the {@linkplain ClassLoader##binary-name binary name} of the class
2856 * or the string representing an array class
2857 * @return the requested class.
2858 * @throws SecurityException if a security manager is present and it
2859 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2860 * @throws LinkageError if the linkage fails
2861 * @throws ClassNotFoundException if the class cannot be loaded by the lookup class' loader.
2862 * @throws IllegalAccessException if the class is not accessible, using the allowed access
2863 * modes.
2864 * @throws NullPointerException if {@code targetName} is null
2865 * @since 9
2866 * @jvms 5.4.3.1 Class and Interface Resolution
2867 */
2868 public Class<?> findClass(String targetName) throws ClassNotFoundException, IllegalAccessException {
2869 Class<?> targetClass = Class.forName(targetName, false, lookupClass.getClassLoader());
2870 return accessClass(targetClass);
2871 }
2872
2873 /**
2874 * Ensures that {@code targetClass} has been initialized. The class
2875 * to be initialized must be {@linkplain #accessClass accessible}
2876 * to this {@code Lookup} object. This method causes {@code targetClass}
2877 * to be initialized if it has not been already initialized,
2878 * as specified in JVMS {@jvms 5.5}.
2879 *
2880 * <p>
2881 * This method returns when {@code targetClass} is fully initialized, or
2882 * when {@code targetClass} is being initialized by the current thread.
2883 *
2884 * @param <T> the type of the class to be initialized
2885 * @param targetClass the class to be initialized
2886 * @return {@code targetClass} that has been initialized, or that is being
2887 * initialized by the current thread.
2888 *
2889 * @throws IllegalArgumentException if {@code targetClass} is a primitive type or {@code void}
2890 * or array class
2891 * @throws IllegalAccessException if {@code targetClass} is not
2892 * {@linkplain #accessClass accessible} to this lookup
2893 * @throws ExceptionInInitializerError if the class initialization provoked
2894 * by this method fails
2895 * @throws SecurityException if a security manager is present and it
2896 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2897 * @since 15
2898 * @jvms 5.5 Initialization
2899 */
2900 public <T> Class<T> ensureInitialized(Class<T> targetClass) throws IllegalAccessException {
2901 if (targetClass.isPrimitive())
2902 throw new IllegalArgumentException(targetClass + " is a primitive class");
2903 if (targetClass.isArray())
2904 throw new IllegalArgumentException(targetClass + " is an array class");
2905
2906 if (!VerifyAccess.isClassAccessible(targetClass, lookupClass, prevLookupClass, allowedModes)) {
2907 throw makeAccessException(targetClass);
2908 }
2909 checkSecurityManager(targetClass);
2910
2911 // ensure class initialization
2912 Unsafe.getUnsafe().ensureClassInitialized(targetClass);
2913 return targetClass;
2914 }
2915
2916 /*
2917 * Returns IllegalAccessException due to access violation to the given targetClass.
2918 *
2919 * This method is called by {@link Lookup#accessClass} and {@link Lookup#ensureInitialized}
2920 * which verifies access to a class rather a member.
2921 */
2922 private IllegalAccessException makeAccessException(Class<?> targetClass) {
2923 String message = "access violation: "+ targetClass;
2924 if (this == MethodHandles.publicLookup()) {
2925 message += ", from public Lookup";
2926 } else {
2927 Module m = lookupClass().getModule();
2928 message += ", from " + lookupClass() + " (" + m + ")";
2929 if (prevLookupClass != null) {
2930 message += ", previous lookup " +
2931 prevLookupClass.getName() + " (" + prevLookupClass.getModule() + ")";
2932 }
2933 }
2934 return new IllegalAccessException(message);
2935 }
2936
2937 /**
2938 * Determines if a class can be accessed from the lookup context defined by
2939 * this {@code Lookup} object. The static initializer of the class is not run.
2940 * If {@code targetClass} is an array class, {@code targetClass} is accessible
2941 * if the element type of the array class is accessible. Otherwise,
2942 * {@code targetClass} is determined as accessible as follows.
2943 *
2944 * <p>
2945 * If {@code targetClass} is in the same module as the lookup class,
2946 * the lookup class is {@code LC} in module {@code M1} and
2947 * the previous lookup class is in module {@code M0} or
2948 * {@code null} if not present,
2949 * {@code targetClass} is accessible if and only if one of the following is true:
2950 * <ul>
2951 * <li>If this lookup has {@link #PRIVATE} access, {@code targetClass} is
2952 * {@code LC} or other class in the same nest of {@code LC}.</li>
2953 * <li>If this lookup has {@link #PACKAGE} access, {@code targetClass} is
2954 * in the same runtime package of {@code LC}.</li>
2955 * <li>If this lookup has {@link #MODULE} access, {@code targetClass} is
2956 * a public type in {@code M1}.</li>
2957 * <li>If this lookup has {@link #PUBLIC} access, {@code targetClass} is
2958 * a public type in a package exported by {@code M1} to at least {@code M0}
2959 * if the previous lookup class is present; otherwise, {@code targetClass}
2960 * is a public type in a package exported by {@code M1} unconditionally.</li>
2961 * </ul>
2962 *
2963 * <p>
2964 * Otherwise, if this lookup has {@link #UNCONDITIONAL} access, this lookup
2965 * can access public types in all modules when the type is in a package
2966 * that is exported unconditionally.
2967 * <p>
2968 * Otherwise, {@code targetClass} is in a different module from {@code lookupClass},
2969 * and if this lookup does not have {@code PUBLIC} access, {@code lookupClass}
2970 * is inaccessible.
2971 * <p>
2972 * Otherwise, if this lookup has no {@linkplain #previousLookupClass() previous lookup class},
2973 * {@code M1} is the module containing {@code lookupClass} and
2974 * {@code M2} is the module containing {@code targetClass},
2975 * then {@code targetClass} is accessible if and only if
2976 * <ul>
2977 * <li>{@code M1} reads {@code M2}, and
2978 * <li>{@code targetClass} is public and in a package exported by
2979 * {@code M2} at least to {@code M1}.
2980 * </ul>
2981 * <p>
2982 * Otherwise, if this lookup has a {@linkplain #previousLookupClass() previous lookup class},
2983 * {@code M1} and {@code M2} are as before, and {@code M0} is the module
2984 * containing the previous lookup class, then {@code targetClass} is accessible
2985 * if and only if one of the following is true:
2986 * <ul>
2987 * <li>{@code targetClass} is in {@code M0} and {@code M1}
2988 * {@linkplain Module#reads reads} {@code M0} and the type is
2989 * in a package that is exported to at least {@code M1}.
2990 * <li>{@code targetClass} is in {@code M1} and {@code M0}
2991 * {@linkplain Module#reads reads} {@code M1} and the type is
2992 * in a package that is exported to at least {@code M0}.
2993 * <li>{@code targetClass} is in a third module {@code M2} and both {@code M0}
2994 * and {@code M1} reads {@code M2} and the type is in a package
2995 * that is exported to at least both {@code M0} and {@code M2}.
2996 * </ul>
2997 * <p>
2998 * Otherwise, {@code targetClass} is not accessible.
2999 *
3000 * @param <T> the type of the class to be access-checked
3001 * @param targetClass the class to be access-checked
3002 * @return {@code targetClass} that has been access-checked
3003 * @throws IllegalAccessException if the class is not accessible from the lookup class
3004 * and previous lookup class, if present, using the allowed access modes.
3005 * @throws SecurityException if a security manager is present and it
3006 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3007 * @throws NullPointerException if {@code targetClass} is {@code null}
3008 * @since 9
3009 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
3010 */
3011 public <T> Class<T> accessClass(Class<T> targetClass) throws IllegalAccessException {
3012 if (!isClassAccessible(targetClass)) {
3013 throw makeAccessException(targetClass);
3014 }
3015 checkSecurityManager(targetClass);
3016 return targetClass;
3017 }
3018
3019 /**
3020 * Produces an early-bound method handle for a virtual method.
3021 * It will bypass checks for overriding methods on the receiver,
3022 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
3023 * instruction from within the explicitly specified {@code specialCaller}.
3024 * The type of the method handle will be that of the method,
3025 * with a suitably restricted receiver type prepended.
3026 * (The receiver type will be {@code specialCaller} or a subtype.)
3027 * The method and all its argument types must be accessible
3028 * to the lookup object.
3029 * <p>
3030 * Before method resolution,
3031 * if the explicitly specified caller class is not identical with the
3032 * lookup class, or if this lookup object does not have
3033 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
3034 * privileges, the access fails.
3035 * <p>
3036 * The returned method handle will have
3037 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3038 * the method's variable arity modifier bit ({@code 0x0080}) is set.
3039 * <p style="font-size:smaller;">
3040 * <em>(Note: JVM internal methods named {@value ConstantDescs#INIT_NAME}
3041 * are not visible to this API,
3042 * even though the {@code invokespecial} instruction can refer to them
3043 * in special circumstances. Use {@link #findConstructor findConstructor}
3044 * to access instance initialization methods in a safe manner.)</em>
3045 * <p><b>Example:</b>
3046 * {@snippet lang="java" :
3047 import static java.lang.invoke.MethodHandles.*;
3048 import static java.lang.invoke.MethodType.*;
3049 ...
3050 static class Listie extends ArrayList {
3051 public String toString() { return "[wee Listie]"; }
3052 static Lookup lookup() { return MethodHandles.lookup(); }
3053 }
3054 ...
3055 // no access to constructor via invokeSpecial:
3056 MethodHandle MH_newListie = Listie.lookup()
3057 .findConstructor(Listie.class, methodType(void.class));
3058 Listie l = (Listie) MH_newListie.invokeExact();
3059 try { assertEquals("impossible", Listie.lookup().findSpecial(
3060 Listie.class, "<init>", methodType(void.class), Listie.class));
3061 } catch (NoSuchMethodException ex) { } // OK
3062 // access to super and self methods via invokeSpecial:
3063 MethodHandle MH_super = Listie.lookup().findSpecial(
3064 ArrayList.class, "toString" , methodType(String.class), Listie.class);
3065 MethodHandle MH_this = Listie.lookup().findSpecial(
3066 Listie.class, "toString" , methodType(String.class), Listie.class);
3067 MethodHandle MH_duper = Listie.lookup().findSpecial(
3068 Object.class, "toString" , methodType(String.class), Listie.class);
3069 assertEquals("[]", (String) MH_super.invokeExact(l));
3070 assertEquals(""+l, (String) MH_this.invokeExact(l));
3071 assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method
3072 try { assertEquals("inaccessible", Listie.lookup().findSpecial(
3073 String.class, "toString", methodType(String.class), Listie.class));
3074 } catch (IllegalAccessException ex) { } // OK
3075 Listie subl = new Listie() { public String toString() { return "[subclass]"; } };
3076 assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method
3077 * }
3078 *
3079 * @param refc the class or interface from which the method is accessed
3080 * @param name the name of the method (which must not be "<init>")
3081 * @param type the type of the method, with the receiver argument omitted
3082 * @param specialCaller the proposed calling class to perform the {@code invokespecial}
3083 * @return the desired method handle
3084 * @throws NoSuchMethodException if the method does not exist
3085 * @throws IllegalAccessException if access checking fails,
3086 * or if the method is {@code static},
3087 * or if the method's variable arity modifier bit
3088 * is set and {@code asVarargsCollector} fails
3089 * @throws SecurityException if a security manager is present and it
3090 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3091 * @throws NullPointerException if any argument is null
3092 */
3093 public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,
3094 Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
3095 checkSpecialCaller(specialCaller, refc);
3096 Lookup specialLookup = this.in(specialCaller);
3097 MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type);
3098 return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerLookup(method));
3099 }
3100
3101 /**
3102 * Produces a method handle giving read access to a non-static field.
3103 * The type of the method handle will have a return type of the field's
3104 * value type.
3105 * The method handle's single argument will be the instance containing
3106 * the field.
3107 * Access checking is performed immediately on behalf of the lookup class.
3108 * @param refc the class or interface from which the method is accessed
3109 * @param name the field's name
3110 * @param type the field's type
3111 * @return a method handle which can load values from the field
3112 * @throws NoSuchFieldException if the field does not exist
3113 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
3114 * @throws SecurityException if a security manager is present and it
3115 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3116 * @throws NullPointerException if any argument is null
3117 * @see #findVarHandle(Class, String, Class)
3118 */
3119 public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3120 MemberName field = resolveOrFail(REF_getField, refc, name, type);
3121 return getDirectField(REF_getField, refc, field);
3122 }
3123
3124 /**
3125 * Produces a method handle giving write access to a non-static field.
3126 * The type of the method handle will have a void return type.
3127 * The method handle will take two arguments, the instance containing
3128 * the field, and the value to be stored.
3129 * The second argument will be of the field's value type.
3130 * Access checking is performed immediately on behalf of the lookup class.
3131 * @param refc the class or interface from which the method is accessed
3132 * @param name the field's name
3133 * @param type the field's type
3134 * @return a method handle which can store values into the field
3135 * @throws NoSuchFieldException if the field does not exist
3136 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
3137 * or {@code final}
3138 * @throws SecurityException if a security manager is present and it
3139 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3140 * @throws NullPointerException if any argument is null
3141 * @see #findVarHandle(Class, String, Class)
3142 */
3143 public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3144 MemberName field = resolveOrFail(REF_putField, refc, name, type);
3145 return getDirectField(REF_putField, refc, field);
3146 }
3147
3148 /**
3149 * Produces a VarHandle giving access to a non-static field {@code name}
3150 * of type {@code type} declared in a class of type {@code recv}.
3151 * The VarHandle's variable type is {@code type} and it has one
3152 * coordinate type, {@code recv}.
3153 * <p>
3154 * Access checking is performed immediately on behalf of the lookup
3155 * class.
3156 * <p>
3157 * Certain access modes of the returned VarHandle are unsupported under
3158 * the following conditions:
3159 * <ul>
3160 * <li>if the field is declared {@code final}, then the write, atomic
3161 * update, numeric atomic update, and bitwise atomic update access
3162 * modes are unsupported.
3163 * <li>if the field type is anything other than {@code byte},
3164 * {@code short}, {@code char}, {@code int}, {@code long},
3165 * {@code float}, or {@code double} then numeric atomic update
3166 * access modes are unsupported.
3167 * <li>if the field type is anything other than {@code boolean},
3168 * {@code byte}, {@code short}, {@code char}, {@code int} or
3169 * {@code long} then bitwise atomic update access modes are
3170 * unsupported.
3171 * </ul>
3172 * <p>
3173 * If the field is declared {@code volatile} then the returned VarHandle
3174 * will override access to the field (effectively ignore the
3175 * {@code volatile} declaration) in accordance to its specified
3176 * access modes.
3177 * <p>
3178 * If the field type is {@code float} or {@code double} then numeric
3179 * and atomic update access modes compare values using their bitwise
3180 * representation (see {@link Float#floatToRawIntBits} and
3181 * {@link Double#doubleToRawLongBits}, respectively).
3182 * @apiNote
3183 * Bitwise comparison of {@code float} values or {@code double} values,
3184 * as performed by the numeric and atomic update access modes, differ
3185 * from the primitive {@code ==} operator and the {@link Float#equals}
3186 * and {@link Double#equals} methods, specifically with respect to
3187 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
3188 * Care should be taken when performing a compare and set or a compare
3189 * and exchange operation with such values since the operation may
3190 * unexpectedly fail.
3191 * There are many possible NaN values that are considered to be
3192 * {@code NaN} in Java, although no IEEE 754 floating-point operation
3193 * provided by Java can distinguish between them. Operation failure can
3194 * occur if the expected or witness value is a NaN value and it is
3195 * transformed (perhaps in a platform specific manner) into another NaN
3196 * value, and thus has a different bitwise representation (see
3197 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
3198 * details).
3199 * The values {@code -0.0} and {@code +0.0} have different bitwise
3200 * representations but are considered equal when using the primitive
3201 * {@code ==} operator. Operation failure can occur if, for example, a
3202 * numeric algorithm computes an expected value to be say {@code -0.0}
3203 * and previously computed the witness value to be say {@code +0.0}.
3204 * @param recv the receiver class, of type {@code R}, that declares the
3205 * non-static field
3206 * @param name the field's name
3207 * @param type the field's type, of type {@code T}
3208 * @return a VarHandle giving access to non-static fields.
3209 * @throws NoSuchFieldException if the field does not exist
3210 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
3211 * @throws SecurityException if a security manager is present and it
3212 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3213 * @throws NullPointerException if any argument is null
3214 * @since 9
3215 */
3216 public VarHandle findVarHandle(Class<?> recv, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3217 MemberName getField = resolveOrFail(REF_getField, recv, name, type);
3218 MemberName putField = resolveOrFail(REF_putField, recv, name, type);
3219 return getFieldVarHandle(REF_getField, REF_putField, recv, getField, putField);
3220 }
3221
3222 /**
3223 * Produces a method handle giving read access to a static field.
3224 * The type of the method handle will have a return type of the field's
3225 * value type.
3226 * The method handle will take no arguments.
3227 * Access checking is performed immediately on behalf of the lookup class.
3228 * <p>
3229 * If the returned method handle is invoked, the field's class will
3230 * be initialized, if it has not already been initialized.
3231 * @param refc the class or interface from which the method is accessed
3232 * @param name the field's name
3233 * @param type the field's type
3234 * @return a method handle which can load values from the field
3235 * @throws NoSuchFieldException if the field does not exist
3236 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
3237 * @throws SecurityException if a security manager is present and it
3238 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3239 * @throws NullPointerException if any argument is null
3240 */
3241 public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3242 MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
3243 return getDirectField(REF_getStatic, refc, field);
3244 }
3245
3246 /**
3247 * Produces a method handle giving write access to a static field.
3248 * The type of the method handle will have a void return type.
3249 * The method handle will take a single
3250 * argument, of the field's value type, the value to be stored.
3251 * Access checking is performed immediately on behalf of the lookup class.
3252 * <p>
3253 * If the returned method handle is invoked, the field's class will
3254 * be initialized, if it has not already been initialized.
3255 * @param refc the class or interface from which the method is accessed
3256 * @param name the field's name
3257 * @param type the field's type
3258 * @return a method handle which can store values into the field
3259 * @throws NoSuchFieldException if the field does not exist
3260 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
3261 * or is {@code final}
3262 * @throws SecurityException if a security manager is present and it
3263 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3264 * @throws NullPointerException if any argument is null
3265 */
3266 public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3267 MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
3268 return getDirectField(REF_putStatic, refc, field);
3269 }
3270
3271 /**
3272 * Produces a VarHandle giving access to a static field {@code name} of
3273 * type {@code type} declared in a class of type {@code decl}.
3274 * The VarHandle's variable type is {@code type} and it has no
3275 * coordinate types.
3276 * <p>
3277 * Access checking is performed immediately on behalf of the lookup
3278 * class.
3279 * <p>
3280 * If the returned VarHandle is operated on, the declaring class will be
3281 * initialized, if it has not already been initialized.
3282 * <p>
3283 * Certain access modes of the returned VarHandle are unsupported under
3284 * the following conditions:
3285 * <ul>
3286 * <li>if the field is declared {@code final}, then the write, atomic
3287 * update, numeric atomic update, and bitwise atomic update access
3288 * modes are unsupported.
3289 * <li>if the field type is anything other than {@code byte},
3290 * {@code short}, {@code char}, {@code int}, {@code long},
3291 * {@code float}, or {@code double}, then numeric atomic update
3292 * access modes are unsupported.
3293 * <li>if the field type is anything other than {@code boolean},
3294 * {@code byte}, {@code short}, {@code char}, {@code int} or
3295 * {@code long} then bitwise atomic update access modes are
3296 * unsupported.
3297 * </ul>
3298 * <p>
3299 * If the field is declared {@code volatile} then the returned VarHandle
3300 * will override access to the field (effectively ignore the
3301 * {@code volatile} declaration) in accordance to its specified
3302 * access modes.
3303 * <p>
3304 * If the field type is {@code float} or {@code double} then numeric
3305 * and atomic update access modes compare values using their bitwise
3306 * representation (see {@link Float#floatToRawIntBits} and
3307 * {@link Double#doubleToRawLongBits}, respectively).
3308 * @apiNote
3309 * Bitwise comparison of {@code float} values or {@code double} values,
3310 * as performed by the numeric and atomic update access modes, differ
3311 * from the primitive {@code ==} operator and the {@link Float#equals}
3312 * and {@link Double#equals} methods, specifically with respect to
3313 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
3314 * Care should be taken when performing a compare and set or a compare
3315 * and exchange operation with such values since the operation may
3316 * unexpectedly fail.
3317 * There are many possible NaN values that are considered to be
3318 * {@code NaN} in Java, although no IEEE 754 floating-point operation
3319 * provided by Java can distinguish between them. Operation failure can
3320 * occur if the expected or witness value is a NaN value and it is
3321 * transformed (perhaps in a platform specific manner) into another NaN
3322 * value, and thus has a different bitwise representation (see
3323 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
3324 * details).
3325 * The values {@code -0.0} and {@code +0.0} have different bitwise
3326 * representations but are considered equal when using the primitive
3327 * {@code ==} operator. Operation failure can occur if, for example, a
3328 * numeric algorithm computes an expected value to be say {@code -0.0}
3329 * and previously computed the witness value to be say {@code +0.0}.
3330 * @param decl the class that declares the static field
3331 * @param name the field's name
3332 * @param type the field's type, of type {@code T}
3333 * @return a VarHandle giving access to a static field
3334 * @throws NoSuchFieldException if the field does not exist
3335 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
3336 * @throws SecurityException if a security manager is present and it
3337 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3338 * @throws NullPointerException if any argument is null
3339 * @since 9
3340 */
3341 public VarHandle findStaticVarHandle(Class<?> decl, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3342 MemberName getField = resolveOrFail(REF_getStatic, decl, name, type);
3343 MemberName putField = resolveOrFail(REF_putStatic, decl, name, type);
3344 return getFieldVarHandle(REF_getStatic, REF_putStatic, decl, getField, putField);
3345 }
3346
3347 /**
3348 * Produces an early-bound method handle for a non-static method.
3349 * The receiver must have a supertype {@code defc} in which a method
3350 * of the given name and type is accessible to the lookup class.
3351 * The method and all its argument types must be accessible to the lookup object.
3352 * The type of the method handle will be that of the method,
3353 * without any insertion of an additional receiver parameter.
3354 * The given receiver will be bound into the method handle,
3355 * so that every call to the method handle will invoke the
3356 * requested method on the given receiver.
3357 * <p>
3358 * The returned method handle will have
3359 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3360 * the method's variable arity modifier bit ({@code 0x0080}) is set
3361 * <em>and</em> the trailing array argument is not the only argument.
3362 * (If the trailing array argument is the only argument,
3363 * the given receiver value will be bound to it.)
3364 * <p>
3365 * This is almost equivalent to the following code, with some differences noted below:
3366 * {@snippet lang="java" :
3367 import static java.lang.invoke.MethodHandles.*;
3368 import static java.lang.invoke.MethodType.*;
3369 ...
3370 MethodHandle mh0 = lookup().findVirtual(defc, name, type);
3371 MethodHandle mh1 = mh0.bindTo(receiver);
3372 mh1 = mh1.withVarargs(mh0.isVarargsCollector());
3373 return mh1;
3374 * }
3375 * where {@code defc} is either {@code receiver.getClass()} or a super
3376 * type of that class, in which the requested method is accessible
3377 * to the lookup class.
3378 * (Unlike {@code bind}, {@code bindTo} does not preserve variable arity.
3379 * Also, {@code bindTo} may throw a {@code ClassCastException} in instances where {@code bind} would
3380 * throw an {@code IllegalAccessException}, as in the case where the member is {@code protected} and
3381 * the receiver is restricted by {@code findVirtual} to the lookup class.)
3382 * @param receiver the object from which the method is accessed
3383 * @param name the name of the method
3384 * @param type the type of the method, with the receiver argument omitted
3385 * @return the desired method handle
3386 * @throws NoSuchMethodException if the method does not exist
3387 * @throws IllegalAccessException if access checking fails
3388 * or if the method's variable arity modifier bit
3389 * is set and {@code asVarargsCollector} fails
3390 * @throws SecurityException if a security manager is present and it
3391 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3392 * @throws NullPointerException if any argument is null
3393 * @see MethodHandle#bindTo
3394 * @see #findVirtual
3395 */
3396 public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
3397 Class<? extends Object> refc = receiver.getClass(); // may get NPE
3398 MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
3399 MethodHandle mh = getDirectMethodNoRestrictInvokeSpecial(refc, method, findBoundCallerLookup(method));
3400 if (!mh.type().leadingReferenceParameter().isAssignableFrom(receiver.getClass())) {
3401 throw new IllegalAccessException("The restricted defining class " +
3402 mh.type().leadingReferenceParameter().getName() +
3403 " is not assignable from receiver class " +
3404 receiver.getClass().getName());
3405 }
3406 return mh.bindArgumentL(0, receiver).setVarargs(method);
3407 }
3408
3409 /**
3410 * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
3411 * to <i>m</i>, if the lookup class has permission.
3412 * If <i>m</i> is non-static, the receiver argument is treated as an initial argument.
3413 * If <i>m</i> is virtual, overriding is respected on every call.
3414 * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped.
3415 * The type of the method handle will be that of the method,
3416 * with the receiver type prepended (but only if it is non-static).
3417 * If the method's {@code accessible} flag is not set,
3418 * access checking is performed immediately on behalf of the lookup class.
3419 * If <i>m</i> is not public, do not share the resulting handle with untrusted parties.
3420 * <p>
3421 * The returned method handle will have
3422 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3423 * the method's variable arity modifier bit ({@code 0x0080}) is set.
3424 * <p>
3425 * If <i>m</i> is static, and
3426 * if the returned method handle is invoked, the method's class will
3427 * be initialized, if it has not already been initialized.
3428 * @param m the reflected method
3429 * @return a method handle which can invoke the reflected method
3430 * @throws IllegalAccessException if access checking fails
3431 * or if the method's variable arity modifier bit
3432 * is set and {@code asVarargsCollector} fails
3433 * @throws NullPointerException if the argument is null
3434 */
3435 public MethodHandle unreflect(Method m) throws IllegalAccessException {
3436 if (m.getDeclaringClass() == MethodHandle.class) {
3437 MethodHandle mh = unreflectForMH(m);
3438 if (mh != null) return mh;
3439 }
3440 if (m.getDeclaringClass() == VarHandle.class) {
3441 MethodHandle mh = unreflectForVH(m);
3442 if (mh != null) return mh;
3443 }
3444 MemberName method = new MemberName(m);
3445 byte refKind = method.getReferenceKind();
3446 if (refKind == REF_invokeSpecial)
3447 refKind = REF_invokeVirtual;
3448 assert(method.isMethod());
3449 @SuppressWarnings("deprecation")
3450 Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
3451 return lookup.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method, findBoundCallerLookup(method));
3452 }
3453 private MethodHandle unreflectForMH(Method m) {
3454 // these names require special lookups because they throw UnsupportedOperationException
3455 if (MemberName.isMethodHandleInvokeName(m.getName()))
3456 return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m));
3457 return null;
3458 }
3459 private MethodHandle unreflectForVH(Method m) {
3460 // these names require special lookups because they throw UnsupportedOperationException
3461 if (MemberName.isVarHandleMethodInvokeName(m.getName()))
3462 return MethodHandleImpl.fakeVarHandleInvoke(new MemberName(m));
3463 return null;
3464 }
3465
3466 /**
3467 * Produces a method handle for a reflected method.
3468 * It will bypass checks for overriding methods on the receiver,
3469 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
3470 * instruction from within the explicitly specified {@code specialCaller}.
3471 * The type of the method handle will be that of the method,
3472 * with a suitably restricted receiver type prepended.
3473 * (The receiver type will be {@code specialCaller} or a subtype.)
3474 * If the method's {@code accessible} flag is not set,
3475 * access checking is performed immediately on behalf of the lookup class,
3476 * as if {@code invokespecial} instruction were being linked.
3477 * <p>
3478 * Before method resolution,
3479 * if the explicitly specified caller class is not identical with the
3480 * lookup class, or if this lookup object does not have
3481 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
3482 * privileges, the access fails.
3483 * <p>
3484 * The returned method handle will have
3485 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3486 * the method's variable arity modifier bit ({@code 0x0080}) is set.
3487 * @param m the reflected method
3488 * @param specialCaller the class nominally calling the method
3489 * @return a method handle which can invoke the reflected method
3490 * @throws IllegalAccessException if access checking fails,
3491 * or if the method is {@code static},
3492 * or if the method's variable arity modifier bit
3493 * is set and {@code asVarargsCollector} fails
3494 * @throws NullPointerException if any argument is null
3495 */
3496 public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException {
3497 checkSpecialCaller(specialCaller, m.getDeclaringClass());
3498 Lookup specialLookup = this.in(specialCaller);
3499 MemberName method = new MemberName(m, true);
3500 assert(method.isMethod());
3501 // ignore m.isAccessible: this is a new kind of access
3502 return specialLookup.getDirectMethodNoSecurityManager(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerLookup(method));
3503 }
3504
3505 /**
3506 * Produces a method handle for a reflected constructor.
3507 * The type of the method handle will be that of the constructor,
3508 * with the return type changed to the declaring class.
3509 * The method handle will perform a {@code newInstance} operation,
3510 * creating a new instance of the constructor's class on the
3511 * arguments passed to the method handle.
3512 * <p>
3513 * If the constructor's {@code accessible} flag is not set,
3514 * access checking is performed immediately on behalf of the lookup class.
3515 * <p>
3516 * The returned method handle will have
3517 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3518 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
3519 * <p>
3520 * If the returned method handle is invoked, the constructor's class will
3521 * be initialized, if it has not already been initialized.
3522 * @param c the reflected constructor
3523 * @return a method handle which can invoke the reflected constructor
3524 * @throws IllegalAccessException if access checking fails
3525 * or if the method's variable arity modifier bit
3526 * is set and {@code asVarargsCollector} fails
3527 * @throws NullPointerException if the argument is null
3528 */
3529 public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException {
3530 MemberName ctor = new MemberName(c);
3531 assert(ctor.isConstructor());
3532 @SuppressWarnings("deprecation")
3533 Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
3534 return lookup.getDirectConstructorNoSecurityManager(ctor.getDeclaringClass(), ctor);
3535 }
3536
3537 /**
3538 * Produces a method handle giving read access to a reflected field.
3539 * The type of the method handle will have a return type of the field's
3540 * value type.
3541 * If the field is {@code static}, the method handle will take no arguments.
3542 * Otherwise, its single argument will be the instance containing
3543 * the field.
3544 * If the {@code Field} object's {@code accessible} flag is not set,
3545 * access checking is performed immediately on behalf of the lookup class.
3546 * <p>
3547 * If the field is static, and
3548 * if the returned method handle is invoked, the field's class will
3549 * be initialized, if it has not already been initialized.
3550 * @param f the reflected field
3551 * @return a method handle which can load values from the reflected field
3552 * @throws IllegalAccessException if access checking fails
3553 * @throws NullPointerException if the argument is null
3554 */
3555 public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
3556 return unreflectField(f, false);
3557 }
3558
3559 /**
3560 * Produces a method handle giving write access to a reflected field.
3561 * The type of the method handle will have a void return type.
3562 * If the field is {@code static}, the method handle will take a single
3563 * argument, of the field's value type, the value to be stored.
3564 * Otherwise, the two arguments will be the instance containing
3565 * the field, and the value to be stored.
3566 * If the {@code Field} object's {@code accessible} flag is not set,
3567 * access checking is performed immediately on behalf of the lookup class.
3568 * <p>
3569 * If the field is {@code final}, write access will not be
3570 * allowed and access checking will fail, except under certain
3571 * narrow circumstances documented for {@link Field#set Field.set}.
3572 * A method handle is returned only if a corresponding call to
3573 * the {@code Field} object's {@code set} method could return
3574 * normally. In particular, fields which are both {@code static}
3575 * and {@code final} may never be set.
3576 * <p>
3577 * If the field is {@code static}, and
3578 * if the returned method handle is invoked, the field's class will
3579 * be initialized, if it has not already been initialized.
3580 * @param f the reflected field
3581 * @return a method handle which can store values into the reflected field
3582 * @throws IllegalAccessException if access checking fails,
3583 * or if the field is {@code final} and write access
3584 * is not enabled on the {@code Field} object
3585 * @throws NullPointerException if the argument is null
3586 */
3587 public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
3588 return unreflectField(f, true);
3589 }
3590
3591 private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
3592 MemberName field = new MemberName(f, isSetter);
3593 if (isSetter && field.isFinal()) {
3594 if (field.isTrustedFinalField()) {
3595 String msg = field.isStatic() ? "static final field has no write access"
3596 : "final field has no write access";
3597 throw field.makeAccessException(msg, this);
3598 }
3599 }
3600 assert(isSetter
3601 ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
3602 : MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
3603 @SuppressWarnings("deprecation")
3604 Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
3605 return lookup.getDirectFieldNoSecurityManager(field.getReferenceKind(), f.getDeclaringClass(), field);
3606 }
3607
3608 /**
3609 * Produces a VarHandle giving access to a reflected field {@code f}
3610 * of type {@code T} declared in a class of type {@code R}.
3611 * The VarHandle's variable type is {@code T}.
3612 * If the field is non-static the VarHandle has one coordinate type,
3613 * {@code R}. Otherwise, the field is static, and the VarHandle has no
3614 * coordinate types.
3615 * <p>
3616 * Access checking is performed immediately on behalf of the lookup
3617 * class, regardless of the value of the field's {@code accessible}
3618 * flag.
3619 * <p>
3620 * If the field is static, and if the returned VarHandle is operated
3621 * on, the field's declaring class will be initialized, if it has not
3622 * already been initialized.
3623 * <p>
3624 * Certain access modes of the returned VarHandle are unsupported under
3625 * the following conditions:
3626 * <ul>
3627 * <li>if the field is declared {@code final}, then the write, atomic
3628 * update, numeric atomic update, and bitwise atomic update access
3629 * modes are unsupported.
3630 * <li>if the field type is anything other than {@code byte},
3631 * {@code short}, {@code char}, {@code int}, {@code long},
3632 * {@code float}, or {@code double} then numeric atomic update
3633 * access modes are unsupported.
3634 * <li>if the field type is anything other than {@code boolean},
3635 * {@code byte}, {@code short}, {@code char}, {@code int} or
3636 * {@code long} then bitwise atomic update access modes are
3637 * unsupported.
3638 * </ul>
3639 * <p>
3640 * If the field is declared {@code volatile} then the returned VarHandle
3641 * will override access to the field (effectively ignore the
3642 * {@code volatile} declaration) in accordance to its specified
3643 * access modes.
3644 * <p>
3645 * If the field type is {@code float} or {@code double} then numeric
3646 * and atomic update access modes compare values using their bitwise
3647 * representation (see {@link Float#floatToRawIntBits} and
3648 * {@link Double#doubleToRawLongBits}, respectively).
3649 * @apiNote
3650 * Bitwise comparison of {@code float} values or {@code double} values,
3651 * as performed by the numeric and atomic update access modes, differ
3652 * from the primitive {@code ==} operator and the {@link Float#equals}
3653 * and {@link Double#equals} methods, specifically with respect to
3654 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
3655 * Care should be taken when performing a compare and set or a compare
3656 * and exchange operation with such values since the operation may
3657 * unexpectedly fail.
3658 * There are many possible NaN values that are considered to be
3659 * {@code NaN} in Java, although no IEEE 754 floating-point operation
3660 * provided by Java can distinguish between them. Operation failure can
3661 * occur if the expected or witness value is a NaN value and it is
3662 * transformed (perhaps in a platform specific manner) into another NaN
3663 * value, and thus has a different bitwise representation (see
3664 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
3665 * details).
3666 * The values {@code -0.0} and {@code +0.0} have different bitwise
3667 * representations but are considered equal when using the primitive
3668 * {@code ==} operator. Operation failure can occur if, for example, a
3669 * numeric algorithm computes an expected value to be say {@code -0.0}
3670 * and previously computed the witness value to be say {@code +0.0}.
3671 * @param f the reflected field, with a field of type {@code T}, and
3672 * a declaring class of type {@code R}
3673 * @return a VarHandle giving access to non-static fields or a static
3674 * field
3675 * @throws IllegalAccessException if access checking fails
3676 * @throws NullPointerException if the argument is null
3677 * @since 9
3678 */
3679 public VarHandle unreflectVarHandle(Field f) throws IllegalAccessException {
3680 MemberName getField = new MemberName(f, false);
3681 MemberName putField = new MemberName(f, true);
3682 return getFieldVarHandleNoSecurityManager(getField.getReferenceKind(), putField.getReferenceKind(),
3683 f.getDeclaringClass(), getField, putField);
3684 }
3685
3686 /**
3687 * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
3688 * created by this lookup object or a similar one.
3689 * Security and access checks are performed to ensure that this lookup object
3690 * is capable of reproducing the target method handle.
3691 * This means that the cracking may fail if target is a direct method handle
3692 * but was created by an unrelated lookup object.
3693 * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a>
3694 * and was created by a lookup object for a different class.
3695 * @param target a direct method handle to crack into symbolic reference components
3696 * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object
3697 * @throws SecurityException if a security manager is present and it
3698 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3699 * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails
3700 * @throws NullPointerException if the target is {@code null}
3701 * @see MethodHandleInfo
3702 * @since 1.8
3703 */
3704 public MethodHandleInfo revealDirect(MethodHandle target) {
3705 if (!target.isCrackable()) {
3706 throw newIllegalArgumentException("not a direct method handle");
3707 }
3708 MemberName member = target.internalMemberName();
3709 Class<?> defc = member.getDeclaringClass();
3710 byte refKind = member.getReferenceKind();
3711 assert(MethodHandleNatives.refKindIsValid(refKind));
3712 if (refKind == REF_invokeSpecial && !target.isInvokeSpecial())
3713 // Devirtualized method invocation is usually formally virtual.
3714 // To avoid creating extra MemberName objects for this common case,
3715 // we encode this extra degree of freedom using MH.isInvokeSpecial.
3716 refKind = REF_invokeVirtual;
3717 if (refKind == REF_invokeVirtual && defc.isInterface())
3718 // Symbolic reference is through interface but resolves to Object method (toString, etc.)
3719 refKind = REF_invokeInterface;
3720 // Check SM permissions and member access before cracking.
3721 try {
3722 checkAccess(refKind, defc, member);
3723 checkSecurityManager(defc, member);
3724 } catch (IllegalAccessException ex) {
3725 throw new IllegalArgumentException(ex);
3726 }
3727 if (allowedModes != TRUSTED && member.isCallerSensitive()) {
3728 Class<?> callerClass = target.internalCallerClass();
3729 if ((lookupModes() & ORIGINAL) == 0 || callerClass != lookupClass())
3730 throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass);
3731 }
3732 // Produce the handle to the results.
3733 return new InfoFromMemberName(this, member, refKind);
3734 }
3735
3736 /// Helper methods, all package-private.
3737
3738 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3739 checkSymbolicClass(refc); // do this before attempting to resolve
3740 Objects.requireNonNull(name);
3741 Objects.requireNonNull(type);
3742 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), allowedModes,
3743 NoSuchFieldException.class);
3744 }
3745
3746 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
3747 checkSymbolicClass(refc); // do this before attempting to resolve
3748 Objects.requireNonNull(type);
3749 checkMethodName(refKind, name); // implicit null-check of name
3750 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), allowedModes,
3751 NoSuchMethodException.class);
3752 }
3753
3754 MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException {
3755 checkSymbolicClass(member.getDeclaringClass()); // do this before attempting to resolve
3756 Objects.requireNonNull(member.getName());
3757 Objects.requireNonNull(member.getType());
3758 return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(), allowedModes,
3759 ReflectiveOperationException.class);
3760 }
3761
3762 MemberName resolveOrNull(byte refKind, MemberName member) {
3763 // do this before attempting to resolve
3764 if (!isClassAccessible(member.getDeclaringClass())) {
3765 return null;
3766 }
3767 Objects.requireNonNull(member.getName());
3768 Objects.requireNonNull(member.getType());
3769 return IMPL_NAMES.resolveOrNull(refKind, member, lookupClassOrNull(), allowedModes);
3770 }
3771
3772 MemberName resolveOrNull(byte refKind, Class<?> refc, String name, MethodType type) {
3773 // do this before attempting to resolve
3774 if (!isClassAccessible(refc)) {
3775 return null;
3776 }
3777 Objects.requireNonNull(type);
3778 // implicit null-check of name
3779 if (name.startsWith("<") && refKind != REF_newInvokeSpecial) {
3780 return null;
3781 }
3782 return IMPL_NAMES.resolveOrNull(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), allowedModes);
3783 }
3784
3785 void checkSymbolicClass(Class<?> refc) throws IllegalAccessException {
3786 if (!isClassAccessible(refc)) {
3787 throw new MemberName(refc).makeAccessException("symbolic reference class is not accessible", this);
3788 }
3789 }
3790
3791 boolean isClassAccessible(Class<?> refc) {
3792 Objects.requireNonNull(refc);
3793 Class<?> caller = lookupClassOrNull();
3794 Class<?> type = refc;
3795 while (type.isArray()) {
3796 type = type.getComponentType();
3797 }
3798 return caller == null || VerifyAccess.isClassAccessible(type, caller, prevLookupClass, allowedModes);
3799 }
3800
3801 /** Check name for an illegal leading "<" character. */
3802 void checkMethodName(byte refKind, String name) throws NoSuchMethodException {
3803 if (name.startsWith("<") && refKind != REF_newInvokeSpecial)
3804 throw new NoSuchMethodException("illegal method name: "+name);
3805 }
3806
3807 /**
3808 * Find my trustable caller class if m is a caller sensitive method.
3809 * If this lookup object has original full privilege access, then the caller class is the lookupClass.
3810 * Otherwise, if m is caller-sensitive, throw IllegalAccessException.
3811 */
3812 Lookup findBoundCallerLookup(MemberName m) throws IllegalAccessException {
3813 if (MethodHandleNatives.isCallerSensitive(m) && (lookupModes() & ORIGINAL) == 0) {
3814 // Only lookups with full privilege access are allowed to resolve caller-sensitive methods
3815 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
3816 }
3817 return this;
3818 }
3819
3820 /**
3821 * Returns {@code true} if this lookup has {@code PRIVATE} and {@code MODULE} access.
3822 * @return {@code true} if this lookup has {@code PRIVATE} and {@code MODULE} access.
3823 *
3824 * @deprecated This method was originally designed to test {@code PRIVATE} access
3825 * that implies full privilege access but {@code MODULE} access has since become
3826 * independent of {@code PRIVATE} access. It is recommended to call
3827 * {@link #hasFullPrivilegeAccess()} instead.
3828 * @since 9
3829 */
3830 @Deprecated(since="14")
3831 public boolean hasPrivateAccess() {
3832 return hasFullPrivilegeAccess();
3833 }
3834
3835 /**
3836 * Returns {@code true} if this lookup has <em>full privilege access</em>,
3837 * i.e. {@code PRIVATE} and {@code MODULE} access.
3838 * A {@code Lookup} object must have full privilege access in order to
3839 * access all members that are allowed to the
3840 * {@linkplain #lookupClass() lookup class}.
3841 *
3842 * @return {@code true} if this lookup has full privilege access.
3843 * @since 14
3844 * @see <a href="MethodHandles.Lookup.html#privacc">private and module access</a>
3845 */
3846 public boolean hasFullPrivilegeAccess() {
3847 return (allowedModes & (PRIVATE|MODULE)) == (PRIVATE|MODULE);
3848 }
3849
3850 /**
3851 * Perform steps 1 and 2b <a href="MethodHandles.Lookup.html#secmgr">access checks</a>
3852 * for ensureInitialized, findClass or accessClass.
3853 */
3854 void checkSecurityManager(Class<?> refc) {
3855 if (allowedModes == TRUSTED) return;
3856
3857 @SuppressWarnings("removal")
3858 SecurityManager smgr = System.getSecurityManager();
3859 if (smgr == null) return;
3860
3861 // Step 1:
3862 boolean fullPrivilegeLookup = hasFullPrivilegeAccess();
3863 if (!fullPrivilegeLookup ||
3864 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
3865 ReflectUtil.checkPackageAccess(refc);
3866 }
3867
3868 // Step 2b:
3869 if (!fullPrivilegeLookup) {
3870 smgr.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
3871 }
3872 }
3873
3874 /**
3875 * Perform steps 1, 2a and 3 <a href="MethodHandles.Lookup.html#secmgr">access checks</a>.
3876 * Determines a trustable caller class to compare with refc, the symbolic reference class.
3877 * If this lookup object has full privilege access except original access,
3878 * then the caller class is the lookupClass.
3879 *
3880 * Lookup object created by {@link MethodHandles#privateLookupIn(Class, Lookup)}
3881 * from the same module skips the security permission check.
3882 */
3883 void checkSecurityManager(Class<?> refc, MemberName m) {
3884 Objects.requireNonNull(refc);
3885 Objects.requireNonNull(m);
3886
3887 if (allowedModes == TRUSTED) return;
3888
3889 @SuppressWarnings("removal")
3890 SecurityManager smgr = System.getSecurityManager();
3891 if (smgr == null) return;
3892
3893 // Step 1:
3894 boolean fullPrivilegeLookup = hasFullPrivilegeAccess();
3895 if (!fullPrivilegeLookup ||
3896 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
3897 ReflectUtil.checkPackageAccess(refc);
3898 }
3899
3900 // Step 2a:
3901 if (m.isPublic()) return;
3902 if (!fullPrivilegeLookup) {
3903 smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION);
3904 }
3905
3906 // Step 3:
3907 Class<?> defc = m.getDeclaringClass();
3908 if (!fullPrivilegeLookup && defc != refc) {
3909 ReflectUtil.checkPackageAccess(defc);
3910 }
3911 }
3912
3913 void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
3914 boolean wantStatic = (refKind == REF_invokeStatic);
3915 String message;
3916 if (m.isConstructor())
3917 message = "expected a method, not a constructor";
3918 else if (!m.isMethod())
3919 message = "expected a method";
3920 else if (wantStatic != m.isStatic())
3921 message = wantStatic ? "expected a static method" : "expected a non-static method";
3922 else
3923 { checkAccess(refKind, refc, m); return; }
3924 throw m.makeAccessException(message, this);
3925 }
3926
3927 void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
3928 boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
3929 String message;
3930 if (wantStatic != m.isStatic())
3931 message = wantStatic ? "expected a static field" : "expected a non-static field";
3932 else
3933 { checkAccess(refKind, refc, m); return; }
3934 throw m.makeAccessException(message, this);
3935 }
3936
3937 private boolean isArrayClone(byte refKind, Class<?> refc, MemberName m) {
3938 return Modifier.isProtected(m.getModifiers()) &&
3939 refKind == REF_invokeVirtual &&
3940 m.getDeclaringClass() == Object.class &&
3941 m.getName().equals("clone") &&
3942 refc.isArray();
3943 }
3944
3945 /** Check public/protected/private bits on the symbolic reference class and its member. */
3946 void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
3947 assert(m.referenceKindIsConsistentWith(refKind) &&
3948 MethodHandleNatives.refKindIsValid(refKind) &&
3949 (MethodHandleNatives.refKindIsField(refKind) == m.isField()));
3950 int allowedModes = this.allowedModes;
3951 if (allowedModes == TRUSTED) return;
3952 int mods = m.getModifiers();
3953 if (isArrayClone(refKind, refc, m)) {
3954 // The JVM does this hack also.
3955 // (See ClassVerifier::verify_invoke_instructions
3956 // and LinkResolver::check_method_accessability.)
3957 // Because the JVM does not allow separate methods on array types,
3958 // there is no separate method for int[].clone.
3959 // All arrays simply inherit Object.clone.
3960 // But for access checking logic, we make Object.clone
3961 // (normally protected) appear to be public.
3962 // Later on, when the DirectMethodHandle is created,
3963 // its leading argument will be restricted to the
3964 // requested array type.
3965 // N.B. The return type is not adjusted, because
3966 // that is *not* the bytecode behavior.
3967 mods ^= Modifier.PROTECTED | Modifier.PUBLIC;
3968 }
3969 if (Modifier.isProtected(mods) && refKind == REF_newInvokeSpecial) {
3970 // cannot "new" a protected ctor in a different package
3971 mods ^= Modifier.PROTECTED;
3972 }
3973 if (Modifier.isFinal(mods) &&
3974 MethodHandleNatives.refKindIsSetter(refKind))
3975 throw m.makeAccessException("unexpected set of a final field", this);
3976 int requestedModes = fixmods(mods); // adjust 0 => PACKAGE
3977 if ((requestedModes & allowedModes) != 0) {
3978 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
3979 mods, lookupClass(), previousLookupClass(), allowedModes))
3980 return;
3981 } else {
3982 // Protected members can also be checked as if they were package-private.
3983 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
3984 && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
3985 return;
3986 }
3987 throw m.makeAccessException(accessFailedMessage(refc, m), this);
3988 }
3989
3990 String accessFailedMessage(Class<?> refc, MemberName m) {
3991 Class<?> defc = m.getDeclaringClass();
3992 int mods = m.getModifiers();
3993 // check the class first:
3994 boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
3995 (defc == refc ||
3996 Modifier.isPublic(refc.getModifiers())));
3997 if (!classOK && (allowedModes & PACKAGE) != 0) {
3998 // ignore previous lookup class to check if default package access
3999 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), null, FULL_POWER_MODES) &&
4000 (defc == refc ||
4001 VerifyAccess.isClassAccessible(refc, lookupClass(), null, FULL_POWER_MODES)));
4002 }
4003 if (!classOK)
4004 return "class is not public";
4005 if (Modifier.isPublic(mods))
4006 return "access to public member failed"; // (how?, module not readable?)
4007 if (Modifier.isPrivate(mods))
4008 return "member is private";
4009 if (Modifier.isProtected(mods))
4010 return "member is protected";
4011 return "member is private to package";
4012 }
4013
4014 private void checkSpecialCaller(Class<?> specialCaller, Class<?> refc) throws IllegalAccessException {
4015 int allowedModes = this.allowedModes;
4016 if (allowedModes == TRUSTED) return;
4017 if ((lookupModes() & PRIVATE) == 0
4018 || (specialCaller != lookupClass()
4019 // ensure non-abstract methods in superinterfaces can be special-invoked
4020 && !(refc != null && refc.isInterface() && refc.isAssignableFrom(specialCaller))))
4021 throw new MemberName(specialCaller).
4022 makeAccessException("no private access for invokespecial", this);
4023 }
4024
4025 private boolean restrictProtectedReceiver(MemberName method) {
4026 // The accessing class only has the right to use a protected member
4027 // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc.
4028 if (!method.isProtected() || method.isStatic()
4029 || allowedModes == TRUSTED
4030 || method.getDeclaringClass() == lookupClass()
4031 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass()))
4032 return false;
4033 return true;
4034 }
4035 private MethodHandle restrictReceiver(MemberName method, DirectMethodHandle mh, Class<?> caller) throws IllegalAccessException {
4036 assert(!method.isStatic());
4037 // receiver type of mh is too wide; narrow to caller
4038 if (!method.getDeclaringClass().isAssignableFrom(caller)) {
4039 throw method.makeAccessException("caller class must be a subclass below the method", caller);
4040 }
4041 MethodType rawType = mh.type();
4042 if (caller.isAssignableFrom(rawType.parameterType(0))) return mh; // no need to restrict; already narrow
4043 MethodType narrowType = rawType.changeParameterType(0, caller);
4044 assert(!mh.isVarargsCollector()); // viewAsType will lose varargs-ness
4045 assert(mh.viewAsTypeChecks(narrowType, true));
4046 return mh.copyWith(narrowType, mh.form);
4047 }
4048
4049 /** Check access and get the requested method. */
4050 private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException {
4051 final boolean doRestrict = true;
4052 final boolean checkSecurity = true;
4053 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerLookup);
4054 }
4055 /** Check access and get the requested method, for invokespecial with no restriction on the application of narrowing rules. */
4056 private MethodHandle getDirectMethodNoRestrictInvokeSpecial(Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException {
4057 final boolean doRestrict = false;
4058 final boolean checkSecurity = true;
4059 return getDirectMethodCommon(REF_invokeSpecial, refc, method, checkSecurity, doRestrict, callerLookup);
4060 }
4061 /** Check access and get the requested method, eliding security manager checks. */
4062 private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException {
4063 final boolean doRestrict = true;
4064 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
4065 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerLookup);
4066 }
4067 /** Common code for all methods; do not call directly except from immediately above. */
4068 private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method,
4069 boolean checkSecurity,
4070 boolean doRestrict,
4071 Lookup boundCaller) throws IllegalAccessException {
4072 checkMethod(refKind, refc, method);
4073 // Optionally check with the security manager; this isn't needed for unreflect* calls.
4074 if (checkSecurity)
4075 checkSecurityManager(refc, method);
4076 assert(!method.isMethodHandleInvoke());
4077
4078 if (refKind == REF_invokeSpecial &&
4079 refc != lookupClass() &&
4080 !refc.isInterface() && !lookupClass().isInterface() &&
4081 refc != lookupClass().getSuperclass() &&
4082 refc.isAssignableFrom(lookupClass())) {
4083 assert(!method.getName().equals(ConstantDescs.INIT_NAME)); // not this code path
4084
4085 // Per JVMS 6.5, desc. of invokespecial instruction:
4086 // If the method is in a superclass of the LC,
4087 // and if our original search was above LC.super,
4088 // repeat the search (symbolic lookup) from LC.super
4089 // and continue with the direct superclass of that class,
4090 // and so forth, until a match is found or no further superclasses exist.
4091 // FIXME: MemberName.resolve should handle this instead.
4092 Class<?> refcAsSuper = lookupClass();
4093 MemberName m2;
4094 do {
4095 refcAsSuper = refcAsSuper.getSuperclass();
4096 m2 = new MemberName(refcAsSuper,
4097 method.getName(),
4098 method.getMethodType(),
4099 REF_invokeSpecial);
4100 m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull(), allowedModes);
4101 } while (m2 == null && // no method is found yet
4102 refc != refcAsSuper); // search up to refc
4103 if (m2 == null) throw new InternalError(method.toString());
4104 method = m2;
4105 refc = refcAsSuper;
4106 // redo basic checks
4107 checkMethod(refKind, refc, method);
4108 }
4109 DirectMethodHandle dmh = DirectMethodHandle.make(refKind, refc, method, lookupClass());
4110 MethodHandle mh = dmh;
4111 // Optionally narrow the receiver argument to lookupClass using restrictReceiver.
4112 if ((doRestrict && refKind == REF_invokeSpecial) ||
4113 (MethodHandleNatives.refKindHasReceiver(refKind) &&
4114 restrictProtectedReceiver(method) &&
4115 // All arrays simply inherit the protected Object.clone method.
4116 // The leading argument is already restricted to the requested
4117 // array type (not the lookup class).
4118 !isArrayClone(refKind, refc, method))) {
4119 mh = restrictReceiver(method, dmh, lookupClass());
4120 }
4121 mh = maybeBindCaller(method, mh, boundCaller);
4122 mh = mh.setVarargs(method);
4123 return mh;
4124 }
4125 private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh, Lookup boundCaller)
4126 throws IllegalAccessException {
4127 if (boundCaller.allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method))
4128 return mh;
4129
4130 // boundCaller must have full privilege access.
4131 // It should have been checked by findBoundCallerLookup. Safe to check this again.
4132 if ((boundCaller.lookupModes() & ORIGINAL) == 0)
4133 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
4134
4135 assert boundCaller.hasFullPrivilegeAccess();
4136
4137 MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, boundCaller.lookupClass);
4138 // Note: caller will apply varargs after this step happens.
4139 return cbmh;
4140 }
4141
4142 /** Check access and get the requested field. */
4143 private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
4144 final boolean checkSecurity = true;
4145 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
4146 }
4147 /** Check access and get the requested field, eliding security manager checks. */
4148 private MethodHandle getDirectFieldNoSecurityManager(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
4149 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
4150 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
4151 }
4152 /** Common code for all fields; do not call directly except from immediately above. */
4153 private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field,
4154 boolean checkSecurity) throws IllegalAccessException {
4155 checkField(refKind, refc, field);
4156 // Optionally check with the security manager; this isn't needed for unreflect* calls.
4157 if (checkSecurity)
4158 checkSecurityManager(refc, field);
4159 DirectMethodHandle dmh = DirectMethodHandle.make(refc, field);
4160 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) &&
4161 restrictProtectedReceiver(field));
4162 if (doRestrict)
4163 return restrictReceiver(field, dmh, lookupClass());
4164 return dmh;
4165 }
4166 private VarHandle getFieldVarHandle(byte getRefKind, byte putRefKind,
4167 Class<?> refc, MemberName getField, MemberName putField)
4168 throws IllegalAccessException {
4169 final boolean checkSecurity = true;
4170 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
4171 }
4172 private VarHandle getFieldVarHandleNoSecurityManager(byte getRefKind, byte putRefKind,
4173 Class<?> refc, MemberName getField, MemberName putField)
4174 throws IllegalAccessException {
4175 final boolean checkSecurity = false;
4176 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
4177 }
4178 private VarHandle getFieldVarHandleCommon(byte getRefKind, byte putRefKind,
4179 Class<?> refc, MemberName getField, MemberName putField,
4180 boolean checkSecurity) throws IllegalAccessException {
4181 assert getField.isStatic() == putField.isStatic();
4182 assert getField.isGetter() && putField.isSetter();
4183 assert MethodHandleNatives.refKindIsStatic(getRefKind) == MethodHandleNatives.refKindIsStatic(putRefKind);
4184 assert MethodHandleNatives.refKindIsGetter(getRefKind) && MethodHandleNatives.refKindIsSetter(putRefKind);
4185
4186 checkField(getRefKind, refc, getField);
4187 if (checkSecurity)
4188 checkSecurityManager(refc, getField);
4189
4190 if (!putField.isFinal()) {
4191 // A VarHandle does not support updates to final fields, any
4192 // such VarHandle to a final field will be read-only and
4193 // therefore the following write-based accessibility checks are
4194 // only required for non-final fields
4195 checkField(putRefKind, refc, putField);
4196 if (checkSecurity)
4197 checkSecurityManager(refc, putField);
4198 }
4199
4200 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(getRefKind) &&
4201 restrictProtectedReceiver(getField));
4202 if (doRestrict) {
4203 assert !getField.isStatic();
4204 // receiver type of VarHandle is too wide; narrow to caller
4205 if (!getField.getDeclaringClass().isAssignableFrom(lookupClass())) {
4206 throw getField.makeAccessException("caller class must be a subclass below the method", lookupClass());
4207 }
4208 refc = lookupClass();
4209 }
4210 return VarHandles.makeFieldHandle(getField, refc,
4211 this.allowedModes == TRUSTED && !getField.isTrustedFinalField());
4212 }
4213 /** Check access and get the requested constructor. */
4214 private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException {
4215 final boolean checkSecurity = true;
4216 return getDirectConstructorCommon(refc, ctor, checkSecurity);
4217 }
4218 /** Check access and get the requested constructor, eliding security manager checks. */
4219 private MethodHandle getDirectConstructorNoSecurityManager(Class<?> refc, MemberName ctor) throws IllegalAccessException {
4220 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
4221 return getDirectConstructorCommon(refc, ctor, checkSecurity);
4222 }
4223 /** Common code for all constructors; do not call directly except from immediately above. */
4224 private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor,
4225 boolean checkSecurity) throws IllegalAccessException {
4226 assert(ctor.isConstructor());
4227 checkAccess(REF_newInvokeSpecial, refc, ctor);
4228 // Optionally check with the security manager; this isn't needed for unreflect* calls.
4229 if (checkSecurity)
4230 checkSecurityManager(refc, ctor);
4231 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
4232 return DirectMethodHandle.make(ctor).setVarargs(ctor);
4233 }
4234
4235 /** Hook called from the JVM (via MethodHandleNatives) to link MH constants:
4236 */
4237 /*non-public*/
4238 MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type)
4239 throws ReflectiveOperationException {
4240 if (!(type instanceof Class || type instanceof MethodType))
4241 throw new InternalError("unresolved MemberName");
4242 MemberName member = new MemberName(refKind, defc, name, type);
4243 MethodHandle mh = LOOKASIDE_TABLE.get(member);
4244 if (mh != null) {
4245 checkSymbolicClass(defc);
4246 return mh;
4247 }
4248 if (defc == MethodHandle.class && refKind == REF_invokeVirtual) {
4249 // Treat MethodHandle.invoke and invokeExact specially.
4250 mh = findVirtualForMH(member.getName(), member.getMethodType());
4251 if (mh != null) {
4252 return mh;
4253 }
4254 } else if (defc == VarHandle.class && refKind == REF_invokeVirtual) {
4255 // Treat signature-polymorphic methods on VarHandle specially.
4256 mh = findVirtualForVH(member.getName(), member.getMethodType());
4257 if (mh != null) {
4258 return mh;
4259 }
4260 }
4261 MemberName resolved = resolveOrFail(refKind, member);
4262 mh = getDirectMethodForConstant(refKind, defc, resolved);
4263 if (mh instanceof DirectMethodHandle dmh
4264 && canBeCached(refKind, defc, resolved)) {
4265 MemberName key = mh.internalMemberName();
4266 if (key != null) {
4267 key = key.asNormalOriginal();
4268 }
4269 if (member.equals(key)) { // better safe than sorry
4270 LOOKASIDE_TABLE.put(key, dmh);
4271 }
4272 }
4273 return mh;
4274 }
4275 private boolean canBeCached(byte refKind, Class<?> defc, MemberName member) {
4276 if (refKind == REF_invokeSpecial) {
4277 return false;
4278 }
4279 if (!Modifier.isPublic(defc.getModifiers()) ||
4280 !Modifier.isPublic(member.getDeclaringClass().getModifiers()) ||
4281 !member.isPublic() ||
4282 member.isCallerSensitive()) {
4283 return false;
4284 }
4285 ClassLoader loader = defc.getClassLoader();
4286 if (loader != null) {
4287 ClassLoader sysl = ClassLoader.getSystemClassLoader();
4288 boolean found = false;
4289 while (sysl != null) {
4290 if (loader == sysl) { found = true; break; }
4291 sysl = sysl.getParent();
4292 }
4293 if (!found) {
4294 return false;
4295 }
4296 }
4297 try {
4298 MemberName resolved2 = publicLookup().resolveOrNull(refKind,
4299 new MemberName(refKind, defc, member.getName(), member.getType()));
4300 if (resolved2 == null) {
4301 return false;
4302 }
4303 checkSecurityManager(defc, resolved2);
4304 } catch (SecurityException ex) {
4305 return false;
4306 }
4307 return true;
4308 }
4309 private MethodHandle getDirectMethodForConstant(byte refKind, Class<?> defc, MemberName member)
4310 throws ReflectiveOperationException {
4311 if (MethodHandleNatives.refKindIsField(refKind)) {
4312 return getDirectFieldNoSecurityManager(refKind, defc, member);
4313 } else if (MethodHandleNatives.refKindIsMethod(refKind)) {
4314 return getDirectMethodNoSecurityManager(refKind, defc, member, findBoundCallerLookup(member));
4315 } else if (refKind == REF_newInvokeSpecial) {
4316 return getDirectConstructorNoSecurityManager(defc, member);
4317 }
4318 // oops
4319 throw newIllegalArgumentException("bad MethodHandle constant #"+member);
4320 }
4321
4322 static ConcurrentHashMap<MemberName, DirectMethodHandle> LOOKASIDE_TABLE = new ConcurrentHashMap<>();
4323 }
4324
4325 /**
4326 * Produces a method handle constructing arrays of a desired type,
4327 * as if by the {@code anewarray} bytecode.
4328 * The return type of the method handle will be the array type.
4329 * The type of its sole argument will be {@code int}, which specifies the size of the array.
4330 *
4331 * <p> If the returned method handle is invoked with a negative
4332 * array size, a {@code NegativeArraySizeException} will be thrown.
4333 *
4334 * @param arrayClass an array type
4335 * @return a method handle which can create arrays of the given type
4336 * @throws NullPointerException if the argument is {@code null}
4337 * @throws IllegalArgumentException if {@code arrayClass} is not an array type
4338 * @see java.lang.reflect.Array#newInstance(Class, int)
4339 * @jvms 6.5 {@code anewarray} Instruction
4340 * @since 9
4341 */
4342 public static MethodHandle arrayConstructor(Class<?> arrayClass) throws IllegalArgumentException {
4343 if (!arrayClass.isArray()) {
4344 throw newIllegalArgumentException("not an array class: " + arrayClass.getName());
4345 }
4346 MethodHandle ani = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_Array_newInstance).
4347 bindTo(arrayClass.getComponentType());
4348 return ani.asType(ani.type().changeReturnType(arrayClass));
4349 }
4350
4351 /**
4352 * Produces a method handle returning the length of an array,
4353 * as if by the {@code arraylength} bytecode.
4354 * The type of the method handle will have {@code int} as return type,
4355 * and its sole argument will be the array type.
4356 *
4357 * <p> If the returned method handle is invoked with a {@code null}
4358 * array reference, a {@code NullPointerException} will be thrown.
4359 *
4360 * @param arrayClass an array type
4361 * @return a method handle which can retrieve the length of an array of the given array type
4362 * @throws NullPointerException if the argument is {@code null}
4363 * @throws IllegalArgumentException if arrayClass is not an array type
4364 * @jvms 6.5 {@code arraylength} Instruction
4365 * @since 9
4366 */
4367 public static MethodHandle arrayLength(Class<?> arrayClass) throws IllegalArgumentException {
4368 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.LENGTH);
4369 }
4370
4371 /**
4372 * Produces a method handle giving read access to elements of an array,
4373 * as if by the {@code aaload} bytecode.
4374 * The type of the method handle will have a return type of the array's
4375 * element type. Its first argument will be the array type,
4376 * and the second will be {@code int}.
4377 *
4378 * <p> When the returned method handle is invoked,
4379 * the array reference and array index are checked.
4380 * A {@code NullPointerException} will be thrown if the array reference
4381 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
4382 * thrown if the index is negative or if it is greater than or equal to
4383 * the length of the array.
4384 *
4385 * @param arrayClass an array type
4386 * @return a method handle which can load values from the given array type
4387 * @throws NullPointerException if the argument is null
4388 * @throws IllegalArgumentException if arrayClass is not an array type
4389 * @jvms 6.5 {@code aaload} Instruction
4390 */
4391 public static MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException {
4392 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.GET);
4393 }
4394
4395 /**
4396 * Produces a method handle giving write access to elements of an array,
4397 * as if by the {@code astore} bytecode.
4398 * The type of the method handle will have a void return type.
4399 * Its last argument will be the array's element type.
4400 * The first and second arguments will be the array type and int.
4401 *
4402 * <p> When the returned method handle is invoked,
4403 * the array reference and array index are checked.
4404 * A {@code NullPointerException} will be thrown if the array reference
4405 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
4406 * thrown if the index is negative or if it is greater than or equal to
4407 * the length of the array.
4408 *
4409 * @param arrayClass the class of an array
4410 * @return a method handle which can store values into the array type
4411 * @throws NullPointerException if the argument is null
4412 * @throws IllegalArgumentException if arrayClass is not an array type
4413 * @jvms 6.5 {@code aastore} Instruction
4414 */
4415 public static MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException {
4416 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.SET);
4417 }
4418
4419 /**
4420 * Produces a VarHandle giving access to elements of an array of type
4421 * {@code arrayClass}. The VarHandle's variable type is the component type
4422 * of {@code arrayClass} and the list of coordinate types is
4423 * {@code (arrayClass, int)}, where the {@code int} coordinate type
4424 * corresponds to an argument that is an index into an array.
4425 * <p>
4426 * Certain access modes of the returned VarHandle are unsupported under
4427 * the following conditions:
4428 * <ul>
4429 * <li>if the component type is anything other than {@code byte},
4430 * {@code short}, {@code char}, {@code int}, {@code long},
4431 * {@code float}, or {@code double} then numeric atomic update access
4432 * modes are unsupported.
4433 * <li>if the component type is anything other than {@code boolean},
4434 * {@code byte}, {@code short}, {@code char}, {@code int} or
4435 * {@code long} then bitwise atomic update access modes are
4436 * unsupported.
4437 * </ul>
4438 * <p>
4439 * If the component type is {@code float} or {@code double} then numeric
4440 * and atomic update access modes compare values using their bitwise
4441 * representation (see {@link Float#floatToRawIntBits} and
4442 * {@link Double#doubleToRawLongBits}, respectively).
4443 *
4444 * <p> When the returned {@code VarHandle} is invoked,
4445 * the array reference and array index are checked.
4446 * A {@code NullPointerException} will be thrown if the array reference
4447 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
4448 * thrown if the index is negative or if it is greater than or equal to
4449 * the length of the array.
4450 *
4451 * @apiNote
4452 * Bitwise comparison of {@code float} values or {@code double} values,
4453 * as performed by the numeric and atomic update access modes, differ
4454 * from the primitive {@code ==} operator and the {@link Float#equals}
4455 * and {@link Double#equals} methods, specifically with respect to
4456 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
4457 * Care should be taken when performing a compare and set or a compare
4458 * and exchange operation with such values since the operation may
4459 * unexpectedly fail.
4460 * There are many possible NaN values that are considered to be
4461 * {@code NaN} in Java, although no IEEE 754 floating-point operation
4462 * provided by Java can distinguish between them. Operation failure can
4463 * occur if the expected or witness value is a NaN value and it is
4464 * transformed (perhaps in a platform specific manner) into another NaN
4465 * value, and thus has a different bitwise representation (see
4466 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
4467 * details).
4468 * The values {@code -0.0} and {@code +0.0} have different bitwise
4469 * representations but are considered equal when using the primitive
4470 * {@code ==} operator. Operation failure can occur if, for example, a
4471 * numeric algorithm computes an expected value to be say {@code -0.0}
4472 * and previously computed the witness value to be say {@code +0.0}.
4473 * @param arrayClass the class of an array, of type {@code T[]}
4474 * @return a VarHandle giving access to elements of an array
4475 * @throws NullPointerException if the arrayClass is null
4476 * @throws IllegalArgumentException if arrayClass is not an array type
4477 * @since 9
4478 */
4479 public static VarHandle arrayElementVarHandle(Class<?> arrayClass) throws IllegalArgumentException {
4480 return VarHandles.makeArrayElementHandle(arrayClass);
4481 }
4482
4483 /**
4484 * Produces a VarHandle giving access to elements of a {@code byte[]} array
4485 * viewed as if it were a different primitive array type, such as
4486 * {@code int[]} or {@code long[]}.
4487 * The VarHandle's variable type is the component type of
4488 * {@code viewArrayClass} and the list of coordinate types is
4489 * {@code (byte[], int)}, where the {@code int} coordinate type
4490 * corresponds to an argument that is an index into a {@code byte[]} array.
4491 * The returned VarHandle accesses bytes at an index in a {@code byte[]}
4492 * array, composing bytes to or from a value of the component type of
4493 * {@code viewArrayClass} according to the given endianness.
4494 * <p>
4495 * The supported component types (variables types) are {@code short},
4496 * {@code char}, {@code int}, {@code long}, {@code float} and
4497 * {@code double}.
4498 * <p>
4499 * Access of bytes at a given index will result in an
4500 * {@code ArrayIndexOutOfBoundsException} if the index is less than {@code 0}
4501 * or greater than the {@code byte[]} array length minus the size (in bytes)
4502 * of {@code T}.
4503 * <p>
4504 * Access of bytes at an index may be aligned or misaligned for {@code T},
4505 * with respect to the underlying memory address, {@code A} say, associated
4506 * with the array and index.
4507 * If access is misaligned then access for anything other than the
4508 * {@code get} and {@code set} access modes will result in an
4509 * {@code IllegalStateException}. In such cases atomic access is only
4510 * guaranteed with respect to the largest power of two that divides the GCD
4511 * of {@code A} and the size (in bytes) of {@code T}.
4512 * If access is aligned then following access modes are supported and are
4513 * guaranteed to support atomic access:
4514 * <ul>
4515 * <li>read write access modes for all {@code T}, with the exception of
4516 * access modes {@code get} and {@code set} for {@code long} and
4517 * {@code double} on 32-bit platforms.
4518 * <li>atomic update access modes for {@code int}, {@code long},
4519 * {@code float} or {@code double}.
4520 * (Future major platform releases of the JDK may support additional
4521 * types for certain currently unsupported access modes.)
4522 * <li>numeric atomic update access modes for {@code int} and {@code long}.
4523 * (Future major platform releases of the JDK may support additional
4524 * numeric types for certain currently unsupported access modes.)
4525 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
4526 * (Future major platform releases of the JDK may support additional
4527 * numeric types for certain currently unsupported access modes.)
4528 * </ul>
4529 * <p>
4530 * Misaligned access, and therefore atomicity guarantees, may be determined
4531 * for {@code byte[]} arrays without operating on a specific array. Given
4532 * an {@code index}, {@code T} and its corresponding boxed type,
4533 * {@code T_BOX}, misalignment may be determined as follows:
4534 * <pre>{@code
4535 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
4536 * int misalignedAtZeroIndex = ByteBuffer.wrap(new byte[0]).
4537 * alignmentOffset(0, sizeOfT);
4538 * int misalignedAtIndex = (misalignedAtZeroIndex + index) % sizeOfT;
4539 * boolean isMisaligned = misalignedAtIndex != 0;
4540 * }</pre>
4541 * <p>
4542 * If the variable type is {@code float} or {@code double} then atomic
4543 * update access modes compare values using their bitwise representation
4544 * (see {@link Float#floatToRawIntBits} and
4545 * {@link Double#doubleToRawLongBits}, respectively).
4546 * @param viewArrayClass the view array class, with a component type of
4547 * type {@code T}
4548 * @param byteOrder the endianness of the view array elements, as
4549 * stored in the underlying {@code byte} array
4550 * @return a VarHandle giving access to elements of a {@code byte[]} array
4551 * viewed as if elements corresponding to the components type of the view
4552 * array class
4553 * @throws NullPointerException if viewArrayClass or byteOrder is null
4554 * @throws IllegalArgumentException if viewArrayClass is not an array type
4555 * @throws UnsupportedOperationException if the component type of
4556 * viewArrayClass is not supported as a variable type
4557 * @since 9
4558 */
4559 public static VarHandle byteArrayViewVarHandle(Class<?> viewArrayClass,
4560 ByteOrder byteOrder) throws IllegalArgumentException {
4561 Objects.requireNonNull(byteOrder);
4562 return VarHandles.byteArrayViewHandle(viewArrayClass,
4563 byteOrder == ByteOrder.BIG_ENDIAN);
4564 }
4565
4566 /**
4567 * Produces a VarHandle giving access to elements of a {@code ByteBuffer}
4568 * viewed as if it were an array of elements of a different primitive
4569 * component type to that of {@code byte}, such as {@code int[]} or
4570 * {@code long[]}.
4571 * The VarHandle's variable type is the component type of
4572 * {@code viewArrayClass} and the list of coordinate types is
4573 * {@code (ByteBuffer, int)}, where the {@code int} coordinate type
4574 * corresponds to an argument that is an index into a {@code byte[]} array.
4575 * The returned VarHandle accesses bytes at an index in a
4576 * {@code ByteBuffer}, composing bytes to or from a value of the component
4577 * type of {@code viewArrayClass} according to the given endianness.
4578 * <p>
4579 * The supported component types (variables types) are {@code short},
4580 * {@code char}, {@code int}, {@code long}, {@code float} and
4581 * {@code double}.
4582 * <p>
4583 * Access will result in a {@code ReadOnlyBufferException} for anything
4584 * other than the read access modes if the {@code ByteBuffer} is read-only.
4585 * <p>
4586 * Access of bytes at a given index will result in an
4587 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
4588 * or greater than the {@code ByteBuffer} limit minus the size (in bytes) of
4589 * {@code T}.
4590 * <p>
4591 * Access of bytes at an index may be aligned or misaligned for {@code T},
4592 * with respect to the underlying memory address, {@code A} say, associated
4593 * with the {@code ByteBuffer} and index.
4594 * If access is misaligned then access for anything other than the
4595 * {@code get} and {@code set} access modes will result in an
4596 * {@code IllegalStateException}. In such cases atomic access is only
4597 * guaranteed with respect to the largest power of two that divides the GCD
4598 * of {@code A} and the size (in bytes) of {@code T}.
4599 * If access is aligned then following access modes are supported and are
4600 * guaranteed to support atomic access:
4601 * <ul>
4602 * <li>read write access modes for all {@code T}, with the exception of
4603 * access modes {@code get} and {@code set} for {@code long} and
4604 * {@code double} on 32-bit platforms.
4605 * <li>atomic update access modes for {@code int}, {@code long},
4606 * {@code float} or {@code double}.
4607 * (Future major platform releases of the JDK may support additional
4608 * types for certain currently unsupported access modes.)
4609 * <li>numeric atomic update access modes for {@code int} and {@code long}.
4610 * (Future major platform releases of the JDK may support additional
4611 * numeric types for certain currently unsupported access modes.)
4612 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
4613 * (Future major platform releases of the JDK may support additional
4614 * numeric types for certain currently unsupported access modes.)
4615 * </ul>
4616 * <p>
4617 * Misaligned access, and therefore atomicity guarantees, may be determined
4618 * for a {@code ByteBuffer}, {@code bb} (direct or otherwise), an
4619 * {@code index}, {@code T} and its corresponding boxed type,
4620 * {@code T_BOX}, as follows:
4621 * <pre>{@code
4622 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
4623 * ByteBuffer bb = ...
4624 * int misalignedAtIndex = bb.alignmentOffset(index, sizeOfT);
4625 * boolean isMisaligned = misalignedAtIndex != 0;
4626 * }</pre>
4627 * <p>
4628 * If the variable type is {@code float} or {@code double} then atomic
4629 * update access modes compare values using their bitwise representation
4630 * (see {@link Float#floatToRawIntBits} and
4631 * {@link Double#doubleToRawLongBits}, respectively).
4632 * @param viewArrayClass the view array class, with a component type of
4633 * type {@code T}
4634 * @param byteOrder the endianness of the view array elements, as
4635 * stored in the underlying {@code ByteBuffer} (Note this overrides the
4636 * endianness of a {@code ByteBuffer})
4637 * @return a VarHandle giving access to elements of a {@code ByteBuffer}
4638 * viewed as if elements corresponding to the components type of the view
4639 * array class
4640 * @throws NullPointerException if viewArrayClass or byteOrder is null
4641 * @throws IllegalArgumentException if viewArrayClass is not an array type
4642 * @throws UnsupportedOperationException if the component type of
4643 * viewArrayClass is not supported as a variable type
4644 * @since 9
4645 */
4646 public static VarHandle byteBufferViewVarHandle(Class<?> viewArrayClass,
4647 ByteOrder byteOrder) throws IllegalArgumentException {
4648 Objects.requireNonNull(byteOrder);
4649 return VarHandles.makeByteBufferViewHandle(viewArrayClass,
4650 byteOrder == ByteOrder.BIG_ENDIAN);
4651 }
4652
4653
4654 /// method handle invocation (reflective style)
4655
4656 /**
4657 * Produces a method handle which will invoke any method handle of the
4658 * given {@code type}, with a given number of trailing arguments replaced by
4659 * a single trailing {@code Object[]} array.
4660 * The resulting invoker will be a method handle with the following
4661 * arguments:
4662 * <ul>
4663 * <li>a single {@code MethodHandle} target
4664 * <li>zero or more leading values (counted by {@code leadingArgCount})
4665 * <li>an {@code Object[]} array containing trailing arguments
4666 * </ul>
4667 * <p>
4668 * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
4669 * the indicated {@code type}.
4670 * That is, if the target is exactly of the given {@code type}, it will behave
4671 * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
4672 * is used to convert the target to the required {@code type}.
4673 * <p>
4674 * The type of the returned invoker will not be the given {@code type}, but rather
4675 * will have all parameters except the first {@code leadingArgCount}
4676 * replaced by a single array of type {@code Object[]}, which will be
4677 * the final parameter.
4678 * <p>
4679 * Before invoking its target, the invoker will spread the final array, apply
4680 * reference casts as necessary, and unbox and widen primitive arguments.
4681 * If, when the invoker is called, the supplied array argument does
4682 * not have the correct number of elements, the invoker will throw
4683 * an {@link IllegalArgumentException} instead of invoking the target.
4684 * <p>
4685 * This method is equivalent to the following code (though it may be more efficient):
4686 * {@snippet lang="java" :
4687 MethodHandle invoker = MethodHandles.invoker(type);
4688 int spreadArgCount = type.parameterCount() - leadingArgCount;
4689 invoker = invoker.asSpreader(Object[].class, spreadArgCount);
4690 return invoker;
4691 * }
4692 * This method throws no reflective or security exceptions.
4693 * @param type the desired target type
4694 * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
4695 * @return a method handle suitable for invoking any method handle of the given type
4696 * @throws NullPointerException if {@code type} is null
4697 * @throws IllegalArgumentException if {@code leadingArgCount} is not in
4698 * the range from 0 to {@code type.parameterCount()} inclusive,
4699 * or if the resulting method handle's type would have
4700 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4701 */
4702 public static MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
4703 if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
4704 throw newIllegalArgumentException("bad argument count", leadingArgCount);
4705 type = type.asSpreaderType(Object[].class, leadingArgCount, type.parameterCount() - leadingArgCount);
4706 return type.invokers().spreadInvoker(leadingArgCount);
4707 }
4708
4709 /**
4710 * Produces a special <em>invoker method handle</em> which can be used to
4711 * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
4712 * The resulting invoker will have a type which is
4713 * exactly equal to the desired type, except that it will accept
4714 * an additional leading argument of type {@code MethodHandle}.
4715 * <p>
4716 * This method is equivalent to the following code (though it may be more efficient):
4717 * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)}
4718 *
4719 * <p style="font-size:smaller;">
4720 * <em>Discussion:</em>
4721 * Invoker method handles can be useful when working with variable method handles
4722 * of unknown types.
4723 * For example, to emulate an {@code invokeExact} call to a variable method
4724 * handle {@code M}, extract its type {@code T},
4725 * look up the invoker method {@code X} for {@code T},
4726 * and call the invoker method, as {@code X.invoke(T, A...)}.
4727 * (It would not work to call {@code X.invokeExact}, since the type {@code T}
4728 * is unknown.)
4729 * If spreading, collecting, or other argument transformations are required,
4730 * they can be applied once to the invoker {@code X} and reused on many {@code M}
4731 * method handle values, as long as they are compatible with the type of {@code X}.
4732 * <p style="font-size:smaller;">
4733 * <em>(Note: The invoker method is not available via the Core Reflection API.
4734 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
4735 * on the declared {@code invokeExact} or {@code invoke} method will raise an
4736 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
4737 * <p>
4738 * This method throws no reflective or security exceptions.
4739 * @param type the desired target type
4740 * @return a method handle suitable for invoking any method handle of the given type
4741 * @throws IllegalArgumentException if the resulting method handle's type would have
4742 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4743 */
4744 public static MethodHandle exactInvoker(MethodType type) {
4745 return type.invokers().exactInvoker();
4746 }
4747
4748 /**
4749 * Produces a special <em>invoker method handle</em> which can be used to
4750 * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
4751 * The resulting invoker will have a type which is
4752 * exactly equal to the desired type, except that it will accept
4753 * an additional leading argument of type {@code MethodHandle}.
4754 * <p>
4755 * Before invoking its target, if the target differs from the expected type,
4756 * the invoker will apply reference casts as
4757 * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
4758 * Similarly, the return value will be converted as necessary.
4759 * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
4760 * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
4761 * <p>
4762 * This method is equivalent to the following code (though it may be more efficient):
4763 * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)}
4764 * <p style="font-size:smaller;">
4765 * <em>Discussion:</em>
4766 * A {@linkplain MethodType#genericMethodType general method type} is one which
4767 * mentions only {@code Object} arguments and return values.
4768 * An invoker for such a type is capable of calling any method handle
4769 * of the same arity as the general type.
4770 * <p style="font-size:smaller;">
4771 * <em>(Note: The invoker method is not available via the Core Reflection API.
4772 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
4773 * on the declared {@code invokeExact} or {@code invoke} method will raise an
4774 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
4775 * <p>
4776 * This method throws no reflective or security exceptions.
4777 * @param type the desired target type
4778 * @return a method handle suitable for invoking any method handle convertible to the given type
4779 * @throws IllegalArgumentException if the resulting method handle's type would have
4780 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4781 */
4782 public static MethodHandle invoker(MethodType type) {
4783 return type.invokers().genericInvoker();
4784 }
4785
4786 /**
4787 * Produces a special <em>invoker method handle</em> which can be used to
4788 * invoke a signature-polymorphic access mode method on any VarHandle whose
4789 * associated access mode type is compatible with the given type.
4790 * The resulting invoker will have a type which is exactly equal to the
4791 * desired given type, except that it will accept an additional leading
4792 * argument of type {@code VarHandle}.
4793 *
4794 * @param accessMode the VarHandle access mode
4795 * @param type the desired target type
4796 * @return a method handle suitable for invoking an access mode method of
4797 * any VarHandle whose access mode type is of the given type.
4798 * @since 9
4799 */
4800 public static MethodHandle varHandleExactInvoker(VarHandle.AccessMode accessMode, MethodType type) {
4801 return type.invokers().varHandleMethodExactInvoker(accessMode);
4802 }
4803
4804 /**
4805 * Produces a special <em>invoker method handle</em> which can be used to
4806 * invoke a signature-polymorphic access mode method on any VarHandle whose
4807 * associated access mode type is compatible with the given type.
4808 * The resulting invoker will have a type which is exactly equal to the
4809 * desired given type, except that it will accept an additional leading
4810 * argument of type {@code VarHandle}.
4811 * <p>
4812 * Before invoking its target, if the access mode type differs from the
4813 * desired given type, the invoker will apply reference casts as necessary
4814 * and box, unbox, or widen primitive values, as if by
4815 * {@link MethodHandle#asType asType}. Similarly, the return value will be
4816 * converted as necessary.
4817 * <p>
4818 * This method is equivalent to the following code (though it may be more
4819 * efficient): {@code publicLookup().findVirtual(VarHandle.class, accessMode.name(), type)}
4820 *
4821 * @param accessMode the VarHandle access mode
4822 * @param type the desired target type
4823 * @return a method handle suitable for invoking an access mode method of
4824 * any VarHandle whose access mode type is convertible to the given
4825 * type.
4826 * @since 9
4827 */
4828 public static MethodHandle varHandleInvoker(VarHandle.AccessMode accessMode, MethodType type) {
4829 return type.invokers().varHandleMethodInvoker(accessMode);
4830 }
4831
4832 /*non-public*/
4833 static MethodHandle basicInvoker(MethodType type) {
4834 return type.invokers().basicInvoker();
4835 }
4836
4837 /// method handle modification (creation from other method handles)
4838
4839 /**
4840 * Produces a method handle which adapts the type of the
4841 * given method handle to a new type by pairwise argument and return type conversion.
4842 * The original type and new type must have the same number of arguments.
4843 * The resulting method handle is guaranteed to report a type
4844 * which is equal to the desired new type.
4845 * <p>
4846 * If the original type and new type are equal, returns target.
4847 * <p>
4848 * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
4849 * and some additional conversions are also applied if those conversions fail.
4850 * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied
4851 * if possible, before or instead of any conversions done by {@code asType}:
4852 * <ul>
4853 * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type,
4854 * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast.
4855 * (This treatment of interfaces follows the usage of the bytecode verifier.)
4856 * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive,
4857 * the boolean is converted to a byte value, 1 for true, 0 for false.
4858 * (This treatment follows the usage of the bytecode verifier.)
4859 * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive,
4860 * <em>T0</em> is converted to byte via Java casting conversion (JLS {@jls 5.5}),
4861 * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}.
4862 * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean,
4863 * then a Java casting conversion (JLS {@jls 5.5}) is applied.
4864 * (Specifically, <em>T0</em> will convert to <em>T1</em> by
4865 * widening and/or narrowing.)
4866 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
4867 * conversion will be applied at runtime, possibly followed
4868 * by a Java casting conversion (JLS {@jls 5.5}) on the primitive value,
4869 * possibly followed by a conversion from byte to boolean by testing
4870 * the low-order bit.
4871 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive,
4872 * and if the reference is null at runtime, a zero value is introduced.
4873 * </ul>
4874 * @param target the method handle to invoke after arguments are retyped
4875 * @param newType the expected type of the new method handle
4876 * @return a method handle which delegates to the target after performing
4877 * any necessary argument conversions, and arranges for any
4878 * necessary return value conversions
4879 * @throws NullPointerException if either argument is null
4880 * @throws WrongMethodTypeException if the conversion cannot be made
4881 * @see MethodHandle#asType
4882 */
4883 public static MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
4884 explicitCastArgumentsChecks(target, newType);
4885 // use the asTypeCache when possible:
4886 MethodType oldType = target.type();
4887 if (oldType == newType) return target;
4888 if (oldType.explicitCastEquivalentToAsType(newType)) {
4889 return target.asFixedArity().asType(newType);
4890 }
4891 return MethodHandleImpl.makePairwiseConvert(target, newType, false);
4892 }
4893
4894 private static void explicitCastArgumentsChecks(MethodHandle target, MethodType newType) {
4895 if (target.type().parameterCount() != newType.parameterCount()) {
4896 throw new WrongMethodTypeException("cannot explicitly cast " + target + " to " + newType);
4897 }
4898 }
4899
4900 /**
4901 * Produces a method handle which adapts the calling sequence of the
4902 * given method handle to a new type, by reordering the arguments.
4903 * The resulting method handle is guaranteed to report a type
4904 * which is equal to the desired new type.
4905 * <p>
4906 * The given array controls the reordering.
4907 * Call {@code #I} the number of incoming parameters (the value
4908 * {@code newType.parameterCount()}, and call {@code #O} the number
4909 * of outgoing parameters (the value {@code target.type().parameterCount()}).
4910 * Then the length of the reordering array must be {@code #O},
4911 * and each element must be a non-negative number less than {@code #I}.
4912 * For every {@code N} less than {@code #O}, the {@code N}-th
4913 * outgoing argument will be taken from the {@code I}-th incoming
4914 * argument, where {@code I} is {@code reorder[N]}.
4915 * <p>
4916 * No argument or return value conversions are applied.
4917 * The type of each incoming argument, as determined by {@code newType},
4918 * must be identical to the type of the corresponding outgoing parameter
4919 * or parameters in the target method handle.
4920 * The return type of {@code newType} must be identical to the return
4921 * type of the original target.
4922 * <p>
4923 * The reordering array need not specify an actual permutation.
4924 * An incoming argument will be duplicated if its index appears
4925 * more than once in the array, and an incoming argument will be dropped
4926 * if its index does not appear in the array.
4927 * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
4928 * incoming arguments which are not mentioned in the reordering array
4929 * may be of any type, as determined only by {@code newType}.
4930 * {@snippet lang="java" :
4931 import static java.lang.invoke.MethodHandles.*;
4932 import static java.lang.invoke.MethodType.*;
4933 ...
4934 MethodType intfn1 = methodType(int.class, int.class);
4935 MethodType intfn2 = methodType(int.class, int.class, int.class);
4936 MethodHandle sub = ... (int x, int y) -> (x-y) ...;
4937 assert(sub.type().equals(intfn2));
4938 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
4939 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
4940 assert((int)rsub.invokeExact(1, 100) == 99);
4941 MethodHandle add = ... (int x, int y) -> (x+y) ...;
4942 assert(add.type().equals(intfn2));
4943 MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
4944 assert(twice.type().equals(intfn1));
4945 assert((int)twice.invokeExact(21) == 42);
4946 * }
4947 * <p>
4948 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4949 * variable-arity method handle}, even if the original target method handle was.
4950 * @param target the method handle to invoke after arguments are reordered
4951 * @param newType the expected type of the new method handle
4952 * @param reorder an index array which controls the reordering
4953 * @return a method handle which delegates to the target after it
4954 * drops unused arguments and moves and/or duplicates the other arguments
4955 * @throws NullPointerException if any argument is null
4956 * @throws IllegalArgumentException if the index array length is not equal to
4957 * the arity of the target, or if any index array element
4958 * not a valid index for a parameter of {@code newType},
4959 * or if two corresponding parameter types in
4960 * {@code target.type()} and {@code newType} are not identical,
4961 */
4962 public static MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
4963 reorder = reorder.clone(); // get a private copy
4964 MethodType oldType = target.type();
4965 permuteArgumentChecks(reorder, newType, oldType);
4966 // first detect dropped arguments and handle them separately
4967 int[] originalReorder = reorder;
4968 BoundMethodHandle result = target.rebind();
4969 LambdaForm form = result.form;
4970 int newArity = newType.parameterCount();
4971 // Normalize the reordering into a real permutation,
4972 // by removing duplicates and adding dropped elements.
4973 // This somewhat improves lambda form caching, as well
4974 // as simplifying the transform by breaking it up into steps.
4975 for (int ddIdx; (ddIdx = findFirstDupOrDrop(reorder, newArity)) != 0; ) {
4976 if (ddIdx > 0) {
4977 // We found a duplicated entry at reorder[ddIdx].
4978 // Example: (x,y,z)->asList(x,y,z)
4979 // permuted by [1*,0,1] => (a0,a1)=>asList(a1,a0,a1)
4980 // permuted by [0,1,0*] => (a0,a1)=>asList(a0,a1,a0)
4981 // The starred element corresponds to the argument
4982 // deleted by the dupArgumentForm transform.
4983 int srcPos = ddIdx, dstPos = srcPos, dupVal = reorder[srcPos];
4984 boolean killFirst = false;
4985 for (int val; (val = reorder[--dstPos]) != dupVal; ) {
4986 // Set killFirst if the dup is larger than an intervening position.
4987 // This will remove at least one inversion from the permutation.
4988 if (dupVal > val) killFirst = true;
4989 }
4990 if (!killFirst) {
4991 srcPos = dstPos;
4992 dstPos = ddIdx;
4993 }
4994 form = form.editor().dupArgumentForm(1 + srcPos, 1 + dstPos);
4995 assert (reorder[srcPos] == reorder[dstPos]);
4996 oldType = oldType.dropParameterTypes(dstPos, dstPos + 1);
4997 // contract the reordering by removing the element at dstPos
4998 int tailPos = dstPos + 1;
4999 System.arraycopy(reorder, tailPos, reorder, dstPos, reorder.length - tailPos);
5000 reorder = Arrays.copyOf(reorder, reorder.length - 1);
5001 } else {
5002 int dropVal = ~ddIdx, insPos = 0;
5003 while (insPos < reorder.length && reorder[insPos] < dropVal) {
5004 // Find first element of reorder larger than dropVal.
5005 // This is where we will insert the dropVal.
5006 insPos += 1;
5007 }
5008 Class<?> ptype = newType.parameterType(dropVal);
5009 form = form.editor().addArgumentForm(1 + insPos, BasicType.basicType(ptype));
5010 oldType = oldType.insertParameterTypes(insPos, ptype);
5011 // expand the reordering by inserting an element at insPos
5012 int tailPos = insPos + 1;
5013 reorder = Arrays.copyOf(reorder, reorder.length + 1);
5014 System.arraycopy(reorder, insPos, reorder, tailPos, reorder.length - tailPos);
5015 reorder[insPos] = dropVal;
5016 }
5017 assert (permuteArgumentChecks(reorder, newType, oldType));
5018 }
5019 assert (reorder.length == newArity); // a perfect permutation
5020 // Note: This may cache too many distinct LFs. Consider backing off to varargs code.
5021 form = form.editor().permuteArgumentsForm(1, reorder);
5022 if (newType == result.type() && form == result.internalForm())
5023 return result;
5024 return result.copyWith(newType, form);
5025 }
5026
5027 /**
5028 * Return an indication of any duplicate or omission in reorder.
5029 * If the reorder contains a duplicate entry, return the index of the second occurrence.
5030 * Otherwise, return ~(n), for the first n in [0..newArity-1] that is not present in reorder.
5031 * Otherwise, return zero.
5032 * If an element not in [0..newArity-1] is encountered, return reorder.length.
5033 */
5034 private static int findFirstDupOrDrop(int[] reorder, int newArity) {
5035 final int BIT_LIMIT = 63; // max number of bits in bit mask
5036 if (newArity < BIT_LIMIT) {
5037 long mask = 0;
5038 for (int i = 0; i < reorder.length; i++) {
5039 int arg = reorder[i];
5040 if (arg >= newArity) {
5041 return reorder.length;
5042 }
5043 long bit = 1L << arg;
5044 if ((mask & bit) != 0) {
5045 return i; // >0 indicates a dup
5046 }
5047 mask |= bit;
5048 }
5049 if (mask == (1L << newArity) - 1) {
5050 assert(Long.numberOfTrailingZeros(Long.lowestOneBit(~mask)) == newArity);
5051 return 0;
5052 }
5053 // find first zero
5054 long zeroBit = Long.lowestOneBit(~mask);
5055 int zeroPos = Long.numberOfTrailingZeros(zeroBit);
5056 assert(zeroPos <= newArity);
5057 if (zeroPos == newArity) {
5058 return 0;
5059 }
5060 return ~zeroPos;
5061 } else {
5062 // same algorithm, different bit set
5063 BitSet mask = new BitSet(newArity);
5064 for (int i = 0; i < reorder.length; i++) {
5065 int arg = reorder[i];
5066 if (arg >= newArity) {
5067 return reorder.length;
5068 }
5069 if (mask.get(arg)) {
5070 return i; // >0 indicates a dup
5071 }
5072 mask.set(arg);
5073 }
5074 int zeroPos = mask.nextClearBit(0);
5075 assert(zeroPos <= newArity);
5076 if (zeroPos == newArity) {
5077 return 0;
5078 }
5079 return ~zeroPos;
5080 }
5081 }
5082
5083 static boolean permuteArgumentChecks(int[] reorder, MethodType newType, MethodType oldType) {
5084 if (newType.returnType() != oldType.returnType())
5085 throw newIllegalArgumentException("return types do not match",
5086 oldType, newType);
5087 if (reorder.length != oldType.parameterCount())
5088 throw newIllegalArgumentException("old type parameter count and reorder array length do not match",
5089 oldType, Arrays.toString(reorder));
5090
5091 int limit = newType.parameterCount();
5092 for (int j = 0; j < reorder.length; j++) {
5093 int i = reorder[j];
5094 if (i < 0 || i >= limit) {
5095 throw newIllegalArgumentException("index is out of bounds for new type",
5096 i, newType);
5097 }
5098 Class<?> src = newType.parameterType(i);
5099 Class<?> dst = oldType.parameterType(j);
5100 if (src != dst)
5101 throw newIllegalArgumentException("parameter types do not match after reorder",
5102 oldType, newType);
5103 }
5104 return true;
5105 }
5106
5107 /**
5108 * Produces a method handle of the requested return type which returns the given
5109 * constant value every time it is invoked.
5110 * <p>
5111 * Before the method handle is returned, the passed-in value is converted to the requested type.
5112 * If the requested type is primitive, widening primitive conversions are attempted,
5113 * else reference conversions are attempted.
5114 * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
5115 * @param type the return type of the desired method handle
5116 * @param value the value to return
5117 * @return a method handle of the given return type and no arguments, which always returns the given value
5118 * @throws NullPointerException if the {@code type} argument is null
5119 * @throws ClassCastException if the value cannot be converted to the required return type
5120 * @throws IllegalArgumentException if the given type is {@code void.class}
5121 */
5122 public static MethodHandle constant(Class<?> type, Object value) {
5123 if (type.isPrimitive()) {
5124 if (type == void.class)
5125 throw newIllegalArgumentException("void type");
5126 Wrapper w = Wrapper.forPrimitiveType(type);
5127 value = w.convert(value, type);
5128 if (w.zero().equals(value))
5129 return zero(w, type);
5130 return insertArguments(identity(type), 0, value);
5131 } else {
5132 if (value == null)
5133 return zero(Wrapper.OBJECT, type);
5134 return identity(type).bindTo(value);
5135 }
5136 }
5137
5138 /**
5139 * Produces a method handle which returns its sole argument when invoked.
5140 * @param type the type of the sole parameter and return value of the desired method handle
5141 * @return a unary method handle which accepts and returns the given type
5142 * @throws NullPointerException if the argument is null
5143 * @throws IllegalArgumentException if the given type is {@code void.class}
5144 */
5145 public static MethodHandle identity(Class<?> type) {
5146 Wrapper btw = (type.isPrimitive() ? Wrapper.forPrimitiveType(type) : Wrapper.OBJECT);
5147 int pos = btw.ordinal();
5148 MethodHandle ident = IDENTITY_MHS[pos];
5149 if (ident == null) {
5150 ident = setCachedMethodHandle(IDENTITY_MHS, pos, makeIdentity(btw.primitiveType()));
5151 }
5152 if (ident.type().returnType() == type)
5153 return ident;
5154 // something like identity(Foo.class); do not bother to intern these
5155 assert (btw == Wrapper.OBJECT);
5156 return makeIdentity(type);
5157 }
5158
5159 /**
5160 * Produces a constant method handle of the requested return type which
5161 * returns the default value for that type every time it is invoked.
5162 * The resulting constant method handle will have no side effects.
5163 * <p>The returned method handle is equivalent to {@code empty(methodType(type))}.
5164 * It is also equivalent to {@code explicitCastArguments(constant(Object.class, null), methodType(type))},
5165 * since {@code explicitCastArguments} converts {@code null} to default values.
5166 * @param type the expected return type of the desired method handle
5167 * @return a constant method handle that takes no arguments
5168 * and returns the default value of the given type (or void, if the type is void)
5169 * @throws NullPointerException if the argument is null
5170 * @see MethodHandles#constant
5171 * @see MethodHandles#empty
5172 * @see MethodHandles#explicitCastArguments
5173 * @since 9
5174 */
5175 public static MethodHandle zero(Class<?> type) {
5176 Objects.requireNonNull(type);
5177 return type.isPrimitive() ? zero(Wrapper.forPrimitiveType(type), type) : zero(Wrapper.OBJECT, type);
5178 }
5179
5180 private static MethodHandle identityOrVoid(Class<?> type) {
5181 return type == void.class ? zero(type) : identity(type);
5182 }
5183
5184 /**
5185 * Produces a method handle of the requested type which ignores any arguments, does nothing,
5186 * and returns a suitable default depending on the return type.
5187 * That is, it returns a zero primitive value, a {@code null}, or {@code void}.
5188 * <p>The returned method handle is equivalent to
5189 * {@code dropArguments(zero(type.returnType()), 0, type.parameterList())}.
5190 *
5191 * @apiNote Given a predicate and target, a useful "if-then" construct can be produced as
5192 * {@code guardWithTest(pred, target, empty(target.type())}.
5193 * @param type the type of the desired method handle
5194 * @return a constant method handle of the given type, which returns a default value of the given return type
5195 * @throws NullPointerException if the argument is null
5196 * @see MethodHandles#zero
5197 * @see MethodHandles#constant
5198 * @since 9
5199 */
5200 public static MethodHandle empty(MethodType type) {
5201 Objects.requireNonNull(type);
5202 return dropArgumentsTrusted(zero(type.returnType()), 0, type.ptypes());
5203 }
5204
5205 private static final MethodHandle[] IDENTITY_MHS = new MethodHandle[Wrapper.COUNT];
5206 private static MethodHandle makeIdentity(Class<?> ptype) {
5207 MethodType mtype = methodType(ptype, ptype);
5208 LambdaForm lform = LambdaForm.identityForm(BasicType.basicType(ptype));
5209 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.IDENTITY);
5210 }
5211
5212 private static MethodHandle zero(Wrapper btw, Class<?> rtype) {
5213 int pos = btw.ordinal();
5214 MethodHandle zero = ZERO_MHS[pos];
5215 if (zero == null) {
5216 zero = setCachedMethodHandle(ZERO_MHS, pos, makeZero(btw.primitiveType()));
5217 }
5218 if (zero.type().returnType() == rtype)
5219 return zero;
5220 assert(btw == Wrapper.OBJECT);
5221 return makeZero(rtype);
5222 }
5223 private static final MethodHandle[] ZERO_MHS = new MethodHandle[Wrapper.COUNT];
5224 private static MethodHandle makeZero(Class<?> rtype) {
5225 MethodType mtype = methodType(rtype);
5226 LambdaForm lform = LambdaForm.zeroForm(BasicType.basicType(rtype));
5227 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.ZERO);
5228 }
5229
5230 private static synchronized MethodHandle setCachedMethodHandle(MethodHandle[] cache, int pos, MethodHandle value) {
5231 // Simulate a CAS, to avoid racy duplication of results.
5232 MethodHandle prev = cache[pos];
5233 if (prev != null) return prev;
5234 return cache[pos] = value;
5235 }
5236
5237 /**
5238 * Provides a target method handle with one or more <em>bound arguments</em>
5239 * in advance of the method handle's invocation.
5240 * The formal parameters to the target corresponding to the bound
5241 * arguments are called <em>bound parameters</em>.
5242 * Returns a new method handle which saves away the bound arguments.
5243 * When it is invoked, it receives arguments for any non-bound parameters,
5244 * binds the saved arguments to their corresponding parameters,
5245 * and calls the original target.
5246 * <p>
5247 * The type of the new method handle will drop the types for the bound
5248 * parameters from the original target type, since the new method handle
5249 * will no longer require those arguments to be supplied by its callers.
5250 * <p>
5251 * Each given argument object must match the corresponding bound parameter type.
5252 * If a bound parameter type is a primitive, the argument object
5253 * must be a wrapper, and will be unboxed to produce the primitive value.
5254 * <p>
5255 * The {@code pos} argument selects which parameters are to be bound.
5256 * It may range between zero and <i>N-L</i> (inclusively),
5257 * where <i>N</i> is the arity of the target method handle
5258 * and <i>L</i> is the length of the values array.
5259 * <p>
5260 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5261 * variable-arity method handle}, even if the original target method handle was.
5262 * @param target the method handle to invoke after the argument is inserted
5263 * @param pos where to insert the argument (zero for the first)
5264 * @param values the series of arguments to insert
5265 * @return a method handle which inserts an additional argument,
5266 * before calling the original method handle
5267 * @throws NullPointerException if the target or the {@code values} array is null
5268 * @throws IllegalArgumentException if {@code pos} is less than {@code 0} or greater than
5269 * {@code N - L} where {@code N} is the arity of the target method handle and {@code L}
5270 * is the length of the values array.
5271 * @throws ClassCastException if an argument does not match the corresponding bound parameter
5272 * type.
5273 * @see MethodHandle#bindTo
5274 */
5275 public static MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
5276 int insCount = values.length;
5277 Class<?>[] ptypes = insertArgumentsChecks(target, insCount, pos);
5278 if (insCount == 0) return target;
5279 BoundMethodHandle result = target.rebind();
5280 for (int i = 0; i < insCount; i++) {
5281 Object value = values[i];
5282 Class<?> ptype = ptypes[pos+i];
5283 if (ptype.isPrimitive()) {
5284 result = insertArgumentPrimitive(result, pos, ptype, value);
5285 } else {
5286 value = ptype.cast(value); // throw CCE if needed
5287 result = result.bindArgumentL(pos, value);
5288 }
5289 }
5290 return result;
5291 }
5292
5293 private static BoundMethodHandle insertArgumentPrimitive(BoundMethodHandle result, int pos,
5294 Class<?> ptype, Object value) {
5295 Wrapper w = Wrapper.forPrimitiveType(ptype);
5296 // perform unboxing and/or primitive conversion
5297 value = w.convert(value, ptype);
5298 return switch (w) {
5299 case INT -> result.bindArgumentI(pos, (int) value);
5300 case LONG -> result.bindArgumentJ(pos, (long) value);
5301 case FLOAT -> result.bindArgumentF(pos, (float) value);
5302 case DOUBLE -> result.bindArgumentD(pos, (double) value);
5303 default -> result.bindArgumentI(pos, ValueConversions.widenSubword(value));
5304 };
5305 }
5306
5307 private static Class<?>[] insertArgumentsChecks(MethodHandle target, int insCount, int pos) throws RuntimeException {
5308 MethodType oldType = target.type();
5309 int outargs = oldType.parameterCount();
5310 int inargs = outargs - insCount;
5311 if (inargs < 0)
5312 throw newIllegalArgumentException("too many values to insert");
5313 if (pos < 0 || pos > inargs)
5314 throw newIllegalArgumentException("no argument type to append");
5315 return oldType.ptypes();
5316 }
5317
5318 /**
5319 * Produces a method handle which will discard some dummy arguments
5320 * before calling some other specified <i>target</i> method handle.
5321 * The type of the new method handle will be the same as the target's type,
5322 * except it will also include the dummy argument types,
5323 * at some given position.
5324 * <p>
5325 * The {@code pos} argument may range between zero and <i>N</i>,
5326 * where <i>N</i> is the arity of the target.
5327 * If {@code pos} is zero, the dummy arguments will precede
5328 * the target's real arguments; if {@code pos} is <i>N</i>
5329 * they will come after.
5330 * <p>
5331 * <b>Example:</b>
5332 * {@snippet lang="java" :
5333 import static java.lang.invoke.MethodHandles.*;
5334 import static java.lang.invoke.MethodType.*;
5335 ...
5336 MethodHandle cat = lookup().findVirtual(String.class,
5337 "concat", methodType(String.class, String.class));
5338 assertEquals("xy", (String) cat.invokeExact("x", "y"));
5339 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
5340 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
5341 assertEquals(bigType, d0.type());
5342 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
5343 * }
5344 * <p>
5345 * This method is also equivalent to the following code:
5346 * <blockquote><pre>
5347 * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))}
5348 * </pre></blockquote>
5349 * @param target the method handle to invoke after the arguments are dropped
5350 * @param pos position of first argument to drop (zero for the leftmost)
5351 * @param valueTypes the type(s) of the argument(s) to drop
5352 * @return a method handle which drops arguments of the given types,
5353 * before calling the original method handle
5354 * @throws NullPointerException if the target is null,
5355 * or if the {@code valueTypes} list or any of its elements is null
5356 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
5357 * or if {@code pos} is negative or greater than the arity of the target,
5358 * or if the new method handle's type would have too many parameters
5359 */
5360 public static MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) {
5361 return dropArgumentsTrusted(target, pos, valueTypes.toArray(new Class<?>[0]).clone());
5362 }
5363
5364 static MethodHandle dropArgumentsTrusted(MethodHandle target, int pos, Class<?>[] valueTypes) {
5365 MethodType oldType = target.type(); // get NPE
5366 int dropped = dropArgumentChecks(oldType, pos, valueTypes);
5367 MethodType newType = oldType.insertParameterTypes(pos, valueTypes);
5368 if (dropped == 0) return target;
5369 BoundMethodHandle result = target.rebind();
5370 LambdaForm lform = result.form;
5371 int insertFormArg = 1 + pos;
5372 for (Class<?> ptype : valueTypes) {
5373 lform = lform.editor().addArgumentForm(insertFormArg++, BasicType.basicType(ptype));
5374 }
5375 result = result.copyWith(newType, lform);
5376 return result;
5377 }
5378
5379 private static int dropArgumentChecks(MethodType oldType, int pos, Class<?>[] valueTypes) {
5380 int dropped = valueTypes.length;
5381 MethodType.checkSlotCount(dropped);
5382 int outargs = oldType.parameterCount();
5383 int inargs = outargs + dropped;
5384 if (pos < 0 || pos > outargs)
5385 throw newIllegalArgumentException("no argument type to remove"
5386 + Arrays.asList(oldType, pos, valueTypes, inargs, outargs)
5387 );
5388 return dropped;
5389 }
5390
5391 /**
5392 * Produces a method handle which will discard some dummy arguments
5393 * before calling some other specified <i>target</i> method handle.
5394 * The type of the new method handle will be the same as the target's type,
5395 * except it will also include the dummy argument types,
5396 * at some given position.
5397 * <p>
5398 * The {@code pos} argument may range between zero and <i>N</i>,
5399 * where <i>N</i> is the arity of the target.
5400 * If {@code pos} is zero, the dummy arguments will precede
5401 * the target's real arguments; if {@code pos} is <i>N</i>
5402 * they will come after.
5403 * @apiNote
5404 * {@snippet lang="java" :
5405 import static java.lang.invoke.MethodHandles.*;
5406 import static java.lang.invoke.MethodType.*;
5407 ...
5408 MethodHandle cat = lookup().findVirtual(String.class,
5409 "concat", methodType(String.class, String.class));
5410 assertEquals("xy", (String) cat.invokeExact("x", "y"));
5411 MethodHandle d0 = dropArguments(cat, 0, String.class);
5412 assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
5413 MethodHandle d1 = dropArguments(cat, 1, String.class);
5414 assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
5415 MethodHandle d2 = dropArguments(cat, 2, String.class);
5416 assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
5417 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
5418 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
5419 * }
5420 * <p>
5421 * This method is also equivalent to the following code:
5422 * <blockquote><pre>
5423 * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))}
5424 * </pre></blockquote>
5425 * @param target the method handle to invoke after the arguments are dropped
5426 * @param pos position of first argument to drop (zero for the leftmost)
5427 * @param valueTypes the type(s) of the argument(s) to drop
5428 * @return a method handle which drops arguments of the given types,
5429 * before calling the original method handle
5430 * @throws NullPointerException if the target is null,
5431 * or if the {@code valueTypes} array or any of its elements is null
5432 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
5433 * or if {@code pos} is negative or greater than the arity of the target,
5434 * or if the new method handle's type would have
5435 * <a href="MethodHandle.html#maxarity">too many parameters</a>
5436 */
5437 public static MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
5438 return dropArgumentsTrusted(target, pos, valueTypes.clone());
5439 }
5440
5441 /* Convenience overloads for trusting internal low-arity call-sites */
5442 static MethodHandle dropArguments(MethodHandle target, int pos, Class<?> valueType1) {
5443 return dropArgumentsTrusted(target, pos, new Class<?>[] { valueType1 });
5444 }
5445 static MethodHandle dropArguments(MethodHandle target, int pos, Class<?> valueType1, Class<?> valueType2) {
5446 return dropArgumentsTrusted(target, pos, new Class<?>[] { valueType1, valueType2 });
5447 }
5448
5449 // private version which allows caller some freedom with error handling
5450 private static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, Class<?>[] newTypes, int pos,
5451 boolean nullOnFailure) {
5452 Class<?>[] oldTypes = target.type().ptypes();
5453 int match = oldTypes.length;
5454 if (skip != 0) {
5455 if (skip < 0 || skip > match) {
5456 throw newIllegalArgumentException("illegal skip", skip, target);
5457 }
5458 oldTypes = Arrays.copyOfRange(oldTypes, skip, match);
5459 match -= skip;
5460 }
5461 Class<?>[] addTypes = newTypes;
5462 int add = addTypes.length;
5463 if (pos != 0) {
5464 if (pos < 0 || pos > add) {
5465 throw newIllegalArgumentException("illegal pos", pos, Arrays.toString(newTypes));
5466 }
5467 addTypes = Arrays.copyOfRange(addTypes, pos, add);
5468 add -= pos;
5469 assert(addTypes.length == add);
5470 }
5471 // Do not add types which already match the existing arguments.
5472 if (match > add || !Arrays.equals(oldTypes, 0, oldTypes.length, addTypes, 0, match)) {
5473 if (nullOnFailure) {
5474 return null;
5475 }
5476 throw newIllegalArgumentException("argument lists do not match",
5477 Arrays.toString(oldTypes), Arrays.toString(newTypes));
5478 }
5479 addTypes = Arrays.copyOfRange(addTypes, match, add);
5480 add -= match;
5481 assert(addTypes.length == add);
5482 // newTypes: ( P*[pos], M*[match], A*[add] )
5483 // target: ( S*[skip], M*[match] )
5484 MethodHandle adapter = target;
5485 if (add > 0) {
5486 adapter = dropArgumentsTrusted(adapter, skip+ match, addTypes);
5487 }
5488 // adapter: (S*[skip], M*[match], A*[add] )
5489 if (pos > 0) {
5490 adapter = dropArgumentsTrusted(adapter, skip, Arrays.copyOfRange(newTypes, 0, pos));
5491 }
5492 // adapter: (S*[skip], P*[pos], M*[match], A*[add] )
5493 return adapter;
5494 }
5495
5496 /**
5497 * Adapts a target method handle to match the given parameter type list. If necessary, adds dummy arguments. Some
5498 * leading parameters can be skipped before matching begins. The remaining types in the {@code target}'s parameter
5499 * type list must be a sub-list of the {@code newTypes} type list at the starting position {@code pos}. The
5500 * resulting handle will have the target handle's parameter type list, with any non-matching parameter types (before
5501 * or after the matching sub-list) inserted in corresponding positions of the target's original parameters, as if by
5502 * {@link #dropArguments(MethodHandle, int, Class[])}.
5503 * <p>
5504 * The resulting handle will have the same return type as the target handle.
5505 * <p>
5506 * In more formal terms, assume these two type lists:<ul>
5507 * <li>The target handle has the parameter type list {@code S..., M...}, with as many types in {@code S} as
5508 * indicated by {@code skip}. The {@code M} types are those that are supposed to match part of the given type list,
5509 * {@code newTypes}.
5510 * <li>The {@code newTypes} list contains types {@code P..., M..., A...}, with as many types in {@code P} as
5511 * indicated by {@code pos}. The {@code M} types are precisely those that the {@code M} types in the target handle's
5512 * parameter type list are supposed to match. The types in {@code A} are additional types found after the matching
5513 * sub-list.
5514 * </ul>
5515 * Given these assumptions, the result of an invocation of {@code dropArgumentsToMatch} will have the parameter type
5516 * list {@code S..., P..., M..., A...}, with the {@code P} and {@code A} types inserted as if by
5517 * {@link #dropArguments(MethodHandle, int, Class[])}.
5518 *
5519 * @apiNote
5520 * Two method handles whose argument lists are "effectively identical" (i.e., identical in a common prefix) may be
5521 * mutually converted to a common type by two calls to {@code dropArgumentsToMatch}, as follows:
5522 * {@snippet lang="java" :
5523 import static java.lang.invoke.MethodHandles.*;
5524 import static java.lang.invoke.MethodType.*;
5525 ...
5526 ...
5527 MethodHandle h0 = constant(boolean.class, true);
5528 MethodHandle h1 = lookup().findVirtual(String.class, "concat", methodType(String.class, String.class));
5529 MethodType bigType = h1.type().insertParameterTypes(1, String.class, int.class);
5530 MethodHandle h2 = dropArguments(h1, 0, bigType.parameterList());
5531 if (h1.type().parameterCount() < h2.type().parameterCount())
5532 h1 = dropArgumentsToMatch(h1, 0, h2.type().parameterList(), 0); // lengthen h1
5533 else
5534 h2 = dropArgumentsToMatch(h2, 0, h1.type().parameterList(), 0); // lengthen h2
5535 MethodHandle h3 = guardWithTest(h0, h1, h2);
5536 assertEquals("xy", h3.invoke("x", "y", 1, "a", "b", "c"));
5537 * }
5538 * @param target the method handle to adapt
5539 * @param skip number of targets parameters to disregard (they will be unchanged)
5540 * @param newTypes the list of types to match {@code target}'s parameter type list to
5541 * @param pos place in {@code newTypes} where the non-skipped target parameters must occur
5542 * @return a possibly adapted method handle
5543 * @throws NullPointerException if either argument is null
5544 * @throws IllegalArgumentException if any element of {@code newTypes} is {@code void.class},
5545 * or if {@code skip} is negative or greater than the arity of the target,
5546 * or if {@code pos} is negative or greater than the newTypes list size,
5547 * or if {@code newTypes} does not contain the {@code target}'s non-skipped parameter types at position
5548 * {@code pos}.
5549 * @since 9
5550 */
5551 public static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos) {
5552 Objects.requireNonNull(target);
5553 Objects.requireNonNull(newTypes);
5554 return dropArgumentsToMatch(target, skip, newTypes.toArray(new Class<?>[0]).clone(), pos, false);
5555 }
5556
5557 /**
5558 * Drop the return value of the target handle (if any).
5559 * The returned method handle will have a {@code void} return type.
5560 *
5561 * @param target the method handle to adapt
5562 * @return a possibly adapted method handle
5563 * @throws NullPointerException if {@code target} is null
5564 * @since 16
5565 */
5566 public static MethodHandle dropReturn(MethodHandle target) {
5567 Objects.requireNonNull(target);
5568 MethodType oldType = target.type();
5569 Class<?> oldReturnType = oldType.returnType();
5570 if (oldReturnType == void.class)
5571 return target;
5572 MethodType newType = oldType.changeReturnType(void.class);
5573 BoundMethodHandle result = target.rebind();
5574 LambdaForm lform = result.editor().filterReturnForm(V_TYPE, true);
5575 result = result.copyWith(newType, lform);
5576 return result;
5577 }
5578
5579 /**
5580 * Adapts a target method handle by pre-processing
5581 * one or more of its arguments, each with its own unary filter function,
5582 * and then calling the target with each pre-processed argument
5583 * replaced by the result of its corresponding filter function.
5584 * <p>
5585 * The pre-processing is performed by one or more method handles,
5586 * specified in the elements of the {@code filters} array.
5587 * The first element of the filter array corresponds to the {@code pos}
5588 * argument of the target, and so on in sequence.
5589 * The filter functions are invoked in left to right order.
5590 * <p>
5591 * Null arguments in the array are treated as identity functions,
5592 * and the corresponding arguments left unchanged.
5593 * (If there are no non-null elements in the array, the original target is returned.)
5594 * Each filter is applied to the corresponding argument of the adapter.
5595 * <p>
5596 * If a filter {@code F} applies to the {@code N}th argument of
5597 * the target, then {@code F} must be a method handle which
5598 * takes exactly one argument. The type of {@code F}'s sole argument
5599 * replaces the corresponding argument type of the target
5600 * in the resulting adapted method handle.
5601 * The return type of {@code F} must be identical to the corresponding
5602 * parameter type of the target.
5603 * <p>
5604 * It is an error if there are elements of {@code filters}
5605 * (null or not)
5606 * which do not correspond to argument positions in the target.
5607 * <p><b>Example:</b>
5608 * {@snippet lang="java" :
5609 import static java.lang.invoke.MethodHandles.*;
5610 import static java.lang.invoke.MethodType.*;
5611 ...
5612 MethodHandle cat = lookup().findVirtual(String.class,
5613 "concat", methodType(String.class, String.class));
5614 MethodHandle upcase = lookup().findVirtual(String.class,
5615 "toUpperCase", methodType(String.class));
5616 assertEquals("xy", (String) cat.invokeExact("x", "y"));
5617 MethodHandle f0 = filterArguments(cat, 0, upcase);
5618 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
5619 MethodHandle f1 = filterArguments(cat, 1, upcase);
5620 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
5621 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
5622 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
5623 * }
5624 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
5625 * denotes the return type of both the {@code target} and resulting adapter.
5626 * {@code P}/{@code p} and {@code B}/{@code b} represent the types and values
5627 * of the parameters and arguments that precede and follow the filter position
5628 * {@code pos}, respectively. {@code A[i]}/{@code a[i]} stand for the types and
5629 * values of the filtered parameters and arguments; they also represent the
5630 * return types of the {@code filter[i]} handles. The latter accept arguments
5631 * {@code v[i]} of type {@code V[i]}, which also appear in the signature of
5632 * the resulting adapter.
5633 * {@snippet lang="java" :
5634 * T target(P... p, A[i]... a[i], B... b);
5635 * A[i] filter[i](V[i]);
5636 * T adapter(P... p, V[i]... v[i], B... b) {
5637 * return target(p..., filter[i](v[i])..., b...);
5638 * }
5639 * }
5640 * <p>
5641 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5642 * variable-arity method handle}, even if the original target method handle was.
5643 *
5644 * @param target the method handle to invoke after arguments are filtered
5645 * @param pos the position of the first argument to filter
5646 * @param filters method handles to call initially on filtered arguments
5647 * @return method handle which incorporates the specified argument filtering logic
5648 * @throws NullPointerException if the target is null
5649 * or if the {@code filters} array is null
5650 * @throws IllegalArgumentException if a non-null element of {@code filters}
5651 * does not match a corresponding argument type of target as described above,
5652 * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()},
5653 * or if the resulting method handle's type would have
5654 * <a href="MethodHandle.html#maxarity">too many parameters</a>
5655 */
5656 public static MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
5657 // In method types arguments start at index 0, while the LF
5658 // editor have the MH receiver at position 0 - adjust appropriately.
5659 final int MH_RECEIVER_OFFSET = 1;
5660 filterArgumentsCheckArity(target, pos, filters);
5661 MethodHandle adapter = target;
5662
5663 // keep track of currently matched filters, as to optimize repeated filters
5664 int index = 0;
5665 int[] positions = new int[filters.length];
5666 MethodHandle filter = null;
5667
5668 // process filters in reverse order so that the invocation of
5669 // the resulting adapter will invoke the filters in left-to-right order
5670 for (int i = filters.length - 1; i >= 0; --i) {
5671 MethodHandle newFilter = filters[i];
5672 if (newFilter == null) continue; // ignore null elements of filters
5673
5674 // flush changes on update
5675 if (filter != newFilter) {
5676 if (filter != null) {
5677 if (index > 1) {
5678 adapter = filterRepeatedArgument(adapter, filter, Arrays.copyOf(positions, index));
5679 } else {
5680 adapter = filterArgument(adapter, positions[0] - 1, filter);
5681 }
5682 }
5683 filter = newFilter;
5684 index = 0;
5685 }
5686
5687 filterArgumentChecks(target, pos + i, newFilter);
5688 positions[index++] = pos + i + MH_RECEIVER_OFFSET;
5689 }
5690 if (index > 1) {
5691 adapter = filterRepeatedArgument(adapter, filter, Arrays.copyOf(positions, index));
5692 } else if (index == 1) {
5693 adapter = filterArgument(adapter, positions[0] - 1, filter);
5694 }
5695 return adapter;
5696 }
5697
5698 private static MethodHandle filterRepeatedArgument(MethodHandle adapter, MethodHandle filter, int[] positions) {
5699 MethodType targetType = adapter.type();
5700 MethodType filterType = filter.type();
5701 BoundMethodHandle result = adapter.rebind();
5702 Class<?> newParamType = filterType.parameterType(0);
5703
5704 Class<?>[] ptypes = targetType.ptypes().clone();
5705 for (int pos : positions) {
5706 ptypes[pos - 1] = newParamType;
5707 }
5708 MethodType newType = MethodType.methodType(targetType.rtype(), ptypes, true);
5709
5710 LambdaForm lform = result.editor().filterRepeatedArgumentForm(BasicType.basicType(newParamType), positions);
5711 return result.copyWithExtendL(newType, lform, filter);
5712 }
5713
5714 /*non-public*/
5715 static MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
5716 filterArgumentChecks(target, pos, filter);
5717 MethodType targetType = target.type();
5718 MethodType filterType = filter.type();
5719 BoundMethodHandle result = target.rebind();
5720 Class<?> newParamType = filterType.parameterType(0);
5721 LambdaForm lform = result.editor().filterArgumentForm(1 + pos, BasicType.basicType(newParamType));
5722 MethodType newType = targetType.changeParameterType(pos, newParamType);
5723 result = result.copyWithExtendL(newType, lform, filter);
5724 return result;
5725 }
5726
5727 private static void filterArgumentsCheckArity(MethodHandle target, int pos, MethodHandle[] filters) {
5728 MethodType targetType = target.type();
5729 int maxPos = targetType.parameterCount();
5730 if (pos + filters.length > maxPos)
5731 throw newIllegalArgumentException("too many filters");
5732 }
5733
5734 private static void filterArgumentChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
5735 MethodType targetType = target.type();
5736 MethodType filterType = filter.type();
5737 if (filterType.parameterCount() != 1
5738 || filterType.returnType() != targetType.parameterType(pos))
5739 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
5740 }
5741
5742 /**
5743 * Adapts a target method handle by pre-processing
5744 * a sub-sequence of its arguments with a filter (another method handle).
5745 * The pre-processed arguments are replaced by the result (if any) of the
5746 * filter function.
5747 * The target is then called on the modified (usually shortened) argument list.
5748 * <p>
5749 * If the filter returns a value, the target must accept that value as
5750 * its argument in position {@code pos}, preceded and/or followed by
5751 * any arguments not passed to the filter.
5752 * If the filter returns void, the target must accept all arguments
5753 * not passed to the filter.
5754 * No arguments are reordered, and a result returned from the filter
5755 * replaces (in order) the whole subsequence of arguments originally
5756 * passed to the adapter.
5757 * <p>
5758 * The argument types (if any) of the filter
5759 * replace zero or one argument types of the target, at position {@code pos},
5760 * in the resulting adapted method handle.
5761 * The return type of the filter (if any) must be identical to the
5762 * argument type of the target at position {@code pos}, and that target argument
5763 * is supplied by the return value of the filter.
5764 * <p>
5765 * In all cases, {@code pos} must be greater than or equal to zero, and
5766 * {@code pos} must also be less than or equal to the target's arity.
5767 * <p><b>Example:</b>
5768 * {@snippet lang="java" :
5769 import static java.lang.invoke.MethodHandles.*;
5770 import static java.lang.invoke.MethodType.*;
5771 ...
5772 MethodHandle deepToString = publicLookup()
5773 .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
5774
5775 MethodHandle ts1 = deepToString.asCollector(String[].class, 1);
5776 assertEquals("[strange]", (String) ts1.invokeExact("strange"));
5777
5778 MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
5779 assertEquals("[up, down]", (String) ts2.invokeExact("up", "down"));
5780
5781 MethodHandle ts3 = deepToString.asCollector(String[].class, 3);
5782 MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2);
5783 assertEquals("[top, [up, down], strange]",
5784 (String) ts3_ts2.invokeExact("top", "up", "down", "strange"));
5785
5786 MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1);
5787 assertEquals("[top, [up, down], [strange]]",
5788 (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange"));
5789
5790 MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3);
5791 assertEquals("[top, [[up, down, strange], charm], bottom]",
5792 (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom"));
5793 * }
5794 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
5795 * represents the return type of the {@code target} and resulting adapter.
5796 * {@code V}/{@code v} stand for the return type and value of the
5797 * {@code filter}, which are also found in the signature and arguments of
5798 * the {@code target}, respectively, unless {@code V} is {@code void}.
5799 * {@code A}/{@code a} and {@code C}/{@code c} represent the parameter types
5800 * and values preceding and following the collection position, {@code pos},
5801 * in the {@code target}'s signature. They also turn up in the resulting
5802 * adapter's signature and arguments, where they surround
5803 * {@code B}/{@code b}, which represent the parameter types and arguments
5804 * to the {@code filter} (if any).
5805 * {@snippet lang="java" :
5806 * T target(A...,V,C...);
5807 * V filter(B...);
5808 * T adapter(A... a,B... b,C... c) {
5809 * V v = filter(b...);
5810 * return target(a...,v,c...);
5811 * }
5812 * // and if the filter has no arguments:
5813 * T target2(A...,V,C...);
5814 * V filter2();
5815 * T adapter2(A... a,C... c) {
5816 * V v = filter2();
5817 * return target2(a...,v,c...);
5818 * }
5819 * // and if the filter has a void return:
5820 * T target3(A...,C...);
5821 * void filter3(B...);
5822 * T adapter3(A... a,B... b,C... c) {
5823 * filter3(b...);
5824 * return target3(a...,c...);
5825 * }
5826 * }
5827 * <p>
5828 * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to
5829 * one which first "folds" the affected arguments, and then drops them, in separate
5830 * steps as follows:
5831 * {@snippet lang="java" :
5832 * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2
5833 * mh = MethodHandles.foldArguments(mh, coll); //step 1
5834 * }
5835 * If the target method handle consumes no arguments besides than the result
5836 * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)}
5837 * is equivalent to {@code filterReturnValue(coll, mh)}.
5838 * If the filter method handle {@code coll} consumes one argument and produces
5839 * a non-void result, then {@code collectArguments(mh, N, coll)}
5840 * is equivalent to {@code filterArguments(mh, N, coll)}.
5841 * Other equivalences are possible but would require argument permutation.
5842 * <p>
5843 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5844 * variable-arity method handle}, even if the original target method handle was.
5845 *
5846 * @param target the method handle to invoke after filtering the subsequence of arguments
5847 * @param pos the position of the first adapter argument to pass to the filter,
5848 * and/or the target argument which receives the result of the filter
5849 * @param filter method handle to call on the subsequence of arguments
5850 * @return method handle which incorporates the specified argument subsequence filtering logic
5851 * @throws NullPointerException if either argument is null
5852 * @throws IllegalArgumentException if the return type of {@code filter}
5853 * is non-void and is not the same as the {@code pos} argument of the target,
5854 * or if {@code pos} is not between 0 and the target's arity, inclusive,
5855 * or if the resulting method handle's type would have
5856 * <a href="MethodHandle.html#maxarity">too many parameters</a>
5857 * @see MethodHandles#foldArguments
5858 * @see MethodHandles#filterArguments
5859 * @see MethodHandles#filterReturnValue
5860 */
5861 public static MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) {
5862 MethodType newType = collectArgumentsChecks(target, pos, filter);
5863 MethodType collectorType = filter.type();
5864 BoundMethodHandle result = target.rebind();
5865 LambdaForm lform = result.editor().collectArgumentsForm(1 + pos, collectorType.basicType());
5866 return result.copyWithExtendL(newType, lform, filter);
5867 }
5868
5869 private static MethodType collectArgumentsChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
5870 MethodType targetType = target.type();
5871 MethodType filterType = filter.type();
5872 Class<?> rtype = filterType.returnType();
5873 Class<?>[] filterArgs = filterType.ptypes();
5874 if (pos < 0 || (rtype == void.class && pos > targetType.parameterCount()) ||
5875 (rtype != void.class && pos >= targetType.parameterCount())) {
5876 throw newIllegalArgumentException("position is out of range for target", target, pos);
5877 }
5878 if (rtype == void.class) {
5879 return targetType.insertParameterTypes(pos, filterArgs);
5880 }
5881 if (rtype != targetType.parameterType(pos)) {
5882 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
5883 }
5884 return targetType.dropParameterTypes(pos, pos + 1).insertParameterTypes(pos, filterArgs);
5885 }
5886
5887 /**
5888 * Adapts a target method handle by post-processing
5889 * its return value (if any) with a filter (another method handle).
5890 * The result of the filter is returned from the adapter.
5891 * <p>
5892 * If the target returns a value, the filter must accept that value as
5893 * its only argument.
5894 * If the target returns void, the filter must accept no arguments.
5895 * <p>
5896 * The return type of the filter
5897 * replaces the return type of the target
5898 * in the resulting adapted method handle.
5899 * The argument type of the filter (if any) must be identical to the
5900 * return type of the target.
5901 * <p><b>Example:</b>
5902 * {@snippet lang="java" :
5903 import static java.lang.invoke.MethodHandles.*;
5904 import static java.lang.invoke.MethodType.*;
5905 ...
5906 MethodHandle cat = lookup().findVirtual(String.class,
5907 "concat", methodType(String.class, String.class));
5908 MethodHandle length = lookup().findVirtual(String.class,
5909 "length", methodType(int.class));
5910 System.out.println((String) cat.invokeExact("x", "y")); // xy
5911 MethodHandle f0 = filterReturnValue(cat, length);
5912 System.out.println((int) f0.invokeExact("x", "y")); // 2
5913 * }
5914 * <p>Here is pseudocode for the resulting adapter. In the code,
5915 * {@code T}/{@code t} represent the result type and value of the
5916 * {@code target}; {@code V}, the result type of the {@code filter}; and
5917 * {@code A}/{@code a}, the types and values of the parameters and arguments
5918 * of the {@code target} as well as the resulting adapter.
5919 * {@snippet lang="java" :
5920 * T target(A...);
5921 * V filter(T);
5922 * V adapter(A... a) {
5923 * T t = target(a...);
5924 * return filter(t);
5925 * }
5926 * // and if the target has a void return:
5927 * void target2(A...);
5928 * V filter2();
5929 * V adapter2(A... a) {
5930 * target2(a...);
5931 * return filter2();
5932 * }
5933 * // and if the filter has a void return:
5934 * T target3(A...);
5935 * void filter3(V);
5936 * void adapter3(A... a) {
5937 * T t = target3(a...);
5938 * filter3(t);
5939 * }
5940 * }
5941 * <p>
5942 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5943 * variable-arity method handle}, even if the original target method handle was.
5944 * @param target the method handle to invoke before filtering the return value
5945 * @param filter method handle to call on the return value
5946 * @return method handle which incorporates the specified return value filtering logic
5947 * @throws NullPointerException if either argument is null
5948 * @throws IllegalArgumentException if the argument list of {@code filter}
5949 * does not match the return type of target as described above
5950 */
5951 public static MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
5952 MethodType targetType = target.type();
5953 MethodType filterType = filter.type();
5954 filterReturnValueChecks(targetType, filterType);
5955 BoundMethodHandle result = target.rebind();
5956 BasicType rtype = BasicType.basicType(filterType.returnType());
5957 LambdaForm lform = result.editor().filterReturnForm(rtype, false);
5958 MethodType newType = targetType.changeReturnType(filterType.returnType());
5959 result = result.copyWithExtendL(newType, lform, filter);
5960 return result;
5961 }
5962
5963 private static void filterReturnValueChecks(MethodType targetType, MethodType filterType) throws RuntimeException {
5964 Class<?> rtype = targetType.returnType();
5965 int filterValues = filterType.parameterCount();
5966 if (filterValues == 0
5967 ? (rtype != void.class)
5968 : (rtype != filterType.parameterType(0) || filterValues != 1))
5969 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
5970 }
5971
5972 /**
5973 * Filter the return value of a target method handle with a filter function. The filter function is
5974 * applied to the return value of the original handle; if the filter specifies more than one parameters,
5975 * then any remaining parameter is appended to the adapter handle. In other words, the adaptation works
5976 * as follows:
5977 * {@snippet lang="java" :
5978 * T target(A...)
5979 * V filter(B... , T)
5980 * V adapter(A... a, B... b) {
5981 * T t = target(a...);
5982 * return filter(b..., t);
5983 * }
5984 * }
5985 * <p>
5986 * If the filter handle is a unary function, then this method behaves like {@link #filterReturnValue(MethodHandle, MethodHandle)}.
5987 *
5988 * @param target the target method handle
5989 * @param filter the filter method handle
5990 * @return the adapter method handle
5991 */
5992 /* package */ static MethodHandle collectReturnValue(MethodHandle target, MethodHandle filter) {
5993 MethodType targetType = target.type();
5994 MethodType filterType = filter.type();
5995 BoundMethodHandle result = target.rebind();
5996 LambdaForm lform = result.editor().collectReturnValueForm(filterType.basicType());
5997 MethodType newType = targetType.changeReturnType(filterType.returnType());
5998 if (filterType.parameterCount() > 1) {
5999 for (int i = 0 ; i < filterType.parameterCount() - 1 ; i++) {
6000 newType = newType.appendParameterTypes(filterType.parameterType(i));
6001 }
6002 }
6003 result = result.copyWithExtendL(newType, lform, filter);
6004 return result;
6005 }
6006
6007 /**
6008 * Adapts a target method handle by pre-processing
6009 * some of its arguments, and then calling the target with
6010 * the result of the pre-processing, inserted into the original
6011 * sequence of arguments.
6012 * <p>
6013 * The pre-processing is performed by {@code combiner}, a second method handle.
6014 * Of the arguments passed to the adapter, the first {@code N} arguments
6015 * are copied to the combiner, which is then called.
6016 * (Here, {@code N} is defined as the parameter count of the combiner.)
6017 * After this, control passes to the target, with any result
6018 * from the combiner inserted before the original {@code N} incoming
6019 * arguments.
6020 * <p>
6021 * If the combiner returns a value, the first parameter type of the target
6022 * must be identical with the return type of the combiner, and the next
6023 * {@code N} parameter types of the target must exactly match the parameters
6024 * of the combiner.
6025 * <p>
6026 * If the combiner has a void return, no result will be inserted,
6027 * and the first {@code N} parameter types of the target
6028 * must exactly match the parameters of the combiner.
6029 * <p>
6030 * The resulting adapter is the same type as the target, except that the
6031 * first parameter type is dropped,
6032 * if it corresponds to the result of the combiner.
6033 * <p>
6034 * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
6035 * that either the combiner or the target does not wish to receive.
6036 * If some of the incoming arguments are destined only for the combiner,
6037 * consider using {@link MethodHandle#asCollector asCollector} instead, since those
6038 * arguments will not need to be live on the stack on entry to the
6039 * target.)
6040 * <p><b>Example:</b>
6041 * {@snippet lang="java" :
6042 import static java.lang.invoke.MethodHandles.*;
6043 import static java.lang.invoke.MethodType.*;
6044 ...
6045 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
6046 "println", methodType(void.class, String.class))
6047 .bindTo(System.out);
6048 MethodHandle cat = lookup().findVirtual(String.class,
6049 "concat", methodType(String.class, String.class));
6050 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
6051 MethodHandle catTrace = foldArguments(cat, trace);
6052 // also prints "boo":
6053 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
6054 * }
6055 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
6056 * represents the result type of the {@code target} and resulting adapter.
6057 * {@code V}/{@code v} represent the type and value of the parameter and argument
6058 * of {@code target} that precedes the folding position; {@code V} also is
6059 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
6060 * types and values of the {@code N} parameters and arguments at the folding
6061 * position. {@code B}/{@code b} represent the types and values of the
6062 * {@code target} parameters and arguments that follow the folded parameters
6063 * and arguments.
6064 * {@snippet lang="java" :
6065 * // there are N arguments in A...
6066 * T target(V, A[N]..., B...);
6067 * V combiner(A...);
6068 * T adapter(A... a, B... b) {
6069 * V v = combiner(a...);
6070 * return target(v, a..., b...);
6071 * }
6072 * // and if the combiner has a void return:
6073 * T target2(A[N]..., B...);
6074 * void combiner2(A...);
6075 * T adapter2(A... a, B... b) {
6076 * combiner2(a...);
6077 * return target2(a..., b...);
6078 * }
6079 * }
6080 * <p>
6081 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
6082 * variable-arity method handle}, even if the original target method handle was.
6083 * @param target the method handle to invoke after arguments are combined
6084 * @param combiner method handle to call initially on the incoming arguments
6085 * @return method handle which incorporates the specified argument folding logic
6086 * @throws NullPointerException if either argument is null
6087 * @throws IllegalArgumentException if {@code combiner}'s return type
6088 * is non-void and not the same as the first argument type of
6089 * the target, or if the initial {@code N} argument types
6090 * of the target
6091 * (skipping one matching the {@code combiner}'s return type)
6092 * are not identical with the argument types of {@code combiner}
6093 */
6094 public static MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
6095 return foldArguments(target, 0, combiner);
6096 }
6097
6098 /**
6099 * Adapts a target method handle by pre-processing some of its arguments, starting at a given position, and then
6100 * calling the target with the result of the pre-processing, inserted into the original sequence of arguments just
6101 * before the folded arguments.
6102 * <p>
6103 * This method is closely related to {@link #foldArguments(MethodHandle, MethodHandle)}, but allows to control the
6104 * position in the parameter list at which folding takes place. The argument controlling this, {@code pos}, is a
6105 * zero-based index. The aforementioned method {@link #foldArguments(MethodHandle, MethodHandle)} assumes position
6106 * 0.
6107 *
6108 * @apiNote Example:
6109 * {@snippet lang="java" :
6110 import static java.lang.invoke.MethodHandles.*;
6111 import static java.lang.invoke.MethodType.*;
6112 ...
6113 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
6114 "println", methodType(void.class, String.class))
6115 .bindTo(System.out);
6116 MethodHandle cat = lookup().findVirtual(String.class,
6117 "concat", methodType(String.class, String.class));
6118 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
6119 MethodHandle catTrace = foldArguments(cat, 1, trace);
6120 // also prints "jum":
6121 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
6122 * }
6123 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
6124 * represents the result type of the {@code target} and resulting adapter.
6125 * {@code V}/{@code v} represent the type and value of the parameter and argument
6126 * of {@code target} that precedes the folding position; {@code V} also is
6127 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
6128 * types and values of the {@code N} parameters and arguments at the folding
6129 * position. {@code Z}/{@code z} and {@code B}/{@code b} represent the types
6130 * and values of the {@code target} parameters and arguments that precede and
6131 * follow the folded parameters and arguments starting at {@code pos},
6132 * respectively.
6133 * {@snippet lang="java" :
6134 * // there are N arguments in A...
6135 * T target(Z..., V, A[N]..., B...);
6136 * V combiner(A...);
6137 * T adapter(Z... z, A... a, B... b) {
6138 * V v = combiner(a...);
6139 * return target(z..., v, a..., b...);
6140 * }
6141 * // and if the combiner has a void return:
6142 * T target2(Z..., A[N]..., B...);
6143 * void combiner2(A...);
6144 * T adapter2(Z... z, A... a, B... b) {
6145 * combiner2(a...);
6146 * return target2(z..., a..., b...);
6147 * }
6148 * }
6149 * <p>
6150 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
6151 * variable-arity method handle}, even if the original target method handle was.
6152 *
6153 * @param target the method handle to invoke after arguments are combined
6154 * @param pos the position at which to start folding and at which to insert the folding result; if this is {@code
6155 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
6156 * @param combiner method handle to call initially on the incoming arguments
6157 * @return method handle which incorporates the specified argument folding logic
6158 * @throws NullPointerException if either argument is null
6159 * @throws IllegalArgumentException if either of the following two conditions holds:
6160 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
6161 * {@code pos} of the target signature;
6162 * (2) the {@code N} argument types at position {@code pos} of the target signature (skipping one matching
6163 * the {@code combiner}'s return type) are not identical with the argument types of {@code combiner}.
6164 *
6165 * @see #foldArguments(MethodHandle, MethodHandle)
6166 * @since 9
6167 */
6168 public static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner) {
6169 MethodType targetType = target.type();
6170 MethodType combinerType = combiner.type();
6171 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType);
6172 BoundMethodHandle result = target.rebind();
6173 boolean dropResult = rtype == void.class;
6174 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType());
6175 MethodType newType = targetType;
6176 if (!dropResult) {
6177 newType = newType.dropParameterTypes(pos, pos + 1);
6178 }
6179 result = result.copyWithExtendL(newType, lform, combiner);
6180 return result;
6181 }
6182
6183 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType) {
6184 int foldArgs = combinerType.parameterCount();
6185 Class<?> rtype = combinerType.returnType();
6186 int foldVals = rtype == void.class ? 0 : 1;
6187 int afterInsertPos = foldPos + foldVals;
6188 boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
6189 if (ok) {
6190 for (int i = 0; i < foldArgs; i++) {
6191 if (combinerType.parameterType(i) != targetType.parameterType(i + afterInsertPos)) {
6192 ok = false;
6193 break;
6194 }
6195 }
6196 }
6197 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos))
6198 ok = false;
6199 if (!ok)
6200 throw misMatchedTypes("target and combiner types", targetType, combinerType);
6201 return rtype;
6202 }
6203
6204 /**
6205 * Adapts a target method handle by pre-processing some of its arguments, then calling the target with the result
6206 * of the pre-processing replacing the argument at the given position.
6207 *
6208 * @param target the method handle to invoke after arguments are combined
6209 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code
6210 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
6211 * @param combiner method handle to call initially on the incoming arguments
6212 * @param argPositions indexes of the target to pick arguments sent to the combiner from
6213 * @return method handle which incorporates the specified argument folding logic
6214 * @throws NullPointerException if either argument is null
6215 * @throws IllegalArgumentException if either of the following two conditions holds:
6216 * (1) {@code combiner}'s return type is not the same as the argument type at position
6217 * {@code pos} of the target signature;
6218 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature are
6219 * not identical with the argument types of {@code combiner}.
6220 */
6221 /*non-public*/
6222 static MethodHandle filterArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
6223 return argumentsWithCombiner(true, target, position, combiner, argPositions);
6224 }
6225
6226 /**
6227 * Adapts a target method handle by pre-processing some of its arguments, calling the target with the result of
6228 * the pre-processing inserted into the original sequence of arguments at the given position.
6229 *
6230 * @param target the method handle to invoke after arguments are combined
6231 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code
6232 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
6233 * @param combiner method handle to call initially on the incoming arguments
6234 * @param argPositions indexes of the target to pick arguments sent to the combiner from
6235 * @return method handle which incorporates the specified argument folding logic
6236 * @throws NullPointerException if either argument is null
6237 * @throws IllegalArgumentException if either of the following two conditions holds:
6238 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
6239 * {@code pos} of the target signature;
6240 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature
6241 * (skipping {@code position} where the {@code combiner}'s return will be folded in) are not identical
6242 * with the argument types of {@code combiner}.
6243 */
6244 /*non-public*/
6245 static MethodHandle foldArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
6246 return argumentsWithCombiner(false, target, position, combiner, argPositions);
6247 }
6248
6249 private static MethodHandle argumentsWithCombiner(boolean filter, MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
6250 MethodType targetType = target.type();
6251 MethodType combinerType = combiner.type();
6252 Class<?> rtype = argumentsWithCombinerChecks(position, filter, targetType, combinerType, argPositions);
6253 BoundMethodHandle result = target.rebind();
6254
6255 MethodType newType = targetType;
6256 LambdaForm lform;
6257 if (filter) {
6258 lform = result.editor().filterArgumentsForm(1 + position, combinerType.basicType(), argPositions);
6259 } else {
6260 boolean dropResult = rtype == void.class;
6261 lform = result.editor().foldArgumentsForm(1 + position, dropResult, combinerType.basicType(), argPositions);
6262 if (!dropResult) {
6263 newType = newType.dropParameterTypes(position, position + 1);
6264 }
6265 }
6266 result = result.copyWithExtendL(newType, lform, combiner);
6267 return result;
6268 }
6269
6270 private static Class<?> argumentsWithCombinerChecks(int position, boolean filter, MethodType targetType, MethodType combinerType, int ... argPos) {
6271 int combinerArgs = combinerType.parameterCount();
6272 if (argPos.length != combinerArgs) {
6273 throw newIllegalArgumentException("combiner and argument map must be equal size", combinerType, argPos.length);
6274 }
6275 Class<?> rtype = combinerType.returnType();
6276
6277 for (int i = 0; i < combinerArgs; i++) {
6278 int arg = argPos[i];
6279 if (arg < 0 || arg > targetType.parameterCount()) {
6280 throw newIllegalArgumentException("arg outside of target parameterRange", targetType, arg);
6281 }
6282 if (combinerType.parameterType(i) != targetType.parameterType(arg)) {
6283 throw newIllegalArgumentException("target argument type at position " + arg
6284 + " must match combiner argument type at index " + i + ": " + targetType
6285 + " -> " + combinerType + ", map: " + Arrays.toString(argPos));
6286 }
6287 }
6288 if (filter && combinerType.returnType() != targetType.parameterType(position)) {
6289 throw misMatchedTypes("target and combiner types", targetType, combinerType);
6290 }
6291 return rtype;
6292 }
6293
6294 /**
6295 * Makes a method handle which adapts a target method handle,
6296 * by guarding it with a test, a boolean-valued method handle.
6297 * If the guard fails, a fallback handle is called instead.
6298 * All three method handles must have the same corresponding
6299 * argument and return types, except that the return type
6300 * of the test must be boolean, and the test is allowed
6301 * to have fewer arguments than the other two method handles.
6302 * <p>
6303 * Here is pseudocode for the resulting adapter. In the code, {@code T}
6304 * represents the uniform result type of the three involved handles;
6305 * {@code A}/{@code a}, the types and values of the {@code target}
6306 * parameters and arguments that are consumed by the {@code test}; and
6307 * {@code B}/{@code b}, those types and values of the {@code target}
6308 * parameters and arguments that are not consumed by the {@code test}.
6309 * {@snippet lang="java" :
6310 * boolean test(A...);
6311 * T target(A...,B...);
6312 * T fallback(A...,B...);
6313 * T adapter(A... a,B... b) {
6314 * if (test(a...))
6315 * return target(a..., b...);
6316 * else
6317 * return fallback(a..., b...);
6318 * }
6319 * }
6320 * Note that the test arguments ({@code a...} in the pseudocode) cannot
6321 * be modified by execution of the test, and so are passed unchanged
6322 * from the caller to the target or fallback as appropriate.
6323 * @param test method handle used for test, must return boolean
6324 * @param target method handle to call if test passes
6325 * @param fallback method handle to call if test fails
6326 * @return method handle which incorporates the specified if/then/else logic
6327 * @throws NullPointerException if any argument is null
6328 * @throws IllegalArgumentException if {@code test} does not return boolean,
6329 * or if all three method types do not match (with the return
6330 * type of {@code test} changed to match that of the target).
6331 */
6332 public static MethodHandle guardWithTest(MethodHandle test,
6333 MethodHandle target,
6334 MethodHandle fallback) {
6335 MethodType gtype = test.type();
6336 MethodType ttype = target.type();
6337 MethodType ftype = fallback.type();
6338 if (!ttype.equals(ftype))
6339 throw misMatchedTypes("target and fallback types", ttype, ftype);
6340 if (gtype.returnType() != boolean.class)
6341 throw newIllegalArgumentException("guard type is not a predicate "+gtype);
6342
6343 test = dropArgumentsToMatch(test, 0, ttype.ptypes(), 0, true);
6344 if (test == null) {
6345 throw misMatchedTypes("target and test types", ttype, gtype);
6346 }
6347 return MethodHandleImpl.makeGuardWithTest(test, target, fallback);
6348 }
6349
6350 static <T> RuntimeException misMatchedTypes(String what, T t1, T t2) {
6351 return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
6352 }
6353
6354 /**
6355 * Makes a method handle which adapts a target method handle,
6356 * by running it inside an exception handler.
6357 * If the target returns normally, the adapter returns that value.
6358 * If an exception matching the specified type is thrown, the fallback
6359 * handle is called instead on the exception, plus the original arguments.
6360 * <p>
6361 * The target and handler must have the same corresponding
6362 * argument and return types, except that handler may omit trailing arguments
6363 * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
6364 * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
6365 * <p>
6366 * Here is pseudocode for the resulting adapter. In the code, {@code T}
6367 * represents the return type of the {@code target} and {@code handler},
6368 * and correspondingly that of the resulting adapter; {@code A}/{@code a},
6369 * the types and values of arguments to the resulting handle consumed by
6370 * {@code handler}; and {@code B}/{@code b}, those of arguments to the
6371 * resulting handle discarded by {@code handler}.
6372 * {@snippet lang="java" :
6373 * T target(A..., B...);
6374 * T handler(ExType, A...);
6375 * T adapter(A... a, B... b) {
6376 * try {
6377 * return target(a..., b...);
6378 * } catch (ExType ex) {
6379 * return handler(ex, a...);
6380 * }
6381 * }
6382 * }
6383 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
6384 * be modified by execution of the target, and so are passed unchanged
6385 * from the caller to the handler, if the handler is invoked.
6386 * <p>
6387 * The target and handler must return the same type, even if the handler
6388 * always throws. (This might happen, for instance, because the handler
6389 * is simulating a {@code finally} clause).
6390 * To create such a throwing handler, compose the handler creation logic
6391 * with {@link #throwException throwException},
6392 * in order to create a method handle of the correct return type.
6393 * @param target method handle to call
6394 * @param exType the type of exception which the handler will catch
6395 * @param handler method handle to call if a matching exception is thrown
6396 * @return method handle which incorporates the specified try/catch logic
6397 * @throws NullPointerException if any argument is null
6398 * @throws IllegalArgumentException if {@code handler} does not accept
6399 * the given exception type, or if the method handle types do
6400 * not match in their return types and their
6401 * corresponding parameters
6402 * @see MethodHandles#tryFinally(MethodHandle, MethodHandle)
6403 */
6404 public static MethodHandle catchException(MethodHandle target,
6405 Class<? extends Throwable> exType,
6406 MethodHandle handler) {
6407 MethodType ttype = target.type();
6408 MethodType htype = handler.type();
6409 if (!Throwable.class.isAssignableFrom(exType))
6410 throw new ClassCastException(exType.getName());
6411 if (htype.parameterCount() < 1 ||
6412 !htype.parameterType(0).isAssignableFrom(exType))
6413 throw newIllegalArgumentException("handler does not accept exception type "+exType);
6414 if (htype.returnType() != ttype.returnType())
6415 throw misMatchedTypes("target and handler return types", ttype, htype);
6416 handler = dropArgumentsToMatch(handler, 1, ttype.ptypes(), 0, true);
6417 if (handler == null) {
6418 throw misMatchedTypes("target and handler types", ttype, htype);
6419 }
6420 return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
6421 }
6422
6423 /**
6424 * Produces a method handle which will throw exceptions of the given {@code exType}.
6425 * The method handle will accept a single argument of {@code exType},
6426 * and immediately throw it as an exception.
6427 * The method type will nominally specify a return of {@code returnType}.
6428 * The return type may be anything convenient: It doesn't matter to the
6429 * method handle's behavior, since it will never return normally.
6430 * @param returnType the return type of the desired method handle
6431 * @param exType the parameter type of the desired method handle
6432 * @return method handle which can throw the given exceptions
6433 * @throws NullPointerException if either argument is null
6434 */
6435 public static MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) {
6436 if (!Throwable.class.isAssignableFrom(exType))
6437 throw new ClassCastException(exType.getName());
6438 return MethodHandleImpl.throwException(methodType(returnType, exType));
6439 }
6440
6441 /**
6442 * Constructs a method handle representing a loop with several loop variables that are updated and checked upon each
6443 * iteration. Upon termination of the loop due to one of the predicates, a corresponding finalizer is run and
6444 * delivers the loop's result, which is the return value of the resulting handle.
6445 * <p>
6446 * Intuitively, every loop is formed by one or more "clauses", each specifying a local <em>iteration variable</em> and/or a loop
6447 * exit. Each iteration of the loop executes each clause in order. A clause can optionally update its iteration
6448 * variable; it can also optionally perform a test and conditional loop exit. In order to express this logic in
6449 * terms of method handles, each clause will specify up to four independent actions:<ul>
6450 * <li><em>init:</em> Before the loop executes, the initialization of an iteration variable {@code v} of type {@code V}.
6451 * <li><em>step:</em> When a clause executes, an update step for the iteration variable {@code v}.
6452 * <li><em>pred:</em> When a clause executes, a predicate execution to test for loop exit.
6453 * <li><em>fini:</em> If a clause causes a loop exit, a finalizer execution to compute the loop's return value.
6454 * </ul>
6455 * The full sequence of all iteration variable types, in clause order, will be notated as {@code (V...)}.
6456 * The values themselves will be {@code (v...)}. When we speak of "parameter lists", we will usually
6457 * be referring to types, but in some contexts (describing execution) the lists will be of actual values.
6458 * <p>
6459 * Some of these clause parts may be omitted according to certain rules, and useful default behavior is provided in
6460 * this case. See below for a detailed description.
6461 * <p>
6462 * <em>Parameters optional everywhere:</em>
6463 * Each clause function is allowed but not required to accept a parameter for each iteration variable {@code v}.
6464 * As an exception, the init functions cannot take any {@code v} parameters,
6465 * because those values are not yet computed when the init functions are executed.
6466 * Any clause function may neglect to take any trailing subsequence of parameters it is entitled to take.
6467 * In fact, any clause function may take no arguments at all.
6468 * <p>
6469 * <em>Loop parameters:</em>
6470 * A clause function may take all the iteration variable values it is entitled to, in which case
6471 * it may also take more trailing parameters. Such extra values are called <em>loop parameters</em>,
6472 * with their types and values notated as {@code (A...)} and {@code (a...)}.
6473 * These become the parameters of the resulting loop handle, to be supplied whenever the loop is executed.
6474 * (Since init functions do not accept iteration variables {@code v}, any parameter to an
6475 * init function is automatically a loop parameter {@code a}.)
6476 * As with iteration variables, clause functions are allowed but not required to accept loop parameters.
6477 * These loop parameters act as loop-invariant values visible across the whole loop.
6478 * <p>
6479 * <em>Parameters visible everywhere:</em>
6480 * Each non-init clause function is permitted to observe the entire loop state, because it can be passed the full
6481 * list {@code (v... a...)} of current iteration variable values and incoming loop parameters.
6482 * The init functions can observe initial pre-loop state, in the form {@code (a...)}.
6483 * Most clause functions will not need all of this information, but they will be formally connected to it
6484 * as if by {@link #dropArguments}.
6485 * <a id="astar"></a>
6486 * More specifically, we shall use the notation {@code (V*)} to express an arbitrary prefix of a full
6487 * sequence {@code (V...)} (and likewise for {@code (v*)}, {@code (A*)}, {@code (a*)}).
6488 * In that notation, the general form of an init function parameter list
6489 * is {@code (A*)}, and the general form of a non-init function parameter list is {@code (V*)} or {@code (V... A*)}.
6490 * <p>
6491 * <em>Checking clause structure:</em>
6492 * Given a set of clauses, there is a number of checks and adjustments performed to connect all the parts of the
6493 * loop. They are spelled out in detail in the steps below. In these steps, every occurrence of the word "must"
6494 * corresponds to a place where {@link IllegalArgumentException} will be thrown if the required constraint is not
6495 * met by the inputs to the loop combinator.
6496 * <p>
6497 * <em>Effectively identical sequences:</em>
6498 * <a id="effid"></a>
6499 * A parameter list {@code A} is defined to be <em>effectively identical</em> to another parameter list {@code B}
6500 * if {@code A} and {@code B} are identical, or if {@code A} is shorter and is identical with a proper prefix of {@code B}.
6501 * When speaking of an unordered set of parameter lists, we say they the set is "effectively identical"
6502 * as a whole if the set contains a longest list, and all members of the set are effectively identical to
6503 * that longest list.
6504 * For example, any set of type sequences of the form {@code (V*)} is effectively identical,
6505 * and the same is true if more sequences of the form {@code (V... A*)} are added.
6506 * <p>
6507 * <em>Step 0: Determine clause structure.</em><ol type="a">
6508 * <li>The clause array (of type {@code MethodHandle[][]}) must be non-{@code null} and contain at least one element.
6509 * <li>The clause array may not contain {@code null}s or sub-arrays longer than four elements.
6510 * <li>Clauses shorter than four elements are treated as if they were padded by {@code null} elements to length
6511 * four. Padding takes place by appending elements to the array.
6512 * <li>Clauses with all {@code null}s are disregarded.
6513 * <li>Each clause is treated as a four-tuple of functions, called "init", "step", "pred", and "fini".
6514 * </ol>
6515 * <p>
6516 * <em>Step 1A: Determine iteration variable types {@code (V...)}.</em><ol type="a">
6517 * <li>The iteration variable type for each clause is determined using the clause's init and step return types.
6518 * <li>If both functions are omitted, there is no iteration variable for the corresponding clause ({@code void} is
6519 * used as the type to indicate that). If one of them is omitted, the other's return type defines the clause's
6520 * iteration variable type. If both are given, the common return type (they must be identical) defines the clause's
6521 * iteration variable type.
6522 * <li>Form the list of return types (in clause order), omitting all occurrences of {@code void}.
6523 * <li>This list of types is called the "iteration variable types" ({@code (V...)}).
6524 * </ol>
6525 * <p>
6526 * <em>Step 1B: Determine loop parameters {@code (A...)}.</em><ul>
6527 * <li>Examine and collect init function parameter lists (which are of the form {@code (A*)}).
6528 * <li>Examine and collect the suffixes of the step, pred, and fini parameter lists, after removing the iteration variable types.
6529 * (They must have the form {@code (V... A*)}; collect the {@code (A*)} parts only.)
6530 * <li>Do not collect suffixes from step, pred, and fini parameter lists that do not begin with all the iteration variable types.
6531 * (These types will be checked in step 2, along with all the clause function types.)
6532 * <li>Omitted clause functions are ignored. (Equivalently, they are deemed to have empty parameter lists.)
6533 * <li>All of the collected parameter lists must be effectively identical.
6534 * <li>The longest parameter list (which is necessarily unique) is called the "external parameter list" ({@code (A...)}).
6535 * <li>If there is no such parameter list, the external parameter list is taken to be the empty sequence.
6536 * <li>The combined list consisting of iteration variable types followed by the external parameter types is called
6537 * the "internal parameter list".
6538 * </ul>
6539 * <p>
6540 * <em>Step 1C: Determine loop return type.</em><ol type="a">
6541 * <li>Examine fini function return types, disregarding omitted fini functions.
6542 * <li>If there are no fini functions, the loop return type is {@code void}.
6543 * <li>Otherwise, the common return type {@code R} of the fini functions (their return types must be identical) defines the loop return
6544 * type.
6545 * </ol>
6546 * <p>
6547 * <em>Step 1D: Check other types.</em><ol type="a">
6548 * <li>There must be at least one non-omitted pred function.
6549 * <li>Every non-omitted pred function must have a {@code boolean} return type.
6550 * </ol>
6551 * <p>
6552 * <em>Step 2: Determine parameter lists.</em><ol type="a">
6553 * <li>The parameter list for the resulting loop handle will be the external parameter list {@code (A...)}.
6554 * <li>The parameter list for init functions will be adjusted to the external parameter list.
6555 * (Note that their parameter lists are already effectively identical to this list.)
6556 * <li>The parameter list for every non-omitted, non-init (step, pred, and fini) function must be
6557 * effectively identical to the internal parameter list {@code (V... A...)}.
6558 * </ol>
6559 * <p>
6560 * <em>Step 3: Fill in omitted functions.</em><ol type="a">
6561 * <li>If an init function is omitted, use a {@linkplain #empty default value} for the clause's iteration variable
6562 * type.
6563 * <li>If a step function is omitted, use an {@linkplain #identity identity function} of the clause's iteration
6564 * variable type; insert dropped argument parameters before the identity function parameter for the non-{@code void}
6565 * iteration variables of preceding clauses. (This will turn the loop variable into a local loop invariant.)
6566 * <li>If a pred function is omitted, use a constant {@code true} function. (This will keep the loop going, as far
6567 * as this clause is concerned. Note that in such cases the corresponding fini function is unreachable.)
6568 * <li>If a fini function is omitted, use a {@linkplain #empty default value} for the
6569 * loop return type.
6570 * </ol>
6571 * <p>
6572 * <em>Step 4: Fill in missing parameter types.</em><ol type="a">
6573 * <li>At this point, every init function parameter list is effectively identical to the external parameter list {@code (A...)},
6574 * but some lists may be shorter. For every init function with a short parameter list, pad out the end of the list.
6575 * <li>At this point, every non-init function parameter list is effectively identical to the internal parameter
6576 * list {@code (V... A...)}, but some lists may be shorter. For every non-init function with a short parameter list,
6577 * pad out the end of the list.
6578 * <li>Argument lists are padded out by {@linkplain #dropArgumentsToMatch(MethodHandle, int, List, int) dropping unused trailing arguments}.
6579 * </ol>
6580 * <p>
6581 * <em>Final observations.</em><ol type="a">
6582 * <li>After these steps, all clauses have been adjusted by supplying omitted functions and arguments.
6583 * <li>All init functions have a common parameter type list {@code (A...)}, which the final loop handle will also have.
6584 * <li>All fini functions have a common return type {@code R}, which the final loop handle will also have.
6585 * <li>All non-init functions have a common parameter type list {@code (V... A...)}, of
6586 * (non-{@code void}) iteration variables {@code V} followed by loop parameters.
6587 * <li>Each pair of init and step functions agrees in their return type {@code V}.
6588 * <li>Each non-init function will be able to observe the current values {@code (v...)} of all iteration variables.
6589 * <li>Every function will be able to observe the incoming values {@code (a...)} of all loop parameters.
6590 * </ol>
6591 * <p>
6592 * <em>Example.</em> As a consequence of step 1A above, the {@code loop} combinator has the following property:
6593 * <ul>
6594 * <li>Given {@code N} clauses {@code Cn = {null, Sn, Pn}} with {@code n = 1..N}.
6595 * <li>Suppose predicate handles {@code Pn} are either {@code null} or have no parameters.
6596 * (Only one {@code Pn} has to be non-{@code null}.)
6597 * <li>Suppose step handles {@code Sn} have signatures {@code (B1..BX)Rn}, for some constant {@code X>=N}.
6598 * <li>Suppose {@code Q} is the count of non-void types {@code Rn}, and {@code (V1...VQ)} is the sequence of those types.
6599 * <li>It must be that {@code Vn == Bn} for {@code n = 1..min(X,Q)}.
6600 * <li>The parameter types {@code Vn} will be interpreted as loop-local state elements {@code (V...)}.
6601 * <li>Any remaining types {@code BQ+1..BX} (if {@code Q<X}) will determine
6602 * the resulting loop handle's parameter types {@code (A...)}.
6603 * </ul>
6604 * In this example, the loop handle parameters {@code (A...)} were derived from the step functions,
6605 * which is natural if most of the loop computation happens in the steps. For some loops,
6606 * the burden of computation might be heaviest in the pred functions, and so the pred functions
6607 * might need to accept the loop parameter values. For loops with complex exit logic, the fini
6608 * functions might need to accept loop parameters, and likewise for loops with complex entry logic,
6609 * where the init functions will need the extra parameters. For such reasons, the rules for
6610 * determining these parameters are as symmetric as possible, across all clause parts.
6611 * In general, the loop parameters function as common invariant values across the whole
6612 * loop, while the iteration variables function as common variant values, or (if there is
6613 * no step function) as internal loop invariant temporaries.
6614 * <p>
6615 * <em>Loop execution.</em><ol type="a">
6616 * <li>When the loop is called, the loop input values are saved in locals, to be passed to
6617 * every clause function. These locals are loop invariant.
6618 * <li>Each init function is executed in clause order (passing the external arguments {@code (a...)})
6619 * and the non-{@code void} values are saved (as the iteration variables {@code (v...)}) into locals.
6620 * These locals will be loop varying (unless their steps behave as identity functions, as noted above).
6621 * <li>All function executions (except init functions) will be passed the internal parameter list, consisting of
6622 * the non-{@code void} iteration values {@code (v...)} (in clause order) and then the loop inputs {@code (a...)}
6623 * (in argument order).
6624 * <li>The step and pred functions are then executed, in clause order (step before pred), until a pred function
6625 * returns {@code false}.
6626 * <li>The non-{@code void} result from a step function call is used to update the corresponding value in the
6627 * sequence {@code (v...)} of loop variables.
6628 * The updated value is immediately visible to all subsequent function calls.
6629 * <li>If a pred function returns {@code false}, the corresponding fini function is called, and the resulting value
6630 * (of type {@code R}) is returned from the loop as a whole.
6631 * <li>If all the pred functions always return true, no fini function is ever invoked, and the loop cannot exit
6632 * except by throwing an exception.
6633 * </ol>
6634 * <p>
6635 * <em>Usage tips.</em>
6636 * <ul>
6637 * <li>Although each step function will receive the current values of <em>all</em> the loop variables,
6638 * sometimes a step function only needs to observe the current value of its own variable.
6639 * In that case, the step function may need to explicitly {@linkplain #dropArguments drop all preceding loop variables}.
6640 * This will require mentioning their types, in an expression like {@code dropArguments(step, 0, V0.class, ...)}.
6641 * <li>Loop variables are not required to vary; they can be loop invariant. A clause can create
6642 * a loop invariant by a suitable init function with no step, pred, or fini function. This may be
6643 * useful to "wire" an incoming loop argument into the step or pred function of an adjacent loop variable.
6644 * <li>If some of the clause functions are virtual methods on an instance, the instance
6645 * itself can be conveniently placed in an initial invariant loop "variable", using an initial clause
6646 * like {@code new MethodHandle[]{identity(ObjType.class)}}. In that case, the instance reference
6647 * will be the first iteration variable value, and it will be easy to use virtual
6648 * methods as clause parts, since all of them will take a leading instance reference matching that value.
6649 * </ul>
6650 * <p>
6651 * Here is pseudocode for the resulting loop handle. As above, {@code V} and {@code v} represent the types
6652 * and values of loop variables; {@code A} and {@code a} represent arguments passed to the whole loop;
6653 * and {@code R} is the common result type of all finalizers as well as of the resulting loop.
6654 * {@snippet lang="java" :
6655 * V... init...(A...);
6656 * boolean pred...(V..., A...);
6657 * V... step...(V..., A...);
6658 * R fini...(V..., A...);
6659 * R loop(A... a) {
6660 * V... v... = init...(a...);
6661 * for (;;) {
6662 * for ((v, p, s, f) in (v..., pred..., step..., fini...)) {
6663 * v = s(v..., a...);
6664 * if (!p(v..., a...)) {
6665 * return f(v..., a...);
6666 * }
6667 * }
6668 * }
6669 * }
6670 * }
6671 * Note that the parameter type lists {@code (V...)} and {@code (A...)} have been expanded
6672 * to their full length, even though individual clause functions may neglect to take them all.
6673 * As noted above, missing parameters are filled in as if by {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}.
6674 *
6675 * @apiNote Example:
6676 * {@snippet lang="java" :
6677 * // iterative implementation of the factorial function as a loop handle
6678 * static int one(int k) { return 1; }
6679 * static int inc(int i, int acc, int k) { return i + 1; }
6680 * static int mult(int i, int acc, int k) { return i * acc; }
6681 * static boolean pred(int i, int acc, int k) { return i < k; }
6682 * static int fin(int i, int acc, int k) { return acc; }
6683 * // assume MH_one, MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
6684 * // null initializer for counter, should initialize to 0
6685 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
6686 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
6687 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
6688 * assertEquals(120, loop.invoke(5));
6689 * }
6690 * The same example, dropping arguments and using combinators:
6691 * {@snippet lang="java" :
6692 * // simplified implementation of the factorial function as a loop handle
6693 * static int inc(int i) { return i + 1; } // drop acc, k
6694 * static int mult(int i, int acc) { return i * acc; } //drop k
6695 * static boolean cmp(int i, int k) { return i < k; }
6696 * // assume MH_inc, MH_mult, and MH_cmp are handles to the above methods
6697 * // null initializer for counter, should initialize to 0
6698 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
6699 * MethodHandle MH_pred = MethodHandles.dropArguments(MH_cmp, 1, int.class); // drop acc
6700 * MethodHandle MH_fin = MethodHandles.dropArguments(MethodHandles.identity(int.class), 0, int.class); // drop i
6701 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
6702 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
6703 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
6704 * assertEquals(720, loop.invoke(6));
6705 * }
6706 * A similar example, using a helper object to hold a loop parameter:
6707 * {@snippet lang="java" :
6708 * // instance-based implementation of the factorial function as a loop handle
6709 * static class FacLoop {
6710 * final int k;
6711 * FacLoop(int k) { this.k = k; }
6712 * int inc(int i) { return i + 1; }
6713 * int mult(int i, int acc) { return i * acc; }
6714 * boolean pred(int i) { return i < k; }
6715 * int fin(int i, int acc) { return acc; }
6716 * }
6717 * // assume MH_FacLoop is a handle to the constructor
6718 * // assume MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
6719 * // null initializer for counter, should initialize to 0
6720 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
6721 * MethodHandle[] instanceClause = new MethodHandle[]{MH_FacLoop};
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(instanceClause, counterClause, accumulatorClause);
6725 * assertEquals(5040, loop.invoke(7));
6726 * }
6727 *
6728 * @param clauses an array of arrays (4-tuples) of {@link MethodHandle}s adhering to the rules described above.
6729 *
6730 * @return a method handle embodying the looping behavior as defined by the arguments.
6731 *
6732 * @throws IllegalArgumentException in case any of the constraints described above is violated.
6733 *
6734 * @see MethodHandles#whileLoop(MethodHandle, MethodHandle, MethodHandle)
6735 * @see MethodHandles#doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
6736 * @see MethodHandles#countedLoop(MethodHandle, MethodHandle, MethodHandle)
6737 * @see MethodHandles#iteratedLoop(MethodHandle, MethodHandle, MethodHandle)
6738 * @since 9
6739 */
6740 public static MethodHandle loop(MethodHandle[]... clauses) {
6741 // Step 0: determine clause structure.
6742 loopChecks0(clauses);
6743
6744 List<MethodHandle> init = new ArrayList<>();
6745 List<MethodHandle> step = new ArrayList<>();
6746 List<MethodHandle> pred = new ArrayList<>();
6747 List<MethodHandle> fini = new ArrayList<>();
6748
6749 Stream.of(clauses).filter(c -> Stream.of(c).anyMatch(Objects::nonNull)).forEach(clause -> {
6750 init.add(clause[0]); // all clauses have at least length 1
6751 step.add(clause.length <= 1 ? null : clause[1]);
6752 pred.add(clause.length <= 2 ? null : clause[2]);
6753 fini.add(clause.length <= 3 ? null : clause[3]);
6754 });
6755
6756 assert Stream.of(init, step, pred, fini).map(List::size).distinct().count() == 1;
6757 final int nclauses = init.size();
6758
6759 // Step 1A: determine iteration variables (V...).
6760 final List<Class<?>> iterationVariableTypes = new ArrayList<>();
6761 for (int i = 0; i < nclauses; ++i) {
6762 MethodHandle in = init.get(i);
6763 MethodHandle st = step.get(i);
6764 if (in == null && st == null) {
6765 iterationVariableTypes.add(void.class);
6766 } else if (in != null && st != null) {
6767 loopChecks1a(i, in, st);
6768 iterationVariableTypes.add(in.type().returnType());
6769 } else {
6770 iterationVariableTypes.add(in == null ? st.type().returnType() : in.type().returnType());
6771 }
6772 }
6773 final List<Class<?>> commonPrefix = iterationVariableTypes.stream().filter(t -> t != void.class).toList();
6774
6775 // Step 1B: determine loop parameters (A...).
6776 final List<Class<?>> commonSuffix = buildCommonSuffix(init, step, pred, fini, commonPrefix.size());
6777 loopChecks1b(init, commonSuffix);
6778
6779 // Step 1C: determine loop return type.
6780 // Step 1D: check other types.
6781 // local variable required here; see JDK-8223553
6782 Stream<Class<?>> cstream = fini.stream().filter(Objects::nonNull).map(MethodHandle::type)
6783 .map(MethodType::returnType);
6784 final Class<?> loopReturnType = cstream.findFirst().orElse(void.class);
6785 loopChecks1cd(pred, fini, loopReturnType);
6786
6787 // Step 2: determine parameter lists.
6788 final List<Class<?>> commonParameterSequence = new ArrayList<>(commonPrefix);
6789 commonParameterSequence.addAll(commonSuffix);
6790 loopChecks2(step, pred, fini, commonParameterSequence);
6791 // Step 3: fill in omitted functions.
6792 for (int i = 0; i < nclauses; ++i) {
6793 Class<?> t = iterationVariableTypes.get(i);
6794 if (init.get(i) == null) {
6795 init.set(i, empty(methodType(t, commonSuffix)));
6796 }
6797 if (step.get(i) == null) {
6798 step.set(i, dropArgumentsToMatch(identityOrVoid(t), 0, commonParameterSequence, i));
6799 }
6800 if (pred.get(i) == null) {
6801 pred.set(i, dropArguments(constant(boolean.class, true), 0, commonParameterSequence));
6802 }
6803 if (fini.get(i) == null) {
6804 fini.set(i, empty(methodType(t, commonParameterSequence)));
6805 }
6806 }
6807
6808 // Step 4: fill in missing parameter types.
6809 // Also convert all handles to fixed-arity handles.
6810 List<MethodHandle> finit = fixArities(fillParameterTypes(init, commonSuffix));
6811 List<MethodHandle> fstep = fixArities(fillParameterTypes(step, commonParameterSequence));
6812 List<MethodHandle> fpred = fixArities(fillParameterTypes(pred, commonParameterSequence));
6813 List<MethodHandle> ffini = fixArities(fillParameterTypes(fini, commonParameterSequence));
6814
6815 assert finit.stream().map(MethodHandle::type).map(MethodType::parameterList).
6816 allMatch(pl -> pl.equals(commonSuffix));
6817 assert Stream.of(fstep, fpred, ffini).flatMap(List::stream).map(MethodHandle::type).map(MethodType::parameterList).
6818 allMatch(pl -> pl.equals(commonParameterSequence));
6819
6820 return MethodHandleImpl.makeLoop(loopReturnType, commonSuffix, finit, fstep, fpred, ffini);
6821 }
6822
6823 private static void loopChecks0(MethodHandle[][] clauses) {
6824 if (clauses == null || clauses.length == 0) {
6825 throw newIllegalArgumentException("null or no clauses passed");
6826 }
6827 if (Stream.of(clauses).anyMatch(Objects::isNull)) {
6828 throw newIllegalArgumentException("null clauses are not allowed");
6829 }
6830 if (Stream.of(clauses).anyMatch(c -> c.length > 4)) {
6831 throw newIllegalArgumentException("All loop clauses must be represented as MethodHandle arrays with at most 4 elements.");
6832 }
6833 }
6834
6835 private static void loopChecks1a(int i, MethodHandle in, MethodHandle st) {
6836 if (in.type().returnType() != st.type().returnType()) {
6837 throw misMatchedTypes("clause " + i + ": init and step return types", in.type().returnType(),
6838 st.type().returnType());
6839 }
6840 }
6841
6842 private static List<Class<?>> longestParameterList(Stream<MethodHandle> mhs, int skipSize) {
6843 return mhs.filter(Objects::nonNull)
6844 // take only those that can contribute to a common suffix because they are longer than the prefix
6845 .map(MethodHandle::type)
6846 .filter(t -> t.parameterCount() > skipSize)
6847 .max(Comparator.comparingInt(MethodType::parameterCount))
6848 .map(methodType -> List.of(Arrays.copyOfRange(methodType.ptypes(), skipSize, methodType.parameterCount())))
6849 .orElse(List.of());
6850 }
6851
6852 private static List<Class<?>> buildCommonSuffix(List<MethodHandle> init, List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, int cpSize) {
6853 final List<Class<?>> longest1 = longestParameterList(Stream.of(step, pred, fini).flatMap(List::stream), cpSize);
6854 final List<Class<?>> longest2 = longestParameterList(init.stream(), 0);
6855 return longest1.size() >= longest2.size() ? longest1 : longest2;
6856 }
6857
6858 private static void loopChecks1b(List<MethodHandle> init, List<Class<?>> commonSuffix) {
6859 if (init.stream().filter(Objects::nonNull).map(MethodHandle::type).
6860 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonSuffix))) {
6861 throw newIllegalArgumentException("found non-effectively identical init parameter type lists: " + init +
6862 " (common suffix: " + commonSuffix + ")");
6863 }
6864 }
6865
6866 private static void loopChecks1cd(List<MethodHandle> pred, List<MethodHandle> fini, Class<?> loopReturnType) {
6867 if (fini.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
6868 anyMatch(t -> t != loopReturnType)) {
6869 throw newIllegalArgumentException("found non-identical finalizer return types: " + fini + " (return type: " +
6870 loopReturnType + ")");
6871 }
6872
6873 if (pred.stream().noneMatch(Objects::nonNull)) {
6874 throw newIllegalArgumentException("no predicate found", pred);
6875 }
6876 if (pred.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
6877 anyMatch(t -> t != boolean.class)) {
6878 throw newIllegalArgumentException("predicates must have boolean return type", pred);
6879 }
6880 }
6881
6882 private static void loopChecks2(List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, List<Class<?>> commonParameterSequence) {
6883 if (Stream.of(step, pred, fini).flatMap(List::stream).filter(Objects::nonNull).map(MethodHandle::type).
6884 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonParameterSequence))) {
6885 throw newIllegalArgumentException("found non-effectively identical parameter type lists:\nstep: " + step +
6886 "\npred: " + pred + "\nfini: " + fini + " (common parameter sequence: " + commonParameterSequence + ")");
6887 }
6888 }
6889
6890 private static List<MethodHandle> fillParameterTypes(List<MethodHandle> hs, final List<Class<?>> targetParams) {
6891 return hs.stream().map(h -> {
6892 int pc = h.type().parameterCount();
6893 int tpsize = targetParams.size();
6894 return pc < tpsize ? dropArguments(h, pc, targetParams.subList(pc, tpsize)) : h;
6895 }).toList();
6896 }
6897
6898 private static List<MethodHandle> fixArities(List<MethodHandle> hs) {
6899 return hs.stream().map(MethodHandle::asFixedArity).toList();
6900 }
6901
6902 /**
6903 * Constructs a {@code while} loop from an initializer, a body, and a predicate.
6904 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
6905 * <p>
6906 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
6907 * method will, in each iteration, first evaluate the predicate and then execute its body (if the predicate
6908 * evaluates to {@code true}).
6909 * The loop will terminate once the predicate evaluates to {@code false} (the body will not be executed in this case).
6910 * <p>
6911 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
6912 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
6913 * and updated with the value returned from its invocation. The result of loop execution will be
6914 * the final value of the additional loop-local variable (if present).
6915 * <p>
6916 * The following rules hold for these argument handles:<ul>
6917 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
6918 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
6919 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
6920 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
6921 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
6922 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
6923 * It will constrain the parameter lists of the other loop parts.
6924 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
6925 * list {@code (A...)} is called the <em>external parameter list</em>.
6926 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
6927 * additional state variable of the loop.
6928 * The body must both accept and return a value of this type {@code V}.
6929 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
6930 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
6931 * <a href="MethodHandles.html#effid">effectively identical</a>
6932 * to the external parameter list {@code (A...)}.
6933 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
6934 * {@linkplain #empty default value}.
6935 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
6936 * Its parameter list (either empty or of the form {@code (V A*)}) must be
6937 * effectively identical to the internal parameter list.
6938 * </ul>
6939 * <p>
6940 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
6941 * <li>The loop handle's result type is the result type {@code V} of the body.
6942 * <li>The loop handle's parameter types are the types {@code (A...)},
6943 * from the external parameter list.
6944 * </ul>
6945 * <p>
6946 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
6947 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
6948 * passed to the loop.
6949 * {@snippet lang="java" :
6950 * V init(A...);
6951 * boolean pred(V, A...);
6952 * V body(V, A...);
6953 * V whileLoop(A... a...) {
6954 * V v = init(a...);
6955 * while (pred(v, a...)) {
6956 * v = body(v, a...);
6957 * }
6958 * return v;
6959 * }
6960 * }
6961 *
6962 * @apiNote Example:
6963 * {@snippet lang="java" :
6964 * // implement the zip function for lists as a loop handle
6965 * static List<String> initZip(Iterator<String> a, Iterator<String> b) { return new ArrayList<>(); }
6966 * static boolean zipPred(List<String> zip, Iterator<String> a, Iterator<String> b) { return a.hasNext() && b.hasNext(); }
6967 * static List<String> zipStep(List<String> zip, Iterator<String> a, Iterator<String> b) {
6968 * zip.add(a.next());
6969 * zip.add(b.next());
6970 * return zip;
6971 * }
6972 * // assume MH_initZip, MH_zipPred, and MH_zipStep are handles to the above methods
6973 * MethodHandle loop = MethodHandles.whileLoop(MH_initZip, MH_zipPred, MH_zipStep);
6974 * List<String> a = Arrays.asList("a", "b", "c", "d");
6975 * List<String> b = Arrays.asList("e", "f", "g", "h");
6976 * List<String> zipped = Arrays.asList("a", "e", "b", "f", "c", "g", "d", "h");
6977 * assertEquals(zipped, (List<String>) loop.invoke(a.iterator(), b.iterator()));
6978 * }
6979 *
6980 *
6981 * @apiNote The implementation of this method can be expressed as follows:
6982 * {@snippet lang="java" :
6983 * MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
6984 * MethodHandle fini = (body.type().returnType() == void.class
6985 * ? null : identity(body.type().returnType()));
6986 * MethodHandle[]
6987 * checkExit = { null, null, pred, fini },
6988 * varBody = { init, body };
6989 * return loop(checkExit, varBody);
6990 * }
6991 * }
6992 *
6993 * @param init optional initializer, providing the initial value of the loop variable.
6994 * May be {@code null}, implying a default initial value. See above for other constraints.
6995 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
6996 * above for other constraints.
6997 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
6998 * See above for other constraints.
6999 *
7000 * @return a method handle implementing the {@code while} loop as described by the arguments.
7001 * @throws IllegalArgumentException if the rules for the arguments are violated.
7002 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
7003 *
7004 * @see #loop(MethodHandle[][])
7005 * @see #doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
7006 * @since 9
7007 */
7008 public static MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
7009 whileLoopChecks(init, pred, body);
7010 MethodHandle fini = identityOrVoid(body.type().returnType());
7011 MethodHandle[] checkExit = { null, null, pred, fini };
7012 MethodHandle[] varBody = { init, body };
7013 return loop(checkExit, varBody);
7014 }
7015
7016 /**
7017 * Constructs a {@code do-while} loop from an initializer, a body, and a predicate.
7018 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
7019 * <p>
7020 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
7021 * method will, in each iteration, first execute its body and then evaluate the predicate.
7022 * The loop will terminate once the predicate evaluates to {@code false} after an execution of the body.
7023 * <p>
7024 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
7025 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
7026 * and updated with the value returned from its invocation. The result of loop execution will be
7027 * the final value of the additional loop-local variable (if present).
7028 * <p>
7029 * The following rules hold for these argument handles:<ul>
7030 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
7031 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
7032 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
7033 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
7034 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
7035 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
7036 * It will constrain the parameter lists of the other loop parts.
7037 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
7038 * list {@code (A...)} is called the <em>external parameter list</em>.
7039 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
7040 * additional state variable of the loop.
7041 * The body must both accept and return a value of this type {@code V}.
7042 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
7043 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
7044 * <a href="MethodHandles.html#effid">effectively identical</a>
7045 * to the external parameter list {@code (A...)}.
7046 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
7047 * {@linkplain #empty default value}.
7048 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
7049 * Its parameter list (either empty or of the form {@code (V A*)}) must be
7050 * effectively identical to the internal parameter list.
7051 * </ul>
7052 * <p>
7053 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
7054 * <li>The loop handle's result type is the result type {@code V} of the body.
7055 * <li>The loop handle's parameter types are the types {@code (A...)},
7056 * from the external parameter list.
7057 * </ul>
7058 * <p>
7059 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
7060 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
7061 * passed to the loop.
7062 * {@snippet lang="java" :
7063 * V init(A...);
7064 * boolean pred(V, A...);
7065 * V body(V, A...);
7066 * V doWhileLoop(A... a...) {
7067 * V v = init(a...);
7068 * do {
7069 * v = body(v, a...);
7070 * } while (pred(v, a...));
7071 * return v;
7072 * }
7073 * }
7074 *
7075 * @apiNote Example:
7076 * {@snippet lang="java" :
7077 * // int i = 0; while (i < limit) { ++i; } return i; => limit
7078 * static int zero(int limit) { return 0; }
7079 * static int step(int i, int limit) { return i + 1; }
7080 * static boolean pred(int i, int limit) { return i < limit; }
7081 * // assume MH_zero, MH_step, and MH_pred are handles to the above methods
7082 * MethodHandle loop = MethodHandles.doWhileLoop(MH_zero, MH_step, MH_pred);
7083 * assertEquals(23, loop.invoke(23));
7084 * }
7085 *
7086 *
7087 * @apiNote The implementation of this method can be expressed as follows:
7088 * {@snippet lang="java" :
7089 * MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
7090 * MethodHandle fini = (body.type().returnType() == void.class
7091 * ? null : identity(body.type().returnType()));
7092 * MethodHandle[] clause = { init, body, pred, fini };
7093 * return loop(clause);
7094 * }
7095 * }
7096 *
7097 * @param init optional initializer, providing the initial value of the loop variable.
7098 * May be {@code null}, implying a default initial value. See above for other constraints.
7099 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
7100 * See above for other constraints.
7101 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
7102 * above for other constraints.
7103 *
7104 * @return a method handle implementing the {@code while} loop as described by the arguments.
7105 * @throws IllegalArgumentException if the rules for the arguments are violated.
7106 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
7107 *
7108 * @see #loop(MethodHandle[][])
7109 * @see #whileLoop(MethodHandle, MethodHandle, MethodHandle)
7110 * @since 9
7111 */
7112 public static MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
7113 whileLoopChecks(init, pred, body);
7114 MethodHandle fini = identityOrVoid(body.type().returnType());
7115 MethodHandle[] clause = {init, body, pred, fini };
7116 return loop(clause);
7117 }
7118
7119 private static void whileLoopChecks(MethodHandle init, MethodHandle pred, MethodHandle body) {
7120 Objects.requireNonNull(pred);
7121 Objects.requireNonNull(body);
7122 MethodType bodyType = body.type();
7123 Class<?> returnType = bodyType.returnType();
7124 List<Class<?>> innerList = bodyType.parameterList();
7125 List<Class<?>> outerList = innerList;
7126 if (returnType == void.class) {
7127 // OK
7128 } else if (innerList.isEmpty() || innerList.get(0) != returnType) {
7129 // leading V argument missing => error
7130 MethodType expected = bodyType.insertParameterTypes(0, returnType);
7131 throw misMatchedTypes("body function", bodyType, expected);
7132 } else {
7133 outerList = innerList.subList(1, innerList.size());
7134 }
7135 MethodType predType = pred.type();
7136 if (predType.returnType() != boolean.class ||
7137 !predType.effectivelyIdenticalParameters(0, innerList)) {
7138 throw misMatchedTypes("loop predicate", predType, methodType(boolean.class, innerList));
7139 }
7140 if (init != null) {
7141 MethodType initType = init.type();
7142 if (initType.returnType() != returnType ||
7143 !initType.effectivelyIdenticalParameters(0, outerList)) {
7144 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
7145 }
7146 }
7147 }
7148
7149 /**
7150 * Constructs a loop that runs a given number of iterations.
7151 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
7152 * <p>
7153 * The number of iterations is determined by the {@code iterations} handle evaluation result.
7154 * The loop counter {@code i} is an extra loop iteration variable of type {@code int}.
7155 * It will be initialized to 0 and incremented by 1 in each iteration.
7156 * <p>
7157 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
7158 * of that type is also present. This variable is initialized using the optional {@code init} handle,
7159 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
7160 * <p>
7161 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
7162 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
7163 * iteration variable.
7164 * The result of the loop handle execution will be the final {@code V} value of that variable
7165 * (or {@code void} if there is no {@code V} variable).
7166 * <p>
7167 * The following rules hold for the argument handles:<ul>
7168 * <li>The {@code iterations} handle must not be {@code null}, and must return
7169 * the type {@code int}, referred to here as {@code I} in parameter type lists.
7170 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
7171 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
7172 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
7173 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
7174 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
7175 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
7176 * of types called the <em>internal parameter list</em>.
7177 * It will constrain the parameter lists of the other loop parts.
7178 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
7179 * with no additional {@code A} types, then the internal parameter list is extended by
7180 * the argument types {@code A...} of the {@code iterations} handle.
7181 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
7182 * list {@code (A...)} is called the <em>external parameter list</em>.
7183 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
7184 * additional state variable of the loop.
7185 * The body must both accept a leading parameter and return a value of this type {@code V}.
7186 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
7187 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
7188 * <a href="MethodHandles.html#effid">effectively identical</a>
7189 * to the external parameter list {@code (A...)}.
7190 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
7191 * {@linkplain #empty default value}.
7192 * <li>The parameter list of {@code iterations} (of some form {@code (A*)}) must be
7193 * effectively identical to the external parameter list {@code (A...)}.
7194 * </ul>
7195 * <p>
7196 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
7197 * <li>The loop handle's result type is the result type {@code V} of the body.
7198 * <li>The loop handle's parameter types are the types {@code (A...)},
7199 * from the external parameter list.
7200 * </ul>
7201 * <p>
7202 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
7203 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
7204 * arguments passed to the loop.
7205 * {@snippet lang="java" :
7206 * int iterations(A...);
7207 * V init(A...);
7208 * V body(V, int, A...);
7209 * V countedLoop(A... a...) {
7210 * int end = iterations(a...);
7211 * V v = init(a...);
7212 * for (int i = 0; i < end; ++i) {
7213 * v = body(v, i, a...);
7214 * }
7215 * return v;
7216 * }
7217 * }
7218 *
7219 * @apiNote Example with a fully conformant body method:
7220 * {@snippet lang="java" :
7221 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
7222 * // => a variation on a well known theme
7223 * static String step(String v, int counter, String init) { return "na " + v; }
7224 * // assume MH_step is a handle to the method above
7225 * MethodHandle fit13 = MethodHandles.constant(int.class, 13);
7226 * MethodHandle start = MethodHandles.identity(String.class);
7227 * MethodHandle loop = MethodHandles.countedLoop(fit13, start, MH_step);
7228 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("Lambdaman!"));
7229 * }
7230 *
7231 * @apiNote Example with the simplest possible body method type,
7232 * and passing the number of iterations to the loop invocation:
7233 * {@snippet lang="java" :
7234 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
7235 * // => a variation on a well known theme
7236 * static String step(String v, int counter ) { return "na " + v; }
7237 * // assume MH_step is a handle to the method above
7238 * MethodHandle count = MethodHandles.dropArguments(MethodHandles.identity(int.class), 1, String.class);
7239 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class);
7240 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i) -> "na " + v
7241 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "Lambdaman!"));
7242 * }
7243 *
7244 * @apiNote Example that treats the number of iterations, string to append to, and string to append
7245 * as loop parameters:
7246 * {@snippet lang="java" :
7247 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
7248 * // => a variation on a well known theme
7249 * static String step(String v, int counter, int iterations_, String pre, String start_) { return pre + " " + v; }
7250 * // assume MH_step is a handle to the method above
7251 * MethodHandle count = MethodHandles.identity(int.class);
7252 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class, String.class);
7253 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i, _, pre, _) -> pre + " " + v
7254 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "na", "Lambdaman!"));
7255 * }
7256 *
7257 * @apiNote Example that illustrates the usage of {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}
7258 * to enforce a loop type:
7259 * {@snippet lang="java" :
7260 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
7261 * // => a variation on a well known theme
7262 * static String step(String v, int counter, String pre) { return pre + " " + v; }
7263 * // assume MH_step is a handle to the method above
7264 * MethodType loopType = methodType(String.class, String.class, int.class, String.class);
7265 * MethodHandle count = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(int.class), 0, loopType.parameterList(), 1);
7266 * MethodHandle start = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(String.class), 0, loopType.parameterList(), 2);
7267 * MethodHandle body = MethodHandles.dropArgumentsToMatch(MH_step, 2, loopType.parameterList(), 0);
7268 * MethodHandle loop = MethodHandles.countedLoop(count, start, body); // (v, i, pre, _, _) -> pre + " " + v
7269 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("na", 13, "Lambdaman!"));
7270 * }
7271 *
7272 * @apiNote The implementation of this method can be expressed as follows:
7273 * {@snippet lang="java" :
7274 * MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
7275 * return countedLoop(empty(iterations.type()), iterations, init, body);
7276 * }
7277 * }
7278 *
7279 * @param iterations a non-{@code null} handle to return the number of iterations this loop should run. The handle's
7280 * result type must be {@code int}. See above for other constraints.
7281 * @param init optional initializer, providing the initial value of the loop variable.
7282 * May be {@code null}, implying a default initial value. See above for other constraints.
7283 * @param body body of the loop, which may not be {@code null}.
7284 * It controls the loop parameters and result type in the standard case (see above for details).
7285 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
7286 * and may accept any number of additional types.
7287 * See above for other constraints.
7288 *
7289 * @return a method handle representing the loop.
7290 * @throws NullPointerException if either of the {@code iterations} or {@code body} handles is {@code null}.
7291 * @throws IllegalArgumentException if any argument violates the rules formulated above.
7292 *
7293 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle, MethodHandle)
7294 * @since 9
7295 */
7296 public static MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
7297 return countedLoop(empty(iterations.type()), iterations, init, body);
7298 }
7299
7300 /**
7301 * Constructs a loop that counts over a range of numbers.
7302 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
7303 * <p>
7304 * The loop counter {@code i} is a loop iteration variable of type {@code int}.
7305 * The {@code start} and {@code end} handles determine the start (inclusive) and end (exclusive)
7306 * values of the loop counter.
7307 * The loop counter will be initialized to the {@code int} value returned from the evaluation of the
7308 * {@code start} handle and run to the value returned from {@code end} (exclusively) with a step width of 1.
7309 * <p>
7310 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
7311 * of that type is also present. This variable is initialized using the optional {@code init} handle,
7312 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
7313 * <p>
7314 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
7315 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
7316 * iteration variable.
7317 * The result of the loop handle execution will be the final {@code V} value of that variable
7318 * (or {@code void} if there is no {@code V} variable).
7319 * <p>
7320 * The following rules hold for the argument handles:<ul>
7321 * <li>The {@code start} and {@code end} handles must not be {@code null}, and must both return
7322 * the common type {@code int}, referred to here as {@code I} in parameter type lists.
7323 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
7324 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
7325 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
7326 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
7327 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
7328 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
7329 * of types called the <em>internal parameter list</em>.
7330 * It will constrain the parameter lists of the other loop parts.
7331 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
7332 * with no additional {@code A} types, then the internal parameter list is extended by
7333 * the argument types {@code A...} of the {@code end} handle.
7334 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
7335 * list {@code (A...)} is called the <em>external parameter list</em>.
7336 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
7337 * additional state variable of the loop.
7338 * The body must both accept a leading parameter and return a value of this type {@code V}.
7339 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
7340 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
7341 * <a href="MethodHandles.html#effid">effectively identical</a>
7342 * to the external parameter list {@code (A...)}.
7343 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
7344 * {@linkplain #empty default value}.
7345 * <li>The parameter list of {@code start} (of some form {@code (A*)}) must be
7346 * effectively identical to the external parameter list {@code (A...)}.
7347 * <li>Likewise, the parameter list of {@code end} must be effectively identical
7348 * to the external parameter list.
7349 * </ul>
7350 * <p>
7351 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
7352 * <li>The loop handle's result type is the result type {@code V} of the body.
7353 * <li>The loop handle's parameter types are the types {@code (A...)},
7354 * from the external parameter list.
7355 * </ul>
7356 * <p>
7357 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
7358 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
7359 * arguments passed to the loop.
7360 * {@snippet lang="java" :
7361 * int start(A...);
7362 * int end(A...);
7363 * V init(A...);
7364 * V body(V, int, A...);
7365 * V countedLoop(A... a...) {
7366 * int e = end(a...);
7367 * int s = start(a...);
7368 * V v = init(a...);
7369 * for (int i = s; i < e; ++i) {
7370 * v = body(v, i, a...);
7371 * }
7372 * return v;
7373 * }
7374 * }
7375 *
7376 * @apiNote The implementation of this method can be expressed as follows:
7377 * {@snippet lang="java" :
7378 * MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
7379 * MethodHandle returnVar = dropArguments(identity(init.type().returnType()), 0, int.class, int.class);
7380 * // assume MH_increment and MH_predicate are handles to implementation-internal methods with
7381 * // the following semantics:
7382 * // MH_increment: (int limit, int counter) -> counter + 1
7383 * // MH_predicate: (int limit, int counter) -> counter < limit
7384 * Class<?> counterType = start.type().returnType(); // int
7385 * Class<?> returnType = body.type().returnType();
7386 * MethodHandle incr = MH_increment, pred = MH_predicate, retv = null;
7387 * if (returnType != void.class) { // ignore the V variable
7388 * incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
7389 * pred = dropArguments(pred, 1, returnType); // ditto
7390 * retv = dropArguments(identity(returnType), 0, counterType); // ignore limit
7391 * }
7392 * body = dropArguments(body, 0, counterType); // ignore the limit variable
7393 * MethodHandle[]
7394 * loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
7395 * bodyClause = { init, body }, // v = init(); v = body(v, i)
7396 * indexVar = { start, incr }; // i = start(); i = i + 1
7397 * return loop(loopLimit, bodyClause, indexVar);
7398 * }
7399 * }
7400 *
7401 * @param start a non-{@code null} handle to return the start value of the loop counter, which must be {@code int}.
7402 * See above for other constraints.
7403 * @param end a non-{@code null} handle to return the end value of the loop counter (the loop will run to
7404 * {@code end-1}). The result type must be {@code int}. See above for other constraints.
7405 * @param init optional initializer, providing the initial value of the loop variable.
7406 * May be {@code null}, implying a default initial value. See above for other constraints.
7407 * @param body body of the loop, which may not be {@code null}.
7408 * It controls the loop parameters and result type in the standard case (see above for details).
7409 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
7410 * and may accept any number of additional types.
7411 * See above for other constraints.
7412 *
7413 * @return a method handle representing the loop.
7414 * @throws NullPointerException if any of the {@code start}, {@code end}, or {@code body} handles is {@code null}.
7415 * @throws IllegalArgumentException if any argument violates the rules formulated above.
7416 *
7417 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle)
7418 * @since 9
7419 */
7420 public static MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
7421 countedLoopChecks(start, end, init, body);
7422 Class<?> counterType = start.type().returnType(); // int, but who's counting?
7423 Class<?> limitType = end.type().returnType(); // yes, int again
7424 Class<?> returnType = body.type().returnType();
7425 MethodHandle incr = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopStep);
7426 MethodHandle pred = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopPred);
7427 MethodHandle retv = null;
7428 if (returnType != void.class) {
7429 incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
7430 pred = dropArguments(pred, 1, returnType); // ditto
7431 retv = dropArguments(identity(returnType), 0, counterType);
7432 }
7433 body = dropArguments(body, 0, counterType); // ignore the limit variable
7434 MethodHandle[]
7435 loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
7436 bodyClause = { init, body }, // v = init(); v = body(v, i)
7437 indexVar = { start, incr }; // i = start(); i = i + 1
7438 return loop(loopLimit, bodyClause, indexVar);
7439 }
7440
7441 private static void countedLoopChecks(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
7442 Objects.requireNonNull(start);
7443 Objects.requireNonNull(end);
7444 Objects.requireNonNull(body);
7445 Class<?> counterType = start.type().returnType();
7446 if (counterType != int.class) {
7447 MethodType expected = start.type().changeReturnType(int.class);
7448 throw misMatchedTypes("start function", start.type(), expected);
7449 } else if (end.type().returnType() != counterType) {
7450 MethodType expected = end.type().changeReturnType(counterType);
7451 throw misMatchedTypes("end function", end.type(), expected);
7452 }
7453 MethodType bodyType = body.type();
7454 Class<?> returnType = bodyType.returnType();
7455 List<Class<?>> innerList = bodyType.parameterList();
7456 // strip leading V value if present
7457 int vsize = (returnType == void.class ? 0 : 1);
7458 if (vsize != 0 && (innerList.isEmpty() || innerList.get(0) != returnType)) {
7459 // argument list has no "V" => error
7460 MethodType expected = bodyType.insertParameterTypes(0, returnType);
7461 throw misMatchedTypes("body function", bodyType, expected);
7462 } else if (innerList.size() <= vsize || innerList.get(vsize) != counterType) {
7463 // missing I type => error
7464 MethodType expected = bodyType.insertParameterTypes(vsize, counterType);
7465 throw misMatchedTypes("body function", bodyType, expected);
7466 }
7467 List<Class<?>> outerList = innerList.subList(vsize + 1, innerList.size());
7468 if (outerList.isEmpty()) {
7469 // special case; take lists from end handle
7470 outerList = end.type().parameterList();
7471 innerList = bodyType.insertParameterTypes(vsize + 1, outerList).parameterList();
7472 }
7473 MethodType expected = methodType(counterType, outerList);
7474 if (!start.type().effectivelyIdenticalParameters(0, outerList)) {
7475 throw misMatchedTypes("start parameter types", start.type(), expected);
7476 }
7477 if (end.type() != start.type() &&
7478 !end.type().effectivelyIdenticalParameters(0, outerList)) {
7479 throw misMatchedTypes("end parameter types", end.type(), expected);
7480 }
7481 if (init != null) {
7482 MethodType initType = init.type();
7483 if (initType.returnType() != returnType ||
7484 !initType.effectivelyIdenticalParameters(0, outerList)) {
7485 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
7486 }
7487 }
7488 }
7489
7490 /**
7491 * Constructs a loop that ranges over the values produced by an {@code Iterator<T>}.
7492 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
7493 * <p>
7494 * The iterator itself will be determined by the evaluation of the {@code iterator} handle.
7495 * Each value it produces will be stored in a loop iteration variable of type {@code T}.
7496 * <p>
7497 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
7498 * of that type is also present. This variable is initialized using the optional {@code init} handle,
7499 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
7500 * <p>
7501 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
7502 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
7503 * iteration variable.
7504 * The result of the loop handle execution will be the final {@code V} value of that variable
7505 * (or {@code void} if there is no {@code V} variable).
7506 * <p>
7507 * The following rules hold for the argument handles:<ul>
7508 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
7509 * {@code (V T A...)V}, where {@code V} is non-{@code void}, or else {@code (T A...)void}.
7510 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
7511 * and we will write {@code (V T A...)V} with the understanding that a {@code void} type {@code V}
7512 * is quietly dropped from the parameter list, leaving {@code (T A...)V}.)
7513 * <li>The parameter list {@code (V T A...)} of the body contributes to a list
7514 * of types called the <em>internal parameter list</em>.
7515 * It will constrain the parameter lists of the other loop parts.
7516 * <li>As a special case, if the body contributes only {@code V} and {@code T} types,
7517 * with no additional {@code A} types, then the internal parameter list is extended by
7518 * the argument types {@code A...} of the {@code iterator} handle; if it is {@code null} the
7519 * single type {@code Iterable} is added and constitutes the {@code A...} list.
7520 * <li>If the iteration variable types {@code (V T)} are dropped from the internal parameter list, the resulting shorter
7521 * list {@code (A...)} is called the <em>external parameter list</em>.
7522 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
7523 * additional state variable of the loop.
7524 * The body must both accept a leading parameter and return a value of this type {@code V}.
7525 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
7526 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
7527 * <a href="MethodHandles.html#effid">effectively identical</a>
7528 * to the external parameter list {@code (A...)}.
7529 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
7530 * {@linkplain #empty default value}.
7531 * <li>If the {@code iterator} handle is non-{@code null}, it must have the return
7532 * type {@code java.util.Iterator} or a subtype thereof.
7533 * The iterator it produces when the loop is executed will be assumed
7534 * to yield values which can be converted to type {@code T}.
7535 * <li>The parameter list of an {@code iterator} that is non-{@code null} (of some form {@code (A*)}) must be
7536 * effectively identical to the external parameter list {@code (A...)}.
7537 * <li>If {@code iterator} is {@code null} it defaults to a method handle which behaves
7538 * like {@link java.lang.Iterable#iterator()}. In that case, the internal parameter list
7539 * {@code (V T A...)} must have at least one {@code A} type, and the default iterator
7540 * handle parameter is adjusted to accept the leading {@code A} type, as if by
7541 * the {@link MethodHandle#asType asType} conversion method.
7542 * The leading {@code A} type must be {@code Iterable} or a subtype thereof.
7543 * This conversion step, done at loop construction time, must not throw a {@code WrongMethodTypeException}.
7544 * </ul>
7545 * <p>
7546 * The type {@code T} may be either a primitive or reference.
7547 * Since type {@code Iterator<T>} is erased in the method handle representation to the raw type {@code Iterator},
7548 * the {@code iteratedLoop} combinator adjusts the leading argument type for {@code body} to {@code Object}
7549 * as if by the {@link MethodHandle#asType asType} conversion method.
7550 * Therefore, if an iterator of the wrong type appears as the loop is executed, runtime exceptions may occur
7551 * as the result of dynamic conversions performed by {@link MethodHandle#asType(MethodType)}.
7552 * <p>
7553 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
7554 * <li>The loop handle's result type is the result type {@code V} of the body.
7555 * <li>The loop handle's parameter types are the types {@code (A...)},
7556 * from the external parameter list.
7557 * </ul>
7558 * <p>
7559 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
7560 * the loop variable as well as the result type of the loop; {@code T}/{@code t}, that of the elements of the
7561 * structure the loop iterates over, and {@code A...}/{@code a...} represent arguments passed to the loop.
7562 * {@snippet lang="java" :
7563 * Iterator<T> iterator(A...); // defaults to Iterable::iterator
7564 * V init(A...);
7565 * V body(V,T,A...);
7566 * V iteratedLoop(A... a...) {
7567 * Iterator<T> it = iterator(a...);
7568 * V v = init(a...);
7569 * while (it.hasNext()) {
7570 * T t = it.next();
7571 * v = body(v, t, a...);
7572 * }
7573 * return v;
7574 * }
7575 * }
7576 *
7577 * @apiNote Example:
7578 * {@snippet lang="java" :
7579 * // get an iterator from a list
7580 * static List<String> reverseStep(List<String> r, String e) {
7581 * r.add(0, e);
7582 * return r;
7583 * }
7584 * static List<String> newArrayList() { return new ArrayList<>(); }
7585 * // assume MH_reverseStep and MH_newArrayList are handles to the above methods
7586 * MethodHandle loop = MethodHandles.iteratedLoop(null, MH_newArrayList, MH_reverseStep);
7587 * List<String> list = Arrays.asList("a", "b", "c", "d", "e");
7588 * List<String> reversedList = Arrays.asList("e", "d", "c", "b", "a");
7589 * assertEquals(reversedList, (List<String>) loop.invoke(list));
7590 * }
7591 *
7592 * @apiNote The implementation of this method can be expressed approximately as follows:
7593 * {@snippet lang="java" :
7594 * MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
7595 * // assume MH_next, MH_hasNext, MH_startIter are handles to methods of Iterator/Iterable
7596 * Class<?> returnType = body.type().returnType();
7597 * Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
7598 * MethodHandle nextVal = MH_next.asType(MH_next.type().changeReturnType(ttype));
7599 * MethodHandle retv = null, step = body, startIter = iterator;
7600 * if (returnType != void.class) {
7601 * // the simple thing first: in (I V A...), drop the I to get V
7602 * retv = dropArguments(identity(returnType), 0, Iterator.class);
7603 * // body type signature (V T A...), internal loop types (I V A...)
7604 * step = swapArguments(body, 0, 1); // swap V <-> T
7605 * }
7606 * if (startIter == null) startIter = MH_getIter;
7607 * MethodHandle[]
7608 * iterVar = { startIter, null, MH_hasNext, retv }, // it = iterator; while (it.hasNext())
7609 * bodyClause = { init, filterArguments(step, 0, nextVal) }; // v = body(v, t, a)
7610 * return loop(iterVar, bodyClause);
7611 * }
7612 * }
7613 *
7614 * @param iterator an optional handle to return the iterator to start the loop.
7615 * If non-{@code null}, the handle must return {@link java.util.Iterator} or a subtype.
7616 * See above for other constraints.
7617 * @param init optional initializer, providing the initial value of the loop variable.
7618 * May be {@code null}, implying a default initial value. See above for other constraints.
7619 * @param body body of the loop, which may not be {@code null}.
7620 * It controls the loop parameters and result type in the standard case (see above for details).
7621 * It must accept its own return type (if non-void) plus a {@code T} parameter (for the iterated values),
7622 * and may accept any number of additional types.
7623 * See above for other constraints.
7624 *
7625 * @return a method handle embodying the iteration loop functionality.
7626 * @throws NullPointerException if the {@code body} handle is {@code null}.
7627 * @throws IllegalArgumentException if any argument violates the above requirements.
7628 *
7629 * @since 9
7630 */
7631 public static MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
7632 Class<?> iterableType = iteratedLoopChecks(iterator, init, body);
7633 Class<?> returnType = body.type().returnType();
7634 MethodHandle hasNext = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iteratePred);
7635 MethodHandle nextRaw = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iterateNext);
7636 MethodHandle startIter;
7637 MethodHandle nextVal;
7638 {
7639 MethodType iteratorType;
7640 if (iterator == null) {
7641 // derive argument type from body, if available, else use Iterable
7642 startIter = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_initIterator);
7643 iteratorType = startIter.type().changeParameterType(0, iterableType);
7644 } else {
7645 // force return type to the internal iterator class
7646 iteratorType = iterator.type().changeReturnType(Iterator.class);
7647 startIter = iterator;
7648 }
7649 Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
7650 MethodType nextValType = nextRaw.type().changeReturnType(ttype);
7651
7652 // perform the asType transforms under an exception transformer, as per spec.:
7653 try {
7654 startIter = startIter.asType(iteratorType);
7655 nextVal = nextRaw.asType(nextValType);
7656 } catch (WrongMethodTypeException ex) {
7657 throw new IllegalArgumentException(ex);
7658 }
7659 }
7660
7661 MethodHandle retv = null, step = body;
7662 if (returnType != void.class) {
7663 // the simple thing first: in (I V A...), drop the I to get V
7664 retv = dropArguments(identity(returnType), 0, Iterator.class);
7665 // body type signature (V T A...), internal loop types (I V A...)
7666 step = swapArguments(body, 0, 1); // swap V <-> T
7667 }
7668
7669 MethodHandle[]
7670 iterVar = { startIter, null, hasNext, retv },
7671 bodyClause = { init, filterArgument(step, 0, nextVal) };
7672 return loop(iterVar, bodyClause);
7673 }
7674
7675 private static Class<?> iteratedLoopChecks(MethodHandle iterator, MethodHandle init, MethodHandle body) {
7676 Objects.requireNonNull(body);
7677 MethodType bodyType = body.type();
7678 Class<?> returnType = bodyType.returnType();
7679 List<Class<?>> internalParamList = bodyType.parameterList();
7680 // strip leading V value if present
7681 int vsize = (returnType == void.class ? 0 : 1);
7682 if (vsize != 0 && (internalParamList.isEmpty() || internalParamList.get(0) != returnType)) {
7683 // argument list has no "V" => error
7684 MethodType expected = bodyType.insertParameterTypes(0, returnType);
7685 throw misMatchedTypes("body function", bodyType, expected);
7686 } else if (internalParamList.size() <= vsize) {
7687 // missing T type => error
7688 MethodType expected = bodyType.insertParameterTypes(vsize, Object.class);
7689 throw misMatchedTypes("body function", bodyType, expected);
7690 }
7691 List<Class<?>> externalParamList = internalParamList.subList(vsize + 1, internalParamList.size());
7692 Class<?> iterableType = null;
7693 if (iterator != null) {
7694 // special case; if the body handle only declares V and T then
7695 // the external parameter list is obtained from iterator handle
7696 if (externalParamList.isEmpty()) {
7697 externalParamList = iterator.type().parameterList();
7698 }
7699 MethodType itype = iterator.type();
7700 if (!Iterator.class.isAssignableFrom(itype.returnType())) {
7701 throw newIllegalArgumentException("iteratedLoop first argument must have Iterator return type");
7702 }
7703 if (!itype.effectivelyIdenticalParameters(0, externalParamList)) {
7704 MethodType expected = methodType(itype.returnType(), externalParamList);
7705 throw misMatchedTypes("iterator parameters", itype, expected);
7706 }
7707 } else {
7708 if (externalParamList.isEmpty()) {
7709 // special case; if the iterator handle is null and the body handle
7710 // only declares V and T then the external parameter list consists
7711 // of Iterable
7712 externalParamList = List.of(Iterable.class);
7713 iterableType = Iterable.class;
7714 } else {
7715 // special case; if the iterator handle is null and the external
7716 // parameter list is not empty then the first parameter must be
7717 // assignable to Iterable
7718 iterableType = externalParamList.get(0);
7719 if (!Iterable.class.isAssignableFrom(iterableType)) {
7720 throw newIllegalArgumentException(
7721 "inferred first loop argument must inherit from Iterable: " + iterableType);
7722 }
7723 }
7724 }
7725 if (init != null) {
7726 MethodType initType = init.type();
7727 if (initType.returnType() != returnType ||
7728 !initType.effectivelyIdenticalParameters(0, externalParamList)) {
7729 throw misMatchedTypes("loop initializer", initType, methodType(returnType, externalParamList));
7730 }
7731 }
7732 return iterableType; // help the caller a bit
7733 }
7734
7735 /*non-public*/
7736 static MethodHandle swapArguments(MethodHandle mh, int i, int j) {
7737 // there should be a better way to uncross my wires
7738 int arity = mh.type().parameterCount();
7739 int[] order = new int[arity];
7740 for (int k = 0; k < arity; k++) order[k] = k;
7741 order[i] = j; order[j] = i;
7742 Class<?>[] types = mh.type().parameterArray();
7743 Class<?> ti = types[i]; types[i] = types[j]; types[j] = ti;
7744 MethodType swapType = methodType(mh.type().returnType(), types);
7745 return permuteArguments(mh, swapType, order);
7746 }
7747
7748 /**
7749 * Makes a method handle that adapts a {@code target} method handle by wrapping it in a {@code try-finally} block.
7750 * Another method handle, {@code cleanup}, represents the functionality of the {@code finally} block. Any exception
7751 * thrown during the execution of the {@code target} handle will be passed to the {@code cleanup} handle. The
7752 * exception will be rethrown, unless {@code cleanup} handle throws an exception first. The
7753 * value returned from the {@code cleanup} handle's execution will be the result of the execution of the
7754 * {@code try-finally} handle.
7755 * <p>
7756 * The {@code cleanup} handle will be passed one or two additional leading arguments.
7757 * The first is the exception thrown during the
7758 * execution of the {@code target} handle, or {@code null} if no exception was thrown.
7759 * The second is the result of the execution of the {@code target} handle, or, if it throws an exception,
7760 * a {@code null}, zero, or {@code false} value of the required type is supplied as a placeholder.
7761 * The second argument is not present if the {@code target} handle has a {@code void} return type.
7762 * (Note that, except for argument type conversions, combinators represent {@code void} values in parameter lists
7763 * by omitting the corresponding paradoxical arguments, not by inserting {@code null} or zero values.)
7764 * <p>
7765 * The {@code target} and {@code cleanup} handles must have the same corresponding argument and return types, except
7766 * that the {@code cleanup} handle may omit trailing arguments. Also, the {@code cleanup} handle must have one or
7767 * two extra leading parameters:<ul>
7768 * <li>a {@code Throwable}, which will carry the exception thrown by the {@code target} handle (if any); and
7769 * <li>a parameter of the same type as the return type of both {@code target} and {@code cleanup}, which will carry
7770 * the result from the execution of the {@code target} handle.
7771 * This parameter is not present if the {@code target} returns {@code void}.
7772 * </ul>
7773 * <p>
7774 * The pseudocode for the resulting adapter looks as follows. In the code, {@code V} represents the result type of
7775 * the {@code try/finally} construct; {@code A}/{@code a}, the types and values of arguments to the resulting
7776 * handle consumed by the cleanup; and {@code B}/{@code b}, those of arguments to the resulting handle discarded by
7777 * the cleanup.
7778 * {@snippet lang="java" :
7779 * V target(A..., B...);
7780 * V cleanup(Throwable, V, A...);
7781 * V adapter(A... a, B... b) {
7782 * V result = (zero value for V);
7783 * Throwable throwable = null;
7784 * try {
7785 * result = target(a..., b...);
7786 * } catch (Throwable t) {
7787 * throwable = t;
7788 * throw t;
7789 * } finally {
7790 * result = cleanup(throwable, result, a...);
7791 * }
7792 * return result;
7793 * }
7794 * }
7795 * <p>
7796 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
7797 * be modified by execution of the target, and so are passed unchanged
7798 * from the caller to the cleanup, if it is invoked.
7799 * <p>
7800 * The target and cleanup must return the same type, even if the cleanup
7801 * always throws.
7802 * To create such a throwing cleanup, compose the cleanup logic
7803 * with {@link #throwException throwException},
7804 * in order to create a method handle of the correct return type.
7805 * <p>
7806 * Note that {@code tryFinally} never converts exceptions into normal returns.
7807 * In rare cases where exceptions must be converted in that way, first wrap
7808 * the target with {@link #catchException(MethodHandle, Class, MethodHandle)}
7809 * to capture an outgoing exception, and then wrap with {@code tryFinally}.
7810 * <p>
7811 * It is recommended that the first parameter type of {@code cleanup} be
7812 * declared {@code Throwable} rather than a narrower subtype. This ensures
7813 * {@code cleanup} will always be invoked with whatever exception that
7814 * {@code target} throws. Declaring a narrower type may result in a
7815 * {@code ClassCastException} being thrown by the {@code try-finally}
7816 * handle if the type of the exception thrown by {@code target} is not
7817 * assignable to the first parameter type of {@code cleanup}. Note that
7818 * various exception types of {@code VirtualMachineError},
7819 * {@code LinkageError}, and {@code RuntimeException} can in principle be
7820 * thrown by almost any kind of Java code, and a finally clause that
7821 * catches (say) only {@code IOException} would mask any of the others
7822 * behind a {@code ClassCastException}.
7823 *
7824 * @param target the handle whose execution is to be wrapped in a {@code try} block.
7825 * @param cleanup the handle that is invoked in the finally block.
7826 *
7827 * @return a method handle embodying the {@code try-finally} block composed of the two arguments.
7828 * @throws NullPointerException if any argument is null
7829 * @throws IllegalArgumentException if {@code cleanup} does not accept
7830 * the required leading arguments, or if the method handle types do
7831 * not match in their return types and their
7832 * corresponding trailing parameters
7833 *
7834 * @see MethodHandles#catchException(MethodHandle, Class, MethodHandle)
7835 * @since 9
7836 */
7837 public static MethodHandle tryFinally(MethodHandle target, MethodHandle cleanup) {
7838 Class<?>[] targetParamTypes = target.type().ptypes();
7839 Class<?> rtype = target.type().returnType();
7840
7841 tryFinallyChecks(target, cleanup);
7842
7843 // Match parameter lists: if the cleanup has a shorter parameter list than the target, add ignored arguments.
7844 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
7845 // target parameter list.
7846 cleanup = dropArgumentsToMatch(cleanup, (rtype == void.class ? 1 : 2), targetParamTypes, 0, false);
7847
7848 // Ensure that the intrinsic type checks the instance thrown by the
7849 // target against the first parameter of cleanup
7850 cleanup = cleanup.asType(cleanup.type().changeParameterType(0, Throwable.class));
7851
7852 // Use asFixedArity() to avoid unnecessary boxing of last argument for VarargsCollector case.
7853 return MethodHandleImpl.makeTryFinally(target.asFixedArity(), cleanup.asFixedArity(), rtype, targetParamTypes);
7854 }
7855
7856 private static void tryFinallyChecks(MethodHandle target, MethodHandle cleanup) {
7857 Class<?> rtype = target.type().returnType();
7858 if (rtype != cleanup.type().returnType()) {
7859 throw misMatchedTypes("target and return types", cleanup.type().returnType(), rtype);
7860 }
7861 MethodType cleanupType = cleanup.type();
7862 if (!Throwable.class.isAssignableFrom(cleanupType.parameterType(0))) {
7863 throw misMatchedTypes("cleanup first argument and Throwable", cleanup.type(), Throwable.class);
7864 }
7865 if (rtype != void.class && cleanupType.parameterType(1) != rtype) {
7866 throw misMatchedTypes("cleanup second argument and target return type", cleanup.type(), rtype);
7867 }
7868 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
7869 // target parameter list.
7870 int cleanupArgIndex = rtype == void.class ? 1 : 2;
7871 if (!cleanupType.effectivelyIdenticalParameters(cleanupArgIndex, target.type().parameterList())) {
7872 throw misMatchedTypes("cleanup parameters after (Throwable,result) and target parameter list prefix",
7873 cleanup.type(), target.type());
7874 }
7875 }
7876
7877 /**
7878 * Creates a table switch method handle, which can be used to switch over a set of target
7879 * method handles, based on a given target index, called selector.
7880 * <p>
7881 * For a selector value of {@code n}, where {@code n} falls in the range {@code [0, N)},
7882 * and where {@code N} is the number of target method handles, the table switch method
7883 * handle will invoke the n-th target method handle from the list of target method handles.
7884 * <p>
7885 * For a selector value that does not fall in the range {@code [0, N)}, the table switch
7886 * method handle will invoke the given fallback method handle.
7887 * <p>
7888 * All method handles passed to this method must have the same type, with the additional
7889 * requirement that the leading parameter be of type {@code int}. The leading parameter
7890 * represents the selector.
7891 * <p>
7892 * Any trailing parameters present in the type will appear on the returned table switch
7893 * method handle as well. Any arguments assigned to these parameters will be forwarded,
7894 * together with the selector value, to the selected method handle when invoking it.
7895 *
7896 * @apiNote Example:
7897 * The cases each drop the {@code selector} value they are given, and take an additional
7898 * {@code String} argument, which is concatenated (using {@link String#concat(String)})
7899 * to a specific constant label string for each case:
7900 * {@snippet lang="java" :
7901 * MethodHandles.Lookup lookup = MethodHandles.lookup();
7902 * MethodHandle caseMh = lookup.findVirtual(String.class, "concat",
7903 * MethodType.methodType(String.class, String.class));
7904 * caseMh = MethodHandles.dropArguments(caseMh, 0, int.class);
7905 *
7906 * MethodHandle caseDefault = MethodHandles.insertArguments(caseMh, 1, "default: ");
7907 * MethodHandle case0 = MethodHandles.insertArguments(caseMh, 1, "case 0: ");
7908 * MethodHandle case1 = MethodHandles.insertArguments(caseMh, 1, "case 1: ");
7909 *
7910 * MethodHandle mhSwitch = MethodHandles.tableSwitch(
7911 * caseDefault,
7912 * case0,
7913 * case1
7914 * );
7915 *
7916 * assertEquals("default: data", (String) mhSwitch.invokeExact(-1, "data"));
7917 * assertEquals("case 0: data", (String) mhSwitch.invokeExact(0, "data"));
7918 * assertEquals("case 1: data", (String) mhSwitch.invokeExact(1, "data"));
7919 * assertEquals("default: data", (String) mhSwitch.invokeExact(2, "data"));
7920 * }
7921 *
7922 * @param fallback the fallback method handle that is called when the selector is not
7923 * within the range {@code [0, N)}.
7924 * @param targets array of target method handles.
7925 * @return the table switch method handle.
7926 * @throws NullPointerException if {@code fallback}, the {@code targets} array, or any
7927 * any of the elements of the {@code targets} array are
7928 * {@code null}.
7929 * @throws IllegalArgumentException if the {@code targets} array is empty, if the leading
7930 * parameter of the fallback handle or any of the target
7931 * handles is not {@code int}, or if the types of
7932 * the fallback handle and all of target handles are
7933 * not the same.
7934 */
7935 public static MethodHandle tableSwitch(MethodHandle fallback, MethodHandle... targets) {
7936 Objects.requireNonNull(fallback);
7937 Objects.requireNonNull(targets);
7938 targets = targets.clone();
7939 MethodType type = tableSwitchChecks(fallback, targets);
7940 return MethodHandleImpl.makeTableSwitch(type, fallback, targets);
7941 }
7942
7943 private static MethodType tableSwitchChecks(MethodHandle defaultCase, MethodHandle[] caseActions) {
7944 if (caseActions.length == 0)
7945 throw new IllegalArgumentException("Not enough cases: " + Arrays.toString(caseActions));
7946
7947 MethodType expectedType = defaultCase.type();
7948
7949 if (!(expectedType.parameterCount() >= 1) || expectedType.parameterType(0) != int.class)
7950 throw new IllegalArgumentException(
7951 "Case actions must have int as leading parameter: " + Arrays.toString(caseActions));
7952
7953 for (MethodHandle mh : caseActions) {
7954 Objects.requireNonNull(mh);
7955 if (mh.type() != expectedType)
7956 throw new IllegalArgumentException(
7957 "Case actions must have the same type: " + Arrays.toString(caseActions));
7958 }
7959
7960 return expectedType;
7961 }
7962
7963 /**
7964 * Creates a var handle object, which can be used to dereference a {@linkplain java.lang.foreign.MemorySegment memory segment}
7965 * at a given byte offset, using the provided value layout.
7966 *
7967 * <p>The provided layout specifies the {@linkplain ValueLayout#carrier() carrier type},
7968 * the {@linkplain ValueLayout#byteSize() byte size},
7969 * the {@linkplain ValueLayout#byteAlignment() byte alignment} and the {@linkplain ValueLayout#order() byte order}
7970 * associated with the returned var handle.
7971 *
7972 * <p>The list of coordinate types associated with the returned var handle is {@code (MemorySegment, long)},
7973 * where the {@code long} coordinate type corresponds to byte offset into the given memory segment coordinate.
7974 * Thus, the returned var handle accesses bytes at an offset in a given memory segment, composing bytes to or from
7975 * a value of the var handle type. Moreover, the access operation will honor the endianness and the
7976 * alignment constraints expressed in the provided layout.
7977 *
7978 * <p>As an example, consider the memory layout expressed by a {@link GroupLayout} instance constructed as follows:
7979 * {@snippet lang="java" :
7980 * GroupLayout seq = java.lang.foreign.MemoryLayout.structLayout(
7981 * MemoryLayout.paddingLayout(4),
7982 * ValueLayout.JAVA_INT.withOrder(ByteOrder.BIG_ENDIAN).withName("value")
7983 * );
7984 * }
7985 * To access the member layout named {@code value}, we can construct a memory segment view var handle as follows:
7986 * {@snippet lang="java" :
7987 * VarHandle handle = MethodHandles.memorySegmentViewVarHandle(ValueLayout.JAVA_INT.withOrder(ByteOrder.BIG_ENDIAN)); //(MemorySegment, long) -> int
7988 * handle = MethodHandles.insertCoordinates(handle, 1, 4); //(MemorySegment) -> int
7989 * }
7990 *
7991 * @apiNote The resulting var handle features certain <i>access mode restrictions</i>,
7992 * which are common to all memory segment view var handles. A memory segment view var handle is associated
7993 * with an access size {@code S} and an alignment constraint {@code B}
7994 * (both expressed in bytes). We say that a memory access operation is <em>fully aligned</em> if it occurs
7995 * at a memory address {@code A} which is compatible with both alignment constraints {@code S} and {@code B}.
7996 * If access is fully aligned then following access modes are supported and are
7997 * guaranteed to support atomic access:
7998 * <ul>
7999 * <li>read write access modes for all {@code T}, with the exception of
8000 * access modes {@code get} and {@code set} for {@code long} and
8001 * {@code double} on 32-bit platforms.
8002 * <li>atomic update access modes for {@code int}, {@code long},
8003 * {@code float}, {@code double} or {@link MemorySegment}.
8004 * (Future major platform releases of the JDK may support additional
8005 * types for certain currently unsupported access modes.)
8006 * <li>numeric atomic update access modes for {@code int}, {@code long} and {@link MemorySegment}.
8007 * (Future major platform releases of the JDK may support additional
8008 * numeric types for certain currently unsupported access modes.)
8009 * <li>bitwise atomic update access modes for {@code int}, {@code long} and {@link MemorySegment}.
8010 * (Future major platform releases of the JDK may support additional
8011 * numeric types for certain currently unsupported access modes.)
8012 * </ul>
8013 *
8014 * If {@code T} is {@code float}, {@code double} or {@link MemorySegment} then atomic
8015 * update access modes compare values using their bitwise representation
8016 * (see {@link Float#floatToRawIntBits},
8017 * {@link Double#doubleToRawLongBits} and {@link MemorySegment#address()}, respectively).
8018 * <p>
8019 * Alternatively, a memory access operation is <em>partially aligned</em> if it occurs at a memory address {@code A}
8020 * which is only compatible with the alignment constraint {@code B}; in such cases, access for anything other than the
8021 * {@code get} and {@code set} access modes will result in an {@code IllegalStateException}. If access is partially aligned,
8022 * atomic access is only guaranteed with respect to the largest power of two that divides the GCD of {@code A} and {@code S}.
8023 * <p>
8024 * In all other cases, we say that a memory access operation is <em>misaligned</em>; in such cases an
8025 * {@code IllegalStateException} is thrown, irrespective of the access mode being used.
8026 * <p>
8027 * Finally, if {@code T} is {@code MemorySegment} all write access modes throw {@link IllegalArgumentException}
8028 * unless the value to be written is a {@linkplain MemorySegment#isNative() native} memory segment.
8029 *
8030 * @param layout the value layout for which a memory access handle is to be obtained.
8031 * @return the new memory segment view var handle.
8032 * @throws NullPointerException if {@code layout} is {@code null}.
8033 * @see MemoryLayout#varHandle(MemoryLayout.PathElement...)
8034 * @since 19
8035 */
8036 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN)
8037 public static VarHandle memorySegmentViewVarHandle(ValueLayout layout) {
8038 Objects.requireNonNull(layout);
8039 return Utils.makeSegmentViewVarHandle(layout);
8040 }
8041
8042 /**
8043 * Adapts a target var handle by pre-processing incoming and outgoing values using a pair of filter functions.
8044 * <p>
8045 * When calling e.g. {@link VarHandle#set(Object...)} on the resulting var handle, the incoming value (of type {@code T}, where
8046 * {@code T} is the <em>last</em> parameter type of the first filter function) is processed using the first filter and then passed
8047 * to the target var handle.
8048 * Conversely, when calling e.g. {@link VarHandle#get(Object...)} on the resulting var handle, the return value obtained from
8049 * the target var handle (of type {@code T}, where {@code T} is the <em>last</em> parameter type of the second filter function)
8050 * is processed using the second filter and returned to the caller. More advanced access mode types, such as
8051 * {@link VarHandle.AccessMode#COMPARE_AND_EXCHANGE} might apply both filters at the same time.
8052 * <p>
8053 * For the boxing and unboxing filters to be well-formed, their types must be of the form {@code (A... , S) -> T} and
8054 * {@code (A... , T) -> S}, respectively, where {@code T} is the type of the target var handle. If this is the case,
8055 * the resulting var handle will have type {@code S} and will feature the additional coordinates {@code A...} (which
8056 * will be appended to the coordinates of the target var handle).
8057 * <p>
8058 * If the boxing and unboxing filters throw any checked exceptions when invoked, the resulting var handle will
8059 * throw an {@link IllegalStateException}.
8060 * <p>
8061 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
8062 * atomic access guarantees as those featured by the target var handle.
8063 *
8064 * @param target the target var handle
8065 * @param filterToTarget a filter to convert some type {@code S} into the type of {@code target}
8066 * @param filterFromTarget a filter to convert the type of {@code target} to some type {@code S}
8067 * @return an adapter var handle which accepts a new type, performing the provided boxing/unboxing conversions.
8068 * @throws IllegalArgumentException if {@code filterFromTarget} and {@code filterToTarget} are not well-formed, that is, they have types
8069 * other than {@code (A... , S) -> T} and {@code (A... , T) -> S}, respectively, where {@code T} is the type of the target var handle,
8070 * or if it's determined that either {@code filterFromTarget} or {@code filterToTarget} throws any checked exceptions.
8071 * @throws NullPointerException if any of the arguments is {@code null}.
8072 * @since 19
8073 */
8074 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN)
8075 public static VarHandle filterValue(VarHandle target, MethodHandle filterToTarget, MethodHandle filterFromTarget) {
8076 return VarHandles.filterValue(target, filterToTarget, filterFromTarget);
8077 }
8078
8079 /**
8080 * Adapts a target var handle by pre-processing incoming coordinate values using unary filter functions.
8081 * <p>
8082 * When calling e.g. {@link VarHandle#get(Object...)} on the resulting var handle, the incoming coordinate values
8083 * starting at position {@code pos} (of type {@code C1, C2 ... Cn}, where {@code C1, C2 ... Cn} are the return types
8084 * of the unary filter functions) are transformed into new values (of type {@code S1, S2 ... Sn}, where {@code S1, S2 ... Sn} are the
8085 * parameter types of the unary filter functions), and then passed (along with any coordinate that was left unaltered
8086 * by the adaptation) to the target var handle.
8087 * <p>
8088 * For the coordinate filters to be well-formed, their types must be of the form {@code S1 -> T1, S2 -> T1 ... Sn -> Tn},
8089 * where {@code T1, T2 ... Tn} are the coordinate types starting at position {@code pos} of the target var handle.
8090 * <p>
8091 * If any of the filters throws a checked exception when invoked, the resulting var handle will
8092 * throw an {@link IllegalStateException}.
8093 * <p>
8094 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
8095 * atomic access guarantees as those featured by the target var handle.
8096 *
8097 * @param target the target var handle
8098 * @param pos the position of the first coordinate to be transformed
8099 * @param filters the unary functions which are used to transform coordinates starting at position {@code pos}
8100 * @return an adapter var handle which accepts new coordinate types, applying the provided transformation
8101 * to the new coordinate values.
8102 * @throws IllegalArgumentException if the handles in {@code filters} are not well-formed, that is, they have types
8103 * other than {@code S1 -> T1, S2 -> T2, ... Sn -> Tn} where {@code T1, T2 ... Tn} are the coordinate types starting
8104 * at position {@code pos} of the target var handle, if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive,
8105 * or if more filters are provided than the actual number of coordinate types available starting at {@code pos},
8106 * or if it's determined that any of the filters throws any checked exceptions.
8107 * @throws NullPointerException if any of the arguments is {@code null} or {@code filters} contains {@code null}.
8108 * @since 19
8109 */
8110 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN)
8111 public static VarHandle filterCoordinates(VarHandle target, int pos, MethodHandle... filters) {
8112 return VarHandles.filterCoordinates(target, pos, filters);
8113 }
8114
8115 /**
8116 * Provides a target var handle with one or more <em>bound coordinates</em>
8117 * in advance of the var handle's invocation. As a consequence, the resulting var handle will feature less
8118 * coordinate types than the target var handle.
8119 * <p>
8120 * When calling e.g. {@link VarHandle#get(Object...)} on the resulting var handle, incoming coordinate values
8121 * are joined with bound coordinate values, and then passed to the target var handle.
8122 * <p>
8123 * For the bound coordinates to be well-formed, their types must be {@code T1, T2 ... Tn },
8124 * where {@code T1, T2 ... Tn} are the coordinate types starting at position {@code pos} of the target var handle.
8125 * <p>
8126 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
8127 * atomic access guarantees as those featured by the target var handle.
8128 *
8129 * @param target the var handle to invoke after the bound coordinates are inserted
8130 * @param pos the position of the first coordinate to be inserted
8131 * @param values the series of bound coordinates to insert
8132 * @return an adapter var handle which inserts additional coordinates,
8133 * before calling the target var handle
8134 * @throws IllegalArgumentException if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive,
8135 * or if more values are provided than the actual number of coordinate types available starting at {@code pos}.
8136 * @throws ClassCastException if the bound coordinates in {@code values} are not well-formed, that is, they have types
8137 * other than {@code T1, T2 ... Tn }, where {@code T1, T2 ... Tn} are the coordinate types starting at position {@code pos}
8138 * of the target var handle.
8139 * @throws NullPointerException if any of the arguments is {@code null} or {@code values} contains {@code null}.
8140 * @since 19
8141 */
8142 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN)
8143 public static VarHandle insertCoordinates(VarHandle target, int pos, Object... values) {
8144 return VarHandles.insertCoordinates(target, pos, values);
8145 }
8146
8147 /**
8148 * Provides a var handle which adapts the coordinate values of the target var handle, by re-arranging them
8149 * so that the new coordinates match the provided ones.
8150 * <p>
8151 * The given array controls the reordering.
8152 * Call {@code #I} the number of incoming coordinates (the value
8153 * {@code newCoordinates.size()}), and call {@code #O} the number
8154 * of outgoing coordinates (the number of coordinates associated with the target var handle).
8155 * Then the length of the reordering array must be {@code #O},
8156 * and each element must be a non-negative number less than {@code #I}.
8157 * For every {@code N} less than {@code #O}, the {@code N}-th
8158 * outgoing coordinate will be taken from the {@code I}-th incoming
8159 * coordinate, where {@code I} is {@code reorder[N]}.
8160 * <p>
8161 * No coordinate value conversions are applied.
8162 * The type of each incoming coordinate, as determined by {@code newCoordinates},
8163 * must be identical to the type of the corresponding outgoing coordinate
8164 * in the target var handle.
8165 * <p>
8166 * The reordering array need not specify an actual permutation.
8167 * An incoming coordinate will be duplicated if its index appears
8168 * more than once in the array, and an incoming coordinate will be dropped
8169 * if its index does not appear in the array.
8170 * <p>
8171 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
8172 * atomic access guarantees as those featured by the target var handle.
8173 * @param target the var handle to invoke after the coordinates have been reordered
8174 * @param newCoordinates the new coordinate types
8175 * @param reorder an index array which controls the reordering
8176 * @return an adapter var handle which re-arranges the incoming coordinate values,
8177 * before calling the target var handle
8178 * @throws IllegalArgumentException if the index array length is not equal to
8179 * the number of coordinates of the target var handle, or if any index array element is not a valid index for
8180 * a coordinate of {@code newCoordinates}, or if two corresponding coordinate types in
8181 * the target var handle and in {@code newCoordinates} are not identical.
8182 * @throws NullPointerException if any of the arguments is {@code null} or {@code newCoordinates} contains {@code null}.
8183 * @since 19
8184 */
8185 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN)
8186 public static VarHandle permuteCoordinates(VarHandle target, List<Class<?>> newCoordinates, int... reorder) {
8187 return VarHandles.permuteCoordinates(target, newCoordinates, reorder);
8188 }
8189
8190 /**
8191 * Adapts a target var handle by pre-processing
8192 * a sub-sequence of its coordinate values with a filter (a method handle).
8193 * The pre-processed coordinates are replaced by the result (if any) of the
8194 * filter function and the target var handle is then called on the modified (usually shortened)
8195 * coordinate list.
8196 * <p>
8197 * If {@code R} is the return type of the filter, then:
8198 * <ul>
8199 * <li>if {@code R} <em>is not</em> {@code void}, the target var handle must have a coordinate of type {@code R} in
8200 * position {@code pos}. The parameter types of the filter will replace the coordinate type at position {@code pos}
8201 * of the target var handle. When the returned var handle is invoked, it will be as if the filter is invoked first,
8202 * and its result is passed in place of the coordinate at position {@code pos} in a downstream invocation of the
8203 * target var handle.</li>
8204 * <li> if {@code R} <em>is</em> {@code void}, the parameter types (if any) of the filter will be inserted in the
8205 * coordinate type list of the target var handle at position {@code pos}. In this case, when the returned var handle
8206 * is invoked, the filter essentially acts as a side effect, consuming some of the coordinate values, before a
8207 * downstream invocation of the target var handle.</li>
8208 * </ul>
8209 * <p>
8210 * If any of the filters throws a checked exception when invoked, the resulting var handle will
8211 * throw an {@link IllegalStateException}.
8212 * <p>
8213 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
8214 * atomic access guarantees as those featured by the target var handle.
8215 *
8216 * @param target the var handle to invoke after the coordinates have been filtered
8217 * @param pos the position in the coordinate list of the target var handle where the filter is to be inserted
8218 * @param filter the filter method handle
8219 * @return an adapter var handle which filters the incoming coordinate values,
8220 * before calling the target var handle
8221 * @throws IllegalArgumentException if the return type of {@code filter}
8222 * is not void, and it is not the same as the {@code pos} coordinate of the target var handle,
8223 * if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive,
8224 * if the resulting var handle's type would have <a href="MethodHandle.html#maxarity">too many coordinates</a>,
8225 * or if it's determined that {@code filter} throws any checked exceptions.
8226 * @throws NullPointerException if any of the arguments is {@code null}.
8227 * @since 19
8228 */
8229 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN)
8230 public static VarHandle collectCoordinates(VarHandle target, int pos, MethodHandle filter) {
8231 return VarHandles.collectCoordinates(target, pos, filter);
8232 }
8233
8234 /**
8235 * Returns a var handle which will discard some dummy coordinates before delegating to the
8236 * target var handle. As a consequence, the resulting var handle will feature more
8237 * coordinate types than the target var handle.
8238 * <p>
8239 * The {@code pos} argument may range between zero and <i>N</i>, where <i>N</i> is the arity of the
8240 * target var handle's coordinate types. If {@code pos} is zero, the dummy coordinates will precede
8241 * the target's real arguments; if {@code pos} is <i>N</i> they will come after.
8242 * <p>
8243 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
8244 * atomic access guarantees as those featured by the target var handle.
8245 *
8246 * @param target the var handle to invoke after the dummy coordinates are dropped
8247 * @param pos position of the first coordinate to drop (zero for the leftmost)
8248 * @param valueTypes the type(s) of the coordinate(s) to drop
8249 * @return an adapter var handle which drops some dummy coordinates,
8250 * before calling the target var handle
8251 * @throws IllegalArgumentException if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive.
8252 * @throws NullPointerException if any of the arguments is {@code null} or {@code valueTypes} contains {@code null}.
8253 * @since 19
8254 */
8255 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN)
8256 public static VarHandle dropCoordinates(VarHandle target, int pos, Class<?>... valueTypes) {
8257 return VarHandles.dropCoordinates(target, pos, valueTypes);
8258 }
8259 }