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 public static Lookup publicLookup() {
180 return Lookup.PUBLIC_LOOKUP;
181 }
182
183 /**
184 * Returns a {@link Lookup lookup} object on a target class to emulate all supported
185 * bytecode behaviors, including <a href="MethodHandles.Lookup.html#privacc">private access</a>.
186 * The returned lookup object can provide access to classes in modules and packages,
187 * and members of those classes, outside the normal rules of Java access control,
188 * instead conforming to the more permissive rules for modular <em>deep reflection</em>.
189 * <p>
190 * A caller, specified as a {@code Lookup} object, in module {@code M1} is
191 * allowed to do deep reflection on module {@code M2} and package of the target class
192 * if and only if all of the following conditions are {@code true}:
193 * <ul>
194 * <li>If there is a security manager, its {@code checkPermission} method is
195 * called to check {@code ReflectPermission("suppressAccessChecks")} and
196 * that must return normally.
197 * <li>The caller lookup object must have {@linkplain Lookup#hasFullPrivilegeAccess()
198 * full privilege access}. Specifically:
199 * <ul>
200 * <li>The caller lookup object must have the {@link Lookup#MODULE MODULE} lookup mode.
201 * (This is because otherwise there would be no way to ensure the original lookup
202 * creator was a member of any particular module, and so any subsequent checks
203 * for readability and qualified exports would become ineffective.)
204 * <li>The caller lookup object must have {@link Lookup#PRIVATE PRIVATE} access.
205 * (This is because an application intending to share intra-module access
206 * using {@link Lookup#MODULE MODULE} alone will inadvertently also share
207 * deep reflection to its own module.)
208 * </ul>
209 * <li>The target class must be a proper class, not a primitive or array class.
210 * (Thus, {@code M2} is well-defined.)
211 * <li>If the caller module {@code M1} differs from
212 * the target module {@code M2} then both of the following must be true:
213 * <ul>
214 * <li>{@code M1} {@link Module#canRead reads} {@code M2}.</li>
215 * <li>{@code M2} {@link Module#isOpen(String,Module) opens} the package
216 * containing the target class to at least {@code M1}.</li>
217 * </ul>
218 * </ul>
219 * <p>
220 * If any of the above checks is violated, this method fails with an
221 * exception.
222 * <p>
223 * Otherwise, if {@code M1} and {@code M2} are the same module, this method
224 * returns a {@code Lookup} on {@code targetClass} with
225 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access}
226 * with {@code null} previous lookup class.
227 * <p>
228 * Otherwise, {@code M1} and {@code M2} are two different modules. This method
229 * returns a {@code Lookup} on {@code targetClass} that records
230 * the lookup class of the caller as the new previous lookup class with
231 * {@code PRIVATE} access but no {@code MODULE} access.
232 * <p>
233 * The resulting {@code Lookup} object has no {@code ORIGINAL} access.
234 *
235 * @apiNote The {@code Lookup} object returned by this method is allowed to
236 * {@linkplain Lookup#defineClass(byte[]) define classes} in the runtime package
237 * of {@code targetClass}. Extreme caution should be taken when opening a package
238 * to another module as such defined classes have the same full privilege
239 * access as other members in {@code targetClass}'s module.
240 *
241 * @param targetClass the target class
242 * @param caller the caller lookup object
243 * @return a lookup object for the target class, with private access
244 * @throws IllegalArgumentException if {@code targetClass} is a primitive type or void or array class
245 * @throws NullPointerException if {@code targetClass} or {@code caller} is {@code null}
246 * @throws SecurityException if denied by the security manager
247 * @throws IllegalAccessException if any of the other access checks specified above fails
248 * @since 9
249 * @see Lookup#dropLookupMode
250 * @see <a href="MethodHandles.Lookup.html#cross-module-lookup">Cross-module lookups</a>
251 */
252 public static Lookup privateLookupIn(Class<?> targetClass, Lookup caller) throws IllegalAccessException {
253 if (caller.allowedModes == Lookup.TRUSTED) {
254 return new Lookup(targetClass);
255 }
256
257 @SuppressWarnings("removal")
258 SecurityManager sm = System.getSecurityManager();
259 if (sm != null) sm.checkPermission(SecurityConstants.ACCESS_PERMISSION);
260 if (targetClass.isPrimitive())
261 throw new IllegalArgumentException(targetClass + " is a primitive class");
262 if (targetClass.isArray())
263 throw new IllegalArgumentException(targetClass + " is an array class");
264 // Ensure that we can reason accurately about private and module access.
265 int requireAccess = Lookup.PRIVATE|Lookup.MODULE;
266 if ((caller.lookupModes() & requireAccess) != requireAccess)
267 throw new IllegalAccessException("caller does not have PRIVATE and MODULE lookup mode");
268
269 // previous lookup class is never set if it has MODULE access
270 assert caller.previousLookupClass() == null;
271
272 Class<?> callerClass = caller.lookupClass();
273 Module callerModule = callerClass.getModule(); // M1
274 Module targetModule = targetClass.getModule(); // M2
275 Class<?> newPreviousClass = null;
276 int newModes = Lookup.FULL_POWER_MODES & ~Lookup.ORIGINAL;
277
278 if (targetModule != callerModule) {
279 if (!callerModule.canRead(targetModule))
280 throw new IllegalAccessException(callerModule + " does not read " + targetModule);
281 if (targetModule.isNamed()) {
282 String pn = targetClass.getPackageName();
283 assert !pn.isEmpty() : "unnamed package cannot be in named module";
284 if (!targetModule.isOpen(pn, callerModule))
285 throw new IllegalAccessException(targetModule + " does not open " + pn + " to " + callerModule);
286 }
287
288 // M2 != M1, set previous lookup class to M1 and drop MODULE access
289 newPreviousClass = callerClass;
290 newModes &= ~Lookup.MODULE;
291 }
292 return Lookup.newLookup(targetClass, newPreviousClass, newModes);
293 }
294
295 /**
296 * Returns the <em>class data</em> associated with the lookup class
297 * of the given {@code caller} lookup object, or {@code null}.
298 *
299 * <p> A hidden class with class data can be created by calling
300 * {@link Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...)
301 * Lookup::defineHiddenClassWithClassData}.
302 * This method will cause the static class initializer of the lookup
303 * class of the given {@code caller} lookup object be executed if
304 * it has not been initialized.
305 *
306 * <p> A hidden class created by {@link Lookup#defineHiddenClass(byte[], boolean, Lookup.ClassOption...)
307 * Lookup::defineHiddenClass} and non-hidden classes have no class data.
308 * {@code null} is returned if this method is called on the lookup object
309 * on these classes.
310 *
311 * <p> The {@linkplain Lookup#lookupModes() lookup modes} for this lookup
312 * must have {@linkplain Lookup#ORIGINAL original access}
313 * in order to retrieve the class data.
314 *
315 * @apiNote
316 * This method can be called as a bootstrap method for a dynamically computed
317 * constant. A framework can create a hidden class with class data, for
318 * example that can be {@code Class} or {@code MethodHandle} object.
319 * The class data is accessible only to the lookup object
320 * created by the original caller but inaccessible to other members
321 * in the same nest. If a framework passes security sensitive objects
322 * to a hidden class via class data, it is recommended to load the value
323 * of class data as a dynamically computed constant instead of storing
324 * the class data in private static field(s) which are accessible to
325 * other nestmates.
326 *
327 * @param <T> the type to cast the class data object to
328 * @param caller the lookup context describing the class performing the
329 * operation (normally stacked by the JVM)
330 * @param name must be {@link ConstantDescs#DEFAULT_NAME}
331 * ({@code "_"})
332 * @param type the type of the class data
333 * @return the value of the class data if present in the lookup class;
334 * otherwise {@code null}
335 * @throws IllegalArgumentException if name is not {@code "_"}
336 * @throws IllegalAccessException if the lookup context does not have
337 * {@linkplain Lookup#ORIGINAL original} access
338 * @throws ClassCastException if the class data cannot be converted to
339 * the given {@code type}
340 * @throws NullPointerException if {@code caller} or {@code type} argument
341 * is {@code null}
342 * @see Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...)
343 * @see MethodHandles#classDataAt(Lookup, String, Class, int)
344 * @since 16
345 * @jvms 5.5 Initialization
346 */
347 public static <T> T classData(Lookup caller, String name, Class<T> type) throws IllegalAccessException {
348 Objects.requireNonNull(caller);
349 Objects.requireNonNull(type);
350 if (!ConstantDescs.DEFAULT_NAME.equals(name)) {
351 throw new IllegalArgumentException("name must be \"_\": " + name);
352 }
353
354 if ((caller.lookupModes() & Lookup.ORIGINAL) != Lookup.ORIGINAL) {
355 throw new IllegalAccessException(caller + " does not have ORIGINAL access");
356 }
357
358 Object classdata = classData(caller.lookupClass());
359 if (classdata == null) return null;
360
361 try {
362 return BootstrapMethodInvoker.widenAndCast(classdata, type);
363 } catch (RuntimeException|Error e) {
364 throw e; // let CCE and other runtime exceptions through
365 } catch (Throwable e) {
366 throw new InternalError(e);
367 }
368 }
369
370 /*
371 * Returns the class data set by the VM in the Class::classData field.
372 *
373 * This is also invoked by LambdaForms as it cannot use condy via
374 * MethodHandles::classData due to bootstrapping issue.
375 */
376 static Object classData(Class<?> c) {
377 UNSAFE.ensureClassInitialized(c);
378 return SharedSecrets.getJavaLangAccess().classData(c);
379 }
380
381 /**
382 * Returns the element at the specified index in the
383 * {@linkplain #classData(Lookup, String, Class) class data},
384 * if the class data associated with the lookup class
385 * of the given {@code caller} lookup object is a {@code List}.
386 * If the class data is not present in this lookup class, this method
387 * returns {@code null}.
388 *
389 * <p> A hidden class with class data can be created by calling
390 * {@link Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...)
391 * Lookup::defineHiddenClassWithClassData}.
392 * This method will cause the static class initializer of the lookup
393 * class of the given {@code caller} lookup object be executed if
394 * it has not been initialized.
395 *
396 * <p> A hidden class created by {@link Lookup#defineHiddenClass(byte[], boolean, Lookup.ClassOption...)
397 * Lookup::defineHiddenClass} and non-hidden classes have no class data.
398 * {@code null} is returned if this method is called on the lookup object
399 * on these classes.
400 *
401 * <p> The {@linkplain Lookup#lookupModes() lookup modes} for this lookup
402 * must have {@linkplain Lookup#ORIGINAL original access}
403 * in order to retrieve the class data.
404 *
405 * @apiNote
406 * This method can be called as a bootstrap method for a dynamically computed
407 * constant. A framework can create a hidden class with class data, for
408 * example that can be {@code List.of(o1, o2, o3....)} containing more than
409 * one object and use this method to load one element at a specific index.
410 * The class data is accessible only to the lookup object
411 * created by the original caller but inaccessible to other members
412 * in the same nest. If a framework passes security sensitive objects
413 * to a hidden class via class data, it is recommended to load the value
414 * of class data as a dynamically computed constant instead of storing
415 * the class data in private static field(s) which are accessible to other
416 * nestmates.
417 *
418 * @param <T> the type to cast the result object to
419 * @param caller the lookup context describing the class performing the
420 * operation (normally stacked by the JVM)
421 * @param name must be {@link java.lang.constant.ConstantDescs#DEFAULT_NAME}
422 * ({@code "_"})
423 * @param type the type of the element at the given index in the class data
424 * @param index index of the element in the class data
425 * @return the element at the given index in the class data
426 * if the class data is present; otherwise {@code null}
427 * @throws IllegalArgumentException if name is not {@code "_"}
428 * @throws IllegalAccessException if the lookup context does not have
429 * {@linkplain Lookup#ORIGINAL original} access
430 * @throws ClassCastException if the class data cannot be converted to {@code List}
431 * or the element at the specified index cannot be converted to the given type
432 * @throws IndexOutOfBoundsException if the index is out of range
433 * @throws NullPointerException if {@code caller} or {@code type} argument is
434 * {@code null}; or if unboxing operation fails because
435 * the element at the given index is {@code null}
436 *
437 * @since 16
438 * @see #classData(Lookup, String, Class)
439 * @see Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...)
440 */
441 public static <T> T classDataAt(Lookup caller, String name, Class<T> type, int index)
442 throws IllegalAccessException
443 {
444 @SuppressWarnings("unchecked")
445 List<Object> classdata = (List<Object>)classData(caller, name, List.class);
446 if (classdata == null) return null;
447
448 try {
449 Object element = classdata.get(index);
450 return BootstrapMethodInvoker.widenAndCast(element, type);
451 } catch (RuntimeException|Error e) {
452 throw e; // let specified exceptions and other runtime exceptions/errors through
453 } catch (Throwable e) {
454 throw new InternalError(e);
455 }
456 }
457
458 /**
459 * Performs an unchecked "crack" of a
460 * <a href="MethodHandleInfo.html#directmh">direct method handle</a>.
461 * The result is as if the user had obtained a lookup object capable enough
462 * to crack the target method handle, called
463 * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect}
464 * on the target to obtain its symbolic reference, and then called
465 * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs}
466 * to resolve the symbolic reference to a member.
467 * <p>
468 * If there is a security manager, its {@code checkPermission} method
469 * is called with a {@code ReflectPermission("suppressAccessChecks")} permission.
470 * @param <T> the desired type of the result, either {@link Member} or a subtype
471 * @param target a direct method handle to crack into symbolic reference components
472 * @param expected a class object representing the desired result type {@code T}
473 * @return a reference to the method, constructor, or field object
474 * @throws SecurityException if the caller is not privileged to call {@code setAccessible}
475 * @throws NullPointerException if either argument is {@code null}
476 * @throws IllegalArgumentException if the target is not a direct method handle
477 * @throws ClassCastException if the member is not of the expected type
478 * @since 1.8
479 */
480 public static <T extends Member> T reflectAs(Class<T> expected, MethodHandle target) {
481 @SuppressWarnings("removal")
482 SecurityManager smgr = System.getSecurityManager();
483 if (smgr != null) smgr.checkPermission(SecurityConstants.ACCESS_PERMISSION);
484 Lookup lookup = Lookup.IMPL_LOOKUP; // use maximally privileged lookup
485 return lookup.revealDirect(target).reflectAs(expected, lookup);
486 }
487
488 /**
489 * A <em>lookup object</em> is a factory for creating method handles,
490 * when the creation requires access checking.
491 * Method handles do not perform
492 * access checks when they are called, but rather when they are created.
493 * Therefore, method handle access
494 * restrictions must be enforced when a method handle is created.
495 * The caller class against which those restrictions are enforced
496 * is known as the {@linkplain #lookupClass() lookup class}.
497 * <p>
498 * A lookup class which needs to create method handles will call
499 * {@link MethodHandles#lookup() MethodHandles.lookup} to create a factory for itself.
500 * When the {@code Lookup} factory object is created, the identity of the lookup class is
501 * determined, and securely stored in the {@code Lookup} object.
502 * The lookup class (or its delegates) may then use factory methods
503 * on the {@code Lookup} object to create method handles for access-checked members.
504 * This includes all methods, constructors, and fields which are allowed to the lookup class,
505 * even private ones.
506 *
507 * <h2><a id="lookups"></a>Lookup Factory Methods</h2>
508 * The factory methods on a {@code Lookup} object correspond to all major
509 * use cases for methods, constructors, and fields.
510 * Each method handle created by a factory method is the functional
511 * equivalent of a particular <em>bytecode behavior</em>.
512 * (Bytecode behaviors are described in section {@jvms 5.4.3.5} of
513 * the Java Virtual Machine Specification.)
514 * Here is a summary of the correspondence between these factory methods and
515 * the behavior of the resulting method handles:
516 * <table class="striped">
517 * <caption style="display:none">lookup method behaviors</caption>
518 * <thead>
519 * <tr>
520 * <th scope="col"><a id="equiv"></a>lookup expression</th>
521 * <th scope="col">member</th>
522 * <th scope="col">bytecode behavior</th>
523 * </tr>
524 * </thead>
525 * <tbody>
526 * <tr>
527 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</th>
528 * <td>{@code FT f;}</td><td>{@code (T) this.f;}</td>
529 * </tr>
530 * <tr>
531 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</th>
532 * <td>{@code static}<br>{@code FT f;}</td><td>{@code (FT) C.f;}</td>
533 * </tr>
534 * <tr>
535 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</th>
536 * <td>{@code FT f;}</td><td>{@code this.f = x;}</td>
537 * </tr>
538 * <tr>
539 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</th>
540 * <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td>
541 * </tr>
542 * <tr>
543 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</th>
544 * <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>
545 * </tr>
546 * <tr>
547 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</th>
548 * <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td>
549 * </tr>
550 * <tr>
551 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</th>
552 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
553 * </tr>
554 * <tr>
555 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</th>
556 * <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td>
557 * </tr>
558 * <tr>
559 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</th>
560 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td>
561 * </tr>
562 * <tr>
563 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</th>
564 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, arg);}</td>
565 * </tr>
566 * <tr>
567 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</th>
568 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
569 * </tr>
570 * <tr>
571 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</th>
572 * <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td>
573 * </tr>
574 * <tr>
575 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSpecial lookup.unreflectSpecial(aMethod,this.class)}</th>
576 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
577 * </tr>
578 * <tr>
579 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findClass lookup.findClass("C")}</th>
580 * <td>{@code class C { ... }}</td><td>{@code C.class;}</td>
581 * </tr>
582 * </tbody>
583 * </table>
584 *
585 * Here, the type {@code C} is the class or interface being searched for a member,
586 * documented as a parameter named {@code refc} in the lookup methods.
587 * The method type {@code MT} is composed from the return type {@code T}
588 * and the sequence of argument types {@code A*}.
589 * The constructor also has a sequence of argument types {@code A*} and
590 * is deemed to return the newly-created object of type {@code C}.
591 * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}.
592 * The formal parameter {@code this} stands for the self-reference of type {@code C};
593 * if it is present, it is always the leading argument to the method handle invocation.
594 * (In the case of some {@code protected} members, {@code this} may be
595 * restricted in type to the lookup class; see below.)
596 * The name {@code arg} stands for all the other method handle arguments.
597 * In the code examples for the Core Reflection API, the name {@code thisOrNull}
598 * stands for a null reference if the accessed method or field is static,
599 * and {@code this} otherwise.
600 * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand
601 * for reflective objects corresponding to the given members declared in type {@code C}.
602 * <p>
603 * The bytecode behavior for a {@code findClass} operation is a load of a constant class,
604 * as if by {@code ldc CONSTANT_Class}.
605 * The behavior is represented, not as a method handle, but directly as a {@code Class} constant.
606 * <p>
607 * In cases where the given member is of variable arity (i.e., a method or constructor)
608 * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}.
609 * In all other cases, the returned method handle will be of fixed arity.
610 * <p style="font-size:smaller;">
611 * <em>Discussion:</em>
612 * The equivalence between looked-up method handles and underlying
613 * class members and bytecode behaviors
614 * can break down in a few ways:
615 * <ul style="font-size:smaller;">
616 * <li>If {@code C} is not symbolically accessible from the lookup class's loader,
617 * the lookup can still succeed, even when there is no equivalent
618 * Java expression or bytecoded constant.
619 * <li>Likewise, if {@code T} or {@code MT}
620 * is not symbolically accessible from the lookup class's loader,
621 * the lookup can still succeed.
622 * For example, lookups for {@code MethodHandle.invokeExact} and
623 * {@code MethodHandle.invoke} will always succeed, regardless of requested type.
624 * <li>If there is a security manager installed, it can forbid the lookup
625 * on various grounds (<a href="MethodHandles.Lookup.html#secmgr">see below</a>).
626 * By contrast, the {@code ldc} instruction on a {@code CONSTANT_MethodHandle}
627 * constant is not subject to security manager checks.
628 * <li>If the looked-up method has a
629 * <a href="MethodHandle.html#maxarity">very large arity</a>,
630 * the method handle creation may fail with an
631 * {@code IllegalArgumentException}, due to the method handle type having
632 * <a href="MethodHandle.html#maxarity">too many parameters.</a>
633 * </ul>
634 *
635 * <h2><a id="access"></a>Access checking</h2>
636 * Access checks are applied in the factory methods of {@code Lookup},
637 * when a method handle is created.
638 * This is a key difference from the Core Reflection API, since
639 * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
640 * performs access checking against every caller, on every call.
641 * <p>
642 * All access checks start from a {@code Lookup} object, which
643 * compares its recorded lookup class against all requests to
644 * create method handles.
645 * A single {@code Lookup} object can be used to create any number
646 * of access-checked method handles, all checked against a single
647 * lookup class.
648 * <p>
649 * A {@code Lookup} object can be shared with other trusted code,
650 * such as a metaobject protocol.
651 * A shared {@code Lookup} object delegates the capability
652 * to create method handles on private members of the lookup class.
653 * Even if privileged code uses the {@code Lookup} object,
654 * the access checking is confined to the privileges of the
655 * original lookup class.
656 * <p>
657 * A lookup can fail, because
658 * the containing class is not accessible to the lookup class, or
659 * because the desired class member is missing, or because the
660 * desired class member is not accessible to the lookup class, or
661 * because the lookup object is not trusted enough to access the member.
662 * In the case of a field setter function on a {@code final} field,
663 * finality enforcement is treated as a kind of access control,
664 * and the lookup will fail, except in special cases of
665 * {@link Lookup#unreflectSetter Lookup.unreflectSetter}.
666 * In any of these cases, a {@code ReflectiveOperationException} will be
667 * thrown from the attempted lookup. The exact class will be one of
668 * the following:
669 * <ul>
670 * <li>NoSuchMethodException — if a method is requested but does not exist
671 * <li>NoSuchFieldException — if a field is requested but does not exist
672 * <li>IllegalAccessException — if the member exists but an access check fails
673 * </ul>
674 * <p>
675 * In general, the conditions under which a method handle may be
676 * looked up for a method {@code M} are no more restrictive than the conditions
677 * under which the lookup class could have compiled, verified, and resolved a call to {@code M}.
678 * Where the JVM would raise exceptions like {@code NoSuchMethodError},
679 * a method handle lookup will generally raise a corresponding
680 * checked exception, such as {@code NoSuchMethodException}.
681 * And the effect of invoking the method handle resulting from the lookup
682 * is <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a>
683 * to executing the compiled, verified, and resolved call to {@code M}.
684 * The same point is true of fields and constructors.
685 * <p style="font-size:smaller;">
686 * <em>Discussion:</em>
687 * Access checks only apply to named and reflected methods,
688 * constructors, and fields.
689 * Other method handle creation methods, such as
690 * {@link MethodHandle#asType MethodHandle.asType},
691 * do not require any access checks, and are used
692 * independently of any {@code Lookup} object.
693 * <p>
694 * If the desired member is {@code protected}, the usual JVM rules apply,
695 * including the requirement that the lookup class must either be in the
696 * same package as the desired member, or must inherit that member.
697 * (See the Java Virtual Machine Specification, sections {@jvms
698 * 4.9.2}, {@jvms 5.4.3.5}, and {@jvms 6.4}.)
699 * In addition, if the desired member is a non-static field or method
700 * in a different package, the resulting method handle may only be applied
701 * to objects of the lookup class or one of its subclasses.
702 * This requirement is enforced by narrowing the type of the leading
703 * {@code this} parameter from {@code C}
704 * (which will necessarily be a superclass of the lookup class)
705 * to the lookup class itself.
706 * <p>
707 * The JVM imposes a similar requirement on {@code invokespecial} instruction,
708 * that the receiver argument must match both the resolved method <em>and</em>
709 * the current class. Again, this requirement is enforced by narrowing the
710 * type of the leading parameter to the resulting method handle.
711 * (See the Java Virtual Machine Specification, section {@jvms 4.10.1.9}.)
712 * <p>
713 * The JVM represents constructors and static initializer blocks as internal methods
714 * with special names ({@value ConstantDescs#INIT_NAME} and {@value
715 * ConstantDescs#CLASS_INIT_NAME}).
716 * The internal syntax of invocation instructions allows them to refer to such internal
717 * methods as if they were normal methods, but the JVM bytecode verifier rejects them.
718 * A lookup of such an internal method will produce a {@code NoSuchMethodException}.
719 * <p>
720 * If the relationship between nested types is expressed directly through the
721 * {@code NestHost} and {@code NestMembers} attributes
722 * (see the Java Virtual Machine Specification, sections {@jvms
723 * 4.7.28} and {@jvms 4.7.29}),
724 * then the associated {@code Lookup} object provides direct access to
725 * the lookup class and all of its nestmates
726 * (see {@link java.lang.Class#getNestHost Class.getNestHost}).
727 * Otherwise, access between nested classes is obtained by the Java compiler creating
728 * a wrapper method to access a private method of another class in the same nest.
729 * For example, a nested class {@code C.D}
730 * can access private members within other related classes such as
731 * {@code C}, {@code C.D.E}, or {@code C.B},
732 * but the Java compiler may need to generate wrapper methods in
733 * those related classes. In such cases, a {@code Lookup} object on
734 * {@code C.E} would be unable to access those private members.
735 * A workaround for this limitation is the {@link Lookup#in Lookup.in} method,
736 * which can transform a lookup on {@code C.E} into one on any of those other
737 * classes, without special elevation of privilege.
738 * <p>
739 * The accesses permitted to a given lookup object may be limited,
740 * according to its set of {@link #lookupModes lookupModes},
741 * to a subset of members normally accessible to the lookup class.
742 * For example, the {@link MethodHandles#publicLookup publicLookup}
743 * method produces a lookup object which is only allowed to access
744 * public members in public classes of exported packages.
745 * The caller sensitive method {@link MethodHandles#lookup lookup}
746 * produces a lookup object with full capabilities relative to
747 * its caller class, to emulate all supported bytecode behaviors.
748 * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object
749 * with fewer access modes than the original lookup object.
750 *
751 * <p style="font-size:smaller;">
752 * <a id="privacc"></a>
753 * <em>Discussion of private and module access:</em>
754 * We say that a lookup has <em>private access</em>
755 * if its {@linkplain #lookupModes lookup modes}
756 * include the possibility of accessing {@code private} members
757 * (which includes the private members of nestmates).
758 * As documented in the relevant methods elsewhere,
759 * only lookups with private access possess the following capabilities:
760 * <ul style="font-size:smaller;">
761 * <li>access private fields, methods, and constructors of the lookup class and its nestmates
762 * <li>create method handles which {@link Lookup#findSpecial emulate invokespecial} instructions
763 * <li>avoid <a href="MethodHandles.Lookup.html#secmgr">package access checks</a>
764 * for classes accessible to the lookup class
765 * <li>create {@link Lookup#in delegated lookup objects} which have private access to other classes
766 * within the same package member
767 * </ul>
768 * <p style="font-size:smaller;">
769 * Similarly, a lookup with module access ensures that the original lookup creator was
770 * a member in the same module as the lookup class.
771 * <p style="font-size:smaller;">
772 * Private and module access are independently determined modes; a lookup may have
773 * either or both or neither. A lookup which possesses both access modes is said to
774 * possess {@linkplain #hasFullPrivilegeAccess() full privilege access}.
775 * <p style="font-size:smaller;">
776 * A lookup with <em>original access</em> ensures that this lookup is created by
777 * the original lookup class and the bootstrap method invoked by the VM.
778 * Such a lookup with original access also has private and module access
779 * which has the following additional capability:
780 * <ul style="font-size:smaller;">
781 * <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> methods,
782 * such as {@code Class.forName}
783 * <li>obtain the {@linkplain MethodHandles#classData(Lookup, String, Class)
784 * class data} associated with the lookup class</li>
785 * </ul>
786 * <p style="font-size:smaller;">
787 * Each of these permissions is a consequence of the fact that a lookup object
788 * with private access can be securely traced back to an originating class,
789 * whose <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> and Java language access permissions
790 * can be reliably determined and emulated by method handles.
791 *
792 * <h2><a id="cross-module-lookup"></a>Cross-module lookups</h2>
793 * When a lookup class in one module {@code M1} accesses a class in another module
794 * {@code M2}, extra access checking is performed beyond the access mode bits.
795 * A {@code Lookup} with {@link #PUBLIC} mode and a lookup class in {@code M1}
796 * can access public types in {@code M2} when {@code M2} is readable to {@code M1}
797 * and when the type is in a package of {@code M2} that is exported to
798 * at least {@code M1}.
799 * <p>
800 * A {@code Lookup} on {@code C} can also <em>teleport</em> to a target class
801 * via {@link #in(Class) Lookup.in} and {@link MethodHandles#privateLookupIn(Class, Lookup)
802 * MethodHandles.privateLookupIn} methods.
803 * Teleporting across modules will always record the original lookup class as
804 * the <em>{@linkplain #previousLookupClass() previous lookup class}</em>
805 * and drops {@link Lookup#MODULE MODULE} access.
806 * If the target class is in the same module as the lookup class {@code C},
807 * then the target class becomes the new lookup class
808 * and there is no change to the previous lookup class.
809 * If the target class is in a different module from {@code M1} ({@code C}'s module),
810 * {@code C} becomes the new previous lookup class
811 * and the target class becomes the new lookup class.
812 * In that case, if there was already a previous lookup class in {@code M0},
813 * and it differs from {@code M1} and {@code M2}, then the resulting lookup
814 * drops all privileges.
815 * For example,
816 * {@snippet lang="java" :
817 * Lookup lookup = MethodHandles.lookup(); // in class C
818 * Lookup lookup2 = lookup.in(D.class);
819 * MethodHandle mh = lookup2.findStatic(E.class, "m", MT);
820 * }
821 * <p>
822 * The {@link #lookup()} factory method produces a {@code Lookup} object
823 * with {@code null} previous lookup class.
824 * {@link Lookup#in lookup.in(D.class)} transforms the {@code lookup} on class {@code C}
825 * to class {@code D} without elevation of privileges.
826 * If {@code C} and {@code D} are in the same module,
827 * {@code lookup2} records {@code D} as the new lookup class and keeps the
828 * same previous lookup class as the original {@code lookup}, or
829 * {@code null} if not present.
830 * <p>
831 * When a {@code Lookup} teleports from a class
832 * in one nest to another nest, {@code PRIVATE} access is dropped.
833 * When a {@code Lookup} teleports from a class in one package to
834 * another package, {@code PACKAGE} access is dropped.
835 * When a {@code Lookup} teleports from a class in one module to another module,
836 * {@code MODULE} access is dropped.
837 * Teleporting across modules drops the ability to access non-exported classes
838 * in both the module of the new lookup class and the module of the old lookup class
839 * and the resulting {@code Lookup} remains only {@code PUBLIC} access.
840 * A {@code Lookup} can teleport back and forth to a class in the module of
841 * the lookup class and the module of the previous class lookup.
842 * Teleporting across modules can only decrease access but cannot increase it.
843 * Teleporting to some third module drops all accesses.
844 * <p>
845 * In the above example, if {@code C} and {@code D} are in different modules,
846 * {@code lookup2} records {@code D} as its lookup class and
847 * {@code C} as its previous lookup class and {@code lookup2} has only
848 * {@code PUBLIC} access. {@code lookup2} can teleport to other class in
849 * {@code C}'s module and {@code D}'s module.
850 * If class {@code E} is in a third module, {@code lookup2.in(E.class)} creates
851 * a {@code Lookup} on {@code E} with no access and {@code lookup2}'s lookup
852 * class {@code D} is recorded as its previous lookup class.
853 * <p>
854 * Teleporting across modules restricts access to the public types that
855 * both the lookup class and the previous lookup class can equally access
856 * (see below).
857 * <p>
858 * {@link MethodHandles#privateLookupIn(Class, Lookup) MethodHandles.privateLookupIn(T.class, lookup)}
859 * can be used to teleport a {@code lookup} from class {@code C} to class {@code T}
860 * and produce a new {@code Lookup} with <a href="#privacc">private access</a>
861 * if the lookup class is allowed to do <em>deep reflection</em> on {@code T}.
862 * The {@code lookup} must have {@link #MODULE} and {@link #PRIVATE} access
863 * to call {@code privateLookupIn}.
864 * A {@code lookup} on {@code C} in module {@code M1} is allowed to do deep reflection
865 * on all classes in {@code M1}. If {@code T} is in {@code M1}, {@code privateLookupIn}
866 * produces a new {@code Lookup} on {@code T} with full capabilities.
867 * A {@code lookup} on {@code C} is also allowed
868 * to do deep reflection on {@code T} in another module {@code M2} if
869 * {@code M1} reads {@code M2} and {@code M2} {@link Module#isOpen(String,Module) opens}
870 * the package containing {@code T} to at least {@code M1}.
871 * {@code T} becomes the new lookup class and {@code C} becomes the new previous
872 * lookup class and {@code MODULE} access is dropped from the resulting {@code Lookup}.
873 * The resulting {@code Lookup} can be used to do member lookup or teleport
874 * to another lookup class by calling {@link #in Lookup::in}. But
875 * it cannot be used to obtain another private {@code Lookup} by calling
876 * {@link MethodHandles#privateLookupIn(Class, Lookup) privateLookupIn}
877 * because it has no {@code MODULE} access.
878 * <p>
879 * The {@code Lookup} object returned by {@code privateLookupIn} is allowed to
880 * {@linkplain Lookup#defineClass(byte[]) define classes} in the runtime package
881 * of {@code T}. Extreme caution should be taken when opening a package
882 * to another module as such defined classes have the same full privilege
883 * access as other members in {@code M2}.
884 *
885 * <h2><a id="module-access-check"></a>Cross-module access checks</h2>
886 *
887 * A {@code Lookup} with {@link #PUBLIC} or with {@link #UNCONDITIONAL} mode
888 * allows cross-module access. The access checking is performed with respect
889 * to both the lookup class and the previous lookup class if present.
890 * <p>
891 * A {@code Lookup} with {@link #UNCONDITIONAL} mode can access public type
892 * in all modules when the type is in a package that is {@linkplain Module#isExported(String)
893 * exported unconditionally}.
894 * <p>
895 * If a {@code Lookup} on {@code LC} in {@code M1} has no previous lookup class,
896 * the lookup with {@link #PUBLIC} mode can access all public types in modules
897 * that are readable to {@code M1} and the type is in a package that is exported
898 * at least to {@code M1}.
899 * <p>
900 * If a {@code Lookup} on {@code LC} in {@code M1} has a previous lookup class
901 * {@code PLC} on {@code M0}, the lookup with {@link #PUBLIC} mode can access
902 * the intersection of all public types that are accessible to {@code M1}
903 * with all public types that are accessible to {@code M0}. {@code M0}
904 * reads {@code M1} and hence the set of accessible types includes:
905 *
906 * <ul>
907 * <li>unconditional-exported packages from {@code M1}</li>
908 * <li>unconditional-exported packages from {@code M0} if {@code M1} reads {@code M0}</li>
909 * <li>
910 * unconditional-exported packages from a third module {@code M2}if both {@code M0}
911 * and {@code M1} read {@code M2}
912 * </li>
913 * <li>qualified-exported packages from {@code M1} to {@code M0}</li>
914 * <li>qualified-exported packages from {@code M0} to {@code M1} if {@code M1} reads {@code M0}</li>
915 * <li>
916 * qualified-exported packages from a third module {@code M2} to both {@code M0} and
917 * {@code M1} if both {@code M0} and {@code M1} read {@code M2}
918 * </li>
919 * </ul>
920 *
921 * <h2><a id="access-modes"></a>Access modes</h2>
922 *
923 * The table below shows the access modes of a {@code Lookup} produced by
924 * any of the following factory or transformation methods:
925 * <ul>
926 * <li>{@link #lookup() MethodHandles::lookup}</li>
927 * <li>{@link #publicLookup() MethodHandles::publicLookup}</li>
928 * <li>{@link #privateLookupIn(Class, Lookup) MethodHandles::privateLookupIn}</li>
929 * <li>{@link Lookup#in Lookup::in}</li>
930 * <li>{@link Lookup#dropLookupMode(int) Lookup::dropLookupMode}</li>
931 * </ul>
932 *
933 * <table class="striped">
934 * <caption style="display:none">
935 * Access mode summary
936 * </caption>
937 * <thead>
938 * <tr>
939 * <th scope="col">Lookup object</th>
940 * <th style="text-align:center">original</th>
941 * <th style="text-align:center">protected</th>
942 * <th style="text-align:center">private</th>
943 * <th style="text-align:center">package</th>
944 * <th style="text-align:center">module</th>
945 * <th style="text-align:center">public</th>
946 * </tr>
947 * </thead>
948 * <tbody>
949 * <tr>
950 * <th scope="row" style="text-align:left">{@code CL = MethodHandles.lookup()} in {@code C}</th>
951 * <td style="text-align:center">ORI</td>
952 * <td style="text-align:center">PRO</td>
953 * <td style="text-align:center">PRI</td>
954 * <td style="text-align:center">PAC</td>
955 * <td style="text-align:center">MOD</td>
956 * <td style="text-align:center">1R</td>
957 * </tr>
958 * <tr>
959 * <th scope="row" style="text-align:left">{@code CL.in(C1)} same package</th>
960 * <td></td>
961 * <td></td>
962 * <td></td>
963 * <td style="text-align:center">PAC</td>
964 * <td style="text-align:center">MOD</td>
965 * <td style="text-align:center">1R</td>
966 * </tr>
967 * <tr>
968 * <th scope="row" style="text-align:left">{@code CL.in(C1)} same module</th>
969 * <td></td>
970 * <td></td>
971 * <td></td>
972 * <td></td>
973 * <td style="text-align:center">MOD</td>
974 * <td style="text-align:center">1R</td>
975 * </tr>
976 * <tr>
977 * <th scope="row" style="text-align:left">{@code CL.in(D)} different module</th>
978 * <td></td>
979 * <td></td>
980 * <td></td>
981 * <td></td>
982 * <td></td>
983 * <td style="text-align:center">2R</td>
984 * </tr>
985 * <tr>
986 * <th scope="row" style="text-align:left">{@code CL.in(D).in(C)} hop back to module</th>
987 * <td></td>
988 * <td></td>
989 * <td></td>
990 * <td></td>
991 * <td></td>
992 * <td style="text-align:center">2R</td>
993 * </tr>
994 * <tr>
995 * <th scope="row" style="text-align:left">{@code PRI1 = privateLookupIn(C1,CL)}</th>
996 * <td></td>
997 * <td style="text-align:center">PRO</td>
998 * <td style="text-align:center">PRI</td>
999 * <td style="text-align:center">PAC</td>
1000 * <td style="text-align:center">MOD</td>
1001 * <td style="text-align:center">1R</td>
1002 * </tr>
1003 * <tr>
1004 * <th scope="row" style="text-align:left">{@code PRI1a = privateLookupIn(C,PRI1)}</th>
1005 * <td></td>
1006 * <td style="text-align:center">PRO</td>
1007 * <td style="text-align:center">PRI</td>
1008 * <td style="text-align:center">PAC</td>
1009 * <td style="text-align:center">MOD</td>
1010 * <td style="text-align:center">1R</td>
1011 * </tr>
1012 * <tr>
1013 * <th scope="row" style="text-align:left">{@code PRI1.in(C1)} same package</th>
1014 * <td></td>
1015 * <td></td>
1016 * <td></td>
1017 * <td style="text-align:center">PAC</td>
1018 * <td style="text-align:center">MOD</td>
1019 * <td style="text-align:center">1R</td>
1020 * </tr>
1021 * <tr>
1022 * <th scope="row" style="text-align:left">{@code PRI1.in(C1)} different package</th>
1023 * <td></td>
1024 * <td></td>
1025 * <td></td>
1026 * <td></td>
1027 * <td style="text-align:center">MOD</td>
1028 * <td style="text-align:center">1R</td>
1029 * </tr>
1030 * <tr>
1031 * <th scope="row" style="text-align:left">{@code PRI1.in(D)} different module</th>
1032 * <td></td>
1033 * <td></td>
1034 * <td></td>
1035 * <td></td>
1036 * <td></td>
1037 * <td style="text-align:center">2R</td>
1038 * </tr>
1039 * <tr>
1040 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PROTECTED)}</th>
1041 * <td></td>
1042 * <td></td>
1043 * <td style="text-align:center">PRI</td>
1044 * <td style="text-align:center">PAC</td>
1045 * <td style="text-align:center">MOD</td>
1046 * <td style="text-align:center">1R</td>
1047 * </tr>
1048 * <tr>
1049 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PRIVATE)}</th>
1050 * <td></td>
1051 * <td></td>
1052 * <td></td>
1053 * <td style="text-align:center">PAC</td>
1054 * <td style="text-align:center">MOD</td>
1055 * <td style="text-align:center">1R</td>
1056 * </tr>
1057 * <tr>
1058 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PACKAGE)}</th>
1059 * <td></td>
1060 * <td></td>
1061 * <td></td>
1062 * <td></td>
1063 * <td style="text-align:center">MOD</td>
1064 * <td style="text-align:center">1R</td>
1065 * </tr>
1066 * <tr>
1067 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(MODULE)}</th>
1068 * <td></td>
1069 * <td></td>
1070 * <td></td>
1071 * <td></td>
1072 * <td></td>
1073 * <td style="text-align:center">1R</td>
1074 * </tr>
1075 * <tr>
1076 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PUBLIC)}</th>
1077 * <td></td>
1078 * <td></td>
1079 * <td></td>
1080 * <td></td>
1081 * <td></td>
1082 * <td style="text-align:center">none</td>
1083 * <tr>
1084 * <th scope="row" style="text-align:left">{@code PRI2 = privateLookupIn(D,CL)}</th>
1085 * <td></td>
1086 * <td style="text-align:center">PRO</td>
1087 * <td style="text-align:center">PRI</td>
1088 * <td style="text-align:center">PAC</td>
1089 * <td></td>
1090 * <td style="text-align:center">2R</td>
1091 * </tr>
1092 * <tr>
1093 * <th scope="row" style="text-align:left">{@code privateLookupIn(D,PRI1)}</th>
1094 * <td></td>
1095 * <td style="text-align:center">PRO</td>
1096 * <td style="text-align:center">PRI</td>
1097 * <td style="text-align:center">PAC</td>
1098 * <td></td>
1099 * <td style="text-align:center">2R</td>
1100 * </tr>
1101 * <tr>
1102 * <th scope="row" style="text-align:left">{@code privateLookupIn(C,PRI2)} fails</th>
1103 * <td></td>
1104 * <td></td>
1105 * <td></td>
1106 * <td></td>
1107 * <td></td>
1108 * <td style="text-align:center">IAE</td>
1109 * </tr>
1110 * <tr>
1111 * <th scope="row" style="text-align:left">{@code PRI2.in(D2)} same package</th>
1112 * <td></td>
1113 * <td></td>
1114 * <td></td>
1115 * <td style="text-align:center">PAC</td>
1116 * <td></td>
1117 * <td style="text-align:center">2R</td>
1118 * </tr>
1119 * <tr>
1120 * <th scope="row" style="text-align:left">{@code PRI2.in(D2)} different package</th>
1121 * <td></td>
1122 * <td></td>
1123 * <td></td>
1124 * <td></td>
1125 * <td></td>
1126 * <td style="text-align:center">2R</td>
1127 * </tr>
1128 * <tr>
1129 * <th scope="row" style="text-align:left">{@code PRI2.in(C1)} hop back to module</th>
1130 * <td></td>
1131 * <td></td>
1132 * <td></td>
1133 * <td></td>
1134 * <td></td>
1135 * <td style="text-align:center">2R</td>
1136 * </tr>
1137 * <tr>
1138 * <th scope="row" style="text-align:left">{@code PRI2.in(E)} hop to third module</th>
1139 * <td></td>
1140 * <td></td>
1141 * <td></td>
1142 * <td></td>
1143 * <td></td>
1144 * <td style="text-align:center">none</td>
1145 * </tr>
1146 * <tr>
1147 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PROTECTED)}</th>
1148 * <td></td>
1149 * <td></td>
1150 * <td style="text-align:center">PRI</td>
1151 * <td style="text-align:center">PAC</td>
1152 * <td></td>
1153 * <td style="text-align:center">2R</td>
1154 * </tr>
1155 * <tr>
1156 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PRIVATE)}</th>
1157 * <td></td>
1158 * <td></td>
1159 * <td></td>
1160 * <td style="text-align:center">PAC</td>
1161 * <td></td>
1162 * <td style="text-align:center">2R</td>
1163 * </tr>
1164 * <tr>
1165 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PACKAGE)}</th>
1166 * <td></td>
1167 * <td></td>
1168 * <td></td>
1169 * <td></td>
1170 * <td></td>
1171 * <td style="text-align:center">2R</td>
1172 * </tr>
1173 * <tr>
1174 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(MODULE)}</th>
1175 * <td></td>
1176 * <td></td>
1177 * <td></td>
1178 * <td></td>
1179 * <td></td>
1180 * <td style="text-align:center">2R</td>
1181 * </tr>
1182 * <tr>
1183 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PUBLIC)}</th>
1184 * <td></td>
1185 * <td></td>
1186 * <td></td>
1187 * <td></td>
1188 * <td></td>
1189 * <td style="text-align:center">none</td>
1190 * </tr>
1191 * <tr>
1192 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PROTECTED)}</th>
1193 * <td></td>
1194 * <td></td>
1195 * <td style="text-align:center">PRI</td>
1196 * <td style="text-align:center">PAC</td>
1197 * <td style="text-align:center">MOD</td>
1198 * <td style="text-align:center">1R</td>
1199 * </tr>
1200 * <tr>
1201 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PRIVATE)}</th>
1202 * <td></td>
1203 * <td></td>
1204 * <td></td>
1205 * <td style="text-align:center">PAC</td>
1206 * <td style="text-align:center">MOD</td>
1207 * <td style="text-align:center">1R</td>
1208 * </tr>
1209 * <tr>
1210 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PACKAGE)}</th>
1211 * <td></td>
1212 * <td></td>
1213 * <td></td>
1214 * <td></td>
1215 * <td style="text-align:center">MOD</td>
1216 * <td style="text-align:center">1R</td>
1217 * </tr>
1218 * <tr>
1219 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(MODULE)}</th>
1220 * <td></td>
1221 * <td></td>
1222 * <td></td>
1223 * <td></td>
1224 * <td></td>
1225 * <td style="text-align:center">1R</td>
1226 * </tr>
1227 * <tr>
1228 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PUBLIC)}</th>
1229 * <td></td>
1230 * <td></td>
1231 * <td></td>
1232 * <td></td>
1233 * <td></td>
1234 * <td style="text-align:center">none</td>
1235 * </tr>
1236 * <tr>
1237 * <th scope="row" style="text-align:left">{@code PUB = publicLookup()}</th>
1238 * <td></td>
1239 * <td></td>
1240 * <td></td>
1241 * <td></td>
1242 * <td></td>
1243 * <td style="text-align:center">U</td>
1244 * </tr>
1245 * <tr>
1246 * <th scope="row" style="text-align:left">{@code PUB.in(D)} different module</th>
1247 * <td></td>
1248 * <td></td>
1249 * <td></td>
1250 * <td></td>
1251 * <td></td>
1252 * <td style="text-align:center">U</td>
1253 * </tr>
1254 * <tr>
1255 * <th scope="row" style="text-align:left">{@code PUB.in(D).in(E)} third module</th>
1256 * <td></td>
1257 * <td></td>
1258 * <td></td>
1259 * <td></td>
1260 * <td></td>
1261 * <td style="text-align:center">U</td>
1262 * </tr>
1263 * <tr>
1264 * <th scope="row" style="text-align:left">{@code PUB.dropLookupMode(UNCONDITIONAL)}</th>
1265 * <td></td>
1266 * <td></td>
1267 * <td></td>
1268 * <td></td>
1269 * <td></td>
1270 * <td style="text-align:center">none</td>
1271 * </tr>
1272 * <tr>
1273 * <th scope="row" style="text-align:left">{@code privateLookupIn(C1,PUB)} fails</th>
1274 * <td></td>
1275 * <td></td>
1276 * <td></td>
1277 * <td></td>
1278 * <td></td>
1279 * <td style="text-align:center">IAE</td>
1280 * </tr>
1281 * <tr>
1282 * <th scope="row" style="text-align:left">{@code ANY.in(X)}, for inaccessible {@code X}</th>
1283 * <td></td>
1284 * <td></td>
1285 * <td></td>
1286 * <td></td>
1287 * <td></td>
1288 * <td style="text-align:center">none</td>
1289 * </tr>
1290 * </tbody>
1291 * </table>
1292 *
1293 * <p>
1294 * Notes:
1295 * <ul>
1296 * <li>Class {@code C} and class {@code C1} are in module {@code M1},
1297 * but {@code D} and {@code D2} are in module {@code M2}, and {@code E}
1298 * is in module {@code M3}. {@code X} stands for class which is inaccessible
1299 * to the lookup. {@code ANY} stands for any of the example lookups.</li>
1300 * <li>{@code ORI} indicates {@link #ORIGINAL} bit set,
1301 * {@code PRO} indicates {@link #PROTECTED} bit set,
1302 * {@code PRI} indicates {@link #PRIVATE} bit set,
1303 * {@code PAC} indicates {@link #PACKAGE} bit set,
1304 * {@code MOD} indicates {@link #MODULE} bit set,
1305 * {@code 1R} and {@code 2R} indicate {@link #PUBLIC} bit set,
1306 * {@code U} indicates {@link #UNCONDITIONAL} bit set,
1307 * {@code IAE} indicates {@code IllegalAccessException} thrown.</li>
1308 * <li>Public access comes in three kinds:
1309 * <ul>
1310 * <li>unconditional ({@code U}): the lookup assumes readability.
1311 * The lookup has {@code null} previous lookup class.
1312 * <li>one-module-reads ({@code 1R}): the module access checking is
1313 * performed with respect to the lookup class. The lookup has {@code null}
1314 * previous lookup class.
1315 * <li>two-module-reads ({@code 2R}): the module access checking is
1316 * performed with respect to the lookup class and the previous lookup class.
1317 * The lookup has a non-null previous lookup class which is in a
1318 * different module from the current lookup class.
1319 * </ul>
1320 * <li>Any attempt to reach a third module loses all access.</li>
1321 * <li>If a target class {@code X} is not accessible to {@code Lookup::in}
1322 * all access modes are dropped.</li>
1323 * </ul>
1324 *
1325 * <h2><a id="secmgr"></a>Security manager interactions</h2>
1326 * Although bytecode instructions can only refer to classes in
1327 * a related class loader, this API can search for methods in any
1328 * class, as long as a reference to its {@code Class} object is
1329 * available. Such cross-loader references are also possible with the
1330 * Core Reflection API, and are impossible to bytecode instructions
1331 * such as {@code invokestatic} or {@code getfield}.
1332 * There is a {@linkplain java.lang.SecurityManager security manager API}
1333 * to allow applications to check such cross-loader references.
1334 * These checks apply to both the {@code MethodHandles.Lookup} API
1335 * and the Core Reflection API
1336 * (as found on {@link java.lang.Class Class}).
1337 * <p>
1338 * If a security manager is present, member and class lookups are subject to
1339 * additional checks.
1340 * From one to three calls are made to the security manager.
1341 * Any of these calls can refuse access by throwing a
1342 * {@link java.lang.SecurityException SecurityException}.
1343 * Define {@code smgr} as the security manager,
1344 * {@code lookc} as the lookup class of the current lookup object,
1345 * {@code refc} as the containing class in which the member
1346 * is being sought, and {@code defc} as the class in which the
1347 * member is actually defined.
1348 * (If a class or other type is being accessed,
1349 * the {@code refc} and {@code defc} values are the class itself.)
1350 * The value {@code lookc} is defined as <em>not present</em>
1351 * if the current lookup object does not have
1352 * {@linkplain #hasFullPrivilegeAccess() full privilege access}.
1353 * The calls are made according to the following rules:
1354 * <ul>
1355 * <li><b>Step 1:</b>
1356 * If {@code lookc} is not present, or if its class loader is not
1357 * the same as or an ancestor of the class loader of {@code refc},
1358 * then {@link SecurityManager#checkPackageAccess
1359 * smgr.checkPackageAccess(refcPkg)} is called,
1360 * where {@code refcPkg} is the package of {@code refc}.
1361 * <li><b>Step 2a:</b>
1362 * If the retrieved member is not public and
1363 * {@code lookc} is not present, then
1364 * {@link SecurityManager#checkPermission smgr.checkPermission}
1365 * with {@code RuntimePermission("accessDeclaredMembers")} is called.
1366 * <li><b>Step 2b:</b>
1367 * If the retrieved class has a {@code null} class loader,
1368 * and {@code lookc} is not present, then
1369 * {@link SecurityManager#checkPermission smgr.checkPermission}
1370 * with {@code RuntimePermission("getClassLoader")} is called.
1371 * <li><b>Step 3:</b>
1372 * If the retrieved member is not public,
1373 * and if {@code lookc} is not present,
1374 * and if {@code defc} and {@code refc} are different,
1375 * then {@link SecurityManager#checkPackageAccess
1376 * smgr.checkPackageAccess(defcPkg)} is called,
1377 * where {@code defcPkg} is the package of {@code defc}.
1378 * </ul>
1379 * Security checks are performed after other access checks have passed.
1380 * Therefore, the above rules presuppose a member or class that is public,
1381 * or else that is being accessed from a lookup class that has
1382 * rights to access the member or class.
1383 * <p>
1384 * If a security manager is present and the current lookup object does not have
1385 * {@linkplain #hasFullPrivilegeAccess() full privilege access}, then
1386 * {@link #defineClass(byte[]) defineClass},
1387 * {@link #defineHiddenClass(byte[], boolean, ClassOption...) defineHiddenClass},
1388 * {@link #defineHiddenClassWithClassData(byte[], Object, boolean, ClassOption...)
1389 * defineHiddenClassWithClassData}
1390 * calls {@link SecurityManager#checkPermission smgr.checkPermission}
1391 * with {@code RuntimePermission("defineClass")}.
1392 *
1393 * <h2><a id="callsens"></a>Caller sensitive methods</h2>
1394 * A small number of Java methods have a special property called caller sensitivity.
1395 * A <em>caller-sensitive</em> method can behave differently depending on the
1396 * identity of its immediate caller.
1397 * <p>
1398 * If a method handle for a caller-sensitive method is requested,
1399 * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> apply,
1400 * but they take account of the lookup class in a special way.
1401 * The resulting method handle behaves as if it were called
1402 * from an instruction contained in the lookup class,
1403 * so that the caller-sensitive method detects the lookup class.
1404 * (By contrast, the invoker of the method handle is disregarded.)
1405 * Thus, in the case of caller-sensitive methods,
1406 * different lookup classes may give rise to
1407 * differently behaving method handles.
1408 * <p>
1409 * In cases where the lookup object is
1410 * {@link MethodHandles#publicLookup() publicLookup()},
1411 * or some other lookup object without the
1412 * {@linkplain #ORIGINAL original access},
1413 * the lookup class is disregarded.
1414 * In such cases, no caller-sensitive method handle can be created,
1415 * access is forbidden, and the lookup fails with an
1416 * {@code IllegalAccessException}.
1417 * <p style="font-size:smaller;">
1418 * <em>Discussion:</em>
1419 * For example, the caller-sensitive method
1420 * {@link java.lang.Class#forName(String) Class.forName(x)}
1421 * can return varying classes or throw varying exceptions,
1422 * depending on the class loader of the class that calls it.
1423 * A public lookup of {@code Class.forName} will fail, because
1424 * there is no reasonable way to determine its bytecode behavior.
1425 * <p style="font-size:smaller;">
1426 * If an application caches method handles for broad sharing,
1427 * it should use {@code publicLookup()} to create them.
1428 * If there is a lookup of {@code Class.forName}, it will fail,
1429 * and the application must take appropriate action in that case.
1430 * It may be that a later lookup, perhaps during the invocation of a
1431 * bootstrap method, can incorporate the specific identity
1432 * of the caller, making the method accessible.
1433 * <p style="font-size:smaller;">
1434 * The function {@code MethodHandles.lookup} is caller sensitive
1435 * so that there can be a secure foundation for lookups.
1436 * Nearly all other methods in the JSR 292 API rely on lookup
1437 * objects to check access requests.
1438 */
1439 public static final
1440 class Lookup {
1441 /** The class on behalf of whom the lookup is being performed. */
1442 private final Class<?> lookupClass;
1443
1444 /** previous lookup class */
1445 private final Class<?> prevLookupClass;
1446
1447 /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */
1448 private final int allowedModes;
1449
1450 static {
1451 Reflection.registerFieldsToFilter(Lookup.class, Set.of("lookupClass", "allowedModes"));
1452 }
1453
1454 /** A single-bit mask representing {@code public} access,
1455 * which may contribute to the result of {@link #lookupModes lookupModes}.
1456 * The value, {@code 0x01}, happens to be the same as the value of the
1457 * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.
1458 * <p>
1459 * A {@code Lookup} with this lookup mode performs cross-module access check
1460 * with respect to the {@linkplain #lookupClass() lookup class} and
1461 * {@linkplain #previousLookupClass() previous lookup class} if present.
1462 */
1463 public static final int PUBLIC = Modifier.PUBLIC;
1464
1465 /** A single-bit mask representing {@code private} access,
1466 * which may contribute to the result of {@link #lookupModes lookupModes}.
1467 * The value, {@code 0x02}, happens to be the same as the value of the
1468 * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.
1469 */
1470 public static final int PRIVATE = Modifier.PRIVATE;
1471
1472 /** A single-bit mask representing {@code protected} access,
1473 * which may contribute to the result of {@link #lookupModes lookupModes}.
1474 * The value, {@code 0x04}, happens to be the same as the value of the
1475 * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.
1476 */
1477 public static final int PROTECTED = Modifier.PROTECTED;
1478
1479 /** A single-bit mask representing {@code package} access (default access),
1480 * which may contribute to the result of {@link #lookupModes lookupModes}.
1481 * The value is {@code 0x08}, which does not correspond meaningfully to
1482 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1483 */
1484 public static final int PACKAGE = Modifier.STATIC;
1485
1486 /** A single-bit mask representing {@code module} access,
1487 * which may contribute to the result of {@link #lookupModes lookupModes}.
1488 * The value is {@code 0x10}, which does not correspond meaningfully to
1489 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1490 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup}
1491 * with this lookup mode can access all public types in the module of the
1492 * lookup class and public types in packages exported by other modules
1493 * to the module of the lookup class.
1494 * <p>
1495 * If this lookup mode is set, the {@linkplain #previousLookupClass()
1496 * previous lookup class} is always {@code null}.
1497 *
1498 * @since 9
1499 */
1500 public static final int MODULE = PACKAGE << 1;
1501
1502 /** A single-bit mask representing {@code unconditional} access
1503 * which may contribute to the result of {@link #lookupModes lookupModes}.
1504 * The value is {@code 0x20}, which does not correspond meaningfully to
1505 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1506 * A {@code Lookup} with this lookup mode assumes {@linkplain
1507 * java.lang.Module#canRead(java.lang.Module) readability}.
1508 * This lookup mode can access all public members of public types
1509 * of all modules when the type is in a package that is {@link
1510 * java.lang.Module#isExported(String) exported unconditionally}.
1511 *
1512 * <p>
1513 * If this lookup mode is set, the {@linkplain #previousLookupClass()
1514 * previous lookup class} is always {@code null}.
1515 *
1516 * @since 9
1517 * @see #publicLookup()
1518 */
1519 public static final int UNCONDITIONAL = PACKAGE << 2;
1520
1521 /** A single-bit mask representing {@code original} access
1522 * which may contribute to the result of {@link #lookupModes lookupModes}.
1523 * The value is {@code 0x40}, which does not correspond meaningfully to
1524 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1525 *
1526 * <p>
1527 * If this lookup mode is set, the {@code Lookup} object must be
1528 * created by the original lookup class by calling
1529 * {@link MethodHandles#lookup()} method or by a bootstrap method
1530 * invoked by the VM. The {@code Lookup} object with this lookup
1531 * mode has {@linkplain #hasFullPrivilegeAccess() full privilege access}.
1532 *
1533 * @since 16
1534 */
1535 public static final int ORIGINAL = PACKAGE << 3;
1536
1537 private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE | MODULE | UNCONDITIONAL | ORIGINAL);
1538 private static final int FULL_POWER_MODES = (ALL_MODES & ~UNCONDITIONAL); // with original access
1539 private static final int TRUSTED = -1;
1540
1541 /*
1542 * Adjust PUBLIC => PUBLIC|MODULE|ORIGINAL|UNCONDITIONAL
1543 * Adjust 0 => PACKAGE
1544 */
1545 private static int fixmods(int mods) {
1546 mods &= (ALL_MODES - PACKAGE - MODULE - ORIGINAL - UNCONDITIONAL);
1547 if (Modifier.isPublic(mods))
1548 mods |= UNCONDITIONAL;
1549 return (mods != 0) ? mods : PACKAGE;
1550 }
1551
1552 /** Tells which class is performing the lookup. It is this class against
1553 * which checks are performed for visibility and access permissions.
1554 * <p>
1555 * If this lookup object has a {@linkplain #previousLookupClass() previous lookup class},
1556 * access checks are performed against both the lookup class and the previous lookup class.
1557 * <p>
1558 * The class implies a maximum level of access permission,
1559 * but the permissions may be additionally limited by the bitmask
1560 * {@link #lookupModes lookupModes}, which controls whether non-public members
1561 * can be accessed.
1562 * @return the lookup class, on behalf of which this lookup object finds members
1563 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1564 */
1565 public Class<?> lookupClass() {
1566 return lookupClass;
1567 }
1568
1569 /** Reports a lookup class in another module that this lookup object
1570 * was previously teleported from, or {@code null}.
1571 * <p>
1572 * A {@code Lookup} object produced by the factory methods, such as the
1573 * {@link #lookup() lookup()} and {@link #publicLookup() publicLookup()} method,
1574 * has {@code null} previous lookup class.
1575 * A {@code Lookup} object has a non-null previous lookup class
1576 * when this lookup was teleported from an old lookup class
1577 * in one module to a new lookup class in another module.
1578 *
1579 * @return the lookup class in another module that this lookup object was
1580 * previously teleported from, or {@code null}
1581 * @since 14
1582 * @see #in(Class)
1583 * @see MethodHandles#privateLookupIn(Class, Lookup)
1584 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1585 */
1586 public Class<?> previousLookupClass() {
1587 return prevLookupClass;
1588 }
1589
1590 // This is just for calling out to MethodHandleImpl.
1591 private Class<?> lookupClassOrNull() {
1592 return (allowedModes == TRUSTED) ? null : lookupClass;
1593 }
1594
1595 /** Tells which access-protection classes of members this lookup object can produce.
1596 * The result is a bit-mask of the bits
1597 * {@linkplain #PUBLIC PUBLIC (0x01)},
1598 * {@linkplain #PRIVATE PRIVATE (0x02)},
1599 * {@linkplain #PROTECTED PROTECTED (0x04)},
1600 * {@linkplain #PACKAGE PACKAGE (0x08)},
1601 * {@linkplain #MODULE MODULE (0x10)},
1602 * {@linkplain #UNCONDITIONAL UNCONDITIONAL (0x20)},
1603 * and {@linkplain #ORIGINAL ORIGINAL (0x40)}.
1604 * <p>
1605 * A freshly-created lookup object
1606 * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class} has
1607 * all possible bits set, except {@code UNCONDITIONAL}.
1608 * A lookup object on a new lookup class
1609 * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object}
1610 * may have some mode bits set to zero.
1611 * Mode bits can also be
1612 * {@linkplain java.lang.invoke.MethodHandles.Lookup#dropLookupMode directly cleared}.
1613 * Once cleared, mode bits cannot be restored from the downgraded lookup object.
1614 * The purpose of this is to restrict access via the new lookup object,
1615 * so that it can access only names which can be reached by the original
1616 * lookup object, and also by the new lookup class.
1617 * @return the lookup modes, which limit the kinds of access performed by this lookup object
1618 * @see #in
1619 * @see #dropLookupMode
1620 */
1621 public int lookupModes() {
1622 return allowedModes & ALL_MODES;
1623 }
1624
1625 /** Embody the current class (the lookupClass) as a lookup class
1626 * for method handle creation.
1627 * Must be called by from a method in this package,
1628 * which in turn is called by a method not in this package.
1629 */
1630 Lookup(Class<?> lookupClass) {
1631 this(lookupClass, null, FULL_POWER_MODES);
1632 }
1633
1634 private Lookup(Class<?> lookupClass, Class<?> prevLookupClass, int allowedModes) {
1635 assert prevLookupClass == null || ((allowedModes & MODULE) == 0
1636 && prevLookupClass.getModule() != lookupClass.getModule());
1637 assert !lookupClass.isArray() && !lookupClass.isPrimitive();
1638 this.lookupClass = lookupClass;
1639 this.prevLookupClass = prevLookupClass;
1640 this.allowedModes = allowedModes;
1641 }
1642
1643 private static Lookup newLookup(Class<?> lookupClass, Class<?> prevLookupClass, int allowedModes) {
1644 // make sure we haven't accidentally picked up a privileged class:
1645 checkUnprivilegedlookupClass(lookupClass);
1646 return new Lookup(lookupClass, prevLookupClass, allowedModes);
1647 }
1648
1649 /**
1650 * Creates a lookup on the specified new lookup class.
1651 * The resulting object will report the specified
1652 * class as its own {@link #lookupClass() lookupClass}.
1653 *
1654 * <p>
1655 * However, the resulting {@code Lookup} object is guaranteed
1656 * to have no more access capabilities than the original.
1657 * In particular, access capabilities can be lost as follows:<ul>
1658 * <li>If the new lookup class is different from the old lookup class,
1659 * i.e. {@link #ORIGINAL ORIGINAL} access is lost.
1660 * <li>If the new lookup class is in a different module from the old one,
1661 * i.e. {@link #MODULE MODULE} access is lost.
1662 * <li>If the new lookup class is in a different package
1663 * than the old one, protected and default (package) members will not be accessible,
1664 * i.e. {@link #PROTECTED PROTECTED} and {@link #PACKAGE PACKAGE} access are lost.
1665 * <li>If the new lookup class is not within the same package member
1666 * as the old one, private members will not be accessible, and protected members
1667 * will not be accessible by virtue of inheritance,
1668 * i.e. {@link #PRIVATE PRIVATE} access is lost.
1669 * (Protected members may continue to be accessible because of package sharing.)
1670 * <li>If the new lookup class is not
1671 * {@linkplain #accessClass(Class) accessible} to this lookup,
1672 * then no members, not even public members, will be accessible
1673 * i.e. all access modes are lost.
1674 * <li>If the new lookup class, the old lookup class and the previous lookup class
1675 * are all in different modules i.e. teleporting to a third module,
1676 * all access modes are lost.
1677 * </ul>
1678 * <p>
1679 * The new previous lookup class is chosen as follows:
1680 * <ul>
1681 * <li>If the new lookup object has {@link #UNCONDITIONAL UNCONDITIONAL} bit,
1682 * the new previous lookup class is {@code null}.
1683 * <li>If the new lookup class is in the same module as the old lookup class,
1684 * the new previous lookup class is the old previous lookup class.
1685 * <li>If the new lookup class is in a different module from the old lookup class,
1686 * the new previous lookup class is the old lookup class.
1687 *</ul>
1688 * <p>
1689 * The resulting lookup's capabilities for loading classes
1690 * (used during {@link #findClass} invocations)
1691 * are determined by the lookup class' loader,
1692 * which may change due to this operation.
1693 *
1694 * @param requestedLookupClass the desired lookup class for the new lookup object
1695 * @return a lookup object which reports the desired lookup class, or the same object
1696 * if there is no change
1697 * @throws IllegalArgumentException if {@code requestedLookupClass} is a primitive type or void or array class
1698 * @throws NullPointerException if the argument is null
1699 *
1700 * @see #accessClass(Class)
1701 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1702 */
1703 public Lookup in(Class<?> requestedLookupClass) {
1704 Objects.requireNonNull(requestedLookupClass);
1705 if (requestedLookupClass.isPrimitive())
1706 throw new IllegalArgumentException(requestedLookupClass + " is a primitive class");
1707 if (requestedLookupClass.isArray())
1708 throw new IllegalArgumentException(requestedLookupClass + " is an array class");
1709
1710 if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all
1711 return new Lookup(requestedLookupClass, null, FULL_POWER_MODES);
1712 if (requestedLookupClass == this.lookupClass)
1713 return this; // keep same capabilities
1714 int newModes = (allowedModes & FULL_POWER_MODES) & ~ORIGINAL;
1715 Module fromModule = this.lookupClass.getModule();
1716 Module targetModule = requestedLookupClass.getModule();
1717 Class<?> plc = this.previousLookupClass();
1718 if ((this.allowedModes & UNCONDITIONAL) != 0) {
1719 assert plc == null;
1720 newModes = UNCONDITIONAL;
1721 } else if (fromModule != targetModule) {
1722 if (plc != null && !VerifyAccess.isSameModule(plc, requestedLookupClass)) {
1723 // allow hopping back and forth between fromModule and plc's module
1724 // but not the third module
1725 newModes = 0;
1726 }
1727 // drop MODULE access
1728 newModes &= ~(MODULE|PACKAGE|PRIVATE|PROTECTED);
1729 // teleport from this lookup class
1730 plc = this.lookupClass;
1731 }
1732 if ((newModes & PACKAGE) != 0
1733 && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {
1734 newModes &= ~(PACKAGE|PRIVATE|PROTECTED);
1735 }
1736 // Allow nestmate lookups to be created without special privilege:
1737 if ((newModes & PRIVATE) != 0
1738 && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {
1739 newModes &= ~(PRIVATE|PROTECTED);
1740 }
1741 if ((newModes & (PUBLIC|UNCONDITIONAL)) != 0
1742 && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, this.prevLookupClass, allowedModes)) {
1743 // The requested class it not accessible from the lookup class.
1744 // No permissions.
1745 newModes = 0;
1746 }
1747 return newLookup(requestedLookupClass, plc, newModes);
1748 }
1749
1750 /**
1751 * Creates a lookup on the same lookup class which this lookup object
1752 * finds members, but with a lookup mode that has lost the given lookup mode.
1753 * The lookup mode to drop is one of {@link #PUBLIC PUBLIC}, {@link #MODULE
1754 * MODULE}, {@link #PACKAGE PACKAGE}, {@link #PROTECTED PROTECTED},
1755 * {@link #PRIVATE PRIVATE}, {@link #ORIGINAL ORIGINAL}, or
1756 * {@link #UNCONDITIONAL UNCONDITIONAL}.
1757 *
1758 * <p> If this lookup is a {@linkplain MethodHandles#publicLookup() public lookup},
1759 * this lookup has {@code UNCONDITIONAL} mode set and it has no other mode set.
1760 * When dropping {@code UNCONDITIONAL} on a public lookup then the resulting
1761 * lookup has no access.
1762 *
1763 * <p> If this lookup is not a public lookup, then the following applies
1764 * regardless of its {@linkplain #lookupModes() lookup modes}.
1765 * {@link #PROTECTED PROTECTED} and {@link #ORIGINAL ORIGINAL} are always
1766 * dropped and so the resulting lookup mode will never have these access
1767 * capabilities. When dropping {@code PACKAGE}
1768 * then the resulting lookup will not have {@code PACKAGE} or {@code PRIVATE}
1769 * access. When dropping {@code MODULE} then the resulting lookup will not
1770 * have {@code MODULE}, {@code PACKAGE}, or {@code PRIVATE} access.
1771 * When dropping {@code PUBLIC} then the resulting lookup has no access.
1772 *
1773 * @apiNote
1774 * A lookup with {@code PACKAGE} but not {@code PRIVATE} mode can safely
1775 * delegate non-public access within the package of the lookup class without
1776 * conferring <a href="MethodHandles.Lookup.html#privacc">private access</a>.
1777 * A lookup with {@code MODULE} but not
1778 * {@code PACKAGE} mode can safely delegate {@code PUBLIC} access within
1779 * the module of the lookup class without conferring package access.
1780 * A lookup with a {@linkplain #previousLookupClass() previous lookup class}
1781 * (and {@code PUBLIC} but not {@code MODULE} mode) can safely delegate access
1782 * to public classes accessible to both the module of the lookup class
1783 * and the module of the previous lookup class.
1784 *
1785 * @param modeToDrop the lookup mode to drop
1786 * @return a lookup object which lacks the indicated mode, or the same object if there is no change
1787 * @throws IllegalArgumentException if {@code modeToDrop} is not one of {@code PUBLIC},
1788 * {@code MODULE}, {@code PACKAGE}, {@code PROTECTED}, {@code PRIVATE}, {@code ORIGINAL}
1789 * or {@code UNCONDITIONAL}
1790 * @see MethodHandles#privateLookupIn
1791 * @since 9
1792 */
1793 public Lookup dropLookupMode(int modeToDrop) {
1794 int oldModes = lookupModes();
1795 int newModes = oldModes & ~(modeToDrop | PROTECTED | ORIGINAL);
1796 switch (modeToDrop) {
1797 case PUBLIC: newModes &= ~(FULL_POWER_MODES); break;
1798 case MODULE: newModes &= ~(PACKAGE | PRIVATE); break;
1799 case PACKAGE: newModes &= ~(PRIVATE); break;
1800 case PROTECTED:
1801 case PRIVATE:
1802 case ORIGINAL:
1803 case UNCONDITIONAL: break;
1804 default: throw new IllegalArgumentException(modeToDrop + " is not a valid mode to drop");
1805 }
1806 if (newModes == oldModes) return this; // return self if no change
1807 return newLookup(lookupClass(), previousLookupClass(), newModes);
1808 }
1809
1810 /**
1811 * Creates and links a class or interface from {@code bytes}
1812 * with the same class loader and in the same runtime package and
1813 * {@linkplain java.security.ProtectionDomain protection domain} as this lookup's
1814 * {@linkplain #lookupClass() lookup class} as if calling
1815 * {@link ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain)
1816 * ClassLoader::defineClass}.
1817 *
1818 * <p> The {@linkplain #lookupModes() lookup modes} for this lookup must include
1819 * {@link #PACKAGE PACKAGE} access as default (package) members will be
1820 * accessible to the class. The {@code PACKAGE} lookup mode serves to authenticate
1821 * that the lookup object was created by a caller in the runtime package (or derived
1822 * from a lookup originally created by suitably privileged code to a target class in
1823 * the runtime package). </p>
1824 *
1825 * <p> The {@code bytes} parameter is the class bytes of a valid class file (as defined
1826 * by the <em>The Java Virtual Machine Specification</em>) with a class name in the
1827 * same package as the lookup class. </p>
1828 *
1829 * <p> This method does not run the class initializer. The class initializer may
1830 * run at a later time, as detailed in section 12.4 of the <em>The Java Language
1831 * Specification</em>. </p>
1832 *
1833 * <p> If there is a security manager and this lookup does not have {@linkplain
1834 * #hasFullPrivilegeAccess() full privilege access}, its {@code checkPermission} method
1835 * is first called to check {@code RuntimePermission("defineClass")}. </p>
1836 *
1837 * @param bytes the class bytes
1838 * @return the {@code Class} object for the class
1839 * @throws IllegalAccessException if this lookup does not have {@code PACKAGE} access
1840 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure
1841 * @throws IllegalArgumentException if {@code bytes} denotes a class in a different package
1842 * than the lookup class or {@code bytes} is not a class or interface
1843 * ({@code ACC_MODULE} flag is set in the value of the {@code access_flags} item)
1844 * @throws VerifyError if the newly created class cannot be verified
1845 * @throws LinkageError if the newly created class cannot be linked for any other reason
1846 * @throws SecurityException if a security manager is present and it
1847 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1848 * @throws NullPointerException if {@code bytes} is {@code null}
1849 * @since 9
1850 * @see Lookup#privateLookupIn
1851 * @see Lookup#dropLookupMode
1852 * @see ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain)
1853 */
1854 public Class<?> defineClass(byte[] bytes) throws IllegalAccessException {
1855 ensureDefineClassPermission();
1856 if ((lookupModes() & PACKAGE) == 0)
1857 throw new IllegalAccessException("Lookup does not have PACKAGE access");
1858 return makeClassDefiner(bytes.clone()).defineClass(false);
1859 }
1860
1861 private void ensureDefineClassPermission() {
1862 if (allowedModes == TRUSTED) return;
1863
1864 if (!hasFullPrivilegeAccess()) {
1865 @SuppressWarnings("removal")
1866 SecurityManager sm = System.getSecurityManager();
1867 if (sm != null)
1868 sm.checkPermission(new RuntimePermission("defineClass"));
1869 }
1870 }
1871
1872 /**
1873 * The set of class options that specify whether a hidden class created by
1874 * {@link Lookup#defineHiddenClass(byte[], boolean, ClassOption...)
1875 * Lookup::defineHiddenClass} method is dynamically added as a new member
1876 * to the nest of a lookup class and/or whether a hidden class has
1877 * a strong relationship with the class loader marked as its defining loader.
1878 *
1879 * @since 15
1880 */
1881 public enum ClassOption {
1882 /**
1883 * Specifies that a hidden class be added to {@linkplain Class#getNestHost nest}
1884 * of a lookup class as a nestmate.
1885 *
1886 * <p> A hidden nestmate class has access to the private members of all
1887 * classes and interfaces in the same nest.
1888 *
1889 * @see Class#getNestHost()
1890 */
1891 NESTMATE(NESTMATE_CLASS),
1892
1893 /**
1894 * Specifies that a hidden class has a <em>strong</em>
1895 * relationship with the class loader marked as its defining loader,
1896 * as a normal class or interface has with its own defining loader.
1897 * This means that the hidden class may be unloaded if and only if
1898 * its defining loader is not reachable and thus may be reclaimed
1899 * by a garbage collector (JLS {@jls 12.7}).
1900 *
1901 * <p> By default, a hidden class or interface may be unloaded
1902 * even if the class loader that is marked as its defining loader is
1903 * <a href="../ref/package-summary.html#reachability">reachable</a>.
1904
1905 *
1906 * @jls 12.7 Unloading of Classes and Interfaces
1907 */
1908 STRONG(STRONG_LOADER_LINK);
1909
1910 /* the flag value is used by VM at define class time */
1911 private final int flag;
1912 ClassOption(int flag) {
1913 this.flag = flag;
1914 }
1915
1916 static int optionsToFlag(Set<ClassOption> options) {
1917 int flags = 0;
1918 for (ClassOption cp : options) {
1919 flags |= cp.flag;
1920 }
1921 return flags;
1922 }
1923 }
1924
1925 /**
1926 * Creates a <em>hidden</em> class or interface from {@code bytes},
1927 * returning a {@code Lookup} on the newly created class or interface.
1928 *
1929 * <p> Ordinarily, a class or interface {@code C} is created by a class loader,
1930 * which either defines {@code C} directly or delegates to another class loader.
1931 * A class loader defines {@code C} directly by invoking
1932 * {@link ClassLoader#defineClass(String, byte[], int, int, ProtectionDomain)
1933 * ClassLoader::defineClass}, which causes the Java Virtual Machine
1934 * to derive {@code C} from a purported representation in {@code class} file format.
1935 * In situations where use of a class loader is undesirable, a class or interface
1936 * {@code C} can be created by this method instead. This method is capable of
1937 * defining {@code C}, and thereby creating it, without invoking
1938 * {@code ClassLoader::defineClass}.
1939 * Instead, this method defines {@code C} as if by arranging for
1940 * the Java Virtual Machine to derive a nonarray class or interface {@code C}
1941 * from a purported representation in {@code class} file format
1942 * using the following rules:
1943 *
1944 * <ol>
1945 * <li> The {@linkplain #lookupModes() lookup modes} for this {@code Lookup}
1946 * must include {@linkplain #hasFullPrivilegeAccess() full privilege} access.
1947 * This level of access is needed to create {@code C} in the module
1948 * of the lookup class of this {@code Lookup}.</li>
1949 *
1950 * <li> The purported representation in {@code bytes} must be a {@code ClassFile}
1951 * structure (JVMS {@jvms 4.1}) of a supported major and minor version.
1952 * The major and minor version may differ from the {@code class} file version
1953 * of the lookup class of this {@code Lookup}.</li>
1954 *
1955 * <li> The value of {@code this_class} must be a valid index in the
1956 * {@code constant_pool} table, and the entry at that index must be a valid
1957 * {@code CONSTANT_Class_info} structure. Let {@code N} be the binary name
1958 * encoded in internal form that is specified by this structure. {@code N} must
1959 * denote a class or interface in the same package as the lookup class.</li>
1960 *
1961 * <li> Let {@code CN} be the string {@code N + "." + <suffix>},
1962 * where {@code <suffix>} is an unqualified name.
1963 *
1964 * <p> Let {@code newBytes} be the {@code ClassFile} structure given by
1965 * {@code bytes} with an additional entry in the {@code constant_pool} table,
1966 * indicating a {@code CONSTANT_Utf8_info} structure for {@code CN}, and
1967 * where the {@code CONSTANT_Class_info} structure indicated by {@code this_class}
1968 * refers to the new {@code CONSTANT_Utf8_info} structure.
1969 *
1970 * <p> Let {@code L} be the defining class loader of the lookup class of this {@code Lookup}.
1971 *
1972 * <p> {@code C} is derived with name {@code CN}, class loader {@code L}, and
1973 * purported representation {@code newBytes} as if by the rules of JVMS {@jvms 5.3.5},
1974 * with the following adjustments:
1975 * <ul>
1976 * <li> The constant indicated by {@code this_class} is permitted to specify a name
1977 * that includes a single {@code "."} character, even though this is not a valid
1978 * binary class or interface name in internal form.</li>
1979 *
1980 * <li> The Java Virtual Machine marks {@code L} as the defining class loader of {@code C},
1981 * but no class loader is recorded as an initiating class loader of {@code C}.</li>
1982 *
1983 * <li> {@code C} is considered to have the same runtime
1984 * {@linkplain Class#getPackage() package}, {@linkplain Class#getModule() module}
1985 * and {@linkplain java.security.ProtectionDomain protection domain}
1986 * as the lookup class of this {@code Lookup}.
1987 * <li> Let {@code GN} be the binary name obtained by taking {@code N}
1988 * (a binary name encoded in internal form) and replacing ASCII forward slashes with
1989 * ASCII periods. For the instance of {@link java.lang.Class} representing {@code C}:
1990 * <ul>
1991 * <li> {@link Class#getName()} returns the string {@code GN + "/" + <suffix>},
1992 * even though this is not a valid binary class or interface name.</li>
1993 * <li> {@link Class#descriptorString()} returns the string
1994 * {@code "L" + N + "." + <suffix> + ";"},
1995 * even though this is not a valid type descriptor name.</li>
1996 * <li> {@link Class#describeConstable()} returns an empty optional as {@code C}
1997 * cannot be described in {@linkplain java.lang.constant.ClassDesc nominal form}.</li>
1998 * </ul>
1999 * </ul>
2000 * </li>
2001 * </ol>
2002 *
2003 * <p> After {@code C} is derived, it is linked by the Java Virtual Machine.
2004 * Linkage occurs as specified in JVMS {@jvms 5.4.3}, with the following adjustments:
2005 * <ul>
2006 * <li> During verification, whenever it is necessary to load the class named
2007 * {@code CN}, the attempt succeeds, producing class {@code C}. No request is
2008 * made of any class loader.</li>
2009 *
2010 * <li> On any attempt to resolve the entry in the run-time constant pool indicated
2011 * by {@code this_class}, the symbolic reference is considered to be resolved to
2012 * {@code C} and resolution always succeeds immediately.</li>
2013 * </ul>
2014 *
2015 * <p> If the {@code initialize} parameter is {@code true},
2016 * then {@code C} is initialized by the Java Virtual Machine.
2017 *
2018 * <p> The newly created class or interface {@code C} serves as the
2019 * {@linkplain #lookupClass() lookup class} of the {@code Lookup} object
2020 * returned by this method. {@code C} is <em>hidden</em> in the sense that
2021 * no other class or interface can refer to {@code C} via a constant pool entry.
2022 * That is, a hidden class or interface cannot be named as a supertype, a field type,
2023 * a method parameter type, or a method return type by any other class.
2024 * This is because a hidden class or interface does not have a binary name, so
2025 * there is no internal form available to record in any class's constant pool.
2026 * A hidden class or interface is not discoverable by {@link Class#forName(String, boolean, ClassLoader)},
2027 * {@link ClassLoader#loadClass(String, boolean)}, or {@link #findClass(String)}, and
2028 * is not {@linkplain java.instrument/java.lang.instrument.Instrumentation#isModifiableClass(Class)
2029 * modifiable} by Java agents or tool agents using the <a href="{@docRoot}/../specs/jvmti.html">
2030 * JVM Tool Interface</a>.
2031 *
2032 * <p> A class or interface created by
2033 * {@linkplain ClassLoader#defineClass(String, byte[], int, int, ProtectionDomain)
2034 * a class loader} has a strong relationship with that class loader.
2035 * That is, every {@code Class} object contains a reference to the {@code ClassLoader}
2036 * that {@linkplain Class#getClassLoader() defined it}.
2037 * This means that a class created by a class loader may be unloaded if and
2038 * only if its defining loader is not reachable and thus may be reclaimed
2039 * by a garbage collector (JLS {@jls 12.7}).
2040 *
2041 * By default, however, a hidden class or interface may be unloaded even if
2042 * the class loader that is marked as its defining loader is
2043 * <a href="../ref/package-summary.html#reachability">reachable</a>.
2044 * This behavior is useful when a hidden class or interface serves multiple
2045 * classes defined by arbitrary class loaders. In other cases, a hidden
2046 * class or interface may be linked to a single class (or a small number of classes)
2047 * with the same defining loader as the hidden class or interface.
2048 * In such cases, where the hidden class or interface must be coterminous
2049 * with a normal class or interface, the {@link ClassOption#STRONG STRONG}
2050 * option may be passed in {@code options}.
2051 * This arranges for a hidden class to have the same strong relationship
2052 * with the class loader marked as its defining loader,
2053 * as a normal class or interface has with its own defining loader.
2054 *
2055 * If {@code STRONG} is not used, then the invoker of {@code defineHiddenClass}
2056 * may still prevent a hidden class or interface from being
2057 * unloaded by ensuring that the {@code Class} object is reachable.
2058 *
2059 * <p> The unloading characteristics are set for each hidden class when it is
2060 * defined, and cannot be changed later. An advantage of allowing hidden classes
2061 * to be unloaded independently of the class loader marked as their defining loader
2062 * is that a very large number of hidden classes may be created by an application.
2063 * In contrast, if {@code STRONG} is used, then the JVM may run out of memory,
2064 * just as if normal classes were created by class loaders.
2065 *
2066 * <p> Classes and interfaces in a nest are allowed to have mutual access to
2067 * their private members. The nest relationship is determined by
2068 * the {@code NestHost} attribute (JVMS {@jvms 4.7.28}) and
2069 * the {@code NestMembers} attribute (JVMS {@jvms 4.7.29}) in a {@code class} file.
2070 * By default, a hidden class belongs to a nest consisting only of itself
2071 * because a hidden class has no binary name.
2072 * The {@link ClassOption#NESTMATE NESTMATE} option can be passed in {@code options}
2073 * to create a hidden class or interface {@code C} as a member of a nest.
2074 * The nest to which {@code C} belongs is not based on any {@code NestHost} attribute
2075 * in the {@code ClassFile} structure from which {@code C} was derived.
2076 * Instead, the following rules determine the nest host of {@code C}:
2077 * <ul>
2078 * <li>If the nest host of the lookup class of this {@code Lookup} has previously
2079 * been determined, then let {@code H} be the nest host of the lookup class.
2080 * Otherwise, the nest host of the lookup class is determined using the
2081 * algorithm in JVMS {@jvms 5.4.4}, yielding {@code H}.</li>
2082 * <li>The nest host of {@code C} is determined to be {@code H},
2083 * the nest host of the lookup class.</li>
2084 * </ul>
2085 *
2086 * <p> A hidden class or interface may be serializable, but this requires a custom
2087 * serialization mechanism in order to ensure that instances are properly serialized
2088 * and deserialized. The default serialization mechanism supports only classes and
2089 * interfaces that are discoverable by their class name.
2090 *
2091 * @param bytes the bytes that make up the class data,
2092 * in the format of a valid {@code class} file as defined by
2093 * <cite>The Java Virtual Machine Specification</cite>.
2094 * @param initialize if {@code true} the class will be initialized.
2095 * @param options {@linkplain ClassOption class options}
2096 * @return the {@code Lookup} object on the hidden class,
2097 * with {@linkplain #ORIGINAL original} and
2098 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege} access
2099 *
2100 * @throws IllegalAccessException if this {@code Lookup} does not have
2101 * {@linkplain #hasFullPrivilegeAccess() full privilege} access
2102 * @throws SecurityException if a security manager is present and it
2103 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2104 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure
2105 * @throws UnsupportedClassVersionError if {@code bytes} is not of a supported major or minor version
2106 * @throws IllegalArgumentException if {@code bytes} denotes a class in a different package
2107 * than the lookup class or {@code bytes} is not a class or interface
2108 * ({@code ACC_MODULE} flag is set in the value of the {@code access_flags} item)
2109 * @throws IncompatibleClassChangeError if the class or interface named as
2110 * the direct superclass of {@code C} is in fact an interface, or if any of the classes
2111 * or interfaces named as direct superinterfaces of {@code C} are not in fact interfaces
2112 * @throws ClassCircularityError if any of the superclasses or superinterfaces of
2113 * {@code C} is {@code C} itself
2114 * @throws VerifyError if the newly created class cannot be verified
2115 * @throws LinkageError if the newly created class cannot be linked for any other reason
2116 * @throws NullPointerException if any parameter is {@code null}
2117 *
2118 * @since 15
2119 * @see Class#isHidden()
2120 * @jvms 4.2.1 Binary Class and Interface Names
2121 * @jvms 4.2.2 Unqualified Names
2122 * @jvms 4.7.28 The {@code NestHost} Attribute
2123 * @jvms 4.7.29 The {@code NestMembers} Attribute
2124 * @jvms 5.4.3.1 Class and Interface Resolution
2125 * @jvms 5.4.4 Access Control
2126 * @jvms 5.3.5 Deriving a {@code Class} from a {@code class} File Representation
2127 * @jvms 5.4 Linking
2128 * @jvms 5.5 Initialization
2129 * @jls 12.7 Unloading of Classes and Interfaces
2130 */
2131 @SuppressWarnings("doclint:reference") // cross-module links
2132 public Lookup defineHiddenClass(byte[] bytes, boolean initialize, ClassOption... options)
2133 throws IllegalAccessException
2134 {
2135 Objects.requireNonNull(bytes);
2136 Objects.requireNonNull(options);
2137
2138 ensureDefineClassPermission();
2139 if (!hasFullPrivilegeAccess()) {
2140 throw new IllegalAccessException(this + " does not have full privilege access");
2141 }
2142
2143 return makeHiddenClassDefiner(bytes.clone(), Set.of(options), false).defineClassAsLookup(initialize);
2144 }
2145
2146 /**
2147 * Creates a <em>hidden</em> class or interface from {@code bytes} with associated
2148 * {@linkplain MethodHandles#classData(Lookup, String, Class) class data},
2149 * returning a {@code Lookup} on the newly created class or interface.
2150 *
2151 * <p> This method is equivalent to calling
2152 * {@link #defineHiddenClass(byte[], boolean, ClassOption...) defineHiddenClass(bytes, initialize, options)}
2153 * as if the hidden class is injected with a private static final <i>unnamed</i>
2154 * field which is initialized with the given {@code classData} at
2155 * the first instruction of the class initializer.
2156 * The newly created class is linked by the Java Virtual Machine.
2157 *
2158 * <p> The {@link MethodHandles#classData(Lookup, String, Class) MethodHandles::classData}
2159 * and {@link MethodHandles#classDataAt(Lookup, String, Class, int) MethodHandles::classDataAt}
2160 * methods can be used to retrieve the {@code classData}.
2161 *
2162 * @apiNote
2163 * A framework can create a hidden class with class data with one or more
2164 * objects and load the class data as dynamically-computed constant(s)
2165 * via a bootstrap method. {@link MethodHandles#classData(Lookup, String, Class)
2166 * Class data} is accessible only to the lookup object created by the newly
2167 * defined hidden class but inaccessible to other members in the same nest
2168 * (unlike private static fields that are accessible to nestmates).
2169 * Care should be taken w.r.t. mutability for example when passing
2170 * an array or other mutable structure through the class data.
2171 * Changing any value stored in the class data at runtime may lead to
2172 * unpredictable behavior.
2173 * If the class data is a {@code List}, it is good practice to make it
2174 * unmodifiable for example via {@link List#of List::of}.
2175 *
2176 * @param bytes the class bytes
2177 * @param classData pre-initialized class data
2178 * @param initialize if {@code true} the class will be initialized.
2179 * @param options {@linkplain ClassOption class options}
2180 * @return the {@code Lookup} object on the hidden class,
2181 * with {@linkplain #ORIGINAL original} and
2182 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege} access
2183 *
2184 * @throws IllegalAccessException if this {@code Lookup} does not have
2185 * {@linkplain #hasFullPrivilegeAccess() full privilege} access
2186 * @throws SecurityException if a security manager is present and it
2187 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2188 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure
2189 * @throws UnsupportedClassVersionError if {@code bytes} is not of a supported major or minor version
2190 * @throws IllegalArgumentException if {@code bytes} denotes a class in a different package
2191 * than the lookup class or {@code bytes} is not a class or interface
2192 * ({@code ACC_MODULE} flag is set in the value of the {@code access_flags} item)
2193 * @throws IncompatibleClassChangeError if the class or interface named as
2194 * the direct superclass of {@code C} is in fact an interface, or if any of the classes
2195 * or interfaces named as direct superinterfaces of {@code C} are not in fact interfaces
2196 * @throws ClassCircularityError if any of the superclasses or superinterfaces of
2197 * {@code C} is {@code C} itself
2198 * @throws VerifyError if the newly created class cannot be verified
2199 * @throws LinkageError if the newly created class cannot be linked for any other reason
2200 * @throws NullPointerException if any parameter is {@code null}
2201 *
2202 * @since 16
2203 * @see Lookup#defineHiddenClass(byte[], boolean, ClassOption...)
2204 * @see Class#isHidden()
2205 * @see MethodHandles#classData(Lookup, String, Class)
2206 * @see MethodHandles#classDataAt(Lookup, String, Class, int)
2207 * @jvms 4.2.1 Binary Class and Interface Names
2208 * @jvms 4.2.2 Unqualified Names
2209 * @jvms 4.7.28 The {@code NestHost} Attribute
2210 * @jvms 4.7.29 The {@code NestMembers} Attribute
2211 * @jvms 5.4.3.1 Class and Interface Resolution
2212 * @jvms 5.4.4 Access Control
2213 * @jvms 5.3.5 Deriving a {@code Class} from a {@code class} File Representation
2214 * @jvms 5.4 Linking
2215 * @jvms 5.5 Initialization
2216 * @jls 12.7 Unloading of Classes and Interface
2217 */
2218 public Lookup defineHiddenClassWithClassData(byte[] bytes, Object classData, boolean initialize, ClassOption... options)
2219 throws IllegalAccessException
2220 {
2221 Objects.requireNonNull(bytes);
2222 Objects.requireNonNull(classData);
2223 Objects.requireNonNull(options);
2224
2225 ensureDefineClassPermission();
2226 if (!hasFullPrivilegeAccess()) {
2227 throw new IllegalAccessException(this + " does not have full privilege access");
2228 }
2229
2230 return makeHiddenClassDefiner(bytes.clone(), Set.of(options), false)
2231 .defineClassAsLookup(initialize, classData);
2232 }
2233
2234 // A default dumper for writing class files passed to Lookup::defineClass
2235 // and Lookup::defineHiddenClass to disk for debugging purposes. To enable,
2236 // set -Djdk.invoke.MethodHandle.dumpHiddenClassFiles or
2237 // -Djdk.invoke.MethodHandle.dumpHiddenClassFiles=true
2238 //
2239 // This default dumper does not dump hidden classes defined by LambdaMetafactory
2240 // and LambdaForms and method handle internals. They are dumped via
2241 // different ClassFileDumpers.
2242 private static ClassFileDumper defaultDumper() {
2243 return DEFAULT_DUMPER;
2244 }
2245
2246 private static final ClassFileDumper DEFAULT_DUMPER = ClassFileDumper.getInstance(
2247 "jdk.invoke.MethodHandle.dumpClassFiles", "DUMP_CLASS_FILES");
2248
2249 static class ClassFile {
2250 final String name; // internal name
2251 final int accessFlags;
2252 final byte[] bytes;
2253 ClassFile(String name, int accessFlags, byte[] bytes) {
2254 this.name = name;
2255 this.accessFlags = accessFlags;
2256 this.bytes = bytes;
2257 }
2258
2259 static ClassFile newInstanceNoCheck(String name, byte[] bytes) {
2260 return new ClassFile(name, 0, bytes);
2261 }
2262
2263 /**
2264 * This method checks the class file version and the structure of `this_class`.
2265 * and checks if the bytes is a class or interface (ACC_MODULE flag not set)
2266 * that is in the named package.
2267 *
2268 * @throws IllegalArgumentException if ACC_MODULE flag is set in access flags
2269 * or the class is not in the given package name.
2270 */
2271 static ClassFile newInstance(byte[] bytes, String pkgName) {
2272 var cf = readClassFile(bytes);
2273
2274 // check if it's in the named package
2275 int index = cf.name.lastIndexOf('/');
2276 String pn = (index == -1) ? "" : cf.name.substring(0, index).replace('/', '.');
2277 if (!pn.equals(pkgName)) {
2278 throw newIllegalArgumentException(cf.name + " not in same package as lookup class");
2279 }
2280 return cf;
2281 }
2282
2283 private static ClassFile readClassFile(byte[] bytes) {
2284 int magic = readInt(bytes, 0);
2285 if (magic != 0xCAFEBABE) {
2286 throw new ClassFormatError("Incompatible magic value: " + magic);
2287 }
2288 int minor = readUnsignedShort(bytes, 4);
2289 int major = readUnsignedShort(bytes, 6);
2290 if (!VM.isSupportedClassFileVersion(major, minor)) {
2291 throw new UnsupportedClassVersionError("Unsupported class file version " + major + "." + minor);
2292 }
2293
2294 String name;
2295 int accessFlags;
2296 try {
2297 ClassReader reader = new ClassReader(bytes);
2298 // ClassReader does not check if `this_class` is CONSTANT_Class_info
2299 // workaround to read `this_class` using readConst and validate the value
2300 int thisClass = reader.readUnsignedShort(reader.header + 2);
2301 Object constant = reader.readConst(thisClass, new char[reader.getMaxStringLength()]);
2302 if (!(constant instanceof Type type)) {
2303 throw new ClassFormatError("this_class item: #" + thisClass + " not a CONSTANT_Class_info");
2304 }
2305 if (!type.getDescriptor().startsWith("L")) {
2306 throw new ClassFormatError("this_class item: #" + thisClass + " not a CONSTANT_Class_info");
2307 }
2308 name = type.getInternalName();
2309 accessFlags = reader.readUnsignedShort(reader.header);
2310 } catch (RuntimeException e) {
2311 // ASM exceptions are poorly specified
2312 ClassFormatError cfe = new ClassFormatError();
2313 cfe.initCause(e);
2314 throw cfe;
2315 }
2316 // must be a class or interface
2317 if ((accessFlags & Opcodes.ACC_MODULE) != 0) {
2318 throw newIllegalArgumentException("Not a class or interface: ACC_MODULE flag is set");
2319 }
2320 return new ClassFile(name, accessFlags, bytes);
2321 }
2322
2323 private static int readInt(byte[] bytes, int offset) {
2324 if ((offset+4) > bytes.length) {
2325 throw new ClassFormatError("Invalid ClassFile structure");
2326 }
2327 return ((bytes[offset] & 0xFF) << 24)
2328 | ((bytes[offset + 1] & 0xFF) << 16)
2329 | ((bytes[offset + 2] & 0xFF) << 8)
2330 | (bytes[offset + 3] & 0xFF);
2331 }
2332
2333 private static int readUnsignedShort(byte[] bytes, int offset) {
2334 if ((offset+2) > bytes.length) {
2335 throw new ClassFormatError("Invalid ClassFile structure");
2336 }
2337 return ((bytes[offset] & 0xFF) << 8) | (bytes[offset + 1] & 0xFF);
2338 }
2339 }
2340
2341 /*
2342 * Returns a ClassDefiner that creates a {@code Class} object of a normal class
2343 * from the given bytes.
2344 *
2345 * Caller should make a defensive copy of the arguments if needed
2346 * before calling this factory method.
2347 *
2348 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or
2349 * {@code bytes} denotes a class in a different package than the lookup class
2350 */
2351 private ClassDefiner makeClassDefiner(byte[] bytes) {
2352 ClassFile cf = ClassFile.newInstance(bytes, lookupClass().getPackageName());
2353 return new ClassDefiner(this, cf, STRONG_LOADER_LINK, defaultDumper());
2354 }
2355
2356 /**
2357 * Returns a ClassDefiner that creates a {@code Class} object of a normal class
2358 * from the given bytes. No package name check on the given bytes.
2359 *
2360 * @param name internal name
2361 * @param bytes class bytes
2362 * @param dumper dumper to write the given bytes to the dumper's output directory
2363 * @return ClassDefiner that defines a normal class of the given bytes.
2364 */
2365 ClassDefiner makeClassDefiner(String name, byte[] bytes, ClassFileDumper dumper) {
2366 // skip package name validation
2367 ClassFile cf = ClassFile.newInstanceNoCheck(name, bytes);
2368 return new ClassDefiner(this, cf, STRONG_LOADER_LINK, dumper);
2369 }
2370
2371 /**
2372 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2373 * from the given bytes. The name must be in the same package as the lookup class.
2374 *
2375 * Caller should make a defensive copy of the arguments if needed
2376 * before calling this factory method.
2377 *
2378 * @param bytes class bytes
2379 * @param dumper dumper to write the given bytes to the dumper's output directory
2380 * @return ClassDefiner that defines a hidden class of the given bytes.
2381 *
2382 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or
2383 * {@code bytes} denotes a class in a different package than the lookup class
2384 */
2385 ClassDefiner makeHiddenClassDefiner(byte[] bytes, ClassFileDumper dumper) {
2386 ClassFile cf = ClassFile.newInstance(bytes, lookupClass().getPackageName());
2387 return makeHiddenClassDefiner(cf, Set.of(), false, dumper);
2388 }
2389
2390 /**
2391 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2392 * from the given bytes and options.
2393 * The name must be in the same package as the lookup class.
2394 *
2395 * Caller should make a defensive copy of the arguments if needed
2396 * before calling this factory method.
2397 *
2398 * @param bytes class bytes
2399 * @param options class options
2400 * @param accessVmAnnotations true to give the hidden class access to VM annotations
2401 * @return ClassDefiner that defines a hidden class of the given bytes and options
2402 *
2403 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or
2404 * {@code bytes} denotes a class in a different package than the lookup class
2405 */
2406 private ClassDefiner makeHiddenClassDefiner(byte[] bytes,
2407 Set<ClassOption> options,
2408 boolean accessVmAnnotations) {
2409 ClassFile cf = ClassFile.newInstance(bytes, lookupClass().getPackageName());
2410 return makeHiddenClassDefiner(cf, options, accessVmAnnotations, defaultDumper());
2411 }
2412
2413 /**
2414 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2415 * from the given bytes and the given options. No package name check on the given bytes.
2416 *
2417 * @param name internal name that specifies the prefix of the hidden class
2418 * @param bytes class bytes
2419 * @param options class options
2420 * @param dumper dumper to write the given bytes to the dumper's output directory
2421 * @return ClassDefiner that defines a hidden class of the given bytes and options.
2422 */
2423 ClassDefiner makeHiddenClassDefiner(String name, byte[] bytes, Set<ClassOption> options, ClassFileDumper dumper) {
2424 Objects.requireNonNull(dumper);
2425 // skip name and access flags validation
2426 return makeHiddenClassDefiner(ClassFile.newInstanceNoCheck(name, bytes), options, false, dumper);
2427 }
2428
2429 /**
2430 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2431 * from the given class file and options.
2432 *
2433 * @param cf ClassFile
2434 * @param options class options
2435 * @param accessVmAnnotations true to give the hidden class access to VM annotations
2436 * @param dumper dumper to write the given bytes to the dumper's output directory
2437 */
2438 private ClassDefiner makeHiddenClassDefiner(ClassFile cf,
2439 Set<ClassOption> options,
2440 boolean accessVmAnnotations,
2441 ClassFileDumper dumper) {
2442 int flags = HIDDEN_CLASS | ClassOption.optionsToFlag(options);
2443 if (accessVmAnnotations | VM.isSystemDomainLoader(lookupClass.getClassLoader())) {
2444 // jdk.internal.vm.annotations are permitted for classes
2445 // defined to boot loader and platform loader
2446 flags |= ACCESS_VM_ANNOTATIONS;
2447 }
2448
2449 return new ClassDefiner(this, cf, flags, dumper);
2450 }
2451
2452 static class ClassDefiner {
2453 private final Lookup lookup;
2454 private final String name; // internal name
2455 private final byte[] bytes;
2456 private final int classFlags;
2457 private final ClassFileDumper dumper;
2458
2459 private ClassDefiner(Lookup lookup, ClassFile cf, int flags, ClassFileDumper dumper) {
2460 assert ((flags & HIDDEN_CLASS) != 0 || (flags & STRONG_LOADER_LINK) == STRONG_LOADER_LINK);
2461 this.lookup = lookup;
2462 this.bytes = cf.bytes;
2463 this.name = cf.name;
2464 this.classFlags = flags;
2465 this.dumper = dumper;
2466 }
2467
2468 String internalName() {
2469 return name;
2470 }
2471
2472 Class<?> defineClass(boolean initialize) {
2473 return defineClass(initialize, null);
2474 }
2475
2476 Lookup defineClassAsLookup(boolean initialize) {
2477 Class<?> c = defineClass(initialize, null);
2478 return new Lookup(c, null, FULL_POWER_MODES);
2479 }
2480
2481 /**
2482 * Defines the class of the given bytes and the given classData.
2483 * If {@code initialize} parameter is true, then the class will be initialized.
2484 *
2485 * @param initialize true if the class to be initialized
2486 * @param classData classData or null
2487 * @return the class
2488 *
2489 * @throws LinkageError linkage error
2490 */
2491 Class<?> defineClass(boolean initialize, Object classData) {
2492 Class<?> lookupClass = lookup.lookupClass();
2493 ClassLoader loader = lookupClass.getClassLoader();
2494 ProtectionDomain pd = (loader != null) ? lookup.lookupClassProtectionDomain() : null;
2495 Class<?> c = null;
2496 try {
2497 c = SharedSecrets.getJavaLangAccess()
2498 .defineClass(loader, lookupClass, name, bytes, pd, initialize, classFlags, classData);
2499 assert !isNestmate() || c.getNestHost() == lookupClass.getNestHost();
2500 return c;
2501 } finally {
2502 // dump the classfile for debugging
2503 if (dumper.isEnabled()) {
2504 String name = internalName();
2505 if (c != null) {
2506 dumper.dumpClass(name, c, bytes);
2507 } else {
2508 dumper.dumpFailedClass(name, bytes);
2509 }
2510 }
2511 }
2512 }
2513
2514 /**
2515 * Defines the class of the given bytes and the given classData.
2516 * If {@code initialize} parameter is true, then the class will be initialized.
2517 *
2518 * @param initialize true if the class to be initialized
2519 * @param classData classData or null
2520 * @return a Lookup for the defined class
2521 *
2522 * @throws LinkageError linkage error
2523 */
2524 Lookup defineClassAsLookup(boolean initialize, Object classData) {
2525 Class<?> c = defineClass(initialize, classData);
2526 return new Lookup(c, null, FULL_POWER_MODES);
2527 }
2528
2529 private boolean isNestmate() {
2530 return (classFlags & NESTMATE_CLASS) != 0;
2531 }
2532 }
2533
2534 private ProtectionDomain lookupClassProtectionDomain() {
2535 ProtectionDomain pd = cachedProtectionDomain;
2536 if (pd == null) {
2537 cachedProtectionDomain = pd = SharedSecrets.getJavaLangAccess().protectionDomain(lookupClass);
2538 }
2539 return pd;
2540 }
2541
2542 // cached protection domain
2543 private volatile ProtectionDomain cachedProtectionDomain;
2544
2545 // Make sure outer class is initialized first.
2546 static { IMPL_NAMES.getClass(); }
2547
2548 /** Package-private version of lookup which is trusted. */
2549 static final Lookup IMPL_LOOKUP = new Lookup(Object.class, null, TRUSTED);
2550
2551 /** Version of lookup which is trusted minimally.
2552 * It can only be used to create method handles to publicly accessible
2553 * members in packages that are exported unconditionally.
2554 */
2555 static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, null, UNCONDITIONAL);
2556
2557 private static void checkUnprivilegedlookupClass(Class<?> lookupClass) {
2558 String name = lookupClass.getName();
2559 if (name.startsWith("java.lang.invoke."))
2560 throw newIllegalArgumentException("illegal lookupClass: "+lookupClass);
2561 }
2562
2563 /**
2564 * Displays the name of the class from which lookups are to be made,
2565 * followed by "/" and the name of the {@linkplain #previousLookupClass()
2566 * previous lookup class} if present.
2567 * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)
2568 * If there are restrictions on the access permitted to this lookup,
2569 * this is indicated by adding a suffix to the class name, consisting
2570 * of a slash and a keyword. The keyword represents the strongest
2571 * allowed access, and is chosen as follows:
2572 * <ul>
2573 * <li>If no access is allowed, the suffix is "/noaccess".
2574 * <li>If only unconditional access is allowed, the suffix is "/publicLookup".
2575 * <li>If only public access to types in exported packages is allowed, the suffix is "/public".
2576 * <li>If only public and module access are allowed, the suffix is "/module".
2577 * <li>If public and package access are allowed, the suffix is "/package".
2578 * <li>If public, package, and private access are allowed, the suffix is "/private".
2579 * </ul>
2580 * If none of the above cases apply, it is the case that
2581 * {@linkplain #hasFullPrivilegeAccess() full privilege access}
2582 * (public, module, package, private, and protected) is allowed.
2583 * In this case, no suffix is added.
2584 * This is true only of an object obtained originally from
2585 * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
2586 * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
2587 * always have restricted access, and will display a suffix.
2588 * <p>
2589 * (It may seem strange that protected access should be
2590 * stronger than private access. Viewed independently from
2591 * package access, protected access is the first to be lost,
2592 * because it requires a direct subclass relationship between
2593 * caller and callee.)
2594 * @see #in
2595 */
2596 @Override
2597 public String toString() {
2598 String cname = lookupClass.getName();
2599 if (prevLookupClass != null)
2600 cname += "/" + prevLookupClass.getName();
2601 switch (allowedModes) {
2602 case 0: // no privileges
2603 return cname + "/noaccess";
2604 case UNCONDITIONAL:
2605 return cname + "/publicLookup";
2606 case PUBLIC:
2607 return cname + "/public";
2608 case PUBLIC|MODULE:
2609 return cname + "/module";
2610 case PUBLIC|PACKAGE:
2611 case PUBLIC|MODULE|PACKAGE:
2612 return cname + "/package";
2613 case PUBLIC|PACKAGE|PRIVATE:
2614 case PUBLIC|MODULE|PACKAGE|PRIVATE:
2615 return cname + "/private";
2616 case PUBLIC|PACKAGE|PRIVATE|PROTECTED:
2617 case PUBLIC|MODULE|PACKAGE|PRIVATE|PROTECTED:
2618 case FULL_POWER_MODES:
2619 return cname;
2620 case TRUSTED:
2621 return "/trusted"; // internal only; not exported
2622 default: // Should not happen, but it's a bitfield...
2623 cname = cname + "/" + Integer.toHexString(allowedModes);
2624 assert(false) : cname;
2625 return cname;
2626 }
2627 }
2628
2629 /**
2630 * Produces a method handle for a static method.
2631 * The type of the method handle will be that of the method.
2632 * (Since static methods do not take receivers, there is no
2633 * additional receiver argument inserted into the method handle type,
2634 * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)
2635 * The method and all its argument types must be accessible to the lookup object.
2636 * <p>
2637 * The returned method handle will have
2638 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2639 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2640 * <p>
2641 * If the returned method handle is invoked, the method's class will
2642 * be initialized, if it has not already been initialized.
2643 * <p><b>Example:</b>
2644 * {@snippet lang="java" :
2645 import static java.lang.invoke.MethodHandles.*;
2646 import static java.lang.invoke.MethodType.*;
2647 ...
2648 MethodHandle MH_asList = publicLookup().findStatic(Arrays.class,
2649 "asList", methodType(List.class, Object[].class));
2650 assertEquals("[x, y]", MH_asList.invoke("x", "y").toString());
2651 * }
2652 * @param refc the class from which the method is accessed
2653 * @param name the name of the method
2654 * @param type the type of the method
2655 * @return the desired method handle
2656 * @throws NoSuchMethodException if the method does not exist
2657 * @throws IllegalAccessException if access checking fails,
2658 * or if the method is not {@code static},
2659 * or if the method's variable arity modifier bit
2660 * is set and {@code asVarargsCollector} fails
2661 * @throws SecurityException if a security manager is present and it
2662 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2663 * @throws NullPointerException if any argument is null
2664 */
2665 public MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2666 MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type);
2667 return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerLookup(method));
2668 }
2669
2670 /**
2671 * Produces a method handle for a virtual method.
2672 * The type of the method handle will be that of the method,
2673 * with the receiver type (usually {@code refc}) prepended.
2674 * The method and all its argument types must be accessible to the lookup object.
2675 * <p>
2676 * When called, the handle will treat the first argument as a receiver
2677 * and, for non-private methods, dispatch on the receiver's type to determine which method
2678 * implementation to enter.
2679 * For private methods the named method in {@code refc} will be invoked on the receiver.
2680 * (The dispatching action is identical with that performed by an
2681 * {@code invokevirtual} or {@code invokeinterface} instruction.)
2682 * <p>
2683 * The first argument will be of type {@code refc} if the lookup
2684 * class has full privileges to access the member. Otherwise
2685 * the member must be {@code protected} and the first argument
2686 * will be restricted in type to the lookup class.
2687 * <p>
2688 * The returned method handle will have
2689 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2690 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2691 * <p>
2692 * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual}
2693 * instructions and method handles produced by {@code findVirtual},
2694 * if the class is {@code MethodHandle} and the name string is
2695 * {@code invokeExact} or {@code invoke}, the resulting
2696 * method handle is equivalent to one produced by
2697 * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or
2698 * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}
2699 * with the same {@code type} argument.
2700 * <p>
2701 * If the class is {@code VarHandle} and the name string corresponds to
2702 * the name of a signature-polymorphic access mode method, the resulting
2703 * method handle is equivalent to one produced by
2704 * {@link java.lang.invoke.MethodHandles#varHandleInvoker} with
2705 * the access mode corresponding to the name string and with the same
2706 * {@code type} arguments.
2707 * <p>
2708 * <b>Example:</b>
2709 * {@snippet lang="java" :
2710 import static java.lang.invoke.MethodHandles.*;
2711 import static java.lang.invoke.MethodType.*;
2712 ...
2713 MethodHandle MH_concat = publicLookup().findVirtual(String.class,
2714 "concat", methodType(String.class, String.class));
2715 MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class,
2716 "hashCode", methodType(int.class));
2717 MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class,
2718 "hashCode", methodType(int.class));
2719 assertEquals("xy", (String) MH_concat.invokeExact("x", "y"));
2720 assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy"));
2721 assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy"));
2722 // interface method:
2723 MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class,
2724 "subSequence", methodType(CharSequence.class, int.class, int.class));
2725 assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString());
2726 // constructor "internal method" must be accessed differently:
2727 MethodType MT_newString = methodType(void.class); //()V for new String()
2728 try { assertEquals("impossible", lookup()
2729 .findVirtual(String.class, "<init>", MT_newString));
2730 } catch (NoSuchMethodException ex) { } // OK
2731 MethodHandle MH_newString = publicLookup()
2732 .findConstructor(String.class, MT_newString);
2733 assertEquals("", (String) MH_newString.invokeExact());
2734 * }
2735 *
2736 * @param refc the class or interface from which the method is accessed
2737 * @param name the name of the method
2738 * @param type the type of the method, with the receiver argument omitted
2739 * @return the desired method handle
2740 * @throws NoSuchMethodException if the method does not exist
2741 * @throws IllegalAccessException if access checking fails,
2742 * or if the method is {@code static},
2743 * or if the method's variable arity modifier bit
2744 * is set and {@code asVarargsCollector} fails
2745 * @throws SecurityException if a security manager is present and it
2746 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2747 * @throws NullPointerException if any argument is null
2748 */
2749 public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2750 if (refc == MethodHandle.class) {
2751 MethodHandle mh = findVirtualForMH(name, type);
2752 if (mh != null) return mh;
2753 } else if (refc == VarHandle.class) {
2754 MethodHandle mh = findVirtualForVH(name, type);
2755 if (mh != null) return mh;
2756 }
2757 byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual);
2758 MemberName method = resolveOrFail(refKind, refc, name, type);
2759 return getDirectMethod(refKind, refc, method, findBoundCallerLookup(method));
2760 }
2761 private MethodHandle findVirtualForMH(String name, MethodType type) {
2762 // these names require special lookups because of the implicit MethodType argument
2763 if ("invoke".equals(name))
2764 return invoker(type);
2765 if ("invokeExact".equals(name))
2766 return exactInvoker(type);
2767 assert(!MemberName.isMethodHandleInvokeName(name));
2768 return null;
2769 }
2770 private MethodHandle findVirtualForVH(String name, MethodType type) {
2771 try {
2772 return varHandleInvoker(VarHandle.AccessMode.valueFromMethodName(name), type);
2773 } catch (IllegalArgumentException e) {
2774 return null;
2775 }
2776 }
2777
2778 /**
2779 * Produces a method handle which creates an object and initializes it, using
2780 * the constructor of the specified type.
2781 * The parameter types of the method handle will be those of the constructor,
2782 * while the return type will be a reference to the constructor's class.
2783 * The constructor and all its argument types must be accessible to the lookup object.
2784 * <p>
2785 * The requested type must have a return type of {@code void}.
2786 * (This is consistent with the JVM's treatment of constructor type descriptors.)
2787 * <p>
2788 * The returned method handle will have
2789 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2790 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
2791 * <p>
2792 * If the returned method handle is invoked, the constructor's class will
2793 * be initialized, if it has not already been initialized.
2794 * <p><b>Example:</b>
2795 * {@snippet lang="java" :
2796 import static java.lang.invoke.MethodHandles.*;
2797 import static java.lang.invoke.MethodType.*;
2798 ...
2799 MethodHandle MH_newArrayList = publicLookup().findConstructor(
2800 ArrayList.class, methodType(void.class, Collection.class));
2801 Collection orig = Arrays.asList("x", "y");
2802 Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig);
2803 assert(orig != copy);
2804 assertEquals(orig, copy);
2805 // a variable-arity constructor:
2806 MethodHandle MH_newProcessBuilder = publicLookup().findConstructor(
2807 ProcessBuilder.class, methodType(void.class, String[].class));
2808 ProcessBuilder pb = (ProcessBuilder)
2809 MH_newProcessBuilder.invoke("x", "y", "z");
2810 assertEquals("[x, y, z]", pb.command().toString());
2811 * }
2812 * @param refc the class or interface from which the method is accessed
2813 * @param type the type of the method, with the receiver argument omitted, and a void return type
2814 * @return the desired method handle
2815 * @throws NoSuchMethodException if the constructor does not exist
2816 * @throws IllegalAccessException if access checking fails
2817 * or if the method's variable arity modifier bit
2818 * is set and {@code asVarargsCollector} fails
2819 * @throws SecurityException if a security manager is present and it
2820 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2821 * @throws NullPointerException if any argument is null
2822 */
2823 public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2824 if (refc.isArray()) {
2825 throw new NoSuchMethodException("no constructor for array class: " + refc.getName());
2826 }
2827 String name = ConstantDescs.INIT_NAME;
2828 MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type);
2829 return getDirectConstructor(refc, ctor);
2830 }
2831
2832 /**
2833 * Looks up a class by name from the lookup context defined by this {@code Lookup} object,
2834 * <a href="MethodHandles.Lookup.html#equiv">as if resolved</a> by an {@code ldc} instruction.
2835 * Such a resolution, as specified in JVMS {@jvms 5.4.3.1}, attempts to locate and load the class,
2836 * and then determines whether the class is accessible to this lookup object.
2837 * <p>
2838 * For a class or an interface, the name is the {@linkplain ClassLoader##binary-name binary name}.
2839 * For an array class of {@code n} dimensions, the name begins with {@code n} occurrences
2840 * of {@code '['} and followed by the element type as encoded in the
2841 * {@linkplain Class##nameFormat table} specified in {@link Class#getName}.
2842 * <p>
2843 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class},
2844 * its class loader, and the {@linkplain #lookupModes() lookup modes}.
2845 *
2846 * @param targetName the {@linkplain ClassLoader##binary-name binary name} of the class
2847 * or the string representing an array class
2848 * @return the requested class.
2849 * @throws SecurityException if a security manager is present and it
2850 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2851 * @throws LinkageError if the linkage fails
2852 * @throws ClassNotFoundException if the class cannot be loaded by the lookup class' loader.
2853 * @throws IllegalAccessException if the class is not accessible, using the allowed access
2854 * modes.
2855 * @throws NullPointerException if {@code targetName} is null
2856 * @since 9
2857 * @jvms 5.4.3.1 Class and Interface Resolution
2858 */
2859 public Class<?> findClass(String targetName) throws ClassNotFoundException, IllegalAccessException {
2860 Class<?> targetClass = Class.forName(targetName, false, lookupClass.getClassLoader());
2861 return accessClass(targetClass);
2862 }
2863
2864 /**
2865 * Ensures that {@code targetClass} has been initialized. The class
2866 * to be initialized must be {@linkplain #accessClass accessible}
2867 * to this {@code Lookup} object. This method causes {@code targetClass}
2868 * to be initialized if it has not been already initialized,
2869 * as specified in JVMS {@jvms 5.5}.
2870 *
2871 * <p>
2872 * This method returns when {@code targetClass} is fully initialized, or
2873 * when {@code targetClass} is being initialized by the current thread.
2874 *
2875 * @param <T> the type of the class to be initialized
2876 * @param targetClass the class to be initialized
2877 * @return {@code targetClass} that has been initialized, or that is being
2878 * initialized by the current thread.
2879 *
2880 * @throws IllegalArgumentException if {@code targetClass} is a primitive type or {@code void}
2881 * or array class
2882 * @throws IllegalAccessException if {@code targetClass} is not
2883 * {@linkplain #accessClass accessible} to this lookup
2884 * @throws ExceptionInInitializerError if the class initialization provoked
2885 * by this method fails
2886 * @throws SecurityException if a security manager is present and it
2887 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2888 * @since 15
2889 * @jvms 5.5 Initialization
2890 */
2891 public <T> Class<T> ensureInitialized(Class<T> targetClass) throws IllegalAccessException {
2892 if (targetClass.isPrimitive())
2893 throw new IllegalArgumentException(targetClass + " is a primitive class");
2894 if (targetClass.isArray())
2895 throw new IllegalArgumentException(targetClass + " is an array class");
2896
2897 if (!VerifyAccess.isClassAccessible(targetClass, lookupClass, prevLookupClass, allowedModes)) {
2898 throw makeAccessException(targetClass);
2899 }
2900 checkSecurityManager(targetClass);
2901
2902 // ensure class initialization
2903 Unsafe.getUnsafe().ensureClassInitialized(targetClass);
2904 return targetClass;
2905 }
2906
2907 /*
2908 * Returns IllegalAccessException due to access violation to the given targetClass.
2909 *
2910 * This method is called by {@link Lookup#accessClass} and {@link Lookup#ensureInitialized}
2911 * which verifies access to a class rather a member.
2912 */
2913 private IllegalAccessException makeAccessException(Class<?> targetClass) {
2914 String message = "access violation: "+ targetClass;
2915 if (this == MethodHandles.publicLookup()) {
2916 message += ", from public Lookup";
2917 } else {
2918 Module m = lookupClass().getModule();
2919 message += ", from " + lookupClass() + " (" + m + ")";
2920 if (prevLookupClass != null) {
2921 message += ", previous lookup " +
2922 prevLookupClass.getName() + " (" + prevLookupClass.getModule() + ")";
2923 }
2924 }
2925 return new IllegalAccessException(message);
2926 }
2927
2928 /**
2929 * Determines if a class can be accessed from the lookup context defined by
2930 * this {@code Lookup} object. The static initializer of the class is not run.
2931 * If {@code targetClass} is an array class, {@code targetClass} is accessible
2932 * if the element type of the array class is accessible. Otherwise,
2933 * {@code targetClass} is determined as accessible as follows.
2934 *
2935 * <p>
2936 * If {@code targetClass} is in the same module as the lookup class,
2937 * the lookup class is {@code LC} in module {@code M1} and
2938 * the previous lookup class is in module {@code M0} or
2939 * {@code null} if not present,
2940 * {@code targetClass} is accessible if and only if one of the following is true:
2941 * <ul>
2942 * <li>If this lookup has {@link #PRIVATE} access, {@code targetClass} is
2943 * {@code LC} or other class in the same nest of {@code LC}.</li>
2944 * <li>If this lookup has {@link #PACKAGE} access, {@code targetClass} is
2945 * in the same runtime package of {@code LC}.</li>
2946 * <li>If this lookup has {@link #MODULE} access, {@code targetClass} is
2947 * a public type in {@code M1}.</li>
2948 * <li>If this lookup has {@link #PUBLIC} access, {@code targetClass} is
2949 * a public type in a package exported by {@code M1} to at least {@code M0}
2950 * if the previous lookup class is present; otherwise, {@code targetClass}
2951 * is a public type in a package exported by {@code M1} unconditionally.</li>
2952 * </ul>
2953 *
2954 * <p>
2955 * Otherwise, if this lookup has {@link #UNCONDITIONAL} access, this lookup
2956 * can access public types in all modules when the type is in a package
2957 * that is exported unconditionally.
2958 * <p>
2959 * Otherwise, {@code targetClass} is in a different module from {@code lookupClass},
2960 * and if this lookup does not have {@code PUBLIC} access, {@code lookupClass}
2961 * is inaccessible.
2962 * <p>
2963 * Otherwise, if this lookup has no {@linkplain #previousLookupClass() previous lookup class},
2964 * {@code M1} is the module containing {@code lookupClass} and
2965 * {@code M2} is the module containing {@code targetClass},
2966 * then {@code targetClass} is accessible if and only if
2967 * <ul>
2968 * <li>{@code M1} reads {@code M2}, and
2969 * <li>{@code targetClass} is public and in a package exported by
2970 * {@code M2} at least to {@code M1}.
2971 * </ul>
2972 * <p>
2973 * Otherwise, if this lookup has a {@linkplain #previousLookupClass() previous lookup class},
2974 * {@code M1} and {@code M2} are as before, and {@code M0} is the module
2975 * containing the previous lookup class, then {@code targetClass} is accessible
2976 * if and only if one of the following is true:
2977 * <ul>
2978 * <li>{@code targetClass} is in {@code M0} and {@code M1}
2979 * {@linkplain Module#reads reads} {@code M0} and the type is
2980 * in a package that is exported to at least {@code M1}.
2981 * <li>{@code targetClass} is in {@code M1} and {@code M0}
2982 * {@linkplain Module#reads reads} {@code M1} and the type is
2983 * in a package that is exported to at least {@code M0}.
2984 * <li>{@code targetClass} is in a third module {@code M2} and both {@code M0}
2985 * and {@code M1} reads {@code M2} and the type is in a package
2986 * that is exported to at least both {@code M0} and {@code M2}.
2987 * </ul>
2988 * <p>
2989 * Otherwise, {@code targetClass} is not accessible.
2990 *
2991 * @param <T> the type of the class to be access-checked
2992 * @param targetClass the class to be access-checked
2993 * @return {@code targetClass} that has been access-checked
2994 * @throws IllegalAccessException if the class is not accessible from the lookup class
2995 * and previous lookup class, if present, using the allowed access modes.
2996 * @throws SecurityException if a security manager is present and it
2997 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2998 * @throws NullPointerException if {@code targetClass} is {@code null}
2999 * @since 9
3000 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
3001 */
3002 public <T> Class<T> accessClass(Class<T> targetClass) throws IllegalAccessException {
3003 if (!isClassAccessible(targetClass)) {
3004 throw makeAccessException(targetClass);
3005 }
3006 checkSecurityManager(targetClass);
3007 return targetClass;
3008 }
3009
3010 /**
3011 * Produces an early-bound method handle for a virtual method.
3012 * It will bypass checks for overriding methods on the receiver,
3013 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
3014 * instruction from within the explicitly specified {@code specialCaller}.
3015 * The type of the method handle will be that of the method,
3016 * with a suitably restricted receiver type prepended.
3017 * (The receiver type will be {@code specialCaller} or a subtype.)
3018 * The method and all its argument types must be accessible
3019 * to the lookup object.
3020 * <p>
3021 * Before method resolution,
3022 * if the explicitly specified caller class is not identical with the
3023 * lookup class, or if this lookup object does not have
3024 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
3025 * privileges, the access fails.
3026 * <p>
3027 * The returned method handle will have
3028 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3029 * the method's variable arity modifier bit ({@code 0x0080}) is set.
3030 * <p style="font-size:smaller;">
3031 * <em>(Note: JVM internal methods named {@value ConstantDescs#INIT_NAME}
3032 * are not visible to this API,
3033 * even though the {@code invokespecial} instruction can refer to them
3034 * in special circumstances. Use {@link #findConstructor findConstructor}
3035 * to access instance initialization methods in a safe manner.)</em>
3036 * <p><b>Example:</b>
3037 * {@snippet lang="java" :
3038 import static java.lang.invoke.MethodHandles.*;
3039 import static java.lang.invoke.MethodType.*;
3040 ...
3041 static class Listie extends ArrayList {
3042 public String toString() { return "[wee Listie]"; }
3043 static Lookup lookup() { return MethodHandles.lookup(); }
3044 }
3045 ...
3046 // no access to constructor via invokeSpecial:
3047 MethodHandle MH_newListie = Listie.lookup()
3048 .findConstructor(Listie.class, methodType(void.class));
3049 Listie l = (Listie) MH_newListie.invokeExact();
3050 try { assertEquals("impossible", Listie.lookup().findSpecial(
3051 Listie.class, "<init>", methodType(void.class), Listie.class));
3052 } catch (NoSuchMethodException ex) { } // OK
3053 // access to super and self methods via invokeSpecial:
3054 MethodHandle MH_super = Listie.lookup().findSpecial(
3055 ArrayList.class, "toString" , methodType(String.class), Listie.class);
3056 MethodHandle MH_this = Listie.lookup().findSpecial(
3057 Listie.class, "toString" , methodType(String.class), Listie.class);
3058 MethodHandle MH_duper = Listie.lookup().findSpecial(
3059 Object.class, "toString" , methodType(String.class), Listie.class);
3060 assertEquals("[]", (String) MH_super.invokeExact(l));
3061 assertEquals(""+l, (String) MH_this.invokeExact(l));
3062 assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method
3063 try { assertEquals("inaccessible", Listie.lookup().findSpecial(
3064 String.class, "toString", methodType(String.class), Listie.class));
3065 } catch (IllegalAccessException ex) { } // OK
3066 Listie subl = new Listie() { public String toString() { return "[subclass]"; } };
3067 assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method
3068 * }
3069 *
3070 * @param refc the class or interface from which the method is accessed
3071 * @param name the name of the method (which must not be "<init>")
3072 * @param type the type of the method, with the receiver argument omitted
3073 * @param specialCaller the proposed calling class to perform the {@code invokespecial}
3074 * @return the desired method handle
3075 * @throws NoSuchMethodException if the method does not exist
3076 * @throws IllegalAccessException if access checking fails,
3077 * or if the method is {@code static},
3078 * or if the method's variable arity modifier bit
3079 * is set and {@code asVarargsCollector} fails
3080 * @throws SecurityException if a security manager is present and it
3081 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3082 * @throws NullPointerException if any argument is null
3083 */
3084 public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,
3085 Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
3086 checkSpecialCaller(specialCaller, refc);
3087 Lookup specialLookup = this.in(specialCaller);
3088 MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type);
3089 return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerLookup(method));
3090 }
3091
3092 /**
3093 * Produces a method handle giving read access to a non-static field.
3094 * The type of the method handle will have a return type of the field's
3095 * value type.
3096 * The method handle's single argument will be the instance containing
3097 * the field.
3098 * Access checking is performed immediately on behalf of the lookup class.
3099 * @param refc the class or interface from which the method is accessed
3100 * @param name the field's name
3101 * @param type the field's type
3102 * @return a method handle which can load values from the field
3103 * @throws NoSuchFieldException if the field does not exist
3104 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
3105 * @throws SecurityException if a security manager is present and it
3106 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3107 * @throws NullPointerException if any argument is null
3108 * @see #findVarHandle(Class, String, Class)
3109 */
3110 public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3111 MemberName field = resolveOrFail(REF_getField, refc, name, type);
3112 return getDirectField(REF_getField, refc, field);
3113 }
3114
3115 /**
3116 * Produces a method handle giving write access to a non-static field.
3117 * The type of the method handle will have a void return type.
3118 * The method handle will take two arguments, the instance containing
3119 * the field, and the value to be stored.
3120 * The second argument will be of the field's value type.
3121 * Access checking is performed immediately on behalf of the lookup class.
3122 * @param refc the class or interface from which the method is accessed
3123 * @param name the field's name
3124 * @param type the field's type
3125 * @return a method handle which can store values into the field
3126 * @throws NoSuchFieldException if the field does not exist
3127 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
3128 * or {@code final}
3129 * @throws SecurityException if a security manager is present and it
3130 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3131 * @throws NullPointerException if any argument is null
3132 * @see #findVarHandle(Class, String, Class)
3133 */
3134 public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3135 MemberName field = resolveOrFail(REF_putField, refc, name, type);
3136 return getDirectField(REF_putField, refc, field);
3137 }
3138
3139 /**
3140 * Produces a VarHandle giving access to a non-static field {@code name}
3141 * of type {@code type} declared in a class of type {@code recv}.
3142 * The VarHandle's variable type is {@code type} and it has one
3143 * coordinate type, {@code recv}.
3144 * <p>
3145 * Access checking is performed immediately on behalf of the lookup
3146 * class.
3147 * <p>
3148 * Certain access modes of the returned VarHandle are unsupported under
3149 * the following conditions:
3150 * <ul>
3151 * <li>if the field is declared {@code final}, then the write, atomic
3152 * update, numeric atomic update, and bitwise atomic update access
3153 * modes are unsupported.
3154 * <li>if the field type is anything other than {@code byte},
3155 * {@code short}, {@code char}, {@code int}, {@code long},
3156 * {@code float}, or {@code double} then numeric atomic update
3157 * access modes are unsupported.
3158 * <li>if the field type is anything other than {@code boolean},
3159 * {@code byte}, {@code short}, {@code char}, {@code int} or
3160 * {@code long} then bitwise atomic update access modes are
3161 * unsupported.
3162 * </ul>
3163 * <p>
3164 * If the field is declared {@code volatile} then the returned VarHandle
3165 * will override access to the field (effectively ignore the
3166 * {@code volatile} declaration) in accordance to its specified
3167 * access modes.
3168 * <p>
3169 * If the field type is {@code float} or {@code double} then numeric
3170 * and atomic update access modes compare values using their bitwise
3171 * representation (see {@link Float#floatToRawIntBits} and
3172 * {@link Double#doubleToRawLongBits}, respectively).
3173 * @apiNote
3174 * Bitwise comparison of {@code float} values or {@code double} values,
3175 * as performed by the numeric and atomic update access modes, differ
3176 * from the primitive {@code ==} operator and the {@link Float#equals}
3177 * and {@link Double#equals} methods, specifically with respect to
3178 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
3179 * Care should be taken when performing a compare and set or a compare
3180 * and exchange operation with such values since the operation may
3181 * unexpectedly fail.
3182 * There are many possible NaN values that are considered to be
3183 * {@code NaN} in Java, although no IEEE 754 floating-point operation
3184 * provided by Java can distinguish between them. Operation failure can
3185 * occur if the expected or witness value is a NaN value and it is
3186 * transformed (perhaps in a platform specific manner) into another NaN
3187 * value, and thus has a different bitwise representation (see
3188 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
3189 * details).
3190 * The values {@code -0.0} and {@code +0.0} have different bitwise
3191 * representations but are considered equal when using the primitive
3192 * {@code ==} operator. Operation failure can occur if, for example, a
3193 * numeric algorithm computes an expected value to be say {@code -0.0}
3194 * and previously computed the witness value to be say {@code +0.0}.
3195 * @param recv the receiver class, of type {@code R}, that declares the
3196 * non-static field
3197 * @param name the field's name
3198 * @param type the field's type, of type {@code T}
3199 * @return a VarHandle giving access to non-static fields.
3200 * @throws NoSuchFieldException if the field does not exist
3201 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
3202 * @throws SecurityException if a security manager is present and it
3203 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3204 * @throws NullPointerException if any argument is null
3205 * @since 9
3206 */
3207 public VarHandle findVarHandle(Class<?> recv, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3208 MemberName getField = resolveOrFail(REF_getField, recv, name, type);
3209 MemberName putField = resolveOrFail(REF_putField, recv, name, type);
3210 return getFieldVarHandle(REF_getField, REF_putField, recv, getField, putField);
3211 }
3212
3213 /**
3214 * Produces a method handle giving read access to a static field.
3215 * The type of the method handle will have a return type of the field's
3216 * value type.
3217 * The method handle will take no arguments.
3218 * Access checking is performed immediately on behalf of the lookup class.
3219 * <p>
3220 * If the returned method handle is invoked, the field's class will
3221 * be initialized, if it has not already been initialized.
3222 * @param refc the class or interface from which the method is accessed
3223 * @param name the field's name
3224 * @param type the field's type
3225 * @return a method handle which can load values from the field
3226 * @throws NoSuchFieldException if the field does not exist
3227 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
3228 * @throws SecurityException if a security manager is present and it
3229 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3230 * @throws NullPointerException if any argument is null
3231 */
3232 public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3233 MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
3234 return getDirectField(REF_getStatic, refc, field);
3235 }
3236
3237 /**
3238 * Produces a method handle giving write access to a static field.
3239 * The type of the method handle will have a void return type.
3240 * The method handle will take a single
3241 * argument, of the field's value type, the value to be stored.
3242 * Access checking is performed immediately on behalf of the lookup class.
3243 * <p>
3244 * If the returned method handle is invoked, the field's class will
3245 * be initialized, if it has not already been initialized.
3246 * @param refc the class or interface from which the method is accessed
3247 * @param name the field's name
3248 * @param type the field's type
3249 * @return a method handle which can store values into the field
3250 * @throws NoSuchFieldException if the field does not exist
3251 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
3252 * or is {@code final}
3253 * @throws SecurityException if a security manager is present and it
3254 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3255 * @throws NullPointerException if any argument is null
3256 */
3257 public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3258 MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
3259 return getDirectField(REF_putStatic, refc, field);
3260 }
3261
3262 /**
3263 * Produces a VarHandle giving access to a static field {@code name} of
3264 * type {@code type} declared in a class of type {@code decl}.
3265 * The VarHandle's variable type is {@code type} and it has no
3266 * coordinate types.
3267 * <p>
3268 * Access checking is performed immediately on behalf of the lookup
3269 * class.
3270 * <p>
3271 * If the returned VarHandle is operated on, the declaring class will be
3272 * initialized, if it has not already been initialized.
3273 * <p>
3274 * Certain access modes of the returned VarHandle are unsupported under
3275 * the following conditions:
3276 * <ul>
3277 * <li>if the field is declared {@code final}, then the write, atomic
3278 * update, numeric atomic update, and bitwise atomic update access
3279 * modes are unsupported.
3280 * <li>if the field type is anything other than {@code byte},
3281 * {@code short}, {@code char}, {@code int}, {@code long},
3282 * {@code float}, or {@code double}, then numeric atomic update
3283 * access modes are unsupported.
3284 * <li>if the field type is anything other than {@code boolean},
3285 * {@code byte}, {@code short}, {@code char}, {@code int} or
3286 * {@code long} then bitwise atomic update access modes are
3287 * unsupported.
3288 * </ul>
3289 * <p>
3290 * If the field is declared {@code volatile} then the returned VarHandle
3291 * will override access to the field (effectively ignore the
3292 * {@code volatile} declaration) in accordance to its specified
3293 * access modes.
3294 * <p>
3295 * If the field type is {@code float} or {@code double} then numeric
3296 * and atomic update access modes compare values using their bitwise
3297 * representation (see {@link Float#floatToRawIntBits} and
3298 * {@link Double#doubleToRawLongBits}, respectively).
3299 * @apiNote
3300 * Bitwise comparison of {@code float} values or {@code double} values,
3301 * as performed by the numeric and atomic update access modes, differ
3302 * from the primitive {@code ==} operator and the {@link Float#equals}
3303 * and {@link Double#equals} methods, specifically with respect to
3304 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
3305 * Care should be taken when performing a compare and set or a compare
3306 * and exchange operation with such values since the operation may
3307 * unexpectedly fail.
3308 * There are many possible NaN values that are considered to be
3309 * {@code NaN} in Java, although no IEEE 754 floating-point operation
3310 * provided by Java can distinguish between them. Operation failure can
3311 * occur if the expected or witness value is a NaN value and it is
3312 * transformed (perhaps in a platform specific manner) into another NaN
3313 * value, and thus has a different bitwise representation (see
3314 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
3315 * details).
3316 * The values {@code -0.0} and {@code +0.0} have different bitwise
3317 * representations but are considered equal when using the primitive
3318 * {@code ==} operator. Operation failure can occur if, for example, a
3319 * numeric algorithm computes an expected value to be say {@code -0.0}
3320 * and previously computed the witness value to be say {@code +0.0}.
3321 * @param decl the class that declares the static field
3322 * @param name the field's name
3323 * @param type the field's type, of type {@code T}
3324 * @return a VarHandle giving access to a static field
3325 * @throws NoSuchFieldException if the field does not exist
3326 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
3327 * @throws SecurityException if a security manager is present and it
3328 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3329 * @throws NullPointerException if any argument is null
3330 * @since 9
3331 */
3332 public VarHandle findStaticVarHandle(Class<?> decl, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3333 MemberName getField = resolveOrFail(REF_getStatic, decl, name, type);
3334 MemberName putField = resolveOrFail(REF_putStatic, decl, name, type);
3335 return getFieldVarHandle(REF_getStatic, REF_putStatic, decl, getField, putField);
3336 }
3337
3338 /**
3339 * Produces an early-bound method handle for a non-static method.
3340 * The receiver must have a supertype {@code defc} in which a method
3341 * of the given name and type is accessible to the lookup class.
3342 * The method and all its argument types must be accessible to the lookup object.
3343 * The type of the method handle will be that of the method,
3344 * without any insertion of an additional receiver parameter.
3345 * The given receiver will be bound into the method handle,
3346 * so that every call to the method handle will invoke the
3347 * requested method on the given receiver.
3348 * <p>
3349 * The returned method handle will have
3350 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3351 * the method's variable arity modifier bit ({@code 0x0080}) is set
3352 * <em>and</em> the trailing array argument is not the only argument.
3353 * (If the trailing array argument is the only argument,
3354 * the given receiver value will be bound to it.)
3355 * <p>
3356 * This is almost equivalent to the following code, with some differences noted below:
3357 * {@snippet lang="java" :
3358 import static java.lang.invoke.MethodHandles.*;
3359 import static java.lang.invoke.MethodType.*;
3360 ...
3361 MethodHandle mh0 = lookup().findVirtual(defc, name, type);
3362 MethodHandle mh1 = mh0.bindTo(receiver);
3363 mh1 = mh1.withVarargs(mh0.isVarargsCollector());
3364 return mh1;
3365 * }
3366 * where {@code defc} is either {@code receiver.getClass()} or a super
3367 * type of that class, in which the requested method is accessible
3368 * to the lookup class.
3369 * (Unlike {@code bind}, {@code bindTo} does not preserve variable arity.
3370 * Also, {@code bindTo} may throw a {@code ClassCastException} in instances where {@code bind} would
3371 * throw an {@code IllegalAccessException}, as in the case where the member is {@code protected} and
3372 * the receiver is restricted by {@code findVirtual} to the lookup class.)
3373 * @param receiver the object from which the method is accessed
3374 * @param name the name of the method
3375 * @param type the type of the method, with the receiver argument omitted
3376 * @return the desired method handle
3377 * @throws NoSuchMethodException if the method does not exist
3378 * @throws IllegalAccessException if access checking fails
3379 * or if the method's variable arity modifier bit
3380 * is set and {@code asVarargsCollector} fails
3381 * @throws SecurityException if a security manager is present and it
3382 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3383 * @throws NullPointerException if any argument is null
3384 * @see MethodHandle#bindTo
3385 * @see #findVirtual
3386 */
3387 public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
3388 Class<? extends Object> refc = receiver.getClass(); // may get NPE
3389 MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
3390 MethodHandle mh = getDirectMethodNoRestrictInvokeSpecial(refc, method, findBoundCallerLookup(method));
3391 if (!mh.type().leadingReferenceParameter().isAssignableFrom(receiver.getClass())) {
3392 throw new IllegalAccessException("The restricted defining class " +
3393 mh.type().leadingReferenceParameter().getName() +
3394 " is not assignable from receiver class " +
3395 receiver.getClass().getName());
3396 }
3397 return mh.bindArgumentL(0, receiver).setVarargs(method);
3398 }
3399
3400 /**
3401 * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
3402 * to <i>m</i>, if the lookup class has permission.
3403 * If <i>m</i> is non-static, the receiver argument is treated as an initial argument.
3404 * If <i>m</i> is virtual, overriding is respected on every call.
3405 * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped.
3406 * The type of the method handle will be that of the method,
3407 * with the receiver type prepended (but only if it is non-static).
3408 * If the method's {@code accessible} flag is not set,
3409 * access checking is performed immediately on behalf of the lookup class.
3410 * If <i>m</i> is not public, do not share the resulting handle with untrusted parties.
3411 * <p>
3412 * The returned method handle will have
3413 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3414 * the method's variable arity modifier bit ({@code 0x0080}) is set.
3415 * <p>
3416 * If <i>m</i> is static, and
3417 * if the returned method handle is invoked, the method's class will
3418 * be initialized, if it has not already been initialized.
3419 * @param m the reflected method
3420 * @return a method handle which can invoke the reflected method
3421 * @throws IllegalAccessException if access checking fails
3422 * or if the method's variable arity modifier bit
3423 * is set and {@code asVarargsCollector} fails
3424 * @throws NullPointerException if the argument is null
3425 */
3426 public MethodHandle unreflect(Method m) throws IllegalAccessException {
3427 if (m.getDeclaringClass() == MethodHandle.class) {
3428 MethodHandle mh = unreflectForMH(m);
3429 if (mh != null) return mh;
3430 }
3431 if (m.getDeclaringClass() == VarHandle.class) {
3432 MethodHandle mh = unreflectForVH(m);
3433 if (mh != null) return mh;
3434 }
3435 MemberName method = new MemberName(m);
3436 byte refKind = method.getReferenceKind();
3437 if (refKind == REF_invokeSpecial)
3438 refKind = REF_invokeVirtual;
3439 assert(method.isMethod());
3440 @SuppressWarnings("deprecation")
3441 Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
3442 return lookup.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method, findBoundCallerLookup(method));
3443 }
3444 private MethodHandle unreflectForMH(Method m) {
3445 // these names require special lookups because they throw UnsupportedOperationException
3446 if (MemberName.isMethodHandleInvokeName(m.getName()))
3447 return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m));
3448 return null;
3449 }
3450 private MethodHandle unreflectForVH(Method m) {
3451 // these names require special lookups because they throw UnsupportedOperationException
3452 if (MemberName.isVarHandleMethodInvokeName(m.getName()))
3453 return MethodHandleImpl.fakeVarHandleInvoke(new MemberName(m));
3454 return null;
3455 }
3456
3457 /**
3458 * Produces a method handle for a reflected method.
3459 * It will bypass checks for overriding methods on the receiver,
3460 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
3461 * instruction from within the explicitly specified {@code specialCaller}.
3462 * The type of the method handle will be that of the method,
3463 * with a suitably restricted receiver type prepended.
3464 * (The receiver type will be {@code specialCaller} or a subtype.)
3465 * If the method's {@code accessible} flag is not set,
3466 * access checking is performed immediately on behalf of the lookup class,
3467 * as if {@code invokespecial} instruction were being linked.
3468 * <p>
3469 * Before method resolution,
3470 * if the explicitly specified caller class is not identical with the
3471 * lookup class, or if this lookup object does not have
3472 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
3473 * privileges, the access fails.
3474 * <p>
3475 * The returned method handle will have
3476 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3477 * the method's variable arity modifier bit ({@code 0x0080}) is set.
3478 * @param m the reflected method
3479 * @param specialCaller the class nominally calling the method
3480 * @return a method handle which can invoke the reflected method
3481 * @throws IllegalAccessException if access checking fails,
3482 * or if the method is {@code static},
3483 * or if the method's variable arity modifier bit
3484 * is set and {@code asVarargsCollector} fails
3485 * @throws NullPointerException if any argument is null
3486 */
3487 public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException {
3488 checkSpecialCaller(specialCaller, m.getDeclaringClass());
3489 Lookup specialLookup = this.in(specialCaller);
3490 MemberName method = new MemberName(m, true);
3491 assert(method.isMethod());
3492 // ignore m.isAccessible: this is a new kind of access
3493 return specialLookup.getDirectMethodNoSecurityManager(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerLookup(method));
3494 }
3495
3496 /**
3497 * Produces a method handle for a reflected constructor.
3498 * The type of the method handle will be that of the constructor,
3499 * with the return type changed to the declaring class.
3500 * The method handle will perform a {@code newInstance} operation,
3501 * creating a new instance of the constructor's class on the
3502 * arguments passed to the method handle.
3503 * <p>
3504 * If the constructor's {@code accessible} flag is not set,
3505 * access checking is performed immediately on behalf of the lookup class.
3506 * <p>
3507 * The returned method handle will have
3508 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3509 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
3510 * <p>
3511 * If the returned method handle is invoked, the constructor's class will
3512 * be initialized, if it has not already been initialized.
3513 * @param c the reflected constructor
3514 * @return a method handle which can invoke the reflected constructor
3515 * @throws IllegalAccessException if access checking fails
3516 * or if the method's variable arity modifier bit
3517 * is set and {@code asVarargsCollector} fails
3518 * @throws NullPointerException if the argument is null
3519 */
3520 public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException {
3521 MemberName ctor = new MemberName(c);
3522 assert(ctor.isConstructor());
3523 @SuppressWarnings("deprecation")
3524 Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
3525 return lookup.getDirectConstructorNoSecurityManager(ctor.getDeclaringClass(), ctor);
3526 }
3527
3528 /*
3529 * Produces a method handle that is capable of creating instances of the given class
3530 * and instantiated by the given constructor. No security manager check.
3531 *
3532 * This method should only be used by ReflectionFactory::newConstructorForSerialization.
3533 */
3534 /* package-private */ MethodHandle serializableConstructor(Class<?> decl, Constructor<?> c) throws IllegalAccessException {
3535 MemberName ctor = new MemberName(c);
3536 assert(ctor.isConstructor() && constructorInSuperclass(decl, c));
3537 checkAccess(REF_newInvokeSpecial, decl, ctor);
3538 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
3539 return DirectMethodHandle.makeAllocator(decl, ctor).setVarargs(ctor);
3540 }
3541
3542 private static boolean constructorInSuperclass(Class<?> decl, Constructor<?> ctor) {
3543 if (decl == ctor.getDeclaringClass())
3544 return true;
3545
3546 Class<?> cl = decl;
3547 while ((cl = cl.getSuperclass()) != null) {
3548 if (cl == ctor.getDeclaringClass()) {
3549 return true;
3550 }
3551 }
3552 return false;
3553 }
3554
3555 /**
3556 * Produces a method handle giving read access to a reflected field.
3557 * The type of the method handle will have a return type of the field's
3558 * value type.
3559 * If the field is {@code static}, the method handle will take no arguments.
3560 * Otherwise, its single argument will be the instance containing
3561 * the field.
3562 * If the {@code Field} object's {@code accessible} flag is not set,
3563 * access checking is performed immediately on behalf of the lookup class.
3564 * <p>
3565 * If the field is static, and
3566 * if the returned method handle is invoked, the field's class will
3567 * be initialized, if it has not already been initialized.
3568 * @param f the reflected field
3569 * @return a method handle which can load values from the reflected field
3570 * @throws IllegalAccessException if access checking fails
3571 * @throws NullPointerException if the argument is null
3572 */
3573 public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
3574 return unreflectField(f, false);
3575 }
3576
3577 /**
3578 * Produces a method handle giving write access to a reflected field.
3579 * The type of the method handle will have a void return type.
3580 * If the field is {@code static}, the method handle will take a single
3581 * argument, of the field's value type, the value to be stored.
3582 * Otherwise, the two arguments will be the instance containing
3583 * the field, and the value to be stored.
3584 * If the {@code Field} object's {@code accessible} flag is not set,
3585 * access checking is performed immediately on behalf of the lookup class.
3586 * <p>
3587 * If the field is {@code final}, write access will not be
3588 * allowed and access checking will fail, except under certain
3589 * narrow circumstances documented for {@link Field#set Field.set}.
3590 * A method handle is returned only if a corresponding call to
3591 * the {@code Field} object's {@code set} method could return
3592 * normally. In particular, fields which are both {@code static}
3593 * and {@code final} may never be set.
3594 * <p>
3595 * If the field is {@code static}, and
3596 * if the returned method handle is invoked, the field's class will
3597 * be initialized, if it has not already been initialized.
3598 * @param f the reflected field
3599 * @return a method handle which can store values into the reflected field
3600 * @throws IllegalAccessException if access checking fails,
3601 * or if the field is {@code final} and write access
3602 * is not enabled on the {@code Field} object
3603 * @throws NullPointerException if the argument is null
3604 */
3605 public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
3606 return unreflectField(f, true);
3607 }
3608
3609 private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
3610 MemberName field = new MemberName(f, isSetter);
3611 if (isSetter && field.isFinal()) {
3612 if (field.isTrustedFinalField()) {
3613 String msg = field.isStatic() ? "static final field has no write access"
3614 : "final field has no write access";
3615 throw field.makeAccessException(msg, this);
3616 }
3617 }
3618 assert(isSetter
3619 ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
3620 : MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
3621 @SuppressWarnings("deprecation")
3622 Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
3623 return lookup.getDirectFieldNoSecurityManager(field.getReferenceKind(), f.getDeclaringClass(), field);
3624 }
3625
3626 /**
3627 * Produces a VarHandle giving access to a reflected field {@code f}
3628 * of type {@code T} declared in a class of type {@code R}.
3629 * The VarHandle's variable type is {@code T}.
3630 * If the field is non-static the VarHandle has one coordinate type,
3631 * {@code R}. Otherwise, the field is static, and the VarHandle has no
3632 * coordinate types.
3633 * <p>
3634 * Access checking is performed immediately on behalf of the lookup
3635 * class, regardless of the value of the field's {@code accessible}
3636 * flag.
3637 * <p>
3638 * If the field is static, and if the returned VarHandle is operated
3639 * on, the field's declaring class will be initialized, if it has not
3640 * already been initialized.
3641 * <p>
3642 * Certain access modes of the returned VarHandle are unsupported under
3643 * the following conditions:
3644 * <ul>
3645 * <li>if the field is declared {@code final}, then the write, atomic
3646 * update, numeric atomic update, and bitwise atomic update access
3647 * modes are unsupported.
3648 * <li>if the field type is anything other than {@code byte},
3649 * {@code short}, {@code char}, {@code int}, {@code long},
3650 * {@code float}, or {@code double} then numeric atomic update
3651 * access modes are unsupported.
3652 * <li>if the field type is anything other than {@code boolean},
3653 * {@code byte}, {@code short}, {@code char}, {@code int} or
3654 * {@code long} then bitwise atomic update access modes are
3655 * unsupported.
3656 * </ul>
3657 * <p>
3658 * If the field is declared {@code volatile} then the returned VarHandle
3659 * will override access to the field (effectively ignore the
3660 * {@code volatile} declaration) in accordance to its specified
3661 * access modes.
3662 * <p>
3663 * If the field type is {@code float} or {@code double} then numeric
3664 * and atomic update access modes compare values using their bitwise
3665 * representation (see {@link Float#floatToRawIntBits} and
3666 * {@link Double#doubleToRawLongBits}, respectively).
3667 * @apiNote
3668 * Bitwise comparison of {@code float} values or {@code double} values,
3669 * as performed by the numeric and atomic update access modes, differ
3670 * from the primitive {@code ==} operator and the {@link Float#equals}
3671 * and {@link Double#equals} methods, specifically with respect to
3672 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
3673 * Care should be taken when performing a compare and set or a compare
3674 * and exchange operation with such values since the operation may
3675 * unexpectedly fail.
3676 * There are many possible NaN values that are considered to be
3677 * {@code NaN} in Java, although no IEEE 754 floating-point operation
3678 * provided by Java can distinguish between them. Operation failure can
3679 * occur if the expected or witness value is a NaN value and it is
3680 * transformed (perhaps in a platform specific manner) into another NaN
3681 * value, and thus has a different bitwise representation (see
3682 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
3683 * details).
3684 * The values {@code -0.0} and {@code +0.0} have different bitwise
3685 * representations but are considered equal when using the primitive
3686 * {@code ==} operator. Operation failure can occur if, for example, a
3687 * numeric algorithm computes an expected value to be say {@code -0.0}
3688 * and previously computed the witness value to be say {@code +0.0}.
3689 * @param f the reflected field, with a field of type {@code T}, and
3690 * a declaring class of type {@code R}
3691 * @return a VarHandle giving access to non-static fields or a static
3692 * field
3693 * @throws IllegalAccessException if access checking fails
3694 * @throws NullPointerException if the argument is null
3695 * @since 9
3696 */
3697 public VarHandle unreflectVarHandle(Field f) throws IllegalAccessException {
3698 MemberName getField = new MemberName(f, false);
3699 MemberName putField = new MemberName(f, true);
3700 return getFieldVarHandleNoSecurityManager(getField.getReferenceKind(), putField.getReferenceKind(),
3701 f.getDeclaringClass(), getField, putField);
3702 }
3703
3704 /**
3705 * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
3706 * created by this lookup object or a similar one.
3707 * Security and access checks are performed to ensure that this lookup object
3708 * is capable of reproducing the target method handle.
3709 * This means that the cracking may fail if target is a direct method handle
3710 * but was created by an unrelated lookup object.
3711 * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a>
3712 * and was created by a lookup object for a different class.
3713 * @param target a direct method handle to crack into symbolic reference components
3714 * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object
3715 * @throws SecurityException if a security manager is present and it
3716 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3717 * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails
3718 * @throws NullPointerException if the target is {@code null}
3719 * @see MethodHandleInfo
3720 * @since 1.8
3721 */
3722 public MethodHandleInfo revealDirect(MethodHandle target) {
3723 if (!target.isCrackable()) {
3724 throw newIllegalArgumentException("not a direct method handle");
3725 }
3726 MemberName member = target.internalMemberName();
3727 Class<?> defc = member.getDeclaringClass();
3728 byte refKind = member.getReferenceKind();
3729 assert(MethodHandleNatives.refKindIsValid(refKind));
3730 if (refKind == REF_invokeSpecial && !target.isInvokeSpecial())
3731 // Devirtualized method invocation is usually formally virtual.
3732 // To avoid creating extra MemberName objects for this common case,
3733 // we encode this extra degree of freedom using MH.isInvokeSpecial.
3734 refKind = REF_invokeVirtual;
3735 if (refKind == REF_invokeVirtual && defc.isInterface())
3736 // Symbolic reference is through interface but resolves to Object method (toString, etc.)
3737 refKind = REF_invokeInterface;
3738 // Check SM permissions and member access before cracking.
3739 try {
3740 checkAccess(refKind, defc, member);
3741 checkSecurityManager(defc, member);
3742 } catch (IllegalAccessException ex) {
3743 throw new IllegalArgumentException(ex);
3744 }
3745 if (allowedModes != TRUSTED && member.isCallerSensitive()) {
3746 Class<?> callerClass = target.internalCallerClass();
3747 if ((lookupModes() & ORIGINAL) == 0 || callerClass != lookupClass())
3748 throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass);
3749 }
3750 // Produce the handle to the results.
3751 return new InfoFromMemberName(this, member, refKind);
3752 }
3753
3754 /// Helper methods, all package-private.
3755
3756 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3757 checkSymbolicClass(refc); // do this before attempting to resolve
3758 Objects.requireNonNull(name);
3759 Objects.requireNonNull(type);
3760 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), allowedModes,
3761 NoSuchFieldException.class);
3762 }
3763
3764 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
3765 checkSymbolicClass(refc); // do this before attempting to resolve
3766 Objects.requireNonNull(type);
3767 checkMethodName(refKind, name); // implicit null-check of name
3768 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), allowedModes,
3769 NoSuchMethodException.class);
3770 }
3771
3772 MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException {
3773 checkSymbolicClass(member.getDeclaringClass()); // do this before attempting to resolve
3774 Objects.requireNonNull(member.getName());
3775 Objects.requireNonNull(member.getType());
3776 return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(), allowedModes,
3777 ReflectiveOperationException.class);
3778 }
3779
3780 MemberName resolveOrNull(byte refKind, MemberName member) {
3781 // do this before attempting to resolve
3782 if (!isClassAccessible(member.getDeclaringClass())) {
3783 return null;
3784 }
3785 Objects.requireNonNull(member.getName());
3786 Objects.requireNonNull(member.getType());
3787 return IMPL_NAMES.resolveOrNull(refKind, member, lookupClassOrNull(), allowedModes);
3788 }
3789
3790 MemberName resolveOrNull(byte refKind, Class<?> refc, String name, MethodType type) {
3791 // do this before attempting to resolve
3792 if (!isClassAccessible(refc)) {
3793 return null;
3794 }
3795 Objects.requireNonNull(type);
3796 // implicit null-check of name
3797 if (name.startsWith("<") && refKind != REF_newInvokeSpecial) {
3798 return null;
3799 }
3800 return IMPL_NAMES.resolveOrNull(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), allowedModes);
3801 }
3802
3803 void checkSymbolicClass(Class<?> refc) throws IllegalAccessException {
3804 if (!isClassAccessible(refc)) {
3805 throw new MemberName(refc).makeAccessException("symbolic reference class is not accessible", this);
3806 }
3807 }
3808
3809 boolean isClassAccessible(Class<?> refc) {
3810 Objects.requireNonNull(refc);
3811 Class<?> caller = lookupClassOrNull();
3812 Class<?> type = refc;
3813 while (type.isArray()) {
3814 type = type.getComponentType();
3815 }
3816 return caller == null || VerifyAccess.isClassAccessible(type, caller, prevLookupClass, allowedModes);
3817 }
3818
3819 /** Check name for an illegal leading "<" character. */
3820 void checkMethodName(byte refKind, String name) throws NoSuchMethodException {
3821 if (name.startsWith("<") && refKind != REF_newInvokeSpecial)
3822 throw new NoSuchMethodException("illegal method name: "+name);
3823 }
3824
3825 /**
3826 * Find my trustable caller class if m is a caller sensitive method.
3827 * If this lookup object has original full privilege access, then the caller class is the lookupClass.
3828 * Otherwise, if m is caller-sensitive, throw IllegalAccessException.
3829 */
3830 Lookup findBoundCallerLookup(MemberName m) throws IllegalAccessException {
3831 if (MethodHandleNatives.isCallerSensitive(m) && (lookupModes() & ORIGINAL) == 0) {
3832 // Only lookups with full privilege access are allowed to resolve caller-sensitive methods
3833 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
3834 }
3835 return this;
3836 }
3837
3838 /**
3839 * Returns {@code true} if this lookup has {@code PRIVATE} and {@code MODULE} access.
3840 * @return {@code true} if this lookup has {@code PRIVATE} and {@code MODULE} access.
3841 *
3842 * @deprecated This method was originally designed to test {@code PRIVATE} access
3843 * that implies full privilege access but {@code MODULE} access has since become
3844 * independent of {@code PRIVATE} access. It is recommended to call
3845 * {@link #hasFullPrivilegeAccess()} instead.
3846 * @since 9
3847 */
3848 @Deprecated(since="14")
3849 public boolean hasPrivateAccess() {
3850 return hasFullPrivilegeAccess();
3851 }
3852
3853 /**
3854 * Returns {@code true} if this lookup has <em>full privilege access</em>,
3855 * i.e. {@code PRIVATE} and {@code MODULE} access.
3856 * A {@code Lookup} object must have full privilege access in order to
3857 * access all members that are allowed to the
3858 * {@linkplain #lookupClass() lookup class}.
3859 *
3860 * @return {@code true} if this lookup has full privilege access.
3861 * @since 14
3862 * @see <a href="MethodHandles.Lookup.html#privacc">private and module access</a>
3863 */
3864 public boolean hasFullPrivilegeAccess() {
3865 return (allowedModes & (PRIVATE|MODULE)) == (PRIVATE|MODULE);
3866 }
3867
3868 /**
3869 * Perform steps 1 and 2b <a href="MethodHandles.Lookup.html#secmgr">access checks</a>
3870 * for ensureInitialized, findClass or accessClass.
3871 */
3872 void checkSecurityManager(Class<?> refc) {
3873 if (allowedModes == TRUSTED) return;
3874
3875 @SuppressWarnings("removal")
3876 SecurityManager smgr = System.getSecurityManager();
3877 if (smgr == null) return;
3878
3879 // Step 1:
3880 boolean fullPrivilegeLookup = hasFullPrivilegeAccess();
3881 if (!fullPrivilegeLookup ||
3882 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
3883 ReflectUtil.checkPackageAccess(refc);
3884 }
3885
3886 // Step 2b:
3887 if (!fullPrivilegeLookup) {
3888 smgr.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
3889 }
3890 }
3891
3892 /**
3893 * Perform steps 1, 2a and 3 <a href="MethodHandles.Lookup.html#secmgr">access checks</a>.
3894 * Determines a trustable caller class to compare with refc, the symbolic reference class.
3895 * If this lookup object has full privilege access except original access,
3896 * then the caller class is the lookupClass.
3897 *
3898 * Lookup object created by {@link MethodHandles#privateLookupIn(Class, Lookup)}
3899 * from the same module skips the security permission check.
3900 */
3901 void checkSecurityManager(Class<?> refc, MemberName m) {
3902 Objects.requireNonNull(refc);
3903 Objects.requireNonNull(m);
3904
3905 if (allowedModes == TRUSTED) return;
3906
3907 @SuppressWarnings("removal")
3908 SecurityManager smgr = System.getSecurityManager();
3909 if (smgr == null) return;
3910
3911 // Step 1:
3912 boolean fullPrivilegeLookup = hasFullPrivilegeAccess();
3913 if (!fullPrivilegeLookup ||
3914 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
3915 ReflectUtil.checkPackageAccess(refc);
3916 }
3917
3918 // Step 2a:
3919 if (m.isPublic()) return;
3920 if (!fullPrivilegeLookup) {
3921 smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION);
3922 }
3923
3924 // Step 3:
3925 Class<?> defc = m.getDeclaringClass();
3926 if (!fullPrivilegeLookup && defc != refc) {
3927 ReflectUtil.checkPackageAccess(defc);
3928 }
3929 }
3930
3931 void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
3932 boolean wantStatic = (refKind == REF_invokeStatic);
3933 String message;
3934 if (m.isConstructor())
3935 message = "expected a method, not a constructor";
3936 else if (!m.isMethod())
3937 message = "expected a method";
3938 else if (wantStatic != m.isStatic())
3939 message = wantStatic ? "expected a static method" : "expected a non-static method";
3940 else
3941 { checkAccess(refKind, refc, m); return; }
3942 throw m.makeAccessException(message, this);
3943 }
3944
3945 void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
3946 boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
3947 String message;
3948 if (wantStatic != m.isStatic())
3949 message = wantStatic ? "expected a static field" : "expected a non-static field";
3950 else
3951 { checkAccess(refKind, refc, m); return; }
3952 throw m.makeAccessException(message, this);
3953 }
3954
3955 private boolean isArrayClone(byte refKind, Class<?> refc, MemberName m) {
3956 return Modifier.isProtected(m.getModifiers()) &&
3957 refKind == REF_invokeVirtual &&
3958 m.getDeclaringClass() == Object.class &&
3959 m.getName().equals("clone") &&
3960 refc.isArray();
3961 }
3962
3963 /** Check public/protected/private bits on the symbolic reference class and its member. */
3964 void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
3965 assert(m.referenceKindIsConsistentWith(refKind) &&
3966 MethodHandleNatives.refKindIsValid(refKind) &&
3967 (MethodHandleNatives.refKindIsField(refKind) == m.isField()));
3968 int allowedModes = this.allowedModes;
3969 if (allowedModes == TRUSTED) return;
3970 int mods = m.getModifiers();
3971 if (isArrayClone(refKind, refc, m)) {
3972 // The JVM does this hack also.
3973 // (See ClassVerifier::verify_invoke_instructions
3974 // and LinkResolver::check_method_accessability.)
3975 // Because the JVM does not allow separate methods on array types,
3976 // there is no separate method for int[].clone.
3977 // All arrays simply inherit Object.clone.
3978 // But for access checking logic, we make Object.clone
3979 // (normally protected) appear to be public.
3980 // Later on, when the DirectMethodHandle is created,
3981 // its leading argument will be restricted to the
3982 // requested array type.
3983 // N.B. The return type is not adjusted, because
3984 // that is *not* the bytecode behavior.
3985 mods ^= Modifier.PROTECTED | Modifier.PUBLIC;
3986 }
3987 if (Modifier.isProtected(mods) && refKind == REF_newInvokeSpecial) {
3988 // cannot "new" a protected ctor in a different package
3989 mods ^= Modifier.PROTECTED;
3990 }
3991 if (Modifier.isFinal(mods) &&
3992 MethodHandleNatives.refKindIsSetter(refKind))
3993 throw m.makeAccessException("unexpected set of a final field", this);
3994 int requestedModes = fixmods(mods); // adjust 0 => PACKAGE
3995 if ((requestedModes & allowedModes) != 0) {
3996 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
3997 mods, lookupClass(), previousLookupClass(), allowedModes))
3998 return;
3999 } else {
4000 // Protected members can also be checked as if they were package-private.
4001 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
4002 && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
4003 return;
4004 }
4005 throw m.makeAccessException(accessFailedMessage(refc, m), this);
4006 }
4007
4008 String accessFailedMessage(Class<?> refc, MemberName m) {
4009 Class<?> defc = m.getDeclaringClass();
4010 int mods = m.getModifiers();
4011 // check the class first:
4012 boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
4013 (defc == refc ||
4014 Modifier.isPublic(refc.getModifiers())));
4015 if (!classOK && (allowedModes & PACKAGE) != 0) {
4016 // ignore previous lookup class to check if default package access
4017 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), null, FULL_POWER_MODES) &&
4018 (defc == refc ||
4019 VerifyAccess.isClassAccessible(refc, lookupClass(), null, FULL_POWER_MODES)));
4020 }
4021 if (!classOK)
4022 return "class is not public";
4023 if (Modifier.isPublic(mods))
4024 return "access to public member failed"; // (how?, module not readable?)
4025 if (Modifier.isPrivate(mods))
4026 return "member is private";
4027 if (Modifier.isProtected(mods))
4028 return "member is protected";
4029 return "member is private to package";
4030 }
4031
4032 private void checkSpecialCaller(Class<?> specialCaller, Class<?> refc) throws IllegalAccessException {
4033 int allowedModes = this.allowedModes;
4034 if (allowedModes == TRUSTED) return;
4035 if ((lookupModes() & PRIVATE) == 0
4036 || (specialCaller != lookupClass()
4037 // ensure non-abstract methods in superinterfaces can be special-invoked
4038 && !(refc != null && refc.isInterface() && refc.isAssignableFrom(specialCaller))))
4039 throw new MemberName(specialCaller).
4040 makeAccessException("no private access for invokespecial", this);
4041 }
4042
4043 private boolean restrictProtectedReceiver(MemberName method) {
4044 // The accessing class only has the right to use a protected member
4045 // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc.
4046 if (!method.isProtected() || method.isStatic()
4047 || allowedModes == TRUSTED
4048 || method.getDeclaringClass() == lookupClass()
4049 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass()))
4050 return false;
4051 return true;
4052 }
4053 private MethodHandle restrictReceiver(MemberName method, DirectMethodHandle mh, Class<?> caller) throws IllegalAccessException {
4054 assert(!method.isStatic());
4055 // receiver type of mh is too wide; narrow to caller
4056 if (!method.getDeclaringClass().isAssignableFrom(caller)) {
4057 throw method.makeAccessException("caller class must be a subclass below the method", caller);
4058 }
4059 MethodType rawType = mh.type();
4060 if (caller.isAssignableFrom(rawType.parameterType(0))) return mh; // no need to restrict; already narrow
4061 MethodType narrowType = rawType.changeParameterType(0, caller);
4062 assert(!mh.isVarargsCollector()); // viewAsType will lose varargs-ness
4063 assert(mh.viewAsTypeChecks(narrowType, true));
4064 return mh.copyWith(narrowType, mh.form);
4065 }
4066
4067 /** Check access and get the requested method. */
4068 private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException {
4069 final boolean doRestrict = true;
4070 final boolean checkSecurity = true;
4071 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerLookup);
4072 }
4073 /** Check access and get the requested method, for invokespecial with no restriction on the application of narrowing rules. */
4074 private MethodHandle getDirectMethodNoRestrictInvokeSpecial(Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException {
4075 final boolean doRestrict = false;
4076 final boolean checkSecurity = true;
4077 return getDirectMethodCommon(REF_invokeSpecial, refc, method, checkSecurity, doRestrict, callerLookup);
4078 }
4079 /** Check access and get the requested method, eliding security manager checks. */
4080 private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException {
4081 final boolean doRestrict = true;
4082 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
4083 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerLookup);
4084 }
4085 /** Common code for all methods; do not call directly except from immediately above. */
4086 private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method,
4087 boolean checkSecurity,
4088 boolean doRestrict,
4089 Lookup boundCaller) throws IllegalAccessException {
4090 checkMethod(refKind, refc, method);
4091 // Optionally check with the security manager; this isn't needed for unreflect* calls.
4092 if (checkSecurity)
4093 checkSecurityManager(refc, method);
4094 assert(!method.isMethodHandleInvoke());
4095
4096 if (refKind == REF_invokeSpecial &&
4097 refc != lookupClass() &&
4098 !refc.isInterface() && !lookupClass().isInterface() &&
4099 refc != lookupClass().getSuperclass() &&
4100 refc.isAssignableFrom(lookupClass())) {
4101 assert(!method.getName().equals(ConstantDescs.INIT_NAME)); // not this code path
4102
4103 // Per JVMS 6.5, desc. of invokespecial instruction:
4104 // If the method is in a superclass of the LC,
4105 // and if our original search was above LC.super,
4106 // repeat the search (symbolic lookup) from LC.super
4107 // and continue with the direct superclass of that class,
4108 // and so forth, until a match is found or no further superclasses exist.
4109 // FIXME: MemberName.resolve should handle this instead.
4110 Class<?> refcAsSuper = lookupClass();
4111 MemberName m2;
4112 do {
4113 refcAsSuper = refcAsSuper.getSuperclass();
4114 m2 = new MemberName(refcAsSuper,
4115 method.getName(),
4116 method.getMethodType(),
4117 REF_invokeSpecial);
4118 m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull(), allowedModes);
4119 } while (m2 == null && // no method is found yet
4120 refc != refcAsSuper); // search up to refc
4121 if (m2 == null) throw new InternalError(method.toString());
4122 method = m2;
4123 refc = refcAsSuper;
4124 // redo basic checks
4125 checkMethod(refKind, refc, method);
4126 }
4127 DirectMethodHandle dmh = DirectMethodHandle.make(refKind, refc, method, lookupClass());
4128 MethodHandle mh = dmh;
4129 // Optionally narrow the receiver argument to lookupClass using restrictReceiver.
4130 if ((doRestrict && refKind == REF_invokeSpecial) ||
4131 (MethodHandleNatives.refKindHasReceiver(refKind) &&
4132 restrictProtectedReceiver(method) &&
4133 // All arrays simply inherit the protected Object.clone method.
4134 // The leading argument is already restricted to the requested
4135 // array type (not the lookup class).
4136 !isArrayClone(refKind, refc, method))) {
4137 mh = restrictReceiver(method, dmh, lookupClass());
4138 }
4139 mh = maybeBindCaller(method, mh, boundCaller);
4140 mh = mh.setVarargs(method);
4141 return mh;
4142 }
4143 private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh, Lookup boundCaller)
4144 throws IllegalAccessException {
4145 if (boundCaller.allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method))
4146 return mh;
4147
4148 // boundCaller must have full privilege access.
4149 // It should have been checked by findBoundCallerLookup. Safe to check this again.
4150 if ((boundCaller.lookupModes() & ORIGINAL) == 0)
4151 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
4152
4153 assert boundCaller.hasFullPrivilegeAccess();
4154
4155 MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, boundCaller.lookupClass);
4156 // Note: caller will apply varargs after this step happens.
4157 return cbmh;
4158 }
4159
4160 /** Check access and get the requested field. */
4161 private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
4162 final boolean checkSecurity = true;
4163 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
4164 }
4165 /** Check access and get the requested field, eliding security manager checks. */
4166 private MethodHandle getDirectFieldNoSecurityManager(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
4167 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
4168 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
4169 }
4170 /** Common code for all fields; do not call directly except from immediately above. */
4171 private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field,
4172 boolean checkSecurity) throws IllegalAccessException {
4173 checkField(refKind, refc, field);
4174 // Optionally check with the security manager; this isn't needed for unreflect* calls.
4175 if (checkSecurity)
4176 checkSecurityManager(refc, field);
4177 DirectMethodHandle dmh = DirectMethodHandle.make(refc, field);
4178 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) &&
4179 restrictProtectedReceiver(field));
4180 if (doRestrict)
4181 return restrictReceiver(field, dmh, lookupClass());
4182 return dmh;
4183 }
4184 private VarHandle getFieldVarHandle(byte getRefKind, byte putRefKind,
4185 Class<?> refc, MemberName getField, MemberName putField)
4186 throws IllegalAccessException {
4187 final boolean checkSecurity = true;
4188 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
4189 }
4190 private VarHandle getFieldVarHandleNoSecurityManager(byte getRefKind, byte putRefKind,
4191 Class<?> refc, MemberName getField, MemberName putField)
4192 throws IllegalAccessException {
4193 final boolean checkSecurity = false;
4194 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
4195 }
4196 private VarHandle getFieldVarHandleCommon(byte getRefKind, byte putRefKind,
4197 Class<?> refc, MemberName getField, MemberName putField,
4198 boolean checkSecurity) throws IllegalAccessException {
4199 assert getField.isStatic() == putField.isStatic();
4200 assert getField.isGetter() && putField.isSetter();
4201 assert MethodHandleNatives.refKindIsStatic(getRefKind) == MethodHandleNatives.refKindIsStatic(putRefKind);
4202 assert MethodHandleNatives.refKindIsGetter(getRefKind) && MethodHandleNatives.refKindIsSetter(putRefKind);
4203
4204 checkField(getRefKind, refc, getField);
4205 if (checkSecurity)
4206 checkSecurityManager(refc, getField);
4207
4208 if (!putField.isFinal()) {
4209 // A VarHandle does not support updates to final fields, any
4210 // such VarHandle to a final field will be read-only and
4211 // therefore the following write-based accessibility checks are
4212 // only required for non-final fields
4213 checkField(putRefKind, refc, putField);
4214 if (checkSecurity)
4215 checkSecurityManager(refc, putField);
4216 }
4217
4218 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(getRefKind) &&
4219 restrictProtectedReceiver(getField));
4220 if (doRestrict) {
4221 assert !getField.isStatic();
4222 // receiver type of VarHandle is too wide; narrow to caller
4223 if (!getField.getDeclaringClass().isAssignableFrom(lookupClass())) {
4224 throw getField.makeAccessException("caller class must be a subclass below the method", lookupClass());
4225 }
4226 refc = lookupClass();
4227 }
4228 return VarHandles.makeFieldHandle(getField, refc,
4229 this.allowedModes == TRUSTED && !getField.isTrustedFinalField());
4230 }
4231 /** Check access and get the requested constructor. */
4232 private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException {
4233 final boolean checkSecurity = true;
4234 return getDirectConstructorCommon(refc, ctor, checkSecurity);
4235 }
4236 /** Check access and get the requested constructor, eliding security manager checks. */
4237 private MethodHandle getDirectConstructorNoSecurityManager(Class<?> refc, MemberName ctor) throws IllegalAccessException {
4238 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
4239 return getDirectConstructorCommon(refc, ctor, checkSecurity);
4240 }
4241 /** Common code for all constructors; do not call directly except from immediately above. */
4242 private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor,
4243 boolean checkSecurity) throws IllegalAccessException {
4244 assert(ctor.isConstructor());
4245 checkAccess(REF_newInvokeSpecial, refc, ctor);
4246 // Optionally check with the security manager; this isn't needed for unreflect* calls.
4247 if (checkSecurity)
4248 checkSecurityManager(refc, ctor);
4249 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
4250 return DirectMethodHandle.make(ctor).setVarargs(ctor);
4251 }
4252
4253 /** Hook called from the JVM (via MethodHandleNatives) to link MH constants:
4254 */
4255 /*non-public*/
4256 MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type)
4257 throws ReflectiveOperationException {
4258 if (!(type instanceof Class || type instanceof MethodType))
4259 throw new InternalError("unresolved MemberName");
4260 MemberName member = new MemberName(refKind, defc, name, type);
4261 MethodHandle mh = LOOKASIDE_TABLE.get(member);
4262 if (mh != null) {
4263 checkSymbolicClass(defc);
4264 return mh;
4265 }
4266 if (defc == MethodHandle.class && refKind == REF_invokeVirtual) {
4267 // Treat MethodHandle.invoke and invokeExact specially.
4268 mh = findVirtualForMH(member.getName(), member.getMethodType());
4269 if (mh != null) {
4270 return mh;
4271 }
4272 } else if (defc == VarHandle.class && refKind == REF_invokeVirtual) {
4273 // Treat signature-polymorphic methods on VarHandle specially.
4274 mh = findVirtualForVH(member.getName(), member.getMethodType());
4275 if (mh != null) {
4276 return mh;
4277 }
4278 }
4279 MemberName resolved = resolveOrFail(refKind, member);
4280 mh = getDirectMethodForConstant(refKind, defc, resolved);
4281 if (mh instanceof DirectMethodHandle dmh
4282 && canBeCached(refKind, defc, resolved)) {
4283 MemberName key = mh.internalMemberName();
4284 if (key != null) {
4285 key = key.asNormalOriginal();
4286 }
4287 if (member.equals(key)) { // better safe than sorry
4288 LOOKASIDE_TABLE.put(key, dmh);
4289 }
4290 }
4291 return mh;
4292 }
4293 private boolean canBeCached(byte refKind, Class<?> defc, MemberName member) {
4294 if (refKind == REF_invokeSpecial) {
4295 return false;
4296 }
4297 if (!Modifier.isPublic(defc.getModifiers()) ||
4298 !Modifier.isPublic(member.getDeclaringClass().getModifiers()) ||
4299 !member.isPublic() ||
4300 member.isCallerSensitive()) {
4301 return false;
4302 }
4303 ClassLoader loader = defc.getClassLoader();
4304 if (loader != null) {
4305 ClassLoader sysl = ClassLoader.getSystemClassLoader();
4306 boolean found = false;
4307 while (sysl != null) {
4308 if (loader == sysl) { found = true; break; }
4309 sysl = sysl.getParent();
4310 }
4311 if (!found) {
4312 return false;
4313 }
4314 }
4315 try {
4316 MemberName resolved2 = publicLookup().resolveOrNull(refKind,
4317 new MemberName(refKind, defc, member.getName(), member.getType()));
4318 if (resolved2 == null) {
4319 return false;
4320 }
4321 checkSecurityManager(defc, resolved2);
4322 } catch (SecurityException ex) {
4323 return false;
4324 }
4325 return true;
4326 }
4327 private MethodHandle getDirectMethodForConstant(byte refKind, Class<?> defc, MemberName member)
4328 throws ReflectiveOperationException {
4329 if (MethodHandleNatives.refKindIsField(refKind)) {
4330 return getDirectFieldNoSecurityManager(refKind, defc, member);
4331 } else if (MethodHandleNatives.refKindIsMethod(refKind)) {
4332 return getDirectMethodNoSecurityManager(refKind, defc, member, findBoundCallerLookup(member));
4333 } else if (refKind == REF_newInvokeSpecial) {
4334 return getDirectConstructorNoSecurityManager(defc, member);
4335 }
4336 // oops
4337 throw newIllegalArgumentException("bad MethodHandle constant #"+member);
4338 }
4339
4340 static ConcurrentHashMap<MemberName, DirectMethodHandle> LOOKASIDE_TABLE = new ConcurrentHashMap<>();
4341 }
4342
4343 /**
4344 * Produces a method handle constructing arrays of a desired type,
4345 * as if by the {@code anewarray} bytecode.
4346 * The return type of the method handle will be the array type.
4347 * The type of its sole argument will be {@code int}, which specifies the size of the array.
4348 *
4349 * <p> If the returned method handle is invoked with a negative
4350 * array size, a {@code NegativeArraySizeException} will be thrown.
4351 *
4352 * @param arrayClass an array type
4353 * @return a method handle which can create arrays of the given type
4354 * @throws NullPointerException if the argument is {@code null}
4355 * @throws IllegalArgumentException if {@code arrayClass} is not an array type
4356 * @see java.lang.reflect.Array#newInstance(Class, int)
4357 * @jvms 6.5 {@code anewarray} Instruction
4358 * @since 9
4359 */
4360 public static MethodHandle arrayConstructor(Class<?> arrayClass) throws IllegalArgumentException {
4361 if (!arrayClass.isArray()) {
4362 throw newIllegalArgumentException("not an array class: " + arrayClass.getName());
4363 }
4364 MethodHandle ani = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_Array_newInstance).
4365 bindTo(arrayClass.getComponentType());
4366 return ani.asType(ani.type().changeReturnType(arrayClass));
4367 }
4368
4369 /**
4370 * Produces a method handle returning the length of an array,
4371 * as if by the {@code arraylength} bytecode.
4372 * The type of the method handle will have {@code int} as return type,
4373 * and its sole argument will be the array type.
4374 *
4375 * <p> If the returned method handle is invoked with a {@code null}
4376 * array reference, a {@code NullPointerException} will be thrown.
4377 *
4378 * @param arrayClass an array type
4379 * @return a method handle which can retrieve the length of an array of the given array type
4380 * @throws NullPointerException if the argument is {@code null}
4381 * @throws IllegalArgumentException if arrayClass is not an array type
4382 * @jvms 6.5 {@code arraylength} Instruction
4383 * @since 9
4384 */
4385 public static MethodHandle arrayLength(Class<?> arrayClass) throws IllegalArgumentException {
4386 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.LENGTH);
4387 }
4388
4389 /**
4390 * Produces a method handle giving read access to elements of an array,
4391 * as if by the {@code aaload} bytecode.
4392 * The type of the method handle will have a return type of the array's
4393 * element type. Its first argument will be the array type,
4394 * and the second will be {@code int}.
4395 *
4396 * <p> When the returned method handle is invoked,
4397 * the array reference and array index are checked.
4398 * A {@code NullPointerException} will be thrown if the array reference
4399 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
4400 * thrown if the index is negative or if it is greater than or equal to
4401 * the length of the array.
4402 *
4403 * @param arrayClass an array type
4404 * @return a method handle which can load values from the given array type
4405 * @throws NullPointerException if the argument is null
4406 * @throws IllegalArgumentException if arrayClass is not an array type
4407 * @jvms 6.5 {@code aaload} Instruction
4408 */
4409 public static MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException {
4410 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.GET);
4411 }
4412
4413 /**
4414 * Produces a method handle giving write access to elements of an array,
4415 * as if by the {@code astore} bytecode.
4416 * The type of the method handle will have a void return type.
4417 * Its last argument will be the array's element type.
4418 * The first and second arguments will be the array type and int.
4419 *
4420 * <p> When the returned method handle is invoked,
4421 * the array reference and array index are checked.
4422 * A {@code NullPointerException} will be thrown if the array reference
4423 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
4424 * thrown if the index is negative or if it is greater than or equal to
4425 * the length of the array.
4426 *
4427 * @param arrayClass the class of an array
4428 * @return a method handle which can store values into the array type
4429 * @throws NullPointerException if the argument is null
4430 * @throws IllegalArgumentException if arrayClass is not an array type
4431 * @jvms 6.5 {@code aastore} Instruction
4432 */
4433 public static MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException {
4434 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.SET);
4435 }
4436
4437 /**
4438 * Produces a VarHandle giving access to elements of an array of type
4439 * {@code arrayClass}. The VarHandle's variable type is the component type
4440 * of {@code arrayClass} and the list of coordinate types is
4441 * {@code (arrayClass, int)}, where the {@code int} coordinate type
4442 * corresponds to an argument that is an index into an array.
4443 * <p>
4444 * Certain access modes of the returned VarHandle are unsupported under
4445 * the following conditions:
4446 * <ul>
4447 * <li>if the component type is anything other than {@code byte},
4448 * {@code short}, {@code char}, {@code int}, {@code long},
4449 * {@code float}, or {@code double} then numeric atomic update access
4450 * modes are unsupported.
4451 * <li>if the component type is anything other than {@code boolean},
4452 * {@code byte}, {@code short}, {@code char}, {@code int} or
4453 * {@code long} then bitwise atomic update access modes are
4454 * unsupported.
4455 * </ul>
4456 * <p>
4457 * If the component type is {@code float} or {@code double} then numeric
4458 * and atomic update access modes compare values using their bitwise
4459 * representation (see {@link Float#floatToRawIntBits} and
4460 * {@link Double#doubleToRawLongBits}, respectively).
4461 *
4462 * <p> When the returned {@code VarHandle} is invoked,
4463 * the array reference and array index are checked.
4464 * A {@code NullPointerException} will be thrown if the array reference
4465 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
4466 * thrown if the index is negative or if it is greater than or equal to
4467 * the length of the array.
4468 *
4469 * @apiNote
4470 * Bitwise comparison of {@code float} values or {@code double} values,
4471 * as performed by the numeric and atomic update access modes, differ
4472 * from the primitive {@code ==} operator and the {@link Float#equals}
4473 * and {@link Double#equals} methods, specifically with respect to
4474 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
4475 * Care should be taken when performing a compare and set or a compare
4476 * and exchange operation with such values since the operation may
4477 * unexpectedly fail.
4478 * There are many possible NaN values that are considered to be
4479 * {@code NaN} in Java, although no IEEE 754 floating-point operation
4480 * provided by Java can distinguish between them. Operation failure can
4481 * occur if the expected or witness value is a NaN value and it is
4482 * transformed (perhaps in a platform specific manner) into another NaN
4483 * value, and thus has a different bitwise representation (see
4484 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
4485 * details).
4486 * The values {@code -0.0} and {@code +0.0} have different bitwise
4487 * representations but are considered equal when using the primitive
4488 * {@code ==} operator. Operation failure can occur if, for example, a
4489 * numeric algorithm computes an expected value to be say {@code -0.0}
4490 * and previously computed the witness value to be say {@code +0.0}.
4491 * @param arrayClass the class of an array, of type {@code T[]}
4492 * @return a VarHandle giving access to elements of an array
4493 * @throws NullPointerException if the arrayClass is null
4494 * @throws IllegalArgumentException if arrayClass is not an array type
4495 * @since 9
4496 */
4497 public static VarHandle arrayElementVarHandle(Class<?> arrayClass) throws IllegalArgumentException {
4498 return VarHandles.makeArrayElementHandle(arrayClass);
4499 }
4500
4501 /**
4502 * Produces a VarHandle giving access to elements of a {@code byte[]} array
4503 * viewed as if it were a different primitive array type, such as
4504 * {@code int[]} or {@code long[]}.
4505 * The VarHandle's variable type is the component type of
4506 * {@code viewArrayClass} and the list of coordinate types is
4507 * {@code (byte[], int)}, where the {@code int} coordinate type
4508 * corresponds to an argument that is an index into a {@code byte[]} array.
4509 * The returned VarHandle accesses bytes at an index in a {@code byte[]}
4510 * array, composing bytes to or from a value of the component type of
4511 * {@code viewArrayClass} according to the given endianness.
4512 * <p>
4513 * The supported component types (variables types) are {@code short},
4514 * {@code char}, {@code int}, {@code long}, {@code float} and
4515 * {@code double}.
4516 * <p>
4517 * Access of bytes at a given index will result in an
4518 * {@code ArrayIndexOutOfBoundsException} if the index is less than {@code 0}
4519 * or greater than the {@code byte[]} array length minus the size (in bytes)
4520 * of {@code T}.
4521 * <p>
4522 * Access of bytes at an index may be aligned or misaligned for {@code T},
4523 * with respect to the underlying memory address, {@code A} say, associated
4524 * with the array and index.
4525 * If access is misaligned then access for anything other than the
4526 * {@code get} and {@code set} access modes will result in an
4527 * {@code IllegalStateException}. In such cases atomic access is only
4528 * guaranteed with respect to the largest power of two that divides the GCD
4529 * of {@code A} and the size (in bytes) of {@code T}.
4530 * If access is aligned then following access modes are supported and are
4531 * guaranteed to support atomic access:
4532 * <ul>
4533 * <li>read write access modes for all {@code T}, with the exception of
4534 * access modes {@code get} and {@code set} for {@code long} and
4535 * {@code double} on 32-bit platforms.
4536 * <li>atomic update access modes for {@code int}, {@code long},
4537 * {@code float} or {@code double}.
4538 * (Future major platform releases of the JDK may support additional
4539 * types for certain currently unsupported access modes.)
4540 * <li>numeric atomic update access modes for {@code int} and {@code long}.
4541 * (Future major platform releases of the JDK may support additional
4542 * numeric types for certain currently unsupported access modes.)
4543 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
4544 * (Future major platform releases of the JDK may support additional
4545 * numeric types for certain currently unsupported access modes.)
4546 * </ul>
4547 * <p>
4548 * Misaligned access, and therefore atomicity guarantees, may be determined
4549 * for {@code byte[]} arrays without operating on a specific array. Given
4550 * an {@code index}, {@code T} and its corresponding boxed type,
4551 * {@code T_BOX}, misalignment may be determined as follows:
4552 * <pre>{@code
4553 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
4554 * int misalignedAtZeroIndex = ByteBuffer.wrap(new byte[0]).
4555 * alignmentOffset(0, sizeOfT);
4556 * int misalignedAtIndex = (misalignedAtZeroIndex + index) % sizeOfT;
4557 * boolean isMisaligned = misalignedAtIndex != 0;
4558 * }</pre>
4559 * <p>
4560 * If the variable type is {@code float} or {@code double} then atomic
4561 * update access modes compare values using their bitwise representation
4562 * (see {@link Float#floatToRawIntBits} and
4563 * {@link Double#doubleToRawLongBits}, respectively).
4564 * @param viewArrayClass the view array class, with a component type of
4565 * type {@code T}
4566 * @param byteOrder the endianness of the view array elements, as
4567 * stored in the underlying {@code byte} array
4568 * @return a VarHandle giving access to elements of a {@code byte[]} array
4569 * viewed as if elements corresponding to the components type of the view
4570 * array class
4571 * @throws NullPointerException if viewArrayClass or byteOrder is null
4572 * @throws IllegalArgumentException if viewArrayClass is not an array type
4573 * @throws UnsupportedOperationException if the component type of
4574 * viewArrayClass is not supported as a variable type
4575 * @since 9
4576 */
4577 public static VarHandle byteArrayViewVarHandle(Class<?> viewArrayClass,
4578 ByteOrder byteOrder) throws IllegalArgumentException {
4579 Objects.requireNonNull(byteOrder);
4580 return VarHandles.byteArrayViewHandle(viewArrayClass,
4581 byteOrder == ByteOrder.BIG_ENDIAN);
4582 }
4583
4584 /**
4585 * Produces a VarHandle giving access to elements of a {@code ByteBuffer}
4586 * viewed as if it were an array of elements of a different primitive
4587 * component type to that of {@code byte}, such as {@code int[]} or
4588 * {@code long[]}.
4589 * The VarHandle's variable type is the component type of
4590 * {@code viewArrayClass} and the list of coordinate types is
4591 * {@code (ByteBuffer, int)}, where the {@code int} coordinate type
4592 * corresponds to an argument that is an index into a {@code byte[]} array.
4593 * The returned VarHandle accesses bytes at an index in a
4594 * {@code ByteBuffer}, composing bytes to or from a value of the component
4595 * type of {@code viewArrayClass} according to the given endianness.
4596 * <p>
4597 * The supported component types (variables types) are {@code short},
4598 * {@code char}, {@code int}, {@code long}, {@code float} and
4599 * {@code double}.
4600 * <p>
4601 * Access will result in a {@code ReadOnlyBufferException} for anything
4602 * other than the read access modes if the {@code ByteBuffer} is read-only.
4603 * <p>
4604 * Access of bytes at a given index will result in an
4605 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
4606 * or greater than the {@code ByteBuffer} limit minus the size (in bytes) of
4607 * {@code T}.
4608 * <p>
4609 * Access of bytes at an index may be aligned or misaligned for {@code T},
4610 * with respect to the underlying memory address, {@code A} say, associated
4611 * with the {@code ByteBuffer} and index.
4612 * If access is misaligned then access for anything other than the
4613 * {@code get} and {@code set} access modes will result in an
4614 * {@code IllegalStateException}. In such cases atomic access is only
4615 * guaranteed with respect to the largest power of two that divides the GCD
4616 * of {@code A} and the size (in bytes) of {@code T}.
4617 * If access is aligned then following access modes are supported and are
4618 * guaranteed to support atomic access:
4619 * <ul>
4620 * <li>read write access modes for all {@code T}, with the exception of
4621 * access modes {@code get} and {@code set} for {@code long} and
4622 * {@code double} on 32-bit platforms.
4623 * <li>atomic update access modes for {@code int}, {@code long},
4624 * {@code float} or {@code double}.
4625 * (Future major platform releases of the JDK may support additional
4626 * types for certain currently unsupported access modes.)
4627 * <li>numeric atomic update access modes for {@code int} and {@code long}.
4628 * (Future major platform releases of the JDK may support additional
4629 * numeric types for certain currently unsupported access modes.)
4630 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
4631 * (Future major platform releases of the JDK may support additional
4632 * numeric types for certain currently unsupported access modes.)
4633 * </ul>
4634 * <p>
4635 * Misaligned access, and therefore atomicity guarantees, may be determined
4636 * for a {@code ByteBuffer}, {@code bb} (direct or otherwise), an
4637 * {@code index}, {@code T} and its corresponding boxed type,
4638 * {@code T_BOX}, as follows:
4639 * <pre>{@code
4640 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
4641 * ByteBuffer bb = ...
4642 * int misalignedAtIndex = bb.alignmentOffset(index, sizeOfT);
4643 * boolean isMisaligned = misalignedAtIndex != 0;
4644 * }</pre>
4645 * <p>
4646 * If the variable type is {@code float} or {@code double} then atomic
4647 * update access modes compare values using their bitwise representation
4648 * (see {@link Float#floatToRawIntBits} and
4649 * {@link Double#doubleToRawLongBits}, respectively).
4650 * @param viewArrayClass the view array class, with a component type of
4651 * type {@code T}
4652 * @param byteOrder the endianness of the view array elements, as
4653 * stored in the underlying {@code ByteBuffer} (Note this overrides the
4654 * endianness of a {@code ByteBuffer})
4655 * @return a VarHandle giving access to elements of a {@code ByteBuffer}
4656 * viewed as if elements corresponding to the components type of the view
4657 * array class
4658 * @throws NullPointerException if viewArrayClass or byteOrder is null
4659 * @throws IllegalArgumentException if viewArrayClass is not an array type
4660 * @throws UnsupportedOperationException if the component type of
4661 * viewArrayClass is not supported as a variable type
4662 * @since 9
4663 */
4664 public static VarHandle byteBufferViewVarHandle(Class<?> viewArrayClass,
4665 ByteOrder byteOrder) throws IllegalArgumentException {
4666 Objects.requireNonNull(byteOrder);
4667 return VarHandles.makeByteBufferViewHandle(viewArrayClass,
4668 byteOrder == ByteOrder.BIG_ENDIAN);
4669 }
4670
4671
4672 /// method handle invocation (reflective style)
4673
4674 /**
4675 * Produces a method handle which will invoke any method handle of the
4676 * given {@code type}, with a given number of trailing arguments replaced by
4677 * a single trailing {@code Object[]} array.
4678 * The resulting invoker will be a method handle with the following
4679 * arguments:
4680 * <ul>
4681 * <li>a single {@code MethodHandle} target
4682 * <li>zero or more leading values (counted by {@code leadingArgCount})
4683 * <li>an {@code Object[]} array containing trailing arguments
4684 * </ul>
4685 * <p>
4686 * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
4687 * the indicated {@code type}.
4688 * That is, if the target is exactly of the given {@code type}, it will behave
4689 * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
4690 * is used to convert the target to the required {@code type}.
4691 * <p>
4692 * The type of the returned invoker will not be the given {@code type}, but rather
4693 * will have all parameters except the first {@code leadingArgCount}
4694 * replaced by a single array of type {@code Object[]}, which will be
4695 * the final parameter.
4696 * <p>
4697 * Before invoking its target, the invoker will spread the final array, apply
4698 * reference casts as necessary, and unbox and widen primitive arguments.
4699 * If, when the invoker is called, the supplied array argument does
4700 * not have the correct number of elements, the invoker will throw
4701 * an {@link IllegalArgumentException} instead of invoking the target.
4702 * <p>
4703 * This method is equivalent to the following code (though it may be more efficient):
4704 * {@snippet lang="java" :
4705 MethodHandle invoker = MethodHandles.invoker(type);
4706 int spreadArgCount = type.parameterCount() - leadingArgCount;
4707 invoker = invoker.asSpreader(Object[].class, spreadArgCount);
4708 return invoker;
4709 * }
4710 * This method throws no reflective or security exceptions.
4711 * @param type the desired target type
4712 * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
4713 * @return a method handle suitable for invoking any method handle of the given type
4714 * @throws NullPointerException if {@code type} is null
4715 * @throws IllegalArgumentException if {@code leadingArgCount} is not in
4716 * the range from 0 to {@code type.parameterCount()} inclusive,
4717 * or if the resulting method handle's type would have
4718 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4719 */
4720 public static MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
4721 if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
4722 throw newIllegalArgumentException("bad argument count", leadingArgCount);
4723 type = type.asSpreaderType(Object[].class, leadingArgCount, type.parameterCount() - leadingArgCount);
4724 return type.invokers().spreadInvoker(leadingArgCount);
4725 }
4726
4727 /**
4728 * Produces a special <em>invoker method handle</em> which can be used to
4729 * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
4730 * The resulting invoker will have a type which is
4731 * exactly equal to the desired type, except that it will accept
4732 * an additional leading argument of type {@code MethodHandle}.
4733 * <p>
4734 * This method is equivalent to the following code (though it may be more efficient):
4735 * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)}
4736 *
4737 * <p style="font-size:smaller;">
4738 * <em>Discussion:</em>
4739 * Invoker method handles can be useful when working with variable method handles
4740 * of unknown types.
4741 * For example, to emulate an {@code invokeExact} call to a variable method
4742 * handle {@code M}, extract its type {@code T},
4743 * look up the invoker method {@code X} for {@code T},
4744 * and call the invoker method, as {@code X.invoke(T, A...)}.
4745 * (It would not work to call {@code X.invokeExact}, since the type {@code T}
4746 * is unknown.)
4747 * If spreading, collecting, or other argument transformations are required,
4748 * they can be applied once to the invoker {@code X} and reused on many {@code M}
4749 * method handle values, as long as they are compatible with the type of {@code X}.
4750 * <p style="font-size:smaller;">
4751 * <em>(Note: The invoker method is not available via the Core Reflection API.
4752 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
4753 * on the declared {@code invokeExact} or {@code invoke} method will raise an
4754 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
4755 * <p>
4756 * This method throws no reflective or security exceptions.
4757 * @param type the desired target type
4758 * @return a method handle suitable for invoking any method handle of the given type
4759 * @throws IllegalArgumentException if the resulting method handle's type would have
4760 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4761 */
4762 public static MethodHandle exactInvoker(MethodType type) {
4763 return type.invokers().exactInvoker();
4764 }
4765
4766 /**
4767 * Produces a special <em>invoker method handle</em> which can be used to
4768 * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
4769 * The resulting invoker will have a type which is
4770 * exactly equal to the desired type, except that it will accept
4771 * an additional leading argument of type {@code MethodHandle}.
4772 * <p>
4773 * Before invoking its target, if the target differs from the expected type,
4774 * the invoker will apply reference casts as
4775 * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
4776 * Similarly, the return value will be converted as necessary.
4777 * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
4778 * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
4779 * <p>
4780 * This method is equivalent to the following code (though it may be more efficient):
4781 * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)}
4782 * <p style="font-size:smaller;">
4783 * <em>Discussion:</em>
4784 * A {@linkplain MethodType#genericMethodType general method type} is one which
4785 * mentions only {@code Object} arguments and return values.
4786 * An invoker for such a type is capable of calling any method handle
4787 * of the same arity as the general type.
4788 * <p style="font-size:smaller;">
4789 * <em>(Note: The invoker method is not available via the Core Reflection API.
4790 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
4791 * on the declared {@code invokeExact} or {@code invoke} method will raise an
4792 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
4793 * <p>
4794 * This method throws no reflective or security exceptions.
4795 * @param type the desired target type
4796 * @return a method handle suitable for invoking any method handle convertible to the given type
4797 * @throws IllegalArgumentException if the resulting method handle's type would have
4798 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4799 */
4800 public static MethodHandle invoker(MethodType type) {
4801 return type.invokers().genericInvoker();
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 *
4812 * @param accessMode the VarHandle access mode
4813 * @param type the desired target type
4814 * @return a method handle suitable for invoking an access mode method of
4815 * any VarHandle whose access mode type is of the given type.
4816 * @since 9
4817 */
4818 public static MethodHandle varHandleExactInvoker(VarHandle.AccessMode accessMode, MethodType type) {
4819 return type.invokers().varHandleMethodExactInvoker(accessMode);
4820 }
4821
4822 /**
4823 * Produces a special <em>invoker method handle</em> which can be used to
4824 * invoke a signature-polymorphic access mode method on any VarHandle whose
4825 * associated access mode type is compatible with the given type.
4826 * The resulting invoker will have a type which is exactly equal to the
4827 * desired given type, except that it will accept an additional leading
4828 * argument of type {@code VarHandle}.
4829 * <p>
4830 * Before invoking its target, if the access mode type differs from the
4831 * desired given type, the invoker will apply reference casts as necessary
4832 * and box, unbox, or widen primitive values, as if by
4833 * {@link MethodHandle#asType asType}. Similarly, the return value will be
4834 * converted as necessary.
4835 * <p>
4836 * This method is equivalent to the following code (though it may be more
4837 * efficient): {@code publicLookup().findVirtual(VarHandle.class, accessMode.name(), type)}
4838 *
4839 * @param accessMode the VarHandle access mode
4840 * @param type the desired target type
4841 * @return a method handle suitable for invoking an access mode method of
4842 * any VarHandle whose access mode type is convertible to the given
4843 * type.
4844 * @since 9
4845 */
4846 public static MethodHandle varHandleInvoker(VarHandle.AccessMode accessMode, MethodType type) {
4847 return type.invokers().varHandleMethodInvoker(accessMode);
4848 }
4849
4850 /*non-public*/
4851 static MethodHandle basicInvoker(MethodType type) {
4852 return type.invokers().basicInvoker();
4853 }
4854
4855 /// method handle modification (creation from other method handles)
4856
4857 /**
4858 * Produces a method handle which adapts the type of the
4859 * given method handle to a new type by pairwise argument and return type conversion.
4860 * The original type and new type must have the same number of arguments.
4861 * The resulting method handle is guaranteed to report a type
4862 * which is equal to the desired new type.
4863 * <p>
4864 * If the original type and new type are equal, returns target.
4865 * <p>
4866 * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
4867 * and some additional conversions are also applied if those conversions fail.
4868 * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied
4869 * if possible, before or instead of any conversions done by {@code asType}:
4870 * <ul>
4871 * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type,
4872 * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast.
4873 * (This treatment of interfaces follows the usage of the bytecode verifier.)
4874 * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive,
4875 * the boolean is converted to a byte value, 1 for true, 0 for false.
4876 * (This treatment follows the usage of the bytecode verifier.)
4877 * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive,
4878 * <em>T0</em> is converted to byte via Java casting conversion (JLS {@jls 5.5}),
4879 * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}.
4880 * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean,
4881 * then a Java casting conversion (JLS {@jls 5.5}) is applied.
4882 * (Specifically, <em>T0</em> will convert to <em>T1</em> by
4883 * widening and/or narrowing.)
4884 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
4885 * conversion will be applied at runtime, possibly followed
4886 * by a Java casting conversion (JLS {@jls 5.5}) on the primitive value,
4887 * possibly followed by a conversion from byte to boolean by testing
4888 * the low-order bit.
4889 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive,
4890 * and if the reference is null at runtime, a zero value is introduced.
4891 * </ul>
4892 * @param target the method handle to invoke after arguments are retyped
4893 * @param newType the expected type of the new method handle
4894 * @return a method handle which delegates to the target after performing
4895 * any necessary argument conversions, and arranges for any
4896 * necessary return value conversions
4897 * @throws NullPointerException if either argument is null
4898 * @throws WrongMethodTypeException if the conversion cannot be made
4899 * @see MethodHandle#asType
4900 */
4901 public static MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
4902 explicitCastArgumentsChecks(target, newType);
4903 // use the asTypeCache when possible:
4904 MethodType oldType = target.type();
4905 if (oldType == newType) return target;
4906 if (oldType.explicitCastEquivalentToAsType(newType)) {
4907 return target.asFixedArity().asType(newType);
4908 }
4909 return MethodHandleImpl.makePairwiseConvert(target, newType, false);
4910 }
4911
4912 private static void explicitCastArgumentsChecks(MethodHandle target, MethodType newType) {
4913 if (target.type().parameterCount() != newType.parameterCount()) {
4914 throw new WrongMethodTypeException("cannot explicitly cast " + target + " to " + newType);
4915 }
4916 }
4917
4918 /**
4919 * Produces a method handle which adapts the calling sequence of the
4920 * given method handle to a new type, by reordering the arguments.
4921 * The resulting method handle is guaranteed to report a type
4922 * which is equal to the desired new type.
4923 * <p>
4924 * The given array controls the reordering.
4925 * Call {@code #I} the number of incoming parameters (the value
4926 * {@code newType.parameterCount()}, and call {@code #O} the number
4927 * of outgoing parameters (the value {@code target.type().parameterCount()}).
4928 * Then the length of the reordering array must be {@code #O},
4929 * and each element must be a non-negative number less than {@code #I}.
4930 * For every {@code N} less than {@code #O}, the {@code N}-th
4931 * outgoing argument will be taken from the {@code I}-th incoming
4932 * argument, where {@code I} is {@code reorder[N]}.
4933 * <p>
4934 * No argument or return value conversions are applied.
4935 * The type of each incoming argument, as determined by {@code newType},
4936 * must be identical to the type of the corresponding outgoing parameter
4937 * or parameters in the target method handle.
4938 * The return type of {@code newType} must be identical to the return
4939 * type of the original target.
4940 * <p>
4941 * The reordering array need not specify an actual permutation.
4942 * An incoming argument will be duplicated if its index appears
4943 * more than once in the array, and an incoming argument will be dropped
4944 * if its index does not appear in the array.
4945 * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
4946 * incoming arguments which are not mentioned in the reordering array
4947 * may be of any type, as determined only by {@code newType}.
4948 * {@snippet lang="java" :
4949 import static java.lang.invoke.MethodHandles.*;
4950 import static java.lang.invoke.MethodType.*;
4951 ...
4952 MethodType intfn1 = methodType(int.class, int.class);
4953 MethodType intfn2 = methodType(int.class, int.class, int.class);
4954 MethodHandle sub = ... (int x, int y) -> (x-y) ...;
4955 assert(sub.type().equals(intfn2));
4956 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
4957 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
4958 assert((int)rsub.invokeExact(1, 100) == 99);
4959 MethodHandle add = ... (int x, int y) -> (x+y) ...;
4960 assert(add.type().equals(intfn2));
4961 MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
4962 assert(twice.type().equals(intfn1));
4963 assert((int)twice.invokeExact(21) == 42);
4964 * }
4965 * <p>
4966 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4967 * variable-arity method handle}, even if the original target method handle was.
4968 * @param target the method handle to invoke after arguments are reordered
4969 * @param newType the expected type of the new method handle
4970 * @param reorder an index array which controls the reordering
4971 * @return a method handle which delegates to the target after it
4972 * drops unused arguments and moves and/or duplicates the other arguments
4973 * @throws NullPointerException if any argument is null
4974 * @throws IllegalArgumentException if the index array length is not equal to
4975 * the arity of the target, or if any index array element
4976 * not a valid index for a parameter of {@code newType},
4977 * or if two corresponding parameter types in
4978 * {@code target.type()} and {@code newType} are not identical,
4979 */
4980 public static MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
4981 reorder = reorder.clone(); // get a private copy
4982 MethodType oldType = target.type();
4983 permuteArgumentChecks(reorder, newType, oldType);
4984 // first detect dropped arguments and handle them separately
4985 int[] originalReorder = reorder;
4986 BoundMethodHandle result = target.rebind();
4987 LambdaForm form = result.form;
4988 int newArity = newType.parameterCount();
4989 // Normalize the reordering into a real permutation,
4990 // by removing duplicates and adding dropped elements.
4991 // This somewhat improves lambda form caching, as well
4992 // as simplifying the transform by breaking it up into steps.
4993 for (int ddIdx; (ddIdx = findFirstDupOrDrop(reorder, newArity)) != 0; ) {
4994 if (ddIdx > 0) {
4995 // We found a duplicated entry at reorder[ddIdx].
4996 // Example: (x,y,z)->asList(x,y,z)
4997 // permuted by [1*,0,1] => (a0,a1)=>asList(a1,a0,a1)
4998 // permuted by [0,1,0*] => (a0,a1)=>asList(a0,a1,a0)
4999 // The starred element corresponds to the argument
5000 // deleted by the dupArgumentForm transform.
5001 int srcPos = ddIdx, dstPos = srcPos, dupVal = reorder[srcPos];
5002 boolean killFirst = false;
5003 for (int val; (val = reorder[--dstPos]) != dupVal; ) {
5004 // Set killFirst if the dup is larger than an intervening position.
5005 // This will remove at least one inversion from the permutation.
5006 if (dupVal > val) killFirst = true;
5007 }
5008 if (!killFirst) {
5009 srcPos = dstPos;
5010 dstPos = ddIdx;
5011 }
5012 form = form.editor().dupArgumentForm(1 + srcPos, 1 + dstPos);
5013 assert (reorder[srcPos] == reorder[dstPos]);
5014 oldType = oldType.dropParameterTypes(dstPos, dstPos + 1);
5015 // contract the reordering by removing the element at dstPos
5016 int tailPos = dstPos + 1;
5017 System.arraycopy(reorder, tailPos, reorder, dstPos, reorder.length - tailPos);
5018 reorder = Arrays.copyOf(reorder, reorder.length - 1);
5019 } else {
5020 int dropVal = ~ddIdx, insPos = 0;
5021 while (insPos < reorder.length && reorder[insPos] < dropVal) {
5022 // Find first element of reorder larger than dropVal.
5023 // This is where we will insert the dropVal.
5024 insPos += 1;
5025 }
5026 Class<?> ptype = newType.parameterType(dropVal);
5027 form = form.editor().addArgumentForm(1 + insPos, BasicType.basicType(ptype));
5028 oldType = oldType.insertParameterTypes(insPos, ptype);
5029 // expand the reordering by inserting an element at insPos
5030 int tailPos = insPos + 1;
5031 reorder = Arrays.copyOf(reorder, reorder.length + 1);
5032 System.arraycopy(reorder, insPos, reorder, tailPos, reorder.length - tailPos);
5033 reorder[insPos] = dropVal;
5034 }
5035 assert (permuteArgumentChecks(reorder, newType, oldType));
5036 }
5037 assert (reorder.length == newArity); // a perfect permutation
5038 // Note: This may cache too many distinct LFs. Consider backing off to varargs code.
5039 form = form.editor().permuteArgumentsForm(1, reorder);
5040 if (newType == result.type() && form == result.internalForm())
5041 return result;
5042 return result.copyWith(newType, form);
5043 }
5044
5045 /**
5046 * Return an indication of any duplicate or omission in reorder.
5047 * If the reorder contains a duplicate entry, return the index of the second occurrence.
5048 * Otherwise, return ~(n), for the first n in [0..newArity-1] that is not present in reorder.
5049 * Otherwise, return zero.
5050 * If an element not in [0..newArity-1] is encountered, return reorder.length.
5051 */
5052 private static int findFirstDupOrDrop(int[] reorder, int newArity) {
5053 final int BIT_LIMIT = 63; // max number of bits in bit mask
5054 if (newArity < BIT_LIMIT) {
5055 long mask = 0;
5056 for (int i = 0; i < reorder.length; i++) {
5057 int arg = reorder[i];
5058 if (arg >= newArity) {
5059 return reorder.length;
5060 }
5061 long bit = 1L << arg;
5062 if ((mask & bit) != 0) {
5063 return i; // >0 indicates a dup
5064 }
5065 mask |= bit;
5066 }
5067 if (mask == (1L << newArity) - 1) {
5068 assert(Long.numberOfTrailingZeros(Long.lowestOneBit(~mask)) == newArity);
5069 return 0;
5070 }
5071 // find first zero
5072 long zeroBit = Long.lowestOneBit(~mask);
5073 int zeroPos = Long.numberOfTrailingZeros(zeroBit);
5074 assert(zeroPos <= newArity);
5075 if (zeroPos == newArity) {
5076 return 0;
5077 }
5078 return ~zeroPos;
5079 } else {
5080 // same algorithm, different bit set
5081 BitSet mask = new BitSet(newArity);
5082 for (int i = 0; i < reorder.length; i++) {
5083 int arg = reorder[i];
5084 if (arg >= newArity) {
5085 return reorder.length;
5086 }
5087 if (mask.get(arg)) {
5088 return i; // >0 indicates a dup
5089 }
5090 mask.set(arg);
5091 }
5092 int zeroPos = mask.nextClearBit(0);
5093 assert(zeroPos <= newArity);
5094 if (zeroPos == newArity) {
5095 return 0;
5096 }
5097 return ~zeroPos;
5098 }
5099 }
5100
5101 static boolean permuteArgumentChecks(int[] reorder, MethodType newType, MethodType oldType) {
5102 if (newType.returnType() != oldType.returnType())
5103 throw newIllegalArgumentException("return types do not match",
5104 oldType, newType);
5105 if (reorder.length != oldType.parameterCount())
5106 throw newIllegalArgumentException("old type parameter count and reorder array length do not match",
5107 oldType, Arrays.toString(reorder));
5108
5109 int limit = newType.parameterCount();
5110 for (int j = 0; j < reorder.length; j++) {
5111 int i = reorder[j];
5112 if (i < 0 || i >= limit) {
5113 throw newIllegalArgumentException("index is out of bounds for new type",
5114 i, newType);
5115 }
5116 Class<?> src = newType.parameterType(i);
5117 Class<?> dst = oldType.parameterType(j);
5118 if (src != dst)
5119 throw newIllegalArgumentException("parameter types do not match after reorder",
5120 oldType, newType);
5121 }
5122 return true;
5123 }
5124
5125 /**
5126 * Produces a method handle of the requested return type which returns the given
5127 * constant value every time it is invoked.
5128 * <p>
5129 * Before the method handle is returned, the passed-in value is converted to the requested type.
5130 * If the requested type is primitive, widening primitive conversions are attempted,
5131 * else reference conversions are attempted.
5132 * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
5133 * @param type the return type of the desired method handle
5134 * @param value the value to return
5135 * @return a method handle of the given return type and no arguments, which always returns the given value
5136 * @throws NullPointerException if the {@code type} argument is null
5137 * @throws ClassCastException if the value cannot be converted to the required return type
5138 * @throws IllegalArgumentException if the given type is {@code void.class}
5139 */
5140 public static MethodHandle constant(Class<?> type, Object value) {
5141 if (type.isPrimitive()) {
5142 if (type == void.class)
5143 throw newIllegalArgumentException("void type");
5144 Wrapper w = Wrapper.forPrimitiveType(type);
5145 value = w.convert(value, type);
5146 if (w.zero().equals(value))
5147 return zero(w, type);
5148 return insertArguments(identity(type), 0, value);
5149 } else {
5150 if (value == null)
5151 return zero(Wrapper.OBJECT, type);
5152 return identity(type).bindTo(value);
5153 }
5154 }
5155
5156 /**
5157 * Produces a method handle which returns its sole argument when invoked.
5158 * @param type the type of the sole parameter and return value of the desired method handle
5159 * @return a unary method handle which accepts and returns the given type
5160 * @throws NullPointerException if the argument is null
5161 * @throws IllegalArgumentException if the given type is {@code void.class}
5162 */
5163 public static MethodHandle identity(Class<?> type) {
5164 Wrapper btw = (type.isPrimitive() ? Wrapper.forPrimitiveType(type) : Wrapper.OBJECT);
5165 int pos = btw.ordinal();
5166 MethodHandle ident = IDENTITY_MHS[pos];
5167 if (ident == null) {
5168 ident = setCachedMethodHandle(IDENTITY_MHS, pos, makeIdentity(btw.primitiveType()));
5169 }
5170 if (ident.type().returnType() == type)
5171 return ident;
5172 // something like identity(Foo.class); do not bother to intern these
5173 assert (btw == Wrapper.OBJECT);
5174 return makeIdentity(type);
5175 }
5176
5177 /**
5178 * Produces a constant method handle of the requested return type which
5179 * returns the default value for that type every time it is invoked.
5180 * The resulting constant method handle will have no side effects.
5181 * <p>The returned method handle is equivalent to {@code empty(methodType(type))}.
5182 * It is also equivalent to {@code explicitCastArguments(constant(Object.class, null), methodType(type))},
5183 * since {@code explicitCastArguments} converts {@code null} to default values.
5184 * @param type the expected return type of the desired method handle
5185 * @return a constant method handle that takes no arguments
5186 * and returns the default value of the given type (or void, if the type is void)
5187 * @throws NullPointerException if the argument is null
5188 * @see MethodHandles#constant
5189 * @see MethodHandles#empty
5190 * @see MethodHandles#explicitCastArguments
5191 * @since 9
5192 */
5193 public static MethodHandle zero(Class<?> type) {
5194 Objects.requireNonNull(type);
5195 return type.isPrimitive() ? zero(Wrapper.forPrimitiveType(type), type) : zero(Wrapper.OBJECT, type);
5196 }
5197
5198 private static MethodHandle identityOrVoid(Class<?> type) {
5199 return type == void.class ? zero(type) : identity(type);
5200 }
5201
5202 /**
5203 * Produces a method handle of the requested type which ignores any arguments, does nothing,
5204 * and returns a suitable default depending on the return type.
5205 * That is, it returns a zero primitive value, a {@code null}, or {@code void}.
5206 * <p>The returned method handle is equivalent to
5207 * {@code dropArguments(zero(type.returnType()), 0, type.parameterList())}.
5208 *
5209 * @apiNote Given a predicate and target, a useful "if-then" construct can be produced as
5210 * {@code guardWithTest(pred, target, empty(target.type())}.
5211 * @param type the type of the desired method handle
5212 * @return a constant method handle of the given type, which returns a default value of the given return type
5213 * @throws NullPointerException if the argument is null
5214 * @see MethodHandles#zero
5215 * @see MethodHandles#constant
5216 * @since 9
5217 */
5218 public static MethodHandle empty(MethodType type) {
5219 Objects.requireNonNull(type);
5220 return dropArgumentsTrusted(zero(type.returnType()), 0, type.ptypes());
5221 }
5222
5223 private static final MethodHandle[] IDENTITY_MHS = new MethodHandle[Wrapper.COUNT];
5224 private static MethodHandle makeIdentity(Class<?> ptype) {
5225 MethodType mtype = methodType(ptype, ptype);
5226 LambdaForm lform = LambdaForm.identityForm(BasicType.basicType(ptype));
5227 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.IDENTITY);
5228 }
5229
5230 private static MethodHandle zero(Wrapper btw, Class<?> rtype) {
5231 int pos = btw.ordinal();
5232 MethodHandle zero = ZERO_MHS[pos];
5233 if (zero == null) {
5234 zero = setCachedMethodHandle(ZERO_MHS, pos, makeZero(btw.primitiveType()));
5235 }
5236 if (zero.type().returnType() == rtype)
5237 return zero;
5238 assert(btw == Wrapper.OBJECT);
5239 return makeZero(rtype);
5240 }
5241 private static final MethodHandle[] ZERO_MHS = new MethodHandle[Wrapper.COUNT];
5242 private static MethodHandle makeZero(Class<?> rtype) {
5243 MethodType mtype = methodType(rtype);
5244 LambdaForm lform = LambdaForm.zeroForm(BasicType.basicType(rtype));
5245 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.ZERO);
5246 }
5247
5248 private static synchronized MethodHandle setCachedMethodHandle(MethodHandle[] cache, int pos, MethodHandle value) {
5249 // Simulate a CAS, to avoid racy duplication of results.
5250 MethodHandle prev = cache[pos];
5251 if (prev != null) return prev;
5252 return cache[pos] = value;
5253 }
5254
5255 /**
5256 * Provides a target method handle with one or more <em>bound arguments</em>
5257 * in advance of the method handle's invocation.
5258 * The formal parameters to the target corresponding to the bound
5259 * arguments are called <em>bound parameters</em>.
5260 * Returns a new method handle which saves away the bound arguments.
5261 * When it is invoked, it receives arguments for any non-bound parameters,
5262 * binds the saved arguments to their corresponding parameters,
5263 * and calls the original target.
5264 * <p>
5265 * The type of the new method handle will drop the types for the bound
5266 * parameters from the original target type, since the new method handle
5267 * will no longer require those arguments to be supplied by its callers.
5268 * <p>
5269 * Each given argument object must match the corresponding bound parameter type.
5270 * If a bound parameter type is a primitive, the argument object
5271 * must be a wrapper, and will be unboxed to produce the primitive value.
5272 * <p>
5273 * The {@code pos} argument selects which parameters are to be bound.
5274 * It may range between zero and <i>N-L</i> (inclusively),
5275 * where <i>N</i> is the arity of the target method handle
5276 * and <i>L</i> is the length of the values array.
5277 * <p>
5278 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5279 * variable-arity method handle}, even if the original target method handle was.
5280 * @param target the method handle to invoke after the argument is inserted
5281 * @param pos where to insert the argument (zero for the first)
5282 * @param values the series of arguments to insert
5283 * @return a method handle which inserts an additional argument,
5284 * before calling the original method handle
5285 * @throws NullPointerException if the target or the {@code values} array is null
5286 * @throws IllegalArgumentException if {@code pos} is less than {@code 0} or greater than
5287 * {@code N - L} where {@code N} is the arity of the target method handle and {@code L}
5288 * is the length of the values array.
5289 * @throws ClassCastException if an argument does not match the corresponding bound parameter
5290 * type.
5291 * @see MethodHandle#bindTo
5292 */
5293 public static MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
5294 int insCount = values.length;
5295 Class<?>[] ptypes = insertArgumentsChecks(target, insCount, pos);
5296 if (insCount == 0) return target;
5297 BoundMethodHandle result = target.rebind();
5298 for (int i = 0; i < insCount; i++) {
5299 Object value = values[i];
5300 Class<?> ptype = ptypes[pos+i];
5301 if (ptype.isPrimitive()) {
5302 result = insertArgumentPrimitive(result, pos, ptype, value);
5303 } else {
5304 value = ptype.cast(value); // throw CCE if needed
5305 result = result.bindArgumentL(pos, value);
5306 }
5307 }
5308 return result;
5309 }
5310
5311 private static BoundMethodHandle insertArgumentPrimitive(BoundMethodHandle result, int pos,
5312 Class<?> ptype, Object value) {
5313 Wrapper w = Wrapper.forPrimitiveType(ptype);
5314 // perform unboxing and/or primitive conversion
5315 value = w.convert(value, ptype);
5316 return switch (w) {
5317 case INT -> result.bindArgumentI(pos, (int) value);
5318 case LONG -> result.bindArgumentJ(pos, (long) value);
5319 case FLOAT -> result.bindArgumentF(pos, (float) value);
5320 case DOUBLE -> result.bindArgumentD(pos, (double) value);
5321 default -> result.bindArgumentI(pos, ValueConversions.widenSubword(value));
5322 };
5323 }
5324
5325 private static Class<?>[] insertArgumentsChecks(MethodHandle target, int insCount, int pos) throws RuntimeException {
5326 MethodType oldType = target.type();
5327 int outargs = oldType.parameterCount();
5328 int inargs = outargs - insCount;
5329 if (inargs < 0)
5330 throw newIllegalArgumentException("too many values to insert");
5331 if (pos < 0 || pos > inargs)
5332 throw newIllegalArgumentException("no argument type to append");
5333 return oldType.ptypes();
5334 }
5335
5336 /**
5337 * Produces a method handle which will discard some dummy arguments
5338 * before calling some other specified <i>target</i> method handle.
5339 * The type of the new method handle will be the same as the target's type,
5340 * except it will also include the dummy argument types,
5341 * at some given position.
5342 * <p>
5343 * The {@code pos} argument may range between zero and <i>N</i>,
5344 * where <i>N</i> is the arity of the target.
5345 * If {@code pos} is zero, the dummy arguments will precede
5346 * the target's real arguments; if {@code pos} is <i>N</i>
5347 * they will come after.
5348 * <p>
5349 * <b>Example:</b>
5350 * {@snippet lang="java" :
5351 import static java.lang.invoke.MethodHandles.*;
5352 import static java.lang.invoke.MethodType.*;
5353 ...
5354 MethodHandle cat = lookup().findVirtual(String.class,
5355 "concat", methodType(String.class, String.class));
5356 assertEquals("xy", (String) cat.invokeExact("x", "y"));
5357 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
5358 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
5359 assertEquals(bigType, d0.type());
5360 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
5361 * }
5362 * <p>
5363 * This method is also equivalent to the following code:
5364 * <blockquote><pre>
5365 * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))}
5366 * </pre></blockquote>
5367 * @param target the method handle to invoke after the arguments are dropped
5368 * @param pos position of first argument to drop (zero for the leftmost)
5369 * @param valueTypes the type(s) of the argument(s) to drop
5370 * @return a method handle which drops arguments of the given types,
5371 * before calling the original method handle
5372 * @throws NullPointerException if the target is null,
5373 * or if the {@code valueTypes} list or any of its elements is null
5374 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
5375 * or if {@code pos} is negative or greater than the arity of the target,
5376 * or if the new method handle's type would have too many parameters
5377 */
5378 public static MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) {
5379 return dropArgumentsTrusted(target, pos, valueTypes.toArray(new Class<?>[0]).clone());
5380 }
5381
5382 static MethodHandle dropArgumentsTrusted(MethodHandle target, int pos, Class<?>[] valueTypes) {
5383 MethodType oldType = target.type(); // get NPE
5384 int dropped = dropArgumentChecks(oldType, pos, valueTypes);
5385 MethodType newType = oldType.insertParameterTypes(pos, valueTypes);
5386 if (dropped == 0) return target;
5387 BoundMethodHandle result = target.rebind();
5388 LambdaForm lform = result.form;
5389 int insertFormArg = 1 + pos;
5390 for (Class<?> ptype : valueTypes) {
5391 lform = lform.editor().addArgumentForm(insertFormArg++, BasicType.basicType(ptype));
5392 }
5393 result = result.copyWith(newType, lform);
5394 return result;
5395 }
5396
5397 private static int dropArgumentChecks(MethodType oldType, int pos, Class<?>[] valueTypes) {
5398 int dropped = valueTypes.length;
5399 MethodType.checkSlotCount(dropped);
5400 int outargs = oldType.parameterCount();
5401 int inargs = outargs + dropped;
5402 if (pos < 0 || pos > outargs)
5403 throw newIllegalArgumentException("no argument type to remove"
5404 + Arrays.asList(oldType, pos, valueTypes, inargs, outargs)
5405 );
5406 return dropped;
5407 }
5408
5409 /**
5410 * Produces a method handle which will discard some dummy arguments
5411 * before calling some other specified <i>target</i> method handle.
5412 * The type of the new method handle will be the same as the target's type,
5413 * except it will also include the dummy argument types,
5414 * at some given position.
5415 * <p>
5416 * The {@code pos} argument may range between zero and <i>N</i>,
5417 * where <i>N</i> is the arity of the target.
5418 * If {@code pos} is zero, the dummy arguments will precede
5419 * the target's real arguments; if {@code pos} is <i>N</i>
5420 * they will come after.
5421 * @apiNote
5422 * {@snippet lang="java" :
5423 import static java.lang.invoke.MethodHandles.*;
5424 import static java.lang.invoke.MethodType.*;
5425 ...
5426 MethodHandle cat = lookup().findVirtual(String.class,
5427 "concat", methodType(String.class, String.class));
5428 assertEquals("xy", (String) cat.invokeExact("x", "y"));
5429 MethodHandle d0 = dropArguments(cat, 0, String.class);
5430 assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
5431 MethodHandle d1 = dropArguments(cat, 1, String.class);
5432 assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
5433 MethodHandle d2 = dropArguments(cat, 2, String.class);
5434 assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
5435 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
5436 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
5437 * }
5438 * <p>
5439 * This method is also equivalent to the following code:
5440 * <blockquote><pre>
5441 * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))}
5442 * </pre></blockquote>
5443 * @param target the method handle to invoke after the arguments are dropped
5444 * @param pos position of first argument to drop (zero for the leftmost)
5445 * @param valueTypes the type(s) of the argument(s) to drop
5446 * @return a method handle which drops arguments of the given types,
5447 * before calling the original method handle
5448 * @throws NullPointerException if the target is null,
5449 * or if the {@code valueTypes} array or any of its elements is null
5450 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
5451 * or if {@code pos} is negative or greater than the arity of the target,
5452 * or if the new method handle's type would have
5453 * <a href="MethodHandle.html#maxarity">too many parameters</a>
5454 */
5455 public static MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
5456 return dropArgumentsTrusted(target, pos, valueTypes.clone());
5457 }
5458
5459 /* Convenience overloads for trusting internal low-arity call-sites */
5460 static MethodHandle dropArguments(MethodHandle target, int pos, Class<?> valueType1) {
5461 return dropArgumentsTrusted(target, pos, new Class<?>[] { valueType1 });
5462 }
5463 static MethodHandle dropArguments(MethodHandle target, int pos, Class<?> valueType1, Class<?> valueType2) {
5464 return dropArgumentsTrusted(target, pos, new Class<?>[] { valueType1, valueType2 });
5465 }
5466
5467 // private version which allows caller some freedom with error handling
5468 private static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, Class<?>[] newTypes, int pos,
5469 boolean nullOnFailure) {
5470 Class<?>[] oldTypes = target.type().ptypes();
5471 int match = oldTypes.length;
5472 if (skip != 0) {
5473 if (skip < 0 || skip > match) {
5474 throw newIllegalArgumentException("illegal skip", skip, target);
5475 }
5476 oldTypes = Arrays.copyOfRange(oldTypes, skip, match);
5477 match -= skip;
5478 }
5479 Class<?>[] addTypes = newTypes;
5480 int add = addTypes.length;
5481 if (pos != 0) {
5482 if (pos < 0 || pos > add) {
5483 throw newIllegalArgumentException("illegal pos", pos, Arrays.toString(newTypes));
5484 }
5485 addTypes = Arrays.copyOfRange(addTypes, pos, add);
5486 add -= pos;
5487 assert(addTypes.length == add);
5488 }
5489 // Do not add types which already match the existing arguments.
5490 if (match > add || !Arrays.equals(oldTypes, 0, oldTypes.length, addTypes, 0, match)) {
5491 if (nullOnFailure) {
5492 return null;
5493 }
5494 throw newIllegalArgumentException("argument lists do not match",
5495 Arrays.toString(oldTypes), Arrays.toString(newTypes));
5496 }
5497 addTypes = Arrays.copyOfRange(addTypes, match, add);
5498 add -= match;
5499 assert(addTypes.length == add);
5500 // newTypes: ( P*[pos], M*[match], A*[add] )
5501 // target: ( S*[skip], M*[match] )
5502 MethodHandle adapter = target;
5503 if (add > 0) {
5504 adapter = dropArgumentsTrusted(adapter, skip+ match, addTypes);
5505 }
5506 // adapter: (S*[skip], M*[match], A*[add] )
5507 if (pos > 0) {
5508 adapter = dropArgumentsTrusted(adapter, skip, Arrays.copyOfRange(newTypes, 0, pos));
5509 }
5510 // adapter: (S*[skip], P*[pos], M*[match], A*[add] )
5511 return adapter;
5512 }
5513
5514 /**
5515 * Adapts a target method handle to match the given parameter type list. If necessary, adds dummy arguments. Some
5516 * leading parameters can be skipped before matching begins. The remaining types in the {@code target}'s parameter
5517 * type list must be a sub-list of the {@code newTypes} type list at the starting position {@code pos}. The
5518 * resulting handle will have the target handle's parameter type list, with any non-matching parameter types (before
5519 * or after the matching sub-list) inserted in corresponding positions of the target's original parameters, as if by
5520 * {@link #dropArguments(MethodHandle, int, Class[])}.
5521 * <p>
5522 * The resulting handle will have the same return type as the target handle.
5523 * <p>
5524 * In more formal terms, assume these two type lists:<ul>
5525 * <li>The target handle has the parameter type list {@code S..., M...}, with as many types in {@code S} as
5526 * indicated by {@code skip}. The {@code M} types are those that are supposed to match part of the given type list,
5527 * {@code newTypes}.
5528 * <li>The {@code newTypes} list contains types {@code P..., M..., A...}, with as many types in {@code P} as
5529 * indicated by {@code pos}. The {@code M} types are precisely those that the {@code M} types in the target handle's
5530 * parameter type list are supposed to match. The types in {@code A} are additional types found after the matching
5531 * sub-list.
5532 * </ul>
5533 * Given these assumptions, the result of an invocation of {@code dropArgumentsToMatch} will have the parameter type
5534 * list {@code S..., P..., M..., A...}, with the {@code P} and {@code A} types inserted as if by
5535 * {@link #dropArguments(MethodHandle, int, Class[])}.
5536 *
5537 * @apiNote
5538 * Two method handles whose argument lists are "effectively identical" (i.e., identical in a common prefix) may be
5539 * mutually converted to a common type by two calls to {@code dropArgumentsToMatch}, as follows:
5540 * {@snippet lang="java" :
5541 import static java.lang.invoke.MethodHandles.*;
5542 import static java.lang.invoke.MethodType.*;
5543 ...
5544 ...
5545 MethodHandle h0 = constant(boolean.class, true);
5546 MethodHandle h1 = lookup().findVirtual(String.class, "concat", methodType(String.class, String.class));
5547 MethodType bigType = h1.type().insertParameterTypes(1, String.class, int.class);
5548 MethodHandle h2 = dropArguments(h1, 0, bigType.parameterList());
5549 if (h1.type().parameterCount() < h2.type().parameterCount())
5550 h1 = dropArgumentsToMatch(h1, 0, h2.type().parameterList(), 0); // lengthen h1
5551 else
5552 h2 = dropArgumentsToMatch(h2, 0, h1.type().parameterList(), 0); // lengthen h2
5553 MethodHandle h3 = guardWithTest(h0, h1, h2);
5554 assertEquals("xy", h3.invoke("x", "y", 1, "a", "b", "c"));
5555 * }
5556 * @param target the method handle to adapt
5557 * @param skip number of targets parameters to disregard (they will be unchanged)
5558 * @param newTypes the list of types to match {@code target}'s parameter type list to
5559 * @param pos place in {@code newTypes} where the non-skipped target parameters must occur
5560 * @return a possibly adapted method handle
5561 * @throws NullPointerException if either argument is null
5562 * @throws IllegalArgumentException if any element of {@code newTypes} is {@code void.class},
5563 * or if {@code skip} is negative or greater than the arity of the target,
5564 * or if {@code pos} is negative or greater than the newTypes list size,
5565 * or if {@code newTypes} does not contain the {@code target}'s non-skipped parameter types at position
5566 * {@code pos}.
5567 * @since 9
5568 */
5569 public static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos) {
5570 Objects.requireNonNull(target);
5571 Objects.requireNonNull(newTypes);
5572 return dropArgumentsToMatch(target, skip, newTypes.toArray(new Class<?>[0]).clone(), pos, false);
5573 }
5574
5575 /**
5576 * Drop the return value of the target handle (if any).
5577 * The returned method handle will have a {@code void} return type.
5578 *
5579 * @param target the method handle to adapt
5580 * @return a possibly adapted method handle
5581 * @throws NullPointerException if {@code target} is null
5582 * @since 16
5583 */
5584 public static MethodHandle dropReturn(MethodHandle target) {
5585 Objects.requireNonNull(target);
5586 MethodType oldType = target.type();
5587 Class<?> oldReturnType = oldType.returnType();
5588 if (oldReturnType == void.class)
5589 return target;
5590 MethodType newType = oldType.changeReturnType(void.class);
5591 BoundMethodHandle result = target.rebind();
5592 LambdaForm lform = result.editor().filterReturnForm(V_TYPE, true);
5593 result = result.copyWith(newType, lform);
5594 return result;
5595 }
5596
5597 /**
5598 * Adapts a target method handle by pre-processing
5599 * one or more of its arguments, each with its own unary filter function,
5600 * and then calling the target with each pre-processed argument
5601 * replaced by the result of its corresponding filter function.
5602 * <p>
5603 * The pre-processing is performed by one or more method handles,
5604 * specified in the elements of the {@code filters} array.
5605 * The first element of the filter array corresponds to the {@code pos}
5606 * argument of the target, and so on in sequence.
5607 * The filter functions are invoked in left to right order.
5608 * <p>
5609 * Null arguments in the array are treated as identity functions,
5610 * and the corresponding arguments left unchanged.
5611 * (If there are no non-null elements in the array, the original target is returned.)
5612 * Each filter is applied to the corresponding argument of the adapter.
5613 * <p>
5614 * If a filter {@code F} applies to the {@code N}th argument of
5615 * the target, then {@code F} must be a method handle which
5616 * takes exactly one argument. The type of {@code F}'s sole argument
5617 * replaces the corresponding argument type of the target
5618 * in the resulting adapted method handle.
5619 * The return type of {@code F} must be identical to the corresponding
5620 * parameter type of the target.
5621 * <p>
5622 * It is an error if there are elements of {@code filters}
5623 * (null or not)
5624 * which do not correspond to argument positions in the target.
5625 * <p><b>Example:</b>
5626 * {@snippet lang="java" :
5627 import static java.lang.invoke.MethodHandles.*;
5628 import static java.lang.invoke.MethodType.*;
5629 ...
5630 MethodHandle cat = lookup().findVirtual(String.class,
5631 "concat", methodType(String.class, String.class));
5632 MethodHandle upcase = lookup().findVirtual(String.class,
5633 "toUpperCase", methodType(String.class));
5634 assertEquals("xy", (String) cat.invokeExact("x", "y"));
5635 MethodHandle f0 = filterArguments(cat, 0, upcase);
5636 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
5637 MethodHandle f1 = filterArguments(cat, 1, upcase);
5638 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
5639 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
5640 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
5641 * }
5642 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
5643 * denotes the return type of both the {@code target} and resulting adapter.
5644 * {@code P}/{@code p} and {@code B}/{@code b} represent the types and values
5645 * of the parameters and arguments that precede and follow the filter position
5646 * {@code pos}, respectively. {@code A[i]}/{@code a[i]} stand for the types and
5647 * values of the filtered parameters and arguments; they also represent the
5648 * return types of the {@code filter[i]} handles. The latter accept arguments
5649 * {@code v[i]} of type {@code V[i]}, which also appear in the signature of
5650 * the resulting adapter.
5651 * {@snippet lang="java" :
5652 * T target(P... p, A[i]... a[i], B... b);
5653 * A[i] filter[i](V[i]);
5654 * T adapter(P... p, V[i]... v[i], B... b) {
5655 * return target(p..., filter[i](v[i])..., b...);
5656 * }
5657 * }
5658 * <p>
5659 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5660 * variable-arity method handle}, even if the original target method handle was.
5661 *
5662 * @param target the method handle to invoke after arguments are filtered
5663 * @param pos the position of the first argument to filter
5664 * @param filters method handles to call initially on filtered arguments
5665 * @return method handle which incorporates the specified argument filtering logic
5666 * @throws NullPointerException if the target is null
5667 * or if the {@code filters} array is null
5668 * @throws IllegalArgumentException if a non-null element of {@code filters}
5669 * does not match a corresponding argument type of target as described above,
5670 * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()},
5671 * or if the resulting method handle's type would have
5672 * <a href="MethodHandle.html#maxarity">too many parameters</a>
5673 */
5674 public static MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
5675 // In method types arguments start at index 0, while the LF
5676 // editor have the MH receiver at position 0 - adjust appropriately.
5677 final int MH_RECEIVER_OFFSET = 1;
5678 filterArgumentsCheckArity(target, pos, filters);
5679 MethodHandle adapter = target;
5680
5681 // keep track of currently matched filters, as to optimize repeated filters
5682 int index = 0;
5683 int[] positions = new int[filters.length];
5684 MethodHandle filter = null;
5685
5686 // process filters in reverse order so that the invocation of
5687 // the resulting adapter will invoke the filters in left-to-right order
5688 for (int i = filters.length - 1; i >= 0; --i) {
5689 MethodHandle newFilter = filters[i];
5690 if (newFilter == null) continue; // ignore null elements of filters
5691
5692 // flush changes on update
5693 if (filter != newFilter) {
5694 if (filter != null) {
5695 if (index > 1) {
5696 adapter = filterRepeatedArgument(adapter, filter, Arrays.copyOf(positions, index));
5697 } else {
5698 adapter = filterArgument(adapter, positions[0] - 1, filter);
5699 }
5700 }
5701 filter = newFilter;
5702 index = 0;
5703 }
5704
5705 filterArgumentChecks(target, pos + i, newFilter);
5706 positions[index++] = pos + i + MH_RECEIVER_OFFSET;
5707 }
5708 if (index > 1) {
5709 adapter = filterRepeatedArgument(adapter, filter, Arrays.copyOf(positions, index));
5710 } else if (index == 1) {
5711 adapter = filterArgument(adapter, positions[0] - 1, filter);
5712 }
5713 return adapter;
5714 }
5715
5716 private static MethodHandle filterRepeatedArgument(MethodHandle adapter, MethodHandle filter, int[] positions) {
5717 MethodType targetType = adapter.type();
5718 MethodType filterType = filter.type();
5719 BoundMethodHandle result = adapter.rebind();
5720 Class<?> newParamType = filterType.parameterType(0);
5721
5722 Class<?>[] ptypes = targetType.ptypes().clone();
5723 for (int pos : positions) {
5724 ptypes[pos - 1] = newParamType;
5725 }
5726 MethodType newType = MethodType.methodType(targetType.rtype(), ptypes, true);
5727
5728 LambdaForm lform = result.editor().filterRepeatedArgumentForm(BasicType.basicType(newParamType), positions);
5729 return result.copyWithExtendL(newType, lform, filter);
5730 }
5731
5732 /*non-public*/
5733 static MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
5734 filterArgumentChecks(target, pos, filter);
5735 MethodType targetType = target.type();
5736 MethodType filterType = filter.type();
5737 BoundMethodHandle result = target.rebind();
5738 Class<?> newParamType = filterType.parameterType(0);
5739 LambdaForm lform = result.editor().filterArgumentForm(1 + pos, BasicType.basicType(newParamType));
5740 MethodType newType = targetType.changeParameterType(pos, newParamType);
5741 result = result.copyWithExtendL(newType, lform, filter);
5742 return result;
5743 }
5744
5745 private static void filterArgumentsCheckArity(MethodHandle target, int pos, MethodHandle[] filters) {
5746 MethodType targetType = target.type();
5747 int maxPos = targetType.parameterCount();
5748 if (pos + filters.length > maxPos)
5749 throw newIllegalArgumentException("too many filters");
5750 }
5751
5752 private static void filterArgumentChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
5753 MethodType targetType = target.type();
5754 MethodType filterType = filter.type();
5755 if (filterType.parameterCount() != 1
5756 || filterType.returnType() != targetType.parameterType(pos))
5757 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
5758 }
5759
5760 /**
5761 * Adapts a target method handle by pre-processing
5762 * a sub-sequence of its arguments with a filter (another method handle).
5763 * The pre-processed arguments are replaced by the result (if any) of the
5764 * filter function.
5765 * The target is then called on the modified (usually shortened) argument list.
5766 * <p>
5767 * If the filter returns a value, the target must accept that value as
5768 * its argument in position {@code pos}, preceded and/or followed by
5769 * any arguments not passed to the filter.
5770 * If the filter returns void, the target must accept all arguments
5771 * not passed to the filter.
5772 * No arguments are reordered, and a result returned from the filter
5773 * replaces (in order) the whole subsequence of arguments originally
5774 * passed to the adapter.
5775 * <p>
5776 * The argument types (if any) of the filter
5777 * replace zero or one argument types of the target, at position {@code pos},
5778 * in the resulting adapted method handle.
5779 * The return type of the filter (if any) must be identical to the
5780 * argument type of the target at position {@code pos}, and that target argument
5781 * is supplied by the return value of the filter.
5782 * <p>
5783 * In all cases, {@code pos} must be greater than or equal to zero, and
5784 * {@code pos} must also be less than or equal to the target's arity.
5785 * <p><b>Example:</b>
5786 * {@snippet lang="java" :
5787 import static java.lang.invoke.MethodHandles.*;
5788 import static java.lang.invoke.MethodType.*;
5789 ...
5790 MethodHandle deepToString = publicLookup()
5791 .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
5792
5793 MethodHandle ts1 = deepToString.asCollector(String[].class, 1);
5794 assertEquals("[strange]", (String) ts1.invokeExact("strange"));
5795
5796 MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
5797 assertEquals("[up, down]", (String) ts2.invokeExact("up", "down"));
5798
5799 MethodHandle ts3 = deepToString.asCollector(String[].class, 3);
5800 MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2);
5801 assertEquals("[top, [up, down], strange]",
5802 (String) ts3_ts2.invokeExact("top", "up", "down", "strange"));
5803
5804 MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1);
5805 assertEquals("[top, [up, down], [strange]]",
5806 (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange"));
5807
5808 MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3);
5809 assertEquals("[top, [[up, down, strange], charm], bottom]",
5810 (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom"));
5811 * }
5812 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
5813 * represents the return type of the {@code target} and resulting adapter.
5814 * {@code V}/{@code v} stand for the return type and value of the
5815 * {@code filter}, which are also found in the signature and arguments of
5816 * the {@code target}, respectively, unless {@code V} is {@code void}.
5817 * {@code A}/{@code a} and {@code C}/{@code c} represent the parameter types
5818 * and values preceding and following the collection position, {@code pos},
5819 * in the {@code target}'s signature. They also turn up in the resulting
5820 * adapter's signature and arguments, where they surround
5821 * {@code B}/{@code b}, which represent the parameter types and arguments
5822 * to the {@code filter} (if any).
5823 * {@snippet lang="java" :
5824 * T target(A...,V,C...);
5825 * V filter(B...);
5826 * T adapter(A... a,B... b,C... c) {
5827 * V v = filter(b...);
5828 * return target(a...,v,c...);
5829 * }
5830 * // and if the filter has no arguments:
5831 * T target2(A...,V,C...);
5832 * V filter2();
5833 * T adapter2(A... a,C... c) {
5834 * V v = filter2();
5835 * return target2(a...,v,c...);
5836 * }
5837 * // and if the filter has a void return:
5838 * T target3(A...,C...);
5839 * void filter3(B...);
5840 * T adapter3(A... a,B... b,C... c) {
5841 * filter3(b...);
5842 * return target3(a...,c...);
5843 * }
5844 * }
5845 * <p>
5846 * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to
5847 * one which first "folds" the affected arguments, and then drops them, in separate
5848 * steps as follows:
5849 * {@snippet lang="java" :
5850 * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2
5851 * mh = MethodHandles.foldArguments(mh, coll); //step 1
5852 * }
5853 * If the target method handle consumes no arguments besides than the result
5854 * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)}
5855 * is equivalent to {@code filterReturnValue(coll, mh)}.
5856 * If the filter method handle {@code coll} consumes one argument and produces
5857 * a non-void result, then {@code collectArguments(mh, N, coll)}
5858 * is equivalent to {@code filterArguments(mh, N, coll)}.
5859 * Other equivalences are possible but would require argument permutation.
5860 * <p>
5861 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5862 * variable-arity method handle}, even if the original target method handle was.
5863 *
5864 * @param target the method handle to invoke after filtering the subsequence of arguments
5865 * @param pos the position of the first adapter argument to pass to the filter,
5866 * and/or the target argument which receives the result of the filter
5867 * @param filter method handle to call on the subsequence of arguments
5868 * @return method handle which incorporates the specified argument subsequence filtering logic
5869 * @throws NullPointerException if either argument is null
5870 * @throws IllegalArgumentException if the return type of {@code filter}
5871 * is non-void and is not the same as the {@code pos} argument of the target,
5872 * or if {@code pos} is not between 0 and the target's arity, inclusive,
5873 * or if the resulting method handle's type would have
5874 * <a href="MethodHandle.html#maxarity">too many parameters</a>
5875 * @see MethodHandles#foldArguments
5876 * @see MethodHandles#filterArguments
5877 * @see MethodHandles#filterReturnValue
5878 */
5879 public static MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) {
5880 MethodType newType = collectArgumentsChecks(target, pos, filter);
5881 MethodType collectorType = filter.type();
5882 BoundMethodHandle result = target.rebind();
5883 LambdaForm lform = result.editor().collectArgumentsForm(1 + pos, collectorType.basicType());
5884 return result.copyWithExtendL(newType, lform, filter);
5885 }
5886
5887 private static MethodType collectArgumentsChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
5888 MethodType targetType = target.type();
5889 MethodType filterType = filter.type();
5890 Class<?> rtype = filterType.returnType();
5891 Class<?>[] filterArgs = filterType.ptypes();
5892 if (pos < 0 || (rtype == void.class && pos > targetType.parameterCount()) ||
5893 (rtype != void.class && pos >= targetType.parameterCount())) {
5894 throw newIllegalArgumentException("position is out of range for target", target, pos);
5895 }
5896 if (rtype == void.class) {
5897 return targetType.insertParameterTypes(pos, filterArgs);
5898 }
5899 if (rtype != targetType.parameterType(pos)) {
5900 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
5901 }
5902 return targetType.dropParameterTypes(pos, pos + 1).insertParameterTypes(pos, filterArgs);
5903 }
5904
5905 /**
5906 * Adapts a target method handle by post-processing
5907 * its return value (if any) with a filter (another method handle).
5908 * The result of the filter is returned from the adapter.
5909 * <p>
5910 * If the target returns a value, the filter must accept that value as
5911 * its only argument.
5912 * If the target returns void, the filter must accept no arguments.
5913 * <p>
5914 * The return type of the filter
5915 * replaces the return type of the target
5916 * in the resulting adapted method handle.
5917 * The argument type of the filter (if any) must be identical to the
5918 * return type of the target.
5919 * <p><b>Example:</b>
5920 * {@snippet lang="java" :
5921 import static java.lang.invoke.MethodHandles.*;
5922 import static java.lang.invoke.MethodType.*;
5923 ...
5924 MethodHandle cat = lookup().findVirtual(String.class,
5925 "concat", methodType(String.class, String.class));
5926 MethodHandle length = lookup().findVirtual(String.class,
5927 "length", methodType(int.class));
5928 System.out.println((String) cat.invokeExact("x", "y")); // xy
5929 MethodHandle f0 = filterReturnValue(cat, length);
5930 System.out.println((int) f0.invokeExact("x", "y")); // 2
5931 * }
5932 * <p>Here is pseudocode for the resulting adapter. In the code,
5933 * {@code T}/{@code t} represent the result type and value of the
5934 * {@code target}; {@code V}, the result type of the {@code filter}; and
5935 * {@code A}/{@code a}, the types and values of the parameters and arguments
5936 * of the {@code target} as well as the resulting adapter.
5937 * {@snippet lang="java" :
5938 * T target(A...);
5939 * V filter(T);
5940 * V adapter(A... a) {
5941 * T t = target(a...);
5942 * return filter(t);
5943 * }
5944 * // and if the target has a void return:
5945 * void target2(A...);
5946 * V filter2();
5947 * V adapter2(A... a) {
5948 * target2(a...);
5949 * return filter2();
5950 * }
5951 * // and if the filter has a void return:
5952 * T target3(A...);
5953 * void filter3(V);
5954 * void adapter3(A... a) {
5955 * T t = target3(a...);
5956 * filter3(t);
5957 * }
5958 * }
5959 * <p>
5960 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5961 * variable-arity method handle}, even if the original target method handle was.
5962 * @param target the method handle to invoke before filtering the return value
5963 * @param filter method handle to call on the return value
5964 * @return method handle which incorporates the specified return value filtering logic
5965 * @throws NullPointerException if either argument is null
5966 * @throws IllegalArgumentException if the argument list of {@code filter}
5967 * does not match the return type of target as described above
5968 */
5969 public static MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
5970 MethodType targetType = target.type();
5971 MethodType filterType = filter.type();
5972 filterReturnValueChecks(targetType, filterType);
5973 BoundMethodHandle result = target.rebind();
5974 BasicType rtype = BasicType.basicType(filterType.returnType());
5975 LambdaForm lform = result.editor().filterReturnForm(rtype, false);
5976 MethodType newType = targetType.changeReturnType(filterType.returnType());
5977 result = result.copyWithExtendL(newType, lform, filter);
5978 return result;
5979 }
5980
5981 private static void filterReturnValueChecks(MethodType targetType, MethodType filterType) throws RuntimeException {
5982 Class<?> rtype = targetType.returnType();
5983 int filterValues = filterType.parameterCount();
5984 if (filterValues == 0
5985 ? (rtype != void.class)
5986 : (rtype != filterType.parameterType(0) || filterValues != 1))
5987 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
5988 }
5989
5990 /**
5991 * Filter the return value of a target method handle with a filter function. The filter function is
5992 * applied to the return value of the original handle; if the filter specifies more than one parameters,
5993 * then any remaining parameter is appended to the adapter handle. In other words, the adaptation works
5994 * as follows:
5995 * {@snippet lang="java" :
5996 * T target(A...)
5997 * V filter(B... , T)
5998 * V adapter(A... a, B... b) {
5999 * T t = target(a...);
6000 * return filter(b..., t);
6001 * }
6002 * }
6003 * <p>
6004 * If the filter handle is a unary function, then this method behaves like {@link #filterReturnValue(MethodHandle, MethodHandle)}.
6005 *
6006 * @param target the target method handle
6007 * @param filter the filter method handle
6008 * @return the adapter method handle
6009 */
6010 /* package */ static MethodHandle collectReturnValue(MethodHandle target, MethodHandle filter) {
6011 MethodType targetType = target.type();
6012 MethodType filterType = filter.type();
6013 BoundMethodHandle result = target.rebind();
6014 LambdaForm lform = result.editor().collectReturnValueForm(filterType.basicType());
6015 MethodType newType = targetType.changeReturnType(filterType.returnType());
6016 if (filterType.parameterCount() > 1) {
6017 for (int i = 0 ; i < filterType.parameterCount() - 1 ; i++) {
6018 newType = newType.appendParameterTypes(filterType.parameterType(i));
6019 }
6020 }
6021 result = result.copyWithExtendL(newType, lform, filter);
6022 return result;
6023 }
6024
6025 /**
6026 * Adapts a target method handle by pre-processing
6027 * some of its arguments, and then calling the target with
6028 * the result of the pre-processing, inserted into the original
6029 * sequence of arguments.
6030 * <p>
6031 * The pre-processing is performed by {@code combiner}, a second method handle.
6032 * Of the arguments passed to the adapter, the first {@code N} arguments
6033 * are copied to the combiner, which is then called.
6034 * (Here, {@code N} is defined as the parameter count of the combiner.)
6035 * After this, control passes to the target, with any result
6036 * from the combiner inserted before the original {@code N} incoming
6037 * arguments.
6038 * <p>
6039 * If the combiner returns a value, the first parameter type of the target
6040 * must be identical with the return type of the combiner, and the next
6041 * {@code N} parameter types of the target must exactly match the parameters
6042 * of the combiner.
6043 * <p>
6044 * If the combiner has a void return, no result will be inserted,
6045 * and the first {@code N} parameter types of the target
6046 * must exactly match the parameters of the combiner.
6047 * <p>
6048 * The resulting adapter is the same type as the target, except that the
6049 * first parameter type is dropped,
6050 * if it corresponds to the result of the combiner.
6051 * <p>
6052 * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
6053 * that either the combiner or the target does not wish to receive.
6054 * If some of the incoming arguments are destined only for the combiner,
6055 * consider using {@link MethodHandle#asCollector asCollector} instead, since those
6056 * arguments will not need to be live on the stack on entry to the
6057 * target.)
6058 * <p><b>Example:</b>
6059 * {@snippet lang="java" :
6060 import static java.lang.invoke.MethodHandles.*;
6061 import static java.lang.invoke.MethodType.*;
6062 ...
6063 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
6064 "println", methodType(void.class, String.class))
6065 .bindTo(System.out);
6066 MethodHandle cat = lookup().findVirtual(String.class,
6067 "concat", methodType(String.class, String.class));
6068 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
6069 MethodHandle catTrace = foldArguments(cat, trace);
6070 // also prints "boo":
6071 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
6072 * }
6073 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
6074 * represents the result type of the {@code target} and resulting adapter.
6075 * {@code V}/{@code v} represent the type and value of the parameter and argument
6076 * of {@code target} that precedes the folding position; {@code V} also is
6077 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
6078 * types and values of the {@code N} parameters and arguments at the folding
6079 * position. {@code B}/{@code b} represent the types and values of the
6080 * {@code target} parameters and arguments that follow the folded parameters
6081 * and arguments.
6082 * {@snippet lang="java" :
6083 * // there are N arguments in A...
6084 * T target(V, A[N]..., B...);
6085 * V combiner(A...);
6086 * T adapter(A... a, B... b) {
6087 * V v = combiner(a...);
6088 * return target(v, a..., b...);
6089 * }
6090 * // and if the combiner has a void return:
6091 * T target2(A[N]..., B...);
6092 * void combiner2(A...);
6093 * T adapter2(A... a, B... b) {
6094 * combiner2(a...);
6095 * return target2(a..., b...);
6096 * }
6097 * }
6098 * <p>
6099 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
6100 * variable-arity method handle}, even if the original target method handle was.
6101 * @param target the method handle to invoke after arguments are combined
6102 * @param combiner method handle to call initially on the incoming arguments
6103 * @return method handle which incorporates the specified argument folding logic
6104 * @throws NullPointerException if either argument is null
6105 * @throws IllegalArgumentException if {@code combiner}'s return type
6106 * is non-void and not the same as the first argument type of
6107 * the target, or if the initial {@code N} argument types
6108 * of the target
6109 * (skipping one matching the {@code combiner}'s return type)
6110 * are not identical with the argument types of {@code combiner}
6111 */
6112 public static MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
6113 return foldArguments(target, 0, combiner);
6114 }
6115
6116 /**
6117 * Adapts a target method handle by pre-processing some of its arguments, starting at a given position, and then
6118 * calling the target with the result of the pre-processing, inserted into the original sequence of arguments just
6119 * before the folded arguments.
6120 * <p>
6121 * This method is closely related to {@link #foldArguments(MethodHandle, MethodHandle)}, but allows to control the
6122 * position in the parameter list at which folding takes place. The argument controlling this, {@code pos}, is a
6123 * zero-based index. The aforementioned method {@link #foldArguments(MethodHandle, MethodHandle)} assumes position
6124 * 0.
6125 *
6126 * @apiNote Example:
6127 * {@snippet lang="java" :
6128 import static java.lang.invoke.MethodHandles.*;
6129 import static java.lang.invoke.MethodType.*;
6130 ...
6131 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
6132 "println", methodType(void.class, String.class))
6133 .bindTo(System.out);
6134 MethodHandle cat = lookup().findVirtual(String.class,
6135 "concat", methodType(String.class, String.class));
6136 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
6137 MethodHandle catTrace = foldArguments(cat, 1, trace);
6138 // also prints "jum":
6139 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
6140 * }
6141 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
6142 * represents the result type of the {@code target} and resulting adapter.
6143 * {@code V}/{@code v} represent the type and value of the parameter and argument
6144 * of {@code target} that precedes the folding position; {@code V} also is
6145 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
6146 * types and values of the {@code N} parameters and arguments at the folding
6147 * position. {@code Z}/{@code z} and {@code B}/{@code b} represent the types
6148 * and values of the {@code target} parameters and arguments that precede and
6149 * follow the folded parameters and arguments starting at {@code pos},
6150 * respectively.
6151 * {@snippet lang="java" :
6152 * // there are N arguments in A...
6153 * T target(Z..., V, A[N]..., B...);
6154 * V combiner(A...);
6155 * T adapter(Z... z, A... a, B... b) {
6156 * V v = combiner(a...);
6157 * return target(z..., v, a..., b...);
6158 * }
6159 * // and if the combiner has a void return:
6160 * T target2(Z..., A[N]..., B...);
6161 * void combiner2(A...);
6162 * T adapter2(Z... z, A... a, B... b) {
6163 * combiner2(a...);
6164 * return target2(z..., a..., b...);
6165 * }
6166 * }
6167 * <p>
6168 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
6169 * variable-arity method handle}, even if the original target method handle was.
6170 *
6171 * @param target the method handle to invoke after arguments are combined
6172 * @param pos the position at which to start folding and at which to insert the folding result; if this is {@code
6173 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
6174 * @param combiner method handle to call initially on the incoming arguments
6175 * @return method handle which incorporates the specified argument folding logic
6176 * @throws NullPointerException if either argument is null
6177 * @throws IllegalArgumentException if either of the following two conditions holds:
6178 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
6179 * {@code pos} of the target signature;
6180 * (2) the {@code N} argument types at position {@code pos} of the target signature (skipping one matching
6181 * the {@code combiner}'s return type) are not identical with the argument types of {@code combiner}.
6182 *
6183 * @see #foldArguments(MethodHandle, MethodHandle)
6184 * @since 9
6185 */
6186 public static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner) {
6187 MethodType targetType = target.type();
6188 MethodType combinerType = combiner.type();
6189 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType);
6190 BoundMethodHandle result = target.rebind();
6191 boolean dropResult = rtype == void.class;
6192 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType());
6193 MethodType newType = targetType;
6194 if (!dropResult) {
6195 newType = newType.dropParameterTypes(pos, pos + 1);
6196 }
6197 result = result.copyWithExtendL(newType, lform, combiner);
6198 return result;
6199 }
6200
6201 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType) {
6202 int foldArgs = combinerType.parameterCount();
6203 Class<?> rtype = combinerType.returnType();
6204 int foldVals = rtype == void.class ? 0 : 1;
6205 int afterInsertPos = foldPos + foldVals;
6206 boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
6207 if (ok) {
6208 for (int i = 0; i < foldArgs; i++) {
6209 if (combinerType.parameterType(i) != targetType.parameterType(i + afterInsertPos)) {
6210 ok = false;
6211 break;
6212 }
6213 }
6214 }
6215 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos))
6216 ok = false;
6217 if (!ok)
6218 throw misMatchedTypes("target and combiner types", targetType, combinerType);
6219 return rtype;
6220 }
6221
6222 /**
6223 * Adapts a target method handle by pre-processing some of its arguments, then calling the target with the result
6224 * of the pre-processing replacing the argument at the given position.
6225 *
6226 * @param target the method handle to invoke after arguments are combined
6227 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code
6228 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
6229 * @param combiner method handle to call initially on the incoming arguments
6230 * @param argPositions indexes of the target to pick arguments sent to the combiner from
6231 * @return method handle which incorporates the specified argument folding logic
6232 * @throws NullPointerException if either argument is null
6233 * @throws IllegalArgumentException if either of the following two conditions holds:
6234 * (1) {@code combiner}'s return type is not the same as the argument type at position
6235 * {@code pos} of the target signature;
6236 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature are
6237 * not identical with the argument types of {@code combiner}.
6238 */
6239 /*non-public*/
6240 static MethodHandle filterArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
6241 return argumentsWithCombiner(true, target, position, combiner, argPositions);
6242 }
6243
6244 /**
6245 * Adapts a target method handle by pre-processing some of its arguments, calling the target with the result of
6246 * the pre-processing inserted into the original sequence of arguments at the given position.
6247 *
6248 * @param target the method handle to invoke after arguments are combined
6249 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code
6250 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
6251 * @param combiner method handle to call initially on the incoming arguments
6252 * @param argPositions indexes of the target to pick arguments sent to the combiner from
6253 * @return method handle which incorporates the specified argument folding logic
6254 * @throws NullPointerException if either argument is null
6255 * @throws IllegalArgumentException if either of the following two conditions holds:
6256 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
6257 * {@code pos} of the target signature;
6258 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature
6259 * (skipping {@code position} where the {@code combiner}'s return will be folded in) are not identical
6260 * with the argument types of {@code combiner}.
6261 */
6262 /*non-public*/
6263 static MethodHandle foldArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
6264 return argumentsWithCombiner(false, target, position, combiner, argPositions);
6265 }
6266
6267 private static MethodHandle argumentsWithCombiner(boolean filter, MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
6268 MethodType targetType = target.type();
6269 MethodType combinerType = combiner.type();
6270 Class<?> rtype = argumentsWithCombinerChecks(position, filter, targetType, combinerType, argPositions);
6271 BoundMethodHandle result = target.rebind();
6272
6273 MethodType newType = targetType;
6274 LambdaForm lform;
6275 if (filter) {
6276 lform = result.editor().filterArgumentsForm(1 + position, combinerType.basicType(), argPositions);
6277 } else {
6278 boolean dropResult = rtype == void.class;
6279 lform = result.editor().foldArgumentsForm(1 + position, dropResult, combinerType.basicType(), argPositions);
6280 if (!dropResult) {
6281 newType = newType.dropParameterTypes(position, position + 1);
6282 }
6283 }
6284 result = result.copyWithExtendL(newType, lform, combiner);
6285 return result;
6286 }
6287
6288 private static Class<?> argumentsWithCombinerChecks(int position, boolean filter, MethodType targetType, MethodType combinerType, int ... argPos) {
6289 int combinerArgs = combinerType.parameterCount();
6290 if (argPos.length != combinerArgs) {
6291 throw newIllegalArgumentException("combiner and argument map must be equal size", combinerType, argPos.length);
6292 }
6293 Class<?> rtype = combinerType.returnType();
6294
6295 for (int i = 0; i < combinerArgs; i++) {
6296 int arg = argPos[i];
6297 if (arg < 0 || arg > targetType.parameterCount()) {
6298 throw newIllegalArgumentException("arg outside of target parameterRange", targetType, arg);
6299 }
6300 if (combinerType.parameterType(i) != targetType.parameterType(arg)) {
6301 throw newIllegalArgumentException("target argument type at position " + arg
6302 + " must match combiner argument type at index " + i + ": " + targetType
6303 + " -> " + combinerType + ", map: " + Arrays.toString(argPos));
6304 }
6305 }
6306 if (filter && combinerType.returnType() != targetType.parameterType(position)) {
6307 throw misMatchedTypes("target and combiner types", targetType, combinerType);
6308 }
6309 return rtype;
6310 }
6311
6312 /**
6313 * Makes a method handle which adapts a target method handle,
6314 * by guarding it with a test, a boolean-valued method handle.
6315 * If the guard fails, a fallback handle is called instead.
6316 * All three method handles must have the same corresponding
6317 * argument and return types, except that the return type
6318 * of the test must be boolean, and the test is allowed
6319 * to have fewer arguments than the other two method handles.
6320 * <p>
6321 * Here is pseudocode for the resulting adapter. In the code, {@code T}
6322 * represents the uniform result type of the three involved handles;
6323 * {@code A}/{@code a}, the types and values of the {@code target}
6324 * parameters and arguments that are consumed by the {@code test}; and
6325 * {@code B}/{@code b}, those types and values of the {@code target}
6326 * parameters and arguments that are not consumed by the {@code test}.
6327 * {@snippet lang="java" :
6328 * boolean test(A...);
6329 * T target(A...,B...);
6330 * T fallback(A...,B...);
6331 * T adapter(A... a,B... b) {
6332 * if (test(a...))
6333 * return target(a..., b...);
6334 * else
6335 * return fallback(a..., b...);
6336 * }
6337 * }
6338 * Note that the test arguments ({@code a...} in the pseudocode) cannot
6339 * be modified by execution of the test, and so are passed unchanged
6340 * from the caller to the target or fallback as appropriate.
6341 * @param test method handle used for test, must return boolean
6342 * @param target method handle to call if test passes
6343 * @param fallback method handle to call if test fails
6344 * @return method handle which incorporates the specified if/then/else logic
6345 * @throws NullPointerException if any argument is null
6346 * @throws IllegalArgumentException if {@code test} does not return boolean,
6347 * or if all three method types do not match (with the return
6348 * type of {@code test} changed to match that of the target).
6349 */
6350 public static MethodHandle guardWithTest(MethodHandle test,
6351 MethodHandle target,
6352 MethodHandle fallback) {
6353 MethodType gtype = test.type();
6354 MethodType ttype = target.type();
6355 MethodType ftype = fallback.type();
6356 if (!ttype.equals(ftype))
6357 throw misMatchedTypes("target and fallback types", ttype, ftype);
6358 if (gtype.returnType() != boolean.class)
6359 throw newIllegalArgumentException("guard type is not a predicate "+gtype);
6360
6361 test = dropArgumentsToMatch(test, 0, ttype.ptypes(), 0, true);
6362 if (test == null) {
6363 throw misMatchedTypes("target and test types", ttype, gtype);
6364 }
6365 return MethodHandleImpl.makeGuardWithTest(test, target, fallback);
6366 }
6367
6368 static <T> RuntimeException misMatchedTypes(String what, T t1, T t2) {
6369 return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
6370 }
6371
6372 /**
6373 * Makes a method handle which adapts a target method handle,
6374 * by running it inside an exception handler.
6375 * If the target returns normally, the adapter returns that value.
6376 * If an exception matching the specified type is thrown, the fallback
6377 * handle is called instead on the exception, plus the original arguments.
6378 * <p>
6379 * The target and handler must have the same corresponding
6380 * argument and return types, except that handler may omit trailing arguments
6381 * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
6382 * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
6383 * <p>
6384 * Here is pseudocode for the resulting adapter. In the code, {@code T}
6385 * represents the return type of the {@code target} and {@code handler},
6386 * and correspondingly that of the resulting adapter; {@code A}/{@code a},
6387 * the types and values of arguments to the resulting handle consumed by
6388 * {@code handler}; and {@code B}/{@code b}, those of arguments to the
6389 * resulting handle discarded by {@code handler}.
6390 * {@snippet lang="java" :
6391 * T target(A..., B...);
6392 * T handler(ExType, A...);
6393 * T adapter(A... a, B... b) {
6394 * try {
6395 * return target(a..., b...);
6396 * } catch (ExType ex) {
6397 * return handler(ex, a...);
6398 * }
6399 * }
6400 * }
6401 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
6402 * be modified by execution of the target, and so are passed unchanged
6403 * from the caller to the handler, if the handler is invoked.
6404 * <p>
6405 * The target and handler must return the same type, even if the handler
6406 * always throws. (This might happen, for instance, because the handler
6407 * is simulating a {@code finally} clause).
6408 * To create such a throwing handler, compose the handler creation logic
6409 * with {@link #throwException throwException},
6410 * in order to create a method handle of the correct return type.
6411 * @param target method handle to call
6412 * @param exType the type of exception which the handler will catch
6413 * @param handler method handle to call if a matching exception is thrown
6414 * @return method handle which incorporates the specified try/catch logic
6415 * @throws NullPointerException if any argument is null
6416 * @throws IllegalArgumentException if {@code handler} does not accept
6417 * the given exception type, or if the method handle types do
6418 * not match in their return types and their
6419 * corresponding parameters
6420 * @see MethodHandles#tryFinally(MethodHandle, MethodHandle)
6421 */
6422 public static MethodHandle catchException(MethodHandle target,
6423 Class<? extends Throwable> exType,
6424 MethodHandle handler) {
6425 MethodType ttype = target.type();
6426 MethodType htype = handler.type();
6427 if (!Throwable.class.isAssignableFrom(exType))
6428 throw new ClassCastException(exType.getName());
6429 if (htype.parameterCount() < 1 ||
6430 !htype.parameterType(0).isAssignableFrom(exType))
6431 throw newIllegalArgumentException("handler does not accept exception type "+exType);
6432 if (htype.returnType() != ttype.returnType())
6433 throw misMatchedTypes("target and handler return types", ttype, htype);
6434 handler = dropArgumentsToMatch(handler, 1, ttype.ptypes(), 0, true);
6435 if (handler == null) {
6436 throw misMatchedTypes("target and handler types", ttype, htype);
6437 }
6438 return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
6439 }
6440
6441 /**
6442 * Produces a method handle which will throw exceptions of the given {@code exType}.
6443 * The method handle will accept a single argument of {@code exType},
6444 * and immediately throw it as an exception.
6445 * The method type will nominally specify a return of {@code returnType}.
6446 * The return type may be anything convenient: It doesn't matter to the
6447 * method handle's behavior, since it will never return normally.
6448 * @param returnType the return type of the desired method handle
6449 * @param exType the parameter type of the desired method handle
6450 * @return method handle which can throw the given exceptions
6451 * @throws NullPointerException if either argument is null
6452 */
6453 public static MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) {
6454 if (!Throwable.class.isAssignableFrom(exType))
6455 throw new ClassCastException(exType.getName());
6456 return MethodHandleImpl.throwException(methodType(returnType, exType));
6457 }
6458
6459 /**
6460 * Constructs a method handle representing a loop with several loop variables that are updated and checked upon each
6461 * iteration. Upon termination of the loop due to one of the predicates, a corresponding finalizer is run and
6462 * delivers the loop's result, which is the return value of the resulting handle.
6463 * <p>
6464 * Intuitively, every loop is formed by one or more "clauses", each specifying a local <em>iteration variable</em> and/or a loop
6465 * exit. Each iteration of the loop executes each clause in order. A clause can optionally update its iteration
6466 * variable; it can also optionally perform a test and conditional loop exit. In order to express this logic in
6467 * terms of method handles, each clause will specify up to four independent actions:<ul>
6468 * <li><em>init:</em> Before the loop executes, the initialization of an iteration variable {@code v} of type {@code V}.
6469 * <li><em>step:</em> When a clause executes, an update step for the iteration variable {@code v}.
6470 * <li><em>pred:</em> When a clause executes, a predicate execution to test for loop exit.
6471 * <li><em>fini:</em> If a clause causes a loop exit, a finalizer execution to compute the loop's return value.
6472 * </ul>
6473 * The full sequence of all iteration variable types, in clause order, will be notated as {@code (V...)}.
6474 * The values themselves will be {@code (v...)}. When we speak of "parameter lists", we will usually
6475 * be referring to types, but in some contexts (describing execution) the lists will be of actual values.
6476 * <p>
6477 * Some of these clause parts may be omitted according to certain rules, and useful default behavior is provided in
6478 * this case. See below for a detailed description.
6479 * <p>
6480 * <em>Parameters optional everywhere:</em>
6481 * Each clause function is allowed but not required to accept a parameter for each iteration variable {@code v}.
6482 * As an exception, the init functions cannot take any {@code v} parameters,
6483 * because those values are not yet computed when the init functions are executed.
6484 * Any clause function may neglect to take any trailing subsequence of parameters it is entitled to take.
6485 * In fact, any clause function may take no arguments at all.
6486 * <p>
6487 * <em>Loop parameters:</em>
6488 * A clause function may take all the iteration variable values it is entitled to, in which case
6489 * it may also take more trailing parameters. Such extra values are called <em>loop parameters</em>,
6490 * with their types and values notated as {@code (A...)} and {@code (a...)}.
6491 * These become the parameters of the resulting loop handle, to be supplied whenever the loop is executed.
6492 * (Since init functions do not accept iteration variables {@code v}, any parameter to an
6493 * init function is automatically a loop parameter {@code a}.)
6494 * As with iteration variables, clause functions are allowed but not required to accept loop parameters.
6495 * These loop parameters act as loop-invariant values visible across the whole loop.
6496 * <p>
6497 * <em>Parameters visible everywhere:</em>
6498 * Each non-init clause function is permitted to observe the entire loop state, because it can be passed the full
6499 * list {@code (v... a...)} of current iteration variable values and incoming loop parameters.
6500 * The init functions can observe initial pre-loop state, in the form {@code (a...)}.
6501 * Most clause functions will not need all of this information, but they will be formally connected to it
6502 * as if by {@link #dropArguments}.
6503 * <a id="astar"></a>
6504 * More specifically, we shall use the notation {@code (V*)} to express an arbitrary prefix of a full
6505 * sequence {@code (V...)} (and likewise for {@code (v*)}, {@code (A*)}, {@code (a*)}).
6506 * In that notation, the general form of an init function parameter list
6507 * is {@code (A*)}, and the general form of a non-init function parameter list is {@code (V*)} or {@code (V... A*)}.
6508 * <p>
6509 * <em>Checking clause structure:</em>
6510 * Given a set of clauses, there is a number of checks and adjustments performed to connect all the parts of the
6511 * loop. They are spelled out in detail in the steps below. In these steps, every occurrence of the word "must"
6512 * corresponds to a place where {@link IllegalArgumentException} will be thrown if the required constraint is not
6513 * met by the inputs to the loop combinator.
6514 * <p>
6515 * <em>Effectively identical sequences:</em>
6516 * <a id="effid"></a>
6517 * A parameter list {@code A} is defined to be <em>effectively identical</em> to another parameter list {@code B}
6518 * if {@code A} and {@code B} are identical, or if {@code A} is shorter and is identical with a proper prefix of {@code B}.
6519 * When speaking of an unordered set of parameter lists, we say they the set is "effectively identical"
6520 * as a whole if the set contains a longest list, and all members of the set are effectively identical to
6521 * that longest list.
6522 * For example, any set of type sequences of the form {@code (V*)} is effectively identical,
6523 * and the same is true if more sequences of the form {@code (V... A*)} are added.
6524 * <p>
6525 * <em>Step 0: Determine clause structure.</em><ol type="a">
6526 * <li>The clause array (of type {@code MethodHandle[][]}) must be non-{@code null} and contain at least one element.
6527 * <li>The clause array may not contain {@code null}s or sub-arrays longer than four elements.
6528 * <li>Clauses shorter than four elements are treated as if they were padded by {@code null} elements to length
6529 * four. Padding takes place by appending elements to the array.
6530 * <li>Clauses with all {@code null}s are disregarded.
6531 * <li>Each clause is treated as a four-tuple of functions, called "init", "step", "pred", and "fini".
6532 * </ol>
6533 * <p>
6534 * <em>Step 1A: Determine iteration variable types {@code (V...)}.</em><ol type="a">
6535 * <li>The iteration variable type for each clause is determined using the clause's init and step return types.
6536 * <li>If both functions are omitted, there is no iteration variable for the corresponding clause ({@code void} is
6537 * used as the type to indicate that). If one of them is omitted, the other's return type defines the clause's
6538 * iteration variable type. If both are given, the common return type (they must be identical) defines the clause's
6539 * iteration variable type.
6540 * <li>Form the list of return types (in clause order), omitting all occurrences of {@code void}.
6541 * <li>This list of types is called the "iteration variable types" ({@code (V...)}).
6542 * </ol>
6543 * <p>
6544 * <em>Step 1B: Determine loop parameters {@code (A...)}.</em><ul>
6545 * <li>Examine and collect init function parameter lists (which are of the form {@code (A*)}).
6546 * <li>Examine and collect the suffixes of the step, pred, and fini parameter lists, after removing the iteration variable types.
6547 * (They must have the form {@code (V... A*)}; collect the {@code (A*)} parts only.)
6548 * <li>Do not collect suffixes from step, pred, and fini parameter lists that do not begin with all the iteration variable types.
6549 * (These types will be checked in step 2, along with all the clause function types.)
6550 * <li>Omitted clause functions are ignored. (Equivalently, they are deemed to have empty parameter lists.)
6551 * <li>All of the collected parameter lists must be effectively identical.
6552 * <li>The longest parameter list (which is necessarily unique) is called the "external parameter list" ({@code (A...)}).
6553 * <li>If there is no such parameter list, the external parameter list is taken to be the empty sequence.
6554 * <li>The combined list consisting of iteration variable types followed by the external parameter types is called
6555 * the "internal parameter list".
6556 * </ul>
6557 * <p>
6558 * <em>Step 1C: Determine loop return type.</em><ol type="a">
6559 * <li>Examine fini function return types, disregarding omitted fini functions.
6560 * <li>If there are no fini functions, the loop return type is {@code void}.
6561 * <li>Otherwise, the common return type {@code R} of the fini functions (their return types must be identical) defines the loop return
6562 * type.
6563 * </ol>
6564 * <p>
6565 * <em>Step 1D: Check other types.</em><ol type="a">
6566 * <li>There must be at least one non-omitted pred function.
6567 * <li>Every non-omitted pred function must have a {@code boolean} return type.
6568 * </ol>
6569 * <p>
6570 * <em>Step 2: Determine parameter lists.</em><ol type="a">
6571 * <li>The parameter list for the resulting loop handle will be the external parameter list {@code (A...)}.
6572 * <li>The parameter list for init functions will be adjusted to the external parameter list.
6573 * (Note that their parameter lists are already effectively identical to this list.)
6574 * <li>The parameter list for every non-omitted, non-init (step, pred, and fini) function must be
6575 * effectively identical to the internal parameter list {@code (V... A...)}.
6576 * </ol>
6577 * <p>
6578 * <em>Step 3: Fill in omitted functions.</em><ol type="a">
6579 * <li>If an init function is omitted, use a {@linkplain #empty default value} for the clause's iteration variable
6580 * type.
6581 * <li>If a step function is omitted, use an {@linkplain #identity identity function} of the clause's iteration
6582 * variable type; insert dropped argument parameters before the identity function parameter for the non-{@code void}
6583 * iteration variables of preceding clauses. (This will turn the loop variable into a local loop invariant.)
6584 * <li>If a pred function is omitted, use a constant {@code true} function. (This will keep the loop going, as far
6585 * as this clause is concerned. Note that in such cases the corresponding fini function is unreachable.)
6586 * <li>If a fini function is omitted, use a {@linkplain #empty default value} for the
6587 * loop return type.
6588 * </ol>
6589 * <p>
6590 * <em>Step 4: Fill in missing parameter types.</em><ol type="a">
6591 * <li>At this point, every init function parameter list is effectively identical to the external parameter list {@code (A...)},
6592 * but some lists may be shorter. For every init function with a short parameter list, pad out the end of the list.
6593 * <li>At this point, every non-init function parameter list is effectively identical to the internal parameter
6594 * list {@code (V... A...)}, but some lists may be shorter. For every non-init function with a short parameter list,
6595 * pad out the end of the list.
6596 * <li>Argument lists are padded out by {@linkplain #dropArgumentsToMatch(MethodHandle, int, List, int) dropping unused trailing arguments}.
6597 * </ol>
6598 * <p>
6599 * <em>Final observations.</em><ol type="a">
6600 * <li>After these steps, all clauses have been adjusted by supplying omitted functions and arguments.
6601 * <li>All init functions have a common parameter type list {@code (A...)}, which the final loop handle will also have.
6602 * <li>All fini functions have a common return type {@code R}, which the final loop handle will also have.
6603 * <li>All non-init functions have a common parameter type list {@code (V... A...)}, of
6604 * (non-{@code void}) iteration variables {@code V} followed by loop parameters.
6605 * <li>Each pair of init and step functions agrees in their return type {@code V}.
6606 * <li>Each non-init function will be able to observe the current values {@code (v...)} of all iteration variables.
6607 * <li>Every function will be able to observe the incoming values {@code (a...)} of all loop parameters.
6608 * </ol>
6609 * <p>
6610 * <em>Example.</em> As a consequence of step 1A above, the {@code loop} combinator has the following property:
6611 * <ul>
6612 * <li>Given {@code N} clauses {@code Cn = {null, Sn, Pn}} with {@code n = 1..N}.
6613 * <li>Suppose predicate handles {@code Pn} are either {@code null} or have no parameters.
6614 * (Only one {@code Pn} has to be non-{@code null}.)
6615 * <li>Suppose step handles {@code Sn} have signatures {@code (B1..BX)Rn}, for some constant {@code X>=N}.
6616 * <li>Suppose {@code Q} is the count of non-void types {@code Rn}, and {@code (V1...VQ)} is the sequence of those types.
6617 * <li>It must be that {@code Vn == Bn} for {@code n = 1..min(X,Q)}.
6618 * <li>The parameter types {@code Vn} will be interpreted as loop-local state elements {@code (V...)}.
6619 * <li>Any remaining types {@code BQ+1..BX} (if {@code Q<X}) will determine
6620 * the resulting loop handle's parameter types {@code (A...)}.
6621 * </ul>
6622 * In this example, the loop handle parameters {@code (A...)} were derived from the step functions,
6623 * which is natural if most of the loop computation happens in the steps. For some loops,
6624 * the burden of computation might be heaviest in the pred functions, and so the pred functions
6625 * might need to accept the loop parameter values. For loops with complex exit logic, the fini
6626 * functions might need to accept loop parameters, and likewise for loops with complex entry logic,
6627 * where the init functions will need the extra parameters. For such reasons, the rules for
6628 * determining these parameters are as symmetric as possible, across all clause parts.
6629 * In general, the loop parameters function as common invariant values across the whole
6630 * loop, while the iteration variables function as common variant values, or (if there is
6631 * no step function) as internal loop invariant temporaries.
6632 * <p>
6633 * <em>Loop execution.</em><ol type="a">
6634 * <li>When the loop is called, the loop input values are saved in locals, to be passed to
6635 * every clause function. These locals are loop invariant.
6636 * <li>Each init function is executed in clause order (passing the external arguments {@code (a...)})
6637 * and the non-{@code void} values are saved (as the iteration variables {@code (v...)}) into locals.
6638 * These locals will be loop varying (unless their steps behave as identity functions, as noted above).
6639 * <li>All function executions (except init functions) will be passed the internal parameter list, consisting of
6640 * the non-{@code void} iteration values {@code (v...)} (in clause order) and then the loop inputs {@code (a...)}
6641 * (in argument order).
6642 * <li>The step and pred functions are then executed, in clause order (step before pred), until a pred function
6643 * returns {@code false}.
6644 * <li>The non-{@code void} result from a step function call is used to update the corresponding value in the
6645 * sequence {@code (v...)} of loop variables.
6646 * The updated value is immediately visible to all subsequent function calls.
6647 * <li>If a pred function returns {@code false}, the corresponding fini function is called, and the resulting value
6648 * (of type {@code R}) is returned from the loop as a whole.
6649 * <li>If all the pred functions always return true, no fini function is ever invoked, and the loop cannot exit
6650 * except by throwing an exception.
6651 * </ol>
6652 * <p>
6653 * <em>Usage tips.</em>
6654 * <ul>
6655 * <li>Although each step function will receive the current values of <em>all</em> the loop variables,
6656 * sometimes a step function only needs to observe the current value of its own variable.
6657 * In that case, the step function may need to explicitly {@linkplain #dropArguments drop all preceding loop variables}.
6658 * This will require mentioning their types, in an expression like {@code dropArguments(step, 0, V0.class, ...)}.
6659 * <li>Loop variables are not required to vary; they can be loop invariant. A clause can create
6660 * a loop invariant by a suitable init function with no step, pred, or fini function. This may be
6661 * useful to "wire" an incoming loop argument into the step or pred function of an adjacent loop variable.
6662 * <li>If some of the clause functions are virtual methods on an instance, the instance
6663 * itself can be conveniently placed in an initial invariant loop "variable", using an initial clause
6664 * like {@code new MethodHandle[]{identity(ObjType.class)}}. In that case, the instance reference
6665 * will be the first iteration variable value, and it will be easy to use virtual
6666 * methods as clause parts, since all of them will take a leading instance reference matching that value.
6667 * </ul>
6668 * <p>
6669 * Here is pseudocode for the resulting loop handle. As above, {@code V} and {@code v} represent the types
6670 * and values of loop variables; {@code A} and {@code a} represent arguments passed to the whole loop;
6671 * and {@code R} is the common result type of all finalizers as well as of the resulting loop.
6672 * {@snippet lang="java" :
6673 * V... init...(A...);
6674 * boolean pred...(V..., A...);
6675 * V... step...(V..., A...);
6676 * R fini...(V..., A...);
6677 * R loop(A... a) {
6678 * V... v... = init...(a...);
6679 * for (;;) {
6680 * for ((v, p, s, f) in (v..., pred..., step..., fini...)) {
6681 * v = s(v..., a...);
6682 * if (!p(v..., a...)) {
6683 * return f(v..., a...);
6684 * }
6685 * }
6686 * }
6687 * }
6688 * }
6689 * Note that the parameter type lists {@code (V...)} and {@code (A...)} have been expanded
6690 * to their full length, even though individual clause functions may neglect to take them all.
6691 * As noted above, missing parameters are filled in as if by {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}.
6692 *
6693 * @apiNote Example:
6694 * {@snippet lang="java" :
6695 * // iterative implementation of the factorial function as a loop handle
6696 * static int one(int k) { return 1; }
6697 * static int inc(int i, int acc, int k) { return i + 1; }
6698 * static int mult(int i, int acc, int k) { return i * acc; }
6699 * static boolean pred(int i, int acc, int k) { return i < k; }
6700 * static int fin(int i, int acc, int k) { return acc; }
6701 * // assume MH_one, MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
6702 * // null initializer for counter, should initialize to 0
6703 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
6704 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
6705 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
6706 * assertEquals(120, loop.invoke(5));
6707 * }
6708 * The same example, dropping arguments and using combinators:
6709 * {@snippet lang="java" :
6710 * // simplified implementation of the factorial function as a loop handle
6711 * static int inc(int i) { return i + 1; } // drop acc, k
6712 * static int mult(int i, int acc) { return i * acc; } //drop k
6713 * static boolean cmp(int i, int k) { return i < k; }
6714 * // assume MH_inc, MH_mult, and MH_cmp are handles to the above methods
6715 * // null initializer for counter, should initialize to 0
6716 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
6717 * MethodHandle MH_pred = MethodHandles.dropArguments(MH_cmp, 1, int.class); // drop acc
6718 * MethodHandle MH_fin = MethodHandles.dropArguments(MethodHandles.identity(int.class), 0, int.class); // drop i
6719 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
6720 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
6721 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
6722 * assertEquals(720, loop.invoke(6));
6723 * }
6724 * A similar example, using a helper object to hold a loop parameter:
6725 * {@snippet lang="java" :
6726 * // instance-based implementation of the factorial function as a loop handle
6727 * static class FacLoop {
6728 * final int k;
6729 * FacLoop(int k) { this.k = k; }
6730 * int inc(int i) { return i + 1; }
6731 * int mult(int i, int acc) { return i * acc; }
6732 * boolean pred(int i) { return i < k; }
6733 * int fin(int i, int acc) { return acc; }
6734 * }
6735 * // assume MH_FacLoop is a handle to the constructor
6736 * // assume MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
6737 * // null initializer for counter, should initialize to 0
6738 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
6739 * MethodHandle[] instanceClause = new MethodHandle[]{MH_FacLoop};
6740 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
6741 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
6742 * MethodHandle loop = MethodHandles.loop(instanceClause, counterClause, accumulatorClause);
6743 * assertEquals(5040, loop.invoke(7));
6744 * }
6745 *
6746 * @param clauses an array of arrays (4-tuples) of {@link MethodHandle}s adhering to the rules described above.
6747 *
6748 * @return a method handle embodying the looping behavior as defined by the arguments.
6749 *
6750 * @throws IllegalArgumentException in case any of the constraints described above is violated.
6751 *
6752 * @see MethodHandles#whileLoop(MethodHandle, MethodHandle, MethodHandle)
6753 * @see MethodHandles#doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
6754 * @see MethodHandles#countedLoop(MethodHandle, MethodHandle, MethodHandle)
6755 * @see MethodHandles#iteratedLoop(MethodHandle, MethodHandle, MethodHandle)
6756 * @since 9
6757 */
6758 public static MethodHandle loop(MethodHandle[]... clauses) {
6759 // Step 0: determine clause structure.
6760 loopChecks0(clauses);
6761
6762 List<MethodHandle> init = new ArrayList<>();
6763 List<MethodHandle> step = new ArrayList<>();
6764 List<MethodHandle> pred = new ArrayList<>();
6765 List<MethodHandle> fini = new ArrayList<>();
6766
6767 Stream.of(clauses).filter(c -> Stream.of(c).anyMatch(Objects::nonNull)).forEach(clause -> {
6768 init.add(clause[0]); // all clauses have at least length 1
6769 step.add(clause.length <= 1 ? null : clause[1]);
6770 pred.add(clause.length <= 2 ? null : clause[2]);
6771 fini.add(clause.length <= 3 ? null : clause[3]);
6772 });
6773
6774 assert Stream.of(init, step, pred, fini).map(List::size).distinct().count() == 1;
6775 final int nclauses = init.size();
6776
6777 // Step 1A: determine iteration variables (V...).
6778 final List<Class<?>> iterationVariableTypes = new ArrayList<>();
6779 for (int i = 0; i < nclauses; ++i) {
6780 MethodHandle in = init.get(i);
6781 MethodHandle st = step.get(i);
6782 if (in == null && st == null) {
6783 iterationVariableTypes.add(void.class);
6784 } else if (in != null && st != null) {
6785 loopChecks1a(i, in, st);
6786 iterationVariableTypes.add(in.type().returnType());
6787 } else {
6788 iterationVariableTypes.add(in == null ? st.type().returnType() : in.type().returnType());
6789 }
6790 }
6791 final List<Class<?>> commonPrefix = iterationVariableTypes.stream().filter(t -> t != void.class).toList();
6792
6793 // Step 1B: determine loop parameters (A...).
6794 final List<Class<?>> commonSuffix = buildCommonSuffix(init, step, pred, fini, commonPrefix.size());
6795 loopChecks1b(init, commonSuffix);
6796
6797 // Step 1C: determine loop return type.
6798 // Step 1D: check other types.
6799 // local variable required here; see JDK-8223553
6800 Stream<Class<?>> cstream = fini.stream().filter(Objects::nonNull).map(MethodHandle::type)
6801 .map(MethodType::returnType);
6802 final Class<?> loopReturnType = cstream.findFirst().orElse(void.class);
6803 loopChecks1cd(pred, fini, loopReturnType);
6804
6805 // Step 2: determine parameter lists.
6806 final List<Class<?>> commonParameterSequence = new ArrayList<>(commonPrefix);
6807 commonParameterSequence.addAll(commonSuffix);
6808 loopChecks2(step, pred, fini, commonParameterSequence);
6809 // Step 3: fill in omitted functions.
6810 for (int i = 0; i < nclauses; ++i) {
6811 Class<?> t = iterationVariableTypes.get(i);
6812 if (init.get(i) == null) {
6813 init.set(i, empty(methodType(t, commonSuffix)));
6814 }
6815 if (step.get(i) == null) {
6816 step.set(i, dropArgumentsToMatch(identityOrVoid(t), 0, commonParameterSequence, i));
6817 }
6818 if (pred.get(i) == null) {
6819 pred.set(i, dropArguments(constant(boolean.class, true), 0, commonParameterSequence));
6820 }
6821 if (fini.get(i) == null) {
6822 fini.set(i, empty(methodType(t, commonParameterSequence)));
6823 }
6824 }
6825
6826 // Step 4: fill in missing parameter types.
6827 // Also convert all handles to fixed-arity handles.
6828 List<MethodHandle> finit = fixArities(fillParameterTypes(init, commonSuffix));
6829 List<MethodHandle> fstep = fixArities(fillParameterTypes(step, commonParameterSequence));
6830 List<MethodHandle> fpred = fixArities(fillParameterTypes(pred, commonParameterSequence));
6831 List<MethodHandle> ffini = fixArities(fillParameterTypes(fini, commonParameterSequence));
6832
6833 assert finit.stream().map(MethodHandle::type).map(MethodType::parameterList).
6834 allMatch(pl -> pl.equals(commonSuffix));
6835 assert Stream.of(fstep, fpred, ffini).flatMap(List::stream).map(MethodHandle::type).map(MethodType::parameterList).
6836 allMatch(pl -> pl.equals(commonParameterSequence));
6837
6838 return MethodHandleImpl.makeLoop(loopReturnType, commonSuffix, finit, fstep, fpred, ffini);
6839 }
6840
6841 private static void loopChecks0(MethodHandle[][] clauses) {
6842 if (clauses == null || clauses.length == 0) {
6843 throw newIllegalArgumentException("null or no clauses passed");
6844 }
6845 if (Stream.of(clauses).anyMatch(Objects::isNull)) {
6846 throw newIllegalArgumentException("null clauses are not allowed");
6847 }
6848 if (Stream.of(clauses).anyMatch(c -> c.length > 4)) {
6849 throw newIllegalArgumentException("All loop clauses must be represented as MethodHandle arrays with at most 4 elements.");
6850 }
6851 }
6852
6853 private static void loopChecks1a(int i, MethodHandle in, MethodHandle st) {
6854 if (in.type().returnType() != st.type().returnType()) {
6855 throw misMatchedTypes("clause " + i + ": init and step return types", in.type().returnType(),
6856 st.type().returnType());
6857 }
6858 }
6859
6860 private static List<Class<?>> longestParameterList(Stream<MethodHandle> mhs, int skipSize) {
6861 return mhs.filter(Objects::nonNull)
6862 // take only those that can contribute to a common suffix because they are longer than the prefix
6863 .map(MethodHandle::type)
6864 .filter(t -> t.parameterCount() > skipSize)
6865 .max(Comparator.comparingInt(MethodType::parameterCount))
6866 .map(methodType -> List.of(Arrays.copyOfRange(methodType.ptypes(), skipSize, methodType.parameterCount())))
6867 .orElse(List.of());
6868 }
6869
6870 private static List<Class<?>> buildCommonSuffix(List<MethodHandle> init, List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, int cpSize) {
6871 final List<Class<?>> longest1 = longestParameterList(Stream.of(step, pred, fini).flatMap(List::stream), cpSize);
6872 final List<Class<?>> longest2 = longestParameterList(init.stream(), 0);
6873 return longest1.size() >= longest2.size() ? longest1 : longest2;
6874 }
6875
6876 private static void loopChecks1b(List<MethodHandle> init, List<Class<?>> commonSuffix) {
6877 if (init.stream().filter(Objects::nonNull).map(MethodHandle::type).
6878 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonSuffix))) {
6879 throw newIllegalArgumentException("found non-effectively identical init parameter type lists: " + init +
6880 " (common suffix: " + commonSuffix + ")");
6881 }
6882 }
6883
6884 private static void loopChecks1cd(List<MethodHandle> pred, List<MethodHandle> fini, Class<?> loopReturnType) {
6885 if (fini.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
6886 anyMatch(t -> t != loopReturnType)) {
6887 throw newIllegalArgumentException("found non-identical finalizer return types: " + fini + " (return type: " +
6888 loopReturnType + ")");
6889 }
6890
6891 if (pred.stream().noneMatch(Objects::nonNull)) {
6892 throw newIllegalArgumentException("no predicate found", pred);
6893 }
6894 if (pred.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
6895 anyMatch(t -> t != boolean.class)) {
6896 throw newIllegalArgumentException("predicates must have boolean return type", pred);
6897 }
6898 }
6899
6900 private static void loopChecks2(List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, List<Class<?>> commonParameterSequence) {
6901 if (Stream.of(step, pred, fini).flatMap(List::stream).filter(Objects::nonNull).map(MethodHandle::type).
6902 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonParameterSequence))) {
6903 throw newIllegalArgumentException("found non-effectively identical parameter type lists:\nstep: " + step +
6904 "\npred: " + pred + "\nfini: " + fini + " (common parameter sequence: " + commonParameterSequence + ")");
6905 }
6906 }
6907
6908 private static List<MethodHandle> fillParameterTypes(List<MethodHandle> hs, final List<Class<?>> targetParams) {
6909 return hs.stream().map(h -> {
6910 int pc = h.type().parameterCount();
6911 int tpsize = targetParams.size();
6912 return pc < tpsize ? dropArguments(h, pc, targetParams.subList(pc, tpsize)) : h;
6913 }).toList();
6914 }
6915
6916 private static List<MethodHandle> fixArities(List<MethodHandle> hs) {
6917 return hs.stream().map(MethodHandle::asFixedArity).toList();
6918 }
6919
6920 /**
6921 * Constructs a {@code while} loop from an initializer, a body, and a predicate.
6922 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
6923 * <p>
6924 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
6925 * method will, in each iteration, first evaluate the predicate and then execute its body (if the predicate
6926 * evaluates to {@code true}).
6927 * The loop will terminate once the predicate evaluates to {@code false} (the body will not be executed in this case).
6928 * <p>
6929 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
6930 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
6931 * and updated with the value returned from its invocation. The result of loop execution will be
6932 * the final value of the additional loop-local variable (if present).
6933 * <p>
6934 * The following rules hold for these argument handles:<ul>
6935 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
6936 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
6937 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
6938 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
6939 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
6940 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
6941 * It will constrain the parameter lists of the other loop parts.
6942 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
6943 * list {@code (A...)} is called the <em>external parameter list</em>.
6944 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
6945 * additional state variable of the loop.
6946 * The body must both accept and return a value of this type {@code V}.
6947 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
6948 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
6949 * <a href="MethodHandles.html#effid">effectively identical</a>
6950 * to the external parameter list {@code (A...)}.
6951 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
6952 * {@linkplain #empty default value}.
6953 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
6954 * Its parameter list (either empty or of the form {@code (V A*)}) must be
6955 * effectively identical to the internal parameter list.
6956 * </ul>
6957 * <p>
6958 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
6959 * <li>The loop handle's result type is the result type {@code V} of the body.
6960 * <li>The loop handle's parameter types are the types {@code (A...)},
6961 * from the external parameter list.
6962 * </ul>
6963 * <p>
6964 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
6965 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
6966 * passed to the loop.
6967 * {@snippet lang="java" :
6968 * V init(A...);
6969 * boolean pred(V, A...);
6970 * V body(V, A...);
6971 * V whileLoop(A... a...) {
6972 * V v = init(a...);
6973 * while (pred(v, a...)) {
6974 * v = body(v, a...);
6975 * }
6976 * return v;
6977 * }
6978 * }
6979 *
6980 * @apiNote Example:
6981 * {@snippet lang="java" :
6982 * // implement the zip function for lists as a loop handle
6983 * static List<String> initZip(Iterator<String> a, Iterator<String> b) { return new ArrayList<>(); }
6984 * static boolean zipPred(List<String> zip, Iterator<String> a, Iterator<String> b) { return a.hasNext() && b.hasNext(); }
6985 * static List<String> zipStep(List<String> zip, Iterator<String> a, Iterator<String> b) {
6986 * zip.add(a.next());
6987 * zip.add(b.next());
6988 * return zip;
6989 * }
6990 * // assume MH_initZip, MH_zipPred, and MH_zipStep are handles to the above methods
6991 * MethodHandle loop = MethodHandles.whileLoop(MH_initZip, MH_zipPred, MH_zipStep);
6992 * List<String> a = Arrays.asList("a", "b", "c", "d");
6993 * List<String> b = Arrays.asList("e", "f", "g", "h");
6994 * List<String> zipped = Arrays.asList("a", "e", "b", "f", "c", "g", "d", "h");
6995 * assertEquals(zipped, (List<String>) loop.invoke(a.iterator(), b.iterator()));
6996 * }
6997 *
6998 *
6999 * @apiNote The implementation of this method can be expressed as follows:
7000 * {@snippet lang="java" :
7001 * MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
7002 * MethodHandle fini = (body.type().returnType() == void.class
7003 * ? null : identity(body.type().returnType()));
7004 * MethodHandle[]
7005 * checkExit = { null, null, pred, fini },
7006 * varBody = { init, body };
7007 * return loop(checkExit, varBody);
7008 * }
7009 * }
7010 *
7011 * @param init optional initializer, providing the initial value of the loop variable.
7012 * May be {@code null}, implying a default initial value. See above for other constraints.
7013 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
7014 * above for other constraints.
7015 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
7016 * See above for other constraints.
7017 *
7018 * @return a method handle implementing the {@code while} loop as described by the arguments.
7019 * @throws IllegalArgumentException if the rules for the arguments are violated.
7020 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
7021 *
7022 * @see #loop(MethodHandle[][])
7023 * @see #doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
7024 * @since 9
7025 */
7026 public static MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
7027 whileLoopChecks(init, pred, body);
7028 MethodHandle fini = identityOrVoid(body.type().returnType());
7029 MethodHandle[] checkExit = { null, null, pred, fini };
7030 MethodHandle[] varBody = { init, body };
7031 return loop(checkExit, varBody);
7032 }
7033
7034 /**
7035 * Constructs a {@code do-while} loop from an initializer, a body, and a predicate.
7036 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
7037 * <p>
7038 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
7039 * method will, in each iteration, first execute its body and then evaluate the predicate.
7040 * The loop will terminate once the predicate evaluates to {@code false} after an execution of the body.
7041 * <p>
7042 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
7043 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
7044 * and updated with the value returned from its invocation. The result of loop execution will be
7045 * the final value of the additional loop-local variable (if present).
7046 * <p>
7047 * The following rules hold for these argument handles:<ul>
7048 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
7049 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
7050 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
7051 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
7052 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
7053 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
7054 * It will constrain the parameter lists of the other loop parts.
7055 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
7056 * list {@code (A...)} is called the <em>external parameter list</em>.
7057 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
7058 * additional state variable of the loop.
7059 * The body must both accept and return a value of this type {@code V}.
7060 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
7061 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
7062 * <a href="MethodHandles.html#effid">effectively identical</a>
7063 * to the external parameter list {@code (A...)}.
7064 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
7065 * {@linkplain #empty default value}.
7066 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
7067 * Its parameter list (either empty or of the form {@code (V A*)}) must be
7068 * effectively identical to the internal parameter list.
7069 * </ul>
7070 * <p>
7071 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
7072 * <li>The loop handle's result type is the result type {@code V} of the body.
7073 * <li>The loop handle's parameter types are the types {@code (A...)},
7074 * from the external parameter list.
7075 * </ul>
7076 * <p>
7077 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
7078 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
7079 * passed to the loop.
7080 * {@snippet lang="java" :
7081 * V init(A...);
7082 * boolean pred(V, A...);
7083 * V body(V, A...);
7084 * V doWhileLoop(A... a...) {
7085 * V v = init(a...);
7086 * do {
7087 * v = body(v, a...);
7088 * } while (pred(v, a...));
7089 * return v;
7090 * }
7091 * }
7092 *
7093 * @apiNote Example:
7094 * {@snippet lang="java" :
7095 * // int i = 0; while (i < limit) { ++i; } return i; => limit
7096 * static int zero(int limit) { return 0; }
7097 * static int step(int i, int limit) { return i + 1; }
7098 * static boolean pred(int i, int limit) { return i < limit; }
7099 * // assume MH_zero, MH_step, and MH_pred are handles to the above methods
7100 * MethodHandle loop = MethodHandles.doWhileLoop(MH_zero, MH_step, MH_pred);
7101 * assertEquals(23, loop.invoke(23));
7102 * }
7103 *
7104 *
7105 * @apiNote The implementation of this method can be expressed as follows:
7106 * {@snippet lang="java" :
7107 * MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
7108 * MethodHandle fini = (body.type().returnType() == void.class
7109 * ? null : identity(body.type().returnType()));
7110 * MethodHandle[] clause = { init, body, pred, fini };
7111 * return loop(clause);
7112 * }
7113 * }
7114 *
7115 * @param init optional initializer, providing the initial value of the loop variable.
7116 * May be {@code null}, implying a default initial value. See above for other constraints.
7117 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
7118 * See above for other constraints.
7119 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
7120 * above for other constraints.
7121 *
7122 * @return a method handle implementing the {@code while} loop as described by the arguments.
7123 * @throws IllegalArgumentException if the rules for the arguments are violated.
7124 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
7125 *
7126 * @see #loop(MethodHandle[][])
7127 * @see #whileLoop(MethodHandle, MethodHandle, MethodHandle)
7128 * @since 9
7129 */
7130 public static MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
7131 whileLoopChecks(init, pred, body);
7132 MethodHandle fini = identityOrVoid(body.type().returnType());
7133 MethodHandle[] clause = {init, body, pred, fini };
7134 return loop(clause);
7135 }
7136
7137 private static void whileLoopChecks(MethodHandle init, MethodHandle pred, MethodHandle body) {
7138 Objects.requireNonNull(pred);
7139 Objects.requireNonNull(body);
7140 MethodType bodyType = body.type();
7141 Class<?> returnType = bodyType.returnType();
7142 List<Class<?>> innerList = bodyType.parameterList();
7143 List<Class<?>> outerList = innerList;
7144 if (returnType == void.class) {
7145 // OK
7146 } else if (innerList.isEmpty() || innerList.get(0) != returnType) {
7147 // leading V argument missing => error
7148 MethodType expected = bodyType.insertParameterTypes(0, returnType);
7149 throw misMatchedTypes("body function", bodyType, expected);
7150 } else {
7151 outerList = innerList.subList(1, innerList.size());
7152 }
7153 MethodType predType = pred.type();
7154 if (predType.returnType() != boolean.class ||
7155 !predType.effectivelyIdenticalParameters(0, innerList)) {
7156 throw misMatchedTypes("loop predicate", predType, methodType(boolean.class, innerList));
7157 }
7158 if (init != null) {
7159 MethodType initType = init.type();
7160 if (initType.returnType() != returnType ||
7161 !initType.effectivelyIdenticalParameters(0, outerList)) {
7162 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
7163 }
7164 }
7165 }
7166
7167 /**
7168 * Constructs a loop that runs a given number of iterations.
7169 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
7170 * <p>
7171 * The number of iterations is determined by the {@code iterations} handle evaluation result.
7172 * The loop counter {@code i} is an extra loop iteration variable of type {@code int}.
7173 * It will be initialized to 0 and incremented by 1 in each iteration.
7174 * <p>
7175 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
7176 * of that type is also present. This variable is initialized using the optional {@code init} handle,
7177 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
7178 * <p>
7179 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
7180 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
7181 * iteration variable.
7182 * The result of the loop handle execution will be the final {@code V} value of that variable
7183 * (or {@code void} if there is no {@code V} variable).
7184 * <p>
7185 * The following rules hold for the argument handles:<ul>
7186 * <li>The {@code iterations} handle must not be {@code null}, and must return
7187 * the type {@code int}, referred to here as {@code I} in parameter type lists.
7188 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
7189 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
7190 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
7191 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
7192 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
7193 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
7194 * of types called the <em>internal parameter list</em>.
7195 * It will constrain the parameter lists of the other loop parts.
7196 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
7197 * with no additional {@code A} types, then the internal parameter list is extended by
7198 * the argument types {@code A...} of the {@code iterations} handle.
7199 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
7200 * list {@code (A...)} is called the <em>external parameter list</em>.
7201 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
7202 * additional state variable of the loop.
7203 * The body must both accept a leading parameter and return a value of this type {@code V}.
7204 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
7205 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
7206 * <a href="MethodHandles.html#effid">effectively identical</a>
7207 * to the external parameter list {@code (A...)}.
7208 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
7209 * {@linkplain #empty default value}.
7210 * <li>The parameter list of {@code iterations} (of some form {@code (A*)}) must be
7211 * effectively identical to the external parameter list {@code (A...)}.
7212 * </ul>
7213 * <p>
7214 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
7215 * <li>The loop handle's result type is the result type {@code V} of the body.
7216 * <li>The loop handle's parameter types are the types {@code (A...)},
7217 * from the external parameter list.
7218 * </ul>
7219 * <p>
7220 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
7221 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
7222 * arguments passed to the loop.
7223 * {@snippet lang="java" :
7224 * int iterations(A...);
7225 * V init(A...);
7226 * V body(V, int, A...);
7227 * V countedLoop(A... a...) {
7228 * int end = iterations(a...);
7229 * V v = init(a...);
7230 * for (int i = 0; i < end; ++i) {
7231 * v = body(v, i, a...);
7232 * }
7233 * return v;
7234 * }
7235 * }
7236 *
7237 * @apiNote Example with a fully conformant body method:
7238 * {@snippet lang="java" :
7239 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
7240 * // => a variation on a well known theme
7241 * static String step(String v, int counter, String init) { return "na " + v; }
7242 * // assume MH_step is a handle to the method above
7243 * MethodHandle fit13 = MethodHandles.constant(int.class, 13);
7244 * MethodHandle start = MethodHandles.identity(String.class);
7245 * MethodHandle loop = MethodHandles.countedLoop(fit13, start, MH_step);
7246 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("Lambdaman!"));
7247 * }
7248 *
7249 * @apiNote Example with the simplest possible body method type,
7250 * and passing the number of iterations to the loop invocation:
7251 * {@snippet lang="java" :
7252 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
7253 * // => a variation on a well known theme
7254 * static String step(String v, int counter ) { return "na " + v; }
7255 * // assume MH_step is a handle to the method above
7256 * MethodHandle count = MethodHandles.dropArguments(MethodHandles.identity(int.class), 1, String.class);
7257 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class);
7258 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i) -> "na " + v
7259 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "Lambdaman!"));
7260 * }
7261 *
7262 * @apiNote Example that treats the number of iterations, string to append to, and string to append
7263 * as loop parameters:
7264 * {@snippet lang="java" :
7265 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
7266 * // => a variation on a well known theme
7267 * static String step(String v, int counter, int iterations_, String pre, String start_) { return pre + " " + v; }
7268 * // assume MH_step is a handle to the method above
7269 * MethodHandle count = MethodHandles.identity(int.class);
7270 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class, String.class);
7271 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i, _, pre, _) -> pre + " " + v
7272 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "na", "Lambdaman!"));
7273 * }
7274 *
7275 * @apiNote Example that illustrates the usage of {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}
7276 * to enforce a loop type:
7277 * {@snippet lang="java" :
7278 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
7279 * // => a variation on a well known theme
7280 * static String step(String v, int counter, String pre) { return pre + " " + v; }
7281 * // assume MH_step is a handle to the method above
7282 * MethodType loopType = methodType(String.class, String.class, int.class, String.class);
7283 * MethodHandle count = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(int.class), 0, loopType.parameterList(), 1);
7284 * MethodHandle start = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(String.class), 0, loopType.parameterList(), 2);
7285 * MethodHandle body = MethodHandles.dropArgumentsToMatch(MH_step, 2, loopType.parameterList(), 0);
7286 * MethodHandle loop = MethodHandles.countedLoop(count, start, body); // (v, i, pre, _, _) -> pre + " " + v
7287 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("na", 13, "Lambdaman!"));
7288 * }
7289 *
7290 * @apiNote The implementation of this method can be expressed as follows:
7291 * {@snippet lang="java" :
7292 * MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
7293 * return countedLoop(empty(iterations.type()), iterations, init, body);
7294 * }
7295 * }
7296 *
7297 * @param iterations a non-{@code null} handle to return the number of iterations this loop should run. The handle's
7298 * result type must be {@code int}. See above for other constraints.
7299 * @param init optional initializer, providing the initial value of the loop variable.
7300 * May be {@code null}, implying a default initial value. See above for other constraints.
7301 * @param body body of the loop, which may not be {@code null}.
7302 * It controls the loop parameters and result type in the standard case (see above for details).
7303 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
7304 * and may accept any number of additional types.
7305 * See above for other constraints.
7306 *
7307 * @return a method handle representing the loop.
7308 * @throws NullPointerException if either of the {@code iterations} or {@code body} handles is {@code null}.
7309 * @throws IllegalArgumentException if any argument violates the rules formulated above.
7310 *
7311 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle, MethodHandle)
7312 * @since 9
7313 */
7314 public static MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
7315 return countedLoop(empty(iterations.type()), iterations, init, body);
7316 }
7317
7318 /**
7319 * Constructs a loop that counts over a range of numbers.
7320 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
7321 * <p>
7322 * The loop counter {@code i} is a loop iteration variable of type {@code int}.
7323 * The {@code start} and {@code end} handles determine the start (inclusive) and end (exclusive)
7324 * values of the loop counter.
7325 * The loop counter will be initialized to the {@code int} value returned from the evaluation of the
7326 * {@code start} handle and run to the value returned from {@code end} (exclusively) with a step width of 1.
7327 * <p>
7328 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
7329 * of that type is also present. This variable is initialized using the optional {@code init} handle,
7330 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
7331 * <p>
7332 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
7333 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
7334 * iteration variable.
7335 * The result of the loop handle execution will be the final {@code V} value of that variable
7336 * (or {@code void} if there is no {@code V} variable).
7337 * <p>
7338 * The following rules hold for the argument handles:<ul>
7339 * <li>The {@code start} and {@code end} handles must not be {@code null}, and must both return
7340 * the common type {@code int}, referred to here as {@code I} in parameter type lists.
7341 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
7342 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
7343 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
7344 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
7345 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
7346 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
7347 * of types called the <em>internal parameter list</em>.
7348 * It will constrain the parameter lists of the other loop parts.
7349 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
7350 * with no additional {@code A} types, then the internal parameter list is extended by
7351 * the argument types {@code A...} of the {@code end} handle.
7352 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
7353 * list {@code (A...)} is called the <em>external parameter list</em>.
7354 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
7355 * additional state variable of the loop.
7356 * The body must both accept a leading parameter and return a value of this type {@code V}.
7357 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
7358 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
7359 * <a href="MethodHandles.html#effid">effectively identical</a>
7360 * to the external parameter list {@code (A...)}.
7361 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
7362 * {@linkplain #empty default value}.
7363 * <li>The parameter list of {@code start} (of some form {@code (A*)}) must be
7364 * effectively identical to the external parameter list {@code (A...)}.
7365 * <li>Likewise, the parameter list of {@code end} must be effectively identical
7366 * to the external parameter list.
7367 * </ul>
7368 * <p>
7369 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
7370 * <li>The loop handle's result type is the result type {@code V} of the body.
7371 * <li>The loop handle's parameter types are the types {@code (A...)},
7372 * from the external parameter list.
7373 * </ul>
7374 * <p>
7375 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
7376 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
7377 * arguments passed to the loop.
7378 * {@snippet lang="java" :
7379 * int start(A...);
7380 * int end(A...);
7381 * V init(A...);
7382 * V body(V, int, A...);
7383 * V countedLoop(A... a...) {
7384 * int e = end(a...);
7385 * int s = start(a...);
7386 * V v = init(a...);
7387 * for (int i = s; i < e; ++i) {
7388 * v = body(v, i, a...);
7389 * }
7390 * return v;
7391 * }
7392 * }
7393 *
7394 * @apiNote The implementation of this method can be expressed as follows:
7395 * {@snippet lang="java" :
7396 * MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
7397 * MethodHandle returnVar = dropArguments(identity(init.type().returnType()), 0, int.class, int.class);
7398 * // assume MH_increment and MH_predicate are handles to implementation-internal methods with
7399 * // the following semantics:
7400 * // MH_increment: (int limit, int counter) -> counter + 1
7401 * // MH_predicate: (int limit, int counter) -> counter < limit
7402 * Class<?> counterType = start.type().returnType(); // int
7403 * Class<?> returnType = body.type().returnType();
7404 * MethodHandle incr = MH_increment, pred = MH_predicate, retv = null;
7405 * if (returnType != void.class) { // ignore the V variable
7406 * incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
7407 * pred = dropArguments(pred, 1, returnType); // ditto
7408 * retv = dropArguments(identity(returnType), 0, counterType); // ignore limit
7409 * }
7410 * body = dropArguments(body, 0, counterType); // ignore the limit variable
7411 * MethodHandle[]
7412 * loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
7413 * bodyClause = { init, body }, // v = init(); v = body(v, i)
7414 * indexVar = { start, incr }; // i = start(); i = i + 1
7415 * return loop(loopLimit, bodyClause, indexVar);
7416 * }
7417 * }
7418 *
7419 * @param start a non-{@code null} handle to return the start value of the loop counter, which must be {@code int}.
7420 * See above for other constraints.
7421 * @param end a non-{@code null} handle to return the end value of the loop counter (the loop will run to
7422 * {@code end-1}). The result type must be {@code int}. See above for other constraints.
7423 * @param init optional initializer, providing the initial value of the loop variable.
7424 * May be {@code null}, implying a default initial value. See above for other constraints.
7425 * @param body body of the loop, which may not be {@code null}.
7426 * It controls the loop parameters and result type in the standard case (see above for details).
7427 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
7428 * and may accept any number of additional types.
7429 * See above for other constraints.
7430 *
7431 * @return a method handle representing the loop.
7432 * @throws NullPointerException if any of the {@code start}, {@code end}, or {@code body} handles is {@code null}.
7433 * @throws IllegalArgumentException if any argument violates the rules formulated above.
7434 *
7435 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle)
7436 * @since 9
7437 */
7438 public static MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
7439 countedLoopChecks(start, end, init, body);
7440 Class<?> counterType = start.type().returnType(); // int, but who's counting?
7441 Class<?> limitType = end.type().returnType(); // yes, int again
7442 Class<?> returnType = body.type().returnType();
7443 MethodHandle incr = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopStep);
7444 MethodHandle pred = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopPred);
7445 MethodHandle retv = null;
7446 if (returnType != void.class) {
7447 incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
7448 pred = dropArguments(pred, 1, returnType); // ditto
7449 retv = dropArguments(identity(returnType), 0, counterType);
7450 }
7451 body = dropArguments(body, 0, counterType); // ignore the limit variable
7452 MethodHandle[]
7453 loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
7454 bodyClause = { init, body }, // v = init(); v = body(v, i)
7455 indexVar = { start, incr }; // i = start(); i = i + 1
7456 return loop(loopLimit, bodyClause, indexVar);
7457 }
7458
7459 private static void countedLoopChecks(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
7460 Objects.requireNonNull(start);
7461 Objects.requireNonNull(end);
7462 Objects.requireNonNull(body);
7463 Class<?> counterType = start.type().returnType();
7464 if (counterType != int.class) {
7465 MethodType expected = start.type().changeReturnType(int.class);
7466 throw misMatchedTypes("start function", start.type(), expected);
7467 } else if (end.type().returnType() != counterType) {
7468 MethodType expected = end.type().changeReturnType(counterType);
7469 throw misMatchedTypes("end function", end.type(), expected);
7470 }
7471 MethodType bodyType = body.type();
7472 Class<?> returnType = bodyType.returnType();
7473 List<Class<?>> innerList = bodyType.parameterList();
7474 // strip leading V value if present
7475 int vsize = (returnType == void.class ? 0 : 1);
7476 if (vsize != 0 && (innerList.isEmpty() || innerList.get(0) != returnType)) {
7477 // argument list has no "V" => error
7478 MethodType expected = bodyType.insertParameterTypes(0, returnType);
7479 throw misMatchedTypes("body function", bodyType, expected);
7480 } else if (innerList.size() <= vsize || innerList.get(vsize) != counterType) {
7481 // missing I type => error
7482 MethodType expected = bodyType.insertParameterTypes(vsize, counterType);
7483 throw misMatchedTypes("body function", bodyType, expected);
7484 }
7485 List<Class<?>> outerList = innerList.subList(vsize + 1, innerList.size());
7486 if (outerList.isEmpty()) {
7487 // special case; take lists from end handle
7488 outerList = end.type().parameterList();
7489 innerList = bodyType.insertParameterTypes(vsize + 1, outerList).parameterList();
7490 }
7491 MethodType expected = methodType(counterType, outerList);
7492 if (!start.type().effectivelyIdenticalParameters(0, outerList)) {
7493 throw misMatchedTypes("start parameter types", start.type(), expected);
7494 }
7495 if (end.type() != start.type() &&
7496 !end.type().effectivelyIdenticalParameters(0, outerList)) {
7497 throw misMatchedTypes("end parameter types", end.type(), expected);
7498 }
7499 if (init != null) {
7500 MethodType initType = init.type();
7501 if (initType.returnType() != returnType ||
7502 !initType.effectivelyIdenticalParameters(0, outerList)) {
7503 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
7504 }
7505 }
7506 }
7507
7508 /**
7509 * Constructs a loop that ranges over the values produced by an {@code Iterator<T>}.
7510 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
7511 * <p>
7512 * The iterator itself will be determined by the evaluation of the {@code iterator} handle.
7513 * Each value it produces will be stored in a loop iteration variable of type {@code T}.
7514 * <p>
7515 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
7516 * of that type is also present. This variable is initialized using the optional {@code init} handle,
7517 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
7518 * <p>
7519 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
7520 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
7521 * iteration variable.
7522 * The result of the loop handle execution will be the final {@code V} value of that variable
7523 * (or {@code void} if there is no {@code V} variable).
7524 * <p>
7525 * The following rules hold for the argument handles:<ul>
7526 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
7527 * {@code (V T A...)V}, where {@code V} is non-{@code void}, or else {@code (T A...)void}.
7528 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
7529 * and we will write {@code (V T A...)V} with the understanding that a {@code void} type {@code V}
7530 * is quietly dropped from the parameter list, leaving {@code (T A...)V}.)
7531 * <li>The parameter list {@code (V T A...)} of the body contributes to a list
7532 * of types called the <em>internal parameter list</em>.
7533 * It will constrain the parameter lists of the other loop parts.
7534 * <li>As a special case, if the body contributes only {@code V} and {@code T} types,
7535 * with no additional {@code A} types, then the internal parameter list is extended by
7536 * the argument types {@code A...} of the {@code iterator} handle; if it is {@code null} the
7537 * single type {@code Iterable} is added and constitutes the {@code A...} list.
7538 * <li>If the iteration variable types {@code (V T)} are dropped from the internal parameter list, the resulting shorter
7539 * list {@code (A...)} is called the <em>external parameter list</em>.
7540 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
7541 * additional state variable of the loop.
7542 * The body must both accept a leading parameter and return a value of this type {@code V}.
7543 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
7544 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
7545 * <a href="MethodHandles.html#effid">effectively identical</a>
7546 * to the external parameter list {@code (A...)}.
7547 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
7548 * {@linkplain #empty default value}.
7549 * <li>If the {@code iterator} handle is non-{@code null}, it must have the return
7550 * type {@code java.util.Iterator} or a subtype thereof.
7551 * The iterator it produces when the loop is executed will be assumed
7552 * to yield values which can be converted to type {@code T}.
7553 * <li>The parameter list of an {@code iterator} that is non-{@code null} (of some form {@code (A*)}) must be
7554 * effectively identical to the external parameter list {@code (A...)}.
7555 * <li>If {@code iterator} is {@code null} it defaults to a method handle which behaves
7556 * like {@link java.lang.Iterable#iterator()}. In that case, the internal parameter list
7557 * {@code (V T A...)} must have at least one {@code A} type, and the default iterator
7558 * handle parameter is adjusted to accept the leading {@code A} type, as if by
7559 * the {@link MethodHandle#asType asType} conversion method.
7560 * The leading {@code A} type must be {@code Iterable} or a subtype thereof.
7561 * This conversion step, done at loop construction time, must not throw a {@code WrongMethodTypeException}.
7562 * </ul>
7563 * <p>
7564 * The type {@code T} may be either a primitive or reference.
7565 * Since type {@code Iterator<T>} is erased in the method handle representation to the raw type {@code Iterator},
7566 * the {@code iteratedLoop} combinator adjusts the leading argument type for {@code body} to {@code Object}
7567 * as if by the {@link MethodHandle#asType asType} conversion method.
7568 * Therefore, if an iterator of the wrong type appears as the loop is executed, runtime exceptions may occur
7569 * as the result of dynamic conversions performed by {@link MethodHandle#asType(MethodType)}.
7570 * <p>
7571 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
7572 * <li>The loop handle's result type is the result type {@code V} of the body.
7573 * <li>The loop handle's parameter types are the types {@code (A...)},
7574 * from the external parameter list.
7575 * </ul>
7576 * <p>
7577 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
7578 * the loop variable as well as the result type of the loop; {@code T}/{@code t}, that of the elements of the
7579 * structure the loop iterates over, and {@code A...}/{@code a...} represent arguments passed to the loop.
7580 * {@snippet lang="java" :
7581 * Iterator<T> iterator(A...); // defaults to Iterable::iterator
7582 * V init(A...);
7583 * V body(V,T,A...);
7584 * V iteratedLoop(A... a...) {
7585 * Iterator<T> it = iterator(a...);
7586 * V v = init(a...);
7587 * while (it.hasNext()) {
7588 * T t = it.next();
7589 * v = body(v, t, a...);
7590 * }
7591 * return v;
7592 * }
7593 * }
7594 *
7595 * @apiNote Example:
7596 * {@snippet lang="java" :
7597 * // get an iterator from a list
7598 * static List<String> reverseStep(List<String> r, String e) {
7599 * r.add(0, e);
7600 * return r;
7601 * }
7602 * static List<String> newArrayList() { return new ArrayList<>(); }
7603 * // assume MH_reverseStep and MH_newArrayList are handles to the above methods
7604 * MethodHandle loop = MethodHandles.iteratedLoop(null, MH_newArrayList, MH_reverseStep);
7605 * List<String> list = Arrays.asList("a", "b", "c", "d", "e");
7606 * List<String> reversedList = Arrays.asList("e", "d", "c", "b", "a");
7607 * assertEquals(reversedList, (List<String>) loop.invoke(list));
7608 * }
7609 *
7610 * @apiNote The implementation of this method can be expressed approximately as follows:
7611 * {@snippet lang="java" :
7612 * MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
7613 * // assume MH_next, MH_hasNext, MH_startIter are handles to methods of Iterator/Iterable
7614 * Class<?> returnType = body.type().returnType();
7615 * Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
7616 * MethodHandle nextVal = MH_next.asType(MH_next.type().changeReturnType(ttype));
7617 * MethodHandle retv = null, step = body, startIter = iterator;
7618 * if (returnType != void.class) {
7619 * // the simple thing first: in (I V A...), drop the I to get V
7620 * retv = dropArguments(identity(returnType), 0, Iterator.class);
7621 * // body type signature (V T A...), internal loop types (I V A...)
7622 * step = swapArguments(body, 0, 1); // swap V <-> T
7623 * }
7624 * if (startIter == null) startIter = MH_getIter;
7625 * MethodHandle[]
7626 * iterVar = { startIter, null, MH_hasNext, retv }, // it = iterator; while (it.hasNext())
7627 * bodyClause = { init, filterArguments(step, 0, nextVal) }; // v = body(v, t, a)
7628 * return loop(iterVar, bodyClause);
7629 * }
7630 * }
7631 *
7632 * @param iterator an optional handle to return the iterator to start the loop.
7633 * If non-{@code null}, the handle must return {@link java.util.Iterator} or a subtype.
7634 * See above for other constraints.
7635 * @param init optional initializer, providing the initial value of the loop variable.
7636 * May be {@code null}, implying a default initial value. See above for other constraints.
7637 * @param body body of the loop, which may not be {@code null}.
7638 * It controls the loop parameters and result type in the standard case (see above for details).
7639 * It must accept its own return type (if non-void) plus a {@code T} parameter (for the iterated values),
7640 * and may accept any number of additional types.
7641 * See above for other constraints.
7642 *
7643 * @return a method handle embodying the iteration loop functionality.
7644 * @throws NullPointerException if the {@code body} handle is {@code null}.
7645 * @throws IllegalArgumentException if any argument violates the above requirements.
7646 *
7647 * @since 9
7648 */
7649 public static MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
7650 Class<?> iterableType = iteratedLoopChecks(iterator, init, body);
7651 Class<?> returnType = body.type().returnType();
7652 MethodHandle hasNext = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iteratePred);
7653 MethodHandle nextRaw = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iterateNext);
7654 MethodHandle startIter;
7655 MethodHandle nextVal;
7656 {
7657 MethodType iteratorType;
7658 if (iterator == null) {
7659 // derive argument type from body, if available, else use Iterable
7660 startIter = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_initIterator);
7661 iteratorType = startIter.type().changeParameterType(0, iterableType);
7662 } else {
7663 // force return type to the internal iterator class
7664 iteratorType = iterator.type().changeReturnType(Iterator.class);
7665 startIter = iterator;
7666 }
7667 Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
7668 MethodType nextValType = nextRaw.type().changeReturnType(ttype);
7669
7670 // perform the asType transforms under an exception transformer, as per spec.:
7671 try {
7672 startIter = startIter.asType(iteratorType);
7673 nextVal = nextRaw.asType(nextValType);
7674 } catch (WrongMethodTypeException ex) {
7675 throw new IllegalArgumentException(ex);
7676 }
7677 }
7678
7679 MethodHandle retv = null, step = body;
7680 if (returnType != void.class) {
7681 // the simple thing first: in (I V A...), drop the I to get V
7682 retv = dropArguments(identity(returnType), 0, Iterator.class);
7683 // body type signature (V T A...), internal loop types (I V A...)
7684 step = swapArguments(body, 0, 1); // swap V <-> T
7685 }
7686
7687 MethodHandle[]
7688 iterVar = { startIter, null, hasNext, retv },
7689 bodyClause = { init, filterArgument(step, 0, nextVal) };
7690 return loop(iterVar, bodyClause);
7691 }
7692
7693 private static Class<?> iteratedLoopChecks(MethodHandle iterator, MethodHandle init, MethodHandle body) {
7694 Objects.requireNonNull(body);
7695 MethodType bodyType = body.type();
7696 Class<?> returnType = bodyType.returnType();
7697 List<Class<?>> internalParamList = bodyType.parameterList();
7698 // strip leading V value if present
7699 int vsize = (returnType == void.class ? 0 : 1);
7700 if (vsize != 0 && (internalParamList.isEmpty() || internalParamList.get(0) != returnType)) {
7701 // argument list has no "V" => error
7702 MethodType expected = bodyType.insertParameterTypes(0, returnType);
7703 throw misMatchedTypes("body function", bodyType, expected);
7704 } else if (internalParamList.size() <= vsize) {
7705 // missing T type => error
7706 MethodType expected = bodyType.insertParameterTypes(vsize, Object.class);
7707 throw misMatchedTypes("body function", bodyType, expected);
7708 }
7709 List<Class<?>> externalParamList = internalParamList.subList(vsize + 1, internalParamList.size());
7710 Class<?> iterableType = null;
7711 if (iterator != null) {
7712 // special case; if the body handle only declares V and T then
7713 // the external parameter list is obtained from iterator handle
7714 if (externalParamList.isEmpty()) {
7715 externalParamList = iterator.type().parameterList();
7716 }
7717 MethodType itype = iterator.type();
7718 if (!Iterator.class.isAssignableFrom(itype.returnType())) {
7719 throw newIllegalArgumentException("iteratedLoop first argument must have Iterator return type");
7720 }
7721 if (!itype.effectivelyIdenticalParameters(0, externalParamList)) {
7722 MethodType expected = methodType(itype.returnType(), externalParamList);
7723 throw misMatchedTypes("iterator parameters", itype, expected);
7724 }
7725 } else {
7726 if (externalParamList.isEmpty()) {
7727 // special case; if the iterator handle is null and the body handle
7728 // only declares V and T then the external parameter list consists
7729 // of Iterable
7730 externalParamList = List.of(Iterable.class);
7731 iterableType = Iterable.class;
7732 } else {
7733 // special case; if the iterator handle is null and the external
7734 // parameter list is not empty then the first parameter must be
7735 // assignable to Iterable
7736 iterableType = externalParamList.get(0);
7737 if (!Iterable.class.isAssignableFrom(iterableType)) {
7738 throw newIllegalArgumentException(
7739 "inferred first loop argument must inherit from Iterable: " + iterableType);
7740 }
7741 }
7742 }
7743 if (init != null) {
7744 MethodType initType = init.type();
7745 if (initType.returnType() != returnType ||
7746 !initType.effectivelyIdenticalParameters(0, externalParamList)) {
7747 throw misMatchedTypes("loop initializer", initType, methodType(returnType, externalParamList));
7748 }
7749 }
7750 return iterableType; // help the caller a bit
7751 }
7752
7753 /*non-public*/
7754 static MethodHandle swapArguments(MethodHandle mh, int i, int j) {
7755 // there should be a better way to uncross my wires
7756 int arity = mh.type().parameterCount();
7757 int[] order = new int[arity];
7758 for (int k = 0; k < arity; k++) order[k] = k;
7759 order[i] = j; order[j] = i;
7760 Class<?>[] types = mh.type().parameterArray();
7761 Class<?> ti = types[i]; types[i] = types[j]; types[j] = ti;
7762 MethodType swapType = methodType(mh.type().returnType(), types);
7763 return permuteArguments(mh, swapType, order);
7764 }
7765
7766 /**
7767 * Makes a method handle that adapts a {@code target} method handle by wrapping it in a {@code try-finally} block.
7768 * Another method handle, {@code cleanup}, represents the functionality of the {@code finally} block. Any exception
7769 * thrown during the execution of the {@code target} handle will be passed to the {@code cleanup} handle. The
7770 * exception will be rethrown, unless {@code cleanup} handle throws an exception first. The
7771 * value returned from the {@code cleanup} handle's execution will be the result of the execution of the
7772 * {@code try-finally} handle.
7773 * <p>
7774 * The {@code cleanup} handle will be passed one or two additional leading arguments.
7775 * The first is the exception thrown during the
7776 * execution of the {@code target} handle, or {@code null} if no exception was thrown.
7777 * The second is the result of the execution of the {@code target} handle, or, if it throws an exception,
7778 * a {@code null}, zero, or {@code false} value of the required type is supplied as a placeholder.
7779 * The second argument is not present if the {@code target} handle has a {@code void} return type.
7780 * (Note that, except for argument type conversions, combinators represent {@code void} values in parameter lists
7781 * by omitting the corresponding paradoxical arguments, not by inserting {@code null} or zero values.)
7782 * <p>
7783 * The {@code target} and {@code cleanup} handles must have the same corresponding argument and return types, except
7784 * that the {@code cleanup} handle may omit trailing arguments. Also, the {@code cleanup} handle must have one or
7785 * two extra leading parameters:<ul>
7786 * <li>a {@code Throwable}, which will carry the exception thrown by the {@code target} handle (if any); and
7787 * <li>a parameter of the same type as the return type of both {@code target} and {@code cleanup}, which will carry
7788 * the result from the execution of the {@code target} handle.
7789 * This parameter is not present if the {@code target} returns {@code void}.
7790 * </ul>
7791 * <p>
7792 * The pseudocode for the resulting adapter looks as follows. In the code, {@code V} represents the result type of
7793 * the {@code try/finally} construct; {@code A}/{@code a}, the types and values of arguments to the resulting
7794 * handle consumed by the cleanup; and {@code B}/{@code b}, those of arguments to the resulting handle discarded by
7795 * the cleanup.
7796 * {@snippet lang="java" :
7797 * V target(A..., B...);
7798 * V cleanup(Throwable, V, A...);
7799 * V adapter(A... a, B... b) {
7800 * V result = (zero value for V);
7801 * Throwable throwable = null;
7802 * try {
7803 * result = target(a..., b...);
7804 * } catch (Throwable t) {
7805 * throwable = t;
7806 * throw t;
7807 * } finally {
7808 * result = cleanup(throwable, result, a...);
7809 * }
7810 * return result;
7811 * }
7812 * }
7813 * <p>
7814 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
7815 * be modified by execution of the target, and so are passed unchanged
7816 * from the caller to the cleanup, if it is invoked.
7817 * <p>
7818 * The target and cleanup must return the same type, even if the cleanup
7819 * always throws.
7820 * To create such a throwing cleanup, compose the cleanup logic
7821 * with {@link #throwException throwException},
7822 * in order to create a method handle of the correct return type.
7823 * <p>
7824 * Note that {@code tryFinally} never converts exceptions into normal returns.
7825 * In rare cases where exceptions must be converted in that way, first wrap
7826 * the target with {@link #catchException(MethodHandle, Class, MethodHandle)}
7827 * to capture an outgoing exception, and then wrap with {@code tryFinally}.
7828 * <p>
7829 * It is recommended that the first parameter type of {@code cleanup} be
7830 * declared {@code Throwable} rather than a narrower subtype. This ensures
7831 * {@code cleanup} will always be invoked with whatever exception that
7832 * {@code target} throws. Declaring a narrower type may result in a
7833 * {@code ClassCastException} being thrown by the {@code try-finally}
7834 * handle if the type of the exception thrown by {@code target} is not
7835 * assignable to the first parameter type of {@code cleanup}. Note that
7836 * various exception types of {@code VirtualMachineError},
7837 * {@code LinkageError}, and {@code RuntimeException} can in principle be
7838 * thrown by almost any kind of Java code, and a finally clause that
7839 * catches (say) only {@code IOException} would mask any of the others
7840 * behind a {@code ClassCastException}.
7841 *
7842 * @param target the handle whose execution is to be wrapped in a {@code try} block.
7843 * @param cleanup the handle that is invoked in the finally block.
7844 *
7845 * @return a method handle embodying the {@code try-finally} block composed of the two arguments.
7846 * @throws NullPointerException if any argument is null
7847 * @throws IllegalArgumentException if {@code cleanup} does not accept
7848 * the required leading arguments, or if the method handle types do
7849 * not match in their return types and their
7850 * corresponding trailing parameters
7851 *
7852 * @see MethodHandles#catchException(MethodHandle, Class, MethodHandle)
7853 * @since 9
7854 */
7855 public static MethodHandle tryFinally(MethodHandle target, MethodHandle cleanup) {
7856 Class<?>[] targetParamTypes = target.type().ptypes();
7857 Class<?> rtype = target.type().returnType();
7858
7859 tryFinallyChecks(target, cleanup);
7860
7861 // Match parameter lists: if the cleanup has a shorter parameter list than the target, add ignored arguments.
7862 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
7863 // target parameter list.
7864 cleanup = dropArgumentsToMatch(cleanup, (rtype == void.class ? 1 : 2), targetParamTypes, 0, false);
7865
7866 // Ensure that the intrinsic type checks the instance thrown by the
7867 // target against the first parameter of cleanup
7868 cleanup = cleanup.asType(cleanup.type().changeParameterType(0, Throwable.class));
7869
7870 // Use asFixedArity() to avoid unnecessary boxing of last argument for VarargsCollector case.
7871 return MethodHandleImpl.makeTryFinally(target.asFixedArity(), cleanup.asFixedArity(), rtype, targetParamTypes);
7872 }
7873
7874 private static void tryFinallyChecks(MethodHandle target, MethodHandle cleanup) {
7875 Class<?> rtype = target.type().returnType();
7876 if (rtype != cleanup.type().returnType()) {
7877 throw misMatchedTypes("target and return types", cleanup.type().returnType(), rtype);
7878 }
7879 MethodType cleanupType = cleanup.type();
7880 if (!Throwable.class.isAssignableFrom(cleanupType.parameterType(0))) {
7881 throw misMatchedTypes("cleanup first argument and Throwable", cleanup.type(), Throwable.class);
7882 }
7883 if (rtype != void.class && cleanupType.parameterType(1) != rtype) {
7884 throw misMatchedTypes("cleanup second argument and target return type", cleanup.type(), rtype);
7885 }
7886 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
7887 // target parameter list.
7888 int cleanupArgIndex = rtype == void.class ? 1 : 2;
7889 if (!cleanupType.effectivelyIdenticalParameters(cleanupArgIndex, target.type().parameterList())) {
7890 throw misMatchedTypes("cleanup parameters after (Throwable,result) and target parameter list prefix",
7891 cleanup.type(), target.type());
7892 }
7893 }
7894
7895 /**
7896 * Creates a table switch method handle, which can be used to switch over a set of target
7897 * method handles, based on a given target index, called selector.
7898 * <p>
7899 * For a selector value of {@code n}, where {@code n} falls in the range {@code [0, N)},
7900 * and where {@code N} is the number of target method handles, the table switch method
7901 * handle will invoke the n-th target method handle from the list of target method handles.
7902 * <p>
7903 * For a selector value that does not fall in the range {@code [0, N)}, the table switch
7904 * method handle will invoke the given fallback method handle.
7905 * <p>
7906 * All method handles passed to this method must have the same type, with the additional
7907 * requirement that the leading parameter be of type {@code int}. The leading parameter
7908 * represents the selector.
7909 * <p>
7910 * Any trailing parameters present in the type will appear on the returned table switch
7911 * method handle as well. Any arguments assigned to these parameters will be forwarded,
7912 * together with the selector value, to the selected method handle when invoking it.
7913 *
7914 * @apiNote Example:
7915 * The cases each drop the {@code selector} value they are given, and take an additional
7916 * {@code String} argument, which is concatenated (using {@link String#concat(String)})
7917 * to a specific constant label string for each case:
7918 * {@snippet lang="java" :
7919 * MethodHandles.Lookup lookup = MethodHandles.lookup();
7920 * MethodHandle caseMh = lookup.findVirtual(String.class, "concat",
7921 * MethodType.methodType(String.class, String.class));
7922 * caseMh = MethodHandles.dropArguments(caseMh, 0, int.class);
7923 *
7924 * MethodHandle caseDefault = MethodHandles.insertArguments(caseMh, 1, "default: ");
7925 * MethodHandle case0 = MethodHandles.insertArguments(caseMh, 1, "case 0: ");
7926 * MethodHandle case1 = MethodHandles.insertArguments(caseMh, 1, "case 1: ");
7927 *
7928 * MethodHandle mhSwitch = MethodHandles.tableSwitch(
7929 * caseDefault,
7930 * case0,
7931 * case1
7932 * );
7933 *
7934 * assertEquals("default: data", (String) mhSwitch.invokeExact(-1, "data"));
7935 * assertEquals("case 0: data", (String) mhSwitch.invokeExact(0, "data"));
7936 * assertEquals("case 1: data", (String) mhSwitch.invokeExact(1, "data"));
7937 * assertEquals("default: data", (String) mhSwitch.invokeExact(2, "data"));
7938 * }
7939 *
7940 * @param fallback the fallback method handle that is called when the selector is not
7941 * within the range {@code [0, N)}.
7942 * @param targets array of target method handles.
7943 * @return the table switch method handle.
7944 * @throws NullPointerException if {@code fallback}, the {@code targets} array, or any
7945 * any of the elements of the {@code targets} array are
7946 * {@code null}.
7947 * @throws IllegalArgumentException if the {@code targets} array is empty, if the leading
7948 * parameter of the fallback handle or any of the target
7949 * handles is not {@code int}, or if the types of
7950 * the fallback handle and all of target handles are
7951 * not the same.
7952 */
7953 public static MethodHandle tableSwitch(MethodHandle fallback, MethodHandle... targets) {
7954 Objects.requireNonNull(fallback);
7955 Objects.requireNonNull(targets);
7956 targets = targets.clone();
7957 MethodType type = tableSwitchChecks(fallback, targets);
7958 return MethodHandleImpl.makeTableSwitch(type, fallback, targets);
7959 }
7960
7961 private static MethodType tableSwitchChecks(MethodHandle defaultCase, MethodHandle[] caseActions) {
7962 if (caseActions.length == 0)
7963 throw new IllegalArgumentException("Not enough cases: " + Arrays.toString(caseActions));
7964
7965 MethodType expectedType = defaultCase.type();
7966
7967 if (!(expectedType.parameterCount() >= 1) || expectedType.parameterType(0) != int.class)
7968 throw new IllegalArgumentException(
7969 "Case actions must have int as leading parameter: " + Arrays.toString(caseActions));
7970
7971 for (MethodHandle mh : caseActions) {
7972 Objects.requireNonNull(mh);
7973 if (mh.type() != expectedType)
7974 throw new IllegalArgumentException(
7975 "Case actions must have the same type: " + Arrays.toString(caseActions));
7976 }
7977
7978 return expectedType;
7979 }
7980
7981 /**
7982 * Creates a var handle object, which can be used to dereference a {@linkplain java.lang.foreign.MemorySegment memory segment}
7983 * at a given byte offset, using the provided value layout.
7984 *
7985 * <p>The provided layout specifies the {@linkplain ValueLayout#carrier() carrier type},
7986 * the {@linkplain ValueLayout#byteSize() byte size},
7987 * the {@linkplain ValueLayout#byteAlignment() byte alignment} and the {@linkplain ValueLayout#order() byte order}
7988 * associated with the returned var handle.
7989 *
7990 * <p>The list of coordinate types associated with the returned var handle is {@code (MemorySegment, long)},
7991 * where the {@code long} coordinate type corresponds to byte offset into the given memory segment coordinate.
7992 * Thus, the returned var handle accesses bytes at an offset in a given memory segment, composing bytes to or from
7993 * a value of the var handle type. Moreover, the access operation will honor the endianness and the
7994 * alignment constraints expressed in the provided layout.
7995 *
7996 * <p>As an example, consider the memory layout expressed by a {@link GroupLayout} instance constructed as follows:
7997 * {@snippet lang="java" :
7998 * GroupLayout seq = java.lang.foreign.MemoryLayout.structLayout(
7999 * MemoryLayout.paddingLayout(4),
8000 * ValueLayout.JAVA_INT.withOrder(ByteOrder.BIG_ENDIAN).withName("value")
8001 * );
8002 * }
8003 * To access the member layout named {@code value}, we can construct a memory segment view var handle as follows:
8004 * {@snippet lang="java" :
8005 * VarHandle handle = MethodHandles.memorySegmentViewVarHandle(ValueLayout.JAVA_INT.withOrder(ByteOrder.BIG_ENDIAN)); //(MemorySegment, long) -> int
8006 * handle = MethodHandles.insertCoordinates(handle, 1, 4); //(MemorySegment) -> int
8007 * }
8008 *
8009 * @apiNote The resulting var handle features certain <i>access mode restrictions</i>,
8010 * which are common to all memory segment view var handles. A memory segment view var handle is associated
8011 * with an access size {@code S} and an alignment constraint {@code B}
8012 * (both expressed in bytes). We say that a memory access operation is <em>fully aligned</em> if it occurs
8013 * at a memory address {@code A} which is compatible with both alignment constraints {@code S} and {@code B}.
8014 * If access is fully aligned then following access modes are supported and are
8015 * guaranteed to support atomic access:
8016 * <ul>
8017 * <li>read write access modes for all {@code T}, with the exception of
8018 * access modes {@code get} and {@code set} for {@code long} and
8019 * {@code double} on 32-bit platforms.
8020 * <li>atomic update access modes for {@code int}, {@code long},
8021 * {@code float}, {@code double} or {@link MemorySegment}.
8022 * (Future major platform releases of the JDK may support additional
8023 * types for certain currently unsupported access modes.)
8024 * <li>numeric atomic update access modes for {@code int}, {@code long} and {@link MemorySegment}.
8025 * (Future major platform releases of the JDK may support additional
8026 * numeric types for certain currently unsupported access modes.)
8027 * <li>bitwise atomic update access modes for {@code int}, {@code long} and {@link MemorySegment}.
8028 * (Future major platform releases of the JDK may support additional
8029 * numeric types for certain currently unsupported access modes.)
8030 * </ul>
8031 *
8032 * If {@code T} is {@code float}, {@code double} or {@link MemorySegment} then atomic
8033 * update access modes compare values using their bitwise representation
8034 * (see {@link Float#floatToRawIntBits},
8035 * {@link Double#doubleToRawLongBits} and {@link MemorySegment#address()}, respectively).
8036 * <p>
8037 * Alternatively, a memory access operation is <em>partially aligned</em> if it occurs at a memory address {@code A}
8038 * which is only compatible with the alignment constraint {@code B}; in such cases, access for anything other than the
8039 * {@code get} and {@code set} access modes will result in an {@code IllegalStateException}. If access is partially aligned,
8040 * atomic access is only guaranteed with respect to the largest power of two that divides the GCD of {@code A} and {@code S}.
8041 * <p>
8042 * In all other cases, we say that a memory access operation is <em>misaligned</em>; in such cases an
8043 * {@code IllegalStateException} is thrown, irrespective of the access mode being used.
8044 * <p>
8045 * Finally, if {@code T} is {@code MemorySegment} all write access modes throw {@link IllegalArgumentException}
8046 * unless the value to be written is a {@linkplain MemorySegment#isNative() native} memory segment.
8047 *
8048 * @param layout the value layout for which a memory access handle is to be obtained.
8049 * @return the new memory segment view var handle.
8050 * @throws NullPointerException if {@code layout} is {@code null}.
8051 * @see MemoryLayout#varHandle(MemoryLayout.PathElement...)
8052 * @since 19
8053 */
8054 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN)
8055 public static VarHandle memorySegmentViewVarHandle(ValueLayout layout) {
8056 Objects.requireNonNull(layout);
8057 return Utils.makeSegmentViewVarHandle(layout);
8058 }
8059
8060 /**
8061 * Adapts a target var handle by pre-processing incoming and outgoing values using a pair of filter functions.
8062 * <p>
8063 * When calling e.g. {@link VarHandle#set(Object...)} on the resulting var handle, the incoming value (of type {@code T}, where
8064 * {@code T} is the <em>last</em> parameter type of the first filter function) is processed using the first filter and then passed
8065 * to the target var handle.
8066 * Conversely, when calling e.g. {@link VarHandle#get(Object...)} on the resulting var handle, the return value obtained from
8067 * the target var handle (of type {@code T}, where {@code T} is the <em>last</em> parameter type of the second filter function)
8068 * is processed using the second filter and returned to the caller. More advanced access mode types, such as
8069 * {@link VarHandle.AccessMode#COMPARE_AND_EXCHANGE} might apply both filters at the same time.
8070 * <p>
8071 * For the boxing and unboxing filters to be well-formed, their types must be of the form {@code (A... , S) -> T} and
8072 * {@code (A... , T) -> S}, respectively, where {@code T} is the type of the target var handle. If this is the case,
8073 * the resulting var handle will have type {@code S} and will feature the additional coordinates {@code A...} (which
8074 * will be appended to the coordinates of the target var handle).
8075 * <p>
8076 * If the boxing and unboxing filters throw any checked exceptions when invoked, the resulting var handle will
8077 * throw an {@link IllegalStateException}.
8078 * <p>
8079 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
8080 * atomic access guarantees as those featured by the target var handle.
8081 *
8082 * @param target the target var handle
8083 * @param filterToTarget a filter to convert some type {@code S} into the type of {@code target}
8084 * @param filterFromTarget a filter to convert the type of {@code target} to some type {@code S}
8085 * @return an adapter var handle which accepts a new type, performing the provided boxing/unboxing conversions.
8086 * @throws IllegalArgumentException if {@code filterFromTarget} and {@code filterToTarget} are not well-formed, that is, they have types
8087 * other than {@code (A... , S) -> T} and {@code (A... , T) -> S}, respectively, where {@code T} is the type of the target var handle,
8088 * or if it's determined that either {@code filterFromTarget} or {@code filterToTarget} throws any checked exceptions.
8089 * @throws NullPointerException if any of the arguments is {@code null}.
8090 * @since 19
8091 */
8092 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN)
8093 public static VarHandle filterValue(VarHandle target, MethodHandle filterToTarget, MethodHandle filterFromTarget) {
8094 return VarHandles.filterValue(target, filterToTarget, filterFromTarget);
8095 }
8096
8097 /**
8098 * Adapts a target var handle by pre-processing incoming coordinate values using unary filter functions.
8099 * <p>
8100 * When calling e.g. {@link VarHandle#get(Object...)} on the resulting var handle, the incoming coordinate values
8101 * starting at position {@code pos} (of type {@code C1, C2 ... Cn}, where {@code C1, C2 ... Cn} are the return types
8102 * of the unary filter functions) are transformed into new values (of type {@code S1, S2 ... Sn}, where {@code S1, S2 ... Sn} are the
8103 * parameter types of the unary filter functions), and then passed (along with any coordinate that was left unaltered
8104 * by the adaptation) to the target var handle.
8105 * <p>
8106 * For the coordinate filters to be well-formed, their types must be of the form {@code S1 -> T1, S2 -> T1 ... Sn -> Tn},
8107 * where {@code T1, T2 ... Tn} are the coordinate types starting at position {@code pos} of the target var handle.
8108 * <p>
8109 * If any of the filters throws a checked exception when invoked, the resulting var handle will
8110 * throw an {@link IllegalStateException}.
8111 * <p>
8112 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
8113 * atomic access guarantees as those featured by the target var handle.
8114 *
8115 * @param target the target var handle
8116 * @param pos the position of the first coordinate to be transformed
8117 * @param filters the unary functions which are used to transform coordinates starting at position {@code pos}
8118 * @return an adapter var handle which accepts new coordinate types, applying the provided transformation
8119 * to the new coordinate values.
8120 * @throws IllegalArgumentException if the handles in {@code filters} are not well-formed, that is, they have types
8121 * other than {@code S1 -> T1, S2 -> T2, ... Sn -> Tn} where {@code T1, T2 ... Tn} are the coordinate types starting
8122 * at position {@code pos} of the target var handle, if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive,
8123 * or if more filters are provided than the actual number of coordinate types available starting at {@code pos},
8124 * or if it's determined that any of the filters throws any checked exceptions.
8125 * @throws NullPointerException if any of the arguments is {@code null} or {@code filters} contains {@code null}.
8126 * @since 19
8127 */
8128 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN)
8129 public static VarHandle filterCoordinates(VarHandle target, int pos, MethodHandle... filters) {
8130 return VarHandles.filterCoordinates(target, pos, filters);
8131 }
8132
8133 /**
8134 * Provides a target var handle with one or more <em>bound coordinates</em>
8135 * in advance of the var handle's invocation. As a consequence, the resulting var handle will feature less
8136 * coordinate types than the target var handle.
8137 * <p>
8138 * When calling e.g. {@link VarHandle#get(Object...)} on the resulting var handle, incoming coordinate values
8139 * are joined with bound coordinate values, and then passed to the target var handle.
8140 * <p>
8141 * For the bound coordinates to be well-formed, their types must be {@code T1, T2 ... Tn },
8142 * where {@code T1, T2 ... Tn} are the coordinate types starting at position {@code pos} of the target var handle.
8143 * <p>
8144 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
8145 * atomic access guarantees as those featured by the target var handle.
8146 *
8147 * @param target the var handle to invoke after the bound coordinates are inserted
8148 * @param pos the position of the first coordinate to be inserted
8149 * @param values the series of bound coordinates to insert
8150 * @return an adapter var handle which inserts additional coordinates,
8151 * before calling the target var handle
8152 * @throws IllegalArgumentException if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive,
8153 * or if more values are provided than the actual number of coordinate types available starting at {@code pos}.
8154 * @throws ClassCastException if the bound coordinates in {@code values} are not well-formed, that is, they have types
8155 * other than {@code T1, T2 ... Tn }, where {@code T1, T2 ... Tn} are the coordinate types starting at position {@code pos}
8156 * of the target var handle.
8157 * @throws NullPointerException if any of the arguments is {@code null} or {@code values} contains {@code null}.
8158 * @since 19
8159 */
8160 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN)
8161 public static VarHandle insertCoordinates(VarHandle target, int pos, Object... values) {
8162 return VarHandles.insertCoordinates(target, pos, values);
8163 }
8164
8165 /**
8166 * Provides a var handle which adapts the coordinate values of the target var handle, by re-arranging them
8167 * so that the new coordinates match the provided ones.
8168 * <p>
8169 * The given array controls the reordering.
8170 * Call {@code #I} the number of incoming coordinates (the value
8171 * {@code newCoordinates.size()}), and call {@code #O} the number
8172 * of outgoing coordinates (the number of coordinates associated with the target var handle).
8173 * Then the length of the reordering array must be {@code #O},
8174 * and each element must be a non-negative number less than {@code #I}.
8175 * For every {@code N} less than {@code #O}, the {@code N}-th
8176 * outgoing coordinate will be taken from the {@code I}-th incoming
8177 * coordinate, where {@code I} is {@code reorder[N]}.
8178 * <p>
8179 * No coordinate value conversions are applied.
8180 * The type of each incoming coordinate, as determined by {@code newCoordinates},
8181 * must be identical to the type of the corresponding outgoing coordinate
8182 * in the target var handle.
8183 * <p>
8184 * The reordering array need not specify an actual permutation.
8185 * An incoming coordinate will be duplicated if its index appears
8186 * more than once in the array, and an incoming coordinate will be dropped
8187 * if its index does not appear in the array.
8188 * <p>
8189 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
8190 * atomic access guarantees as those featured by the target var handle.
8191 * @param target the var handle to invoke after the coordinates have been reordered
8192 * @param newCoordinates the new coordinate types
8193 * @param reorder an index array which controls the reordering
8194 * @return an adapter var handle which re-arranges the incoming coordinate values,
8195 * before calling the target var handle
8196 * @throws IllegalArgumentException if the index array length is not equal to
8197 * the number of coordinates of the target var handle, or if any index array element is not a valid index for
8198 * a coordinate of {@code newCoordinates}, or if two corresponding coordinate types in
8199 * the target var handle and in {@code newCoordinates} are not identical.
8200 * @throws NullPointerException if any of the arguments is {@code null} or {@code newCoordinates} contains {@code null}.
8201 * @since 19
8202 */
8203 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN)
8204 public static VarHandle permuteCoordinates(VarHandle target, List<Class<?>> newCoordinates, int... reorder) {
8205 return VarHandles.permuteCoordinates(target, newCoordinates, reorder);
8206 }
8207
8208 /**
8209 * Adapts a target var handle by pre-processing
8210 * a sub-sequence of its coordinate values with a filter (a method handle).
8211 * The pre-processed coordinates are replaced by the result (if any) of the
8212 * filter function and the target var handle is then called on the modified (usually shortened)
8213 * coordinate list.
8214 * <p>
8215 * If {@code R} is the return type of the filter, then:
8216 * <ul>
8217 * <li>if {@code R} <em>is not</em> {@code void}, the target var handle must have a coordinate of type {@code R} in
8218 * position {@code pos}. The parameter types of the filter will replace the coordinate type at position {@code pos}
8219 * of the target var handle. When the returned var handle is invoked, it will be as if the filter is invoked first,
8220 * and its result is passed in place of the coordinate at position {@code pos} in a downstream invocation of the
8221 * target var handle.</li>
8222 * <li> if {@code R} <em>is</em> {@code void}, the parameter types (if any) of the filter will be inserted in the
8223 * coordinate type list of the target var handle at position {@code pos}. In this case, when the returned var handle
8224 * is invoked, the filter essentially acts as a side effect, consuming some of the coordinate values, before a
8225 * downstream invocation of the target var handle.</li>
8226 * </ul>
8227 * <p>
8228 * If any of the filters throws a checked exception when invoked, the resulting var handle will
8229 * throw an {@link IllegalStateException}.
8230 * <p>
8231 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
8232 * atomic access guarantees as those featured by the target var handle.
8233 *
8234 * @param target the var handle to invoke after the coordinates have been filtered
8235 * @param pos the position in the coordinate list of the target var handle where the filter is to be inserted
8236 * @param filter the filter method handle
8237 * @return an adapter var handle which filters the incoming coordinate values,
8238 * before calling the target var handle
8239 * @throws IllegalArgumentException if the return type of {@code filter}
8240 * is not void, and it is not the same as the {@code pos} coordinate of the target var handle,
8241 * if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive,
8242 * if the resulting var handle's type would have <a href="MethodHandle.html#maxarity">too many coordinates</a>,
8243 * or if it's determined that {@code filter} throws any checked exceptions.
8244 * @throws NullPointerException if any of the arguments is {@code null}.
8245 * @since 19
8246 */
8247 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN)
8248 public static VarHandle collectCoordinates(VarHandle target, int pos, MethodHandle filter) {
8249 return VarHandles.collectCoordinates(target, pos, filter);
8250 }
8251
8252 /**
8253 * Returns a var handle which will discard some dummy coordinates before delegating to the
8254 * target var handle. As a consequence, the resulting var handle will feature more
8255 * coordinate types than the target var handle.
8256 * <p>
8257 * The {@code pos} argument may range between zero and <i>N</i>, where <i>N</i> is the arity of the
8258 * target var handle's coordinate types. If {@code pos} is zero, the dummy coordinates will precede
8259 * the target's real arguments; if {@code pos} is <i>N</i> they will come after.
8260 * <p>
8261 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
8262 * atomic access guarantees as those featured by the target var handle.
8263 *
8264 * @param target the var handle to invoke after the dummy coordinates are dropped
8265 * @param pos position of the first coordinate to drop (zero for the leftmost)
8266 * @param valueTypes the type(s) of the coordinate(s) to drop
8267 * @return an adapter var handle which drops some dummy coordinates,
8268 * before calling the target var handle
8269 * @throws IllegalArgumentException if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive.
8270 * @throws NullPointerException if any of the arguments is {@code null} or {@code valueTypes} contains {@code null}.
8271 * @since 19
8272 */
8273 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN)
8274 public static VarHandle dropCoordinates(VarHandle target, int pos, Class<?>... valueTypes) {
8275 return VarHandles.dropCoordinates(target, pos, valueTypes);
8276 }
8277 }