1 /*
2 * Copyright (c) 2008, 2025, 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.misc.Unsafe;
30 import jdk.internal.misc.VM;
31 import jdk.internal.reflect.CallerSensitive;
32 import jdk.internal.reflect.CallerSensitiveAdapter;
33 import jdk.internal.reflect.Reflection;
34 import jdk.internal.util.ClassFileDumper;
35 import jdk.internal.vm.annotation.ForceInline;
36 import jdk.internal.vm.annotation.Stable;
37 import sun.invoke.util.ValueConversions;
38 import sun.invoke.util.VerifyAccess;
39 import sun.invoke.util.Wrapper;
40
41 import java.lang.classfile.ClassFile;
42 import java.lang.classfile.ClassModel;
43 import java.lang.constant.ClassDesc;
44 import java.lang.constant.ConstantDescs;
45 import java.lang.invoke.LambdaForm.BasicType;
46 import java.lang.invoke.MethodHandleImpl.Intrinsic;
47 import java.lang.reflect.Constructor;
48 import java.lang.reflect.Field;
49 import java.lang.reflect.Member;
50 import java.lang.reflect.Method;
51 import java.lang.reflect.Modifier;
52 import java.nio.ByteOrder;
53 import java.security.ProtectionDomain;
54 import java.util.ArrayList;
55 import java.util.Arrays;
56 import java.util.BitSet;
57 import java.util.Comparator;
58 import java.util.Iterator;
59 import java.util.List;
60 import java.util.Objects;
61 import java.util.Set;
62 import java.util.concurrent.ConcurrentHashMap;
63 import java.util.stream.Stream;
64
65 import static java.lang.classfile.ClassFile.*;
66 import static java.lang.invoke.LambdaForm.BasicType.V_TYPE;
67 import static java.lang.invoke.MethodHandleNatives.Constants.*;
68 import static java.lang.invoke.MethodHandleStatics.*;
69 import static java.lang.invoke.MethodType.methodType;
70
71 /**
72 * This class consists exclusively of static methods that operate on or return
73 * method handles. They fall into several categories:
74 * <ul>
75 * <li>Lookup methods which help create method handles for methods and fields.
76 * <li>Combinator methods, which combine or transform pre-existing method handles into new ones.
77 * <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns.
78 * </ul>
79 * A lookup, combinator, or factory method will fail and throw an
80 * {@code IllegalArgumentException} if the created method handle's type
81 * would have <a href="MethodHandle.html#maxarity">too many parameters</a>.
82 *
83 * @author John Rose, JSR 292 EG
84 * @since 1.7
85 */
86 public final class MethodHandles {
87
88 private MethodHandles() { } // do not instantiate
89
90 static final MemberName.Factory IMPL_NAMES = MemberName.getFactory();
91
92 // See IMPL_LOOKUP below.
93
94 //--- Method handle creation from ordinary methods.
95
96 /**
97 * Returns a {@link Lookup lookup object} with
98 * full capabilities to emulate all supported bytecode behaviors of the caller.
99 * These capabilities include {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access} to the caller.
100 * Factory methods on the lookup object can create
101 * <a href="MethodHandleInfo.html#directmh">direct method handles</a>
102 * for any member that the caller has access to via bytecodes,
103 * including protected and private fields and methods.
104 * This lookup object is created by the original lookup class
105 * and has the {@link Lookup#ORIGINAL ORIGINAL} bit set.
106 * This lookup object is a <em>capability</em> which may be delegated to trusted agents.
107 * Do not store it in place where untrusted code can access it.
108 * <p>
109 * This method is caller sensitive, which means that it may return different
110 * values to different callers.
111 * In cases where {@code MethodHandles.lookup} is called from a context where
112 * there is no caller frame on the stack (e.g. when called directly
113 * from a JNI attached thread), {@code IllegalCallerException} is thrown.
114 * To obtain a {@link Lookup lookup object} in such a context, use an auxiliary class that will
115 * implicitly be identified as the caller, or use {@link MethodHandles#publicLookup()}
116 * to obtain a low-privileged lookup instead.
117 * @return a lookup object for the caller of this method, with
118 * {@linkplain Lookup#ORIGINAL original} and
119 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access}.
120 * @throws IllegalCallerException if there is no caller frame on the stack.
121 */
122 @CallerSensitive
123 @ForceInline // to ensure Reflection.getCallerClass optimization
124 public static Lookup lookup() {
125 final Class<?> c = Reflection.getCallerClass();
126 if (c == null) {
127 throw new IllegalCallerException("no caller frame");
128 }
129 return new Lookup(c);
130 }
131
132 /**
133 * This lookup method is the alternate implementation of
134 * the lookup method with a leading caller class argument which is
135 * non-caller-sensitive. This method is only invoked by reflection
136 * and method handle.
137 */
138 @CallerSensitiveAdapter
139 private static Lookup lookup(Class<?> caller) {
140 if (caller.getClassLoader() == null) {
141 throw newInternalError("calling lookup() reflectively is not supported: "+caller);
142 }
143 return new Lookup(caller);
144 }
145
146 /**
147 * Returns a {@link Lookup lookup object} which is trusted minimally.
148 * The lookup has the {@code UNCONDITIONAL} mode.
149 * It can only be used to create method handles to public members of
150 * public classes in packages that are exported unconditionally.
151 * <p>
152 * As a matter of pure convention, the {@linkplain Lookup#lookupClass() lookup class}
153 * of this lookup object will be {@link java.lang.Object}.
154 *
155 * @apiNote The use of Object is conventional, and because the lookup modes are
156 * limited, there is no special access provided to the internals of Object, its package
157 * or its module. This public lookup object or other lookup object with
158 * {@code UNCONDITIONAL} mode assumes readability. Consequently, the lookup class
159 * is not used to determine the lookup context.
160 *
161 * <p style="font-size:smaller;">
162 * <em>Discussion:</em>
163 * The lookup class can be changed to any other class {@code C} using an expression of the form
164 * {@link Lookup#in publicLookup().in(C.class)}.
165 * Also, it cannot access
166 * <a href="MethodHandles.Lookup.html#callsens">caller sensitive methods</a>.
167 * @return a lookup object which is trusted minimally
168 */
169 public static Lookup publicLookup() {
170 return Lookup.PUBLIC_LOOKUP;
171 }
172
173 /**
174 * Returns a {@link Lookup lookup} object on a target class to emulate all supported
175 * bytecode behaviors, including <a href="MethodHandles.Lookup.html#privacc">private access</a>.
176 * The returned lookup object can provide access to classes in modules and packages,
177 * and members of those classes, outside the normal rules of Java access control,
178 * instead conforming to the more permissive rules for modular <em>deep reflection</em>.
179 * <p>
180 * A caller, specified as a {@code Lookup} object, in module {@code M1} is
181 * allowed to do deep reflection on module {@code M2} and package of the target class
182 * if and only if all of the following conditions are {@code true}:
183 * <ul>
184 * <li>The caller lookup object must have {@linkplain Lookup#hasFullPrivilegeAccess()
185 * full privilege access}. Specifically:
186 * <ul>
187 * <li>The caller lookup object must have the {@link Lookup#MODULE MODULE} lookup mode.
188 * (This is because otherwise there would be no way to ensure the original lookup
189 * creator was a member of any particular module, and so any subsequent checks
190 * for readability and qualified exports would become ineffective.)
191 * <li>The caller lookup object must have {@link Lookup#PRIVATE PRIVATE} access.
192 * (This is because an application intending to share intra-module access
193 * using {@link Lookup#MODULE MODULE} alone will inadvertently also share
194 * deep reflection to its own module.)
195 * </ul>
196 * <li>The target class must be a proper class, not a primitive or array class.
197 * (Thus, {@code M2} is well-defined.)
198 * <li>If the caller module {@code M1} differs from
199 * the target module {@code M2} then both of the following must be true:
200 * <ul>
201 * <li>{@code M1} {@link Module#canRead reads} {@code M2}.</li>
202 * <li>{@code M2} {@link Module#isOpen(String,Module) opens} the package
203 * containing the target class to at least {@code M1}.</li>
204 * </ul>
205 * </ul>
206 * <p>
207 * If any of the above checks is violated, this method fails with an
208 * exception.
209 * <p>
210 * Otherwise, if {@code M1} and {@code M2} are the same module, this method
211 * returns a {@code Lookup} on {@code targetClass} with
212 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access}
213 * with {@code null} previous lookup class.
214 * <p>
215 * Otherwise, {@code M1} and {@code M2} are two different modules. This method
216 * returns a {@code Lookup} on {@code targetClass} that records
217 * the lookup class of the caller as the new previous lookup class with
218 * {@code PRIVATE} access but no {@code MODULE} access.
219 * <p>
220 * The resulting {@code Lookup} object has no {@code ORIGINAL} access.
221 *
222 * @apiNote The {@code Lookup} object returned by this method is allowed to
223 * {@linkplain Lookup#defineClass(byte[]) define classes} in the runtime package
224 * of {@code targetClass}. Extreme caution should be taken when opening a package
225 * to another module as such defined classes have the same full privilege
226 * access as other members in {@code targetClass}'s module.
227 *
228 * @param targetClass the target class
229 * @param caller the caller lookup object
230 * @return a lookup object for the target class, with private access
231 * @throws IllegalArgumentException if {@code targetClass} is a primitive type or void or array class
232 * @throws NullPointerException if {@code targetClass} or {@code caller} is {@code null}
233 * @throws IllegalAccessException if any of the other access checks specified above fails
234 * @since 9
235 * @see Lookup#dropLookupMode
236 * @see <a href="MethodHandles.Lookup.html#cross-module-lookup">Cross-module lookups</a>
237 */
238 public static Lookup privateLookupIn(Class<?> targetClass, Lookup caller) throws IllegalAccessException {
239 if (caller.allowedModes == Lookup.TRUSTED) {
240 return new Lookup(targetClass);
241 }
242
243 if (targetClass.isPrimitive())
244 throw new IllegalArgumentException(targetClass + " is a primitive class");
245 if (targetClass.isArray())
246 throw new IllegalArgumentException(targetClass + " is an array class");
247 // Ensure that we can reason accurately about private and module access.
248 int requireAccess = Lookup.PRIVATE|Lookup.MODULE;
249 if ((caller.lookupModes() & requireAccess) != requireAccess)
250 throw new IllegalAccessException("caller does not have PRIVATE and MODULE lookup mode");
251
252 // previous lookup class is never set if it has MODULE access
253 assert caller.previousLookupClass() == null;
254
255 Class<?> callerClass = caller.lookupClass();
256 Module callerModule = callerClass.getModule(); // M1
257 Module targetModule = targetClass.getModule(); // M2
258 Class<?> newPreviousClass = null;
259 int newModes = Lookup.FULL_POWER_MODES & ~Lookup.ORIGINAL;
260
261 if (targetModule != callerModule) {
262 if (!callerModule.canRead(targetModule))
263 throw new IllegalAccessException(callerModule + " does not read " + targetModule);
264 if (targetModule.isNamed()) {
265 String pn = targetClass.getPackageName();
266 assert !pn.isEmpty() : "unnamed package cannot be in named module";
267 if (!targetModule.isOpen(pn, callerModule))
268 throw new IllegalAccessException(targetModule + " does not open " + pn + " to " + callerModule);
269 }
270
271 // M2 != M1, set previous lookup class to M1 and drop MODULE access
272 newPreviousClass = callerClass;
273 newModes &= ~Lookup.MODULE;
274 }
275 return Lookup.newLookup(targetClass, newPreviousClass, newModes);
276 }
277
278 /**
279 * Returns the <em>class data</em> associated with the lookup class
280 * of the given {@code caller} lookup object, or {@code null}.
281 *
282 * <p> A hidden class with class data can be created by calling
283 * {@link Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...)
284 * Lookup::defineHiddenClassWithClassData}.
285 * This method will cause the static class initializer of the lookup
286 * class of the given {@code caller} lookup object be executed if
287 * it has not been initialized.
288 *
289 * <p> A hidden class created by {@link Lookup#defineHiddenClass(byte[], boolean, Lookup.ClassOption...)
290 * Lookup::defineHiddenClass} and non-hidden classes have no class data.
291 * {@code null} is returned if this method is called on the lookup object
292 * on these classes.
293 *
294 * <p> The {@linkplain Lookup#lookupModes() lookup modes} for this lookup
295 * must have {@linkplain Lookup#ORIGINAL original access}
296 * in order to retrieve the class data.
297 *
298 * @apiNote
299 * This method can be called as a bootstrap method for a dynamically computed
300 * constant. A framework can create a hidden class with class data, for
301 * example that can be {@code Class} or {@code MethodHandle} object.
302 * The class data is accessible only to the lookup object
303 * created by the original caller but inaccessible to other members
304 * in the same nest. If a framework passes security sensitive objects
305 * to a hidden class via class data, it is recommended to load the value
306 * of class data as a dynamically computed constant instead of storing
307 * the class data in private static field(s) which are accessible to
308 * other nestmates.
309 *
310 * @param <T> the type to cast the class data object to
311 * @param caller the lookup context describing the class performing the
312 * operation (normally stacked by the JVM)
313 * @param name must be {@link ConstantDescs#DEFAULT_NAME}
314 * ({@code "_"})
315 * @param type the type of the class data
316 * @return the value of the class data if present in the lookup class;
317 * otherwise {@code null}
318 * @throws IllegalArgumentException if name is not {@code "_"}
319 * @throws IllegalAccessException if the lookup context does not have
320 * {@linkplain Lookup#ORIGINAL original} access
321 * @throws ClassCastException if the class data cannot be converted to
322 * the given {@code type}
323 * @throws NullPointerException if {@code caller} or {@code type} argument
324 * is {@code null}
325 * @see Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...)
326 * @see MethodHandles#classDataAt(Lookup, String, Class, int)
327 * @since 16
328 * @jvms 5.5 Initialization
329 */
330 public static <T> T classData(Lookup caller, String name, Class<T> type) throws IllegalAccessException {
331 Objects.requireNonNull(caller);
332 Objects.requireNonNull(type);
333 if (!ConstantDescs.DEFAULT_NAME.equals(name)) {
334 throw new IllegalArgumentException("name must be \"_\": " + name);
335 }
336
337 if ((caller.lookupModes() & Lookup.ORIGINAL) != Lookup.ORIGINAL) {
338 throw new IllegalAccessException(caller + " does not have ORIGINAL access");
339 }
340
341 Object classdata = classData(caller.lookupClass());
342 if (classdata == null) return null;
343
344 try {
345 return BootstrapMethodInvoker.widenAndCast(classdata, type);
346 } catch (RuntimeException|Error e) {
347 throw e; // let CCE and other runtime exceptions through
348 } catch (Throwable e) {
349 throw new InternalError(e);
350 }
351 }
352
353 /*
354 * Returns the class data set by the VM in the Class::classData field.
355 *
356 * This is also invoked by LambdaForms as it cannot use condy via
357 * MethodHandles::classData due to bootstrapping issue.
358 */
359 static Object classData(Class<?> c) {
360 UNSAFE.ensureClassInitialized(c);
361 return SharedSecrets.getJavaLangAccess().classData(c);
362 }
363
364 /**
365 * Returns the element at the specified index in the
366 * {@linkplain #classData(Lookup, String, Class) class data},
367 * if the class data associated with the lookup class
368 * of the given {@code caller} lookup object is a {@code List}.
369 * If the class data is not present in this lookup class, this method
370 * returns {@code null}.
371 *
372 * <p> A hidden class with class data can be created by calling
373 * {@link Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...)
374 * Lookup::defineHiddenClassWithClassData}.
375 * This method will cause the static class initializer of the lookup
376 * class of the given {@code caller} lookup object be executed if
377 * it has not been initialized.
378 *
379 * <p> A hidden class created by {@link Lookup#defineHiddenClass(byte[], boolean, Lookup.ClassOption...)
380 * Lookup::defineHiddenClass} and non-hidden classes have no class data.
381 * {@code null} is returned if this method is called on the lookup object
382 * on these classes.
383 *
384 * <p> The {@linkplain Lookup#lookupModes() lookup modes} for this lookup
385 * must have {@linkplain Lookup#ORIGINAL original access}
386 * in order to retrieve the class data.
387 *
388 * @apiNote
389 * This method can be called as a bootstrap method for a dynamically computed
390 * constant. A framework can create a hidden class with class data, for
391 * example that can be {@code List.of(o1, o2, o3....)} containing more than
392 * one object and use this method to load one element at a specific index.
393 * The class data is accessible only to the lookup object
394 * created by the original caller but inaccessible to other members
395 * in the same nest. If a framework passes security sensitive objects
396 * to a hidden class via class data, it is recommended to load the value
397 * of class data as a dynamically computed constant instead of storing
398 * the class data in private static field(s) which are accessible to other
399 * nestmates.
400 *
401 * @param <T> the type to cast the result object to
402 * @param caller the lookup context describing the class performing the
403 * operation (normally stacked by the JVM)
404 * @param name must be {@link java.lang.constant.ConstantDescs#DEFAULT_NAME}
405 * ({@code "_"})
406 * @param type the type of the element at the given index in the class data
407 * @param index index of the element in the class data
408 * @return the element at the given index in the class data
409 * if the class data is present; otherwise {@code null}
410 * @throws IllegalArgumentException if name is not {@code "_"}
411 * @throws IllegalAccessException if the lookup context does not have
412 * {@linkplain Lookup#ORIGINAL original} access
413 * @throws ClassCastException if the class data cannot be converted to {@code List}
414 * or the element at the specified index cannot be converted to the given type
415 * @throws IndexOutOfBoundsException if the index is out of range
416 * @throws NullPointerException if {@code caller} or {@code type} argument is
417 * {@code null}; or if unboxing operation fails because
418 * the element at the given index is {@code null}
419 *
420 * @since 16
421 * @see #classData(Lookup, String, Class)
422 * @see Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...)
423 */
424 public static <T> T classDataAt(Lookup caller, String name, Class<T> type, int index)
425 throws IllegalAccessException
426 {
427 @SuppressWarnings("unchecked")
428 List<Object> classdata = (List<Object>)classData(caller, name, List.class);
429 if (classdata == null) return null;
430
431 try {
432 Object element = classdata.get(index);
433 return BootstrapMethodInvoker.widenAndCast(element, type);
434 } catch (RuntimeException|Error e) {
435 throw e; // let specified exceptions and other runtime exceptions/errors through
436 } catch (Throwable e) {
437 throw new InternalError(e);
438 }
439 }
440
441 /**
442 * Performs an unchecked "crack" of a
443 * <a href="MethodHandleInfo.html#directmh">direct method handle</a>.
444 * The result is as if the user had obtained a lookup object capable enough
445 * to crack the target method handle, called
446 * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect}
447 * on the target to obtain its symbolic reference, and then called
448 * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs}
449 * to resolve the symbolic reference to a member.
450 * @param <T> the desired type of the result, either {@link Member} or a subtype
451 * @param expected a class object representing the desired result type {@code T}
452 * @param target a direct method handle to crack into symbolic reference components
453 * @return a reference to the method, constructor, or field object
454 * @throws NullPointerException if either argument is {@code null}
455 * @throws IllegalArgumentException if the target is not a direct method handle
456 * @throws ClassCastException if the member is not of the expected type
457 * @since 1.8
458 */
459 public static <T extends Member> T reflectAs(Class<T> expected, MethodHandle target) {
460 Lookup lookup = Lookup.IMPL_LOOKUP; // use maximally privileged lookup
461 return lookup.revealDirect(target).reflectAs(expected, lookup);
462 }
463
464 /**
465 * A <em>lookup object</em> is a factory for creating method handles,
466 * when the creation requires access checking.
467 * Method handles do not perform
468 * access checks when they are called, but rather when they are created.
469 * Therefore, method handle access
470 * restrictions must be enforced when a method handle is created.
471 * The caller class against which those restrictions are enforced
472 * is known as the {@linkplain #lookupClass() lookup class}.
473 * <p>
474 * A lookup class which needs to create method handles will call
475 * {@link MethodHandles#lookup() MethodHandles.lookup} to create a factory for itself.
476 * When the {@code Lookup} factory object is created, the identity of the lookup class is
477 * determined, and securely stored in the {@code Lookup} object.
478 * The lookup class (or its delegates) may then use factory methods
479 * on the {@code Lookup} object to create method handles for access-checked members.
480 * This includes all methods, constructors, and fields which are allowed to the lookup class,
481 * even private ones.
482 *
483 * <h2><a id="lookups"></a>Lookup Factory Methods</h2>
484 * The factory methods on a {@code Lookup} object correspond to all major
485 * use cases for methods, constructors, and fields.
486 * Each method handle created by a factory method is the functional
487 * equivalent of a particular <em>bytecode behavior</em>.
488 * (Bytecode behaviors are described in section {@jvms 5.4.3.5} of
489 * the Java Virtual Machine Specification.)
490 * Here is a summary of the correspondence between these factory methods and
491 * the behavior of the resulting method handles:
492 * <table class="striped">
493 * <caption style="display:none">lookup method behaviors</caption>
494 * <thead>
495 * <tr>
496 * <th scope="col"><a id="equiv"></a>lookup expression</th>
497 * <th scope="col">member</th>
498 * <th scope="col">bytecode behavior</th>
499 * </tr>
500 * </thead>
501 * <tbody>
502 * <tr>
503 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</th>
504 * <td>{@code FT f;}</td><td>{@code (T) this.f;}</td>
505 * </tr>
506 * <tr>
507 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</th>
508 * <td>{@code static}<br>{@code FT f;}</td><td>{@code (FT) C.f;}</td>
509 * </tr>
510 * <tr>
511 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</th>
512 * <td>{@code FT f;}</td><td>{@code this.f = x;}</td>
513 * </tr>
514 * <tr>
515 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</th>
516 * <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td>
517 * </tr>
518 * <tr>
519 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</th>
520 * <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>
521 * </tr>
522 * <tr>
523 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</th>
524 * <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td>
525 * </tr>
526 * <tr>
527 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</th>
528 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
529 * </tr>
530 * <tr>
531 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</th>
532 * <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td>
533 * </tr>
534 * <tr>
535 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</th>
536 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td>
537 * </tr>
538 * <tr>
539 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</th>
540 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, arg);}</td>
541 * </tr>
542 * <tr>
543 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</th>
544 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
545 * </tr>
546 * <tr>
547 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</th>
548 * <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td>
549 * </tr>
550 * <tr>
551 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSpecial lookup.unreflectSpecial(aMethod,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#findClass lookup.findClass("C")}</th>
556 * <td>{@code class C { ... }}</td><td>{@code C.class;}</td>
557 * </tr>
558 * </tbody>
559 * </table>
560 *
561 * Here, the type {@code C} is the class or interface being searched for a member,
562 * documented as a parameter named {@code refc} in the lookup methods.
563 * The method type {@code MT} is composed from the return type {@code T}
564 * and the sequence of argument types {@code A*}.
565 * The constructor also has a sequence of argument types {@code A*} and
566 * is deemed to return the newly-created object of type {@code C}.
567 * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}.
568 * The formal parameter {@code this} stands for the self-reference of type {@code C};
569 * if it is present, it is always the leading argument to the method handle invocation.
570 * (In the case of some {@code protected} members, {@code this} may be
571 * restricted in type to the lookup class; see below.)
572 * The name {@code arg} stands for all the other method handle arguments.
573 * In the code examples for the Core Reflection API, the name {@code thisOrNull}
574 * stands for a null reference if the accessed method or field is static,
575 * and {@code this} otherwise.
576 * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand
577 * for reflective objects corresponding to the given members declared in type {@code C}.
578 * <p>
579 * The bytecode behavior for a {@code findClass} operation is a load of a constant class,
580 * as if by {@code ldc CONSTANT_Class}.
581 * The behavior is represented, not as a method handle, but directly as a {@code Class} constant.
582 * <p>
583 * In cases where the given member is of variable arity (i.e., a method or constructor)
584 * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}.
585 * In all other cases, the returned method handle will be of fixed arity.
586 * <p style="font-size:smaller;">
587 * <em>Discussion:</em>
588 * The equivalence between looked-up method handles and underlying
589 * class members and bytecode behaviors
590 * can break down in a few ways:
591 * <ul style="font-size:smaller;">
592 * <li>If {@code C} is not symbolically accessible from the lookup class's loader,
593 * the lookup can still succeed, even when there is no equivalent
594 * Java expression or bytecoded constant.
595 * <li>Likewise, if {@code T} or {@code MT}
596 * is not symbolically accessible from the lookup class's loader,
597 * the lookup can still succeed.
598 * For example, lookups for {@code MethodHandle.invokeExact} and
599 * {@code MethodHandle.invoke} will always succeed, regardless of requested type.
600 * <li>If the looked-up method has a
601 * <a href="MethodHandle.html#maxarity">very large arity</a>,
602 * the method handle creation may fail with an
603 * {@code IllegalArgumentException}, due to the method handle type having
604 * <a href="MethodHandle.html#maxarity">too many parameters.</a>
605 * </ul>
606 *
607 * <h2><a id="access"></a>Access checking</h2>
608 * Access checks are applied in the factory methods of {@code Lookup},
609 * when a method handle is created.
610 * This is a key difference from the Core Reflection API, since
611 * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
612 * performs access checking against every caller, on every call.
613 * <p>
614 * All access checks start from a {@code Lookup} object, which
615 * compares its recorded lookup class against all requests to
616 * create method handles.
617 * A single {@code Lookup} object can be used to create any number
618 * of access-checked method handles, all checked against a single
619 * lookup class.
620 * <p>
621 * A {@code Lookup} object can be shared with other trusted code,
622 * such as a metaobject protocol.
623 * A shared {@code Lookup} object delegates the capability
624 * to create method handles on private members of the lookup class.
625 * Even if privileged code uses the {@code Lookup} object,
626 * the access checking is confined to the privileges of the
627 * original lookup class.
628 * <p>
629 * A lookup can fail, because
630 * the containing class is not accessible to the lookup class, or
631 * because the desired class member is missing, or because the
632 * desired class member is not accessible to the lookup class, or
633 * because the lookup object is not trusted enough to access the member.
634 * In the case of a field setter function on a {@code final} field,
635 * finality enforcement is treated as a kind of access control,
636 * and the lookup will fail, except in special cases of
637 * {@link Lookup#unreflectSetter Lookup.unreflectSetter}.
638 * In any of these cases, a {@code ReflectiveOperationException} will be
639 * thrown from the attempted lookup. The exact class will be one of
640 * the following:
641 * <ul>
642 * <li>NoSuchMethodException — if a method is requested but does not exist
643 * <li>NoSuchFieldException — if a field is requested but does not exist
644 * <li>IllegalAccessException — if the member exists but an access check fails
645 * </ul>
646 * <p>
647 * In general, the conditions under which a method handle may be
648 * looked up for a method {@code M} are no more restrictive than the conditions
649 * under which the lookup class could have compiled, verified, and resolved a call to {@code M}.
650 * Where the JVM would raise exceptions like {@code NoSuchMethodError},
651 * a method handle lookup will generally raise a corresponding
652 * checked exception, such as {@code NoSuchMethodException}.
653 * And the effect of invoking the method handle resulting from the lookup
654 * is <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a>
655 * to executing the compiled, verified, and resolved call to {@code M}.
656 * The same point is true of fields and constructors.
657 * <p style="font-size:smaller;">
658 * <em>Discussion:</em>
659 * Access checks only apply to named and reflected methods,
660 * constructors, and fields.
661 * Other method handle creation methods, such as
662 * {@link MethodHandle#asType MethodHandle.asType},
663 * do not require any access checks, and are used
664 * independently of any {@code Lookup} object.
665 * <p>
666 * If the desired member is {@code protected}, the usual JVM rules apply,
667 * including the requirement that the lookup class must either be in the
668 * same package as the desired member, or must inherit that member.
669 * (See the Java Virtual Machine Specification, sections {@jvms
670 * 4.9.2}, {@jvms 5.4.3.5}, and {@jvms 6.4}.)
671 * In addition, if the desired member is a non-static field or method
672 * in a different package, the resulting method handle may only be applied
673 * to objects of the lookup class or one of its subclasses.
674 * This requirement is enforced by narrowing the type of the leading
675 * {@code this} parameter from {@code C}
676 * (which will necessarily be a superclass of the lookup class)
677 * to the lookup class itself.
678 * <p>
679 * The JVM imposes a similar requirement on {@code invokespecial} instruction,
680 * that the receiver argument must match both the resolved method <em>and</em>
681 * the current class. Again, this requirement is enforced by narrowing the
682 * type of the leading parameter to the resulting method handle.
683 * (See the Java Virtual Machine Specification, section {@jvms 4.10.1.9}.)
684 * <p>
685 * The JVM represents constructors and static initializer blocks as internal methods
686 * with special names ({@value ConstantDescs#INIT_NAME} and {@value
687 * ConstantDescs#CLASS_INIT_NAME}).
688 * The internal syntax of invocation instructions allows them to refer to such internal
689 * methods as if they were normal methods, but the JVM bytecode verifier rejects them.
690 * A lookup of such an internal method will produce a {@code NoSuchMethodException}.
691 * <p>
692 * If the relationship between nested types is expressed directly through the
693 * {@code NestHost} and {@code NestMembers} attributes
694 * (see the Java Virtual Machine Specification, sections {@jvms
695 * 4.7.28} and {@jvms 4.7.29}),
696 * then the associated {@code Lookup} object provides direct access to
697 * the lookup class and all of its nestmates
698 * (see {@link java.lang.Class#getNestHost Class.getNestHost}).
699 * Otherwise, access between nested classes is obtained by the Java compiler creating
700 * a wrapper method to access a private method of another class in the same nest.
701 * For example, a nested class {@code C.D}
702 * can access private members within other related classes such as
703 * {@code C}, {@code C.D.E}, or {@code C.B},
704 * but the Java compiler may need to generate wrapper methods in
705 * those related classes. In such cases, a {@code Lookup} object on
706 * {@code C.E} would be unable to access those private members.
707 * A workaround for this limitation is the {@link Lookup#in Lookup.in} method,
708 * which can transform a lookup on {@code C.E} into one on any of those other
709 * classes, without special elevation of privilege.
710 * <p>
711 * The accesses permitted to a given lookup object may be limited,
712 * according to its set of {@link #lookupModes lookupModes},
713 * to a subset of members normally accessible to the lookup class.
714 * For example, the {@link MethodHandles#publicLookup publicLookup}
715 * method produces a lookup object which is only allowed to access
716 * public members in public classes of exported packages.
717 * The caller sensitive method {@link MethodHandles#lookup lookup}
718 * produces a lookup object with full capabilities relative to
719 * its caller class, to emulate all supported bytecode behaviors.
720 * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object
721 * with fewer access modes than the original lookup object.
722 *
723 * <p style="font-size:smaller;">
724 * <a id="privacc"></a>
725 * <em>Discussion of private and module access:</em>
726 * We say that a lookup has <em>private access</em>
727 * if its {@linkplain #lookupModes lookup modes}
728 * include the possibility of accessing {@code private} members
729 * (which includes the private members of nestmates).
730 * As documented in the relevant methods elsewhere,
731 * only lookups with private access possess the following capabilities:
732 * <ul style="font-size:smaller;">
733 * <li>access private fields, methods, and constructors of the lookup class and its nestmates
734 * <li>create method handles which {@link Lookup#findSpecial emulate invokespecial} instructions
735 * <li>create {@link Lookup#in delegated lookup objects} which have private access to other classes
736 * within the same package member
737 * </ul>
738 * <p style="font-size:smaller;">
739 * Similarly, a lookup with module access ensures that the original lookup creator was
740 * a member in the same module as the lookup class.
741 * <p style="font-size:smaller;">
742 * Private and module access are independently determined modes; a lookup may have
743 * either or both or neither. A lookup which possesses both access modes is said to
744 * possess {@linkplain #hasFullPrivilegeAccess() full privilege access}.
745 * <p style="font-size:smaller;">
746 * A lookup with <em>original access</em> ensures that this lookup is created by
747 * the original lookup class and the bootstrap method invoked by the VM.
748 * Such a lookup with original access also has private and module access
749 * which has the following additional capability:
750 * <ul style="font-size:smaller;">
751 * <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> methods,
752 * such as {@code Class.forName}
753 * <li>obtain the {@linkplain MethodHandles#classData(Lookup, String, Class)
754 * class data} associated with the lookup class</li>
755 * </ul>
756 * <p style="font-size:smaller;">
757 * Each of these permissions is a consequence of the fact that a lookup object
758 * with private access can be securely traced back to an originating class,
759 * whose <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> and Java language access permissions
760 * can be reliably determined and emulated by method handles.
761 *
762 * <h2><a id="cross-module-lookup"></a>Cross-module lookups</h2>
763 * When a lookup class in one module {@code M1} accesses a class in another module
764 * {@code M2}, extra access checking is performed beyond the access mode bits.
765 * A {@code Lookup} with {@link #PUBLIC} mode and a lookup class in {@code M1}
766 * can access public types in {@code M2} when {@code M2} is readable to {@code M1}
767 * and when the type is in a package of {@code M2} that is exported to
768 * at least {@code M1}.
769 * <p>
770 * A {@code Lookup} on {@code C} can also <em>teleport</em> to a target class
771 * via {@link #in(Class) Lookup.in} and {@link MethodHandles#privateLookupIn(Class, Lookup)
772 * MethodHandles.privateLookupIn} methods.
773 * Teleporting across modules will always record the original lookup class as
774 * the <em>{@linkplain #previousLookupClass() previous lookup class}</em>
775 * and drops {@link Lookup#MODULE MODULE} access.
776 * If the target class is in the same module as the lookup class {@code C},
777 * then the target class becomes the new lookup class
778 * and there is no change to the previous lookup class.
779 * If the target class is in a different module from {@code M1} ({@code C}'s module),
780 * {@code C} becomes the new previous lookup class
781 * and the target class becomes the new lookup class.
782 * In that case, if there was already a previous lookup class in {@code M0},
783 * and it differs from {@code M1} and {@code M2}, then the resulting lookup
784 * drops all privileges.
785 * For example,
786 * {@snippet lang="java" :
787 * Lookup lookup = MethodHandles.lookup(); // in class C
788 * Lookup lookup2 = lookup.in(D.class);
789 * MethodHandle mh = lookup2.findStatic(E.class, "m", MT);
790 * }
791 * <p>
792 * The {@link #lookup()} factory method produces a {@code Lookup} object
793 * with {@code null} previous lookup class.
794 * {@link Lookup#in lookup.in(D.class)} transforms the {@code lookup} on class {@code C}
795 * to class {@code D} without elevation of privileges.
796 * If {@code C} and {@code D} are in the same module,
797 * {@code lookup2} records {@code D} as the new lookup class and keeps the
798 * same previous lookup class as the original {@code lookup}, or
799 * {@code null} if not present.
800 * <p>
801 * When a {@code Lookup} teleports from a class
802 * in one nest to another nest, {@code PRIVATE} access is dropped.
803 * When a {@code Lookup} teleports from a class in one package to
804 * another package, {@code PACKAGE} access is dropped.
805 * When a {@code Lookup} teleports from a class in one module to another module,
806 * {@code MODULE} access is dropped.
807 * Teleporting across modules drops the ability to access non-exported classes
808 * in both the module of the new lookup class and the module of the old lookup class
809 * and the resulting {@code Lookup} remains only {@code PUBLIC} access.
810 * A {@code Lookup} can teleport back and forth to a class in the module of
811 * the lookup class and the module of the previous class lookup.
812 * Teleporting across modules can only decrease access but cannot increase it.
813 * Teleporting to some third module drops all accesses.
814 * <p>
815 * In the above example, if {@code C} and {@code D} are in different modules,
816 * {@code lookup2} records {@code D} as its lookup class and
817 * {@code C} as its previous lookup class and {@code lookup2} has only
818 * {@code PUBLIC} access. {@code lookup2} can teleport to other class in
819 * {@code C}'s module and {@code D}'s module.
820 * If class {@code E} is in a third module, {@code lookup2.in(E.class)} creates
821 * a {@code Lookup} on {@code E} with no access and {@code lookup2}'s lookup
822 * class {@code D} is recorded as its previous lookup class.
823 * <p>
824 * Teleporting across modules restricts access to the public types that
825 * both the lookup class and the previous lookup class can equally access
826 * (see below).
827 * <p>
828 * {@link MethodHandles#privateLookupIn(Class, Lookup) MethodHandles.privateLookupIn(T.class, lookup)}
829 * can be used to teleport a {@code lookup} from class {@code C} to class {@code T}
830 * and produce a new {@code Lookup} with <a href="#privacc">private access</a>
831 * if the lookup class is allowed to do <em>deep reflection</em> on {@code T}.
832 * The {@code lookup} must have {@link #MODULE} and {@link #PRIVATE} access
833 * to call {@code privateLookupIn}.
834 * A {@code lookup} on {@code C} in module {@code M1} is allowed to do deep reflection
835 * on all classes in {@code M1}. If {@code T} is in {@code M1}, {@code privateLookupIn}
836 * produces a new {@code Lookup} on {@code T} with full capabilities.
837 * A {@code lookup} on {@code C} is also allowed
838 * to do deep reflection on {@code T} in another module {@code M2} if
839 * {@code M1} reads {@code M2} and {@code M2} {@link Module#isOpen(String,Module) opens}
840 * the package containing {@code T} to at least {@code M1}.
841 * {@code T} becomes the new lookup class and {@code C} becomes the new previous
842 * lookup class and {@code MODULE} access is dropped from the resulting {@code Lookup}.
843 * The resulting {@code Lookup} can be used to do member lookup or teleport
844 * to another lookup class by calling {@link #in Lookup::in}. But
845 * it cannot be used to obtain another private {@code Lookup} by calling
846 * {@link MethodHandles#privateLookupIn(Class, Lookup) privateLookupIn}
847 * because it has no {@code MODULE} access.
848 * <p>
849 * The {@code Lookup} object returned by {@code privateLookupIn} is allowed to
850 * {@linkplain Lookup#defineClass(byte[]) define classes} in the runtime package
851 * of {@code T}. Extreme caution should be taken when opening a package
852 * to another module as such defined classes have the same full privilege
853 * access as other members in {@code M2}.
854 *
855 * <h2><a id="module-access-check"></a>Cross-module access checks</h2>
856 *
857 * A {@code Lookup} with {@link #PUBLIC} or with {@link #UNCONDITIONAL} mode
858 * allows cross-module access. The access checking is performed with respect
859 * to both the lookup class and the previous lookup class if present.
860 * <p>
861 * A {@code Lookup} with {@link #UNCONDITIONAL} mode can access public type
862 * in all modules when the type is in a package that is {@linkplain Module#isExported(String)
863 * exported unconditionally}.
864 * <p>
865 * If a {@code Lookup} on {@code LC} in {@code M1} has no previous lookup class,
866 * the lookup with {@link #PUBLIC} mode can access all public types in modules
867 * that are readable to {@code M1} and the type is in a package that is exported
868 * at least to {@code M1}.
869 * <p>
870 * If a {@code Lookup} on {@code LC} in {@code M1} has a previous lookup class
871 * {@code PLC} on {@code M0}, the lookup with {@link #PUBLIC} mode can access
872 * the intersection of all public types that are accessible to {@code M1}
873 * with all public types that are accessible to {@code M0}. {@code M0}
874 * reads {@code M1} and hence the set of accessible types includes:
875 *
876 * <ul>
877 * <li>unconditional-exported packages from {@code M1}</li>
878 * <li>unconditional-exported packages from {@code M0} if {@code M1} reads {@code M0}</li>
879 * <li>
880 * unconditional-exported packages from a third module {@code M2}if both {@code M0}
881 * and {@code M1} read {@code M2}
882 * </li>
883 * <li>qualified-exported packages from {@code M1} to {@code M0}</li>
884 * <li>qualified-exported packages from {@code M0} to {@code M1} if {@code M1} reads {@code M0}</li>
885 * <li>
886 * qualified-exported packages from a third module {@code M2} to both {@code M0} and
887 * {@code M1} if both {@code M0} and {@code M1} read {@code M2}
888 * </li>
889 * </ul>
890 *
891 * <h2><a id="access-modes"></a>Access modes</h2>
892 *
893 * The table below shows the access modes of a {@code Lookup} produced by
894 * any of the following factory or transformation methods:
895 * <ul>
896 * <li>{@link #lookup() MethodHandles::lookup}</li>
897 * <li>{@link #publicLookup() MethodHandles::publicLookup}</li>
898 * <li>{@link #privateLookupIn(Class, Lookup) MethodHandles::privateLookupIn}</li>
899 * <li>{@link Lookup#in Lookup::in}</li>
900 * <li>{@link Lookup#dropLookupMode(int) Lookup::dropLookupMode}</li>
901 * </ul>
902 *
903 * <table class="striped">
904 * <caption style="display:none">
905 * Access mode summary
906 * </caption>
907 * <thead>
908 * <tr>
909 * <th scope="col">Lookup object</th>
910 * <th style="text-align:center">original</th>
911 * <th style="text-align:center">protected</th>
912 * <th style="text-align:center">private</th>
913 * <th style="text-align:center">package</th>
914 * <th style="text-align:center">module</th>
915 * <th style="text-align:center">public</th>
916 * </tr>
917 * </thead>
918 * <tbody>
919 * <tr>
920 * <th scope="row" style="text-align:left">{@code CL = MethodHandles.lookup()} in {@code C}</th>
921 * <td style="text-align:center">ORI</td>
922 * <td style="text-align:center">PRO</td>
923 * <td style="text-align:center">PRI</td>
924 * <td style="text-align:center">PAC</td>
925 * <td style="text-align:center">MOD</td>
926 * <td style="text-align:center">1R</td>
927 * </tr>
928 * <tr>
929 * <th scope="row" style="text-align:left">{@code CL.in(C1)} same package</th>
930 * <td></td>
931 * <td></td>
932 * <td></td>
933 * <td style="text-align:center">PAC</td>
934 * <td style="text-align:center">MOD</td>
935 * <td style="text-align:center">1R</td>
936 * </tr>
937 * <tr>
938 * <th scope="row" style="text-align:left">{@code CL.in(C1)} same module</th>
939 * <td></td>
940 * <td></td>
941 * <td></td>
942 * <td></td>
943 * <td style="text-align:center">MOD</td>
944 * <td style="text-align:center">1R</td>
945 * </tr>
946 * <tr>
947 * <th scope="row" style="text-align:left">{@code CL.in(D)} different module</th>
948 * <td></td>
949 * <td></td>
950 * <td></td>
951 * <td></td>
952 * <td></td>
953 * <td style="text-align:center">2R</td>
954 * </tr>
955 * <tr>
956 * <th scope="row" style="text-align:left">{@code CL.in(D).in(C)} hop back to module</th>
957 * <td></td>
958 * <td></td>
959 * <td></td>
960 * <td></td>
961 * <td></td>
962 * <td style="text-align:center">2R</td>
963 * </tr>
964 * <tr>
965 * <th scope="row" style="text-align:left">{@code PRI1 = privateLookupIn(C1,CL)}</th>
966 * <td></td>
967 * <td style="text-align:center">PRO</td>
968 * <td style="text-align:center">PRI</td>
969 * <td style="text-align:center">PAC</td>
970 * <td style="text-align:center">MOD</td>
971 * <td style="text-align:center">1R</td>
972 * </tr>
973 * <tr>
974 * <th scope="row" style="text-align:left">{@code PRI1a = privateLookupIn(C,PRI1)}</th>
975 * <td></td>
976 * <td style="text-align:center">PRO</td>
977 * <td style="text-align:center">PRI</td>
978 * <td style="text-align:center">PAC</td>
979 * <td style="text-align:center">MOD</td>
980 * <td style="text-align:center">1R</td>
981 * </tr>
982 * <tr>
983 * <th scope="row" style="text-align:left">{@code PRI1.in(C1)} same package</th>
984 * <td></td>
985 * <td></td>
986 * <td></td>
987 * <td style="text-align:center">PAC</td>
988 * <td style="text-align:center">MOD</td>
989 * <td style="text-align:center">1R</td>
990 * </tr>
991 * <tr>
992 * <th scope="row" style="text-align:left">{@code PRI1.in(C1)} different package</th>
993 * <td></td>
994 * <td></td>
995 * <td></td>
996 * <td></td>
997 * <td style="text-align:center">MOD</td>
998 * <td style="text-align:center">1R</td>
999 * </tr>
1000 * <tr>
1001 * <th scope="row" style="text-align:left">{@code PRI1.in(D)} different module</th>
1002 * <td></td>
1003 * <td></td>
1004 * <td></td>
1005 * <td></td>
1006 * <td></td>
1007 * <td style="text-align:center">2R</td>
1008 * </tr>
1009 * <tr>
1010 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PROTECTED)}</th>
1011 * <td></td>
1012 * <td></td>
1013 * <td style="text-align:center">PRI</td>
1014 * <td style="text-align:center">PAC</td>
1015 * <td style="text-align:center">MOD</td>
1016 * <td style="text-align:center">1R</td>
1017 * </tr>
1018 * <tr>
1019 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PRIVATE)}</th>
1020 * <td></td>
1021 * <td></td>
1022 * <td></td>
1023 * <td style="text-align:center">PAC</td>
1024 * <td style="text-align:center">MOD</td>
1025 * <td style="text-align:center">1R</td>
1026 * </tr>
1027 * <tr>
1028 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PACKAGE)}</th>
1029 * <td></td>
1030 * <td></td>
1031 * <td></td>
1032 * <td></td>
1033 * <td style="text-align:center">MOD</td>
1034 * <td style="text-align:center">1R</td>
1035 * </tr>
1036 * <tr>
1037 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(MODULE)}</th>
1038 * <td></td>
1039 * <td></td>
1040 * <td></td>
1041 * <td></td>
1042 * <td></td>
1043 * <td style="text-align:center">1R</td>
1044 * </tr>
1045 * <tr>
1046 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PUBLIC)}</th>
1047 * <td></td>
1048 * <td></td>
1049 * <td></td>
1050 * <td></td>
1051 * <td></td>
1052 * <td style="text-align:center">none</td>
1053 * <tr>
1054 * <th scope="row" style="text-align:left">{@code PRI2 = privateLookupIn(D,CL)}</th>
1055 * <td></td>
1056 * <td style="text-align:center">PRO</td>
1057 * <td style="text-align:center">PRI</td>
1058 * <td style="text-align:center">PAC</td>
1059 * <td></td>
1060 * <td style="text-align:center">2R</td>
1061 * </tr>
1062 * <tr>
1063 * <th scope="row" style="text-align:left">{@code privateLookupIn(D,PRI1)}</th>
1064 * <td></td>
1065 * <td style="text-align:center">PRO</td>
1066 * <td style="text-align:center">PRI</td>
1067 * <td style="text-align:center">PAC</td>
1068 * <td></td>
1069 * <td style="text-align:center">2R</td>
1070 * </tr>
1071 * <tr>
1072 * <th scope="row" style="text-align:left">{@code privateLookupIn(C,PRI2)} fails</th>
1073 * <td></td>
1074 * <td></td>
1075 * <td></td>
1076 * <td></td>
1077 * <td></td>
1078 * <td style="text-align:center">IAE</td>
1079 * </tr>
1080 * <tr>
1081 * <th scope="row" style="text-align:left">{@code PRI2.in(D2)} same package</th>
1082 * <td></td>
1083 * <td></td>
1084 * <td></td>
1085 * <td style="text-align:center">PAC</td>
1086 * <td></td>
1087 * <td style="text-align:center">2R</td>
1088 * </tr>
1089 * <tr>
1090 * <th scope="row" style="text-align:left">{@code PRI2.in(D2)} different package</th>
1091 * <td></td>
1092 * <td></td>
1093 * <td></td>
1094 * <td></td>
1095 * <td></td>
1096 * <td style="text-align:center">2R</td>
1097 * </tr>
1098 * <tr>
1099 * <th scope="row" style="text-align:left">{@code PRI2.in(C1)} hop back to module</th>
1100 * <td></td>
1101 * <td></td>
1102 * <td></td>
1103 * <td></td>
1104 * <td></td>
1105 * <td style="text-align:center">2R</td>
1106 * </tr>
1107 * <tr>
1108 * <th scope="row" style="text-align:left">{@code PRI2.in(E)} hop to third module</th>
1109 * <td></td>
1110 * <td></td>
1111 * <td></td>
1112 * <td></td>
1113 * <td></td>
1114 * <td style="text-align:center">none</td>
1115 * </tr>
1116 * <tr>
1117 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PROTECTED)}</th>
1118 * <td></td>
1119 * <td></td>
1120 * <td style="text-align:center">PRI</td>
1121 * <td style="text-align:center">PAC</td>
1122 * <td></td>
1123 * <td style="text-align:center">2R</td>
1124 * </tr>
1125 * <tr>
1126 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PRIVATE)}</th>
1127 * <td></td>
1128 * <td></td>
1129 * <td></td>
1130 * <td style="text-align:center">PAC</td>
1131 * <td></td>
1132 * <td style="text-align:center">2R</td>
1133 * </tr>
1134 * <tr>
1135 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PACKAGE)}</th>
1136 * <td></td>
1137 * <td></td>
1138 * <td></td>
1139 * <td></td>
1140 * <td></td>
1141 * <td style="text-align:center">2R</td>
1142 * </tr>
1143 * <tr>
1144 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(MODULE)}</th>
1145 * <td></td>
1146 * <td></td>
1147 * <td></td>
1148 * <td></td>
1149 * <td></td>
1150 * <td style="text-align:center">2R</td>
1151 * </tr>
1152 * <tr>
1153 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PUBLIC)}</th>
1154 * <td></td>
1155 * <td></td>
1156 * <td></td>
1157 * <td></td>
1158 * <td></td>
1159 * <td style="text-align:center">none</td>
1160 * </tr>
1161 * <tr>
1162 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PROTECTED)}</th>
1163 * <td></td>
1164 * <td></td>
1165 * <td style="text-align:center">PRI</td>
1166 * <td style="text-align:center">PAC</td>
1167 * <td style="text-align:center">MOD</td>
1168 * <td style="text-align:center">1R</td>
1169 * </tr>
1170 * <tr>
1171 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PRIVATE)}</th>
1172 * <td></td>
1173 * <td></td>
1174 * <td></td>
1175 * <td style="text-align:center">PAC</td>
1176 * <td style="text-align:center">MOD</td>
1177 * <td style="text-align:center">1R</td>
1178 * </tr>
1179 * <tr>
1180 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PACKAGE)}</th>
1181 * <td></td>
1182 * <td></td>
1183 * <td></td>
1184 * <td></td>
1185 * <td style="text-align:center">MOD</td>
1186 * <td style="text-align:center">1R</td>
1187 * </tr>
1188 * <tr>
1189 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(MODULE)}</th>
1190 * <td></td>
1191 * <td></td>
1192 * <td></td>
1193 * <td></td>
1194 * <td></td>
1195 * <td style="text-align:center">1R</td>
1196 * </tr>
1197 * <tr>
1198 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PUBLIC)}</th>
1199 * <td></td>
1200 * <td></td>
1201 * <td></td>
1202 * <td></td>
1203 * <td></td>
1204 * <td style="text-align:center">none</td>
1205 * </tr>
1206 * <tr>
1207 * <th scope="row" style="text-align:left">{@code PUB = publicLookup()}</th>
1208 * <td></td>
1209 * <td></td>
1210 * <td></td>
1211 * <td></td>
1212 * <td></td>
1213 * <td style="text-align:center">U</td>
1214 * </tr>
1215 * <tr>
1216 * <th scope="row" style="text-align:left">{@code PUB.in(D)} different module</th>
1217 * <td></td>
1218 * <td></td>
1219 * <td></td>
1220 * <td></td>
1221 * <td></td>
1222 * <td style="text-align:center">U</td>
1223 * </tr>
1224 * <tr>
1225 * <th scope="row" style="text-align:left">{@code PUB.in(D).in(E)} third module</th>
1226 * <td></td>
1227 * <td></td>
1228 * <td></td>
1229 * <td></td>
1230 * <td></td>
1231 * <td style="text-align:center">U</td>
1232 * </tr>
1233 * <tr>
1234 * <th scope="row" style="text-align:left">{@code PUB.dropLookupMode(UNCONDITIONAL)}</th>
1235 * <td></td>
1236 * <td></td>
1237 * <td></td>
1238 * <td></td>
1239 * <td></td>
1240 * <td style="text-align:center">none</td>
1241 * </tr>
1242 * <tr>
1243 * <th scope="row" style="text-align:left">{@code privateLookupIn(C1,PUB)} fails</th>
1244 * <td></td>
1245 * <td></td>
1246 * <td></td>
1247 * <td></td>
1248 * <td></td>
1249 * <td style="text-align:center">IAE</td>
1250 * </tr>
1251 * <tr>
1252 * <th scope="row" style="text-align:left">{@code ANY.in(X)}, for inaccessible {@code X}</th>
1253 * <td></td>
1254 * <td></td>
1255 * <td></td>
1256 * <td></td>
1257 * <td></td>
1258 * <td style="text-align:center">none</td>
1259 * </tr>
1260 * </tbody>
1261 * </table>
1262 *
1263 * <p>
1264 * Notes:
1265 * <ul>
1266 * <li>Class {@code C} and class {@code C1} are in module {@code M1},
1267 * but {@code D} and {@code D2} are in module {@code M2}, and {@code E}
1268 * is in module {@code M3}. {@code X} stands for class which is inaccessible
1269 * to the lookup. {@code ANY} stands for any of the example lookups.</li>
1270 * <li>{@code ORI} indicates {@link #ORIGINAL} bit set,
1271 * {@code PRO} indicates {@link #PROTECTED} bit set,
1272 * {@code PRI} indicates {@link #PRIVATE} bit set,
1273 * {@code PAC} indicates {@link #PACKAGE} bit set,
1274 * {@code MOD} indicates {@link #MODULE} bit set,
1275 * {@code 1R} and {@code 2R} indicate {@link #PUBLIC} bit set,
1276 * {@code U} indicates {@link #UNCONDITIONAL} bit set,
1277 * {@code IAE} indicates {@code IllegalAccessException} thrown.</li>
1278 * <li>Public access comes in three kinds:
1279 * <ul>
1280 * <li>unconditional ({@code U}): the lookup assumes readability.
1281 * The lookup has {@code null} previous lookup class.
1282 * <li>one-module-reads ({@code 1R}): the module access checking is
1283 * performed with respect to the lookup class. The lookup has {@code null}
1284 * previous lookup class.
1285 * <li>two-module-reads ({@code 2R}): the module access checking is
1286 * performed with respect to the lookup class and the previous lookup class.
1287 * The lookup has a non-null previous lookup class which is in a
1288 * different module from the current lookup class.
1289 * </ul>
1290 * <li>Any attempt to reach a third module loses all access.</li>
1291 * <li>If a target class {@code X} is not accessible to {@code Lookup::in}
1292 * all access modes are dropped.</li>
1293 * </ul>
1294 *
1295 * <h2><a id="callsens"></a>Caller sensitive methods</h2>
1296 * A small number of Java methods have a special property called caller sensitivity.
1297 * A <em>caller-sensitive</em> method can behave differently depending on the
1298 * identity of its immediate caller.
1299 * <p>
1300 * If a method handle for a caller-sensitive method is requested,
1301 * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> apply,
1302 * but they take account of the lookup class in a special way.
1303 * The resulting method handle behaves as if it were called
1304 * from an instruction contained in the lookup class,
1305 * so that the caller-sensitive method detects the lookup class.
1306 * (By contrast, the invoker of the method handle is disregarded.)
1307 * Thus, in the case of caller-sensitive methods,
1308 * different lookup classes may give rise to
1309 * differently behaving method handles.
1310 * <p>
1311 * In cases where the lookup object is
1312 * {@link MethodHandles#publicLookup() publicLookup()},
1313 * or some other lookup object without the
1314 * {@linkplain #ORIGINAL original access},
1315 * the lookup class is disregarded.
1316 * In such cases, no caller-sensitive method handle can be created,
1317 * access is forbidden, and the lookup fails with an
1318 * {@code IllegalAccessException}.
1319 * <p style="font-size:smaller;">
1320 * <em>Discussion:</em>
1321 * For example, the caller-sensitive method
1322 * {@link java.lang.Class#forName(String) Class.forName(x)}
1323 * can return varying classes or throw varying exceptions,
1324 * depending on the class loader of the class that calls it.
1325 * A public lookup of {@code Class.forName} will fail, because
1326 * there is no reasonable way to determine its bytecode behavior.
1327 * <p style="font-size:smaller;">
1328 * If an application caches method handles for broad sharing,
1329 * it should use {@code publicLookup()} to create them.
1330 * If there is a lookup of {@code Class.forName}, it will fail,
1331 * and the application must take appropriate action in that case.
1332 * It may be that a later lookup, perhaps during the invocation of a
1333 * bootstrap method, can incorporate the specific identity
1334 * of the caller, making the method accessible.
1335 * <p style="font-size:smaller;">
1336 * The function {@code MethodHandles.lookup} is caller sensitive
1337 * so that there can be a secure foundation for lookups.
1338 * Nearly all other methods in the JSR 292 API rely on lookup
1339 * objects to check access requests.
1340 */
1341 public static final
1342 class Lookup {
1343 /** The class on behalf of whom the lookup is being performed. */
1344 private final Class<?> lookupClass;
1345
1346 /** previous lookup class */
1347 private final Class<?> prevLookupClass;
1348
1349 /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */
1350 private final int allowedModes;
1351
1352 static {
1353 Reflection.registerFieldsToFilter(Lookup.class, Set.of("lookupClass", "allowedModes"));
1354 }
1355
1356 /** A single-bit mask representing {@code public} access,
1357 * which may contribute to the result of {@link #lookupModes lookupModes}.
1358 * The value, {@code 0x01}, happens to be the same as the value of the
1359 * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.
1360 * <p>
1361 * A {@code Lookup} with this lookup mode performs cross-module access check
1362 * with respect to the {@linkplain #lookupClass() lookup class} and
1363 * {@linkplain #previousLookupClass() previous lookup class} if present.
1364 */
1365 public static final int PUBLIC = Modifier.PUBLIC;
1366
1367 /** A single-bit mask representing {@code private} access,
1368 * which may contribute to the result of {@link #lookupModes lookupModes}.
1369 * The value, {@code 0x02}, happens to be the same as the value of the
1370 * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.
1371 */
1372 public static final int PRIVATE = Modifier.PRIVATE;
1373
1374 /** A single-bit mask representing {@code protected} access,
1375 * which may contribute to the result of {@link #lookupModes lookupModes}.
1376 * The value, {@code 0x04}, happens to be the same as the value of the
1377 * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.
1378 */
1379 public static final int PROTECTED = Modifier.PROTECTED;
1380
1381 /** A single-bit mask representing {@code package} access (default access),
1382 * which may contribute to the result of {@link #lookupModes lookupModes}.
1383 * The value is {@code 0x08}, which does not correspond meaningfully to
1384 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1385 */
1386 public static final int PACKAGE = Modifier.STATIC;
1387
1388 /** A single-bit mask representing {@code module} access,
1389 * which may contribute to the result of {@link #lookupModes lookupModes}.
1390 * The value is {@code 0x10}, which does not correspond meaningfully to
1391 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1392 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup}
1393 * with this lookup mode can access all public types in the module of the
1394 * lookup class and public types in packages exported by other modules
1395 * to the module of the lookup class.
1396 * <p>
1397 * If this lookup mode is set, the {@linkplain #previousLookupClass()
1398 * previous lookup class} is always {@code null}.
1399 *
1400 * @since 9
1401 */
1402 public static final int MODULE = PACKAGE << 1;
1403
1404 /** A single-bit mask representing {@code unconditional} access
1405 * which may contribute to the result of {@link #lookupModes lookupModes}.
1406 * The value is {@code 0x20}, which does not correspond meaningfully to
1407 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1408 * A {@code Lookup} with this lookup mode assumes {@linkplain
1409 * java.lang.Module#canRead(java.lang.Module) readability}.
1410 * This lookup mode can access all public members of public types
1411 * of all modules when the type is in a package that is {@link
1412 * java.lang.Module#isExported(String) exported unconditionally}.
1413 *
1414 * <p>
1415 * If this lookup mode is set, the {@linkplain #previousLookupClass()
1416 * previous lookup class} is always {@code null}.
1417 *
1418 * @since 9
1419 * @see #publicLookup()
1420 */
1421 public static final int UNCONDITIONAL = PACKAGE << 2;
1422
1423 /** A single-bit mask representing {@code original} access
1424 * which may contribute to the result of {@link #lookupModes lookupModes}.
1425 * The value is {@code 0x40}, which does not correspond meaningfully to
1426 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1427 *
1428 * <p>
1429 * If this lookup mode is set, the {@code Lookup} object must be
1430 * created by the original lookup class by calling
1431 * {@link MethodHandles#lookup()} method or by a bootstrap method
1432 * invoked by the VM. The {@code Lookup} object with this lookup
1433 * mode has {@linkplain #hasFullPrivilegeAccess() full privilege access}.
1434 *
1435 * @since 16
1436 */
1437 public static final int ORIGINAL = PACKAGE << 3;
1438
1439 private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE | MODULE | UNCONDITIONAL | ORIGINAL);
1440 private static final int FULL_POWER_MODES = (ALL_MODES & ~UNCONDITIONAL); // with original access
1441 private static final int TRUSTED = -1;
1442
1443 /*
1444 * Adjust PUBLIC => PUBLIC|MODULE|ORIGINAL|UNCONDITIONAL
1445 * Adjust 0 => PACKAGE
1446 */
1447 private static int fixmods(int mods) {
1448 mods &= (ALL_MODES - PACKAGE - MODULE - ORIGINAL - UNCONDITIONAL);
1449 if (Modifier.isPublic(mods))
1450 mods |= UNCONDITIONAL;
1451 return (mods != 0) ? mods : PACKAGE;
1452 }
1453
1454 /** Tells which class is performing the lookup. It is this class against
1455 * which checks are performed for visibility and access permissions.
1456 * <p>
1457 * If this lookup object has a {@linkplain #previousLookupClass() previous lookup class},
1458 * access checks are performed against both the lookup class and the previous lookup class.
1459 * <p>
1460 * The class implies a maximum level of access permission,
1461 * but the permissions may be additionally limited by the bitmask
1462 * {@link #lookupModes lookupModes}, which controls whether non-public members
1463 * can be accessed.
1464 * @return the lookup class, on behalf of which this lookup object finds members
1465 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1466 */
1467 public Class<?> lookupClass() {
1468 return lookupClass;
1469 }
1470
1471 /** Reports a lookup class in another module that this lookup object
1472 * was previously teleported from, or {@code null}.
1473 * <p>
1474 * A {@code Lookup} object produced by the factory methods, such as the
1475 * {@link #lookup() lookup()} and {@link #publicLookup() publicLookup()} method,
1476 * has {@code null} previous lookup class.
1477 * A {@code Lookup} object has a non-null previous lookup class
1478 * when this lookup was teleported from an old lookup class
1479 * in one module to a new lookup class in another module.
1480 *
1481 * @return the lookup class in another module that this lookup object was
1482 * previously teleported from, or {@code null}
1483 * @since 14
1484 * @see #in(Class)
1485 * @see MethodHandles#privateLookupIn(Class, Lookup)
1486 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1487 */
1488 public Class<?> previousLookupClass() {
1489 return prevLookupClass;
1490 }
1491
1492 // This is just for calling out to MethodHandleImpl.
1493 private Class<?> lookupClassOrNull() {
1494 return (allowedModes == TRUSTED) ? null : lookupClass;
1495 }
1496
1497 /** Tells which access-protection classes of members this lookup object can produce.
1498 * The result is a bit-mask of the bits
1499 * {@linkplain #PUBLIC PUBLIC (0x01)},
1500 * {@linkplain #PRIVATE PRIVATE (0x02)},
1501 * {@linkplain #PROTECTED PROTECTED (0x04)},
1502 * {@linkplain #PACKAGE PACKAGE (0x08)},
1503 * {@linkplain #MODULE MODULE (0x10)},
1504 * {@linkplain #UNCONDITIONAL UNCONDITIONAL (0x20)},
1505 * and {@linkplain #ORIGINAL ORIGINAL (0x40)}.
1506 * <p>
1507 * A freshly-created lookup object
1508 * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class} has
1509 * all possible bits set, except {@code UNCONDITIONAL}.
1510 * A lookup object on a new lookup class
1511 * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object}
1512 * may have some mode bits set to zero.
1513 * Mode bits can also be
1514 * {@linkplain java.lang.invoke.MethodHandles.Lookup#dropLookupMode directly cleared}.
1515 * Once cleared, mode bits cannot be restored from the downgraded lookup object.
1516 * The purpose of this is to restrict access via the new lookup object,
1517 * so that it can access only names which can be reached by the original
1518 * lookup object, and also by the new lookup class.
1519 * @return the lookup modes, which limit the kinds of access performed by this lookup object
1520 * @see #in
1521 * @see #dropLookupMode
1522 */
1523 public int lookupModes() {
1524 return allowedModes & ALL_MODES;
1525 }
1526
1527 /** Embody the current class (the lookupClass) as a lookup class
1528 * for method handle creation.
1529 * Must be called by from a method in this package,
1530 * which in turn is called by a method not in this package.
1531 */
1532 Lookup(Class<?> lookupClass) {
1533 this(lookupClass, null, FULL_POWER_MODES);
1534 }
1535
1536 private Lookup(Class<?> lookupClass, Class<?> prevLookupClass, int allowedModes) {
1537 assert prevLookupClass == null || ((allowedModes & MODULE) == 0
1538 && prevLookupClass.getModule() != lookupClass.getModule());
1539 assert !lookupClass.isArray() && !lookupClass.isPrimitive();
1540 this.lookupClass = lookupClass;
1541 this.prevLookupClass = prevLookupClass;
1542 this.allowedModes = allowedModes;
1543 }
1544
1545 private static Lookup newLookup(Class<?> lookupClass, Class<?> prevLookupClass, int allowedModes) {
1546 // make sure we haven't accidentally picked up a privileged class:
1547 checkUnprivilegedlookupClass(lookupClass);
1548 return new Lookup(lookupClass, prevLookupClass, allowedModes);
1549 }
1550
1551 /**
1552 * Creates a lookup on the specified new lookup class.
1553 * The resulting object will report the specified
1554 * class as its own {@link #lookupClass() lookupClass}.
1555 *
1556 * <p>
1557 * However, the resulting {@code Lookup} object is guaranteed
1558 * to have no more access capabilities than the original.
1559 * In particular, access capabilities can be lost as follows:<ul>
1560 * <li>If the new lookup class is different from the old lookup class,
1561 * i.e. {@link #ORIGINAL ORIGINAL} access is lost.
1562 * <li>If the new lookup class is in a different module from the old one,
1563 * i.e. {@link #MODULE MODULE} access is lost.
1564 * <li>If the new lookup class is in a different package
1565 * than the old one, protected and default (package) members will not be accessible,
1566 * i.e. {@link #PROTECTED PROTECTED} and {@link #PACKAGE PACKAGE} access are lost.
1567 * <li>If the new lookup class is not within the same package member
1568 * as the old one, private members will not be accessible, and protected members
1569 * will not be accessible by virtue of inheritance,
1570 * i.e. {@link #PRIVATE PRIVATE} access is lost.
1571 * (Protected members may continue to be accessible because of package sharing.)
1572 * <li>If the new lookup class is not
1573 * {@linkplain #accessClass(Class) accessible} to this lookup,
1574 * then no members, not even public members, will be accessible
1575 * i.e. all access modes are lost.
1576 * <li>If the new lookup class, the old lookup class and the previous lookup class
1577 * are all in different modules i.e. teleporting to a third module,
1578 * all access modes are lost.
1579 * </ul>
1580 * <p>
1581 * The new previous lookup class is chosen as follows:
1582 * <ul>
1583 * <li>If the new lookup object has {@link #UNCONDITIONAL UNCONDITIONAL} bit,
1584 * the new previous lookup class is {@code null}.
1585 * <li>If the new lookup class is in the same module as the old lookup class,
1586 * the new previous lookup class is the old previous lookup class.
1587 * <li>If the new lookup class is in a different module from the old lookup class,
1588 * the new previous lookup class is the old lookup class.
1589 *</ul>
1590 * <p>
1591 * The resulting lookup's capabilities for loading classes
1592 * (used during {@link #findClass} invocations)
1593 * are determined by the lookup class' loader,
1594 * which may change due to this operation.
1595 *
1596 * @param requestedLookupClass the desired lookup class for the new lookup object
1597 * @return a lookup object which reports the desired lookup class, or the same object
1598 * if there is no change
1599 * @throws IllegalArgumentException if {@code requestedLookupClass} is a primitive type or void or array class
1600 * @throws NullPointerException if the argument is null
1601 *
1602 * @see #accessClass(Class)
1603 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1604 */
1605 public Lookup in(Class<?> requestedLookupClass) {
1606 Objects.requireNonNull(requestedLookupClass);
1607 if (requestedLookupClass.isPrimitive())
1608 throw new IllegalArgumentException(requestedLookupClass + " is a primitive class");
1609 if (requestedLookupClass.isArray())
1610 throw new IllegalArgumentException(requestedLookupClass + " is an array class");
1611
1612 if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all
1613 return new Lookup(requestedLookupClass, null, FULL_POWER_MODES);
1614 if (requestedLookupClass == this.lookupClass)
1615 return this; // keep same capabilities
1616 int newModes = (allowedModes & FULL_POWER_MODES) & ~ORIGINAL;
1617 Module fromModule = this.lookupClass.getModule();
1618 Module targetModule = requestedLookupClass.getModule();
1619 Class<?> plc = this.previousLookupClass();
1620 if ((this.allowedModes & UNCONDITIONAL) != 0) {
1621 assert plc == null;
1622 newModes = UNCONDITIONAL;
1623 } else if (fromModule != targetModule) {
1624 if (plc != null && !VerifyAccess.isSameModule(plc, requestedLookupClass)) {
1625 // allow hopping back and forth between fromModule and plc's module
1626 // but not the third module
1627 newModes = 0;
1628 }
1629 // drop MODULE access
1630 newModes &= ~(MODULE|PACKAGE|PRIVATE|PROTECTED);
1631 // teleport from this lookup class
1632 plc = this.lookupClass;
1633 }
1634 if ((newModes & PACKAGE) != 0
1635 && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {
1636 newModes &= ~(PACKAGE|PRIVATE|PROTECTED);
1637 }
1638 // Allow nestmate lookups to be created without special privilege:
1639 if ((newModes & PRIVATE) != 0
1640 && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {
1641 newModes &= ~(PRIVATE|PROTECTED);
1642 }
1643 if ((newModes & (PUBLIC|UNCONDITIONAL)) != 0
1644 && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, this.prevLookupClass, allowedModes)) {
1645 // The requested class it not accessible from the lookup class.
1646 // No permissions.
1647 newModes = 0;
1648 }
1649 return newLookup(requestedLookupClass, plc, newModes);
1650 }
1651
1652 /**
1653 * Creates a lookup on the same lookup class which this lookup object
1654 * finds members, but with a lookup mode that has lost the given lookup mode.
1655 * The lookup mode to drop is one of {@link #PUBLIC PUBLIC}, {@link #MODULE
1656 * MODULE}, {@link #PACKAGE PACKAGE}, {@link #PROTECTED PROTECTED},
1657 * {@link #PRIVATE PRIVATE}, {@link #ORIGINAL ORIGINAL}, or
1658 * {@link #UNCONDITIONAL UNCONDITIONAL}.
1659 *
1660 * <p> If this lookup is a {@linkplain MethodHandles#publicLookup() public lookup},
1661 * this lookup has {@code UNCONDITIONAL} mode set and it has no other mode set.
1662 * When dropping {@code UNCONDITIONAL} on a public lookup then the resulting
1663 * lookup has no access.
1664 *
1665 * <p> If this lookup is not a public lookup, then the following applies
1666 * regardless of its {@linkplain #lookupModes() lookup modes}.
1667 * {@link #PROTECTED PROTECTED} and {@link #ORIGINAL ORIGINAL} are always
1668 * dropped and so the resulting lookup mode will never have these access
1669 * capabilities. When dropping {@code PACKAGE}
1670 * then the resulting lookup will not have {@code PACKAGE} or {@code PRIVATE}
1671 * access. When dropping {@code MODULE} then the resulting lookup will not
1672 * have {@code MODULE}, {@code PACKAGE}, or {@code PRIVATE} access.
1673 * When dropping {@code PUBLIC} then the resulting lookup has no access.
1674 *
1675 * @apiNote
1676 * A lookup with {@code PACKAGE} but not {@code PRIVATE} mode can safely
1677 * delegate non-public access within the package of the lookup class without
1678 * conferring <a href="MethodHandles.Lookup.html#privacc">private access</a>.
1679 * A lookup with {@code MODULE} but not
1680 * {@code PACKAGE} mode can safely delegate {@code PUBLIC} access within
1681 * the module of the lookup class without conferring package access.
1682 * A lookup with a {@linkplain #previousLookupClass() previous lookup class}
1683 * (and {@code PUBLIC} but not {@code MODULE} mode) can safely delegate access
1684 * to public classes accessible to both the module of the lookup class
1685 * and the module of the previous lookup class.
1686 *
1687 * @param modeToDrop the lookup mode to drop
1688 * @return a lookup object which lacks the indicated mode, or the same object if there is no change
1689 * @throws IllegalArgumentException if {@code modeToDrop} is not one of {@code PUBLIC},
1690 * {@code MODULE}, {@code PACKAGE}, {@code PROTECTED}, {@code PRIVATE}, {@code ORIGINAL}
1691 * or {@code UNCONDITIONAL}
1692 * @see MethodHandles#privateLookupIn
1693 * @since 9
1694 */
1695 public Lookup dropLookupMode(int modeToDrop) {
1696 int oldModes = lookupModes();
1697 int newModes = oldModes & ~(modeToDrop | PROTECTED | ORIGINAL);
1698 switch (modeToDrop) {
1699 case PUBLIC: newModes &= ~(FULL_POWER_MODES); break;
1700 case MODULE: newModes &= ~(PACKAGE | PRIVATE); break;
1701 case PACKAGE: newModes &= ~(PRIVATE); break;
1702 case PROTECTED:
1703 case PRIVATE:
1704 case ORIGINAL:
1705 case UNCONDITIONAL: break;
1706 default: throw new IllegalArgumentException(modeToDrop + " is not a valid mode to drop");
1707 }
1708 if (newModes == oldModes) return this; // return self if no change
1709 return newLookup(lookupClass(), previousLookupClass(), newModes);
1710 }
1711
1712 /**
1713 * Creates and links a class or interface from {@code bytes}
1714 * with the same class loader and in the same runtime package and
1715 * {@linkplain java.security.ProtectionDomain protection domain} as this lookup's
1716 * {@linkplain #lookupClass() lookup class} as if calling
1717 * {@link ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain)
1718 * ClassLoader::defineClass}.
1719 *
1720 * <p> The {@linkplain #lookupModes() lookup modes} for this lookup must include
1721 * {@link #PACKAGE PACKAGE} access as default (package) members will be
1722 * accessible to the class. The {@code PACKAGE} lookup mode serves to authenticate
1723 * that the lookup object was created by a caller in the runtime package (or derived
1724 * from a lookup originally created by suitably privileged code to a target class in
1725 * the runtime package). </p>
1726 *
1727 * <p> The {@code bytes} parameter is the class bytes of a valid class file (as defined
1728 * by the <em>The Java Virtual Machine Specification</em>) with a class name in the
1729 * same package as the lookup class. </p>
1730 *
1731 * <p> This method does not run the class initializer. The class initializer may
1732 * run at a later time, as detailed in section 12.4 of the <em>The Java Language
1733 * Specification</em>. </p>
1734 *
1735 * @param bytes the class bytes
1736 * @return the {@code Class} object for the class
1737 * @throws IllegalAccessException if this lookup does not have {@code PACKAGE} access
1738 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure
1739 * @throws IllegalArgumentException if {@code bytes} denotes a class in a different package
1740 * than the lookup class or {@code bytes} is not a class or interface
1741 * ({@code ACC_MODULE} flag is set in the value of the {@code access_flags} item)
1742 * @throws VerifyError if the newly created class cannot be verified
1743 * @throws LinkageError if the newly created class cannot be linked for any other reason
1744 * @throws NullPointerException if {@code bytes} is {@code null}
1745 * @since 9
1746 * @see MethodHandles#privateLookupIn
1747 * @see Lookup#dropLookupMode
1748 * @see ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain)
1749 */
1750 public Class<?> defineClass(byte[] bytes) throws IllegalAccessException {
1751 if ((lookupModes() & PACKAGE) == 0)
1752 throw new IllegalAccessException("Lookup does not have PACKAGE access");
1753 return makeClassDefiner(bytes.clone()).defineClass(false);
1754 }
1755
1756 /**
1757 * The set of class options that specify whether a hidden class created by
1758 * {@link Lookup#defineHiddenClass(byte[], boolean, ClassOption...)
1759 * Lookup::defineHiddenClass} method is dynamically added as a new member
1760 * to the nest of a lookup class and/or whether a hidden class has
1761 * a strong relationship with the class loader marked as its defining loader.
1762 *
1763 * @since 15
1764 */
1765 public enum ClassOption {
1766 /**
1767 * Specifies that a hidden class be added to {@linkplain Class#getNestHost nest}
1768 * of a lookup class as a nestmate.
1769 *
1770 * <p> A hidden nestmate class has access to the private members of all
1771 * classes and interfaces in the same nest.
1772 *
1773 * @see Class#getNestHost()
1774 */
1775 NESTMATE(NESTMATE_CLASS),
1776
1777 /**
1778 * Specifies that a hidden class has a <em>strong</em>
1779 * relationship with the class loader marked as its defining loader,
1780 * as a normal class or interface has with its own defining loader.
1781 * This means that the hidden class may be unloaded if and only if
1782 * its defining loader is not reachable and thus may be reclaimed
1783 * by a garbage collector (JLS {@jls 12.7}).
1784 *
1785 * <p> By default, a hidden class or interface may be unloaded
1786 * even if the class loader that is marked as its defining loader is
1787 * <a href="../ref/package-summary.html#reachability">reachable</a>.
1788
1789 *
1790 * @jls 12.7 Unloading of Classes and Interfaces
1791 */
1792 STRONG(STRONG_LOADER_LINK);
1793
1794 /* the flag value is used by VM at define class time */
1795 private final int flag;
1796 ClassOption(int flag) {
1797 this.flag = flag;
1798 }
1799
1800 static int optionsToFlag(ClassOption[] options) {
1801 int flags = 0;
1802 for (ClassOption cp : options) {
1803 if ((flags & cp.flag) != 0) {
1804 throw new IllegalArgumentException("Duplicate ClassOption " + cp);
1805 }
1806 flags |= cp.flag;
1807 }
1808 return flags;
1809 }
1810 }
1811
1812 /**
1813 * Creates a <em>hidden</em> class or interface from {@code bytes},
1814 * returning a {@code Lookup} on the newly created class or interface.
1815 *
1816 * <p> Ordinarily, a class or interface {@code C} is created by a class loader,
1817 * which either defines {@code C} directly or delegates to another class loader.
1818 * A class loader defines {@code C} directly by invoking
1819 * {@link ClassLoader#defineClass(String, byte[], int, int, ProtectionDomain)
1820 * ClassLoader::defineClass}, which causes the Java Virtual Machine
1821 * to derive {@code C} from a purported representation in {@code class} file format.
1822 * In situations where use of a class loader is undesirable, a class or interface
1823 * {@code C} can be created by this method instead. This method is capable of
1824 * defining {@code C}, and thereby creating it, without invoking
1825 * {@code ClassLoader::defineClass}.
1826 * Instead, this method defines {@code C} as if by arranging for
1827 * the Java Virtual Machine to derive a nonarray class or interface {@code C}
1828 * from a purported representation in {@code class} file format
1829 * using the following rules:
1830 *
1831 * <ol>
1832 * <li> The {@linkplain #lookupModes() lookup modes} for this {@code Lookup}
1833 * must include {@linkplain #hasFullPrivilegeAccess() full privilege} access.
1834 * This level of access is needed to create {@code C} in the module
1835 * of the lookup class of this {@code Lookup}.</li>
1836 *
1837 * <li> The purported representation in {@code bytes} must be a {@code ClassFile}
1838 * structure (JVMS {@jvms 4.1}) of a supported major and minor version.
1839 * The major and minor version may differ from the {@code class} file version
1840 * of the lookup class of this {@code Lookup}.</li>
1841 *
1842 * <li> The value of {@code this_class} must be a valid index in the
1843 * {@code constant_pool} table, and the entry at that index must be a valid
1844 * {@code CONSTANT_Class_info} structure. Let {@code N} be the binary name
1845 * encoded in internal form that is specified by this structure. {@code N} must
1846 * denote a class or interface in the same package as the lookup class.</li>
1847 *
1848 * <li> Let {@code CN} be the string {@code N + "." + <suffix>},
1849 * where {@code <suffix>} is an unqualified name.
1850 *
1851 * <p> Let {@code newBytes} be the {@code ClassFile} structure given by
1852 * {@code bytes} with an additional entry in the {@code constant_pool} table,
1853 * indicating a {@code CONSTANT_Utf8_info} structure for {@code CN}, and
1854 * where the {@code CONSTANT_Class_info} structure indicated by {@code this_class}
1855 * refers to the new {@code CONSTANT_Utf8_info} structure.
1856 *
1857 * <p> Let {@code L} be the defining class loader of the lookup class of this {@code Lookup}.
1858 *
1859 * <p> {@code C} is derived with name {@code CN}, class loader {@code L}, and
1860 * purported representation {@code newBytes} as if by the rules of JVMS {@jvms 5.3.5},
1861 * with the following adjustments:
1862 * <ul>
1863 * <li> The constant indicated by {@code this_class} is permitted to specify a name
1864 * that includes a single {@code "."} character, even though this is not a valid
1865 * binary class or interface name in internal form.</li>
1866 *
1867 * <li> The Java Virtual Machine marks {@code L} as the defining class loader of {@code C},
1868 * but no class loader is recorded as an initiating class loader of {@code C}.</li>
1869 *
1870 * <li> {@code C} is considered to have the same runtime
1871 * {@linkplain Class#getPackage() package}, {@linkplain Class#getModule() module}
1872 * and {@linkplain java.security.ProtectionDomain protection domain}
1873 * as the lookup class of this {@code Lookup}.
1874 * <li> Let {@code GN} be the binary name obtained by taking {@code N}
1875 * (a binary name encoded in internal form) and replacing ASCII forward slashes with
1876 * ASCII periods. For the instance of {@link java.lang.Class} representing {@code C}:
1877 * <ul>
1878 * <li> {@link Class#getName()} returns the string {@code GN + "/" + <suffix>},
1879 * even though this is not a valid binary class or interface name.</li>
1880 * <li> {@link Class#descriptorString()} returns the string
1881 * {@code "L" + N + "." + <suffix> + ";"},
1882 * even though this is not a valid type descriptor name.</li>
1883 * <li> {@link Class#describeConstable()} returns an empty optional as {@code C}
1884 * cannot be described in {@linkplain java.lang.constant.ClassDesc nominal form}.</li>
1885 * </ul>
1886 * </ul>
1887 * </li>
1888 * </ol>
1889 *
1890 * <p> After {@code C} is derived, it is linked by the Java Virtual Machine.
1891 * Linkage occurs as specified in JVMS {@jvms 5.4.3}, with the following adjustments:
1892 * <ul>
1893 * <li> During verification, whenever it is necessary to load the class named
1894 * {@code CN}, the attempt succeeds, producing class {@code C}. No request is
1895 * made of any class loader.</li>
1896 *
1897 * <li> On any attempt to resolve the entry in the run-time constant pool indicated
1898 * by {@code this_class}, the symbolic reference is considered to be resolved to
1899 * {@code C} and resolution always succeeds immediately.</li>
1900 * </ul>
1901 *
1902 * <p> If the {@code initialize} parameter is {@code true},
1903 * then {@code C} is initialized by the Java Virtual Machine.
1904 *
1905 * <p> The newly created class or interface {@code C} serves as the
1906 * {@linkplain #lookupClass() lookup class} of the {@code Lookup} object
1907 * returned by this method. {@code C} is <em>hidden</em> in the sense that
1908 * no other class or interface can refer to {@code C} via a constant pool entry.
1909 * That is, a hidden class or interface cannot be named as a supertype, a field type,
1910 * a method parameter type, or a method return type by any other class.
1911 * This is because a hidden class or interface does not have a binary name, so
1912 * there is no internal form available to record in any class's constant pool.
1913 * A hidden class or interface is not discoverable by {@link Class#forName(String, boolean, ClassLoader)},
1914 * {@link ClassLoader#loadClass(String, boolean)}, or {@link #findClass(String)}, and
1915 * is not {@linkplain java.instrument/java.lang.instrument.Instrumentation#isModifiableClass(Class)
1916 * modifiable} by Java agents or tool agents using the <a href="{@docRoot}/../specs/jvmti.html">
1917 * JVM Tool Interface</a>.
1918 *
1919 * <p> A class or interface created by
1920 * {@linkplain ClassLoader#defineClass(String, byte[], int, int, ProtectionDomain)
1921 * a class loader} has a strong relationship with that class loader.
1922 * That is, every {@code Class} object contains a reference to the {@code ClassLoader}
1923 * that {@linkplain Class#getClassLoader() defined it}.
1924 * This means that a class created by a class loader may be unloaded if and
1925 * only if its defining loader is not reachable and thus may be reclaimed
1926 * by a garbage collector (JLS {@jls 12.7}).
1927 *
1928 * By default, however, a hidden class or interface may be unloaded even if
1929 * the class loader that is marked as its defining loader is
1930 * <a href="../ref/package-summary.html#reachability">reachable</a>.
1931 * This behavior is useful when a hidden class or interface serves multiple
1932 * classes defined by arbitrary class loaders. In other cases, a hidden
1933 * class or interface may be linked to a single class (or a small number of classes)
1934 * with the same defining loader as the hidden class or interface.
1935 * In such cases, where the hidden class or interface must be coterminous
1936 * with a normal class or interface, the {@link ClassOption#STRONG STRONG}
1937 * option may be passed in {@code options}.
1938 * This arranges for a hidden class to have the same strong relationship
1939 * with the class loader marked as its defining loader,
1940 * as a normal class or interface has with its own defining loader.
1941 *
1942 * If {@code STRONG} is not used, then the invoker of {@code defineHiddenClass}
1943 * may still prevent a hidden class or interface from being
1944 * unloaded by ensuring that the {@code Class} object is reachable.
1945 *
1946 * <p> The unloading characteristics are set for each hidden class when it is
1947 * defined, and cannot be changed later. An advantage of allowing hidden classes
1948 * to be unloaded independently of the class loader marked as their defining loader
1949 * is that a very large number of hidden classes may be created by an application.
1950 * In contrast, if {@code STRONG} is used, then the JVM may run out of memory,
1951 * just as if normal classes were created by class loaders.
1952 *
1953 * <p> Classes and interfaces in a nest are allowed to have mutual access to
1954 * their private members. The nest relationship is determined by
1955 * the {@code NestHost} attribute (JVMS {@jvms 4.7.28}) and
1956 * the {@code NestMembers} attribute (JVMS {@jvms 4.7.29}) in a {@code class} file.
1957 * By default, a hidden class belongs to a nest consisting only of itself
1958 * because a hidden class has no binary name.
1959 * The {@link ClassOption#NESTMATE NESTMATE} option can be passed in {@code options}
1960 * to create a hidden class or interface {@code C} as a member of a nest.
1961 * The nest to which {@code C} belongs is not based on any {@code NestHost} attribute
1962 * in the {@code ClassFile} structure from which {@code C} was derived.
1963 * Instead, the following rules determine the nest host of {@code C}:
1964 * <ul>
1965 * <li>If the nest host of the lookup class of this {@code Lookup} has previously
1966 * been determined, then let {@code H} be the nest host of the lookup class.
1967 * Otherwise, the nest host of the lookup class is determined using the
1968 * algorithm in JVMS {@jvms 5.4.4}, yielding {@code H}.</li>
1969 * <li>The nest host of {@code C} is determined to be {@code H},
1970 * the nest host of the lookup class.</li>
1971 * </ul>
1972 *
1973 * <p> A hidden class or interface may be serializable, but this requires a custom
1974 * serialization mechanism in order to ensure that instances are properly serialized
1975 * and deserialized. The default serialization mechanism supports only classes and
1976 * interfaces that are discoverable by their class name.
1977 *
1978 * @param bytes the bytes that make up the class data,
1979 * in the format of a valid {@code class} file as defined by
1980 * <cite>The Java Virtual Machine Specification</cite>.
1981 * @param initialize if {@code true} the class will be initialized.
1982 * @param options {@linkplain ClassOption class options}
1983 * @return the {@code Lookup} object on the hidden class,
1984 * with {@linkplain #ORIGINAL original} and
1985 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege} access
1986 *
1987 * @throws IllegalAccessException if this {@code Lookup} does not have
1988 * {@linkplain #hasFullPrivilegeAccess() full privilege} access
1989 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure
1990 * @throws UnsupportedClassVersionError if {@code bytes} is not of a supported major or minor version
1991 * @throws IllegalArgumentException if {@code bytes} denotes a class in a different package
1992 * than the lookup class or {@code bytes} is not a class or interface
1993 * ({@code ACC_MODULE} flag is set in the value of the {@code access_flags} item)
1994 * @throws IncompatibleClassChangeError if the class or interface named as
1995 * the direct superclass of {@code C} is in fact an interface, or if any of the classes
1996 * or interfaces named as direct superinterfaces of {@code C} are not in fact interfaces
1997 * @throws ClassCircularityError if any of the superclasses or superinterfaces of
1998 * {@code C} is {@code C} itself
1999 * @throws VerifyError if the newly created class cannot be verified
2000 * @throws LinkageError if the newly created class cannot be linked for any other reason
2001 * @throws NullPointerException if any parameter is {@code null}
2002 *
2003 * @since 15
2004 * @see Class#isHidden()
2005 * @jvms 4.2.1 Binary Class and Interface Names
2006 * @jvms 4.2.2 Unqualified Names
2007 * @jvms 4.7.28 The {@code NestHost} Attribute
2008 * @jvms 4.7.29 The {@code NestMembers} Attribute
2009 * @jvms 5.4.3.1 Class and Interface Resolution
2010 * @jvms 5.4.4 Access Control
2011 * @jvms 5.3.5 Deriving a {@code Class} from a {@code class} File Representation
2012 * @jvms 5.4 Linking
2013 * @jvms 5.5 Initialization
2014 * @jls 12.7 Unloading of Classes and Interfaces
2015 */
2016 @SuppressWarnings("doclint:reference") // cross-module links
2017 public Lookup defineHiddenClass(byte[] bytes, boolean initialize, ClassOption... options)
2018 throws IllegalAccessException
2019 {
2020 Objects.requireNonNull(bytes);
2021 int flags = ClassOption.optionsToFlag(options);
2022 if (!hasFullPrivilegeAccess()) {
2023 throw new IllegalAccessException(this + " does not have full privilege access");
2024 }
2025
2026 return makeHiddenClassDefiner(bytes.clone(), false, flags).defineClassAsLookup(initialize);
2027 }
2028
2029 /**
2030 * Creates a <em>hidden</em> class or interface from {@code bytes} with associated
2031 * {@linkplain MethodHandles#classData(Lookup, String, Class) class data},
2032 * returning a {@code Lookup} on the newly created class or interface.
2033 *
2034 * <p> This method is equivalent to calling
2035 * {@link #defineHiddenClass(byte[], boolean, ClassOption...) defineHiddenClass(bytes, initialize, options)}
2036 * as if the hidden class is injected with a private static final <i>unnamed</i>
2037 * field which is initialized with the given {@code classData} at
2038 * the first instruction of the class initializer.
2039 * The newly created class is linked by the Java Virtual Machine.
2040 *
2041 * <p> The {@link MethodHandles#classData(Lookup, String, Class) MethodHandles::classData}
2042 * and {@link MethodHandles#classDataAt(Lookup, String, Class, int) MethodHandles::classDataAt}
2043 * methods can be used to retrieve the {@code classData}.
2044 *
2045 * @apiNote
2046 * A framework can create a hidden class with class data with one or more
2047 * objects and load the class data as dynamically-computed constant(s)
2048 * via a bootstrap method. {@link MethodHandles#classData(Lookup, String, Class)
2049 * Class data} is accessible only to the lookup object created by the newly
2050 * defined hidden class but inaccessible to other members in the same nest
2051 * (unlike private static fields that are accessible to nestmates).
2052 * Care should be taken w.r.t. mutability for example when passing
2053 * an array or other mutable structure through the class data.
2054 * Changing any value stored in the class data at runtime may lead to
2055 * unpredictable behavior.
2056 * If the class data is a {@code List}, it is good practice to make it
2057 * unmodifiable for example via {@link List#of List::of}.
2058 *
2059 * @param bytes the class bytes
2060 * @param classData pre-initialized class data
2061 * @param initialize if {@code true} the class will be initialized.
2062 * @param options {@linkplain ClassOption class options}
2063 * @return the {@code Lookup} object on the hidden class,
2064 * with {@linkplain #ORIGINAL original} and
2065 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege} access
2066 *
2067 * @throws IllegalAccessException if this {@code Lookup} does not have
2068 * {@linkplain #hasFullPrivilegeAccess() full privilege} access
2069 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure
2070 * @throws UnsupportedClassVersionError if {@code bytes} is not of a supported major or minor version
2071 * @throws IllegalArgumentException if {@code bytes} denotes a class in a different package
2072 * than the lookup class or {@code bytes} is not a class or interface
2073 * ({@code ACC_MODULE} flag is set in the value of the {@code access_flags} item)
2074 * @throws IncompatibleClassChangeError if the class or interface named as
2075 * the direct superclass of {@code C} is in fact an interface, or if any of the classes
2076 * or interfaces named as direct superinterfaces of {@code C} are not in fact interfaces
2077 * @throws ClassCircularityError if any of the superclasses or superinterfaces of
2078 * {@code C} is {@code C} itself
2079 * @throws VerifyError if the newly created class cannot be verified
2080 * @throws LinkageError if the newly created class cannot be linked for any other reason
2081 * @throws NullPointerException if any parameter is {@code null}
2082 *
2083 * @since 16
2084 * @see Lookup#defineHiddenClass(byte[], boolean, ClassOption...)
2085 * @see Class#isHidden()
2086 * @see MethodHandles#classData(Lookup, String, Class)
2087 * @see MethodHandles#classDataAt(Lookup, String, Class, int)
2088 * @jvms 4.2.1 Binary Class and Interface Names
2089 * @jvms 4.2.2 Unqualified Names
2090 * @jvms 4.7.28 The {@code NestHost} Attribute
2091 * @jvms 4.7.29 The {@code NestMembers} Attribute
2092 * @jvms 5.4.3.1 Class and Interface Resolution
2093 * @jvms 5.4.4 Access Control
2094 * @jvms 5.3.5 Deriving a {@code Class} from a {@code class} File Representation
2095 * @jvms 5.4 Linking
2096 * @jvms 5.5 Initialization
2097 * @jls 12.7 Unloading of Classes and Interfaces
2098 */
2099 public Lookup defineHiddenClassWithClassData(byte[] bytes, Object classData, boolean initialize, ClassOption... options)
2100 throws IllegalAccessException
2101 {
2102 Objects.requireNonNull(bytes);
2103 Objects.requireNonNull(classData);
2104
2105 int flags = ClassOption.optionsToFlag(options);
2106
2107 if (!hasFullPrivilegeAccess()) {
2108 throw new IllegalAccessException(this + " does not have full privilege access");
2109 }
2110
2111 return makeHiddenClassDefiner(bytes.clone(), false, flags)
2112 .defineClassAsLookup(initialize, classData);
2113 }
2114
2115 // A default dumper for writing class files passed to Lookup::defineClass
2116 // and Lookup::defineHiddenClass to disk for debugging purposes. To enable,
2117 // set -Djdk.invoke.MethodHandle.dumpHiddenClassFiles or
2118 // -Djdk.invoke.MethodHandle.dumpHiddenClassFiles=true
2119 //
2120 // This default dumper does not dump hidden classes defined by LambdaMetafactory
2121 // and LambdaForms and method handle internals. They are dumped via
2122 // different ClassFileDumpers.
2123 private static ClassFileDumper defaultDumper() {
2124 return DEFAULT_DUMPER;
2125 }
2126
2127 private static final ClassFileDumper DEFAULT_DUMPER = ClassFileDumper.getInstance(
2128 "jdk.invoke.MethodHandle.dumpClassFiles", "DUMP_CLASS_FILES");
2129
2130 /**
2131 * This method checks the class file version and the structure of `this_class`.
2132 * and checks if the bytes is a class or interface (ACC_MODULE flag not set)
2133 * that is in the named package.
2134 *
2135 * @throws IllegalArgumentException if ACC_MODULE flag is set in access flags
2136 * or the class is not in the given package name.
2137 */
2138 static String validateAndFindInternalName(byte[] bytes, String pkgName) {
2139 int magic = readInt(bytes, 0);
2140 if (magic != ClassFile.MAGIC_NUMBER) {
2141 throw new ClassFormatError("Incompatible magic value: " + magic);
2142 }
2143 // We have to read major and minor this way as ClassFile API throws IAE
2144 // yet we want distinct ClassFormatError and UnsupportedClassVersionError
2145 int minor = readUnsignedShort(bytes, 4);
2146 int major = readUnsignedShort(bytes, 6);
2147
2148 if (!VM.isSupportedClassFileVersion(major, minor)) {
2149 throw new UnsupportedClassVersionError("Unsupported class file version " + major + "." + minor);
2150 }
2151
2152 String name;
2153 ClassDesc sym;
2154 int accessFlags;
2155 try {
2156 ClassModel cm = ClassFile.of().parse(bytes);
2157 var thisClass = cm.thisClass();
2158 name = thisClass.asInternalName();
2159 sym = thisClass.asSymbol();
2160 accessFlags = cm.flags().flagsMask();
2161 } catch (IllegalArgumentException e) {
2162 ClassFormatError cfe = new ClassFormatError();
2163 cfe.initCause(e);
2164 throw cfe;
2165 }
2166 // must be a class or interface
2167 if ((accessFlags & ACC_MODULE) != 0) {
2168 throw newIllegalArgumentException("Not a class or interface: ACC_MODULE flag is set");
2169 }
2170
2171 String pn = sym.packageName();
2172 if (!pn.equals(pkgName)) {
2173 throw newIllegalArgumentException(name + " not in same package as lookup class");
2174 }
2175
2176 return name;
2177 }
2178
2179 private static int readInt(byte[] bytes, int offset) {
2180 if ((offset + 4) > bytes.length) {
2181 throw new ClassFormatError("Invalid ClassFile structure");
2182 }
2183 return ((bytes[offset] & 0xFF) << 24)
2184 | ((bytes[offset + 1] & 0xFF) << 16)
2185 | ((bytes[offset + 2] & 0xFF) << 8)
2186 | (bytes[offset + 3] & 0xFF);
2187 }
2188
2189 private static int readUnsignedShort(byte[] bytes, int offset) {
2190 if ((offset+2) > bytes.length) {
2191 throw new ClassFormatError("Invalid ClassFile structure");
2192 }
2193 return ((bytes[offset] & 0xFF) << 8) | (bytes[offset + 1] & 0xFF);
2194 }
2195
2196 /*
2197 * Returns a ClassDefiner that creates a {@code Class} object of a normal class
2198 * from the given bytes.
2199 *
2200 * Caller should make a defensive copy of the arguments if needed
2201 * before calling this factory method.
2202 *
2203 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or
2204 * {@code bytes} denotes a class in a different package than the lookup class
2205 */
2206 private ClassDefiner makeClassDefiner(byte[] bytes) {
2207 var internalName = validateAndFindInternalName(bytes, lookupClass().getPackageName());
2208 return new ClassDefiner(this, internalName, bytes, STRONG_LOADER_LINK, defaultDumper());
2209 }
2210
2211 /**
2212 * Returns a ClassDefiner that creates a {@code Class} object of a normal class
2213 * from the given bytes. No package name check on the given bytes.
2214 *
2215 * @param internalName internal name
2216 * @param bytes class bytes
2217 * @param dumper dumper to write the given bytes to the dumper's output directory
2218 * @return ClassDefiner that defines a normal class of the given bytes.
2219 */
2220 ClassDefiner makeClassDefiner(String internalName, byte[] bytes, ClassFileDumper dumper) {
2221 // skip package name validation
2222 return new ClassDefiner(this, internalName, bytes, STRONG_LOADER_LINK, dumper);
2223 }
2224
2225 /**
2226 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2227 * from the given bytes. The name must be in the same package as the lookup class.
2228 *
2229 * Caller should make a defensive copy of the arguments if needed
2230 * before calling this factory method.
2231 *
2232 * @param bytes class bytes
2233 * @param dumper dumper to write the given bytes to the dumper's output directory
2234 * @return ClassDefiner that defines a hidden class of the given bytes.
2235 *
2236 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or
2237 * {@code bytes} denotes a class in a different package than the lookup class
2238 */
2239 ClassDefiner makeHiddenClassDefiner(byte[] bytes, ClassFileDumper dumper) {
2240 var internalName = validateAndFindInternalName(bytes, lookupClass().getPackageName());
2241 return makeHiddenClassDefiner(internalName, bytes, false, dumper, 0);
2242 }
2243
2244 /**
2245 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2246 * from the given bytes and options.
2247 * The name must be in the same package as the lookup class.
2248 *
2249 * Caller should make a defensive copy of the arguments if needed
2250 * before calling this factory method.
2251 *
2252 * @param bytes class bytes
2253 * @param flags class option flag mask
2254 * @param accessVmAnnotations true to give the hidden class access to VM annotations
2255 * @return ClassDefiner that defines a hidden class of the given bytes and options
2256 *
2257 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or
2258 * {@code bytes} denotes a class in a different package than the lookup class
2259 */
2260 private ClassDefiner makeHiddenClassDefiner(byte[] bytes,
2261 boolean accessVmAnnotations,
2262 int flags) {
2263 var internalName = validateAndFindInternalName(bytes, lookupClass().getPackageName());
2264 return makeHiddenClassDefiner(internalName, bytes, accessVmAnnotations, defaultDumper(), flags);
2265 }
2266
2267 /**
2268 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2269 * from the given bytes and the given options. No package name check on the given bytes.
2270 *
2271 * @param internalName internal name that specifies the prefix of the hidden class
2272 * @param bytes class bytes
2273 * @param dumper dumper to write the given bytes to the dumper's output directory
2274 * @return ClassDefiner that defines a hidden class of the given bytes and options.
2275 */
2276 ClassDefiner makeHiddenClassDefiner(String internalName, byte[] bytes, ClassFileDumper dumper) {
2277 Objects.requireNonNull(dumper);
2278 // skip name and access flags validation
2279 return makeHiddenClassDefiner(internalName, bytes, false, dumper, 0);
2280 }
2281
2282 /**
2283 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2284 * from the given bytes and the given options. No package name check on the given bytes.
2285 *
2286 * @param internalName internal name that specifies the prefix of the hidden class
2287 * @param bytes class bytes
2288 * @param flags class options flag mask
2289 * @param dumper dumper to write the given bytes to the dumper's output directory
2290 * @return ClassDefiner that defines a hidden class of the given bytes and options.
2291 */
2292 ClassDefiner makeHiddenClassDefiner(String internalName, byte[] bytes, ClassFileDumper dumper, int flags) {
2293 Objects.requireNonNull(dumper);
2294 // skip name and access flags validation
2295 return makeHiddenClassDefiner(internalName, bytes, false, dumper, flags);
2296 }
2297
2298 /**
2299 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2300 * from the given class file and options.
2301 *
2302 * @param internalName internal name
2303 * @param bytes Class byte array
2304 * @param flags class option flag mask
2305 * @param accessVmAnnotations true to give the hidden class access to VM annotations
2306 * @param dumper dumper to write the given bytes to the dumper's output directory
2307 */
2308 private ClassDefiner makeHiddenClassDefiner(String internalName,
2309 byte[] bytes,
2310 boolean accessVmAnnotations,
2311 ClassFileDumper dumper,
2312 int flags) {
2313 flags |= HIDDEN_CLASS;
2314 if (accessVmAnnotations | VM.isSystemDomainLoader(lookupClass.getClassLoader())) {
2315 // jdk.internal.vm.annotations are permitted for classes
2316 // defined to boot loader and platform loader
2317 flags |= ACCESS_VM_ANNOTATIONS;
2318 }
2319
2320 return new ClassDefiner(this, internalName, bytes, flags, dumper);
2321 }
2322
2323 record ClassDefiner(Lookup lookup, String internalName, byte[] bytes, int classFlags, ClassFileDumper dumper) {
2324 ClassDefiner {
2325 assert ((classFlags & HIDDEN_CLASS) != 0 || (classFlags & STRONG_LOADER_LINK) == STRONG_LOADER_LINK);
2326 }
2327
2328 Class<?> defineClass(boolean initialize) {
2329 return defineClass(initialize, null);
2330 }
2331
2332 Lookup defineClassAsLookup(boolean initialize) {
2333 Class<?> c = defineClass(initialize, null);
2334 return new Lookup(c, null, FULL_POWER_MODES);
2335 }
2336
2337 /**
2338 * Defines the class of the given bytes and the given classData.
2339 * If {@code initialize} parameter is true, then the class will be initialized.
2340 *
2341 * @param initialize true if the class to be initialized
2342 * @param classData classData or null
2343 * @return the class
2344 *
2345 * @throws LinkageError linkage error
2346 */
2347 Class<?> defineClass(boolean initialize, Object classData) {
2348 Class<?> lookupClass = lookup.lookupClass();
2349 ClassLoader loader = lookupClass.getClassLoader();
2350 ProtectionDomain pd = (loader != null) ? lookup.lookupClassProtectionDomain() : null;
2351 Class<?> c = null;
2352 try {
2353 c = SharedSecrets.getJavaLangAccess()
2354 .defineClass(loader, lookupClass, internalName, bytes, pd, initialize, classFlags, classData);
2355 assert !isNestmate() || c.getNestHost() == lookupClass.getNestHost();
2356 return c;
2357 } finally {
2358 // dump the classfile for debugging
2359 if (dumper.isEnabled()) {
2360 String name = internalName();
2361 if (c != null) {
2362 dumper.dumpClass(name, c, bytes);
2363 } else {
2364 dumper.dumpFailedClass(name, bytes);
2365 }
2366 }
2367 }
2368 }
2369
2370 /**
2371 * Defines the class of the given bytes and the given classData.
2372 * If {@code initialize} parameter is true, then the class will be initialized.
2373 *
2374 * @param initialize true if the class to be initialized
2375 * @param classData classData or null
2376 * @return a Lookup for the defined class
2377 *
2378 * @throws LinkageError linkage error
2379 */
2380 Lookup defineClassAsLookup(boolean initialize, Object classData) {
2381 Class<?> c = defineClass(initialize, classData);
2382 return new Lookup(c, null, FULL_POWER_MODES);
2383 }
2384
2385 private boolean isNestmate() {
2386 return (classFlags & NESTMATE_CLASS) != 0;
2387 }
2388 }
2389
2390 private ProtectionDomain lookupClassProtectionDomain() {
2391 ProtectionDomain pd = cachedProtectionDomain;
2392 if (pd == null) {
2393 cachedProtectionDomain = pd = SharedSecrets.getJavaLangAccess().protectionDomain(lookupClass);
2394 }
2395 return pd;
2396 }
2397
2398 // cached protection domain
2399 private volatile ProtectionDomain cachedProtectionDomain;
2400
2401 // Make sure outer class is initialized first.
2402 static { IMPL_NAMES.getClass(); }
2403
2404 /** Package-private version of lookup which is trusted. */
2405 static final Lookup IMPL_LOOKUP = new Lookup(Object.class, null, TRUSTED);
2406
2407 /** Version of lookup which is trusted minimally.
2408 * It can only be used to create method handles to publicly accessible
2409 * members in packages that are exported unconditionally.
2410 */
2411 static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, null, UNCONDITIONAL);
2412
2413 private static void checkUnprivilegedlookupClass(Class<?> lookupClass) {
2414 String name = lookupClass.getName();
2415 if (name.startsWith("java.lang.invoke."))
2416 throw newIllegalArgumentException("illegal lookupClass: "+lookupClass);
2417 }
2418
2419 /**
2420 * Displays the name of the class from which lookups are to be made,
2421 * followed by "/" and the name of the {@linkplain #previousLookupClass()
2422 * previous lookup class} if present.
2423 * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)
2424 * If there are restrictions on the access permitted to this lookup,
2425 * this is indicated by adding a suffix to the class name, consisting
2426 * of a slash and a keyword. The keyword represents the strongest
2427 * allowed access, and is chosen as follows:
2428 * <ul>
2429 * <li>If no access is allowed, the suffix is "/noaccess".
2430 * <li>If only unconditional access is allowed, the suffix is "/publicLookup".
2431 * <li>If only public access to types in exported packages is allowed, the suffix is "/public".
2432 * <li>If only public and module access are allowed, the suffix is "/module".
2433 * <li>If public and package access are allowed, the suffix is "/package".
2434 * <li>If public, package, and private access are allowed, the suffix is "/private".
2435 * </ul>
2436 * If none of the above cases apply, it is the case that
2437 * {@linkplain #hasFullPrivilegeAccess() full privilege access}
2438 * (public, module, package, private, and protected) is allowed.
2439 * In this case, no suffix is added.
2440 * This is true only of an object obtained originally from
2441 * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
2442 * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
2443 * always have restricted access, and will display a suffix.
2444 * <p>
2445 * (It may seem strange that protected access should be
2446 * stronger than private access. Viewed independently from
2447 * package access, protected access is the first to be lost,
2448 * because it requires a direct subclass relationship between
2449 * caller and callee.)
2450 * @see #in
2451 */
2452 @Override
2453 public String toString() {
2454 String cname = lookupClass.getName();
2455 if (prevLookupClass != null)
2456 cname += "/" + prevLookupClass.getName();
2457 switch (allowedModes) {
2458 case 0: // no privileges
2459 return cname + "/noaccess";
2460 case UNCONDITIONAL:
2461 return cname + "/publicLookup";
2462 case PUBLIC:
2463 return cname + "/public";
2464 case PUBLIC|MODULE:
2465 return cname + "/module";
2466 case PUBLIC|PACKAGE:
2467 case PUBLIC|MODULE|PACKAGE:
2468 return cname + "/package";
2469 case PUBLIC|PACKAGE|PRIVATE:
2470 case PUBLIC|MODULE|PACKAGE|PRIVATE:
2471 return cname + "/private";
2472 case PUBLIC|PACKAGE|PRIVATE|PROTECTED:
2473 case PUBLIC|MODULE|PACKAGE|PRIVATE|PROTECTED:
2474 case FULL_POWER_MODES:
2475 return cname;
2476 case TRUSTED:
2477 return "/trusted"; // internal only; not exported
2478 default: // Should not happen, but it's a bitfield...
2479 cname = cname + "/" + Integer.toHexString(allowedModes);
2480 assert(false) : cname;
2481 return cname;
2482 }
2483 }
2484
2485 /**
2486 * Produces a method handle for a static method.
2487 * The type of the method handle will be that of the method.
2488 * (Since static methods do not take receivers, there is no
2489 * additional receiver argument inserted into the method handle type,
2490 * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)
2491 * The method and all its argument types must be accessible to the lookup object.
2492 * <p>
2493 * The returned method handle will have
2494 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2495 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2496 * <p>
2497 * If the returned method handle is invoked, the method's class will
2498 * be initialized, if it has not already been initialized.
2499 * <p><b>Example:</b>
2500 * {@snippet lang="java" :
2501 import static java.lang.invoke.MethodHandles.*;
2502 import static java.lang.invoke.MethodType.*;
2503 ...
2504 MethodHandle MH_asList = publicLookup().findStatic(Arrays.class,
2505 "asList", methodType(List.class, Object[].class));
2506 assertEquals("[x, y]", MH_asList.invoke("x", "y").toString());
2507 * }
2508 * @param refc the class from which the method is accessed
2509 * @param name the name of the method
2510 * @param type the type of the method
2511 * @return the desired method handle
2512 * @throws NoSuchMethodException if the method does not exist
2513 * @throws IllegalAccessException if access checking fails,
2514 * or if the method is not {@code static},
2515 * or if the method's variable arity modifier bit
2516 * is set and {@code asVarargsCollector} fails
2517 * @throws NullPointerException if any argument is null
2518 */
2519 public MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2520 MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type);
2521 return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerLookup(method));
2522 }
2523
2524 /**
2525 * Produces a method handle for a virtual method.
2526 * The type of the method handle will be that of the method,
2527 * with the receiver type (usually {@code refc}) prepended.
2528 * The method and all its argument types must be accessible to the lookup object.
2529 * <p>
2530 * When called, the handle will treat the first argument as a receiver
2531 * and, for non-private methods, dispatch on the receiver's type to determine which method
2532 * implementation to enter.
2533 * For private methods the named method in {@code refc} will be invoked on the receiver.
2534 * (The dispatching action is identical with that performed by an
2535 * {@code invokevirtual} or {@code invokeinterface} instruction.)
2536 * <p>
2537 * The first argument will be of type {@code refc} if the lookup
2538 * class has full privileges to access the member. Otherwise
2539 * the member must be {@code protected} and the first argument
2540 * will be restricted in type to the lookup class.
2541 * <p>
2542 * The returned method handle will have
2543 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2544 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2545 * <p>
2546 * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual}
2547 * instructions and method handles produced by {@code findVirtual},
2548 * if the class is {@code MethodHandle} and the name string is
2549 * {@code invokeExact} or {@code invoke}, the resulting
2550 * method handle is equivalent to one produced by
2551 * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or
2552 * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}
2553 * with the same {@code type} argument.
2554 * <p>
2555 * If the class is {@code VarHandle} and the name string corresponds to
2556 * the name of a signature-polymorphic access mode method, the resulting
2557 * method handle is equivalent to one produced by
2558 * {@link java.lang.invoke.MethodHandles#varHandleInvoker} with
2559 * the access mode corresponding to the name string and with the same
2560 * {@code type} arguments.
2561 * <p>
2562 * <b>Example:</b>
2563 * {@snippet lang="java" :
2564 import static java.lang.invoke.MethodHandles.*;
2565 import static java.lang.invoke.MethodType.*;
2566 ...
2567 MethodHandle MH_concat = publicLookup().findVirtual(String.class,
2568 "concat", methodType(String.class, String.class));
2569 MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class,
2570 "hashCode", methodType(int.class));
2571 MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class,
2572 "hashCode", methodType(int.class));
2573 assertEquals("xy", (String) MH_concat.invokeExact("x", "y"));
2574 assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy"));
2575 assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy"));
2576 // interface method:
2577 MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class,
2578 "subSequence", methodType(CharSequence.class, int.class, int.class));
2579 assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString());
2580 // constructor "internal method" must be accessed differently:
2581 MethodType MT_newString = methodType(void.class); //()V for new String()
2582 try { assertEquals("impossible", lookup()
2583 .findVirtual(String.class, "<init>", MT_newString));
2584 } catch (NoSuchMethodException ex) { } // OK
2585 MethodHandle MH_newString = publicLookup()
2586 .findConstructor(String.class, MT_newString);
2587 assertEquals("", (String) MH_newString.invokeExact());
2588 * }
2589 *
2590 * @param refc the class or interface from which the method is accessed
2591 * @param name the name of the method
2592 * @param type the type of the method, with the receiver argument omitted
2593 * @return the desired method handle
2594 * @throws NoSuchMethodException if the method does not exist
2595 * @throws IllegalAccessException if access checking fails,
2596 * or if the method is {@code static},
2597 * or if the method's variable arity modifier bit
2598 * is set and {@code asVarargsCollector} fails
2599 * @throws NullPointerException if any argument is null
2600 */
2601 public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2602 if (refc == MethodHandle.class) {
2603 MethodHandle mh = findVirtualForMH(name, type);
2604 if (mh != null) return mh;
2605 } else if (refc == VarHandle.class) {
2606 MethodHandle mh = findVirtualForVH(name, type);
2607 if (mh != null) return mh;
2608 }
2609 byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual);
2610 MemberName method = resolveOrFail(refKind, refc, name, type);
2611 return getDirectMethod(refKind, refc, method, findBoundCallerLookup(method));
2612 }
2613 private MethodHandle findVirtualForMH(String name, MethodType type) {
2614 // these names require special lookups because of the implicit MethodType argument
2615 if ("invoke".equals(name))
2616 return invoker(type);
2617 if ("invokeExact".equals(name))
2618 return exactInvoker(type);
2619 assert(!MemberName.isMethodHandleInvokeName(name));
2620 return null;
2621 }
2622 private MethodHandle findVirtualForVH(String name, MethodType type) {
2623 try {
2624 return varHandleInvoker(VarHandle.AccessMode.valueFromMethodName(name), type);
2625 } catch (IllegalArgumentException e) {
2626 return null;
2627 }
2628 }
2629
2630 /**
2631 * Produces a method handle which creates an object and initializes it, using
2632 * the constructor of the specified type.
2633 * The parameter types of the method handle will be those of the constructor,
2634 * while the return type will be a reference to the constructor's class.
2635 * The constructor and all its argument types must be accessible to the lookup object.
2636 * <p>
2637 * The requested type must have a return type of {@code void}.
2638 * (This is consistent with the JVM's treatment of constructor type descriptors.)
2639 * <p>
2640 * The returned method handle will have
2641 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2642 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
2643 * <p>
2644 * If the returned method handle is invoked, the constructor's class will
2645 * be initialized, if it has not already been initialized.
2646 * <p><b>Example:</b>
2647 * {@snippet lang="java" :
2648 import static java.lang.invoke.MethodHandles.*;
2649 import static java.lang.invoke.MethodType.*;
2650 ...
2651 MethodHandle MH_newArrayList = publicLookup().findConstructor(
2652 ArrayList.class, methodType(void.class, Collection.class));
2653 Collection orig = Arrays.asList("x", "y");
2654 Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig);
2655 assert(orig != copy);
2656 assertEquals(orig, copy);
2657 // a variable-arity constructor:
2658 MethodHandle MH_newProcessBuilder = publicLookup().findConstructor(
2659 ProcessBuilder.class, methodType(void.class, String[].class));
2660 ProcessBuilder pb = (ProcessBuilder)
2661 MH_newProcessBuilder.invoke("x", "y", "z");
2662 assertEquals("[x, y, z]", pb.command().toString());
2663 * }
2664 *
2665 *
2666 * @param refc the class or interface from which the method is accessed
2667 * @param type the type of the method, with the receiver argument omitted, and a void return type
2668 * @return the desired method handle
2669 * @throws NoSuchMethodException if the constructor does not exist
2670 * @throws IllegalAccessException if access checking fails
2671 * or if the method's variable arity modifier bit
2672 * is set and {@code asVarargsCollector} fails
2673 * @throws NullPointerException if any argument is null
2674 */
2675 public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2676 if (refc.isArray()) {
2677 throw new NoSuchMethodException("no constructor for array class: " + refc.getName());
2678 }
2679 if (type.returnType() != void.class) {
2680 throw new NoSuchMethodException("Constructors must have void return type: " + refc.getName());
2681 }
2682 String name = ConstantDescs.INIT_NAME;
2683 MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type);
2684 return getDirectConstructor(refc, ctor);
2685 }
2686
2687 /**
2688 * Looks up a class by name from the lookup context defined by this {@code Lookup} object,
2689 * <a href="MethodHandles.Lookup.html#equiv">as if resolved</a> by an {@code ldc} instruction.
2690 * Such a resolution, as specified in JVMS {@jvms 5.4.3.1}, attempts to locate and load the class,
2691 * and then determines whether the class is accessible to this lookup object.
2692 * <p>
2693 * For a class or an interface, the name is the {@linkplain ClassLoader##binary-name binary name}.
2694 * For an array class of {@code n} dimensions, the name begins with {@code n} occurrences
2695 * of {@code '['} and followed by the element type as encoded in the
2696 * {@linkplain Class##nameFormat table} specified in {@link Class#getName}.
2697 * <p>
2698 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class},
2699 * its class loader, and the {@linkplain #lookupModes() lookup modes}.
2700 *
2701 * @param targetName the {@linkplain ClassLoader##binary-name binary name} of the class
2702 * or the string representing an array class
2703 * @return the requested class.
2704 * @throws LinkageError if the linkage fails
2705 * @throws ClassNotFoundException if the class cannot be loaded by the lookup class' loader.
2706 * @throws IllegalAccessException if the class is not accessible, using the allowed access
2707 * modes.
2708 * @throws NullPointerException if {@code targetName} is null
2709 * @since 9
2710 * @jvms 5.4.3.1 Class and Interface Resolution
2711 */
2712 public Class<?> findClass(String targetName) throws ClassNotFoundException, IllegalAccessException {
2713 Class<?> targetClass = Class.forName(targetName, false, lookupClass.getClassLoader());
2714 return accessClass(targetClass);
2715 }
2716
2717 /**
2718 * Ensures that {@code targetClass} has been initialized. The class
2719 * to be initialized must be {@linkplain #accessClass accessible}
2720 * to this {@code Lookup} object. This method causes {@code targetClass}
2721 * to be initialized if it has not been already initialized,
2722 * as specified in JVMS {@jvms 5.5}.
2723 *
2724 * <p>
2725 * This method returns when {@code targetClass} is fully initialized, or
2726 * when {@code targetClass} is being initialized by the current thread.
2727 *
2728 * @param <T> the type of the class to be initialized
2729 * @param targetClass the class to be initialized
2730 * @return {@code targetClass} that has been initialized, or that is being
2731 * initialized by the current thread.
2732 *
2733 * @throws IllegalArgumentException if {@code targetClass} is a primitive type or {@code void}
2734 * or array class
2735 * @throws IllegalAccessException if {@code targetClass} is not
2736 * {@linkplain #accessClass accessible} to this lookup
2737 * @throws ExceptionInInitializerError if the class initialization provoked
2738 * by this method fails
2739 * @since 15
2740 * @jvms 5.5 Initialization
2741 */
2742 public <T> Class<T> ensureInitialized(Class<T> targetClass) throws IllegalAccessException {
2743 if (targetClass.isPrimitive())
2744 throw new IllegalArgumentException(targetClass + " is a primitive class");
2745 if (targetClass.isArray())
2746 throw new IllegalArgumentException(targetClass + " is an array class");
2747
2748 if (!VerifyAccess.isClassAccessible(targetClass, lookupClass, prevLookupClass, allowedModes)) {
2749 throw makeAccessException(targetClass);
2750 }
2751
2752 // ensure class initialization
2753 Unsafe.getUnsafe().ensureClassInitialized(targetClass);
2754 return targetClass;
2755 }
2756
2757 /*
2758 * Returns IllegalAccessException due to access violation to the given targetClass.
2759 *
2760 * This method is called by {@link Lookup#accessClass} and {@link Lookup#ensureInitialized}
2761 * which verifies access to a class rather a member.
2762 */
2763 private IllegalAccessException makeAccessException(Class<?> targetClass) {
2764 String message = "access violation: "+ targetClass;
2765 if (this == MethodHandles.publicLookup()) {
2766 message += ", from public Lookup";
2767 } else {
2768 Module m = lookupClass().getModule();
2769 message += ", from " + lookupClass() + " (" + m + ")";
2770 if (prevLookupClass != null) {
2771 message += ", previous lookup " +
2772 prevLookupClass.getName() + " (" + prevLookupClass.getModule() + ")";
2773 }
2774 }
2775 return new IllegalAccessException(message);
2776 }
2777
2778 /**
2779 * Determines if a class can be accessed from the lookup context defined by
2780 * this {@code Lookup} object. The static initializer of the class is not run.
2781 * If {@code targetClass} is an array class, {@code targetClass} is accessible
2782 * if the element type of the array class is accessible. Otherwise,
2783 * {@code targetClass} is determined as accessible as follows.
2784 *
2785 * <p>
2786 * If {@code targetClass} is in the same module as the lookup class,
2787 * the lookup class is {@code LC} in module {@code M1} and
2788 * the previous lookup class is in module {@code M0} or
2789 * {@code null} if not present,
2790 * {@code targetClass} is accessible if and only if one of the following is true:
2791 * <ul>
2792 * <li>If this lookup has {@link #PRIVATE} access, {@code targetClass} is
2793 * {@code LC} or other class in the same nest of {@code LC}.</li>
2794 * <li>If this lookup has {@link #PACKAGE} access, {@code targetClass} is
2795 * in the same runtime package of {@code LC}.</li>
2796 * <li>If this lookup has {@link #MODULE} access, {@code targetClass} is
2797 * a public type in {@code M1}.</li>
2798 * <li>If this lookup has {@link #PUBLIC} access, {@code targetClass} is
2799 * a public type in a package exported by {@code M1} to at least {@code M0}
2800 * if the previous lookup class is present; otherwise, {@code targetClass}
2801 * is a public type in a package exported by {@code M1} unconditionally.</li>
2802 * </ul>
2803 *
2804 * <p>
2805 * Otherwise, if this lookup has {@link #UNCONDITIONAL} access, this lookup
2806 * can access public types in all modules when the type is in a package
2807 * that is exported unconditionally.
2808 * <p>
2809 * Otherwise, {@code targetClass} is in a different module from {@code lookupClass},
2810 * and if this lookup does not have {@code PUBLIC} access, {@code lookupClass}
2811 * is inaccessible.
2812 * <p>
2813 * Otherwise, if this lookup has no {@linkplain #previousLookupClass() previous lookup class},
2814 * {@code M1} is the module containing {@code lookupClass} and
2815 * {@code M2} is the module containing {@code targetClass},
2816 * then {@code targetClass} is accessible if and only if
2817 * <ul>
2818 * <li>{@code M1} reads {@code M2}, and
2819 * <li>{@code targetClass} is public and in a package exported by
2820 * {@code M2} at least to {@code M1}.
2821 * </ul>
2822 * <p>
2823 * Otherwise, if this lookup has a {@linkplain #previousLookupClass() previous lookup class},
2824 * {@code M1} and {@code M2} are as before, and {@code M0} is the module
2825 * containing the previous lookup class, then {@code targetClass} is accessible
2826 * if and only if one of the following is true:
2827 * <ul>
2828 * <li>{@code targetClass} is in {@code M0} and {@code M1}
2829 * {@linkplain Module#reads reads} {@code M0} and the type is
2830 * in a package that is exported to at least {@code M1}.
2831 * <li>{@code targetClass} is in {@code M1} and {@code M0}
2832 * {@linkplain Module#reads reads} {@code M1} and the type is
2833 * in a package that is exported to at least {@code M0}.
2834 * <li>{@code targetClass} is in a third module {@code M2} and both {@code M0}
2835 * and {@code M1} reads {@code M2} and the type is in a package
2836 * that is exported to at least both {@code M0} and {@code M2}.
2837 * </ul>
2838 * <p>
2839 * Otherwise, {@code targetClass} is not accessible.
2840 *
2841 * @param <T> the type of the class to be access-checked
2842 * @param targetClass the class to be access-checked
2843 * @return {@code targetClass} that has been access-checked
2844 * @throws IllegalAccessException if the class is not accessible from the lookup class
2845 * and previous lookup class, if present, using the allowed access modes.
2846 * @throws NullPointerException if {@code targetClass} is {@code null}
2847 * @since 9
2848 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
2849 */
2850 public <T> Class<T> accessClass(Class<T> targetClass) throws IllegalAccessException {
2851 if (!isClassAccessible(targetClass)) {
2852 throw makeAccessException(targetClass);
2853 }
2854 return targetClass;
2855 }
2856
2857 /**
2858 * Produces an early-bound method handle for a virtual method.
2859 * It will bypass checks for overriding methods on the receiver,
2860 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
2861 * instruction from within the explicitly specified {@code specialCaller}.
2862 * The type of the method handle will be that of the method,
2863 * with a suitably restricted receiver type prepended.
2864 * (The receiver type will be {@code specialCaller} or a subtype.)
2865 * The method and all its argument types must be accessible
2866 * to the lookup object.
2867 * <p>
2868 * Before method resolution,
2869 * if the explicitly specified caller class is not identical with the
2870 * lookup class, or if this lookup object does not have
2871 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
2872 * privileges, the access fails.
2873 * <p>
2874 * The returned method handle will have
2875 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2876 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2877 * <p style="font-size:smaller;">
2878 * <em>(Note: JVM internal methods named {@value ConstantDescs#INIT_NAME}
2879 * are not visible to this API,
2880 * even though the {@code invokespecial} instruction can refer to them
2881 * in special circumstances. Use {@link #findConstructor findConstructor}
2882 * to access instance initialization methods in a safe manner.)</em>
2883 * <p><b>Example:</b>
2884 * {@snippet lang="java" :
2885 import static java.lang.invoke.MethodHandles.*;
2886 import static java.lang.invoke.MethodType.*;
2887 ...
2888 static class Listie extends ArrayList {
2889 public String toString() { return "[wee Listie]"; }
2890 static Lookup lookup() { return MethodHandles.lookup(); }
2891 }
2892 ...
2893 // no access to constructor via invokeSpecial:
2894 MethodHandle MH_newListie = Listie.lookup()
2895 .findConstructor(Listie.class, methodType(void.class));
2896 Listie l = (Listie) MH_newListie.invokeExact();
2897 try { assertEquals("impossible", Listie.lookup().findSpecial(
2898 Listie.class, "<init>", methodType(void.class), Listie.class));
2899 } catch (NoSuchMethodException ex) { } // OK
2900 // access to super and self methods via invokeSpecial:
2901 MethodHandle MH_super = Listie.lookup().findSpecial(
2902 ArrayList.class, "toString" , methodType(String.class), Listie.class);
2903 MethodHandle MH_this = Listie.lookup().findSpecial(
2904 Listie.class, "toString" , methodType(String.class), Listie.class);
2905 MethodHandle MH_duper = Listie.lookup().findSpecial(
2906 Object.class, "toString" , methodType(String.class), Listie.class);
2907 assertEquals("[]", (String) MH_super.invokeExact(l));
2908 assertEquals(""+l, (String) MH_this.invokeExact(l));
2909 assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method
2910 try { assertEquals("inaccessible", Listie.lookup().findSpecial(
2911 String.class, "toString", methodType(String.class), Listie.class));
2912 } catch (IllegalAccessException ex) { } // OK
2913 Listie subl = new Listie() { public String toString() { return "[subclass]"; } };
2914 assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method
2915 * }
2916 *
2917 * @param refc the class or interface from which the method is accessed
2918 * @param name the name of the method (which must not be "<init>")
2919 * @param type the type of the method, with the receiver argument omitted
2920 * @param specialCaller the proposed calling class to perform the {@code invokespecial}
2921 * @return the desired method handle
2922 * @throws NoSuchMethodException if the method does not exist
2923 * @throws IllegalAccessException if access checking fails,
2924 * or if the method is {@code static},
2925 * or if the method's variable arity modifier bit
2926 * is set and {@code asVarargsCollector} fails
2927 * @throws NullPointerException if any argument is null
2928 */
2929 public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,
2930 Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
2931 checkSpecialCaller(specialCaller, refc);
2932 Lookup specialLookup = this.in(specialCaller);
2933 MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type);
2934 return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerLookup(method));
2935 }
2936
2937 /**
2938 * Produces a method handle giving read access to a non-static field.
2939 * The type of the method handle will have a return type of the field's
2940 * value type.
2941 * The method handle's single argument will be the instance containing
2942 * the field.
2943 * Access checking is performed immediately on behalf of the lookup class.
2944 * @param refc the class or interface from which the method is accessed
2945 * @param name the field's name
2946 * @param type the field's type
2947 * @return a method handle which can load values from the field
2948 * @throws NoSuchFieldException if the field does not exist
2949 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
2950 * @throws NullPointerException if any argument is null
2951 * @see #findVarHandle(Class, String, Class)
2952 */
2953 public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2954 MemberName field = resolveOrFail(REF_getField, refc, name, type);
2955 return getDirectField(REF_getField, refc, field);
2956 }
2957
2958 /**
2959 * Produces a method handle giving write access to a non-static field.
2960 * The type of the method handle will have a void return type.
2961 * The method handle will take two arguments, the instance containing
2962 * the field, and the value to be stored.
2963 * The second argument will be of the field's value type.
2964 * Access checking is performed immediately on behalf of the lookup class.
2965 * @param refc the class or interface from which the method is accessed
2966 * @param name the field's name
2967 * @param type the field's type
2968 * @return a method handle which can store values into the field
2969 * @throws NoSuchFieldException if the field does not exist
2970 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
2971 * or {@code final}
2972 * @throws NullPointerException if any argument is null
2973 * @see #findVarHandle(Class, String, Class)
2974 */
2975 public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2976 MemberName field = resolveOrFail(REF_putField, refc, name, type);
2977 return getDirectField(REF_putField, refc, field);
2978 }
2979
2980 /**
2981 * Produces a VarHandle giving access to a non-static field {@code name}
2982 * of type {@code type} declared in a class of type {@code recv}.
2983 * The VarHandle's variable type is {@code type} and it has one
2984 * coordinate type, {@code recv}.
2985 * <p>
2986 * Access checking is performed immediately on behalf of the lookup
2987 * class.
2988 * <p>
2989 * Certain access modes of the returned VarHandle are unsupported under
2990 * the following conditions:
2991 * <ul>
2992 * <li>if the field is declared {@code final}, then the write, atomic
2993 * update, numeric atomic update, and bitwise atomic update access
2994 * modes are unsupported.
2995 * <li>if the field type is anything other than {@code byte},
2996 * {@code short}, {@code char}, {@code int}, {@code long},
2997 * {@code float}, or {@code double} then numeric atomic update
2998 * access modes are unsupported.
2999 * <li>if the field type is anything other than {@code boolean},
3000 * {@code byte}, {@code short}, {@code char}, {@code int} or
3001 * {@code long} then bitwise atomic update access modes are
3002 * unsupported.
3003 * </ul>
3004 * <p>
3005 * If the field is declared {@code volatile} then the returned VarHandle
3006 * will override access to the field (effectively ignore the
3007 * {@code volatile} declaration) in accordance to its specified
3008 * access modes.
3009 * <p>
3010 * If the field type is {@code float} or {@code double} then numeric
3011 * and atomic update access modes compare values using their bitwise
3012 * representation (see {@link Float#floatToRawIntBits} and
3013 * {@link Double#doubleToRawLongBits}, respectively).
3014 * @apiNote
3015 * Bitwise comparison of {@code float} values or {@code double} values,
3016 * as performed by the numeric and atomic update access modes, differ
3017 * from the primitive {@code ==} operator and the {@link Float#equals}
3018 * and {@link Double#equals} methods, specifically with respect to
3019 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
3020 * Care should be taken when performing a compare and set or a compare
3021 * and exchange operation with such values since the operation may
3022 * unexpectedly fail.
3023 * There are many possible NaN values that are considered to be
3024 * {@code NaN} in Java, although no IEEE 754 floating-point operation
3025 * provided by Java can distinguish between them. Operation failure can
3026 * occur if the expected or witness value is a NaN value and it is
3027 * transformed (perhaps in a platform specific manner) into another NaN
3028 * value, and thus has a different bitwise representation (see
3029 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
3030 * details).
3031 * The values {@code -0.0} and {@code +0.0} have different bitwise
3032 * representations but are considered equal when using the primitive
3033 * {@code ==} operator. Operation failure can occur if, for example, a
3034 * numeric algorithm computes an expected value to be say {@code -0.0}
3035 * and previously computed the witness value to be say {@code +0.0}.
3036 * @param recv the receiver class, of type {@code R}, that declares the
3037 * non-static field
3038 * @param name the field's name
3039 * @param type the field's type, of type {@code T}
3040 * @return a VarHandle giving access to non-static fields.
3041 * @throws NoSuchFieldException if the field does not exist
3042 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
3043 * @throws NullPointerException if any argument is null
3044 * @since 9
3045 */
3046 public VarHandle findVarHandle(Class<?> recv, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3047 MemberName getField = resolveOrFail(REF_getField, recv, name, type);
3048 MemberName putField = resolveOrFail(REF_putField, recv, name, type);
3049 return getFieldVarHandle(REF_getField, REF_putField, recv, getField, putField);
3050 }
3051
3052 /**
3053 * Produces a method handle giving read access to a static field.
3054 * The type of the method handle will have a return type of the field's
3055 * value type.
3056 * The method handle will take no arguments.
3057 * Access checking is performed immediately on behalf of the lookup class.
3058 * <p>
3059 * If the returned method handle is invoked, the field's class will
3060 * be initialized, if it has not already been initialized.
3061 * @param refc the class or interface from which the method is accessed
3062 * @param name the field's name
3063 * @param type the field's type
3064 * @return a method handle which can load values from the field
3065 * @throws NoSuchFieldException if the field does not exist
3066 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
3067 * @throws NullPointerException if any argument is null
3068 */
3069 public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3070 MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
3071 return getDirectField(REF_getStatic, refc, field);
3072 }
3073
3074 /**
3075 * Produces a method handle giving write access to a static field.
3076 * The type of the method handle will have a void return type.
3077 * The method handle will take a single
3078 * argument, of the field's value type, the value to be stored.
3079 * Access checking is performed immediately on behalf of the lookup class.
3080 * <p>
3081 * If the returned method handle is invoked, the field's class will
3082 * be initialized, if it has not already been initialized.
3083 * @param refc the class or interface from which the method is accessed
3084 * @param name the field's name
3085 * @param type the field's type
3086 * @return a method handle which can store values into the field
3087 * @throws NoSuchFieldException if the field does not exist
3088 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
3089 * or is {@code final}
3090 * @throws NullPointerException if any argument is null
3091 */
3092 public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3093 MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
3094 return getDirectField(REF_putStatic, refc, field);
3095 }
3096
3097 /**
3098 * Produces a VarHandle giving access to a static field {@code name} of
3099 * type {@code type} declared in a class of type {@code decl}.
3100 * The VarHandle's variable type is {@code type} and it has no
3101 * coordinate types.
3102 * <p>
3103 * Access checking is performed immediately on behalf of the lookup
3104 * class.
3105 * <p>
3106 * If the returned VarHandle is operated on, the declaring class will be
3107 * initialized, if it has not already been initialized.
3108 * <p>
3109 * Certain access modes of the returned VarHandle are unsupported under
3110 * the following conditions:
3111 * <ul>
3112 * <li>if the field is declared {@code final}, then the write, atomic
3113 * update, numeric atomic update, and bitwise atomic update access
3114 * modes are unsupported.
3115 * <li>if the field type is anything other than {@code byte},
3116 * {@code short}, {@code char}, {@code int}, {@code long},
3117 * {@code float}, or {@code double}, then numeric atomic update
3118 * access modes are unsupported.
3119 * <li>if the field type is anything other than {@code boolean},
3120 * {@code byte}, {@code short}, {@code char}, {@code int} or
3121 * {@code long} then bitwise atomic update access modes are
3122 * unsupported.
3123 * </ul>
3124 * <p>
3125 * If the field is declared {@code volatile} then the returned VarHandle
3126 * will override access to the field (effectively ignore the
3127 * {@code volatile} declaration) in accordance to its specified
3128 * access modes.
3129 * <p>
3130 * If the field type is {@code float} or {@code double} then numeric
3131 * and atomic update access modes compare values using their bitwise
3132 * representation (see {@link Float#floatToRawIntBits} and
3133 * {@link Double#doubleToRawLongBits}, respectively).
3134 * @apiNote
3135 * Bitwise comparison of {@code float} values or {@code double} values,
3136 * as performed by the numeric and atomic update access modes, differ
3137 * from the primitive {@code ==} operator and the {@link Float#equals}
3138 * and {@link Double#equals} methods, specifically with respect to
3139 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
3140 * Care should be taken when performing a compare and set or a compare
3141 * and exchange operation with such values since the operation may
3142 * unexpectedly fail.
3143 * There are many possible NaN values that are considered to be
3144 * {@code NaN} in Java, although no IEEE 754 floating-point operation
3145 * provided by Java can distinguish between them. Operation failure can
3146 * occur if the expected or witness value is a NaN value and it is
3147 * transformed (perhaps in a platform specific manner) into another NaN
3148 * value, and thus has a different bitwise representation (see
3149 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
3150 * details).
3151 * The values {@code -0.0} and {@code +0.0} have different bitwise
3152 * representations but are considered equal when using the primitive
3153 * {@code ==} operator. Operation failure can occur if, for example, a
3154 * numeric algorithm computes an expected value to be say {@code -0.0}
3155 * and previously computed the witness value to be say {@code +0.0}.
3156 * @param decl the class that declares the static field
3157 * @param name the field's name
3158 * @param type the field's type, of type {@code T}
3159 * @return a VarHandle giving access to a static field
3160 * @throws NoSuchFieldException if the field does not exist
3161 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
3162 * @throws NullPointerException if any argument is null
3163 * @since 9
3164 */
3165 public VarHandle findStaticVarHandle(Class<?> decl, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3166 MemberName getField = resolveOrFail(REF_getStatic, decl, name, type);
3167 MemberName putField = resolveOrFail(REF_putStatic, decl, name, type);
3168 return getFieldVarHandle(REF_getStatic, REF_putStatic, decl, getField, putField);
3169 }
3170
3171 /**
3172 * Produces an early-bound method handle for a non-static method.
3173 * The receiver must have a supertype {@code defc} in which a method
3174 * of the given name and type is accessible to the lookup class.
3175 * The method and all its argument types must be accessible to the lookup object.
3176 * The type of the method handle will be that of the method,
3177 * without any insertion of an additional receiver parameter.
3178 * The given receiver will be bound into the method handle,
3179 * so that every call to the method handle will invoke the
3180 * requested method on the given receiver.
3181 * <p>
3182 * The returned method handle will have
3183 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3184 * the method's variable arity modifier bit ({@code 0x0080}) is set
3185 * <em>and</em> the trailing array argument is not the only argument.
3186 * (If the trailing array argument is the only argument,
3187 * the given receiver value will be bound to it.)
3188 * <p>
3189 * This is almost equivalent to the following code, with some differences noted below:
3190 * {@snippet lang="java" :
3191 import static java.lang.invoke.MethodHandles.*;
3192 import static java.lang.invoke.MethodType.*;
3193 ...
3194 MethodHandle mh0 = lookup().findVirtual(defc, name, type);
3195 MethodHandle mh1 = mh0.bindTo(receiver);
3196 mh1 = mh1.withVarargs(mh0.isVarargsCollector());
3197 return mh1;
3198 * }
3199 * where {@code defc} is either {@code receiver.getClass()} or a super
3200 * type of that class, in which the requested method is accessible
3201 * to the lookup class.
3202 * (Unlike {@code bind}, {@code bindTo} does not preserve variable arity.
3203 * Also, {@code bindTo} may throw a {@code ClassCastException} in instances where {@code bind} would
3204 * throw an {@code IllegalAccessException}, as in the case where the member is {@code protected} and
3205 * the receiver is restricted by {@code findVirtual} to the lookup class.)
3206 * @param receiver the object from which the method is accessed
3207 * @param name the name of the method
3208 * @param type the type of the method, with the receiver argument omitted
3209 * @return the desired method handle
3210 * @throws NoSuchMethodException if the method does not exist
3211 * @throws IllegalAccessException if access checking fails
3212 * or if the method's variable arity modifier bit
3213 * is set and {@code asVarargsCollector} fails
3214 * @throws NullPointerException if any argument is null
3215 * @see MethodHandle#bindTo
3216 * @see #findVirtual
3217 */
3218 public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
3219 Class<? extends Object> refc = receiver.getClass(); // may get NPE
3220 MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
3221 MethodHandle mh = getDirectMethodNoRestrictInvokeSpecial(refc, method, findBoundCallerLookup(method));
3222 if (!mh.type().leadingReferenceParameter().isAssignableFrom(receiver.getClass())) {
3223 throw new IllegalAccessException("The restricted defining class " +
3224 mh.type().leadingReferenceParameter().getName() +
3225 " is not assignable from receiver class " +
3226 receiver.getClass().getName());
3227 }
3228 return mh.bindArgumentL(0, receiver).setVarargs(method);
3229 }
3230
3231 /**
3232 * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
3233 * to <i>m</i>, if the lookup class has permission.
3234 * If <i>m</i> is non-static, the receiver argument is treated as an initial argument.
3235 * If <i>m</i> is virtual, overriding is respected on every call.
3236 * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped.
3237 * The type of the method handle will be that of the method,
3238 * with the receiver type prepended (but only if it is non-static).
3239 * If the method's {@code accessible} flag is not set,
3240 * access checking is performed immediately on behalf of the lookup class.
3241 * If <i>m</i> is not public, do not share the resulting handle with untrusted parties.
3242 * <p>
3243 * The returned method handle will have
3244 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3245 * the method's variable arity modifier bit ({@code 0x0080}) is set.
3246 * <p>
3247 * If <i>m</i> is static, and
3248 * if the returned method handle is invoked, the method's class will
3249 * be initialized, if it has not already been initialized.
3250 * @param m the reflected method
3251 * @return a method handle which can invoke the reflected method
3252 * @throws IllegalAccessException if access checking fails
3253 * or if the method's variable arity modifier bit
3254 * is set and {@code asVarargsCollector} fails
3255 * @throws NullPointerException if the argument is null
3256 */
3257 public MethodHandle unreflect(Method m) throws IllegalAccessException {
3258 if (m.getDeclaringClass() == MethodHandle.class) {
3259 MethodHandle mh = unreflectForMH(m);
3260 if (mh != null) return mh;
3261 }
3262 if (m.getDeclaringClass() == VarHandle.class) {
3263 MethodHandle mh = unreflectForVH(m);
3264 if (mh != null) return mh;
3265 }
3266 MemberName method = new MemberName(m);
3267 byte refKind = method.getReferenceKind();
3268 if (refKind == REF_invokeSpecial)
3269 refKind = REF_invokeVirtual;
3270 assert(method.isMethod());
3271 @SuppressWarnings("deprecation")
3272 Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
3273 return lookup.getDirectMethod(refKind, method.getDeclaringClass(), method, findBoundCallerLookup(method));
3274 }
3275 private MethodHandle unreflectForMH(Method m) {
3276 // these names require special lookups because they throw UnsupportedOperationException
3277 if (MemberName.isMethodHandleInvokeName(m.getName()))
3278 return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m));
3279 return null;
3280 }
3281 private MethodHandle unreflectForVH(Method m) {
3282 // these names require special lookups because they throw UnsupportedOperationException
3283 if (MemberName.isVarHandleMethodInvokeName(m.getName()))
3284 return MethodHandleImpl.fakeVarHandleInvoke(new MemberName(m));
3285 return null;
3286 }
3287
3288 /**
3289 * Produces a method handle for a reflected method.
3290 * It will bypass checks for overriding methods on the receiver,
3291 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
3292 * instruction from within the explicitly specified {@code specialCaller}.
3293 * The type of the method handle will be that of the method,
3294 * with a suitably restricted receiver type prepended.
3295 * (The receiver type will be {@code specialCaller} or a subtype.)
3296 * If the method's {@code accessible} flag is not set,
3297 * access checking is performed immediately on behalf of the lookup class,
3298 * as if {@code invokespecial} instruction were being linked.
3299 * <p>
3300 * Before method resolution,
3301 * if the explicitly specified caller class is not identical with the
3302 * lookup class, or if this lookup object does not have
3303 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
3304 * privileges, the access fails.
3305 * <p>
3306 * The returned method handle will have
3307 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3308 * the method's variable arity modifier bit ({@code 0x0080}) is set.
3309 * @param m the reflected method
3310 * @param specialCaller the class nominally calling the method
3311 * @return a method handle which can invoke the reflected method
3312 * @throws IllegalAccessException if access checking fails,
3313 * or if the method is {@code static},
3314 * or if the method's variable arity modifier bit
3315 * is set and {@code asVarargsCollector} fails
3316 * @throws NullPointerException if any argument is null
3317 */
3318 public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException {
3319 checkSpecialCaller(specialCaller, m.getDeclaringClass());
3320 Lookup specialLookup = this.in(specialCaller);
3321 MemberName method = new MemberName(m, true);
3322 assert(method.isMethod());
3323 // ignore m.isAccessible: this is a new kind of access
3324 return specialLookup.getDirectMethod(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerLookup(method));
3325 }
3326
3327 /**
3328 * Produces a method handle for a reflected constructor.
3329 * The type of the method handle will be that of the constructor,
3330 * with the return type changed to the declaring class.
3331 * The method handle will perform a {@code newInstance} operation,
3332 * creating a new instance of the constructor's class on the
3333 * arguments passed to the method handle.
3334 * <p>
3335 * If the constructor's {@code accessible} flag is not set,
3336 * access checking is performed immediately on behalf of the lookup class.
3337 * <p>
3338 * The returned method handle will have
3339 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3340 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
3341 * <p>
3342 * If the returned method handle is invoked, the constructor's class will
3343 * be initialized, if it has not already been initialized.
3344 * @param c the reflected constructor
3345 * @return a method handle which can invoke the reflected constructor
3346 * @throws IllegalAccessException if access checking fails
3347 * or if the method's variable arity modifier bit
3348 * is set and {@code asVarargsCollector} fails
3349 * @throws NullPointerException if the argument is null
3350 */
3351 public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException {
3352 MemberName ctor = new MemberName(c);
3353 assert(ctor.isConstructor());
3354 @SuppressWarnings("deprecation")
3355 Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
3356 return lookup.getDirectConstructor(ctor.getDeclaringClass(), ctor);
3357 }
3358
3359 /*
3360 * Produces a method handle that is capable of creating instances of the given class
3361 * and instantiated by the given constructor.
3362 *
3363 * This method should only be used by ReflectionFactory::newConstructorForSerialization.
3364 */
3365 /* package-private */ MethodHandle serializableConstructor(Class<?> decl, Constructor<?> c) throws IllegalAccessException {
3366 MemberName ctor = new MemberName(c);
3367 assert(ctor.isConstructor() && constructorInSuperclass(decl, c));
3368 checkAccess(REF_newInvokeSpecial, decl, ctor);
3369 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
3370 return DirectMethodHandle.makeAllocator(decl, ctor).setVarargs(ctor);
3371 }
3372
3373 private static boolean constructorInSuperclass(Class<?> decl, Constructor<?> ctor) {
3374 if (decl == ctor.getDeclaringClass())
3375 return true;
3376
3377 Class<?> cl = decl;
3378 while ((cl = cl.getSuperclass()) != null) {
3379 if (cl == ctor.getDeclaringClass()) {
3380 return true;
3381 }
3382 }
3383 return false;
3384 }
3385
3386 /**
3387 * Produces a method handle giving read access to a reflected field.
3388 * The type of the method handle will have a return type of the field's
3389 * value type.
3390 * If the field is {@code static}, the method handle will take no arguments.
3391 * Otherwise, its single argument will be the instance containing
3392 * the field.
3393 * If the {@code Field} object's {@code accessible} flag is not set,
3394 * access checking is performed immediately on behalf of the lookup class.
3395 * <p>
3396 * If the field is static, and
3397 * if the returned method handle is invoked, the field's class will
3398 * be initialized, if it has not already been initialized.
3399 * @param f the reflected field
3400 * @return a method handle which can load values from the reflected field
3401 * @throws IllegalAccessException if access checking fails
3402 * @throws NullPointerException if the argument is null
3403 */
3404 public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
3405 return unreflectField(f, false);
3406 }
3407
3408 /**
3409 * Produces a method handle giving write access to a reflected field.
3410 * The type of the method handle will have a void return type.
3411 * If the field is {@code static}, the method handle will take a single
3412 * argument, of the field's value type, the value to be stored.
3413 * Otherwise, the two arguments will be the instance containing
3414 * the field, and the value to be stored.
3415 * If the {@code Field} object's {@code accessible} flag is not set,
3416 * access checking is performed immediately on behalf of the lookup class.
3417 * <p>
3418 * If the field is {@code final}, write access will not be
3419 * allowed and access checking will fail, except under certain
3420 * narrow circumstances documented for {@link Field#set Field.set}.
3421 * A method handle is returned only if a corresponding call to
3422 * the {@code Field} object's {@code set} method could return
3423 * normally. In particular, fields which are both {@code static}
3424 * and {@code final} may never be set.
3425 * <p>
3426 * If the field is {@code static}, and
3427 * if the returned method handle is invoked, the field's class will
3428 * be initialized, if it has not already been initialized.
3429 * @param f the reflected field
3430 * @return a method handle which can store values into the reflected field
3431 * @throws IllegalAccessException if access checking fails,
3432 * or if the field is {@code final} and write access
3433 * is not enabled on the {@code Field} object
3434 * @throws NullPointerException if the argument is null
3435 */
3436 public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
3437 return unreflectField(f, true);
3438 }
3439
3440 private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
3441 MemberName field = new MemberName(f, isSetter);
3442 if (isSetter && field.isFinal()) {
3443 if (field.isTrustedFinalField()) {
3444 String msg = field.isStatic() ? "static final field has no write access"
3445 : "final field has no write access";
3446 throw field.makeAccessException(msg, this);
3447 }
3448 }
3449 assert(isSetter
3450 ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
3451 : MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
3452 @SuppressWarnings("deprecation")
3453 Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
3454 return lookup.getDirectField(field.getReferenceKind(), f.getDeclaringClass(), field);
3455 }
3456
3457 /**
3458 * Produces a VarHandle giving access to a reflected field {@code f}
3459 * of type {@code T} declared in a class of type {@code R}.
3460 * The VarHandle's variable type is {@code T}.
3461 * If the field is non-static the VarHandle has one coordinate type,
3462 * {@code R}. Otherwise, the field is static, and the VarHandle has no
3463 * coordinate types.
3464 * <p>
3465 * Access checking is performed immediately on behalf of the lookup
3466 * class, regardless of the value of the field's {@code accessible}
3467 * flag.
3468 * <p>
3469 * If the field is static, and if the returned VarHandle is operated
3470 * on, the field's declaring class will be initialized, if it has not
3471 * already been initialized.
3472 * <p>
3473 * Certain access modes of the returned VarHandle are unsupported under
3474 * the following conditions:
3475 * <ul>
3476 * <li>if the field is declared {@code final}, then the write, atomic
3477 * update, numeric atomic update, and bitwise atomic update access
3478 * modes are unsupported.
3479 * <li>if the field type is anything other than {@code byte},
3480 * {@code short}, {@code char}, {@code int}, {@code long},
3481 * {@code float}, or {@code double} then numeric atomic update
3482 * access modes are unsupported.
3483 * <li>if the field type is anything other than {@code boolean},
3484 * {@code byte}, {@code short}, {@code char}, {@code int} or
3485 * {@code long} then bitwise atomic update access modes are
3486 * unsupported.
3487 * </ul>
3488 * <p>
3489 * If the field is declared {@code volatile} then the returned VarHandle
3490 * will override access to the field (effectively ignore the
3491 * {@code volatile} declaration) in accordance to its specified
3492 * access modes.
3493 * <p>
3494 * If the field type is {@code float} or {@code double} then numeric
3495 * and atomic update access modes compare values using their bitwise
3496 * representation (see {@link Float#floatToRawIntBits} and
3497 * {@link Double#doubleToRawLongBits}, respectively).
3498 * @apiNote
3499 * Bitwise comparison of {@code float} values or {@code double} values,
3500 * as performed by the numeric and atomic update access modes, differ
3501 * from the primitive {@code ==} operator and the {@link Float#equals}
3502 * and {@link Double#equals} methods, specifically with respect to
3503 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
3504 * Care should be taken when performing a compare and set or a compare
3505 * and exchange operation with such values since the operation may
3506 * unexpectedly fail.
3507 * There are many possible NaN values that are considered to be
3508 * {@code NaN} in Java, although no IEEE 754 floating-point operation
3509 * provided by Java can distinguish between them. Operation failure can
3510 * occur if the expected or witness value is a NaN value and it is
3511 * transformed (perhaps in a platform specific manner) into another NaN
3512 * value, and thus has a different bitwise representation (see
3513 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
3514 * details).
3515 * The values {@code -0.0} and {@code +0.0} have different bitwise
3516 * representations but are considered equal when using the primitive
3517 * {@code ==} operator. Operation failure can occur if, for example, a
3518 * numeric algorithm computes an expected value to be say {@code -0.0}
3519 * and previously computed the witness value to be say {@code +0.0}.
3520 * @param f the reflected field, with a field of type {@code T}, and
3521 * a declaring class of type {@code R}
3522 * @return a VarHandle giving access to non-static fields or a static
3523 * field
3524 * @throws IllegalAccessException if access checking fails
3525 * @throws NullPointerException if the argument is null
3526 * @since 9
3527 */
3528 public VarHandle unreflectVarHandle(Field f) throws IllegalAccessException {
3529 MemberName getField = new MemberName(f, false);
3530 MemberName putField = new MemberName(f, true);
3531 return getFieldVarHandle(getField.getReferenceKind(), putField.getReferenceKind(),
3532 f.getDeclaringClass(), getField, putField);
3533 }
3534
3535 /**
3536 * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
3537 * created by this lookup object or a similar one.
3538 * Security and access checks are performed to ensure that this lookup object
3539 * is capable of reproducing the target method handle.
3540 * This means that the cracking may fail if target is a direct method handle
3541 * but was created by an unrelated lookup object.
3542 * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a>
3543 * and was created by a lookup object for a different class.
3544 * @param target a direct method handle to crack into symbolic reference components
3545 * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object
3546 * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails
3547 * @throws NullPointerException if the target is {@code null}
3548 * @see MethodHandleInfo
3549 * @since 1.8
3550 */
3551 public MethodHandleInfo revealDirect(MethodHandle target) {
3552 if (!target.isCrackable()) {
3553 throw newIllegalArgumentException("not a direct method handle");
3554 }
3555 MemberName member = target.internalMemberName();
3556 Class<?> defc = member.getDeclaringClass();
3557 byte refKind = member.getReferenceKind();
3558 assert(MethodHandleNatives.refKindIsValid(refKind));
3559 if (refKind == REF_invokeSpecial && !target.isInvokeSpecial())
3560 // Devirtualized method invocation is usually formally virtual.
3561 // To avoid creating extra MemberName objects for this common case,
3562 // we encode this extra degree of freedom using MH.isInvokeSpecial.
3563 refKind = REF_invokeVirtual;
3564 if (refKind == REF_invokeVirtual && defc.isInterface())
3565 // Symbolic reference is through interface but resolves to Object method (toString, etc.)
3566 refKind = REF_invokeInterface;
3567 // Check member access before cracking.
3568 try {
3569 checkAccess(refKind, defc, member);
3570 } catch (IllegalAccessException ex) {
3571 throw new IllegalArgumentException(ex);
3572 }
3573 if (allowedModes != TRUSTED && member.isCallerSensitive()) {
3574 Class<?> callerClass = target.internalCallerClass();
3575 if ((lookupModes() & ORIGINAL) == 0 || callerClass != lookupClass())
3576 throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass);
3577 }
3578 // Produce the handle to the results.
3579 return new InfoFromMemberName(this, member, refKind);
3580 }
3581
3582 //--- Helper methods, all package-private.
3583
3584 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3585 checkSymbolicClass(refc); // do this before attempting to resolve
3586 Objects.requireNonNull(name);
3587 Objects.requireNonNull(type);
3588 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), allowedModes,
3589 NoSuchFieldException.class);
3590 }
3591
3592 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
3593 checkSymbolicClass(refc); // do this before attempting to resolve
3594 Objects.requireNonNull(type);
3595 checkMethodName(refKind, name); // implicit null-check of name
3596 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), allowedModes,
3597 NoSuchMethodException.class);
3598 }
3599
3600 MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException {
3601 checkSymbolicClass(member.getDeclaringClass()); // do this before attempting to resolve
3602 Objects.requireNonNull(member.getName());
3603 Objects.requireNonNull(member.getType());
3604 return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(), allowedModes,
3605 ReflectiveOperationException.class);
3606 }
3607
3608 MemberName resolveOrNull(byte refKind, MemberName member) {
3609 // do this before attempting to resolve
3610 if (!isClassAccessible(member.getDeclaringClass())) {
3611 return null;
3612 }
3613 Objects.requireNonNull(member.getName());
3614 Objects.requireNonNull(member.getType());
3615 return IMPL_NAMES.resolveOrNull(refKind, member, lookupClassOrNull(), allowedModes);
3616 }
3617
3618 MemberName resolveOrNull(byte refKind, Class<?> refc, String name, MethodType type) {
3619 // do this before attempting to resolve
3620 if (!isClassAccessible(refc)) {
3621 return null;
3622 }
3623 Objects.requireNonNull(type);
3624 // implicit null-check of name
3625 if (name.startsWith("<") && refKind != REF_newInvokeSpecial) {
3626 return null;
3627 }
3628 return IMPL_NAMES.resolveOrNull(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), allowedModes);
3629 }
3630
3631 void checkSymbolicClass(Class<?> refc) throws IllegalAccessException {
3632 if (!isClassAccessible(refc)) {
3633 throw new MemberName(refc).makeAccessException("symbolic reference class is not accessible", this);
3634 }
3635 }
3636
3637 boolean isClassAccessible(Class<?> refc) {
3638 Objects.requireNonNull(refc);
3639 Class<?> caller = lookupClassOrNull();
3640 Class<?> type = refc;
3641 while (type.isArray()) {
3642 type = type.getComponentType();
3643 }
3644 return caller == null || VerifyAccess.isClassAccessible(type, caller, prevLookupClass, allowedModes);
3645 }
3646
3647 /** Check name for an illegal leading "<" character. */
3648 void checkMethodName(byte refKind, String name) throws NoSuchMethodException {
3649 if (name.startsWith("<") && refKind != REF_newInvokeSpecial)
3650 throw new NoSuchMethodException("illegal method name: "+name);
3651 }
3652
3653 /**
3654 * Find my trustable caller class if m is a caller sensitive method.
3655 * If this lookup object has original full privilege access, then the caller class is the lookupClass.
3656 * Otherwise, if m is caller-sensitive, throw IllegalAccessException.
3657 */
3658 Lookup findBoundCallerLookup(MemberName m) throws IllegalAccessException {
3659 if (MethodHandleNatives.isCallerSensitive(m) && (lookupModes() & ORIGINAL) == 0) {
3660 // Only lookups with full privilege access are allowed to resolve caller-sensitive methods
3661 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
3662 }
3663 return this;
3664 }
3665
3666 /**
3667 * Returns {@code true} if this lookup has {@code PRIVATE} and {@code MODULE} access.
3668 * @return {@code true} if this lookup has {@code PRIVATE} and {@code MODULE} access.
3669 *
3670 * @deprecated This method was originally designed to test {@code PRIVATE} access
3671 * that implies full privilege access but {@code MODULE} access has since become
3672 * independent of {@code PRIVATE} access. It is recommended to call
3673 * {@link #hasFullPrivilegeAccess()} instead.
3674 * @since 9
3675 */
3676 @Deprecated(since="14")
3677 public boolean hasPrivateAccess() {
3678 return hasFullPrivilegeAccess();
3679 }
3680
3681 /**
3682 * Returns {@code true} if this lookup has <em>full privilege access</em>,
3683 * i.e. {@code PRIVATE} and {@code MODULE} access.
3684 * A {@code Lookup} object must have full privilege access in order to
3685 * access all members that are allowed to the
3686 * {@linkplain #lookupClass() lookup class}.
3687 *
3688 * @return {@code true} if this lookup has full privilege access.
3689 * @since 14
3690 * @see <a href="MethodHandles.Lookup.html#privacc">private and module access</a>
3691 */
3692 public boolean hasFullPrivilegeAccess() {
3693 return (allowedModes & (PRIVATE|MODULE)) == (PRIVATE|MODULE);
3694 }
3695
3696 void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
3697 boolean wantStatic = (refKind == REF_invokeStatic);
3698 String message;
3699 if (m.isConstructor())
3700 message = "expected a method, not a constructor";
3701 else if (!m.isMethod())
3702 message = "expected a method";
3703 else if (wantStatic != m.isStatic())
3704 message = wantStatic ? "expected a static method" : "expected a non-static method";
3705 else
3706 { checkAccess(refKind, refc, m); return; }
3707 throw m.makeAccessException(message, this);
3708 }
3709
3710 void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
3711 boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
3712 String message;
3713 if (wantStatic != m.isStatic())
3714 message = wantStatic ? "expected a static field" : "expected a non-static field";
3715 else
3716 { checkAccess(refKind, refc, m); return; }
3717 throw m.makeAccessException(message, this);
3718 }
3719
3720 private boolean isArrayClone(byte refKind, Class<?> refc, MemberName m) {
3721 return Modifier.isProtected(m.getModifiers()) &&
3722 refKind == REF_invokeVirtual &&
3723 m.getDeclaringClass() == Object.class &&
3724 m.getName().equals("clone") &&
3725 refc.isArray();
3726 }
3727
3728 /** Check public/protected/private bits on the symbolic reference class and its member. */
3729 void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
3730 assert(m.referenceKindIsConsistentWith(refKind) &&
3731 MethodHandleNatives.refKindIsValid(refKind) &&
3732 (MethodHandleNatives.refKindIsField(refKind) == m.isField()));
3733 int allowedModes = this.allowedModes;
3734 if (allowedModes == TRUSTED) return;
3735 int mods = m.getModifiers();
3736 if (isArrayClone(refKind, refc, m)) {
3737 // The JVM does this hack also.
3738 // (See ClassVerifier::verify_invoke_instructions
3739 // and LinkResolver::check_method_accessability.)
3740 // Because the JVM does not allow separate methods on array types,
3741 // there is no separate method for int[].clone.
3742 // All arrays simply inherit Object.clone.
3743 // But for access checking logic, we make Object.clone
3744 // (normally protected) appear to be public.
3745 // Later on, when the DirectMethodHandle is created,
3746 // its leading argument will be restricted to the
3747 // requested array type.
3748 // N.B. The return type is not adjusted, because
3749 // that is *not* the bytecode behavior.
3750 mods ^= Modifier.PROTECTED | Modifier.PUBLIC;
3751 }
3752 if (Modifier.isProtected(mods) && refKind == REF_newInvokeSpecial) {
3753 // cannot "new" a protected ctor in a different package
3754 mods ^= Modifier.PROTECTED;
3755 }
3756 if (Modifier.isFinal(mods) &&
3757 MethodHandleNatives.refKindIsSetter(refKind))
3758 throw m.makeAccessException("unexpected set of a final field", this);
3759 int requestedModes = fixmods(mods); // adjust 0 => PACKAGE
3760 if ((requestedModes & allowedModes) != 0) {
3761 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
3762 mods, lookupClass(), previousLookupClass(), allowedModes))
3763 return;
3764 } else {
3765 // Protected members can also be checked as if they were package-private.
3766 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
3767 && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
3768 return;
3769 }
3770 throw m.makeAccessException(accessFailedMessage(refc, m), this);
3771 }
3772
3773 String accessFailedMessage(Class<?> refc, MemberName m) {
3774 Class<?> defc = m.getDeclaringClass();
3775 int mods = m.getModifiers();
3776 // check the class first:
3777 boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
3778 (defc == refc ||
3779 Modifier.isPublic(refc.getModifiers())));
3780 if (!classOK && (allowedModes & PACKAGE) != 0) {
3781 // ignore previous lookup class to check if default package access
3782 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), null, FULL_POWER_MODES) &&
3783 (defc == refc ||
3784 VerifyAccess.isClassAccessible(refc, lookupClass(), null, FULL_POWER_MODES)));
3785 }
3786 if (!classOK)
3787 return "class is not public";
3788 if (Modifier.isPublic(mods))
3789 return "access to public member failed"; // (how?, module not readable?)
3790 if (Modifier.isPrivate(mods))
3791 return "member is private";
3792 if (Modifier.isProtected(mods))
3793 return "member is protected";
3794 return "member is private to package";
3795 }
3796
3797 private void checkSpecialCaller(Class<?> specialCaller, Class<?> refc) throws IllegalAccessException {
3798 int allowedModes = this.allowedModes;
3799 if (allowedModes == TRUSTED) return;
3800 if ((lookupModes() & PRIVATE) == 0
3801 || (specialCaller != lookupClass()
3802 // ensure non-abstract methods in superinterfaces can be special-invoked
3803 && !(refc != null && refc.isInterface() && refc.isAssignableFrom(specialCaller))))
3804 throw new MemberName(specialCaller).
3805 makeAccessException("no private access for invokespecial", this);
3806 }
3807
3808 private boolean restrictProtectedReceiver(MemberName method) {
3809 // The accessing class only has the right to use a protected member
3810 // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc.
3811 if (!method.isProtected() || method.isStatic()
3812 || allowedModes == TRUSTED
3813 || method.getDeclaringClass() == lookupClass()
3814 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass()))
3815 return false;
3816 return true;
3817 }
3818 private MethodHandle restrictReceiver(MemberName method, DirectMethodHandle mh, Class<?> caller) throws IllegalAccessException {
3819 assert(!method.isStatic());
3820 // receiver type of mh is too wide; narrow to caller
3821 if (!method.getDeclaringClass().isAssignableFrom(caller)) {
3822 throw method.makeAccessException("caller class must be a subclass below the method", caller);
3823 }
3824 MethodType rawType = mh.type();
3825 if (caller.isAssignableFrom(rawType.parameterType(0))) return mh; // no need to restrict; already narrow
3826 MethodType narrowType = rawType.changeParameterType(0, caller);
3827 assert(!mh.isVarargsCollector()); // viewAsType will lose varargs-ness
3828 assert(mh.viewAsTypeChecks(narrowType, true));
3829 return mh.copyWith(narrowType, mh.form);
3830 }
3831
3832 /** Check access and get the requested method. */
3833 private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException {
3834 final boolean doRestrict = true;
3835 return getDirectMethodCommon(refKind, refc, method, doRestrict, callerLookup);
3836 }
3837 /** Check access and get the requested method, for invokespecial with no restriction on the application of narrowing rules. */
3838 private MethodHandle getDirectMethodNoRestrictInvokeSpecial(Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException {
3839 final boolean doRestrict = false;
3840 return getDirectMethodCommon(REF_invokeSpecial, refc, method, doRestrict, callerLookup);
3841 }
3842 /** Common code for all methods; do not call directly except from immediately above. */
3843 private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method,
3844 boolean doRestrict,
3845 Lookup boundCaller) throws IllegalAccessException {
3846 checkMethod(refKind, refc, method);
3847 assert(!method.isMethodHandleInvoke());
3848 if (refKind == REF_invokeSpecial &&
3849 refc != lookupClass() &&
3850 !refc.isInterface() && !lookupClass().isInterface() &&
3851 refc != lookupClass().getSuperclass() &&
3852 refc.isAssignableFrom(lookupClass())) {
3853 assert(!method.getName().equals(ConstantDescs.INIT_NAME)); // not this code path
3854
3855 // Per JVMS 6.5, desc. of invokespecial instruction:
3856 // If the method is in a superclass of the LC,
3857 // and if our original search was above LC.super,
3858 // repeat the search (symbolic lookup) from LC.super
3859 // and continue with the direct superclass of that class,
3860 // and so forth, until a match is found or no further superclasses exist.
3861 // FIXME: MemberName.resolve should handle this instead.
3862 Class<?> refcAsSuper = lookupClass();
3863 MemberName m2;
3864 do {
3865 refcAsSuper = refcAsSuper.getSuperclass();
3866 m2 = new MemberName(refcAsSuper,
3867 method.getName(),
3868 method.getMethodType(),
3869 REF_invokeSpecial);
3870 m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull(), allowedModes);
3871 } while (m2 == null && // no method is found yet
3872 refc != refcAsSuper); // search up to refc
3873 if (m2 == null) throw new InternalError(method.toString());
3874 method = m2;
3875 refc = refcAsSuper;
3876 // redo basic checks
3877 checkMethod(refKind, refc, method);
3878 }
3879 DirectMethodHandle dmh = DirectMethodHandle.make(refKind, refc, method, lookupClass());
3880 MethodHandle mh = dmh;
3881 // Optionally narrow the receiver argument to lookupClass using restrictReceiver.
3882 if ((doRestrict && refKind == REF_invokeSpecial) ||
3883 (MethodHandleNatives.refKindHasReceiver(refKind) &&
3884 restrictProtectedReceiver(method) &&
3885 // All arrays simply inherit the protected Object.clone method.
3886 // The leading argument is already restricted to the requested
3887 // array type (not the lookup class).
3888 !isArrayClone(refKind, refc, method))) {
3889 mh = restrictReceiver(method, dmh, lookupClass());
3890 }
3891 mh = maybeBindCaller(method, mh, boundCaller);
3892 mh = mh.setVarargs(method);
3893 return mh;
3894 }
3895 private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh, Lookup boundCaller)
3896 throws IllegalAccessException {
3897 if (boundCaller.allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method))
3898 return mh;
3899
3900 // boundCaller must have full privilege access.
3901 // It should have been checked by findBoundCallerLookup. Safe to check this again.
3902 if ((boundCaller.lookupModes() & ORIGINAL) == 0)
3903 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
3904
3905 assert boundCaller.hasFullPrivilegeAccess();
3906
3907 MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, boundCaller.lookupClass);
3908 // Note: caller will apply varargs after this step happens.
3909 return cbmh;
3910 }
3911
3912 /** Check access and get the requested field. */
3913 private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
3914 return getDirectFieldCommon(refKind, refc, field);
3915 }
3916 /** Common code for all fields; do not call directly except from immediately above. */
3917 private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
3918 checkField(refKind, refc, field);
3919 DirectMethodHandle dmh = DirectMethodHandle.make(refc, field);
3920 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) &&
3921 restrictProtectedReceiver(field));
3922 if (doRestrict)
3923 return restrictReceiver(field, dmh, lookupClass());
3924 return dmh;
3925 }
3926 private VarHandle getFieldVarHandle(byte getRefKind, byte putRefKind,
3927 Class<?> refc, MemberName getField, MemberName putField)
3928 throws IllegalAccessException {
3929 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField);
3930 }
3931 private VarHandle getFieldVarHandleCommon(byte getRefKind, byte putRefKind,
3932 Class<?> refc, MemberName getField,
3933 MemberName putField) throws IllegalAccessException {
3934 assert getField.isStatic() == putField.isStatic();
3935 assert getField.isGetter() && putField.isSetter();
3936 assert MethodHandleNatives.refKindIsStatic(getRefKind) == MethodHandleNatives.refKindIsStatic(putRefKind);
3937 assert MethodHandleNatives.refKindIsGetter(getRefKind) && MethodHandleNatives.refKindIsSetter(putRefKind);
3938
3939 checkField(getRefKind, refc, getField);
3940
3941 if (!putField.isFinal()) {
3942 // A VarHandle does not support updates to final fields, any
3943 // such VarHandle to a final field will be read-only and
3944 // therefore the following write-based accessibility checks are
3945 // only required for non-final fields
3946 checkField(putRefKind, refc, putField);
3947 }
3948
3949 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(getRefKind) &&
3950 restrictProtectedReceiver(getField));
3951 if (doRestrict) {
3952 assert !getField.isStatic();
3953 // receiver type of VarHandle is too wide; narrow to caller
3954 if (!getField.getDeclaringClass().isAssignableFrom(lookupClass())) {
3955 throw getField.makeAccessException("caller class must be a subclass below the method", lookupClass());
3956 }
3957 refc = lookupClass();
3958 }
3959 return VarHandles.makeFieldHandle(getField, refc,
3960 this.allowedModes == TRUSTED && !getField.isTrustedFinalField());
3961 }
3962 /** Check access and get the requested constructor. */
3963 private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException {
3964 return getDirectConstructorCommon(refc, ctor);
3965 }
3966 /** Common code for all constructors; do not call directly except from immediately above. */
3967 private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor) throws IllegalAccessException {
3968 assert(ctor.isConstructor());
3969 checkAccess(REF_newInvokeSpecial, refc, ctor);
3970 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
3971 return DirectMethodHandle.make(ctor).setVarargs(ctor);
3972 }
3973
3974 /** Hook called from the JVM (via MethodHandleNatives) to link MH constants:
3975 */
3976 /*non-public*/
3977 MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type)
3978 throws ReflectiveOperationException {
3979 if (!(type instanceof Class || type instanceof MethodType))
3980 throw new InternalError("unresolved MemberName");
3981 MemberName member = new MemberName(refKind, defc, name, type);
3982 MethodHandle mh = LOOKASIDE_TABLE.get(member);
3983 if (mh != null) {
3984 checkSymbolicClass(defc);
3985 return mh;
3986 }
3987 if (defc == MethodHandle.class && refKind == REF_invokeVirtual) {
3988 // Treat MethodHandle.invoke and invokeExact specially.
3989 mh = findVirtualForMH(member.getName(), member.getMethodType());
3990 if (mh != null) {
3991 return mh;
3992 }
3993 } else if (defc == VarHandle.class && refKind == REF_invokeVirtual) {
3994 // Treat signature-polymorphic methods on VarHandle specially.
3995 mh = findVirtualForVH(member.getName(), member.getMethodType());
3996 if (mh != null) {
3997 return mh;
3998 }
3999 }
4000 MemberName resolved = resolveOrFail(refKind, member);
4001 mh = getDirectMethodForConstant(refKind, defc, resolved);
4002 if (mh instanceof DirectMethodHandle dmh
4003 && canBeCached(refKind, defc, resolved)) {
4004 MemberName key = mh.internalMemberName();
4005 if (key != null) {
4006 key = key.asNormalOriginal();
4007 }
4008 if (member.equals(key)) { // better safe than sorry
4009 LOOKASIDE_TABLE.put(key, dmh);
4010 }
4011 }
4012 return mh;
4013 }
4014 private boolean canBeCached(byte refKind, Class<?> defc, MemberName member) {
4015 if (refKind == REF_invokeSpecial) {
4016 return false;
4017 }
4018 if (!Modifier.isPublic(defc.getModifiers()) ||
4019 !Modifier.isPublic(member.getDeclaringClass().getModifiers()) ||
4020 !member.isPublic() ||
4021 member.isCallerSensitive()) {
4022 return false;
4023 }
4024 ClassLoader loader = defc.getClassLoader();
4025 if (loader != null) {
4026 ClassLoader sysl = ClassLoader.getSystemClassLoader();
4027 boolean found = false;
4028 while (sysl != null) {
4029 if (loader == sysl) { found = true; break; }
4030 sysl = sysl.getParent();
4031 }
4032 if (!found) {
4033 return false;
4034 }
4035 }
4036 MemberName resolved2 = publicLookup().resolveOrNull(refKind,
4037 new MemberName(refKind, defc, member.getName(), member.getType()));
4038 if (resolved2 == null) {
4039 return false;
4040 }
4041 return true;
4042 }
4043 private MethodHandle getDirectMethodForConstant(byte refKind, Class<?> defc, MemberName member)
4044 throws ReflectiveOperationException {
4045 if (MethodHandleNatives.refKindIsField(refKind)) {
4046 return getDirectField(refKind, defc, member);
4047 } else if (MethodHandleNatives.refKindIsMethod(refKind)) {
4048 return getDirectMethod(refKind, defc, member, findBoundCallerLookup(member));
4049 } else if (refKind == REF_newInvokeSpecial) {
4050 return getDirectConstructor(defc, member);
4051 }
4052 // oops
4053 throw newIllegalArgumentException("bad MethodHandle constant #"+member);
4054 }
4055
4056 static ConcurrentHashMap<MemberName, DirectMethodHandle> LOOKASIDE_TABLE = new ConcurrentHashMap<>();
4057 }
4058
4059 /**
4060 * Produces a method handle constructing arrays of a desired type,
4061 * as if by the {@code anewarray} bytecode.
4062 * The return type of the method handle will be the array type.
4063 * The type of its sole argument will be {@code int}, which specifies the size of the array.
4064 *
4065 * <p> If the returned method handle is invoked with a negative
4066 * array size, a {@code NegativeArraySizeException} will be thrown.
4067 *
4068 * @param arrayClass an array type
4069 * @return a method handle which can create arrays of the given type
4070 * @throws NullPointerException if the argument is {@code null}
4071 * @throws IllegalArgumentException if {@code arrayClass} is not an array type
4072 * @see java.lang.reflect.Array#newInstance(Class, int)
4073 * @jvms 6.5 {@code anewarray} Instruction
4074 * @since 9
4075 */
4076 public static MethodHandle arrayConstructor(Class<?> arrayClass) throws IllegalArgumentException {
4077 if (!arrayClass.isArray()) {
4078 throw newIllegalArgumentException("not an array class: " + arrayClass.getName());
4079 }
4080 MethodHandle ani = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_Array_newInstance).
4081 bindTo(arrayClass.getComponentType());
4082 return ani.asType(ani.type().changeReturnType(arrayClass));
4083 }
4084
4085 /**
4086 * Produces a method handle returning the length of an array,
4087 * as if by the {@code arraylength} bytecode.
4088 * The type of the method handle will have {@code int} as return type,
4089 * and its sole argument will be the array type.
4090 *
4091 * <p> If the returned method handle is invoked with a {@code null}
4092 * array reference, a {@code NullPointerException} will be thrown.
4093 *
4094 * @param arrayClass an array type
4095 * @return a method handle which can retrieve the length of an array of the given array type
4096 * @throws NullPointerException if the argument is {@code null}
4097 * @throws IllegalArgumentException if arrayClass is not an array type
4098 * @jvms 6.5 {@code arraylength} Instruction
4099 * @since 9
4100 */
4101 public static MethodHandle arrayLength(Class<?> arrayClass) throws IllegalArgumentException {
4102 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.LENGTH);
4103 }
4104
4105 /**
4106 * Produces a method handle giving read access to elements of an array,
4107 * as if by the {@code aaload} bytecode.
4108 * The type of the method handle will have a return type of the array's
4109 * element type. Its first argument will be the array type,
4110 * and the second will be {@code int}.
4111 *
4112 * <p> When the returned method handle is invoked,
4113 * the array reference and array index are checked.
4114 * A {@code NullPointerException} will be thrown if the array reference
4115 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
4116 * thrown if the index is negative or if it is greater than or equal to
4117 * the length of the array.
4118 *
4119 * @param arrayClass an array type
4120 * @return a method handle which can load values from the given array type
4121 * @throws NullPointerException if the argument is null
4122 * @throws IllegalArgumentException if arrayClass is not an array type
4123 * @jvms 6.5 {@code aaload} Instruction
4124 */
4125 public static MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException {
4126 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.GET);
4127 }
4128
4129 /**
4130 * Produces a method handle giving write access to elements of an array,
4131 * as if by the {@code astore} bytecode.
4132 * The type of the method handle will have a void return type.
4133 * Its last argument will be the array's element type.
4134 * The first and second arguments will be the array type and int.
4135 *
4136 * <p> When the returned method handle is invoked,
4137 * the array reference and array index are checked.
4138 * A {@code NullPointerException} will be thrown if the array reference
4139 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
4140 * thrown if the index is negative or if it is greater than or equal to
4141 * the length of the array.
4142 *
4143 * @param arrayClass the class of an array
4144 * @return a method handle which can store values into the array type
4145 * @throws NullPointerException if the argument is null
4146 * @throws IllegalArgumentException if arrayClass is not an array type
4147 * @jvms 6.5 {@code aastore} Instruction
4148 */
4149 public static MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException {
4150 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.SET);
4151 }
4152
4153 /**
4154 * Produces a VarHandle giving access to elements of an array of type
4155 * {@code arrayClass}. The VarHandle's variable type is the component type
4156 * of {@code arrayClass} and the list of coordinate types is
4157 * {@code (arrayClass, int)}, where the {@code int} coordinate type
4158 * corresponds to an argument that is an index into an array.
4159 * <p>
4160 * Certain access modes of the returned VarHandle are unsupported under
4161 * the following conditions:
4162 * <ul>
4163 * <li>if the component type is anything other than {@code byte},
4164 * {@code short}, {@code char}, {@code int}, {@code long},
4165 * {@code float}, or {@code double} then numeric atomic update access
4166 * modes are unsupported.
4167 * <li>if the component type is anything other than {@code boolean},
4168 * {@code byte}, {@code short}, {@code char}, {@code int} or
4169 * {@code long} then bitwise atomic update access modes are
4170 * unsupported.
4171 * </ul>
4172 * <p>
4173 * If the component type is {@code float} or {@code double} then numeric
4174 * and atomic update access modes compare values using their bitwise
4175 * representation (see {@link Float#floatToRawIntBits} and
4176 * {@link Double#doubleToRawLongBits}, respectively).
4177 *
4178 * <p> When the returned {@code VarHandle} is invoked,
4179 * the array reference and array index are checked.
4180 * A {@code NullPointerException} will be thrown if the array reference
4181 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
4182 * thrown if the index is negative or if it is greater than or equal to
4183 * the length of the array.
4184 *
4185 * @apiNote
4186 * Bitwise comparison of {@code float} values or {@code double} values,
4187 * as performed by the numeric and atomic update access modes, differ
4188 * from the primitive {@code ==} operator and the {@link Float#equals}
4189 * and {@link Double#equals} methods, specifically with respect to
4190 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
4191 * Care should be taken when performing a compare and set or a compare
4192 * and exchange operation with such values since the operation may
4193 * unexpectedly fail.
4194 * There are many possible NaN values that are considered to be
4195 * {@code NaN} in Java, although no IEEE 754 floating-point operation
4196 * provided by Java can distinguish between them. Operation failure can
4197 * occur if the expected or witness value is a NaN value and it is
4198 * transformed (perhaps in a platform specific manner) into another NaN
4199 * value, and thus has a different bitwise representation (see
4200 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
4201 * details).
4202 * The values {@code -0.0} and {@code +0.0} have different bitwise
4203 * representations but are considered equal when using the primitive
4204 * {@code ==} operator. Operation failure can occur if, for example, a
4205 * numeric algorithm computes an expected value to be say {@code -0.0}
4206 * and previously computed the witness value to be say {@code +0.0}.
4207 * @param arrayClass the class of an array, of type {@code T[]}
4208 * @return a VarHandle giving access to elements of an array
4209 * @throws NullPointerException if the arrayClass is null
4210 * @throws IllegalArgumentException if arrayClass is not an array type
4211 * @since 9
4212 */
4213 public static VarHandle arrayElementVarHandle(Class<?> arrayClass) throws IllegalArgumentException {
4214 return VarHandles.makeArrayElementHandle(arrayClass);
4215 }
4216
4217 /**
4218 * Produces a VarHandle giving access to elements of a {@code byte[]} array
4219 * viewed as if it were a different primitive array type, such as
4220 * {@code int[]} or {@code long[]}.
4221 * The VarHandle's variable type is the component type of
4222 * {@code viewArrayClass} and the list of coordinate types is
4223 * {@code (byte[], int)}, where the {@code int} coordinate type
4224 * corresponds to an argument that is an index into a {@code byte[]} array.
4225 * The returned VarHandle accesses bytes at an index in a {@code byte[]}
4226 * array, composing bytes to or from a value of the component type of
4227 * {@code viewArrayClass} according to the given endianness.
4228 * <p>
4229 * The supported component types (variables types) are {@code short},
4230 * {@code char}, {@code int}, {@code long}, {@code float} and
4231 * {@code double}.
4232 * <p>
4233 * Access of bytes at a given index will result in an
4234 * {@code ArrayIndexOutOfBoundsException} if the index is less than {@code 0}
4235 * or greater than the {@code byte[]} array length minus the size (in bytes)
4236 * of {@code T}.
4237 * <p>
4238 * Only plain {@linkplain VarHandle.AccessMode#GET get} and {@linkplain VarHandle.AccessMode#SET set}
4239 * access modes are supported by the returned var handle. For all other access modes, an
4240 * {@link UnsupportedOperationException} will be thrown.
4241 *
4242 * @apiNote if access modes other than plain access are required, clients should
4243 * consider using off-heap memory through
4244 * {@linkplain java.nio.ByteBuffer#allocateDirect(int) direct byte buffers} or
4245 * off-heap {@linkplain java.lang.foreign.MemorySegment memory segments},
4246 * or memory segments backed by a
4247 * {@linkplain java.lang.foreign.MemorySegment#ofArray(long[]) {@code long[]}},
4248 * for which stronger alignment guarantees can be made.
4249 *
4250 * @param viewArrayClass the view array class, with a component type of
4251 * type {@code T}
4252 * @param byteOrder the endianness of the view array elements, as
4253 * stored in the underlying {@code byte} array
4254 * @return a VarHandle giving access to elements of a {@code byte[]} array
4255 * viewed as if elements corresponding to the components type of the view
4256 * array class
4257 * @throws NullPointerException if viewArrayClass or byteOrder is null
4258 * @throws IllegalArgumentException if viewArrayClass is not an array type
4259 * @throws UnsupportedOperationException if the component type of
4260 * viewArrayClass is not supported as a variable type
4261 * @since 9
4262 */
4263 public static VarHandle byteArrayViewVarHandle(Class<?> viewArrayClass,
4264 ByteOrder byteOrder) throws IllegalArgumentException {
4265 Objects.requireNonNull(byteOrder);
4266 return VarHandles.byteArrayViewHandle(viewArrayClass,
4267 byteOrder == ByteOrder.BIG_ENDIAN);
4268 }
4269
4270 /**
4271 * Produces a VarHandle giving access to elements of a {@code ByteBuffer}
4272 * viewed as if it were an array of elements of a different primitive
4273 * component type to that of {@code byte}, such as {@code int[]} or
4274 * {@code long[]}.
4275 * The VarHandle's variable type is the component type of
4276 * {@code viewArrayClass} and the list of coordinate types is
4277 * {@code (ByteBuffer, int)}, where the {@code int} coordinate type
4278 * corresponds to an argument that is an index into a {@code byte[]} array.
4279 * The returned VarHandle accesses bytes at an index in a
4280 * {@code ByteBuffer}, composing bytes to or from a value of the component
4281 * type of {@code viewArrayClass} according to the given endianness.
4282 * <p>
4283 * The supported component types (variables types) are {@code short},
4284 * {@code char}, {@code int}, {@code long}, {@code float} and
4285 * {@code double}.
4286 * <p>
4287 * Access will result in a {@code ReadOnlyBufferException} for anything
4288 * other than the read access modes if the {@code ByteBuffer} is read-only.
4289 * <p>
4290 * Access of bytes at a given index will result in an
4291 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
4292 * or greater than the {@code ByteBuffer} limit minus the size (in bytes) of
4293 * {@code T}.
4294 * <p>
4295 * For heap byte buffers, access is always unaligned. As a result, only the plain
4296 * {@linkplain VarHandle.AccessMode#GET get}
4297 * and {@linkplain VarHandle.AccessMode#SET set} access modes are supported by the
4298 * returned var handle. For all other access modes, an {@link IllegalStateException}
4299 * will be thrown.
4300 * <p>
4301 * For direct buffers only, access of bytes at an index may be aligned or misaligned for {@code T},
4302 * with respect to the underlying memory address, {@code A} say, associated
4303 * with the {@code ByteBuffer} and index.
4304 * If access is misaligned then access for anything other than the
4305 * {@code get} and {@code set} access modes will result in an
4306 * {@code IllegalStateException}. In such cases atomic access is only
4307 * guaranteed with respect to the largest power of two that divides the GCD
4308 * of {@code A} and the size (in bytes) of {@code T}.
4309 * If access is aligned then following access modes are supported and are
4310 * guaranteed to support atomic access:
4311 * <ul>
4312 * <li>read write access modes for all {@code T}, with the exception of
4313 * access modes {@code get} and {@code set} for {@code long} and
4314 * {@code double} on 32-bit platforms.
4315 * <li>atomic update access modes for {@code int}, {@code long},
4316 * {@code float} or {@code double}.
4317 * (Future major platform releases of the JDK may support additional
4318 * types for certain currently unsupported access modes.)
4319 * <li>numeric atomic update access modes for {@code int} and {@code long}.
4320 * (Future major platform releases of the JDK may support additional
4321 * numeric types for certain currently unsupported access modes.)
4322 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
4323 * (Future major platform releases of the JDK may support additional
4324 * numeric types for certain currently unsupported access modes.)
4325 * </ul>
4326 * <p>
4327 * Misaligned access, and therefore atomicity guarantees, may be determined
4328 * for a {@code ByteBuffer}, {@code bb} (direct or otherwise), an
4329 * {@code index}, {@code T} and its corresponding boxed type,
4330 * {@code T_BOX}, as follows:
4331 * <pre>{@code
4332 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
4333 * ByteBuffer bb = ...
4334 * int misalignedAtIndex = bb.alignmentOffset(index, sizeOfT);
4335 * boolean isMisaligned = misalignedAtIndex != 0;
4336 * }</pre>
4337 * <p>
4338 * If the variable type is {@code float} or {@code double} then atomic
4339 * update access modes compare values using their bitwise representation
4340 * (see {@link Float#floatToRawIntBits} and
4341 * {@link Double#doubleToRawLongBits}, respectively).
4342 * @param viewArrayClass the view array class, with a component type of
4343 * type {@code T}
4344 * @param byteOrder the endianness of the view array elements, as
4345 * stored in the underlying {@code ByteBuffer} (Note this overrides the
4346 * endianness of a {@code ByteBuffer})
4347 * @return a VarHandle giving access to elements of a {@code ByteBuffer}
4348 * viewed as if elements corresponding to the components type of the view
4349 * array class
4350 * @throws NullPointerException if viewArrayClass or byteOrder is null
4351 * @throws IllegalArgumentException if viewArrayClass is not an array type
4352 * @throws UnsupportedOperationException if the component type of
4353 * viewArrayClass is not supported as a variable type
4354 * @since 9
4355 */
4356 public static VarHandle byteBufferViewVarHandle(Class<?> viewArrayClass,
4357 ByteOrder byteOrder) throws IllegalArgumentException {
4358 Objects.requireNonNull(byteOrder);
4359 return VarHandles.makeByteBufferViewHandle(viewArrayClass,
4360 byteOrder == ByteOrder.BIG_ENDIAN);
4361 }
4362
4363
4364 //--- method handle invocation (reflective style)
4365
4366 /**
4367 * Produces a method handle which will invoke any method handle of the
4368 * given {@code type}, with a given number of trailing arguments replaced by
4369 * a single trailing {@code Object[]} array.
4370 * The resulting invoker will be a method handle with the following
4371 * arguments:
4372 * <ul>
4373 * <li>a single {@code MethodHandle} target
4374 * <li>zero or more leading values (counted by {@code leadingArgCount})
4375 * <li>an {@code Object[]} array containing trailing arguments
4376 * </ul>
4377 * <p>
4378 * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
4379 * the indicated {@code type}.
4380 * That is, if the target is exactly of the given {@code type}, it will behave
4381 * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
4382 * is used to convert the target to the required {@code type}.
4383 * <p>
4384 * The type of the returned invoker will not be the given {@code type}, but rather
4385 * will have all parameters except the first {@code leadingArgCount}
4386 * replaced by a single array of type {@code Object[]}, which will be
4387 * the final parameter.
4388 * <p>
4389 * Before invoking its target, the invoker will spread the final array, apply
4390 * reference casts as necessary, and unbox and widen primitive arguments.
4391 * If, when the invoker is called, the supplied array argument does
4392 * not have the correct number of elements, the invoker will throw
4393 * an {@link IllegalArgumentException} instead of invoking the target.
4394 * <p>
4395 * This method is equivalent to the following code (though it may be more efficient):
4396 * {@snippet lang="java" :
4397 MethodHandle invoker = MethodHandles.invoker(type);
4398 int spreadArgCount = type.parameterCount() - leadingArgCount;
4399 invoker = invoker.asSpreader(Object[].class, spreadArgCount);
4400 return invoker;
4401 * }
4402 * This method throws no reflective exceptions.
4403 * @param type the desired target type
4404 * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
4405 * @return a method handle suitable for invoking any method handle of the given type
4406 * @throws NullPointerException if {@code type} is null
4407 * @throws IllegalArgumentException if {@code leadingArgCount} is not in
4408 * the range from 0 to {@code type.parameterCount()} inclusive,
4409 * or if the resulting method handle's type would have
4410 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4411 */
4412 public static MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
4413 if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
4414 throw newIllegalArgumentException("bad argument count", leadingArgCount);
4415 type = type.asSpreaderType(Object[].class, leadingArgCount, type.parameterCount() - leadingArgCount);
4416 return type.invokers().spreadInvoker(leadingArgCount);
4417 }
4418
4419 /**
4420 * Produces a special <em>invoker method handle</em> which can be used to
4421 * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
4422 * The resulting invoker will have a type which is
4423 * exactly equal to the desired type, except that it will accept
4424 * an additional leading argument of type {@code MethodHandle}.
4425 * <p>
4426 * This method is equivalent to the following code (though it may be more efficient):
4427 * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)}
4428 *
4429 * <p style="font-size:smaller;">
4430 * <em>Discussion:</em>
4431 * Invoker method handles can be useful when working with variable method handles
4432 * of unknown types.
4433 * For example, to emulate an {@code invokeExact} call to a variable method
4434 * handle {@code M}, extract its type {@code T},
4435 * look up the invoker method {@code X} for {@code T},
4436 * and call the invoker method, as {@code X.invoke(T, A...)}.
4437 * (It would not work to call {@code X.invokeExact}, since the type {@code T}
4438 * is unknown.)
4439 * If spreading, collecting, or other argument transformations are required,
4440 * they can be applied once to the invoker {@code X} and reused on many {@code M}
4441 * method handle values, as long as they are compatible with the type of {@code X}.
4442 * <p style="font-size:smaller;">
4443 * <em>(Note: The invoker method is not available via the Core Reflection API.
4444 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
4445 * on the declared {@code invokeExact} or {@code invoke} method will raise an
4446 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
4447 * <p>
4448 * This method throws no reflective exceptions.
4449 * @param type the desired target type
4450 * @return a method handle suitable for invoking any method handle of the given type
4451 * @throws IllegalArgumentException if the resulting method handle's type would have
4452 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4453 */
4454 public static MethodHandle exactInvoker(MethodType type) {
4455 return type.invokers().exactInvoker();
4456 }
4457
4458 /**
4459 * Produces a special <em>invoker method handle</em> which can be used to
4460 * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
4461 * The resulting invoker will have a type which is
4462 * exactly equal to the desired type, except that it will accept
4463 * an additional leading argument of type {@code MethodHandle}.
4464 * <p>
4465 * Before invoking its target, if the target differs from the expected type,
4466 * the invoker will apply reference casts as
4467 * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
4468 * Similarly, the return value will be converted as necessary.
4469 * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
4470 * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
4471 * <p>
4472 * This method is equivalent to the following code (though it may be more efficient):
4473 * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)}
4474 * <p style="font-size:smaller;">
4475 * <em>Discussion:</em>
4476 * A {@linkplain MethodType#genericMethodType general method type} is one which
4477 * mentions only {@code Object} arguments and return values.
4478 * An invoker for such a type is capable of calling any method handle
4479 * of the same arity as the general type.
4480 * <p style="font-size:smaller;">
4481 * <em>(Note: The invoker method is not available via the Core Reflection API.
4482 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
4483 * on the declared {@code invokeExact} or {@code invoke} method will raise an
4484 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
4485 * <p>
4486 * This method throws no reflective exceptions.
4487 * @param type the desired target type
4488 * @return a method handle suitable for invoking any method handle convertible to the given type
4489 * @throws IllegalArgumentException if the resulting method handle's type would have
4490 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4491 */
4492 public static MethodHandle invoker(MethodType type) {
4493 return type.invokers().genericInvoker();
4494 }
4495
4496 /**
4497 * Produces a special <em>invoker method handle</em> which can be used to
4498 * invoke a signature-polymorphic access mode method on any VarHandle whose
4499 * associated access mode type is compatible with the given type.
4500 * The resulting invoker will have a type which is exactly equal to the
4501 * desired given type, except that it will accept an additional leading
4502 * argument of type {@code VarHandle}.
4503 *
4504 * @param accessMode the VarHandle access mode
4505 * @param type the desired target type
4506 * @return a method handle suitable for invoking an access mode method of
4507 * any VarHandle whose access mode type is of the given type.
4508 * @since 9
4509 */
4510 public static MethodHandle varHandleExactInvoker(VarHandle.AccessMode accessMode, MethodType type) {
4511 return type.invokers().varHandleMethodExactInvoker(accessMode);
4512 }
4513
4514 /**
4515 * Produces a special <em>invoker method handle</em> which can be used to
4516 * invoke a signature-polymorphic access mode method on any VarHandle whose
4517 * associated access mode type is compatible with the given type.
4518 * The resulting invoker will have a type which is exactly equal to the
4519 * desired given type, except that it will accept an additional leading
4520 * argument of type {@code VarHandle}.
4521 * <p>
4522 * Before invoking its target, if the access mode type differs from the
4523 * desired given type, the invoker will apply reference casts as necessary
4524 * and box, unbox, or widen primitive values, as if by
4525 * {@link MethodHandle#asType asType}. Similarly, the return value will be
4526 * converted as necessary.
4527 * <p>
4528 * This method is equivalent to the following code (though it may be more
4529 * efficient): {@code publicLookup().findVirtual(VarHandle.class, accessMode.name(), type)}
4530 *
4531 * @param accessMode the VarHandle access mode
4532 * @param type the desired target type
4533 * @return a method handle suitable for invoking an access mode method of
4534 * any VarHandle whose access mode type is convertible to the given
4535 * type.
4536 * @since 9
4537 */
4538 public static MethodHandle varHandleInvoker(VarHandle.AccessMode accessMode, MethodType type) {
4539 return type.invokers().varHandleMethodInvoker(accessMode);
4540 }
4541
4542 /*non-public*/
4543 static MethodHandle basicInvoker(MethodType type) {
4544 return type.invokers().basicInvoker();
4545 }
4546
4547 //--- method handle modification (creation from other method handles)
4548
4549 /**
4550 * Produces a method handle which adapts the type of the
4551 * given method handle to a new type by pairwise argument and return type conversion.
4552 * The original type and new type must have the same number of arguments.
4553 * The resulting method handle is guaranteed to report a type
4554 * which is equal to the desired new type.
4555 * <p>
4556 * If the original type and new type are equal, returns target.
4557 * <p>
4558 * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
4559 * and some additional conversions are also applied if those conversions fail.
4560 * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied
4561 * if possible, before or instead of any conversions done by {@code asType}:
4562 * <ul>
4563 * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type,
4564 * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast.
4565 * (This treatment of interfaces follows the usage of the bytecode verifier.)
4566 * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive,
4567 * the boolean is converted to a byte value, 1 for true, 0 for false.
4568 * (This treatment follows the usage of the bytecode verifier.)
4569 * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive,
4570 * <em>T0</em> is converted to byte via Java casting conversion (JLS {@jls 5.5}),
4571 * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}.
4572 * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean,
4573 * then a Java casting conversion (JLS {@jls 5.5}) is applied.
4574 * (Specifically, <em>T0</em> will convert to <em>T1</em> by
4575 * widening and/or narrowing.)
4576 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
4577 * conversion will be applied at runtime, possibly followed
4578 * by a Java casting conversion (JLS {@jls 5.5}) on the primitive value,
4579 * possibly followed by a conversion from byte to boolean by testing
4580 * the low-order bit.
4581 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive,
4582 * and if the reference is null at runtime, a zero value is introduced.
4583 * </ul>
4584 * @param target the method handle to invoke after arguments are retyped
4585 * @param newType the expected type of the new method handle
4586 * @return a method handle which delegates to the target after performing
4587 * any necessary argument conversions, and arranges for any
4588 * necessary return value conversions
4589 * @throws NullPointerException if either argument is null
4590 * @throws WrongMethodTypeException if the conversion cannot be made
4591 * @see MethodHandle#asType
4592 */
4593 public static MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
4594 explicitCastArgumentsChecks(target, newType);
4595 // use the asTypeCache when possible:
4596 MethodType oldType = target.type();
4597 if (oldType == newType) return target;
4598 if (oldType.explicitCastEquivalentToAsType(newType)) {
4599 return target.asFixedArity().asType(newType);
4600 }
4601 return MethodHandleImpl.makePairwiseConvert(target, newType, false);
4602 }
4603
4604 private static void explicitCastArgumentsChecks(MethodHandle target, MethodType newType) {
4605 if (target.type().parameterCount() != newType.parameterCount()) {
4606 throw new WrongMethodTypeException("cannot explicitly cast " + target + " to " + newType);
4607 }
4608 }
4609
4610 /**
4611 * Produces a method handle which adapts the calling sequence of the
4612 * given method handle to a new type, by reordering the arguments.
4613 * The resulting method handle is guaranteed to report a type
4614 * which is equal to the desired new type.
4615 * <p>
4616 * The given array controls the reordering.
4617 * Call {@code #I} the number of incoming parameters (the value
4618 * {@code newType.parameterCount()}, and call {@code #O} the number
4619 * of outgoing parameters (the value {@code target.type().parameterCount()}).
4620 * Then the length of the reordering array must be {@code #O},
4621 * and each element must be a non-negative number less than {@code #I}.
4622 * For every {@code N} less than {@code #O}, the {@code N}-th
4623 * outgoing argument will be taken from the {@code I}-th incoming
4624 * argument, where {@code I} is {@code reorder[N]}.
4625 * <p>
4626 * No argument or return value conversions are applied.
4627 * The type of each incoming argument, as determined by {@code newType},
4628 * must be identical to the type of the corresponding outgoing parameter
4629 * or parameters in the target method handle.
4630 * The return type of {@code newType} must be identical to the return
4631 * type of the original target.
4632 * <p>
4633 * The reordering array need not specify an actual permutation.
4634 * An incoming argument will be duplicated if its index appears
4635 * more than once in the array, and an incoming argument will be dropped
4636 * if its index does not appear in the array.
4637 * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
4638 * incoming arguments which are not mentioned in the reordering array
4639 * may be of any type, as determined only by {@code newType}.
4640 * {@snippet lang="java" :
4641 import static java.lang.invoke.MethodHandles.*;
4642 import static java.lang.invoke.MethodType.*;
4643 ...
4644 MethodType intfn1 = methodType(int.class, int.class);
4645 MethodType intfn2 = methodType(int.class, int.class, int.class);
4646 MethodHandle sub = ... (int x, int y) -> (x-y) ...;
4647 assert(sub.type().equals(intfn2));
4648 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
4649 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
4650 assert((int)rsub.invokeExact(1, 100) == 99);
4651 MethodHandle add = ... (int x, int y) -> (x+y) ...;
4652 assert(add.type().equals(intfn2));
4653 MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
4654 assert(twice.type().equals(intfn1));
4655 assert((int)twice.invokeExact(21) == 42);
4656 * }
4657 * <p>
4658 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4659 * variable-arity method handle}, even if the original target method handle was.
4660 * @param target the method handle to invoke after arguments are reordered
4661 * @param newType the expected type of the new method handle
4662 * @param reorder an index array which controls the reordering
4663 * @return a method handle which delegates to the target after it
4664 * drops unused arguments and moves and/or duplicates the other arguments
4665 * @throws NullPointerException if any argument is null
4666 * @throws IllegalArgumentException if the index array length is not equal to
4667 * the arity of the target, or if any index array element
4668 * not a valid index for a parameter of {@code newType},
4669 * or if two corresponding parameter types in
4670 * {@code target.type()} and {@code newType} are not identical,
4671 */
4672 public static MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
4673 reorder = reorder.clone(); // get a private copy
4674 MethodType oldType = target.type();
4675 permuteArgumentChecks(reorder, newType, oldType);
4676 // first detect dropped arguments and handle them separately
4677 int[] originalReorder = reorder;
4678 BoundMethodHandle result = target.rebind();
4679 LambdaForm form = result.form;
4680 int newArity = newType.parameterCount();
4681 // Normalize the reordering into a real permutation,
4682 // by removing duplicates and adding dropped elements.
4683 // This somewhat improves lambda form caching, as well
4684 // as simplifying the transform by breaking it up into steps.
4685 for (int ddIdx; (ddIdx = findFirstDupOrDrop(reorder, newArity)) != 0; ) {
4686 if (ddIdx > 0) {
4687 // We found a duplicated entry at reorder[ddIdx].
4688 // Example: (x,y,z)->asList(x,y,z)
4689 // permuted by [1*,0,1] => (a0,a1)=>asList(a1,a0,a1)
4690 // permuted by [0,1,0*] => (a0,a1)=>asList(a0,a1,a0)
4691 // The starred element corresponds to the argument
4692 // deleted by the dupArgumentForm transform.
4693 int srcPos = ddIdx, dstPos = srcPos, dupVal = reorder[srcPos];
4694 boolean killFirst = false;
4695 for (int val; (val = reorder[--dstPos]) != dupVal; ) {
4696 // Set killFirst if the dup is larger than an intervening position.
4697 // This will remove at least one inversion from the permutation.
4698 if (dupVal > val) killFirst = true;
4699 }
4700 if (!killFirst) {
4701 srcPos = dstPos;
4702 dstPos = ddIdx;
4703 }
4704 form = form.editor().dupArgumentForm(1 + srcPos, 1 + dstPos);
4705 assert (reorder[srcPos] == reorder[dstPos]);
4706 oldType = oldType.dropParameterTypes(dstPos, dstPos + 1);
4707 // contract the reordering by removing the element at dstPos
4708 int tailPos = dstPos + 1;
4709 System.arraycopy(reorder, tailPos, reorder, dstPos, reorder.length - tailPos);
4710 reorder = Arrays.copyOf(reorder, reorder.length - 1);
4711 } else {
4712 int dropVal = ~ddIdx, insPos = 0;
4713 while (insPos < reorder.length && reorder[insPos] < dropVal) {
4714 // Find first element of reorder larger than dropVal.
4715 // This is where we will insert the dropVal.
4716 insPos += 1;
4717 }
4718 Class<?> ptype = newType.parameterType(dropVal);
4719 form = form.editor().addArgumentForm(1 + insPos, BasicType.basicType(ptype));
4720 oldType = oldType.insertParameterTypes(insPos, ptype);
4721 // expand the reordering by inserting an element at insPos
4722 int tailPos = insPos + 1;
4723 reorder = Arrays.copyOf(reorder, reorder.length + 1);
4724 System.arraycopy(reorder, insPos, reorder, tailPos, reorder.length - tailPos);
4725 reorder[insPos] = dropVal;
4726 }
4727 assert (permuteArgumentChecks(reorder, newType, oldType));
4728 }
4729 assert (reorder.length == newArity); // a perfect permutation
4730 // Note: This may cache too many distinct LFs. Consider backing off to varargs code.
4731 form = form.editor().permuteArgumentsForm(1, reorder);
4732 if (newType == result.type() && form == result.internalForm())
4733 return result;
4734 return result.copyWith(newType, form);
4735 }
4736
4737 /**
4738 * Return an indication of any duplicate or omission in reorder.
4739 * If the reorder contains a duplicate entry, return the index of the second occurrence.
4740 * Otherwise, return ~(n), for the first n in [0..newArity-1] that is not present in reorder.
4741 * Otherwise, return zero.
4742 * If an element not in [0..newArity-1] is encountered, return reorder.length.
4743 */
4744 private static int findFirstDupOrDrop(int[] reorder, int newArity) {
4745 final int BIT_LIMIT = 63; // max number of bits in bit mask
4746 if (newArity < BIT_LIMIT) {
4747 long mask = 0;
4748 for (int i = 0; i < reorder.length; i++) {
4749 int arg = reorder[i];
4750 if (arg >= newArity) {
4751 return reorder.length;
4752 }
4753 long bit = 1L << arg;
4754 if ((mask & bit) != 0) {
4755 return i; // >0 indicates a dup
4756 }
4757 mask |= bit;
4758 }
4759 if (mask == (1L << newArity) - 1) {
4760 assert(Long.numberOfTrailingZeros(Long.lowestOneBit(~mask)) == newArity);
4761 return 0;
4762 }
4763 // find first zero
4764 long zeroBit = Long.lowestOneBit(~mask);
4765 int zeroPos = Long.numberOfTrailingZeros(zeroBit);
4766 assert(zeroPos <= newArity);
4767 if (zeroPos == newArity) {
4768 return 0;
4769 }
4770 return ~zeroPos;
4771 } else {
4772 // same algorithm, different bit set
4773 BitSet mask = new BitSet(newArity);
4774 for (int i = 0; i < reorder.length; i++) {
4775 int arg = reorder[i];
4776 if (arg >= newArity) {
4777 return reorder.length;
4778 }
4779 if (mask.get(arg)) {
4780 return i; // >0 indicates a dup
4781 }
4782 mask.set(arg);
4783 }
4784 int zeroPos = mask.nextClearBit(0);
4785 assert(zeroPos <= newArity);
4786 if (zeroPos == newArity) {
4787 return 0;
4788 }
4789 return ~zeroPos;
4790 }
4791 }
4792
4793 static boolean permuteArgumentChecks(int[] reorder, MethodType newType, MethodType oldType) {
4794 if (newType.returnType() != oldType.returnType())
4795 throw newIllegalArgumentException("return types do not match",
4796 oldType, newType);
4797 if (reorder.length != oldType.parameterCount())
4798 throw newIllegalArgumentException("old type parameter count and reorder array length do not match",
4799 oldType, Arrays.toString(reorder));
4800
4801 int limit = newType.parameterCount();
4802 for (int j = 0; j < reorder.length; j++) {
4803 int i = reorder[j];
4804 if (i < 0 || i >= limit) {
4805 throw newIllegalArgumentException("index is out of bounds for new type",
4806 i, newType);
4807 }
4808 Class<?> src = newType.parameterType(i);
4809 Class<?> dst = oldType.parameterType(j);
4810 if (src != dst)
4811 throw newIllegalArgumentException("parameter types do not match after reorder",
4812 oldType, newType);
4813 }
4814 return true;
4815 }
4816
4817 /**
4818 * Produces a method handle of the requested return type which returns the given
4819 * constant value every time it is invoked.
4820 * <p>
4821 * Before the method handle is returned, the passed-in value is converted to the requested type.
4822 * If the requested type is primitive, widening primitive conversions are attempted,
4823 * else reference conversions are attempted.
4824 * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
4825 * @param type the return type of the desired method handle
4826 * @param value the value to return
4827 * @return a method handle of the given return type and no arguments, which always returns the given value
4828 * @throws NullPointerException if the {@code type} argument is null
4829 * @throws ClassCastException if the value cannot be converted to the required return type
4830 * @throws IllegalArgumentException if the given type is {@code void.class}
4831 */
4832 public static MethodHandle constant(Class<?> type, Object value) {
4833 if (Objects.requireNonNull(type) == void.class)
4834 throw newIllegalArgumentException("void type");
4835 return MethodHandleImpl.makeConstantReturning(type, value);
4836 }
4837
4838 /**
4839 * Produces a method handle which returns its sole argument when invoked.
4840 * @param type the type of the sole parameter and return value of the desired method handle
4841 * @return a unary method handle which accepts and returns the given type
4842 * @throws NullPointerException if the argument is null
4843 * @throws IllegalArgumentException if the given type is {@code void.class}
4844 */
4845 public static MethodHandle identity(Class<?> type) {
4846 Wrapper btw = (type.isPrimitive() ? Wrapper.forPrimitiveType(type) : Wrapper.OBJECT);
4847 int pos = btw.ordinal();
4848 MethodHandle ident = IDENTITY_MHS[pos];
4849 if (ident == null) {
4850 ident = setCachedMethodHandle(IDENTITY_MHS, pos, makeIdentity(btw.primitiveType()));
4851 }
4852 if (ident.type().returnType() == type)
4853 return ident;
4854 // something like identity(Foo.class); do not bother to intern these
4855 assert (btw == Wrapper.OBJECT);
4856 return makeIdentity(type);
4857 }
4858
4859 /**
4860 * Produces a constant method handle of the requested return type which
4861 * returns the default value for that type every time it is invoked.
4862 * The resulting constant method handle will have no side effects.
4863 * <p>The returned method handle is equivalent to {@code empty(methodType(type))}.
4864 * It is also equivalent to {@code explicitCastArguments(constant(Object.class, null), methodType(type))},
4865 * since {@code explicitCastArguments} converts {@code null} to default values.
4866 * @param type the expected return type of the desired method handle
4867 * @return a constant method handle that takes no arguments
4868 * and returns the default value of the given type (or void, if the type is void)
4869 * @throws NullPointerException if the argument is null
4870 * @see MethodHandles#constant
4871 * @see MethodHandles#empty
4872 * @see MethodHandles#explicitCastArguments
4873 * @since 9
4874 */
4875 public static MethodHandle zero(Class<?> type) {
4876 Objects.requireNonNull(type);
4877 return type.isPrimitive() ? primitiveZero(Wrapper.forPrimitiveType(type))
4878 : MethodHandleImpl.makeConstantReturning(type, null);
4879 }
4880
4881 private static MethodHandle identityOrVoid(Class<?> type) {
4882 return type == void.class ? zero(type) : identity(type);
4883 }
4884
4885 /**
4886 * Produces a method handle of the requested type which ignores any arguments, does nothing,
4887 * and returns a suitable default depending on the return type.
4888 * That is, it returns a zero primitive value, a {@code null}, or {@code void}.
4889 * <p>The returned method handle is equivalent to
4890 * {@code dropArguments(zero(type.returnType()), 0, type.parameterList())}.
4891 *
4892 * @apiNote Given a predicate and target, a useful "if-then" construct can be produced as
4893 * {@code guardWithTest(pred, target, empty(target.type())}.
4894 * @param type the type of the desired method handle
4895 * @return a constant method handle of the given type, which returns a default value of the given return type
4896 * @throws NullPointerException if the argument is null
4897 * @see MethodHandles#primitiveZero
4898 * @see MethodHandles#constant
4899 * @since 9
4900 */
4901 public static MethodHandle empty(MethodType type) {
4902 Objects.requireNonNull(type);
4903 return dropArgumentsTrusted(zero(type.returnType()), 0, type.ptypes());
4904 }
4905
4906 private static final MethodHandle[] IDENTITY_MHS = new MethodHandle[Wrapper.COUNT];
4907 private static MethodHandle makeIdentity(Class<?> ptype) {
4908 MethodType mtype = methodType(ptype, ptype); // throws IAE for void
4909 LambdaForm lform = LambdaForm.identityForm(BasicType.basicType(ptype));
4910 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.IDENTITY);
4911 }
4912
4913 private static MethodHandle primitiveZero(Wrapper w) {
4914 assert w != Wrapper.OBJECT : w;
4915 int pos = w.ordinal();
4916 MethodHandle mh = PRIMITIVE_ZERO_MHS[pos];
4917 if (mh == null) {
4918 mh = setCachedMethodHandle(PRIMITIVE_ZERO_MHS, pos, makePrimitiveZero(w));
4919 }
4920 assert (mh.type().returnType() == w.primitiveType()) : mh;
4921 return mh;
4922 }
4923
4924 private static MethodHandle makePrimitiveZero(Wrapper w) {
4925 if (w == Wrapper.VOID) {
4926 var lf = LambdaForm.identityForm(V_TYPE); // ensures BMH & SimpleMH are initialized
4927 return SimpleMethodHandle.make(MethodType.methodType(void.class), lf);
4928 } else {
4929 return MethodHandleImpl.makeConstantReturning(w.primitiveType(), w.zero());
4930 }
4931 }
4932
4933 private static final @Stable MethodHandle[] PRIMITIVE_ZERO_MHS = new MethodHandle[Wrapper.COUNT];
4934
4935 private static synchronized MethodHandle setCachedMethodHandle(MethodHandle[] cache, int pos, MethodHandle value) {
4936 // Simulate a CAS, to avoid racy duplication of results.
4937 MethodHandle prev = cache[pos];
4938 if (prev != null) return prev;
4939 return cache[pos] = value;
4940 }
4941
4942 /**
4943 * Provides a target method handle with one or more <em>bound arguments</em>
4944 * in advance of the method handle's invocation.
4945 * The formal parameters to the target corresponding to the bound
4946 * arguments are called <em>bound parameters</em>.
4947 * Returns a new method handle which saves away the bound arguments.
4948 * When it is invoked, it receives arguments for any non-bound parameters,
4949 * binds the saved arguments to their corresponding parameters,
4950 * and calls the original target.
4951 * <p>
4952 * The type of the new method handle will drop the types for the bound
4953 * parameters from the original target type, since the new method handle
4954 * will no longer require those arguments to be supplied by its callers.
4955 * <p>
4956 * Each given argument object must match the corresponding bound parameter type.
4957 * If a bound parameter type is a primitive, the argument object
4958 * must be a wrapper, and will be unboxed to produce the primitive value.
4959 * <p>
4960 * The {@code pos} argument selects which parameters are to be bound.
4961 * It may range between zero and <i>N-L</i> (inclusively),
4962 * where <i>N</i> is the arity of the target method handle
4963 * and <i>L</i> is the length of the values array.
4964 * <p>
4965 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4966 * variable-arity method handle}, even if the original target method handle was.
4967 * @param target the method handle to invoke after the argument is inserted
4968 * @param pos where to insert the argument (zero for the first)
4969 * @param values the series of arguments to insert
4970 * @return a method handle which inserts an additional argument,
4971 * before calling the original method handle
4972 * @throws NullPointerException if the target or the {@code values} array is null
4973 * @throws IllegalArgumentException if {@code pos} is less than {@code 0} or greater than
4974 * {@code N - L} where {@code N} is the arity of the target method handle and {@code L}
4975 * is the length of the values array.
4976 * @throws ClassCastException if an argument does not match the corresponding bound parameter
4977 * type.
4978 * @see MethodHandle#bindTo
4979 */
4980 public static MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
4981 int insCount = values.length;
4982 Class<?>[] ptypes = insertArgumentsChecks(target, insCount, pos);
4983 if (insCount == 0) return target;
4984 BoundMethodHandle result = target.rebind();
4985 for (int i = 0; i < insCount; i++) {
4986 Object value = values[i];
4987 Class<?> ptype = ptypes[pos+i];
4988 if (ptype.isPrimitive()) {
4989 result = insertArgumentPrimitive(result, pos, ptype, value);
4990 } else {
4991 value = ptype.cast(value); // throw CCE if needed
4992 result = result.bindArgumentL(pos, value);
4993 }
4994 }
4995 return result;
4996 }
4997
4998 private static BoundMethodHandle insertArgumentPrimitive(BoundMethodHandle result, int pos,
4999 Class<?> ptype, Object value) {
5000 Wrapper w = Wrapper.forPrimitiveType(ptype);
5001 // perform unboxing and/or primitive conversion
5002 value = w.convert(value, ptype);
5003 return switch (w) {
5004 case INT -> result.bindArgumentI(pos, (int) value);
5005 case LONG -> result.bindArgumentJ(pos, (long) value);
5006 case FLOAT -> result.bindArgumentF(pos, (float) value);
5007 case DOUBLE -> result.bindArgumentD(pos, (double) value);
5008 default -> result.bindArgumentI(pos, ValueConversions.widenSubword(value));
5009 };
5010 }
5011
5012 private static Class<?>[] insertArgumentsChecks(MethodHandle target, int insCount, int pos) throws RuntimeException {
5013 MethodType oldType = target.type();
5014 int outargs = oldType.parameterCount();
5015 int inargs = outargs - insCount;
5016 if (inargs < 0)
5017 throw newIllegalArgumentException("too many values to insert");
5018 if (pos < 0 || pos > inargs)
5019 throw newIllegalArgumentException("no argument type to append");
5020 return oldType.ptypes();
5021 }
5022
5023 /**
5024 * Produces a method handle which will discard some dummy arguments
5025 * before calling some other specified <i>target</i> method handle.
5026 * The type of the new method handle will be the same as the target's type,
5027 * except it will also include the dummy argument types,
5028 * at some given position.
5029 * <p>
5030 * The {@code pos} argument may range between zero and <i>N</i>,
5031 * where <i>N</i> is the arity of the target.
5032 * If {@code pos} is zero, the dummy arguments will precede
5033 * the target's real arguments; if {@code pos} is <i>N</i>
5034 * they will come after.
5035 * <p>
5036 * <b>Example:</b>
5037 * {@snippet lang="java" :
5038 import static java.lang.invoke.MethodHandles.*;
5039 import static java.lang.invoke.MethodType.*;
5040 ...
5041 MethodHandle cat = lookup().findVirtual(String.class,
5042 "concat", methodType(String.class, String.class));
5043 assertEquals("xy", (String) cat.invokeExact("x", "y"));
5044 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
5045 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
5046 assertEquals(bigType, d0.type());
5047 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
5048 * }
5049 * <p>
5050 * This method is also equivalent to the following code:
5051 * <blockquote><pre>
5052 * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))}
5053 * </pre></blockquote>
5054 * @param target the method handle to invoke after the arguments are dropped
5055 * @param pos position of first argument to drop (zero for the leftmost)
5056 * @param valueTypes the type(s) of the argument(s) to drop
5057 * @return a method handle which drops arguments of the given types,
5058 * before calling the original method handle
5059 * @throws NullPointerException if the target is null,
5060 * or if the {@code valueTypes} list or any of its elements is null
5061 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
5062 * or if {@code pos} is negative or greater than the arity of the target,
5063 * or if the new method handle's type would have too many parameters
5064 */
5065 public static MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) {
5066 return dropArgumentsTrusted(target, pos, valueTypes.toArray(new Class<?>[0]).clone());
5067 }
5068
5069 static MethodHandle dropArgumentsTrusted(MethodHandle target, int pos, Class<?>[] valueTypes) {
5070 MethodType oldType = target.type(); // get NPE
5071 int dropped = dropArgumentChecks(oldType, pos, valueTypes);
5072 MethodType newType = oldType.insertParameterTypes(pos, valueTypes);
5073 if (dropped == 0) return target;
5074 BoundMethodHandle result = target.rebind();
5075 LambdaForm lform = result.form;
5076 int insertFormArg = 1 + pos;
5077 for (Class<?> ptype : valueTypes) {
5078 lform = lform.editor().addArgumentForm(insertFormArg++, BasicType.basicType(ptype));
5079 }
5080 result = result.copyWith(newType, lform);
5081 return result;
5082 }
5083
5084 private static int dropArgumentChecks(MethodType oldType, int pos, Class<?>[] valueTypes) {
5085 int dropped = valueTypes.length;
5086 MethodType.checkSlotCount(dropped);
5087 int outargs = oldType.parameterCount();
5088 int inargs = outargs + dropped;
5089 if (pos < 0 || pos > outargs)
5090 throw newIllegalArgumentException("no argument type to remove"
5091 + Arrays.asList(oldType, pos, valueTypes, inargs, outargs)
5092 );
5093 return dropped;
5094 }
5095
5096 /**
5097 * Produces a method handle which will discard some dummy arguments
5098 * before calling some other specified <i>target</i> method handle.
5099 * The type of the new method handle will be the same as the target's type,
5100 * except it will also include the dummy argument types,
5101 * at some given position.
5102 * <p>
5103 * The {@code pos} argument may range between zero and <i>N</i>,
5104 * where <i>N</i> is the arity of the target.
5105 * If {@code pos} is zero, the dummy arguments will precede
5106 * the target's real arguments; if {@code pos} is <i>N</i>
5107 * they will come after.
5108 * @apiNote
5109 * {@snippet lang="java" :
5110 import static java.lang.invoke.MethodHandles.*;
5111 import static java.lang.invoke.MethodType.*;
5112 ...
5113 MethodHandle cat = lookup().findVirtual(String.class,
5114 "concat", methodType(String.class, String.class));
5115 assertEquals("xy", (String) cat.invokeExact("x", "y"));
5116 MethodHandle d0 = dropArguments(cat, 0, String.class);
5117 assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
5118 MethodHandle d1 = dropArguments(cat, 1, String.class);
5119 assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
5120 MethodHandle d2 = dropArguments(cat, 2, String.class);
5121 assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
5122 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
5123 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
5124 * }
5125 * <p>
5126 * This method is also equivalent to the following code:
5127 * <blockquote><pre>
5128 * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))}
5129 * </pre></blockquote>
5130 * @param target the method handle to invoke after the arguments are dropped
5131 * @param pos position of first argument to drop (zero for the leftmost)
5132 * @param valueTypes the type(s) of the argument(s) to drop
5133 * @return a method handle which drops arguments of the given types,
5134 * before calling the original method handle
5135 * @throws NullPointerException if the target is null,
5136 * or if the {@code valueTypes} array or any of its elements is null
5137 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
5138 * or if {@code pos} is negative or greater than the arity of the target,
5139 * or if the new method handle's type would have
5140 * <a href="MethodHandle.html#maxarity">too many parameters</a>
5141 */
5142 public static MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
5143 return dropArgumentsTrusted(target, pos, valueTypes.clone());
5144 }
5145
5146 /* Convenience overloads for trusting internal low-arity call-sites */
5147 static MethodHandle dropArguments(MethodHandle target, int pos, Class<?> valueType1) {
5148 return dropArgumentsTrusted(target, pos, new Class<?>[] { valueType1 });
5149 }
5150 static MethodHandle dropArguments(MethodHandle target, int pos, Class<?> valueType1, Class<?> valueType2) {
5151 return dropArgumentsTrusted(target, pos, new Class<?>[] { valueType1, valueType2 });
5152 }
5153
5154 // private version which allows caller some freedom with error handling
5155 private static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, Class<?>[] newTypes, int pos,
5156 boolean nullOnFailure) {
5157 Class<?>[] oldTypes = target.type().ptypes();
5158 int match = oldTypes.length;
5159 if (skip != 0) {
5160 if (skip < 0 || skip > match) {
5161 throw newIllegalArgumentException("illegal skip", skip, target);
5162 }
5163 oldTypes = Arrays.copyOfRange(oldTypes, skip, match);
5164 match -= skip;
5165 }
5166 Class<?>[] addTypes = newTypes;
5167 int add = addTypes.length;
5168 if (pos != 0) {
5169 if (pos < 0 || pos > add) {
5170 throw newIllegalArgumentException("illegal pos", pos, Arrays.toString(newTypes));
5171 }
5172 addTypes = Arrays.copyOfRange(addTypes, pos, add);
5173 add -= pos;
5174 assert(addTypes.length == add);
5175 }
5176 // Do not add types which already match the existing arguments.
5177 if (match > add || !Arrays.equals(oldTypes, 0, oldTypes.length, addTypes, 0, match)) {
5178 if (nullOnFailure) {
5179 return null;
5180 }
5181 throw newIllegalArgumentException("argument lists do not match",
5182 Arrays.toString(oldTypes), Arrays.toString(newTypes));
5183 }
5184 addTypes = Arrays.copyOfRange(addTypes, match, add);
5185 add -= match;
5186 assert(addTypes.length == add);
5187 // newTypes: ( P*[pos], M*[match], A*[add] )
5188 // target: ( S*[skip], M*[match] )
5189 MethodHandle adapter = target;
5190 if (add > 0) {
5191 adapter = dropArgumentsTrusted(adapter, skip+ match, addTypes);
5192 }
5193 // adapter: (S*[skip], M*[match], A*[add] )
5194 if (pos > 0) {
5195 adapter = dropArgumentsTrusted(adapter, skip, Arrays.copyOfRange(newTypes, 0, pos));
5196 }
5197 // adapter: (S*[skip], P*[pos], M*[match], A*[add] )
5198 return adapter;
5199 }
5200
5201 /**
5202 * Adapts a target method handle to match the given parameter type list. If necessary, adds dummy arguments. Some
5203 * leading parameters can be skipped before matching begins. The remaining types in the {@code target}'s parameter
5204 * type list must be a sub-list of the {@code newTypes} type list at the starting position {@code pos}. The
5205 * resulting handle will have the target handle's parameter type list, with any non-matching parameter types (before
5206 * or after the matching sub-list) inserted in corresponding positions of the target's original parameters, as if by
5207 * {@link #dropArguments(MethodHandle, int, Class[])}.
5208 * <p>
5209 * The resulting handle will have the same return type as the target handle.
5210 * <p>
5211 * In more formal terms, assume these two type lists:<ul>
5212 * <li>The target handle has the parameter type list {@code S..., M...}, with as many types in {@code S} as
5213 * indicated by {@code skip}. The {@code M} types are those that are supposed to match part of the given type list,
5214 * {@code newTypes}.
5215 * <li>The {@code newTypes} list contains types {@code P..., M..., A...}, with as many types in {@code P} as
5216 * indicated by {@code pos}. The {@code M} types are precisely those that the {@code M} types in the target handle's
5217 * parameter type list are supposed to match. The types in {@code A} are additional types found after the matching
5218 * sub-list.
5219 * </ul>
5220 * Given these assumptions, the result of an invocation of {@code dropArgumentsToMatch} will have the parameter type
5221 * list {@code S..., P..., M..., A...}, with the {@code P} and {@code A} types inserted as if by
5222 * {@link #dropArguments(MethodHandle, int, Class[])}.
5223 *
5224 * @apiNote
5225 * Two method handles whose argument lists are "effectively identical" (i.e., identical in a common prefix) may be
5226 * mutually converted to a common type by two calls to {@code dropArgumentsToMatch}, as follows:
5227 * {@snippet lang="java" :
5228 import static java.lang.invoke.MethodHandles.*;
5229 import static java.lang.invoke.MethodType.*;
5230 ...
5231 ...
5232 MethodHandle h0 = constant(boolean.class, true);
5233 MethodHandle h1 = lookup().findVirtual(String.class, "concat", methodType(String.class, String.class));
5234 MethodType bigType = h1.type().insertParameterTypes(1, String.class, int.class);
5235 MethodHandle h2 = dropArguments(h1, 0, bigType.parameterList());
5236 if (h1.type().parameterCount() < h2.type().parameterCount())
5237 h1 = dropArgumentsToMatch(h1, 0, h2.type().parameterList(), 0); // lengthen h1
5238 else
5239 h2 = dropArgumentsToMatch(h2, 0, h1.type().parameterList(), 0); // lengthen h2
5240 MethodHandle h3 = guardWithTest(h0, h1, h2);
5241 assertEquals("xy", h3.invoke("x", "y", 1, "a", "b", "c"));
5242 * }
5243 * @param target the method handle to adapt
5244 * @param skip number of targets parameters to disregard (they will be unchanged)
5245 * @param newTypes the list of types to match {@code target}'s parameter type list to
5246 * @param pos place in {@code newTypes} where the non-skipped target parameters must occur
5247 * @return a possibly adapted method handle
5248 * @throws NullPointerException if either argument is null
5249 * @throws IllegalArgumentException if any element of {@code newTypes} is {@code void.class},
5250 * or if {@code skip} is negative or greater than the arity of the target,
5251 * or if {@code pos} is negative or greater than the newTypes list size,
5252 * or if {@code newTypes} does not contain the {@code target}'s non-skipped parameter types at position
5253 * {@code pos}.
5254 * @since 9
5255 */
5256 public static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos) {
5257 Objects.requireNonNull(target);
5258 Objects.requireNonNull(newTypes);
5259 return dropArgumentsToMatch(target, skip, newTypes.toArray(new Class<?>[0]).clone(), pos, false);
5260 }
5261
5262 /**
5263 * Drop the return value of the target handle (if any).
5264 * The returned method handle will have a {@code void} return type.
5265 *
5266 * @param target the method handle to adapt
5267 * @return a possibly adapted method handle
5268 * @throws NullPointerException if {@code target} is null
5269 * @since 16
5270 */
5271 public static MethodHandle dropReturn(MethodHandle target) {
5272 Objects.requireNonNull(target);
5273 MethodType oldType = target.type();
5274 Class<?> oldReturnType = oldType.returnType();
5275 if (oldReturnType == void.class)
5276 return target;
5277 MethodType newType = oldType.changeReturnType(void.class);
5278 BoundMethodHandle result = target.rebind();
5279 LambdaForm lform = result.editor().filterReturnForm(V_TYPE, true);
5280 result = result.copyWith(newType, lform);
5281 return result;
5282 }
5283
5284 /**
5285 * Adapts a target method handle by pre-processing
5286 * one or more of its arguments, each with its own unary filter function,
5287 * and then calling the target with each pre-processed argument
5288 * replaced by the result of its corresponding filter function.
5289 * <p>
5290 * The pre-processing is performed by one or more method handles,
5291 * specified in the elements of the {@code filters} array.
5292 * The first element of the filter array corresponds to the {@code pos}
5293 * argument of the target, and so on in sequence.
5294 * The filter functions are invoked in left to right order.
5295 * <p>
5296 * Null arguments in the array are treated as identity functions,
5297 * and the corresponding arguments left unchanged.
5298 * (If there are no non-null elements in the array, the original target is returned.)
5299 * Each filter is applied to the corresponding argument of the adapter.
5300 * <p>
5301 * If a filter {@code F} applies to the {@code N}th argument of
5302 * the target, then {@code F} must be a method handle which
5303 * takes exactly one argument. The type of {@code F}'s sole argument
5304 * replaces the corresponding argument type of the target
5305 * in the resulting adapted method handle.
5306 * The return type of {@code F} must be identical to the corresponding
5307 * parameter type of the target.
5308 * <p>
5309 * It is an error if there are elements of {@code filters}
5310 * (null or not)
5311 * which do not correspond to argument positions in the target.
5312 * <p><b>Example:</b>
5313 * {@snippet lang="java" :
5314 import static java.lang.invoke.MethodHandles.*;
5315 import static java.lang.invoke.MethodType.*;
5316 ...
5317 MethodHandle cat = lookup().findVirtual(String.class,
5318 "concat", methodType(String.class, String.class));
5319 MethodHandle upcase = lookup().findVirtual(String.class,
5320 "toUpperCase", methodType(String.class));
5321 assertEquals("xy", (String) cat.invokeExact("x", "y"));
5322 MethodHandle f0 = filterArguments(cat, 0, upcase);
5323 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
5324 MethodHandle f1 = filterArguments(cat, 1, upcase);
5325 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
5326 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
5327 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
5328 * }
5329 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
5330 * denotes the return type of both the {@code target} and resulting adapter.
5331 * {@code P}/{@code p} and {@code B}/{@code b} represent the types and values
5332 * of the parameters and arguments that precede and follow the filter position
5333 * {@code pos}, respectively. {@code A[i]}/{@code a[i]} stand for the types and
5334 * values of the filtered parameters and arguments; they also represent the
5335 * return types of the {@code filter[i]} handles. The latter accept arguments
5336 * {@code v[i]} of type {@code V[i]}, which also appear in the signature of
5337 * the resulting adapter.
5338 * {@snippet lang="java" :
5339 * T target(P... p, A[i]... a[i], B... b);
5340 * A[i] filter[i](V[i]);
5341 * T adapter(P... p, V[i]... v[i], B... b) {
5342 * return target(p..., filter[i](v[i])..., b...);
5343 * }
5344 * }
5345 * <p>
5346 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5347 * variable-arity method handle}, even if the original target method handle was.
5348 *
5349 * @param target the method handle to invoke after arguments are filtered
5350 * @param pos the position of the first argument to filter
5351 * @param filters method handles to call initially on filtered arguments
5352 * @return method handle which incorporates the specified argument filtering logic
5353 * @throws NullPointerException if the target is null
5354 * or if the {@code filters} array is null
5355 * @throws IllegalArgumentException if a non-null element of {@code filters}
5356 * does not match a corresponding argument type of target as described above,
5357 * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()},
5358 * or if the resulting method handle's type would have
5359 * <a href="MethodHandle.html#maxarity">too many parameters</a>
5360 */
5361 public static MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
5362 // In method types arguments start at index 0, while the LF
5363 // editor have the MH receiver at position 0 - adjust appropriately.
5364 final int MH_RECEIVER_OFFSET = 1;
5365 filterArgumentsCheckArity(target, pos, filters);
5366 MethodHandle adapter = target;
5367
5368 // keep track of currently matched filters, as to optimize repeated filters
5369 int index = 0;
5370 int[] positions = new int[filters.length];
5371 MethodHandle filter = null;
5372
5373 // process filters in reverse order so that the invocation of
5374 // the resulting adapter will invoke the filters in left-to-right order
5375 for (int i = filters.length - 1; i >= 0; --i) {
5376 MethodHandle newFilter = filters[i];
5377 if (newFilter == null) continue; // ignore null elements of filters
5378
5379 // flush changes on update
5380 if (filter != newFilter) {
5381 if (filter != null) {
5382 if (index > 1) {
5383 adapter = filterRepeatedArgument(adapter, filter, Arrays.copyOf(positions, index));
5384 } else {
5385 adapter = filterArgument(adapter, positions[0] - 1, filter);
5386 }
5387 }
5388 filter = newFilter;
5389 index = 0;
5390 }
5391
5392 filterArgumentChecks(target, pos + i, newFilter);
5393 positions[index++] = pos + i + MH_RECEIVER_OFFSET;
5394 }
5395 if (index > 1) {
5396 adapter = filterRepeatedArgument(adapter, filter, Arrays.copyOf(positions, index));
5397 } else if (index == 1) {
5398 adapter = filterArgument(adapter, positions[0] - 1, filter);
5399 }
5400 return adapter;
5401 }
5402
5403 private static MethodHandle filterRepeatedArgument(MethodHandle adapter, MethodHandle filter, int[] positions) {
5404 MethodType targetType = adapter.type();
5405 MethodType filterType = filter.type();
5406 BoundMethodHandle result = adapter.rebind();
5407 Class<?> newParamType = filterType.parameterType(0);
5408
5409 Class<?>[] ptypes = targetType.ptypes().clone();
5410 for (int pos : positions) {
5411 ptypes[pos - 1] = newParamType;
5412 }
5413 MethodType newType = MethodType.methodType(targetType.rtype(), ptypes, true);
5414
5415 LambdaForm lform = result.editor().filterRepeatedArgumentForm(BasicType.basicType(newParamType), positions);
5416 return result.copyWithExtendL(newType, lform, filter);
5417 }
5418
5419 /*non-public*/
5420 static MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
5421 filterArgumentChecks(target, pos, filter);
5422 MethodType targetType = target.type();
5423 MethodType filterType = filter.type();
5424 BoundMethodHandle result = target.rebind();
5425 Class<?> newParamType = filterType.parameterType(0);
5426 LambdaForm lform = result.editor().filterArgumentForm(1 + pos, BasicType.basicType(newParamType));
5427 MethodType newType = targetType.changeParameterType(pos, newParamType);
5428 result = result.copyWithExtendL(newType, lform, filter);
5429 return result;
5430 }
5431
5432 private static void filterArgumentsCheckArity(MethodHandle target, int pos, MethodHandle[] filters) {
5433 MethodType targetType = target.type();
5434 int maxPos = targetType.parameterCount();
5435 if (pos + filters.length > maxPos)
5436 throw newIllegalArgumentException("too many filters");
5437 }
5438
5439 private static void filterArgumentChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
5440 MethodType targetType = target.type();
5441 MethodType filterType = filter.type();
5442 if (filterType.parameterCount() != 1
5443 || filterType.returnType() != targetType.parameterType(pos))
5444 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
5445 }
5446
5447 /**
5448 * Adapts a target method handle by pre-processing
5449 * a sub-sequence of its arguments with a filter (another method handle).
5450 * The pre-processed arguments are replaced by the result (if any) of the
5451 * filter function.
5452 * The target is then called on the modified (usually shortened) argument list.
5453 * <p>
5454 * If the filter returns a value, the target must accept that value as
5455 * its argument in position {@code pos}, preceded and/or followed by
5456 * any arguments not passed to the filter.
5457 * If the filter returns void, the target must accept all arguments
5458 * not passed to the filter.
5459 * No arguments are reordered, and a result returned from the filter
5460 * replaces (in order) the whole subsequence of arguments originally
5461 * passed to the adapter.
5462 * <p>
5463 * The argument types (if any) of the filter
5464 * replace zero or one argument types of the target, at position {@code pos},
5465 * in the resulting adapted method handle.
5466 * The return type of the filter (if any) must be identical to the
5467 * argument type of the target at position {@code pos}, and that target argument
5468 * is supplied by the return value of the filter.
5469 * <p>
5470 * In all cases, {@code pos} must be greater than or equal to zero, and
5471 * {@code pos} must also be less than or equal to the target's arity.
5472 * <p><b>Example:</b>
5473 * {@snippet lang="java" :
5474 import static java.lang.invoke.MethodHandles.*;
5475 import static java.lang.invoke.MethodType.*;
5476 ...
5477 MethodHandle deepToString = publicLookup()
5478 .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
5479
5480 MethodHandle ts1 = deepToString.asCollector(String[].class, 1);
5481 assertEquals("[strange]", (String) ts1.invokeExact("strange"));
5482
5483 MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
5484 assertEquals("[up, down]", (String) ts2.invokeExact("up", "down"));
5485
5486 MethodHandle ts3 = deepToString.asCollector(String[].class, 3);
5487 MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2);
5488 assertEquals("[top, [up, down], strange]",
5489 (String) ts3_ts2.invokeExact("top", "up", "down", "strange"));
5490
5491 MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1);
5492 assertEquals("[top, [up, down], [strange]]",
5493 (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange"));
5494
5495 MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3);
5496 assertEquals("[top, [[up, down, strange], charm], bottom]",
5497 (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom"));
5498 * }
5499 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
5500 * represents the return type of the {@code target} and resulting adapter.
5501 * {@code V}/{@code v} stand for the return type and value of the
5502 * {@code filter}, which are also found in the signature and arguments of
5503 * the {@code target}, respectively, unless {@code V} is {@code void}.
5504 * {@code A}/{@code a} and {@code C}/{@code c} represent the parameter types
5505 * and values preceding and following the collection position, {@code pos},
5506 * in the {@code target}'s signature. They also turn up in the resulting
5507 * adapter's signature and arguments, where they surround
5508 * {@code B}/{@code b}, which represent the parameter types and arguments
5509 * to the {@code filter} (if any).
5510 * {@snippet lang="java" :
5511 * T target(A...,V,C...);
5512 * V filter(B...);
5513 * T adapter(A... a,B... b,C... c) {
5514 * V v = filter(b...);
5515 * return target(a...,v,c...);
5516 * }
5517 * // and if the filter has no arguments:
5518 * T target2(A...,V,C...);
5519 * V filter2();
5520 * T adapter2(A... a,C... c) {
5521 * V v = filter2();
5522 * return target2(a...,v,c...);
5523 * }
5524 * // and if the filter has a void return:
5525 * T target3(A...,C...);
5526 * void filter3(B...);
5527 * T adapter3(A... a,B... b,C... c) {
5528 * filter3(b...);
5529 * return target3(a...,c...);
5530 * }
5531 * }
5532 * <p>
5533 * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to
5534 * one which first "folds" the affected arguments, and then drops them, in separate
5535 * steps as follows:
5536 * {@snippet lang="java" :
5537 * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2
5538 * mh = MethodHandles.foldArguments(mh, coll); //step 1
5539 * }
5540 * If the target method handle consumes no arguments besides than the result
5541 * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)}
5542 * is equivalent to {@code filterReturnValue(coll, mh)}.
5543 * If the filter method handle {@code coll} consumes one argument and produces
5544 * a non-void result, then {@code collectArguments(mh, N, coll)}
5545 * is equivalent to {@code filterArguments(mh, N, coll)}.
5546 * Other equivalences are possible but would require argument permutation.
5547 * <p>
5548 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5549 * variable-arity method handle}, even if the original target method handle was.
5550 *
5551 * @param target the method handle to invoke after filtering the subsequence of arguments
5552 * @param pos the position of the first adapter argument to pass to the filter,
5553 * and/or the target argument which receives the result of the filter
5554 * @param filter method handle to call on the subsequence of arguments
5555 * @return method handle which incorporates the specified argument subsequence filtering logic
5556 * @throws NullPointerException if either argument is null
5557 * @throws IllegalArgumentException if the return type of {@code filter}
5558 * is non-void and is not the same as the {@code pos} argument of the target,
5559 * or if {@code pos} is not between 0 and the target's arity, inclusive,
5560 * or if the resulting method handle's type would have
5561 * <a href="MethodHandle.html#maxarity">too many parameters</a>
5562 * @see MethodHandles#foldArguments
5563 * @see MethodHandles#filterArguments
5564 * @see MethodHandles#filterReturnValue
5565 */
5566 public static MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) {
5567 MethodType newType = collectArgumentsChecks(target, pos, filter);
5568 MethodType collectorType = filter.type();
5569 BoundMethodHandle result = target.rebind();
5570 LambdaForm lform = result.editor().collectArgumentsForm(1 + pos, collectorType.basicType());
5571 return result.copyWithExtendL(newType, lform, filter);
5572 }
5573
5574 private static MethodType collectArgumentsChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
5575 MethodType targetType = target.type();
5576 MethodType filterType = filter.type();
5577 Class<?> rtype = filterType.returnType();
5578 Class<?>[] filterArgs = filterType.ptypes();
5579 if (pos < 0 || (rtype == void.class && pos > targetType.parameterCount()) ||
5580 (rtype != void.class && pos >= targetType.parameterCount())) {
5581 throw newIllegalArgumentException("position is out of range for target", target, pos);
5582 }
5583 if (rtype == void.class) {
5584 return targetType.insertParameterTypes(pos, filterArgs);
5585 }
5586 if (rtype != targetType.parameterType(pos)) {
5587 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
5588 }
5589 return targetType.dropParameterTypes(pos, pos + 1).insertParameterTypes(pos, filterArgs);
5590 }
5591
5592 /**
5593 * Adapts a target method handle by post-processing
5594 * its return value (if any) with a filter (another method handle).
5595 * The result of the filter is returned from the adapter.
5596 * <p>
5597 * If the target returns a value, the filter must accept that value as
5598 * its only argument.
5599 * If the target returns void, the filter must accept no arguments.
5600 * <p>
5601 * The return type of the filter
5602 * replaces the return type of the target
5603 * in the resulting adapted method handle.
5604 * The argument type of the filter (if any) must be identical to the
5605 * return type of the target.
5606 * <p><b>Example:</b>
5607 * {@snippet lang="java" :
5608 import static java.lang.invoke.MethodHandles.*;
5609 import static java.lang.invoke.MethodType.*;
5610 ...
5611 MethodHandle cat = lookup().findVirtual(String.class,
5612 "concat", methodType(String.class, String.class));
5613 MethodHandle length = lookup().findVirtual(String.class,
5614 "length", methodType(int.class));
5615 System.out.println((String) cat.invokeExact("x", "y")); // xy
5616 MethodHandle f0 = filterReturnValue(cat, length);
5617 System.out.println((int) f0.invokeExact("x", "y")); // 2
5618 * }
5619 * <p>Here is pseudocode for the resulting adapter. In the code,
5620 * {@code T}/{@code t} represent the result type and value of the
5621 * {@code target}; {@code V}, the result type of the {@code filter}; and
5622 * {@code A}/{@code a}, the types and values of the parameters and arguments
5623 * of the {@code target} as well as the resulting adapter.
5624 * {@snippet lang="java" :
5625 * T target(A...);
5626 * V filter(T);
5627 * V adapter(A... a) {
5628 * T t = target(a...);
5629 * return filter(t);
5630 * }
5631 * // and if the target has a void return:
5632 * void target2(A...);
5633 * V filter2();
5634 * V adapter2(A... a) {
5635 * target2(a...);
5636 * return filter2();
5637 * }
5638 * // and if the filter has a void return:
5639 * T target3(A...);
5640 * void filter3(V);
5641 * void adapter3(A... a) {
5642 * T t = target3(a...);
5643 * filter3(t);
5644 * }
5645 * }
5646 * <p>
5647 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5648 * variable-arity method handle}, even if the original target method handle was.
5649 * @param target the method handle to invoke before filtering the return value
5650 * @param filter method handle to call on the return value
5651 * @return method handle which incorporates the specified return value filtering logic
5652 * @throws NullPointerException if either argument is null
5653 * @throws IllegalArgumentException if the argument list of {@code filter}
5654 * does not match the return type of target as described above
5655 */
5656 public static MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
5657 MethodType targetType = target.type();
5658 MethodType filterType = filter.type();
5659 filterReturnValueChecks(targetType, filterType);
5660 BoundMethodHandle result = target.rebind();
5661 BasicType rtype = BasicType.basicType(filterType.returnType());
5662 LambdaForm lform = result.editor().filterReturnForm(rtype, false);
5663 MethodType newType = targetType.changeReturnType(filterType.returnType());
5664 result = result.copyWithExtendL(newType, lform, filter);
5665 return result;
5666 }
5667
5668 private static void filterReturnValueChecks(MethodType targetType, MethodType filterType) throws RuntimeException {
5669 Class<?> rtype = targetType.returnType();
5670 int filterValues = filterType.parameterCount();
5671 if (filterValues == 0
5672 ? (rtype != void.class)
5673 : (rtype != filterType.parameterType(0) || filterValues != 1))
5674 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
5675 }
5676
5677 /**
5678 * Filter the return value of a target method handle with a filter function. The filter function is
5679 * applied to the return value of the original handle; if the filter specifies more than one parameters,
5680 * then any remaining parameter is appended to the adapter handle. In other words, the adaptation works
5681 * as follows:
5682 * {@snippet lang="java" :
5683 * T target(A...)
5684 * V filter(B... , T)
5685 * V adapter(A... a, B... b) {
5686 * T t = target(a...);
5687 * return filter(b..., t);
5688 * }
5689 * }
5690 * <p>
5691 * If the filter handle is a unary function, then this method behaves like {@link #filterReturnValue(MethodHandle, MethodHandle)}.
5692 *
5693 * @param target the target method handle
5694 * @param filter the filter method handle
5695 * @return the adapter method handle
5696 */
5697 /* package */ static MethodHandle collectReturnValue(MethodHandle target, MethodHandle filter) {
5698 MethodType targetType = target.type();
5699 MethodType filterType = filter.type();
5700 BoundMethodHandle result = target.rebind();
5701 LambdaForm lform = result.editor().collectReturnValueForm(filterType.basicType());
5702 MethodType newType = targetType.changeReturnType(filterType.returnType());
5703 if (filterType.parameterCount() > 1) {
5704 for (int i = 0 ; i < filterType.parameterCount() - 1 ; i++) {
5705 newType = newType.appendParameterTypes(filterType.parameterType(i));
5706 }
5707 }
5708 result = result.copyWithExtendL(newType, lform, filter);
5709 return result;
5710 }
5711
5712 /**
5713 * Adapts a target method handle by pre-processing
5714 * some of its arguments, and then calling the target with
5715 * the result of the pre-processing, inserted into the original
5716 * sequence of arguments.
5717 * <p>
5718 * The pre-processing is performed by {@code combiner}, a second method handle.
5719 * Of the arguments passed to the adapter, the first {@code N} arguments
5720 * are copied to the combiner, which is then called.
5721 * (Here, {@code N} is defined as the parameter count of the combiner.)
5722 * After this, control passes to the target, with any result
5723 * from the combiner inserted before the original {@code N} incoming
5724 * arguments.
5725 * <p>
5726 * If the combiner returns a value, the first parameter type of the target
5727 * must be identical with the return type of the combiner, and the next
5728 * {@code N} parameter types of the target must exactly match the parameters
5729 * of the combiner.
5730 * <p>
5731 * If the combiner has a void return, no result will be inserted,
5732 * and the first {@code N} parameter types of the target
5733 * must exactly match the parameters of the combiner.
5734 * <p>
5735 * The resulting adapter is the same type as the target, except that the
5736 * first parameter type is dropped,
5737 * if it corresponds to the result of the combiner.
5738 * <p>
5739 * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
5740 * that either the combiner or the target does not wish to receive.
5741 * If some of the incoming arguments are destined only for the combiner,
5742 * consider using {@link MethodHandle#asCollector asCollector} instead, since those
5743 * arguments will not need to be live on the stack on entry to the
5744 * target.)
5745 * <p><b>Example:</b>
5746 * {@snippet lang="java" :
5747 import static java.lang.invoke.MethodHandles.*;
5748 import static java.lang.invoke.MethodType.*;
5749 ...
5750 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
5751 "println", methodType(void.class, String.class))
5752 .bindTo(System.out);
5753 MethodHandle cat = lookup().findVirtual(String.class,
5754 "concat", methodType(String.class, String.class));
5755 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
5756 MethodHandle catTrace = foldArguments(cat, trace);
5757 // also prints "boo":
5758 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
5759 * }
5760 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
5761 * represents the result type of the {@code target} and resulting adapter.
5762 * {@code V}/{@code v} represent the type and value of the parameter and argument
5763 * of {@code target} that precedes the folding position; {@code V} also is
5764 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
5765 * types and values of the {@code N} parameters and arguments at the folding
5766 * position. {@code B}/{@code b} represent the types and values of the
5767 * {@code target} parameters and arguments that follow the folded parameters
5768 * and arguments.
5769 * {@snippet lang="java" :
5770 * // there are N arguments in A...
5771 * T target(V, A[N]..., B...);
5772 * V combiner(A...);
5773 * T adapter(A... a, B... b) {
5774 * V v = combiner(a...);
5775 * return target(v, a..., b...);
5776 * }
5777 * // and if the combiner has a void return:
5778 * T target2(A[N]..., B...);
5779 * void combiner2(A...);
5780 * T adapter2(A... a, B... b) {
5781 * combiner2(a...);
5782 * return target2(a..., b...);
5783 * }
5784 * }
5785 * <p>
5786 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5787 * variable-arity method handle}, even if the original target method handle was.
5788 * @param target the method handle to invoke after arguments are combined
5789 * @param combiner method handle to call initially on the incoming arguments
5790 * @return method handle which incorporates the specified argument folding logic
5791 * @throws NullPointerException if either argument is null
5792 * @throws IllegalArgumentException if {@code combiner}'s return type
5793 * is non-void and not the same as the first argument type of
5794 * the target, or if the initial {@code N} argument types
5795 * of the target
5796 * (skipping one matching the {@code combiner}'s return type)
5797 * are not identical with the argument types of {@code combiner}
5798 */
5799 public static MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
5800 return foldArguments(target, 0, combiner);
5801 }
5802
5803 /**
5804 * Adapts a target method handle by pre-processing some of its arguments, starting at a given position, and then
5805 * calling the target with the result of the pre-processing, inserted into the original sequence of arguments just
5806 * before the folded arguments.
5807 * <p>
5808 * This method is closely related to {@link #foldArguments(MethodHandle, MethodHandle)}, but allows to control the
5809 * position in the parameter list at which folding takes place. The argument controlling this, {@code pos}, is a
5810 * zero-based index. The aforementioned method {@link #foldArguments(MethodHandle, MethodHandle)} assumes position
5811 * 0.
5812 *
5813 * @apiNote Example:
5814 * {@snippet lang="java" :
5815 import static java.lang.invoke.MethodHandles.*;
5816 import static java.lang.invoke.MethodType.*;
5817 ...
5818 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
5819 "println", methodType(void.class, String.class))
5820 .bindTo(System.out);
5821 MethodHandle cat = lookup().findVirtual(String.class,
5822 "concat", methodType(String.class, String.class));
5823 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
5824 MethodHandle catTrace = foldArguments(cat, 1, trace);
5825 // also prints "jum":
5826 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
5827 * }
5828 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
5829 * represents the result type of the {@code target} and resulting adapter.
5830 * {@code V}/{@code v} represent the type and value of the parameter and argument
5831 * of {@code target} that precedes the folding position; {@code V} also is
5832 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
5833 * types and values of the {@code N} parameters and arguments at the folding
5834 * position. {@code Z}/{@code z} and {@code B}/{@code b} represent the types
5835 * and values of the {@code target} parameters and arguments that precede and
5836 * follow the folded parameters and arguments starting at {@code pos},
5837 * respectively.
5838 * {@snippet lang="java" :
5839 * // there are N arguments in A...
5840 * T target(Z..., V, A[N]..., B...);
5841 * V combiner(A...);
5842 * T adapter(Z... z, A... a, B... b) {
5843 * V v = combiner(a...);
5844 * return target(z..., v, a..., b...);
5845 * }
5846 * // and if the combiner has a void return:
5847 * T target2(Z..., A[N]..., B...);
5848 * void combiner2(A...);
5849 * T adapter2(Z... z, A... a, B... b) {
5850 * combiner2(a...);
5851 * return target2(z..., a..., b...);
5852 * }
5853 * }
5854 * <p>
5855 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5856 * variable-arity method handle}, even if the original target method handle was.
5857 *
5858 * @param target the method handle to invoke after arguments are combined
5859 * @param pos the position at which to start folding and at which to insert the folding result; if this is {@code
5860 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
5861 * @param combiner method handle to call initially on the incoming arguments
5862 * @return method handle which incorporates the specified argument folding logic
5863 * @throws NullPointerException if either argument is null
5864 * @throws IllegalArgumentException if either of the following two conditions holds:
5865 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
5866 * {@code pos} of the target signature;
5867 * (2) the {@code N} argument types at position {@code pos} of the target signature (skipping one matching
5868 * the {@code combiner}'s return type) are not identical with the argument types of {@code combiner}.
5869 *
5870 * @see #foldArguments(MethodHandle, MethodHandle)
5871 * @since 9
5872 */
5873 public static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner) {
5874 MethodType targetType = target.type();
5875 MethodType combinerType = combiner.type();
5876 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType);
5877 BoundMethodHandle result = target.rebind();
5878 boolean dropResult = rtype == void.class;
5879 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType());
5880 MethodType newType = targetType;
5881 if (!dropResult) {
5882 newType = newType.dropParameterTypes(pos, pos + 1);
5883 }
5884 result = result.copyWithExtendL(newType, lform, combiner);
5885 return result;
5886 }
5887
5888 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType) {
5889 int foldArgs = combinerType.parameterCount();
5890 Class<?> rtype = combinerType.returnType();
5891 int foldVals = rtype == void.class ? 0 : 1;
5892 int afterInsertPos = foldPos + foldVals;
5893 boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
5894 if (ok) {
5895 for (int i = 0; i < foldArgs; i++) {
5896 if (combinerType.parameterType(i) != targetType.parameterType(i + afterInsertPos)) {
5897 ok = false;
5898 break;
5899 }
5900 }
5901 }
5902 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos))
5903 ok = false;
5904 if (!ok)
5905 throw misMatchedTypes("target and combiner types", targetType, combinerType);
5906 return rtype;
5907 }
5908
5909 /**
5910 * Adapts a target method handle by pre-processing some of its arguments, then calling the target with the result
5911 * of the pre-processing replacing the argument at the given position.
5912 *
5913 * @param target the method handle to invoke after arguments are combined
5914 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code
5915 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
5916 * @param combiner method handle to call initially on the incoming arguments
5917 * @param argPositions indexes of the target to pick arguments sent to the combiner from
5918 * @return method handle which incorporates the specified argument folding logic
5919 * @throws NullPointerException if either argument is null
5920 * @throws IllegalArgumentException if either of the following two conditions holds:
5921 * (1) {@code combiner}'s return type is not the same as the argument type at position
5922 * {@code pos} of the target signature;
5923 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature are
5924 * not identical with the argument types of {@code combiner}.
5925 */
5926 /*non-public*/
5927 static MethodHandle filterArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
5928 return argumentsWithCombiner(true, target, position, combiner, argPositions);
5929 }
5930
5931 /**
5932 * Adapts a target method handle by pre-processing some of its arguments, calling the target with the result of
5933 * the pre-processing inserted into the original sequence of arguments at the given position.
5934 *
5935 * @param target the method handle to invoke after arguments are combined
5936 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code
5937 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
5938 * @param combiner method handle to call initially on the incoming arguments
5939 * @param argPositions indexes of the target to pick arguments sent to the combiner from
5940 * @return method handle which incorporates the specified argument folding logic
5941 * @throws NullPointerException if either argument is null
5942 * @throws IllegalArgumentException if either of the following two conditions holds:
5943 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
5944 * {@code pos} of the target signature;
5945 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature
5946 * (skipping {@code position} where the {@code combiner}'s return will be folded in) are not identical
5947 * with the argument types of {@code combiner}.
5948 */
5949 /*non-public*/
5950 static MethodHandle foldArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
5951 return argumentsWithCombiner(false, target, position, combiner, argPositions);
5952 }
5953
5954 private static MethodHandle argumentsWithCombiner(boolean filter, MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
5955 MethodType targetType = target.type();
5956 MethodType combinerType = combiner.type();
5957 Class<?> rtype = argumentsWithCombinerChecks(position, filter, targetType, combinerType, argPositions);
5958 BoundMethodHandle result = target.rebind();
5959
5960 MethodType newType = targetType;
5961 LambdaForm lform;
5962 if (filter) {
5963 lform = result.editor().filterArgumentsForm(1 + position, combinerType.basicType(), argPositions);
5964 } else {
5965 boolean dropResult = rtype == void.class;
5966 lform = result.editor().foldArgumentsForm(1 + position, dropResult, combinerType.basicType(), argPositions);
5967 if (!dropResult) {
5968 newType = newType.dropParameterTypes(position, position + 1);
5969 }
5970 }
5971 result = result.copyWithExtendL(newType, lform, combiner);
5972 return result;
5973 }
5974
5975 private static Class<?> argumentsWithCombinerChecks(int position, boolean filter, MethodType targetType, MethodType combinerType, int ... argPos) {
5976 int combinerArgs = combinerType.parameterCount();
5977 if (argPos.length != combinerArgs) {
5978 throw newIllegalArgumentException("combiner and argument map must be equal size", combinerType, argPos.length);
5979 }
5980 Class<?> rtype = combinerType.returnType();
5981
5982 for (int i = 0; i < combinerArgs; i++) {
5983 int arg = argPos[i];
5984 if (arg < 0 || arg > targetType.parameterCount()) {
5985 throw newIllegalArgumentException("arg outside of target parameterRange", targetType, arg);
5986 }
5987 if (combinerType.parameterType(i) != targetType.parameterType(arg)) {
5988 throw newIllegalArgumentException("target argument type at position " + arg
5989 + " must match combiner argument type at index " + i + ": " + targetType
5990 + " -> " + combinerType + ", map: " + Arrays.toString(argPos));
5991 }
5992 }
5993 if (filter && combinerType.returnType() != targetType.parameterType(position)) {
5994 throw misMatchedTypes("target and combiner types", targetType, combinerType);
5995 }
5996 return rtype;
5997 }
5998
5999 /**
6000 * Makes a method handle which adapts a target method handle,
6001 * by guarding it with a test, a boolean-valued method handle.
6002 * If the guard fails, a fallback handle is called instead.
6003 * All three method handles must have the same corresponding
6004 * argument and return types, except that the return type
6005 * of the test must be boolean, and the test is allowed
6006 * to have fewer arguments than the other two method handles.
6007 * <p>
6008 * Here is pseudocode for the resulting adapter. In the code, {@code T}
6009 * represents the uniform result type of the three involved handles;
6010 * {@code A}/{@code a}, the types and values of the {@code target}
6011 * parameters and arguments that are consumed by the {@code test}; and
6012 * {@code B}/{@code b}, those types and values of the {@code target}
6013 * parameters and arguments that are not consumed by the {@code test}.
6014 * {@snippet lang="java" :
6015 * boolean test(A...);
6016 * T target(A...,B...);
6017 * T fallback(A...,B...);
6018 * T adapter(A... a,B... b) {
6019 * if (test(a...))
6020 * return target(a..., b...);
6021 * else
6022 * return fallback(a..., b...);
6023 * }
6024 * }
6025 * Note that the test arguments ({@code a...} in the pseudocode) cannot
6026 * be modified by execution of the test, and so are passed unchanged
6027 * from the caller to the target or fallback as appropriate.
6028 * @param test method handle used for test, must return boolean
6029 * @param target method handle to call if test passes
6030 * @param fallback method handle to call if test fails
6031 * @return method handle which incorporates the specified if/then/else logic
6032 * @throws NullPointerException if any argument is null
6033 * @throws IllegalArgumentException if {@code test} does not return boolean,
6034 * or if all three method types do not match (with the return
6035 * type of {@code test} changed to match that of the target).
6036 */
6037 public static MethodHandle guardWithTest(MethodHandle test,
6038 MethodHandle target,
6039 MethodHandle fallback) {
6040 MethodType gtype = test.type();
6041 MethodType ttype = target.type();
6042 MethodType ftype = fallback.type();
6043 if (!ttype.equals(ftype))
6044 throw misMatchedTypes("target and fallback types", ttype, ftype);
6045 if (gtype.returnType() != boolean.class)
6046 throw newIllegalArgumentException("guard type is not a predicate "+gtype);
6047
6048 test = dropArgumentsToMatch(test, 0, ttype.ptypes(), 0, true);
6049 if (test == null) {
6050 throw misMatchedTypes("target and test types", ttype, gtype);
6051 }
6052 return MethodHandleImpl.makeGuardWithTest(test, target, fallback);
6053 }
6054
6055 static <T> RuntimeException misMatchedTypes(String what, T t1, T t2) {
6056 return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
6057 }
6058
6059 /**
6060 * Makes a method handle which adapts a target method handle,
6061 * by running it inside an exception handler.
6062 * If the target returns normally, the adapter returns that value.
6063 * If an exception matching the specified type is thrown, the fallback
6064 * handle is called instead on the exception, plus the original arguments.
6065 * <p>
6066 * The target and handler must have the same corresponding
6067 * argument and return types, except that handler may omit trailing arguments
6068 * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
6069 * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
6070 * <p>
6071 * Here is pseudocode for the resulting adapter. In the code, {@code T}
6072 * represents the return type of the {@code target} and {@code handler},
6073 * and correspondingly that of the resulting adapter; {@code A}/{@code a},
6074 * the types and values of arguments to the resulting handle consumed by
6075 * {@code handler}; and {@code B}/{@code b}, those of arguments to the
6076 * resulting handle discarded by {@code handler}.
6077 * {@snippet lang="java" :
6078 * T target(A..., B...);
6079 * T handler(ExType, A...);
6080 * T adapter(A... a, B... b) {
6081 * try {
6082 * return target(a..., b...);
6083 * } catch (ExType ex) {
6084 * return handler(ex, a...);
6085 * }
6086 * }
6087 * }
6088 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
6089 * be modified by execution of the target, and so are passed unchanged
6090 * from the caller to the handler, if the handler is invoked.
6091 * <p>
6092 * The target and handler must return the same type, even if the handler
6093 * always throws. (This might happen, for instance, because the handler
6094 * is simulating a {@code finally} clause).
6095 * To create such a throwing handler, compose the handler creation logic
6096 * with {@link #throwException throwException},
6097 * in order to create a method handle of the correct return type.
6098 * @param target method handle to call
6099 * @param exType the type of exception which the handler will catch
6100 * @param handler method handle to call if a matching exception is thrown
6101 * @return method handle which incorporates the specified try/catch logic
6102 * @throws NullPointerException if any argument is null
6103 * @throws IllegalArgumentException if {@code handler} does not accept
6104 * the given exception type, or if the method handle types do
6105 * not match in their return types and their
6106 * corresponding parameters
6107 * @see MethodHandles#tryFinally(MethodHandle, MethodHandle)
6108 */
6109 public static MethodHandle catchException(MethodHandle target,
6110 Class<? extends Throwable> exType,
6111 MethodHandle handler) {
6112 MethodType ttype = target.type();
6113 MethodType htype = handler.type();
6114 if (!Throwable.class.isAssignableFrom(exType))
6115 throw new ClassCastException(exType.getName());
6116 if (htype.parameterCount() < 1 ||
6117 !htype.parameterType(0).isAssignableFrom(exType))
6118 throw newIllegalArgumentException("handler does not accept exception type "+exType);
6119 if (htype.returnType() != ttype.returnType())
6120 throw misMatchedTypes("target and handler return types", ttype, htype);
6121 handler = dropArgumentsToMatch(handler, 1, ttype.ptypes(), 0, true);
6122 if (handler == null) {
6123 throw misMatchedTypes("target and handler types", ttype, htype);
6124 }
6125 return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
6126 }
6127
6128 /**
6129 * Produces a method handle which will throw exceptions of the given {@code exType}.
6130 * The method handle will accept a single argument of {@code exType},
6131 * and immediately throw it as an exception.
6132 * The method type will nominally specify a return of {@code returnType}.
6133 * The return type may be anything convenient: It doesn't matter to the
6134 * method handle's behavior, since it will never return normally.
6135 * @param returnType the return type of the desired method handle
6136 * @param exType the parameter type of the desired method handle
6137 * @return method handle which can throw the given exceptions
6138 * @throws NullPointerException if either argument is null
6139 */
6140 public static MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) {
6141 if (!Throwable.class.isAssignableFrom(exType))
6142 throw new ClassCastException(exType.getName());
6143 return MethodHandleImpl.throwException(methodType(returnType, exType));
6144 }
6145
6146 /**
6147 * Constructs a method handle representing a loop with several loop variables that are updated and checked upon each
6148 * iteration. Upon termination of the loop due to one of the predicates, a corresponding finalizer is run and
6149 * delivers the loop's result, which is the return value of the resulting handle.
6150 * <p>
6151 * Intuitively, every loop is formed by one or more "clauses", each specifying a local <em>iteration variable</em> and/or a loop
6152 * exit. Each iteration of the loop executes each clause in order. A clause can optionally update its iteration
6153 * variable; it can also optionally perform a test and conditional loop exit. In order to express this logic in
6154 * terms of method handles, each clause will specify up to four independent actions:<ul>
6155 * <li><em>init:</em> Before the loop executes, the initialization of an iteration variable {@code v} of type {@code V}.
6156 * <li><em>step:</em> When a clause executes, an update step for the iteration variable {@code v}.
6157 * <li><em>pred:</em> When a clause executes, a predicate execution to test for loop exit.
6158 * <li><em>fini:</em> If a clause causes a loop exit, a finalizer execution to compute the loop's return value.
6159 * </ul>
6160 * The full sequence of all iteration variable types, in clause order, will be notated as {@code (V...)}.
6161 * The values themselves will be {@code (v...)}. When we speak of "parameter lists", we will usually
6162 * be referring to types, but in some contexts (describing execution) the lists will be of actual values.
6163 * <p>
6164 * Some of these clause parts may be omitted according to certain rules, and useful default behavior is provided in
6165 * this case. See below for a detailed description.
6166 * <p>
6167 * <em>Parameters optional everywhere:</em>
6168 * Each clause function is allowed but not required to accept a parameter for each iteration variable {@code v}.
6169 * As an exception, the init functions cannot take any {@code v} parameters,
6170 * because those values are not yet computed when the init functions are executed.
6171 * Any clause function may neglect to take any trailing subsequence of parameters it is entitled to take.
6172 * In fact, any clause function may take no arguments at all.
6173 * <p>
6174 * <em>Loop parameters:</em>
6175 * A clause function may take all the iteration variable values it is entitled to, in which case
6176 * it may also take more trailing parameters. Such extra values are called <em>loop parameters</em>,
6177 * with their types and values notated as {@code (A...)} and {@code (a...)}.
6178 * These become the parameters of the resulting loop handle, to be supplied whenever the loop is executed.
6179 * (Since init functions do not accept iteration variables {@code v}, any parameter to an
6180 * init function is automatically a loop parameter {@code a}.)
6181 * As with iteration variables, clause functions are allowed but not required to accept loop parameters.
6182 * These loop parameters act as loop-invariant values visible across the whole loop.
6183 * <p>
6184 * <em>Parameters visible everywhere:</em>
6185 * Each non-init clause function is permitted to observe the entire loop state, because it can be passed the full
6186 * list {@code (v... a...)} of current iteration variable values and incoming loop parameters.
6187 * The init functions can observe initial pre-loop state, in the form {@code (a...)}.
6188 * Most clause functions will not need all of this information, but they will be formally connected to it
6189 * as if by {@link #dropArguments}.
6190 * <a id="astar"></a>
6191 * More specifically, we shall use the notation {@code (V*)} to express an arbitrary prefix of a full
6192 * sequence {@code (V...)} (and likewise for {@code (v*)}, {@code (A*)}, {@code (a*)}).
6193 * In that notation, the general form of an init function parameter list
6194 * is {@code (A*)}, and the general form of a non-init function parameter list is {@code (V*)} or {@code (V... A*)}.
6195 * <p>
6196 * <em>Checking clause structure:</em>
6197 * Given a set of clauses, there is a number of checks and adjustments performed to connect all the parts of the
6198 * loop. They are spelled out in detail in the steps below. In these steps, every occurrence of the word "must"
6199 * corresponds to a place where {@link IllegalArgumentException} will be thrown if the required constraint is not
6200 * met by the inputs to the loop combinator.
6201 * <p>
6202 * <em>Effectively identical sequences:</em>
6203 * <a id="effid"></a>
6204 * A parameter list {@code A} is defined to be <em>effectively identical</em> to another parameter list {@code B}
6205 * if {@code A} and {@code B} are identical, or if {@code A} is shorter and is identical with a proper prefix of {@code B}.
6206 * When speaking of an unordered set of parameter lists, we say they the set is "effectively identical"
6207 * as a whole if the set contains a longest list, and all members of the set are effectively identical to
6208 * that longest list.
6209 * For example, any set of type sequences of the form {@code (V*)} is effectively identical,
6210 * and the same is true if more sequences of the form {@code (V... A*)} are added.
6211 * <p>
6212 * <em>Step 0: Determine clause structure.</em><ol type="a">
6213 * <li>The clause array (of type {@code MethodHandle[][]}) must be non-{@code null} and contain at least one element.
6214 * <li>The clause array may not contain {@code null}s or sub-arrays longer than four elements.
6215 * <li>Clauses shorter than four elements are treated as if they were padded by {@code null} elements to length
6216 * four. Padding takes place by appending elements to the array.
6217 * <li>Clauses with all {@code null}s are disregarded.
6218 * <li>Each clause is treated as a four-tuple of functions, called "init", "step", "pred", and "fini".
6219 * </ol>
6220 * <p>
6221 * <em>Step 1A: Determine iteration variable types {@code (V...)}.</em><ol type="a">
6222 * <li>The iteration variable type for each clause is determined using the clause's init and step return types.
6223 * <li>If both functions are omitted, there is no iteration variable for the corresponding clause ({@code void} is
6224 * used as the type to indicate that). If one of them is omitted, the other's return type defines the clause's
6225 * iteration variable type. If both are given, the common return type (they must be identical) defines the clause's
6226 * iteration variable type.
6227 * <li>Form the list of return types (in clause order), omitting all occurrences of {@code void}.
6228 * <li>This list of types is called the "iteration variable types" ({@code (V...)}).
6229 * </ol>
6230 * <p>
6231 * <em>Step 1B: Determine loop parameters {@code (A...)}.</em><ul>
6232 * <li>Examine and collect init function parameter lists (which are of the form {@code (A*)}).
6233 * <li>Examine and collect the suffixes of the step, pred, and fini parameter lists, after removing the iteration variable types.
6234 * (They must have the form {@code (V... A*)}; collect the {@code (A*)} parts only.)
6235 * <li>Do not collect suffixes from step, pred, and fini parameter lists that do not begin with all the iteration variable types.
6236 * (These types will be checked in step 2, along with all the clause function types.)
6237 * <li>Omitted clause functions are ignored. (Equivalently, they are deemed to have empty parameter lists.)
6238 * <li>All of the collected parameter lists must be effectively identical.
6239 * <li>The longest parameter list (which is necessarily unique) is called the "external parameter list" ({@code (A...)}).
6240 * <li>If there is no such parameter list, the external parameter list is taken to be the empty sequence.
6241 * <li>The combined list consisting of iteration variable types followed by the external parameter types is called
6242 * the "internal parameter list".
6243 * </ul>
6244 * <p>
6245 * <em>Step 1C: Determine loop return type.</em><ol type="a">
6246 * <li>Examine fini function return types, disregarding omitted fini functions.
6247 * <li>If there are no fini functions, the loop return type is {@code void}.
6248 * <li>Otherwise, the common return type {@code R} of the fini functions (their return types must be identical) defines the loop return
6249 * type.
6250 * </ol>
6251 * <p>
6252 * <em>Step 1D: Check other types.</em><ol type="a">
6253 * <li>There must be at least one non-omitted pred function.
6254 * <li>Every non-omitted pred function must have a {@code boolean} return type.
6255 * </ol>
6256 * <p>
6257 * <em>Step 2: Determine parameter lists.</em><ol type="a">
6258 * <li>The parameter list for the resulting loop handle will be the external parameter list {@code (A...)}.
6259 * <li>The parameter list for init functions will be adjusted to the external parameter list.
6260 * (Note that their parameter lists are already effectively identical to this list.)
6261 * <li>The parameter list for every non-omitted, non-init (step, pred, and fini) function must be
6262 * effectively identical to the internal parameter list {@code (V... A...)}.
6263 * </ol>
6264 * <p>
6265 * <em>Step 3: Fill in omitted functions.</em><ol type="a">
6266 * <li>If an init function is omitted, use a {@linkplain #empty default value} for the clause's iteration variable
6267 * type.
6268 * <li>If a step function is omitted, use an {@linkplain #identity identity function} of the clause's iteration
6269 * variable type; insert dropped argument parameters before the identity function parameter for the non-{@code void}
6270 * iteration variables of preceding clauses. (This will turn the loop variable into a local loop invariant.)
6271 * <li>If a pred function is omitted, use a constant {@code true} function. (This will keep the loop going, as far
6272 * as this clause is concerned. Note that in such cases the corresponding fini function is unreachable.)
6273 * <li>If a fini function is omitted, use a {@linkplain #empty default value} for the
6274 * loop return type.
6275 * </ol>
6276 * <p>
6277 * <em>Step 4: Fill in missing parameter types.</em><ol type="a">
6278 * <li>At this point, every init function parameter list is effectively identical to the external parameter list {@code (A...)},
6279 * but some lists may be shorter. For every init function with a short parameter list, pad out the end of the list.
6280 * <li>At this point, every non-init function parameter list is effectively identical to the internal parameter
6281 * list {@code (V... A...)}, but some lists may be shorter. For every non-init function with a short parameter list,
6282 * pad out the end of the list.
6283 * <li>Argument lists are padded out by {@linkplain #dropArgumentsToMatch(MethodHandle, int, List, int) dropping unused trailing arguments}.
6284 * </ol>
6285 * <p>
6286 * <em>Final observations.</em><ol type="a">
6287 * <li>After these steps, all clauses have been adjusted by supplying omitted functions and arguments.
6288 * <li>All init functions have a common parameter type list {@code (A...)}, which the final loop handle will also have.
6289 * <li>All fini functions have a common return type {@code R}, which the final loop handle will also have.
6290 * <li>All non-init functions have a common parameter type list {@code (V... A...)}, of
6291 * (non-{@code void}) iteration variables {@code V} followed by loop parameters.
6292 * <li>Each pair of init and step functions agrees in their return type {@code V}.
6293 * <li>Each non-init function will be able to observe the current values {@code (v...)} of all iteration variables.
6294 * <li>Every function will be able to observe the incoming values {@code (a...)} of all loop parameters.
6295 * </ol>
6296 * <p>
6297 * <em>Example.</em> As a consequence of step 1A above, the {@code loop} combinator has the following property:
6298 * <ul>
6299 * <li>Given {@code N} clauses {@code Cn = {null, Sn, Pn}} with {@code n = 1..N}.
6300 * <li>Suppose predicate handles {@code Pn} are either {@code null} or have no parameters.
6301 * (Only one {@code Pn} has to be non-{@code null}.)
6302 * <li>Suppose step handles {@code Sn} have signatures {@code (B1..BX)Rn}, for some constant {@code X>=N}.
6303 * <li>Suppose {@code Q} is the count of non-void types {@code Rn}, and {@code (V1...VQ)} is the sequence of those types.
6304 * <li>It must be that {@code Vn == Bn} for {@code n = 1..min(X,Q)}.
6305 * <li>The parameter types {@code Vn} will be interpreted as loop-local state elements {@code (V...)}.
6306 * <li>Any remaining types {@code BQ+1..BX} (if {@code Q<X}) will determine
6307 * the resulting loop handle's parameter types {@code (A...)}.
6308 * </ul>
6309 * In this example, the loop handle parameters {@code (A...)} were derived from the step functions,
6310 * which is natural if most of the loop computation happens in the steps. For some loops,
6311 * the burden of computation might be heaviest in the pred functions, and so the pred functions
6312 * might need to accept the loop parameter values. For loops with complex exit logic, the fini
6313 * functions might need to accept loop parameters, and likewise for loops with complex entry logic,
6314 * where the init functions will need the extra parameters. For such reasons, the rules for
6315 * determining these parameters are as symmetric as possible, across all clause parts.
6316 * In general, the loop parameters function as common invariant values across the whole
6317 * loop, while the iteration variables function as common variant values, or (if there is
6318 * no step function) as internal loop invariant temporaries.
6319 * <p>
6320 * <em>Loop execution.</em><ol type="a">
6321 * <li>When the loop is called, the loop input values are saved in locals, to be passed to
6322 * every clause function. These locals are loop invariant.
6323 * <li>Each init function is executed in clause order (passing the external arguments {@code (a...)})
6324 * and the non-{@code void} values are saved (as the iteration variables {@code (v...)}) into locals.
6325 * These locals will be loop varying (unless their steps behave as identity functions, as noted above).
6326 * <li>All function executions (except init functions) will be passed the internal parameter list, consisting of
6327 * the non-{@code void} iteration values {@code (v...)} (in clause order) and then the loop inputs {@code (a...)}
6328 * (in argument order).
6329 * <li>The step and pred functions are then executed, in clause order (step before pred), until a pred function
6330 * returns {@code false}.
6331 * <li>The non-{@code void} result from a step function call is used to update the corresponding value in the
6332 * sequence {@code (v...)} of loop variables.
6333 * The updated value is immediately visible to all subsequent function calls.
6334 * <li>If a pred function returns {@code false}, the corresponding fini function is called, and the resulting value
6335 * (of type {@code R}) is returned from the loop as a whole.
6336 * <li>If all the pred functions always return true, no fini function is ever invoked, and the loop cannot exit
6337 * except by throwing an exception.
6338 * </ol>
6339 * <p>
6340 * <em>Usage tips.</em>
6341 * <ul>
6342 * <li>Although each step function will receive the current values of <em>all</em> the loop variables,
6343 * sometimes a step function only needs to observe the current value of its own variable.
6344 * In that case, the step function may need to explicitly {@linkplain #dropArguments drop all preceding loop variables}.
6345 * This will require mentioning their types, in an expression like {@code dropArguments(step, 0, V0.class, ...)}.
6346 * <li>Loop variables are not required to vary; they can be loop invariant. A clause can create
6347 * a loop invariant by a suitable init function with no step, pred, or fini function. This may be
6348 * useful to "wire" an incoming loop argument into the step or pred function of an adjacent loop variable.
6349 * <li>If some of the clause functions are virtual methods on an instance, the instance
6350 * itself can be conveniently placed in an initial invariant loop "variable", using an initial clause
6351 * like {@code new MethodHandle[]{identity(ObjType.class)}}. In that case, the instance reference
6352 * will be the first iteration variable value, and it will be easy to use virtual
6353 * methods as clause parts, since all of them will take a leading instance reference matching that value.
6354 * </ul>
6355 * <p>
6356 * Here is pseudocode for the resulting loop handle. As above, {@code V} and {@code v} represent the types
6357 * and values of loop variables; {@code A} and {@code a} represent arguments passed to the whole loop;
6358 * and {@code R} is the common result type of all finalizers as well as of the resulting loop.
6359 * {@snippet lang="java" :
6360 * V... init...(A...);
6361 * boolean pred...(V..., A...);
6362 * V... step...(V..., A...);
6363 * R fini...(V..., A...);
6364 * R loop(A... a) {
6365 * V... v... = init...(a...);
6366 * for (;;) {
6367 * for ((v, p, s, f) in (v..., pred..., step..., fini...)) {
6368 * v = s(v..., a...);
6369 * if (!p(v..., a...)) {
6370 * return f(v..., a...);
6371 * }
6372 * }
6373 * }
6374 * }
6375 * }
6376 * Note that the parameter type lists {@code (V...)} and {@code (A...)} have been expanded
6377 * to their full length, even though individual clause functions may neglect to take them all.
6378 * As noted above, missing parameters are filled in as if by {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}.
6379 *
6380 * @apiNote Example:
6381 * {@snippet lang="java" :
6382 * // iterative implementation of the factorial function as a loop handle
6383 * static int one(int k) { return 1; }
6384 * static int inc(int i, int acc, int k) { return i + 1; }
6385 * static int mult(int i, int acc, int k) { return i * acc; }
6386 * static boolean pred(int i, int acc, int k) { return i < k; }
6387 * static int fin(int i, int acc, int k) { return acc; }
6388 * // assume MH_one, MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
6389 * // null initializer for counter, should initialize to 0
6390 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
6391 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
6392 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
6393 * assertEquals(120, loop.invoke(5));
6394 * }
6395 * The same example, dropping arguments and using combinators:
6396 * {@snippet lang="java" :
6397 * // simplified implementation of the factorial function as a loop handle
6398 * static int inc(int i) { return i + 1; } // drop acc, k
6399 * static int mult(int i, int acc) { return i * acc; } //drop k
6400 * static boolean cmp(int i, int k) { return i < k; }
6401 * // assume MH_inc, MH_mult, and MH_cmp are handles to the above methods
6402 * // null initializer for counter, should initialize to 0
6403 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
6404 * MethodHandle MH_pred = MethodHandles.dropArguments(MH_cmp, 1, int.class); // drop acc
6405 * MethodHandle MH_fin = MethodHandles.dropArguments(MethodHandles.identity(int.class), 0, int.class); // drop i
6406 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
6407 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
6408 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
6409 * assertEquals(720, loop.invoke(6));
6410 * }
6411 * A similar example, using a helper object to hold a loop parameter:
6412 * {@snippet lang="java" :
6413 * // instance-based implementation of the factorial function as a loop handle
6414 * static class FacLoop {
6415 * final int k;
6416 * FacLoop(int k) { this.k = k; }
6417 * int inc(int i) { return i + 1; }
6418 * int mult(int i, int acc) { return i * acc; }
6419 * boolean pred(int i) { return i < k; }
6420 * int fin(int i, int acc) { return acc; }
6421 * }
6422 * // assume MH_FacLoop is a handle to the constructor
6423 * // assume MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
6424 * // null initializer for counter, should initialize to 0
6425 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
6426 * MethodHandle[] instanceClause = new MethodHandle[]{MH_FacLoop};
6427 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
6428 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
6429 * MethodHandle loop = MethodHandles.loop(instanceClause, counterClause, accumulatorClause);
6430 * assertEquals(5040, loop.invoke(7));
6431 * }
6432 *
6433 * @param clauses an array of arrays (4-tuples) of {@link MethodHandle}s adhering to the rules described above.
6434 *
6435 * @return a method handle embodying the looping behavior as defined by the arguments.
6436 *
6437 * @throws IllegalArgumentException in case any of the constraints described above is violated.
6438 *
6439 * @see MethodHandles#whileLoop(MethodHandle, MethodHandle, MethodHandle)
6440 * @see MethodHandles#doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
6441 * @see MethodHandles#countedLoop(MethodHandle, MethodHandle, MethodHandle)
6442 * @see MethodHandles#iteratedLoop(MethodHandle, MethodHandle, MethodHandle)
6443 * @since 9
6444 */
6445 public static MethodHandle loop(MethodHandle[]... clauses) {
6446 // Step 0: determine clause structure.
6447 loopChecks0(clauses);
6448
6449 List<MethodHandle> init = new ArrayList<>();
6450 List<MethodHandle> step = new ArrayList<>();
6451 List<MethodHandle> pred = new ArrayList<>();
6452 List<MethodHandle> fini = new ArrayList<>();
6453
6454 Stream.of(clauses).filter(c -> Stream.of(c).anyMatch(Objects::nonNull)).forEach(clause -> {
6455 init.add(clause[0]); // all clauses have at least length 1
6456 step.add(clause.length <= 1 ? null : clause[1]);
6457 pred.add(clause.length <= 2 ? null : clause[2]);
6458 fini.add(clause.length <= 3 ? null : clause[3]);
6459 });
6460
6461 assert Stream.of(init, step, pred, fini).map(List::size).distinct().count() == 1;
6462 final int nclauses = init.size();
6463
6464 // Step 1A: determine iteration variables (V...).
6465 final List<Class<?>> iterationVariableTypes = new ArrayList<>();
6466 for (int i = 0; i < nclauses; ++i) {
6467 MethodHandle in = init.get(i);
6468 MethodHandle st = step.get(i);
6469 if (in == null && st == null) {
6470 iterationVariableTypes.add(void.class);
6471 } else if (in != null && st != null) {
6472 loopChecks1a(i, in, st);
6473 iterationVariableTypes.add(in.type().returnType());
6474 } else {
6475 iterationVariableTypes.add(in == null ? st.type().returnType() : in.type().returnType());
6476 }
6477 }
6478 final List<Class<?>> commonPrefix = iterationVariableTypes.stream().filter(t -> t != void.class).toList();
6479
6480 // Step 1B: determine loop parameters (A...).
6481 final List<Class<?>> commonSuffix = buildCommonSuffix(init, step, pred, fini, commonPrefix.size());
6482 loopChecks1b(init, commonSuffix);
6483
6484 // Step 1C: determine loop return type.
6485 // Step 1D: check other types.
6486 // local variable required here; see JDK-8223553
6487 Stream<Class<?>> cstream = fini.stream().filter(Objects::nonNull).map(MethodHandle::type)
6488 .map(MethodType::returnType);
6489 final Class<?> loopReturnType = cstream.findFirst().orElse(void.class);
6490 loopChecks1cd(pred, fini, loopReturnType);
6491
6492 // Step 2: determine parameter lists.
6493 final List<Class<?>> commonParameterSequence = new ArrayList<>(commonPrefix);
6494 commonParameterSequence.addAll(commonSuffix);
6495 loopChecks2(step, pred, fini, commonParameterSequence);
6496 // Step 3: fill in omitted functions.
6497 for (int i = 0; i < nclauses; ++i) {
6498 Class<?> t = iterationVariableTypes.get(i);
6499 if (init.get(i) == null) {
6500 init.set(i, empty(methodType(t, commonSuffix)));
6501 }
6502 if (step.get(i) == null) {
6503 step.set(i, dropArgumentsToMatch(identityOrVoid(t), 0, commonParameterSequence, i));
6504 }
6505 if (pred.get(i) == null) {
6506 pred.set(i, dropArguments(constant(boolean.class, true), 0, commonParameterSequence));
6507 }
6508 if (fini.get(i) == null) {
6509 fini.set(i, empty(methodType(t, commonParameterSequence)));
6510 }
6511 }
6512
6513 // Step 4: fill in missing parameter types.
6514 // Also convert all handles to fixed-arity handles.
6515 List<MethodHandle> finit = fixArities(fillParameterTypes(init, commonSuffix));
6516 List<MethodHandle> fstep = fixArities(fillParameterTypes(step, commonParameterSequence));
6517 List<MethodHandle> fpred = fixArities(fillParameterTypes(pred, commonParameterSequence));
6518 List<MethodHandle> ffini = fixArities(fillParameterTypes(fini, commonParameterSequence));
6519
6520 assert finit.stream().map(MethodHandle::type).map(MethodType::parameterList).
6521 allMatch(pl -> pl.equals(commonSuffix));
6522 assert Stream.of(fstep, fpred, ffini).flatMap(List::stream).map(MethodHandle::type).map(MethodType::parameterList).
6523 allMatch(pl -> pl.equals(commonParameterSequence));
6524
6525 return MethodHandleImpl.makeLoop(loopReturnType, commonSuffix, finit, fstep, fpred, ffini);
6526 }
6527
6528 private static void loopChecks0(MethodHandle[][] clauses) {
6529 if (clauses == null || clauses.length == 0) {
6530 throw newIllegalArgumentException("null or no clauses passed");
6531 }
6532 if (Stream.of(clauses).anyMatch(Objects::isNull)) {
6533 throw newIllegalArgumentException("null clauses are not allowed");
6534 }
6535 if (Stream.of(clauses).anyMatch(c -> c.length > 4)) {
6536 throw newIllegalArgumentException("All loop clauses must be represented as MethodHandle arrays with at most 4 elements.");
6537 }
6538 }
6539
6540 private static void loopChecks1a(int i, MethodHandle in, MethodHandle st) {
6541 if (in.type().returnType() != st.type().returnType()) {
6542 throw misMatchedTypes("clause " + i + ": init and step return types", in.type().returnType(),
6543 st.type().returnType());
6544 }
6545 }
6546
6547 private static List<Class<?>> longestParameterList(Stream<MethodHandle> mhs, int skipSize) {
6548 return mhs.filter(Objects::nonNull)
6549 // take only those that can contribute to a common suffix because they are longer than the prefix
6550 .map(MethodHandle::type)
6551 .filter(t -> t.parameterCount() > skipSize)
6552 .max(Comparator.comparingInt(MethodType::parameterCount))
6553 .map(methodType -> List.of(Arrays.copyOfRange(methodType.ptypes(), skipSize, methodType.parameterCount())))
6554 .orElse(List.of());
6555 }
6556
6557 private static List<Class<?>> buildCommonSuffix(List<MethodHandle> init, List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, int cpSize) {
6558 final List<Class<?>> longest1 = longestParameterList(Stream.of(step, pred, fini).flatMap(List::stream), cpSize);
6559 final List<Class<?>> longest2 = longestParameterList(init.stream(), 0);
6560 return longest1.size() >= longest2.size() ? longest1 : longest2;
6561 }
6562
6563 private static void loopChecks1b(List<MethodHandle> init, List<Class<?>> commonSuffix) {
6564 if (init.stream().filter(Objects::nonNull).map(MethodHandle::type).
6565 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonSuffix))) {
6566 throw newIllegalArgumentException("found non-effectively identical init parameter type lists: " + init +
6567 " (common suffix: " + commonSuffix + ")");
6568 }
6569 }
6570
6571 private static void loopChecks1cd(List<MethodHandle> pred, List<MethodHandle> fini, Class<?> loopReturnType) {
6572 if (fini.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
6573 anyMatch(t -> t != loopReturnType)) {
6574 throw newIllegalArgumentException("found non-identical finalizer return types: " + fini + " (return type: " +
6575 loopReturnType + ")");
6576 }
6577
6578 if (pred.stream().noneMatch(Objects::nonNull)) {
6579 throw newIllegalArgumentException("no predicate found", pred);
6580 }
6581 if (pred.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
6582 anyMatch(t -> t != boolean.class)) {
6583 throw newIllegalArgumentException("predicates must have boolean return type", pred);
6584 }
6585 }
6586
6587 private static void loopChecks2(List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, List<Class<?>> commonParameterSequence) {
6588 if (Stream.of(step, pred, fini).flatMap(List::stream).filter(Objects::nonNull).map(MethodHandle::type).
6589 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonParameterSequence))) {
6590 throw newIllegalArgumentException("found non-effectively identical parameter type lists:\nstep: " + step +
6591 "\npred: " + pred + "\nfini: " + fini + " (common parameter sequence: " + commonParameterSequence + ")");
6592 }
6593 }
6594
6595 private static List<MethodHandle> fillParameterTypes(List<MethodHandle> hs, final List<Class<?>> targetParams) {
6596 return hs.stream().map(h -> {
6597 int pc = h.type().parameterCount();
6598 int tpsize = targetParams.size();
6599 return pc < tpsize ? dropArguments(h, pc, targetParams.subList(pc, tpsize)) : h;
6600 }).toList();
6601 }
6602
6603 private static List<MethodHandle> fixArities(List<MethodHandle> hs) {
6604 return hs.stream().map(MethodHandle::asFixedArity).toList();
6605 }
6606
6607 /**
6608 * Constructs a {@code while} loop from an initializer, a body, and a predicate.
6609 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
6610 * <p>
6611 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
6612 * method will, in each iteration, first evaluate the predicate and then execute its body (if the predicate
6613 * evaluates to {@code true}).
6614 * The loop will terminate once the predicate evaluates to {@code false} (the body will not be executed in this case).
6615 * <p>
6616 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
6617 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
6618 * and updated with the value returned from its invocation. The result of loop execution will be
6619 * the final value of the additional loop-local variable (if present).
6620 * <p>
6621 * The following rules hold for these argument handles:<ul>
6622 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
6623 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
6624 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
6625 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
6626 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
6627 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
6628 * It will constrain the parameter lists of the other loop parts.
6629 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
6630 * list {@code (A...)} is called the <em>external parameter list</em>.
6631 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
6632 * additional state variable of the loop.
6633 * The body must both accept and return a value of this type {@code V}.
6634 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
6635 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
6636 * <a href="MethodHandles.html#effid">effectively identical</a>
6637 * to the external parameter list {@code (A...)}.
6638 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
6639 * {@linkplain #empty default value}.
6640 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
6641 * Its parameter list (either empty or of the form {@code (V A*)}) must be
6642 * effectively identical to the internal parameter list.
6643 * </ul>
6644 * <p>
6645 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
6646 * <li>The loop handle's result type is the result type {@code V} of the body.
6647 * <li>The loop handle's parameter types are the types {@code (A...)},
6648 * from the external parameter list.
6649 * </ul>
6650 * <p>
6651 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
6652 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
6653 * passed to the loop.
6654 * {@snippet lang="java" :
6655 * V init(A...);
6656 * boolean pred(V, A...);
6657 * V body(V, A...);
6658 * V whileLoop(A... a...) {
6659 * V v = init(a...);
6660 * while (pred(v, a...)) {
6661 * v = body(v, a...);
6662 * }
6663 * return v;
6664 * }
6665 * }
6666 *
6667 * @apiNote Example:
6668 * {@snippet lang="java" :
6669 * // implement the zip function for lists as a loop handle
6670 * static List<String> initZip(Iterator<String> a, Iterator<String> b) { return new ArrayList<>(); }
6671 * static boolean zipPred(List<String> zip, Iterator<String> a, Iterator<String> b) { return a.hasNext() && b.hasNext(); }
6672 * static List<String> zipStep(List<String> zip, Iterator<String> a, Iterator<String> b) {
6673 * zip.add(a.next());
6674 * zip.add(b.next());
6675 * return zip;
6676 * }
6677 * // assume MH_initZip, MH_zipPred, and MH_zipStep are handles to the above methods
6678 * MethodHandle loop = MethodHandles.whileLoop(MH_initZip, MH_zipPred, MH_zipStep);
6679 * List<String> a = Arrays.asList("a", "b", "c", "d");
6680 * List<String> b = Arrays.asList("e", "f", "g", "h");
6681 * List<String> zipped = Arrays.asList("a", "e", "b", "f", "c", "g", "d", "h");
6682 * assertEquals(zipped, (List<String>) loop.invoke(a.iterator(), b.iterator()));
6683 * }
6684 *
6685 *
6686 * @apiNote The implementation of this method can be expressed as follows:
6687 * {@snippet lang="java" :
6688 * MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
6689 * MethodHandle fini = (body.type().returnType() == void.class
6690 * ? null : identity(body.type().returnType()));
6691 * MethodHandle[]
6692 * checkExit = { null, null, pred, fini },
6693 * varBody = { init, body };
6694 * return loop(checkExit, varBody);
6695 * }
6696 * }
6697 *
6698 * @param init optional initializer, providing the initial value of the loop variable.
6699 * May be {@code null}, implying a default initial value. See above for other constraints.
6700 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
6701 * above for other constraints.
6702 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
6703 * See above for other constraints.
6704 *
6705 * @return a method handle implementing the {@code while} loop as described by the arguments.
6706 * @throws IllegalArgumentException if the rules for the arguments are violated.
6707 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
6708 *
6709 * @see #loop(MethodHandle[][])
6710 * @see #doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
6711 * @since 9
6712 */
6713 public static MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
6714 whileLoopChecks(init, pred, body);
6715 MethodHandle fini = identityOrVoid(body.type().returnType());
6716 MethodHandle[] checkExit = { null, null, pred, fini };
6717 MethodHandle[] varBody = { init, body };
6718 return loop(checkExit, varBody);
6719 }
6720
6721 /**
6722 * Constructs a {@code do-while} loop from an initializer, a body, and a predicate.
6723 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
6724 * <p>
6725 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
6726 * method will, in each iteration, first execute its body and then evaluate the predicate.
6727 * The loop will terminate once the predicate evaluates to {@code false} after an execution of the body.
6728 * <p>
6729 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
6730 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
6731 * and updated with the value returned from its invocation. The result of loop execution will be
6732 * the final value of the additional loop-local variable (if present).
6733 * <p>
6734 * The following rules hold for these argument handles:<ul>
6735 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
6736 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
6737 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
6738 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
6739 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
6740 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
6741 * It will constrain the parameter lists of the other loop parts.
6742 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
6743 * list {@code (A...)} is called the <em>external parameter list</em>.
6744 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
6745 * additional state variable of the loop.
6746 * The body must both accept and return a value of this type {@code V}.
6747 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
6748 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
6749 * <a href="MethodHandles.html#effid">effectively identical</a>
6750 * to the external parameter list {@code (A...)}.
6751 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
6752 * {@linkplain #empty default value}.
6753 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
6754 * Its parameter list (either empty or of the form {@code (V A*)}) must be
6755 * effectively identical to the internal parameter list.
6756 * </ul>
6757 * <p>
6758 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
6759 * <li>The loop handle's result type is the result type {@code V} of the body.
6760 * <li>The loop handle's parameter types are the types {@code (A...)},
6761 * from the external parameter list.
6762 * </ul>
6763 * <p>
6764 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
6765 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
6766 * passed to the loop.
6767 * {@snippet lang="java" :
6768 * V init(A...);
6769 * boolean pred(V, A...);
6770 * V body(V, A...);
6771 * V doWhileLoop(A... a...) {
6772 * V v = init(a...);
6773 * do {
6774 * v = body(v, a...);
6775 * } while (pred(v, a...));
6776 * return v;
6777 * }
6778 * }
6779 *
6780 * @apiNote Example:
6781 * {@snippet lang="java" :
6782 * // int i = 0; while (i < limit) { ++i; } return i; => limit
6783 * static int zero(int limit) { return 0; }
6784 * static int step(int i, int limit) { return i + 1; }
6785 * static boolean pred(int i, int limit) { return i < limit; }
6786 * // assume MH_zero, MH_step, and MH_pred are handles to the above methods
6787 * MethodHandle loop = MethodHandles.doWhileLoop(MH_zero, MH_step, MH_pred);
6788 * assertEquals(23, loop.invoke(23));
6789 * }
6790 *
6791 *
6792 * @apiNote The implementation of this method can be expressed as follows:
6793 * {@snippet lang="java" :
6794 * MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
6795 * MethodHandle fini = (body.type().returnType() == void.class
6796 * ? null : identity(body.type().returnType()));
6797 * MethodHandle[] clause = { init, body, pred, fini };
6798 * return loop(clause);
6799 * }
6800 * }
6801 *
6802 * @param init optional initializer, providing the initial value of the loop variable.
6803 * May be {@code null}, implying a default initial value. See above for other constraints.
6804 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
6805 * See above for other constraints.
6806 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
6807 * above for other constraints.
6808 *
6809 * @return a method handle implementing the {@code while} loop as described by the arguments.
6810 * @throws IllegalArgumentException if the rules for the arguments are violated.
6811 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
6812 *
6813 * @see #loop(MethodHandle[][])
6814 * @see #whileLoop(MethodHandle, MethodHandle, MethodHandle)
6815 * @since 9
6816 */
6817 public static MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
6818 whileLoopChecks(init, pred, body);
6819 MethodHandle fini = identityOrVoid(body.type().returnType());
6820 MethodHandle[] clause = {init, body, pred, fini };
6821 return loop(clause);
6822 }
6823
6824 private static void whileLoopChecks(MethodHandle init, MethodHandle pred, MethodHandle body) {
6825 Objects.requireNonNull(pred);
6826 Objects.requireNonNull(body);
6827 MethodType bodyType = body.type();
6828 Class<?> returnType = bodyType.returnType();
6829 List<Class<?>> innerList = bodyType.parameterList();
6830 List<Class<?>> outerList = innerList;
6831 if (returnType == void.class) {
6832 // OK
6833 } else if (innerList.isEmpty() || innerList.get(0) != returnType) {
6834 // leading V argument missing => error
6835 MethodType expected = bodyType.insertParameterTypes(0, returnType);
6836 throw misMatchedTypes("body function", bodyType, expected);
6837 } else {
6838 outerList = innerList.subList(1, innerList.size());
6839 }
6840 MethodType predType = pred.type();
6841 if (predType.returnType() != boolean.class ||
6842 !predType.effectivelyIdenticalParameters(0, innerList)) {
6843 throw misMatchedTypes("loop predicate", predType, methodType(boolean.class, innerList));
6844 }
6845 if (init != null) {
6846 MethodType initType = init.type();
6847 if (initType.returnType() != returnType ||
6848 !initType.effectivelyIdenticalParameters(0, outerList)) {
6849 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
6850 }
6851 }
6852 }
6853
6854 /**
6855 * Constructs a loop that runs a given number of iterations.
6856 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
6857 * <p>
6858 * The number of iterations is determined by the {@code iterations} handle evaluation result.
6859 * The loop counter {@code i} is an extra loop iteration variable of type {@code int}.
6860 * It will be initialized to 0 and incremented by 1 in each iteration.
6861 * <p>
6862 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
6863 * of that type is also present. This variable is initialized using the optional {@code init} handle,
6864 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
6865 * <p>
6866 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
6867 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
6868 * iteration variable.
6869 * The result of the loop handle execution will be the final {@code V} value of that variable
6870 * (or {@code void} if there is no {@code V} variable).
6871 * <p>
6872 * The following rules hold for the argument handles:<ul>
6873 * <li>The {@code iterations} handle must not be {@code null}, and must return
6874 * the type {@code int}, referred to here as {@code I} in parameter type lists.
6875 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
6876 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
6877 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
6878 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
6879 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
6880 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
6881 * of types called the <em>internal parameter list</em>.
6882 * It will constrain the parameter lists of the other loop parts.
6883 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
6884 * with no additional {@code A} types, then the internal parameter list is extended by
6885 * the argument types {@code A...} of the {@code iterations} handle.
6886 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
6887 * list {@code (A...)} is called the <em>external parameter list</em>.
6888 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
6889 * additional state variable of the loop.
6890 * The body must both accept a leading parameter and return a value of this type {@code V}.
6891 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
6892 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
6893 * <a href="MethodHandles.html#effid">effectively identical</a>
6894 * to the external parameter list {@code (A...)}.
6895 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
6896 * {@linkplain #empty default value}.
6897 * <li>The parameter list of {@code iterations} (of some form {@code (A*)}) must be
6898 * effectively identical to the external parameter list {@code (A...)}.
6899 * </ul>
6900 * <p>
6901 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
6902 * <li>The loop handle's result type is the result type {@code V} of the body.
6903 * <li>The loop handle's parameter types are the types {@code (A...)},
6904 * from the external parameter list.
6905 * </ul>
6906 * <p>
6907 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
6908 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
6909 * arguments passed to the loop.
6910 * {@snippet lang="java" :
6911 * int iterations(A...);
6912 * V init(A...);
6913 * V body(V, int, A...);
6914 * V countedLoop(A... a...) {
6915 * int end = iterations(a...);
6916 * V v = init(a...);
6917 * for (int i = 0; i < end; ++i) {
6918 * v = body(v, i, a...);
6919 * }
6920 * return v;
6921 * }
6922 * }
6923 *
6924 * @apiNote Example with a fully conformant body method:
6925 * {@snippet lang="java" :
6926 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
6927 * // => a variation on a well known theme
6928 * static String step(String v, int counter, String init) { return "na " + v; }
6929 * // assume MH_step is a handle to the method above
6930 * MethodHandle fit13 = MethodHandles.constant(int.class, 13);
6931 * MethodHandle start = MethodHandles.identity(String.class);
6932 * MethodHandle loop = MethodHandles.countedLoop(fit13, start, MH_step);
6933 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("Lambdaman!"));
6934 * }
6935 *
6936 * @apiNote Example with the simplest possible body method type,
6937 * and passing the number of iterations to the loop invocation:
6938 * {@snippet lang="java" :
6939 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
6940 * // => a variation on a well known theme
6941 * static String step(String v, int counter ) { return "na " + v; }
6942 * // assume MH_step is a handle to the method above
6943 * MethodHandle count = MethodHandles.dropArguments(MethodHandles.identity(int.class), 1, String.class);
6944 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class);
6945 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i) -> "na " + v
6946 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "Lambdaman!"));
6947 * }
6948 *
6949 * @apiNote Example that treats the number of iterations, string to append to, and string to append
6950 * as loop parameters:
6951 * {@snippet lang="java" :
6952 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
6953 * // => a variation on a well known theme
6954 * static String step(String v, int counter, int iterations_, String pre, String start_) { return pre + " " + v; }
6955 * // assume MH_step is a handle to the method above
6956 * MethodHandle count = MethodHandles.identity(int.class);
6957 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class, String.class);
6958 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i, _, pre, _) -> pre + " " + v
6959 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "na", "Lambdaman!"));
6960 * }
6961 *
6962 * @apiNote Example that illustrates the usage of {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}
6963 * to enforce a loop type:
6964 * {@snippet lang="java" :
6965 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
6966 * // => a variation on a well known theme
6967 * static String step(String v, int counter, String pre) { return pre + " " + v; }
6968 * // assume MH_step is a handle to the method above
6969 * MethodType loopType = methodType(String.class, String.class, int.class, String.class);
6970 * MethodHandle count = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(int.class), 0, loopType.parameterList(), 1);
6971 * MethodHandle start = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(String.class), 0, loopType.parameterList(), 2);
6972 * MethodHandle body = MethodHandles.dropArgumentsToMatch(MH_step, 2, loopType.parameterList(), 0);
6973 * MethodHandle loop = MethodHandles.countedLoop(count, start, body); // (v, i, pre, _, _) -> pre + " " + v
6974 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("na", 13, "Lambdaman!"));
6975 * }
6976 *
6977 * @apiNote The implementation of this method can be expressed as follows:
6978 * {@snippet lang="java" :
6979 * MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
6980 * return countedLoop(empty(iterations.type()), iterations, init, body);
6981 * }
6982 * }
6983 *
6984 * @param iterations a non-{@code null} handle to return the number of iterations this loop should run. The handle's
6985 * result type must be {@code int}. See above for other constraints.
6986 * @param init optional initializer, providing the initial value of the loop variable.
6987 * May be {@code null}, implying a default initial value. See above for other constraints.
6988 * @param body body of the loop, which may not be {@code null}.
6989 * It controls the loop parameters and result type in the standard case (see above for details).
6990 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
6991 * and may accept any number of additional types.
6992 * See above for other constraints.
6993 *
6994 * @return a method handle representing the loop.
6995 * @throws NullPointerException if either of the {@code iterations} or {@code body} handles is {@code null}.
6996 * @throws IllegalArgumentException if any argument violates the rules formulated above.
6997 *
6998 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle, MethodHandle)
6999 * @since 9
7000 */
7001 public static MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
7002 return countedLoop(empty(iterations.type()), iterations, init, body);
7003 }
7004
7005 /**
7006 * Constructs a loop that counts over a range of numbers.
7007 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
7008 * <p>
7009 * The loop counter {@code i} is a loop iteration variable of type {@code int}.
7010 * The {@code start} and {@code end} handles determine the start (inclusive) and end (exclusive)
7011 * values of the loop counter.
7012 * The loop counter will be initialized to the {@code int} value returned from the evaluation of the
7013 * {@code start} handle and run to the value returned from {@code end} (exclusively) with a step width of 1.
7014 * <p>
7015 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
7016 * of that type is also present. This variable is initialized using the optional {@code init} handle,
7017 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
7018 * <p>
7019 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
7020 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
7021 * iteration variable.
7022 * The result of the loop handle execution will be the final {@code V} value of that variable
7023 * (or {@code void} if there is no {@code V} variable).
7024 * <p>
7025 * The following rules hold for the argument handles:<ul>
7026 * <li>The {@code start} and {@code end} handles must not be {@code null}, and must both return
7027 * the common type {@code int}, referred to here as {@code I} in parameter type lists.
7028 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
7029 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
7030 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
7031 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
7032 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
7033 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
7034 * of types called the <em>internal parameter list</em>.
7035 * It will constrain the parameter lists of the other loop parts.
7036 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
7037 * with no additional {@code A} types, then the internal parameter list is extended by
7038 * the argument types {@code A...} of the {@code end} handle.
7039 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
7040 * list {@code (A...)} is called the <em>external parameter list</em>.
7041 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
7042 * additional state variable of the loop.
7043 * The body must both accept a leading parameter and return a value of this type {@code V}.
7044 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
7045 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
7046 * <a href="MethodHandles.html#effid">effectively identical</a>
7047 * to the external parameter list {@code (A...)}.
7048 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
7049 * {@linkplain #empty default value}.
7050 * <li>The parameter list of {@code start} (of some form {@code (A*)}) must be
7051 * effectively identical to the external parameter list {@code (A...)}.
7052 * <li>Likewise, the parameter list of {@code end} must be effectively identical
7053 * to the external parameter list.
7054 * </ul>
7055 * <p>
7056 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
7057 * <li>The loop handle's result type is the result type {@code V} of the body.
7058 * <li>The loop handle's parameter types are the types {@code (A...)},
7059 * from the external parameter list.
7060 * </ul>
7061 * <p>
7062 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
7063 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
7064 * arguments passed to the loop.
7065 * {@snippet lang="java" :
7066 * int start(A...);
7067 * int end(A...);
7068 * V init(A...);
7069 * V body(V, int, A...);
7070 * V countedLoop(A... a...) {
7071 * int e = end(a...);
7072 * int s = start(a...);
7073 * V v = init(a...);
7074 * for (int i = s; i < e; ++i) {
7075 * v = body(v, i, a...);
7076 * }
7077 * return v;
7078 * }
7079 * }
7080 *
7081 * @apiNote The implementation of this method can be expressed as follows:
7082 * {@snippet lang="java" :
7083 * MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
7084 * MethodHandle returnVar = dropArguments(identity(init.type().returnType()), 0, int.class, int.class);
7085 * // assume MH_increment and MH_predicate are handles to implementation-internal methods with
7086 * // the following semantics:
7087 * // MH_increment: (int limit, int counter) -> counter + 1
7088 * // MH_predicate: (int limit, int counter) -> counter < limit
7089 * Class<?> counterType = start.type().returnType(); // int
7090 * Class<?> returnType = body.type().returnType();
7091 * MethodHandle incr = MH_increment, pred = MH_predicate, retv = null;
7092 * if (returnType != void.class) { // ignore the V variable
7093 * incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
7094 * pred = dropArguments(pred, 1, returnType); // ditto
7095 * retv = dropArguments(identity(returnType), 0, counterType); // ignore limit
7096 * }
7097 * body = dropArguments(body, 0, counterType); // ignore the limit variable
7098 * MethodHandle[]
7099 * loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
7100 * bodyClause = { init, body }, // v = init(); v = body(v, i)
7101 * indexVar = { start, incr }; // i = start(); i = i + 1
7102 * return loop(loopLimit, bodyClause, indexVar);
7103 * }
7104 * }
7105 *
7106 * @param start a non-{@code null} handle to return the start value of the loop counter, which must be {@code int}.
7107 * See above for other constraints.
7108 * @param end a non-{@code null} handle to return the end value of the loop counter (the loop will run to
7109 * {@code end-1}). The result type must be {@code int}. See above for other constraints.
7110 * @param init optional initializer, providing the initial value of the loop variable.
7111 * May be {@code null}, implying a default initial value. See above for other constraints.
7112 * @param body body of the loop, which may not be {@code null}.
7113 * It controls the loop parameters and result type in the standard case (see above for details).
7114 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
7115 * and may accept any number of additional types.
7116 * See above for other constraints.
7117 *
7118 * @return a method handle representing the loop.
7119 * @throws NullPointerException if any of the {@code start}, {@code end}, or {@code body} handles is {@code null}.
7120 * @throws IllegalArgumentException if any argument violates the rules formulated above.
7121 *
7122 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle)
7123 * @since 9
7124 */
7125 public static MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
7126 countedLoopChecks(start, end, init, body);
7127 Class<?> counterType = start.type().returnType(); // int, but who's counting?
7128 Class<?> limitType = end.type().returnType(); // yes, int again
7129 Class<?> returnType = body.type().returnType();
7130 MethodHandle incr = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopStep);
7131 MethodHandle pred = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopPred);
7132 MethodHandle retv = null;
7133 if (returnType != void.class) {
7134 incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
7135 pred = dropArguments(pred, 1, returnType); // ditto
7136 retv = dropArguments(identity(returnType), 0, counterType);
7137 }
7138 body = dropArguments(body, 0, counterType); // ignore the limit variable
7139 MethodHandle[]
7140 loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
7141 bodyClause = { init, body }, // v = init(); v = body(v, i)
7142 indexVar = { start, incr }; // i = start(); i = i + 1
7143 return loop(loopLimit, bodyClause, indexVar);
7144 }
7145
7146 private static void countedLoopChecks(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
7147 Objects.requireNonNull(start);
7148 Objects.requireNonNull(end);
7149 Objects.requireNonNull(body);
7150 Class<?> counterType = start.type().returnType();
7151 if (counterType != int.class) {
7152 MethodType expected = start.type().changeReturnType(int.class);
7153 throw misMatchedTypes("start function", start.type(), expected);
7154 } else if (end.type().returnType() != counterType) {
7155 MethodType expected = end.type().changeReturnType(counterType);
7156 throw misMatchedTypes("end function", end.type(), expected);
7157 }
7158 MethodType bodyType = body.type();
7159 Class<?> returnType = bodyType.returnType();
7160 List<Class<?>> innerList = bodyType.parameterList();
7161 // strip leading V value if present
7162 int vsize = (returnType == void.class ? 0 : 1);
7163 if (vsize != 0 && (innerList.isEmpty() || innerList.get(0) != returnType)) {
7164 // argument list has no "V" => error
7165 MethodType expected = bodyType.insertParameterTypes(0, returnType);
7166 throw misMatchedTypes("body function", bodyType, expected);
7167 } else if (innerList.size() <= vsize || innerList.get(vsize) != counterType) {
7168 // missing I type => error
7169 MethodType expected = bodyType.insertParameterTypes(vsize, counterType);
7170 throw misMatchedTypes("body function", bodyType, expected);
7171 }
7172 List<Class<?>> outerList = innerList.subList(vsize + 1, innerList.size());
7173 if (outerList.isEmpty()) {
7174 // special case; take lists from end handle
7175 outerList = end.type().parameterList();
7176 innerList = bodyType.insertParameterTypes(vsize + 1, outerList).parameterList();
7177 }
7178 MethodType expected = methodType(counterType, outerList);
7179 if (!start.type().effectivelyIdenticalParameters(0, outerList)) {
7180 throw misMatchedTypes("start parameter types", start.type(), expected);
7181 }
7182 if (end.type() != start.type() &&
7183 !end.type().effectivelyIdenticalParameters(0, outerList)) {
7184 throw misMatchedTypes("end parameter types", end.type(), expected);
7185 }
7186 if (init != null) {
7187 MethodType initType = init.type();
7188 if (initType.returnType() != returnType ||
7189 !initType.effectivelyIdenticalParameters(0, outerList)) {
7190 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
7191 }
7192 }
7193 }
7194
7195 /**
7196 * Constructs a loop that ranges over the values produced by an {@code Iterator<T>}.
7197 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
7198 * <p>
7199 * The iterator itself will be determined by the evaluation of the {@code iterator} handle.
7200 * Each value it produces will be stored in a loop iteration variable of type {@code T}.
7201 * <p>
7202 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
7203 * of that type is also present. This variable is initialized using the optional {@code init} handle,
7204 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
7205 * <p>
7206 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
7207 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
7208 * iteration variable.
7209 * The result of the loop handle execution will be the final {@code V} value of that variable
7210 * (or {@code void} if there is no {@code V} variable).
7211 * <p>
7212 * The following rules hold for the argument handles:<ul>
7213 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
7214 * {@code (V T A...)V}, where {@code V} is non-{@code void}, or else {@code (T A...)void}.
7215 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
7216 * and we will write {@code (V T A...)V} with the understanding that a {@code void} type {@code V}
7217 * is quietly dropped from the parameter list, leaving {@code (T A...)V}.)
7218 * <li>The parameter list {@code (V T A...)} of the body contributes to a list
7219 * of types called the <em>internal parameter list</em>.
7220 * It will constrain the parameter lists of the other loop parts.
7221 * <li>As a special case, if the body contributes only {@code V} and {@code T} types,
7222 * with no additional {@code A} types, then the internal parameter list is extended by
7223 * the argument types {@code A...} of the {@code iterator} handle; if it is {@code null} the
7224 * single type {@code Iterable} is added and constitutes the {@code A...} list.
7225 * <li>If the iteration variable types {@code (V T)} are dropped from the internal parameter list, the resulting shorter
7226 * list {@code (A...)} is called the <em>external parameter list</em>.
7227 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
7228 * additional state variable of the loop.
7229 * The body must both accept a leading parameter and return a value of this type {@code V}.
7230 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
7231 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
7232 * <a href="MethodHandles.html#effid">effectively identical</a>
7233 * to the external parameter list {@code (A...)}.
7234 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
7235 * {@linkplain #empty default value}.
7236 * <li>If the {@code iterator} handle is non-{@code null}, it must have the return
7237 * type {@code java.util.Iterator} or a subtype thereof.
7238 * The iterator it produces when the loop is executed will be assumed
7239 * to yield values which can be converted to type {@code T}.
7240 * <li>The parameter list of an {@code iterator} that is non-{@code null} (of some form {@code (A*)}) must be
7241 * effectively identical to the external parameter list {@code (A...)}.
7242 * <li>If {@code iterator} is {@code null} it defaults to a method handle which behaves
7243 * like {@link java.lang.Iterable#iterator()}. In that case, the internal parameter list
7244 * {@code (V T A...)} must have at least one {@code A} type, and the default iterator
7245 * handle parameter is adjusted to accept the leading {@code A} type, as if by
7246 * the {@link MethodHandle#asType asType} conversion method.
7247 * The leading {@code A} type must be {@code Iterable} or a subtype thereof.
7248 * This conversion step, done at loop construction time, must not throw a {@code WrongMethodTypeException}.
7249 * </ul>
7250 * <p>
7251 * The type {@code T} may be either a primitive or reference.
7252 * Since type {@code Iterator<T>} is erased in the method handle representation to the raw type {@code Iterator},
7253 * the {@code iteratedLoop} combinator adjusts the leading argument type for {@code body} to {@code Object}
7254 * as if by the {@link MethodHandle#asType asType} conversion method.
7255 * Therefore, if an iterator of the wrong type appears as the loop is executed, runtime exceptions may occur
7256 * as the result of dynamic conversions performed by {@link MethodHandle#asType(MethodType)}.
7257 * <p>
7258 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
7259 * <li>The loop handle's result type is the result type {@code V} of the body.
7260 * <li>The loop handle's parameter types are the types {@code (A...)},
7261 * from the external parameter list.
7262 * </ul>
7263 * <p>
7264 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
7265 * the loop variable as well as the result type of the loop; {@code T}/{@code t}, that of the elements of the
7266 * structure the loop iterates over, and {@code A...}/{@code a...} represent arguments passed to the loop.
7267 * {@snippet lang="java" :
7268 * Iterator<T> iterator(A...); // defaults to Iterable::iterator
7269 * V init(A...);
7270 * V body(V,T,A...);
7271 * V iteratedLoop(A... a...) {
7272 * Iterator<T> it = iterator(a...);
7273 * V v = init(a...);
7274 * while (it.hasNext()) {
7275 * T t = it.next();
7276 * v = body(v, t, a...);
7277 * }
7278 * return v;
7279 * }
7280 * }
7281 *
7282 * @apiNote Example:
7283 * {@snippet lang="java" :
7284 * // get an iterator from a list
7285 * static List<String> reverseStep(List<String> r, String e) {
7286 * r.add(0, e);
7287 * return r;
7288 * }
7289 * static List<String> newArrayList() { return new ArrayList<>(); }
7290 * // assume MH_reverseStep and MH_newArrayList are handles to the above methods
7291 * MethodHandle loop = MethodHandles.iteratedLoop(null, MH_newArrayList, MH_reverseStep);
7292 * List<String> list = Arrays.asList("a", "b", "c", "d", "e");
7293 * List<String> reversedList = Arrays.asList("e", "d", "c", "b", "a");
7294 * assertEquals(reversedList, (List<String>) loop.invoke(list));
7295 * }
7296 *
7297 * @apiNote The implementation of this method can be expressed approximately as follows:
7298 * {@snippet lang="java" :
7299 * MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
7300 * // assume MH_next, MH_hasNext, MH_startIter are handles to methods of Iterator/Iterable
7301 * Class<?> returnType = body.type().returnType();
7302 * Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
7303 * MethodHandle nextVal = MH_next.asType(MH_next.type().changeReturnType(ttype));
7304 * MethodHandle retv = null, step = body, startIter = iterator;
7305 * if (returnType != void.class) {
7306 * // the simple thing first: in (I V A...), drop the I to get V
7307 * retv = dropArguments(identity(returnType), 0, Iterator.class);
7308 * // body type signature (V T A...), internal loop types (I V A...)
7309 * step = swapArguments(body, 0, 1); // swap V <-> T
7310 * }
7311 * if (startIter == null) startIter = MH_getIter;
7312 * MethodHandle[]
7313 * iterVar = { startIter, null, MH_hasNext, retv }, // it = iterator; while (it.hasNext())
7314 * bodyClause = { init, filterArguments(step, 0, nextVal) }; // v = body(v, t, a)
7315 * return loop(iterVar, bodyClause);
7316 * }
7317 * }
7318 *
7319 * @param iterator an optional handle to return the iterator to start the loop.
7320 * If non-{@code null}, the handle must return {@link java.util.Iterator} or a subtype.
7321 * See above for other constraints.
7322 * @param init optional initializer, providing the initial value of the loop variable.
7323 * May be {@code null}, implying a default initial value. See above for other constraints.
7324 * @param body body of the loop, which may not be {@code null}.
7325 * It controls the loop parameters and result type in the standard case (see above for details).
7326 * It must accept its own return type (if non-void) plus a {@code T} parameter (for the iterated values),
7327 * and may accept any number of additional types.
7328 * See above for other constraints.
7329 *
7330 * @return a method handle embodying the iteration loop functionality.
7331 * @throws NullPointerException if the {@code body} handle is {@code null}.
7332 * @throws IllegalArgumentException if any argument violates the above requirements.
7333 *
7334 * @since 9
7335 */
7336 public static MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
7337 Class<?> iterableType = iteratedLoopChecks(iterator, init, body);
7338 Class<?> returnType = body.type().returnType();
7339 MethodHandle hasNext = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iteratePred);
7340 MethodHandle nextRaw = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iterateNext);
7341 MethodHandle startIter;
7342 MethodHandle nextVal;
7343 {
7344 MethodType iteratorType;
7345 if (iterator == null) {
7346 // derive argument type from body, if available, else use Iterable
7347 startIter = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_initIterator);
7348 iteratorType = startIter.type().changeParameterType(0, iterableType);
7349 } else {
7350 // force return type to the internal iterator class
7351 iteratorType = iterator.type().changeReturnType(Iterator.class);
7352 startIter = iterator;
7353 }
7354 Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
7355 MethodType nextValType = nextRaw.type().changeReturnType(ttype);
7356
7357 // perform the asType transforms under an exception transformer, as per spec.:
7358 try {
7359 startIter = startIter.asType(iteratorType);
7360 nextVal = nextRaw.asType(nextValType);
7361 } catch (WrongMethodTypeException ex) {
7362 throw new IllegalArgumentException(ex);
7363 }
7364 }
7365
7366 MethodHandle retv = null, step = body;
7367 if (returnType != void.class) {
7368 // the simple thing first: in (I V A...), drop the I to get V
7369 retv = dropArguments(identity(returnType), 0, Iterator.class);
7370 // body type signature (V T A...), internal loop types (I V A...)
7371 step = swapArguments(body, 0, 1); // swap V <-> T
7372 }
7373
7374 MethodHandle[]
7375 iterVar = { startIter, null, hasNext, retv },
7376 bodyClause = { init, filterArgument(step, 0, nextVal) };
7377 return loop(iterVar, bodyClause);
7378 }
7379
7380 private static Class<?> iteratedLoopChecks(MethodHandle iterator, MethodHandle init, MethodHandle body) {
7381 Objects.requireNonNull(body);
7382 MethodType bodyType = body.type();
7383 Class<?> returnType = bodyType.returnType();
7384 List<Class<?>> internalParamList = bodyType.parameterList();
7385 // strip leading V value if present
7386 int vsize = (returnType == void.class ? 0 : 1);
7387 if (vsize != 0 && (internalParamList.isEmpty() || internalParamList.get(0) != returnType)) {
7388 // argument list has no "V" => error
7389 MethodType expected = bodyType.insertParameterTypes(0, returnType);
7390 throw misMatchedTypes("body function", bodyType, expected);
7391 } else if (internalParamList.size() <= vsize) {
7392 // missing T type => error
7393 MethodType expected = bodyType.insertParameterTypes(vsize, Object.class);
7394 throw misMatchedTypes("body function", bodyType, expected);
7395 }
7396 List<Class<?>> externalParamList = internalParamList.subList(vsize + 1, internalParamList.size());
7397 Class<?> iterableType = null;
7398 if (iterator != null) {
7399 // special case; if the body handle only declares V and T then
7400 // the external parameter list is obtained from iterator handle
7401 if (externalParamList.isEmpty()) {
7402 externalParamList = iterator.type().parameterList();
7403 }
7404 MethodType itype = iterator.type();
7405 if (!Iterator.class.isAssignableFrom(itype.returnType())) {
7406 throw newIllegalArgumentException("iteratedLoop first argument must have Iterator return type");
7407 }
7408 if (!itype.effectivelyIdenticalParameters(0, externalParamList)) {
7409 MethodType expected = methodType(itype.returnType(), externalParamList);
7410 throw misMatchedTypes("iterator parameters", itype, expected);
7411 }
7412 } else {
7413 if (externalParamList.isEmpty()) {
7414 // special case; if the iterator handle is null and the body handle
7415 // only declares V and T then the external parameter list consists
7416 // of Iterable
7417 externalParamList = List.of(Iterable.class);
7418 iterableType = Iterable.class;
7419 } else {
7420 // special case; if the iterator handle is null and the external
7421 // parameter list is not empty then the first parameter must be
7422 // assignable to Iterable
7423 iterableType = externalParamList.get(0);
7424 if (!Iterable.class.isAssignableFrom(iterableType)) {
7425 throw newIllegalArgumentException(
7426 "inferred first loop argument must inherit from Iterable: " + iterableType);
7427 }
7428 }
7429 }
7430 if (init != null) {
7431 MethodType initType = init.type();
7432 if (initType.returnType() != returnType ||
7433 !initType.effectivelyIdenticalParameters(0, externalParamList)) {
7434 throw misMatchedTypes("loop initializer", initType, methodType(returnType, externalParamList));
7435 }
7436 }
7437 return iterableType; // help the caller a bit
7438 }
7439
7440 /*non-public*/
7441 static MethodHandle swapArguments(MethodHandle mh, int i, int j) {
7442 // there should be a better way to uncross my wires
7443 int arity = mh.type().parameterCount();
7444 int[] order = new int[arity];
7445 for (int k = 0; k < arity; k++) order[k] = k;
7446 order[i] = j; order[j] = i;
7447 Class<?>[] types = mh.type().parameterArray();
7448 Class<?> ti = types[i]; types[i] = types[j]; types[j] = ti;
7449 MethodType swapType = methodType(mh.type().returnType(), types);
7450 return permuteArguments(mh, swapType, order);
7451 }
7452
7453 /**
7454 * Makes a method handle that adapts a {@code target} method handle by wrapping it in a {@code try-finally} block.
7455 * Another method handle, {@code cleanup}, represents the functionality of the {@code finally} block. Any exception
7456 * thrown during the execution of the {@code target} handle will be passed to the {@code cleanup} handle. The
7457 * exception will be rethrown, unless {@code cleanup} handle throws an exception first. The
7458 * value returned from the {@code cleanup} handle's execution will be the result of the execution of the
7459 * {@code try-finally} handle.
7460 * <p>
7461 * The {@code cleanup} handle will be passed one or two additional leading arguments.
7462 * The first is the exception thrown during the
7463 * execution of the {@code target} handle, or {@code null} if no exception was thrown.
7464 * The second is the result of the execution of the {@code target} handle, or, if it throws an exception,
7465 * a {@code null}, zero, or {@code false} value of the required type is supplied as a placeholder.
7466 * The second argument is not present if the {@code target} handle has a {@code void} return type.
7467 * (Note that, except for argument type conversions, combinators represent {@code void} values in parameter lists
7468 * by omitting the corresponding paradoxical arguments, not by inserting {@code null} or zero values.)
7469 * <p>
7470 * The {@code target} and {@code cleanup} handles must have the same corresponding argument and return types, except
7471 * that the {@code cleanup} handle may omit trailing arguments. Also, the {@code cleanup} handle must have one or
7472 * two extra leading parameters:<ul>
7473 * <li>a {@code Throwable}, which will carry the exception thrown by the {@code target} handle (if any); and
7474 * <li>a parameter of the same type as the return type of both {@code target} and {@code cleanup}, which will carry
7475 * the result from the execution of the {@code target} handle.
7476 * This parameter is not present if the {@code target} returns {@code void}.
7477 * </ul>
7478 * <p>
7479 * The pseudocode for the resulting adapter looks as follows. In the code, {@code V} represents the result type of
7480 * the {@code try/finally} construct; {@code A}/{@code a}, the types and values of arguments to the resulting
7481 * handle consumed by the cleanup; and {@code B}/{@code b}, those of arguments to the resulting handle discarded by
7482 * the cleanup.
7483 * {@snippet lang="java" :
7484 * V target(A..., B...);
7485 * V cleanup(Throwable, V, A...);
7486 * V adapter(A... a, B... b) {
7487 * V result = (zero value for V);
7488 * Throwable throwable = null;
7489 * try {
7490 * result = target(a..., b...);
7491 * } catch (Throwable t) {
7492 * throwable = t;
7493 * throw t;
7494 * } finally {
7495 * result = cleanup(throwable, result, a...);
7496 * }
7497 * return result;
7498 * }
7499 * }
7500 * <p>
7501 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
7502 * be modified by execution of the target, and so are passed unchanged
7503 * from the caller to the cleanup, if it is invoked.
7504 * <p>
7505 * The target and cleanup must return the same type, even if the cleanup
7506 * always throws.
7507 * To create such a throwing cleanup, compose the cleanup logic
7508 * with {@link #throwException throwException},
7509 * in order to create a method handle of the correct return type.
7510 * <p>
7511 * Note that {@code tryFinally} never converts exceptions into normal returns.
7512 * In rare cases where exceptions must be converted in that way, first wrap
7513 * the target with {@link #catchException(MethodHandle, Class, MethodHandle)}
7514 * to capture an outgoing exception, and then wrap with {@code tryFinally}.
7515 * <p>
7516 * It is recommended that the first parameter type of {@code cleanup} be
7517 * declared {@code Throwable} rather than a narrower subtype. This ensures
7518 * {@code cleanup} will always be invoked with whatever exception that
7519 * {@code target} throws. Declaring a narrower type may result in a
7520 * {@code ClassCastException} being thrown by the {@code try-finally}
7521 * handle if the type of the exception thrown by {@code target} is not
7522 * assignable to the first parameter type of {@code cleanup}. Note that
7523 * various exception types of {@code VirtualMachineError},
7524 * {@code LinkageError}, and {@code RuntimeException} can in principle be
7525 * thrown by almost any kind of Java code, and a finally clause that
7526 * catches (say) only {@code IOException} would mask any of the others
7527 * behind a {@code ClassCastException}.
7528 *
7529 * @param target the handle whose execution is to be wrapped in a {@code try} block.
7530 * @param cleanup the handle that is invoked in the finally block.
7531 *
7532 * @return a method handle embodying the {@code try-finally} block composed of the two arguments.
7533 * @throws NullPointerException if any argument is null
7534 * @throws IllegalArgumentException if {@code cleanup} does not accept
7535 * the required leading arguments, or if the method handle types do
7536 * not match in their return types and their
7537 * corresponding trailing parameters
7538 *
7539 * @see MethodHandles#catchException(MethodHandle, Class, MethodHandle)
7540 * @since 9
7541 */
7542 public static MethodHandle tryFinally(MethodHandle target, MethodHandle cleanup) {
7543 Class<?>[] targetParamTypes = target.type().ptypes();
7544 Class<?> rtype = target.type().returnType();
7545
7546 tryFinallyChecks(target, cleanup);
7547
7548 // Match parameter lists: if the cleanup has a shorter parameter list than the target, add ignored arguments.
7549 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
7550 // target parameter list.
7551 cleanup = dropArgumentsToMatch(cleanup, (rtype == void.class ? 1 : 2), targetParamTypes, 0, false);
7552
7553 // Ensure that the intrinsic type checks the instance thrown by the
7554 // target against the first parameter of cleanup
7555 cleanup = cleanup.asType(cleanup.type().changeParameterType(0, Throwable.class));
7556
7557 // Use asFixedArity() to avoid unnecessary boxing of last argument for VarargsCollector case.
7558 return MethodHandleImpl.makeTryFinally(target.asFixedArity(), cleanup.asFixedArity(), rtype, targetParamTypes);
7559 }
7560
7561 private static void tryFinallyChecks(MethodHandle target, MethodHandle cleanup) {
7562 Class<?> rtype = target.type().returnType();
7563 if (rtype != cleanup.type().returnType()) {
7564 throw misMatchedTypes("target and return types", cleanup.type().returnType(), rtype);
7565 }
7566 MethodType cleanupType = cleanup.type();
7567 if (!Throwable.class.isAssignableFrom(cleanupType.parameterType(0))) {
7568 throw misMatchedTypes("cleanup first argument and Throwable", cleanup.type(), Throwable.class);
7569 }
7570 if (rtype != void.class && cleanupType.parameterType(1) != rtype) {
7571 throw misMatchedTypes("cleanup second argument and target return type", cleanup.type(), rtype);
7572 }
7573 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
7574 // target parameter list.
7575 int cleanupArgIndex = rtype == void.class ? 1 : 2;
7576 if (!cleanupType.effectivelyIdenticalParameters(cleanupArgIndex, target.type().parameterList())) {
7577 throw misMatchedTypes("cleanup parameters after (Throwable,result) and target parameter list prefix",
7578 cleanup.type(), target.type());
7579 }
7580 }
7581
7582 /**
7583 * Creates a table switch method handle, which can be used to switch over a set of target
7584 * method handles, based on a given target index, called selector.
7585 * <p>
7586 * For a selector value of {@code n}, where {@code n} falls in the range {@code [0, N)},
7587 * and where {@code N} is the number of target method handles, the table switch method
7588 * handle will invoke the n-th target method handle from the list of target method handles.
7589 * <p>
7590 * For a selector value that does not fall in the range {@code [0, N)}, the table switch
7591 * method handle will invoke the given fallback method handle.
7592 * <p>
7593 * All method handles passed to this method must have the same type, with the additional
7594 * requirement that the leading parameter be of type {@code int}. The leading parameter
7595 * represents the selector.
7596 * <p>
7597 * Any trailing parameters present in the type will appear on the returned table switch
7598 * method handle as well. Any arguments assigned to these parameters will be forwarded,
7599 * together with the selector value, to the selected method handle when invoking it.
7600 *
7601 * @apiNote Example:
7602 * The cases each drop the {@code selector} value they are given, and take an additional
7603 * {@code String} argument, which is concatenated (using {@link String#concat(String)})
7604 * to a specific constant label string for each case:
7605 * {@snippet lang="java" :
7606 * MethodHandles.Lookup lookup = MethodHandles.lookup();
7607 * MethodHandle caseMh = lookup.findVirtual(String.class, "concat",
7608 * MethodType.methodType(String.class, String.class));
7609 * caseMh = MethodHandles.dropArguments(caseMh, 0, int.class);
7610 *
7611 * MethodHandle caseDefault = MethodHandles.insertArguments(caseMh, 1, "default: ");
7612 * MethodHandle case0 = MethodHandles.insertArguments(caseMh, 1, "case 0: ");
7613 * MethodHandle case1 = MethodHandles.insertArguments(caseMh, 1, "case 1: ");
7614 *
7615 * MethodHandle mhSwitch = MethodHandles.tableSwitch(
7616 * caseDefault,
7617 * case0,
7618 * case1
7619 * );
7620 *
7621 * assertEquals("default: data", (String) mhSwitch.invokeExact(-1, "data"));
7622 * assertEquals("case 0: data", (String) mhSwitch.invokeExact(0, "data"));
7623 * assertEquals("case 1: data", (String) mhSwitch.invokeExact(1, "data"));
7624 * assertEquals("default: data", (String) mhSwitch.invokeExact(2, "data"));
7625 * }
7626 *
7627 * @param fallback the fallback method handle that is called when the selector is not
7628 * within the range {@code [0, N)}.
7629 * @param targets array of target method handles.
7630 * @return the table switch method handle.
7631 * @throws NullPointerException if {@code fallback}, the {@code targets} array, or any
7632 * any of the elements of the {@code targets} array are
7633 * {@code null}.
7634 * @throws IllegalArgumentException if the {@code targets} array is empty, if the leading
7635 * parameter of the fallback handle or any of the target
7636 * handles is not {@code int}, or if the types of
7637 * the fallback handle and all of target handles are
7638 * not the same.
7639 *
7640 * @since 17
7641 */
7642 public static MethodHandle tableSwitch(MethodHandle fallback, MethodHandle... targets) {
7643 Objects.requireNonNull(fallback);
7644 Objects.requireNonNull(targets);
7645 targets = targets.clone();
7646 MethodType type = tableSwitchChecks(fallback, targets);
7647 return MethodHandleImpl.makeTableSwitch(type, fallback, targets);
7648 }
7649
7650 private static MethodType tableSwitchChecks(MethodHandle defaultCase, MethodHandle[] caseActions) {
7651 if (caseActions.length == 0)
7652 throw new IllegalArgumentException("Not enough cases: " + Arrays.toString(caseActions));
7653
7654 MethodType expectedType = defaultCase.type();
7655
7656 if (!(expectedType.parameterCount() >= 1) || expectedType.parameterType(0) != int.class)
7657 throw new IllegalArgumentException(
7658 "Case actions must have int as leading parameter: " + Arrays.toString(caseActions));
7659
7660 for (MethodHandle mh : caseActions) {
7661 Objects.requireNonNull(mh);
7662 if (mh.type() != expectedType)
7663 throw new IllegalArgumentException(
7664 "Case actions must have the same type: " + Arrays.toString(caseActions));
7665 }
7666
7667 return expectedType;
7668 }
7669
7670 /**
7671 * Adapts a target var handle by pre-processing incoming and outgoing values using a pair of filter functions.
7672 * <p>
7673 * When calling e.g. {@link VarHandle#set(Object...)} on the resulting var handle, the incoming value (of type {@code T}, where
7674 * {@code T} is the <em>last</em> parameter type of the first filter function) is processed using the first filter and then passed
7675 * to the target var handle.
7676 * Conversely, when calling e.g. {@link VarHandle#get(Object...)} on the resulting var handle, the return value obtained from
7677 * the target var handle (of type {@code T}, where {@code T} is the <em>last</em> parameter type of the second filter function)
7678 * is processed using the second filter and returned to the caller. More advanced access mode types, such as
7679 * {@link VarHandle.AccessMode#COMPARE_AND_EXCHANGE} might apply both filters at the same time.
7680 * <p>
7681 * For the boxing and unboxing filters to be well-formed, their types must be of the form {@code (A... , S) -> T} and
7682 * {@code (A... , T) -> S}, respectively, where {@code T} is the type of the target var handle. If this is the case,
7683 * the resulting var handle will have type {@code S} and will feature the additional coordinates {@code A...} (which
7684 * will be appended to the coordinates of the target var handle).
7685 * <p>
7686 * If the boxing and unboxing filters throw any checked exceptions when invoked, the resulting var handle will
7687 * throw an {@link IllegalStateException}.
7688 * <p>
7689 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
7690 * atomic access guarantees as those featured by the target var handle.
7691 *
7692 * @param target the target var handle
7693 * @param filterToTarget a filter to convert some type {@code S} into the type of {@code target}
7694 * @param filterFromTarget a filter to convert the type of {@code target} to some type {@code S}
7695 * @return an adapter var handle which accepts a new type, performing the provided boxing/unboxing conversions.
7696 * @throws IllegalArgumentException if {@code filterFromTarget} and {@code filterToTarget} are not well-formed, that is, they have types
7697 * other than {@code (A... , S) -> T} and {@code (A... , T) -> S}, respectively, where {@code T} is the type of the target var handle,
7698 * or if it's determined that either {@code filterFromTarget} or {@code filterToTarget} throws any checked exceptions.
7699 * @throws NullPointerException if any of the arguments is {@code null}.
7700 * @since 22
7701 */
7702 public static VarHandle filterValue(VarHandle target, MethodHandle filterToTarget, MethodHandle filterFromTarget) {
7703 return VarHandles.filterValue(target, filterToTarget, filterFromTarget);
7704 }
7705
7706 /**
7707 * Adapts a target var handle by pre-processing incoming coordinate values using unary filter functions.
7708 * <p>
7709 * When calling e.g. {@link VarHandle#get(Object...)} on the resulting var handle, the incoming coordinate values
7710 * starting at position {@code pos} (of type {@code C1, C2 ... Cn}, where {@code C1, C2 ... Cn} are the return types
7711 * of the unary filter functions) are transformed into new values (of type {@code S1, S2 ... Sn}, where {@code S1, S2 ... Sn} are the
7712 * parameter types of the unary filter functions), and then passed (along with any coordinate that was left unaltered
7713 * by the adaptation) to the target var handle.
7714 * <p>
7715 * For the coordinate filters to be well-formed, their types must be of the form {@code S1 -> T1, S2 -> T1 ... Sn -> Tn},
7716 * where {@code T1, T2 ... Tn} are the coordinate types starting at position {@code pos} of the target var handle.
7717 * <p>
7718 * If any of the filters throws a checked exception when invoked, the resulting var handle will
7719 * throw an {@link IllegalStateException}.
7720 * <p>
7721 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
7722 * atomic access guarantees as those featured by the target var handle.
7723 *
7724 * @param target the target var handle
7725 * @param pos the position of the first coordinate to be transformed
7726 * @param filters the unary functions which are used to transform coordinates starting at position {@code pos}
7727 * @return an adapter var handle which accepts new coordinate types, applying the provided transformation
7728 * to the new coordinate values.
7729 * @throws IllegalArgumentException if the handles in {@code filters} are not well-formed, that is, they have types
7730 * other than {@code S1 -> T1, S2 -> T2, ... Sn -> Tn} where {@code T1, T2 ... Tn} are the coordinate types starting
7731 * at position {@code pos} of the target var handle, if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive,
7732 * or if more filters are provided than the actual number of coordinate types available starting at {@code pos},
7733 * or if it's determined that any of the filters throws any checked exceptions.
7734 * @throws NullPointerException if any of the arguments is {@code null} or {@code filters} contains {@code null}.
7735 * @since 22
7736 */
7737 public static VarHandle filterCoordinates(VarHandle target, int pos, MethodHandle... filters) {
7738 return VarHandles.filterCoordinates(target, pos, filters);
7739 }
7740
7741 /**
7742 * Provides a target var handle with one or more <em>bound coordinates</em>
7743 * in advance of the var handle's invocation. As a consequence, the resulting var handle will feature less
7744 * coordinate types than the target var handle.
7745 * <p>
7746 * When calling e.g. {@link VarHandle#get(Object...)} on the resulting var handle, incoming coordinate values
7747 * are joined with bound coordinate values, and then passed to the target var handle.
7748 * <p>
7749 * For the bound coordinates to be well-formed, their types must be {@code T1, T2 ... Tn },
7750 * where {@code T1, T2 ... Tn} are the coordinate types starting at position {@code pos} of the target var handle.
7751 * <p>
7752 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
7753 * atomic access guarantees as those featured by the target var handle.
7754 *
7755 * @param target the var handle to invoke after the bound coordinates are inserted
7756 * @param pos the position of the first coordinate to be inserted
7757 * @param values the series of bound coordinates to insert
7758 * @return an adapter var handle which inserts additional coordinates,
7759 * before calling the target var handle
7760 * @throws IllegalArgumentException if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive,
7761 * or if more values are provided than the actual number of coordinate types available starting at {@code pos}.
7762 * @throws ClassCastException if the bound coordinates in {@code values} are not well-formed, that is, they have types
7763 * other than {@code T1, T2 ... Tn }, where {@code T1, T2 ... Tn} are the coordinate types starting at position {@code pos}
7764 * of the target var handle.
7765 * @throws NullPointerException if any of the arguments is {@code null} or {@code values} contains {@code null}.
7766 * @since 22
7767 */
7768 public static VarHandle insertCoordinates(VarHandle target, int pos, Object... values) {
7769 return VarHandles.insertCoordinates(target, pos, values);
7770 }
7771
7772 /**
7773 * Provides a var handle which adapts the coordinate values of the target var handle, by re-arranging them
7774 * so that the new coordinates match the provided ones.
7775 * <p>
7776 * The given array controls the reordering.
7777 * Call {@code #I} the number of incoming coordinates (the value
7778 * {@code newCoordinates.size()}), and call {@code #O} the number
7779 * of outgoing coordinates (the number of coordinates associated with the target var handle).
7780 * Then the length of the reordering array must be {@code #O},
7781 * and each element must be a non-negative number less than {@code #I}.
7782 * For every {@code N} less than {@code #O}, the {@code N}-th
7783 * outgoing coordinate will be taken from the {@code I}-th incoming
7784 * coordinate, where {@code I} is {@code reorder[N]}.
7785 * <p>
7786 * No coordinate value conversions are applied.
7787 * The type of each incoming coordinate, as determined by {@code newCoordinates},
7788 * must be identical to the type of the corresponding outgoing coordinate
7789 * in the target var handle.
7790 * <p>
7791 * The reordering array need not specify an actual permutation.
7792 * An incoming coordinate will be duplicated if its index appears
7793 * more than once in the array, and an incoming coordinate will be dropped
7794 * if its index does not appear in the array.
7795 * <p>
7796 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
7797 * atomic access guarantees as those featured by the target var handle.
7798 * @param target the var handle to invoke after the coordinates have been reordered
7799 * @param newCoordinates the new coordinate types
7800 * @param reorder an index array which controls the reordering
7801 * @return an adapter var handle which re-arranges the incoming coordinate values,
7802 * before calling the target var handle
7803 * @throws IllegalArgumentException if the index array length is not equal to
7804 * the number of coordinates of the target var handle, or if any index array element is not a valid index for
7805 * a coordinate of {@code newCoordinates}, or if two corresponding coordinate types in
7806 * the target var handle and in {@code newCoordinates} are not identical.
7807 * @throws NullPointerException if any of the arguments is {@code null} or {@code newCoordinates} contains {@code null}.
7808 * @since 22
7809 */
7810 public static VarHandle permuteCoordinates(VarHandle target, List<Class<?>> newCoordinates, int... reorder) {
7811 return VarHandles.permuteCoordinates(target, newCoordinates, reorder);
7812 }
7813
7814 /**
7815 * Adapts a target var handle by pre-processing
7816 * a sub-sequence of its coordinate values with a filter (a method handle).
7817 * The pre-processed coordinates are replaced by the result (if any) of the
7818 * filter function and the target var handle is then called on the modified (usually shortened)
7819 * coordinate list.
7820 * <p>
7821 * If {@code R} is the return type of the filter, then:
7822 * <ul>
7823 * <li>if {@code R} <em>is not</em> {@code void}, the target var handle must have a coordinate of type {@code R} in
7824 * position {@code pos}. The parameter types of the filter will replace the coordinate type at position {@code pos}
7825 * of the target var handle. When the returned var handle is invoked, it will be as if the filter is invoked first,
7826 * and its result is passed in place of the coordinate at position {@code pos} in a downstream invocation of the
7827 * target var handle.</li>
7828 * <li> if {@code R} <em>is</em> {@code void}, the parameter types (if any) of the filter will be inserted in the
7829 * coordinate type list of the target var handle at position {@code pos}. In this case, when the returned var handle
7830 * is invoked, the filter essentially acts as a side effect, consuming some of the coordinate values, before a
7831 * downstream invocation of the target var handle.</li>
7832 * </ul>
7833 * <p>
7834 * If any of the filters throws a checked exception when invoked, the resulting var handle will
7835 * throw an {@link IllegalStateException}.
7836 * <p>
7837 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
7838 * atomic access guarantees as those featured by the target var handle.
7839 *
7840 * @param target the var handle to invoke after the coordinates have been filtered
7841 * @param pos the position in the coordinate list of the target var handle where the filter is to be inserted
7842 * @param filter the filter method handle
7843 * @return an adapter var handle which filters the incoming coordinate values,
7844 * before calling the target var handle
7845 * @throws IllegalArgumentException if the return type of {@code filter}
7846 * is not void, and it is not the same as the {@code pos} coordinate of the target var handle,
7847 * if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive,
7848 * if the resulting var handle's type would have <a href="MethodHandle.html#maxarity">too many coordinates</a>,
7849 * or if it's determined that {@code filter} throws any checked exceptions.
7850 * @throws NullPointerException if any of the arguments is {@code null}.
7851 * @since 22
7852 */
7853 public static VarHandle collectCoordinates(VarHandle target, int pos, MethodHandle filter) {
7854 return VarHandles.collectCoordinates(target, pos, filter);
7855 }
7856
7857 /**
7858 * Returns a var handle which will discard some dummy coordinates before delegating to the
7859 * target var handle. As a consequence, the resulting var handle will feature more
7860 * coordinate types than the target var handle.
7861 * <p>
7862 * The {@code pos} argument may range between zero and <i>N</i>, where <i>N</i> is the arity of the
7863 * target var handle's coordinate types. If {@code pos} is zero, the dummy coordinates will precede
7864 * the target's real arguments; if {@code pos} is <i>N</i> they will come after.
7865 * <p>
7866 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
7867 * atomic access guarantees as those featured by the target var handle.
7868 *
7869 * @param target the var handle to invoke after the dummy coordinates are dropped
7870 * @param pos position of the first coordinate to drop (zero for the leftmost)
7871 * @param valueTypes the type(s) of the coordinate(s) to drop
7872 * @return an adapter var handle which drops some dummy coordinates,
7873 * before calling the target var handle
7874 * @throws IllegalArgumentException if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive.
7875 * @throws NullPointerException if any of the arguments is {@code null} or {@code valueTypes} contains {@code null}.
7876 * @since 22
7877 */
7878 public static VarHandle dropCoordinates(VarHandle target, int pos, Class<?>... valueTypes) {
7879 return VarHandles.dropCoordinates(target, pos, valueTypes);
7880 }
7881 }