1 /*
2 * Copyright (c) 2008, 2023, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package java.lang.invoke;
27
28 import jdk.internal.access.SharedSecrets;
29 import jdk.internal.misc.Unsafe;
30 import jdk.internal.misc.VM;
31 import jdk.internal.org.objectweb.asm.ClassReader;
32 import jdk.internal.org.objectweb.asm.Opcodes;
33 import jdk.internal.org.objectweb.asm.Type;
34 import jdk.internal.reflect.CallerSensitive;
35 import jdk.internal.reflect.CallerSensitiveAdapter;
36 import jdk.internal.reflect.Reflection;
37 import jdk.internal.util.ClassFileDumper;
38 import jdk.internal.vm.annotation.ForceInline;
39 import sun.invoke.util.ValueConversions;
40 import sun.invoke.util.VerifyAccess;
41 import sun.invoke.util.Wrapper;
42 import sun.reflect.misc.ReflectUtil;
43 import sun.security.util.SecurityConstants;
44
45 import java.lang.constant.ConstantDescs;
46 import java.lang.invoke.LambdaForm.BasicType;
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.invoke.LambdaForm.BasicType.V_TYPE;
66 import static java.lang.invoke.MethodHandleImpl.Intrinsic;
67 import static java.lang.invoke.MethodHandleNatives.Constants.*;
68 import static java.lang.invoke.MethodHandleStatics.UNSAFE;
69 import static java.lang.invoke.MethodHandleStatics.newIllegalArgumentException;
70 import static java.lang.invoke.MethodHandleStatics.newInternalError;
71 import static java.lang.invoke.MethodType.methodType;
72
73 /**
74 * This class consists exclusively of static methods that operate on or return
75 * method handles. They fall into several categories:
76 * <ul>
77 * <li>Lookup methods which help create method handles for methods and fields.
78 * <li>Combinator methods, which combine or transform pre-existing method handles into new ones.
79 * <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns.
80 * </ul>
81 * A lookup, combinator, or factory method will fail and throw an
82 * {@code IllegalArgumentException} if the created method handle's type
83 * would have <a href="MethodHandle.html#maxarity">too many parameters</a>.
84 *
85 * @author John Rose, JSR 292 EG
86 * @since 1.7
87 */
88 public class MethodHandles {
89
90 private MethodHandles() { } // do not instantiate
91
92 static final MemberName.Factory IMPL_NAMES = MemberName.getFactory();
93
94 // See IMPL_LOOKUP below.
95
96 //// Method handle creation from ordinary methods.
97
98 /**
99 * Returns a {@link Lookup lookup object} with
100 * full capabilities to emulate all supported bytecode behaviors of the caller.
101 * These capabilities include {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access} to the caller.
102 * Factory methods on the lookup object can create
103 * <a href="MethodHandleInfo.html#directmh">direct method handles</a>
104 * for any member that the caller has access to via bytecodes,
105 * including protected and private fields and methods.
106 * This lookup object is created by the original lookup class
107 * and has the {@link Lookup#ORIGINAL ORIGINAL} bit set.
108 * This lookup object is a <em>capability</em> which may be delegated to trusted agents.
109 * Do not store it in place where untrusted code can access it.
110 * <p>
111 * This method is caller sensitive, which means that it may return different
112 * values to different callers.
113 * In cases where {@code MethodHandles.lookup} is called from a context where
114 * there is no caller frame on the stack (e.g. when called directly
115 * from a JNI attached thread), {@code IllegalCallerException} is thrown.
116 * To obtain a {@link Lookup lookup object} in such a context, use an auxiliary class that will
117 * implicitly be identified as the caller, or use {@link MethodHandles#publicLookup()}
118 * to obtain a low-privileged lookup instead.
119 * @return a lookup object for the caller of this method, with
120 * {@linkplain Lookup#ORIGINAL original} and
121 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access}.
122 * @throws IllegalCallerException if there is no caller frame on the stack.
123 */
124 @CallerSensitive
125 @ForceInline // to ensure Reflection.getCallerClass optimization
126 public static Lookup lookup() {
127 final Class<?> c = Reflection.getCallerClass();
128 if (c == null) {
129 throw new IllegalCallerException("no caller frame");
130 }
131 return new Lookup(c);
132 }
133
134 /**
135 * This lookup method is the alternate implementation of
136 * the lookup method with a leading caller class argument which is
137 * non-caller-sensitive. This method is only invoked by reflection
138 * and method handle.
139 */
140 @CallerSensitiveAdapter
141 private static Lookup lookup(Class<?> caller) {
142 if (caller.getClassLoader() == null) {
143 throw newInternalError("calling lookup() reflectively is not supported: "+caller);
144 }
145 return new Lookup(caller);
146 }
147
148 /**
149 * Returns a {@link Lookup lookup object} which is trusted minimally.
150 * The lookup has the {@code UNCONDITIONAL} mode.
151 * It can only be used to create method handles to public members of
152 * public classes in packages that are exported unconditionally.
153 * <p>
154 * As a matter of pure convention, the {@linkplain Lookup#lookupClass() lookup class}
155 * of this lookup object will be {@link java.lang.Object}.
156 *
157 * @apiNote The use of Object is conventional, and because the lookup modes are
158 * limited, there is no special access provided to the internals of Object, its package
159 * or its module. This public lookup object or other lookup object with
160 * {@code UNCONDITIONAL} mode assumes readability. Consequently, the lookup class
161 * is not used to determine the lookup context.
162 *
163 * <p style="font-size:smaller;">
164 * <em>Discussion:</em>
165 * The lookup class can be changed to any other class {@code C} using an expression of the form
166 * {@link Lookup#in publicLookup().in(C.class)}.
167 * A public lookup object is always subject to
168 * <a href="MethodHandles.Lookup.html#secmgr">security manager checks</a>.
169 * Also, it cannot access
170 * <a href="MethodHandles.Lookup.html#callsens">caller sensitive methods</a>.
171 * @return a lookup object which is trusted minimally
172 */
173 public static Lookup publicLookup() {
174 return Lookup.PUBLIC_LOOKUP;
175 }
176
177 /**
178 * Returns a {@link Lookup lookup} object on a target class to emulate all supported
179 * bytecode behaviors, including <a href="MethodHandles.Lookup.html#privacc">private access</a>.
180 * The returned lookup object can provide access to classes in modules and packages,
181 * and members of those classes, outside the normal rules of Java access control,
182 * instead conforming to the more permissive rules for modular <em>deep reflection</em>.
183 * <p>
184 * A caller, specified as a {@code Lookup} object, in module {@code M1} is
185 * allowed to do deep reflection on module {@code M2} and package of the target class
186 * if and only if all of the following conditions are {@code true}:
187 * <ul>
188 * <li>If there is a security manager, its {@code checkPermission} method is
189 * called to check {@code ReflectPermission("suppressAccessChecks")} and
190 * that must return normally.
191 * <li>The caller lookup object must have {@linkplain Lookup#hasFullPrivilegeAccess()
192 * full privilege access}. Specifically:
193 * <ul>
194 * <li>The caller lookup object must have the {@link Lookup#MODULE MODULE} lookup mode.
195 * (This is because otherwise there would be no way to ensure the original lookup
196 * creator was a member of any particular module, and so any subsequent checks
197 * for readability and qualified exports would become ineffective.)
198 * <li>The caller lookup object must have {@link Lookup#PRIVATE PRIVATE} access.
199 * (This is because an application intending to share intra-module access
200 * using {@link Lookup#MODULE MODULE} alone will inadvertently also share
201 * deep reflection to its own module.)
202 * </ul>
203 * <li>The target class must be a proper class, not a primitive or array class.
204 * (Thus, {@code M2} is well-defined.)
205 * <li>If the caller module {@code M1} differs from
206 * the target module {@code M2} then both of the following must be true:
207 * <ul>
208 * <li>{@code M1} {@link Module#canRead reads} {@code M2}.</li>
209 * <li>{@code M2} {@link Module#isOpen(String,Module) opens} the package
210 * containing the target class to at least {@code M1}.</li>
211 * </ul>
212 * </ul>
213 * <p>
214 * If any of the above checks is violated, this method fails with an
215 * exception.
216 * <p>
217 * Otherwise, if {@code M1} and {@code M2} are the same module, this method
218 * returns a {@code Lookup} on {@code targetClass} with
219 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access}
220 * with {@code null} previous lookup class.
221 * <p>
222 * Otherwise, {@code M1} and {@code M2} are two different modules. This method
223 * returns a {@code Lookup} on {@code targetClass} that records
224 * the lookup class of the caller as the new previous lookup class with
225 * {@code PRIVATE} access but no {@code MODULE} access.
226 * <p>
227 * The resulting {@code Lookup} object has no {@code ORIGINAL} access.
228 *
229 * @apiNote The {@code Lookup} object returned by this method is allowed to
230 * {@linkplain Lookup#defineClass(byte[]) define classes} in the runtime package
231 * of {@code targetClass}. Extreme caution should be taken when opening a package
232 * to another module as such defined classes have the same full privilege
233 * access as other members in {@code targetClass}'s module.
234 *
235 * @param targetClass the target class
236 * @param caller the caller lookup object
237 * @return a lookup object for the target class, with private access
238 * @throws IllegalArgumentException if {@code targetClass} is a primitive type or void or array class
239 * @throws NullPointerException if {@code targetClass} or {@code caller} is {@code null}
240 * @throws SecurityException if denied by the security manager
241 * @throws IllegalAccessException if any of the other access checks specified above fails
242 * @since 9
243 * @see Lookup#dropLookupMode
244 * @see <a href="MethodHandles.Lookup.html#cross-module-lookup">Cross-module lookups</a>
245 */
246 public static Lookup privateLookupIn(Class<?> targetClass, Lookup caller) throws IllegalAccessException {
247 if (caller.allowedModes == Lookup.TRUSTED) {
248 return new Lookup(targetClass);
249 }
250
251 @SuppressWarnings("removal")
252 SecurityManager sm = System.getSecurityManager();
253 if (sm != null) sm.checkPermission(SecurityConstants.ACCESS_PERMISSION);
254 if (targetClass.isPrimitive())
255 throw new IllegalArgumentException(targetClass + " is a primitive class");
256 if (targetClass.isArray())
257 throw new IllegalArgumentException(targetClass + " is an array class");
258 // Ensure that we can reason accurately about private and module access.
259 int requireAccess = Lookup.PRIVATE|Lookup.MODULE;
260 if ((caller.lookupModes() & requireAccess) != requireAccess)
261 throw new IllegalAccessException("caller does not have PRIVATE and MODULE lookup mode");
262
263 // previous lookup class is never set if it has MODULE access
264 assert caller.previousLookupClass() == null;
265
266 Class<?> callerClass = caller.lookupClass();
267 Module callerModule = callerClass.getModule(); // M1
268 Module targetModule = targetClass.getModule(); // M2
269 Class<?> newPreviousClass = null;
270 int newModes = Lookup.FULL_POWER_MODES & ~Lookup.ORIGINAL;
271
272 if (targetModule != callerModule) {
273 if (!callerModule.canRead(targetModule))
274 throw new IllegalAccessException(callerModule + " does not read " + targetModule);
275 if (targetModule.isNamed()) {
276 String pn = targetClass.getPackageName();
277 assert !pn.isEmpty() : "unnamed package cannot be in named module";
278 if (!targetModule.isOpen(pn, callerModule))
279 throw new IllegalAccessException(targetModule + " does not open " + pn + " to " + callerModule);
280 }
281
282 // M2 != M1, set previous lookup class to M1 and drop MODULE access
283 newPreviousClass = callerClass;
284 newModes &= ~Lookup.MODULE;
285 }
286 return Lookup.newLookup(targetClass, newPreviousClass, newModes);
287 }
288
289 /**
290 * Returns the <em>class data</em> associated with the lookup class
291 * of the given {@code caller} lookup object, or {@code null}.
292 *
293 * <p> A hidden class with class data can be created by calling
294 * {@link Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...)
295 * Lookup::defineHiddenClassWithClassData}.
296 * This method will cause the static class initializer of the lookup
297 * class of the given {@code caller} lookup object be executed if
298 * it has not been initialized.
299 *
300 * <p> A hidden class created by {@link Lookup#defineHiddenClass(byte[], boolean, Lookup.ClassOption...)
301 * Lookup::defineHiddenClass} and non-hidden classes have no class data.
302 * {@code null} is returned if this method is called on the lookup object
303 * on these classes.
304 *
305 * <p> The {@linkplain Lookup#lookupModes() lookup modes} for this lookup
306 * must have {@linkplain Lookup#ORIGINAL original access}
307 * in order to retrieve the class data.
308 *
309 * @apiNote
310 * This method can be called as a bootstrap method for a dynamically computed
311 * constant. A framework can create a hidden class with class data, for
312 * example that can be {@code Class} or {@code MethodHandle} object.
313 * The class data is accessible only to the lookup object
314 * created by the original caller but inaccessible to other members
315 * in the same nest. If a framework passes security sensitive objects
316 * to a hidden class via class data, it is recommended to load the value
317 * of class data as a dynamically computed constant instead of storing
318 * the class data in private static field(s) which are accessible to
319 * other nestmates.
320 *
321 * @param <T> the type to cast the class data object to
322 * @param caller the lookup context describing the class performing the
323 * operation (normally stacked by the JVM)
324 * @param name must be {@link ConstantDescs#DEFAULT_NAME}
325 * ({@code "_"})
326 * @param type the type of the class data
327 * @return the value of the class data if present in the lookup class;
328 * otherwise {@code null}
329 * @throws IllegalArgumentException if name is not {@code "_"}
330 * @throws IllegalAccessException if the lookup context does not have
331 * {@linkplain Lookup#ORIGINAL original} access
332 * @throws ClassCastException if the class data cannot be converted to
333 * the given {@code type}
334 * @throws NullPointerException if {@code caller} or {@code type} argument
335 * is {@code null}
336 * @see Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...)
337 * @see MethodHandles#classDataAt(Lookup, String, Class, int)
338 * @since 16
339 * @jvms 5.5 Initialization
340 */
341 public static <T> T classData(Lookup caller, String name, Class<T> type) throws IllegalAccessException {
342 Objects.requireNonNull(caller);
343 Objects.requireNonNull(type);
344 if (!ConstantDescs.DEFAULT_NAME.equals(name)) {
345 throw new IllegalArgumentException("name must be \"_\": " + name);
346 }
347
348 if ((caller.lookupModes() & Lookup.ORIGINAL) != Lookup.ORIGINAL) {
349 throw new IllegalAccessException(caller + " does not have ORIGINAL access");
350 }
351
352 Object classdata = classData(caller.lookupClass());
353 if (classdata == null) return null;
354
355 try {
356 return BootstrapMethodInvoker.widenAndCast(classdata, type);
357 } catch (RuntimeException|Error e) {
358 throw e; // let CCE and other runtime exceptions through
359 } catch (Throwable e) {
360 throw new InternalError(e);
361 }
362 }
363
364 /*
365 * Returns the class data set by the VM in the Class::classData field.
366 *
367 * This is also invoked by LambdaForms as it cannot use condy via
368 * MethodHandles::classData due to bootstrapping issue.
369 */
370 static Object classData(Class<?> c) {
371 UNSAFE.ensureClassInitialized(c);
372 return SharedSecrets.getJavaLangAccess().classData(c);
373 }
374
375 /**
376 * Returns the element at the specified index in the
377 * {@linkplain #classData(Lookup, String, Class) class data},
378 * if the class data associated with the lookup class
379 * of the given {@code caller} lookup object is a {@code List}.
380 * If the class data is not present in this lookup class, this method
381 * returns {@code null}.
382 *
383 * <p> A hidden class with class data can be created by calling
384 * {@link Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...)
385 * Lookup::defineHiddenClassWithClassData}.
386 * This method will cause the static class initializer of the lookup
387 * class of the given {@code caller} lookup object be executed if
388 * it has not been initialized.
389 *
390 * <p> A hidden class created by {@link Lookup#defineHiddenClass(byte[], boolean, Lookup.ClassOption...)
391 * Lookup::defineHiddenClass} and non-hidden classes have no class data.
392 * {@code null} is returned if this method is called on the lookup object
393 * on these classes.
394 *
395 * <p> The {@linkplain Lookup#lookupModes() lookup modes} for this lookup
396 * must have {@linkplain Lookup#ORIGINAL original access}
397 * in order to retrieve the class data.
398 *
399 * @apiNote
400 * This method can be called as a bootstrap method for a dynamically computed
401 * constant. A framework can create a hidden class with class data, for
402 * example that can be {@code List.of(o1, o2, o3....)} containing more than
403 * one object and use this method to load one element at a specific index.
404 * The class data is accessible only to the lookup object
405 * created by the original caller but inaccessible to other members
406 * in the same nest. If a framework passes security sensitive objects
407 * to a hidden class via class data, it is recommended to load the value
408 * of class data as a dynamically computed constant instead of storing
409 * the class data in private static field(s) which are accessible to other
410 * nestmates.
411 *
412 * @param <T> the type to cast the result object to
413 * @param caller the lookup context describing the class performing the
414 * operation (normally stacked by the JVM)
415 * @param name must be {@link java.lang.constant.ConstantDescs#DEFAULT_NAME}
416 * ({@code "_"})
417 * @param type the type of the element at the given index in the class data
418 * @param index index of the element in the class data
419 * @return the element at the given index in the class data
420 * if the class data is present; otherwise {@code null}
421 * @throws IllegalArgumentException if name is not {@code "_"}
422 * @throws IllegalAccessException if the lookup context does not have
423 * {@linkplain Lookup#ORIGINAL original} access
424 * @throws ClassCastException if the class data cannot be converted to {@code List}
425 * or the element at the specified index cannot be converted to the given type
426 * @throws IndexOutOfBoundsException if the index is out of range
427 * @throws NullPointerException if {@code caller} or {@code type} argument is
428 * {@code null}; or if unboxing operation fails because
429 * the element at the given index is {@code null}
430 *
431 * @since 16
432 * @see #classData(Lookup, String, Class)
433 * @see Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...)
434 */
435 public static <T> T classDataAt(Lookup caller, String name, Class<T> type, int index)
436 throws IllegalAccessException
437 {
438 @SuppressWarnings("unchecked")
439 List<Object> classdata = (List<Object>)classData(caller, name, List.class);
440 if (classdata == null) return null;
441
442 try {
443 Object element = classdata.get(index);
444 return BootstrapMethodInvoker.widenAndCast(element, type);
445 } catch (RuntimeException|Error e) {
446 throw e; // let specified exceptions and other runtime exceptions/errors through
447 } catch (Throwable e) {
448 throw new InternalError(e);
449 }
450 }
451
452 /**
453 * Performs an unchecked "crack" of a
454 * <a href="MethodHandleInfo.html#directmh">direct method handle</a>.
455 * The result is as if the user had obtained a lookup object capable enough
456 * to crack the target method handle, called
457 * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect}
458 * on the target to obtain its symbolic reference, and then called
459 * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs}
460 * to resolve the symbolic reference to a member.
461 * <p>
462 * If there is a security manager, its {@code checkPermission} method
463 * is called with a {@code ReflectPermission("suppressAccessChecks")} permission.
464 * @param <T> the desired type of the result, either {@link Member} or a subtype
465 * @param target a direct method handle to crack into symbolic reference components
466 * @param expected a class object representing the desired result type {@code T}
467 * @return a reference to the method, constructor, or field object
468 * @throws SecurityException if the caller is not privileged to call {@code setAccessible}
469 * @throws NullPointerException if either argument is {@code null}
470 * @throws IllegalArgumentException if the target is not a direct method handle
471 * @throws ClassCastException if the member is not of the expected type
472 * @since 1.8
473 */
474 public static <T extends Member> T reflectAs(Class<T> expected, MethodHandle target) {
475 @SuppressWarnings("removal")
476 SecurityManager smgr = System.getSecurityManager();
477 if (smgr != null) smgr.checkPermission(SecurityConstants.ACCESS_PERMISSION);
478 Lookup lookup = Lookup.IMPL_LOOKUP; // use maximally privileged lookup
479 return lookup.revealDirect(target).reflectAs(expected, lookup);
480 }
481
482 /**
483 * A <em>lookup object</em> is a factory for creating method handles,
484 * when the creation requires access checking.
485 * Method handles do not perform
486 * access checks when they are called, but rather when they are created.
487 * Therefore, method handle access
488 * restrictions must be enforced when a method handle is created.
489 * The caller class against which those restrictions are enforced
490 * is known as the {@linkplain #lookupClass() lookup class}.
491 * <p>
492 * A lookup class which needs to create method handles will call
493 * {@link MethodHandles#lookup() MethodHandles.lookup} to create a factory for itself.
494 * When the {@code Lookup} factory object is created, the identity of the lookup class is
495 * determined, and securely stored in the {@code Lookup} object.
496 * The lookup class (or its delegates) may then use factory methods
497 * on the {@code Lookup} object to create method handles for access-checked members.
498 * This includes all methods, constructors, and fields which are allowed to the lookup class,
499 * even private ones.
500 *
501 * <h2><a id="lookups"></a>Lookup Factory Methods</h2>
502 * The factory methods on a {@code Lookup} object correspond to all major
503 * use cases for methods, constructors, and fields.
504 * Each method handle created by a factory method is the functional
505 * equivalent of a particular <em>bytecode behavior</em>.
506 * (Bytecode behaviors are described in section {@jvms 5.4.3.5} of
507 * the Java Virtual Machine Specification.)
508 * Here is a summary of the correspondence between these factory methods and
509 * the behavior of the resulting method handles:
510 * <table class="striped">
511 * <caption style="display:none">lookup method behaviors</caption>
512 * <thead>
513 * <tr>
514 * <th scope="col"><a id="equiv"></a>lookup expression</th>
515 * <th scope="col">member</th>
516 * <th scope="col">bytecode behavior</th>
517 * </tr>
518 * </thead>
519 * <tbody>
520 * <tr>
521 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</th>
522 * <td>{@code FT f;}</td><td>{@code (T) this.f;}</td>
523 * </tr>
524 * <tr>
525 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</th>
526 * <td>{@code static}<br>{@code FT f;}</td><td>{@code (FT) C.f;}</td>
527 * </tr>
528 * <tr>
529 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</th>
530 * <td>{@code FT f;}</td><td>{@code this.f = x;}</td>
531 * </tr>
532 * <tr>
533 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</th>
534 * <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td>
535 * </tr>
536 * <tr>
537 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</th>
538 * <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>
539 * </tr>
540 * <tr>
541 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</th>
542 * <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td>
543 * </tr>
544 * <tr>
545 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</th>
546 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
547 * </tr>
548 * <tr>
549 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</th>
550 * <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td>
551 * </tr>
552 * <tr>
553 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</th>
554 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td>
555 * </tr>
556 * <tr>
557 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</th>
558 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, arg);}</td>
559 * </tr>
560 * <tr>
561 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</th>
562 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
563 * </tr>
564 * <tr>
565 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</th>
566 * <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td>
567 * </tr>
568 * <tr>
569 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSpecial lookup.unreflectSpecial(aMethod,this.class)}</th>
570 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
571 * </tr>
572 * <tr>
573 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findClass lookup.findClass("C")}</th>
574 * <td>{@code class C { ... }}</td><td>{@code C.class;}</td>
575 * </tr>
576 * </tbody>
577 * </table>
578 *
579 * Here, the type {@code C} is the class or interface being searched for a member,
580 * documented as a parameter named {@code refc} in the lookup methods.
581 * The method type {@code MT} is composed from the return type {@code T}
582 * and the sequence of argument types {@code A*}.
583 * The constructor also has a sequence of argument types {@code A*} and
584 * is deemed to return the newly-created object of type {@code C}.
585 * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}.
586 * The formal parameter {@code this} stands for the self-reference of type {@code C};
587 * if it is present, it is always the leading argument to the method handle invocation.
588 * (In the case of some {@code protected} members, {@code this} may be
589 * restricted in type to the lookup class; see below.)
590 * The name {@code arg} stands for all the other method handle arguments.
591 * In the code examples for the Core Reflection API, the name {@code thisOrNull}
592 * stands for a null reference if the accessed method or field is static,
593 * and {@code this} otherwise.
594 * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand
595 * for reflective objects corresponding to the given members declared in type {@code C}.
596 * <p>
597 * The bytecode behavior for a {@code findClass} operation is a load of a constant class,
598 * as if by {@code ldc CONSTANT_Class}.
599 * The behavior is represented, not as a method handle, but directly as a {@code Class} constant.
600 * <p>
601 * In cases where the given member is of variable arity (i.e., a method or constructor)
602 * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}.
603 * In all other cases, the returned method handle will be of fixed arity.
604 * <p style="font-size:smaller;">
605 * <em>Discussion:</em>
606 * The equivalence between looked-up method handles and underlying
607 * class members and bytecode behaviors
608 * can break down in a few ways:
609 * <ul style="font-size:smaller;">
610 * <li>If {@code C} is not symbolically accessible from the lookup class's loader,
611 * the lookup can still succeed, even when there is no equivalent
612 * Java expression or bytecoded constant.
613 * <li>Likewise, if {@code T} or {@code MT}
614 * is not symbolically accessible from the lookup class's loader,
615 * the lookup can still succeed.
616 * For example, lookups for {@code MethodHandle.invokeExact} and
617 * {@code MethodHandle.invoke} will always succeed, regardless of requested type.
618 * <li>If there is a security manager installed, it can forbid the lookup
619 * on various grounds (<a href="MethodHandles.Lookup.html#secmgr">see below</a>).
620 * By contrast, the {@code ldc} instruction on a {@code CONSTANT_MethodHandle}
621 * constant is not subject to security manager checks.
622 * <li>If the looked-up method has a
623 * <a href="MethodHandle.html#maxarity">very large arity</a>,
624 * the method handle creation may fail with an
625 * {@code IllegalArgumentException}, due to the method handle type having
626 * <a href="MethodHandle.html#maxarity">too many parameters.</a>
627 * </ul>
628 *
629 * <h2><a id="access"></a>Access checking</h2>
630 * Access checks are applied in the factory methods of {@code Lookup},
631 * when a method handle is created.
632 * This is a key difference from the Core Reflection API, since
633 * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
634 * performs access checking against every caller, on every call.
635 * <p>
636 * All access checks start from a {@code Lookup} object, which
637 * compares its recorded lookup class against all requests to
638 * create method handles.
639 * A single {@code Lookup} object can be used to create any number
640 * of access-checked method handles, all checked against a single
641 * lookup class.
642 * <p>
643 * A {@code Lookup} object can be shared with other trusted code,
644 * such as a metaobject protocol.
645 * A shared {@code Lookup} object delegates the capability
646 * to create method handles on private members of the lookup class.
647 * Even if privileged code uses the {@code Lookup} object,
648 * the access checking is confined to the privileges of the
649 * original lookup class.
650 * <p>
651 * A lookup can fail, because
652 * the containing class is not accessible to the lookup class, or
653 * because the desired class member is missing, or because the
654 * desired class member is not accessible to the lookup class, or
655 * because the lookup object is not trusted enough to access the member.
656 * In the case of a field setter function on a {@code final} field,
657 * finality enforcement is treated as a kind of access control,
658 * and the lookup will fail, except in special cases of
659 * {@link Lookup#unreflectSetter Lookup.unreflectSetter}.
660 * In any of these cases, a {@code ReflectiveOperationException} will be
661 * thrown from the attempted lookup. The exact class will be one of
662 * the following:
663 * <ul>
664 * <li>NoSuchMethodException — if a method is requested but does not exist
665 * <li>NoSuchFieldException — if a field is requested but does not exist
666 * <li>IllegalAccessException — if the member exists but an access check fails
667 * </ul>
668 * <p>
669 * In general, the conditions under which a method handle may be
670 * looked up for a method {@code M} are no more restrictive than the conditions
671 * under which the lookup class could have compiled, verified, and resolved a call to {@code M}.
672 * Where the JVM would raise exceptions like {@code NoSuchMethodError},
673 * a method handle lookup will generally raise a corresponding
674 * checked exception, such as {@code NoSuchMethodException}.
675 * And the effect of invoking the method handle resulting from the lookup
676 * is <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a>
677 * to executing the compiled, verified, and resolved call to {@code M}.
678 * The same point is true of fields and constructors.
679 * <p style="font-size:smaller;">
680 * <em>Discussion:</em>
681 * Access checks only apply to named and reflected methods,
682 * constructors, and fields.
683 * Other method handle creation methods, such as
684 * {@link MethodHandle#asType MethodHandle.asType},
685 * do not require any access checks, and are used
686 * independently of any {@code Lookup} object.
687 * <p>
688 * If the desired member is {@code protected}, the usual JVM rules apply,
689 * including the requirement that the lookup class must either be in the
690 * same package as the desired member, or must inherit that member.
691 * (See the Java Virtual Machine Specification, sections {@jvms
692 * 4.9.2}, {@jvms 5.4.3.5}, and {@jvms 6.4}.)
693 * In addition, if the desired member is a non-static field or method
694 * in a different package, the resulting method handle may only be applied
695 * to objects of the lookup class or one of its subclasses.
696 * This requirement is enforced by narrowing the type of the leading
697 * {@code this} parameter from {@code C}
698 * (which will necessarily be a superclass of the lookup class)
699 * to the lookup class itself.
700 * <p>
701 * The JVM imposes a similar requirement on {@code invokespecial} instruction,
702 * that the receiver argument must match both the resolved method <em>and</em>
703 * the current class. Again, this requirement is enforced by narrowing the
704 * type of the leading parameter to the resulting method handle.
705 * (See the Java Virtual Machine Specification, section {@jvms 4.10.1.9}.)
706 * <p>
707 * The JVM represents constructors and static initializer blocks as internal methods
708 * with special names ({@value ConstantDescs#INIT_NAME} and {@value
709 * ConstantDescs#CLASS_INIT_NAME}).
710 * The internal syntax of invocation instructions allows them to refer to such internal
711 * methods as if they were normal methods, but the JVM bytecode verifier rejects them.
712 * A lookup of such an internal method will produce a {@code NoSuchMethodException}.
713 * <p>
714 * If the relationship between nested types is expressed directly through the
715 * {@code NestHost} and {@code NestMembers} attributes
716 * (see the Java Virtual Machine Specification, sections {@jvms
717 * 4.7.28} and {@jvms 4.7.29}),
718 * then the associated {@code Lookup} object provides direct access to
719 * the lookup class and all of its nestmates
720 * (see {@link java.lang.Class#getNestHost Class.getNestHost}).
721 * Otherwise, access between nested classes is obtained by the Java compiler creating
722 * a wrapper method to access a private method of another class in the same nest.
723 * For example, a nested class {@code C.D}
724 * can access private members within other related classes such as
725 * {@code C}, {@code C.D.E}, or {@code C.B},
726 * but the Java compiler may need to generate wrapper methods in
727 * those related classes. In such cases, a {@code Lookup} object on
728 * {@code C.E} would be unable to access those private members.
729 * A workaround for this limitation is the {@link Lookup#in Lookup.in} method,
730 * which can transform a lookup on {@code C.E} into one on any of those other
731 * classes, without special elevation of privilege.
732 * <p>
733 * The accesses permitted to a given lookup object may be limited,
734 * according to its set of {@link #lookupModes lookupModes},
735 * to a subset of members normally accessible to the lookup class.
736 * For example, the {@link MethodHandles#publicLookup publicLookup}
737 * method produces a lookup object which is only allowed to access
738 * public members in public classes of exported packages.
739 * The caller sensitive method {@link MethodHandles#lookup lookup}
740 * produces a lookup object with full capabilities relative to
741 * its caller class, to emulate all supported bytecode behaviors.
742 * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object
743 * with fewer access modes than the original lookup object.
744 *
745 * <p style="font-size:smaller;">
746 * <a id="privacc"></a>
747 * <em>Discussion of private and module access:</em>
748 * We say that a lookup has <em>private access</em>
749 * if its {@linkplain #lookupModes lookup modes}
750 * include the possibility of accessing {@code private} members
751 * (which includes the private members of nestmates).
752 * As documented in the relevant methods elsewhere,
753 * only lookups with private access possess the following capabilities:
754 * <ul style="font-size:smaller;">
755 * <li>access private fields, methods, and constructors of the lookup class and its nestmates
756 * <li>create method handles which {@link Lookup#findSpecial emulate invokespecial} instructions
757 * <li>avoid <a href="MethodHandles.Lookup.html#secmgr">package access checks</a>
758 * for classes accessible to the lookup class
759 * <li>create {@link Lookup#in delegated lookup objects} which have private access to other classes
760 * within the same package member
761 * </ul>
762 * <p style="font-size:smaller;">
763 * Similarly, a lookup with module access ensures that the original lookup creator was
764 * a member in the same module as the lookup class.
765 * <p style="font-size:smaller;">
766 * Private and module access are independently determined modes; a lookup may have
767 * either or both or neither. A lookup which possesses both access modes is said to
768 * possess {@linkplain #hasFullPrivilegeAccess() full privilege access}.
769 * <p style="font-size:smaller;">
770 * A lookup with <em>original access</em> ensures that this lookup is created by
771 * the original lookup class and the bootstrap method invoked by the VM.
772 * Such a lookup with original access also has private and module access
773 * which has the following additional capability:
774 * <ul style="font-size:smaller;">
775 * <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> methods,
776 * such as {@code Class.forName}
777 * <li>obtain the {@linkplain MethodHandles#classData(Lookup, String, Class)
778 * class data} associated with the lookup class</li>
779 * </ul>
780 * <p style="font-size:smaller;">
781 * Each of these permissions is a consequence of the fact that a lookup object
782 * with private access can be securely traced back to an originating class,
783 * whose <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> and Java language access permissions
784 * can be reliably determined and emulated by method handles.
785 *
786 * <h2><a id="cross-module-lookup"></a>Cross-module lookups</h2>
787 * When a lookup class in one module {@code M1} accesses a class in another module
788 * {@code M2}, extra access checking is performed beyond the access mode bits.
789 * A {@code Lookup} with {@link #PUBLIC} mode and a lookup class in {@code M1}
790 * can access public types in {@code M2} when {@code M2} is readable to {@code M1}
791 * and when the type is in a package of {@code M2} that is exported to
792 * at least {@code M1}.
793 * <p>
794 * A {@code Lookup} on {@code C} can also <em>teleport</em> to a target class
795 * via {@link #in(Class) Lookup.in} and {@link MethodHandles#privateLookupIn(Class, Lookup)
796 * MethodHandles.privateLookupIn} methods.
797 * Teleporting across modules will always record the original lookup class as
798 * the <em>{@linkplain #previousLookupClass() previous lookup class}</em>
799 * and drops {@link Lookup#MODULE MODULE} access.
800 * If the target class is in the same module as the lookup class {@code C},
801 * then the target class becomes the new lookup class
802 * and there is no change to the previous lookup class.
803 * If the target class is in a different module from {@code M1} ({@code C}'s module),
804 * {@code C} becomes the new previous lookup class
805 * and the target class becomes the new lookup class.
806 * In that case, if there was already a previous lookup class in {@code M0},
807 * and it differs from {@code M1} and {@code M2}, then the resulting lookup
808 * drops all privileges.
809 * For example,
810 * {@snippet lang="java" :
811 * Lookup lookup = MethodHandles.lookup(); // in class C
812 * Lookup lookup2 = lookup.in(D.class);
813 * MethodHandle mh = lookup2.findStatic(E.class, "m", MT);
814 * }
815 * <p>
816 * The {@link #lookup()} factory method produces a {@code Lookup} object
817 * with {@code null} previous lookup class.
818 * {@link Lookup#in lookup.in(D.class)} transforms the {@code lookup} on class {@code C}
819 * to class {@code D} without elevation of privileges.
820 * If {@code C} and {@code D} are in the same module,
821 * {@code lookup2} records {@code D} as the new lookup class and keeps the
822 * same previous lookup class as the original {@code lookup}, or
823 * {@code null} if not present.
824 * <p>
825 * When a {@code Lookup} teleports from a class
826 * in one nest to another nest, {@code PRIVATE} access is dropped.
827 * When a {@code Lookup} teleports from a class in one package to
828 * another package, {@code PACKAGE} access is dropped.
829 * When a {@code Lookup} teleports from a class in one module to another module,
830 * {@code MODULE} access is dropped.
831 * Teleporting across modules drops the ability to access non-exported classes
832 * in both the module of the new lookup class and the module of the old lookup class
833 * and the resulting {@code Lookup} remains only {@code PUBLIC} access.
834 * A {@code Lookup} can teleport back and forth to a class in the module of
835 * the lookup class and the module of the previous class lookup.
836 * Teleporting across modules can only decrease access but cannot increase it.
837 * Teleporting to some third module drops all accesses.
838 * <p>
839 * In the above example, if {@code C} and {@code D} are in different modules,
840 * {@code lookup2} records {@code D} as its lookup class and
841 * {@code C} as its previous lookup class and {@code lookup2} has only
842 * {@code PUBLIC} access. {@code lookup2} can teleport to other class in
843 * {@code C}'s module and {@code D}'s module.
844 * If class {@code E} is in a third module, {@code lookup2.in(E.class)} creates
845 * a {@code Lookup} on {@code E} with no access and {@code lookup2}'s lookup
846 * class {@code D} is recorded as its previous lookup class.
847 * <p>
848 * Teleporting across modules restricts access to the public types that
849 * both the lookup class and the previous lookup class can equally access
850 * (see below).
851 * <p>
852 * {@link MethodHandles#privateLookupIn(Class, Lookup) MethodHandles.privateLookupIn(T.class, lookup)}
853 * can be used to teleport a {@code lookup} from class {@code C} to class {@code T}
854 * and produce a new {@code Lookup} with <a href="#privacc">private access</a>
855 * if the lookup class is allowed to do <em>deep reflection</em> on {@code T}.
856 * The {@code lookup} must have {@link #MODULE} and {@link #PRIVATE} access
857 * to call {@code privateLookupIn}.
858 * A {@code lookup} on {@code C} in module {@code M1} is allowed to do deep reflection
859 * on all classes in {@code M1}. If {@code T} is in {@code M1}, {@code privateLookupIn}
860 * produces a new {@code Lookup} on {@code T} with full capabilities.
861 * A {@code lookup} on {@code C} is also allowed
862 * to do deep reflection on {@code T} in another module {@code M2} if
863 * {@code M1} reads {@code M2} and {@code M2} {@link Module#isOpen(String,Module) opens}
864 * the package containing {@code T} to at least {@code M1}.
865 * {@code T} becomes the new lookup class and {@code C} becomes the new previous
866 * lookup class and {@code MODULE} access is dropped from the resulting {@code Lookup}.
867 * The resulting {@code Lookup} can be used to do member lookup or teleport
868 * to another lookup class by calling {@link #in Lookup::in}. But
869 * it cannot be used to obtain another private {@code Lookup} by calling
870 * {@link MethodHandles#privateLookupIn(Class, Lookup) privateLookupIn}
871 * because it has no {@code MODULE} access.
872 * <p>
873 * The {@code Lookup} object returned by {@code privateLookupIn} is allowed to
874 * {@linkplain Lookup#defineClass(byte[]) define classes} in the runtime package
875 * of {@code T}. Extreme caution should be taken when opening a package
876 * to another module as such defined classes have the same full privilege
877 * access as other members in {@code M2}.
878 *
879 * <h2><a id="module-access-check"></a>Cross-module access checks</h2>
880 *
881 * A {@code Lookup} with {@link #PUBLIC} or with {@link #UNCONDITIONAL} mode
882 * allows cross-module access. The access checking is performed with respect
883 * to both the lookup class and the previous lookup class if present.
884 * <p>
885 * A {@code Lookup} with {@link #UNCONDITIONAL} mode can access public type
886 * in all modules when the type is in a package that is {@linkplain Module#isExported(String)
887 * exported unconditionally}.
888 * <p>
889 * If a {@code Lookup} on {@code LC} in {@code M1} has no previous lookup class,
890 * the lookup with {@link #PUBLIC} mode can access all public types in modules
891 * that are readable to {@code M1} and the type is in a package that is exported
892 * at least to {@code M1}.
893 * <p>
894 * If a {@code Lookup} on {@code LC} in {@code M1} has a previous lookup class
895 * {@code PLC} on {@code M0}, the lookup with {@link #PUBLIC} mode can access
896 * the intersection of all public types that are accessible to {@code M1}
897 * with all public types that are accessible to {@code M0}. {@code M0}
898 * reads {@code M1} and hence the set of accessible types includes:
899 *
900 * <ul>
901 * <li>unconditional-exported packages from {@code M1}</li>
902 * <li>unconditional-exported packages from {@code M0} if {@code M1} reads {@code M0}</li>
903 * <li>
904 * unconditional-exported packages from a third module {@code M2}if both {@code M0}
905 * and {@code M1} read {@code M2}
906 * </li>
907 * <li>qualified-exported packages from {@code M1} to {@code M0}</li>
908 * <li>qualified-exported packages from {@code M0} to {@code M1} if {@code M1} reads {@code M0}</li>
909 * <li>
910 * qualified-exported packages from a third module {@code M2} to both {@code M0} and
911 * {@code M1} if both {@code M0} and {@code M1} read {@code M2}
912 * </li>
913 * </ul>
914 *
915 * <h2><a id="access-modes"></a>Access modes</h2>
916 *
917 * The table below shows the access modes of a {@code Lookup} produced by
918 * any of the following factory or transformation methods:
919 * <ul>
920 * <li>{@link #lookup() MethodHandles::lookup}</li>
921 * <li>{@link #publicLookup() MethodHandles::publicLookup}</li>
922 * <li>{@link #privateLookupIn(Class, Lookup) MethodHandles::privateLookupIn}</li>
923 * <li>{@link Lookup#in Lookup::in}</li>
924 * <li>{@link Lookup#dropLookupMode(int) Lookup::dropLookupMode}</li>
925 * </ul>
926 *
927 * <table class="striped">
928 * <caption style="display:none">
929 * Access mode summary
930 * </caption>
931 * <thead>
932 * <tr>
933 * <th scope="col">Lookup object</th>
934 * <th style="text-align:center">original</th>
935 * <th style="text-align:center">protected</th>
936 * <th style="text-align:center">private</th>
937 * <th style="text-align:center">package</th>
938 * <th style="text-align:center">module</th>
939 * <th style="text-align:center">public</th>
940 * </tr>
941 * </thead>
942 * <tbody>
943 * <tr>
944 * <th scope="row" style="text-align:left">{@code CL = MethodHandles.lookup()} in {@code C}</th>
945 * <td style="text-align:center">ORI</td>
946 * <td style="text-align:center">PRO</td>
947 * <td style="text-align:center">PRI</td>
948 * <td style="text-align:center">PAC</td>
949 * <td style="text-align:center">MOD</td>
950 * <td style="text-align:center">1R</td>
951 * </tr>
952 * <tr>
953 * <th scope="row" style="text-align:left">{@code CL.in(C1)} same package</th>
954 * <td></td>
955 * <td></td>
956 * <td></td>
957 * <td style="text-align:center">PAC</td>
958 * <td style="text-align:center">MOD</td>
959 * <td style="text-align:center">1R</td>
960 * </tr>
961 * <tr>
962 * <th scope="row" style="text-align:left">{@code CL.in(C1)} same module</th>
963 * <td></td>
964 * <td></td>
965 * <td></td>
966 * <td></td>
967 * <td style="text-align:center">MOD</td>
968 * <td style="text-align:center">1R</td>
969 * </tr>
970 * <tr>
971 * <th scope="row" style="text-align:left">{@code CL.in(D)} different module</th>
972 * <td></td>
973 * <td></td>
974 * <td></td>
975 * <td></td>
976 * <td></td>
977 * <td style="text-align:center">2R</td>
978 * </tr>
979 * <tr>
980 * <th scope="row" style="text-align:left">{@code CL.in(D).in(C)} hop back to module</th>
981 * <td></td>
982 * <td></td>
983 * <td></td>
984 * <td></td>
985 * <td></td>
986 * <td style="text-align:center">2R</td>
987 * </tr>
988 * <tr>
989 * <th scope="row" style="text-align:left">{@code PRI1 = privateLookupIn(C1,CL)}</th>
990 * <td></td>
991 * <td style="text-align:center">PRO</td>
992 * <td style="text-align:center">PRI</td>
993 * <td style="text-align:center">PAC</td>
994 * <td style="text-align:center">MOD</td>
995 * <td style="text-align:center">1R</td>
996 * </tr>
997 * <tr>
998 * <th scope="row" style="text-align:left">{@code PRI1a = privateLookupIn(C,PRI1)}</th>
999 * <td></td>
1000 * <td style="text-align:center">PRO</td>
1001 * <td style="text-align:center">PRI</td>
1002 * <td style="text-align:center">PAC</td>
1003 * <td style="text-align:center">MOD</td>
1004 * <td style="text-align:center">1R</td>
1005 * </tr>
1006 * <tr>
1007 * <th scope="row" style="text-align:left">{@code PRI1.in(C1)} same package</th>
1008 * <td></td>
1009 * <td></td>
1010 * <td></td>
1011 * <td style="text-align:center">PAC</td>
1012 * <td style="text-align:center">MOD</td>
1013 * <td style="text-align:center">1R</td>
1014 * </tr>
1015 * <tr>
1016 * <th scope="row" style="text-align:left">{@code PRI1.in(C1)} different package</th>
1017 * <td></td>
1018 * <td></td>
1019 * <td></td>
1020 * <td></td>
1021 * <td style="text-align:center">MOD</td>
1022 * <td style="text-align:center">1R</td>
1023 * </tr>
1024 * <tr>
1025 * <th scope="row" style="text-align:left">{@code PRI1.in(D)} different module</th>
1026 * <td></td>
1027 * <td></td>
1028 * <td></td>
1029 * <td></td>
1030 * <td></td>
1031 * <td style="text-align:center">2R</td>
1032 * </tr>
1033 * <tr>
1034 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PROTECTED)}</th>
1035 * <td></td>
1036 * <td></td>
1037 * <td style="text-align:center">PRI</td>
1038 * <td style="text-align:center">PAC</td>
1039 * <td style="text-align:center">MOD</td>
1040 * <td style="text-align:center">1R</td>
1041 * </tr>
1042 * <tr>
1043 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PRIVATE)}</th>
1044 * <td></td>
1045 * <td></td>
1046 * <td></td>
1047 * <td style="text-align:center">PAC</td>
1048 * <td style="text-align:center">MOD</td>
1049 * <td style="text-align:center">1R</td>
1050 * </tr>
1051 * <tr>
1052 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PACKAGE)}</th>
1053 * <td></td>
1054 * <td></td>
1055 * <td></td>
1056 * <td></td>
1057 * <td style="text-align:center">MOD</td>
1058 * <td style="text-align:center">1R</td>
1059 * </tr>
1060 * <tr>
1061 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(MODULE)}</th>
1062 * <td></td>
1063 * <td></td>
1064 * <td></td>
1065 * <td></td>
1066 * <td></td>
1067 * <td style="text-align:center">1R</td>
1068 * </tr>
1069 * <tr>
1070 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PUBLIC)}</th>
1071 * <td></td>
1072 * <td></td>
1073 * <td></td>
1074 * <td></td>
1075 * <td></td>
1076 * <td style="text-align:center">none</td>
1077 * <tr>
1078 * <th scope="row" style="text-align:left">{@code PRI2 = privateLookupIn(D,CL)}</th>
1079 * <td></td>
1080 * <td style="text-align:center">PRO</td>
1081 * <td style="text-align:center">PRI</td>
1082 * <td style="text-align:center">PAC</td>
1083 * <td></td>
1084 * <td style="text-align:center">2R</td>
1085 * </tr>
1086 * <tr>
1087 * <th scope="row" style="text-align:left">{@code privateLookupIn(D,PRI1)}</th>
1088 * <td></td>
1089 * <td style="text-align:center">PRO</td>
1090 * <td style="text-align:center">PRI</td>
1091 * <td style="text-align:center">PAC</td>
1092 * <td></td>
1093 * <td style="text-align:center">2R</td>
1094 * </tr>
1095 * <tr>
1096 * <th scope="row" style="text-align:left">{@code privateLookupIn(C,PRI2)} fails</th>
1097 * <td></td>
1098 * <td></td>
1099 * <td></td>
1100 * <td></td>
1101 * <td></td>
1102 * <td style="text-align:center">IAE</td>
1103 * </tr>
1104 * <tr>
1105 * <th scope="row" style="text-align:left">{@code PRI2.in(D2)} same package</th>
1106 * <td></td>
1107 * <td></td>
1108 * <td></td>
1109 * <td style="text-align:center">PAC</td>
1110 * <td></td>
1111 * <td style="text-align:center">2R</td>
1112 * </tr>
1113 * <tr>
1114 * <th scope="row" style="text-align:left">{@code PRI2.in(D2)} different package</th>
1115 * <td></td>
1116 * <td></td>
1117 * <td></td>
1118 * <td></td>
1119 * <td></td>
1120 * <td style="text-align:center">2R</td>
1121 * </tr>
1122 * <tr>
1123 * <th scope="row" style="text-align:left">{@code PRI2.in(C1)} hop back to module</th>
1124 * <td></td>
1125 * <td></td>
1126 * <td></td>
1127 * <td></td>
1128 * <td></td>
1129 * <td style="text-align:center">2R</td>
1130 * </tr>
1131 * <tr>
1132 * <th scope="row" style="text-align:left">{@code PRI2.in(E)} hop to third module</th>
1133 * <td></td>
1134 * <td></td>
1135 * <td></td>
1136 * <td></td>
1137 * <td></td>
1138 * <td style="text-align:center">none</td>
1139 * </tr>
1140 * <tr>
1141 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PROTECTED)}</th>
1142 * <td></td>
1143 * <td></td>
1144 * <td style="text-align:center">PRI</td>
1145 * <td style="text-align:center">PAC</td>
1146 * <td></td>
1147 * <td style="text-align:center">2R</td>
1148 * </tr>
1149 * <tr>
1150 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PRIVATE)}</th>
1151 * <td></td>
1152 * <td></td>
1153 * <td></td>
1154 * <td style="text-align:center">PAC</td>
1155 * <td></td>
1156 * <td style="text-align:center">2R</td>
1157 * </tr>
1158 * <tr>
1159 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PACKAGE)}</th>
1160 * <td></td>
1161 * <td></td>
1162 * <td></td>
1163 * <td></td>
1164 * <td></td>
1165 * <td style="text-align:center">2R</td>
1166 * </tr>
1167 * <tr>
1168 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(MODULE)}</th>
1169 * <td></td>
1170 * <td></td>
1171 * <td></td>
1172 * <td></td>
1173 * <td></td>
1174 * <td style="text-align:center">2R</td>
1175 * </tr>
1176 * <tr>
1177 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PUBLIC)}</th>
1178 * <td></td>
1179 * <td></td>
1180 * <td></td>
1181 * <td></td>
1182 * <td></td>
1183 * <td style="text-align:center">none</td>
1184 * </tr>
1185 * <tr>
1186 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PROTECTED)}</th>
1187 * <td></td>
1188 * <td></td>
1189 * <td style="text-align:center">PRI</td>
1190 * <td style="text-align:center">PAC</td>
1191 * <td style="text-align:center">MOD</td>
1192 * <td style="text-align:center">1R</td>
1193 * </tr>
1194 * <tr>
1195 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PRIVATE)}</th>
1196 * <td></td>
1197 * <td></td>
1198 * <td></td>
1199 * <td style="text-align:center">PAC</td>
1200 * <td style="text-align:center">MOD</td>
1201 * <td style="text-align:center">1R</td>
1202 * </tr>
1203 * <tr>
1204 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PACKAGE)}</th>
1205 * <td></td>
1206 * <td></td>
1207 * <td></td>
1208 * <td></td>
1209 * <td style="text-align:center">MOD</td>
1210 * <td style="text-align:center">1R</td>
1211 * </tr>
1212 * <tr>
1213 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(MODULE)}</th>
1214 * <td></td>
1215 * <td></td>
1216 * <td></td>
1217 * <td></td>
1218 * <td></td>
1219 * <td style="text-align:center">1R</td>
1220 * </tr>
1221 * <tr>
1222 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PUBLIC)}</th>
1223 * <td></td>
1224 * <td></td>
1225 * <td></td>
1226 * <td></td>
1227 * <td></td>
1228 * <td style="text-align:center">none</td>
1229 * </tr>
1230 * <tr>
1231 * <th scope="row" style="text-align:left">{@code PUB = publicLookup()}</th>
1232 * <td></td>
1233 * <td></td>
1234 * <td></td>
1235 * <td></td>
1236 * <td></td>
1237 * <td style="text-align:center">U</td>
1238 * </tr>
1239 * <tr>
1240 * <th scope="row" style="text-align:left">{@code PUB.in(D)} different module</th>
1241 * <td></td>
1242 * <td></td>
1243 * <td></td>
1244 * <td></td>
1245 * <td></td>
1246 * <td style="text-align:center">U</td>
1247 * </tr>
1248 * <tr>
1249 * <th scope="row" style="text-align:left">{@code PUB.in(D).in(E)} third module</th>
1250 * <td></td>
1251 * <td></td>
1252 * <td></td>
1253 * <td></td>
1254 * <td></td>
1255 * <td style="text-align:center">U</td>
1256 * </tr>
1257 * <tr>
1258 * <th scope="row" style="text-align:left">{@code PUB.dropLookupMode(UNCONDITIONAL)}</th>
1259 * <td></td>
1260 * <td></td>
1261 * <td></td>
1262 * <td></td>
1263 * <td></td>
1264 * <td style="text-align:center">none</td>
1265 * </tr>
1266 * <tr>
1267 * <th scope="row" style="text-align:left">{@code privateLookupIn(C1,PUB)} fails</th>
1268 * <td></td>
1269 * <td></td>
1270 * <td></td>
1271 * <td></td>
1272 * <td></td>
1273 * <td style="text-align:center">IAE</td>
1274 * </tr>
1275 * <tr>
1276 * <th scope="row" style="text-align:left">{@code ANY.in(X)}, for inaccessible {@code X}</th>
1277 * <td></td>
1278 * <td></td>
1279 * <td></td>
1280 * <td></td>
1281 * <td></td>
1282 * <td style="text-align:center">none</td>
1283 * </tr>
1284 * </tbody>
1285 * </table>
1286 *
1287 * <p>
1288 * Notes:
1289 * <ul>
1290 * <li>Class {@code C} and class {@code C1} are in module {@code M1},
1291 * but {@code D} and {@code D2} are in module {@code M2}, and {@code E}
1292 * is in module {@code M3}. {@code X} stands for class which is inaccessible
1293 * to the lookup. {@code ANY} stands for any of the example lookups.</li>
1294 * <li>{@code ORI} indicates {@link #ORIGINAL} bit set,
1295 * {@code PRO} indicates {@link #PROTECTED} bit set,
1296 * {@code PRI} indicates {@link #PRIVATE} bit set,
1297 * {@code PAC} indicates {@link #PACKAGE} bit set,
1298 * {@code MOD} indicates {@link #MODULE} bit set,
1299 * {@code 1R} and {@code 2R} indicate {@link #PUBLIC} bit set,
1300 * {@code U} indicates {@link #UNCONDITIONAL} bit set,
1301 * {@code IAE} indicates {@code IllegalAccessException} thrown.</li>
1302 * <li>Public access comes in three kinds:
1303 * <ul>
1304 * <li>unconditional ({@code U}): the lookup assumes readability.
1305 * The lookup has {@code null} previous lookup class.
1306 * <li>one-module-reads ({@code 1R}): the module access checking is
1307 * performed with respect to the lookup class. The lookup has {@code null}
1308 * previous lookup class.
1309 * <li>two-module-reads ({@code 2R}): the module access checking is
1310 * performed with respect to the lookup class and the previous lookup class.
1311 * The lookup has a non-null previous lookup class which is in a
1312 * different module from the current lookup class.
1313 * </ul>
1314 * <li>Any attempt to reach a third module loses all access.</li>
1315 * <li>If a target class {@code X} is not accessible to {@code Lookup::in}
1316 * all access modes are dropped.</li>
1317 * </ul>
1318 *
1319 * <h2><a id="secmgr"></a>Security manager interactions</h2>
1320 * Although bytecode instructions can only refer to classes in
1321 * a related class loader, this API can search for methods in any
1322 * class, as long as a reference to its {@code Class} object is
1323 * available. Such cross-loader references are also possible with the
1324 * Core Reflection API, and are impossible to bytecode instructions
1325 * such as {@code invokestatic} or {@code getfield}.
1326 * There is a {@linkplain java.lang.SecurityManager security manager API}
1327 * to allow applications to check such cross-loader references.
1328 * These checks apply to both the {@code MethodHandles.Lookup} API
1329 * and the Core Reflection API
1330 * (as found on {@link java.lang.Class Class}).
1331 * <p>
1332 * If a security manager is present, member and class lookups are subject to
1333 * additional checks.
1334 * From one to three calls are made to the security manager.
1335 * Any of these calls can refuse access by throwing a
1336 * {@link java.lang.SecurityException SecurityException}.
1337 * Define {@code smgr} as the security manager,
1338 * {@code lookc} as the lookup class of the current lookup object,
1339 * {@code refc} as the containing class in which the member
1340 * is being sought, and {@code defc} as the class in which the
1341 * member is actually defined.
1342 * (If a class or other type is being accessed,
1343 * the {@code refc} and {@code defc} values are the class itself.)
1344 * The value {@code lookc} is defined as <em>not present</em>
1345 * if the current lookup object does not have
1346 * {@linkplain #hasFullPrivilegeAccess() full privilege access}.
1347 * The calls are made according to the following rules:
1348 * <ul>
1349 * <li><b>Step 1:</b>
1350 * If {@code lookc} is not present, or if its class loader is not
1351 * the same as or an ancestor of the class loader of {@code refc},
1352 * then {@link SecurityManager#checkPackageAccess
1353 * smgr.checkPackageAccess(refcPkg)} is called,
1354 * where {@code refcPkg} is the package of {@code refc}.
1355 * <li><b>Step 2a:</b>
1356 * If the retrieved member is not public and
1357 * {@code lookc} is not present, then
1358 * {@link SecurityManager#checkPermission smgr.checkPermission}
1359 * with {@code RuntimePermission("accessDeclaredMembers")} is called.
1360 * <li><b>Step 2b:</b>
1361 * If the retrieved class has a {@code null} class loader,
1362 * and {@code lookc} is not present, then
1363 * {@link SecurityManager#checkPermission smgr.checkPermission}
1364 * with {@code RuntimePermission("getClassLoader")} is called.
1365 * <li><b>Step 3:</b>
1366 * If the retrieved member is not public,
1367 * and if {@code lookc} is not present,
1368 * and if {@code defc} and {@code refc} are different,
1369 * then {@link SecurityManager#checkPackageAccess
1370 * smgr.checkPackageAccess(defcPkg)} is called,
1371 * where {@code defcPkg} is the package of {@code defc}.
1372 * </ul>
1373 * Security checks are performed after other access checks have passed.
1374 * Therefore, the above rules presuppose a member or class that is public,
1375 * or else that is being accessed from a lookup class that has
1376 * rights to access the member or class.
1377 * <p>
1378 * If a security manager is present and the current lookup object does not have
1379 * {@linkplain #hasFullPrivilegeAccess() full privilege access}, then
1380 * {@link #defineClass(byte[]) defineClass},
1381 * {@link #defineHiddenClass(byte[], boolean, ClassOption...) defineHiddenClass},
1382 * {@link #defineHiddenClassWithClassData(byte[], Object, boolean, ClassOption...)
1383 * defineHiddenClassWithClassData}
1384 * calls {@link SecurityManager#checkPermission smgr.checkPermission}
1385 * with {@code RuntimePermission("defineClass")}.
1386 *
1387 * <h2><a id="callsens"></a>Caller sensitive methods</h2>
1388 * A small number of Java methods have a special property called caller sensitivity.
1389 * A <em>caller-sensitive</em> method can behave differently depending on the
1390 * identity of its immediate caller.
1391 * <p>
1392 * If a method handle for a caller-sensitive method is requested,
1393 * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> apply,
1394 * but they take account of the lookup class in a special way.
1395 * The resulting method handle behaves as if it were called
1396 * from an instruction contained in the lookup class,
1397 * so that the caller-sensitive method detects the lookup class.
1398 * (By contrast, the invoker of the method handle is disregarded.)
1399 * Thus, in the case of caller-sensitive methods,
1400 * different lookup classes may give rise to
1401 * differently behaving method handles.
1402 * <p>
1403 * In cases where the lookup object is
1404 * {@link MethodHandles#publicLookup() publicLookup()},
1405 * or some other lookup object without the
1406 * {@linkplain #ORIGINAL original access},
1407 * the lookup class is disregarded.
1408 * In such cases, no caller-sensitive method handle can be created,
1409 * access is forbidden, and the lookup fails with an
1410 * {@code IllegalAccessException}.
1411 * <p style="font-size:smaller;">
1412 * <em>Discussion:</em>
1413 * For example, the caller-sensitive method
1414 * {@link java.lang.Class#forName(String) Class.forName(x)}
1415 * can return varying classes or throw varying exceptions,
1416 * depending on the class loader of the class that calls it.
1417 * A public lookup of {@code Class.forName} will fail, because
1418 * there is no reasonable way to determine its bytecode behavior.
1419 * <p style="font-size:smaller;">
1420 * If an application caches method handles for broad sharing,
1421 * it should use {@code publicLookup()} to create them.
1422 * If there is a lookup of {@code Class.forName}, it will fail,
1423 * and the application must take appropriate action in that case.
1424 * It may be that a later lookup, perhaps during the invocation of a
1425 * bootstrap method, can incorporate the specific identity
1426 * of the caller, making the method accessible.
1427 * <p style="font-size:smaller;">
1428 * The function {@code MethodHandles.lookup} is caller sensitive
1429 * so that there can be a secure foundation for lookups.
1430 * Nearly all other methods in the JSR 292 API rely on lookup
1431 * objects to check access requests.
1432 */
1433 public static final
1434 class Lookup {
1435 /** The class on behalf of whom the lookup is being performed. */
1436 private final Class<?> lookupClass;
1437
1438 /** previous lookup class */
1439 private final Class<?> prevLookupClass;
1440
1441 /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */
1442 private final int allowedModes;
1443
1444 static {
1445 Reflection.registerFieldsToFilter(Lookup.class, Set.of("lookupClass", "allowedModes"));
1446 }
1447
1448 /** A single-bit mask representing {@code public} access,
1449 * which may contribute to the result of {@link #lookupModes lookupModes}.
1450 * The value, {@code 0x01}, happens to be the same as the value of the
1451 * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.
1452 * <p>
1453 * A {@code Lookup} with this lookup mode performs cross-module access check
1454 * with respect to the {@linkplain #lookupClass() lookup class} and
1455 * {@linkplain #previousLookupClass() previous lookup class} if present.
1456 */
1457 public static final int PUBLIC = Modifier.PUBLIC;
1458
1459 /** A single-bit mask representing {@code private} access,
1460 * which may contribute to the result of {@link #lookupModes lookupModes}.
1461 * The value, {@code 0x02}, happens to be the same as the value of the
1462 * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.
1463 */
1464 public static final int PRIVATE = Modifier.PRIVATE;
1465
1466 /** A single-bit mask representing {@code protected} access,
1467 * which may contribute to the result of {@link #lookupModes lookupModes}.
1468 * The value, {@code 0x04}, happens to be the same as the value of the
1469 * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.
1470 */
1471 public static final int PROTECTED = Modifier.PROTECTED;
1472
1473 /** A single-bit mask representing {@code package} access (default access),
1474 * which may contribute to the result of {@link #lookupModes lookupModes}.
1475 * The value is {@code 0x08}, which does not correspond meaningfully to
1476 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1477 */
1478 public static final int PACKAGE = Modifier.STATIC;
1479
1480 /** A single-bit mask representing {@code module} access,
1481 * which may contribute to the result of {@link #lookupModes lookupModes}.
1482 * The value is {@code 0x10}, which does not correspond meaningfully to
1483 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1484 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup}
1485 * with this lookup mode can access all public types in the module of the
1486 * lookup class and public types in packages exported by other modules
1487 * to the module of the lookup class.
1488 * <p>
1489 * If this lookup mode is set, the {@linkplain #previousLookupClass()
1490 * previous lookup class} is always {@code null}.
1491 *
1492 * @since 9
1493 */
1494 public static final int MODULE = PACKAGE << 1;
1495
1496 /** A single-bit mask representing {@code unconditional} access
1497 * which may contribute to the result of {@link #lookupModes lookupModes}.
1498 * The value is {@code 0x20}, which does not correspond meaningfully to
1499 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1500 * A {@code Lookup} with this lookup mode assumes {@linkplain
1501 * java.lang.Module#canRead(java.lang.Module) readability}.
1502 * This lookup mode can access all public members of public types
1503 * of all modules when the type is in a package that is {@link
1504 * java.lang.Module#isExported(String) exported unconditionally}.
1505 *
1506 * <p>
1507 * If this lookup mode is set, the {@linkplain #previousLookupClass()
1508 * previous lookup class} is always {@code null}.
1509 *
1510 * @since 9
1511 * @see #publicLookup()
1512 */
1513 public static final int UNCONDITIONAL = PACKAGE << 2;
1514
1515 /** A single-bit mask representing {@code original} access
1516 * which may contribute to the result of {@link #lookupModes lookupModes}.
1517 * The value is {@code 0x40}, which does not correspond meaningfully to
1518 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1519 *
1520 * <p>
1521 * If this lookup mode is set, the {@code Lookup} object must be
1522 * created by the original lookup class by calling
1523 * {@link MethodHandles#lookup()} method or by a bootstrap method
1524 * invoked by the VM. The {@code Lookup} object with this lookup
1525 * mode has {@linkplain #hasFullPrivilegeAccess() full privilege access}.
1526 *
1527 * @since 16
1528 */
1529 public static final int ORIGINAL = PACKAGE << 3;
1530
1531 private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE | MODULE | UNCONDITIONAL | ORIGINAL);
1532 private static final int FULL_POWER_MODES = (ALL_MODES & ~UNCONDITIONAL); // with original access
1533 private static final int TRUSTED = -1;
1534
1535 /*
1536 * Adjust PUBLIC => PUBLIC|MODULE|ORIGINAL|UNCONDITIONAL
1537 * Adjust 0 => PACKAGE
1538 */
1539 private static int fixmods(int mods) {
1540 mods &= (ALL_MODES - PACKAGE - MODULE - ORIGINAL - UNCONDITIONAL);
1541 if (Modifier.isPublic(mods))
1542 mods |= UNCONDITIONAL;
1543 return (mods != 0) ? mods : PACKAGE;
1544 }
1545
1546 /** Tells which class is performing the lookup. It is this class against
1547 * which checks are performed for visibility and access permissions.
1548 * <p>
1549 * If this lookup object has a {@linkplain #previousLookupClass() previous lookup class},
1550 * access checks are performed against both the lookup class and the previous lookup class.
1551 * <p>
1552 * The class implies a maximum level of access permission,
1553 * but the permissions may be additionally limited by the bitmask
1554 * {@link #lookupModes lookupModes}, which controls whether non-public members
1555 * can be accessed.
1556 * @return the lookup class, on behalf of which this lookup object finds members
1557 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1558 */
1559 public Class<?> lookupClass() {
1560 return lookupClass;
1561 }
1562
1563 /** Reports a lookup class in another module that this lookup object
1564 * was previously teleported from, or {@code null}.
1565 * <p>
1566 * A {@code Lookup} object produced by the factory methods, such as the
1567 * {@link #lookup() lookup()} and {@link #publicLookup() publicLookup()} method,
1568 * has {@code null} previous lookup class.
1569 * A {@code Lookup} object has a non-null previous lookup class
1570 * when this lookup was teleported from an old lookup class
1571 * in one module to a new lookup class in another module.
1572 *
1573 * @return the lookup class in another module that this lookup object was
1574 * previously teleported from, or {@code null}
1575 * @since 14
1576 * @see #in(Class)
1577 * @see MethodHandles#privateLookupIn(Class, Lookup)
1578 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1579 */
1580 public Class<?> previousLookupClass() {
1581 return prevLookupClass;
1582 }
1583
1584 // This is just for calling out to MethodHandleImpl.
1585 private Class<?> lookupClassOrNull() {
1586 return (allowedModes == TRUSTED) ? null : lookupClass;
1587 }
1588
1589 /** Tells which access-protection classes of members this lookup object can produce.
1590 * The result is a bit-mask of the bits
1591 * {@linkplain #PUBLIC PUBLIC (0x01)},
1592 * {@linkplain #PRIVATE PRIVATE (0x02)},
1593 * {@linkplain #PROTECTED PROTECTED (0x04)},
1594 * {@linkplain #PACKAGE PACKAGE (0x08)},
1595 * {@linkplain #MODULE MODULE (0x10)},
1596 * {@linkplain #UNCONDITIONAL UNCONDITIONAL (0x20)},
1597 * and {@linkplain #ORIGINAL ORIGINAL (0x40)}.
1598 * <p>
1599 * A freshly-created lookup object
1600 * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class} has
1601 * all possible bits set, except {@code UNCONDITIONAL}.
1602 * A lookup object on a new lookup class
1603 * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object}
1604 * may have some mode bits set to zero.
1605 * Mode bits can also be
1606 * {@linkplain java.lang.invoke.MethodHandles.Lookup#dropLookupMode directly cleared}.
1607 * Once cleared, mode bits cannot be restored from the downgraded lookup object.
1608 * The purpose of this is to restrict access via the new lookup object,
1609 * so that it can access only names which can be reached by the original
1610 * lookup object, and also by the new lookup class.
1611 * @return the lookup modes, which limit the kinds of access performed by this lookup object
1612 * @see #in
1613 * @see #dropLookupMode
1614 */
1615 public int lookupModes() {
1616 return allowedModes & ALL_MODES;
1617 }
1618
1619 /** Embody the current class (the lookupClass) as a lookup class
1620 * for method handle creation.
1621 * Must be called by from a method in this package,
1622 * which in turn is called by a method not in this package.
1623 */
1624 Lookup(Class<?> lookupClass) {
1625 this(lookupClass, null, FULL_POWER_MODES);
1626 }
1627
1628 private Lookup(Class<?> lookupClass, Class<?> prevLookupClass, int allowedModes) {
1629 assert prevLookupClass == null || ((allowedModes & MODULE) == 0
1630 && prevLookupClass.getModule() != lookupClass.getModule());
1631 assert !lookupClass.isArray() && !lookupClass.isPrimitive();
1632 this.lookupClass = lookupClass;
1633 this.prevLookupClass = prevLookupClass;
1634 this.allowedModes = allowedModes;
1635 }
1636
1637 private static Lookup newLookup(Class<?> lookupClass, Class<?> prevLookupClass, int allowedModes) {
1638 // make sure we haven't accidentally picked up a privileged class:
1639 checkUnprivilegedlookupClass(lookupClass);
1640 return new Lookup(lookupClass, prevLookupClass, allowedModes);
1641 }
1642
1643 /**
1644 * Creates a lookup on the specified new lookup class.
1645 * The resulting object will report the specified
1646 * class as its own {@link #lookupClass() lookupClass}.
1647 *
1648 * <p>
1649 * However, the resulting {@code Lookup} object is guaranteed
1650 * to have no more access capabilities than the original.
1651 * In particular, access capabilities can be lost as follows:<ul>
1652 * <li>If the new lookup class is different from the old lookup class,
1653 * i.e. {@link #ORIGINAL ORIGINAL} access is lost.
1654 * <li>If the new lookup class is in a different module from the old one,
1655 * i.e. {@link #MODULE MODULE} access is lost.
1656 * <li>If the new lookup class is in a different package
1657 * than the old one, protected and default (package) members will not be accessible,
1658 * i.e. {@link #PROTECTED PROTECTED} and {@link #PACKAGE PACKAGE} access are lost.
1659 * <li>If the new lookup class is not within the same package member
1660 * as the old one, private members will not be accessible, and protected members
1661 * will not be accessible by virtue of inheritance,
1662 * i.e. {@link #PRIVATE PRIVATE} access is lost.
1663 * (Protected members may continue to be accessible because of package sharing.)
1664 * <li>If the new lookup class is not
1665 * {@linkplain #accessClass(Class) accessible} to this lookup,
1666 * then no members, not even public members, will be accessible
1667 * i.e. all access modes are lost.
1668 * <li>If the new lookup class, the old lookup class and the previous lookup class
1669 * are all in different modules i.e. teleporting to a third module,
1670 * all access modes are lost.
1671 * </ul>
1672 * <p>
1673 * The new previous lookup class is chosen as follows:
1674 * <ul>
1675 * <li>If the new lookup object has {@link #UNCONDITIONAL UNCONDITIONAL} bit,
1676 * the new previous lookup class is {@code null}.
1677 * <li>If the new lookup class is in the same module as the old lookup class,
1678 * the new previous lookup class is the old previous lookup class.
1679 * <li>If the new lookup class is in a different module from the old lookup class,
1680 * the new previous lookup class is the old lookup class.
1681 *</ul>
1682 * <p>
1683 * The resulting lookup's capabilities for loading classes
1684 * (used during {@link #findClass} invocations)
1685 * are determined by the lookup class' loader,
1686 * which may change due to this operation.
1687 *
1688 * @param requestedLookupClass the desired lookup class for the new lookup object
1689 * @return a lookup object which reports the desired lookup class, or the same object
1690 * if there is no change
1691 * @throws IllegalArgumentException if {@code requestedLookupClass} is a primitive type or void or array class
1692 * @throws NullPointerException if the argument is null
1693 *
1694 * @see #accessClass(Class)
1695 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1696 */
1697 public Lookup in(Class<?> requestedLookupClass) {
1698 Objects.requireNonNull(requestedLookupClass);
1699 if (requestedLookupClass.isPrimitive())
1700 throw new IllegalArgumentException(requestedLookupClass + " is a primitive class");
1701 if (requestedLookupClass.isArray())
1702 throw new IllegalArgumentException(requestedLookupClass + " is an array class");
1703
1704 if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all
1705 return new Lookup(requestedLookupClass, null, FULL_POWER_MODES);
1706 if (requestedLookupClass == this.lookupClass)
1707 return this; // keep same capabilities
1708 int newModes = (allowedModes & FULL_POWER_MODES) & ~ORIGINAL;
1709 Module fromModule = this.lookupClass.getModule();
1710 Module targetModule = requestedLookupClass.getModule();
1711 Class<?> plc = this.previousLookupClass();
1712 if ((this.allowedModes & UNCONDITIONAL) != 0) {
1713 assert plc == null;
1714 newModes = UNCONDITIONAL;
1715 } else if (fromModule != targetModule) {
1716 if (plc != null && !VerifyAccess.isSameModule(plc, requestedLookupClass)) {
1717 // allow hopping back and forth between fromModule and plc's module
1718 // but not the third module
1719 newModes = 0;
1720 }
1721 // drop MODULE access
1722 newModes &= ~(MODULE|PACKAGE|PRIVATE|PROTECTED);
1723 // teleport from this lookup class
1724 plc = this.lookupClass;
1725 }
1726 if ((newModes & PACKAGE) != 0
1727 && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {
1728 newModes &= ~(PACKAGE|PRIVATE|PROTECTED);
1729 }
1730 // Allow nestmate lookups to be created without special privilege:
1731 if ((newModes & PRIVATE) != 0
1732 && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {
1733 newModes &= ~(PRIVATE|PROTECTED);
1734 }
1735 if ((newModes & (PUBLIC|UNCONDITIONAL)) != 0
1736 && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, this.prevLookupClass, allowedModes)) {
1737 // The requested class it not accessible from the lookup class.
1738 // No permissions.
1739 newModes = 0;
1740 }
1741 return newLookup(requestedLookupClass, plc, newModes);
1742 }
1743
1744 /**
1745 * Creates a lookup on the same lookup class which this lookup object
1746 * finds members, but with a lookup mode that has lost the given lookup mode.
1747 * The lookup mode to drop is one of {@link #PUBLIC PUBLIC}, {@link #MODULE
1748 * MODULE}, {@link #PACKAGE PACKAGE}, {@link #PROTECTED PROTECTED},
1749 * {@link #PRIVATE PRIVATE}, {@link #ORIGINAL ORIGINAL}, or
1750 * {@link #UNCONDITIONAL UNCONDITIONAL}.
1751 *
1752 * <p> If this lookup is a {@linkplain MethodHandles#publicLookup() public lookup},
1753 * this lookup has {@code UNCONDITIONAL} mode set and it has no other mode set.
1754 * When dropping {@code UNCONDITIONAL} on a public lookup then the resulting
1755 * lookup has no access.
1756 *
1757 * <p> If this lookup is not a public lookup, then the following applies
1758 * regardless of its {@linkplain #lookupModes() lookup modes}.
1759 * {@link #PROTECTED PROTECTED} and {@link #ORIGINAL ORIGINAL} are always
1760 * dropped and so the resulting lookup mode will never have these access
1761 * capabilities. When dropping {@code PACKAGE}
1762 * then the resulting lookup will not have {@code PACKAGE} or {@code PRIVATE}
1763 * access. When dropping {@code MODULE} then the resulting lookup will not
1764 * have {@code MODULE}, {@code PACKAGE}, or {@code PRIVATE} access.
1765 * When dropping {@code PUBLIC} then the resulting lookup has no access.
1766 *
1767 * @apiNote
1768 * A lookup with {@code PACKAGE} but not {@code PRIVATE} mode can safely
1769 * delegate non-public access within the package of the lookup class without
1770 * conferring <a href="MethodHandles.Lookup.html#privacc">private access</a>.
1771 * A lookup with {@code MODULE} but not
1772 * {@code PACKAGE} mode can safely delegate {@code PUBLIC} access within
1773 * the module of the lookup class without conferring package access.
1774 * A lookup with a {@linkplain #previousLookupClass() previous lookup class}
1775 * (and {@code PUBLIC} but not {@code MODULE} mode) can safely delegate access
1776 * to public classes accessible to both the module of the lookup class
1777 * and the module of the previous lookup class.
1778 *
1779 * @param modeToDrop the lookup mode to drop
1780 * @return a lookup object which lacks the indicated mode, or the same object if there is no change
1781 * @throws IllegalArgumentException if {@code modeToDrop} is not one of {@code PUBLIC},
1782 * {@code MODULE}, {@code PACKAGE}, {@code PROTECTED}, {@code PRIVATE}, {@code ORIGINAL}
1783 * or {@code UNCONDITIONAL}
1784 * @see MethodHandles#privateLookupIn
1785 * @since 9
1786 */
1787 public Lookup dropLookupMode(int modeToDrop) {
1788 int oldModes = lookupModes();
1789 int newModes = oldModes & ~(modeToDrop | PROTECTED | ORIGINAL);
1790 switch (modeToDrop) {
1791 case PUBLIC: newModes &= ~(FULL_POWER_MODES); break;
1792 case MODULE: newModes &= ~(PACKAGE | PRIVATE); break;
1793 case PACKAGE: newModes &= ~(PRIVATE); break;
1794 case PROTECTED:
1795 case PRIVATE:
1796 case ORIGINAL:
1797 case UNCONDITIONAL: break;
1798 default: throw new IllegalArgumentException(modeToDrop + " is not a valid mode to drop");
1799 }
1800 if (newModes == oldModes) return this; // return self if no change
1801 return newLookup(lookupClass(), previousLookupClass(), newModes);
1802 }
1803
1804 /**
1805 * Creates and links a class or interface from {@code bytes}
1806 * with the same class loader and in the same runtime package and
1807 * {@linkplain java.security.ProtectionDomain protection domain} as this lookup's
1808 * {@linkplain #lookupClass() lookup class} as if calling
1809 * {@link ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain)
1810 * ClassLoader::defineClass}.
1811 *
1812 * <p> The {@linkplain #lookupModes() lookup modes} for this lookup must include
1813 * {@link #PACKAGE PACKAGE} access as default (package) members will be
1814 * accessible to the class. The {@code PACKAGE} lookup mode serves to authenticate
1815 * that the lookup object was created by a caller in the runtime package (or derived
1816 * from a lookup originally created by suitably privileged code to a target class in
1817 * the runtime package). </p>
1818 *
1819 * <p> The {@code bytes} parameter is the class bytes of a valid class file (as defined
1820 * by the <em>The Java Virtual Machine Specification</em>) with a class name in the
1821 * same package as the lookup class. </p>
1822 *
1823 * <p> This method does not run the class initializer. The class initializer may
1824 * run at a later time, as detailed in section 12.4 of the <em>The Java Language
1825 * Specification</em>. </p>
1826 *
1827 * <p> If there is a security manager and this lookup does not have {@linkplain
1828 * #hasFullPrivilegeAccess() full privilege access}, its {@code checkPermission} method
1829 * is first called to check {@code RuntimePermission("defineClass")}. </p>
1830 *
1831 * @param bytes the class bytes
1832 * @return the {@code Class} object for the class
1833 * @throws IllegalAccessException if this lookup does not have {@code PACKAGE} access
1834 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure
1835 * @throws IllegalArgumentException if {@code bytes} denotes a class in a different package
1836 * than the lookup class or {@code bytes} is not a class or interface
1837 * ({@code ACC_MODULE} flag is set in the value of the {@code access_flags} item)
1838 * @throws VerifyError if the newly created class cannot be verified
1839 * @throws LinkageError if the newly created class cannot be linked for any other reason
1840 * @throws SecurityException if a security manager is present and it
1841 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1842 * @throws NullPointerException if {@code bytes} is {@code null}
1843 * @since 9
1844 * @see Lookup#privateLookupIn
1845 * @see Lookup#dropLookupMode
1846 * @see ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain)
1847 */
1848 public Class<?> defineClass(byte[] bytes) throws IllegalAccessException {
1849 ensureDefineClassPermission();
1850 if ((lookupModes() & PACKAGE) == 0)
1851 throw new IllegalAccessException("Lookup does not have PACKAGE access");
1852 return makeClassDefiner(bytes.clone()).defineClass(false);
1853 }
1854
1855 private void ensureDefineClassPermission() {
1856 if (allowedModes == TRUSTED) return;
1857
1858 if (!hasFullPrivilegeAccess()) {
1859 @SuppressWarnings("removal")
1860 SecurityManager sm = System.getSecurityManager();
1861 if (sm != null)
1862 sm.checkPermission(new RuntimePermission("defineClass"));
1863 }
1864 }
1865
1866 /**
1867 * The set of class options that specify whether a hidden class created by
1868 * {@link Lookup#defineHiddenClass(byte[], boolean, ClassOption...)
1869 * Lookup::defineHiddenClass} method is dynamically added as a new member
1870 * to the nest of a lookup class and/or whether a hidden class has
1871 * a strong relationship with the class loader marked as its defining loader.
1872 *
1873 * @since 15
1874 */
1875 public enum ClassOption {
1876 /**
1877 * Specifies that a hidden class be added to {@linkplain Class#getNestHost nest}
1878 * of a lookup class as a nestmate.
1879 *
1880 * <p> A hidden nestmate class has access to the private members of all
1881 * classes and interfaces in the same nest.
1882 *
1883 * @see Class#getNestHost()
1884 */
1885 NESTMATE(NESTMATE_CLASS),
1886
1887 /**
1888 * Specifies that a hidden class has a <em>strong</em>
1889 * relationship with the class loader marked as its defining loader,
1890 * as a normal class or interface has with its own defining loader.
1891 * This means that the hidden class may be unloaded if and only if
1892 * its defining loader is not reachable and thus may be reclaimed
1893 * by a garbage collector (JLS {@jls 12.7}).
1894 *
1895 * <p> By default, a hidden class or interface may be unloaded
1896 * even if the class loader that is marked as its defining loader is
1897 * <a href="../ref/package-summary.html#reachability">reachable</a>.
1898
1899 *
1900 * @jls 12.7 Unloading of Classes and Interfaces
1901 */
1902 STRONG(STRONG_LOADER_LINK);
1903
1904 /* the flag value is used by VM at define class time */
1905 private final int flag;
1906 ClassOption(int flag) {
1907 this.flag = flag;
1908 }
1909
1910 static int optionsToFlag(Set<ClassOption> options) {
1911 int flags = 0;
1912 for (ClassOption cp : options) {
1913 flags |= cp.flag;
1914 }
1915 return flags;
1916 }
1917 }
1918
1919 /**
1920 * Creates a <em>hidden</em> class or interface from {@code bytes},
1921 * returning a {@code Lookup} on the newly created class or interface.
1922 *
1923 * <p> Ordinarily, a class or interface {@code C} is created by a class loader,
1924 * which either defines {@code C} directly or delegates to another class loader.
1925 * A class loader defines {@code C} directly by invoking
1926 * {@link ClassLoader#defineClass(String, byte[], int, int, ProtectionDomain)
1927 * ClassLoader::defineClass}, which causes the Java Virtual Machine
1928 * to derive {@code C} from a purported representation in {@code class} file format.
1929 * In situations where use of a class loader is undesirable, a class or interface
1930 * {@code C} can be created by this method instead. This method is capable of
1931 * defining {@code C}, and thereby creating it, without invoking
1932 * {@code ClassLoader::defineClass}.
1933 * Instead, this method defines {@code C} as if by arranging for
1934 * the Java Virtual Machine to derive a nonarray class or interface {@code C}
1935 * from a purported representation in {@code class} file format
1936 * using the following rules:
1937 *
1938 * <ol>
1939 * <li> The {@linkplain #lookupModes() lookup modes} for this {@code Lookup}
1940 * must include {@linkplain #hasFullPrivilegeAccess() full privilege} access.
1941 * This level of access is needed to create {@code C} in the module
1942 * of the lookup class of this {@code Lookup}.</li>
1943 *
1944 * <li> The purported representation in {@code bytes} must be a {@code ClassFile}
1945 * structure (JVMS {@jvms 4.1}) of a supported major and minor version.
1946 * The major and minor version may differ from the {@code class} file version
1947 * of the lookup class of this {@code Lookup}.</li>
1948 *
1949 * <li> The value of {@code this_class} must be a valid index in the
1950 * {@code constant_pool} table, and the entry at that index must be a valid
1951 * {@code CONSTANT_Class_info} structure. Let {@code N} be the binary name
1952 * encoded in internal form that is specified by this structure. {@code N} must
1953 * denote a class or interface in the same package as the lookup class.</li>
1954 *
1955 * <li> Let {@code CN} be the string {@code N + "." + <suffix>},
1956 * where {@code <suffix>} is an unqualified name.
1957 *
1958 * <p> Let {@code newBytes} be the {@code ClassFile} structure given by
1959 * {@code bytes} with an additional entry in the {@code constant_pool} table,
1960 * indicating a {@code CONSTANT_Utf8_info} structure for {@code CN}, and
1961 * where the {@code CONSTANT_Class_info} structure indicated by {@code this_class}
1962 * refers to the new {@code CONSTANT_Utf8_info} structure.
1963 *
1964 * <p> Let {@code L} be the defining class loader of the lookup class of this {@code Lookup}.
1965 *
1966 * <p> {@code C} is derived with name {@code CN}, class loader {@code L}, and
1967 * purported representation {@code newBytes} as if by the rules of JVMS {@jvms 5.3.5},
1968 * with the following adjustments:
1969 * <ul>
1970 * <li> The constant indicated by {@code this_class} is permitted to specify a name
1971 * that includes a single {@code "."} character, even though this is not a valid
1972 * binary class or interface name in internal form.</li>
1973 *
1974 * <li> The Java Virtual Machine marks {@code L} as the defining class loader of {@code C},
1975 * but no class loader is recorded as an initiating class loader of {@code C}.</li>
1976 *
1977 * <li> {@code C} is considered to have the same runtime
1978 * {@linkplain Class#getPackage() package}, {@linkplain Class#getModule() module}
1979 * and {@linkplain java.security.ProtectionDomain protection domain}
1980 * as the lookup class of this {@code Lookup}.
1981 * <li> Let {@code GN} be the binary name obtained by taking {@code N}
1982 * (a binary name encoded in internal form) and replacing ASCII forward slashes with
1983 * ASCII periods. For the instance of {@link java.lang.Class} representing {@code C}:
1984 * <ul>
1985 * <li> {@link Class#getName()} returns the string {@code GN + "/" + <suffix>},
1986 * even though this is not a valid binary class or interface name.</li>
1987 * <li> {@link Class#descriptorString()} returns the string
1988 * {@code "L" + N + "." + <suffix> + ";"},
1989 * even though this is not a valid type descriptor name.</li>
1990 * <li> {@link Class#describeConstable()} returns an empty optional as {@code C}
1991 * cannot be described in {@linkplain java.lang.constant.ClassDesc nominal form}.</li>
1992 * </ul>
1993 * </ul>
1994 * </li>
1995 * </ol>
1996 *
1997 * <p> After {@code C} is derived, it is linked by the Java Virtual Machine.
1998 * Linkage occurs as specified in JVMS {@jvms 5.4.3}, with the following adjustments:
1999 * <ul>
2000 * <li> During verification, whenever it is necessary to load the class named
2001 * {@code CN}, the attempt succeeds, producing class {@code C}. No request is
2002 * made of any class loader.</li>
2003 *
2004 * <li> On any attempt to resolve the entry in the run-time constant pool indicated
2005 * by {@code this_class}, the symbolic reference is considered to be resolved to
2006 * {@code C} and resolution always succeeds immediately.</li>
2007 * </ul>
2008 *
2009 * <p> If the {@code initialize} parameter is {@code true},
2010 * then {@code C} is initialized by the Java Virtual Machine.
2011 *
2012 * <p> The newly created class or interface {@code C} serves as the
2013 * {@linkplain #lookupClass() lookup class} of the {@code Lookup} object
2014 * returned by this method. {@code C} is <em>hidden</em> in the sense that
2015 * no other class or interface can refer to {@code C} via a constant pool entry.
2016 * That is, a hidden class or interface cannot be named as a supertype, a field type,
2017 * a method parameter type, or a method return type by any other class.
2018 * This is because a hidden class or interface does not have a binary name, so
2019 * there is no internal form available to record in any class's constant pool.
2020 * A hidden class or interface is not discoverable by {@link Class#forName(String, boolean, ClassLoader)},
2021 * {@link ClassLoader#loadClass(String, boolean)}, or {@link #findClass(String)}, and
2022 * is not {@linkplain java.instrument/java.lang.instrument.Instrumentation#isModifiableClass(Class)
2023 * modifiable} by Java agents or tool agents using the <a href="{@docRoot}/../specs/jvmti.html">
2024 * JVM Tool Interface</a>.
2025 *
2026 * <p> A class or interface created by
2027 * {@linkplain ClassLoader#defineClass(String, byte[], int, int, ProtectionDomain)
2028 * a class loader} has a strong relationship with that class loader.
2029 * That is, every {@code Class} object contains a reference to the {@code ClassLoader}
2030 * that {@linkplain Class#getClassLoader() defined it}.
2031 * This means that a class created by a class loader may be unloaded if and
2032 * only if its defining loader is not reachable and thus may be reclaimed
2033 * by a garbage collector (JLS {@jls 12.7}).
2034 *
2035 * By default, however, a hidden class or interface may be unloaded even if
2036 * the class loader that is marked as its defining loader is
2037 * <a href="../ref/package-summary.html#reachability">reachable</a>.
2038 * This behavior is useful when a hidden class or interface serves multiple
2039 * classes defined by arbitrary class loaders. In other cases, a hidden
2040 * class or interface may be linked to a single class (or a small number of classes)
2041 * with the same defining loader as the hidden class or interface.
2042 * In such cases, where the hidden class or interface must be coterminous
2043 * with a normal class or interface, the {@link ClassOption#STRONG STRONG}
2044 * option may be passed in {@code options}.
2045 * This arranges for a hidden class to have the same strong relationship
2046 * with the class loader marked as its defining loader,
2047 * as a normal class or interface has with its own defining loader.
2048 *
2049 * If {@code STRONG} is not used, then the invoker of {@code defineHiddenClass}
2050 * may still prevent a hidden class or interface from being
2051 * unloaded by ensuring that the {@code Class} object is reachable.
2052 *
2053 * <p> The unloading characteristics are set for each hidden class when it is
2054 * defined, and cannot be changed later. An advantage of allowing hidden classes
2055 * to be unloaded independently of the class loader marked as their defining loader
2056 * is that a very large number of hidden classes may be created by an application.
2057 * In contrast, if {@code STRONG} is used, then the JVM may run out of memory,
2058 * just as if normal classes were created by class loaders.
2059 *
2060 * <p> Classes and interfaces in a nest are allowed to have mutual access to
2061 * their private members. The nest relationship is determined by
2062 * the {@code NestHost} attribute (JVMS {@jvms 4.7.28}) and
2063 * the {@code NestMembers} attribute (JVMS {@jvms 4.7.29}) in a {@code class} file.
2064 * By default, a hidden class belongs to a nest consisting only of itself
2065 * because a hidden class has no binary name.
2066 * The {@link ClassOption#NESTMATE NESTMATE} option can be passed in {@code options}
2067 * to create a hidden class or interface {@code C} as a member of a nest.
2068 * The nest to which {@code C} belongs is not based on any {@code NestHost} attribute
2069 * in the {@code ClassFile} structure from which {@code C} was derived.
2070 * Instead, the following rules determine the nest host of {@code C}:
2071 * <ul>
2072 * <li>If the nest host of the lookup class of this {@code Lookup} has previously
2073 * been determined, then let {@code H} be the nest host of the lookup class.
2074 * Otherwise, the nest host of the lookup class is determined using the
2075 * algorithm in JVMS {@jvms 5.4.4}, yielding {@code H}.</li>
2076 * <li>The nest host of {@code C} is determined to be {@code H},
2077 * the nest host of the lookup class.</li>
2078 * </ul>
2079 *
2080 * <p> A hidden class or interface may be serializable, but this requires a custom
2081 * serialization mechanism in order to ensure that instances are properly serialized
2082 * and deserialized. The default serialization mechanism supports only classes and
2083 * interfaces that are discoverable by their class name.
2084 *
2085 * @param bytes the bytes that make up the class data,
2086 * in the format of a valid {@code class} file as defined by
2087 * <cite>The Java Virtual Machine Specification</cite>.
2088 * @param initialize if {@code true} the class will be initialized.
2089 * @param options {@linkplain ClassOption class options}
2090 * @return the {@code Lookup} object on the hidden class,
2091 * with {@linkplain #ORIGINAL original} and
2092 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege} access
2093 *
2094 * @throws IllegalAccessException if this {@code Lookup} does not have
2095 * {@linkplain #hasFullPrivilegeAccess() full privilege} access
2096 * @throws SecurityException if a security manager is present and it
2097 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2098 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure
2099 * @throws UnsupportedClassVersionError if {@code bytes} is not of a supported major or minor version
2100 * @throws IllegalArgumentException if {@code bytes} denotes a class in a different package
2101 * than the lookup class or {@code bytes} is not a class or interface
2102 * ({@code ACC_MODULE} flag is set in the value of the {@code access_flags} item)
2103 * @throws IncompatibleClassChangeError if the class or interface named as
2104 * the direct superclass of {@code C} is in fact an interface, or if any of the classes
2105 * or interfaces named as direct superinterfaces of {@code C} are not in fact interfaces
2106 * @throws ClassCircularityError if any of the superclasses or superinterfaces of
2107 * {@code C} is {@code C} itself
2108 * @throws VerifyError if the newly created class cannot be verified
2109 * @throws LinkageError if the newly created class cannot be linked for any other reason
2110 * @throws NullPointerException if any parameter is {@code null}
2111 *
2112 * @since 15
2113 * @see Class#isHidden()
2114 * @jvms 4.2.1 Binary Class and Interface Names
2115 * @jvms 4.2.2 Unqualified Names
2116 * @jvms 4.7.28 The {@code NestHost} Attribute
2117 * @jvms 4.7.29 The {@code NestMembers} Attribute
2118 * @jvms 5.4.3.1 Class and Interface Resolution
2119 * @jvms 5.4.4 Access Control
2120 * @jvms 5.3.5 Deriving a {@code Class} from a {@code class} File Representation
2121 * @jvms 5.4 Linking
2122 * @jvms 5.5 Initialization
2123 * @jls 12.7 Unloading of Classes and Interfaces
2124 */
2125 @SuppressWarnings("doclint:reference") // cross-module links
2126 public Lookup defineHiddenClass(byte[] bytes, boolean initialize, ClassOption... options)
2127 throws IllegalAccessException
2128 {
2129 Objects.requireNonNull(bytes);
2130 Objects.requireNonNull(options);
2131
2132 ensureDefineClassPermission();
2133 if (!hasFullPrivilegeAccess()) {
2134 throw new IllegalAccessException(this + " does not have full privilege access");
2135 }
2136
2137 return makeHiddenClassDefiner(bytes.clone(), Set.of(options), false).defineClassAsLookup(initialize);
2138 }
2139
2140 /**
2141 * Creates a <em>hidden</em> class or interface from {@code bytes} with associated
2142 * {@linkplain MethodHandles#classData(Lookup, String, Class) class data},
2143 * returning a {@code Lookup} on the newly created class or interface.
2144 *
2145 * <p> This method is equivalent to calling
2146 * {@link #defineHiddenClass(byte[], boolean, ClassOption...) defineHiddenClass(bytes, initialize, options)}
2147 * as if the hidden class is injected with a private static final <i>unnamed</i>
2148 * field which is initialized with the given {@code classData} at
2149 * the first instruction of the class initializer.
2150 * The newly created class is linked by the Java Virtual Machine.
2151 *
2152 * <p> The {@link MethodHandles#classData(Lookup, String, Class) MethodHandles::classData}
2153 * and {@link MethodHandles#classDataAt(Lookup, String, Class, int) MethodHandles::classDataAt}
2154 * methods can be used to retrieve the {@code classData}.
2155 *
2156 * @apiNote
2157 * A framework can create a hidden class with class data with one or more
2158 * objects and load the class data as dynamically-computed constant(s)
2159 * via a bootstrap method. {@link MethodHandles#classData(Lookup, String, Class)
2160 * Class data} is accessible only to the lookup object created by the newly
2161 * defined hidden class but inaccessible to other members in the same nest
2162 * (unlike private static fields that are accessible to nestmates).
2163 * Care should be taken w.r.t. mutability for example when passing
2164 * an array or other mutable structure through the class data.
2165 * Changing any value stored in the class data at runtime may lead to
2166 * unpredictable behavior.
2167 * If the class data is a {@code List}, it is good practice to make it
2168 * unmodifiable for example via {@link List#of List::of}.
2169 *
2170 * @param bytes the class bytes
2171 * @param classData pre-initialized class data
2172 * @param initialize if {@code true} the class will be initialized.
2173 * @param options {@linkplain ClassOption class options}
2174 * @return the {@code Lookup} object on the hidden class,
2175 * with {@linkplain #ORIGINAL original} and
2176 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege} access
2177 *
2178 * @throws IllegalAccessException if this {@code Lookup} does not have
2179 * {@linkplain #hasFullPrivilegeAccess() full privilege} access
2180 * @throws SecurityException if a security manager is present and it
2181 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2182 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure
2183 * @throws UnsupportedClassVersionError if {@code bytes} is not of a supported major or minor version
2184 * @throws IllegalArgumentException if {@code bytes} denotes a class in a different package
2185 * than the lookup class or {@code bytes} is not a class or interface
2186 * ({@code ACC_MODULE} flag is set in the value of the {@code access_flags} item)
2187 * @throws IncompatibleClassChangeError if the class or interface named as
2188 * the direct superclass of {@code C} is in fact an interface, or if any of the classes
2189 * or interfaces named as direct superinterfaces of {@code C} are not in fact interfaces
2190 * @throws ClassCircularityError if any of the superclasses or superinterfaces of
2191 * {@code C} is {@code C} itself
2192 * @throws VerifyError if the newly created class cannot be verified
2193 * @throws LinkageError if the newly created class cannot be linked for any other reason
2194 * @throws NullPointerException if any parameter is {@code null}
2195 *
2196 * @since 16
2197 * @see Lookup#defineHiddenClass(byte[], boolean, ClassOption...)
2198 * @see Class#isHidden()
2199 * @see MethodHandles#classData(Lookup, String, Class)
2200 * @see MethodHandles#classDataAt(Lookup, String, Class, int)
2201 * @jvms 4.2.1 Binary Class and Interface Names
2202 * @jvms 4.2.2 Unqualified Names
2203 * @jvms 4.7.28 The {@code NestHost} Attribute
2204 * @jvms 4.7.29 The {@code NestMembers} Attribute
2205 * @jvms 5.4.3.1 Class and Interface Resolution
2206 * @jvms 5.4.4 Access Control
2207 * @jvms 5.3.5 Deriving a {@code Class} from a {@code class} File Representation
2208 * @jvms 5.4 Linking
2209 * @jvms 5.5 Initialization
2210 * @jls 12.7 Unloading of Classes and Interface
2211 */
2212 public Lookup defineHiddenClassWithClassData(byte[] bytes, Object classData, boolean initialize, ClassOption... options)
2213 throws IllegalAccessException
2214 {
2215 Objects.requireNonNull(bytes);
2216 Objects.requireNonNull(classData);
2217 Objects.requireNonNull(options);
2218
2219 ensureDefineClassPermission();
2220 if (!hasFullPrivilegeAccess()) {
2221 throw new IllegalAccessException(this + " does not have full privilege access");
2222 }
2223
2224 return makeHiddenClassDefiner(bytes.clone(), Set.of(options), false)
2225 .defineClassAsLookup(initialize, classData);
2226 }
2227
2228 // A default dumper for writing class files passed to Lookup::defineClass
2229 // and Lookup::defineHiddenClass to disk for debugging purposes. To enable,
2230 // set -Djdk.invoke.MethodHandle.dumpHiddenClassFiles or
2231 // -Djdk.invoke.MethodHandle.dumpHiddenClassFiles=true
2232 //
2233 // This default dumper does not dump hidden classes defined by LambdaMetafactory
2234 // and LambdaForms and method handle internals. They are dumped via
2235 // different ClassFileDumpers.
2236 private static ClassFileDumper defaultDumper() {
2237 return DEFAULT_DUMPER;
2238 }
2239
2240 private static final ClassFileDumper DEFAULT_DUMPER = ClassFileDumper.getInstance(
2241 "jdk.invoke.MethodHandle.dumpClassFiles", "DUMP_CLASS_FILES");
2242
2243 static class ClassFile {
2244 final String name; // internal name
2245 final int accessFlags;
2246 final byte[] bytes;
2247 ClassFile(String name, int accessFlags, byte[] bytes) {
2248 this.name = name;
2249 this.accessFlags = accessFlags;
2250 this.bytes = bytes;
2251 }
2252
2253 static ClassFile newInstanceNoCheck(String name, byte[] bytes) {
2254 return new ClassFile(name, 0, bytes);
2255 }
2256
2257 /**
2258 * This method checks the class file version and the structure of `this_class`.
2259 * and checks if the bytes is a class or interface (ACC_MODULE flag not set)
2260 * that is in the named package.
2261 *
2262 * @throws IllegalArgumentException if ACC_MODULE flag is set in access flags
2263 * or the class is not in the given package name.
2264 */
2265 static ClassFile newInstance(byte[] bytes, String pkgName) {
2266 var cf = readClassFile(bytes);
2267
2268 // check if it's in the named package
2269 int index = cf.name.lastIndexOf('/');
2270 String pn = (index == -1) ? "" : cf.name.substring(0, index).replace('/', '.');
2271 if (!pn.equals(pkgName)) {
2272 throw newIllegalArgumentException(cf.name + " not in same package as lookup class");
2273 }
2274 return cf;
2275 }
2276
2277 private static ClassFile readClassFile(byte[] bytes) {
2278 int magic = readInt(bytes, 0);
2279 if (magic != 0xCAFEBABE) {
2280 throw new ClassFormatError("Incompatible magic value: " + magic);
2281 }
2282 int minor = readUnsignedShort(bytes, 4);
2283 int major = readUnsignedShort(bytes, 6);
2284 if (!VM.isSupportedClassFileVersion(major, minor)) {
2285 throw new UnsupportedClassVersionError("Unsupported class file version " + major + "." + minor);
2286 }
2287
2288 String name;
2289 int accessFlags;
2290 try {
2291 ClassReader reader = new ClassReader(bytes);
2292 // ClassReader does not check if `this_class` is CONSTANT_Class_info
2293 // workaround to read `this_class` using readConst and validate the value
2294 int thisClass = reader.readUnsignedShort(reader.header + 2);
2295 Object constant = reader.readConst(thisClass, new char[reader.getMaxStringLength()]);
2296 if (!(constant instanceof Type type)) {
2297 throw new ClassFormatError("this_class item: #" + thisClass + " not a CONSTANT_Class_info");
2298 }
2299 if (!type.getDescriptor().startsWith("L")) {
2300 throw new ClassFormatError("this_class item: #" + thisClass + " not a CONSTANT_Class_info");
2301 }
2302 name = type.getInternalName();
2303 accessFlags = reader.readUnsignedShort(reader.header);
2304 } catch (RuntimeException e) {
2305 // ASM exceptions are poorly specified
2306 ClassFormatError cfe = new ClassFormatError();
2307 cfe.initCause(e);
2308 throw cfe;
2309 }
2310 // must be a class or interface
2311 if ((accessFlags & Opcodes.ACC_MODULE) != 0) {
2312 throw newIllegalArgumentException("Not a class or interface: ACC_MODULE flag is set");
2313 }
2314 return new ClassFile(name, accessFlags, bytes);
2315 }
2316
2317 private static int readInt(byte[] bytes, int offset) {
2318 if ((offset+4) > bytes.length) {
2319 throw new ClassFormatError("Invalid ClassFile structure");
2320 }
2321 return ((bytes[offset] & 0xFF) << 24)
2322 | ((bytes[offset + 1] & 0xFF) << 16)
2323 | ((bytes[offset + 2] & 0xFF) << 8)
2324 | (bytes[offset + 3] & 0xFF);
2325 }
2326
2327 private static int readUnsignedShort(byte[] bytes, int offset) {
2328 if ((offset+2) > bytes.length) {
2329 throw new ClassFormatError("Invalid ClassFile structure");
2330 }
2331 return ((bytes[offset] & 0xFF) << 8) | (bytes[offset + 1] & 0xFF);
2332 }
2333 }
2334
2335 /*
2336 * Returns a ClassDefiner that creates a {@code Class} object of a normal class
2337 * from the given bytes.
2338 *
2339 * Caller should make a defensive copy of the arguments if needed
2340 * before calling this factory method.
2341 *
2342 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or
2343 * {@code bytes} denotes a class in a different package than the lookup class
2344 */
2345 private ClassDefiner makeClassDefiner(byte[] bytes) {
2346 ClassFile cf = ClassFile.newInstance(bytes, lookupClass().getPackageName());
2347 return new ClassDefiner(this, cf, STRONG_LOADER_LINK, defaultDumper());
2348 }
2349
2350 /**
2351 * Returns a ClassDefiner that creates a {@code Class} object of a normal class
2352 * from the given bytes. No package name check on the given bytes.
2353 *
2354 * @param name internal name
2355 * @param bytes class bytes
2356 * @param dumper dumper to write the given bytes to the dumper's output directory
2357 * @return ClassDefiner that defines a normal class of the given bytes.
2358 */
2359 ClassDefiner makeClassDefiner(String name, byte[] bytes, ClassFileDumper dumper) {
2360 // skip package name validation
2361 ClassFile cf = ClassFile.newInstanceNoCheck(name, bytes);
2362 return new ClassDefiner(this, cf, STRONG_LOADER_LINK, dumper);
2363 }
2364
2365 /**
2366 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2367 * from the given bytes. The name must be in the same package as the lookup class.
2368 *
2369 * Caller should make a defensive copy of the arguments if needed
2370 * before calling this factory method.
2371 *
2372 * @param bytes class bytes
2373 * @param dumper dumper to write the given bytes to the dumper's output directory
2374 * @return ClassDefiner that defines a hidden class of the given bytes.
2375 *
2376 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or
2377 * {@code bytes} denotes a class in a different package than the lookup class
2378 */
2379 ClassDefiner makeHiddenClassDefiner(byte[] bytes, ClassFileDumper dumper) {
2380 ClassFile cf = ClassFile.newInstance(bytes, lookupClass().getPackageName());
2381 return makeHiddenClassDefiner(cf, Set.of(), false, dumper);
2382 }
2383
2384 /**
2385 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2386 * from the given bytes and options.
2387 * The name must be in the same package as the lookup class.
2388 *
2389 * Caller should make a defensive copy of the arguments if needed
2390 * before calling this factory method.
2391 *
2392 * @param bytes class bytes
2393 * @param options class options
2394 * @param accessVmAnnotations true to give the hidden class access to VM annotations
2395 * @return ClassDefiner that defines a hidden class of the given bytes and options
2396 *
2397 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or
2398 * {@code bytes} denotes a class in a different package than the lookup class
2399 */
2400 private ClassDefiner makeHiddenClassDefiner(byte[] bytes,
2401 Set<ClassOption> options,
2402 boolean accessVmAnnotations) {
2403 ClassFile cf = ClassFile.newInstance(bytes, lookupClass().getPackageName());
2404 return makeHiddenClassDefiner(cf, options, accessVmAnnotations, defaultDumper());
2405 }
2406
2407 /**
2408 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2409 * from the given bytes and the given options. No package name check on the given bytes.
2410 *
2411 * @param name internal name that specifies the prefix of the hidden class
2412 * @param bytes class bytes
2413 * @param options class options
2414 * @param dumper dumper to write the given bytes to the dumper's output directory
2415 * @return ClassDefiner that defines a hidden class of the given bytes and options.
2416 */
2417 ClassDefiner makeHiddenClassDefiner(String name, byte[] bytes, Set<ClassOption> options, ClassFileDumper dumper) {
2418 Objects.requireNonNull(dumper);
2419 // skip name and access flags validation
2420 return makeHiddenClassDefiner(ClassFile.newInstanceNoCheck(name, bytes), options, false, dumper);
2421 }
2422
2423 /**
2424 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2425 * from the given class file and options.
2426 *
2427 * @param cf ClassFile
2428 * @param options class options
2429 * @param accessVmAnnotations true to give the hidden class access to VM annotations
2430 * @param dumper dumper to write the given bytes to the dumper's output directory
2431 */
2432 private ClassDefiner makeHiddenClassDefiner(ClassFile cf,
2433 Set<ClassOption> options,
2434 boolean accessVmAnnotations,
2435 ClassFileDumper dumper) {
2436 int flags = HIDDEN_CLASS | ClassOption.optionsToFlag(options);
2437 if (accessVmAnnotations | VM.isSystemDomainLoader(lookupClass.getClassLoader())) {
2438 // jdk.internal.vm.annotations are permitted for classes
2439 // defined to boot loader and platform loader
2440 flags |= ACCESS_VM_ANNOTATIONS;
2441 }
2442
2443 return new ClassDefiner(this, cf, flags, dumper);
2444 }
2445
2446 static class ClassDefiner {
2447 private final Lookup lookup;
2448 private final String name; // internal name
2449 private final byte[] bytes;
2450 private final int classFlags;
2451 private final ClassFileDumper dumper;
2452
2453 private ClassDefiner(Lookup lookup, ClassFile cf, int flags, ClassFileDumper dumper) {
2454 assert ((flags & HIDDEN_CLASS) != 0 || (flags & STRONG_LOADER_LINK) == STRONG_LOADER_LINK);
2455 this.lookup = lookup;
2456 this.bytes = cf.bytes;
2457 this.name = cf.name;
2458 this.classFlags = flags;
2459 this.dumper = dumper;
2460 }
2461
2462 String internalName() {
2463 return name;
2464 }
2465
2466 Class<?> defineClass(boolean initialize) {
2467 return defineClass(initialize, null);
2468 }
2469
2470 Lookup defineClassAsLookup(boolean initialize) {
2471 Class<?> c = defineClass(initialize, null);
2472 return new Lookup(c, null, FULL_POWER_MODES);
2473 }
2474
2475 /**
2476 * Defines the class of the given bytes and the given classData.
2477 * If {@code initialize} parameter is true, then the class will be initialized.
2478 *
2479 * @param initialize true if the class to be initialized
2480 * @param classData classData or null
2481 * @return the class
2482 *
2483 * @throws LinkageError linkage error
2484 */
2485 Class<?> defineClass(boolean initialize, Object classData) {
2486 Class<?> lookupClass = lookup.lookupClass();
2487 ClassLoader loader = lookupClass.getClassLoader();
2488 ProtectionDomain pd = (loader != null) ? lookup.lookupClassProtectionDomain() : null;
2489 Class<?> c = null;
2490 try {
2491 c = SharedSecrets.getJavaLangAccess()
2492 .defineClass(loader, lookupClass, name, bytes, pd, initialize, classFlags, classData);
2493 assert !isNestmate() || c.getNestHost() == lookupClass.getNestHost();
2494 return c;
2495 } finally {
2496 // dump the classfile for debugging
2497 if (dumper.isEnabled()) {
2498 String name = internalName();
2499 if (c != null) {
2500 dumper.dumpClass(name, c, bytes);
2501 } else {
2502 dumper.dumpFailedClass(name, bytes);
2503 }
2504 }
2505 }
2506 }
2507
2508 /**
2509 * Defines the class of the given bytes and the given classData.
2510 * If {@code initialize} parameter is true, then the class will be initialized.
2511 *
2512 * @param initialize true if the class to be initialized
2513 * @param classData classData or null
2514 * @return a Lookup for the defined class
2515 *
2516 * @throws LinkageError linkage error
2517 */
2518 Lookup defineClassAsLookup(boolean initialize, Object classData) {
2519 Class<?> c = defineClass(initialize, classData);
2520 return new Lookup(c, null, FULL_POWER_MODES);
2521 }
2522
2523 private boolean isNestmate() {
2524 return (classFlags & NESTMATE_CLASS) != 0;
2525 }
2526 }
2527
2528 private ProtectionDomain lookupClassProtectionDomain() {
2529 ProtectionDomain pd = cachedProtectionDomain;
2530 if (pd == null) {
2531 cachedProtectionDomain = pd = SharedSecrets.getJavaLangAccess().protectionDomain(lookupClass);
2532 }
2533 return pd;
2534 }
2535
2536 // cached protection domain
2537 private volatile ProtectionDomain cachedProtectionDomain;
2538
2539 // Make sure outer class is initialized first.
2540 static { IMPL_NAMES.getClass(); }
2541
2542 /** Package-private version of lookup which is trusted. */
2543 static final Lookup IMPL_LOOKUP = new Lookup(Object.class, null, TRUSTED);
2544
2545 /** Version of lookup which is trusted minimally.
2546 * It can only be used to create method handles to publicly accessible
2547 * members in packages that are exported unconditionally.
2548 */
2549 static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, null, UNCONDITIONAL);
2550
2551 private static void checkUnprivilegedlookupClass(Class<?> lookupClass) {
2552 String name = lookupClass.getName();
2553 if (name.startsWith("java.lang.invoke."))
2554 throw newIllegalArgumentException("illegal lookupClass: "+lookupClass);
2555 }
2556
2557 /**
2558 * Displays the name of the class from which lookups are to be made,
2559 * followed by "/" and the name of the {@linkplain #previousLookupClass()
2560 * previous lookup class} if present.
2561 * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)
2562 * If there are restrictions on the access permitted to this lookup,
2563 * this is indicated by adding a suffix to the class name, consisting
2564 * of a slash and a keyword. The keyword represents the strongest
2565 * allowed access, and is chosen as follows:
2566 * <ul>
2567 * <li>If no access is allowed, the suffix is "/noaccess".
2568 * <li>If only unconditional access is allowed, the suffix is "/publicLookup".
2569 * <li>If only public access to types in exported packages is allowed, the suffix is "/public".
2570 * <li>If only public and module access are allowed, the suffix is "/module".
2571 * <li>If public and package access are allowed, the suffix is "/package".
2572 * <li>If public, package, and private access are allowed, the suffix is "/private".
2573 * </ul>
2574 * If none of the above cases apply, it is the case that
2575 * {@linkplain #hasFullPrivilegeAccess() full privilege access}
2576 * (public, module, package, private, and protected) is allowed.
2577 * In this case, no suffix is added.
2578 * This is true only of an object obtained originally from
2579 * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
2580 * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
2581 * always have restricted access, and will display a suffix.
2582 * <p>
2583 * (It may seem strange that protected access should be
2584 * stronger than private access. Viewed independently from
2585 * package access, protected access is the first to be lost,
2586 * because it requires a direct subclass relationship between
2587 * caller and callee.)
2588 * @see #in
2589 */
2590 @Override
2591 public String toString() {
2592 String cname = lookupClass.getName();
2593 if (prevLookupClass != null)
2594 cname += "/" + prevLookupClass.getName();
2595 switch (allowedModes) {
2596 case 0: // no privileges
2597 return cname + "/noaccess";
2598 case UNCONDITIONAL:
2599 return cname + "/publicLookup";
2600 case PUBLIC:
2601 return cname + "/public";
2602 case PUBLIC|MODULE:
2603 return cname + "/module";
2604 case PUBLIC|PACKAGE:
2605 case PUBLIC|MODULE|PACKAGE:
2606 return cname + "/package";
2607 case PUBLIC|PACKAGE|PRIVATE:
2608 case PUBLIC|MODULE|PACKAGE|PRIVATE:
2609 return cname + "/private";
2610 case PUBLIC|PACKAGE|PRIVATE|PROTECTED:
2611 case PUBLIC|MODULE|PACKAGE|PRIVATE|PROTECTED:
2612 case FULL_POWER_MODES:
2613 return cname;
2614 case TRUSTED:
2615 return "/trusted"; // internal only; not exported
2616 default: // Should not happen, but it's a bitfield...
2617 cname = cname + "/" + Integer.toHexString(allowedModes);
2618 assert(false) : cname;
2619 return cname;
2620 }
2621 }
2622
2623 /**
2624 * Produces a method handle for a static method.
2625 * The type of the method handle will be that of the method.
2626 * (Since static methods do not take receivers, there is no
2627 * additional receiver argument inserted into the method handle type,
2628 * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)
2629 * The method and all its argument types must be accessible to the lookup object.
2630 * <p>
2631 * The returned method handle will have
2632 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2633 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2634 * <p>
2635 * If the returned method handle is invoked, the method's class will
2636 * be initialized, if it has not already been initialized.
2637 * <p><b>Example:</b>
2638 * {@snippet lang="java" :
2639 import static java.lang.invoke.MethodHandles.*;
2640 import static java.lang.invoke.MethodType.*;
2641 ...
2642 MethodHandle MH_asList = publicLookup().findStatic(Arrays.class,
2643 "asList", methodType(List.class, Object[].class));
2644 assertEquals("[x, y]", MH_asList.invoke("x", "y").toString());
2645 * }
2646 * @param refc the class from which the method is accessed
2647 * @param name the name of the method
2648 * @param type the type of the method
2649 * @return the desired method handle
2650 * @throws NoSuchMethodException if the method does not exist
2651 * @throws IllegalAccessException if access checking fails,
2652 * or if the method is not {@code static},
2653 * or if the method's variable arity modifier bit
2654 * is set and {@code asVarargsCollector} fails
2655 * @throws SecurityException if a security manager is present and it
2656 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2657 * @throws NullPointerException if any argument is null
2658 */
2659 public MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2660 MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type);
2661 return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerLookup(method));
2662 }
2663
2664 /**
2665 * Produces a method handle for a virtual method.
2666 * The type of the method handle will be that of the method,
2667 * with the receiver type (usually {@code refc}) prepended.
2668 * The method and all its argument types must be accessible to the lookup object.
2669 * <p>
2670 * When called, the handle will treat the first argument as a receiver
2671 * and, for non-private methods, dispatch on the receiver's type to determine which method
2672 * implementation to enter.
2673 * For private methods the named method in {@code refc} will be invoked on the receiver.
2674 * (The dispatching action is identical with that performed by an
2675 * {@code invokevirtual} or {@code invokeinterface} instruction.)
2676 * <p>
2677 * The first argument will be of type {@code refc} if the lookup
2678 * class has full privileges to access the member. Otherwise
2679 * the member must be {@code protected} and the first argument
2680 * will be restricted in type to the lookup class.
2681 * <p>
2682 * The returned method handle will have
2683 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2684 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2685 * <p>
2686 * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual}
2687 * instructions and method handles produced by {@code findVirtual},
2688 * if the class is {@code MethodHandle} and the name string is
2689 * {@code invokeExact} or {@code invoke}, the resulting
2690 * method handle is equivalent to one produced by
2691 * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or
2692 * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}
2693 * with the same {@code type} argument.
2694 * <p>
2695 * If the class is {@code VarHandle} and the name string corresponds to
2696 * the name of a signature-polymorphic access mode method, the resulting
2697 * method handle is equivalent to one produced by
2698 * {@link java.lang.invoke.MethodHandles#varHandleInvoker} with
2699 * the access mode corresponding to the name string and with the same
2700 * {@code type} arguments.
2701 * <p>
2702 * <b>Example:</b>
2703 * {@snippet lang="java" :
2704 import static java.lang.invoke.MethodHandles.*;
2705 import static java.lang.invoke.MethodType.*;
2706 ...
2707 MethodHandle MH_concat = publicLookup().findVirtual(String.class,
2708 "concat", methodType(String.class, String.class));
2709 MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class,
2710 "hashCode", methodType(int.class));
2711 MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class,
2712 "hashCode", methodType(int.class));
2713 assertEquals("xy", (String) MH_concat.invokeExact("x", "y"));
2714 assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy"));
2715 assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy"));
2716 // interface method:
2717 MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class,
2718 "subSequence", methodType(CharSequence.class, int.class, int.class));
2719 assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString());
2720 // constructor "internal method" must be accessed differently:
2721 MethodType MT_newString = methodType(void.class); //()V for new String()
2722 try { assertEquals("impossible", lookup()
2723 .findVirtual(String.class, "<init>", MT_newString));
2724 } catch (NoSuchMethodException ex) { } // OK
2725 MethodHandle MH_newString = publicLookup()
2726 .findConstructor(String.class, MT_newString);
2727 assertEquals("", (String) MH_newString.invokeExact());
2728 * }
2729 *
2730 * @param refc the class or interface from which the method is accessed
2731 * @param name the name of the method
2732 * @param type the type of the method, with the receiver argument omitted
2733 * @return the desired method handle
2734 * @throws NoSuchMethodException if the method does not exist
2735 * @throws IllegalAccessException if access checking fails,
2736 * or if the method is {@code static},
2737 * or if the method's variable arity modifier bit
2738 * is set and {@code asVarargsCollector} fails
2739 * @throws SecurityException if a security manager is present and it
2740 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2741 * @throws NullPointerException if any argument is null
2742 */
2743 public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2744 if (refc == MethodHandle.class) {
2745 MethodHandle mh = findVirtualForMH(name, type);
2746 if (mh != null) return mh;
2747 } else if (refc == VarHandle.class) {
2748 MethodHandle mh = findVirtualForVH(name, type);
2749 if (mh != null) return mh;
2750 }
2751 byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual);
2752 MemberName method = resolveOrFail(refKind, refc, name, type);
2753 return getDirectMethod(refKind, refc, method, findBoundCallerLookup(method));
2754 }
2755 private MethodHandle findVirtualForMH(String name, MethodType type) {
2756 // these names require special lookups because of the implicit MethodType argument
2757 if ("invoke".equals(name))
2758 return invoker(type);
2759 if ("invokeExact".equals(name))
2760 return exactInvoker(type);
2761 assert(!MemberName.isMethodHandleInvokeName(name));
2762 return null;
2763 }
2764 private MethodHandle findVirtualForVH(String name, MethodType type) {
2765 try {
2766 return varHandleInvoker(VarHandle.AccessMode.valueFromMethodName(name), type);
2767 } catch (IllegalArgumentException e) {
2768 return null;
2769 }
2770 }
2771
2772 /**
2773 * Produces a method handle which creates an object and initializes it, using
2774 * the constructor of the specified type.
2775 * The parameter types of the method handle will be those of the constructor,
2776 * while the return type will be a reference to the constructor's class.
2777 * The constructor and all its argument types must be accessible to the lookup object.
2778 * <p>
2779 * The requested type must have a return type of {@code void}.
2780 * (This is consistent with the JVM's treatment of constructor type descriptors.)
2781 * <p>
2782 * The returned method handle will have
2783 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2784 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
2785 * <p>
2786 * If the returned method handle is invoked, the constructor's class will
2787 * be initialized, if it has not already been initialized.
2788 * <p><b>Example:</b>
2789 * {@snippet lang="java" :
2790 import static java.lang.invoke.MethodHandles.*;
2791 import static java.lang.invoke.MethodType.*;
2792 ...
2793 MethodHandle MH_newArrayList = publicLookup().findConstructor(
2794 ArrayList.class, methodType(void.class, Collection.class));
2795 Collection orig = Arrays.asList("x", "y");
2796 Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig);
2797 assert(orig != copy);
2798 assertEquals(orig, copy);
2799 // a variable-arity constructor:
2800 MethodHandle MH_newProcessBuilder = publicLookup().findConstructor(
2801 ProcessBuilder.class, methodType(void.class, String[].class));
2802 ProcessBuilder pb = (ProcessBuilder)
2803 MH_newProcessBuilder.invoke("x", "y", "z");
2804 assertEquals("[x, y, z]", pb.command().toString());
2805 * }
2806 *
2807 *
2808 * @param refc the class or interface from which the method is accessed
2809 * @param type the type of the method, with the receiver argument omitted, and a void return type
2810 * @return the desired method handle
2811 * @throws NoSuchMethodException if the constructor does not exist
2812 * @throws IllegalAccessException if access checking fails
2813 * or if the method's variable arity modifier bit
2814 * is set and {@code asVarargsCollector} fails
2815 * @throws SecurityException if a security manager is present and it
2816 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2817 * @throws NullPointerException if any argument is null
2818 */
2819 public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2820 if (refc.isArray()) {
2821 throw new NoSuchMethodException("no constructor for array class: " + refc.getName());
2822 }
2823 if (type.returnType() != void.class) {
2824 throw new NoSuchMethodException("Constructors must have void return type: " + refc.getName());
2825 }
2826 String name = ConstantDescs.INIT_NAME;
2827 MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type);
2828 return getDirectConstructor(refc, ctor);
2829 }
2830
2831 /**
2832 * Looks up a class by name from the lookup context defined by this {@code Lookup} object,
2833 * <a href="MethodHandles.Lookup.html#equiv">as if resolved</a> by an {@code ldc} instruction.
2834 * Such a resolution, as specified in JVMS {@jvms 5.4.3.1}, attempts to locate and load the class,
2835 * and then determines whether the class is accessible to this lookup object.
2836 * <p>
2837 * For a class or an interface, the name is the {@linkplain ClassLoader##binary-name binary name}.
2838 * For an array class of {@code n} dimensions, the name begins with {@code n} occurrences
2839 * of {@code '['} and followed by the element type as encoded in the
2840 * {@linkplain Class##nameFormat table} specified in {@link Class#getName}.
2841 * <p>
2842 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class},
2843 * its class loader, and the {@linkplain #lookupModes() lookup modes}.
2844 *
2845 * @param targetName the {@linkplain ClassLoader##binary-name binary name} of the class
2846 * or the string representing an array class
2847 * @return the requested class.
2848 * @throws SecurityException if a security manager is present and it
2849 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2850 * @throws LinkageError if the linkage fails
2851 * @throws ClassNotFoundException if the class cannot be loaded by the lookup class' loader.
2852 * @throws IllegalAccessException if the class is not accessible, using the allowed access
2853 * modes.
2854 * @throws NullPointerException if {@code targetName} is null
2855 * @since 9
2856 * @jvms 5.4.3.1 Class and Interface Resolution
2857 */
2858 public Class<?> findClass(String targetName) throws ClassNotFoundException, IllegalAccessException {
2859 Class<?> targetClass = Class.forName(targetName, false, lookupClass.getClassLoader());
2860 return accessClass(targetClass);
2861 }
2862
2863 /**
2864 * Ensures that {@code targetClass} has been initialized. The class
2865 * to be initialized must be {@linkplain #accessClass accessible}
2866 * to this {@code Lookup} object. This method causes {@code targetClass}
2867 * to be initialized if it has not been already initialized,
2868 * as specified in JVMS {@jvms 5.5}.
2869 *
2870 * <p>
2871 * This method returns when {@code targetClass} is fully initialized, or
2872 * when {@code targetClass} is being initialized by the current thread.
2873 *
2874 * @param <T> the type of the class to be initialized
2875 * @param targetClass the class to be initialized
2876 * @return {@code targetClass} that has been initialized, or that is being
2877 * initialized by the current thread.
2878 *
2879 * @throws IllegalArgumentException if {@code targetClass} is a primitive type or {@code void}
2880 * or array class
2881 * @throws IllegalAccessException if {@code targetClass} is not
2882 * {@linkplain #accessClass accessible} to this lookup
2883 * @throws ExceptionInInitializerError if the class initialization provoked
2884 * by this method fails
2885 * @throws SecurityException if a security manager is present and it
2886 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2887 * @since 15
2888 * @jvms 5.5 Initialization
2889 */
2890 public <T> Class<T> ensureInitialized(Class<T> targetClass) throws IllegalAccessException {
2891 if (targetClass.isPrimitive())
2892 throw new IllegalArgumentException(targetClass + " is a primitive class");
2893 if (targetClass.isArray())
2894 throw new IllegalArgumentException(targetClass + " is an array class");
2895
2896 if (!VerifyAccess.isClassAccessible(targetClass, lookupClass, prevLookupClass, allowedModes)) {
2897 throw makeAccessException(targetClass);
2898 }
2899 checkSecurityManager(targetClass);
2900
2901 // ensure class initialization
2902 Unsafe.getUnsafe().ensureClassInitialized(targetClass);
2903 return targetClass;
2904 }
2905
2906 /*
2907 * Returns IllegalAccessException due to access violation to the given targetClass.
2908 *
2909 * This method is called by {@link Lookup#accessClass} and {@link Lookup#ensureInitialized}
2910 * which verifies access to a class rather a member.
2911 */
2912 private IllegalAccessException makeAccessException(Class<?> targetClass) {
2913 String message = "access violation: "+ targetClass;
2914 if (this == MethodHandles.publicLookup()) {
2915 message += ", from public Lookup";
2916 } else {
2917 Module m = lookupClass().getModule();
2918 message += ", from " + lookupClass() + " (" + m + ")";
2919 if (prevLookupClass != null) {
2920 message += ", previous lookup " +
2921 prevLookupClass.getName() + " (" + prevLookupClass.getModule() + ")";
2922 }
2923 }
2924 return new IllegalAccessException(message);
2925 }
2926
2927 /**
2928 * Determines if a class can be accessed from the lookup context defined by
2929 * this {@code Lookup} object. The static initializer of the class is not run.
2930 * If {@code targetClass} is an array class, {@code targetClass} is accessible
2931 * if the element type of the array class is accessible. Otherwise,
2932 * {@code targetClass} is determined as accessible as follows.
2933 *
2934 * <p>
2935 * If {@code targetClass} is in the same module as the lookup class,
2936 * the lookup class is {@code LC} in module {@code M1} and
2937 * the previous lookup class is in module {@code M0} or
2938 * {@code null} if not present,
2939 * {@code targetClass} is accessible if and only if one of the following is true:
2940 * <ul>
2941 * <li>If this lookup has {@link #PRIVATE} access, {@code targetClass} is
2942 * {@code LC} or other class in the same nest of {@code LC}.</li>
2943 * <li>If this lookup has {@link #PACKAGE} access, {@code targetClass} is
2944 * in the same runtime package of {@code LC}.</li>
2945 * <li>If this lookup has {@link #MODULE} access, {@code targetClass} is
2946 * a public type in {@code M1}.</li>
2947 * <li>If this lookup has {@link #PUBLIC} access, {@code targetClass} is
2948 * a public type in a package exported by {@code M1} to at least {@code M0}
2949 * if the previous lookup class is present; otherwise, {@code targetClass}
2950 * is a public type in a package exported by {@code M1} unconditionally.</li>
2951 * </ul>
2952 *
2953 * <p>
2954 * Otherwise, if this lookup has {@link #UNCONDITIONAL} access, this lookup
2955 * can access public types in all modules when the type is in a package
2956 * that is exported unconditionally.
2957 * <p>
2958 * Otherwise, {@code targetClass} is in a different module from {@code lookupClass},
2959 * and if this lookup does not have {@code PUBLIC} access, {@code lookupClass}
2960 * is inaccessible.
2961 * <p>
2962 * Otherwise, if this lookup has no {@linkplain #previousLookupClass() previous lookup class},
2963 * {@code M1} is the module containing {@code lookupClass} and
2964 * {@code M2} is the module containing {@code targetClass},
2965 * then {@code targetClass} is accessible if and only if
2966 * <ul>
2967 * <li>{@code M1} reads {@code M2}, and
2968 * <li>{@code targetClass} is public and in a package exported by
2969 * {@code M2} at least to {@code M1}.
2970 * </ul>
2971 * <p>
2972 * Otherwise, if this lookup has a {@linkplain #previousLookupClass() previous lookup class},
2973 * {@code M1} and {@code M2} are as before, and {@code M0} is the module
2974 * containing the previous lookup class, then {@code targetClass} is accessible
2975 * if and only if one of the following is true:
2976 * <ul>
2977 * <li>{@code targetClass} is in {@code M0} and {@code M1}
2978 * {@linkplain Module#reads reads} {@code M0} and the type is
2979 * in a package that is exported to at least {@code M1}.
2980 * <li>{@code targetClass} is in {@code M1} and {@code M0}
2981 * {@linkplain Module#reads reads} {@code M1} and the type is
2982 * in a package that is exported to at least {@code M0}.
2983 * <li>{@code targetClass} is in a third module {@code M2} and both {@code M0}
2984 * and {@code M1} reads {@code M2} and the type is in a package
2985 * that is exported to at least both {@code M0} and {@code M2}.
2986 * </ul>
2987 * <p>
2988 * Otherwise, {@code targetClass} is not accessible.
2989 *
2990 * @param <T> the type of the class to be access-checked
2991 * @param targetClass the class to be access-checked
2992 * @return {@code targetClass} that has been access-checked
2993 * @throws IllegalAccessException if the class is not accessible from the lookup class
2994 * and previous lookup class, if present, using the allowed access modes.
2995 * @throws SecurityException if a security manager is present and it
2996 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2997 * @throws NullPointerException if {@code targetClass} is {@code null}
2998 * @since 9
2999 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
3000 */
3001 public <T> Class<T> accessClass(Class<T> targetClass) throws IllegalAccessException {
3002 if (!isClassAccessible(targetClass)) {
3003 throw makeAccessException(targetClass);
3004 }
3005 checkSecurityManager(targetClass);
3006 return targetClass;
3007 }
3008
3009 /**
3010 * Produces an early-bound method handle for a virtual method.
3011 * It will bypass checks for overriding methods on the receiver,
3012 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
3013 * instruction from within the explicitly specified {@code specialCaller}.
3014 * The type of the method handle will be that of the method,
3015 * with a suitably restricted receiver type prepended.
3016 * (The receiver type will be {@code specialCaller} or a subtype.)
3017 * The method and all its argument types must be accessible
3018 * to the lookup object.
3019 * <p>
3020 * Before method resolution,
3021 * if the explicitly specified caller class is not identical with the
3022 * lookup class, or if this lookup object does not have
3023 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
3024 * privileges, the access fails.
3025 * <p>
3026 * The returned method handle will have
3027 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3028 * the method's variable arity modifier bit ({@code 0x0080}) is set.
3029 * <p style="font-size:smaller;">
3030 * <em>(Note: JVM internal methods named {@value ConstantDescs#INIT_NAME}
3031 * are not visible to this API,
3032 * even though the {@code invokespecial} instruction can refer to them
3033 * in special circumstances. Use {@link #findConstructor findConstructor}
3034 * to access instance initialization methods in a safe manner.)</em>
3035 * <p><b>Example:</b>
3036 * {@snippet lang="java" :
3037 import static java.lang.invoke.MethodHandles.*;
3038 import static java.lang.invoke.MethodType.*;
3039 ...
3040 static class Listie extends ArrayList {
3041 public String toString() { return "[wee Listie]"; }
3042 static Lookup lookup() { return MethodHandles.lookup(); }
3043 }
3044 ...
3045 // no access to constructor via invokeSpecial:
3046 MethodHandle MH_newListie = Listie.lookup()
3047 .findConstructor(Listie.class, methodType(void.class));
3048 Listie l = (Listie) MH_newListie.invokeExact();
3049 try { assertEquals("impossible", Listie.lookup().findSpecial(
3050 Listie.class, "<init>", methodType(void.class), Listie.class));
3051 } catch (NoSuchMethodException ex) { } // OK
3052 // access to super and self methods via invokeSpecial:
3053 MethodHandle MH_super = Listie.lookup().findSpecial(
3054 ArrayList.class, "toString" , methodType(String.class), Listie.class);
3055 MethodHandle MH_this = Listie.lookup().findSpecial(
3056 Listie.class, "toString" , methodType(String.class), Listie.class);
3057 MethodHandle MH_duper = Listie.lookup().findSpecial(
3058 Object.class, "toString" , methodType(String.class), Listie.class);
3059 assertEquals("[]", (String) MH_super.invokeExact(l));
3060 assertEquals(""+l, (String) MH_this.invokeExact(l));
3061 assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method
3062 try { assertEquals("inaccessible", Listie.lookup().findSpecial(
3063 String.class, "toString", methodType(String.class), Listie.class));
3064 } catch (IllegalAccessException ex) { } // OK
3065 Listie subl = new Listie() { public String toString() { return "[subclass]"; } };
3066 assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method
3067 * }
3068 *
3069 * @param refc the class or interface from which the method is accessed
3070 * @param name the name of the method (which must not be "<init>")
3071 * @param type the type of the method, with the receiver argument omitted
3072 * @param specialCaller the proposed calling class to perform the {@code invokespecial}
3073 * @return the desired method handle
3074 * @throws NoSuchMethodException if the method does not exist
3075 * @throws IllegalAccessException if access checking fails,
3076 * or if the method is {@code static},
3077 * or if the method's variable arity modifier bit
3078 * is set and {@code asVarargsCollector} fails
3079 * @throws SecurityException if a security manager is present and it
3080 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3081 * @throws NullPointerException if any argument is null
3082 */
3083 public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,
3084 Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
3085 checkSpecialCaller(specialCaller, refc);
3086 Lookup specialLookup = this.in(specialCaller);
3087 MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type);
3088 return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerLookup(method));
3089 }
3090
3091 /**
3092 * Produces a method handle giving read access to a non-static field.
3093 * The type of the method handle will have a return type of the field's
3094 * value type.
3095 * The method handle's single argument will be the instance containing
3096 * the field.
3097 * Access checking is performed immediately on behalf of the lookup class.
3098 * @param refc the class or interface from which the method is accessed
3099 * @param name the field's name
3100 * @param type the field's type
3101 * @return a method handle which can load values from the field
3102 * @throws NoSuchFieldException if the field does not exist
3103 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
3104 * @throws SecurityException if a security manager is present and it
3105 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3106 * @throws NullPointerException if any argument is null
3107 * @see #findVarHandle(Class, String, Class)
3108 */
3109 public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3110 MemberName field = resolveOrFail(REF_getField, refc, name, type);
3111 return getDirectField(REF_getField, refc, field);
3112 }
3113
3114 /**
3115 * Produces a method handle giving write access to a non-static field.
3116 * The type of the method handle will have a void return type.
3117 * The method handle will take two arguments, the instance containing
3118 * the field, and the value to be stored.
3119 * The second argument will be of the field's value type.
3120 * Access checking is performed immediately on behalf of the lookup class.
3121 * @param refc the class or interface from which the method is accessed
3122 * @param name the field's name
3123 * @param type the field's type
3124 * @return a method handle which can store values into the field
3125 * @throws NoSuchFieldException if the field does not exist
3126 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
3127 * or {@code final}
3128 * @throws SecurityException if a security manager is present and it
3129 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3130 * @throws NullPointerException if any argument is null
3131 * @see #findVarHandle(Class, String, Class)
3132 */
3133 public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3134 MemberName field = resolveOrFail(REF_putField, refc, name, type);
3135 return getDirectField(REF_putField, refc, field);
3136 }
3137
3138 /**
3139 * Produces a VarHandle giving access to a non-static field {@code name}
3140 * of type {@code type} declared in a class of type {@code recv}.
3141 * The VarHandle's variable type is {@code type} and it has one
3142 * coordinate type, {@code recv}.
3143 * <p>
3144 * Access checking is performed immediately on behalf of the lookup
3145 * class.
3146 * <p>
3147 * Certain access modes of the returned VarHandle are unsupported under
3148 * the following conditions:
3149 * <ul>
3150 * <li>if the field is declared {@code final}, then the write, atomic
3151 * update, numeric atomic update, and bitwise atomic update access
3152 * modes are unsupported.
3153 * <li>if the field type is anything other than {@code byte},
3154 * {@code short}, {@code char}, {@code int}, {@code long},
3155 * {@code float}, or {@code double} then numeric atomic update
3156 * access modes are unsupported.
3157 * <li>if the field type is anything other than {@code boolean},
3158 * {@code byte}, {@code short}, {@code char}, {@code int} or
3159 * {@code long} then bitwise atomic update access modes are
3160 * unsupported.
3161 * </ul>
3162 * <p>
3163 * If the field is declared {@code volatile} then the returned VarHandle
3164 * will override access to the field (effectively ignore the
3165 * {@code volatile} declaration) in accordance to its specified
3166 * access modes.
3167 * <p>
3168 * If the field type is {@code float} or {@code double} then numeric
3169 * and atomic update access modes compare values using their bitwise
3170 * representation (see {@link Float#floatToRawIntBits} and
3171 * {@link Double#doubleToRawLongBits}, respectively).
3172 * @apiNote
3173 * Bitwise comparison of {@code float} values or {@code double} values,
3174 * as performed by the numeric and atomic update access modes, differ
3175 * from the primitive {@code ==} operator and the {@link Float#equals}
3176 * and {@link Double#equals} methods, specifically with respect to
3177 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
3178 * Care should be taken when performing a compare and set or a compare
3179 * and exchange operation with such values since the operation may
3180 * unexpectedly fail.
3181 * There are many possible NaN values that are considered to be
3182 * {@code NaN} in Java, although no IEEE 754 floating-point operation
3183 * provided by Java can distinguish between them. Operation failure can
3184 * occur if the expected or witness value is a NaN value and it is
3185 * transformed (perhaps in a platform specific manner) into another NaN
3186 * value, and thus has a different bitwise representation (see
3187 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
3188 * details).
3189 * The values {@code -0.0} and {@code +0.0} have different bitwise
3190 * representations but are considered equal when using the primitive
3191 * {@code ==} operator. Operation failure can occur if, for example, a
3192 * numeric algorithm computes an expected value to be say {@code -0.0}
3193 * and previously computed the witness value to be say {@code +0.0}.
3194 * @param recv the receiver class, of type {@code R}, that declares the
3195 * non-static field
3196 * @param name the field's name
3197 * @param type the field's type, of type {@code T}
3198 * @return a VarHandle giving access to non-static fields.
3199 * @throws NoSuchFieldException if the field does not exist
3200 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
3201 * @throws SecurityException if a security manager is present and it
3202 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3203 * @throws NullPointerException if any argument is null
3204 * @since 9
3205 */
3206 public VarHandle findVarHandle(Class<?> recv, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3207 MemberName getField = resolveOrFail(REF_getField, recv, name, type);
3208 MemberName putField = resolveOrFail(REF_putField, recv, name, type);
3209 return getFieldVarHandle(REF_getField, REF_putField, recv, getField, putField);
3210 }
3211
3212 /**
3213 * Produces a method handle giving read access to a static field.
3214 * The type of the method handle will have a return type of the field's
3215 * value type.
3216 * The method handle will take no arguments.
3217 * Access checking is performed immediately on behalf of the lookup class.
3218 * <p>
3219 * If the returned method handle is invoked, the field's class will
3220 * be initialized, if it has not already been initialized.
3221 * @param refc the class or interface from which the method is accessed
3222 * @param name the field's name
3223 * @param type the field's type
3224 * @return a method handle which can load values from the field
3225 * @throws NoSuchFieldException if the field does not exist
3226 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
3227 * @throws SecurityException if a security manager is present and it
3228 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3229 * @throws NullPointerException if any argument is null
3230 */
3231 public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3232 MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
3233 return getDirectField(REF_getStatic, refc, field);
3234 }
3235
3236 /**
3237 * Produces a method handle giving write access to a static field.
3238 * The type of the method handle will have a void return type.
3239 * The method handle will take a single
3240 * argument, of the field's value type, the value to be stored.
3241 * Access checking is performed immediately on behalf of the lookup class.
3242 * <p>
3243 * If the returned method handle is invoked, the field's class will
3244 * be initialized, if it has not already been initialized.
3245 * @param refc the class or interface from which the method is accessed
3246 * @param name the field's name
3247 * @param type the field's type
3248 * @return a method handle which can store values into the field
3249 * @throws NoSuchFieldException if the field does not exist
3250 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
3251 * or is {@code final}
3252 * @throws SecurityException if a security manager is present and it
3253 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3254 * @throws NullPointerException if any argument is null
3255 */
3256 public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3257 MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
3258 return getDirectField(REF_putStatic, refc, field);
3259 }
3260
3261 /**
3262 * Produces a VarHandle giving access to a static field {@code name} of
3263 * type {@code type} declared in a class of type {@code decl}.
3264 * The VarHandle's variable type is {@code type} and it has no
3265 * coordinate types.
3266 * <p>
3267 * Access checking is performed immediately on behalf of the lookup
3268 * class.
3269 * <p>
3270 * If the returned VarHandle is operated on, the declaring class will be
3271 * initialized, if it has not already been initialized.
3272 * <p>
3273 * Certain access modes of the returned VarHandle are unsupported under
3274 * the following conditions:
3275 * <ul>
3276 * <li>if the field is declared {@code final}, then the write, atomic
3277 * update, numeric atomic update, and bitwise atomic update access
3278 * modes are unsupported.
3279 * <li>if the field type is anything other than {@code byte},
3280 * {@code short}, {@code char}, {@code int}, {@code long},
3281 * {@code float}, or {@code double}, then numeric atomic update
3282 * access modes are unsupported.
3283 * <li>if the field type is anything other than {@code boolean},
3284 * {@code byte}, {@code short}, {@code char}, {@code int} or
3285 * {@code long} then bitwise atomic update access modes are
3286 * unsupported.
3287 * </ul>
3288 * <p>
3289 * If the field is declared {@code volatile} then the returned VarHandle
3290 * will override access to the field (effectively ignore the
3291 * {@code volatile} declaration) in accordance to its specified
3292 * access modes.
3293 * <p>
3294 * If the field type is {@code float} or {@code double} then numeric
3295 * and atomic update access modes compare values using their bitwise
3296 * representation (see {@link Float#floatToRawIntBits} and
3297 * {@link Double#doubleToRawLongBits}, respectively).
3298 * @apiNote
3299 * Bitwise comparison of {@code float} values or {@code double} values,
3300 * as performed by the numeric and atomic update access modes, differ
3301 * from the primitive {@code ==} operator and the {@link Float#equals}
3302 * and {@link Double#equals} methods, specifically with respect to
3303 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
3304 * Care should be taken when performing a compare and set or a compare
3305 * and exchange operation with such values since the operation may
3306 * unexpectedly fail.
3307 * There are many possible NaN values that are considered to be
3308 * {@code NaN} in Java, although no IEEE 754 floating-point operation
3309 * provided by Java can distinguish between them. Operation failure can
3310 * occur if the expected or witness value is a NaN value and it is
3311 * transformed (perhaps in a platform specific manner) into another NaN
3312 * value, and thus has a different bitwise representation (see
3313 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
3314 * details).
3315 * The values {@code -0.0} and {@code +0.0} have different bitwise
3316 * representations but are considered equal when using the primitive
3317 * {@code ==} operator. Operation failure can occur if, for example, a
3318 * numeric algorithm computes an expected value to be say {@code -0.0}
3319 * and previously computed the witness value to be say {@code +0.0}.
3320 * @param decl the class that declares the static field
3321 * @param name the field's name
3322 * @param type the field's type, of type {@code T}
3323 * @return a VarHandle giving access to a static field
3324 * @throws NoSuchFieldException if the field does not exist
3325 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
3326 * @throws SecurityException if a security manager is present and it
3327 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3328 * @throws NullPointerException if any argument is null
3329 * @since 9
3330 */
3331 public VarHandle findStaticVarHandle(Class<?> decl, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3332 MemberName getField = resolveOrFail(REF_getStatic, decl, name, type);
3333 MemberName putField = resolveOrFail(REF_putStatic, decl, name, type);
3334 return getFieldVarHandle(REF_getStatic, REF_putStatic, decl, getField, putField);
3335 }
3336
3337 /**
3338 * Produces an early-bound method handle for a non-static method.
3339 * The receiver must have a supertype {@code defc} in which a method
3340 * of the given name and type is accessible to the lookup class.
3341 * The method and all its argument types must be accessible to the lookup object.
3342 * The type of the method handle will be that of the method,
3343 * without any insertion of an additional receiver parameter.
3344 * The given receiver will be bound into the method handle,
3345 * so that every call to the method handle will invoke the
3346 * requested method on the given receiver.
3347 * <p>
3348 * The returned method handle will have
3349 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3350 * the method's variable arity modifier bit ({@code 0x0080}) is set
3351 * <em>and</em> the trailing array argument is not the only argument.
3352 * (If the trailing array argument is the only argument,
3353 * the given receiver value will be bound to it.)
3354 * <p>
3355 * This is almost equivalent to the following code, with some differences noted below:
3356 * {@snippet lang="java" :
3357 import static java.lang.invoke.MethodHandles.*;
3358 import static java.lang.invoke.MethodType.*;
3359 ...
3360 MethodHandle mh0 = lookup().findVirtual(defc, name, type);
3361 MethodHandle mh1 = mh0.bindTo(receiver);
3362 mh1 = mh1.withVarargs(mh0.isVarargsCollector());
3363 return mh1;
3364 * }
3365 * where {@code defc} is either {@code receiver.getClass()} or a super
3366 * type of that class, in which the requested method is accessible
3367 * to the lookup class.
3368 * (Unlike {@code bind}, {@code bindTo} does not preserve variable arity.
3369 * Also, {@code bindTo} may throw a {@code ClassCastException} in instances where {@code bind} would
3370 * throw an {@code IllegalAccessException}, as in the case where the member is {@code protected} and
3371 * the receiver is restricted by {@code findVirtual} to the lookup class.)
3372 * @param receiver the object from which the method is accessed
3373 * @param name the name of the method
3374 * @param type the type of the method, with the receiver argument omitted
3375 * @return the desired method handle
3376 * @throws NoSuchMethodException if the method does not exist
3377 * @throws IllegalAccessException if access checking fails
3378 * or if the method's variable arity modifier bit
3379 * is set and {@code asVarargsCollector} fails
3380 * @throws SecurityException if a security manager is present and it
3381 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3382 * @throws NullPointerException if any argument is null
3383 * @see MethodHandle#bindTo
3384 * @see #findVirtual
3385 */
3386 public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
3387 Class<? extends Object> refc = receiver.getClass(); // may get NPE
3388 MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
3389 MethodHandle mh = getDirectMethodNoRestrictInvokeSpecial(refc, method, findBoundCallerLookup(method));
3390 if (!mh.type().leadingReferenceParameter().isAssignableFrom(receiver.getClass())) {
3391 throw new IllegalAccessException("The restricted defining class " +
3392 mh.type().leadingReferenceParameter().getName() +
3393 " is not assignable from receiver class " +
3394 receiver.getClass().getName());
3395 }
3396 return mh.bindArgumentL(0, receiver).setVarargs(method);
3397 }
3398
3399 /**
3400 * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
3401 * to <i>m</i>, if the lookup class has permission.
3402 * If <i>m</i> is non-static, the receiver argument is treated as an initial argument.
3403 * If <i>m</i> is virtual, overriding is respected on every call.
3404 * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped.
3405 * The type of the method handle will be that of the method,
3406 * with the receiver type prepended (but only if it is non-static).
3407 * If the method's {@code accessible} flag is not set,
3408 * access checking is performed immediately on behalf of the lookup class.
3409 * If <i>m</i> is not public, do not share the resulting handle with untrusted parties.
3410 * <p>
3411 * The returned method handle will have
3412 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3413 * the method's variable arity modifier bit ({@code 0x0080}) is set.
3414 * <p>
3415 * If <i>m</i> is static, and
3416 * if the returned method handle is invoked, the method's class will
3417 * be initialized, if it has not already been initialized.
3418 * @param m the reflected method
3419 * @return a method handle which can invoke the reflected method
3420 * @throws IllegalAccessException if access checking fails
3421 * or if the method's variable arity modifier bit
3422 * is set and {@code asVarargsCollector} fails
3423 * @throws NullPointerException if the argument is null
3424 */
3425 public MethodHandle unreflect(Method m) throws IllegalAccessException {
3426 if (m.getDeclaringClass() == MethodHandle.class) {
3427 MethodHandle mh = unreflectForMH(m);
3428 if (mh != null) return mh;
3429 }
3430 if (m.getDeclaringClass() == VarHandle.class) {
3431 MethodHandle mh = unreflectForVH(m);
3432 if (mh != null) return mh;
3433 }
3434 MemberName method = new MemberName(m);
3435 byte refKind = method.getReferenceKind();
3436 if (refKind == REF_invokeSpecial)
3437 refKind = REF_invokeVirtual;
3438 assert(method.isMethod());
3439 @SuppressWarnings("deprecation")
3440 Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
3441 return lookup.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method, findBoundCallerLookup(method));
3442 }
3443 private MethodHandle unreflectForMH(Method m) {
3444 // these names require special lookups because they throw UnsupportedOperationException
3445 if (MemberName.isMethodHandleInvokeName(m.getName()))
3446 return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m));
3447 return null;
3448 }
3449 private MethodHandle unreflectForVH(Method m) {
3450 // these names require special lookups because they throw UnsupportedOperationException
3451 if (MemberName.isVarHandleMethodInvokeName(m.getName()))
3452 return MethodHandleImpl.fakeVarHandleInvoke(new MemberName(m));
3453 return null;
3454 }
3455
3456 /**
3457 * Produces a method handle for a reflected method.
3458 * It will bypass checks for overriding methods on the receiver,
3459 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
3460 * instruction from within the explicitly specified {@code specialCaller}.
3461 * The type of the method handle will be that of the method,
3462 * with a suitably restricted receiver type prepended.
3463 * (The receiver type will be {@code specialCaller} or a subtype.)
3464 * If the method's {@code accessible} flag is not set,
3465 * access checking is performed immediately on behalf of the lookup class,
3466 * as if {@code invokespecial} instruction were being linked.
3467 * <p>
3468 * Before method resolution,
3469 * if the explicitly specified caller class is not identical with the
3470 * lookup class, or if this lookup object does not have
3471 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
3472 * privileges, the access fails.
3473 * <p>
3474 * The returned method handle will have
3475 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3476 * the method's variable arity modifier bit ({@code 0x0080}) is set.
3477 * @param m the reflected method
3478 * @param specialCaller the class nominally calling the method
3479 * @return a method handle which can invoke the reflected method
3480 * @throws IllegalAccessException if access checking fails,
3481 * or if the method is {@code static},
3482 * or if the method's variable arity modifier bit
3483 * is set and {@code asVarargsCollector} fails
3484 * @throws NullPointerException if any argument is null
3485 */
3486 public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException {
3487 checkSpecialCaller(specialCaller, m.getDeclaringClass());
3488 Lookup specialLookup = this.in(specialCaller);
3489 MemberName method = new MemberName(m, true);
3490 assert(method.isMethod());
3491 // ignore m.isAccessible: this is a new kind of access
3492 return specialLookup.getDirectMethodNoSecurityManager(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerLookup(method));
3493 }
3494
3495 /**
3496 * Produces a method handle for a reflected constructor.
3497 * The type of the method handle will be that of the constructor,
3498 * with the return type changed to the declaring class.
3499 * The method handle will perform a {@code newInstance} operation,
3500 * creating a new instance of the constructor's class on the
3501 * arguments passed to the method handle.
3502 * <p>
3503 * If the constructor's {@code accessible} flag is not set,
3504 * access checking is performed immediately on behalf of the lookup class.
3505 * <p>
3506 * The returned method handle will have
3507 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3508 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
3509 * <p>
3510 * If the returned method handle is invoked, the constructor's class will
3511 * be initialized, if it has not already been initialized.
3512 * @param c the reflected constructor
3513 * @return a method handle which can invoke the reflected constructor
3514 * @throws IllegalAccessException if access checking fails
3515 * or if the method's variable arity modifier bit
3516 * is set and {@code asVarargsCollector} fails
3517 * @throws NullPointerException if the argument is null
3518 */
3519 public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException {
3520 MemberName ctor = new MemberName(c);
3521 assert(ctor.isConstructor());
3522 @SuppressWarnings("deprecation")
3523 Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
3524 return lookup.getDirectConstructorNoSecurityManager(ctor.getDeclaringClass(), ctor);
3525 }
3526
3527 /*
3528 * Produces a method handle that is capable of creating instances of the given class
3529 * and instantiated by the given constructor. No security manager check.
3530 *
3531 * This method should only be used by ReflectionFactory::newConstructorForSerialization.
3532 */
3533 /* package-private */ MethodHandle serializableConstructor(Class<?> decl, Constructor<?> c) throws IllegalAccessException {
3534 MemberName ctor = new MemberName(c);
3535 assert(ctor.isConstructor() && constructorInSuperclass(decl, c));
3536 checkAccess(REF_newInvokeSpecial, decl, ctor);
3537 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
3538 return DirectMethodHandle.makeAllocator(decl, ctor).setVarargs(ctor);
3539 }
3540
3541 private static boolean constructorInSuperclass(Class<?> decl, Constructor<?> ctor) {
3542 if (decl == ctor.getDeclaringClass())
3543 return true;
3544
3545 Class<?> cl = decl;
3546 while ((cl = cl.getSuperclass()) != null) {
3547 if (cl == ctor.getDeclaringClass()) {
3548 return true;
3549 }
3550 }
3551 return false;
3552 }
3553
3554 /**
3555 * Produces a method handle giving read access to a reflected field.
3556 * The type of the method handle will have a return type of the field's
3557 * value type.
3558 * If the field is {@code static}, the method handle will take no arguments.
3559 * Otherwise, its single argument will be the instance containing
3560 * the field.
3561 * If the {@code Field} object's {@code accessible} flag is not set,
3562 * access checking is performed immediately on behalf of the lookup class.
3563 * <p>
3564 * If the field is static, and
3565 * if the returned method handle is invoked, the field's class will
3566 * be initialized, if it has not already been initialized.
3567 * @param f the reflected field
3568 * @return a method handle which can load values from the reflected field
3569 * @throws IllegalAccessException if access checking fails
3570 * @throws NullPointerException if the argument is null
3571 */
3572 public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
3573 return unreflectField(f, false);
3574 }
3575
3576 /**
3577 * Produces a method handle giving write access to a reflected field.
3578 * The type of the method handle will have a void return type.
3579 * If the field is {@code static}, the method handle will take a single
3580 * argument, of the field's value type, the value to be stored.
3581 * Otherwise, the two arguments will be the instance containing
3582 * the field, and the value to be stored.
3583 * If the {@code Field} object's {@code accessible} flag is not set,
3584 * access checking is performed immediately on behalf of the lookup class.
3585 * <p>
3586 * If the field is {@code final}, write access will not be
3587 * allowed and access checking will fail, except under certain
3588 * narrow circumstances documented for {@link Field#set Field.set}.
3589 * A method handle is returned only if a corresponding call to
3590 * the {@code Field} object's {@code set} method could return
3591 * normally. In particular, fields which are both {@code static}
3592 * and {@code final} may never be set.
3593 * <p>
3594 * If the field is {@code static}, and
3595 * if the returned method handle is invoked, the field's class will
3596 * be initialized, if it has not already been initialized.
3597 * @param f the reflected field
3598 * @return a method handle which can store values into the reflected field
3599 * @throws IllegalAccessException if access checking fails,
3600 * or if the field is {@code final} and write access
3601 * is not enabled on the {@code Field} object
3602 * @throws NullPointerException if the argument is null
3603 */
3604 public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
3605 return unreflectField(f, true);
3606 }
3607
3608 private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
3609 MemberName field = new MemberName(f, isSetter);
3610 if (isSetter && field.isFinal()) {
3611 if (field.isTrustedFinalField()) {
3612 String msg = field.isStatic() ? "static final field has no write access"
3613 : "final field has no write access";
3614 throw field.makeAccessException(msg, this);
3615 }
3616 }
3617 assert(isSetter
3618 ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
3619 : MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
3620 @SuppressWarnings("deprecation")
3621 Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
3622 return lookup.getDirectFieldNoSecurityManager(field.getReferenceKind(), f.getDeclaringClass(), field);
3623 }
3624
3625 /**
3626 * Produces a VarHandle giving access to a reflected field {@code f}
3627 * of type {@code T} declared in a class of type {@code R}.
3628 * The VarHandle's variable type is {@code T}.
3629 * If the field is non-static the VarHandle has one coordinate type,
3630 * {@code R}. Otherwise, the field is static, and the VarHandle has no
3631 * coordinate types.
3632 * <p>
3633 * Access checking is performed immediately on behalf of the lookup
3634 * class, regardless of the value of the field's {@code accessible}
3635 * flag.
3636 * <p>
3637 * If the field is static, and if the returned VarHandle is operated
3638 * on, the field's declaring class will be initialized, if it has not
3639 * already been initialized.
3640 * <p>
3641 * Certain access modes of the returned VarHandle are unsupported under
3642 * the following conditions:
3643 * <ul>
3644 * <li>if the field is declared {@code final}, then the write, atomic
3645 * update, numeric atomic update, and bitwise atomic update access
3646 * modes are unsupported.
3647 * <li>if the field type is anything other than {@code byte},
3648 * {@code short}, {@code char}, {@code int}, {@code long},
3649 * {@code float}, or {@code double} then numeric atomic update
3650 * access modes are unsupported.
3651 * <li>if the field type is anything other than {@code boolean},
3652 * {@code byte}, {@code short}, {@code char}, {@code int} or
3653 * {@code long} then bitwise atomic update access modes are
3654 * unsupported.
3655 * </ul>
3656 * <p>
3657 * If the field is declared {@code volatile} then the returned VarHandle
3658 * will override access to the field (effectively ignore the
3659 * {@code volatile} declaration) in accordance to its specified
3660 * access modes.
3661 * <p>
3662 * If the field type is {@code float} or {@code double} then numeric
3663 * and atomic update access modes compare values using their bitwise
3664 * representation (see {@link Float#floatToRawIntBits} and
3665 * {@link Double#doubleToRawLongBits}, respectively).
3666 * @apiNote
3667 * Bitwise comparison of {@code float} values or {@code double} values,
3668 * as performed by the numeric and atomic update access modes, differ
3669 * from the primitive {@code ==} operator and the {@link Float#equals}
3670 * and {@link Double#equals} methods, specifically with respect to
3671 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
3672 * Care should be taken when performing a compare and set or a compare
3673 * and exchange operation with such values since the operation may
3674 * unexpectedly fail.
3675 * There are many possible NaN values that are considered to be
3676 * {@code NaN} in Java, although no IEEE 754 floating-point operation
3677 * provided by Java can distinguish between them. Operation failure can
3678 * occur if the expected or witness value is a NaN value and it is
3679 * transformed (perhaps in a platform specific manner) into another NaN
3680 * value, and thus has a different bitwise representation (see
3681 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
3682 * details).
3683 * The values {@code -0.0} and {@code +0.0} have different bitwise
3684 * representations but are considered equal when using the primitive
3685 * {@code ==} operator. Operation failure can occur if, for example, a
3686 * numeric algorithm computes an expected value to be say {@code -0.0}
3687 * and previously computed the witness value to be say {@code +0.0}.
3688 * @param f the reflected field, with a field of type {@code T}, and
3689 * a declaring class of type {@code R}
3690 * @return a VarHandle giving access to non-static fields or a static
3691 * field
3692 * @throws IllegalAccessException if access checking fails
3693 * @throws NullPointerException if the argument is null
3694 * @since 9
3695 */
3696 public VarHandle unreflectVarHandle(Field f) throws IllegalAccessException {
3697 MemberName getField = new MemberName(f, false);
3698 MemberName putField = new MemberName(f, true);
3699 return getFieldVarHandleNoSecurityManager(getField.getReferenceKind(), putField.getReferenceKind(),
3700 f.getDeclaringClass(), getField, putField);
3701 }
3702
3703 /**
3704 * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
3705 * created by this lookup object or a similar one.
3706 * Security and access checks are performed to ensure that this lookup object
3707 * is capable of reproducing the target method handle.
3708 * This means that the cracking may fail if target is a direct method handle
3709 * but was created by an unrelated lookup object.
3710 * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a>
3711 * and was created by a lookup object for a different class.
3712 * @param target a direct method handle to crack into symbolic reference components
3713 * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object
3714 * @throws SecurityException if a security manager is present and it
3715 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3716 * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails
3717 * @throws NullPointerException if the target is {@code null}
3718 * @see MethodHandleInfo
3719 * @since 1.8
3720 */
3721 public MethodHandleInfo revealDirect(MethodHandle target) {
3722 if (!target.isCrackable()) {
3723 throw newIllegalArgumentException("not a direct method handle");
3724 }
3725 MemberName member = target.internalMemberName();
3726 Class<?> defc = member.getDeclaringClass();
3727 byte refKind = member.getReferenceKind();
3728 assert(MethodHandleNatives.refKindIsValid(refKind));
3729 if (refKind == REF_invokeSpecial && !target.isInvokeSpecial())
3730 // Devirtualized method invocation is usually formally virtual.
3731 // To avoid creating extra MemberName objects for this common case,
3732 // we encode this extra degree of freedom using MH.isInvokeSpecial.
3733 refKind = REF_invokeVirtual;
3734 if (refKind == REF_invokeVirtual && defc.isInterface())
3735 // Symbolic reference is through interface but resolves to Object method (toString, etc.)
3736 refKind = REF_invokeInterface;
3737 // Check SM permissions and member access before cracking.
3738 try {
3739 checkAccess(refKind, defc, member);
3740 checkSecurityManager(defc, member);
3741 } catch (IllegalAccessException ex) {
3742 throw new IllegalArgumentException(ex);
3743 }
3744 if (allowedModes != TRUSTED && member.isCallerSensitive()) {
3745 Class<?> callerClass = target.internalCallerClass();
3746 if ((lookupModes() & ORIGINAL) == 0 || callerClass != lookupClass())
3747 throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass);
3748 }
3749 // Produce the handle to the results.
3750 return new InfoFromMemberName(this, member, refKind);
3751 }
3752
3753 /// Helper methods, all package-private.
3754
3755 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3756 checkSymbolicClass(refc); // do this before attempting to resolve
3757 Objects.requireNonNull(name);
3758 Objects.requireNonNull(type);
3759 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), allowedModes,
3760 NoSuchFieldException.class);
3761 }
3762
3763 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
3764 checkSymbolicClass(refc); // do this before attempting to resolve
3765 Objects.requireNonNull(type);
3766 checkMethodName(refKind, name); // implicit null-check of name
3767 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), allowedModes,
3768 NoSuchMethodException.class);
3769 }
3770
3771 MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException {
3772 checkSymbolicClass(member.getDeclaringClass()); // do this before attempting to resolve
3773 Objects.requireNonNull(member.getName());
3774 Objects.requireNonNull(member.getType());
3775 return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(), allowedModes,
3776 ReflectiveOperationException.class);
3777 }
3778
3779 MemberName resolveOrNull(byte refKind, MemberName member) {
3780 // do this before attempting to resolve
3781 if (!isClassAccessible(member.getDeclaringClass())) {
3782 return null;
3783 }
3784 Objects.requireNonNull(member.getName());
3785 Objects.requireNonNull(member.getType());
3786 return IMPL_NAMES.resolveOrNull(refKind, member, lookupClassOrNull(), allowedModes);
3787 }
3788
3789 MemberName resolveOrNull(byte refKind, Class<?> refc, String name, MethodType type) {
3790 // do this before attempting to resolve
3791 if (!isClassAccessible(refc)) {
3792 return null;
3793 }
3794 Objects.requireNonNull(type);
3795 // implicit null-check of name
3796 if (name.startsWith("<") && refKind != REF_newInvokeSpecial) {
3797 return null;
3798 }
3799 return IMPL_NAMES.resolveOrNull(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), allowedModes);
3800 }
3801
3802 void checkSymbolicClass(Class<?> refc) throws IllegalAccessException {
3803 if (!isClassAccessible(refc)) {
3804 throw new MemberName(refc).makeAccessException("symbolic reference class is not accessible", this);
3805 }
3806 }
3807
3808 boolean isClassAccessible(Class<?> refc) {
3809 Objects.requireNonNull(refc);
3810 Class<?> caller = lookupClassOrNull();
3811 Class<?> type = refc;
3812 while (type.isArray()) {
3813 type = type.getComponentType();
3814 }
3815 return caller == null || VerifyAccess.isClassAccessible(type, caller, prevLookupClass, allowedModes);
3816 }
3817
3818 /** Check name for an illegal leading "<" character. */
3819 void checkMethodName(byte refKind, String name) throws NoSuchMethodException {
3820 if (name.startsWith("<") && refKind != REF_newInvokeSpecial)
3821 throw new NoSuchMethodException("illegal method name: "+name);
3822 }
3823
3824 /**
3825 * Find my trustable caller class if m is a caller sensitive method.
3826 * If this lookup object has original full privilege access, then the caller class is the lookupClass.
3827 * Otherwise, if m is caller-sensitive, throw IllegalAccessException.
3828 */
3829 Lookup findBoundCallerLookup(MemberName m) throws IllegalAccessException {
3830 if (MethodHandleNatives.isCallerSensitive(m) && (lookupModes() & ORIGINAL) == 0) {
3831 // Only lookups with full privilege access are allowed to resolve caller-sensitive methods
3832 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
3833 }
3834 return this;
3835 }
3836
3837 /**
3838 * Returns {@code true} if this lookup has {@code PRIVATE} and {@code MODULE} access.
3839 * @return {@code true} if this lookup has {@code PRIVATE} and {@code MODULE} access.
3840 *
3841 * @deprecated This method was originally designed to test {@code PRIVATE} access
3842 * that implies full privilege access but {@code MODULE} access has since become
3843 * independent of {@code PRIVATE} access. It is recommended to call
3844 * {@link #hasFullPrivilegeAccess()} instead.
3845 * @since 9
3846 */
3847 @Deprecated(since="14")
3848 public boolean hasPrivateAccess() {
3849 return hasFullPrivilegeAccess();
3850 }
3851
3852 /**
3853 * Returns {@code true} if this lookup has <em>full privilege access</em>,
3854 * i.e. {@code PRIVATE} and {@code MODULE} access.
3855 * A {@code Lookup} object must have full privilege access in order to
3856 * access all members that are allowed to the
3857 * {@linkplain #lookupClass() lookup class}.
3858 *
3859 * @return {@code true} if this lookup has full privilege access.
3860 * @since 14
3861 * @see <a href="MethodHandles.Lookup.html#privacc">private and module access</a>
3862 */
3863 public boolean hasFullPrivilegeAccess() {
3864 return (allowedModes & (PRIVATE|MODULE)) == (PRIVATE|MODULE);
3865 }
3866
3867 /**
3868 * Perform steps 1 and 2b <a href="MethodHandles.Lookup.html#secmgr">access checks</a>
3869 * for ensureInitialized, findClass or accessClass.
3870 */
3871 void checkSecurityManager(Class<?> refc) {
3872 if (allowedModes == TRUSTED) return;
3873
3874 @SuppressWarnings("removal")
3875 SecurityManager smgr = System.getSecurityManager();
3876 if (smgr == null) return;
3877
3878 // Step 1:
3879 boolean fullPrivilegeLookup = hasFullPrivilegeAccess();
3880 if (!fullPrivilegeLookup ||
3881 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
3882 ReflectUtil.checkPackageAccess(refc);
3883 }
3884
3885 // Step 2b:
3886 if (!fullPrivilegeLookup) {
3887 smgr.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
3888 }
3889 }
3890
3891 /**
3892 * Perform steps 1, 2a and 3 <a href="MethodHandles.Lookup.html#secmgr">access checks</a>.
3893 * Determines a trustable caller class to compare with refc, the symbolic reference class.
3894 * If this lookup object has full privilege access except original access,
3895 * then the caller class is the lookupClass.
3896 *
3897 * Lookup object created by {@link MethodHandles#privateLookupIn(Class, Lookup)}
3898 * from the same module skips the security permission check.
3899 */
3900 void checkSecurityManager(Class<?> refc, MemberName m) {
3901 Objects.requireNonNull(refc);
3902 Objects.requireNonNull(m);
3903
3904 if (allowedModes == TRUSTED) return;
3905
3906 @SuppressWarnings("removal")
3907 SecurityManager smgr = System.getSecurityManager();
3908 if (smgr == null) return;
3909
3910 // Step 1:
3911 boolean fullPrivilegeLookup = hasFullPrivilegeAccess();
3912 if (!fullPrivilegeLookup ||
3913 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
3914 ReflectUtil.checkPackageAccess(refc);
3915 }
3916
3917 // Step 2a:
3918 if (m.isPublic()) return;
3919 if (!fullPrivilegeLookup) {
3920 smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION);
3921 }
3922
3923 // Step 3:
3924 Class<?> defc = m.getDeclaringClass();
3925 if (!fullPrivilegeLookup && defc != refc) {
3926 ReflectUtil.checkPackageAccess(defc);
3927 }
3928 }
3929
3930 void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
3931 boolean wantStatic = (refKind == REF_invokeStatic);
3932 String message;
3933 if (m.isConstructor())
3934 message = "expected a method, not a constructor";
3935 else if (!m.isMethod())
3936 message = "expected a method";
3937 else if (wantStatic != m.isStatic())
3938 message = wantStatic ? "expected a static method" : "expected a non-static method";
3939 else
3940 { checkAccess(refKind, refc, m); return; }
3941 throw m.makeAccessException(message, this);
3942 }
3943
3944 void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
3945 boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
3946 String message;
3947 if (wantStatic != m.isStatic())
3948 message = wantStatic ? "expected a static field" : "expected a non-static field";
3949 else
3950 { checkAccess(refKind, refc, m); return; }
3951 throw m.makeAccessException(message, this);
3952 }
3953
3954 private boolean isArrayClone(byte refKind, Class<?> refc, MemberName m) {
3955 return Modifier.isProtected(m.getModifiers()) &&
3956 refKind == REF_invokeVirtual &&
3957 m.getDeclaringClass() == Object.class &&
3958 m.getName().equals("clone") &&
3959 refc.isArray();
3960 }
3961
3962 /** Check public/protected/private bits on the symbolic reference class and its member. */
3963 void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
3964 assert(m.referenceKindIsConsistentWith(refKind) &&
3965 MethodHandleNatives.refKindIsValid(refKind) &&
3966 (MethodHandleNatives.refKindIsField(refKind) == m.isField()));
3967 int allowedModes = this.allowedModes;
3968 if (allowedModes == TRUSTED) return;
3969 int mods = m.getModifiers();
3970 if (isArrayClone(refKind, refc, m)) {
3971 // The JVM does this hack also.
3972 // (See ClassVerifier::verify_invoke_instructions
3973 // and LinkResolver::check_method_accessability.)
3974 // Because the JVM does not allow separate methods on array types,
3975 // there is no separate method for int[].clone.
3976 // All arrays simply inherit Object.clone.
3977 // But for access checking logic, we make Object.clone
3978 // (normally protected) appear to be public.
3979 // Later on, when the DirectMethodHandle is created,
3980 // its leading argument will be restricted to the
3981 // requested array type.
3982 // N.B. The return type is not adjusted, because
3983 // that is *not* the bytecode behavior.
3984 mods ^= Modifier.PROTECTED | Modifier.PUBLIC;
3985 }
3986 if (Modifier.isProtected(mods) && refKind == REF_newInvokeSpecial) {
3987 // cannot "new" a protected ctor in a different package
3988 mods ^= Modifier.PROTECTED;
3989 }
3990 if (Modifier.isFinal(mods) &&
3991 MethodHandleNatives.refKindIsSetter(refKind))
3992 throw m.makeAccessException("unexpected set of a final field", this);
3993 int requestedModes = fixmods(mods); // adjust 0 => PACKAGE
3994 if ((requestedModes & allowedModes) != 0) {
3995 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
3996 mods, lookupClass(), previousLookupClass(), allowedModes))
3997 return;
3998 } else {
3999 // Protected members can also be checked as if they were package-private.
4000 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
4001 && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
4002 return;
4003 }
4004 throw m.makeAccessException(accessFailedMessage(refc, m), this);
4005 }
4006
4007 String accessFailedMessage(Class<?> refc, MemberName m) {
4008 Class<?> defc = m.getDeclaringClass();
4009 int mods = m.getModifiers();
4010 // check the class first:
4011 boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
4012 (defc == refc ||
4013 Modifier.isPublic(refc.getModifiers())));
4014 if (!classOK && (allowedModes & PACKAGE) != 0) {
4015 // ignore previous lookup class to check if default package access
4016 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), null, FULL_POWER_MODES) &&
4017 (defc == refc ||
4018 VerifyAccess.isClassAccessible(refc, lookupClass(), null, FULL_POWER_MODES)));
4019 }
4020 if (!classOK)
4021 return "class is not public";
4022 if (Modifier.isPublic(mods))
4023 return "access to public member failed"; // (how?, module not readable?)
4024 if (Modifier.isPrivate(mods))
4025 return "member is private";
4026 if (Modifier.isProtected(mods))
4027 return "member is protected";
4028 return "member is private to package";
4029 }
4030
4031 private void checkSpecialCaller(Class<?> specialCaller, Class<?> refc) throws IllegalAccessException {
4032 int allowedModes = this.allowedModes;
4033 if (allowedModes == TRUSTED) return;
4034 if ((lookupModes() & PRIVATE) == 0
4035 || (specialCaller != lookupClass()
4036 // ensure non-abstract methods in superinterfaces can be special-invoked
4037 && !(refc != null && refc.isInterface() && refc.isAssignableFrom(specialCaller))))
4038 throw new MemberName(specialCaller).
4039 makeAccessException("no private access for invokespecial", this);
4040 }
4041
4042 private boolean restrictProtectedReceiver(MemberName method) {
4043 // The accessing class only has the right to use a protected member
4044 // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc.
4045 if (!method.isProtected() || method.isStatic()
4046 || allowedModes == TRUSTED
4047 || method.getDeclaringClass() == lookupClass()
4048 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass()))
4049 return false;
4050 return true;
4051 }
4052 private MethodHandle restrictReceiver(MemberName method, DirectMethodHandle mh, Class<?> caller) throws IllegalAccessException {
4053 assert(!method.isStatic());
4054 // receiver type of mh is too wide; narrow to caller
4055 if (!method.getDeclaringClass().isAssignableFrom(caller)) {
4056 throw method.makeAccessException("caller class must be a subclass below the method", caller);
4057 }
4058 MethodType rawType = mh.type();
4059 if (caller.isAssignableFrom(rawType.parameterType(0))) return mh; // no need to restrict; already narrow
4060 MethodType narrowType = rawType.changeParameterType(0, caller);
4061 assert(!mh.isVarargsCollector()); // viewAsType will lose varargs-ness
4062 assert(mh.viewAsTypeChecks(narrowType, true));
4063 return mh.copyWith(narrowType, mh.form);
4064 }
4065
4066 /** Check access and get the requested method. */
4067 private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException {
4068 final boolean doRestrict = true;
4069 final boolean checkSecurity = true;
4070 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerLookup);
4071 }
4072 /** Check access and get the requested method, for invokespecial with no restriction on the application of narrowing rules. */
4073 private MethodHandle getDirectMethodNoRestrictInvokeSpecial(Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException {
4074 final boolean doRestrict = false;
4075 final boolean checkSecurity = true;
4076 return getDirectMethodCommon(REF_invokeSpecial, refc, method, checkSecurity, doRestrict, callerLookup);
4077 }
4078 /** Check access and get the requested method, eliding security manager checks. */
4079 private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException {
4080 final boolean doRestrict = true;
4081 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
4082 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerLookup);
4083 }
4084 /** Common code for all methods; do not call directly except from immediately above. */
4085 private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method,
4086 boolean checkSecurity,
4087 boolean doRestrict,
4088 Lookup boundCaller) throws IllegalAccessException {
4089 checkMethod(refKind, refc, method);
4090 // Optionally check with the security manager; this isn't needed for unreflect* calls.
4091 if (checkSecurity)
4092 checkSecurityManager(refc, method);
4093 assert(!method.isMethodHandleInvoke());
4094 if (refKind == REF_invokeSpecial &&
4095 refc != lookupClass() &&
4096 !refc.isInterface() && !lookupClass().isInterface() &&
4097 refc != lookupClass().getSuperclass() &&
4098 refc.isAssignableFrom(lookupClass())) {
4099 assert(!method.getName().equals(ConstantDescs.INIT_NAME)); // not this code path
4100
4101 // Per JVMS 6.5, desc. of invokespecial instruction:
4102 // If the method is in a superclass of the LC,
4103 // and if our original search was above LC.super,
4104 // repeat the search (symbolic lookup) from LC.super
4105 // and continue with the direct superclass of that class,
4106 // and so forth, until a match is found or no further superclasses exist.
4107 // FIXME: MemberName.resolve should handle this instead.
4108 Class<?> refcAsSuper = lookupClass();
4109 MemberName m2;
4110 do {
4111 refcAsSuper = refcAsSuper.getSuperclass();
4112 m2 = new MemberName(refcAsSuper,
4113 method.getName(),
4114 method.getMethodType(),
4115 REF_invokeSpecial);
4116 m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull(), allowedModes);
4117 } while (m2 == null && // no method is found yet
4118 refc != refcAsSuper); // search up to refc
4119 if (m2 == null) throw new InternalError(method.toString());
4120 method = m2;
4121 refc = refcAsSuper;
4122 // redo basic checks
4123 checkMethod(refKind, refc, method);
4124 }
4125 DirectMethodHandle dmh = DirectMethodHandle.make(refKind, refc, method, lookupClass());
4126 MethodHandle mh = dmh;
4127 // Optionally narrow the receiver argument to lookupClass using restrictReceiver.
4128 if ((doRestrict && refKind == REF_invokeSpecial) ||
4129 (MethodHandleNatives.refKindHasReceiver(refKind) &&
4130 restrictProtectedReceiver(method) &&
4131 // All arrays simply inherit the protected Object.clone method.
4132 // The leading argument is already restricted to the requested
4133 // array type (not the lookup class).
4134 !isArrayClone(refKind, refc, method))) {
4135 mh = restrictReceiver(method, dmh, lookupClass());
4136 }
4137 mh = maybeBindCaller(method, mh, boundCaller);
4138 mh = mh.setVarargs(method);
4139 return mh;
4140 }
4141 private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh, Lookup boundCaller)
4142 throws IllegalAccessException {
4143 if (boundCaller.allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method))
4144 return mh;
4145
4146 // boundCaller must have full privilege access.
4147 // It should have been checked by findBoundCallerLookup. Safe to check this again.
4148 if ((boundCaller.lookupModes() & ORIGINAL) == 0)
4149 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
4150
4151 assert boundCaller.hasFullPrivilegeAccess();
4152
4153 MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, boundCaller.lookupClass);
4154 // Note: caller will apply varargs after this step happens.
4155 return cbmh;
4156 }
4157
4158 /** Check access and get the requested field. */
4159 private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
4160 final boolean checkSecurity = true;
4161 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
4162 }
4163 /** Check access and get the requested field, eliding security manager checks. */
4164 private MethodHandle getDirectFieldNoSecurityManager(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
4165 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
4166 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
4167 }
4168 /** Common code for all fields; do not call directly except from immediately above. */
4169 private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field,
4170 boolean checkSecurity) throws IllegalAccessException {
4171 checkField(refKind, refc, field);
4172 // Optionally check with the security manager; this isn't needed for unreflect* calls.
4173 if (checkSecurity)
4174 checkSecurityManager(refc, field);
4175 DirectMethodHandle dmh = DirectMethodHandle.make(refc, field);
4176 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) &&
4177 restrictProtectedReceiver(field));
4178 if (doRestrict)
4179 return restrictReceiver(field, dmh, lookupClass());
4180 return dmh;
4181 }
4182 private VarHandle getFieldVarHandle(byte getRefKind, byte putRefKind,
4183 Class<?> refc, MemberName getField, MemberName putField)
4184 throws IllegalAccessException {
4185 final boolean checkSecurity = true;
4186 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
4187 }
4188 private VarHandle getFieldVarHandleNoSecurityManager(byte getRefKind, byte putRefKind,
4189 Class<?> refc, MemberName getField, MemberName putField)
4190 throws IllegalAccessException {
4191 final boolean checkSecurity = false;
4192 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
4193 }
4194 private VarHandle getFieldVarHandleCommon(byte getRefKind, byte putRefKind,
4195 Class<?> refc, MemberName getField, MemberName putField,
4196 boolean checkSecurity) throws IllegalAccessException {
4197 assert getField.isStatic() == putField.isStatic();
4198 assert getField.isGetter() && putField.isSetter();
4199 assert MethodHandleNatives.refKindIsStatic(getRefKind) == MethodHandleNatives.refKindIsStatic(putRefKind);
4200 assert MethodHandleNatives.refKindIsGetter(getRefKind) && MethodHandleNatives.refKindIsSetter(putRefKind);
4201
4202 checkField(getRefKind, refc, getField);
4203 if (checkSecurity)
4204 checkSecurityManager(refc, getField);
4205
4206 if (!putField.isFinal()) {
4207 // A VarHandle does not support updates to final fields, any
4208 // such VarHandle to a final field will be read-only and
4209 // therefore the following write-based accessibility checks are
4210 // only required for non-final fields
4211 checkField(putRefKind, refc, putField);
4212 if (checkSecurity)
4213 checkSecurityManager(refc, putField);
4214 }
4215
4216 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(getRefKind) &&
4217 restrictProtectedReceiver(getField));
4218 if (doRestrict) {
4219 assert !getField.isStatic();
4220 // receiver type of VarHandle is too wide; narrow to caller
4221 if (!getField.getDeclaringClass().isAssignableFrom(lookupClass())) {
4222 throw getField.makeAccessException("caller class must be a subclass below the method", lookupClass());
4223 }
4224 refc = lookupClass();
4225 }
4226 return VarHandles.makeFieldHandle(getField, refc,
4227 this.allowedModes == TRUSTED && !getField.isTrustedFinalField());
4228 }
4229 /** Check access and get the requested constructor. */
4230 private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException {
4231 final boolean checkSecurity = true;
4232 return getDirectConstructorCommon(refc, ctor, checkSecurity);
4233 }
4234 /** Check access and get the requested constructor, eliding security manager checks. */
4235 private MethodHandle getDirectConstructorNoSecurityManager(Class<?> refc, MemberName ctor) throws IllegalAccessException {
4236 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
4237 return getDirectConstructorCommon(refc, ctor, checkSecurity);
4238 }
4239 /** Common code for all constructors; do not call directly except from immediately above. */
4240 private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor,
4241 boolean checkSecurity) throws IllegalAccessException {
4242 assert(ctor.isConstructor());
4243 checkAccess(REF_newInvokeSpecial, refc, ctor);
4244 // Optionally check with the security manager; this isn't needed for unreflect* calls.
4245 if (checkSecurity)
4246 checkSecurityManager(refc, ctor);
4247 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
4248 return DirectMethodHandle.make(ctor).setVarargs(ctor);
4249 }
4250
4251 /** Hook called from the JVM (via MethodHandleNatives) to link MH constants:
4252 */
4253 /*non-public*/
4254 MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type)
4255 throws ReflectiveOperationException {
4256 if (!(type instanceof Class || type instanceof MethodType))
4257 throw new InternalError("unresolved MemberName");
4258 MemberName member = new MemberName(refKind, defc, name, type);
4259 MethodHandle mh = LOOKASIDE_TABLE.get(member);
4260 if (mh != null) {
4261 checkSymbolicClass(defc);
4262 return mh;
4263 }
4264 if (defc == MethodHandle.class && refKind == REF_invokeVirtual) {
4265 // Treat MethodHandle.invoke and invokeExact specially.
4266 mh = findVirtualForMH(member.getName(), member.getMethodType());
4267 if (mh != null) {
4268 return mh;
4269 }
4270 } else if (defc == VarHandle.class && refKind == REF_invokeVirtual) {
4271 // Treat signature-polymorphic methods on VarHandle specially.
4272 mh = findVirtualForVH(member.getName(), member.getMethodType());
4273 if (mh != null) {
4274 return mh;
4275 }
4276 }
4277 MemberName resolved = resolveOrFail(refKind, member);
4278 mh = getDirectMethodForConstant(refKind, defc, resolved);
4279 if (mh instanceof DirectMethodHandle dmh
4280 && canBeCached(refKind, defc, resolved)) {
4281 MemberName key = mh.internalMemberName();
4282 if (key != null) {
4283 key = key.asNormalOriginal();
4284 }
4285 if (member.equals(key)) { // better safe than sorry
4286 LOOKASIDE_TABLE.put(key, dmh);
4287 }
4288 }
4289 return mh;
4290 }
4291 private boolean canBeCached(byte refKind, Class<?> defc, MemberName member) {
4292 if (refKind == REF_invokeSpecial) {
4293 return false;
4294 }
4295 if (!Modifier.isPublic(defc.getModifiers()) ||
4296 !Modifier.isPublic(member.getDeclaringClass().getModifiers()) ||
4297 !member.isPublic() ||
4298 member.isCallerSensitive()) {
4299 return false;
4300 }
4301 ClassLoader loader = defc.getClassLoader();
4302 if (loader != null) {
4303 ClassLoader sysl = ClassLoader.getSystemClassLoader();
4304 boolean found = false;
4305 while (sysl != null) {
4306 if (loader == sysl) { found = true; break; }
4307 sysl = sysl.getParent();
4308 }
4309 if (!found) {
4310 return false;
4311 }
4312 }
4313 try {
4314 MemberName resolved2 = publicLookup().resolveOrNull(refKind,
4315 new MemberName(refKind, defc, member.getName(), member.getType()));
4316 if (resolved2 == null) {
4317 return false;
4318 }
4319 checkSecurityManager(defc, resolved2);
4320 } catch (SecurityException ex) {
4321 return false;
4322 }
4323 return true;
4324 }
4325 private MethodHandle getDirectMethodForConstant(byte refKind, Class<?> defc, MemberName member)
4326 throws ReflectiveOperationException {
4327 if (MethodHandleNatives.refKindIsField(refKind)) {
4328 return getDirectFieldNoSecurityManager(refKind, defc, member);
4329 } else if (MethodHandleNatives.refKindIsMethod(refKind)) {
4330 return getDirectMethodNoSecurityManager(refKind, defc, member, findBoundCallerLookup(member));
4331 } else if (refKind == REF_newInvokeSpecial) {
4332 return getDirectConstructorNoSecurityManager(defc, member);
4333 }
4334 // oops
4335 throw newIllegalArgumentException("bad MethodHandle constant #"+member);
4336 }
4337
4338 static ConcurrentHashMap<MemberName, DirectMethodHandle> LOOKASIDE_TABLE = new ConcurrentHashMap<>();
4339 }
4340
4341 /**
4342 * Produces a method handle constructing arrays of a desired type,
4343 * as if by the {@code anewarray} bytecode.
4344 * The return type of the method handle will be the array type.
4345 * The type of its sole argument will be {@code int}, which specifies the size of the array.
4346 *
4347 * <p> If the returned method handle is invoked with a negative
4348 * array size, a {@code NegativeArraySizeException} will be thrown.
4349 *
4350 * @param arrayClass an array type
4351 * @return a method handle which can create arrays of the given type
4352 * @throws NullPointerException if the argument is {@code null}
4353 * @throws IllegalArgumentException if {@code arrayClass} is not an array type
4354 * @see java.lang.reflect.Array#newInstance(Class, int)
4355 * @jvms 6.5 {@code anewarray} Instruction
4356 * @since 9
4357 */
4358 public static MethodHandle arrayConstructor(Class<?> arrayClass) throws IllegalArgumentException {
4359 if (!arrayClass.isArray()) {
4360 throw newIllegalArgumentException("not an array class: " + arrayClass.getName());
4361 }
4362 MethodHandle ani = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_Array_newInstance).
4363 bindTo(arrayClass.getComponentType());
4364 return ani.asType(ani.type().changeReturnType(arrayClass));
4365 }
4366
4367 /**
4368 * Produces a method handle returning the length of an array,
4369 * as if by the {@code arraylength} bytecode.
4370 * The type of the method handle will have {@code int} as return type,
4371 * and its sole argument will be the array type.
4372 *
4373 * <p> If the returned method handle is invoked with a {@code null}
4374 * array reference, a {@code NullPointerException} will be thrown.
4375 *
4376 * @param arrayClass an array type
4377 * @return a method handle which can retrieve the length of an array of the given array type
4378 * @throws NullPointerException if the argument is {@code null}
4379 * @throws IllegalArgumentException if arrayClass is not an array type
4380 * @jvms 6.5 {@code arraylength} Instruction
4381 * @since 9
4382 */
4383 public static MethodHandle arrayLength(Class<?> arrayClass) throws IllegalArgumentException {
4384 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.LENGTH);
4385 }
4386
4387 /**
4388 * Produces a method handle giving read access to elements of an array,
4389 * as if by the {@code aaload} bytecode.
4390 * The type of the method handle will have a return type of the array's
4391 * element type. Its first argument will be the array type,
4392 * and the second will be {@code int}.
4393 *
4394 * <p> When the returned method handle is invoked,
4395 * the array reference and array index are checked.
4396 * A {@code NullPointerException} will be thrown if the array reference
4397 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
4398 * thrown if the index is negative or if it is greater than or equal to
4399 * the length of the array.
4400 *
4401 * @param arrayClass an array type
4402 * @return a method handle which can load values from the given array type
4403 * @throws NullPointerException if the argument is null
4404 * @throws IllegalArgumentException if arrayClass is not an array type
4405 * @jvms 6.5 {@code aaload} Instruction
4406 */
4407 public static MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException {
4408 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.GET);
4409 }
4410
4411 /**
4412 * Produces a method handle giving write access to elements of an array,
4413 * as if by the {@code astore} bytecode.
4414 * The type of the method handle will have a void return type.
4415 * Its last argument will be the array's element type.
4416 * The first and second arguments will be the array type and int.
4417 *
4418 * <p> When the returned method handle is invoked,
4419 * the array reference and array index are checked.
4420 * A {@code NullPointerException} will be thrown if the array reference
4421 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
4422 * thrown if the index is negative or if it is greater than or equal to
4423 * the length of the array.
4424 *
4425 * @param arrayClass the class of an array
4426 * @return a method handle which can store values into the array type
4427 * @throws NullPointerException if the argument is null
4428 * @throws IllegalArgumentException if arrayClass is not an array type
4429 * @jvms 6.5 {@code aastore} Instruction
4430 */
4431 public static MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException {
4432 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.SET);
4433 }
4434
4435 /**
4436 * Produces a VarHandle giving access to elements of an array of type
4437 * {@code arrayClass}. The VarHandle's variable type is the component type
4438 * of {@code arrayClass} and the list of coordinate types is
4439 * {@code (arrayClass, int)}, where the {@code int} coordinate type
4440 * corresponds to an argument that is an index into an array.
4441 * <p>
4442 * Certain access modes of the returned VarHandle are unsupported under
4443 * the following conditions:
4444 * <ul>
4445 * <li>if the component type is anything other than {@code byte},
4446 * {@code short}, {@code char}, {@code int}, {@code long},
4447 * {@code float}, or {@code double} then numeric atomic update access
4448 * modes are unsupported.
4449 * <li>if the component type is anything other than {@code boolean},
4450 * {@code byte}, {@code short}, {@code char}, {@code int} or
4451 * {@code long} then bitwise atomic update access modes are
4452 * unsupported.
4453 * </ul>
4454 * <p>
4455 * If the component type is {@code float} or {@code double} then numeric
4456 * and atomic update access modes compare values using their bitwise
4457 * representation (see {@link Float#floatToRawIntBits} and
4458 * {@link Double#doubleToRawLongBits}, respectively).
4459 *
4460 * <p> When the returned {@code VarHandle} is invoked,
4461 * the array reference and array index are checked.
4462 * A {@code NullPointerException} will be thrown if the array reference
4463 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
4464 * thrown if the index is negative or if it is greater than or equal to
4465 * the length of the array.
4466 *
4467 * @apiNote
4468 * Bitwise comparison of {@code float} values or {@code double} values,
4469 * as performed by the numeric and atomic update access modes, differ
4470 * from the primitive {@code ==} operator and the {@link Float#equals}
4471 * and {@link Double#equals} methods, specifically with respect to
4472 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
4473 * Care should be taken when performing a compare and set or a compare
4474 * and exchange operation with such values since the operation may
4475 * unexpectedly fail.
4476 * There are many possible NaN values that are considered to be
4477 * {@code NaN} in Java, although no IEEE 754 floating-point operation
4478 * provided by Java can distinguish between them. Operation failure can
4479 * occur if the expected or witness value is a NaN value and it is
4480 * transformed (perhaps in a platform specific manner) into another NaN
4481 * value, and thus has a different bitwise representation (see
4482 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
4483 * details).
4484 * The values {@code -0.0} and {@code +0.0} have different bitwise
4485 * representations but are considered equal when using the primitive
4486 * {@code ==} operator. Operation failure can occur if, for example, a
4487 * numeric algorithm computes an expected value to be say {@code -0.0}
4488 * and previously computed the witness value to be say {@code +0.0}.
4489 * @param arrayClass the class of an array, of type {@code T[]}
4490 * @return a VarHandle giving access to elements of an array
4491 * @throws NullPointerException if the arrayClass is null
4492 * @throws IllegalArgumentException if arrayClass is not an array type
4493 * @since 9
4494 */
4495 public static VarHandle arrayElementVarHandle(Class<?> arrayClass) throws IllegalArgumentException {
4496 return VarHandles.makeArrayElementHandle(arrayClass);
4497 }
4498
4499 /**
4500 * Produces a VarHandle giving access to elements of a {@code byte[]} array
4501 * viewed as if it were a different primitive array type, such as
4502 * {@code int[]} or {@code long[]}.
4503 * The VarHandle's variable type is the component type of
4504 * {@code viewArrayClass} and the list of coordinate types is
4505 * {@code (byte[], int)}, where the {@code int} coordinate type
4506 * corresponds to an argument that is an index into a {@code byte[]} array.
4507 * The returned VarHandle accesses bytes at an index in a {@code byte[]}
4508 * array, composing bytes to or from a value of the component type of
4509 * {@code viewArrayClass} according to the given endianness.
4510 * <p>
4511 * The supported component types (variables types) are {@code short},
4512 * {@code char}, {@code int}, {@code long}, {@code float} and
4513 * {@code double}.
4514 * <p>
4515 * Access of bytes at a given index will result in an
4516 * {@code ArrayIndexOutOfBoundsException} if the index is less than {@code 0}
4517 * or greater than the {@code byte[]} array length minus the size (in bytes)
4518 * of {@code T}.
4519 * <p>
4520 * Access of bytes at an index may be aligned or misaligned for {@code T},
4521 * with respect to the underlying memory address, {@code A} say, associated
4522 * with the array and index.
4523 * If access is misaligned then access for anything other than the
4524 * {@code get} and {@code set} access modes will result in an
4525 * {@code IllegalStateException}. In such cases atomic access is only
4526 * guaranteed with respect to the largest power of two that divides the GCD
4527 * of {@code A} and the size (in bytes) of {@code T}.
4528 * If access is aligned then following access modes are supported and are
4529 * guaranteed to support atomic access:
4530 * <ul>
4531 * <li>read write access modes for all {@code T}, with the exception of
4532 * access modes {@code get} and {@code set} for {@code long} and
4533 * {@code double} on 32-bit platforms.
4534 * <li>atomic update access modes for {@code int}, {@code long},
4535 * {@code float} or {@code double}.
4536 * (Future major platform releases of the JDK may support additional
4537 * types for certain currently unsupported access modes.)
4538 * <li>numeric atomic update access modes for {@code int} and {@code long}.
4539 * (Future major platform releases of the JDK may support additional
4540 * numeric types for certain currently unsupported access modes.)
4541 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
4542 * (Future major platform releases of the JDK may support additional
4543 * numeric types for certain currently unsupported access modes.)
4544 * </ul>
4545 * <p>
4546 * Misaligned access, and therefore atomicity guarantees, may be determined
4547 * for {@code byte[]} arrays without operating on a specific array. Given
4548 * an {@code index}, {@code T} and its corresponding boxed type,
4549 * {@code T_BOX}, misalignment may be determined as follows:
4550 * <pre>{@code
4551 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
4552 * int misalignedAtZeroIndex = ByteBuffer.wrap(new byte[0]).
4553 * alignmentOffset(0, sizeOfT);
4554 * int misalignedAtIndex = (misalignedAtZeroIndex + index) % sizeOfT;
4555 * boolean isMisaligned = misalignedAtIndex != 0;
4556 * }</pre>
4557 * <p>
4558 * If the variable type is {@code float} or {@code double} then atomic
4559 * update access modes compare values using their bitwise representation
4560 * (see {@link Float#floatToRawIntBits} and
4561 * {@link Double#doubleToRawLongBits}, respectively).
4562 * @param viewArrayClass the view array class, with a component type of
4563 * type {@code T}
4564 * @param byteOrder the endianness of the view array elements, as
4565 * stored in the underlying {@code byte} array
4566 * @return a VarHandle giving access to elements of a {@code byte[]} array
4567 * viewed as if elements corresponding to the components type of the view
4568 * array class
4569 * @throws NullPointerException if viewArrayClass or byteOrder is null
4570 * @throws IllegalArgumentException if viewArrayClass is not an array type
4571 * @throws UnsupportedOperationException if the component type of
4572 * viewArrayClass is not supported as a variable type
4573 * @since 9
4574 */
4575 public static VarHandle byteArrayViewVarHandle(Class<?> viewArrayClass,
4576 ByteOrder byteOrder) throws IllegalArgumentException {
4577 Objects.requireNonNull(byteOrder);
4578 return VarHandles.byteArrayViewHandle(viewArrayClass,
4579 byteOrder == ByteOrder.BIG_ENDIAN);
4580 }
4581
4582 /**
4583 * Produces a VarHandle giving access to elements of a {@code ByteBuffer}
4584 * viewed as if it were an array of elements of a different primitive
4585 * component type to that of {@code byte}, such as {@code int[]} or
4586 * {@code long[]}.
4587 * The VarHandle's variable type is the component type of
4588 * {@code viewArrayClass} and the list of coordinate types is
4589 * {@code (ByteBuffer, int)}, where the {@code int} coordinate type
4590 * corresponds to an argument that is an index into a {@code byte[]} array.
4591 * The returned VarHandle accesses bytes at an index in a
4592 * {@code ByteBuffer}, composing bytes to or from a value of the component
4593 * type of {@code viewArrayClass} according to the given endianness.
4594 * <p>
4595 * The supported component types (variables types) are {@code short},
4596 * {@code char}, {@code int}, {@code long}, {@code float} and
4597 * {@code double}.
4598 * <p>
4599 * Access will result in a {@code ReadOnlyBufferException} for anything
4600 * other than the read access modes if the {@code ByteBuffer} is read-only.
4601 * <p>
4602 * Access of bytes at a given index will result in an
4603 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
4604 * or greater than the {@code ByteBuffer} limit minus the size (in bytes) of
4605 * {@code T}.
4606 * <p>
4607 * Access of bytes at an index may be aligned or misaligned for {@code T},
4608 * with respect to the underlying memory address, {@code A} say, associated
4609 * with the {@code ByteBuffer} and index.
4610 * If access is misaligned then access for anything other than the
4611 * {@code get} and {@code set} access modes will result in an
4612 * {@code IllegalStateException}. In such cases atomic access is only
4613 * guaranteed with respect to the largest power of two that divides the GCD
4614 * of {@code A} and the size (in bytes) of {@code T}.
4615 * If access is aligned then following access modes are supported and are
4616 * guaranteed to support atomic access:
4617 * <ul>
4618 * <li>read write access modes for all {@code T}, with the exception of
4619 * access modes {@code get} and {@code set} for {@code long} and
4620 * {@code double} on 32-bit platforms.
4621 * <li>atomic update access modes for {@code int}, {@code long},
4622 * {@code float} or {@code double}.
4623 * (Future major platform releases of the JDK may support additional
4624 * types for certain currently unsupported access modes.)
4625 * <li>numeric atomic update access modes for {@code int} and {@code long}.
4626 * (Future major platform releases of the JDK may support additional
4627 * numeric types for certain currently unsupported access modes.)
4628 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
4629 * (Future major platform releases of the JDK may support additional
4630 * numeric types for certain currently unsupported access modes.)
4631 * </ul>
4632 * <p>
4633 * Misaligned access, and therefore atomicity guarantees, may be determined
4634 * for a {@code ByteBuffer}, {@code bb} (direct or otherwise), an
4635 * {@code index}, {@code T} and its corresponding boxed type,
4636 * {@code T_BOX}, as follows:
4637 * <pre>{@code
4638 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
4639 * ByteBuffer bb = ...
4640 * int misalignedAtIndex = bb.alignmentOffset(index, sizeOfT);
4641 * boolean isMisaligned = misalignedAtIndex != 0;
4642 * }</pre>
4643 * <p>
4644 * If the variable type is {@code float} or {@code double} then atomic
4645 * update access modes compare values using their bitwise representation
4646 * (see {@link Float#floatToRawIntBits} and
4647 * {@link Double#doubleToRawLongBits}, respectively).
4648 * @param viewArrayClass the view array class, with a component type of
4649 * type {@code T}
4650 * @param byteOrder the endianness of the view array elements, as
4651 * stored in the underlying {@code ByteBuffer} (Note this overrides the
4652 * endianness of a {@code ByteBuffer})
4653 * @return a VarHandle giving access to elements of a {@code ByteBuffer}
4654 * viewed as if elements corresponding to the components type of the view
4655 * array class
4656 * @throws NullPointerException if viewArrayClass or byteOrder is null
4657 * @throws IllegalArgumentException if viewArrayClass is not an array type
4658 * @throws UnsupportedOperationException if the component type of
4659 * viewArrayClass is not supported as a variable type
4660 * @since 9
4661 */
4662 public static VarHandle byteBufferViewVarHandle(Class<?> viewArrayClass,
4663 ByteOrder byteOrder) throws IllegalArgumentException {
4664 Objects.requireNonNull(byteOrder);
4665 return VarHandles.makeByteBufferViewHandle(viewArrayClass,
4666 byteOrder == ByteOrder.BIG_ENDIAN);
4667 }
4668
4669
4670 /// method handle invocation (reflective style)
4671
4672 /**
4673 * Produces a method handle which will invoke any method handle of the
4674 * given {@code type}, with a given number of trailing arguments replaced by
4675 * a single trailing {@code Object[]} array.
4676 * The resulting invoker will be a method handle with the following
4677 * arguments:
4678 * <ul>
4679 * <li>a single {@code MethodHandle} target
4680 * <li>zero or more leading values (counted by {@code leadingArgCount})
4681 * <li>an {@code Object[]} array containing trailing arguments
4682 * </ul>
4683 * <p>
4684 * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
4685 * the indicated {@code type}.
4686 * That is, if the target is exactly of the given {@code type}, it will behave
4687 * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
4688 * is used to convert the target to the required {@code type}.
4689 * <p>
4690 * The type of the returned invoker will not be the given {@code type}, but rather
4691 * will have all parameters except the first {@code leadingArgCount}
4692 * replaced by a single array of type {@code Object[]}, which will be
4693 * the final parameter.
4694 * <p>
4695 * Before invoking its target, the invoker will spread the final array, apply
4696 * reference casts as necessary, and unbox and widen primitive arguments.
4697 * If, when the invoker is called, the supplied array argument does
4698 * not have the correct number of elements, the invoker will throw
4699 * an {@link IllegalArgumentException} instead of invoking the target.
4700 * <p>
4701 * This method is equivalent to the following code (though it may be more efficient):
4702 * {@snippet lang="java" :
4703 MethodHandle invoker = MethodHandles.invoker(type);
4704 int spreadArgCount = type.parameterCount() - leadingArgCount;
4705 invoker = invoker.asSpreader(Object[].class, spreadArgCount);
4706 return invoker;
4707 * }
4708 * This method throws no reflective or security exceptions.
4709 * @param type the desired target type
4710 * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
4711 * @return a method handle suitable for invoking any method handle of the given type
4712 * @throws NullPointerException if {@code type} is null
4713 * @throws IllegalArgumentException if {@code leadingArgCount} is not in
4714 * the range from 0 to {@code type.parameterCount()} inclusive,
4715 * or if the resulting method handle's type would have
4716 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4717 */
4718 public static MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
4719 if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
4720 throw newIllegalArgumentException("bad argument count", leadingArgCount);
4721 type = type.asSpreaderType(Object[].class, leadingArgCount, type.parameterCount() - leadingArgCount);
4722 return type.invokers().spreadInvoker(leadingArgCount);
4723 }
4724
4725 /**
4726 * Produces a special <em>invoker method handle</em> which can be used to
4727 * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
4728 * The resulting invoker will have a type which is
4729 * exactly equal to the desired type, except that it will accept
4730 * an additional leading argument of type {@code MethodHandle}.
4731 * <p>
4732 * This method is equivalent to the following code (though it may be more efficient):
4733 * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)}
4734 *
4735 * <p style="font-size:smaller;">
4736 * <em>Discussion:</em>
4737 * Invoker method handles can be useful when working with variable method handles
4738 * of unknown types.
4739 * For example, to emulate an {@code invokeExact} call to a variable method
4740 * handle {@code M}, extract its type {@code T},
4741 * look up the invoker method {@code X} for {@code T},
4742 * and call the invoker method, as {@code X.invoke(T, A...)}.
4743 * (It would not work to call {@code X.invokeExact}, since the type {@code T}
4744 * is unknown.)
4745 * If spreading, collecting, or other argument transformations are required,
4746 * they can be applied once to the invoker {@code X} and reused on many {@code M}
4747 * method handle values, as long as they are compatible with the type of {@code X}.
4748 * <p style="font-size:smaller;">
4749 * <em>(Note: The invoker method is not available via the Core Reflection API.
4750 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
4751 * on the declared {@code invokeExact} or {@code invoke} method will raise an
4752 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
4753 * <p>
4754 * This method throws no reflective or security exceptions.
4755 * @param type the desired target type
4756 * @return a method handle suitable for invoking any method handle of the given type
4757 * @throws IllegalArgumentException if the resulting method handle's type would have
4758 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4759 */
4760 public static MethodHandle exactInvoker(MethodType type) {
4761 return type.invokers().exactInvoker();
4762 }
4763
4764 /**
4765 * Produces a special <em>invoker method handle</em> which can be used to
4766 * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
4767 * The resulting invoker will have a type which is
4768 * exactly equal to the desired type, except that it will accept
4769 * an additional leading argument of type {@code MethodHandle}.
4770 * <p>
4771 * Before invoking its target, if the target differs from the expected type,
4772 * the invoker will apply reference casts as
4773 * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
4774 * Similarly, the return value will be converted as necessary.
4775 * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
4776 * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
4777 * <p>
4778 * This method is equivalent to the following code (though it may be more efficient):
4779 * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)}
4780 * <p style="font-size:smaller;">
4781 * <em>Discussion:</em>
4782 * A {@linkplain MethodType#genericMethodType general method type} is one which
4783 * mentions only {@code Object} arguments and return values.
4784 * An invoker for such a type is capable of calling any method handle
4785 * of the same arity as the general type.
4786 * <p style="font-size:smaller;">
4787 * <em>(Note: The invoker method is not available via the Core Reflection API.
4788 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
4789 * on the declared {@code invokeExact} or {@code invoke} method will raise an
4790 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
4791 * <p>
4792 * This method throws no reflective or security exceptions.
4793 * @param type the desired target type
4794 * @return a method handle suitable for invoking any method handle convertible to the given type
4795 * @throws IllegalArgumentException if the resulting method handle's type would have
4796 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4797 */
4798 public static MethodHandle invoker(MethodType type) {
4799 return type.invokers().genericInvoker();
4800 }
4801
4802 /**
4803 * Produces a special <em>invoker method handle</em> which can be used to
4804 * invoke a signature-polymorphic access mode method on any VarHandle whose
4805 * associated access mode type is compatible with the given type.
4806 * The resulting invoker will have a type which is exactly equal to the
4807 * desired given type, except that it will accept an additional leading
4808 * argument of type {@code VarHandle}.
4809 *
4810 * @param accessMode the VarHandle access mode
4811 * @param type the desired target type
4812 * @return a method handle suitable for invoking an access mode method of
4813 * any VarHandle whose access mode type is of the given type.
4814 * @since 9
4815 */
4816 public static MethodHandle varHandleExactInvoker(VarHandle.AccessMode accessMode, MethodType type) {
4817 return type.invokers().varHandleMethodExactInvoker(accessMode);
4818 }
4819
4820 /**
4821 * Produces a special <em>invoker method handle</em> which can be used to
4822 * invoke a signature-polymorphic access mode method on any VarHandle whose
4823 * associated access mode type is compatible with the given type.
4824 * The resulting invoker will have a type which is exactly equal to the
4825 * desired given type, except that it will accept an additional leading
4826 * argument of type {@code VarHandle}.
4827 * <p>
4828 * Before invoking its target, if the access mode type differs from the
4829 * desired given type, the invoker will apply reference casts as necessary
4830 * and box, unbox, or widen primitive values, as if by
4831 * {@link MethodHandle#asType asType}. Similarly, the return value will be
4832 * converted as necessary.
4833 * <p>
4834 * This method is equivalent to the following code (though it may be more
4835 * efficient): {@code publicLookup().findVirtual(VarHandle.class, accessMode.name(), type)}
4836 *
4837 * @param accessMode the VarHandle access mode
4838 * @param type the desired target type
4839 * @return a method handle suitable for invoking an access mode method of
4840 * any VarHandle whose access mode type is convertible to the given
4841 * type.
4842 * @since 9
4843 */
4844 public static MethodHandle varHandleInvoker(VarHandle.AccessMode accessMode, MethodType type) {
4845 return type.invokers().varHandleMethodInvoker(accessMode);
4846 }
4847
4848 /*non-public*/
4849 static MethodHandle basicInvoker(MethodType type) {
4850 return type.invokers().basicInvoker();
4851 }
4852
4853 /// method handle modification (creation from other method handles)
4854
4855 /**
4856 * Produces a method handle which adapts the type of the
4857 * given method handle to a new type by pairwise argument and return type conversion.
4858 * The original type and new type must have the same number of arguments.
4859 * The resulting method handle is guaranteed to report a type
4860 * which is equal to the desired new type.
4861 * <p>
4862 * If the original type and new type are equal, returns target.
4863 * <p>
4864 * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
4865 * and some additional conversions are also applied if those conversions fail.
4866 * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied
4867 * if possible, before or instead of any conversions done by {@code asType}:
4868 * <ul>
4869 * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type,
4870 * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast.
4871 * (This treatment of interfaces follows the usage of the bytecode verifier.)
4872 * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive,
4873 * the boolean is converted to a byte value, 1 for true, 0 for false.
4874 * (This treatment follows the usage of the bytecode verifier.)
4875 * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive,
4876 * <em>T0</em> is converted to byte via Java casting conversion (JLS {@jls 5.5}),
4877 * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}.
4878 * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean,
4879 * then a Java casting conversion (JLS {@jls 5.5}) is applied.
4880 * (Specifically, <em>T0</em> will convert to <em>T1</em> by
4881 * widening and/or narrowing.)
4882 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
4883 * conversion will be applied at runtime, possibly followed
4884 * by a Java casting conversion (JLS {@jls 5.5}) on the primitive value,
4885 * possibly followed by a conversion from byte to boolean by testing
4886 * the low-order bit.
4887 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive,
4888 * and if the reference is null at runtime, a zero value is introduced.
4889 * </ul>
4890 * @param target the method handle to invoke after arguments are retyped
4891 * @param newType the expected type of the new method handle
4892 * @return a method handle which delegates to the target after performing
4893 * any necessary argument conversions, and arranges for any
4894 * necessary return value conversions
4895 * @throws NullPointerException if either argument is null
4896 * @throws WrongMethodTypeException if the conversion cannot be made
4897 * @see MethodHandle#asType
4898 */
4899 public static MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
4900 explicitCastArgumentsChecks(target, newType);
4901 // use the asTypeCache when possible:
4902 MethodType oldType = target.type();
4903 if (oldType == newType) return target;
4904 if (oldType.explicitCastEquivalentToAsType(newType)) {
4905 return target.asFixedArity().asType(newType);
4906 }
4907 return MethodHandleImpl.makePairwiseConvert(target, newType, false);
4908 }
4909
4910 private static void explicitCastArgumentsChecks(MethodHandle target, MethodType newType) {
4911 if (target.type().parameterCount() != newType.parameterCount()) {
4912 throw new WrongMethodTypeException("cannot explicitly cast " + target + " to " + newType);
4913 }
4914 }
4915
4916 /**
4917 * Produces a method handle which adapts the calling sequence of the
4918 * given method handle to a new type, by reordering the arguments.
4919 * The resulting method handle is guaranteed to report a type
4920 * which is equal to the desired new type.
4921 * <p>
4922 * The given array controls the reordering.
4923 * Call {@code #I} the number of incoming parameters (the value
4924 * {@code newType.parameterCount()}, and call {@code #O} the number
4925 * of outgoing parameters (the value {@code target.type().parameterCount()}).
4926 * Then the length of the reordering array must be {@code #O},
4927 * and each element must be a non-negative number less than {@code #I}.
4928 * For every {@code N} less than {@code #O}, the {@code N}-th
4929 * outgoing argument will be taken from the {@code I}-th incoming
4930 * argument, where {@code I} is {@code reorder[N]}.
4931 * <p>
4932 * No argument or return value conversions are applied.
4933 * The type of each incoming argument, as determined by {@code newType},
4934 * must be identical to the type of the corresponding outgoing parameter
4935 * or parameters in the target method handle.
4936 * The return type of {@code newType} must be identical to the return
4937 * type of the original target.
4938 * <p>
4939 * The reordering array need not specify an actual permutation.
4940 * An incoming argument will be duplicated if its index appears
4941 * more than once in the array, and an incoming argument will be dropped
4942 * if its index does not appear in the array.
4943 * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
4944 * incoming arguments which are not mentioned in the reordering array
4945 * may be of any type, as determined only by {@code newType}.
4946 * {@snippet lang="java" :
4947 import static java.lang.invoke.MethodHandles.*;
4948 import static java.lang.invoke.MethodType.*;
4949 ...
4950 MethodType intfn1 = methodType(int.class, int.class);
4951 MethodType intfn2 = methodType(int.class, int.class, int.class);
4952 MethodHandle sub = ... (int x, int y) -> (x-y) ...;
4953 assert(sub.type().equals(intfn2));
4954 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
4955 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
4956 assert((int)rsub.invokeExact(1, 100) == 99);
4957 MethodHandle add = ... (int x, int y) -> (x+y) ...;
4958 assert(add.type().equals(intfn2));
4959 MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
4960 assert(twice.type().equals(intfn1));
4961 assert((int)twice.invokeExact(21) == 42);
4962 * }
4963 * <p>
4964 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4965 * variable-arity method handle}, even if the original target method handle was.
4966 * @param target the method handle to invoke after arguments are reordered
4967 * @param newType the expected type of the new method handle
4968 * @param reorder an index array which controls the reordering
4969 * @return a method handle which delegates to the target after it
4970 * drops unused arguments and moves and/or duplicates the other arguments
4971 * @throws NullPointerException if any argument is null
4972 * @throws IllegalArgumentException if the index array length is not equal to
4973 * the arity of the target, or if any index array element
4974 * not a valid index for a parameter of {@code newType},
4975 * or if two corresponding parameter types in
4976 * {@code target.type()} and {@code newType} are not identical,
4977 */
4978 public static MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
4979 reorder = reorder.clone(); // get a private copy
4980 MethodType oldType = target.type();
4981 permuteArgumentChecks(reorder, newType, oldType);
4982 // first detect dropped arguments and handle them separately
4983 int[] originalReorder = reorder;
4984 BoundMethodHandle result = target.rebind();
4985 LambdaForm form = result.form;
4986 int newArity = newType.parameterCount();
4987 // Normalize the reordering into a real permutation,
4988 // by removing duplicates and adding dropped elements.
4989 // This somewhat improves lambda form caching, as well
4990 // as simplifying the transform by breaking it up into steps.
4991 for (int ddIdx; (ddIdx = findFirstDupOrDrop(reorder, newArity)) != 0; ) {
4992 if (ddIdx > 0) {
4993 // We found a duplicated entry at reorder[ddIdx].
4994 // Example: (x,y,z)->asList(x,y,z)
4995 // permuted by [1*,0,1] => (a0,a1)=>asList(a1,a0,a1)
4996 // permuted by [0,1,0*] => (a0,a1)=>asList(a0,a1,a0)
4997 // The starred element corresponds to the argument
4998 // deleted by the dupArgumentForm transform.
4999 int srcPos = ddIdx, dstPos = srcPos, dupVal = reorder[srcPos];
5000 boolean killFirst = false;
5001 for (int val; (val = reorder[--dstPos]) != dupVal; ) {
5002 // Set killFirst if the dup is larger than an intervening position.
5003 // This will remove at least one inversion from the permutation.
5004 if (dupVal > val) killFirst = true;
5005 }
5006 if (!killFirst) {
5007 srcPos = dstPos;
5008 dstPos = ddIdx;
5009 }
5010 form = form.editor().dupArgumentForm(1 + srcPos, 1 + dstPos);
5011 assert (reorder[srcPos] == reorder[dstPos]);
5012 oldType = oldType.dropParameterTypes(dstPos, dstPos + 1);
5013 // contract the reordering by removing the element at dstPos
5014 int tailPos = dstPos + 1;
5015 System.arraycopy(reorder, tailPos, reorder, dstPos, reorder.length - tailPos);
5016 reorder = Arrays.copyOf(reorder, reorder.length - 1);
5017 } else {
5018 int dropVal = ~ddIdx, insPos = 0;
5019 while (insPos < reorder.length && reorder[insPos] < dropVal) {
5020 // Find first element of reorder larger than dropVal.
5021 // This is where we will insert the dropVal.
5022 insPos += 1;
5023 }
5024 Class<?> ptype = newType.parameterType(dropVal);
5025 form = form.editor().addArgumentForm(1 + insPos, BasicType.basicType(ptype));
5026 oldType = oldType.insertParameterTypes(insPos, ptype);
5027 // expand the reordering by inserting an element at insPos
5028 int tailPos = insPos + 1;
5029 reorder = Arrays.copyOf(reorder, reorder.length + 1);
5030 System.arraycopy(reorder, insPos, reorder, tailPos, reorder.length - tailPos);
5031 reorder[insPos] = dropVal;
5032 }
5033 assert (permuteArgumentChecks(reorder, newType, oldType));
5034 }
5035 assert (reorder.length == newArity); // a perfect permutation
5036 // Note: This may cache too many distinct LFs. Consider backing off to varargs code.
5037 form = form.editor().permuteArgumentsForm(1, reorder);
5038 if (newType == result.type() && form == result.internalForm())
5039 return result;
5040 return result.copyWith(newType, form);
5041 }
5042
5043 /**
5044 * Return an indication of any duplicate or omission in reorder.
5045 * If the reorder contains a duplicate entry, return the index of the second occurrence.
5046 * Otherwise, return ~(n), for the first n in [0..newArity-1] that is not present in reorder.
5047 * Otherwise, return zero.
5048 * If an element not in [0..newArity-1] is encountered, return reorder.length.
5049 */
5050 private static int findFirstDupOrDrop(int[] reorder, int newArity) {
5051 final int BIT_LIMIT = 63; // max number of bits in bit mask
5052 if (newArity < BIT_LIMIT) {
5053 long mask = 0;
5054 for (int i = 0; i < reorder.length; i++) {
5055 int arg = reorder[i];
5056 if (arg >= newArity) {
5057 return reorder.length;
5058 }
5059 long bit = 1L << arg;
5060 if ((mask & bit) != 0) {
5061 return i; // >0 indicates a dup
5062 }
5063 mask |= bit;
5064 }
5065 if (mask == (1L << newArity) - 1) {
5066 assert(Long.numberOfTrailingZeros(Long.lowestOneBit(~mask)) == newArity);
5067 return 0;
5068 }
5069 // find first zero
5070 long zeroBit = Long.lowestOneBit(~mask);
5071 int zeroPos = Long.numberOfTrailingZeros(zeroBit);
5072 assert(zeroPos <= newArity);
5073 if (zeroPos == newArity) {
5074 return 0;
5075 }
5076 return ~zeroPos;
5077 } else {
5078 // same algorithm, different bit set
5079 BitSet mask = new BitSet(newArity);
5080 for (int i = 0; i < reorder.length; i++) {
5081 int arg = reorder[i];
5082 if (arg >= newArity) {
5083 return reorder.length;
5084 }
5085 if (mask.get(arg)) {
5086 return i; // >0 indicates a dup
5087 }
5088 mask.set(arg);
5089 }
5090 int zeroPos = mask.nextClearBit(0);
5091 assert(zeroPos <= newArity);
5092 if (zeroPos == newArity) {
5093 return 0;
5094 }
5095 return ~zeroPos;
5096 }
5097 }
5098
5099 static boolean permuteArgumentChecks(int[] reorder, MethodType newType, MethodType oldType) {
5100 if (newType.returnType() != oldType.returnType())
5101 throw newIllegalArgumentException("return types do not match",
5102 oldType, newType);
5103 if (reorder.length != oldType.parameterCount())
5104 throw newIllegalArgumentException("old type parameter count and reorder array length do not match",
5105 oldType, Arrays.toString(reorder));
5106
5107 int limit = newType.parameterCount();
5108 for (int j = 0; j < reorder.length; j++) {
5109 int i = reorder[j];
5110 if (i < 0 || i >= limit) {
5111 throw newIllegalArgumentException("index is out of bounds for new type",
5112 i, newType);
5113 }
5114 Class<?> src = newType.parameterType(i);
5115 Class<?> dst = oldType.parameterType(j);
5116 if (src != dst)
5117 throw newIllegalArgumentException("parameter types do not match after reorder",
5118 oldType, newType);
5119 }
5120 return true;
5121 }
5122
5123 /**
5124 * Produces a method handle of the requested return type which returns the given
5125 * constant value every time it is invoked.
5126 * <p>
5127 * Before the method handle is returned, the passed-in value is converted to the requested type.
5128 * If the requested type is primitive, widening primitive conversions are attempted,
5129 * else reference conversions are attempted.
5130 * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
5131 * @param type the return type of the desired method handle
5132 * @param value the value to return
5133 * @return a method handle of the given return type and no arguments, which always returns the given value
5134 * @throws NullPointerException if the {@code type} argument is null
5135 * @throws ClassCastException if the value cannot be converted to the required return type
5136 * @throws IllegalArgumentException if the given type is {@code void.class}
5137 */
5138 public static MethodHandle constant(Class<?> type, Object value) {
5139 if (type.isPrimitive()) {
5140 if (type == void.class)
5141 throw newIllegalArgumentException("void type");
5142 Wrapper w = Wrapper.forPrimitiveType(type);
5143 value = w.convert(value, type);
5144 if (w.zero().equals(value))
5145 return zero(w, type);
5146 return insertArguments(identity(type), 0, value);
5147 } else {
5148 if (value == null)
5149 return zero(Wrapper.OBJECT, type);
5150 return identity(type).bindTo(value);
5151 }
5152 }
5153
5154 /**
5155 * Produces a method handle which returns its sole argument when invoked.
5156 * @param type the type of the sole parameter and return value of the desired method handle
5157 * @return a unary method handle which accepts and returns the given type
5158 * @throws NullPointerException if the argument is null
5159 * @throws IllegalArgumentException if the given type is {@code void.class}
5160 */
5161 public static MethodHandle identity(Class<?> type) {
5162 Wrapper btw = (type.isPrimitive() ? Wrapper.forPrimitiveType(type) : Wrapper.OBJECT);
5163 int pos = btw.ordinal();
5164 MethodHandle ident = IDENTITY_MHS[pos];
5165 if (ident == null) {
5166 ident = setCachedMethodHandle(IDENTITY_MHS, pos, makeIdentity(btw.primitiveType()));
5167 }
5168 if (ident.type().returnType() == type)
5169 return ident;
5170 // something like identity(Foo.class); do not bother to intern these
5171 assert (btw == Wrapper.OBJECT);
5172 return makeIdentity(type);
5173 }
5174
5175 /**
5176 * Produces a constant method handle of the requested return type which
5177 * returns the default value for that type every time it is invoked.
5178 * The resulting constant method handle will have no side effects.
5179 * <p>The returned method handle is equivalent to {@code empty(methodType(type))}.
5180 * It is also equivalent to {@code explicitCastArguments(constant(Object.class, null), methodType(type))},
5181 * since {@code explicitCastArguments} converts {@code null} to default values.
5182 * @param type the expected return type of the desired method handle
5183 * @return a constant method handle that takes no arguments
5184 * and returns the default value of the given type (or void, if the type is void)
5185 * @throws NullPointerException if the argument is null
5186 * @see MethodHandles#constant
5187 * @see MethodHandles#empty
5188 * @see MethodHandles#explicitCastArguments
5189 * @since 9
5190 */
5191 public static MethodHandle zero(Class<?> type) {
5192 Objects.requireNonNull(type);
5193 if (type.isPrimitive()) {
5194 return zero(Wrapper.forPrimitiveType(type), type);
5195 } else {
5196 return zero(Wrapper.OBJECT, type);
5197 }
5198 }
5199
5200 private static MethodHandle identityOrVoid(Class<?> type) {
5201 return type == void.class ? zero(type) : identity(type);
5202 }
5203
5204 /**
5205 * Produces a method handle of the requested type which ignores any arguments, does nothing,
5206 * and returns a suitable default depending on the return type.
5207 * That is, it returns a zero primitive value, a {@code null}, or {@code void}.
5208 * <p>The returned method handle is equivalent to
5209 * {@code dropArguments(zero(type.returnType()), 0, type.parameterList())}.
5210 *
5211 * @apiNote Given a predicate and target, a useful "if-then" construct can be produced as
5212 * {@code guardWithTest(pred, target, empty(target.type())}.
5213 * @param type the type of the desired method handle
5214 * @return a constant method handle of the given type, which returns a default value of the given return type
5215 * @throws NullPointerException if the argument is null
5216 * @see MethodHandles#zero
5217 * @see MethodHandles#constant
5218 * @since 9
5219 */
5220 public static MethodHandle empty(MethodType type) {
5221 Objects.requireNonNull(type);
5222 return dropArgumentsTrusted(zero(type.returnType()), 0, type.ptypes());
5223 }
5224
5225 private static final MethodHandle[] IDENTITY_MHS = new MethodHandle[Wrapper.COUNT];
5226 private static MethodHandle makeIdentity(Class<?> ptype) {
5227 MethodType mtype = methodType(ptype, ptype);
5228 LambdaForm lform = LambdaForm.identityForm(BasicType.basicType(ptype));
5229 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.IDENTITY);
5230 }
5231
5232 private static MethodHandle zero(Wrapper btw, Class<?> rtype) {
5233 int pos = btw.ordinal();
5234 MethodHandle zero = ZERO_MHS[pos];
5235 if (zero == null) {
5236 zero = setCachedMethodHandle(ZERO_MHS, pos, makeZero(btw.primitiveType()));
5237 }
5238 if (zero.type().returnType() == rtype)
5239 return zero;
5240 assert(btw == Wrapper.OBJECT);
5241 return makeZero(rtype);
5242 }
5243 private static final MethodHandle[] ZERO_MHS = new MethodHandle[Wrapper.COUNT];
5244 private static MethodHandle makeZero(Class<?> rtype) {
5245 MethodType mtype = methodType(rtype);
5246 LambdaForm lform = LambdaForm.zeroForm(BasicType.basicType(rtype));
5247 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.ZERO);
5248 }
5249
5250 private static synchronized MethodHandle setCachedMethodHandle(MethodHandle[] cache, int pos, MethodHandle value) {
5251 // Simulate a CAS, to avoid racy duplication of results.
5252 MethodHandle prev = cache[pos];
5253 if (prev != null) return prev;
5254 return cache[pos] = value;
5255 }
5256
5257 /**
5258 * Provides a target method handle with one or more <em>bound arguments</em>
5259 * in advance of the method handle's invocation.
5260 * The formal parameters to the target corresponding to the bound
5261 * arguments are called <em>bound parameters</em>.
5262 * Returns a new method handle which saves away the bound arguments.
5263 * When it is invoked, it receives arguments for any non-bound parameters,
5264 * binds the saved arguments to their corresponding parameters,
5265 * and calls the original target.
5266 * <p>
5267 * The type of the new method handle will drop the types for the bound
5268 * parameters from the original target type, since the new method handle
5269 * will no longer require those arguments to be supplied by its callers.
5270 * <p>
5271 * Each given argument object must match the corresponding bound parameter type.
5272 * If a bound parameter type is a primitive, the argument object
5273 * must be a wrapper, and will be unboxed to produce the primitive value.
5274 * <p>
5275 * The {@code pos} argument selects which parameters are to be bound.
5276 * It may range between zero and <i>N-L</i> (inclusively),
5277 * where <i>N</i> is the arity of the target method handle
5278 * and <i>L</i> is the length of the values array.
5279 * <p>
5280 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5281 * variable-arity method handle}, even if the original target method handle was.
5282 * @param target the method handle to invoke after the argument is inserted
5283 * @param pos where to insert the argument (zero for the first)
5284 * @param values the series of arguments to insert
5285 * @return a method handle which inserts an additional argument,
5286 * before calling the original method handle
5287 * @throws NullPointerException if the target or the {@code values} array is null
5288 * @throws IllegalArgumentException if {@code pos} is less than {@code 0} or greater than
5289 * {@code N - L} where {@code N} is the arity of the target method handle and {@code L}
5290 * is the length of the values array.
5291 * @throws ClassCastException if an argument does not match the corresponding bound parameter
5292 * type.
5293 * @see MethodHandle#bindTo
5294 */
5295 public static MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
5296 int insCount = values.length;
5297 Class<?>[] ptypes = insertArgumentsChecks(target, insCount, pos);
5298 if (insCount == 0) return target;
5299 BoundMethodHandle result = target.rebind();
5300 for (int i = 0; i < insCount; i++) {
5301 Object value = values[i];
5302 Class<?> ptype = ptypes[pos+i];
5303 if (ptype.isPrimitive()) {
5304 result = insertArgumentPrimitive(result, pos, ptype, value);
5305 } else {
5306 value = ptype.cast(value); // throw CCE if needed
5307 result = result.bindArgumentL(pos, value);
5308 }
5309 }
5310 return result;
5311 }
5312
5313 private static BoundMethodHandle insertArgumentPrimitive(BoundMethodHandle result, int pos,
5314 Class<?> ptype, Object value) {
5315 Wrapper w = Wrapper.forPrimitiveType(ptype);
5316 // perform unboxing and/or primitive conversion
5317 value = w.convert(value, ptype);
5318 return switch (w) {
5319 case INT -> result.bindArgumentI(pos, (int) value);
5320 case LONG -> result.bindArgumentJ(pos, (long) value);
5321 case FLOAT -> result.bindArgumentF(pos, (float) value);
5322 case DOUBLE -> result.bindArgumentD(pos, (double) value);
5323 default -> result.bindArgumentI(pos, ValueConversions.widenSubword(value));
5324 };
5325 }
5326
5327 private static Class<?>[] insertArgumentsChecks(MethodHandle target, int insCount, int pos) throws RuntimeException {
5328 MethodType oldType = target.type();
5329 int outargs = oldType.parameterCount();
5330 int inargs = outargs - insCount;
5331 if (inargs < 0)
5332 throw newIllegalArgumentException("too many values to insert");
5333 if (pos < 0 || pos > inargs)
5334 throw newIllegalArgumentException("no argument type to append");
5335 return oldType.ptypes();
5336 }
5337
5338 /**
5339 * Produces a method handle which will discard some dummy arguments
5340 * before calling some other specified <i>target</i> method handle.
5341 * The type of the new method handle will be the same as the target's type,
5342 * except it will also include the dummy argument types,
5343 * at some given position.
5344 * <p>
5345 * The {@code pos} argument may range between zero and <i>N</i>,
5346 * where <i>N</i> is the arity of the target.
5347 * If {@code pos} is zero, the dummy arguments will precede
5348 * the target's real arguments; if {@code pos} is <i>N</i>
5349 * they will come after.
5350 * <p>
5351 * <b>Example:</b>
5352 * {@snippet lang="java" :
5353 import static java.lang.invoke.MethodHandles.*;
5354 import static java.lang.invoke.MethodType.*;
5355 ...
5356 MethodHandle cat = lookup().findVirtual(String.class,
5357 "concat", methodType(String.class, String.class));
5358 assertEquals("xy", (String) cat.invokeExact("x", "y"));
5359 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
5360 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
5361 assertEquals(bigType, d0.type());
5362 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
5363 * }
5364 * <p>
5365 * This method is also equivalent to the following code:
5366 * <blockquote><pre>
5367 * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))}
5368 * </pre></blockquote>
5369 * @param target the method handle to invoke after the arguments are dropped
5370 * @param pos position of first argument to drop (zero for the leftmost)
5371 * @param valueTypes the type(s) of the argument(s) to drop
5372 * @return a method handle which drops arguments of the given types,
5373 * before calling the original method handle
5374 * @throws NullPointerException if the target is null,
5375 * or if the {@code valueTypes} list or any of its elements is null
5376 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
5377 * or if {@code pos} is negative or greater than the arity of the target,
5378 * or if the new method handle's type would have too many parameters
5379 */
5380 public static MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) {
5381 return dropArgumentsTrusted(target, pos, valueTypes.toArray(new Class<?>[0]).clone());
5382 }
5383
5384 static MethodHandle dropArgumentsTrusted(MethodHandle target, int pos, Class<?>[] valueTypes) {
5385 MethodType oldType = target.type(); // get NPE
5386 int dropped = dropArgumentChecks(oldType, pos, valueTypes);
5387 MethodType newType = oldType.insertParameterTypes(pos, valueTypes);
5388 if (dropped == 0) return target;
5389 BoundMethodHandle result = target.rebind();
5390 LambdaForm lform = result.form;
5391 int insertFormArg = 1 + pos;
5392 for (Class<?> ptype : valueTypes) {
5393 lform = lform.editor().addArgumentForm(insertFormArg++, BasicType.basicType(ptype));
5394 }
5395 result = result.copyWith(newType, lform);
5396 return result;
5397 }
5398
5399 private static int dropArgumentChecks(MethodType oldType, int pos, Class<?>[] valueTypes) {
5400 int dropped = valueTypes.length;
5401 MethodType.checkSlotCount(dropped);
5402 int outargs = oldType.parameterCount();
5403 int inargs = outargs + dropped;
5404 if (pos < 0 || pos > outargs)
5405 throw newIllegalArgumentException("no argument type to remove"
5406 + Arrays.asList(oldType, pos, valueTypes, inargs, outargs)
5407 );
5408 return dropped;
5409 }
5410
5411 /**
5412 * Produces a method handle which will discard some dummy arguments
5413 * before calling some other specified <i>target</i> method handle.
5414 * The type of the new method handle will be the same as the target's type,
5415 * except it will also include the dummy argument types,
5416 * at some given position.
5417 * <p>
5418 * The {@code pos} argument may range between zero and <i>N</i>,
5419 * where <i>N</i> is the arity of the target.
5420 * If {@code pos} is zero, the dummy arguments will precede
5421 * the target's real arguments; if {@code pos} is <i>N</i>
5422 * they will come after.
5423 * @apiNote
5424 * {@snippet lang="java" :
5425 import static java.lang.invoke.MethodHandles.*;
5426 import static java.lang.invoke.MethodType.*;
5427 ...
5428 MethodHandle cat = lookup().findVirtual(String.class,
5429 "concat", methodType(String.class, String.class));
5430 assertEquals("xy", (String) cat.invokeExact("x", "y"));
5431 MethodHandle d0 = dropArguments(cat, 0, String.class);
5432 assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
5433 MethodHandle d1 = dropArguments(cat, 1, String.class);
5434 assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
5435 MethodHandle d2 = dropArguments(cat, 2, String.class);
5436 assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
5437 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
5438 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
5439 * }
5440 * <p>
5441 * This method is also equivalent to the following code:
5442 * <blockquote><pre>
5443 * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))}
5444 * </pre></blockquote>
5445 * @param target the method handle to invoke after the arguments are dropped
5446 * @param pos position of first argument to drop (zero for the leftmost)
5447 * @param valueTypes the type(s) of the argument(s) to drop
5448 * @return a method handle which drops arguments of the given types,
5449 * before calling the original method handle
5450 * @throws NullPointerException if the target is null,
5451 * or if the {@code valueTypes} array or any of its elements is null
5452 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
5453 * or if {@code pos} is negative or greater than the arity of the target,
5454 * or if the new method handle's type would have
5455 * <a href="MethodHandle.html#maxarity">too many parameters</a>
5456 */
5457 public static MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
5458 return dropArgumentsTrusted(target, pos, valueTypes.clone());
5459 }
5460
5461 /* Convenience overloads for trusting internal low-arity call-sites */
5462 static MethodHandle dropArguments(MethodHandle target, int pos, Class<?> valueType1) {
5463 return dropArgumentsTrusted(target, pos, new Class<?>[] { valueType1 });
5464 }
5465 static MethodHandle dropArguments(MethodHandle target, int pos, Class<?> valueType1, Class<?> valueType2) {
5466 return dropArgumentsTrusted(target, pos, new Class<?>[] { valueType1, valueType2 });
5467 }
5468
5469 // private version which allows caller some freedom with error handling
5470 private static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, Class<?>[] newTypes, int pos,
5471 boolean nullOnFailure) {
5472 Class<?>[] oldTypes = target.type().ptypes();
5473 int match = oldTypes.length;
5474 if (skip != 0) {
5475 if (skip < 0 || skip > match) {
5476 throw newIllegalArgumentException("illegal skip", skip, target);
5477 }
5478 oldTypes = Arrays.copyOfRange(oldTypes, skip, match);
5479 match -= skip;
5480 }
5481 Class<?>[] addTypes = newTypes;
5482 int add = addTypes.length;
5483 if (pos != 0) {
5484 if (pos < 0 || pos > add) {
5485 throw newIllegalArgumentException("illegal pos", pos, Arrays.toString(newTypes));
5486 }
5487 addTypes = Arrays.copyOfRange(addTypes, pos, add);
5488 add -= pos;
5489 assert(addTypes.length == add);
5490 }
5491 // Do not add types which already match the existing arguments.
5492 if (match > add || !Arrays.equals(oldTypes, 0, oldTypes.length, addTypes, 0, match)) {
5493 if (nullOnFailure) {
5494 return null;
5495 }
5496 throw newIllegalArgumentException("argument lists do not match",
5497 Arrays.toString(oldTypes), Arrays.toString(newTypes));
5498 }
5499 addTypes = Arrays.copyOfRange(addTypes, match, add);
5500 add -= match;
5501 assert(addTypes.length == add);
5502 // newTypes: ( P*[pos], M*[match], A*[add] )
5503 // target: ( S*[skip], M*[match] )
5504 MethodHandle adapter = target;
5505 if (add > 0) {
5506 adapter = dropArgumentsTrusted(adapter, skip+ match, addTypes);
5507 }
5508 // adapter: (S*[skip], M*[match], A*[add] )
5509 if (pos > 0) {
5510 adapter = dropArgumentsTrusted(adapter, skip, Arrays.copyOfRange(newTypes, 0, pos));
5511 }
5512 // adapter: (S*[skip], P*[pos], M*[match], A*[add] )
5513 return adapter;
5514 }
5515
5516 /**
5517 * Adapts a target method handle to match the given parameter type list. If necessary, adds dummy arguments. Some
5518 * leading parameters can be skipped before matching begins. The remaining types in the {@code target}'s parameter
5519 * type list must be a sub-list of the {@code newTypes} type list at the starting position {@code pos}. The
5520 * resulting handle will have the target handle's parameter type list, with any non-matching parameter types (before
5521 * or after the matching sub-list) inserted in corresponding positions of the target's original parameters, as if by
5522 * {@link #dropArguments(MethodHandle, int, Class[])}.
5523 * <p>
5524 * The resulting handle will have the same return type as the target handle.
5525 * <p>
5526 * In more formal terms, assume these two type lists:<ul>
5527 * <li>The target handle has the parameter type list {@code S..., M...}, with as many types in {@code S} as
5528 * indicated by {@code skip}. The {@code M} types are those that are supposed to match part of the given type list,
5529 * {@code newTypes}.
5530 * <li>The {@code newTypes} list contains types {@code P..., M..., A...}, with as many types in {@code P} as
5531 * indicated by {@code pos}. The {@code M} types are precisely those that the {@code M} types in the target handle's
5532 * parameter type list are supposed to match. The types in {@code A} are additional types found after the matching
5533 * sub-list.
5534 * </ul>
5535 * Given these assumptions, the result of an invocation of {@code dropArgumentsToMatch} will have the parameter type
5536 * list {@code S..., P..., M..., A...}, with the {@code P} and {@code A} types inserted as if by
5537 * {@link #dropArguments(MethodHandle, int, Class[])}.
5538 *
5539 * @apiNote
5540 * Two method handles whose argument lists are "effectively identical" (i.e., identical in a common prefix) may be
5541 * mutually converted to a common type by two calls to {@code dropArgumentsToMatch}, as follows:
5542 * {@snippet lang="java" :
5543 import static java.lang.invoke.MethodHandles.*;
5544 import static java.lang.invoke.MethodType.*;
5545 ...
5546 ...
5547 MethodHandle h0 = constant(boolean.class, true);
5548 MethodHandle h1 = lookup().findVirtual(String.class, "concat", methodType(String.class, String.class));
5549 MethodType bigType = h1.type().insertParameterTypes(1, String.class, int.class);
5550 MethodHandle h2 = dropArguments(h1, 0, bigType.parameterList());
5551 if (h1.type().parameterCount() < h2.type().parameterCount())
5552 h1 = dropArgumentsToMatch(h1, 0, h2.type().parameterList(), 0); // lengthen h1
5553 else
5554 h2 = dropArgumentsToMatch(h2, 0, h1.type().parameterList(), 0); // lengthen h2
5555 MethodHandle h3 = guardWithTest(h0, h1, h2);
5556 assertEquals("xy", h3.invoke("x", "y", 1, "a", "b", "c"));
5557 * }
5558 * @param target the method handle to adapt
5559 * @param skip number of targets parameters to disregard (they will be unchanged)
5560 * @param newTypes the list of types to match {@code target}'s parameter type list to
5561 * @param pos place in {@code newTypes} where the non-skipped target parameters must occur
5562 * @return a possibly adapted method handle
5563 * @throws NullPointerException if either argument is null
5564 * @throws IllegalArgumentException if any element of {@code newTypes} is {@code void.class},
5565 * or if {@code skip} is negative or greater than the arity of the target,
5566 * or if {@code pos} is negative or greater than the newTypes list size,
5567 * or if {@code newTypes} does not contain the {@code target}'s non-skipped parameter types at position
5568 * {@code pos}.
5569 * @since 9
5570 */
5571 public static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos) {
5572 Objects.requireNonNull(target);
5573 Objects.requireNonNull(newTypes);
5574 return dropArgumentsToMatch(target, skip, newTypes.toArray(new Class<?>[0]).clone(), pos, false);
5575 }
5576
5577 /**
5578 * Drop the return value of the target handle (if any).
5579 * The returned method handle will have a {@code void} return type.
5580 *
5581 * @param target the method handle to adapt
5582 * @return a possibly adapted method handle
5583 * @throws NullPointerException if {@code target} is null
5584 * @since 16
5585 */
5586 public static MethodHandle dropReturn(MethodHandle target) {
5587 Objects.requireNonNull(target);
5588 MethodType oldType = target.type();
5589 Class<?> oldReturnType = oldType.returnType();
5590 if (oldReturnType == void.class)
5591 return target;
5592 MethodType newType = oldType.changeReturnType(void.class);
5593 BoundMethodHandle result = target.rebind();
5594 LambdaForm lform = result.editor().filterReturnForm(V_TYPE, true);
5595 result = result.copyWith(newType, lform);
5596 return result;
5597 }
5598
5599 /**
5600 * Adapts a target method handle by pre-processing
5601 * one or more of its arguments, each with its own unary filter function,
5602 * and then calling the target with each pre-processed argument
5603 * replaced by the result of its corresponding filter function.
5604 * <p>
5605 * The pre-processing is performed by one or more method handles,
5606 * specified in the elements of the {@code filters} array.
5607 * The first element of the filter array corresponds to the {@code pos}
5608 * argument of the target, and so on in sequence.
5609 * The filter functions are invoked in left to right order.
5610 * <p>
5611 * Null arguments in the array are treated as identity functions,
5612 * and the corresponding arguments left unchanged.
5613 * (If there are no non-null elements in the array, the original target is returned.)
5614 * Each filter is applied to the corresponding argument of the adapter.
5615 * <p>
5616 * If a filter {@code F} applies to the {@code N}th argument of
5617 * the target, then {@code F} must be a method handle which
5618 * takes exactly one argument. The type of {@code F}'s sole argument
5619 * replaces the corresponding argument type of the target
5620 * in the resulting adapted method handle.
5621 * The return type of {@code F} must be identical to the corresponding
5622 * parameter type of the target.
5623 * <p>
5624 * It is an error if there are elements of {@code filters}
5625 * (null or not)
5626 * which do not correspond to argument positions in the target.
5627 * <p><b>Example:</b>
5628 * {@snippet lang="java" :
5629 import static java.lang.invoke.MethodHandles.*;
5630 import static java.lang.invoke.MethodType.*;
5631 ...
5632 MethodHandle cat = lookup().findVirtual(String.class,
5633 "concat", methodType(String.class, String.class));
5634 MethodHandle upcase = lookup().findVirtual(String.class,
5635 "toUpperCase", methodType(String.class));
5636 assertEquals("xy", (String) cat.invokeExact("x", "y"));
5637 MethodHandle f0 = filterArguments(cat, 0, upcase);
5638 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
5639 MethodHandle f1 = filterArguments(cat, 1, upcase);
5640 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
5641 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
5642 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
5643 * }
5644 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
5645 * denotes the return type of both the {@code target} and resulting adapter.
5646 * {@code P}/{@code p} and {@code B}/{@code b} represent the types and values
5647 * of the parameters and arguments that precede and follow the filter position
5648 * {@code pos}, respectively. {@code A[i]}/{@code a[i]} stand for the types and
5649 * values of the filtered parameters and arguments; they also represent the
5650 * return types of the {@code filter[i]} handles. The latter accept arguments
5651 * {@code v[i]} of type {@code V[i]}, which also appear in the signature of
5652 * the resulting adapter.
5653 * {@snippet lang="java" :
5654 * T target(P... p, A[i]... a[i], B... b);
5655 * A[i] filter[i](V[i]);
5656 * T adapter(P... p, V[i]... v[i], B... b) {
5657 * return target(p..., filter[i](v[i])..., b...);
5658 * }
5659 * }
5660 * <p>
5661 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5662 * variable-arity method handle}, even if the original target method handle was.
5663 *
5664 * @param target the method handle to invoke after arguments are filtered
5665 * @param pos the position of the first argument to filter
5666 * @param filters method handles to call initially on filtered arguments
5667 * @return method handle which incorporates the specified argument filtering logic
5668 * @throws NullPointerException if the target is null
5669 * or if the {@code filters} array is null
5670 * @throws IllegalArgumentException if a non-null element of {@code filters}
5671 * does not match a corresponding argument type of target as described above,
5672 * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()},
5673 * or if the resulting method handle's type would have
5674 * <a href="MethodHandle.html#maxarity">too many parameters</a>
5675 */
5676 public static MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
5677 // In method types arguments start at index 0, while the LF
5678 // editor have the MH receiver at position 0 - adjust appropriately.
5679 final int MH_RECEIVER_OFFSET = 1;
5680 filterArgumentsCheckArity(target, pos, filters);
5681 MethodHandle adapter = target;
5682
5683 // keep track of currently matched filters, as to optimize repeated filters
5684 int index = 0;
5685 int[] positions = new int[filters.length];
5686 MethodHandle filter = null;
5687
5688 // process filters in reverse order so that the invocation of
5689 // the resulting adapter will invoke the filters in left-to-right order
5690 for (int i = filters.length - 1; i >= 0; --i) {
5691 MethodHandle newFilter = filters[i];
5692 if (newFilter == null) continue; // ignore null elements of filters
5693
5694 // flush changes on update
5695 if (filter != newFilter) {
5696 if (filter != null) {
5697 if (index > 1) {
5698 adapter = filterRepeatedArgument(adapter, filter, Arrays.copyOf(positions, index));
5699 } else {
5700 adapter = filterArgument(adapter, positions[0] - 1, filter);
5701 }
5702 }
5703 filter = newFilter;
5704 index = 0;
5705 }
5706
5707 filterArgumentChecks(target, pos + i, newFilter);
5708 positions[index++] = pos + i + MH_RECEIVER_OFFSET;
5709 }
5710 if (index > 1) {
5711 adapter = filterRepeatedArgument(adapter, filter, Arrays.copyOf(positions, index));
5712 } else if (index == 1) {
5713 adapter = filterArgument(adapter, positions[0] - 1, filter);
5714 }
5715 return adapter;
5716 }
5717
5718 private static MethodHandle filterRepeatedArgument(MethodHandle adapter, MethodHandle filter, int[] positions) {
5719 MethodType targetType = adapter.type();
5720 MethodType filterType = filter.type();
5721 BoundMethodHandle result = adapter.rebind();
5722 Class<?> newParamType = filterType.parameterType(0);
5723
5724 Class<?>[] ptypes = targetType.ptypes().clone();
5725 for (int pos : positions) {
5726 ptypes[pos - 1] = newParamType;
5727 }
5728 MethodType newType = MethodType.methodType(targetType.rtype(), ptypes, true);
5729
5730 LambdaForm lform = result.editor().filterRepeatedArgumentForm(BasicType.basicType(newParamType), positions);
5731 return result.copyWithExtendL(newType, lform, filter);
5732 }
5733
5734 /*non-public*/
5735 static MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
5736 filterArgumentChecks(target, pos, filter);
5737 MethodType targetType = target.type();
5738 MethodType filterType = filter.type();
5739 BoundMethodHandle result = target.rebind();
5740 Class<?> newParamType = filterType.parameterType(0);
5741 LambdaForm lform = result.editor().filterArgumentForm(1 + pos, BasicType.basicType(newParamType));
5742 MethodType newType = targetType.changeParameterType(pos, newParamType);
5743 result = result.copyWithExtendL(newType, lform, filter);
5744 return result;
5745 }
5746
5747 private static void filterArgumentsCheckArity(MethodHandle target, int pos, MethodHandle[] filters) {
5748 MethodType targetType = target.type();
5749 int maxPos = targetType.parameterCount();
5750 if (pos + filters.length > maxPos)
5751 throw newIllegalArgumentException("too many filters");
5752 }
5753
5754 private static void filterArgumentChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
5755 MethodType targetType = target.type();
5756 MethodType filterType = filter.type();
5757 if (filterType.parameterCount() != 1
5758 || filterType.returnType() != targetType.parameterType(pos))
5759 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
5760 }
5761
5762 /**
5763 * Adapts a target method handle by pre-processing
5764 * a sub-sequence of its arguments with a filter (another method handle).
5765 * The pre-processed arguments are replaced by the result (if any) of the
5766 * filter function.
5767 * The target is then called on the modified (usually shortened) argument list.
5768 * <p>
5769 * If the filter returns a value, the target must accept that value as
5770 * its argument in position {@code pos}, preceded and/or followed by
5771 * any arguments not passed to the filter.
5772 * If the filter returns void, the target must accept all arguments
5773 * not passed to the filter.
5774 * No arguments are reordered, and a result returned from the filter
5775 * replaces (in order) the whole subsequence of arguments originally
5776 * passed to the adapter.
5777 * <p>
5778 * The argument types (if any) of the filter
5779 * replace zero or one argument types of the target, at position {@code pos},
5780 * in the resulting adapted method handle.
5781 * The return type of the filter (if any) must be identical to the
5782 * argument type of the target at position {@code pos}, and that target argument
5783 * is supplied by the return value of the filter.
5784 * <p>
5785 * In all cases, {@code pos} must be greater than or equal to zero, and
5786 * {@code pos} must also be less than or equal to the target's arity.
5787 * <p><b>Example:</b>
5788 * {@snippet lang="java" :
5789 import static java.lang.invoke.MethodHandles.*;
5790 import static java.lang.invoke.MethodType.*;
5791 ...
5792 MethodHandle deepToString = publicLookup()
5793 .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
5794
5795 MethodHandle ts1 = deepToString.asCollector(String[].class, 1);
5796 assertEquals("[strange]", (String) ts1.invokeExact("strange"));
5797
5798 MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
5799 assertEquals("[up, down]", (String) ts2.invokeExact("up", "down"));
5800
5801 MethodHandle ts3 = deepToString.asCollector(String[].class, 3);
5802 MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2);
5803 assertEquals("[top, [up, down], strange]",
5804 (String) ts3_ts2.invokeExact("top", "up", "down", "strange"));
5805
5806 MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1);
5807 assertEquals("[top, [up, down], [strange]]",
5808 (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange"));
5809
5810 MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3);
5811 assertEquals("[top, [[up, down, strange], charm], bottom]",
5812 (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom"));
5813 * }
5814 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
5815 * represents the return type of the {@code target} and resulting adapter.
5816 * {@code V}/{@code v} stand for the return type and value of the
5817 * {@code filter}, which are also found in the signature and arguments of
5818 * the {@code target}, respectively, unless {@code V} is {@code void}.
5819 * {@code A}/{@code a} and {@code C}/{@code c} represent the parameter types
5820 * and values preceding and following the collection position, {@code pos},
5821 * in the {@code target}'s signature. They also turn up in the resulting
5822 * adapter's signature and arguments, where they surround
5823 * {@code B}/{@code b}, which represent the parameter types and arguments
5824 * to the {@code filter} (if any).
5825 * {@snippet lang="java" :
5826 * T target(A...,V,C...);
5827 * V filter(B...);
5828 * T adapter(A... a,B... b,C... c) {
5829 * V v = filter(b...);
5830 * return target(a...,v,c...);
5831 * }
5832 * // and if the filter has no arguments:
5833 * T target2(A...,V,C...);
5834 * V filter2();
5835 * T adapter2(A... a,C... c) {
5836 * V v = filter2();
5837 * return target2(a...,v,c...);
5838 * }
5839 * // and if the filter has a void return:
5840 * T target3(A...,C...);
5841 * void filter3(B...);
5842 * T adapter3(A... a,B... b,C... c) {
5843 * filter3(b...);
5844 * return target3(a...,c...);
5845 * }
5846 * }
5847 * <p>
5848 * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to
5849 * one which first "folds" the affected arguments, and then drops them, in separate
5850 * steps as follows:
5851 * {@snippet lang="java" :
5852 * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2
5853 * mh = MethodHandles.foldArguments(mh, coll); //step 1
5854 * }
5855 * If the target method handle consumes no arguments besides than the result
5856 * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)}
5857 * is equivalent to {@code filterReturnValue(coll, mh)}.
5858 * If the filter method handle {@code coll} consumes one argument and produces
5859 * a non-void result, then {@code collectArguments(mh, N, coll)}
5860 * is equivalent to {@code filterArguments(mh, N, coll)}.
5861 * Other equivalences are possible but would require argument permutation.
5862 * <p>
5863 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5864 * variable-arity method handle}, even if the original target method handle was.
5865 *
5866 * @param target the method handle to invoke after filtering the subsequence of arguments
5867 * @param pos the position of the first adapter argument to pass to the filter,
5868 * and/or the target argument which receives the result of the filter
5869 * @param filter method handle to call on the subsequence of arguments
5870 * @return method handle which incorporates the specified argument subsequence filtering logic
5871 * @throws NullPointerException if either argument is null
5872 * @throws IllegalArgumentException if the return type of {@code filter}
5873 * is non-void and is not the same as the {@code pos} argument of the target,
5874 * or if {@code pos} is not between 0 and the target's arity, inclusive,
5875 * or if the resulting method handle's type would have
5876 * <a href="MethodHandle.html#maxarity">too many parameters</a>
5877 * @see MethodHandles#foldArguments
5878 * @see MethodHandles#filterArguments
5879 * @see MethodHandles#filterReturnValue
5880 */
5881 public static MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) {
5882 MethodType newType = collectArgumentsChecks(target, pos, filter);
5883 MethodType collectorType = filter.type();
5884 BoundMethodHandle result = target.rebind();
5885 LambdaForm lform = result.editor().collectArgumentsForm(1 + pos, collectorType.basicType());
5886 return result.copyWithExtendL(newType, lform, filter);
5887 }
5888
5889 private static MethodType collectArgumentsChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
5890 MethodType targetType = target.type();
5891 MethodType filterType = filter.type();
5892 Class<?> rtype = filterType.returnType();
5893 Class<?>[] filterArgs = filterType.ptypes();
5894 if (pos < 0 || (rtype == void.class && pos > targetType.parameterCount()) ||
5895 (rtype != void.class && pos >= targetType.parameterCount())) {
5896 throw newIllegalArgumentException("position is out of range for target", target, pos);
5897 }
5898 if (rtype == void.class) {
5899 return targetType.insertParameterTypes(pos, filterArgs);
5900 }
5901 if (rtype != targetType.parameterType(pos)) {
5902 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
5903 }
5904 return targetType.dropParameterTypes(pos, pos + 1).insertParameterTypes(pos, filterArgs);
5905 }
5906
5907 /**
5908 * Adapts a target method handle by post-processing
5909 * its return value (if any) with a filter (another method handle).
5910 * The result of the filter is returned from the adapter.
5911 * <p>
5912 * If the target returns a value, the filter must accept that value as
5913 * its only argument.
5914 * If the target returns void, the filter must accept no arguments.
5915 * <p>
5916 * The return type of the filter
5917 * replaces the return type of the target
5918 * in the resulting adapted method handle.
5919 * The argument type of the filter (if any) must be identical to the
5920 * return type of the target.
5921 * <p><b>Example:</b>
5922 * {@snippet lang="java" :
5923 import static java.lang.invoke.MethodHandles.*;
5924 import static java.lang.invoke.MethodType.*;
5925 ...
5926 MethodHandle cat = lookup().findVirtual(String.class,
5927 "concat", methodType(String.class, String.class));
5928 MethodHandle length = lookup().findVirtual(String.class,
5929 "length", methodType(int.class));
5930 System.out.println((String) cat.invokeExact("x", "y")); // xy
5931 MethodHandle f0 = filterReturnValue(cat, length);
5932 System.out.println((int) f0.invokeExact("x", "y")); // 2
5933 * }
5934 * <p>Here is pseudocode for the resulting adapter. In the code,
5935 * {@code T}/{@code t} represent the result type and value of the
5936 * {@code target}; {@code V}, the result type of the {@code filter}; and
5937 * {@code A}/{@code a}, the types and values of the parameters and arguments
5938 * of the {@code target} as well as the resulting adapter.
5939 * {@snippet lang="java" :
5940 * T target(A...);
5941 * V filter(T);
5942 * V adapter(A... a) {
5943 * T t = target(a...);
5944 * return filter(t);
5945 * }
5946 * // and if the target has a void return:
5947 * void target2(A...);
5948 * V filter2();
5949 * V adapter2(A... a) {
5950 * target2(a...);
5951 * return filter2();
5952 * }
5953 * // and if the filter has a void return:
5954 * T target3(A...);
5955 * void filter3(V);
5956 * void adapter3(A... a) {
5957 * T t = target3(a...);
5958 * filter3(t);
5959 * }
5960 * }
5961 * <p>
5962 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5963 * variable-arity method handle}, even if the original target method handle was.
5964 * @param target the method handle to invoke before filtering the return value
5965 * @param filter method handle to call on the return value
5966 * @return method handle which incorporates the specified return value filtering logic
5967 * @throws NullPointerException if either argument is null
5968 * @throws IllegalArgumentException if the argument list of {@code filter}
5969 * does not match the return type of target as described above
5970 */
5971 public static MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
5972 MethodType targetType = target.type();
5973 MethodType filterType = filter.type();
5974 filterReturnValueChecks(targetType, filterType);
5975 BoundMethodHandle result = target.rebind();
5976 BasicType rtype = BasicType.basicType(filterType.returnType());
5977 LambdaForm lform = result.editor().filterReturnForm(rtype, false);
5978 MethodType newType = targetType.changeReturnType(filterType.returnType());
5979 result = result.copyWithExtendL(newType, lform, filter);
5980 return result;
5981 }
5982
5983 private static void filterReturnValueChecks(MethodType targetType, MethodType filterType) throws RuntimeException {
5984 Class<?> rtype = targetType.returnType();
5985 int filterValues = filterType.parameterCount();
5986 if (filterValues == 0
5987 ? (rtype != void.class)
5988 : (rtype != filterType.parameterType(0) || filterValues != 1))
5989 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
5990 }
5991
5992 /**
5993 * Filter the return value of a target method handle with a filter function. The filter function is
5994 * applied to the return value of the original handle; if the filter specifies more than one parameters,
5995 * then any remaining parameter is appended to the adapter handle. In other words, the adaptation works
5996 * as follows:
5997 * {@snippet lang="java" :
5998 * T target(A...)
5999 * V filter(B... , T)
6000 * V adapter(A... a, B... b) {
6001 * T t = target(a...);
6002 * return filter(b..., t);
6003 * }
6004 * }
6005 * <p>
6006 * If the filter handle is a unary function, then this method behaves like {@link #filterReturnValue(MethodHandle, MethodHandle)}.
6007 *
6008 * @param target the target method handle
6009 * @param filter the filter method handle
6010 * @return the adapter method handle
6011 */
6012 /* package */ static MethodHandle collectReturnValue(MethodHandle target, MethodHandle filter) {
6013 MethodType targetType = target.type();
6014 MethodType filterType = filter.type();
6015 BoundMethodHandle result = target.rebind();
6016 LambdaForm lform = result.editor().collectReturnValueForm(filterType.basicType());
6017 MethodType newType = targetType.changeReturnType(filterType.returnType());
6018 if (filterType.parameterCount() > 1) {
6019 for (int i = 0 ; i < filterType.parameterCount() - 1 ; i++) {
6020 newType = newType.appendParameterTypes(filterType.parameterType(i));
6021 }
6022 }
6023 result = result.copyWithExtendL(newType, lform, filter);
6024 return result;
6025 }
6026
6027 /**
6028 * Adapts a target method handle by pre-processing
6029 * some of its arguments, and then calling the target with
6030 * the result of the pre-processing, inserted into the original
6031 * sequence of arguments.
6032 * <p>
6033 * The pre-processing is performed by {@code combiner}, a second method handle.
6034 * Of the arguments passed to the adapter, the first {@code N} arguments
6035 * are copied to the combiner, which is then called.
6036 * (Here, {@code N} is defined as the parameter count of the combiner.)
6037 * After this, control passes to the target, with any result
6038 * from the combiner inserted before the original {@code N} incoming
6039 * arguments.
6040 * <p>
6041 * If the combiner returns a value, the first parameter type of the target
6042 * must be identical with the return type of the combiner, and the next
6043 * {@code N} parameter types of the target must exactly match the parameters
6044 * of the combiner.
6045 * <p>
6046 * If the combiner has a void return, no result will be inserted,
6047 * and the first {@code N} parameter types of the target
6048 * must exactly match the parameters of the combiner.
6049 * <p>
6050 * The resulting adapter is the same type as the target, except that the
6051 * first parameter type is dropped,
6052 * if it corresponds to the result of the combiner.
6053 * <p>
6054 * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
6055 * that either the combiner or the target does not wish to receive.
6056 * If some of the incoming arguments are destined only for the combiner,
6057 * consider using {@link MethodHandle#asCollector asCollector} instead, since those
6058 * arguments will not need to be live on the stack on entry to the
6059 * target.)
6060 * <p><b>Example:</b>
6061 * {@snippet lang="java" :
6062 import static java.lang.invoke.MethodHandles.*;
6063 import static java.lang.invoke.MethodType.*;
6064 ...
6065 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
6066 "println", methodType(void.class, String.class))
6067 .bindTo(System.out);
6068 MethodHandle cat = lookup().findVirtual(String.class,
6069 "concat", methodType(String.class, String.class));
6070 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
6071 MethodHandle catTrace = foldArguments(cat, trace);
6072 // also prints "boo":
6073 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
6074 * }
6075 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
6076 * represents the result type of the {@code target} and resulting adapter.
6077 * {@code V}/{@code v} represent the type and value of the parameter and argument
6078 * of {@code target} that precedes the folding position; {@code V} also is
6079 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
6080 * types and values of the {@code N} parameters and arguments at the folding
6081 * position. {@code B}/{@code b} represent the types and values of the
6082 * {@code target} parameters and arguments that follow the folded parameters
6083 * and arguments.
6084 * {@snippet lang="java" :
6085 * // there are N arguments in A...
6086 * T target(V, A[N]..., B...);
6087 * V combiner(A...);
6088 * T adapter(A... a, B... b) {
6089 * V v = combiner(a...);
6090 * return target(v, a..., b...);
6091 * }
6092 * // and if the combiner has a void return:
6093 * T target2(A[N]..., B...);
6094 * void combiner2(A...);
6095 * T adapter2(A... a, B... b) {
6096 * combiner2(a...);
6097 * return target2(a..., b...);
6098 * }
6099 * }
6100 * <p>
6101 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
6102 * variable-arity method handle}, even if the original target method handle was.
6103 * @param target the method handle to invoke after arguments are combined
6104 * @param combiner method handle to call initially on the incoming arguments
6105 * @return method handle which incorporates the specified argument folding logic
6106 * @throws NullPointerException if either argument is null
6107 * @throws IllegalArgumentException if {@code combiner}'s return type
6108 * is non-void and not the same as the first argument type of
6109 * the target, or if the initial {@code N} argument types
6110 * of the target
6111 * (skipping one matching the {@code combiner}'s return type)
6112 * are not identical with the argument types of {@code combiner}
6113 */
6114 public static MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
6115 return foldArguments(target, 0, combiner);
6116 }
6117
6118 /**
6119 * Adapts a target method handle by pre-processing some of its arguments, starting at a given position, and then
6120 * calling the target with the result of the pre-processing, inserted into the original sequence of arguments just
6121 * before the folded arguments.
6122 * <p>
6123 * This method is closely related to {@link #foldArguments(MethodHandle, MethodHandle)}, but allows to control the
6124 * position in the parameter list at which folding takes place. The argument controlling this, {@code pos}, is a
6125 * zero-based index. The aforementioned method {@link #foldArguments(MethodHandle, MethodHandle)} assumes position
6126 * 0.
6127 *
6128 * @apiNote Example:
6129 * {@snippet lang="java" :
6130 import static java.lang.invoke.MethodHandles.*;
6131 import static java.lang.invoke.MethodType.*;
6132 ...
6133 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
6134 "println", methodType(void.class, String.class))
6135 .bindTo(System.out);
6136 MethodHandle cat = lookup().findVirtual(String.class,
6137 "concat", methodType(String.class, String.class));
6138 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
6139 MethodHandle catTrace = foldArguments(cat, 1, trace);
6140 // also prints "jum":
6141 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
6142 * }
6143 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
6144 * represents the result type of the {@code target} and resulting adapter.
6145 * {@code V}/{@code v} represent the type and value of the parameter and argument
6146 * of {@code target} that precedes the folding position; {@code V} also is
6147 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
6148 * types and values of the {@code N} parameters and arguments at the folding
6149 * position. {@code Z}/{@code z} and {@code B}/{@code b} represent the types
6150 * and values of the {@code target} parameters and arguments that precede and
6151 * follow the folded parameters and arguments starting at {@code pos},
6152 * respectively.
6153 * {@snippet lang="java" :
6154 * // there are N arguments in A...
6155 * T target(Z..., V, A[N]..., B...);
6156 * V combiner(A...);
6157 * T adapter(Z... z, A... a, B... b) {
6158 * V v = combiner(a...);
6159 * return target(z..., v, a..., b...);
6160 * }
6161 * // and if the combiner has a void return:
6162 * T target2(Z..., A[N]..., B...);
6163 * void combiner2(A...);
6164 * T adapter2(Z... z, A... a, B... b) {
6165 * combiner2(a...);
6166 * return target2(z..., a..., b...);
6167 * }
6168 * }
6169 * <p>
6170 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
6171 * variable-arity method handle}, even if the original target method handle was.
6172 *
6173 * @param target the method handle to invoke after arguments are combined
6174 * @param pos the position at which to start folding and at which to insert the folding result; if this is {@code
6175 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
6176 * @param combiner method handle to call initially on the incoming arguments
6177 * @return method handle which incorporates the specified argument folding logic
6178 * @throws NullPointerException if either argument is null
6179 * @throws IllegalArgumentException if either of the following two conditions holds:
6180 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
6181 * {@code pos} of the target signature;
6182 * (2) the {@code N} argument types at position {@code pos} of the target signature (skipping one matching
6183 * the {@code combiner}'s return type) are not identical with the argument types of {@code combiner}.
6184 *
6185 * @see #foldArguments(MethodHandle, MethodHandle)
6186 * @since 9
6187 */
6188 public static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner) {
6189 MethodType targetType = target.type();
6190 MethodType combinerType = combiner.type();
6191 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType);
6192 BoundMethodHandle result = target.rebind();
6193 boolean dropResult = rtype == void.class;
6194 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType());
6195 MethodType newType = targetType;
6196 if (!dropResult) {
6197 newType = newType.dropParameterTypes(pos, pos + 1);
6198 }
6199 result = result.copyWithExtendL(newType, lform, combiner);
6200 return result;
6201 }
6202
6203 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType) {
6204 int foldArgs = combinerType.parameterCount();
6205 Class<?> rtype = combinerType.returnType();
6206 int foldVals = rtype == void.class ? 0 : 1;
6207 int afterInsertPos = foldPos + foldVals;
6208 boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
6209 if (ok) {
6210 for (int i = 0; i < foldArgs; i++) {
6211 if (combinerType.parameterType(i) != targetType.parameterType(i + afterInsertPos)) {
6212 ok = false;
6213 break;
6214 }
6215 }
6216 }
6217 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos))
6218 ok = false;
6219 if (!ok)
6220 throw misMatchedTypes("target and combiner types", targetType, combinerType);
6221 return rtype;
6222 }
6223
6224 /**
6225 * Adapts a target method handle by pre-processing some of its arguments, then calling the target with the result
6226 * of the pre-processing replacing the argument at the given position.
6227 *
6228 * @param target the method handle to invoke after arguments are combined
6229 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code
6230 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
6231 * @param combiner method handle to call initially on the incoming arguments
6232 * @param argPositions indexes of the target to pick arguments sent to the combiner from
6233 * @return method handle which incorporates the specified argument folding logic
6234 * @throws NullPointerException if either argument is null
6235 * @throws IllegalArgumentException if either of the following two conditions holds:
6236 * (1) {@code combiner}'s return type is not the same as the argument type at position
6237 * {@code pos} of the target signature;
6238 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature are
6239 * not identical with the argument types of {@code combiner}.
6240 */
6241 /*non-public*/
6242 static MethodHandle filterArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
6243 return argumentsWithCombiner(true, target, position, combiner, argPositions);
6244 }
6245
6246 /**
6247 * Adapts a target method handle by pre-processing some of its arguments, calling the target with the result of
6248 * the pre-processing inserted into the original sequence of arguments at the given position.
6249 *
6250 * @param target the method handle to invoke after arguments are combined
6251 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code
6252 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
6253 * @param combiner method handle to call initially on the incoming arguments
6254 * @param argPositions indexes of the target to pick arguments sent to the combiner from
6255 * @return method handle which incorporates the specified argument folding logic
6256 * @throws NullPointerException if either argument is null
6257 * @throws IllegalArgumentException if either of the following two conditions holds:
6258 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
6259 * {@code pos} of the target signature;
6260 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature
6261 * (skipping {@code position} where the {@code combiner}'s return will be folded in) are not identical
6262 * with the argument types of {@code combiner}.
6263 */
6264 /*non-public*/
6265 static MethodHandle foldArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
6266 return argumentsWithCombiner(false, target, position, combiner, argPositions);
6267 }
6268
6269 private static MethodHandle argumentsWithCombiner(boolean filter, MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
6270 MethodType targetType = target.type();
6271 MethodType combinerType = combiner.type();
6272 Class<?> rtype = argumentsWithCombinerChecks(position, filter, targetType, combinerType, argPositions);
6273 BoundMethodHandle result = target.rebind();
6274
6275 MethodType newType = targetType;
6276 LambdaForm lform;
6277 if (filter) {
6278 lform = result.editor().filterArgumentsForm(1 + position, combinerType.basicType(), argPositions);
6279 } else {
6280 boolean dropResult = rtype == void.class;
6281 lform = result.editor().foldArgumentsForm(1 + position, dropResult, combinerType.basicType(), argPositions);
6282 if (!dropResult) {
6283 newType = newType.dropParameterTypes(position, position + 1);
6284 }
6285 }
6286 result = result.copyWithExtendL(newType, lform, combiner);
6287 return result;
6288 }
6289
6290 private static Class<?> argumentsWithCombinerChecks(int position, boolean filter, MethodType targetType, MethodType combinerType, int ... argPos) {
6291 int combinerArgs = combinerType.parameterCount();
6292 if (argPos.length != combinerArgs) {
6293 throw newIllegalArgumentException("combiner and argument map must be equal size", combinerType, argPos.length);
6294 }
6295 Class<?> rtype = combinerType.returnType();
6296
6297 for (int i = 0; i < combinerArgs; i++) {
6298 int arg = argPos[i];
6299 if (arg < 0 || arg > targetType.parameterCount()) {
6300 throw newIllegalArgumentException("arg outside of target parameterRange", targetType, arg);
6301 }
6302 if (combinerType.parameterType(i) != targetType.parameterType(arg)) {
6303 throw newIllegalArgumentException("target argument type at position " + arg
6304 + " must match combiner argument type at index " + i + ": " + targetType
6305 + " -> " + combinerType + ", map: " + Arrays.toString(argPos));
6306 }
6307 }
6308 if (filter && combinerType.returnType() != targetType.parameterType(position)) {
6309 throw misMatchedTypes("target and combiner types", targetType, combinerType);
6310 }
6311 return rtype;
6312 }
6313
6314 /**
6315 * Makes a method handle which adapts a target method handle,
6316 * by guarding it with a test, a boolean-valued method handle.
6317 * If the guard fails, a fallback handle is called instead.
6318 * All three method handles must have the same corresponding
6319 * argument and return types, except that the return type
6320 * of the test must be boolean, and the test is allowed
6321 * to have fewer arguments than the other two method handles.
6322 * <p>
6323 * Here is pseudocode for the resulting adapter. In the code, {@code T}
6324 * represents the uniform result type of the three involved handles;
6325 * {@code A}/{@code a}, the types and values of the {@code target}
6326 * parameters and arguments that are consumed by the {@code test}; and
6327 * {@code B}/{@code b}, those types and values of the {@code target}
6328 * parameters and arguments that are not consumed by the {@code test}.
6329 * {@snippet lang="java" :
6330 * boolean test(A...);
6331 * T target(A...,B...);
6332 * T fallback(A...,B...);
6333 * T adapter(A... a,B... b) {
6334 * if (test(a...))
6335 * return target(a..., b...);
6336 * else
6337 * return fallback(a..., b...);
6338 * }
6339 * }
6340 * Note that the test arguments ({@code a...} in the pseudocode) cannot
6341 * be modified by execution of the test, and so are passed unchanged
6342 * from the caller to the target or fallback as appropriate.
6343 * @param test method handle used for test, must return boolean
6344 * @param target method handle to call if test passes
6345 * @param fallback method handle to call if test fails
6346 * @return method handle which incorporates the specified if/then/else logic
6347 * @throws NullPointerException if any argument is null
6348 * @throws IllegalArgumentException if {@code test} does not return boolean,
6349 * or if all three method types do not match (with the return
6350 * type of {@code test} changed to match that of the target).
6351 */
6352 public static MethodHandle guardWithTest(MethodHandle test,
6353 MethodHandle target,
6354 MethodHandle fallback) {
6355 MethodType gtype = test.type();
6356 MethodType ttype = target.type();
6357 MethodType ftype = fallback.type();
6358 if (!ttype.equals(ftype))
6359 throw misMatchedTypes("target and fallback types", ttype, ftype);
6360 if (gtype.returnType() != boolean.class)
6361 throw newIllegalArgumentException("guard type is not a predicate "+gtype);
6362
6363 test = dropArgumentsToMatch(test, 0, ttype.ptypes(), 0, true);
6364 if (test == null) {
6365 throw misMatchedTypes("target and test types", ttype, gtype);
6366 }
6367 return MethodHandleImpl.makeGuardWithTest(test, target, fallback);
6368 }
6369
6370 static <T> RuntimeException misMatchedTypes(String what, T t1, T t2) {
6371 return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
6372 }
6373
6374 /**
6375 * Makes a method handle which adapts a target method handle,
6376 * by running it inside an exception handler.
6377 * If the target returns normally, the adapter returns that value.
6378 * If an exception matching the specified type is thrown, the fallback
6379 * handle is called instead on the exception, plus the original arguments.
6380 * <p>
6381 * The target and handler must have the same corresponding
6382 * argument and return types, except that handler may omit trailing arguments
6383 * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
6384 * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
6385 * <p>
6386 * Here is pseudocode for the resulting adapter. In the code, {@code T}
6387 * represents the return type of the {@code target} and {@code handler},
6388 * and correspondingly that of the resulting adapter; {@code A}/{@code a},
6389 * the types and values of arguments to the resulting handle consumed by
6390 * {@code handler}; and {@code B}/{@code b}, those of arguments to the
6391 * resulting handle discarded by {@code handler}.
6392 * {@snippet lang="java" :
6393 * T target(A..., B...);
6394 * T handler(ExType, A...);
6395 * T adapter(A... a, B... b) {
6396 * try {
6397 * return target(a..., b...);
6398 * } catch (ExType ex) {
6399 * return handler(ex, a...);
6400 * }
6401 * }
6402 * }
6403 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
6404 * be modified by execution of the target, and so are passed unchanged
6405 * from the caller to the handler, if the handler is invoked.
6406 * <p>
6407 * The target and handler must return the same type, even if the handler
6408 * always throws. (This might happen, for instance, because the handler
6409 * is simulating a {@code finally} clause).
6410 * To create such a throwing handler, compose the handler creation logic
6411 * with {@link #throwException throwException},
6412 * in order to create a method handle of the correct return type.
6413 * @param target method handle to call
6414 * @param exType the type of exception which the handler will catch
6415 * @param handler method handle to call if a matching exception is thrown
6416 * @return method handle which incorporates the specified try/catch logic
6417 * @throws NullPointerException if any argument is null
6418 * @throws IllegalArgumentException if {@code handler} does not accept
6419 * the given exception type, or if the method handle types do
6420 * not match in their return types and their
6421 * corresponding parameters
6422 * @see MethodHandles#tryFinally(MethodHandle, MethodHandle)
6423 */
6424 public static MethodHandle catchException(MethodHandle target,
6425 Class<? extends Throwable> exType,
6426 MethodHandle handler) {
6427 MethodType ttype = target.type();
6428 MethodType htype = handler.type();
6429 if (!Throwable.class.isAssignableFrom(exType))
6430 throw new ClassCastException(exType.getName());
6431 if (htype.parameterCount() < 1 ||
6432 !htype.parameterType(0).isAssignableFrom(exType))
6433 throw newIllegalArgumentException("handler does not accept exception type "+exType);
6434 if (htype.returnType() != ttype.returnType())
6435 throw misMatchedTypes("target and handler return types", ttype, htype);
6436 handler = dropArgumentsToMatch(handler, 1, ttype.ptypes(), 0, true);
6437 if (handler == null) {
6438 throw misMatchedTypes("target and handler types", ttype, htype);
6439 }
6440 return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
6441 }
6442
6443 /**
6444 * Produces a method handle which will throw exceptions of the given {@code exType}.
6445 * The method handle will accept a single argument of {@code exType},
6446 * and immediately throw it as an exception.
6447 * The method type will nominally specify a return of {@code returnType}.
6448 * The return type may be anything convenient: It doesn't matter to the
6449 * method handle's behavior, since it will never return normally.
6450 * @param returnType the return type of the desired method handle
6451 * @param exType the parameter type of the desired method handle
6452 * @return method handle which can throw the given exceptions
6453 * @throws NullPointerException if either argument is null
6454 */
6455 public static MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) {
6456 if (!Throwable.class.isAssignableFrom(exType))
6457 throw new ClassCastException(exType.getName());
6458 return MethodHandleImpl.throwException(methodType(returnType, exType));
6459 }
6460
6461 /**
6462 * Constructs a method handle representing a loop with several loop variables that are updated and checked upon each
6463 * iteration. Upon termination of the loop due to one of the predicates, a corresponding finalizer is run and
6464 * delivers the loop's result, which is the return value of the resulting handle.
6465 * <p>
6466 * Intuitively, every loop is formed by one or more "clauses", each specifying a local <em>iteration variable</em> and/or a loop
6467 * exit. Each iteration of the loop executes each clause in order. A clause can optionally update its iteration
6468 * variable; it can also optionally perform a test and conditional loop exit. In order to express this logic in
6469 * terms of method handles, each clause will specify up to four independent actions:<ul>
6470 * <li><em>init:</em> Before the loop executes, the initialization of an iteration variable {@code v} of type {@code V}.
6471 * <li><em>step:</em> When a clause executes, an update step for the iteration variable {@code v}.
6472 * <li><em>pred:</em> When a clause executes, a predicate execution to test for loop exit.
6473 * <li><em>fini:</em> If a clause causes a loop exit, a finalizer execution to compute the loop's return value.
6474 * </ul>
6475 * The full sequence of all iteration variable types, in clause order, will be notated as {@code (V...)}.
6476 * The values themselves will be {@code (v...)}. When we speak of "parameter lists", we will usually
6477 * be referring to types, but in some contexts (describing execution) the lists will be of actual values.
6478 * <p>
6479 * Some of these clause parts may be omitted according to certain rules, and useful default behavior is provided in
6480 * this case. See below for a detailed description.
6481 * <p>
6482 * <em>Parameters optional everywhere:</em>
6483 * Each clause function is allowed but not required to accept a parameter for each iteration variable {@code v}.
6484 * As an exception, the init functions cannot take any {@code v} parameters,
6485 * because those values are not yet computed when the init functions are executed.
6486 * Any clause function may neglect to take any trailing subsequence of parameters it is entitled to take.
6487 * In fact, any clause function may take no arguments at all.
6488 * <p>
6489 * <em>Loop parameters:</em>
6490 * A clause function may take all the iteration variable values it is entitled to, in which case
6491 * it may also take more trailing parameters. Such extra values are called <em>loop parameters</em>,
6492 * with their types and values notated as {@code (A...)} and {@code (a...)}.
6493 * These become the parameters of the resulting loop handle, to be supplied whenever the loop is executed.
6494 * (Since init functions do not accept iteration variables {@code v}, any parameter to an
6495 * init function is automatically a loop parameter {@code a}.)
6496 * As with iteration variables, clause functions are allowed but not required to accept loop parameters.
6497 * These loop parameters act as loop-invariant values visible across the whole loop.
6498 * <p>
6499 * <em>Parameters visible everywhere:</em>
6500 * Each non-init clause function is permitted to observe the entire loop state, because it can be passed the full
6501 * list {@code (v... a...)} of current iteration variable values and incoming loop parameters.
6502 * The init functions can observe initial pre-loop state, in the form {@code (a...)}.
6503 * Most clause functions will not need all of this information, but they will be formally connected to it
6504 * as if by {@link #dropArguments}.
6505 * <a id="astar"></a>
6506 * More specifically, we shall use the notation {@code (V*)} to express an arbitrary prefix of a full
6507 * sequence {@code (V...)} (and likewise for {@code (v*)}, {@code (A*)}, {@code (a*)}).
6508 * In that notation, the general form of an init function parameter list
6509 * is {@code (A*)}, and the general form of a non-init function parameter list is {@code (V*)} or {@code (V... A*)}.
6510 * <p>
6511 * <em>Checking clause structure:</em>
6512 * Given a set of clauses, there is a number of checks and adjustments performed to connect all the parts of the
6513 * loop. They are spelled out in detail in the steps below. In these steps, every occurrence of the word "must"
6514 * corresponds to a place where {@link IllegalArgumentException} will be thrown if the required constraint is not
6515 * met by the inputs to the loop combinator.
6516 * <p>
6517 * <em>Effectively identical sequences:</em>
6518 * <a id="effid"></a>
6519 * A parameter list {@code A} is defined to be <em>effectively identical</em> to another parameter list {@code B}
6520 * if {@code A} and {@code B} are identical, or if {@code A} is shorter and is identical with a proper prefix of {@code B}.
6521 * When speaking of an unordered set of parameter lists, we say they the set is "effectively identical"
6522 * as a whole if the set contains a longest list, and all members of the set are effectively identical to
6523 * that longest list.
6524 * For example, any set of type sequences of the form {@code (V*)} is effectively identical,
6525 * and the same is true if more sequences of the form {@code (V... A*)} are added.
6526 * <p>
6527 * <em>Step 0: Determine clause structure.</em><ol type="a">
6528 * <li>The clause array (of type {@code MethodHandle[][]}) must be non-{@code null} and contain at least one element.
6529 * <li>The clause array may not contain {@code null}s or sub-arrays longer than four elements.
6530 * <li>Clauses shorter than four elements are treated as if they were padded by {@code null} elements to length
6531 * four. Padding takes place by appending elements to the array.
6532 * <li>Clauses with all {@code null}s are disregarded.
6533 * <li>Each clause is treated as a four-tuple of functions, called "init", "step", "pred", and "fini".
6534 * </ol>
6535 * <p>
6536 * <em>Step 1A: Determine iteration variable types {@code (V...)}.</em><ol type="a">
6537 * <li>The iteration variable type for each clause is determined using the clause's init and step return types.
6538 * <li>If both functions are omitted, there is no iteration variable for the corresponding clause ({@code void} is
6539 * used as the type to indicate that). If one of them is omitted, the other's return type defines the clause's
6540 * iteration variable type. If both are given, the common return type (they must be identical) defines the clause's
6541 * iteration variable type.
6542 * <li>Form the list of return types (in clause order), omitting all occurrences of {@code void}.
6543 * <li>This list of types is called the "iteration variable types" ({@code (V...)}).
6544 * </ol>
6545 * <p>
6546 * <em>Step 1B: Determine loop parameters {@code (A...)}.</em><ul>
6547 * <li>Examine and collect init function parameter lists (which are of the form {@code (A*)}).
6548 * <li>Examine and collect the suffixes of the step, pred, and fini parameter lists, after removing the iteration variable types.
6549 * (They must have the form {@code (V... A*)}; collect the {@code (A*)} parts only.)
6550 * <li>Do not collect suffixes from step, pred, and fini parameter lists that do not begin with all the iteration variable types.
6551 * (These types will be checked in step 2, along with all the clause function types.)
6552 * <li>Omitted clause functions are ignored. (Equivalently, they are deemed to have empty parameter lists.)
6553 * <li>All of the collected parameter lists must be effectively identical.
6554 * <li>The longest parameter list (which is necessarily unique) is called the "external parameter list" ({@code (A...)}).
6555 * <li>If there is no such parameter list, the external parameter list is taken to be the empty sequence.
6556 * <li>The combined list consisting of iteration variable types followed by the external parameter types is called
6557 * the "internal parameter list".
6558 * </ul>
6559 * <p>
6560 * <em>Step 1C: Determine loop return type.</em><ol type="a">
6561 * <li>Examine fini function return types, disregarding omitted fini functions.
6562 * <li>If there are no fini functions, the loop return type is {@code void}.
6563 * <li>Otherwise, the common return type {@code R} of the fini functions (their return types must be identical) defines the loop return
6564 * type.
6565 * </ol>
6566 * <p>
6567 * <em>Step 1D: Check other types.</em><ol type="a">
6568 * <li>There must be at least one non-omitted pred function.
6569 * <li>Every non-omitted pred function must have a {@code boolean} return type.
6570 * </ol>
6571 * <p>
6572 * <em>Step 2: Determine parameter lists.</em><ol type="a">
6573 * <li>The parameter list for the resulting loop handle will be the external parameter list {@code (A...)}.
6574 * <li>The parameter list for init functions will be adjusted to the external parameter list.
6575 * (Note that their parameter lists are already effectively identical to this list.)
6576 * <li>The parameter list for every non-omitted, non-init (step, pred, and fini) function must be
6577 * effectively identical to the internal parameter list {@code (V... A...)}.
6578 * </ol>
6579 * <p>
6580 * <em>Step 3: Fill in omitted functions.</em><ol type="a">
6581 * <li>If an init function is omitted, use a {@linkplain #empty default value} for the clause's iteration variable
6582 * type.
6583 * <li>If a step function is omitted, use an {@linkplain #identity identity function} of the clause's iteration
6584 * variable type; insert dropped argument parameters before the identity function parameter for the non-{@code void}
6585 * iteration variables of preceding clauses. (This will turn the loop variable into a local loop invariant.)
6586 * <li>If a pred function is omitted, use a constant {@code true} function. (This will keep the loop going, as far
6587 * as this clause is concerned. Note that in such cases the corresponding fini function is unreachable.)
6588 * <li>If a fini function is omitted, use a {@linkplain #empty default value} for the
6589 * loop return type.
6590 * </ol>
6591 * <p>
6592 * <em>Step 4: Fill in missing parameter types.</em><ol type="a">
6593 * <li>At this point, every init function parameter list is effectively identical to the external parameter list {@code (A...)},
6594 * but some lists may be shorter. For every init function with a short parameter list, pad out the end of the list.
6595 * <li>At this point, every non-init function parameter list is effectively identical to the internal parameter
6596 * list {@code (V... A...)}, but some lists may be shorter. For every non-init function with a short parameter list,
6597 * pad out the end of the list.
6598 * <li>Argument lists are padded out by {@linkplain #dropArgumentsToMatch(MethodHandle, int, List, int) dropping unused trailing arguments}.
6599 * </ol>
6600 * <p>
6601 * <em>Final observations.</em><ol type="a">
6602 * <li>After these steps, all clauses have been adjusted by supplying omitted functions and arguments.
6603 * <li>All init functions have a common parameter type list {@code (A...)}, which the final loop handle will also have.
6604 * <li>All fini functions have a common return type {@code R}, which the final loop handle will also have.
6605 * <li>All non-init functions have a common parameter type list {@code (V... A...)}, of
6606 * (non-{@code void}) iteration variables {@code V} followed by loop parameters.
6607 * <li>Each pair of init and step functions agrees in their return type {@code V}.
6608 * <li>Each non-init function will be able to observe the current values {@code (v...)} of all iteration variables.
6609 * <li>Every function will be able to observe the incoming values {@code (a...)} of all loop parameters.
6610 * </ol>
6611 * <p>
6612 * <em>Example.</em> As a consequence of step 1A above, the {@code loop} combinator has the following property:
6613 * <ul>
6614 * <li>Given {@code N} clauses {@code Cn = {null, Sn, Pn}} with {@code n = 1..N}.
6615 * <li>Suppose predicate handles {@code Pn} are either {@code null} or have no parameters.
6616 * (Only one {@code Pn} has to be non-{@code null}.)
6617 * <li>Suppose step handles {@code Sn} have signatures {@code (B1..BX)Rn}, for some constant {@code X>=N}.
6618 * <li>Suppose {@code Q} is the count of non-void types {@code Rn}, and {@code (V1...VQ)} is the sequence of those types.
6619 * <li>It must be that {@code Vn == Bn} for {@code n = 1..min(X,Q)}.
6620 * <li>The parameter types {@code Vn} will be interpreted as loop-local state elements {@code (V...)}.
6621 * <li>Any remaining types {@code BQ+1..BX} (if {@code Q<X}) will determine
6622 * the resulting loop handle's parameter types {@code (A...)}.
6623 * </ul>
6624 * In this example, the loop handle parameters {@code (A...)} were derived from the step functions,
6625 * which is natural if most of the loop computation happens in the steps. For some loops,
6626 * the burden of computation might be heaviest in the pred functions, and so the pred functions
6627 * might need to accept the loop parameter values. For loops with complex exit logic, the fini
6628 * functions might need to accept loop parameters, and likewise for loops with complex entry logic,
6629 * where the init functions will need the extra parameters. For such reasons, the rules for
6630 * determining these parameters are as symmetric as possible, across all clause parts.
6631 * In general, the loop parameters function as common invariant values across the whole
6632 * loop, while the iteration variables function as common variant values, or (if there is
6633 * no step function) as internal loop invariant temporaries.
6634 * <p>
6635 * <em>Loop execution.</em><ol type="a">
6636 * <li>When the loop is called, the loop input values are saved in locals, to be passed to
6637 * every clause function. These locals are loop invariant.
6638 * <li>Each init function is executed in clause order (passing the external arguments {@code (a...)})
6639 * and the non-{@code void} values are saved (as the iteration variables {@code (v...)}) into locals.
6640 * These locals will be loop varying (unless their steps behave as identity functions, as noted above).
6641 * <li>All function executions (except init functions) will be passed the internal parameter list, consisting of
6642 * the non-{@code void} iteration values {@code (v...)} (in clause order) and then the loop inputs {@code (a...)}
6643 * (in argument order).
6644 * <li>The step and pred functions are then executed, in clause order (step before pred), until a pred function
6645 * returns {@code false}.
6646 * <li>The non-{@code void} result from a step function call is used to update the corresponding value in the
6647 * sequence {@code (v...)} of loop variables.
6648 * The updated value is immediately visible to all subsequent function calls.
6649 * <li>If a pred function returns {@code false}, the corresponding fini function is called, and the resulting value
6650 * (of type {@code R}) is returned from the loop as a whole.
6651 * <li>If all the pred functions always return true, no fini function is ever invoked, and the loop cannot exit
6652 * except by throwing an exception.
6653 * </ol>
6654 * <p>
6655 * <em>Usage tips.</em>
6656 * <ul>
6657 * <li>Although each step function will receive the current values of <em>all</em> the loop variables,
6658 * sometimes a step function only needs to observe the current value of its own variable.
6659 * In that case, the step function may need to explicitly {@linkplain #dropArguments drop all preceding loop variables}.
6660 * This will require mentioning their types, in an expression like {@code dropArguments(step, 0, V0.class, ...)}.
6661 * <li>Loop variables are not required to vary; they can be loop invariant. A clause can create
6662 * a loop invariant by a suitable init function with no step, pred, or fini function. This may be
6663 * useful to "wire" an incoming loop argument into the step or pred function of an adjacent loop variable.
6664 * <li>If some of the clause functions are virtual methods on an instance, the instance
6665 * itself can be conveniently placed in an initial invariant loop "variable", using an initial clause
6666 * like {@code new MethodHandle[]{identity(ObjType.class)}}. In that case, the instance reference
6667 * will be the first iteration variable value, and it will be easy to use virtual
6668 * methods as clause parts, since all of them will take a leading instance reference matching that value.
6669 * </ul>
6670 * <p>
6671 * Here is pseudocode for the resulting loop handle. As above, {@code V} and {@code v} represent the types
6672 * and values of loop variables; {@code A} and {@code a} represent arguments passed to the whole loop;
6673 * and {@code R} is the common result type of all finalizers as well as of the resulting loop.
6674 * {@snippet lang="java" :
6675 * V... init...(A...);
6676 * boolean pred...(V..., A...);
6677 * V... step...(V..., A...);
6678 * R fini...(V..., A...);
6679 * R loop(A... a) {
6680 * V... v... = init...(a...);
6681 * for (;;) {
6682 * for ((v, p, s, f) in (v..., pred..., step..., fini...)) {
6683 * v = s(v..., a...);
6684 * if (!p(v..., a...)) {
6685 * return f(v..., a...);
6686 * }
6687 * }
6688 * }
6689 * }
6690 * }
6691 * Note that the parameter type lists {@code (V...)} and {@code (A...)} have been expanded
6692 * to their full length, even though individual clause functions may neglect to take them all.
6693 * As noted above, missing parameters are filled in as if by {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}.
6694 *
6695 * @apiNote Example:
6696 * {@snippet lang="java" :
6697 * // iterative implementation of the factorial function as a loop handle
6698 * static int one(int k) { return 1; }
6699 * static int inc(int i, int acc, int k) { return i + 1; }
6700 * static int mult(int i, int acc, int k) { return i * acc; }
6701 * static boolean pred(int i, int acc, int k) { return i < k; }
6702 * static int fin(int i, int acc, int k) { return acc; }
6703 * // assume MH_one, MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
6704 * // null initializer for counter, should initialize to 0
6705 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
6706 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
6707 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
6708 * assertEquals(120, loop.invoke(5));
6709 * }
6710 * The same example, dropping arguments and using combinators:
6711 * {@snippet lang="java" :
6712 * // simplified implementation of the factorial function as a loop handle
6713 * static int inc(int i) { return i + 1; } // drop acc, k
6714 * static int mult(int i, int acc) { return i * acc; } //drop k
6715 * static boolean cmp(int i, int k) { return i < k; }
6716 * // assume MH_inc, MH_mult, and MH_cmp are handles to the above methods
6717 * // null initializer for counter, should initialize to 0
6718 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
6719 * MethodHandle MH_pred = MethodHandles.dropArguments(MH_cmp, 1, int.class); // drop acc
6720 * MethodHandle MH_fin = MethodHandles.dropArguments(MethodHandles.identity(int.class), 0, int.class); // drop i
6721 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
6722 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
6723 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
6724 * assertEquals(720, loop.invoke(6));
6725 * }
6726 * A similar example, using a helper object to hold a loop parameter:
6727 * {@snippet lang="java" :
6728 * // instance-based implementation of the factorial function as a loop handle
6729 * static class FacLoop {
6730 * final int k;
6731 * FacLoop(int k) { this.k = k; }
6732 * int inc(int i) { return i + 1; }
6733 * int mult(int i, int acc) { return i * acc; }
6734 * boolean pred(int i) { return i < k; }
6735 * int fin(int i, int acc) { return acc; }
6736 * }
6737 * // assume MH_FacLoop is a handle to the constructor
6738 * // assume MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
6739 * // null initializer for counter, should initialize to 0
6740 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
6741 * MethodHandle[] instanceClause = new MethodHandle[]{MH_FacLoop};
6742 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
6743 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
6744 * MethodHandle loop = MethodHandles.loop(instanceClause, counterClause, accumulatorClause);
6745 * assertEquals(5040, loop.invoke(7));
6746 * }
6747 *
6748 * @param clauses an array of arrays (4-tuples) of {@link MethodHandle}s adhering to the rules described above.
6749 *
6750 * @return a method handle embodying the looping behavior as defined by the arguments.
6751 *
6752 * @throws IllegalArgumentException in case any of the constraints described above is violated.
6753 *
6754 * @see MethodHandles#whileLoop(MethodHandle, MethodHandle, MethodHandle)
6755 * @see MethodHandles#doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
6756 * @see MethodHandles#countedLoop(MethodHandle, MethodHandle, MethodHandle)
6757 * @see MethodHandles#iteratedLoop(MethodHandle, MethodHandle, MethodHandle)
6758 * @since 9
6759 */
6760 public static MethodHandle loop(MethodHandle[]... clauses) {
6761 // Step 0: determine clause structure.
6762 loopChecks0(clauses);
6763
6764 List<MethodHandle> init = new ArrayList<>();
6765 List<MethodHandle> step = new ArrayList<>();
6766 List<MethodHandle> pred = new ArrayList<>();
6767 List<MethodHandle> fini = new ArrayList<>();
6768
6769 Stream.of(clauses).filter(c -> Stream.of(c).anyMatch(Objects::nonNull)).forEach(clause -> {
6770 init.add(clause[0]); // all clauses have at least length 1
6771 step.add(clause.length <= 1 ? null : clause[1]);
6772 pred.add(clause.length <= 2 ? null : clause[2]);
6773 fini.add(clause.length <= 3 ? null : clause[3]);
6774 });
6775
6776 assert Stream.of(init, step, pred, fini).map(List::size).distinct().count() == 1;
6777 final int nclauses = init.size();
6778
6779 // Step 1A: determine iteration variables (V...).
6780 final List<Class<?>> iterationVariableTypes = new ArrayList<>();
6781 for (int i = 0; i < nclauses; ++i) {
6782 MethodHandle in = init.get(i);
6783 MethodHandle st = step.get(i);
6784 if (in == null && st == null) {
6785 iterationVariableTypes.add(void.class);
6786 } else if (in != null && st != null) {
6787 loopChecks1a(i, in, st);
6788 iterationVariableTypes.add(in.type().returnType());
6789 } else {
6790 iterationVariableTypes.add(in == null ? st.type().returnType() : in.type().returnType());
6791 }
6792 }
6793 final List<Class<?>> commonPrefix = iterationVariableTypes.stream().filter(t -> t != void.class).toList();
6794
6795 // Step 1B: determine loop parameters (A...).
6796 final List<Class<?>> commonSuffix = buildCommonSuffix(init, step, pred, fini, commonPrefix.size());
6797 loopChecks1b(init, commonSuffix);
6798
6799 // Step 1C: determine loop return type.
6800 // Step 1D: check other types.
6801 // local variable required here; see JDK-8223553
6802 Stream<Class<?>> cstream = fini.stream().filter(Objects::nonNull).map(MethodHandle::type)
6803 .map(MethodType::returnType);
6804 final Class<?> loopReturnType = cstream.findFirst().orElse(void.class);
6805 loopChecks1cd(pred, fini, loopReturnType);
6806
6807 // Step 2: determine parameter lists.
6808 final List<Class<?>> commonParameterSequence = new ArrayList<>(commonPrefix);
6809 commonParameterSequence.addAll(commonSuffix);
6810 loopChecks2(step, pred, fini, commonParameterSequence);
6811 // Step 3: fill in omitted functions.
6812 for (int i = 0; i < nclauses; ++i) {
6813 Class<?> t = iterationVariableTypes.get(i);
6814 if (init.get(i) == null) {
6815 init.set(i, empty(methodType(t, commonSuffix)));
6816 }
6817 if (step.get(i) == null) {
6818 step.set(i, dropArgumentsToMatch(identityOrVoid(t), 0, commonParameterSequence, i));
6819 }
6820 if (pred.get(i) == null) {
6821 pred.set(i, dropArguments(constant(boolean.class, true), 0, commonParameterSequence));
6822 }
6823 if (fini.get(i) == null) {
6824 fini.set(i, empty(methodType(t, commonParameterSequence)));
6825 }
6826 }
6827
6828 // Step 4: fill in missing parameter types.
6829 // Also convert all handles to fixed-arity handles.
6830 List<MethodHandle> finit = fixArities(fillParameterTypes(init, commonSuffix));
6831 List<MethodHandle> fstep = fixArities(fillParameterTypes(step, commonParameterSequence));
6832 List<MethodHandle> fpred = fixArities(fillParameterTypes(pred, commonParameterSequence));
6833 List<MethodHandle> ffini = fixArities(fillParameterTypes(fini, commonParameterSequence));
6834
6835 assert finit.stream().map(MethodHandle::type).map(MethodType::parameterList).
6836 allMatch(pl -> pl.equals(commonSuffix));
6837 assert Stream.of(fstep, fpred, ffini).flatMap(List::stream).map(MethodHandle::type).map(MethodType::parameterList).
6838 allMatch(pl -> pl.equals(commonParameterSequence));
6839
6840 return MethodHandleImpl.makeLoop(loopReturnType, commonSuffix, finit, fstep, fpred, ffini);
6841 }
6842
6843 private static void loopChecks0(MethodHandle[][] clauses) {
6844 if (clauses == null || clauses.length == 0) {
6845 throw newIllegalArgumentException("null or no clauses passed");
6846 }
6847 if (Stream.of(clauses).anyMatch(Objects::isNull)) {
6848 throw newIllegalArgumentException("null clauses are not allowed");
6849 }
6850 if (Stream.of(clauses).anyMatch(c -> c.length > 4)) {
6851 throw newIllegalArgumentException("All loop clauses must be represented as MethodHandle arrays with at most 4 elements.");
6852 }
6853 }
6854
6855 private static void loopChecks1a(int i, MethodHandle in, MethodHandle st) {
6856 if (in.type().returnType() != st.type().returnType()) {
6857 throw misMatchedTypes("clause " + i + ": init and step return types", in.type().returnType(),
6858 st.type().returnType());
6859 }
6860 }
6861
6862 private static List<Class<?>> longestParameterList(Stream<MethodHandle> mhs, int skipSize) {
6863 return mhs.filter(Objects::nonNull)
6864 // take only those that can contribute to a common suffix because they are longer than the prefix
6865 .map(MethodHandle::type)
6866 .filter(t -> t.parameterCount() > skipSize)
6867 .max(Comparator.comparingInt(MethodType::parameterCount))
6868 .map(methodType -> List.of(Arrays.copyOfRange(methodType.ptypes(), skipSize, methodType.parameterCount())))
6869 .orElse(List.of());
6870 }
6871
6872 private static List<Class<?>> buildCommonSuffix(List<MethodHandle> init, List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, int cpSize) {
6873 final List<Class<?>> longest1 = longestParameterList(Stream.of(step, pred, fini).flatMap(List::stream), cpSize);
6874 final List<Class<?>> longest2 = longestParameterList(init.stream(), 0);
6875 return longest1.size() >= longest2.size() ? longest1 : longest2;
6876 }
6877
6878 private static void loopChecks1b(List<MethodHandle> init, List<Class<?>> commonSuffix) {
6879 if (init.stream().filter(Objects::nonNull).map(MethodHandle::type).
6880 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonSuffix))) {
6881 throw newIllegalArgumentException("found non-effectively identical init parameter type lists: " + init +
6882 " (common suffix: " + commonSuffix + ")");
6883 }
6884 }
6885
6886 private static void loopChecks1cd(List<MethodHandle> pred, List<MethodHandle> fini, Class<?> loopReturnType) {
6887 if (fini.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
6888 anyMatch(t -> t != loopReturnType)) {
6889 throw newIllegalArgumentException("found non-identical finalizer return types: " + fini + " (return type: " +
6890 loopReturnType + ")");
6891 }
6892
6893 if (pred.stream().noneMatch(Objects::nonNull)) {
6894 throw newIllegalArgumentException("no predicate found", pred);
6895 }
6896 if (pred.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
6897 anyMatch(t -> t != boolean.class)) {
6898 throw newIllegalArgumentException("predicates must have boolean return type", pred);
6899 }
6900 }
6901
6902 private static void loopChecks2(List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, List<Class<?>> commonParameterSequence) {
6903 if (Stream.of(step, pred, fini).flatMap(List::stream).filter(Objects::nonNull).map(MethodHandle::type).
6904 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonParameterSequence))) {
6905 throw newIllegalArgumentException("found non-effectively identical parameter type lists:\nstep: " + step +
6906 "\npred: " + pred + "\nfini: " + fini + " (common parameter sequence: " + commonParameterSequence + ")");
6907 }
6908 }
6909
6910 private static List<MethodHandle> fillParameterTypes(List<MethodHandle> hs, final List<Class<?>> targetParams) {
6911 return hs.stream().map(h -> {
6912 int pc = h.type().parameterCount();
6913 int tpsize = targetParams.size();
6914 return pc < tpsize ? dropArguments(h, pc, targetParams.subList(pc, tpsize)) : h;
6915 }).toList();
6916 }
6917
6918 private static List<MethodHandle> fixArities(List<MethodHandle> hs) {
6919 return hs.stream().map(MethodHandle::asFixedArity).toList();
6920 }
6921
6922 /**
6923 * Constructs a {@code while} loop from an initializer, a body, and a predicate.
6924 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
6925 * <p>
6926 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
6927 * method will, in each iteration, first evaluate the predicate and then execute its body (if the predicate
6928 * evaluates to {@code true}).
6929 * The loop will terminate once the predicate evaluates to {@code false} (the body will not be executed in this case).
6930 * <p>
6931 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
6932 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
6933 * and updated with the value returned from its invocation. The result of loop execution will be
6934 * the final value of the additional loop-local variable (if present).
6935 * <p>
6936 * The following rules hold for these argument handles:<ul>
6937 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
6938 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
6939 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
6940 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
6941 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
6942 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
6943 * It will constrain the parameter lists of the other loop parts.
6944 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
6945 * list {@code (A...)} is called the <em>external parameter list</em>.
6946 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
6947 * additional state variable of the loop.
6948 * The body must both accept and return a value of this type {@code V}.
6949 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
6950 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
6951 * <a href="MethodHandles.html#effid">effectively identical</a>
6952 * to the external parameter list {@code (A...)}.
6953 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
6954 * {@linkplain #empty default value}.
6955 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
6956 * Its parameter list (either empty or of the form {@code (V A*)}) must be
6957 * effectively identical to the internal parameter list.
6958 * </ul>
6959 * <p>
6960 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
6961 * <li>The loop handle's result type is the result type {@code V} of the body.
6962 * <li>The loop handle's parameter types are the types {@code (A...)},
6963 * from the external parameter list.
6964 * </ul>
6965 * <p>
6966 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
6967 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
6968 * passed to the loop.
6969 * {@snippet lang="java" :
6970 * V init(A...);
6971 * boolean pred(V, A...);
6972 * V body(V, A...);
6973 * V whileLoop(A... a...) {
6974 * V v = init(a...);
6975 * while (pred(v, a...)) {
6976 * v = body(v, a...);
6977 * }
6978 * return v;
6979 * }
6980 * }
6981 *
6982 * @apiNote Example:
6983 * {@snippet lang="java" :
6984 * // implement the zip function for lists as a loop handle
6985 * static List<String> initZip(Iterator<String> a, Iterator<String> b) { return new ArrayList<>(); }
6986 * static boolean zipPred(List<String> zip, Iterator<String> a, Iterator<String> b) { return a.hasNext() && b.hasNext(); }
6987 * static List<String> zipStep(List<String> zip, Iterator<String> a, Iterator<String> b) {
6988 * zip.add(a.next());
6989 * zip.add(b.next());
6990 * return zip;
6991 * }
6992 * // assume MH_initZip, MH_zipPred, and MH_zipStep are handles to the above methods
6993 * MethodHandle loop = MethodHandles.whileLoop(MH_initZip, MH_zipPred, MH_zipStep);
6994 * List<String> a = Arrays.asList("a", "b", "c", "d");
6995 * List<String> b = Arrays.asList("e", "f", "g", "h");
6996 * List<String> zipped = Arrays.asList("a", "e", "b", "f", "c", "g", "d", "h");
6997 * assertEquals(zipped, (List<String>) loop.invoke(a.iterator(), b.iterator()));
6998 * }
6999 *
7000 *
7001 * @apiNote The implementation of this method can be expressed as follows:
7002 * {@snippet lang="java" :
7003 * MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
7004 * MethodHandle fini = (body.type().returnType() == void.class
7005 * ? null : identity(body.type().returnType()));
7006 * MethodHandle[]
7007 * checkExit = { null, null, pred, fini },
7008 * varBody = { init, body };
7009 * return loop(checkExit, varBody);
7010 * }
7011 * }
7012 *
7013 * @param init optional initializer, providing the initial value of the loop variable.
7014 * May be {@code null}, implying a default initial value. See above for other constraints.
7015 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
7016 * above for other constraints.
7017 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
7018 * See above for other constraints.
7019 *
7020 * @return a method handle implementing the {@code while} loop as described by the arguments.
7021 * @throws IllegalArgumentException if the rules for the arguments are violated.
7022 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
7023 *
7024 * @see #loop(MethodHandle[][])
7025 * @see #doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
7026 * @since 9
7027 */
7028 public static MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
7029 whileLoopChecks(init, pred, body);
7030 MethodHandle fini = identityOrVoid(body.type().returnType());
7031 MethodHandle[] checkExit = { null, null, pred, fini };
7032 MethodHandle[] varBody = { init, body };
7033 return loop(checkExit, varBody);
7034 }
7035
7036 /**
7037 * Constructs a {@code do-while} loop from an initializer, a body, and a predicate.
7038 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
7039 * <p>
7040 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
7041 * method will, in each iteration, first execute its body and then evaluate the predicate.
7042 * The loop will terminate once the predicate evaluates to {@code false} after an execution of the body.
7043 * <p>
7044 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
7045 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
7046 * and updated with the value returned from its invocation. The result of loop execution will be
7047 * the final value of the additional loop-local variable (if present).
7048 * <p>
7049 * The following rules hold for these argument handles:<ul>
7050 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
7051 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
7052 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
7053 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
7054 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
7055 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
7056 * It will constrain the parameter lists of the other loop parts.
7057 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
7058 * list {@code (A...)} is called the <em>external parameter list</em>.
7059 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
7060 * additional state variable of the loop.
7061 * The body must both accept and return a value of this type {@code V}.
7062 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
7063 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
7064 * <a href="MethodHandles.html#effid">effectively identical</a>
7065 * to the external parameter list {@code (A...)}.
7066 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
7067 * {@linkplain #empty default value}.
7068 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
7069 * Its parameter list (either empty or of the form {@code (V A*)}) must be
7070 * effectively identical to the internal parameter list.
7071 * </ul>
7072 * <p>
7073 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
7074 * <li>The loop handle's result type is the result type {@code V} of the body.
7075 * <li>The loop handle's parameter types are the types {@code (A...)},
7076 * from the external parameter list.
7077 * </ul>
7078 * <p>
7079 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
7080 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
7081 * passed to the loop.
7082 * {@snippet lang="java" :
7083 * V init(A...);
7084 * boolean pred(V, A...);
7085 * V body(V, A...);
7086 * V doWhileLoop(A... a...) {
7087 * V v = init(a...);
7088 * do {
7089 * v = body(v, a...);
7090 * } while (pred(v, a...));
7091 * return v;
7092 * }
7093 * }
7094 *
7095 * @apiNote Example:
7096 * {@snippet lang="java" :
7097 * // int i = 0; while (i < limit) { ++i; } return i; => limit
7098 * static int zero(int limit) { return 0; }
7099 * static int step(int i, int limit) { return i + 1; }
7100 * static boolean pred(int i, int limit) { return i < limit; }
7101 * // assume MH_zero, MH_step, and MH_pred are handles to the above methods
7102 * MethodHandle loop = MethodHandles.doWhileLoop(MH_zero, MH_step, MH_pred);
7103 * assertEquals(23, loop.invoke(23));
7104 * }
7105 *
7106 *
7107 * @apiNote The implementation of this method can be expressed as follows:
7108 * {@snippet lang="java" :
7109 * MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
7110 * MethodHandle fini = (body.type().returnType() == void.class
7111 * ? null : identity(body.type().returnType()));
7112 * MethodHandle[] clause = { init, body, pred, fini };
7113 * return loop(clause);
7114 * }
7115 * }
7116 *
7117 * @param init optional initializer, providing the initial value of the loop variable.
7118 * May be {@code null}, implying a default initial value. See above for other constraints.
7119 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
7120 * See above for other constraints.
7121 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
7122 * above for other constraints.
7123 *
7124 * @return a method handle implementing the {@code while} loop as described by the arguments.
7125 * @throws IllegalArgumentException if the rules for the arguments are violated.
7126 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
7127 *
7128 * @see #loop(MethodHandle[][])
7129 * @see #whileLoop(MethodHandle, MethodHandle, MethodHandle)
7130 * @since 9
7131 */
7132 public static MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
7133 whileLoopChecks(init, pred, body);
7134 MethodHandle fini = identityOrVoid(body.type().returnType());
7135 MethodHandle[] clause = {init, body, pred, fini };
7136 return loop(clause);
7137 }
7138
7139 private static void whileLoopChecks(MethodHandle init, MethodHandle pred, MethodHandle body) {
7140 Objects.requireNonNull(pred);
7141 Objects.requireNonNull(body);
7142 MethodType bodyType = body.type();
7143 Class<?> returnType = bodyType.returnType();
7144 List<Class<?>> innerList = bodyType.parameterList();
7145 List<Class<?>> outerList = innerList;
7146 if (returnType == void.class) {
7147 // OK
7148 } else if (innerList.isEmpty() || innerList.get(0) != returnType) {
7149 // leading V argument missing => error
7150 MethodType expected = bodyType.insertParameterTypes(0, returnType);
7151 throw misMatchedTypes("body function", bodyType, expected);
7152 } else {
7153 outerList = innerList.subList(1, innerList.size());
7154 }
7155 MethodType predType = pred.type();
7156 if (predType.returnType() != boolean.class ||
7157 !predType.effectivelyIdenticalParameters(0, innerList)) {
7158 throw misMatchedTypes("loop predicate", predType, methodType(boolean.class, innerList));
7159 }
7160 if (init != null) {
7161 MethodType initType = init.type();
7162 if (initType.returnType() != returnType ||
7163 !initType.effectivelyIdenticalParameters(0, outerList)) {
7164 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
7165 }
7166 }
7167 }
7168
7169 /**
7170 * Constructs a loop that runs a given number of iterations.
7171 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
7172 * <p>
7173 * The number of iterations is determined by the {@code iterations} handle evaluation result.
7174 * The loop counter {@code i} is an extra loop iteration variable of type {@code int}.
7175 * It will be initialized to 0 and incremented by 1 in each iteration.
7176 * <p>
7177 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
7178 * of that type is also present. This variable is initialized using the optional {@code init} handle,
7179 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
7180 * <p>
7181 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
7182 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
7183 * iteration variable.
7184 * The result of the loop handle execution will be the final {@code V} value of that variable
7185 * (or {@code void} if there is no {@code V} variable).
7186 * <p>
7187 * The following rules hold for the argument handles:<ul>
7188 * <li>The {@code iterations} handle must not be {@code null}, and must return
7189 * the type {@code int}, referred to here as {@code I} in parameter type lists.
7190 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
7191 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
7192 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
7193 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
7194 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
7195 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
7196 * of types called the <em>internal parameter list</em>.
7197 * It will constrain the parameter lists of the other loop parts.
7198 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
7199 * with no additional {@code A} types, then the internal parameter list is extended by
7200 * the argument types {@code A...} of the {@code iterations} handle.
7201 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
7202 * list {@code (A...)} is called the <em>external parameter list</em>.
7203 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
7204 * additional state variable of the loop.
7205 * The body must both accept a leading parameter and return a value of this type {@code V}.
7206 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
7207 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
7208 * <a href="MethodHandles.html#effid">effectively identical</a>
7209 * to the external parameter list {@code (A...)}.
7210 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
7211 * {@linkplain #empty default value}.
7212 * <li>The parameter list of {@code iterations} (of some form {@code (A*)}) must be
7213 * effectively identical to the external parameter list {@code (A...)}.
7214 * </ul>
7215 * <p>
7216 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
7217 * <li>The loop handle's result type is the result type {@code V} of the body.
7218 * <li>The loop handle's parameter types are the types {@code (A...)},
7219 * from the external parameter list.
7220 * </ul>
7221 * <p>
7222 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
7223 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
7224 * arguments passed to the loop.
7225 * {@snippet lang="java" :
7226 * int iterations(A...);
7227 * V init(A...);
7228 * V body(V, int, A...);
7229 * V countedLoop(A... a...) {
7230 * int end = iterations(a...);
7231 * V v = init(a...);
7232 * for (int i = 0; i < end; ++i) {
7233 * v = body(v, i, a...);
7234 * }
7235 * return v;
7236 * }
7237 * }
7238 *
7239 * @apiNote Example with a fully conformant body method:
7240 * {@snippet lang="java" :
7241 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
7242 * // => a variation on a well known theme
7243 * static String step(String v, int counter, String init) { return "na " + v; }
7244 * // assume MH_step is a handle to the method above
7245 * MethodHandle fit13 = MethodHandles.constant(int.class, 13);
7246 * MethodHandle start = MethodHandles.identity(String.class);
7247 * MethodHandle loop = MethodHandles.countedLoop(fit13, start, MH_step);
7248 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("Lambdaman!"));
7249 * }
7250 *
7251 * @apiNote Example with the simplest possible body method type,
7252 * and passing the number of iterations to the loop invocation:
7253 * {@snippet lang="java" :
7254 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
7255 * // => a variation on a well known theme
7256 * static String step(String v, int counter ) { return "na " + v; }
7257 * // assume MH_step is a handle to the method above
7258 * MethodHandle count = MethodHandles.dropArguments(MethodHandles.identity(int.class), 1, String.class);
7259 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class);
7260 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i) -> "na " + v
7261 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "Lambdaman!"));
7262 * }
7263 *
7264 * @apiNote Example that treats the number of iterations, string to append to, and string to append
7265 * as loop parameters:
7266 * {@snippet lang="java" :
7267 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
7268 * // => a variation on a well known theme
7269 * static String step(String v, int counter, int iterations_, String pre, String start_) { return pre + " " + v; }
7270 * // assume MH_step is a handle to the method above
7271 * MethodHandle count = MethodHandles.identity(int.class);
7272 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class, String.class);
7273 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i, _, pre, _) -> pre + " " + v
7274 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "na", "Lambdaman!"));
7275 * }
7276 *
7277 * @apiNote Example that illustrates the usage of {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}
7278 * to enforce a loop type:
7279 * {@snippet lang="java" :
7280 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
7281 * // => a variation on a well known theme
7282 * static String step(String v, int counter, String pre) { return pre + " " + v; }
7283 * // assume MH_step is a handle to the method above
7284 * MethodType loopType = methodType(String.class, String.class, int.class, String.class);
7285 * MethodHandle count = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(int.class), 0, loopType.parameterList(), 1);
7286 * MethodHandle start = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(String.class), 0, loopType.parameterList(), 2);
7287 * MethodHandle body = MethodHandles.dropArgumentsToMatch(MH_step, 2, loopType.parameterList(), 0);
7288 * MethodHandle loop = MethodHandles.countedLoop(count, start, body); // (v, i, pre, _, _) -> pre + " " + v
7289 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("na", 13, "Lambdaman!"));
7290 * }
7291 *
7292 * @apiNote The implementation of this method can be expressed as follows:
7293 * {@snippet lang="java" :
7294 * MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
7295 * return countedLoop(empty(iterations.type()), iterations, init, body);
7296 * }
7297 * }
7298 *
7299 * @param iterations a non-{@code null} handle to return the number of iterations this loop should run. The handle's
7300 * result type must be {@code int}. See above for other constraints.
7301 * @param init optional initializer, providing the initial value of the loop variable.
7302 * May be {@code null}, implying a default initial value. See above for other constraints.
7303 * @param body body of the loop, which may not be {@code null}.
7304 * It controls the loop parameters and result type in the standard case (see above for details).
7305 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
7306 * and may accept any number of additional types.
7307 * See above for other constraints.
7308 *
7309 * @return a method handle representing the loop.
7310 * @throws NullPointerException if either of the {@code iterations} or {@code body} handles is {@code null}.
7311 * @throws IllegalArgumentException if any argument violates the rules formulated above.
7312 *
7313 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle, MethodHandle)
7314 * @since 9
7315 */
7316 public static MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
7317 return countedLoop(empty(iterations.type()), iterations, init, body);
7318 }
7319
7320 /**
7321 * Constructs a loop that counts over a range of numbers.
7322 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
7323 * <p>
7324 * The loop counter {@code i} is a loop iteration variable of type {@code int}.
7325 * The {@code start} and {@code end} handles determine the start (inclusive) and end (exclusive)
7326 * values of the loop counter.
7327 * The loop counter will be initialized to the {@code int} value returned from the evaluation of the
7328 * {@code start} handle and run to the value returned from {@code end} (exclusively) with a step width of 1.
7329 * <p>
7330 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
7331 * of that type is also present. This variable is initialized using the optional {@code init} handle,
7332 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
7333 * <p>
7334 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
7335 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
7336 * iteration variable.
7337 * The result of the loop handle execution will be the final {@code V} value of that variable
7338 * (or {@code void} if there is no {@code V} variable).
7339 * <p>
7340 * The following rules hold for the argument handles:<ul>
7341 * <li>The {@code start} and {@code end} handles must not be {@code null}, and must both return
7342 * the common type {@code int}, referred to here as {@code I} in parameter type lists.
7343 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
7344 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
7345 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
7346 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
7347 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
7348 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
7349 * of types called the <em>internal parameter list</em>.
7350 * It will constrain the parameter lists of the other loop parts.
7351 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
7352 * with no additional {@code A} types, then the internal parameter list is extended by
7353 * the argument types {@code A...} of the {@code end} handle.
7354 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
7355 * list {@code (A...)} is called the <em>external parameter list</em>.
7356 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
7357 * additional state variable of the loop.
7358 * The body must both accept a leading parameter and return a value of this type {@code V}.
7359 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
7360 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
7361 * <a href="MethodHandles.html#effid">effectively identical</a>
7362 * to the external parameter list {@code (A...)}.
7363 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
7364 * {@linkplain #empty default value}.
7365 * <li>The parameter list of {@code start} (of some form {@code (A*)}) must be
7366 * effectively identical to the external parameter list {@code (A...)}.
7367 * <li>Likewise, the parameter list of {@code end} must be effectively identical
7368 * to the external parameter list.
7369 * </ul>
7370 * <p>
7371 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
7372 * <li>The loop handle's result type is the result type {@code V} of the body.
7373 * <li>The loop handle's parameter types are the types {@code (A...)},
7374 * from the external parameter list.
7375 * </ul>
7376 * <p>
7377 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
7378 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
7379 * arguments passed to the loop.
7380 * {@snippet lang="java" :
7381 * int start(A...);
7382 * int end(A...);
7383 * V init(A...);
7384 * V body(V, int, A...);
7385 * V countedLoop(A... a...) {
7386 * int e = end(a...);
7387 * int s = start(a...);
7388 * V v = init(a...);
7389 * for (int i = s; i < e; ++i) {
7390 * v = body(v, i, a...);
7391 * }
7392 * return v;
7393 * }
7394 * }
7395 *
7396 * @apiNote The implementation of this method can be expressed as follows:
7397 * {@snippet lang="java" :
7398 * MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
7399 * MethodHandle returnVar = dropArguments(identity(init.type().returnType()), 0, int.class, int.class);
7400 * // assume MH_increment and MH_predicate are handles to implementation-internal methods with
7401 * // the following semantics:
7402 * // MH_increment: (int limit, int counter) -> counter + 1
7403 * // MH_predicate: (int limit, int counter) -> counter < limit
7404 * Class<?> counterType = start.type().returnType(); // int
7405 * Class<?> returnType = body.type().returnType();
7406 * MethodHandle incr = MH_increment, pred = MH_predicate, retv = null;
7407 * if (returnType != void.class) { // ignore the V variable
7408 * incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
7409 * pred = dropArguments(pred, 1, returnType); // ditto
7410 * retv = dropArguments(identity(returnType), 0, counterType); // ignore limit
7411 * }
7412 * body = dropArguments(body, 0, counterType); // ignore the limit variable
7413 * MethodHandle[]
7414 * loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
7415 * bodyClause = { init, body }, // v = init(); v = body(v, i)
7416 * indexVar = { start, incr }; // i = start(); i = i + 1
7417 * return loop(loopLimit, bodyClause, indexVar);
7418 * }
7419 * }
7420 *
7421 * @param start a non-{@code null} handle to return the start value of the loop counter, which must be {@code int}.
7422 * See above for other constraints.
7423 * @param end a non-{@code null} handle to return the end value of the loop counter (the loop will run to
7424 * {@code end-1}). The result type must be {@code int}. See above for other constraints.
7425 * @param init optional initializer, providing the initial value of the loop variable.
7426 * May be {@code null}, implying a default initial value. See above for other constraints.
7427 * @param body body of the loop, which may not be {@code null}.
7428 * It controls the loop parameters and result type in the standard case (see above for details).
7429 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
7430 * and may accept any number of additional types.
7431 * See above for other constraints.
7432 *
7433 * @return a method handle representing the loop.
7434 * @throws NullPointerException if any of the {@code start}, {@code end}, or {@code body} handles is {@code null}.
7435 * @throws IllegalArgumentException if any argument violates the rules formulated above.
7436 *
7437 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle)
7438 * @since 9
7439 */
7440 public static MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
7441 countedLoopChecks(start, end, init, body);
7442 Class<?> counterType = start.type().returnType(); // int, but who's counting?
7443 Class<?> limitType = end.type().returnType(); // yes, int again
7444 Class<?> returnType = body.type().returnType();
7445 MethodHandle incr = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopStep);
7446 MethodHandle pred = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopPred);
7447 MethodHandle retv = null;
7448 if (returnType != void.class) {
7449 incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
7450 pred = dropArguments(pred, 1, returnType); // ditto
7451 retv = dropArguments(identity(returnType), 0, counterType);
7452 }
7453 body = dropArguments(body, 0, counterType); // ignore the limit variable
7454 MethodHandle[]
7455 loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
7456 bodyClause = { init, body }, // v = init(); v = body(v, i)
7457 indexVar = { start, incr }; // i = start(); i = i + 1
7458 return loop(loopLimit, bodyClause, indexVar);
7459 }
7460
7461 private static void countedLoopChecks(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
7462 Objects.requireNonNull(start);
7463 Objects.requireNonNull(end);
7464 Objects.requireNonNull(body);
7465 Class<?> counterType = start.type().returnType();
7466 if (counterType != int.class) {
7467 MethodType expected = start.type().changeReturnType(int.class);
7468 throw misMatchedTypes("start function", start.type(), expected);
7469 } else if (end.type().returnType() != counterType) {
7470 MethodType expected = end.type().changeReturnType(counterType);
7471 throw misMatchedTypes("end function", end.type(), expected);
7472 }
7473 MethodType bodyType = body.type();
7474 Class<?> returnType = bodyType.returnType();
7475 List<Class<?>> innerList = bodyType.parameterList();
7476 // strip leading V value if present
7477 int vsize = (returnType == void.class ? 0 : 1);
7478 if (vsize != 0 && (innerList.isEmpty() || innerList.get(0) != returnType)) {
7479 // argument list has no "V" => error
7480 MethodType expected = bodyType.insertParameterTypes(0, returnType);
7481 throw misMatchedTypes("body function", bodyType, expected);
7482 } else if (innerList.size() <= vsize || innerList.get(vsize) != counterType) {
7483 // missing I type => error
7484 MethodType expected = bodyType.insertParameterTypes(vsize, counterType);
7485 throw misMatchedTypes("body function", bodyType, expected);
7486 }
7487 List<Class<?>> outerList = innerList.subList(vsize + 1, innerList.size());
7488 if (outerList.isEmpty()) {
7489 // special case; take lists from end handle
7490 outerList = end.type().parameterList();
7491 innerList = bodyType.insertParameterTypes(vsize + 1, outerList).parameterList();
7492 }
7493 MethodType expected = methodType(counterType, outerList);
7494 if (!start.type().effectivelyIdenticalParameters(0, outerList)) {
7495 throw misMatchedTypes("start parameter types", start.type(), expected);
7496 }
7497 if (end.type() != start.type() &&
7498 !end.type().effectivelyIdenticalParameters(0, outerList)) {
7499 throw misMatchedTypes("end parameter types", end.type(), expected);
7500 }
7501 if (init != null) {
7502 MethodType initType = init.type();
7503 if (initType.returnType() != returnType ||
7504 !initType.effectivelyIdenticalParameters(0, outerList)) {
7505 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
7506 }
7507 }
7508 }
7509
7510 /**
7511 * Constructs a loop that ranges over the values produced by an {@code Iterator<T>}.
7512 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
7513 * <p>
7514 * The iterator itself will be determined by the evaluation of the {@code iterator} handle.
7515 * Each value it produces will be stored in a loop iteration variable of type {@code T}.
7516 * <p>
7517 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
7518 * of that type is also present. This variable is initialized using the optional {@code init} handle,
7519 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
7520 * <p>
7521 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
7522 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
7523 * iteration variable.
7524 * The result of the loop handle execution will be the final {@code V} value of that variable
7525 * (or {@code void} if there is no {@code V} variable).
7526 * <p>
7527 * The following rules hold for the argument handles:<ul>
7528 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
7529 * {@code (V T A...)V}, where {@code V} is non-{@code void}, or else {@code (T A...)void}.
7530 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
7531 * and we will write {@code (V T A...)V} with the understanding that a {@code void} type {@code V}
7532 * is quietly dropped from the parameter list, leaving {@code (T A...)V}.)
7533 * <li>The parameter list {@code (V T A...)} of the body contributes to a list
7534 * of types called the <em>internal parameter list</em>.
7535 * It will constrain the parameter lists of the other loop parts.
7536 * <li>As a special case, if the body contributes only {@code V} and {@code T} types,
7537 * with no additional {@code A} types, then the internal parameter list is extended by
7538 * the argument types {@code A...} of the {@code iterator} handle; if it is {@code null} the
7539 * single type {@code Iterable} is added and constitutes the {@code A...} list.
7540 * <li>If the iteration variable types {@code (V T)} are dropped from the internal parameter list, the resulting shorter
7541 * list {@code (A...)} is called the <em>external parameter list</em>.
7542 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
7543 * additional state variable of the loop.
7544 * The body must both accept a leading parameter and return a value of this type {@code V}.
7545 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
7546 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
7547 * <a href="MethodHandles.html#effid">effectively identical</a>
7548 * to the external parameter list {@code (A...)}.
7549 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
7550 * {@linkplain #empty default value}.
7551 * <li>If the {@code iterator} handle is non-{@code null}, it must have the return
7552 * type {@code java.util.Iterator} or a subtype thereof.
7553 * The iterator it produces when the loop is executed will be assumed
7554 * to yield values which can be converted to type {@code T}.
7555 * <li>The parameter list of an {@code iterator} that is non-{@code null} (of some form {@code (A*)}) must be
7556 * effectively identical to the external parameter list {@code (A...)}.
7557 * <li>If {@code iterator} is {@code null} it defaults to a method handle which behaves
7558 * like {@link java.lang.Iterable#iterator()}. In that case, the internal parameter list
7559 * {@code (V T A...)} must have at least one {@code A} type, and the default iterator
7560 * handle parameter is adjusted to accept the leading {@code A} type, as if by
7561 * the {@link MethodHandle#asType asType} conversion method.
7562 * The leading {@code A} type must be {@code Iterable} or a subtype thereof.
7563 * This conversion step, done at loop construction time, must not throw a {@code WrongMethodTypeException}.
7564 * </ul>
7565 * <p>
7566 * The type {@code T} may be either a primitive or reference.
7567 * Since type {@code Iterator<T>} is erased in the method handle representation to the raw type {@code Iterator},
7568 * the {@code iteratedLoop} combinator adjusts the leading argument type for {@code body} to {@code Object}
7569 * as if by the {@link MethodHandle#asType asType} conversion method.
7570 * Therefore, if an iterator of the wrong type appears as the loop is executed, runtime exceptions may occur
7571 * as the result of dynamic conversions performed by {@link MethodHandle#asType(MethodType)}.
7572 * <p>
7573 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
7574 * <li>The loop handle's result type is the result type {@code V} of the body.
7575 * <li>The loop handle's parameter types are the types {@code (A...)},
7576 * from the external parameter list.
7577 * </ul>
7578 * <p>
7579 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
7580 * the loop variable as well as the result type of the loop; {@code T}/{@code t}, that of the elements of the
7581 * structure the loop iterates over, and {@code A...}/{@code a...} represent arguments passed to the loop.
7582 * {@snippet lang="java" :
7583 * Iterator<T> iterator(A...); // defaults to Iterable::iterator
7584 * V init(A...);
7585 * V body(V,T,A...);
7586 * V iteratedLoop(A... a...) {
7587 * Iterator<T> it = iterator(a...);
7588 * V v = init(a...);
7589 * while (it.hasNext()) {
7590 * T t = it.next();
7591 * v = body(v, t, a...);
7592 * }
7593 * return v;
7594 * }
7595 * }
7596 *
7597 * @apiNote Example:
7598 * {@snippet lang="java" :
7599 * // get an iterator from a list
7600 * static List<String> reverseStep(List<String> r, String e) {
7601 * r.add(0, e);
7602 * return r;
7603 * }
7604 * static List<String> newArrayList() { return new ArrayList<>(); }
7605 * // assume MH_reverseStep and MH_newArrayList are handles to the above methods
7606 * MethodHandle loop = MethodHandles.iteratedLoop(null, MH_newArrayList, MH_reverseStep);
7607 * List<String> list = Arrays.asList("a", "b", "c", "d", "e");
7608 * List<String> reversedList = Arrays.asList("e", "d", "c", "b", "a");
7609 * assertEquals(reversedList, (List<String>) loop.invoke(list));
7610 * }
7611 *
7612 * @apiNote The implementation of this method can be expressed approximately as follows:
7613 * {@snippet lang="java" :
7614 * MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
7615 * // assume MH_next, MH_hasNext, MH_startIter are handles to methods of Iterator/Iterable
7616 * Class<?> returnType = body.type().returnType();
7617 * Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
7618 * MethodHandle nextVal = MH_next.asType(MH_next.type().changeReturnType(ttype));
7619 * MethodHandle retv = null, step = body, startIter = iterator;
7620 * if (returnType != void.class) {
7621 * // the simple thing first: in (I V A...), drop the I to get V
7622 * retv = dropArguments(identity(returnType), 0, Iterator.class);
7623 * // body type signature (V T A...), internal loop types (I V A...)
7624 * step = swapArguments(body, 0, 1); // swap V <-> T
7625 * }
7626 * if (startIter == null) startIter = MH_getIter;
7627 * MethodHandle[]
7628 * iterVar = { startIter, null, MH_hasNext, retv }, // it = iterator; while (it.hasNext())
7629 * bodyClause = { init, filterArguments(step, 0, nextVal) }; // v = body(v, t, a)
7630 * return loop(iterVar, bodyClause);
7631 * }
7632 * }
7633 *
7634 * @param iterator an optional handle to return the iterator to start the loop.
7635 * If non-{@code null}, the handle must return {@link java.util.Iterator} or a subtype.
7636 * See above for other constraints.
7637 * @param init optional initializer, providing the initial value of the loop variable.
7638 * May be {@code null}, implying a default initial value. See above for other constraints.
7639 * @param body body of the loop, which may not be {@code null}.
7640 * It controls the loop parameters and result type in the standard case (see above for details).
7641 * It must accept its own return type (if non-void) plus a {@code T} parameter (for the iterated values),
7642 * and may accept any number of additional types.
7643 * See above for other constraints.
7644 *
7645 * @return a method handle embodying the iteration loop functionality.
7646 * @throws NullPointerException if the {@code body} handle is {@code null}.
7647 * @throws IllegalArgumentException if any argument violates the above requirements.
7648 *
7649 * @since 9
7650 */
7651 public static MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
7652 Class<?> iterableType = iteratedLoopChecks(iterator, init, body);
7653 Class<?> returnType = body.type().returnType();
7654 MethodHandle hasNext = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iteratePred);
7655 MethodHandle nextRaw = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iterateNext);
7656 MethodHandle startIter;
7657 MethodHandle nextVal;
7658 {
7659 MethodType iteratorType;
7660 if (iterator == null) {
7661 // derive argument type from body, if available, else use Iterable
7662 startIter = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_initIterator);
7663 iteratorType = startIter.type().changeParameterType(0, iterableType);
7664 } else {
7665 // force return type to the internal iterator class
7666 iteratorType = iterator.type().changeReturnType(Iterator.class);
7667 startIter = iterator;
7668 }
7669 Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
7670 MethodType nextValType = nextRaw.type().changeReturnType(ttype);
7671
7672 // perform the asType transforms under an exception transformer, as per spec.:
7673 try {
7674 startIter = startIter.asType(iteratorType);
7675 nextVal = nextRaw.asType(nextValType);
7676 } catch (WrongMethodTypeException ex) {
7677 throw new IllegalArgumentException(ex);
7678 }
7679 }
7680
7681 MethodHandle retv = null, step = body;
7682 if (returnType != void.class) {
7683 // the simple thing first: in (I V A...), drop the I to get V
7684 retv = dropArguments(identity(returnType), 0, Iterator.class);
7685 // body type signature (V T A...), internal loop types (I V A...)
7686 step = swapArguments(body, 0, 1); // swap V <-> T
7687 }
7688
7689 MethodHandle[]
7690 iterVar = { startIter, null, hasNext, retv },
7691 bodyClause = { init, filterArgument(step, 0, nextVal) };
7692 return loop(iterVar, bodyClause);
7693 }
7694
7695 private static Class<?> iteratedLoopChecks(MethodHandle iterator, MethodHandle init, MethodHandle body) {
7696 Objects.requireNonNull(body);
7697 MethodType bodyType = body.type();
7698 Class<?> returnType = bodyType.returnType();
7699 List<Class<?>> internalParamList = bodyType.parameterList();
7700 // strip leading V value if present
7701 int vsize = (returnType == void.class ? 0 : 1);
7702 if (vsize != 0 && (internalParamList.isEmpty() || internalParamList.get(0) != returnType)) {
7703 // argument list has no "V" => error
7704 MethodType expected = bodyType.insertParameterTypes(0, returnType);
7705 throw misMatchedTypes("body function", bodyType, expected);
7706 } else if (internalParamList.size() <= vsize) {
7707 // missing T type => error
7708 MethodType expected = bodyType.insertParameterTypes(vsize, Object.class);
7709 throw misMatchedTypes("body function", bodyType, expected);
7710 }
7711 List<Class<?>> externalParamList = internalParamList.subList(vsize + 1, internalParamList.size());
7712 Class<?> iterableType = null;
7713 if (iterator != null) {
7714 // special case; if the body handle only declares V and T then
7715 // the external parameter list is obtained from iterator handle
7716 if (externalParamList.isEmpty()) {
7717 externalParamList = iterator.type().parameterList();
7718 }
7719 MethodType itype = iterator.type();
7720 if (!Iterator.class.isAssignableFrom(itype.returnType())) {
7721 throw newIllegalArgumentException("iteratedLoop first argument must have Iterator return type");
7722 }
7723 if (!itype.effectivelyIdenticalParameters(0, externalParamList)) {
7724 MethodType expected = methodType(itype.returnType(), externalParamList);
7725 throw misMatchedTypes("iterator parameters", itype, expected);
7726 }
7727 } else {
7728 if (externalParamList.isEmpty()) {
7729 // special case; if the iterator handle is null and the body handle
7730 // only declares V and T then the external parameter list consists
7731 // of Iterable
7732 externalParamList = List.of(Iterable.class);
7733 iterableType = Iterable.class;
7734 } else {
7735 // special case; if the iterator handle is null and the external
7736 // parameter list is not empty then the first parameter must be
7737 // assignable to Iterable
7738 iterableType = externalParamList.get(0);
7739 if (!Iterable.class.isAssignableFrom(iterableType)) {
7740 throw newIllegalArgumentException(
7741 "inferred first loop argument must inherit from Iterable: " + iterableType);
7742 }
7743 }
7744 }
7745 if (init != null) {
7746 MethodType initType = init.type();
7747 if (initType.returnType() != returnType ||
7748 !initType.effectivelyIdenticalParameters(0, externalParamList)) {
7749 throw misMatchedTypes("loop initializer", initType, methodType(returnType, externalParamList));
7750 }
7751 }
7752 return iterableType; // help the caller a bit
7753 }
7754
7755 /*non-public*/
7756 static MethodHandle swapArguments(MethodHandle mh, int i, int j) {
7757 // there should be a better way to uncross my wires
7758 int arity = mh.type().parameterCount();
7759 int[] order = new int[arity];
7760 for (int k = 0; k < arity; k++) order[k] = k;
7761 order[i] = j; order[j] = i;
7762 Class<?>[] types = mh.type().parameterArray();
7763 Class<?> ti = types[i]; types[i] = types[j]; types[j] = ti;
7764 MethodType swapType = methodType(mh.type().returnType(), types);
7765 return permuteArguments(mh, swapType, order);
7766 }
7767
7768 /**
7769 * Makes a method handle that adapts a {@code target} method handle by wrapping it in a {@code try-finally} block.
7770 * Another method handle, {@code cleanup}, represents the functionality of the {@code finally} block. Any exception
7771 * thrown during the execution of the {@code target} handle will be passed to the {@code cleanup} handle. The
7772 * exception will be rethrown, unless {@code cleanup} handle throws an exception first. The
7773 * value returned from the {@code cleanup} handle's execution will be the result of the execution of the
7774 * {@code try-finally} handle.
7775 * <p>
7776 * The {@code cleanup} handle will be passed one or two additional leading arguments.
7777 * The first is the exception thrown during the
7778 * execution of the {@code target} handle, or {@code null} if no exception was thrown.
7779 * The second is the result of the execution of the {@code target} handle, or, if it throws an exception,
7780 * a {@code null}, zero, or {@code false} value of the required type is supplied as a placeholder.
7781 * The second argument is not present if the {@code target} handle has a {@code void} return type.
7782 * (Note that, except for argument type conversions, combinators represent {@code void} values in parameter lists
7783 * by omitting the corresponding paradoxical arguments, not by inserting {@code null} or zero values.)
7784 * <p>
7785 * The {@code target} and {@code cleanup} handles must have the same corresponding argument and return types, except
7786 * that the {@code cleanup} handle may omit trailing arguments. Also, the {@code cleanup} handle must have one or
7787 * two extra leading parameters:<ul>
7788 * <li>a {@code Throwable}, which will carry the exception thrown by the {@code target} handle (if any); and
7789 * <li>a parameter of the same type as the return type of both {@code target} and {@code cleanup}, which will carry
7790 * the result from the execution of the {@code target} handle.
7791 * This parameter is not present if the {@code target} returns {@code void}.
7792 * </ul>
7793 * <p>
7794 * The pseudocode for the resulting adapter looks as follows. In the code, {@code V} represents the result type of
7795 * the {@code try/finally} construct; {@code A}/{@code a}, the types and values of arguments to the resulting
7796 * handle consumed by the cleanup; and {@code B}/{@code b}, those of arguments to the resulting handle discarded by
7797 * the cleanup.
7798 * {@snippet lang="java" :
7799 * V target(A..., B...);
7800 * V cleanup(Throwable, V, A...);
7801 * V adapter(A... a, B... b) {
7802 * V result = (zero value for V);
7803 * Throwable throwable = null;
7804 * try {
7805 * result = target(a..., b...);
7806 * } catch (Throwable t) {
7807 * throwable = t;
7808 * throw t;
7809 * } finally {
7810 * result = cleanup(throwable, result, a...);
7811 * }
7812 * return result;
7813 * }
7814 * }
7815 * <p>
7816 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
7817 * be modified by execution of the target, and so are passed unchanged
7818 * from the caller to the cleanup, if it is invoked.
7819 * <p>
7820 * The target and cleanup must return the same type, even if the cleanup
7821 * always throws.
7822 * To create such a throwing cleanup, compose the cleanup logic
7823 * with {@link #throwException throwException},
7824 * in order to create a method handle of the correct return type.
7825 * <p>
7826 * Note that {@code tryFinally} never converts exceptions into normal returns.
7827 * In rare cases where exceptions must be converted in that way, first wrap
7828 * the target with {@link #catchException(MethodHandle, Class, MethodHandle)}
7829 * to capture an outgoing exception, and then wrap with {@code tryFinally}.
7830 * <p>
7831 * It is recommended that the first parameter type of {@code cleanup} be
7832 * declared {@code Throwable} rather than a narrower subtype. This ensures
7833 * {@code cleanup} will always be invoked with whatever exception that
7834 * {@code target} throws. Declaring a narrower type may result in a
7835 * {@code ClassCastException} being thrown by the {@code try-finally}
7836 * handle if the type of the exception thrown by {@code target} is not
7837 * assignable to the first parameter type of {@code cleanup}. Note that
7838 * various exception types of {@code VirtualMachineError},
7839 * {@code LinkageError}, and {@code RuntimeException} can in principle be
7840 * thrown by almost any kind of Java code, and a finally clause that
7841 * catches (say) only {@code IOException} would mask any of the others
7842 * behind a {@code ClassCastException}.
7843 *
7844 * @param target the handle whose execution is to be wrapped in a {@code try} block.
7845 * @param cleanup the handle that is invoked in the finally block.
7846 *
7847 * @return a method handle embodying the {@code try-finally} block composed of the two arguments.
7848 * @throws NullPointerException if any argument is null
7849 * @throws IllegalArgumentException if {@code cleanup} does not accept
7850 * the required leading arguments, or if the method handle types do
7851 * not match in their return types and their
7852 * corresponding trailing parameters
7853 *
7854 * @see MethodHandles#catchException(MethodHandle, Class, MethodHandle)
7855 * @since 9
7856 */
7857 public static MethodHandle tryFinally(MethodHandle target, MethodHandle cleanup) {
7858 Class<?>[] targetParamTypes = target.type().ptypes();
7859 Class<?> rtype = target.type().returnType();
7860
7861 tryFinallyChecks(target, cleanup);
7862
7863 // Match parameter lists: if the cleanup has a shorter parameter list than the target, add ignored arguments.
7864 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
7865 // target parameter list.
7866 cleanup = dropArgumentsToMatch(cleanup, (rtype == void.class ? 1 : 2), targetParamTypes, 0, false);
7867
7868 // Ensure that the intrinsic type checks the instance thrown by the
7869 // target against the first parameter of cleanup
7870 cleanup = cleanup.asType(cleanup.type().changeParameterType(0, Throwable.class));
7871
7872 // Use asFixedArity() to avoid unnecessary boxing of last argument for VarargsCollector case.
7873 return MethodHandleImpl.makeTryFinally(target.asFixedArity(), cleanup.asFixedArity(), rtype, targetParamTypes);
7874 }
7875
7876 private static void tryFinallyChecks(MethodHandle target, MethodHandle cleanup) {
7877 Class<?> rtype = target.type().returnType();
7878 if (rtype != cleanup.type().returnType()) {
7879 throw misMatchedTypes("target and return types", cleanup.type().returnType(), rtype);
7880 }
7881 MethodType cleanupType = cleanup.type();
7882 if (!Throwable.class.isAssignableFrom(cleanupType.parameterType(0))) {
7883 throw misMatchedTypes("cleanup first argument and Throwable", cleanup.type(), Throwable.class);
7884 }
7885 if (rtype != void.class && cleanupType.parameterType(1) != rtype) {
7886 throw misMatchedTypes("cleanup second argument and target return type", cleanup.type(), rtype);
7887 }
7888 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
7889 // target parameter list.
7890 int cleanupArgIndex = rtype == void.class ? 1 : 2;
7891 if (!cleanupType.effectivelyIdenticalParameters(cleanupArgIndex, target.type().parameterList())) {
7892 throw misMatchedTypes("cleanup parameters after (Throwable,result) and target parameter list prefix",
7893 cleanup.type(), target.type());
7894 }
7895 }
7896
7897 /**
7898 * Creates a table switch method handle, which can be used to switch over a set of target
7899 * method handles, based on a given target index, called selector.
7900 * <p>
7901 * For a selector value of {@code n}, where {@code n} falls in the range {@code [0, N)},
7902 * and where {@code N} is the number of target method handles, the table switch method
7903 * handle will invoke the n-th target method handle from the list of target method handles.
7904 * <p>
7905 * For a selector value that does not fall in the range {@code [0, N)}, the table switch
7906 * method handle will invoke the given fallback method handle.
7907 * <p>
7908 * All method handles passed to this method must have the same type, with the additional
7909 * requirement that the leading parameter be of type {@code int}. The leading parameter
7910 * represents the selector.
7911 * <p>
7912 * Any trailing parameters present in the type will appear on the returned table switch
7913 * method handle as well. Any arguments assigned to these parameters will be forwarded,
7914 * together with the selector value, to the selected method handle when invoking it.
7915 *
7916 * @apiNote Example:
7917 * The cases each drop the {@code selector} value they are given, and take an additional
7918 * {@code String} argument, which is concatenated (using {@link String#concat(String)})
7919 * to a specific constant label string for each case:
7920 * {@snippet lang="java" :
7921 * MethodHandles.Lookup lookup = MethodHandles.lookup();
7922 * MethodHandle caseMh = lookup.findVirtual(String.class, "concat",
7923 * MethodType.methodType(String.class, String.class));
7924 * caseMh = MethodHandles.dropArguments(caseMh, 0, int.class);
7925 *
7926 * MethodHandle caseDefault = MethodHandles.insertArguments(caseMh, 1, "default: ");
7927 * MethodHandle case0 = MethodHandles.insertArguments(caseMh, 1, "case 0: ");
7928 * MethodHandle case1 = MethodHandles.insertArguments(caseMh, 1, "case 1: ");
7929 *
7930 * MethodHandle mhSwitch = MethodHandles.tableSwitch(
7931 * caseDefault,
7932 * case0,
7933 * case1
7934 * );
7935 *
7936 * assertEquals("default: data", (String) mhSwitch.invokeExact(-1, "data"));
7937 * assertEquals("case 0: data", (String) mhSwitch.invokeExact(0, "data"));
7938 * assertEquals("case 1: data", (String) mhSwitch.invokeExact(1, "data"));
7939 * assertEquals("default: data", (String) mhSwitch.invokeExact(2, "data"));
7940 * }
7941 *
7942 * @param fallback the fallback method handle that is called when the selector is not
7943 * within the range {@code [0, N)}.
7944 * @param targets array of target method handles.
7945 * @return the table switch method handle.
7946 * @throws NullPointerException if {@code fallback}, the {@code targets} array, or any
7947 * any of the elements of the {@code targets} array are
7948 * {@code null}.
7949 * @throws IllegalArgumentException if the {@code targets} array is empty, if the leading
7950 * parameter of the fallback handle or any of the target
7951 * handles is not {@code int}, or if the types of
7952 * the fallback handle and all of target handles are
7953 * not the same.
7954 */
7955 public static MethodHandle tableSwitch(MethodHandle fallback, MethodHandle... targets) {
7956 Objects.requireNonNull(fallback);
7957 Objects.requireNonNull(targets);
7958 targets = targets.clone();
7959 MethodType type = tableSwitchChecks(fallback, targets);
7960 return MethodHandleImpl.makeTableSwitch(type, fallback, targets);
7961 }
7962
7963 private static MethodType tableSwitchChecks(MethodHandle defaultCase, MethodHandle[] caseActions) {
7964 if (caseActions.length == 0)
7965 throw new IllegalArgumentException("Not enough cases: " + Arrays.toString(caseActions));
7966
7967 MethodType expectedType = defaultCase.type();
7968
7969 if (!(expectedType.parameterCount() >= 1) || expectedType.parameterType(0) != int.class)
7970 throw new IllegalArgumentException(
7971 "Case actions must have int as leading parameter: " + Arrays.toString(caseActions));
7972
7973 for (MethodHandle mh : caseActions) {
7974 Objects.requireNonNull(mh);
7975 if (mh.type() != expectedType)
7976 throw new IllegalArgumentException(
7977 "Case actions must have the same type: " + Arrays.toString(caseActions));
7978 }
7979
7980 return expectedType;
7981 }
7982
7983 /**
7984 * Adapts a target var handle by pre-processing incoming and outgoing values using a pair of filter functions.
7985 * <p>
7986 * When calling e.g. {@link VarHandle#set(Object...)} on the resulting var handle, the incoming value (of type {@code T}, where
7987 * {@code T} is the <em>last</em> parameter type of the first filter function) is processed using the first filter and then passed
7988 * to the target var handle.
7989 * Conversely, when calling e.g. {@link VarHandle#get(Object...)} on the resulting var handle, the return value obtained from
7990 * the target var handle (of type {@code T}, where {@code T} is the <em>last</em> parameter type of the second filter function)
7991 * is processed using the second filter and returned to the caller. More advanced access mode types, such as
7992 * {@link VarHandle.AccessMode#COMPARE_AND_EXCHANGE} might apply both filters at the same time.
7993 * <p>
7994 * For the boxing and unboxing filters to be well-formed, their types must be of the form {@code (A... , S) -> T} and
7995 * {@code (A... , T) -> S}, respectively, where {@code T} is the type of the target var handle. If this is the case,
7996 * the resulting var handle will have type {@code S} and will feature the additional coordinates {@code A...} (which
7997 * will be appended to the coordinates of the target var handle).
7998 * <p>
7999 * If the boxing and unboxing filters throw any checked exceptions when invoked, the resulting var handle will
8000 * throw an {@link IllegalStateException}.
8001 * <p>
8002 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
8003 * atomic access guarantees as those featured by the target var handle.
8004 *
8005 * @param target the target var handle
8006 * @param filterToTarget a filter to convert some type {@code S} into the type of {@code target}
8007 * @param filterFromTarget a filter to convert the type of {@code target} to some type {@code S}
8008 * @return an adapter var handle which accepts a new type, performing the provided boxing/unboxing conversions.
8009 * @throws IllegalArgumentException if {@code filterFromTarget} and {@code filterToTarget} are not well-formed, that is, they have types
8010 * other than {@code (A... , S) -> T} and {@code (A... , T) -> S}, respectively, where {@code T} is the type of the target var handle,
8011 * or if it's determined that either {@code filterFromTarget} or {@code filterToTarget} throws any checked exceptions.
8012 * @throws NullPointerException if any of the arguments is {@code null}.
8013 * @since 22
8014 */
8015 public static VarHandle filterValue(VarHandle target, MethodHandle filterToTarget, MethodHandle filterFromTarget) {
8016 return VarHandles.filterValue(target, filterToTarget, filterFromTarget);
8017 }
8018
8019 /**
8020 * Adapts a target var handle by pre-processing incoming coordinate values using unary filter functions.
8021 * <p>
8022 * When calling e.g. {@link VarHandle#get(Object...)} on the resulting var handle, the incoming coordinate values
8023 * starting at position {@code pos} (of type {@code C1, C2 ... Cn}, where {@code C1, C2 ... Cn} are the return types
8024 * of the unary filter functions) are transformed into new values (of type {@code S1, S2 ... Sn}, where {@code S1, S2 ... Sn} are the
8025 * parameter types of the unary filter functions), and then passed (along with any coordinate that was left unaltered
8026 * by the adaptation) to the target var handle.
8027 * <p>
8028 * For the coordinate filters to be well-formed, their types must be of the form {@code S1 -> T1, S2 -> T1 ... Sn -> Tn},
8029 * where {@code T1, T2 ... Tn} are the coordinate types starting at position {@code pos} of the target var handle.
8030 * <p>
8031 * If any of the filters throws a checked exception when invoked, the resulting var handle will
8032 * throw an {@link IllegalStateException}.
8033 * <p>
8034 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
8035 * atomic access guarantees as those featured by the target var handle.
8036 *
8037 * @param target the target var handle
8038 * @param pos the position of the first coordinate to be transformed
8039 * @param filters the unary functions which are used to transform coordinates starting at position {@code pos}
8040 * @return an adapter var handle which accepts new coordinate types, applying the provided transformation
8041 * to the new coordinate values.
8042 * @throws IllegalArgumentException if the handles in {@code filters} are not well-formed, that is, they have types
8043 * other than {@code S1 -> T1, S2 -> T2, ... Sn -> Tn} where {@code T1, T2 ... Tn} are the coordinate types starting
8044 * at position {@code pos} of the target var handle, if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive,
8045 * or if more filters are provided than the actual number of coordinate types available starting at {@code pos},
8046 * or if it's determined that any of the filters throws any checked exceptions.
8047 * @throws NullPointerException if any of the arguments is {@code null} or {@code filters} contains {@code null}.
8048 * @since 22
8049 */
8050 public static VarHandle filterCoordinates(VarHandle target, int pos, MethodHandle... filters) {
8051 return VarHandles.filterCoordinates(target, pos, filters);
8052 }
8053
8054 /**
8055 * Provides a target var handle with one or more <em>bound coordinates</em>
8056 * in advance of the var handle's invocation. As a consequence, the resulting var handle will feature less
8057 * coordinate types than the target var handle.
8058 * <p>
8059 * When calling e.g. {@link VarHandle#get(Object...)} on the resulting var handle, incoming coordinate values
8060 * are joined with bound coordinate values, and then passed to the target var handle.
8061 * <p>
8062 * For the bound coordinates to be well-formed, their types must be {@code T1, T2 ... Tn },
8063 * where {@code T1, T2 ... Tn} are the coordinate types starting at position {@code pos} of the target var handle.
8064 * <p>
8065 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
8066 * atomic access guarantees as those featured by the target var handle.
8067 *
8068 * @param target the var handle to invoke after the bound coordinates are inserted
8069 * @param pos the position of the first coordinate to be inserted
8070 * @param values the series of bound coordinates to insert
8071 * @return an adapter var handle which inserts additional coordinates,
8072 * before calling the target var handle
8073 * @throws IllegalArgumentException if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive,
8074 * or if more values are provided than the actual number of coordinate types available starting at {@code pos}.
8075 * @throws ClassCastException if the bound coordinates in {@code values} are not well-formed, that is, they have types
8076 * other than {@code T1, T2 ... Tn }, where {@code T1, T2 ... Tn} are the coordinate types starting at position {@code pos}
8077 * of the target var handle.
8078 * @throws NullPointerException if any of the arguments is {@code null} or {@code values} contains {@code null}.
8079 * @since 22
8080 */
8081 public static VarHandle insertCoordinates(VarHandle target, int pos, Object... values) {
8082 return VarHandles.insertCoordinates(target, pos, values);
8083 }
8084
8085 /**
8086 * Provides a var handle which adapts the coordinate values of the target var handle, by re-arranging them
8087 * so that the new coordinates match the provided ones.
8088 * <p>
8089 * The given array controls the reordering.
8090 * Call {@code #I} the number of incoming coordinates (the value
8091 * {@code newCoordinates.size()}), and call {@code #O} the number
8092 * of outgoing coordinates (the number of coordinates associated with the target var handle).
8093 * Then the length of the reordering array must be {@code #O},
8094 * and each element must be a non-negative number less than {@code #I}.
8095 * For every {@code N} less than {@code #O}, the {@code N}-th
8096 * outgoing coordinate will be taken from the {@code I}-th incoming
8097 * coordinate, where {@code I} is {@code reorder[N]}.
8098 * <p>
8099 * No coordinate value conversions are applied.
8100 * The type of each incoming coordinate, as determined by {@code newCoordinates},
8101 * must be identical to the type of the corresponding outgoing coordinate
8102 * in the target var handle.
8103 * <p>
8104 * The reordering array need not specify an actual permutation.
8105 * An incoming coordinate will be duplicated if its index appears
8106 * more than once in the array, and an incoming coordinate will be dropped
8107 * if its index does not appear in the array.
8108 * <p>
8109 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
8110 * atomic access guarantees as those featured by the target var handle.
8111 * @param target the var handle to invoke after the coordinates have been reordered
8112 * @param newCoordinates the new coordinate types
8113 * @param reorder an index array which controls the reordering
8114 * @return an adapter var handle which re-arranges the incoming coordinate values,
8115 * before calling the target var handle
8116 * @throws IllegalArgumentException if the index array length is not equal to
8117 * the number of coordinates of the target var handle, or if any index array element is not a valid index for
8118 * a coordinate of {@code newCoordinates}, or if two corresponding coordinate types in
8119 * the target var handle and in {@code newCoordinates} are not identical.
8120 * @throws NullPointerException if any of the arguments is {@code null} or {@code newCoordinates} contains {@code null}.
8121 * @since 22
8122 */
8123 public static VarHandle permuteCoordinates(VarHandle target, List<Class<?>> newCoordinates, int... reorder) {
8124 return VarHandles.permuteCoordinates(target, newCoordinates, reorder);
8125 }
8126
8127 /**
8128 * Adapts a target var handle by pre-processing
8129 * a sub-sequence of its coordinate values with a filter (a method handle).
8130 * The pre-processed coordinates are replaced by the result (if any) of the
8131 * filter function and the target var handle is then called on the modified (usually shortened)
8132 * coordinate list.
8133 * <p>
8134 * If {@code R} is the return type of the filter, then:
8135 * <ul>
8136 * <li>if {@code R} <em>is not</em> {@code void}, the target var handle must have a coordinate of type {@code R} in
8137 * position {@code pos}. The parameter types of the filter will replace the coordinate type at position {@code pos}
8138 * of the target var handle. When the returned var handle is invoked, it will be as if the filter is invoked first,
8139 * and its result is passed in place of the coordinate at position {@code pos} in a downstream invocation of the
8140 * target var handle.</li>
8141 * <li> if {@code R} <em>is</em> {@code void}, the parameter types (if any) of the filter will be inserted in the
8142 * coordinate type list of the target var handle at position {@code pos}. In this case, when the returned var handle
8143 * is invoked, the filter essentially acts as a side effect, consuming some of the coordinate values, before a
8144 * downstream invocation of the target var handle.</li>
8145 * </ul>
8146 * <p>
8147 * If any of the filters throws a checked exception when invoked, the resulting var handle will
8148 * throw an {@link IllegalStateException}.
8149 * <p>
8150 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
8151 * atomic access guarantees as those featured by the target var handle.
8152 *
8153 * @param target the var handle to invoke after the coordinates have been filtered
8154 * @param pos the position in the coordinate list of the target var handle where the filter is to be inserted
8155 * @param filter the filter method handle
8156 * @return an adapter var handle which filters the incoming coordinate values,
8157 * before calling the target var handle
8158 * @throws IllegalArgumentException if the return type of {@code filter}
8159 * is not void, and it is not the same as the {@code pos} coordinate of the target var handle,
8160 * if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive,
8161 * if the resulting var handle's type would have <a href="MethodHandle.html#maxarity">too many coordinates</a>,
8162 * or if it's determined that {@code filter} throws any checked exceptions.
8163 * @throws NullPointerException if any of the arguments is {@code null}.
8164 * @since 22
8165 */
8166 public static VarHandle collectCoordinates(VarHandle target, int pos, MethodHandle filter) {
8167 return VarHandles.collectCoordinates(target, pos, filter);
8168 }
8169
8170 /**
8171 * Returns a var handle which will discard some dummy coordinates before delegating to the
8172 * target var handle. As a consequence, the resulting var handle will feature more
8173 * coordinate types than the target var handle.
8174 * <p>
8175 * The {@code pos} argument may range between zero and <i>N</i>, where <i>N</i> is the arity of the
8176 * target var handle's coordinate types. If {@code pos} is zero, the dummy coordinates will precede
8177 * the target's real arguments; if {@code pos} is <i>N</i> they will come after.
8178 * <p>
8179 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
8180 * atomic access guarantees as those featured by the target var handle.
8181 *
8182 * @param target the var handle to invoke after the dummy coordinates are dropped
8183 * @param pos position of the first coordinate to drop (zero for the leftmost)
8184 * @param valueTypes the type(s) of the coordinate(s) to drop
8185 * @return an adapter var handle which drops some dummy coordinates,
8186 * before calling the target var handle
8187 * @throws IllegalArgumentException if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive.
8188 * @throws NullPointerException if any of the arguments is {@code null} or {@code valueTypes} contains {@code null}.
8189 * @since 22
8190 */
8191 public static VarHandle dropCoordinates(VarHandle target, int pos, Class<?>... valueTypes) {
8192 return VarHandles.dropCoordinates(target, pos, valueTypes);
8193 }
8194 }