1 /*
2 * Copyright (c) 2008, 2022, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package java.lang.invoke;
27
28 import jdk.internal.access.SharedSecrets;
29 import jdk.internal.foreign.Utils;
30 import jdk.internal.javac.PreviewFeature;
31 import jdk.internal.misc.Unsafe;
32 import jdk.internal.misc.VM;
33 import jdk.internal.org.objectweb.asm.ClassReader;
34 import jdk.internal.org.objectweb.asm.Opcodes;
35 import jdk.internal.org.objectweb.asm.Type;
36 import jdk.internal.reflect.CallerSensitive;
37 import jdk.internal.reflect.CallerSensitiveAdapter;
38 import jdk.internal.reflect.Reflection;
39 import jdk.internal.vm.annotation.ForceInline;
40 import sun.invoke.util.ValueConversions;
41 import sun.invoke.util.VerifyAccess;
42 import sun.invoke.util.Wrapper;
43 import sun.reflect.misc.ReflectUtil;
44 import sun.security.util.SecurityConstants;
45
46 import java.lang.constant.ConstantDescs;
47 import java.lang.foreign.GroupLayout;
48 import java.lang.foreign.MemoryLayout;
49 import java.lang.foreign.MemorySegment;
50 import java.lang.foreign.ValueLayout;
51 import java.lang.invoke.LambdaForm.BasicType;
52 import java.lang.reflect.Constructor;
53 import java.lang.reflect.Field;
54 import java.lang.reflect.Member;
55 import java.lang.reflect.Method;
56 import java.lang.reflect.Modifier;
57 import java.nio.ByteOrder;
58 import java.security.ProtectionDomain;
59 import java.util.ArrayList;
60 import java.util.Arrays;
61 import java.util.BitSet;
62 import java.util.Iterator;
63 import java.util.List;
64 import java.util.Objects;
65 import java.util.Set;
66 import java.util.concurrent.ConcurrentHashMap;
67 import java.util.stream.Stream;
68
69 import static java.lang.invoke.LambdaForm.BasicType.V_TYPE;
70 import static java.lang.invoke.MethodHandleImpl.Intrinsic;
71 import static java.lang.invoke.MethodHandleNatives.Constants.*;
72 import static java.lang.invoke.MethodHandleStatics.UNSAFE;
73 import static java.lang.invoke.MethodHandleStatics.newIllegalArgumentException;
74 import static java.lang.invoke.MethodHandleStatics.newInternalError;
75 import static java.lang.invoke.MethodType.methodType;
76
77 /**
78 * This class consists exclusively of static methods that operate on or return
79 * method handles. They fall into several categories:
80 * <ul>
81 * <li>Lookup methods which help create method handles for methods and fields.
82 * <li>Combinator methods, which combine or transform pre-existing method handles into new ones.
83 * <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns.
84 * </ul>
85 * A lookup, combinator, or factory method will fail and throw an
86 * {@code IllegalArgumentException} if the created method handle's type
87 * would have <a href="MethodHandle.html#maxarity">too many parameters</a>.
88 *
89 * @author John Rose, JSR 292 EG
90 * @since 1.7
91 */
92 public class MethodHandles {
93
94 private MethodHandles() { } // do not instantiate
95
96 static final MemberName.Factory IMPL_NAMES = MemberName.getFactory();
97
98 // See IMPL_LOOKUP below.
99
100 //// Method handle creation from ordinary methods.
101
102 /**
103 * Returns a {@link Lookup lookup object} with
104 * full capabilities to emulate all supported bytecode behaviors of the caller.
105 * These capabilities include {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access} to the caller.
106 * Factory methods on the lookup object can create
107 * <a href="MethodHandleInfo.html#directmh">direct method handles</a>
108 * for any member that the caller has access to via bytecodes,
109 * including protected and private fields and methods.
110 * This lookup object is created by the original lookup class
111 * and has the {@link Lookup#ORIGINAL ORIGINAL} bit set.
112 * This lookup object is a <em>capability</em> which may be delegated to trusted agents.
113 * Do not store it in place where untrusted code can access it.
114 * <p>
115 * This method is caller sensitive, which means that it may return different
116 * values to different callers.
117 * In cases where {@code MethodHandles.lookup} is called from a context where
118 * there is no caller frame on the stack (e.g. when called directly
119 * from a JNI attached thread), {@code IllegalCallerException} is thrown.
120 * To obtain a {@link Lookup lookup object} in such a context, use an auxiliary class that will
121 * implicitly be identified as the caller, or use {@link MethodHandles#publicLookup()}
122 * to obtain a low-privileged lookup instead.
123 * @return a lookup object for the caller of this method, with
124 * {@linkplain Lookup#ORIGINAL original} and
125 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access}.
126 * @throws IllegalCallerException if there is no caller frame on the stack.
127 */
128 @CallerSensitive
129 @ForceInline // to ensure Reflection.getCallerClass optimization
130 public static Lookup lookup() {
131 final Class<?> c = Reflection.getCallerClass();
132 if (c == null) {
133 throw new IllegalCallerException("no caller frame");
134 }
135 return new Lookup(c);
136 }
137
138 /**
139 * This lookup method is the alternate implementation of
140 * the lookup method with a leading caller class argument which is
141 * non-caller-sensitive. This method is only invoked by reflection
142 * and method handle.
143 */
144 @CallerSensitiveAdapter
145 private static Lookup lookup(Class<?> caller) {
146 if (caller.getClassLoader() == null) {
147 throw newInternalError("calling lookup() reflectively is not supported: "+caller);
148 }
149 return new Lookup(caller);
150 }
151
152 /**
153 * Returns a {@link Lookup lookup object} which is trusted minimally.
154 * The lookup has the {@code UNCONDITIONAL} mode.
155 * It can only be used to create method handles to public members of
156 * public classes in packages that are exported unconditionally.
157 * <p>
158 * As a matter of pure convention, the {@linkplain Lookup#lookupClass() lookup class}
159 * of this lookup object will be {@link java.lang.Object}.
160 *
161 * @apiNote The use of Object is conventional, and because the lookup modes are
162 * limited, there is no special access provided to the internals of Object, its package
163 * or its module. This public lookup object or other lookup object with
164 * {@code UNCONDITIONAL} mode assumes readability. Consequently, the lookup class
165 * is not used to determine the lookup context.
166 *
167 * <p style="font-size:smaller;">
168 * <em>Discussion:</em>
169 * The lookup class can be changed to any other class {@code C} using an expression of the form
170 * {@link Lookup#in publicLookup().in(C.class)}.
171 * A public lookup object is always subject to
172 * <a href="MethodHandles.Lookup.html#secmgr">security manager checks</a>.
173 * Also, it cannot access
174 * <a href="MethodHandles.Lookup.html#callsens">caller sensitive methods</a>.
175 * @return a lookup object which is trusted minimally
176 *
177 * @revised 9
178 */
179 public static Lookup publicLookup() {
180 return Lookup.PUBLIC_LOOKUP;
181 }
182
183 /**
184 * Returns a {@link Lookup lookup} object on a target class to emulate all supported
185 * bytecode behaviors, including <a href="MethodHandles.Lookup.html#privacc">private access</a>.
186 * The returned lookup object can provide access to classes in modules and packages,
187 * and members of those classes, outside the normal rules of Java access control,
188 * instead conforming to the more permissive rules for modular <em>deep reflection</em>.
189 * <p>
190 * A caller, specified as a {@code Lookup} object, in module {@code M1} is
191 * allowed to do deep reflection on module {@code M2} and package of the target class
192 * if and only if all of the following conditions are {@code true}:
193 * <ul>
194 * <li>If there is a security manager, its {@code checkPermission} method is
195 * called to check {@code ReflectPermission("suppressAccessChecks")} and
196 * that must return normally.
197 * <li>The caller lookup object must have {@linkplain Lookup#hasFullPrivilegeAccess()
198 * full privilege access}. Specifically:
199 * <ul>
200 * <li>The caller lookup object must have the {@link Lookup#MODULE MODULE} lookup mode.
201 * (This is because otherwise there would be no way to ensure the original lookup
202 * creator was a member of any particular module, and so any subsequent checks
203 * for readability and qualified exports would become ineffective.)
204 * <li>The caller lookup object must have {@link Lookup#PRIVATE PRIVATE} access.
205 * (This is because an application intending to share intra-module access
206 * using {@link Lookup#MODULE MODULE} alone will inadvertently also share
207 * deep reflection to its own module.)
208 * </ul>
209 * <li>The target class must be a proper class, not a primitive or array class.
210 * (Thus, {@code M2} is well-defined.)
211 * <li>If the caller module {@code M1} differs from
212 * the target module {@code M2} then both of the following must be true:
213 * <ul>
214 * <li>{@code M1} {@link Module#canRead reads} {@code M2}.</li>
215 * <li>{@code M2} {@link Module#isOpen(String,Module) opens} the package
216 * containing the target class to at least {@code M1}.</li>
217 * </ul>
218 * </ul>
219 * <p>
220 * If any of the above checks is violated, this method fails with an
221 * exception.
222 * <p>
223 * Otherwise, if {@code M1} and {@code M2} are the same module, this method
224 * returns a {@code Lookup} on {@code targetClass} with
225 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access}
226 * with {@code null} previous lookup class.
227 * <p>
228 * Otherwise, {@code M1} and {@code M2} are two different modules. This method
229 * returns a {@code Lookup} on {@code targetClass} that records
230 * the lookup class of the caller as the new previous lookup class with
231 * {@code PRIVATE} access but no {@code MODULE} access.
232 * <p>
233 * The resulting {@code Lookup} object has no {@code ORIGINAL} access.
234 *
235 * @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 ({@code "<init>"} and {@code "<clinit>"}).
709 * The internal syntax of invocation instructions allows them to refer to such internal
710 * methods as if they were normal methods, but the JVM bytecode verifier rejects them.
711 * A lookup of such an internal method will produce a {@code NoSuchMethodException}.
712 * <p>
713 * If the relationship between nested types is expressed directly through the
714 * {@code NestHost} and {@code NestMembers} attributes
715 * (see the Java Virtual Machine Specification, sections {@jvms
716 * 4.7.28} and {@jvms 4.7.29}),
717 * then the associated {@code Lookup} object provides direct access to
718 * the lookup class and all of its nestmates
719 * (see {@link java.lang.Class#getNestHost Class.getNestHost}).
720 * Otherwise, access between nested classes is obtained by the Java compiler creating
721 * a wrapper method to access a private method of another class in the same nest.
722 * For example, a nested class {@code C.D}
723 * can access private members within other related classes such as
724 * {@code C}, {@code C.D.E}, or {@code C.B},
725 * but the Java compiler may need to generate wrapper methods in
726 * those related classes. In such cases, a {@code Lookup} object on
727 * {@code C.E} would be unable to access those private members.
728 * A workaround for this limitation is the {@link Lookup#in Lookup.in} method,
729 * which can transform a lookup on {@code C.E} into one on any of those other
730 * classes, without special elevation of privilege.
731 * <p>
732 * The accesses permitted to a given lookup object may be limited,
733 * according to its set of {@link #lookupModes lookupModes},
734 * to a subset of members normally accessible to the lookup class.
735 * For example, the {@link MethodHandles#publicLookup publicLookup}
736 * method produces a lookup object which is only allowed to access
737 * public members in public classes of exported packages.
738 * The caller sensitive method {@link MethodHandles#lookup lookup}
739 * produces a lookup object with full capabilities relative to
740 * its caller class, to emulate all supported bytecode behaviors.
741 * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object
742 * with fewer access modes than the original lookup object.
743 *
744 * <p style="font-size:smaller;">
745 * <a id="privacc"></a>
746 * <em>Discussion of private and module access:</em>
747 * We say that a lookup has <em>private access</em>
748 * if its {@linkplain #lookupModes lookup modes}
749 * include the possibility of accessing {@code private} members
750 * (which includes the private members of nestmates).
751 * As documented in the relevant methods elsewhere,
752 * only lookups with private access possess the following capabilities:
753 * <ul style="font-size:smaller;">
754 * <li>access private fields, methods, and constructors of the lookup class and its nestmates
755 * <li>create method handles which {@link Lookup#findSpecial emulate invokespecial} instructions
756 * <li>avoid <a href="MethodHandles.Lookup.html#secmgr">package access checks</a>
757 * for classes accessible to the lookup class
758 * <li>create {@link Lookup#in delegated lookup objects} which have private access to other classes
759 * within the same package member
760 * </ul>
761 * <p style="font-size:smaller;">
762 * Similarly, a lookup with module access ensures that the original lookup creator was
763 * a member in the same module as the lookup class.
764 * <p style="font-size:smaller;">
765 * Private and module access are independently determined modes; a lookup may have
766 * either or both or neither. A lookup which possesses both access modes is said to
767 * possess {@linkplain #hasFullPrivilegeAccess() full privilege access}.
768 * <p style="font-size:smaller;">
769 * A lookup with <em>original access</em> ensures that this lookup is created by
770 * the original lookup class and the bootstrap method invoked by the VM.
771 * Such a lookup with original access also has private and module access
772 * which has the following additional capability:
773 * <ul style="font-size:smaller;">
774 * <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> methods,
775 * such as {@code Class.forName}
776 * <li>obtain the {@linkplain MethodHandles#classData(Lookup, String, Class)
777 * class data} associated with the lookup class</li>
778 * </ul>
779 * <p style="font-size:smaller;">
780 * Each of these permissions is a consequence of the fact that a lookup object
781 * with private access can be securely traced back to an originating class,
782 * whose <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> and Java language access permissions
783 * can be reliably determined and emulated by method handles.
784 *
785 * <h2><a id="cross-module-lookup"></a>Cross-module lookups</h2>
786 * When a lookup class in one module {@code M1} accesses a class in another module
787 * {@code M2}, extra access checking is performed beyond the access mode bits.
788 * A {@code Lookup} with {@link #PUBLIC} mode and a lookup class in {@code M1}
789 * can access public types in {@code M2} when {@code M2} is readable to {@code M1}
790 * and when the type is in a package of {@code M2} that is exported to
791 * at least {@code M1}.
792 * <p>
793 * A {@code Lookup} on {@code C} can also <em>teleport</em> to a target class
794 * via {@link #in(Class) Lookup.in} and {@link MethodHandles#privateLookupIn(Class, Lookup)
795 * MethodHandles.privateLookupIn} methods.
796 * Teleporting across modules will always record the original lookup class as
797 * the <em>{@linkplain #previousLookupClass() previous lookup class}</em>
798 * and drops {@link Lookup#MODULE MODULE} access.
799 * If the target class is in the same module as the lookup class {@code C},
800 * then the target class becomes the new lookup class
801 * and there is no change to the previous lookup class.
802 * If the target class is in a different module from {@code M1} ({@code C}'s module),
803 * {@code C} becomes the new previous lookup class
804 * and the target class becomes the new lookup class.
805 * In that case, if there was already a previous lookup class in {@code M0},
806 * and it differs from {@code M1} and {@code M2}, then the resulting lookup
807 * drops all privileges.
808 * For example,
809 * {@snippet lang="java" :
810 * Lookup lookup = MethodHandles.lookup(); // in class C
811 * Lookup lookup2 = lookup.in(D.class);
812 * MethodHandle mh = lookup2.findStatic(E.class, "m", MT);
813 * }
814 * <p>
815 * The {@link #lookup()} factory method produces a {@code Lookup} object
816 * with {@code null} previous lookup class.
817 * {@link Lookup#in lookup.in(D.class)} transforms the {@code lookup} on class {@code C}
818 * to class {@code D} without elevation of privileges.
819 * If {@code C} and {@code D} are in the same module,
820 * {@code lookup2} records {@code D} as the new lookup class and keeps the
821 * same previous lookup class as the original {@code lookup}, or
822 * {@code null} if not present.
823 * <p>
824 * When a {@code Lookup} teleports from a class
825 * in one nest to another nest, {@code PRIVATE} access is dropped.
826 * When a {@code Lookup} teleports from a class in one package to
827 * another package, {@code PACKAGE} access is dropped.
828 * When a {@code Lookup} teleports from a class in one module to another module,
829 * {@code MODULE} access is dropped.
830 * Teleporting across modules drops the ability to access non-exported classes
831 * in both the module of the new lookup class and the module of the old lookup class
832 * and the resulting {@code Lookup} remains only {@code PUBLIC} access.
833 * A {@code Lookup} can teleport back and forth to a class in the module of
834 * the lookup class and the module of the previous class lookup.
835 * Teleporting across modules can only decrease access but cannot increase it.
836 * Teleporting to some third module drops all accesses.
837 * <p>
838 * In the above example, if {@code C} and {@code D} are in different modules,
839 * {@code lookup2} records {@code D} as its lookup class and
840 * {@code C} as its previous lookup class and {@code lookup2} has only
841 * {@code PUBLIC} access. {@code lookup2} can teleport to other class in
842 * {@code C}'s module and {@code D}'s module.
843 * If class {@code E} is in a third module, {@code lookup2.in(E.class)} creates
844 * a {@code Lookup} on {@code E} with no access and {@code lookup2}'s lookup
845 * class {@code D} is recorded as its previous lookup class.
846 * <p>
847 * Teleporting across modules restricts access to the public types that
848 * both the lookup class and the previous lookup class can equally access
849 * (see below).
850 * <p>
851 * {@link MethodHandles#privateLookupIn(Class, Lookup) MethodHandles.privateLookupIn(T.class, lookup)}
852 * can be used to teleport a {@code lookup} from class {@code C} to class {@code T}
853 * and create a new {@code Lookup} with <a href="#privacc">private access</a>
854 * if the lookup class is allowed to do <em>deep reflection</em> on {@code T}.
855 * The {@code lookup} must have {@link #MODULE} and {@link #PRIVATE} access
856 * to call {@code privateLookupIn}.
857 * A {@code lookup} on {@code C} in module {@code M1} is allowed to do deep reflection
858 * on all classes in {@code M1}. If {@code T} is in {@code M1}, {@code privateLookupIn}
859 * produces a new {@code Lookup} on {@code T} with full capabilities.
860 * A {@code lookup} on {@code C} is also allowed
861 * to do deep reflection on {@code T} in another module {@code M2} if
862 * {@code M1} reads {@code M2} and {@code M2} {@link Module#isOpen(String,Module) opens}
863 * the package containing {@code T} to at least {@code M1}.
864 * {@code T} becomes the new lookup class and {@code C} becomes the new previous
865 * lookup class and {@code MODULE} access is dropped from the resulting {@code Lookup}.
866 * The resulting {@code Lookup} can be used to do member lookup or teleport
867 * to another lookup class by calling {@link #in Lookup::in}. But
868 * it cannot be used to obtain another private {@code Lookup} by calling
869 * {@link MethodHandles#privateLookupIn(Class, Lookup) privateLookupIn}
870 * because it has no {@code MODULE} access.
871 *
872 * <h2><a id="module-access-check"></a>Cross-module access checks</h2>
873 *
874 * A {@code Lookup} with {@link #PUBLIC} or with {@link #UNCONDITIONAL} mode
875 * allows cross-module access. The access checking is performed with respect
876 * to both the lookup class and the previous lookup class if present.
877 * <p>
878 * A {@code Lookup} with {@link #UNCONDITIONAL} mode can access public type
879 * in all modules when the type is in a package that is {@linkplain Module#isExported(String)
880 * exported unconditionally}.
881 * <p>
882 * If a {@code Lookup} on {@code LC} in {@code M1} has no previous lookup class,
883 * the lookup with {@link #PUBLIC} mode can access all public types in modules
884 * that are readable to {@code M1} and the type is in a package that is exported
885 * at least to {@code M1}.
886 * <p>
887 * If a {@code Lookup} on {@code LC} in {@code M1} has a previous lookup class
888 * {@code PLC} on {@code M0}, the lookup with {@link #PUBLIC} mode can access
889 * the intersection of all public types that are accessible to {@code M1}
890 * with all public types that are accessible to {@code M0}. {@code M0}
891 * reads {@code M1} and hence the set of accessible types includes:
892 *
893 * <ul>
894 * <li>unconditional-exported packages from {@code M1}</li>
895 * <li>unconditional-exported packages from {@code M0} if {@code M1} reads {@code M0}</li>
896 * <li>
897 * unconditional-exported packages from a third module {@code M2}if both {@code M0}
898 * and {@code M1} read {@code M2}
899 * </li>
900 * <li>qualified-exported packages from {@code M1} to {@code M0}</li>
901 * <li>qualified-exported packages from {@code M0} to {@code M1} if {@code M1} reads {@code M0}</li>
902 * <li>
903 * qualified-exported packages from a third module {@code M2} to both {@code M0} and
904 * {@code M1} if both {@code M0} and {@code M1} read {@code M2}
905 * </li>
906 * </ul>
907 *
908 * <h2><a id="access-modes"></a>Access modes</h2>
909 *
910 * The table below shows the access modes of a {@code Lookup} produced by
911 * any of the following factory or transformation methods:
912 * <ul>
913 * <li>{@link #lookup() MethodHandles::lookup}</li>
914 * <li>{@link #publicLookup() MethodHandles::publicLookup}</li>
915 * <li>{@link #privateLookupIn(Class, Lookup) MethodHandles::privateLookupIn}</li>
916 * <li>{@link Lookup#in Lookup::in}</li>
917 * <li>{@link Lookup#dropLookupMode(int) Lookup::dropLookupMode}</li>
918 * </ul>
919 *
920 * <table class="striped">
921 * <caption style="display:none">
922 * Access mode summary
923 * </caption>
924 * <thead>
925 * <tr>
926 * <th scope="col">Lookup object</th>
927 * <th style="text-align:center">original</th>
928 * <th style="text-align:center">protected</th>
929 * <th style="text-align:center">private</th>
930 * <th style="text-align:center">package</th>
931 * <th style="text-align:center">module</th>
932 * <th style="text-align:center">public</th>
933 * </tr>
934 * </thead>
935 * <tbody>
936 * <tr>
937 * <th scope="row" style="text-align:left">{@code CL = MethodHandles.lookup()} in {@code C}</th>
938 * <td style="text-align:center">ORI</td>
939 * <td style="text-align:center">PRO</td>
940 * <td style="text-align:center">PRI</td>
941 * <td style="text-align:center">PAC</td>
942 * <td style="text-align:center">MOD</td>
943 * <td style="text-align:center">1R</td>
944 * </tr>
945 * <tr>
946 * <th scope="row" style="text-align:left">{@code CL.in(C1)} same package</th>
947 * <td></td>
948 * <td></td>
949 * <td></td>
950 * <td style="text-align:center">PAC</td>
951 * <td style="text-align:center">MOD</td>
952 * <td style="text-align:center">1R</td>
953 * </tr>
954 * <tr>
955 * <th scope="row" style="text-align:left">{@code CL.in(C1)} same module</th>
956 * <td></td>
957 * <td></td>
958 * <td></td>
959 * <td></td>
960 * <td style="text-align:center">MOD</td>
961 * <td style="text-align:center">1R</td>
962 * </tr>
963 * <tr>
964 * <th scope="row" style="text-align:left">{@code CL.in(D)} different module</th>
965 * <td></td>
966 * <td></td>
967 * <td></td>
968 * <td></td>
969 * <td></td>
970 * <td style="text-align:center">2R</td>
971 * </tr>
972 * <tr>
973 * <th scope="row" style="text-align:left">{@code CL.in(D).in(C)} hop back to module</th>
974 * <td></td>
975 * <td></td>
976 * <td></td>
977 * <td></td>
978 * <td></td>
979 * <td style="text-align:center">2R</td>
980 * </tr>
981 * <tr>
982 * <th scope="row" style="text-align:left">{@code PRI1 = privateLookupIn(C1,CL)}</th>
983 * <td></td>
984 * <td style="text-align:center">PRO</td>
985 * <td style="text-align:center">PRI</td>
986 * <td style="text-align:center">PAC</td>
987 * <td style="text-align:center">MOD</td>
988 * <td style="text-align:center">1R</td>
989 * </tr>
990 * <tr>
991 * <th scope="row" style="text-align:left">{@code PRI1a = privateLookupIn(C,PRI1)}</th>
992 * <td></td>
993 * <td style="text-align:center">PRO</td>
994 * <td style="text-align:center">PRI</td>
995 * <td style="text-align:center">PAC</td>
996 * <td style="text-align:center">MOD</td>
997 * <td style="text-align:center">1R</td>
998 * </tr>
999 * <tr>
1000 * <th scope="row" style="text-align:left">{@code PRI1.in(C1)} same package</th>
1001 * <td></td>
1002 * <td></td>
1003 * <td></td>
1004 * <td style="text-align:center">PAC</td>
1005 * <td style="text-align:center">MOD</td>
1006 * <td style="text-align:center">1R</td>
1007 * </tr>
1008 * <tr>
1009 * <th scope="row" style="text-align:left">{@code PRI1.in(C1)} different package</th>
1010 * <td></td>
1011 * <td></td>
1012 * <td></td>
1013 * <td></td>
1014 * <td style="text-align:center">MOD</td>
1015 * <td style="text-align:center">1R</td>
1016 * </tr>
1017 * <tr>
1018 * <th scope="row" style="text-align:left">{@code PRI1.in(D)} different module</th>
1019 * <td></td>
1020 * <td></td>
1021 * <td></td>
1022 * <td></td>
1023 * <td></td>
1024 * <td style="text-align:center">2R</td>
1025 * </tr>
1026 * <tr>
1027 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PROTECTED)}</th>
1028 * <td></td>
1029 * <td></td>
1030 * <td style="text-align:center">PRI</td>
1031 * <td style="text-align:center">PAC</td>
1032 * <td style="text-align:center">MOD</td>
1033 * <td style="text-align:center">1R</td>
1034 * </tr>
1035 * <tr>
1036 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PRIVATE)}</th>
1037 * <td></td>
1038 * <td></td>
1039 * <td></td>
1040 * <td style="text-align:center">PAC</td>
1041 * <td style="text-align:center">MOD</td>
1042 * <td style="text-align:center">1R</td>
1043 * </tr>
1044 * <tr>
1045 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PACKAGE)}</th>
1046 * <td></td>
1047 * <td></td>
1048 * <td></td>
1049 * <td></td>
1050 * <td style="text-align:center">MOD</td>
1051 * <td style="text-align:center">1R</td>
1052 * </tr>
1053 * <tr>
1054 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(MODULE)}</th>
1055 * <td></td>
1056 * <td></td>
1057 * <td></td>
1058 * <td></td>
1059 * <td></td>
1060 * <td style="text-align:center">1R</td>
1061 * </tr>
1062 * <tr>
1063 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PUBLIC)}</th>
1064 * <td></td>
1065 * <td></td>
1066 * <td></td>
1067 * <td></td>
1068 * <td></td>
1069 * <td style="text-align:center">none</td>
1070 * <tr>
1071 * <th scope="row" style="text-align:left">{@code PRI2 = privateLookupIn(D,CL)}</th>
1072 * <td></td>
1073 * <td style="text-align:center">PRO</td>
1074 * <td style="text-align:center">PRI</td>
1075 * <td style="text-align:center">PAC</td>
1076 * <td></td>
1077 * <td style="text-align:center">2R</td>
1078 * </tr>
1079 * <tr>
1080 * <th scope="row" style="text-align:left">{@code privateLookupIn(D,PRI1)}</th>
1081 * <td></td>
1082 * <td style="text-align:center">PRO</td>
1083 * <td style="text-align:center">PRI</td>
1084 * <td style="text-align:center">PAC</td>
1085 * <td></td>
1086 * <td style="text-align:center">2R</td>
1087 * </tr>
1088 * <tr>
1089 * <th scope="row" style="text-align:left">{@code privateLookupIn(C,PRI2)} fails</th>
1090 * <td></td>
1091 * <td></td>
1092 * <td></td>
1093 * <td></td>
1094 * <td></td>
1095 * <td style="text-align:center">IAE</td>
1096 * </tr>
1097 * <tr>
1098 * <th scope="row" style="text-align:left">{@code PRI2.in(D2)} same package</th>
1099 * <td></td>
1100 * <td></td>
1101 * <td></td>
1102 * <td style="text-align:center">PAC</td>
1103 * <td></td>
1104 * <td style="text-align:center">2R</td>
1105 * </tr>
1106 * <tr>
1107 * <th scope="row" style="text-align:left">{@code PRI2.in(D2)} different package</th>
1108 * <td></td>
1109 * <td></td>
1110 * <td></td>
1111 * <td></td>
1112 * <td></td>
1113 * <td style="text-align:center">2R</td>
1114 * </tr>
1115 * <tr>
1116 * <th scope="row" style="text-align:left">{@code PRI2.in(C1)} hop back to module</th>
1117 * <td></td>
1118 * <td></td>
1119 * <td></td>
1120 * <td></td>
1121 * <td></td>
1122 * <td style="text-align:center">2R</td>
1123 * </tr>
1124 * <tr>
1125 * <th scope="row" style="text-align:left">{@code PRI2.in(E)} hop to third module</th>
1126 * <td></td>
1127 * <td></td>
1128 * <td></td>
1129 * <td></td>
1130 * <td></td>
1131 * <td style="text-align:center">none</td>
1132 * </tr>
1133 * <tr>
1134 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PROTECTED)}</th>
1135 * <td></td>
1136 * <td></td>
1137 * <td style="text-align:center">PRI</td>
1138 * <td style="text-align:center">PAC</td>
1139 * <td></td>
1140 * <td style="text-align:center">2R</td>
1141 * </tr>
1142 * <tr>
1143 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PRIVATE)}</th>
1144 * <td></td>
1145 * <td></td>
1146 * <td></td>
1147 * <td style="text-align:center">PAC</td>
1148 * <td></td>
1149 * <td style="text-align:center">2R</td>
1150 * </tr>
1151 * <tr>
1152 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PACKAGE)}</th>
1153 * <td></td>
1154 * <td></td>
1155 * <td></td>
1156 * <td></td>
1157 * <td></td>
1158 * <td style="text-align:center">2R</td>
1159 * </tr>
1160 * <tr>
1161 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(MODULE)}</th>
1162 * <td></td>
1163 * <td></td>
1164 * <td></td>
1165 * <td></td>
1166 * <td></td>
1167 * <td style="text-align:center">2R</td>
1168 * </tr>
1169 * <tr>
1170 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PUBLIC)}</th>
1171 * <td></td>
1172 * <td></td>
1173 * <td></td>
1174 * <td></td>
1175 * <td></td>
1176 * <td style="text-align:center">none</td>
1177 * </tr>
1178 * <tr>
1179 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PROTECTED)}</th>
1180 * <td></td>
1181 * <td></td>
1182 * <td style="text-align:center">PRI</td>
1183 * <td style="text-align:center">PAC</td>
1184 * <td style="text-align:center">MOD</td>
1185 * <td style="text-align:center">1R</td>
1186 * </tr>
1187 * <tr>
1188 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PRIVATE)}</th>
1189 * <td></td>
1190 * <td></td>
1191 * <td></td>
1192 * <td style="text-align:center">PAC</td>
1193 * <td style="text-align:center">MOD</td>
1194 * <td style="text-align:center">1R</td>
1195 * </tr>
1196 * <tr>
1197 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PACKAGE)}</th>
1198 * <td></td>
1199 * <td></td>
1200 * <td></td>
1201 * <td></td>
1202 * <td style="text-align:center">MOD</td>
1203 * <td style="text-align:center">1R</td>
1204 * </tr>
1205 * <tr>
1206 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(MODULE)}</th>
1207 * <td></td>
1208 * <td></td>
1209 * <td></td>
1210 * <td></td>
1211 * <td></td>
1212 * <td style="text-align:center">1R</td>
1213 * </tr>
1214 * <tr>
1215 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PUBLIC)}</th>
1216 * <td></td>
1217 * <td></td>
1218 * <td></td>
1219 * <td></td>
1220 * <td></td>
1221 * <td style="text-align:center">none</td>
1222 * </tr>
1223 * <tr>
1224 * <th scope="row" style="text-align:left">{@code PUB = publicLookup()}</th>
1225 * <td></td>
1226 * <td></td>
1227 * <td></td>
1228 * <td></td>
1229 * <td></td>
1230 * <td style="text-align:center">U</td>
1231 * </tr>
1232 * <tr>
1233 * <th scope="row" style="text-align:left">{@code PUB.in(D)} different module</th>
1234 * <td></td>
1235 * <td></td>
1236 * <td></td>
1237 * <td></td>
1238 * <td></td>
1239 * <td style="text-align:center">U</td>
1240 * </tr>
1241 * <tr>
1242 * <th scope="row" style="text-align:left">{@code PUB.in(D).in(E)} third module</th>
1243 * <td></td>
1244 * <td></td>
1245 * <td></td>
1246 * <td></td>
1247 * <td></td>
1248 * <td style="text-align:center">U</td>
1249 * </tr>
1250 * <tr>
1251 * <th scope="row" style="text-align:left">{@code PUB.dropLookupMode(UNCONDITIONAL)}</th>
1252 * <td></td>
1253 * <td></td>
1254 * <td></td>
1255 * <td></td>
1256 * <td></td>
1257 * <td style="text-align:center">none</td>
1258 * </tr>
1259 * <tr>
1260 * <th scope="row" style="text-align:left">{@code privateLookupIn(C1,PUB)} fails</th>
1261 * <td></td>
1262 * <td></td>
1263 * <td></td>
1264 * <td></td>
1265 * <td></td>
1266 * <td style="text-align:center">IAE</td>
1267 * </tr>
1268 * <tr>
1269 * <th scope="row" style="text-align:left">{@code ANY.in(X)}, for inaccessible {@code X}</th>
1270 * <td></td>
1271 * <td></td>
1272 * <td></td>
1273 * <td></td>
1274 * <td></td>
1275 * <td style="text-align:center">none</td>
1276 * </tr>
1277 * </tbody>
1278 * </table>
1279 *
1280 * <p>
1281 * Notes:
1282 * <ul>
1283 * <li>Class {@code C} and class {@code C1} are in module {@code M1},
1284 * but {@code D} and {@code D2} are in module {@code M2}, and {@code E}
1285 * is in module {@code M3}. {@code X} stands for class which is inaccessible
1286 * to the lookup. {@code ANY} stands for any of the example lookups.</li>
1287 * <li>{@code ORI} indicates {@link #ORIGINAL} bit set,
1288 * {@code PRO} indicates {@link #PROTECTED} bit set,
1289 * {@code PRI} indicates {@link #PRIVATE} bit set,
1290 * {@code PAC} indicates {@link #PACKAGE} bit set,
1291 * {@code MOD} indicates {@link #MODULE} bit set,
1292 * {@code 1R} and {@code 2R} indicate {@link #PUBLIC} bit set,
1293 * {@code U} indicates {@link #UNCONDITIONAL} bit set,
1294 * {@code IAE} indicates {@code IllegalAccessException} thrown.</li>
1295 * <li>Public access comes in three kinds:
1296 * <ul>
1297 * <li>unconditional ({@code U}): the lookup assumes readability.
1298 * The lookup has {@code null} previous lookup class.
1299 * <li>one-module-reads ({@code 1R}): the module access checking is
1300 * performed with respect to the lookup class. The lookup has {@code null}
1301 * previous lookup class.
1302 * <li>two-module-reads ({@code 2R}): the module access checking is
1303 * performed with respect to the lookup class and the previous lookup class.
1304 * The lookup has a non-null previous lookup class which is in a
1305 * different module from the current lookup class.
1306 * </ul>
1307 * <li>Any attempt to reach a third module loses all access.</li>
1308 * <li>If a target class {@code X} is not accessible to {@code Lookup::in}
1309 * all access modes are dropped.</li>
1310 * </ul>
1311 *
1312 * <h2><a id="secmgr"></a>Security manager interactions</h2>
1313 * Although bytecode instructions can only refer to classes in
1314 * a related class loader, this API can search for methods in any
1315 * class, as long as a reference to its {@code Class} object is
1316 * available. Such cross-loader references are also possible with the
1317 * Core Reflection API, and are impossible to bytecode instructions
1318 * such as {@code invokestatic} or {@code getfield}.
1319 * There is a {@linkplain java.lang.SecurityManager security manager API}
1320 * to allow applications to check such cross-loader references.
1321 * These checks apply to both the {@code MethodHandles.Lookup} API
1322 * and the Core Reflection API
1323 * (as found on {@link java.lang.Class Class}).
1324 * <p>
1325 * If a security manager is present, member and class lookups are subject to
1326 * additional checks.
1327 * From one to three calls are made to the security manager.
1328 * Any of these calls can refuse access by throwing a
1329 * {@link java.lang.SecurityException SecurityException}.
1330 * Define {@code smgr} as the security manager,
1331 * {@code lookc} as the lookup class of the current lookup object,
1332 * {@code refc} as the containing class in which the member
1333 * is being sought, and {@code defc} as the class in which the
1334 * member is actually defined.
1335 * (If a class or other type is being accessed,
1336 * the {@code refc} and {@code defc} values are the class itself.)
1337 * The value {@code lookc} is defined as <em>not present</em>
1338 * if the current lookup object does not have
1339 * {@linkplain #hasFullPrivilegeAccess() full privilege access}.
1340 * The calls are made according to the following rules:
1341 * <ul>
1342 * <li><b>Step 1:</b>
1343 * If {@code lookc} is not present, or if its class loader is not
1344 * the same as or an ancestor of the class loader of {@code refc},
1345 * then {@link SecurityManager#checkPackageAccess
1346 * smgr.checkPackageAccess(refcPkg)} is called,
1347 * where {@code refcPkg} is the package of {@code refc}.
1348 * <li><b>Step 2a:</b>
1349 * If the retrieved member is not public and
1350 * {@code lookc} is not present, then
1351 * {@link SecurityManager#checkPermission smgr.checkPermission}
1352 * with {@code RuntimePermission("accessDeclaredMembers")} is called.
1353 * <li><b>Step 2b:</b>
1354 * If the retrieved class has a {@code null} class loader,
1355 * and {@code lookc} is not present, then
1356 * {@link SecurityManager#checkPermission smgr.checkPermission}
1357 * with {@code RuntimePermission("getClassLoader")} is called.
1358 * <li><b>Step 3:</b>
1359 * If the retrieved member is not public,
1360 * and if {@code lookc} is not present,
1361 * and if {@code defc} and {@code refc} are different,
1362 * then {@link SecurityManager#checkPackageAccess
1363 * smgr.checkPackageAccess(defcPkg)} is called,
1364 * where {@code defcPkg} is the package of {@code defc}.
1365 * </ul>
1366 * Security checks are performed after other access checks have passed.
1367 * Therefore, the above rules presuppose a member or class that is public,
1368 * or else that is being accessed from a lookup class that has
1369 * rights to access the member or class.
1370 * <p>
1371 * If a security manager is present and the current lookup object does not have
1372 * {@linkplain #hasFullPrivilegeAccess() full privilege access}, then
1373 * {@link #defineClass(byte[]) defineClass},
1374 * {@link #defineHiddenClass(byte[], boolean, ClassOption...) defineHiddenClass},
1375 * {@link #defineHiddenClassWithClassData(byte[], Object, boolean, ClassOption...)
1376 * defineHiddenClassWithClassData}
1377 * calls {@link SecurityManager#checkPermission smgr.checkPermission}
1378 * with {@code RuntimePermission("defineClass")}.
1379 *
1380 * <h2><a id="callsens"></a>Caller sensitive methods</h2>
1381 * A small number of Java methods have a special property called caller sensitivity.
1382 * A <em>caller-sensitive</em> method can behave differently depending on the
1383 * identity of its immediate caller.
1384 * <p>
1385 * If a method handle for a caller-sensitive method is requested,
1386 * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> apply,
1387 * but they take account of the lookup class in a special way.
1388 * The resulting method handle behaves as if it were called
1389 * from an instruction contained in the lookup class,
1390 * so that the caller-sensitive method detects the lookup class.
1391 * (By contrast, the invoker of the method handle is disregarded.)
1392 * Thus, in the case of caller-sensitive methods,
1393 * different lookup classes may give rise to
1394 * differently behaving method handles.
1395 * <p>
1396 * In cases where the lookup object is
1397 * {@link MethodHandles#publicLookup() publicLookup()},
1398 * or some other lookup object without the
1399 * {@linkplain #ORIGINAL original access},
1400 * the lookup class is disregarded.
1401 * In such cases, no caller-sensitive method handle can be created,
1402 * access is forbidden, and the lookup fails with an
1403 * {@code IllegalAccessException}.
1404 * <p style="font-size:smaller;">
1405 * <em>Discussion:</em>
1406 * For example, the caller-sensitive method
1407 * {@link java.lang.Class#forName(String) Class.forName(x)}
1408 * can return varying classes or throw varying exceptions,
1409 * depending on the class loader of the class that calls it.
1410 * A public lookup of {@code Class.forName} will fail, because
1411 * there is no reasonable way to determine its bytecode behavior.
1412 * <p style="font-size:smaller;">
1413 * If an application caches method handles for broad sharing,
1414 * it should use {@code publicLookup()} to create them.
1415 * If there is a lookup of {@code Class.forName}, it will fail,
1416 * and the application must take appropriate action in that case.
1417 * It may be that a later lookup, perhaps during the invocation of a
1418 * bootstrap method, can incorporate the specific identity
1419 * of the caller, making the method accessible.
1420 * <p style="font-size:smaller;">
1421 * The function {@code MethodHandles.lookup} is caller sensitive
1422 * so that there can be a secure foundation for lookups.
1423 * Nearly all other methods in the JSR 292 API rely on lookup
1424 * objects to check access requests.
1425 *
1426 * @revised 9
1427 */
1428 public static final
1429 class Lookup {
1430 /** The class on behalf of whom the lookup is being performed. */
1431 private final Class<?> lookupClass;
1432
1433 /** previous lookup class */
1434 private final Class<?> prevLookupClass;
1435
1436 /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */
1437 private final int allowedModes;
1438
1439 static {
1440 Reflection.registerFieldsToFilter(Lookup.class, Set.of("lookupClass", "allowedModes"));
1441 }
1442
1443 /** A single-bit mask representing {@code public} access,
1444 * which may contribute to the result of {@link #lookupModes lookupModes}.
1445 * The value, {@code 0x01}, happens to be the same as the value of the
1446 * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.
1447 * <p>
1448 * A {@code Lookup} with this lookup mode performs cross-module access check
1449 * with respect to the {@linkplain #lookupClass() lookup class} and
1450 * {@linkplain #previousLookupClass() previous lookup class} if present.
1451 */
1452 public static final int PUBLIC = Modifier.PUBLIC;
1453
1454 /** A single-bit mask representing {@code private} access,
1455 * which may contribute to the result of {@link #lookupModes lookupModes}.
1456 * The value, {@code 0x02}, happens to be the same as the value of the
1457 * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.
1458 */
1459 public static final int PRIVATE = Modifier.PRIVATE;
1460
1461 /** A single-bit mask representing {@code protected} access,
1462 * which may contribute to the result of {@link #lookupModes lookupModes}.
1463 * The value, {@code 0x04}, happens to be the same as the value of the
1464 * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.
1465 */
1466 public static final int PROTECTED = Modifier.PROTECTED;
1467
1468 /** A single-bit mask representing {@code package} access (default access),
1469 * which may contribute to the result of {@link #lookupModes lookupModes}.
1470 * The value is {@code 0x08}, which does not correspond meaningfully to
1471 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1472 */
1473 public static final int PACKAGE = Modifier.STATIC;
1474
1475 /** A single-bit mask representing {@code module} access,
1476 * which may contribute to the result of {@link #lookupModes lookupModes}.
1477 * The value is {@code 0x10}, which does not correspond meaningfully to
1478 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1479 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup}
1480 * with this lookup mode can access all public types in the module of the
1481 * lookup class and public types in packages exported by other modules
1482 * to the module of the lookup class.
1483 * <p>
1484 * If this lookup mode is set, the {@linkplain #previousLookupClass()
1485 * previous lookup class} is always {@code null}.
1486 *
1487 * @since 9
1488 */
1489 public static final int MODULE = PACKAGE << 1;
1490
1491 /** A single-bit mask representing {@code unconditional} access
1492 * which may contribute to the result of {@link #lookupModes lookupModes}.
1493 * The value is {@code 0x20}, which does not correspond meaningfully to
1494 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1495 * A {@code Lookup} with this lookup mode assumes {@linkplain
1496 * java.lang.Module#canRead(java.lang.Module) readability}.
1497 * This lookup mode can access all public members of public types
1498 * of all modules when the type is in a package that is {@link
1499 * java.lang.Module#isExported(String) exported unconditionally}.
1500 *
1501 * <p>
1502 * If this lookup mode is set, the {@linkplain #previousLookupClass()
1503 * previous lookup class} is always {@code null}.
1504 *
1505 * @since 9
1506 * @see #publicLookup()
1507 */
1508 public static final int UNCONDITIONAL = PACKAGE << 2;
1509
1510 /** A single-bit mask representing {@code original} access
1511 * which may contribute to the result of {@link #lookupModes lookupModes}.
1512 * The value is {@code 0x40}, which does not correspond meaningfully to
1513 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1514 *
1515 * <p>
1516 * If this lookup mode is set, the {@code Lookup} object must be
1517 * created by the original lookup class by calling
1518 * {@link MethodHandles#lookup()} method or by a bootstrap method
1519 * invoked by the VM. The {@code Lookup} object with this lookup
1520 * mode has {@linkplain #hasFullPrivilegeAccess() full privilege access}.
1521 *
1522 * @since 16
1523 */
1524 public static final int ORIGINAL = PACKAGE << 3;
1525
1526 private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE | MODULE | UNCONDITIONAL | ORIGINAL);
1527 private static final int FULL_POWER_MODES = (ALL_MODES & ~UNCONDITIONAL); // with original access
1528 private static final int TRUSTED = -1;
1529
1530 /*
1531 * Adjust PUBLIC => PUBLIC|MODULE|ORIGINAL|UNCONDITIONAL
1532 * Adjust 0 => PACKAGE
1533 */
1534 private static int fixmods(int mods) {
1535 mods &= (ALL_MODES - PACKAGE - MODULE - ORIGINAL - UNCONDITIONAL);
1536 if (Modifier.isPublic(mods))
1537 mods |= UNCONDITIONAL;
1538 return (mods != 0) ? mods : PACKAGE;
1539 }
1540
1541 /** Tells which class is performing the lookup. It is this class against
1542 * which checks are performed for visibility and access permissions.
1543 * <p>
1544 * If this lookup object has a {@linkplain #previousLookupClass() previous lookup class},
1545 * access checks are performed against both the lookup class and the previous lookup class.
1546 * <p>
1547 * The class implies a maximum level of access permission,
1548 * but the permissions may be additionally limited by the bitmask
1549 * {@link #lookupModes lookupModes}, which controls whether non-public members
1550 * can be accessed.
1551 * @return the lookup class, on behalf of which this lookup object finds members
1552 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1553 */
1554 public Class<?> lookupClass() {
1555 return lookupClass;
1556 }
1557
1558 /** Reports a lookup class in another module that this lookup object
1559 * was previously teleported from, or {@code null}.
1560 * <p>
1561 * A {@code Lookup} object produced by the factory methods, such as the
1562 * {@link #lookup() lookup()} and {@link #publicLookup() publicLookup()} method,
1563 * has {@code null} previous lookup class.
1564 * A {@code Lookup} object has a non-null previous lookup class
1565 * when this lookup was teleported from an old lookup class
1566 * in one module to a new lookup class in another module.
1567 *
1568 * @return the lookup class in another module that this lookup object was
1569 * previously teleported from, or {@code null}
1570 * @since 14
1571 * @see #in(Class)
1572 * @see MethodHandles#privateLookupIn(Class, Lookup)
1573 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1574 */
1575 public Class<?> previousLookupClass() {
1576 return prevLookupClass;
1577 }
1578
1579 // This is just for calling out to MethodHandleImpl.
1580 private Class<?> lookupClassOrNull() {
1581 return (allowedModes == TRUSTED) ? null : lookupClass;
1582 }
1583
1584 /** Tells which access-protection classes of members this lookup object can produce.
1585 * The result is a bit-mask of the bits
1586 * {@linkplain #PUBLIC PUBLIC (0x01)},
1587 * {@linkplain #PRIVATE PRIVATE (0x02)},
1588 * {@linkplain #PROTECTED PROTECTED (0x04)},
1589 * {@linkplain #PACKAGE PACKAGE (0x08)},
1590 * {@linkplain #MODULE MODULE (0x10)},
1591 * {@linkplain #UNCONDITIONAL UNCONDITIONAL (0x20)},
1592 * and {@linkplain #ORIGINAL ORIGINAL (0x40)}.
1593 * <p>
1594 * A freshly-created lookup object
1595 * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class} has
1596 * all possible bits set, except {@code UNCONDITIONAL}.
1597 * A lookup object on a new lookup class
1598 * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object}
1599 * may have some mode bits set to zero.
1600 * Mode bits can also be
1601 * {@linkplain java.lang.invoke.MethodHandles.Lookup#dropLookupMode directly cleared}.
1602 * Once cleared, mode bits cannot be restored from the downgraded lookup object.
1603 * The purpose of this is to restrict access via the new lookup object,
1604 * so that it can access only names which can be reached by the original
1605 * lookup object, and also by the new lookup class.
1606 * @return the lookup modes, which limit the kinds of access performed by this lookup object
1607 * @see #in
1608 * @see #dropLookupMode
1609 *
1610 * @revised 9
1611 */
1612 public int lookupModes() {
1613 return allowedModes & ALL_MODES;
1614 }
1615
1616 /** Embody the current class (the lookupClass) as a lookup class
1617 * for method handle creation.
1618 * Must be called by from a method in this package,
1619 * which in turn is called by a method not in this package.
1620 */
1621 Lookup(Class<?> lookupClass) {
1622 this(lookupClass, null, FULL_POWER_MODES);
1623 }
1624
1625 private Lookup(Class<?> lookupClass, Class<?> prevLookupClass, int allowedModes) {
1626 assert prevLookupClass == null || ((allowedModes & MODULE) == 0
1627 && prevLookupClass.getModule() != lookupClass.getModule());
1628 assert !lookupClass.isArray() && !lookupClass.isPrimitive();
1629 this.lookupClass = lookupClass;
1630 this.prevLookupClass = prevLookupClass;
1631 this.allowedModes = allowedModes;
1632 }
1633
1634 private static Lookup newLookup(Class<?> lookupClass, Class<?> prevLookupClass, int allowedModes) {
1635 // make sure we haven't accidentally picked up a privileged class:
1636 checkUnprivilegedlookupClass(lookupClass);
1637 return new Lookup(lookupClass, prevLookupClass, allowedModes);
1638 }
1639
1640 /**
1641 * Creates a lookup on the specified new lookup class.
1642 * The resulting object will report the specified
1643 * class as its own {@link #lookupClass() lookupClass}.
1644 *
1645 * <p>
1646 * However, the resulting {@code Lookup} object is guaranteed
1647 * to have no more access capabilities than the original.
1648 * In particular, access capabilities can be lost as follows:<ul>
1649 * <li>If the new lookup class is different from the old lookup class,
1650 * i.e. {@link #ORIGINAL ORIGINAL} access is lost.
1651 * <li>If the new lookup class is in a different module from the old one,
1652 * i.e. {@link #MODULE MODULE} access is lost.
1653 * <li>If the new lookup class is in a different package
1654 * than the old one, protected and default (package) members will not be accessible,
1655 * i.e. {@link #PROTECTED PROTECTED} and {@link #PACKAGE PACKAGE} access are lost.
1656 * <li>If the new lookup class is not within the same package member
1657 * as the old one, private members will not be accessible, and protected members
1658 * will not be accessible by virtue of inheritance,
1659 * i.e. {@link #PRIVATE PRIVATE} access is lost.
1660 * (Protected members may continue to be accessible because of package sharing.)
1661 * <li>If the new lookup class is not
1662 * {@linkplain #accessClass(Class) accessible} to this lookup,
1663 * then no members, not even public members, will be accessible
1664 * i.e. all access modes are lost.
1665 * <li>If the new lookup class, the old lookup class and the previous lookup class
1666 * are all in different modules i.e. teleporting to a third module,
1667 * all access modes are lost.
1668 * </ul>
1669 * <p>
1670 * The new previous lookup class is chosen as follows:
1671 * <ul>
1672 * <li>If the new lookup object has {@link #UNCONDITIONAL UNCONDITIONAL} bit,
1673 * the new previous lookup class is {@code null}.
1674 * <li>If the new lookup class is in the same module as the old lookup class,
1675 * the new previous lookup class is the old previous lookup class.
1676 * <li>If the new lookup class is in a different module from the old lookup class,
1677 * the new previous lookup class is the old lookup class.
1678 *</ul>
1679 * <p>
1680 * The resulting lookup's capabilities for loading classes
1681 * (used during {@link #findClass} invocations)
1682 * are determined by the lookup class' loader,
1683 * which may change due to this operation.
1684 *
1685 * @param requestedLookupClass the desired lookup class for the new lookup object
1686 * @return a lookup object which reports the desired lookup class, or the same object
1687 * if there is no change
1688 * @throws IllegalArgumentException if {@code requestedLookupClass} is a primitive type or void or array class
1689 * @throws NullPointerException if the argument is null
1690 *
1691 * @revised 9
1692 * @see #accessClass(Class)
1693 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1694 */
1695 public Lookup in(Class<?> requestedLookupClass) {
1696 Objects.requireNonNull(requestedLookupClass);
1697 if (requestedLookupClass.isPrimitive())
1698 throw new IllegalArgumentException(requestedLookupClass + " is a primitive class");
1699 if (requestedLookupClass.isArray())
1700 throw new IllegalArgumentException(requestedLookupClass + " is an array class");
1701
1702 if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all
1703 return new Lookup(requestedLookupClass, null, FULL_POWER_MODES);
1704 if (requestedLookupClass == this.lookupClass)
1705 return this; // keep same capabilities
1706 int newModes = (allowedModes & FULL_POWER_MODES) & ~ORIGINAL;
1707 Module fromModule = this.lookupClass.getModule();
1708 Module targetModule = requestedLookupClass.getModule();
1709 Class<?> plc = this.previousLookupClass();
1710 if ((this.allowedModes & UNCONDITIONAL) != 0) {
1711 assert plc == null;
1712 newModes = UNCONDITIONAL;
1713 } else if (fromModule != targetModule) {
1714 if (plc != null && !VerifyAccess.isSameModule(plc, requestedLookupClass)) {
1715 // allow hopping back and forth between fromModule and plc's module
1716 // but not the third module
1717 newModes = 0;
1718 }
1719 // drop MODULE access
1720 newModes &= ~(MODULE|PACKAGE|PRIVATE|PROTECTED);
1721 // teleport from this lookup class
1722 plc = this.lookupClass;
1723 }
1724 if ((newModes & PACKAGE) != 0
1725 && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {
1726 newModes &= ~(PACKAGE|PRIVATE|PROTECTED);
1727 }
1728 // Allow nestmate lookups to be created without special privilege:
1729 if ((newModes & PRIVATE) != 0
1730 && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {
1731 newModes &= ~(PRIVATE|PROTECTED);
1732 }
1733 if ((newModes & (PUBLIC|UNCONDITIONAL)) != 0
1734 && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, this.prevLookupClass, allowedModes)) {
1735 // The requested class it not accessible from the lookup class.
1736 // No permissions.
1737 newModes = 0;
1738 }
1739 return newLookup(requestedLookupClass, plc, newModes);
1740 }
1741
1742 /**
1743 * Creates a lookup on the same lookup class which this lookup object
1744 * finds members, but with a lookup mode that has lost the given lookup mode.
1745 * The lookup mode to drop is one of {@link #PUBLIC PUBLIC}, {@link #MODULE
1746 * MODULE}, {@link #PACKAGE PACKAGE}, {@link #PROTECTED PROTECTED},
1747 * {@link #PRIVATE PRIVATE}, {@link #ORIGINAL ORIGINAL}, or
1748 * {@link #UNCONDITIONAL UNCONDITIONAL}.
1749 *
1750 * <p> If this lookup is a {@linkplain MethodHandles#publicLookup() public lookup},
1751 * this lookup has {@code UNCONDITIONAL} mode set and it has no other mode set.
1752 * When dropping {@code UNCONDITIONAL} on a public lookup then the resulting
1753 * lookup has no access.
1754 *
1755 * <p> If this lookup is not a public lookup, then the following applies
1756 * regardless of its {@linkplain #lookupModes() lookup modes}.
1757 * {@link #PROTECTED PROTECTED} and {@link #ORIGINAL ORIGINAL} are always
1758 * dropped and so the resulting lookup mode will never have these access
1759 * capabilities. When dropping {@code PACKAGE}
1760 * then the resulting lookup will not have {@code PACKAGE} or {@code PRIVATE}
1761 * access. When dropping {@code MODULE} then the resulting lookup will not
1762 * have {@code MODULE}, {@code PACKAGE}, or {@code PRIVATE} access.
1763 * When dropping {@code PUBLIC} then the resulting lookup has no access.
1764 *
1765 * @apiNote
1766 * A lookup with {@code PACKAGE} but not {@code PRIVATE} mode can safely
1767 * delegate non-public access within the package of the lookup class without
1768 * conferring <a href="MethodHandles.Lookup.html#privacc">private access</a>.
1769 * A lookup with {@code MODULE} but not
1770 * {@code PACKAGE} mode can safely delegate {@code PUBLIC} access within
1771 * the module of the lookup class without conferring package access.
1772 * A lookup with a {@linkplain #previousLookupClass() previous lookup class}
1773 * (and {@code PUBLIC} but not {@code MODULE} mode) can safely delegate access
1774 * to public classes accessible to both the module of the lookup class
1775 * and the module of the previous lookup class.
1776 *
1777 * @param modeToDrop the lookup mode to drop
1778 * @return a lookup object which lacks the indicated mode, or the same object if there is no change
1779 * @throws IllegalArgumentException if {@code modeToDrop} is not one of {@code PUBLIC},
1780 * {@code MODULE}, {@code PACKAGE}, {@code PROTECTED}, {@code PRIVATE}, {@code ORIGINAL}
1781 * or {@code UNCONDITIONAL}
1782 * @see MethodHandles#privateLookupIn
1783 * @since 9
1784 */
1785 public Lookup dropLookupMode(int modeToDrop) {
1786 int oldModes = lookupModes();
1787 int newModes = oldModes & ~(modeToDrop | PROTECTED | ORIGINAL);
1788 switch (modeToDrop) {
1789 case PUBLIC: newModes &= ~(FULL_POWER_MODES); break;
1790 case MODULE: newModes &= ~(PACKAGE | PRIVATE); break;
1791 case PACKAGE: newModes &= ~(PRIVATE); break;
1792 case PROTECTED:
1793 case PRIVATE:
1794 case ORIGINAL:
1795 case UNCONDITIONAL: break;
1796 default: throw new IllegalArgumentException(modeToDrop + " is not a valid mode to drop");
1797 }
1798 if (newModes == oldModes) return this; // return self if no change
1799 return newLookup(lookupClass(), previousLookupClass(), newModes);
1800 }
1801
1802 /**
1803 * Creates and links a class or interface from {@code bytes}
1804 * with the same class loader and in the same runtime package and
1805 * {@linkplain java.security.ProtectionDomain protection domain} as this lookup's
1806 * {@linkplain #lookupClass() lookup class} as if calling
1807 * {@link ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain)
1808 * ClassLoader::defineClass}.
1809 *
1810 * <p> The {@linkplain #lookupModes() lookup modes} for this lookup must include
1811 * {@link #PACKAGE PACKAGE} access as default (package) members will be
1812 * accessible to the class. The {@code PACKAGE} lookup mode serves to authenticate
1813 * that the lookup object was created by a caller in the runtime package (or derived
1814 * from a lookup originally created by suitably privileged code to a target class in
1815 * the runtime package). </p>
1816 *
1817 * <p> The {@code bytes} parameter is the class bytes of a valid class file (as defined
1818 * by the <em>The Java Virtual Machine Specification</em>) with a class name in the
1819 * same package as the lookup class. </p>
1820 *
1821 * <p> This method does not run the class initializer. The class initializer may
1822 * run at a later time, as detailed in section 12.4 of the <em>The Java Language
1823 * Specification</em>. </p>
1824 *
1825 * <p> If there is a security manager and this lookup does not have {@linkplain
1826 * #hasFullPrivilegeAccess() full privilege access}, its {@code checkPermission} method
1827 * is first called to check {@code RuntimePermission("defineClass")}. </p>
1828 *
1829 * @param bytes the class bytes
1830 * @return the {@code Class} object for the class
1831 * @throws IllegalAccessException if this lookup does not have {@code PACKAGE} access
1832 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure
1833 * @throws IllegalArgumentException if {@code bytes} denotes a class in a different package
1834 * than the lookup class or {@code bytes} is not a class or interface
1835 * ({@code ACC_MODULE} flag is set in the value of the {@code access_flags} item)
1836 * @throws VerifyError if the newly created class cannot be verified
1837 * @throws LinkageError if the newly created class cannot be linked for any other reason
1838 * @throws SecurityException if a security manager is present and it
1839 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1840 * @throws NullPointerException if {@code bytes} is {@code null}
1841 * @since 9
1842 * @see Lookup#privateLookupIn
1843 * @see Lookup#dropLookupMode
1844 * @see ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain)
1845 */
1846 public Class<?> defineClass(byte[] bytes) throws IllegalAccessException {
1847 ensureDefineClassPermission();
1848 if ((lookupModes() & PACKAGE) == 0)
1849 throw new IllegalAccessException("Lookup does not have PACKAGE access");
1850 return makeClassDefiner(bytes.clone()).defineClass(false);
1851 }
1852
1853 private void ensureDefineClassPermission() {
1854 if (allowedModes == TRUSTED) return;
1855
1856 if (!hasFullPrivilegeAccess()) {
1857 @SuppressWarnings("removal")
1858 SecurityManager sm = System.getSecurityManager();
1859 if (sm != null)
1860 sm.checkPermission(new RuntimePermission("defineClass"));
1861 }
1862 }
1863
1864 /**
1865 * The set of class options that specify whether a hidden class created by
1866 * {@link Lookup#defineHiddenClass(byte[], boolean, ClassOption...)
1867 * Lookup::defineHiddenClass} method is dynamically added as a new member
1868 * to the nest of a lookup class and/or whether a hidden class has
1869 * a strong relationship with the class loader marked as its defining loader.
1870 *
1871 * @since 15
1872 */
1873 public enum ClassOption {
1874 /**
1875 * Specifies that a hidden class be added to {@linkplain Class#getNestHost nest}
1876 * of a lookup class as a nestmate.
1877 *
1878 * <p> A hidden nestmate class has access to the private members of all
1879 * classes and interfaces in the same nest.
1880 *
1881 * @see Class#getNestHost()
1882 */
1883 NESTMATE(NESTMATE_CLASS),
1884
1885 /**
1886 * Specifies that a hidden class has a <em>strong</em>
1887 * relationship with the class loader marked as its defining loader,
1888 * as a normal class or interface has with its own defining loader.
1889 * This means that the hidden class may be unloaded if and only if
1890 * its defining loader is not reachable and thus may be reclaimed
1891 * by a garbage collector (JLS {@jls 12.7}).
1892 *
1893 * <p> By default, a hidden class or interface may be unloaded
1894 * even if the class loader that is marked as its defining loader is
1895 * <a href="../ref/package-summary.html#reachability">reachable</a>.
1896
1897 *
1898 * @jls 12.7 Unloading of Classes and Interfaces
1899 */
1900 STRONG(STRONG_LOADER_LINK);
1901
1902 /* the flag value is used by VM at define class time */
1903 private final int flag;
1904 ClassOption(int flag) {
1905 this.flag = flag;
1906 }
1907
1908 static int optionsToFlag(Set<ClassOption> options) {
1909 int flags = 0;
1910 for (ClassOption cp : options) {
1911 flags |= cp.flag;
1912 }
1913 return flags;
1914 }
1915 }
1916
1917 /**
1918 * Creates a <em>hidden</em> class or interface from {@code bytes},
1919 * returning a {@code Lookup} on the newly created class or interface.
1920 *
1921 * <p> Ordinarily, a class or interface {@code C} is created by a class loader,
1922 * which either defines {@code C} directly or delegates to another class loader.
1923 * A class loader defines {@code C} directly by invoking
1924 * {@link ClassLoader#defineClass(String, byte[], int, int, ProtectionDomain)
1925 * ClassLoader::defineClass}, which causes the Java Virtual Machine
1926 * to derive {@code C} from a purported representation in {@code class} file format.
1927 * In situations where use of a class loader is undesirable, a class or interface
1928 * {@code C} can be created by this method instead. This method is capable of
1929 * defining {@code C}, and thereby creating it, without invoking
1930 * {@code ClassLoader::defineClass}.
1931 * Instead, this method defines {@code C} as if by arranging for
1932 * the Java Virtual Machine to derive a nonarray class or interface {@code C}
1933 * from a purported representation in {@code class} file format
1934 * using the following rules:
1935 *
1936 * <ol>
1937 * <li> The {@linkplain #lookupModes() lookup modes} for this {@code Lookup}
1938 * must include {@linkplain #hasFullPrivilegeAccess() full privilege} access.
1939 * This level of access is needed to create {@code C} in the module
1940 * of the lookup class of this {@code Lookup}.</li>
1941 *
1942 * <li> The purported representation in {@code bytes} must be a {@code ClassFile}
1943 * structure (JVMS {@jvms 4.1}) of a supported major and minor version.
1944 * The major and minor version may differ from the {@code class} file version
1945 * of the lookup class of this {@code Lookup}.</li>
1946 *
1947 * <li> The value of {@code this_class} must be a valid index in the
1948 * {@code constant_pool} table, and the entry at that index must be a valid
1949 * {@code CONSTANT_Class_info} structure. Let {@code N} be the binary name
1950 * encoded in internal form that is specified by this structure. {@code N} must
1951 * denote a class or interface in the same package as the lookup class.</li>
1952 *
1953 * <li> Let {@code CN} be the string {@code N + "." + <suffix>},
1954 * where {@code <suffix>} is an unqualified name.
1955 *
1956 * <p> Let {@code newBytes} be the {@code ClassFile} structure given by
1957 * {@code bytes} with an additional entry in the {@code constant_pool} table,
1958 * indicating a {@code CONSTANT_Utf8_info} structure for {@code CN}, and
1959 * where the {@code CONSTANT_Class_info} structure indicated by {@code this_class}
1960 * refers to the new {@code CONSTANT_Utf8_info} structure.
1961 *
1962 * <p> Let {@code L} be the defining class loader of the lookup class of this {@code Lookup}.
1963 *
1964 * <p> {@code C} is derived with name {@code CN}, class loader {@code L}, and
1965 * purported representation {@code newBytes} as if by the rules of JVMS {@jvms 5.3.5},
1966 * with the following adjustments:
1967 * <ul>
1968 * <li> The constant indicated by {@code this_class} is permitted to specify a name
1969 * that includes a single {@code "."} character, even though this is not a valid
1970 * binary class or interface name in internal form.</li>
1971 *
1972 * <li> The Java Virtual Machine marks {@code L} as the defining class loader of {@code C},
1973 * but no class loader is recorded as an initiating class loader of {@code C}.</li>
1974 *
1975 * <li> {@code C} is considered to have the same runtime
1976 * {@linkplain Class#getPackage() package}, {@linkplain Class#getModule() module}
1977 * and {@linkplain java.security.ProtectionDomain protection domain}
1978 * as the lookup class of this {@code Lookup}.
1979 * <li> Let {@code GN} be the binary name obtained by taking {@code N}
1980 * (a binary name encoded in internal form) and replacing ASCII forward slashes with
1981 * ASCII periods. For the instance of {@link java.lang.Class} representing {@code C}:
1982 * <ul>
1983 * <li> {@link Class#getName()} returns the string {@code GN + "/" + <suffix>},
1984 * even though this is not a valid binary class or interface name.</li>
1985 * <li> {@link Class#descriptorString()} returns the string
1986 * {@code "L" + N + "." + <suffix> + ";"},
1987 * even though this is not a valid type descriptor name.</li>
1988 * <li> {@link Class#describeConstable()} returns an empty optional as {@code C}
1989 * cannot be described in {@linkplain java.lang.constant.ClassDesc nominal form}.</li>
1990 * </ul>
1991 * </ul>
1992 * </li>
1993 * </ol>
1994 *
1995 * <p> After {@code C} is derived, it is linked by the Java Virtual Machine.
1996 * Linkage occurs as specified in JVMS {@jvms 5.4.3}, with the following adjustments:
1997 * <ul>
1998 * <li> During verification, whenever it is necessary to load the class named
1999 * {@code CN}, the attempt succeeds, producing class {@code C}. No request is
2000 * made of any class loader.</li>
2001 *
2002 * <li> On any attempt to resolve the entry in the run-time constant pool indicated
2003 * by {@code this_class}, the symbolic reference is considered to be resolved to
2004 * {@code C} and resolution always succeeds immediately.</li>
2005 * </ul>
2006 *
2007 * <p> If the {@code initialize} parameter is {@code true},
2008 * then {@code C} is initialized by the Java Virtual Machine.
2009 *
2010 * <p> The newly created class or interface {@code C} serves as the
2011 * {@linkplain #lookupClass() lookup class} of the {@code Lookup} object
2012 * returned by this method. {@code C} is <em>hidden</em> in the sense that
2013 * no other class or interface can refer to {@code C} via a constant pool entry.
2014 * That is, a hidden class or interface cannot be named as a supertype, a field type,
2015 * a method parameter type, or a method return type by any other class.
2016 * This is because a hidden class or interface does not have a binary name, so
2017 * there is no internal form available to record in any class's constant pool.
2018 * A hidden class or interface is not discoverable by {@link Class#forName(String, boolean, ClassLoader)},
2019 * {@link ClassLoader#loadClass(String, boolean)}, or {@link #findClass(String)}, and
2020 * is not {@linkplain java.instrument/java.lang.instrument.Instrumentation#isModifiableClass(Class)
2021 * modifiable} by Java agents or tool agents using the <a href="{@docRoot}/../specs/jvmti.html">
2022 * JVM Tool Interface</a>.
2023 *
2024 * <p> A class or interface created by
2025 * {@linkplain ClassLoader#defineClass(String, byte[], int, int, ProtectionDomain)
2026 * a class loader} has a strong relationship with that class loader.
2027 * That is, every {@code Class} object contains a reference to the {@code ClassLoader}
2028 * that {@linkplain Class#getClassLoader() defined it}.
2029 * This means that a class created by a class loader may be unloaded if and
2030 * only if its defining loader is not reachable and thus may be reclaimed
2031 * by a garbage collector (JLS {@jls 12.7}).
2032 *
2033 * By default, however, a hidden class or interface may be unloaded even if
2034 * the class loader that is marked as its defining loader is
2035 * <a href="../ref/package-summary.html#reachability">reachable</a>.
2036 * This behavior is useful when a hidden class or interface serves multiple
2037 * classes defined by arbitrary class loaders. In other cases, a hidden
2038 * class or interface may be linked to a single class (or a small number of classes)
2039 * with the same defining loader as the hidden class or interface.
2040 * In such cases, where the hidden class or interface must be coterminous
2041 * with a normal class or interface, the {@link ClassOption#STRONG STRONG}
2042 * option may be passed in {@code options}.
2043 * This arranges for a hidden class to have the same strong relationship
2044 * with the class loader marked as its defining loader,
2045 * as a normal class or interface has with its own defining loader.
2046 *
2047 * If {@code STRONG} is not used, then the invoker of {@code defineHiddenClass}
2048 * may still prevent a hidden class or interface from being
2049 * unloaded by ensuring that the {@code Class} object is reachable.
2050 *
2051 * <p> The unloading characteristics are set for each hidden class when it is
2052 * defined, and cannot be changed later. An advantage of allowing hidden classes
2053 * to be unloaded independently of the class loader marked as their defining loader
2054 * is that a very large number of hidden classes may be created by an application.
2055 * In contrast, if {@code STRONG} is used, then the JVM may run out of memory,
2056 * just as if normal classes were created by class loaders.
2057 *
2058 * <p> Classes and interfaces in a nest are allowed to have mutual access to
2059 * their private members. The nest relationship is determined by
2060 * the {@code NestHost} attribute (JVMS {@jvms 4.7.28}) and
2061 * the {@code NestMembers} attribute (JVMS {@jvms 4.7.29}) in a {@code class} file.
2062 * By default, a hidden class belongs to a nest consisting only of itself
2063 * because a hidden class has no binary name.
2064 * The {@link ClassOption#NESTMATE NESTMATE} option can be passed in {@code options}
2065 * to create a hidden class or interface {@code C} as a member of a nest.
2066 * The nest to which {@code C} belongs is not based on any {@code NestHost} attribute
2067 * in the {@code ClassFile} structure from which {@code C} was derived.
2068 * Instead, the following rules determine the nest host of {@code C}:
2069 * <ul>
2070 * <li>If the nest host of the lookup class of this {@code Lookup} has previously
2071 * been determined, then let {@code H} be the nest host of the lookup class.
2072 * Otherwise, the nest host of the lookup class is determined using the
2073 * algorithm in JVMS {@jvms 5.4.4}, yielding {@code H}.</li>
2074 * <li>The nest host of {@code C} is determined to be {@code H},
2075 * the nest host of the lookup class.</li>
2076 * </ul>
2077 *
2078 * <p> A hidden class or interface may be serializable, but this requires a custom
2079 * serialization mechanism in order to ensure that instances are properly serialized
2080 * and deserialized. The default serialization mechanism supports only classes and
2081 * interfaces that are discoverable by their class name.
2082 *
2083 * @param bytes the bytes that make up the class data,
2084 * in the format of a valid {@code class} file as defined by
2085 * <cite>The Java Virtual Machine Specification</cite>.
2086 * @param initialize if {@code true} the class will be initialized.
2087 * @param options {@linkplain ClassOption class options}
2088 * @return the {@code Lookup} object on the hidden class,
2089 * with {@linkplain #ORIGINAL original} and
2090 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege} access
2091 *
2092 * @throws IllegalAccessException if this {@code Lookup} does not have
2093 * {@linkplain #hasFullPrivilegeAccess() full privilege} access
2094 * @throws SecurityException if a security manager is present and it
2095 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2096 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure
2097 * @throws UnsupportedClassVersionError if {@code bytes} is not of a supported major or minor version
2098 * @throws IllegalArgumentException if {@code bytes} denotes a class in a different package
2099 * than the lookup class or {@code bytes} is not a class or interface
2100 * ({@code ACC_MODULE} flag is set in the value of the {@code access_flags} item)
2101 * @throws IncompatibleClassChangeError if the class or interface named as
2102 * the direct superclass of {@code C} is in fact an interface, or if any of the classes
2103 * or interfaces named as direct superinterfaces of {@code C} are not in fact interfaces
2104 * @throws ClassCircularityError if any of the superclasses or superinterfaces of
2105 * {@code C} is {@code C} itself
2106 * @throws VerifyError if the newly created class cannot be verified
2107 * @throws LinkageError if the newly created class cannot be linked for any other reason
2108 * @throws NullPointerException if any parameter is {@code null}
2109 *
2110 * @since 15
2111 * @see Class#isHidden()
2112 * @jvms 4.2.1 Binary Class and Interface Names
2113 * @jvms 4.2.2 Unqualified Names
2114 * @jvms 4.7.28 The {@code NestHost} Attribute
2115 * @jvms 4.7.29 The {@code NestMembers} Attribute
2116 * @jvms 5.4.3.1 Class and Interface Resolution
2117 * @jvms 5.4.4 Access Control
2118 * @jvms 5.3.5 Deriving a {@code Class} from a {@code class} File Representation
2119 * @jvms 5.4 Linking
2120 * @jvms 5.5 Initialization
2121 * @jls 12.7 Unloading of Classes and Interfaces
2122 */
2123 @SuppressWarnings("doclint:reference") // cross-module links
2124 public Lookup defineHiddenClass(byte[] bytes, boolean initialize, ClassOption... options)
2125 throws IllegalAccessException
2126 {
2127 Objects.requireNonNull(bytes);
2128 Objects.requireNonNull(options);
2129
2130 ensureDefineClassPermission();
2131 if (!hasFullPrivilegeAccess()) {
2132 throw new IllegalAccessException(this + " does not have full privilege access");
2133 }
2134
2135 return makeHiddenClassDefiner(bytes.clone(), Set.of(options), false).defineClassAsLookup(initialize);
2136 }
2137
2138 /**
2139 * Creates a <em>hidden</em> class or interface from {@code bytes} with associated
2140 * {@linkplain MethodHandles#classData(Lookup, String, Class) class data},
2141 * returning a {@code Lookup} on the newly created class or interface.
2142 *
2143 * <p> This method is equivalent to calling
2144 * {@link #defineHiddenClass(byte[], boolean, ClassOption...) defineHiddenClass(bytes, initialize, options)}
2145 * as if the hidden class is injected with a private static final <i>unnamed</i>
2146 * field which is initialized with the given {@code classData} at
2147 * the first instruction of the class initializer.
2148 * The newly created class is linked by the Java Virtual Machine.
2149 *
2150 * <p> The {@link MethodHandles#classData(Lookup, String, Class) MethodHandles::classData}
2151 * and {@link MethodHandles#classDataAt(Lookup, String, Class, int) MethodHandles::classDataAt}
2152 * methods can be used to retrieve the {@code classData}.
2153 *
2154 * @apiNote
2155 * A framework can create a hidden class with class data with one or more
2156 * objects and load the class data as dynamically-computed constant(s)
2157 * via a bootstrap method. {@link MethodHandles#classData(Lookup, String, Class)
2158 * Class data} is accessible only to the lookup object created by the newly
2159 * defined hidden class but inaccessible to other members in the same nest
2160 * (unlike private static fields that are accessible to nestmates).
2161 * Care should be taken w.r.t. mutability for example when passing
2162 * an array or other mutable structure through the class data.
2163 * Changing any value stored in the class data at runtime may lead to
2164 * unpredictable behavior.
2165 * If the class data is a {@code List}, it is good practice to make it
2166 * unmodifiable for example via {@link List#of List::of}.
2167 *
2168 * @param bytes the class bytes
2169 * @param classData pre-initialized class data
2170 * @param initialize if {@code true} the class will be initialized.
2171 * @param options {@linkplain ClassOption class options}
2172 * @return the {@code Lookup} object on the hidden class,
2173 * with {@linkplain #ORIGINAL original} and
2174 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege} access
2175 *
2176 * @throws IllegalAccessException if this {@code Lookup} does not have
2177 * {@linkplain #hasFullPrivilegeAccess() full privilege} access
2178 * @throws SecurityException if a security manager is present and it
2179 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2180 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure
2181 * @throws UnsupportedClassVersionError if {@code bytes} is not of a supported major or minor version
2182 * @throws IllegalArgumentException if {@code bytes} denotes a class in a different package
2183 * than the lookup class or {@code bytes} is not a class or interface
2184 * ({@code ACC_MODULE} flag is set in the value of the {@code access_flags} item)
2185 * @throws IncompatibleClassChangeError if the class or interface named as
2186 * the direct superclass of {@code C} is in fact an interface, or if any of the classes
2187 * or interfaces named as direct superinterfaces of {@code C} are not in fact interfaces
2188 * @throws ClassCircularityError if any of the superclasses or superinterfaces of
2189 * {@code C} is {@code C} itself
2190 * @throws VerifyError if the newly created class cannot be verified
2191 * @throws LinkageError if the newly created class cannot be linked for any other reason
2192 * @throws NullPointerException if any parameter is {@code null}
2193 *
2194 * @since 16
2195 * @see Lookup#defineHiddenClass(byte[], boolean, ClassOption...)
2196 * @see Class#isHidden()
2197 * @see MethodHandles#classData(Lookup, String, Class)
2198 * @see MethodHandles#classDataAt(Lookup, String, Class, int)
2199 * @jvms 4.2.1 Binary Class and Interface Names
2200 * @jvms 4.2.2 Unqualified Names
2201 * @jvms 4.7.28 The {@code NestHost} Attribute
2202 * @jvms 4.7.29 The {@code NestMembers} Attribute
2203 * @jvms 5.4.3.1 Class and Interface Resolution
2204 * @jvms 5.4.4 Access Control
2205 * @jvms 5.3.5 Deriving a {@code Class} from a {@code class} File Representation
2206 * @jvms 5.4 Linking
2207 * @jvms 5.5 Initialization
2208 * @jls 12.7 Unloading of Classes and Interface
2209 */
2210 public Lookup defineHiddenClassWithClassData(byte[] bytes, Object classData, boolean initialize, ClassOption... options)
2211 throws IllegalAccessException
2212 {
2213 Objects.requireNonNull(bytes);
2214 Objects.requireNonNull(classData);
2215 Objects.requireNonNull(options);
2216
2217 ensureDefineClassPermission();
2218 if (!hasFullPrivilegeAccess()) {
2219 throw new IllegalAccessException(this + " does not have full privilege access");
2220 }
2221
2222 return makeHiddenClassDefiner(bytes.clone(), Set.of(options), false)
2223 .defineClassAsLookup(initialize, classData);
2224 }
2225
2226 static class ClassFile {
2227 final String name;
2228 final int accessFlags;
2229 final byte[] bytes;
2230 ClassFile(String name, int accessFlags, byte[] bytes) {
2231 this.name = name;
2232 this.accessFlags = accessFlags;
2233 this.bytes = bytes;
2234 }
2235
2236 static ClassFile newInstanceNoCheck(String name, byte[] bytes) {
2237 return new ClassFile(name, 0, bytes);
2238 }
2239
2240 /**
2241 * This method checks the class file version and the structure of `this_class`.
2242 * and checks if the bytes is a class or interface (ACC_MODULE flag not set)
2243 * that is in the named package.
2244 *
2245 * @throws IllegalArgumentException if ACC_MODULE flag is set in access flags
2246 * or the class is not in the given package name.
2247 */
2248 static ClassFile newInstance(byte[] bytes, String pkgName) {
2249 int magic = readInt(bytes, 0);
2250 if (magic != 0xCAFEBABE) {
2251 throw new ClassFormatError("Incompatible magic value: " + magic);
2252 }
2253 int minor = readUnsignedShort(bytes, 4);
2254 int major = readUnsignedShort(bytes, 6);
2255 if (!VM.isSupportedClassFileVersion(major, minor)) {
2256 throw new UnsupportedClassVersionError("Unsupported class file version " + major + "." + minor);
2257 }
2258
2259 String name;
2260 int accessFlags;
2261 try {
2262 ClassReader reader = new ClassReader(bytes);
2263 // ClassReader::getClassName does not check if `this_class` is CONSTANT_Class_info
2264 // workaround to read `this_class` using readConst and validate the value
2265 int thisClass = reader.readUnsignedShort(reader.header + 2);
2266 Object constant = reader.readConst(thisClass, new char[reader.getMaxStringLength()]);
2267 if (!(constant instanceof Type type)) {
2268 throw new ClassFormatError("this_class item: #" + thisClass + " not a CONSTANT_Class_info");
2269 }
2270 if (!type.getDescriptor().startsWith("L")) {
2271 throw new ClassFormatError("this_class item: #" + thisClass + " not a CONSTANT_Class_info");
2272 }
2273 name = type.getClassName();
2274 accessFlags = reader.readUnsignedShort(reader.header);
2275 } catch (RuntimeException e) {
2276 // ASM exceptions are poorly specified
2277 ClassFormatError cfe = new ClassFormatError();
2278 cfe.initCause(e);
2279 throw cfe;
2280 }
2281
2282 // must be a class or interface
2283 if ((accessFlags & Opcodes.ACC_MODULE) != 0) {
2284 throw newIllegalArgumentException("Not a class or interface: ACC_MODULE flag is set");
2285 }
2286
2287 // check if it's in the named package
2288 int index = name.lastIndexOf('.');
2289 String pn = (index == -1) ? "" : name.substring(0, index);
2290 if (!pn.equals(pkgName)) {
2291 throw newIllegalArgumentException(name + " not in same package as lookup class");
2292 }
2293
2294 return new ClassFile(name, accessFlags, bytes);
2295 }
2296
2297 private static int readInt(byte[] bytes, int offset) {
2298 if ((offset+4) > bytes.length) {
2299 throw new ClassFormatError("Invalid ClassFile structure");
2300 }
2301 return ((bytes[offset] & 0xFF) << 24)
2302 | ((bytes[offset + 1] & 0xFF) << 16)
2303 | ((bytes[offset + 2] & 0xFF) << 8)
2304 | (bytes[offset + 3] & 0xFF);
2305 }
2306
2307 private static int readUnsignedShort(byte[] bytes, int offset) {
2308 if ((offset+2) > bytes.length) {
2309 throw new ClassFormatError("Invalid ClassFile structure");
2310 }
2311 return ((bytes[offset] & 0xFF) << 8) | (bytes[offset + 1] & 0xFF);
2312 }
2313 }
2314
2315 /*
2316 * Returns a ClassDefiner that creates a {@code Class} object of a normal class
2317 * from the given bytes.
2318 *
2319 * Caller should make a defensive copy of the arguments if needed
2320 * before calling this factory method.
2321 *
2322 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or
2323 * {@bytes} denotes a class in a different package than the lookup class
2324 */
2325 private ClassDefiner makeClassDefiner(byte[] bytes) {
2326 ClassFile cf = ClassFile.newInstance(bytes, lookupClass().getPackageName());
2327 return new ClassDefiner(this, cf, STRONG_LOADER_LINK);
2328 }
2329
2330 /**
2331 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2332 * from the given bytes. The name must be in the same package as the lookup class.
2333 *
2334 * Caller should make a defensive copy of the arguments if needed
2335 * before calling this factory method.
2336 *
2337 * @param bytes class bytes
2338 * @return ClassDefiner that defines a hidden class of the given bytes.
2339 *
2340 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or
2341 * {@bytes} denotes a class in a different package than the lookup class
2342 */
2343 ClassDefiner makeHiddenClassDefiner(byte[] bytes) {
2344 ClassFile cf = ClassFile.newInstance(bytes, lookupClass().getPackageName());
2345 return makeHiddenClassDefiner(cf, Set.of(), false);
2346 }
2347
2348 /**
2349 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2350 * from the given bytes and options.
2351 * The name must be in the same package as the lookup class.
2352 *
2353 * Caller should make a defensive copy of the arguments if needed
2354 * before calling this factory method.
2355 *
2356 * @param bytes class bytes
2357 * @param options class options
2358 * @param accessVmAnnotations true to give the hidden class access to VM annotations
2359 * @return ClassDefiner that defines a hidden class of the given bytes and options
2360 *
2361 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or
2362 * {@bytes} denotes a class in a different package than the lookup class
2363 */
2364 ClassDefiner makeHiddenClassDefiner(byte[] bytes,
2365 Set<ClassOption> options,
2366 boolean accessVmAnnotations) {
2367 ClassFile cf = ClassFile.newInstance(bytes, lookupClass().getPackageName());
2368 return makeHiddenClassDefiner(cf, options, accessVmAnnotations);
2369 }
2370
2371 /**
2372 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2373 * from the given bytes and the given options. No package name check on the given name.
2374 *
2375 * @param name fully-qualified name that specifies the prefix of the hidden class
2376 * @param bytes class bytes
2377 * @param options class options
2378 * @return ClassDefiner that defines a hidden class of the given bytes and options.
2379 */
2380 ClassDefiner makeHiddenClassDefiner(String name, byte[] bytes, Set<ClassOption> options) {
2381 // skip name and access flags validation
2382 return makeHiddenClassDefiner(ClassFile.newInstanceNoCheck(name, bytes), options, false);
2383 }
2384
2385 /**
2386 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2387 * from the given class file and options.
2388 *
2389 * @param cf ClassFile
2390 * @param options class options
2391 * @param accessVmAnnotations true to give the hidden class access to VM annotations
2392 */
2393 private ClassDefiner makeHiddenClassDefiner(ClassFile cf,
2394 Set<ClassOption> options,
2395 boolean accessVmAnnotations) {
2396 int flags = HIDDEN_CLASS | ClassOption.optionsToFlag(options);
2397 if (accessVmAnnotations | VM.isSystemDomainLoader(lookupClass.getClassLoader())) {
2398 // jdk.internal.vm.annotations are permitted for classes
2399 // defined to boot loader and platform loader
2400 flags |= ACCESS_VM_ANNOTATIONS;
2401 }
2402
2403 return new ClassDefiner(this, cf, flags);
2404 }
2405
2406 static class ClassDefiner {
2407 private final Lookup lookup;
2408 private final String name;
2409 private final byte[] bytes;
2410 private final int classFlags;
2411
2412 private ClassDefiner(Lookup lookup, ClassFile cf, int flags) {
2413 assert ((flags & HIDDEN_CLASS) != 0 || (flags & STRONG_LOADER_LINK) == STRONG_LOADER_LINK);
2414 this.lookup = lookup;
2415 this.bytes = cf.bytes;
2416 this.name = cf.name;
2417 this.classFlags = flags;
2418 }
2419
2420 String className() {
2421 return name;
2422 }
2423
2424 Class<?> defineClass(boolean initialize) {
2425 return defineClass(initialize, null);
2426 }
2427
2428 Lookup defineClassAsLookup(boolean initialize) {
2429 Class<?> c = defineClass(initialize, null);
2430 return new Lookup(c, null, FULL_POWER_MODES);
2431 }
2432
2433 /**
2434 * Defines the class of the given bytes and the given classData.
2435 * If {@code initialize} parameter is true, then the class will be initialized.
2436 *
2437 * @param initialize true if the class to be initialized
2438 * @param classData classData or null
2439 * @return the class
2440 *
2441 * @throws LinkageError linkage error
2442 */
2443 Class<?> defineClass(boolean initialize, Object classData) {
2444 Class<?> lookupClass = lookup.lookupClass();
2445 ClassLoader loader = lookupClass.getClassLoader();
2446 ProtectionDomain pd = (loader != null) ? lookup.lookupClassProtectionDomain() : null;
2447 Class<?> c = SharedSecrets.getJavaLangAccess()
2448 .defineClass(loader, lookupClass, name, bytes, pd, initialize, classFlags, classData);
2449 assert !isNestmate() || c.getNestHost() == lookupClass.getNestHost();
2450 return c;
2451 }
2452
2453 Lookup defineClassAsLookup(boolean initialize, Object classData) {
2454 Class<?> c = defineClass(initialize, classData);
2455 return new Lookup(c, null, FULL_POWER_MODES);
2456 }
2457
2458 private boolean isNestmate() {
2459 return (classFlags & NESTMATE_CLASS) != 0;
2460 }
2461 }
2462
2463 private ProtectionDomain lookupClassProtectionDomain() {
2464 ProtectionDomain pd = cachedProtectionDomain;
2465 if (pd == null) {
2466 cachedProtectionDomain = pd = SharedSecrets.getJavaLangAccess().protectionDomain(lookupClass);
2467 }
2468 return pd;
2469 }
2470
2471 // cached protection domain
2472 private volatile ProtectionDomain cachedProtectionDomain;
2473
2474 // Make sure outer class is initialized first.
2475 static { IMPL_NAMES.getClass(); }
2476
2477 /** Package-private version of lookup which is trusted. */
2478 static final Lookup IMPL_LOOKUP = new Lookup(Object.class, null, TRUSTED);
2479
2480 /** Version of lookup which is trusted minimally.
2481 * It can only be used to create method handles to publicly accessible
2482 * members in packages that are exported unconditionally.
2483 */
2484 static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, null, UNCONDITIONAL);
2485
2486 private static void checkUnprivilegedlookupClass(Class<?> lookupClass) {
2487 String name = lookupClass.getName();
2488 if (name.startsWith("java.lang.invoke."))
2489 throw newIllegalArgumentException("illegal lookupClass: "+lookupClass);
2490 }
2491
2492 /**
2493 * Displays the name of the class from which lookups are to be made,
2494 * followed by "/" and the name of the {@linkplain #previousLookupClass()
2495 * previous lookup class} if present.
2496 * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)
2497 * If there are restrictions on the access permitted to this lookup,
2498 * this is indicated by adding a suffix to the class name, consisting
2499 * of a slash and a keyword. The keyword represents the strongest
2500 * allowed access, and is chosen as follows:
2501 * <ul>
2502 * <li>If no access is allowed, the suffix is "/noaccess".
2503 * <li>If only unconditional access is allowed, the suffix is "/publicLookup".
2504 * <li>If only public access to types in exported packages is allowed, the suffix is "/public".
2505 * <li>If only public and module access are allowed, the suffix is "/module".
2506 * <li>If public and package access are allowed, the suffix is "/package".
2507 * <li>If public, package, and private access are allowed, the suffix is "/private".
2508 * </ul>
2509 * If none of the above cases apply, it is the case that
2510 * {@linkplain #hasFullPrivilegeAccess() full privilege access}
2511 * (public, module, package, private, and protected) is allowed.
2512 * In this case, no suffix is added.
2513 * This is true only of an object obtained originally from
2514 * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
2515 * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
2516 * always have restricted access, and will display a suffix.
2517 * <p>
2518 * (It may seem strange that protected access should be
2519 * stronger than private access. Viewed independently from
2520 * package access, protected access is the first to be lost,
2521 * because it requires a direct subclass relationship between
2522 * caller and callee.)
2523 * @see #in
2524 *
2525 * @revised 9
2526 */
2527 @Override
2528 public String toString() {
2529 String cname = lookupClass.getName();
2530 if (prevLookupClass != null)
2531 cname += "/" + prevLookupClass.getName();
2532 switch (allowedModes) {
2533 case 0: // no privileges
2534 return cname + "/noaccess";
2535 case UNCONDITIONAL:
2536 return cname + "/publicLookup";
2537 case PUBLIC:
2538 return cname + "/public";
2539 case PUBLIC|MODULE:
2540 return cname + "/module";
2541 case PUBLIC|PACKAGE:
2542 case PUBLIC|MODULE|PACKAGE:
2543 return cname + "/package";
2544 case PUBLIC|PACKAGE|PRIVATE:
2545 case PUBLIC|MODULE|PACKAGE|PRIVATE:
2546 return cname + "/private";
2547 case PUBLIC|PACKAGE|PRIVATE|PROTECTED:
2548 case PUBLIC|MODULE|PACKAGE|PRIVATE|PROTECTED:
2549 case FULL_POWER_MODES:
2550 return cname;
2551 case TRUSTED:
2552 return "/trusted"; // internal only; not exported
2553 default: // Should not happen, but it's a bitfield...
2554 cname = cname + "/" + Integer.toHexString(allowedModes);
2555 assert(false) : cname;
2556 return cname;
2557 }
2558 }
2559
2560 /**
2561 * Produces a method handle for a static method.
2562 * The type of the method handle will be that of the method.
2563 * (Since static methods do not take receivers, there is no
2564 * additional receiver argument inserted into the method handle type,
2565 * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)
2566 * The method and all its argument types must be accessible to the lookup object.
2567 * <p>
2568 * The returned method handle will have
2569 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2570 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2571 * <p>
2572 * If the returned method handle is invoked, the method's class will
2573 * be initialized, if it has not already been initialized.
2574 * <p><b>Example:</b>
2575 * {@snippet lang="java" :
2576 import static java.lang.invoke.MethodHandles.*;
2577 import static java.lang.invoke.MethodType.*;
2578 ...
2579 MethodHandle MH_asList = publicLookup().findStatic(Arrays.class,
2580 "asList", methodType(List.class, Object[].class));
2581 assertEquals("[x, y]", MH_asList.invoke("x", "y").toString());
2582 * }
2583 * @param refc the class from which the method is accessed
2584 * @param name the name of the method
2585 * @param type the type of the method
2586 * @return the desired method handle
2587 * @throws NoSuchMethodException if the method does not exist
2588 * @throws IllegalAccessException if access checking fails,
2589 * or if the method is not {@code static},
2590 * or if the method's variable arity modifier bit
2591 * is set and {@code asVarargsCollector} fails
2592 * @throws SecurityException if a security manager is present and it
2593 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2594 * @throws NullPointerException if any argument is null
2595 */
2596 public MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2597 MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type);
2598 return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerLookup(method));
2599 }
2600
2601 /**
2602 * Produces a method handle for a virtual method.
2603 * The type of the method handle will be that of the method,
2604 * with the receiver type (usually {@code refc}) prepended.
2605 * The method and all its argument types must be accessible to the lookup object.
2606 * <p>
2607 * When called, the handle will treat the first argument as a receiver
2608 * and, for non-private methods, dispatch on the receiver's type to determine which method
2609 * implementation to enter.
2610 * For private methods the named method in {@code refc} will be invoked on the receiver.
2611 * (The dispatching action is identical with that performed by an
2612 * {@code invokevirtual} or {@code invokeinterface} instruction.)
2613 * <p>
2614 * The first argument will be of type {@code refc} if the lookup
2615 * class has full privileges to access the member. Otherwise
2616 * the member must be {@code protected} and the first argument
2617 * will be restricted in type to the lookup class.
2618 * <p>
2619 * The returned method handle will have
2620 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2621 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2622 * <p>
2623 * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual}
2624 * instructions and method handles produced by {@code findVirtual},
2625 * if the class is {@code MethodHandle} and the name string is
2626 * {@code invokeExact} or {@code invoke}, the resulting
2627 * method handle is equivalent to one produced by
2628 * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or
2629 * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}
2630 * with the same {@code type} argument.
2631 * <p>
2632 * If the class is {@code VarHandle} and the name string corresponds to
2633 * the name of a signature-polymorphic access mode method, the resulting
2634 * method handle is equivalent to one produced by
2635 * {@link java.lang.invoke.MethodHandles#varHandleInvoker} with
2636 * the access mode corresponding to the name string and with the same
2637 * {@code type} arguments.
2638 * <p>
2639 * <b>Example:</b>
2640 * {@snippet lang="java" :
2641 import static java.lang.invoke.MethodHandles.*;
2642 import static java.lang.invoke.MethodType.*;
2643 ...
2644 MethodHandle MH_concat = publicLookup().findVirtual(String.class,
2645 "concat", methodType(String.class, String.class));
2646 MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class,
2647 "hashCode", methodType(int.class));
2648 MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class,
2649 "hashCode", methodType(int.class));
2650 assertEquals("xy", (String) MH_concat.invokeExact("x", "y"));
2651 assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy"));
2652 assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy"));
2653 // interface method:
2654 MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class,
2655 "subSequence", methodType(CharSequence.class, int.class, int.class));
2656 assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString());
2657 // constructor "internal method" must be accessed differently:
2658 MethodType MT_newString = methodType(void.class); //()V for new String()
2659 try { assertEquals("impossible", lookup()
2660 .findVirtual(String.class, "<init>", MT_newString));
2661 } catch (NoSuchMethodException ex) { } // OK
2662 MethodHandle MH_newString = publicLookup()
2663 .findConstructor(String.class, MT_newString);
2664 assertEquals("", (String) MH_newString.invokeExact());
2665 * }
2666 *
2667 * @param refc the class or interface from which the method is accessed
2668 * @param name the name of the method
2669 * @param type the type of the method, with the receiver argument omitted
2670 * @return the desired method handle
2671 * @throws NoSuchMethodException if the method does not exist
2672 * @throws IllegalAccessException if access checking fails,
2673 * or if the method is {@code static},
2674 * or if the method's variable arity modifier bit
2675 * is set and {@code asVarargsCollector} fails
2676 * @throws SecurityException if a security manager is present and it
2677 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2678 * @throws NullPointerException if any argument is null
2679 */
2680 public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2681 if (refc == MethodHandle.class) {
2682 MethodHandle mh = findVirtualForMH(name, type);
2683 if (mh != null) return mh;
2684 } else if (refc == VarHandle.class) {
2685 MethodHandle mh = findVirtualForVH(name, type);
2686 if (mh != null) return mh;
2687 }
2688 byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual);
2689 MemberName method = resolveOrFail(refKind, refc, name, type);
2690 return getDirectMethod(refKind, refc, method, findBoundCallerLookup(method));
2691 }
2692 private MethodHandle findVirtualForMH(String name, MethodType type) {
2693 // these names require special lookups because of the implicit MethodType argument
2694 if ("invoke".equals(name))
2695 return invoker(type);
2696 if ("invokeExact".equals(name))
2697 return exactInvoker(type);
2698 assert(!MemberName.isMethodHandleInvokeName(name));
2699 return null;
2700 }
2701 private MethodHandle findVirtualForVH(String name, MethodType type) {
2702 try {
2703 return varHandleInvoker(VarHandle.AccessMode.valueFromMethodName(name), type);
2704 } catch (IllegalArgumentException e) {
2705 return null;
2706 }
2707 }
2708
2709 /**
2710 * Produces a method handle which creates an object and initializes it, using
2711 * the constructor of the specified type.
2712 * The parameter types of the method handle will be those of the constructor,
2713 * while the return type will be a reference to the constructor's class.
2714 * The constructor and all its argument types must be accessible to the lookup object.
2715 * <p>
2716 * The requested type must have a return type of {@code void}.
2717 * (This is consistent with the JVM's treatment of constructor type descriptors.)
2718 * <p>
2719 * The returned method handle will have
2720 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2721 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
2722 * <p>
2723 * If the returned method handle is invoked, the constructor's class will
2724 * be initialized, if it has not already been initialized.
2725 * <p><b>Example:</b>
2726 * {@snippet lang="java" :
2727 import static java.lang.invoke.MethodHandles.*;
2728 import static java.lang.invoke.MethodType.*;
2729 ...
2730 MethodHandle MH_newArrayList = publicLookup().findConstructor(
2731 ArrayList.class, methodType(void.class, Collection.class));
2732 Collection orig = Arrays.asList("x", "y");
2733 Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig);
2734 assert(orig != copy);
2735 assertEquals(orig, copy);
2736 // a variable-arity constructor:
2737 MethodHandle MH_newProcessBuilder = publicLookup().findConstructor(
2738 ProcessBuilder.class, methodType(void.class, String[].class));
2739 ProcessBuilder pb = (ProcessBuilder)
2740 MH_newProcessBuilder.invoke("x", "y", "z");
2741 assertEquals("[x, y, z]", pb.command().toString());
2742 * }
2743 * @param refc the class or interface from which the method is accessed
2744 * @param type the type of the method, with the receiver argument omitted, and a void return type
2745 * @return the desired method handle
2746 * @throws NoSuchMethodException if the constructor does not exist
2747 * @throws IllegalAccessException if access checking fails
2748 * or if the method's variable arity modifier bit
2749 * is set and {@code asVarargsCollector} fails
2750 * @throws SecurityException if a security manager is present and it
2751 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2752 * @throws NullPointerException if any argument is null
2753 */
2754 public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2755 if (refc.isArray()) {
2756 throw new NoSuchMethodException("no constructor for array class: " + refc.getName());
2757 }
2758 String name = "<init>";
2759 MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type);
2760 return getDirectConstructor(refc, ctor);
2761 }
2762
2763 /**
2764 * Looks up a class by name from the lookup context defined by this {@code Lookup} object,
2765 * <a href="MethodHandles.Lookup.html#equiv">as if resolved</a> by an {@code ldc} instruction.
2766 * Such a resolution, as specified in JVMS {@jvms 5.4.3.1}, attempts to locate and load the class,
2767 * and then determines whether the class is accessible to this lookup object.
2768 * <p>
2769 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class},
2770 * its class loader, and the {@linkplain #lookupModes() lookup modes}.
2771 *
2772 * @param targetName the fully qualified name of the class to be looked up.
2773 * @return the requested class.
2774 * @throws SecurityException if a security manager is present and it
2775 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2776 * @throws LinkageError if the linkage fails
2777 * @throws ClassNotFoundException if the class cannot be loaded by the lookup class' loader.
2778 * @throws IllegalAccessException if the class is not accessible, using the allowed access
2779 * modes.
2780 * @throws NullPointerException if {@code targetName} is null
2781 * @since 9
2782 * @jvms 5.4.3.1 Class and Interface Resolution
2783 */
2784 public Class<?> findClass(String targetName) throws ClassNotFoundException, IllegalAccessException {
2785 Class<?> targetClass = Class.forName(targetName, false, lookupClass.getClassLoader());
2786 return accessClass(targetClass);
2787 }
2788
2789 /**
2790 * Ensures that {@code targetClass} has been initialized. The class
2791 * to be initialized must be {@linkplain #accessClass accessible}
2792 * to this {@code Lookup} object. This method causes {@code targetClass}
2793 * to be initialized if it has not been already initialized,
2794 * as specified in JVMS {@jvms 5.5}.
2795 *
2796 * <p>
2797 * This method returns when {@code targetClass} is fully initialized, or
2798 * when {@code targetClass} is being initialized by the current thread.
2799 *
2800 * @param targetClass the class to be initialized
2801 * @return {@code targetClass} that has been initialized, or that is being
2802 * initialized by the current thread.
2803 *
2804 * @throws IllegalArgumentException if {@code targetClass} is a primitive type or {@code void}
2805 * or array class
2806 * @throws IllegalAccessException if {@code targetClass} is not
2807 * {@linkplain #accessClass accessible} to this lookup
2808 * @throws ExceptionInInitializerError if the class initialization provoked
2809 * by this method fails
2810 * @throws SecurityException if a security manager is present and it
2811 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2812 * @since 15
2813 * @jvms 5.5 Initialization
2814 */
2815 public Class<?> ensureInitialized(Class<?> targetClass) throws IllegalAccessException {
2816 if (targetClass.isPrimitive())
2817 throw new IllegalArgumentException(targetClass + " is a primitive class");
2818 if (targetClass.isArray())
2819 throw new IllegalArgumentException(targetClass + " is an array class");
2820
2821 if (!VerifyAccess.isClassAccessible(targetClass, lookupClass, prevLookupClass, allowedModes)) {
2822 throw makeAccessException(targetClass);
2823 }
2824 checkSecurityManager(targetClass);
2825
2826 // ensure class initialization
2827 Unsafe.getUnsafe().ensureClassInitialized(targetClass);
2828 return targetClass;
2829 }
2830
2831 /*
2832 * Returns IllegalAccessException due to access violation to the given targetClass.
2833 *
2834 * This method is called by {@link Lookup#accessClass} and {@link Lookup#ensureInitialized}
2835 * which verifies access to a class rather a member.
2836 */
2837 private IllegalAccessException makeAccessException(Class<?> targetClass) {
2838 String message = "access violation: "+ targetClass;
2839 if (this == MethodHandles.publicLookup()) {
2840 message += ", from public Lookup";
2841 } else {
2842 Module m = lookupClass().getModule();
2843 message += ", from " + lookupClass() + " (" + m + ")";
2844 if (prevLookupClass != null) {
2845 message += ", previous lookup " +
2846 prevLookupClass.getName() + " (" + prevLookupClass.getModule() + ")";
2847 }
2848 }
2849 return new IllegalAccessException(message);
2850 }
2851
2852 /**
2853 * Determines if a class can be accessed from the lookup context defined by
2854 * this {@code Lookup} object. The static initializer of the class is not run.
2855 * If {@code targetClass} is an array class, {@code targetClass} is accessible
2856 * if the element type of the array class is accessible. Otherwise,
2857 * {@code targetClass} is determined as accessible as follows.
2858 *
2859 * <p>
2860 * If {@code targetClass} is in the same module as the lookup class,
2861 * the lookup class is {@code LC} in module {@code M1} and
2862 * the previous lookup class is in module {@code M0} or
2863 * {@code null} if not present,
2864 * {@code targetClass} is accessible if and only if one of the following is true:
2865 * <ul>
2866 * <li>If this lookup has {@link #PRIVATE} access, {@code targetClass} is
2867 * {@code LC} or other class in the same nest of {@code LC}.</li>
2868 * <li>If this lookup has {@link #PACKAGE} access, {@code targetClass} is
2869 * in the same runtime package of {@code LC}.</li>
2870 * <li>If this lookup has {@link #MODULE} access, {@code targetClass} is
2871 * a public type in {@code M1}.</li>
2872 * <li>If this lookup has {@link #PUBLIC} access, {@code targetClass} is
2873 * a public type in a package exported by {@code M1} to at least {@code M0}
2874 * if the previous lookup class is present; otherwise, {@code targetClass}
2875 * is a public type in a package exported by {@code M1} unconditionally.</li>
2876 * </ul>
2877 *
2878 * <p>
2879 * Otherwise, if this lookup has {@link #UNCONDITIONAL} access, this lookup
2880 * can access public types in all modules when the type is in a package
2881 * that is exported unconditionally.
2882 * <p>
2883 * Otherwise, {@code targetClass} is in a different module from {@code lookupClass},
2884 * and if this lookup does not have {@code PUBLIC} access, {@code lookupClass}
2885 * is inaccessible.
2886 * <p>
2887 * Otherwise, if this lookup has no {@linkplain #previousLookupClass() previous lookup class},
2888 * {@code M1} is the module containing {@code lookupClass} and
2889 * {@code M2} is the module containing {@code targetClass},
2890 * then {@code targetClass} is accessible if and only if
2891 * <ul>
2892 * <li>{@code M1} reads {@code M2}, and
2893 * <li>{@code targetClass} is public and in a package exported by
2894 * {@code M2} at least to {@code M1}.
2895 * </ul>
2896 * <p>
2897 * Otherwise, if this lookup has a {@linkplain #previousLookupClass() previous lookup class},
2898 * {@code M1} and {@code M2} are as before, and {@code M0} is the module
2899 * containing the previous lookup class, then {@code targetClass} is accessible
2900 * if and only if one of the following is true:
2901 * <ul>
2902 * <li>{@code targetClass} is in {@code M0} and {@code M1}
2903 * {@linkplain Module#reads reads} {@code M0} and the type is
2904 * in a package that is exported to at least {@code M1}.
2905 * <li>{@code targetClass} is in {@code M1} and {@code M0}
2906 * {@linkplain Module#reads reads} {@code M1} and the type is
2907 * in a package that is exported to at least {@code M0}.
2908 * <li>{@code targetClass} is in a third module {@code M2} and both {@code M0}
2909 * and {@code M1} reads {@code M2} and the type is in a package
2910 * that is exported to at least both {@code M0} and {@code M2}.
2911 * </ul>
2912 * <p>
2913 * Otherwise, {@code targetClass} is not accessible.
2914 *
2915 * @param targetClass the class to be access-checked
2916 * @return the class that has been access-checked
2917 * @throws IllegalAccessException if the class is not accessible from the lookup class
2918 * and previous lookup class, if present, using the allowed access modes.
2919 * @throws SecurityException if a security manager is present and it
2920 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2921 * @throws NullPointerException if {@code targetClass} is {@code null}
2922 * @since 9
2923 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
2924 */
2925 public Class<?> accessClass(Class<?> targetClass) throws IllegalAccessException {
2926 if (!isClassAccessible(targetClass)) {
2927 throw makeAccessException(targetClass);
2928 }
2929 checkSecurityManager(targetClass);
2930 return targetClass;
2931 }
2932
2933 /**
2934 * Produces an early-bound method handle for a virtual method.
2935 * It will bypass checks for overriding methods on the receiver,
2936 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
2937 * instruction from within the explicitly specified {@code specialCaller}.
2938 * The type of the method handle will be that of the method,
2939 * with a suitably restricted receiver type prepended.
2940 * (The receiver type will be {@code specialCaller} or a subtype.)
2941 * The method and all its argument types must be accessible
2942 * to the lookup object.
2943 * <p>
2944 * Before method resolution,
2945 * if the explicitly specified caller class is not identical with the
2946 * lookup class, or if this lookup object does not have
2947 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
2948 * privileges, the access fails.
2949 * <p>
2950 * The returned method handle will have
2951 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2952 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2953 * <p style="font-size:smaller;">
2954 * <em>(Note: JVM internal methods named {@code "<init>"} are not visible to this API,
2955 * even though the {@code invokespecial} instruction can refer to them
2956 * in special circumstances. Use {@link #findConstructor findConstructor}
2957 * to access instance initialization methods in a safe manner.)</em>
2958 * <p><b>Example:</b>
2959 * {@snippet lang="java" :
2960 import static java.lang.invoke.MethodHandles.*;
2961 import static java.lang.invoke.MethodType.*;
2962 ...
2963 static class Listie extends ArrayList {
2964 public String toString() { return "[wee Listie]"; }
2965 static Lookup lookup() { return MethodHandles.lookup(); }
2966 }
2967 ...
2968 // no access to constructor via invokeSpecial:
2969 MethodHandle MH_newListie = Listie.lookup()
2970 .findConstructor(Listie.class, methodType(void.class));
2971 Listie l = (Listie) MH_newListie.invokeExact();
2972 try { assertEquals("impossible", Listie.lookup().findSpecial(
2973 Listie.class, "<init>", methodType(void.class), Listie.class));
2974 } catch (NoSuchMethodException ex) { } // OK
2975 // access to super and self methods via invokeSpecial:
2976 MethodHandle MH_super = Listie.lookup().findSpecial(
2977 ArrayList.class, "toString" , methodType(String.class), Listie.class);
2978 MethodHandle MH_this = Listie.lookup().findSpecial(
2979 Listie.class, "toString" , methodType(String.class), Listie.class);
2980 MethodHandle MH_duper = Listie.lookup().findSpecial(
2981 Object.class, "toString" , methodType(String.class), Listie.class);
2982 assertEquals("[]", (String) MH_super.invokeExact(l));
2983 assertEquals(""+l, (String) MH_this.invokeExact(l));
2984 assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method
2985 try { assertEquals("inaccessible", Listie.lookup().findSpecial(
2986 String.class, "toString", methodType(String.class), Listie.class));
2987 } catch (IllegalAccessException ex) { } // OK
2988 Listie subl = new Listie() { public String toString() { return "[subclass]"; } };
2989 assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method
2990 * }
2991 *
2992 * @param refc the class or interface from which the method is accessed
2993 * @param name the name of the method (which must not be "<init>")
2994 * @param type the type of the method, with the receiver argument omitted
2995 * @param specialCaller the proposed calling class to perform the {@code invokespecial}
2996 * @return the desired method handle
2997 * @throws NoSuchMethodException if the method does not exist
2998 * @throws IllegalAccessException if access checking fails,
2999 * or if the method is {@code static},
3000 * or if the method's variable arity modifier bit
3001 * is set and {@code asVarargsCollector} fails
3002 * @throws SecurityException if a security manager is present and it
3003 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3004 * @throws NullPointerException if any argument is null
3005 */
3006 public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,
3007 Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
3008 checkSpecialCaller(specialCaller, refc);
3009 Lookup specialLookup = this.in(specialCaller);
3010 MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type);
3011 return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerLookup(method));
3012 }
3013
3014 /**
3015 * Produces a method handle giving read access to a non-static field.
3016 * The type of the method handle will have a return type of the field's
3017 * value type.
3018 * The method handle's single argument will be the instance containing
3019 * the field.
3020 * Access checking is performed immediately on behalf of the lookup class.
3021 * @param refc the class or interface from which the method is accessed
3022 * @param name the field's name
3023 * @param type the field's type
3024 * @return a method handle which can load values from the field
3025 * @throws NoSuchFieldException if the field does not exist
3026 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
3027 * @throws SecurityException if a security manager is present and it
3028 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3029 * @throws NullPointerException if any argument is null
3030 * @see #findVarHandle(Class, String, Class)
3031 */
3032 public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3033 MemberName field = resolveOrFail(REF_getField, refc, name, type);
3034 return getDirectField(REF_getField, refc, field);
3035 }
3036
3037 /**
3038 * Produces a method handle giving write access to a non-static field.
3039 * The type of the method handle will have a void return type.
3040 * The method handle will take two arguments, the instance containing
3041 * the field, and the value to be stored.
3042 * The second argument will be of the field's value type.
3043 * Access checking is performed immediately on behalf of the lookup class.
3044 * @param refc the class or interface from which the method is accessed
3045 * @param name the field's name
3046 * @param type the field's type
3047 * @return a method handle which can store values into the field
3048 * @throws NoSuchFieldException if the field does not exist
3049 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
3050 * or {@code final}
3051 * @throws SecurityException if a security manager is present and it
3052 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3053 * @throws NullPointerException if any argument is null
3054 * @see #findVarHandle(Class, String, Class)
3055 */
3056 public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3057 MemberName field = resolveOrFail(REF_putField, refc, name, type);
3058 return getDirectField(REF_putField, refc, field);
3059 }
3060
3061 /**
3062 * Produces a VarHandle giving access to a non-static field {@code name}
3063 * of type {@code type} declared in a class of type {@code recv}.
3064 * The VarHandle's variable type is {@code type} and it has one
3065 * coordinate type, {@code recv}.
3066 * <p>
3067 * Access checking is performed immediately on behalf of the lookup
3068 * class.
3069 * <p>
3070 * Certain access modes of the returned VarHandle are unsupported under
3071 * the following conditions:
3072 * <ul>
3073 * <li>if the field is declared {@code final}, then the write, atomic
3074 * update, numeric atomic update, and bitwise atomic update access
3075 * modes are unsupported.
3076 * <li>if the field type is anything other than {@code byte},
3077 * {@code short}, {@code char}, {@code int}, {@code long},
3078 * {@code float}, or {@code double} then numeric atomic update
3079 * access modes are unsupported.
3080 * <li>if the field type is anything other than {@code boolean},
3081 * {@code byte}, {@code short}, {@code char}, {@code int} or
3082 * {@code long} then bitwise atomic update access modes are
3083 * unsupported.
3084 * </ul>
3085 * <p>
3086 * If the field is declared {@code volatile} then the returned VarHandle
3087 * will override access to the field (effectively ignore the
3088 * {@code volatile} declaration) in accordance to its specified
3089 * access modes.
3090 * <p>
3091 * If the field type is {@code float} or {@code double} then numeric
3092 * and atomic update access modes compare values using their bitwise
3093 * representation (see {@link Float#floatToRawIntBits} and
3094 * {@link Double#doubleToRawLongBits}, respectively).
3095 * @apiNote
3096 * Bitwise comparison of {@code float} values or {@code double} values,
3097 * as performed by the numeric and atomic update access modes, differ
3098 * from the primitive {@code ==} operator and the {@link Float#equals}
3099 * and {@link Double#equals} methods, specifically with respect to
3100 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
3101 * Care should be taken when performing a compare and set or a compare
3102 * and exchange operation with such values since the operation may
3103 * unexpectedly fail.
3104 * There are many possible NaN values that are considered to be
3105 * {@code NaN} in Java, although no IEEE 754 floating-point operation
3106 * provided by Java can distinguish between them. Operation failure can
3107 * occur if the expected or witness value is a NaN value and it is
3108 * transformed (perhaps in a platform specific manner) into another NaN
3109 * value, and thus has a different bitwise representation (see
3110 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
3111 * details).
3112 * The values {@code -0.0} and {@code +0.0} have different bitwise
3113 * representations but are considered equal when using the primitive
3114 * {@code ==} operator. Operation failure can occur if, for example, a
3115 * numeric algorithm computes an expected value to be say {@code -0.0}
3116 * and previously computed the witness value to be say {@code +0.0}.
3117 * @param recv the receiver class, of type {@code R}, that declares the
3118 * non-static field
3119 * @param name the field's name
3120 * @param type the field's type, of type {@code T}
3121 * @return a VarHandle giving access to non-static fields.
3122 * @throws NoSuchFieldException if the field does not exist
3123 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
3124 * @throws SecurityException if a security manager is present and it
3125 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3126 * @throws NullPointerException if any argument is null
3127 * @since 9
3128 */
3129 public VarHandle findVarHandle(Class<?> recv, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3130 MemberName getField = resolveOrFail(REF_getField, recv, name, type);
3131 MemberName putField = resolveOrFail(REF_putField, recv, name, type);
3132 return getFieldVarHandle(REF_getField, REF_putField, recv, getField, putField);
3133 }
3134
3135 /**
3136 * Produces a method handle giving read access to a static field.
3137 * The type of the method handle will have a return type of the field's
3138 * value type.
3139 * The method handle will take no arguments.
3140 * Access checking is performed immediately on behalf of the lookup class.
3141 * <p>
3142 * If the returned method handle is invoked, the field's class will
3143 * be initialized, if it has not already been initialized.
3144 * @param refc the class or interface from which the method is accessed
3145 * @param name the field's name
3146 * @param type the field's type
3147 * @return a method handle which can load values from the field
3148 * @throws NoSuchFieldException if the field does not exist
3149 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
3150 * @throws SecurityException if a security manager is present and it
3151 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3152 * @throws NullPointerException if any argument is null
3153 */
3154 public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3155 MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
3156 return getDirectField(REF_getStatic, refc, field);
3157 }
3158
3159 /**
3160 * Produces a method handle giving write access to a static field.
3161 * The type of the method handle will have a void return type.
3162 * The method handle will take a single
3163 * argument, of the field's value type, the value to be stored.
3164 * Access checking is performed immediately on behalf of the lookup class.
3165 * <p>
3166 * If the returned method handle is invoked, the field's class will
3167 * be initialized, if it has not already been initialized.
3168 * @param refc the class or interface from which the method is accessed
3169 * @param name the field's name
3170 * @param type the field's type
3171 * @return a method handle which can store values into the field
3172 * @throws NoSuchFieldException if the field does not exist
3173 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
3174 * or is {@code final}
3175 * @throws SecurityException if a security manager is present and it
3176 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3177 * @throws NullPointerException if any argument is null
3178 */
3179 public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3180 MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
3181 return getDirectField(REF_putStatic, refc, field);
3182 }
3183
3184 /**
3185 * Produces a VarHandle giving access to a static field {@code name} of
3186 * type {@code type} declared in a class of type {@code decl}.
3187 * The VarHandle's variable type is {@code type} and it has no
3188 * coordinate types.
3189 * <p>
3190 * Access checking is performed immediately on behalf of the lookup
3191 * class.
3192 * <p>
3193 * If the returned VarHandle is operated on, the declaring class will be
3194 * initialized, if it has not already been initialized.
3195 * <p>
3196 * Certain access modes of the returned VarHandle are unsupported under
3197 * the following conditions:
3198 * <ul>
3199 * <li>if the field is declared {@code final}, then the write, atomic
3200 * update, numeric atomic update, and bitwise atomic update access
3201 * modes are unsupported.
3202 * <li>if the field type is anything other than {@code byte},
3203 * {@code short}, {@code char}, {@code int}, {@code long},
3204 * {@code float}, or {@code double}, then numeric atomic update
3205 * access modes are unsupported.
3206 * <li>if the field type is anything other than {@code boolean},
3207 * {@code byte}, {@code short}, {@code char}, {@code int} or
3208 * {@code long} then bitwise atomic update access modes are
3209 * unsupported.
3210 * </ul>
3211 * <p>
3212 * If the field is declared {@code volatile} then the returned VarHandle
3213 * will override access to the field (effectively ignore the
3214 * {@code volatile} declaration) in accordance to its specified
3215 * access modes.
3216 * <p>
3217 * If the field type is {@code float} or {@code double} then numeric
3218 * and atomic update access modes compare values using their bitwise
3219 * representation (see {@link Float#floatToRawIntBits} and
3220 * {@link Double#doubleToRawLongBits}, respectively).
3221 * @apiNote
3222 * Bitwise comparison of {@code float} values or {@code double} values,
3223 * as performed by the numeric and atomic update access modes, differ
3224 * from the primitive {@code ==} operator and the {@link Float#equals}
3225 * and {@link Double#equals} methods, specifically with respect to
3226 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
3227 * Care should be taken when performing a compare and set or a compare
3228 * and exchange operation with such values since the operation may
3229 * unexpectedly fail.
3230 * There are many possible NaN values that are considered to be
3231 * {@code NaN} in Java, although no IEEE 754 floating-point operation
3232 * provided by Java can distinguish between them. Operation failure can
3233 * occur if the expected or witness value is a NaN value and it is
3234 * transformed (perhaps in a platform specific manner) into another NaN
3235 * value, and thus has a different bitwise representation (see
3236 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
3237 * details).
3238 * The values {@code -0.0} and {@code +0.0} have different bitwise
3239 * representations but are considered equal when using the primitive
3240 * {@code ==} operator. Operation failure can occur if, for example, a
3241 * numeric algorithm computes an expected value to be say {@code -0.0}
3242 * and previously computed the witness value to be say {@code +0.0}.
3243 * @param decl the class that declares the static field
3244 * @param name the field's name
3245 * @param type the field's type, of type {@code T}
3246 * @return a VarHandle giving access to a static field
3247 * @throws NoSuchFieldException if the field does not exist
3248 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
3249 * @throws SecurityException if a security manager is present and it
3250 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3251 * @throws NullPointerException if any argument is null
3252 * @since 9
3253 */
3254 public VarHandle findStaticVarHandle(Class<?> decl, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3255 MemberName getField = resolveOrFail(REF_getStatic, decl, name, type);
3256 MemberName putField = resolveOrFail(REF_putStatic, decl, name, type);
3257 return getFieldVarHandle(REF_getStatic, REF_putStatic, decl, getField, putField);
3258 }
3259
3260 /**
3261 * Produces an early-bound method handle for a non-static method.
3262 * The receiver must have a supertype {@code defc} in which a method
3263 * of the given name and type is accessible to the lookup class.
3264 * The method and all its argument types must be accessible to the lookup object.
3265 * The type of the method handle will be that of the method,
3266 * without any insertion of an additional receiver parameter.
3267 * The given receiver will be bound into the method handle,
3268 * so that every call to the method handle will invoke the
3269 * requested method on the given receiver.
3270 * <p>
3271 * The returned method handle will have
3272 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3273 * the method's variable arity modifier bit ({@code 0x0080}) is set
3274 * <em>and</em> the trailing array argument is not the only argument.
3275 * (If the trailing array argument is the only argument,
3276 * the given receiver value will be bound to it.)
3277 * <p>
3278 * This is almost equivalent to the following code, with some differences noted below:
3279 * {@snippet lang="java" :
3280 import static java.lang.invoke.MethodHandles.*;
3281 import static java.lang.invoke.MethodType.*;
3282 ...
3283 MethodHandle mh0 = lookup().findVirtual(defc, name, type);
3284 MethodHandle mh1 = mh0.bindTo(receiver);
3285 mh1 = mh1.withVarargs(mh0.isVarargsCollector());
3286 return mh1;
3287 * }
3288 * where {@code defc} is either {@code receiver.getClass()} or a super
3289 * type of that class, in which the requested method is accessible
3290 * to the lookup class.
3291 * (Unlike {@code bind}, {@code bindTo} does not preserve variable arity.
3292 * Also, {@code bindTo} may throw a {@code ClassCastException} in instances where {@code bind} would
3293 * throw an {@code IllegalAccessException}, as in the case where the member is {@code protected} and
3294 * the receiver is restricted by {@code findVirtual} to the lookup class.)
3295 * @param receiver the object from which the method is accessed
3296 * @param name the name of the method
3297 * @param type the type of the method, with the receiver argument omitted
3298 * @return the desired method handle
3299 * @throws NoSuchMethodException if the method does not exist
3300 * @throws IllegalAccessException if access checking fails
3301 * or if the method's variable arity modifier bit
3302 * is set and {@code asVarargsCollector} fails
3303 * @throws SecurityException if a security manager is present and it
3304 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3305 * @throws NullPointerException if any argument is null
3306 * @see MethodHandle#bindTo
3307 * @see #findVirtual
3308 */
3309 public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
3310 Class<? extends Object> refc = receiver.getClass(); // may get NPE
3311 MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
3312 MethodHandle mh = getDirectMethodNoRestrictInvokeSpecial(refc, method, findBoundCallerLookup(method));
3313 if (!mh.type().leadingReferenceParameter().isAssignableFrom(receiver.getClass())) {
3314 throw new IllegalAccessException("The restricted defining class " +
3315 mh.type().leadingReferenceParameter().getName() +
3316 " is not assignable from receiver class " +
3317 receiver.getClass().getName());
3318 }
3319 return mh.bindArgumentL(0, receiver).setVarargs(method);
3320 }
3321
3322 /**
3323 * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
3324 * to <i>m</i>, if the lookup class has permission.
3325 * If <i>m</i> is non-static, the receiver argument is treated as an initial argument.
3326 * If <i>m</i> is virtual, overriding is respected on every call.
3327 * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped.
3328 * The type of the method handle will be that of the method,
3329 * with the receiver type prepended (but only if it is non-static).
3330 * If the method's {@code accessible} flag is not set,
3331 * access checking is performed immediately on behalf of the lookup class.
3332 * If <i>m</i> is not public, do not share the resulting handle with untrusted parties.
3333 * <p>
3334 * The returned method handle will have
3335 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3336 * the method's variable arity modifier bit ({@code 0x0080}) is set.
3337 * <p>
3338 * If <i>m</i> is static, and
3339 * if the returned method handle is invoked, the method's class will
3340 * be initialized, if it has not already been initialized.
3341 * @param m the reflected method
3342 * @return a method handle which can invoke the reflected method
3343 * @throws IllegalAccessException if access checking fails
3344 * or if the method's variable arity modifier bit
3345 * is set and {@code asVarargsCollector} fails
3346 * @throws NullPointerException if the argument is null
3347 */
3348 public MethodHandle unreflect(Method m) throws IllegalAccessException {
3349 if (m.getDeclaringClass() == MethodHandle.class) {
3350 MethodHandle mh = unreflectForMH(m);
3351 if (mh != null) return mh;
3352 }
3353 if (m.getDeclaringClass() == VarHandle.class) {
3354 MethodHandle mh = unreflectForVH(m);
3355 if (mh != null) return mh;
3356 }
3357 MemberName method = new MemberName(m);
3358 byte refKind = method.getReferenceKind();
3359 if (refKind == REF_invokeSpecial)
3360 refKind = REF_invokeVirtual;
3361 assert(method.isMethod());
3362 @SuppressWarnings("deprecation")
3363 Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
3364 return lookup.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method, findBoundCallerLookup(method));
3365 }
3366 private MethodHandle unreflectForMH(Method m) {
3367 // these names require special lookups because they throw UnsupportedOperationException
3368 if (MemberName.isMethodHandleInvokeName(m.getName()))
3369 return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m));
3370 return null;
3371 }
3372 private MethodHandle unreflectForVH(Method m) {
3373 // these names require special lookups because they throw UnsupportedOperationException
3374 if (MemberName.isVarHandleMethodInvokeName(m.getName()))
3375 return MethodHandleImpl.fakeVarHandleInvoke(new MemberName(m));
3376 return null;
3377 }
3378
3379 /**
3380 * Produces a method handle for a reflected method.
3381 * It will bypass checks for overriding methods on the receiver,
3382 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
3383 * instruction from within the explicitly specified {@code specialCaller}.
3384 * The type of the method handle will be that of the method,
3385 * with a suitably restricted receiver type prepended.
3386 * (The receiver type will be {@code specialCaller} or a subtype.)
3387 * If the method's {@code accessible} flag is not set,
3388 * access checking is performed immediately on behalf of the lookup class,
3389 * as if {@code invokespecial} instruction were being linked.
3390 * <p>
3391 * Before method resolution,
3392 * if the explicitly specified caller class is not identical with the
3393 * lookup class, or if this lookup object does not have
3394 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
3395 * privileges, the access fails.
3396 * <p>
3397 * The returned method handle will have
3398 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3399 * the method's variable arity modifier bit ({@code 0x0080}) is set.
3400 * @param m the reflected method
3401 * @param specialCaller the class nominally calling the method
3402 * @return a method handle which can invoke the reflected method
3403 * @throws IllegalAccessException if access checking fails,
3404 * or if the method is {@code static},
3405 * or if the method's variable arity modifier bit
3406 * is set and {@code asVarargsCollector} fails
3407 * @throws NullPointerException if any argument is null
3408 */
3409 public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException {
3410 checkSpecialCaller(specialCaller, m.getDeclaringClass());
3411 Lookup specialLookup = this.in(specialCaller);
3412 MemberName method = new MemberName(m, true);
3413 assert(method.isMethod());
3414 // ignore m.isAccessible: this is a new kind of access
3415 return specialLookup.getDirectMethodNoSecurityManager(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerLookup(method));
3416 }
3417
3418 /**
3419 * Produces a method handle for a reflected constructor.
3420 * The type of the method handle will be that of the constructor,
3421 * with the return type changed to the declaring class.
3422 * The method handle will perform a {@code newInstance} operation,
3423 * creating a new instance of the constructor's class on the
3424 * arguments passed to the method handle.
3425 * <p>
3426 * If the constructor's {@code accessible} flag is not set,
3427 * access checking is performed immediately on behalf of the lookup class.
3428 * <p>
3429 * The returned method handle will have
3430 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3431 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
3432 * <p>
3433 * If the returned method handle is invoked, the constructor's class will
3434 * be initialized, if it has not already been initialized.
3435 * @param c the reflected constructor
3436 * @return a method handle which can invoke the reflected constructor
3437 * @throws IllegalAccessException if access checking fails
3438 * or if the method's variable arity modifier bit
3439 * is set and {@code asVarargsCollector} fails
3440 * @throws NullPointerException if the argument is null
3441 */
3442 public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException {
3443 MemberName ctor = new MemberName(c);
3444 assert(ctor.isConstructor());
3445 @SuppressWarnings("deprecation")
3446 Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
3447 return lookup.getDirectConstructorNoSecurityManager(ctor.getDeclaringClass(), ctor);
3448 }
3449
3450 /**
3451 * Produces a method handle giving read access to a reflected field.
3452 * The type of the method handle will have a return type of the field's
3453 * value type.
3454 * If the field is {@code static}, the method handle will take no arguments.
3455 * Otherwise, its single argument will be the instance containing
3456 * the field.
3457 * If the {@code Field} object's {@code accessible} flag is not set,
3458 * access checking is performed immediately on behalf of the lookup class.
3459 * <p>
3460 * If the field is static, and
3461 * if the returned method handle is invoked, the field's class will
3462 * be initialized, if it has not already been initialized.
3463 * @param f the reflected field
3464 * @return a method handle which can load values from the reflected field
3465 * @throws IllegalAccessException if access checking fails
3466 * @throws NullPointerException if the argument is null
3467 */
3468 public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
3469 return unreflectField(f, false);
3470 }
3471
3472 /**
3473 * Produces a method handle giving write access to a reflected field.
3474 * The type of the method handle will have a void return type.
3475 * If the field is {@code static}, the method handle will take a single
3476 * argument, of the field's value type, the value to be stored.
3477 * Otherwise, the two arguments will be the instance containing
3478 * the field, and the value to be stored.
3479 * If the {@code Field} object's {@code accessible} flag is not set,
3480 * access checking is performed immediately on behalf of the lookup class.
3481 * <p>
3482 * If the field is {@code final}, write access will not be
3483 * allowed and access checking will fail, except under certain
3484 * narrow circumstances documented for {@link Field#set Field.set}.
3485 * A method handle is returned only if a corresponding call to
3486 * the {@code Field} object's {@code set} method could return
3487 * normally. In particular, fields which are both {@code static}
3488 * and {@code final} may never be set.
3489 * <p>
3490 * If the field is {@code static}, and
3491 * if the returned method handle is invoked, the field's class will
3492 * be initialized, if it has not already been initialized.
3493 * @param f the reflected field
3494 * @return a method handle which can store values into the reflected field
3495 * @throws IllegalAccessException if access checking fails,
3496 * or if the field is {@code final} and write access
3497 * is not enabled on the {@code Field} object
3498 * @throws NullPointerException if the argument is null
3499 */
3500 public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
3501 return unreflectField(f, true);
3502 }
3503
3504 private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
3505 MemberName field = new MemberName(f, isSetter);
3506 if (isSetter && field.isFinal()) {
3507 if (field.isTrustedFinalField()) {
3508 String msg = field.isStatic() ? "static final field has no write access"
3509 : "final field has no write access";
3510 throw field.makeAccessException(msg, this);
3511 }
3512 }
3513 assert(isSetter
3514 ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
3515 : MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
3516 @SuppressWarnings("deprecation")
3517 Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
3518 return lookup.getDirectFieldNoSecurityManager(field.getReferenceKind(), f.getDeclaringClass(), field);
3519 }
3520
3521 /**
3522 * Produces a VarHandle giving access to a reflected field {@code f}
3523 * of type {@code T} declared in a class of type {@code R}.
3524 * The VarHandle's variable type is {@code T}.
3525 * If the field is non-static the VarHandle has one coordinate type,
3526 * {@code R}. Otherwise, the field is static, and the VarHandle has no
3527 * coordinate types.
3528 * <p>
3529 * Access checking is performed immediately on behalf of the lookup
3530 * class, regardless of the value of the field's {@code accessible}
3531 * flag.
3532 * <p>
3533 * If the field is static, and if the returned VarHandle is operated
3534 * on, the field's declaring class will be initialized, if it has not
3535 * already been initialized.
3536 * <p>
3537 * Certain access modes of the returned VarHandle are unsupported under
3538 * the following conditions:
3539 * <ul>
3540 * <li>if the field is declared {@code final}, then the write, atomic
3541 * update, numeric atomic update, and bitwise atomic update access
3542 * modes are unsupported.
3543 * <li>if the field type is anything other than {@code byte},
3544 * {@code short}, {@code char}, {@code int}, {@code long},
3545 * {@code float}, or {@code double} then numeric atomic update
3546 * access modes are unsupported.
3547 * <li>if the field type is anything other than {@code boolean},
3548 * {@code byte}, {@code short}, {@code char}, {@code int} or
3549 * {@code long} then bitwise atomic update access modes are
3550 * unsupported.
3551 * </ul>
3552 * <p>
3553 * If the field is declared {@code volatile} then the returned VarHandle
3554 * will override access to the field (effectively ignore the
3555 * {@code volatile} declaration) in accordance to its specified
3556 * access modes.
3557 * <p>
3558 * If the field type is {@code float} or {@code double} then numeric
3559 * and atomic update access modes compare values using their bitwise
3560 * representation (see {@link Float#floatToRawIntBits} and
3561 * {@link Double#doubleToRawLongBits}, respectively).
3562 * @apiNote
3563 * Bitwise comparison of {@code float} values or {@code double} values,
3564 * as performed by the numeric and atomic update access modes, differ
3565 * from the primitive {@code ==} operator and the {@link Float#equals}
3566 * and {@link Double#equals} methods, specifically with respect to
3567 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
3568 * Care should be taken when performing a compare and set or a compare
3569 * and exchange operation with such values since the operation may
3570 * unexpectedly fail.
3571 * There are many possible NaN values that are considered to be
3572 * {@code NaN} in Java, although no IEEE 754 floating-point operation
3573 * provided by Java can distinguish between them. Operation failure can
3574 * occur if the expected or witness value is a NaN value and it is
3575 * transformed (perhaps in a platform specific manner) into another NaN
3576 * value, and thus has a different bitwise representation (see
3577 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
3578 * details).
3579 * The values {@code -0.0} and {@code +0.0} have different bitwise
3580 * representations but are considered equal when using the primitive
3581 * {@code ==} operator. Operation failure can occur if, for example, a
3582 * numeric algorithm computes an expected value to be say {@code -0.0}
3583 * and previously computed the witness value to be say {@code +0.0}.
3584 * @param f the reflected field, with a field of type {@code T}, and
3585 * a declaring class of type {@code R}
3586 * @return a VarHandle giving access to non-static fields or a static
3587 * field
3588 * @throws IllegalAccessException if access checking fails
3589 * @throws NullPointerException if the argument is null
3590 * @since 9
3591 */
3592 public VarHandle unreflectVarHandle(Field f) throws IllegalAccessException {
3593 MemberName getField = new MemberName(f, false);
3594 MemberName putField = new MemberName(f, true);
3595 return getFieldVarHandleNoSecurityManager(getField.getReferenceKind(), putField.getReferenceKind(),
3596 f.getDeclaringClass(), getField, putField);
3597 }
3598
3599 /**
3600 * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
3601 * created by this lookup object or a similar one.
3602 * Security and access checks are performed to ensure that this lookup object
3603 * is capable of reproducing the target method handle.
3604 * This means that the cracking may fail if target is a direct method handle
3605 * but was created by an unrelated lookup object.
3606 * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a>
3607 * and was created by a lookup object for a different class.
3608 * @param target a direct method handle to crack into symbolic reference components
3609 * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object
3610 * @throws SecurityException if a security manager is present and it
3611 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3612 * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails
3613 * @throws NullPointerException if the target is {@code null}
3614 * @see MethodHandleInfo
3615 * @since 1.8
3616 */
3617 public MethodHandleInfo revealDirect(MethodHandle target) {
3618 if (!target.isCrackable()) {
3619 throw newIllegalArgumentException("not a direct method handle");
3620 }
3621 MemberName member = target.internalMemberName();
3622 Class<?> defc = member.getDeclaringClass();
3623 byte refKind = member.getReferenceKind();
3624 assert(MethodHandleNatives.refKindIsValid(refKind));
3625 if (refKind == REF_invokeSpecial && !target.isInvokeSpecial())
3626 // Devirtualized method invocation is usually formally virtual.
3627 // To avoid creating extra MemberName objects for this common case,
3628 // we encode this extra degree of freedom using MH.isInvokeSpecial.
3629 refKind = REF_invokeVirtual;
3630 if (refKind == REF_invokeVirtual && defc.isInterface())
3631 // Symbolic reference is through interface but resolves to Object method (toString, etc.)
3632 refKind = REF_invokeInterface;
3633 // Check SM permissions and member access before cracking.
3634 try {
3635 checkAccess(refKind, defc, member);
3636 checkSecurityManager(defc, member);
3637 } catch (IllegalAccessException ex) {
3638 throw new IllegalArgumentException(ex);
3639 }
3640 if (allowedModes != TRUSTED && member.isCallerSensitive()) {
3641 Class<?> callerClass = target.internalCallerClass();
3642 if ((lookupModes() & ORIGINAL) == 0 || callerClass != lookupClass())
3643 throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass);
3644 }
3645 // Produce the handle to the results.
3646 return new InfoFromMemberName(this, member, refKind);
3647 }
3648
3649 /// Helper methods, all package-private.
3650
3651 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3652 checkSymbolicClass(refc); // do this before attempting to resolve
3653 Objects.requireNonNull(name);
3654 Objects.requireNonNull(type);
3655 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), allowedModes,
3656 NoSuchFieldException.class);
3657 }
3658
3659 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
3660 checkSymbolicClass(refc); // do this before attempting to resolve
3661 Objects.requireNonNull(type);
3662 checkMethodName(refKind, name); // implicit null-check of name
3663 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), allowedModes,
3664 NoSuchMethodException.class);
3665 }
3666
3667 MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException {
3668 checkSymbolicClass(member.getDeclaringClass()); // do this before attempting to resolve
3669 Objects.requireNonNull(member.getName());
3670 Objects.requireNonNull(member.getType());
3671 return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(), allowedModes,
3672 ReflectiveOperationException.class);
3673 }
3674
3675 MemberName resolveOrNull(byte refKind, MemberName member) {
3676 // do this before attempting to resolve
3677 if (!isClassAccessible(member.getDeclaringClass())) {
3678 return null;
3679 }
3680 Objects.requireNonNull(member.getName());
3681 Objects.requireNonNull(member.getType());
3682 return IMPL_NAMES.resolveOrNull(refKind, member, lookupClassOrNull(), allowedModes);
3683 }
3684
3685 MemberName resolveOrNull(byte refKind, Class<?> refc, String name, MethodType type) {
3686 // do this before attempting to resolve
3687 if (!isClassAccessible(refc)) {
3688 return null;
3689 }
3690 Objects.requireNonNull(type);
3691 // implicit null-check of name
3692 if (name.startsWith("<") && refKind != REF_newInvokeSpecial) {
3693 return null;
3694 }
3695 return IMPL_NAMES.resolveOrNull(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), allowedModes);
3696 }
3697
3698 void checkSymbolicClass(Class<?> refc) throws IllegalAccessException {
3699 if (!isClassAccessible(refc)) {
3700 throw new MemberName(refc).makeAccessException("symbolic reference class is not accessible", this);
3701 }
3702 }
3703
3704 boolean isClassAccessible(Class<?> refc) {
3705 Objects.requireNonNull(refc);
3706 Class<?> caller = lookupClassOrNull();
3707 Class<?> type = refc;
3708 while (type.isArray()) {
3709 type = type.getComponentType();
3710 }
3711 return caller == null || VerifyAccess.isClassAccessible(type, caller, prevLookupClass, allowedModes);
3712 }
3713
3714 /** Check name for an illegal leading "<" character. */
3715 void checkMethodName(byte refKind, String name) throws NoSuchMethodException {
3716 if (name.startsWith("<") && refKind != REF_newInvokeSpecial)
3717 throw new NoSuchMethodException("illegal method name: "+name);
3718 }
3719
3720 /**
3721 * Find my trustable caller class if m is a caller sensitive method.
3722 * If this lookup object has original full privilege access, then the caller class is the lookupClass.
3723 * Otherwise, if m is caller-sensitive, throw IllegalAccessException.
3724 */
3725 Lookup findBoundCallerLookup(MemberName m) throws IllegalAccessException {
3726 if (MethodHandleNatives.isCallerSensitive(m) && (lookupModes() & ORIGINAL) == 0) {
3727 // Only lookups with full privilege access are allowed to resolve caller-sensitive methods
3728 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
3729 }
3730 return this;
3731 }
3732
3733 /**
3734 * Returns {@code true} if this lookup has {@code PRIVATE} and {@code MODULE} access.
3735 * @return {@code true} if this lookup has {@code PRIVATE} and {@code MODULE} access.
3736 *
3737 * @deprecated This method was originally designed to test {@code PRIVATE} access
3738 * that implies full privilege access but {@code MODULE} access has since become
3739 * independent of {@code PRIVATE} access. It is recommended to call
3740 * {@link #hasFullPrivilegeAccess()} instead.
3741 * @since 9
3742 */
3743 @Deprecated(since="14")
3744 public boolean hasPrivateAccess() {
3745 return hasFullPrivilegeAccess();
3746 }
3747
3748 /**
3749 * Returns {@code true} if this lookup has <em>full privilege access</em>,
3750 * i.e. {@code PRIVATE} and {@code MODULE} access.
3751 * A {@code Lookup} object must have full privilege access in order to
3752 * access all members that are allowed to the
3753 * {@linkplain #lookupClass() lookup class}.
3754 *
3755 * @return {@code true} if this lookup has full privilege access.
3756 * @since 14
3757 * @see <a href="MethodHandles.Lookup.html#privacc">private and module access</a>
3758 */
3759 public boolean hasFullPrivilegeAccess() {
3760 return (allowedModes & (PRIVATE|MODULE)) == (PRIVATE|MODULE);
3761 }
3762
3763 /**
3764 * Perform steps 1 and 2b <a href="MethodHandles.Lookup.html#secmgr">access checks</a>
3765 * for ensureInitialzed, findClass or accessClass.
3766 */
3767 void checkSecurityManager(Class<?> refc) {
3768 if (allowedModes == TRUSTED) return;
3769
3770 @SuppressWarnings("removal")
3771 SecurityManager smgr = System.getSecurityManager();
3772 if (smgr == null) return;
3773
3774 // Step 1:
3775 boolean fullPrivilegeLookup = hasFullPrivilegeAccess();
3776 if (!fullPrivilegeLookup ||
3777 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
3778 ReflectUtil.checkPackageAccess(refc);
3779 }
3780
3781 // Step 2b:
3782 if (!fullPrivilegeLookup) {
3783 smgr.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
3784 }
3785 }
3786
3787 /**
3788 * Perform steps 1, 2a and 3 <a href="MethodHandles.Lookup.html#secmgr">access checks</a>.
3789 * Determines a trustable caller class to compare with refc, the symbolic reference class.
3790 * If this lookup object has full privilege access except original access,
3791 * then the caller class is the lookupClass.
3792 *
3793 * Lookup object created by {@link MethodHandles#privateLookupIn(Class, Lookup)}
3794 * from the same module skips the security permission check.
3795 */
3796 void checkSecurityManager(Class<?> refc, MemberName m) {
3797 Objects.requireNonNull(refc);
3798 Objects.requireNonNull(m);
3799
3800 if (allowedModes == TRUSTED) return;
3801
3802 @SuppressWarnings("removal")
3803 SecurityManager smgr = System.getSecurityManager();
3804 if (smgr == null) return;
3805
3806 // Step 1:
3807 boolean fullPrivilegeLookup = hasFullPrivilegeAccess();
3808 if (!fullPrivilegeLookup ||
3809 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
3810 ReflectUtil.checkPackageAccess(refc);
3811 }
3812
3813 // Step 2a:
3814 if (m.isPublic()) return;
3815 if (!fullPrivilegeLookup) {
3816 smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION);
3817 }
3818
3819 // Step 3:
3820 Class<?> defc = m.getDeclaringClass();
3821 if (!fullPrivilegeLookup && defc != refc) {
3822 ReflectUtil.checkPackageAccess(defc);
3823 }
3824 }
3825
3826 void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
3827 boolean wantStatic = (refKind == REF_invokeStatic);
3828 String message;
3829 if (m.isConstructor())
3830 message = "expected a method, not a constructor";
3831 else if (!m.isMethod())
3832 message = "expected a method";
3833 else if (wantStatic != m.isStatic())
3834 message = wantStatic ? "expected a static method" : "expected a non-static method";
3835 else
3836 { checkAccess(refKind, refc, m); return; }
3837 throw m.makeAccessException(message, this);
3838 }
3839
3840 void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
3841 boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
3842 String message;
3843 if (wantStatic != m.isStatic())
3844 message = wantStatic ? "expected a static field" : "expected a non-static field";
3845 else
3846 { checkAccess(refKind, refc, m); return; }
3847 throw m.makeAccessException(message, this);
3848 }
3849
3850 /** Check public/protected/private bits on the symbolic reference class and its member. */
3851 void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
3852 assert(m.referenceKindIsConsistentWith(refKind) &&
3853 MethodHandleNatives.refKindIsValid(refKind) &&
3854 (MethodHandleNatives.refKindIsField(refKind) == m.isField()));
3855 int allowedModes = this.allowedModes;
3856 if (allowedModes == TRUSTED) return;
3857 int mods = m.getModifiers();
3858 if (Modifier.isProtected(mods) &&
3859 refKind == REF_invokeVirtual &&
3860 m.getDeclaringClass() == Object.class &&
3861 m.getName().equals("clone") &&
3862 refc.isArray()) {
3863 // The JVM does this hack also.
3864 // (See ClassVerifier::verify_invoke_instructions
3865 // and LinkResolver::check_method_accessability.)
3866 // Because the JVM does not allow separate methods on array types,
3867 // there is no separate method for int[].clone.
3868 // All arrays simply inherit Object.clone.
3869 // But for access checking logic, we make Object.clone
3870 // (normally protected) appear to be public.
3871 // Later on, when the DirectMethodHandle is created,
3872 // its leading argument will be restricted to the
3873 // requested array type.
3874 // N.B. The return type is not adjusted, because
3875 // that is *not* the bytecode behavior.
3876 mods ^= Modifier.PROTECTED | Modifier.PUBLIC;
3877 }
3878 if (Modifier.isProtected(mods) && refKind == REF_newInvokeSpecial) {
3879 // cannot "new" a protected ctor in a different package
3880 mods ^= Modifier.PROTECTED;
3881 }
3882 if (Modifier.isFinal(mods) &&
3883 MethodHandleNatives.refKindIsSetter(refKind))
3884 throw m.makeAccessException("unexpected set of a final field", this);
3885 int requestedModes = fixmods(mods); // adjust 0 => PACKAGE
3886 if ((requestedModes & allowedModes) != 0) {
3887 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
3888 mods, lookupClass(), previousLookupClass(), allowedModes))
3889 return;
3890 } else {
3891 // Protected members can also be checked as if they were package-private.
3892 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
3893 && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
3894 return;
3895 }
3896 throw m.makeAccessException(accessFailedMessage(refc, m), this);
3897 }
3898
3899 String accessFailedMessage(Class<?> refc, MemberName m) {
3900 Class<?> defc = m.getDeclaringClass();
3901 int mods = m.getModifiers();
3902 // check the class first:
3903 boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
3904 (defc == refc ||
3905 Modifier.isPublic(refc.getModifiers())));
3906 if (!classOK && (allowedModes & PACKAGE) != 0) {
3907 // ignore previous lookup class to check if default package access
3908 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), null, FULL_POWER_MODES) &&
3909 (defc == refc ||
3910 VerifyAccess.isClassAccessible(refc, lookupClass(), null, FULL_POWER_MODES)));
3911 }
3912 if (!classOK)
3913 return "class is not public";
3914 if (Modifier.isPublic(mods))
3915 return "access to public member failed"; // (how?, module not readable?)
3916 if (Modifier.isPrivate(mods))
3917 return "member is private";
3918 if (Modifier.isProtected(mods))
3919 return "member is protected";
3920 return "member is private to package";
3921 }
3922
3923 private void checkSpecialCaller(Class<?> specialCaller, Class<?> refc) throws IllegalAccessException {
3924 int allowedModes = this.allowedModes;
3925 if (allowedModes == TRUSTED) return;
3926 if ((lookupModes() & PRIVATE) == 0
3927 || (specialCaller != lookupClass()
3928 // ensure non-abstract methods in superinterfaces can be special-invoked
3929 && !(refc != null && refc.isInterface() && refc.isAssignableFrom(specialCaller))))
3930 throw new MemberName(specialCaller).
3931 makeAccessException("no private access for invokespecial", this);
3932 }
3933
3934 private boolean restrictProtectedReceiver(MemberName method) {
3935 // The accessing class only has the right to use a protected member
3936 // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc.
3937 if (!method.isProtected() || method.isStatic()
3938 || allowedModes == TRUSTED
3939 || method.getDeclaringClass() == lookupClass()
3940 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass()))
3941 return false;
3942 return true;
3943 }
3944 private MethodHandle restrictReceiver(MemberName method, DirectMethodHandle mh, Class<?> caller) throws IllegalAccessException {
3945 assert(!method.isStatic());
3946 // receiver type of mh is too wide; narrow to caller
3947 if (!method.getDeclaringClass().isAssignableFrom(caller)) {
3948 throw method.makeAccessException("caller class must be a subclass below the method", caller);
3949 }
3950 MethodType rawType = mh.type();
3951 if (caller.isAssignableFrom(rawType.parameterType(0))) return mh; // no need to restrict; already narrow
3952 MethodType narrowType = rawType.changeParameterType(0, caller);
3953 assert(!mh.isVarargsCollector()); // viewAsType will lose varargs-ness
3954 assert(mh.viewAsTypeChecks(narrowType, true));
3955 return mh.copyWith(narrowType, mh.form);
3956 }
3957
3958 /** Check access and get the requested method. */
3959 private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException {
3960 final boolean doRestrict = true;
3961 final boolean checkSecurity = true;
3962 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerLookup);
3963 }
3964 /** Check access and get the requested method, for invokespecial with no restriction on the application of narrowing rules. */
3965 private MethodHandle getDirectMethodNoRestrictInvokeSpecial(Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException {
3966 final boolean doRestrict = false;
3967 final boolean checkSecurity = true;
3968 return getDirectMethodCommon(REF_invokeSpecial, refc, method, checkSecurity, doRestrict, callerLookup);
3969 }
3970 /** Check access and get the requested method, eliding security manager checks. */
3971 private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException {
3972 final boolean doRestrict = true;
3973 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
3974 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerLookup);
3975 }
3976 /** Common code for all methods; do not call directly except from immediately above. */
3977 private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method,
3978 boolean checkSecurity,
3979 boolean doRestrict,
3980 Lookup boundCaller) throws IllegalAccessException {
3981 checkMethod(refKind, refc, method);
3982 // Optionally check with the security manager; this isn't needed for unreflect* calls.
3983 if (checkSecurity)
3984 checkSecurityManager(refc, method);
3985 assert(!method.isMethodHandleInvoke());
3986
3987 if (refKind == REF_invokeSpecial &&
3988 refc != lookupClass() &&
3989 !refc.isInterface() &&
3990 refc != lookupClass().getSuperclass() &&
3991 refc.isAssignableFrom(lookupClass())) {
3992 assert(!method.getName().equals("<init>")); // not this code path
3993
3994 // Per JVMS 6.5, desc. of invokespecial instruction:
3995 // If the method is in a superclass of the LC,
3996 // and if our original search was above LC.super,
3997 // repeat the search (symbolic lookup) from LC.super
3998 // and continue with the direct superclass of that class,
3999 // and so forth, until a match is found or no further superclasses exist.
4000 // FIXME: MemberName.resolve should handle this instead.
4001 Class<?> refcAsSuper = lookupClass();
4002 MemberName m2;
4003 do {
4004 refcAsSuper = refcAsSuper.getSuperclass();
4005 m2 = new MemberName(refcAsSuper,
4006 method.getName(),
4007 method.getMethodType(),
4008 REF_invokeSpecial);
4009 m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull(), allowedModes);
4010 } while (m2 == null && // no method is found yet
4011 refc != refcAsSuper); // search up to refc
4012 if (m2 == null) throw new InternalError(method.toString());
4013 method = m2;
4014 refc = refcAsSuper;
4015 // redo basic checks
4016 checkMethod(refKind, refc, method);
4017 }
4018 DirectMethodHandle dmh = DirectMethodHandle.make(refKind, refc, method, lookupClass());
4019 MethodHandle mh = dmh;
4020 // Optionally narrow the receiver argument to lookupClass using restrictReceiver.
4021 if ((doRestrict && refKind == REF_invokeSpecial) ||
4022 (MethodHandleNatives.refKindHasReceiver(refKind) && restrictProtectedReceiver(method))) {
4023 mh = restrictReceiver(method, dmh, lookupClass());
4024 }
4025 mh = maybeBindCaller(method, mh, boundCaller);
4026 mh = mh.setVarargs(method);
4027 return mh;
4028 }
4029 private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh, Lookup boundCaller)
4030 throws IllegalAccessException {
4031 if (boundCaller.allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method))
4032 return mh;
4033
4034 // boundCaller must have full privilege access.
4035 // It should have been checked by findBoundCallerLookup. Safe to check this again.
4036 if ((boundCaller.lookupModes() & ORIGINAL) == 0)
4037 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
4038
4039 assert boundCaller.hasFullPrivilegeAccess();
4040
4041 MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, boundCaller.lookupClass);
4042 // Note: caller will apply varargs after this step happens.
4043 return cbmh;
4044 }
4045
4046 /** Check access and get the requested field. */
4047 private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
4048 final boolean checkSecurity = true;
4049 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
4050 }
4051 /** Check access and get the requested field, eliding security manager checks. */
4052 private MethodHandle getDirectFieldNoSecurityManager(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
4053 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
4054 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
4055 }
4056 /** Common code for all fields; do not call directly except from immediately above. */
4057 private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field,
4058 boolean checkSecurity) throws IllegalAccessException {
4059 checkField(refKind, refc, field);
4060 // Optionally check with the security manager; this isn't needed for unreflect* calls.
4061 if (checkSecurity)
4062 checkSecurityManager(refc, field);
4063 DirectMethodHandle dmh = DirectMethodHandle.make(refc, field);
4064 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) &&
4065 restrictProtectedReceiver(field));
4066 if (doRestrict)
4067 return restrictReceiver(field, dmh, lookupClass());
4068 return dmh;
4069 }
4070 private VarHandle getFieldVarHandle(byte getRefKind, byte putRefKind,
4071 Class<?> refc, MemberName getField, MemberName putField)
4072 throws IllegalAccessException {
4073 final boolean checkSecurity = true;
4074 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
4075 }
4076 private VarHandle getFieldVarHandleNoSecurityManager(byte getRefKind, byte putRefKind,
4077 Class<?> refc, MemberName getField, MemberName putField)
4078 throws IllegalAccessException {
4079 final boolean checkSecurity = false;
4080 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
4081 }
4082 private VarHandle getFieldVarHandleCommon(byte getRefKind, byte putRefKind,
4083 Class<?> refc, MemberName getField, MemberName putField,
4084 boolean checkSecurity) throws IllegalAccessException {
4085 assert getField.isStatic() == putField.isStatic();
4086 assert getField.isGetter() && putField.isSetter();
4087 assert MethodHandleNatives.refKindIsStatic(getRefKind) == MethodHandleNatives.refKindIsStatic(putRefKind);
4088 assert MethodHandleNatives.refKindIsGetter(getRefKind) && MethodHandleNatives.refKindIsSetter(putRefKind);
4089
4090 checkField(getRefKind, refc, getField);
4091 if (checkSecurity)
4092 checkSecurityManager(refc, getField);
4093
4094 if (!putField.isFinal()) {
4095 // A VarHandle does not support updates to final fields, any
4096 // such VarHandle to a final field will be read-only and
4097 // therefore the following write-based accessibility checks are
4098 // only required for non-final fields
4099 checkField(putRefKind, refc, putField);
4100 if (checkSecurity)
4101 checkSecurityManager(refc, putField);
4102 }
4103
4104 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(getRefKind) &&
4105 restrictProtectedReceiver(getField));
4106 if (doRestrict) {
4107 assert !getField.isStatic();
4108 // receiver type of VarHandle is too wide; narrow to caller
4109 if (!getField.getDeclaringClass().isAssignableFrom(lookupClass())) {
4110 throw getField.makeAccessException("caller class must be a subclass below the method", lookupClass());
4111 }
4112 refc = lookupClass();
4113 }
4114 return VarHandles.makeFieldHandle(getField, refc, getField.getFieldType(),
4115 this.allowedModes == TRUSTED && !getField.isTrustedFinalField());
4116 }
4117 /** Check access and get the requested constructor. */
4118 private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException {
4119 final boolean checkSecurity = true;
4120 return getDirectConstructorCommon(refc, ctor, checkSecurity);
4121 }
4122 /** Check access and get the requested constructor, eliding security manager checks. */
4123 private MethodHandle getDirectConstructorNoSecurityManager(Class<?> refc, MemberName ctor) throws IllegalAccessException {
4124 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
4125 return getDirectConstructorCommon(refc, ctor, checkSecurity);
4126 }
4127 /** Common code for all constructors; do not call directly except from immediately above. */
4128 private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor,
4129 boolean checkSecurity) throws IllegalAccessException {
4130 assert(ctor.isConstructor());
4131 checkAccess(REF_newInvokeSpecial, refc, ctor);
4132 // Optionally check with the security manager; this isn't needed for unreflect* calls.
4133 if (checkSecurity)
4134 checkSecurityManager(refc, ctor);
4135 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
4136 return DirectMethodHandle.make(ctor).setVarargs(ctor);
4137 }
4138
4139 /** Hook called from the JVM (via MethodHandleNatives) to link MH constants:
4140 */
4141 /*non-public*/
4142 MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type)
4143 throws ReflectiveOperationException {
4144 if (!(type instanceof Class || type instanceof MethodType))
4145 throw new InternalError("unresolved MemberName");
4146 MemberName member = new MemberName(refKind, defc, name, type);
4147 MethodHandle mh = LOOKASIDE_TABLE.get(member);
4148 if (mh != null) {
4149 checkSymbolicClass(defc);
4150 return mh;
4151 }
4152 if (defc == MethodHandle.class && refKind == REF_invokeVirtual) {
4153 // Treat MethodHandle.invoke and invokeExact specially.
4154 mh = findVirtualForMH(member.getName(), member.getMethodType());
4155 if (mh != null) {
4156 return mh;
4157 }
4158 } else if (defc == VarHandle.class && refKind == REF_invokeVirtual) {
4159 // Treat signature-polymorphic methods on VarHandle specially.
4160 mh = findVirtualForVH(member.getName(), member.getMethodType());
4161 if (mh != null) {
4162 return mh;
4163 }
4164 }
4165 MemberName resolved = resolveOrFail(refKind, member);
4166 mh = getDirectMethodForConstant(refKind, defc, resolved);
4167 if (mh instanceof DirectMethodHandle
4168 && canBeCached(refKind, defc, resolved)) {
4169 MemberName key = mh.internalMemberName();
4170 if (key != null) {
4171 key = key.asNormalOriginal();
4172 }
4173 if (member.equals(key)) { // better safe than sorry
4174 LOOKASIDE_TABLE.put(key, (DirectMethodHandle) mh);
4175 }
4176 }
4177 return mh;
4178 }
4179 private boolean canBeCached(byte refKind, Class<?> defc, MemberName member) {
4180 if (refKind == REF_invokeSpecial) {
4181 return false;
4182 }
4183 if (!Modifier.isPublic(defc.getModifiers()) ||
4184 !Modifier.isPublic(member.getDeclaringClass().getModifiers()) ||
4185 !member.isPublic() ||
4186 member.isCallerSensitive()) {
4187 return false;
4188 }
4189 ClassLoader loader = defc.getClassLoader();
4190 if (loader != null) {
4191 ClassLoader sysl = ClassLoader.getSystemClassLoader();
4192 boolean found = false;
4193 while (sysl != null) {
4194 if (loader == sysl) { found = true; break; }
4195 sysl = sysl.getParent();
4196 }
4197 if (!found) {
4198 return false;
4199 }
4200 }
4201 try {
4202 MemberName resolved2 = publicLookup().resolveOrNull(refKind,
4203 new MemberName(refKind, defc, member.getName(), member.getType()));
4204 if (resolved2 == null) {
4205 return false;
4206 }
4207 checkSecurityManager(defc, resolved2);
4208 } catch (SecurityException ex) {
4209 return false;
4210 }
4211 return true;
4212 }
4213 private MethodHandle getDirectMethodForConstant(byte refKind, Class<?> defc, MemberName member)
4214 throws ReflectiveOperationException {
4215 if (MethodHandleNatives.refKindIsField(refKind)) {
4216 return getDirectFieldNoSecurityManager(refKind, defc, member);
4217 } else if (MethodHandleNatives.refKindIsMethod(refKind)) {
4218 return getDirectMethodNoSecurityManager(refKind, defc, member, findBoundCallerLookup(member));
4219 } else if (refKind == REF_newInvokeSpecial) {
4220 return getDirectConstructorNoSecurityManager(defc, member);
4221 }
4222 // oops
4223 throw newIllegalArgumentException("bad MethodHandle constant #"+member);
4224 }
4225
4226 static ConcurrentHashMap<MemberName, DirectMethodHandle> LOOKASIDE_TABLE = new ConcurrentHashMap<>();
4227 }
4228
4229 /**
4230 * Produces a method handle constructing arrays of a desired type,
4231 * as if by the {@code anewarray} bytecode.
4232 * The return type of the method handle will be the array type.
4233 * The type of its sole argument will be {@code int}, which specifies the size of the array.
4234 *
4235 * <p> If the returned method handle is invoked with a negative
4236 * array size, a {@code NegativeArraySizeException} will be thrown.
4237 *
4238 * @param arrayClass an array type
4239 * @return a method handle which can create arrays of the given type
4240 * @throws NullPointerException if the argument is {@code null}
4241 * @throws IllegalArgumentException if {@code arrayClass} is not an array type
4242 * @see java.lang.reflect.Array#newInstance(Class, int)
4243 * @jvms 6.5 {@code anewarray} Instruction
4244 * @since 9
4245 */
4246 public static MethodHandle arrayConstructor(Class<?> arrayClass) throws IllegalArgumentException {
4247 if (!arrayClass.isArray()) {
4248 throw newIllegalArgumentException("not an array class: " + arrayClass.getName());
4249 }
4250 MethodHandle ani = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_Array_newInstance).
4251 bindTo(arrayClass.getComponentType());
4252 return ani.asType(ani.type().changeReturnType(arrayClass));
4253 }
4254
4255 /**
4256 * Produces a method handle returning the length of an array,
4257 * as if by the {@code arraylength} bytecode.
4258 * The type of the method handle will have {@code int} as return type,
4259 * and its sole argument will be the array type.
4260 *
4261 * <p> If the returned method handle is invoked with a {@code null}
4262 * array reference, a {@code NullPointerException} will be thrown.
4263 *
4264 * @param arrayClass an array type
4265 * @return a method handle which can retrieve the length of an array of the given array type
4266 * @throws NullPointerException if the argument is {@code null}
4267 * @throws IllegalArgumentException if arrayClass is not an array type
4268 * @jvms 6.5 {@code arraylength} Instruction
4269 * @since 9
4270 */
4271 public static MethodHandle arrayLength(Class<?> arrayClass) throws IllegalArgumentException {
4272 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.LENGTH);
4273 }
4274
4275 /**
4276 * Produces a method handle giving read access to elements of an array,
4277 * as if by the {@code aaload} bytecode.
4278 * The type of the method handle will have a return type of the array's
4279 * element type. Its first argument will be the array type,
4280 * and the second will be {@code int}.
4281 *
4282 * <p> When the returned method handle is invoked,
4283 * the array reference and array index are checked.
4284 * A {@code NullPointerException} will be thrown if the array reference
4285 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
4286 * thrown if the index is negative or if it is greater than or equal to
4287 * the length of the array.
4288 *
4289 * @param arrayClass an array type
4290 * @return a method handle which can load values from the given array type
4291 * @throws NullPointerException if the argument is null
4292 * @throws IllegalArgumentException if arrayClass is not an array type
4293 * @jvms 6.5 {@code aaload} Instruction
4294 */
4295 public static MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException {
4296 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.GET);
4297 }
4298
4299 /**
4300 * Produces a method handle giving write access to elements of an array,
4301 * as if by the {@code astore} bytecode.
4302 * The type of the method handle will have a void return type.
4303 * Its last argument will be the array's element type.
4304 * The first and second arguments will be the array type and int.
4305 *
4306 * <p> When the returned method handle is invoked,
4307 * the array reference and array index are checked.
4308 * A {@code NullPointerException} will be thrown if the array reference
4309 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
4310 * thrown if the index is negative or if it is greater than or equal to
4311 * the length of the array.
4312 *
4313 * @param arrayClass the class of an array
4314 * @return a method handle which can store values into the array type
4315 * @throws NullPointerException if the argument is null
4316 * @throws IllegalArgumentException if arrayClass is not an array type
4317 * @jvms 6.5 {@code aastore} Instruction
4318 */
4319 public static MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException {
4320 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.SET);
4321 }
4322
4323 /**
4324 * Produces a VarHandle giving access to elements of an array of type
4325 * {@code arrayClass}. The VarHandle's variable type is the component type
4326 * of {@code arrayClass} and the list of coordinate types is
4327 * {@code (arrayClass, int)}, where the {@code int} coordinate type
4328 * corresponds to an argument that is an index into an array.
4329 * <p>
4330 * Certain access modes of the returned VarHandle are unsupported under
4331 * the following conditions:
4332 * <ul>
4333 * <li>if the component type is anything other than {@code byte},
4334 * {@code short}, {@code char}, {@code int}, {@code long},
4335 * {@code float}, or {@code double} then numeric atomic update access
4336 * modes are unsupported.
4337 * <li>if the component type is anything other than {@code boolean},
4338 * {@code byte}, {@code short}, {@code char}, {@code int} or
4339 * {@code long} then bitwise atomic update access modes are
4340 * unsupported.
4341 * </ul>
4342 * <p>
4343 * If the component type is {@code float} or {@code double} then numeric
4344 * and atomic update access modes compare values using their bitwise
4345 * representation (see {@link Float#floatToRawIntBits} and
4346 * {@link Double#doubleToRawLongBits}, respectively).
4347 *
4348 * <p> When the returned {@code VarHandle} is invoked,
4349 * the array reference and array index are checked.
4350 * A {@code NullPointerException} will be thrown if the array reference
4351 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
4352 * thrown if the index is negative or if it is greater than or equal to
4353 * the length of the array.
4354 *
4355 * @apiNote
4356 * Bitwise comparison of {@code float} values or {@code double} values,
4357 * as performed by the numeric and atomic update access modes, differ
4358 * from the primitive {@code ==} operator and the {@link Float#equals}
4359 * and {@link Double#equals} methods, specifically with respect to
4360 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
4361 * Care should be taken when performing a compare and set or a compare
4362 * and exchange operation with such values since the operation may
4363 * unexpectedly fail.
4364 * There are many possible NaN values that are considered to be
4365 * {@code NaN} in Java, although no IEEE 754 floating-point operation
4366 * provided by Java can distinguish between them. Operation failure can
4367 * occur if the expected or witness value is a NaN value and it is
4368 * transformed (perhaps in a platform specific manner) into another NaN
4369 * value, and thus has a different bitwise representation (see
4370 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
4371 * details).
4372 * The values {@code -0.0} and {@code +0.0} have different bitwise
4373 * representations but are considered equal when using the primitive
4374 * {@code ==} operator. Operation failure can occur if, for example, a
4375 * numeric algorithm computes an expected value to be say {@code -0.0}
4376 * and previously computed the witness value to be say {@code +0.0}.
4377 * @param arrayClass the class of an array, of type {@code T[]}
4378 * @return a VarHandle giving access to elements of an array
4379 * @throws NullPointerException if the arrayClass is null
4380 * @throws IllegalArgumentException if arrayClass is not an array type
4381 * @since 9
4382 */
4383 public static VarHandle arrayElementVarHandle(Class<?> arrayClass) throws IllegalArgumentException {
4384 return VarHandles.makeArrayElementHandle(arrayClass);
4385 }
4386
4387 /**
4388 * Produces a VarHandle giving access to elements of a {@code byte[]} array
4389 * viewed as if it were a different primitive array type, such as
4390 * {@code int[]} or {@code long[]}.
4391 * The VarHandle's variable type is the component type of
4392 * {@code viewArrayClass} and the list of coordinate types is
4393 * {@code (byte[], int)}, where the {@code int} coordinate type
4394 * corresponds to an argument that is an index into a {@code byte[]} array.
4395 * The returned VarHandle accesses bytes at an index in a {@code byte[]}
4396 * array, composing bytes to or from a value of the component type of
4397 * {@code viewArrayClass} according to the given endianness.
4398 * <p>
4399 * The supported component types (variables types) are {@code short},
4400 * {@code char}, {@code int}, {@code long}, {@code float} and
4401 * {@code double}.
4402 * <p>
4403 * Access of bytes at a given index will result in an
4404 * {@code ArrayIndexOutOfBoundsException} if the index is less than {@code 0}
4405 * or greater than the {@code byte[]} array length minus the size (in bytes)
4406 * of {@code T}.
4407 * <p>
4408 * Access of bytes at an index may be aligned or misaligned for {@code T},
4409 * with respect to the underlying memory address, {@code A} say, associated
4410 * with the array and index.
4411 * If access is misaligned then access for anything other than the
4412 * {@code get} and {@code set} access modes will result in an
4413 * {@code IllegalStateException}. In such cases atomic access is only
4414 * guaranteed with respect to the largest power of two that divides the GCD
4415 * of {@code A} and the size (in bytes) of {@code T}.
4416 * If access is aligned then following access modes are supported and are
4417 * guaranteed to support atomic access:
4418 * <ul>
4419 * <li>read write access modes for all {@code T}, with the exception of
4420 * access modes {@code get} and {@code set} for {@code long} and
4421 * {@code double} on 32-bit platforms.
4422 * <li>atomic update access modes for {@code int}, {@code long},
4423 * {@code float} or {@code double}.
4424 * (Future major platform releases of the JDK may support additional
4425 * types for certain currently unsupported access modes.)
4426 * <li>numeric atomic update access modes for {@code int} and {@code long}.
4427 * (Future major platform releases of the JDK may support additional
4428 * numeric types for certain currently unsupported access modes.)
4429 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
4430 * (Future major platform releases of the JDK may support additional
4431 * numeric types for certain currently unsupported access modes.)
4432 * </ul>
4433 * <p>
4434 * Misaligned access, and therefore atomicity guarantees, may be determined
4435 * for {@code byte[]} arrays without operating on a specific array. Given
4436 * an {@code index}, {@code T} and its corresponding boxed type,
4437 * {@code T_BOX}, misalignment may be determined as follows:
4438 * <pre>{@code
4439 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
4440 * int misalignedAtZeroIndex = ByteBuffer.wrap(new byte[0]).
4441 * alignmentOffset(0, sizeOfT);
4442 * int misalignedAtIndex = (misalignedAtZeroIndex + index) % sizeOfT;
4443 * boolean isMisaligned = misalignedAtIndex != 0;
4444 * }</pre>
4445 * <p>
4446 * If the variable type is {@code float} or {@code double} then atomic
4447 * update access modes compare values using their bitwise representation
4448 * (see {@link Float#floatToRawIntBits} and
4449 * {@link Double#doubleToRawLongBits}, respectively).
4450 * @param viewArrayClass the view array class, with a component type of
4451 * type {@code T}
4452 * @param byteOrder the endianness of the view array elements, as
4453 * stored in the underlying {@code byte} array
4454 * @return a VarHandle giving access to elements of a {@code byte[]} array
4455 * viewed as if elements corresponding to the components type of the view
4456 * array class
4457 * @throws NullPointerException if viewArrayClass or byteOrder is null
4458 * @throws IllegalArgumentException if viewArrayClass is not an array type
4459 * @throws UnsupportedOperationException if the component type of
4460 * viewArrayClass is not supported as a variable type
4461 * @since 9
4462 */
4463 public static VarHandle byteArrayViewVarHandle(Class<?> viewArrayClass,
4464 ByteOrder byteOrder) throws IllegalArgumentException {
4465 Objects.requireNonNull(byteOrder);
4466 return VarHandles.byteArrayViewHandle(viewArrayClass,
4467 byteOrder == ByteOrder.BIG_ENDIAN);
4468 }
4469
4470 /**
4471 * Produces a VarHandle giving access to elements of a {@code ByteBuffer}
4472 * viewed as if it were an array of elements of a different primitive
4473 * component type to that of {@code byte}, such as {@code int[]} or
4474 * {@code long[]}.
4475 * The VarHandle's variable type is the component type of
4476 * {@code viewArrayClass} and the list of coordinate types is
4477 * {@code (ByteBuffer, int)}, where the {@code int} coordinate type
4478 * corresponds to an argument that is an index into a {@code byte[]} array.
4479 * The returned VarHandle accesses bytes at an index in a
4480 * {@code ByteBuffer}, composing bytes to or from a value of the component
4481 * type of {@code viewArrayClass} according to the given endianness.
4482 * <p>
4483 * The supported component types (variables types) are {@code short},
4484 * {@code char}, {@code int}, {@code long}, {@code float} and
4485 * {@code double}.
4486 * <p>
4487 * Access will result in a {@code ReadOnlyBufferException} for anything
4488 * other than the read access modes if the {@code ByteBuffer} is read-only.
4489 * <p>
4490 * Access of bytes at a given index will result in an
4491 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
4492 * or greater than the {@code ByteBuffer} limit minus the size (in bytes) of
4493 * {@code T}.
4494 * <p>
4495 * Access of bytes at an index may be aligned or misaligned for {@code T},
4496 * with respect to the underlying memory address, {@code A} say, associated
4497 * with the {@code ByteBuffer} and index.
4498 * If access is misaligned then access for anything other than the
4499 * {@code get} and {@code set} access modes will result in an
4500 * {@code IllegalStateException}. In such cases atomic access is only
4501 * guaranteed with respect to the largest power of two that divides the GCD
4502 * of {@code A} and the size (in bytes) of {@code T}.
4503 * If access is aligned then following access modes are supported and are
4504 * guaranteed to support atomic access:
4505 * <ul>
4506 * <li>read write access modes for all {@code T}, with the exception of
4507 * access modes {@code get} and {@code set} for {@code long} and
4508 * {@code double} on 32-bit platforms.
4509 * <li>atomic update access modes for {@code int}, {@code long},
4510 * {@code float} or {@code double}.
4511 * (Future major platform releases of the JDK may support additional
4512 * types for certain currently unsupported access modes.)
4513 * <li>numeric atomic update access modes for {@code int} and {@code long}.
4514 * (Future major platform releases of the JDK may support additional
4515 * numeric types for certain currently unsupported access modes.)
4516 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
4517 * (Future major platform releases of the JDK may support additional
4518 * numeric types for certain currently unsupported access modes.)
4519 * </ul>
4520 * <p>
4521 * Misaligned access, and therefore atomicity guarantees, may be determined
4522 * for a {@code ByteBuffer}, {@code bb} (direct or otherwise), an
4523 * {@code index}, {@code T} and its corresponding boxed type,
4524 * {@code T_BOX}, as follows:
4525 * <pre>{@code
4526 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
4527 * ByteBuffer bb = ...
4528 * int misalignedAtIndex = bb.alignmentOffset(index, sizeOfT);
4529 * boolean isMisaligned = misalignedAtIndex != 0;
4530 * }</pre>
4531 * <p>
4532 * If the variable type is {@code float} or {@code double} then atomic
4533 * update access modes compare values using their bitwise representation
4534 * (see {@link Float#floatToRawIntBits} and
4535 * {@link Double#doubleToRawLongBits}, respectively).
4536 * @param viewArrayClass the view array class, with a component type of
4537 * type {@code T}
4538 * @param byteOrder the endianness of the view array elements, as
4539 * stored in the underlying {@code ByteBuffer} (Note this overrides the
4540 * endianness of a {@code ByteBuffer})
4541 * @return a VarHandle giving access to elements of a {@code ByteBuffer}
4542 * viewed as if elements corresponding to the components type of the view
4543 * array class
4544 * @throws NullPointerException if viewArrayClass or byteOrder is null
4545 * @throws IllegalArgumentException if viewArrayClass is not an array type
4546 * @throws UnsupportedOperationException if the component type of
4547 * viewArrayClass is not supported as a variable type
4548 * @since 9
4549 */
4550 public static VarHandle byteBufferViewVarHandle(Class<?> viewArrayClass,
4551 ByteOrder byteOrder) throws IllegalArgumentException {
4552 Objects.requireNonNull(byteOrder);
4553 return VarHandles.makeByteBufferViewHandle(viewArrayClass,
4554 byteOrder == ByteOrder.BIG_ENDIAN);
4555 }
4556
4557
4558 /// method handle invocation (reflective style)
4559
4560 /**
4561 * Produces a method handle which will invoke any method handle of the
4562 * given {@code type}, with a given number of trailing arguments replaced by
4563 * a single trailing {@code Object[]} array.
4564 * The resulting invoker will be a method handle with the following
4565 * arguments:
4566 * <ul>
4567 * <li>a single {@code MethodHandle} target
4568 * <li>zero or more leading values (counted by {@code leadingArgCount})
4569 * <li>an {@code Object[]} array containing trailing arguments
4570 * </ul>
4571 * <p>
4572 * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
4573 * the indicated {@code type}.
4574 * That is, if the target is exactly of the given {@code type}, it will behave
4575 * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
4576 * is used to convert the target to the required {@code type}.
4577 * <p>
4578 * The type of the returned invoker will not be the given {@code type}, but rather
4579 * will have all parameters except the first {@code leadingArgCount}
4580 * replaced by a single array of type {@code Object[]}, which will be
4581 * the final parameter.
4582 * <p>
4583 * Before invoking its target, the invoker will spread the final array, apply
4584 * reference casts as necessary, and unbox and widen primitive arguments.
4585 * If, when the invoker is called, the supplied array argument does
4586 * not have the correct number of elements, the invoker will throw
4587 * an {@link IllegalArgumentException} instead of invoking the target.
4588 * <p>
4589 * This method is equivalent to the following code (though it may be more efficient):
4590 * {@snippet lang="java" :
4591 MethodHandle invoker = MethodHandles.invoker(type);
4592 int spreadArgCount = type.parameterCount() - leadingArgCount;
4593 invoker = invoker.asSpreader(Object[].class, spreadArgCount);
4594 return invoker;
4595 * }
4596 * This method throws no reflective or security exceptions.
4597 * @param type the desired target type
4598 * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
4599 * @return a method handle suitable for invoking any method handle of the given type
4600 * @throws NullPointerException if {@code type} is null
4601 * @throws IllegalArgumentException if {@code leadingArgCount} is not in
4602 * the range from 0 to {@code type.parameterCount()} inclusive,
4603 * or if the resulting method handle's type would have
4604 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4605 */
4606 public static MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
4607 if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
4608 throw newIllegalArgumentException("bad argument count", leadingArgCount);
4609 type = type.asSpreaderType(Object[].class, leadingArgCount, type.parameterCount() - leadingArgCount);
4610 return type.invokers().spreadInvoker(leadingArgCount);
4611 }
4612
4613 /**
4614 * Produces a special <em>invoker method handle</em> which can be used to
4615 * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
4616 * The resulting invoker will have a type which is
4617 * exactly equal to the desired type, except that it will accept
4618 * an additional leading argument of type {@code MethodHandle}.
4619 * <p>
4620 * This method is equivalent to the following code (though it may be more efficient):
4621 * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)}
4622 *
4623 * <p style="font-size:smaller;">
4624 * <em>Discussion:</em>
4625 * Invoker method handles can be useful when working with variable method handles
4626 * of unknown types.
4627 * For example, to emulate an {@code invokeExact} call to a variable method
4628 * handle {@code M}, extract its type {@code T},
4629 * look up the invoker method {@code X} for {@code T},
4630 * and call the invoker method, as {@code X.invoke(T, A...)}.
4631 * (It would not work to call {@code X.invokeExact}, since the type {@code T}
4632 * is unknown.)
4633 * If spreading, collecting, or other argument transformations are required,
4634 * they can be applied once to the invoker {@code X} and reused on many {@code M}
4635 * method handle values, as long as they are compatible with the type of {@code X}.
4636 * <p style="font-size:smaller;">
4637 * <em>(Note: The invoker method is not available via the Core Reflection API.
4638 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
4639 * on the declared {@code invokeExact} or {@code invoke} method will raise an
4640 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
4641 * <p>
4642 * This method throws no reflective or security exceptions.
4643 * @param type the desired target type
4644 * @return a method handle suitable for invoking any method handle of the given type
4645 * @throws IllegalArgumentException if the resulting method handle's type would have
4646 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4647 */
4648 public static MethodHandle exactInvoker(MethodType type) {
4649 return type.invokers().exactInvoker();
4650 }
4651
4652 /**
4653 * Produces a special <em>invoker method handle</em> which can be used to
4654 * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
4655 * The resulting invoker will have a type which is
4656 * exactly equal to the desired type, except that it will accept
4657 * an additional leading argument of type {@code MethodHandle}.
4658 * <p>
4659 * Before invoking its target, if the target differs from the expected type,
4660 * the invoker will apply reference casts as
4661 * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
4662 * Similarly, the return value will be converted as necessary.
4663 * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
4664 * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
4665 * <p>
4666 * This method is equivalent to the following code (though it may be more efficient):
4667 * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)}
4668 * <p style="font-size:smaller;">
4669 * <em>Discussion:</em>
4670 * A {@linkplain MethodType#genericMethodType general method type} is one which
4671 * mentions only {@code Object} arguments and return values.
4672 * An invoker for such a type is capable of calling any method handle
4673 * of the same arity as the general type.
4674 * <p style="font-size:smaller;">
4675 * <em>(Note: The invoker method is not available via the Core Reflection API.
4676 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
4677 * on the declared {@code invokeExact} or {@code invoke} method will raise an
4678 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
4679 * <p>
4680 * This method throws no reflective or security exceptions.
4681 * @param type the desired target type
4682 * @return a method handle suitable for invoking any method handle convertible to the given type
4683 * @throws IllegalArgumentException if the resulting method handle's type would have
4684 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4685 */
4686 public static MethodHandle invoker(MethodType type) {
4687 return type.invokers().genericInvoker();
4688 }
4689
4690 /**
4691 * Produces a special <em>invoker method handle</em> which can be used to
4692 * invoke a signature-polymorphic access mode method on any VarHandle whose
4693 * associated access mode type is compatible with the given type.
4694 * The resulting invoker will have a type which is exactly equal to the
4695 * desired given type, except that it will accept an additional leading
4696 * argument of type {@code VarHandle}.
4697 *
4698 * @param accessMode the VarHandle access mode
4699 * @param type the desired target type
4700 * @return a method handle suitable for invoking an access mode method of
4701 * any VarHandle whose access mode type is of the given type.
4702 * @since 9
4703 */
4704 public static MethodHandle varHandleExactInvoker(VarHandle.AccessMode accessMode, MethodType type) {
4705 return type.invokers().varHandleMethodExactInvoker(accessMode);
4706 }
4707
4708 /**
4709 * Produces a special <em>invoker method handle</em> which can be used to
4710 * invoke a signature-polymorphic access mode method on any VarHandle whose
4711 * associated access mode type is compatible with the given type.
4712 * The resulting invoker will have a type which is exactly equal to the
4713 * desired given type, except that it will accept an additional leading
4714 * argument of type {@code VarHandle}.
4715 * <p>
4716 * Before invoking its target, if the access mode type differs from the
4717 * desired given type, the invoker will apply reference casts as necessary
4718 * and box, unbox, or widen primitive values, as if by
4719 * {@link MethodHandle#asType asType}. Similarly, the return value will be
4720 * converted as necessary.
4721 * <p>
4722 * This method is equivalent to the following code (though it may be more
4723 * efficient): {@code publicLookup().findVirtual(VarHandle.class, accessMode.name(), type)}
4724 *
4725 * @param accessMode the VarHandle access mode
4726 * @param type the desired target type
4727 * @return a method handle suitable for invoking an access mode method of
4728 * any VarHandle whose access mode type is convertible to the given
4729 * type.
4730 * @since 9
4731 */
4732 public static MethodHandle varHandleInvoker(VarHandle.AccessMode accessMode, MethodType type) {
4733 return type.invokers().varHandleMethodInvoker(accessMode);
4734 }
4735
4736 /*non-public*/
4737 static MethodHandle basicInvoker(MethodType type) {
4738 return type.invokers().basicInvoker();
4739 }
4740
4741 /// method handle modification (creation from other method handles)
4742
4743 /**
4744 * Produces a method handle which adapts the type of the
4745 * given method handle to a new type by pairwise argument and return type conversion.
4746 * The original type and new type must have the same number of arguments.
4747 * The resulting method handle is guaranteed to report a type
4748 * which is equal to the desired new type.
4749 * <p>
4750 * If the original type and new type are equal, returns target.
4751 * <p>
4752 * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
4753 * and some additional conversions are also applied if those conversions fail.
4754 * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied
4755 * if possible, before or instead of any conversions done by {@code asType}:
4756 * <ul>
4757 * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type,
4758 * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast.
4759 * (This treatment of interfaces follows the usage of the bytecode verifier.)
4760 * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive,
4761 * the boolean is converted to a byte value, 1 for true, 0 for false.
4762 * (This treatment follows the usage of the bytecode verifier.)
4763 * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive,
4764 * <em>T0</em> is converted to byte via Java casting conversion (JLS {@jls 5.5}),
4765 * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}.
4766 * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean,
4767 * then a Java casting conversion (JLS {@jls 5.5}) is applied.
4768 * (Specifically, <em>T0</em> will convert to <em>T1</em> by
4769 * widening and/or narrowing.)
4770 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
4771 * conversion will be applied at runtime, possibly followed
4772 * by a Java casting conversion (JLS {@jls 5.5}) on the primitive value,
4773 * possibly followed by a conversion from byte to boolean by testing
4774 * the low-order bit.
4775 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive,
4776 * and if the reference is null at runtime, a zero value is introduced.
4777 * </ul>
4778 * @param target the method handle to invoke after arguments are retyped
4779 * @param newType the expected type of the new method handle
4780 * @return a method handle which delegates to the target after performing
4781 * any necessary argument conversions, and arranges for any
4782 * necessary return value conversions
4783 * @throws NullPointerException if either argument is null
4784 * @throws WrongMethodTypeException if the conversion cannot be made
4785 * @see MethodHandle#asType
4786 */
4787 public static MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
4788 explicitCastArgumentsChecks(target, newType);
4789 // use the asTypeCache when possible:
4790 MethodType oldType = target.type();
4791 if (oldType == newType) return target;
4792 if (oldType.explicitCastEquivalentToAsType(newType)) {
4793 return target.asFixedArity().asType(newType);
4794 }
4795 return MethodHandleImpl.makePairwiseConvert(target, newType, false);
4796 }
4797
4798 private static void explicitCastArgumentsChecks(MethodHandle target, MethodType newType) {
4799 if (target.type().parameterCount() != newType.parameterCount()) {
4800 throw new WrongMethodTypeException("cannot explicitly cast " + target + " to " + newType);
4801 }
4802 }
4803
4804 /**
4805 * Produces a method handle which adapts the calling sequence of the
4806 * given method handle to a new type, by reordering the arguments.
4807 * The resulting method handle is guaranteed to report a type
4808 * which is equal to the desired new type.
4809 * <p>
4810 * The given array controls the reordering.
4811 * Call {@code #I} the number of incoming parameters (the value
4812 * {@code newType.parameterCount()}, and call {@code #O} the number
4813 * of outgoing parameters (the value {@code target.type().parameterCount()}).
4814 * Then the length of the reordering array must be {@code #O},
4815 * and each element must be a non-negative number less than {@code #I}.
4816 * For every {@code N} less than {@code #O}, the {@code N}-th
4817 * outgoing argument will be taken from the {@code I}-th incoming
4818 * argument, where {@code I} is {@code reorder[N]}.
4819 * <p>
4820 * No argument or return value conversions are applied.
4821 * The type of each incoming argument, as determined by {@code newType},
4822 * must be identical to the type of the corresponding outgoing parameter
4823 * or parameters in the target method handle.
4824 * The return type of {@code newType} must be identical to the return
4825 * type of the original target.
4826 * <p>
4827 * The reordering array need not specify an actual permutation.
4828 * An incoming argument will be duplicated if its index appears
4829 * more than once in the array, and an incoming argument will be dropped
4830 * if its index does not appear in the array.
4831 * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
4832 * incoming arguments which are not mentioned in the reordering array
4833 * may be of any type, as determined only by {@code newType}.
4834 * {@snippet lang="java" :
4835 import static java.lang.invoke.MethodHandles.*;
4836 import static java.lang.invoke.MethodType.*;
4837 ...
4838 MethodType intfn1 = methodType(int.class, int.class);
4839 MethodType intfn2 = methodType(int.class, int.class, int.class);
4840 MethodHandle sub = ... (int x, int y) -> (x-y) ...;
4841 assert(sub.type().equals(intfn2));
4842 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
4843 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
4844 assert((int)rsub.invokeExact(1, 100) == 99);
4845 MethodHandle add = ... (int x, int y) -> (x+y) ...;
4846 assert(add.type().equals(intfn2));
4847 MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
4848 assert(twice.type().equals(intfn1));
4849 assert((int)twice.invokeExact(21) == 42);
4850 * }
4851 * <p>
4852 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4853 * variable-arity method handle}, even if the original target method handle was.
4854 * @param target the method handle to invoke after arguments are reordered
4855 * @param newType the expected type of the new method handle
4856 * @param reorder an index array which controls the reordering
4857 * @return a method handle which delegates to the target after it
4858 * drops unused arguments and moves and/or duplicates the other arguments
4859 * @throws NullPointerException if any argument is null
4860 * @throws IllegalArgumentException if the index array length is not equal to
4861 * the arity of the target, or if any index array element
4862 * not a valid index for a parameter of {@code newType},
4863 * or if two corresponding parameter types in
4864 * {@code target.type()} and {@code newType} are not identical,
4865 */
4866 public static MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
4867 reorder = reorder.clone(); // get a private copy
4868 MethodType oldType = target.type();
4869 permuteArgumentChecks(reorder, newType, oldType);
4870 // first detect dropped arguments and handle them separately
4871 int[] originalReorder = reorder;
4872 BoundMethodHandle result = target.rebind();
4873 LambdaForm form = result.form;
4874 int newArity = newType.parameterCount();
4875 // Normalize the reordering into a real permutation,
4876 // by removing duplicates and adding dropped elements.
4877 // This somewhat improves lambda form caching, as well
4878 // as simplifying the transform by breaking it up into steps.
4879 for (int ddIdx; (ddIdx = findFirstDupOrDrop(reorder, newArity)) != 0; ) {
4880 if (ddIdx > 0) {
4881 // We found a duplicated entry at reorder[ddIdx].
4882 // Example: (x,y,z)->asList(x,y,z)
4883 // permuted by [1*,0,1] => (a0,a1)=>asList(a1,a0,a1)
4884 // permuted by [0,1,0*] => (a0,a1)=>asList(a0,a1,a0)
4885 // The starred element corresponds to the argument
4886 // deleted by the dupArgumentForm transform.
4887 int srcPos = ddIdx, dstPos = srcPos, dupVal = reorder[srcPos];
4888 boolean killFirst = false;
4889 for (int val; (val = reorder[--dstPos]) != dupVal; ) {
4890 // Set killFirst if the dup is larger than an intervening position.
4891 // This will remove at least one inversion from the permutation.
4892 if (dupVal > val) killFirst = true;
4893 }
4894 if (!killFirst) {
4895 srcPos = dstPos;
4896 dstPos = ddIdx;
4897 }
4898 form = form.editor().dupArgumentForm(1 + srcPos, 1 + dstPos);
4899 assert (reorder[srcPos] == reorder[dstPos]);
4900 oldType = oldType.dropParameterTypes(dstPos, dstPos + 1);
4901 // contract the reordering by removing the element at dstPos
4902 int tailPos = dstPos + 1;
4903 System.arraycopy(reorder, tailPos, reorder, dstPos, reorder.length - tailPos);
4904 reorder = Arrays.copyOf(reorder, reorder.length - 1);
4905 } else {
4906 int dropVal = ~ddIdx, insPos = 0;
4907 while (insPos < reorder.length && reorder[insPos] < dropVal) {
4908 // Find first element of reorder larger than dropVal.
4909 // This is where we will insert the dropVal.
4910 insPos += 1;
4911 }
4912 Class<?> ptype = newType.parameterType(dropVal);
4913 form = form.editor().addArgumentForm(1 + insPos, BasicType.basicType(ptype));
4914 oldType = oldType.insertParameterTypes(insPos, ptype);
4915 // expand the reordering by inserting an element at insPos
4916 int tailPos = insPos + 1;
4917 reorder = Arrays.copyOf(reorder, reorder.length + 1);
4918 System.arraycopy(reorder, insPos, reorder, tailPos, reorder.length - tailPos);
4919 reorder[insPos] = dropVal;
4920 }
4921 assert (permuteArgumentChecks(reorder, newType, oldType));
4922 }
4923 assert (reorder.length == newArity); // a perfect permutation
4924 // Note: This may cache too many distinct LFs. Consider backing off to varargs code.
4925 form = form.editor().permuteArgumentsForm(1, reorder);
4926 if (newType == result.type() && form == result.internalForm())
4927 return result;
4928 return result.copyWith(newType, form);
4929 }
4930
4931 /**
4932 * Return an indication of any duplicate or omission in reorder.
4933 * If the reorder contains a duplicate entry, return the index of the second occurrence.
4934 * Otherwise, return ~(n), for the first n in [0..newArity-1] that is not present in reorder.
4935 * Otherwise, return zero.
4936 * If an element not in [0..newArity-1] is encountered, return reorder.length.
4937 */
4938 private static int findFirstDupOrDrop(int[] reorder, int newArity) {
4939 final int BIT_LIMIT = 63; // max number of bits in bit mask
4940 if (newArity < BIT_LIMIT) {
4941 long mask = 0;
4942 for (int i = 0; i < reorder.length; i++) {
4943 int arg = reorder[i];
4944 if (arg >= newArity) {
4945 return reorder.length;
4946 }
4947 long bit = 1L << arg;
4948 if ((mask & bit) != 0) {
4949 return i; // >0 indicates a dup
4950 }
4951 mask |= bit;
4952 }
4953 if (mask == (1L << newArity) - 1) {
4954 assert(Long.numberOfTrailingZeros(Long.lowestOneBit(~mask)) == newArity);
4955 return 0;
4956 }
4957 // find first zero
4958 long zeroBit = Long.lowestOneBit(~mask);
4959 int zeroPos = Long.numberOfTrailingZeros(zeroBit);
4960 assert(zeroPos <= newArity);
4961 if (zeroPos == newArity) {
4962 return 0;
4963 }
4964 return ~zeroPos;
4965 } else {
4966 // same algorithm, different bit set
4967 BitSet mask = new BitSet(newArity);
4968 for (int i = 0; i < reorder.length; i++) {
4969 int arg = reorder[i];
4970 if (arg >= newArity) {
4971 return reorder.length;
4972 }
4973 if (mask.get(arg)) {
4974 return i; // >0 indicates a dup
4975 }
4976 mask.set(arg);
4977 }
4978 int zeroPos = mask.nextClearBit(0);
4979 assert(zeroPos <= newArity);
4980 if (zeroPos == newArity) {
4981 return 0;
4982 }
4983 return ~zeroPos;
4984 }
4985 }
4986
4987 static boolean permuteArgumentChecks(int[] reorder, MethodType newType, MethodType oldType) {
4988 if (newType.returnType() != oldType.returnType())
4989 throw newIllegalArgumentException("return types do not match",
4990 oldType, newType);
4991 if (reorder.length != oldType.parameterCount())
4992 throw newIllegalArgumentException("old type parameter count and reorder array length do not match",
4993 oldType, Arrays.toString(reorder));
4994
4995 int limit = newType.parameterCount();
4996 for (int j = 0; j < reorder.length; j++) {
4997 int i = reorder[j];
4998 if (i < 0 || i >= limit) {
4999 throw newIllegalArgumentException("index is out of bounds for new type",
5000 i, newType);
5001 }
5002 Class<?> src = newType.parameterType(i);
5003 Class<?> dst = oldType.parameterType(j);
5004 if (src != dst)
5005 throw newIllegalArgumentException("parameter types do not match after reorder",
5006 oldType, newType);
5007 }
5008 return true;
5009 }
5010
5011 /**
5012 * Produces a method handle of the requested return type which returns the given
5013 * constant value every time it is invoked.
5014 * <p>
5015 * Before the method handle is returned, the passed-in value is converted to the requested type.
5016 * If the requested type is primitive, widening primitive conversions are attempted,
5017 * else reference conversions are attempted.
5018 * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
5019 * @param type the return type of the desired method handle
5020 * @param value the value to return
5021 * @return a method handle of the given return type and no arguments, which always returns the given value
5022 * @throws NullPointerException if the {@code type} argument is null
5023 * @throws ClassCastException if the value cannot be converted to the required return type
5024 * @throws IllegalArgumentException if the given type is {@code void.class}
5025 */
5026 public static MethodHandle constant(Class<?> type, Object value) {
5027 if (type.isPrimitive()) {
5028 if (type == void.class)
5029 throw newIllegalArgumentException("void type");
5030 Wrapper w = Wrapper.forPrimitiveType(type);
5031 value = w.convert(value, type);
5032 if (w.zero().equals(value))
5033 return zero(w, type);
5034 return insertArguments(identity(type), 0, value);
5035 } else {
5036 if (value == null)
5037 return zero(Wrapper.OBJECT, type);
5038 return identity(type).bindTo(value);
5039 }
5040 }
5041
5042 /**
5043 * Produces a method handle which returns its sole argument when invoked.
5044 * @param type the type of the sole parameter and return value of the desired method handle
5045 * @return a unary method handle which accepts and returns the given type
5046 * @throws NullPointerException if the argument is null
5047 * @throws IllegalArgumentException if the given type is {@code void.class}
5048 */
5049 public static MethodHandle identity(Class<?> type) {
5050 Wrapper btw = (type.isPrimitive() ? Wrapper.forPrimitiveType(type) : Wrapper.OBJECT);
5051 int pos = btw.ordinal();
5052 MethodHandle ident = IDENTITY_MHS[pos];
5053 if (ident == null) {
5054 ident = setCachedMethodHandle(IDENTITY_MHS, pos, makeIdentity(btw.primitiveType()));
5055 }
5056 if (ident.type().returnType() == type)
5057 return ident;
5058 // something like identity(Foo.class); do not bother to intern these
5059 assert (btw == Wrapper.OBJECT);
5060 return makeIdentity(type);
5061 }
5062
5063 /**
5064 * Produces a constant method handle of the requested return type which
5065 * returns the default value for that type every time it is invoked.
5066 * The resulting constant method handle will have no side effects.
5067 * <p>The returned method handle is equivalent to {@code empty(methodType(type))}.
5068 * It is also equivalent to {@code explicitCastArguments(constant(Object.class, null), methodType(type))},
5069 * since {@code explicitCastArguments} converts {@code null} to default values.
5070 * @param type the expected return type of the desired method handle
5071 * @return a constant method handle that takes no arguments
5072 * and returns the default value of the given type (or void, if the type is void)
5073 * @throws NullPointerException if the argument is null
5074 * @see MethodHandles#constant
5075 * @see MethodHandles#empty
5076 * @see MethodHandles#explicitCastArguments
5077 * @since 9
5078 */
5079 public static MethodHandle zero(Class<?> type) {
5080 Objects.requireNonNull(type);
5081 return type.isPrimitive() ? zero(Wrapper.forPrimitiveType(type), type) : zero(Wrapper.OBJECT, type);
5082 }
5083
5084 private static MethodHandle identityOrVoid(Class<?> type) {
5085 return type == void.class ? zero(type) : identity(type);
5086 }
5087
5088 /**
5089 * Produces a method handle of the requested type which ignores any arguments, does nothing,
5090 * and returns a suitable default depending on the return type.
5091 * That is, it returns a zero primitive value, a {@code null}, or {@code void}.
5092 * <p>The returned method handle is equivalent to
5093 * {@code dropArguments(zero(type.returnType()), 0, type.parameterList())}.
5094 *
5095 * @apiNote Given a predicate and target, a useful "if-then" construct can be produced as
5096 * {@code guardWithTest(pred, target, empty(target.type())}.
5097 * @param type the type of the desired method handle
5098 * @return a constant method handle of the given type, which returns a default value of the given return type
5099 * @throws NullPointerException if the argument is null
5100 * @see MethodHandles#zero
5101 * @see MethodHandles#constant
5102 * @since 9
5103 */
5104 public static MethodHandle empty(MethodType type) {
5105 Objects.requireNonNull(type);
5106 return dropArgumentsTrusted(zero(type.returnType()), 0, type.ptypes());
5107 }
5108
5109 private static final MethodHandle[] IDENTITY_MHS = new MethodHandle[Wrapper.COUNT];
5110 private static MethodHandle makeIdentity(Class<?> ptype) {
5111 MethodType mtype = methodType(ptype, ptype);
5112 LambdaForm lform = LambdaForm.identityForm(BasicType.basicType(ptype));
5113 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.IDENTITY);
5114 }
5115
5116 private static MethodHandle zero(Wrapper btw, Class<?> rtype) {
5117 int pos = btw.ordinal();
5118 MethodHandle zero = ZERO_MHS[pos];
5119 if (zero == null) {
5120 zero = setCachedMethodHandle(ZERO_MHS, pos, makeZero(btw.primitiveType()));
5121 }
5122 if (zero.type().returnType() == rtype)
5123 return zero;
5124 assert(btw == Wrapper.OBJECT);
5125 return makeZero(rtype);
5126 }
5127 private static final MethodHandle[] ZERO_MHS = new MethodHandle[Wrapper.COUNT];
5128 private static MethodHandle makeZero(Class<?> rtype) {
5129 MethodType mtype = methodType(rtype);
5130 LambdaForm lform = LambdaForm.zeroForm(BasicType.basicType(rtype));
5131 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.ZERO);
5132 }
5133
5134 private static synchronized MethodHandle setCachedMethodHandle(MethodHandle[] cache, int pos, MethodHandle value) {
5135 // Simulate a CAS, to avoid racy duplication of results.
5136 MethodHandle prev = cache[pos];
5137 if (prev != null) return prev;
5138 return cache[pos] = value;
5139 }
5140
5141 /**
5142 * Provides a target method handle with one or more <em>bound arguments</em>
5143 * in advance of the method handle's invocation.
5144 * The formal parameters to the target corresponding to the bound
5145 * arguments are called <em>bound parameters</em>.
5146 * Returns a new method handle which saves away the bound arguments.
5147 * When it is invoked, it receives arguments for any non-bound parameters,
5148 * binds the saved arguments to their corresponding parameters,
5149 * and calls the original target.
5150 * <p>
5151 * The type of the new method handle will drop the types for the bound
5152 * parameters from the original target type, since the new method handle
5153 * will no longer require those arguments to be supplied by its callers.
5154 * <p>
5155 * Each given argument object must match the corresponding bound parameter type.
5156 * If a bound parameter type is a primitive, the argument object
5157 * must be a wrapper, and will be unboxed to produce the primitive value.
5158 * <p>
5159 * The {@code pos} argument selects which parameters are to be bound.
5160 * It may range between zero and <i>N-L</i> (inclusively),
5161 * where <i>N</i> is the arity of the target method handle
5162 * and <i>L</i> is the length of the values array.
5163 * <p>
5164 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5165 * variable-arity method handle}, even if the original target method handle was.
5166 * @param target the method handle to invoke after the argument is inserted
5167 * @param pos where to insert the argument (zero for the first)
5168 * @param values the series of arguments to insert
5169 * @return a method handle which inserts an additional argument,
5170 * before calling the original method handle
5171 * @throws NullPointerException if the target or the {@code values} array is null
5172 * @throws IllegalArgumentException if (@code pos) is less than {@code 0} or greater than
5173 * {@code N - L} where {@code N} is the arity of the target method handle and {@code L}
5174 * is the length of the values array.
5175 * @throws ClassCastException if an argument does not match the corresponding bound parameter
5176 * type.
5177 * @see MethodHandle#bindTo
5178 */
5179 public static MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
5180 int insCount = values.length;
5181 Class<?>[] ptypes = insertArgumentsChecks(target, insCount, pos);
5182 if (insCount == 0) return target;
5183 BoundMethodHandle result = target.rebind();
5184 for (int i = 0; i < insCount; i++) {
5185 Object value = values[i];
5186 Class<?> ptype = ptypes[pos+i];
5187 if (ptype.isPrimitive()) {
5188 result = insertArgumentPrimitive(result, pos, ptype, value);
5189 } else {
5190 value = ptype.cast(value); // throw CCE if needed
5191 result = result.bindArgumentL(pos, value);
5192 }
5193 }
5194 return result;
5195 }
5196
5197 private static BoundMethodHandle insertArgumentPrimitive(BoundMethodHandle result, int pos,
5198 Class<?> ptype, Object value) {
5199 Wrapper w = Wrapper.forPrimitiveType(ptype);
5200 // perform unboxing and/or primitive conversion
5201 value = w.convert(value, ptype);
5202 return switch (w) {
5203 case INT -> result.bindArgumentI(pos, (int) value);
5204 case LONG -> result.bindArgumentJ(pos, (long) value);
5205 case FLOAT -> result.bindArgumentF(pos, (float) value);
5206 case DOUBLE -> result.bindArgumentD(pos, (double) value);
5207 default -> result.bindArgumentI(pos, ValueConversions.widenSubword(value));
5208 };
5209 }
5210
5211 private static Class<?>[] insertArgumentsChecks(MethodHandle target, int insCount, int pos) throws RuntimeException {
5212 MethodType oldType = target.type();
5213 int outargs = oldType.parameterCount();
5214 int inargs = outargs - insCount;
5215 if (inargs < 0)
5216 throw newIllegalArgumentException("too many values to insert");
5217 if (pos < 0 || pos > inargs)
5218 throw newIllegalArgumentException("no argument type to append");
5219 return oldType.ptypes();
5220 }
5221
5222 /**
5223 * Produces a method handle which will discard some dummy arguments
5224 * before calling some other specified <i>target</i> method handle.
5225 * The type of the new method handle will be the same as the target's type,
5226 * except it will also include the dummy argument types,
5227 * at some given position.
5228 * <p>
5229 * The {@code pos} argument may range between zero and <i>N</i>,
5230 * where <i>N</i> is the arity of the target.
5231 * If {@code pos} is zero, the dummy arguments will precede
5232 * the target's real arguments; if {@code pos} is <i>N</i>
5233 * they will come after.
5234 * <p>
5235 * <b>Example:</b>
5236 * {@snippet lang="java" :
5237 import static java.lang.invoke.MethodHandles.*;
5238 import static java.lang.invoke.MethodType.*;
5239 ...
5240 MethodHandle cat = lookup().findVirtual(String.class,
5241 "concat", methodType(String.class, String.class));
5242 assertEquals("xy", (String) cat.invokeExact("x", "y"));
5243 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
5244 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
5245 assertEquals(bigType, d0.type());
5246 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
5247 * }
5248 * <p>
5249 * This method is also equivalent to the following code:
5250 * <blockquote><pre>
5251 * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))}
5252 * </pre></blockquote>
5253 * @param target the method handle to invoke after the arguments are dropped
5254 * @param pos position of first argument to drop (zero for the leftmost)
5255 * @param valueTypes the type(s) of the argument(s) to drop
5256 * @return a method handle which drops arguments of the given types,
5257 * before calling the original method handle
5258 * @throws NullPointerException if the target is null,
5259 * or if the {@code valueTypes} list or any of its elements is null
5260 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
5261 * or if {@code pos} is negative or greater than the arity of the target,
5262 * or if the new method handle's type would have too many parameters
5263 */
5264 public static MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) {
5265 return dropArgumentsTrusted(target, pos, valueTypes.toArray(new Class<?>[0]).clone());
5266 }
5267
5268 static MethodHandle dropArgumentsTrusted(MethodHandle target, int pos, Class<?>[] valueTypes) {
5269 MethodType oldType = target.type(); // get NPE
5270 int dropped = dropArgumentChecks(oldType, pos, valueTypes);
5271 MethodType newType = oldType.insertParameterTypes(pos, valueTypes);
5272 if (dropped == 0) return target;
5273 BoundMethodHandle result = target.rebind();
5274 LambdaForm lform = result.form;
5275 int insertFormArg = 1 + pos;
5276 for (Class<?> ptype : valueTypes) {
5277 lform = lform.editor().addArgumentForm(insertFormArg++, BasicType.basicType(ptype));
5278 }
5279 result = result.copyWith(newType, lform);
5280 return result;
5281 }
5282
5283 private static int dropArgumentChecks(MethodType oldType, int pos, Class<?>[] valueTypes) {
5284 int dropped = valueTypes.length;
5285 MethodType.checkSlotCount(dropped);
5286 int outargs = oldType.parameterCount();
5287 int inargs = outargs + dropped;
5288 if (pos < 0 || pos > outargs)
5289 throw newIllegalArgumentException("no argument type to remove"
5290 + Arrays.asList(oldType, pos, valueTypes, inargs, outargs)
5291 );
5292 return dropped;
5293 }
5294
5295 /**
5296 * Produces a method handle which will discard some dummy arguments
5297 * before calling some other specified <i>target</i> method handle.
5298 * The type of the new method handle will be the same as the target's type,
5299 * except it will also include the dummy argument types,
5300 * at some given position.
5301 * <p>
5302 * The {@code pos} argument may range between zero and <i>N</i>,
5303 * where <i>N</i> is the arity of the target.
5304 * If {@code pos} is zero, the dummy arguments will precede
5305 * the target's real arguments; if {@code pos} is <i>N</i>
5306 * they will come after.
5307 * @apiNote
5308 * {@snippet lang="java" :
5309 import static java.lang.invoke.MethodHandles.*;
5310 import static java.lang.invoke.MethodType.*;
5311 ...
5312 MethodHandle cat = lookup().findVirtual(String.class,
5313 "concat", methodType(String.class, String.class));
5314 assertEquals("xy", (String) cat.invokeExact("x", "y"));
5315 MethodHandle d0 = dropArguments(cat, 0, String.class);
5316 assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
5317 MethodHandle d1 = dropArguments(cat, 1, String.class);
5318 assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
5319 MethodHandle d2 = dropArguments(cat, 2, String.class);
5320 assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
5321 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
5322 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
5323 * }
5324 * <p>
5325 * This method is also equivalent to the following code:
5326 * <blockquote><pre>
5327 * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))}
5328 * </pre></blockquote>
5329 * @param target the method handle to invoke after the arguments are dropped
5330 * @param pos position of first argument to drop (zero for the leftmost)
5331 * @param valueTypes the type(s) of the argument(s) to drop
5332 * @return a method handle which drops arguments of the given types,
5333 * before calling the original method handle
5334 * @throws NullPointerException if the target is null,
5335 * or if the {@code valueTypes} array or any of its elements is null
5336 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
5337 * or if {@code pos} is negative or greater than the arity of the target,
5338 * or if the new method handle's type would have
5339 * <a href="MethodHandle.html#maxarity">too many parameters</a>
5340 */
5341 public static MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
5342 return dropArgumentsTrusted(target, pos, valueTypes.clone());
5343 }
5344
5345 /* Convenience overloads for trusting internal low-arity call-sites */
5346 static MethodHandle dropArguments(MethodHandle target, int pos, Class<?> valueType1) {
5347 return dropArgumentsTrusted(target, pos, new Class<?>[] { valueType1 });
5348 }
5349 static MethodHandle dropArguments(MethodHandle target, int pos, Class<?> valueType1, Class<?> valueType2) {
5350 return dropArgumentsTrusted(target, pos, new Class<?>[] { valueType1, valueType2 });
5351 }
5352
5353 // private version which allows caller some freedom with error handling
5354 private static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, Class<?>[] newTypes, int pos,
5355 boolean nullOnFailure) {
5356 Class<?>[] oldTypes = target.type().ptypes();
5357 int match = oldTypes.length;
5358 if (skip != 0) {
5359 if (skip < 0 || skip > match) {
5360 throw newIllegalArgumentException("illegal skip", skip, target);
5361 }
5362 oldTypes = Arrays.copyOfRange(oldTypes, skip, match);
5363 match -= skip;
5364 }
5365 Class<?>[] addTypes = newTypes;
5366 int add = addTypes.length;
5367 if (pos != 0) {
5368 if (pos < 0 || pos > add) {
5369 throw newIllegalArgumentException("illegal pos", pos, Arrays.toString(newTypes));
5370 }
5371 addTypes = Arrays.copyOfRange(addTypes, pos, add);
5372 add -= pos;
5373 assert(addTypes.length == add);
5374 }
5375 // Do not add types which already match the existing arguments.
5376 if (match > add || !Arrays.equals(oldTypes, 0, oldTypes.length, addTypes, 0, match)) {
5377 if (nullOnFailure) {
5378 return null;
5379 }
5380 throw newIllegalArgumentException("argument lists do not match",
5381 Arrays.toString(oldTypes), Arrays.toString(newTypes));
5382 }
5383 addTypes = Arrays.copyOfRange(addTypes, match, add);
5384 add -= match;
5385 assert(addTypes.length == add);
5386 // newTypes: ( P*[pos], M*[match], A*[add] )
5387 // target: ( S*[skip], M*[match] )
5388 MethodHandle adapter = target;
5389 if (add > 0) {
5390 adapter = dropArgumentsTrusted(adapter, skip+ match, addTypes);
5391 }
5392 // adapter: (S*[skip], M*[match], A*[add] )
5393 if (pos > 0) {
5394 adapter = dropArgumentsTrusted(adapter, skip, Arrays.copyOfRange(newTypes, 0, pos));
5395 }
5396 // adapter: (S*[skip], P*[pos], M*[match], A*[add] )
5397 return adapter;
5398 }
5399
5400 /**
5401 * Adapts a target method handle to match the given parameter type list. If necessary, adds dummy arguments. Some
5402 * leading parameters can be skipped before matching begins. The remaining types in the {@code target}'s parameter
5403 * type list must be a sub-list of the {@code newTypes} type list at the starting position {@code pos}. The
5404 * resulting handle will have the target handle's parameter type list, with any non-matching parameter types (before
5405 * or after the matching sub-list) inserted in corresponding positions of the target's original parameters, as if by
5406 * {@link #dropArguments(MethodHandle, int, Class[])}.
5407 * <p>
5408 * The resulting handle will have the same return type as the target handle.
5409 * <p>
5410 * In more formal terms, assume these two type lists:<ul>
5411 * <li>The target handle has the parameter type list {@code S..., M...}, with as many types in {@code S} as
5412 * indicated by {@code skip}. The {@code M} types are those that are supposed to match part of the given type list,
5413 * {@code newTypes}.
5414 * <li>The {@code newTypes} list contains types {@code P..., M..., A...}, with as many types in {@code P} as
5415 * indicated by {@code pos}. The {@code M} types are precisely those that the {@code M} types in the target handle's
5416 * parameter type list are supposed to match. The types in {@code A} are additional types found after the matching
5417 * sub-list.
5418 * </ul>
5419 * Given these assumptions, the result of an invocation of {@code dropArgumentsToMatch} will have the parameter type
5420 * list {@code S..., P..., M..., A...}, with the {@code P} and {@code A} types inserted as if by
5421 * {@link #dropArguments(MethodHandle, int, Class[])}.
5422 *
5423 * @apiNote
5424 * Two method handles whose argument lists are "effectively identical" (i.e., identical in a common prefix) may be
5425 * mutually converted to a common type by two calls to {@code dropArgumentsToMatch}, as follows:
5426 * {@snippet lang="java" :
5427 import static java.lang.invoke.MethodHandles.*;
5428 import static java.lang.invoke.MethodType.*;
5429 ...
5430 ...
5431 MethodHandle h0 = constant(boolean.class, true);
5432 MethodHandle h1 = lookup().findVirtual(String.class, "concat", methodType(String.class, String.class));
5433 MethodType bigType = h1.type().insertParameterTypes(1, String.class, int.class);
5434 MethodHandle h2 = dropArguments(h1, 0, bigType.parameterList());
5435 if (h1.type().parameterCount() < h2.type().parameterCount())
5436 h1 = dropArgumentsToMatch(h1, 0, h2.type().parameterList(), 0); // lengthen h1
5437 else
5438 h2 = dropArgumentsToMatch(h2, 0, h1.type().parameterList(), 0); // lengthen h2
5439 MethodHandle h3 = guardWithTest(h0, h1, h2);
5440 assertEquals("xy", h3.invoke("x", "y", 1, "a", "b", "c"));
5441 * }
5442 * @param target the method handle to adapt
5443 * @param skip number of targets parameters to disregard (they will be unchanged)
5444 * @param newTypes the list of types to match {@code target}'s parameter type list to
5445 * @param pos place in {@code newTypes} where the non-skipped target parameters must occur
5446 * @return a possibly adapted method handle
5447 * @throws NullPointerException if either argument is null
5448 * @throws IllegalArgumentException if any element of {@code newTypes} is {@code void.class},
5449 * or if {@code skip} is negative or greater than the arity of the target,
5450 * or if {@code pos} is negative or greater than the newTypes list size,
5451 * or if {@code newTypes} does not contain the {@code target}'s non-skipped parameter types at position
5452 * {@code pos}.
5453 * @since 9
5454 */
5455 public static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos) {
5456 Objects.requireNonNull(target);
5457 Objects.requireNonNull(newTypes);
5458 return dropArgumentsToMatch(target, skip, newTypes.toArray(new Class<?>[0]).clone(), pos, false);
5459 }
5460
5461 /**
5462 * Drop the return value of the target handle (if any).
5463 * The returned method handle will have a {@code void} return type.
5464 *
5465 * @param target the method handle to adapt
5466 * @return a possibly adapted method handle
5467 * @throws NullPointerException if {@code target} is null
5468 * @since 16
5469 */
5470 public static MethodHandle dropReturn(MethodHandle target) {
5471 Objects.requireNonNull(target);
5472 MethodType oldType = target.type();
5473 Class<?> oldReturnType = oldType.returnType();
5474 if (oldReturnType == void.class)
5475 return target;
5476 MethodType newType = oldType.changeReturnType(void.class);
5477 BoundMethodHandle result = target.rebind();
5478 LambdaForm lform = result.editor().filterReturnForm(V_TYPE, true);
5479 result = result.copyWith(newType, lform);
5480 return result;
5481 }
5482
5483 /**
5484 * Adapts a target method handle by pre-processing
5485 * one or more of its arguments, each with its own unary filter function,
5486 * and then calling the target with each pre-processed argument
5487 * replaced by the result of its corresponding filter function.
5488 * <p>
5489 * The pre-processing is performed by one or more method handles,
5490 * specified in the elements of the {@code filters} array.
5491 * The first element of the filter array corresponds to the {@code pos}
5492 * argument of the target, and so on in sequence.
5493 * The filter functions are invoked in left to right order.
5494 * <p>
5495 * Null arguments in the array are treated as identity functions,
5496 * and the corresponding arguments left unchanged.
5497 * (If there are no non-null elements in the array, the original target is returned.)
5498 * Each filter is applied to the corresponding argument of the adapter.
5499 * <p>
5500 * If a filter {@code F} applies to the {@code N}th argument of
5501 * the target, then {@code F} must be a method handle which
5502 * takes exactly one argument. The type of {@code F}'s sole argument
5503 * replaces the corresponding argument type of the target
5504 * in the resulting adapted method handle.
5505 * The return type of {@code F} must be identical to the corresponding
5506 * parameter type of the target.
5507 * <p>
5508 * It is an error if there are elements of {@code filters}
5509 * (null or not)
5510 * which do not correspond to argument positions in the target.
5511 * <p><b>Example:</b>
5512 * {@snippet lang="java" :
5513 import static java.lang.invoke.MethodHandles.*;
5514 import static java.lang.invoke.MethodType.*;
5515 ...
5516 MethodHandle cat = lookup().findVirtual(String.class,
5517 "concat", methodType(String.class, String.class));
5518 MethodHandle upcase = lookup().findVirtual(String.class,
5519 "toUpperCase", methodType(String.class));
5520 assertEquals("xy", (String) cat.invokeExact("x", "y"));
5521 MethodHandle f0 = filterArguments(cat, 0, upcase);
5522 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
5523 MethodHandle f1 = filterArguments(cat, 1, upcase);
5524 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
5525 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
5526 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
5527 * }
5528 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
5529 * denotes the return type of both the {@code target} and resulting adapter.
5530 * {@code P}/{@code p} and {@code B}/{@code b} represent the types and values
5531 * of the parameters and arguments that precede and follow the filter position
5532 * {@code pos}, respectively. {@code A[i]}/{@code a[i]} stand for the types and
5533 * values of the filtered parameters and arguments; they also represent the
5534 * return types of the {@code filter[i]} handles. The latter accept arguments
5535 * {@code v[i]} of type {@code V[i]}, which also appear in the signature of
5536 * the resulting adapter.
5537 * {@snippet lang="java" :
5538 * T target(P... p, A[i]... a[i], B... b);
5539 * A[i] filter[i](V[i]);
5540 * T adapter(P... p, V[i]... v[i], B... b) {
5541 * return target(p..., filter[i](v[i])..., b...);
5542 * }
5543 * }
5544 * <p>
5545 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5546 * variable-arity method handle}, even if the original target method handle was.
5547 *
5548 * @param target the method handle to invoke after arguments are filtered
5549 * @param pos the position of the first argument to filter
5550 * @param filters method handles to call initially on filtered arguments
5551 * @return method handle which incorporates the specified argument filtering logic
5552 * @throws NullPointerException if the target is null
5553 * or if the {@code filters} array is null
5554 * @throws IllegalArgumentException if a non-null element of {@code filters}
5555 * does not match a corresponding argument type of target as described above,
5556 * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()},
5557 * or if the resulting method handle's type would have
5558 * <a href="MethodHandle.html#maxarity">too many parameters</a>
5559 */
5560 public static MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
5561 // In method types arguments start at index 0, while the LF
5562 // editor have the MH receiver at position 0 - adjust appropriately.
5563 final int MH_RECEIVER_OFFSET = 1;
5564 filterArgumentsCheckArity(target, pos, filters);
5565 MethodHandle adapter = target;
5566
5567 // keep track of currently matched filters, as to optimize repeated filters
5568 int index = 0;
5569 int[] positions = new int[filters.length];
5570 MethodHandle filter = null;
5571
5572 // process filters in reverse order so that the invocation of
5573 // the resulting adapter will invoke the filters in left-to-right order
5574 for (int i = filters.length - 1; i >= 0; --i) {
5575 MethodHandle newFilter = filters[i];
5576 if (newFilter == null) continue; // ignore null elements of filters
5577
5578 // flush changes on update
5579 if (filter != newFilter) {
5580 if (filter != null) {
5581 if (index > 1) {
5582 adapter = filterRepeatedArgument(adapter, filter, Arrays.copyOf(positions, index));
5583 } else {
5584 adapter = filterArgument(adapter, positions[0] - 1, filter);
5585 }
5586 }
5587 filter = newFilter;
5588 index = 0;
5589 }
5590
5591 filterArgumentChecks(target, pos + i, newFilter);
5592 positions[index++] = pos + i + MH_RECEIVER_OFFSET;
5593 }
5594 if (index > 1) {
5595 adapter = filterRepeatedArgument(adapter, filter, Arrays.copyOf(positions, index));
5596 } else if (index == 1) {
5597 adapter = filterArgument(adapter, positions[0] - 1, filter);
5598 }
5599 return adapter;
5600 }
5601
5602 private static MethodHandle filterRepeatedArgument(MethodHandle adapter, MethodHandle filter, int[] positions) {
5603 MethodType targetType = adapter.type();
5604 MethodType filterType = filter.type();
5605 BoundMethodHandle result = adapter.rebind();
5606 Class<?> newParamType = filterType.parameterType(0);
5607
5608 Class<?>[] ptypes = targetType.ptypes().clone();
5609 for (int pos : positions) {
5610 ptypes[pos - 1] = newParamType;
5611 }
5612 MethodType newType = MethodType.methodType(targetType.rtype(), ptypes, true);
5613
5614 LambdaForm lform = result.editor().filterRepeatedArgumentForm(BasicType.basicType(newParamType), positions);
5615 return result.copyWithExtendL(newType, lform, filter);
5616 }
5617
5618 /*non-public*/
5619 static MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
5620 filterArgumentChecks(target, pos, filter);
5621 MethodType targetType = target.type();
5622 MethodType filterType = filter.type();
5623 BoundMethodHandle result = target.rebind();
5624 Class<?> newParamType = filterType.parameterType(0);
5625 LambdaForm lform = result.editor().filterArgumentForm(1 + pos, BasicType.basicType(newParamType));
5626 MethodType newType = targetType.changeParameterType(pos, newParamType);
5627 result = result.copyWithExtendL(newType, lform, filter);
5628 return result;
5629 }
5630
5631 private static void filterArgumentsCheckArity(MethodHandle target, int pos, MethodHandle[] filters) {
5632 MethodType targetType = target.type();
5633 int maxPos = targetType.parameterCount();
5634 if (pos + filters.length > maxPos)
5635 throw newIllegalArgumentException("too many filters");
5636 }
5637
5638 private static void filterArgumentChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
5639 MethodType targetType = target.type();
5640 MethodType filterType = filter.type();
5641 if (filterType.parameterCount() != 1
5642 || filterType.returnType() != targetType.parameterType(pos))
5643 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
5644 }
5645
5646 /**
5647 * Adapts a target method handle by pre-processing
5648 * a sub-sequence of its arguments with a filter (another method handle).
5649 * The pre-processed arguments are replaced by the result (if any) of the
5650 * filter function.
5651 * The target is then called on the modified (usually shortened) argument list.
5652 * <p>
5653 * If the filter returns a value, the target must accept that value as
5654 * its argument in position {@code pos}, preceded and/or followed by
5655 * any arguments not passed to the filter.
5656 * If the filter returns void, the target must accept all arguments
5657 * not passed to the filter.
5658 * No arguments are reordered, and a result returned from the filter
5659 * replaces (in order) the whole subsequence of arguments originally
5660 * passed to the adapter.
5661 * <p>
5662 * The argument types (if any) of the filter
5663 * replace zero or one argument types of the target, at position {@code pos},
5664 * in the resulting adapted method handle.
5665 * The return type of the filter (if any) must be identical to the
5666 * argument type of the target at position {@code pos}, and that target argument
5667 * is supplied by the return value of the filter.
5668 * <p>
5669 * In all cases, {@code pos} must be greater than or equal to zero, and
5670 * {@code pos} must also be less than or equal to the target's arity.
5671 * <p><b>Example:</b>
5672 * {@snippet lang="java" :
5673 import static java.lang.invoke.MethodHandles.*;
5674 import static java.lang.invoke.MethodType.*;
5675 ...
5676 MethodHandle deepToString = publicLookup()
5677 .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
5678
5679 MethodHandle ts1 = deepToString.asCollector(String[].class, 1);
5680 assertEquals("[strange]", (String) ts1.invokeExact("strange"));
5681
5682 MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
5683 assertEquals("[up, down]", (String) ts2.invokeExact("up", "down"));
5684
5685 MethodHandle ts3 = deepToString.asCollector(String[].class, 3);
5686 MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2);
5687 assertEquals("[top, [up, down], strange]",
5688 (String) ts3_ts2.invokeExact("top", "up", "down", "strange"));
5689
5690 MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1);
5691 assertEquals("[top, [up, down], [strange]]",
5692 (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange"));
5693
5694 MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3);
5695 assertEquals("[top, [[up, down, strange], charm], bottom]",
5696 (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom"));
5697 * }
5698 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
5699 * represents the return type of the {@code target} and resulting adapter.
5700 * {@code V}/{@code v} stand for the return type and value of the
5701 * {@code filter}, which are also found in the signature and arguments of
5702 * the {@code target}, respectively, unless {@code V} is {@code void}.
5703 * {@code A}/{@code a} and {@code C}/{@code c} represent the parameter types
5704 * and values preceding and following the collection position, {@code pos},
5705 * in the {@code target}'s signature. They also turn up in the resulting
5706 * adapter's signature and arguments, where they surround
5707 * {@code B}/{@code b}, which represent the parameter types and arguments
5708 * to the {@code filter} (if any).
5709 * {@snippet lang="java" :
5710 * T target(A...,V,C...);
5711 * V filter(B...);
5712 * T adapter(A... a,B... b,C... c) {
5713 * V v = filter(b...);
5714 * return target(a...,v,c...);
5715 * }
5716 * // and if the filter has no arguments:
5717 * T target2(A...,V,C...);
5718 * V filter2();
5719 * T adapter2(A... a,C... c) {
5720 * V v = filter2();
5721 * return target2(a...,v,c...);
5722 * }
5723 * // and if the filter has a void return:
5724 * T target3(A...,C...);
5725 * void filter3(B...);
5726 * T adapter3(A... a,B... b,C... c) {
5727 * filter3(b...);
5728 * return target3(a...,c...);
5729 * }
5730 * }
5731 * <p>
5732 * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to
5733 * one which first "folds" the affected arguments, and then drops them, in separate
5734 * steps as follows:
5735 * {@snippet lang="java" :
5736 * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2
5737 * mh = MethodHandles.foldArguments(mh, coll); //step 1
5738 * }
5739 * If the target method handle consumes no arguments besides than the result
5740 * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)}
5741 * is equivalent to {@code filterReturnValue(coll, mh)}.
5742 * If the filter method handle {@code coll} consumes one argument and produces
5743 * a non-void result, then {@code collectArguments(mh, N, coll)}
5744 * is equivalent to {@code filterArguments(mh, N, coll)}.
5745 * Other equivalences are possible but would require argument permutation.
5746 * <p>
5747 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5748 * variable-arity method handle}, even if the original target method handle was.
5749 *
5750 * @param target the method handle to invoke after filtering the subsequence of arguments
5751 * @param pos the position of the first adapter argument to pass to the filter,
5752 * and/or the target argument which receives the result of the filter
5753 * @param filter method handle to call on the subsequence of arguments
5754 * @return method handle which incorporates the specified argument subsequence filtering logic
5755 * @throws NullPointerException if either argument is null
5756 * @throws IllegalArgumentException if the return type of {@code filter}
5757 * is non-void and is not the same as the {@code pos} argument of the target,
5758 * or if {@code pos} is not between 0 and the target's arity, inclusive,
5759 * or if the resulting method handle's type would have
5760 * <a href="MethodHandle.html#maxarity">too many parameters</a>
5761 * @see MethodHandles#foldArguments
5762 * @see MethodHandles#filterArguments
5763 * @see MethodHandles#filterReturnValue
5764 */
5765 public static MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) {
5766 MethodType newType = collectArgumentsChecks(target, pos, filter);
5767 MethodType collectorType = filter.type();
5768 BoundMethodHandle result = target.rebind();
5769 LambdaForm lform = result.editor().collectArgumentsForm(1 + pos, collectorType.basicType());
5770 return result.copyWithExtendL(newType, lform, filter);
5771 }
5772
5773 private static MethodType collectArgumentsChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
5774 MethodType targetType = target.type();
5775 MethodType filterType = filter.type();
5776 Class<?> rtype = filterType.returnType();
5777 Class<?>[] filterArgs = filterType.ptypes();
5778 if (pos < 0 || (rtype == void.class && pos > targetType.parameterCount()) ||
5779 (rtype != void.class && pos >= targetType.parameterCount())) {
5780 throw newIllegalArgumentException("position is out of range for target", target, pos);
5781 }
5782 if (rtype == void.class) {
5783 return targetType.insertParameterTypes(pos, filterArgs);
5784 }
5785 if (rtype != targetType.parameterType(pos)) {
5786 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
5787 }
5788 return targetType.dropParameterTypes(pos, pos + 1).insertParameterTypes(pos, filterArgs);
5789 }
5790
5791 /**
5792 * Adapts a target method handle by post-processing
5793 * its return value (if any) with a filter (another method handle).
5794 * The result of the filter is returned from the adapter.
5795 * <p>
5796 * If the target returns a value, the filter must accept that value as
5797 * its only argument.
5798 * If the target returns void, the filter must accept no arguments.
5799 * <p>
5800 * The return type of the filter
5801 * replaces the return type of the target
5802 * in the resulting adapted method handle.
5803 * The argument type of the filter (if any) must be identical to the
5804 * return type of the target.
5805 * <p><b>Example:</b>
5806 * {@snippet lang="java" :
5807 import static java.lang.invoke.MethodHandles.*;
5808 import static java.lang.invoke.MethodType.*;
5809 ...
5810 MethodHandle cat = lookup().findVirtual(String.class,
5811 "concat", methodType(String.class, String.class));
5812 MethodHandle length = lookup().findVirtual(String.class,
5813 "length", methodType(int.class));
5814 System.out.println((String) cat.invokeExact("x", "y")); // xy
5815 MethodHandle f0 = filterReturnValue(cat, length);
5816 System.out.println((int) f0.invokeExact("x", "y")); // 2
5817 * }
5818 * <p>Here is pseudocode for the resulting adapter. In the code,
5819 * {@code T}/{@code t} represent the result type and value of the
5820 * {@code target}; {@code V}, the result type of the {@code filter}; and
5821 * {@code A}/{@code a}, the types and values of the parameters and arguments
5822 * of the {@code target} as well as the resulting adapter.
5823 * {@snippet lang="java" :
5824 * T target(A...);
5825 * V filter(T);
5826 * V adapter(A... a) {
5827 * T t = target(a...);
5828 * return filter(t);
5829 * }
5830 * // and if the target has a void return:
5831 * void target2(A...);
5832 * V filter2();
5833 * V adapter2(A... a) {
5834 * target2(a...);
5835 * return filter2();
5836 * }
5837 * // and if the filter has a void return:
5838 * T target3(A...);
5839 * void filter3(V);
5840 * void adapter3(A... a) {
5841 * T t = target3(a...);
5842 * filter3(t);
5843 * }
5844 * }
5845 * <p>
5846 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5847 * variable-arity method handle}, even if the original target method handle was.
5848 * @param target the method handle to invoke before filtering the return value
5849 * @param filter method handle to call on the return value
5850 * @return method handle which incorporates the specified return value filtering logic
5851 * @throws NullPointerException if either argument is null
5852 * @throws IllegalArgumentException if the argument list of {@code filter}
5853 * does not match the return type of target as described above
5854 */
5855 public static MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
5856 MethodType targetType = target.type();
5857 MethodType filterType = filter.type();
5858 filterReturnValueChecks(targetType, filterType);
5859 BoundMethodHandle result = target.rebind();
5860 BasicType rtype = BasicType.basicType(filterType.returnType());
5861 LambdaForm lform = result.editor().filterReturnForm(rtype, false);
5862 MethodType newType = targetType.changeReturnType(filterType.returnType());
5863 result = result.copyWithExtendL(newType, lform, filter);
5864 return result;
5865 }
5866
5867 private static void filterReturnValueChecks(MethodType targetType, MethodType filterType) throws RuntimeException {
5868 Class<?> rtype = targetType.returnType();
5869 int filterValues = filterType.parameterCount();
5870 if (filterValues == 0
5871 ? (rtype != void.class)
5872 : (rtype != filterType.parameterType(0) || filterValues != 1))
5873 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
5874 }
5875
5876 /**
5877 * Filter the return value of a target method handle with a filter function. The filter function is
5878 * applied to the return value of the original handle; if the filter specifies more than one parameters,
5879 * then any remaining parameter is appended to the adapter handle. In other words, the adaptation works
5880 * as follows:
5881 * {@snippet lang="java" :
5882 * T target(A...)
5883 * V filter(B... , T)
5884 * V adapter(A... a, B... b) {
5885 * T t = target(a...);
5886 * return filter(b..., t);
5887 * }
5888 * }
5889 * <p>
5890 * If the filter handle is a unary function, then this method behaves like {@link #filterReturnValue(MethodHandle, MethodHandle)}.
5891 *
5892 * @param target the target method handle
5893 * @param filter the filter method handle
5894 * @return the adapter method handle
5895 */
5896 /* package */ static MethodHandle collectReturnValue(MethodHandle target, MethodHandle filter) {
5897 MethodType targetType = target.type();
5898 MethodType filterType = filter.type();
5899 BoundMethodHandle result = target.rebind();
5900 LambdaForm lform = result.editor().collectReturnValueForm(filterType.basicType());
5901 MethodType newType = targetType.changeReturnType(filterType.returnType());
5902 if (filterType.parameterCount() > 1) {
5903 for (int i = 0 ; i < filterType.parameterCount() - 1 ; i++) {
5904 newType = newType.appendParameterTypes(filterType.parameterType(i));
5905 }
5906 }
5907 result = result.copyWithExtendL(newType, lform, filter);
5908 return result;
5909 }
5910
5911 /**
5912 * Adapts a target method handle by pre-processing
5913 * some of its arguments, and then calling the target with
5914 * the result of the pre-processing, inserted into the original
5915 * sequence of arguments.
5916 * <p>
5917 * The pre-processing is performed by {@code combiner}, a second method handle.
5918 * Of the arguments passed to the adapter, the first {@code N} arguments
5919 * are copied to the combiner, which is then called.
5920 * (Here, {@code N} is defined as the parameter count of the combiner.)
5921 * After this, control passes to the target, with any result
5922 * from the combiner inserted before the original {@code N} incoming
5923 * arguments.
5924 * <p>
5925 * If the combiner returns a value, the first parameter type of the target
5926 * must be identical with the return type of the combiner, and the next
5927 * {@code N} parameter types of the target must exactly match the parameters
5928 * of the combiner.
5929 * <p>
5930 * If the combiner has a void return, no result will be inserted,
5931 * and the first {@code N} parameter types of the target
5932 * must exactly match the parameters of the combiner.
5933 * <p>
5934 * The resulting adapter is the same type as the target, except that the
5935 * first parameter type is dropped,
5936 * if it corresponds to the result of the combiner.
5937 * <p>
5938 * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
5939 * that either the combiner or the target does not wish to receive.
5940 * If some of the incoming arguments are destined only for the combiner,
5941 * consider using {@link MethodHandle#asCollector asCollector} instead, since those
5942 * arguments will not need to be live on the stack on entry to the
5943 * target.)
5944 * <p><b>Example:</b>
5945 * {@snippet lang="java" :
5946 import static java.lang.invoke.MethodHandles.*;
5947 import static java.lang.invoke.MethodType.*;
5948 ...
5949 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
5950 "println", methodType(void.class, String.class))
5951 .bindTo(System.out);
5952 MethodHandle cat = lookup().findVirtual(String.class,
5953 "concat", methodType(String.class, String.class));
5954 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
5955 MethodHandle catTrace = foldArguments(cat, trace);
5956 // also prints "boo":
5957 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
5958 * }
5959 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
5960 * represents the result type of the {@code target} and resulting adapter.
5961 * {@code V}/{@code v} represent the type and value of the parameter and argument
5962 * of {@code target} that precedes the folding position; {@code V} also is
5963 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
5964 * types and values of the {@code N} parameters and arguments at the folding
5965 * position. {@code B}/{@code b} represent the types and values of the
5966 * {@code target} parameters and arguments that follow the folded parameters
5967 * and arguments.
5968 * {@snippet lang="java" :
5969 * // there are N arguments in A...
5970 * T target(V, A[N]..., B...);
5971 * V combiner(A...);
5972 * T adapter(A... a, B... b) {
5973 * V v = combiner(a...);
5974 * return target(v, a..., b...);
5975 * }
5976 * // and if the combiner has a void return:
5977 * T target2(A[N]..., B...);
5978 * void combiner2(A...);
5979 * T adapter2(A... a, B... b) {
5980 * combiner2(a...);
5981 * return target2(a..., b...);
5982 * }
5983 * }
5984 * <p>
5985 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5986 * variable-arity method handle}, even if the original target method handle was.
5987 * @param target the method handle to invoke after arguments are combined
5988 * @param combiner method handle to call initially on the incoming arguments
5989 * @return method handle which incorporates the specified argument folding logic
5990 * @throws NullPointerException if either argument is null
5991 * @throws IllegalArgumentException if {@code combiner}'s return type
5992 * is non-void and not the same as the first argument type of
5993 * the target, or if the initial {@code N} argument types
5994 * of the target
5995 * (skipping one matching the {@code combiner}'s return type)
5996 * are not identical with the argument types of {@code combiner}
5997 */
5998 public static MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
5999 return foldArguments(target, 0, combiner);
6000 }
6001
6002 /**
6003 * Adapts a target method handle by pre-processing some of its arguments, starting at a given position, and then
6004 * calling the target with the result of the pre-processing, inserted into the original sequence of arguments just
6005 * before the folded arguments.
6006 * <p>
6007 * This method is closely related to {@link #foldArguments(MethodHandle, MethodHandle)}, but allows to control the
6008 * position in the parameter list at which folding takes place. The argument controlling this, {@code pos}, is a
6009 * zero-based index. The aforementioned method {@link #foldArguments(MethodHandle, MethodHandle)} assumes position
6010 * 0.
6011 *
6012 * @apiNote Example:
6013 * {@snippet lang="java" :
6014 import static java.lang.invoke.MethodHandles.*;
6015 import static java.lang.invoke.MethodType.*;
6016 ...
6017 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
6018 "println", methodType(void.class, String.class))
6019 .bindTo(System.out);
6020 MethodHandle cat = lookup().findVirtual(String.class,
6021 "concat", methodType(String.class, String.class));
6022 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
6023 MethodHandle catTrace = foldArguments(cat, 1, trace);
6024 // also prints "jum":
6025 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
6026 * }
6027 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
6028 * represents the result type of the {@code target} and resulting adapter.
6029 * {@code V}/{@code v} represent the type and value of the parameter and argument
6030 * of {@code target} that precedes the folding position; {@code V} also is
6031 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
6032 * types and values of the {@code N} parameters and arguments at the folding
6033 * position. {@code Z}/{@code z} and {@code B}/{@code b} represent the types
6034 * and values of the {@code target} parameters and arguments that precede and
6035 * follow the folded parameters and arguments starting at {@code pos},
6036 * respectively.
6037 * {@snippet lang="java" :
6038 * // there are N arguments in A...
6039 * T target(Z..., V, A[N]..., B...);
6040 * V combiner(A...);
6041 * T adapter(Z... z, A... a, B... b) {
6042 * V v = combiner(a...);
6043 * return target(z..., v, a..., b...);
6044 * }
6045 * // and if the combiner has a void return:
6046 * T target2(Z..., A[N]..., B...);
6047 * void combiner2(A...);
6048 * T adapter2(Z... z, A... a, B... b) {
6049 * combiner2(a...);
6050 * return target2(z..., a..., b...);
6051 * }
6052 * }
6053 * <p>
6054 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
6055 * variable-arity method handle}, even if the original target method handle was.
6056 *
6057 * @param target the method handle to invoke after arguments are combined
6058 * @param pos the position at which to start folding and at which to insert the folding result; if this is {@code
6059 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
6060 * @param combiner method handle to call initially on the incoming arguments
6061 * @return method handle which incorporates the specified argument folding logic
6062 * @throws NullPointerException if either argument is null
6063 * @throws IllegalArgumentException if either of the following two conditions holds:
6064 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
6065 * {@code pos} of the target signature;
6066 * (2) the {@code N} argument types at position {@code pos} of the target signature (skipping one matching
6067 * the {@code combiner}'s return type) are not identical with the argument types of {@code combiner}.
6068 *
6069 * @see #foldArguments(MethodHandle, MethodHandle)
6070 * @since 9
6071 */
6072 public static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner) {
6073 MethodType targetType = target.type();
6074 MethodType combinerType = combiner.type();
6075 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType);
6076 BoundMethodHandle result = target.rebind();
6077 boolean dropResult = rtype == void.class;
6078 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType());
6079 MethodType newType = targetType;
6080 if (!dropResult) {
6081 newType = newType.dropParameterTypes(pos, pos + 1);
6082 }
6083 result = result.copyWithExtendL(newType, lform, combiner);
6084 return result;
6085 }
6086
6087 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType) {
6088 int foldArgs = combinerType.parameterCount();
6089 Class<?> rtype = combinerType.returnType();
6090 int foldVals = rtype == void.class ? 0 : 1;
6091 int afterInsertPos = foldPos + foldVals;
6092 boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
6093 if (ok) {
6094 for (int i = 0; i < foldArgs; i++) {
6095 if (combinerType.parameterType(i) != targetType.parameterType(i + afterInsertPos)) {
6096 ok = false;
6097 break;
6098 }
6099 }
6100 }
6101 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos))
6102 ok = false;
6103 if (!ok)
6104 throw misMatchedTypes("target and combiner types", targetType, combinerType);
6105 return rtype;
6106 }
6107
6108 /**
6109 * Adapts a target method handle by pre-processing some of its arguments, then calling the target with the result
6110 * of the pre-processing replacing the argument at the given position.
6111 *
6112 * @param target the method handle to invoke after arguments are combined
6113 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code
6114 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
6115 * @param combiner method handle to call initially on the incoming arguments
6116 * @param argPositions indexes of the target to pick arguments sent to the combiner from
6117 * @return method handle which incorporates the specified argument folding logic
6118 * @throws NullPointerException if either argument is null
6119 * @throws IllegalArgumentException if either of the following two conditions holds:
6120 * (1) {@code combiner}'s return type is not the same as the argument type at position
6121 * {@code pos} of the target signature;
6122 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature are
6123 * not identical with the argument types of {@code combiner}.
6124 */
6125 /*non-public*/
6126 static MethodHandle filterArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
6127 return argumentsWithCombiner(true, target, position, combiner, argPositions);
6128 }
6129
6130 /**
6131 * Adapts a target method handle by pre-processing some of its arguments, calling the target with the result of
6132 * the pre-processing inserted into the original sequence of arguments at the given position.
6133 *
6134 * @param target the method handle to invoke after arguments are combined
6135 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code
6136 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
6137 * @param combiner method handle to call initially on the incoming arguments
6138 * @param argPositions indexes of the target to pick arguments sent to the combiner from
6139 * @return method handle which incorporates the specified argument folding logic
6140 * @throws NullPointerException if either argument is null
6141 * @throws IllegalArgumentException if either of the following two conditions holds:
6142 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
6143 * {@code pos} of the target signature;
6144 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature
6145 * (skipping {@code position} where the {@code combiner}'s return will be folded in) are not identical
6146 * with the argument types of {@code combiner}.
6147 */
6148 /*non-public*/
6149 static MethodHandle foldArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
6150 return argumentsWithCombiner(false, target, position, combiner, argPositions);
6151 }
6152
6153 private static MethodHandle argumentsWithCombiner(boolean filter, MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
6154 MethodType targetType = target.type();
6155 MethodType combinerType = combiner.type();
6156 Class<?> rtype = argumentsWithCombinerChecks(position, filter, targetType, combinerType, argPositions);
6157 BoundMethodHandle result = target.rebind();
6158
6159 MethodType newType = targetType;
6160 LambdaForm lform;
6161 if (filter) {
6162 lform = result.editor().filterArgumentsForm(1 + position, combinerType.basicType(), argPositions);
6163 } else {
6164 boolean dropResult = rtype == void.class;
6165 lform = result.editor().foldArgumentsForm(1 + position, dropResult, combinerType.basicType(), argPositions);
6166 if (!dropResult) {
6167 newType = newType.dropParameterTypes(position, position + 1);
6168 }
6169 }
6170 result = result.copyWithExtendL(newType, lform, combiner);
6171 return result;
6172 }
6173
6174 private static Class<?> argumentsWithCombinerChecks(int position, boolean filter, MethodType targetType, MethodType combinerType, int ... argPos) {
6175 int combinerArgs = combinerType.parameterCount();
6176 if (argPos.length != combinerArgs) {
6177 throw newIllegalArgumentException("combiner and argument map must be equal size", combinerType, argPos.length);
6178 }
6179 Class<?> rtype = combinerType.returnType();
6180
6181 for (int i = 0; i < combinerArgs; i++) {
6182 int arg = argPos[i];
6183 if (arg < 0 || arg > targetType.parameterCount()) {
6184 throw newIllegalArgumentException("arg outside of target parameterRange", targetType, arg);
6185 }
6186 if (combinerType.parameterType(i) != targetType.parameterType(arg)) {
6187 throw newIllegalArgumentException("target argument type at position " + arg
6188 + " must match combiner argument type at index " + i + ": " + targetType
6189 + " -> " + combinerType + ", map: " + Arrays.toString(argPos));
6190 }
6191 }
6192 if (filter && combinerType.returnType() != targetType.parameterType(position)) {
6193 throw misMatchedTypes("target and combiner types", targetType, combinerType);
6194 }
6195 return rtype;
6196 }
6197
6198 /**
6199 * Makes a method handle which adapts a target method handle,
6200 * by guarding it with a test, a boolean-valued method handle.
6201 * If the guard fails, a fallback handle is called instead.
6202 * All three method handles must have the same corresponding
6203 * argument and return types, except that the return type
6204 * of the test must be boolean, and the test is allowed
6205 * to have fewer arguments than the other two method handles.
6206 * <p>
6207 * Here is pseudocode for the resulting adapter. In the code, {@code T}
6208 * represents the uniform result type of the three involved handles;
6209 * {@code A}/{@code a}, the types and values of the {@code target}
6210 * parameters and arguments that are consumed by the {@code test}; and
6211 * {@code B}/{@code b}, those types and values of the {@code target}
6212 * parameters and arguments that are not consumed by the {@code test}.
6213 * {@snippet lang="java" :
6214 * boolean test(A...);
6215 * T target(A...,B...);
6216 * T fallback(A...,B...);
6217 * T adapter(A... a,B... b) {
6218 * if (test(a...))
6219 * return target(a..., b...);
6220 * else
6221 * return fallback(a..., b...);
6222 * }
6223 * }
6224 * Note that the test arguments ({@code a...} in the pseudocode) cannot
6225 * be modified by execution of the test, and so are passed unchanged
6226 * from the caller to the target or fallback as appropriate.
6227 * @param test method handle used for test, must return boolean
6228 * @param target method handle to call if test passes
6229 * @param fallback method handle to call if test fails
6230 * @return method handle which incorporates the specified if/then/else logic
6231 * @throws NullPointerException if any argument is null
6232 * @throws IllegalArgumentException if {@code test} does not return boolean,
6233 * or if all three method types do not match (with the return
6234 * type of {@code test} changed to match that of the target).
6235 */
6236 public static MethodHandle guardWithTest(MethodHandle test,
6237 MethodHandle target,
6238 MethodHandle fallback) {
6239 MethodType gtype = test.type();
6240 MethodType ttype = target.type();
6241 MethodType ftype = fallback.type();
6242 if (!ttype.equals(ftype))
6243 throw misMatchedTypes("target and fallback types", ttype, ftype);
6244 if (gtype.returnType() != boolean.class)
6245 throw newIllegalArgumentException("guard type is not a predicate "+gtype);
6246
6247 test = dropArgumentsToMatch(test, 0, ttype.ptypes(), 0, true);
6248 if (test == null) {
6249 throw misMatchedTypes("target and test types", ttype, gtype);
6250 }
6251 return MethodHandleImpl.makeGuardWithTest(test, target, fallback);
6252 }
6253
6254 static <T> RuntimeException misMatchedTypes(String what, T t1, T t2) {
6255 return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
6256 }
6257
6258 /**
6259 * Makes a method handle which adapts a target method handle,
6260 * by running it inside an exception handler.
6261 * If the target returns normally, the adapter returns that value.
6262 * If an exception matching the specified type is thrown, the fallback
6263 * handle is called instead on the exception, plus the original arguments.
6264 * <p>
6265 * The target and handler must have the same corresponding
6266 * argument and return types, except that handler may omit trailing arguments
6267 * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
6268 * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
6269 * <p>
6270 * Here is pseudocode for the resulting adapter. In the code, {@code T}
6271 * represents the return type of the {@code target} and {@code handler},
6272 * and correspondingly that of the resulting adapter; {@code A}/{@code a},
6273 * the types and values of arguments to the resulting handle consumed by
6274 * {@code handler}; and {@code B}/{@code b}, those of arguments to the
6275 * resulting handle discarded by {@code handler}.
6276 * {@snippet lang="java" :
6277 * T target(A..., B...);
6278 * T handler(ExType, A...);
6279 * T adapter(A... a, B... b) {
6280 * try {
6281 * return target(a..., b...);
6282 * } catch (ExType ex) {
6283 * return handler(ex, a...);
6284 * }
6285 * }
6286 * }
6287 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
6288 * be modified by execution of the target, and so are passed unchanged
6289 * from the caller to the handler, if the handler is invoked.
6290 * <p>
6291 * The target and handler must return the same type, even if the handler
6292 * always throws. (This might happen, for instance, because the handler
6293 * is simulating a {@code finally} clause).
6294 * To create such a throwing handler, compose the handler creation logic
6295 * with {@link #throwException throwException},
6296 * in order to create a method handle of the correct return type.
6297 * @param target method handle to call
6298 * @param exType the type of exception which the handler will catch
6299 * @param handler method handle to call if a matching exception is thrown
6300 * @return method handle which incorporates the specified try/catch logic
6301 * @throws NullPointerException if any argument is null
6302 * @throws IllegalArgumentException if {@code handler} does not accept
6303 * the given exception type, or if the method handle types do
6304 * not match in their return types and their
6305 * corresponding parameters
6306 * @see MethodHandles#tryFinally(MethodHandle, MethodHandle)
6307 */
6308 public static MethodHandle catchException(MethodHandle target,
6309 Class<? extends Throwable> exType,
6310 MethodHandle handler) {
6311 MethodType ttype = target.type();
6312 MethodType htype = handler.type();
6313 if (!Throwable.class.isAssignableFrom(exType))
6314 throw new ClassCastException(exType.getName());
6315 if (htype.parameterCount() < 1 ||
6316 !htype.parameterType(0).isAssignableFrom(exType))
6317 throw newIllegalArgumentException("handler does not accept exception type "+exType);
6318 if (htype.returnType() != ttype.returnType())
6319 throw misMatchedTypes("target and handler return types", ttype, htype);
6320 handler = dropArgumentsToMatch(handler, 1, ttype.ptypes(), 0, true);
6321 if (handler == null) {
6322 throw misMatchedTypes("target and handler types", ttype, htype);
6323 }
6324 return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
6325 }
6326
6327 /**
6328 * Produces a method handle which will throw exceptions of the given {@code exType}.
6329 * The method handle will accept a single argument of {@code exType},
6330 * and immediately throw it as an exception.
6331 * The method type will nominally specify a return of {@code returnType}.
6332 * The return type may be anything convenient: It doesn't matter to the
6333 * method handle's behavior, since it will never return normally.
6334 * @param returnType the return type of the desired method handle
6335 * @param exType the parameter type of the desired method handle
6336 * @return method handle which can throw the given exceptions
6337 * @throws NullPointerException if either argument is null
6338 */
6339 public static MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) {
6340 if (!Throwable.class.isAssignableFrom(exType))
6341 throw new ClassCastException(exType.getName());
6342 return MethodHandleImpl.throwException(methodType(returnType, exType));
6343 }
6344
6345 /**
6346 * Constructs a method handle representing a loop with several loop variables that are updated and checked upon each
6347 * iteration. Upon termination of the loop due to one of the predicates, a corresponding finalizer is run and
6348 * delivers the loop's result, which is the return value of the resulting handle.
6349 * <p>
6350 * Intuitively, every loop is formed by one or more "clauses", each specifying a local <em>iteration variable</em> and/or a loop
6351 * exit. Each iteration of the loop executes each clause in order. A clause can optionally update its iteration
6352 * variable; it can also optionally perform a test and conditional loop exit. In order to express this logic in
6353 * terms of method handles, each clause will specify up to four independent actions:<ul>
6354 * <li><em>init:</em> Before the loop executes, the initialization of an iteration variable {@code v} of type {@code V}.
6355 * <li><em>step:</em> When a clause executes, an update step for the iteration variable {@code v}.
6356 * <li><em>pred:</em> When a clause executes, a predicate execution to test for loop exit.
6357 * <li><em>fini:</em> If a clause causes a loop exit, a finalizer execution to compute the loop's return value.
6358 * </ul>
6359 * The full sequence of all iteration variable types, in clause order, will be notated as {@code (V...)}.
6360 * The values themselves will be {@code (v...)}. When we speak of "parameter lists", we will usually
6361 * be referring to types, but in some contexts (describing execution) the lists will be of actual values.
6362 * <p>
6363 * Some of these clause parts may be omitted according to certain rules, and useful default behavior is provided in
6364 * this case. See below for a detailed description.
6365 * <p>
6366 * <em>Parameters optional everywhere:</em>
6367 * Each clause function is allowed but not required to accept a parameter for each iteration variable {@code v}.
6368 * As an exception, the init functions cannot take any {@code v} parameters,
6369 * because those values are not yet computed when the init functions are executed.
6370 * Any clause function may neglect to take any trailing subsequence of parameters it is entitled to take.
6371 * In fact, any clause function may take no arguments at all.
6372 * <p>
6373 * <em>Loop parameters:</em>
6374 * A clause function may take all the iteration variable values it is entitled to, in which case
6375 * it may also take more trailing parameters. Such extra values are called <em>loop parameters</em>,
6376 * with their types and values notated as {@code (A...)} and {@code (a...)}.
6377 * These become the parameters of the resulting loop handle, to be supplied whenever the loop is executed.
6378 * (Since init functions do not accept iteration variables {@code v}, any parameter to an
6379 * init function is automatically a loop parameter {@code a}.)
6380 * As with iteration variables, clause functions are allowed but not required to accept loop parameters.
6381 * These loop parameters act as loop-invariant values visible across the whole loop.
6382 * <p>
6383 * <em>Parameters visible everywhere:</em>
6384 * Each non-init clause function is permitted to observe the entire loop state, because it can be passed the full
6385 * list {@code (v... a...)} of current iteration variable values and incoming loop parameters.
6386 * The init functions can observe initial pre-loop state, in the form {@code (a...)}.
6387 * Most clause functions will not need all of this information, but they will be formally connected to it
6388 * as if by {@link #dropArguments}.
6389 * <a id="astar"></a>
6390 * More specifically, we shall use the notation {@code (V*)} to express an arbitrary prefix of a full
6391 * sequence {@code (V...)} (and likewise for {@code (v*)}, {@code (A*)}, {@code (a*)}).
6392 * In that notation, the general form of an init function parameter list
6393 * is {@code (A*)}, and the general form of a non-init function parameter list is {@code (V*)} or {@code (V... A*)}.
6394 * <p>
6395 * <em>Checking clause structure:</em>
6396 * Given a set of clauses, there is a number of checks and adjustments performed to connect all the parts of the
6397 * loop. They are spelled out in detail in the steps below. In these steps, every occurrence of the word "must"
6398 * corresponds to a place where {@link IllegalArgumentException} will be thrown if the required constraint is not
6399 * met by the inputs to the loop combinator.
6400 * <p>
6401 * <em>Effectively identical sequences:</em>
6402 * <a id="effid"></a>
6403 * A parameter list {@code A} is defined to be <em>effectively identical</em> to another parameter list {@code B}
6404 * if {@code A} and {@code B} are identical, or if {@code A} is shorter and is identical with a proper prefix of {@code B}.
6405 * When speaking of an unordered set of parameter lists, we say they the set is "effectively identical"
6406 * as a whole if the set contains a longest list, and all members of the set are effectively identical to
6407 * that longest list.
6408 * For example, any set of type sequences of the form {@code (V*)} is effectively identical,
6409 * and the same is true if more sequences of the form {@code (V... A*)} are added.
6410 * <p>
6411 * <em>Step 0: Determine clause structure.</em><ol type="a">
6412 * <li>The clause array (of type {@code MethodHandle[][]}) must be non-{@code null} and contain at least one element.
6413 * <li>The clause array may not contain {@code null}s or sub-arrays longer than four elements.
6414 * <li>Clauses shorter than four elements are treated as if they were padded by {@code null} elements to length
6415 * four. Padding takes place by appending elements to the array.
6416 * <li>Clauses with all {@code null}s are disregarded.
6417 * <li>Each clause is treated as a four-tuple of functions, called "init", "step", "pred", and "fini".
6418 * </ol>
6419 * <p>
6420 * <em>Step 1A: Determine iteration variable types {@code (V...)}.</em><ol type="a">
6421 * <li>The iteration variable type for each clause is determined using the clause's init and step return types.
6422 * <li>If both functions are omitted, there is no iteration variable for the corresponding clause ({@code void} is
6423 * used as the type to indicate that). If one of them is omitted, the other's return type defines the clause's
6424 * iteration variable type. If both are given, the common return type (they must be identical) defines the clause's
6425 * iteration variable type.
6426 * <li>Form the list of return types (in clause order), omitting all occurrences of {@code void}.
6427 * <li>This list of types is called the "iteration variable types" ({@code (V...)}).
6428 * </ol>
6429 * <p>
6430 * <em>Step 1B: Determine loop parameters {@code (A...)}.</em><ul>
6431 * <li>Examine and collect init function parameter lists (which are of the form {@code (A*)}).
6432 * <li>Examine and collect the suffixes of the step, pred, and fini parameter lists, after removing the iteration variable types.
6433 * (They must have the form {@code (V... A*)}; collect the {@code (A*)} parts only.)
6434 * <li>Do not collect suffixes from step, pred, and fini parameter lists that do not begin with all the iteration variable types.
6435 * (These types will be checked in step 2, along with all the clause function types.)
6436 * <li>Omitted clause functions are ignored. (Equivalently, they are deemed to have empty parameter lists.)
6437 * <li>All of the collected parameter lists must be effectively identical.
6438 * <li>The longest parameter list (which is necessarily unique) is called the "external parameter list" ({@code (A...)}).
6439 * <li>If there is no such parameter list, the external parameter list is taken to be the empty sequence.
6440 * <li>The combined list consisting of iteration variable types followed by the external parameter types is called
6441 * the "internal parameter list".
6442 * </ul>
6443 * <p>
6444 * <em>Step 1C: Determine loop return type.</em><ol type="a">
6445 * <li>Examine fini function return types, disregarding omitted fini functions.
6446 * <li>If there are no fini functions, the loop return type is {@code void}.
6447 * <li>Otherwise, the common return type {@code R} of the fini functions (their return types must be identical) defines the loop return
6448 * type.
6449 * </ol>
6450 * <p>
6451 * <em>Step 1D: Check other types.</em><ol type="a">
6452 * <li>There must be at least one non-omitted pred function.
6453 * <li>Every non-omitted pred function must have a {@code boolean} return type.
6454 * </ol>
6455 * <p>
6456 * <em>Step 2: Determine parameter lists.</em><ol type="a">
6457 * <li>The parameter list for the resulting loop handle will be the external parameter list {@code (A...)}.
6458 * <li>The parameter list for init functions will be adjusted to the external parameter list.
6459 * (Note that their parameter lists are already effectively identical to this list.)
6460 * <li>The parameter list for every non-omitted, non-init (step, pred, and fini) function must be
6461 * effectively identical to the internal parameter list {@code (V... A...)}.
6462 * </ol>
6463 * <p>
6464 * <em>Step 3: Fill in omitted functions.</em><ol type="a">
6465 * <li>If an init function is omitted, use a {@linkplain #empty default value} for the clause's iteration variable
6466 * type.
6467 * <li>If a step function is omitted, use an {@linkplain #identity identity function} of the clause's iteration
6468 * variable type; insert dropped argument parameters before the identity function parameter for the non-{@code void}
6469 * iteration variables of preceding clauses. (This will turn the loop variable into a local loop invariant.)
6470 * <li>If a pred function is omitted, use a constant {@code true} function. (This will keep the loop going, as far
6471 * as this clause is concerned. Note that in such cases the corresponding fini function is unreachable.)
6472 * <li>If a fini function is omitted, use a {@linkplain #empty default value} for the
6473 * loop return type.
6474 * </ol>
6475 * <p>
6476 * <em>Step 4: Fill in missing parameter types.</em><ol type="a">
6477 * <li>At this point, every init function parameter list is effectively identical to the external parameter list {@code (A...)},
6478 * but some lists may be shorter. For every init function with a short parameter list, pad out the end of the list.
6479 * <li>At this point, every non-init function parameter list is effectively identical to the internal parameter
6480 * list {@code (V... A...)}, but some lists may be shorter. For every non-init function with a short parameter list,
6481 * pad out the end of the list.
6482 * <li>Argument lists are padded out by {@linkplain #dropArgumentsToMatch(MethodHandle, int, List, int) dropping unused trailing arguments}.
6483 * </ol>
6484 * <p>
6485 * <em>Final observations.</em><ol type="a">
6486 * <li>After these steps, all clauses have been adjusted by supplying omitted functions and arguments.
6487 * <li>All init functions have a common parameter type list {@code (A...)}, which the final loop handle will also have.
6488 * <li>All fini functions have a common return type {@code R}, which the final loop handle will also have.
6489 * <li>All non-init functions have a common parameter type list {@code (V... A...)}, of
6490 * (non-{@code void}) iteration variables {@code V} followed by loop parameters.
6491 * <li>Each pair of init and step functions agrees in their return type {@code V}.
6492 * <li>Each non-init function will be able to observe the current values {@code (v...)} of all iteration variables.
6493 * <li>Every function will be able to observe the incoming values {@code (a...)} of all loop parameters.
6494 * </ol>
6495 * <p>
6496 * <em>Example.</em> As a consequence of step 1A above, the {@code loop} combinator has the following property:
6497 * <ul>
6498 * <li>Given {@code N} clauses {@code Cn = {null, Sn, Pn}} with {@code n = 1..N}.
6499 * <li>Suppose predicate handles {@code Pn} are either {@code null} or have no parameters.
6500 * (Only one {@code Pn} has to be non-{@code null}.)
6501 * <li>Suppose step handles {@code Sn} have signatures {@code (B1..BX)Rn}, for some constant {@code X>=N}.
6502 * <li>Suppose {@code Q} is the count of non-void types {@code Rn}, and {@code (V1...VQ)} is the sequence of those types.
6503 * <li>It must be that {@code Vn == Bn} for {@code n = 1..min(X,Q)}.
6504 * <li>The parameter types {@code Vn} will be interpreted as loop-local state elements {@code (V...)}.
6505 * <li>Any remaining types {@code BQ+1..BX} (if {@code Q<X}) will determine
6506 * the resulting loop handle's parameter types {@code (A...)}.
6507 * </ul>
6508 * In this example, the loop handle parameters {@code (A...)} were derived from the step functions,
6509 * which is natural if most of the loop computation happens in the steps. For some loops,
6510 * the burden of computation might be heaviest in the pred functions, and so the pred functions
6511 * might need to accept the loop parameter values. For loops with complex exit logic, the fini
6512 * functions might need to accept loop parameters, and likewise for loops with complex entry logic,
6513 * where the init functions will need the extra parameters. For such reasons, the rules for
6514 * determining these parameters are as symmetric as possible, across all clause parts.
6515 * In general, the loop parameters function as common invariant values across the whole
6516 * loop, while the iteration variables function as common variant values, or (if there is
6517 * no step function) as internal loop invariant temporaries.
6518 * <p>
6519 * <em>Loop execution.</em><ol type="a">
6520 * <li>When the loop is called, the loop input values are saved in locals, to be passed to
6521 * every clause function. These locals are loop invariant.
6522 * <li>Each init function is executed in clause order (passing the external arguments {@code (a...)})
6523 * and the non-{@code void} values are saved (as the iteration variables {@code (v...)}) into locals.
6524 * These locals will be loop varying (unless their steps behave as identity functions, as noted above).
6525 * <li>All function executions (except init functions) will be passed the internal parameter list, consisting of
6526 * the non-{@code void} iteration values {@code (v...)} (in clause order) and then the loop inputs {@code (a...)}
6527 * (in argument order).
6528 * <li>The step and pred functions are then executed, in clause order (step before pred), until a pred function
6529 * returns {@code false}.
6530 * <li>The non-{@code void} result from a step function call is used to update the corresponding value in the
6531 * sequence {@code (v...)} of loop variables.
6532 * The updated value is immediately visible to all subsequent function calls.
6533 * <li>If a pred function returns {@code false}, the corresponding fini function is called, and the resulting value
6534 * (of type {@code R}) is returned from the loop as a whole.
6535 * <li>If all the pred functions always return true, no fini function is ever invoked, and the loop cannot exit
6536 * except by throwing an exception.
6537 * </ol>
6538 * <p>
6539 * <em>Usage tips.</em>
6540 * <ul>
6541 * <li>Although each step function will receive the current values of <em>all</em> the loop variables,
6542 * sometimes a step function only needs to observe the current value of its own variable.
6543 * In that case, the step function may need to explicitly {@linkplain #dropArguments drop all preceding loop variables}.
6544 * This will require mentioning their types, in an expression like {@code dropArguments(step, 0, V0.class, ...)}.
6545 * <li>Loop variables are not required to vary; they can be loop invariant. A clause can create
6546 * a loop invariant by a suitable init function with no step, pred, or fini function. This may be
6547 * useful to "wire" an incoming loop argument into the step or pred function of an adjacent loop variable.
6548 * <li>If some of the clause functions are virtual methods on an instance, the instance
6549 * itself can be conveniently placed in an initial invariant loop "variable", using an initial clause
6550 * like {@code new MethodHandle[]{identity(ObjType.class)}}. In that case, the instance reference
6551 * will be the first iteration variable value, and it will be easy to use virtual
6552 * methods as clause parts, since all of them will take a leading instance reference matching that value.
6553 * </ul>
6554 * <p>
6555 * Here is pseudocode for the resulting loop handle. As above, {@code V} and {@code v} represent the types
6556 * and values of loop variables; {@code A} and {@code a} represent arguments passed to the whole loop;
6557 * and {@code R} is the common result type of all finalizers as well as of the resulting loop.
6558 * {@snippet lang="java" :
6559 * V... init...(A...);
6560 * boolean pred...(V..., A...);
6561 * V... step...(V..., A...);
6562 * R fini...(V..., A...);
6563 * R loop(A... a) {
6564 * V... v... = init...(a...);
6565 * for (;;) {
6566 * for ((v, p, s, f) in (v..., pred..., step..., fini...)) {
6567 * v = s(v..., a...);
6568 * if (!p(v..., a...)) {
6569 * return f(v..., a...);
6570 * }
6571 * }
6572 * }
6573 * }
6574 * }
6575 * Note that the parameter type lists {@code (V...)} and {@code (A...)} have been expanded
6576 * to their full length, even though individual clause functions may neglect to take them all.
6577 * As noted above, missing parameters are filled in as if by {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}.
6578 *
6579 * @apiNote Example:
6580 * {@snippet lang="java" :
6581 * // iterative implementation of the factorial function as a loop handle
6582 * static int one(int k) { return 1; }
6583 * static int inc(int i, int acc, int k) { return i + 1; }
6584 * static int mult(int i, int acc, int k) { return i * acc; }
6585 * static boolean pred(int i, int acc, int k) { return i < k; }
6586 * static int fin(int i, int acc, int k) { return acc; }
6587 * // assume MH_one, MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
6588 * // null initializer for counter, should initialize to 0
6589 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
6590 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
6591 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
6592 * assertEquals(120, loop.invoke(5));
6593 * }
6594 * The same example, dropping arguments and using combinators:
6595 * {@snippet lang="java" :
6596 * // simplified implementation of the factorial function as a loop handle
6597 * static int inc(int i) { return i + 1; } // drop acc, k
6598 * static int mult(int i, int acc) { return i * acc; } //drop k
6599 * static boolean cmp(int i, int k) { return i < k; }
6600 * // assume MH_inc, MH_mult, and MH_cmp are handles to the above methods
6601 * // null initializer for counter, should initialize to 0
6602 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
6603 * MethodHandle MH_pred = MethodHandles.dropArguments(MH_cmp, 1, int.class); // drop acc
6604 * MethodHandle MH_fin = MethodHandles.dropArguments(MethodHandles.identity(int.class), 0, int.class); // drop i
6605 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
6606 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
6607 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
6608 * assertEquals(720, loop.invoke(6));
6609 * }
6610 * A similar example, using a helper object to hold a loop parameter:
6611 * {@snippet lang="java" :
6612 * // instance-based implementation of the factorial function as a loop handle
6613 * static class FacLoop {
6614 * final int k;
6615 * FacLoop(int k) { this.k = k; }
6616 * int inc(int i) { return i + 1; }
6617 * int mult(int i, int acc) { return i * acc; }
6618 * boolean pred(int i) { return i < k; }
6619 * int fin(int i, int acc) { return acc; }
6620 * }
6621 * // assume MH_FacLoop is a handle to the constructor
6622 * // assume MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
6623 * // null initializer for counter, should initialize to 0
6624 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
6625 * MethodHandle[] instanceClause = new MethodHandle[]{MH_FacLoop};
6626 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
6627 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
6628 * MethodHandle loop = MethodHandles.loop(instanceClause, counterClause, accumulatorClause);
6629 * assertEquals(5040, loop.invoke(7));
6630 * }
6631 *
6632 * @param clauses an array of arrays (4-tuples) of {@link MethodHandle}s adhering to the rules described above.
6633 *
6634 * @return a method handle embodying the looping behavior as defined by the arguments.
6635 *
6636 * @throws IllegalArgumentException in case any of the constraints described above is violated.
6637 *
6638 * @see MethodHandles#whileLoop(MethodHandle, MethodHandle, MethodHandle)
6639 * @see MethodHandles#doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
6640 * @see MethodHandles#countedLoop(MethodHandle, MethodHandle, MethodHandle)
6641 * @see MethodHandles#iteratedLoop(MethodHandle, MethodHandle, MethodHandle)
6642 * @since 9
6643 */
6644 public static MethodHandle loop(MethodHandle[]... clauses) {
6645 // Step 0: determine clause structure.
6646 loopChecks0(clauses);
6647
6648 List<MethodHandle> init = new ArrayList<>();
6649 List<MethodHandle> step = new ArrayList<>();
6650 List<MethodHandle> pred = new ArrayList<>();
6651 List<MethodHandle> fini = new ArrayList<>();
6652
6653 Stream.of(clauses).filter(c -> Stream.of(c).anyMatch(Objects::nonNull)).forEach(clause -> {
6654 init.add(clause[0]); // all clauses have at least length 1
6655 step.add(clause.length <= 1 ? null : clause[1]);
6656 pred.add(clause.length <= 2 ? null : clause[2]);
6657 fini.add(clause.length <= 3 ? null : clause[3]);
6658 });
6659
6660 assert Stream.of(init, step, pred, fini).map(List::size).distinct().count() == 1;
6661 final int nclauses = init.size();
6662
6663 // Step 1A: determine iteration variables (V...).
6664 final List<Class<?>> iterationVariableTypes = new ArrayList<>();
6665 for (int i = 0; i < nclauses; ++i) {
6666 MethodHandle in = init.get(i);
6667 MethodHandle st = step.get(i);
6668 if (in == null && st == null) {
6669 iterationVariableTypes.add(void.class);
6670 } else if (in != null && st != null) {
6671 loopChecks1a(i, in, st);
6672 iterationVariableTypes.add(in.type().returnType());
6673 } else {
6674 iterationVariableTypes.add(in == null ? st.type().returnType() : in.type().returnType());
6675 }
6676 }
6677 final List<Class<?>> commonPrefix = iterationVariableTypes.stream().filter(t -> t != void.class).toList();
6678
6679 // Step 1B: determine loop parameters (A...).
6680 final List<Class<?>> commonSuffix = buildCommonSuffix(init, step, pred, fini, commonPrefix.size());
6681 loopChecks1b(init, commonSuffix);
6682
6683 // Step 1C: determine loop return type.
6684 // Step 1D: check other types.
6685 // local variable required here; see JDK-8223553
6686 Stream<Class<?>> cstream = fini.stream().filter(Objects::nonNull).map(MethodHandle::type)
6687 .map(MethodType::returnType);
6688 final Class<?> loopReturnType = cstream.findFirst().orElse(void.class);
6689 loopChecks1cd(pred, fini, loopReturnType);
6690
6691 // Step 2: determine parameter lists.
6692 final List<Class<?>> commonParameterSequence = new ArrayList<>(commonPrefix);
6693 commonParameterSequence.addAll(commonSuffix);
6694 loopChecks2(step, pred, fini, commonParameterSequence);
6695 // Step 3: fill in omitted functions.
6696 for (int i = 0; i < nclauses; ++i) {
6697 Class<?> t = iterationVariableTypes.get(i);
6698 if (init.get(i) == null) {
6699 init.set(i, empty(methodType(t, commonSuffix)));
6700 }
6701 if (step.get(i) == null) {
6702 step.set(i, dropArgumentsToMatch(identityOrVoid(t), 0, commonParameterSequence, i));
6703 }
6704 if (pred.get(i) == null) {
6705 pred.set(i, dropArguments(constant(boolean.class, true), 0, commonParameterSequence));
6706 }
6707 if (fini.get(i) == null) {
6708 fini.set(i, empty(methodType(t, commonParameterSequence)));
6709 }
6710 }
6711
6712 // Step 4: fill in missing parameter types.
6713 // Also convert all handles to fixed-arity handles.
6714 List<MethodHandle> finit = fixArities(fillParameterTypes(init, commonSuffix));
6715 List<MethodHandle> fstep = fixArities(fillParameterTypes(step, commonParameterSequence));
6716 List<MethodHandle> fpred = fixArities(fillParameterTypes(pred, commonParameterSequence));
6717 List<MethodHandle> ffini = fixArities(fillParameterTypes(fini, commonParameterSequence));
6718
6719 assert finit.stream().map(MethodHandle::type).map(MethodType::parameterList).
6720 allMatch(pl -> pl.equals(commonSuffix));
6721 assert Stream.of(fstep, fpred, ffini).flatMap(List::stream).map(MethodHandle::type).map(MethodType::parameterList).
6722 allMatch(pl -> pl.equals(commonParameterSequence));
6723
6724 return MethodHandleImpl.makeLoop(loopReturnType, commonSuffix, finit, fstep, fpred, ffini);
6725 }
6726
6727 private static void loopChecks0(MethodHandle[][] clauses) {
6728 if (clauses == null || clauses.length == 0) {
6729 throw newIllegalArgumentException("null or no clauses passed");
6730 }
6731 if (Stream.of(clauses).anyMatch(Objects::isNull)) {
6732 throw newIllegalArgumentException("null clauses are not allowed");
6733 }
6734 if (Stream.of(clauses).anyMatch(c -> c.length > 4)) {
6735 throw newIllegalArgumentException("All loop clauses must be represented as MethodHandle arrays with at most 4 elements.");
6736 }
6737 }
6738
6739 private static void loopChecks1a(int i, MethodHandle in, MethodHandle st) {
6740 if (in.type().returnType() != st.type().returnType()) {
6741 throw misMatchedTypes("clause " + i + ": init and step return types", in.type().returnType(),
6742 st.type().returnType());
6743 }
6744 }
6745
6746 private static List<Class<?>> longestParameterList(Stream<MethodHandle> mhs, int skipSize) {
6747 final List<Class<?>> empty = List.of();
6748 final List<Class<?>> longest = mhs.filter(Objects::nonNull).
6749 // take only those that can contribute to a common suffix because they are longer than the prefix
6750 map(MethodHandle::type).
6751 filter(t -> t.parameterCount() > skipSize).
6752 map(MethodType::parameterList).
6753 reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
6754 return longest.isEmpty() ? empty : longest.subList(skipSize, longest.size());
6755 }
6756
6757 private static List<Class<?>> longestParameterList(List<List<Class<?>>> lists) {
6758 final List<Class<?>> empty = List.of();
6759 return lists.stream().reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
6760 }
6761
6762 private static List<Class<?>> buildCommonSuffix(List<MethodHandle> init, List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, int cpSize) {
6763 final List<Class<?>> longest1 = longestParameterList(Stream.of(step, pred, fini).flatMap(List::stream), cpSize);
6764 final List<Class<?>> longest2 = longestParameterList(init.stream(), 0);
6765 return longestParameterList(List.of(longest1, longest2));
6766 }
6767
6768 private static void loopChecks1b(List<MethodHandle> init, List<Class<?>> commonSuffix) {
6769 if (init.stream().filter(Objects::nonNull).map(MethodHandle::type).
6770 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonSuffix))) {
6771 throw newIllegalArgumentException("found non-effectively identical init parameter type lists: " + init +
6772 " (common suffix: " + commonSuffix + ")");
6773 }
6774 }
6775
6776 private static void loopChecks1cd(List<MethodHandle> pred, List<MethodHandle> fini, Class<?> loopReturnType) {
6777 if (fini.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
6778 anyMatch(t -> t != loopReturnType)) {
6779 throw newIllegalArgumentException("found non-identical finalizer return types: " + fini + " (return type: " +
6780 loopReturnType + ")");
6781 }
6782
6783 if (pred.stream().noneMatch(Objects::nonNull)) {
6784 throw newIllegalArgumentException("no predicate found", pred);
6785 }
6786 if (pred.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
6787 anyMatch(t -> t != boolean.class)) {
6788 throw newIllegalArgumentException("predicates must have boolean return type", pred);
6789 }
6790 }
6791
6792 private static void loopChecks2(List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, List<Class<?>> commonParameterSequence) {
6793 if (Stream.of(step, pred, fini).flatMap(List::stream).filter(Objects::nonNull).map(MethodHandle::type).
6794 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonParameterSequence))) {
6795 throw newIllegalArgumentException("found non-effectively identical parameter type lists:\nstep: " + step +
6796 "\npred: " + pred + "\nfini: " + fini + " (common parameter sequence: " + commonParameterSequence + ")");
6797 }
6798 }
6799
6800 private static List<MethodHandle> fillParameterTypes(List<MethodHandle> hs, final List<Class<?>> targetParams) {
6801 return hs.stream().map(h -> {
6802 int pc = h.type().parameterCount();
6803 int tpsize = targetParams.size();
6804 return pc < tpsize ? dropArguments(h, pc, targetParams.subList(pc, tpsize)) : h;
6805 }).toList();
6806 }
6807
6808 private static List<MethodHandle> fixArities(List<MethodHandle> hs) {
6809 return hs.stream().map(MethodHandle::asFixedArity).toList();
6810 }
6811
6812 /**
6813 * Constructs a {@code while} loop from an initializer, a body, and a predicate.
6814 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
6815 * <p>
6816 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
6817 * method will, in each iteration, first evaluate the predicate and then execute its body (if the predicate
6818 * evaluates to {@code true}).
6819 * The loop will terminate once the predicate evaluates to {@code false} (the body will not be executed in this case).
6820 * <p>
6821 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
6822 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
6823 * and updated with the value returned from its invocation. The result of loop execution will be
6824 * the final value of the additional loop-local variable (if present).
6825 * <p>
6826 * The following rules hold for these argument handles:<ul>
6827 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
6828 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
6829 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
6830 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
6831 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
6832 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
6833 * It will constrain the parameter lists of the other loop parts.
6834 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
6835 * list {@code (A...)} is called the <em>external parameter list</em>.
6836 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
6837 * additional state variable of the loop.
6838 * The body must both accept and return a value of this type {@code V}.
6839 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
6840 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
6841 * <a href="MethodHandles.html#effid">effectively identical</a>
6842 * to the external parameter list {@code (A...)}.
6843 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
6844 * {@linkplain #empty default value}.
6845 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
6846 * Its parameter list (either empty or of the form {@code (V A*)}) must be
6847 * effectively identical to the internal parameter list.
6848 * </ul>
6849 * <p>
6850 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
6851 * <li>The loop handle's result type is the result type {@code V} of the body.
6852 * <li>The loop handle's parameter types are the types {@code (A...)},
6853 * from the external parameter list.
6854 * </ul>
6855 * <p>
6856 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
6857 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
6858 * passed to the loop.
6859 * {@snippet lang="java" :
6860 * V init(A...);
6861 * boolean pred(V, A...);
6862 * V body(V, A...);
6863 * V whileLoop(A... a...) {
6864 * V v = init(a...);
6865 * while (pred(v, a...)) {
6866 * v = body(v, a...);
6867 * }
6868 * return v;
6869 * }
6870 * }
6871 *
6872 * @apiNote Example:
6873 * {@snippet lang="java" :
6874 * // implement the zip function for lists as a loop handle
6875 * static List<String> initZip(Iterator<String> a, Iterator<String> b) { return new ArrayList<>(); }
6876 * static boolean zipPred(List<String> zip, Iterator<String> a, Iterator<String> b) { return a.hasNext() && b.hasNext(); }
6877 * static List<String> zipStep(List<String> zip, Iterator<String> a, Iterator<String> b) {
6878 * zip.add(a.next());
6879 * zip.add(b.next());
6880 * return zip;
6881 * }
6882 * // assume MH_initZip, MH_zipPred, and MH_zipStep are handles to the above methods
6883 * MethodHandle loop = MethodHandles.whileLoop(MH_initZip, MH_zipPred, MH_zipStep);
6884 * List<String> a = Arrays.asList("a", "b", "c", "d");
6885 * List<String> b = Arrays.asList("e", "f", "g", "h");
6886 * List<String> zipped = Arrays.asList("a", "e", "b", "f", "c", "g", "d", "h");
6887 * assertEquals(zipped, (List<String>) loop.invoke(a.iterator(), b.iterator()));
6888 * }
6889 *
6890 *
6891 * @apiNote The implementation of this method can be expressed as follows:
6892 * {@snippet lang="java" :
6893 * MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
6894 * MethodHandle fini = (body.type().returnType() == void.class
6895 * ? null : identity(body.type().returnType()));
6896 * MethodHandle[]
6897 * checkExit = { null, null, pred, fini },
6898 * varBody = { init, body };
6899 * return loop(checkExit, varBody);
6900 * }
6901 * }
6902 *
6903 * @param init optional initializer, providing the initial value of the loop variable.
6904 * May be {@code null}, implying a default initial value. See above for other constraints.
6905 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
6906 * above for other constraints.
6907 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
6908 * See above for other constraints.
6909 *
6910 * @return a method handle implementing the {@code while} loop as described by the arguments.
6911 * @throws IllegalArgumentException if the rules for the arguments are violated.
6912 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
6913 *
6914 * @see #loop(MethodHandle[][])
6915 * @see #doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
6916 * @since 9
6917 */
6918 public static MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
6919 whileLoopChecks(init, pred, body);
6920 MethodHandle fini = identityOrVoid(body.type().returnType());
6921 MethodHandle[] checkExit = { null, null, pred, fini };
6922 MethodHandle[] varBody = { init, body };
6923 return loop(checkExit, varBody);
6924 }
6925
6926 /**
6927 * Constructs a {@code do-while} loop from an initializer, a body, and a predicate.
6928 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
6929 * <p>
6930 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
6931 * method will, in each iteration, first execute its body and then evaluate the predicate.
6932 * The loop will terminate once the predicate evaluates to {@code false} after an execution of the body.
6933 * <p>
6934 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
6935 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
6936 * and updated with the value returned from its invocation. The result of loop execution will be
6937 * the final value of the additional loop-local variable (if present).
6938 * <p>
6939 * The following rules hold for these argument handles:<ul>
6940 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
6941 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
6942 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
6943 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
6944 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
6945 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
6946 * It will constrain the parameter lists of the other loop parts.
6947 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
6948 * list {@code (A...)} is called the <em>external parameter list</em>.
6949 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
6950 * additional state variable of the loop.
6951 * The body must both accept and return a value of this type {@code V}.
6952 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
6953 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
6954 * <a href="MethodHandles.html#effid">effectively identical</a>
6955 * to the external parameter list {@code (A...)}.
6956 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
6957 * {@linkplain #empty default value}.
6958 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
6959 * Its parameter list (either empty or of the form {@code (V A*)}) must be
6960 * effectively identical to the internal parameter list.
6961 * </ul>
6962 * <p>
6963 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
6964 * <li>The loop handle's result type is the result type {@code V} of the body.
6965 * <li>The loop handle's parameter types are the types {@code (A...)},
6966 * from the external parameter list.
6967 * </ul>
6968 * <p>
6969 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
6970 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
6971 * passed to the loop.
6972 * {@snippet lang="java" :
6973 * V init(A...);
6974 * boolean pred(V, A...);
6975 * V body(V, A...);
6976 * V doWhileLoop(A... a...) {
6977 * V v = init(a...);
6978 * do {
6979 * v = body(v, a...);
6980 * } while (pred(v, a...));
6981 * return v;
6982 * }
6983 * }
6984 *
6985 * @apiNote Example:
6986 * {@snippet lang="java" :
6987 * // int i = 0; while (i < limit) { ++i; } return i; => limit
6988 * static int zero(int limit) { return 0; }
6989 * static int step(int i, int limit) { return i + 1; }
6990 * static boolean pred(int i, int limit) { return i < limit; }
6991 * // assume MH_zero, MH_step, and MH_pred are handles to the above methods
6992 * MethodHandle loop = MethodHandles.doWhileLoop(MH_zero, MH_step, MH_pred);
6993 * assertEquals(23, loop.invoke(23));
6994 * }
6995 *
6996 *
6997 * @apiNote The implementation of this method can be expressed as follows:
6998 * {@snippet lang="java" :
6999 * MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
7000 * MethodHandle fini = (body.type().returnType() == void.class
7001 * ? null : identity(body.type().returnType()));
7002 * MethodHandle[] clause = { init, body, pred, fini };
7003 * return loop(clause);
7004 * }
7005 * }
7006 *
7007 * @param init optional initializer, providing the initial value of the loop variable.
7008 * May be {@code null}, implying a default initial value. See above for other constraints.
7009 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
7010 * See above for other constraints.
7011 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
7012 * above for other constraints.
7013 *
7014 * @return a method handle implementing the {@code while} loop as described by the arguments.
7015 * @throws IllegalArgumentException if the rules for the arguments are violated.
7016 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
7017 *
7018 * @see #loop(MethodHandle[][])
7019 * @see #whileLoop(MethodHandle, MethodHandle, MethodHandle)
7020 * @since 9
7021 */
7022 public static MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
7023 whileLoopChecks(init, pred, body);
7024 MethodHandle fini = identityOrVoid(body.type().returnType());
7025 MethodHandle[] clause = {init, body, pred, fini };
7026 return loop(clause);
7027 }
7028
7029 private static void whileLoopChecks(MethodHandle init, MethodHandle pred, MethodHandle body) {
7030 Objects.requireNonNull(pred);
7031 Objects.requireNonNull(body);
7032 MethodType bodyType = body.type();
7033 Class<?> returnType = bodyType.returnType();
7034 List<Class<?>> innerList = bodyType.parameterList();
7035 List<Class<?>> outerList = innerList;
7036 if (returnType == void.class) {
7037 // OK
7038 } else if (innerList.isEmpty() || innerList.get(0) != returnType) {
7039 // leading V argument missing => error
7040 MethodType expected = bodyType.insertParameterTypes(0, returnType);
7041 throw misMatchedTypes("body function", bodyType, expected);
7042 } else {
7043 outerList = innerList.subList(1, innerList.size());
7044 }
7045 MethodType predType = pred.type();
7046 if (predType.returnType() != boolean.class ||
7047 !predType.effectivelyIdenticalParameters(0, innerList)) {
7048 throw misMatchedTypes("loop predicate", predType, methodType(boolean.class, innerList));
7049 }
7050 if (init != null) {
7051 MethodType initType = init.type();
7052 if (initType.returnType() != returnType ||
7053 !initType.effectivelyIdenticalParameters(0, outerList)) {
7054 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
7055 }
7056 }
7057 }
7058
7059 /**
7060 * Constructs a loop that runs a given number of iterations.
7061 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
7062 * <p>
7063 * The number of iterations is determined by the {@code iterations} handle evaluation result.
7064 * The loop counter {@code i} is an extra loop iteration variable of type {@code int}.
7065 * It will be initialized to 0 and incremented by 1 in each iteration.
7066 * <p>
7067 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
7068 * of that type is also present. This variable is initialized using the optional {@code init} handle,
7069 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
7070 * <p>
7071 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
7072 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
7073 * iteration variable.
7074 * The result of the loop handle execution will be the final {@code V} value of that variable
7075 * (or {@code void} if there is no {@code V} variable).
7076 * <p>
7077 * The following rules hold for the argument handles:<ul>
7078 * <li>The {@code iterations} handle must not be {@code null}, and must return
7079 * the type {@code int}, referred to here as {@code I} in parameter type lists.
7080 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
7081 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
7082 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
7083 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
7084 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
7085 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
7086 * of types called the <em>internal parameter list</em>.
7087 * It will constrain the parameter lists of the other loop parts.
7088 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
7089 * with no additional {@code A} types, then the internal parameter list is extended by
7090 * the argument types {@code A...} of the {@code iterations} handle.
7091 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
7092 * list {@code (A...)} is called the <em>external parameter list</em>.
7093 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
7094 * additional state variable of the loop.
7095 * The body must both accept a leading parameter and return a value of this type {@code V}.
7096 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
7097 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
7098 * <a href="MethodHandles.html#effid">effectively identical</a>
7099 * to the external parameter list {@code (A...)}.
7100 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
7101 * {@linkplain #empty default value}.
7102 * <li>The parameter list of {@code iterations} (of some form {@code (A*)}) must be
7103 * effectively identical to the external parameter list {@code (A...)}.
7104 * </ul>
7105 * <p>
7106 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
7107 * <li>The loop handle's result type is the result type {@code V} of the body.
7108 * <li>The loop handle's parameter types are the types {@code (A...)},
7109 * from the external parameter list.
7110 * </ul>
7111 * <p>
7112 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
7113 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
7114 * arguments passed to the loop.
7115 * {@snippet lang="java" :
7116 * int iterations(A...);
7117 * V init(A...);
7118 * V body(V, int, A...);
7119 * V countedLoop(A... a...) {
7120 * int end = iterations(a...);
7121 * V v = init(a...);
7122 * for (int i = 0; i < end; ++i) {
7123 * v = body(v, i, a...);
7124 * }
7125 * return v;
7126 * }
7127 * }
7128 *
7129 * @apiNote Example with a fully conformant body method:
7130 * {@snippet lang="java" :
7131 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
7132 * // => a variation on a well known theme
7133 * static String step(String v, int counter, String init) { return "na " + v; }
7134 * // assume MH_step is a handle to the method above
7135 * MethodHandle fit13 = MethodHandles.constant(int.class, 13);
7136 * MethodHandle start = MethodHandles.identity(String.class);
7137 * MethodHandle loop = MethodHandles.countedLoop(fit13, start, MH_step);
7138 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("Lambdaman!"));
7139 * }
7140 *
7141 * @apiNote Example with the simplest possible body method type,
7142 * and passing the number of iterations to the loop invocation:
7143 * {@snippet lang="java" :
7144 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
7145 * // => a variation on a well known theme
7146 * static String step(String v, int counter ) { return "na " + v; }
7147 * // assume MH_step is a handle to the method above
7148 * MethodHandle count = MethodHandles.dropArguments(MethodHandles.identity(int.class), 1, String.class);
7149 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class);
7150 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i) -> "na " + v
7151 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "Lambdaman!"));
7152 * }
7153 *
7154 * @apiNote Example that treats the number of iterations, string to append to, and string to append
7155 * as loop parameters:
7156 * {@snippet lang="java" :
7157 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
7158 * // => a variation on a well known theme
7159 * static String step(String v, int counter, int iterations_, String pre, String start_) { return pre + " " + v; }
7160 * // assume MH_step is a handle to the method above
7161 * MethodHandle count = MethodHandles.identity(int.class);
7162 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class, String.class);
7163 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i, _, pre, _) -> pre + " " + v
7164 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "na", "Lambdaman!"));
7165 * }
7166 *
7167 * @apiNote Example that illustrates the usage of {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}
7168 * to enforce a loop type:
7169 * {@snippet lang="java" :
7170 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
7171 * // => a variation on a well known theme
7172 * static String step(String v, int counter, String pre) { return pre + " " + v; }
7173 * // assume MH_step is a handle to the method above
7174 * MethodType loopType = methodType(String.class, String.class, int.class, String.class);
7175 * MethodHandle count = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(int.class), 0, loopType.parameterList(), 1);
7176 * MethodHandle start = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(String.class), 0, loopType.parameterList(), 2);
7177 * MethodHandle body = MethodHandles.dropArgumentsToMatch(MH_step, 2, loopType.parameterList(), 0);
7178 * MethodHandle loop = MethodHandles.countedLoop(count, start, body); // (v, i, pre, _, _) -> pre + " " + v
7179 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("na", 13, "Lambdaman!"));
7180 * }
7181 *
7182 * @apiNote The implementation of this method can be expressed as follows:
7183 * {@snippet lang="java" :
7184 * MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
7185 * return countedLoop(empty(iterations.type()), iterations, init, body);
7186 * }
7187 * }
7188 *
7189 * @param iterations a non-{@code null} handle to return the number of iterations this loop should run. The handle's
7190 * result type must be {@code int}. See above for other constraints.
7191 * @param init optional initializer, providing the initial value of the loop variable.
7192 * May be {@code null}, implying a default initial value. See above for other constraints.
7193 * @param body body of the loop, which may not be {@code null}.
7194 * It controls the loop parameters and result type in the standard case (see above for details).
7195 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
7196 * and may accept any number of additional types.
7197 * See above for other constraints.
7198 *
7199 * @return a method handle representing the loop.
7200 * @throws NullPointerException if either of the {@code iterations} or {@code body} handles is {@code null}.
7201 * @throws IllegalArgumentException if any argument violates the rules formulated above.
7202 *
7203 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle, MethodHandle)
7204 * @since 9
7205 */
7206 public static MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
7207 return countedLoop(empty(iterations.type()), iterations, init, body);
7208 }
7209
7210 /**
7211 * Constructs a loop that counts over a range of numbers.
7212 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
7213 * <p>
7214 * The loop counter {@code i} is a loop iteration variable of type {@code int}.
7215 * The {@code start} and {@code end} handles determine the start (inclusive) and end (exclusive)
7216 * values of the loop counter.
7217 * The loop counter will be initialized to the {@code int} value returned from the evaluation of the
7218 * {@code start} handle and run to the value returned from {@code end} (exclusively) with a step width of 1.
7219 * <p>
7220 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
7221 * of that type is also present. This variable is initialized using the optional {@code init} handle,
7222 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
7223 * <p>
7224 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
7225 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
7226 * iteration variable.
7227 * The result of the loop handle execution will be the final {@code V} value of that variable
7228 * (or {@code void} if there is no {@code V} variable).
7229 * <p>
7230 * The following rules hold for the argument handles:<ul>
7231 * <li>The {@code start} and {@code end} handles must not be {@code null}, and must both return
7232 * the common type {@code int}, referred to here as {@code I} in parameter type lists.
7233 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
7234 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
7235 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
7236 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
7237 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
7238 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
7239 * of types called the <em>internal parameter list</em>.
7240 * It will constrain the parameter lists of the other loop parts.
7241 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
7242 * with no additional {@code A} types, then the internal parameter list is extended by
7243 * the argument types {@code A...} of the {@code end} handle.
7244 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
7245 * list {@code (A...)} is called the <em>external parameter list</em>.
7246 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
7247 * additional state variable of the loop.
7248 * The body must both accept a leading parameter and return a value of this type {@code V}.
7249 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
7250 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
7251 * <a href="MethodHandles.html#effid">effectively identical</a>
7252 * to the external parameter list {@code (A...)}.
7253 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
7254 * {@linkplain #empty default value}.
7255 * <li>The parameter list of {@code start} (of some form {@code (A*)}) must be
7256 * effectively identical to the external parameter list {@code (A...)}.
7257 * <li>Likewise, the parameter list of {@code end} must be effectively identical
7258 * to the external parameter list.
7259 * </ul>
7260 * <p>
7261 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
7262 * <li>The loop handle's result type is the result type {@code V} of the body.
7263 * <li>The loop handle's parameter types are the types {@code (A...)},
7264 * from the external parameter list.
7265 * </ul>
7266 * <p>
7267 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
7268 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
7269 * arguments passed to the loop.
7270 * {@snippet lang="java" :
7271 * int start(A...);
7272 * int end(A...);
7273 * V init(A...);
7274 * V body(V, int, A...);
7275 * V countedLoop(A... a...) {
7276 * int e = end(a...);
7277 * int s = start(a...);
7278 * V v = init(a...);
7279 * for (int i = s; i < e; ++i) {
7280 * v = body(v, i, a...);
7281 * }
7282 * return v;
7283 * }
7284 * }
7285 *
7286 * @apiNote The implementation of this method can be expressed as follows:
7287 * {@snippet lang="java" :
7288 * MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
7289 * MethodHandle returnVar = dropArguments(identity(init.type().returnType()), 0, int.class, int.class);
7290 * // assume MH_increment and MH_predicate are handles to implementation-internal methods with
7291 * // the following semantics:
7292 * // MH_increment: (int limit, int counter) -> counter + 1
7293 * // MH_predicate: (int limit, int counter) -> counter < limit
7294 * Class<?> counterType = start.type().returnType(); // int
7295 * Class<?> returnType = body.type().returnType();
7296 * MethodHandle incr = MH_increment, pred = MH_predicate, retv = null;
7297 * if (returnType != void.class) { // ignore the V variable
7298 * incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
7299 * pred = dropArguments(pred, 1, returnType); // ditto
7300 * retv = dropArguments(identity(returnType), 0, counterType); // ignore limit
7301 * }
7302 * body = dropArguments(body, 0, counterType); // ignore the limit variable
7303 * MethodHandle[]
7304 * loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
7305 * bodyClause = { init, body }, // v = init(); v = body(v, i)
7306 * indexVar = { start, incr }; // i = start(); i = i + 1
7307 * return loop(loopLimit, bodyClause, indexVar);
7308 * }
7309 * }
7310 *
7311 * @param start a non-{@code null} handle to return the start value of the loop counter, which must be {@code int}.
7312 * See above for other constraints.
7313 * @param end a non-{@code null} handle to return the end value of the loop counter (the loop will run to
7314 * {@code end-1}). The result type must be {@code int}. See above for other constraints.
7315 * @param init optional initializer, providing the initial value of the loop variable.
7316 * May be {@code null}, implying a default initial value. See above for other constraints.
7317 * @param body body of the loop, which may not be {@code null}.
7318 * It controls the loop parameters and result type in the standard case (see above for details).
7319 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
7320 * and may accept any number of additional types.
7321 * See above for other constraints.
7322 *
7323 * @return a method handle representing the loop.
7324 * @throws NullPointerException if any of the {@code start}, {@code end}, or {@code body} handles is {@code null}.
7325 * @throws IllegalArgumentException if any argument violates the rules formulated above.
7326 *
7327 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle)
7328 * @since 9
7329 */
7330 public static MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
7331 countedLoopChecks(start, end, init, body);
7332 Class<?> counterType = start.type().returnType(); // int, but who's counting?
7333 Class<?> limitType = end.type().returnType(); // yes, int again
7334 Class<?> returnType = body.type().returnType();
7335 MethodHandle incr = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopStep);
7336 MethodHandle pred = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopPred);
7337 MethodHandle retv = null;
7338 if (returnType != void.class) {
7339 incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
7340 pred = dropArguments(pred, 1, returnType); // ditto
7341 retv = dropArguments(identity(returnType), 0, counterType);
7342 }
7343 body = dropArguments(body, 0, counterType); // ignore the limit variable
7344 MethodHandle[]
7345 loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
7346 bodyClause = { init, body }, // v = init(); v = body(v, i)
7347 indexVar = { start, incr }; // i = start(); i = i + 1
7348 return loop(loopLimit, bodyClause, indexVar);
7349 }
7350
7351 private static void countedLoopChecks(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
7352 Objects.requireNonNull(start);
7353 Objects.requireNonNull(end);
7354 Objects.requireNonNull(body);
7355 Class<?> counterType = start.type().returnType();
7356 if (counterType != int.class) {
7357 MethodType expected = start.type().changeReturnType(int.class);
7358 throw misMatchedTypes("start function", start.type(), expected);
7359 } else if (end.type().returnType() != counterType) {
7360 MethodType expected = end.type().changeReturnType(counterType);
7361 throw misMatchedTypes("end function", end.type(), expected);
7362 }
7363 MethodType bodyType = body.type();
7364 Class<?> returnType = bodyType.returnType();
7365 List<Class<?>> innerList = bodyType.parameterList();
7366 // strip leading V value if present
7367 int vsize = (returnType == void.class ? 0 : 1);
7368 if (vsize != 0 && (innerList.isEmpty() || innerList.get(0) != returnType)) {
7369 // argument list has no "V" => error
7370 MethodType expected = bodyType.insertParameterTypes(0, returnType);
7371 throw misMatchedTypes("body function", bodyType, expected);
7372 } else if (innerList.size() <= vsize || innerList.get(vsize) != counterType) {
7373 // missing I type => error
7374 MethodType expected = bodyType.insertParameterTypes(vsize, counterType);
7375 throw misMatchedTypes("body function", bodyType, expected);
7376 }
7377 List<Class<?>> outerList = innerList.subList(vsize + 1, innerList.size());
7378 if (outerList.isEmpty()) {
7379 // special case; take lists from end handle
7380 outerList = end.type().parameterList();
7381 innerList = bodyType.insertParameterTypes(vsize + 1, outerList).parameterList();
7382 }
7383 MethodType expected = methodType(counterType, outerList);
7384 if (!start.type().effectivelyIdenticalParameters(0, outerList)) {
7385 throw misMatchedTypes("start parameter types", start.type(), expected);
7386 }
7387 if (end.type() != start.type() &&
7388 !end.type().effectivelyIdenticalParameters(0, outerList)) {
7389 throw misMatchedTypes("end parameter types", end.type(), expected);
7390 }
7391 if (init != null) {
7392 MethodType initType = init.type();
7393 if (initType.returnType() != returnType ||
7394 !initType.effectivelyIdenticalParameters(0, outerList)) {
7395 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
7396 }
7397 }
7398 }
7399
7400 /**
7401 * Constructs a loop that ranges over the values produced by an {@code Iterator<T>}.
7402 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
7403 * <p>
7404 * The iterator itself will be determined by the evaluation of the {@code iterator} handle.
7405 * Each value it produces will be stored in a loop iteration variable of type {@code T}.
7406 * <p>
7407 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
7408 * of that type is also present. This variable is initialized using the optional {@code init} handle,
7409 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
7410 * <p>
7411 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
7412 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
7413 * iteration variable.
7414 * The result of the loop handle execution will be the final {@code V} value of that variable
7415 * (or {@code void} if there is no {@code V} variable).
7416 * <p>
7417 * The following rules hold for the argument handles:<ul>
7418 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
7419 * {@code (V T A...)V}, where {@code V} is non-{@code void}, or else {@code (T A...)void}.
7420 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
7421 * and we will write {@code (V T A...)V} with the understanding that a {@code void} type {@code V}
7422 * is quietly dropped from the parameter list, leaving {@code (T A...)V}.)
7423 * <li>The parameter list {@code (V T A...)} of the body contributes to a list
7424 * of types called the <em>internal parameter list</em>.
7425 * It will constrain the parameter lists of the other loop parts.
7426 * <li>As a special case, if the body contributes only {@code V} and {@code T} types,
7427 * with no additional {@code A} types, then the internal parameter list is extended by
7428 * the argument types {@code A...} of the {@code iterator} handle; if it is {@code null} the
7429 * single type {@code Iterable} is added and constitutes the {@code A...} list.
7430 * <li>If the iteration variable types {@code (V T)} are dropped from the internal parameter list, the resulting shorter
7431 * list {@code (A...)} is called the <em>external parameter list</em>.
7432 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
7433 * additional state variable of the loop.
7434 * The body must both accept a leading parameter and return a value of this type {@code V}.
7435 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
7436 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
7437 * <a href="MethodHandles.html#effid">effectively identical</a>
7438 * to the external parameter list {@code (A...)}.
7439 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
7440 * {@linkplain #empty default value}.
7441 * <li>If the {@code iterator} handle is non-{@code null}, it must have the return
7442 * type {@code java.util.Iterator} or a subtype thereof.
7443 * The iterator it produces when the loop is executed will be assumed
7444 * to yield values which can be converted to type {@code T}.
7445 * <li>The parameter list of an {@code iterator} that is non-{@code null} (of some form {@code (A*)}) must be
7446 * effectively identical to the external parameter list {@code (A...)}.
7447 * <li>If {@code iterator} is {@code null} it defaults to a method handle which behaves
7448 * like {@link java.lang.Iterable#iterator()}. In that case, the internal parameter list
7449 * {@code (V T A...)} must have at least one {@code A} type, and the default iterator
7450 * handle parameter is adjusted to accept the leading {@code A} type, as if by
7451 * the {@link MethodHandle#asType asType} conversion method.
7452 * The leading {@code A} type must be {@code Iterable} or a subtype thereof.
7453 * This conversion step, done at loop construction time, must not throw a {@code WrongMethodTypeException}.
7454 * </ul>
7455 * <p>
7456 * The type {@code T} may be either a primitive or reference.
7457 * Since type {@code Iterator<T>} is erased in the method handle representation to the raw type {@code Iterator},
7458 * the {@code iteratedLoop} combinator adjusts the leading argument type for {@code body} to {@code Object}
7459 * as if by the {@link MethodHandle#asType asType} conversion method.
7460 * Therefore, if an iterator of the wrong type appears as the loop is executed, runtime exceptions may occur
7461 * as the result of dynamic conversions performed by {@link MethodHandle#asType(MethodType)}.
7462 * <p>
7463 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
7464 * <li>The loop handle's result type is the result type {@code V} of the body.
7465 * <li>The loop handle's parameter types are the types {@code (A...)},
7466 * from the external parameter list.
7467 * </ul>
7468 * <p>
7469 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
7470 * the loop variable as well as the result type of the loop; {@code T}/{@code t}, that of the elements of the
7471 * structure the loop iterates over, and {@code A...}/{@code a...} represent arguments passed to the loop.
7472 * {@snippet lang="java" :
7473 * Iterator<T> iterator(A...); // defaults to Iterable::iterator
7474 * V init(A...);
7475 * V body(V,T,A...);
7476 * V iteratedLoop(A... a...) {
7477 * Iterator<T> it = iterator(a...);
7478 * V v = init(a...);
7479 * while (it.hasNext()) {
7480 * T t = it.next();
7481 * v = body(v, t, a...);
7482 * }
7483 * return v;
7484 * }
7485 * }
7486 *
7487 * @apiNote Example:
7488 * {@snippet lang="java" :
7489 * // get an iterator from a list
7490 * static List<String> reverseStep(List<String> r, String e) {
7491 * r.add(0, e);
7492 * return r;
7493 * }
7494 * static List<String> newArrayList() { return new ArrayList<>(); }
7495 * // assume MH_reverseStep and MH_newArrayList are handles to the above methods
7496 * MethodHandle loop = MethodHandles.iteratedLoop(null, MH_newArrayList, MH_reverseStep);
7497 * List<String> list = Arrays.asList("a", "b", "c", "d", "e");
7498 * List<String> reversedList = Arrays.asList("e", "d", "c", "b", "a");
7499 * assertEquals(reversedList, (List<String>) loop.invoke(list));
7500 * }
7501 *
7502 * @apiNote The implementation of this method can be expressed approximately as follows:
7503 * {@snippet lang="java" :
7504 * MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
7505 * // assume MH_next, MH_hasNext, MH_startIter are handles to methods of Iterator/Iterable
7506 * Class<?> returnType = body.type().returnType();
7507 * Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
7508 * MethodHandle nextVal = MH_next.asType(MH_next.type().changeReturnType(ttype));
7509 * MethodHandle retv = null, step = body, startIter = iterator;
7510 * if (returnType != void.class) {
7511 * // the simple thing first: in (I V A...), drop the I to get V
7512 * retv = dropArguments(identity(returnType), 0, Iterator.class);
7513 * // body type signature (V T A...), internal loop types (I V A...)
7514 * step = swapArguments(body, 0, 1); // swap V <-> T
7515 * }
7516 * if (startIter == null) startIter = MH_getIter;
7517 * MethodHandle[]
7518 * iterVar = { startIter, null, MH_hasNext, retv }, // it = iterator; while (it.hasNext())
7519 * bodyClause = { init, filterArguments(step, 0, nextVal) }; // v = body(v, t, a)
7520 * return loop(iterVar, bodyClause);
7521 * }
7522 * }
7523 *
7524 * @param iterator an optional handle to return the iterator to start the loop.
7525 * If non-{@code null}, the handle must return {@link java.util.Iterator} or a subtype.
7526 * See above for other constraints.
7527 * @param init optional initializer, providing the initial value of the loop variable.
7528 * May be {@code null}, implying a default initial value. See above for other constraints.
7529 * @param body body of the loop, which may not be {@code null}.
7530 * It controls the loop parameters and result type in the standard case (see above for details).
7531 * It must accept its own return type (if non-void) plus a {@code T} parameter (for the iterated values),
7532 * and may accept any number of additional types.
7533 * See above for other constraints.
7534 *
7535 * @return a method handle embodying the iteration loop functionality.
7536 * @throws NullPointerException if the {@code body} handle is {@code null}.
7537 * @throws IllegalArgumentException if any argument violates the above requirements.
7538 *
7539 * @since 9
7540 */
7541 public static MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
7542 Class<?> iterableType = iteratedLoopChecks(iterator, init, body);
7543 Class<?> returnType = body.type().returnType();
7544 MethodHandle hasNext = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iteratePred);
7545 MethodHandle nextRaw = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iterateNext);
7546 MethodHandle startIter;
7547 MethodHandle nextVal;
7548 {
7549 MethodType iteratorType;
7550 if (iterator == null) {
7551 // derive argument type from body, if available, else use Iterable
7552 startIter = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_initIterator);
7553 iteratorType = startIter.type().changeParameterType(0, iterableType);
7554 } else {
7555 // force return type to the internal iterator class
7556 iteratorType = iterator.type().changeReturnType(Iterator.class);
7557 startIter = iterator;
7558 }
7559 Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
7560 MethodType nextValType = nextRaw.type().changeReturnType(ttype);
7561
7562 // perform the asType transforms under an exception transformer, as per spec.:
7563 try {
7564 startIter = startIter.asType(iteratorType);
7565 nextVal = nextRaw.asType(nextValType);
7566 } catch (WrongMethodTypeException ex) {
7567 throw new IllegalArgumentException(ex);
7568 }
7569 }
7570
7571 MethodHandle retv = null, step = body;
7572 if (returnType != void.class) {
7573 // the simple thing first: in (I V A...), drop the I to get V
7574 retv = dropArguments(identity(returnType), 0, Iterator.class);
7575 // body type signature (V T A...), internal loop types (I V A...)
7576 step = swapArguments(body, 0, 1); // swap V <-> T
7577 }
7578
7579 MethodHandle[]
7580 iterVar = { startIter, null, hasNext, retv },
7581 bodyClause = { init, filterArgument(step, 0, nextVal) };
7582 return loop(iterVar, bodyClause);
7583 }
7584
7585 private static Class<?> iteratedLoopChecks(MethodHandle iterator, MethodHandle init, MethodHandle body) {
7586 Objects.requireNonNull(body);
7587 MethodType bodyType = body.type();
7588 Class<?> returnType = bodyType.returnType();
7589 List<Class<?>> internalParamList = bodyType.parameterList();
7590 // strip leading V value if present
7591 int vsize = (returnType == void.class ? 0 : 1);
7592 if (vsize != 0 && (internalParamList.isEmpty() || internalParamList.get(0) != returnType)) {
7593 // argument list has no "V" => error
7594 MethodType expected = bodyType.insertParameterTypes(0, returnType);
7595 throw misMatchedTypes("body function", bodyType, expected);
7596 } else if (internalParamList.size() <= vsize) {
7597 // missing T type => error
7598 MethodType expected = bodyType.insertParameterTypes(vsize, Object.class);
7599 throw misMatchedTypes("body function", bodyType, expected);
7600 }
7601 List<Class<?>> externalParamList = internalParamList.subList(vsize + 1, internalParamList.size());
7602 Class<?> iterableType = null;
7603 if (iterator != null) {
7604 // special case; if the body handle only declares V and T then
7605 // the external parameter list is obtained from iterator handle
7606 if (externalParamList.isEmpty()) {
7607 externalParamList = iterator.type().parameterList();
7608 }
7609 MethodType itype = iterator.type();
7610 if (!Iterator.class.isAssignableFrom(itype.returnType())) {
7611 throw newIllegalArgumentException("iteratedLoop first argument must have Iterator return type");
7612 }
7613 if (!itype.effectivelyIdenticalParameters(0, externalParamList)) {
7614 MethodType expected = methodType(itype.returnType(), externalParamList);
7615 throw misMatchedTypes("iterator parameters", itype, expected);
7616 }
7617 } else {
7618 if (externalParamList.isEmpty()) {
7619 // special case; if the iterator handle is null and the body handle
7620 // only declares V and T then the external parameter list consists
7621 // of Iterable
7622 externalParamList = List.of(Iterable.class);
7623 iterableType = Iterable.class;
7624 } else {
7625 // special case; if the iterator handle is null and the external
7626 // parameter list is not empty then the first parameter must be
7627 // assignable to Iterable
7628 iterableType = externalParamList.get(0);
7629 if (!Iterable.class.isAssignableFrom(iterableType)) {
7630 throw newIllegalArgumentException(
7631 "inferred first loop argument must inherit from Iterable: " + iterableType);
7632 }
7633 }
7634 }
7635 if (init != null) {
7636 MethodType initType = init.type();
7637 if (initType.returnType() != returnType ||
7638 !initType.effectivelyIdenticalParameters(0, externalParamList)) {
7639 throw misMatchedTypes("loop initializer", initType, methodType(returnType, externalParamList));
7640 }
7641 }
7642 return iterableType; // help the caller a bit
7643 }
7644
7645 /*non-public*/
7646 static MethodHandle swapArguments(MethodHandle mh, int i, int j) {
7647 // there should be a better way to uncross my wires
7648 int arity = mh.type().parameterCount();
7649 int[] order = new int[arity];
7650 for (int k = 0; k < arity; k++) order[k] = k;
7651 order[i] = j; order[j] = i;
7652 Class<?>[] types = mh.type().parameterArray();
7653 Class<?> ti = types[i]; types[i] = types[j]; types[j] = ti;
7654 MethodType swapType = methodType(mh.type().returnType(), types);
7655 return permuteArguments(mh, swapType, order);
7656 }
7657
7658 /**
7659 * Makes a method handle that adapts a {@code target} method handle by wrapping it in a {@code try-finally} block.
7660 * Another method handle, {@code cleanup}, represents the functionality of the {@code finally} block. Any exception
7661 * thrown during the execution of the {@code target} handle will be passed to the {@code cleanup} handle. The
7662 * exception will be rethrown, unless {@code cleanup} handle throws an exception first. The
7663 * value returned from the {@code cleanup} handle's execution will be the result of the execution of the
7664 * {@code try-finally} handle.
7665 * <p>
7666 * The {@code cleanup} handle will be passed one or two additional leading arguments.
7667 * The first is the exception thrown during the
7668 * execution of the {@code target} handle, or {@code null} if no exception was thrown.
7669 * The second is the result of the execution of the {@code target} handle, or, if it throws an exception,
7670 * a {@code null}, zero, or {@code false} value of the required type is supplied as a placeholder.
7671 * The second argument is not present if the {@code target} handle has a {@code void} return type.
7672 * (Note that, except for argument type conversions, combinators represent {@code void} values in parameter lists
7673 * by omitting the corresponding paradoxical arguments, not by inserting {@code null} or zero values.)
7674 * <p>
7675 * The {@code target} and {@code cleanup} handles must have the same corresponding argument and return types, except
7676 * that the {@code cleanup} handle may omit trailing arguments. Also, the {@code cleanup} handle must have one or
7677 * two extra leading parameters:<ul>
7678 * <li>a {@code Throwable}, which will carry the exception thrown by the {@code target} handle (if any); and
7679 * <li>a parameter of the same type as the return type of both {@code target} and {@code cleanup}, which will carry
7680 * the result from the execution of the {@code target} handle.
7681 * This parameter is not present if the {@code target} returns {@code void}.
7682 * </ul>
7683 * <p>
7684 * The pseudocode for the resulting adapter looks as follows. In the code, {@code V} represents the result type of
7685 * the {@code try/finally} construct; {@code A}/{@code a}, the types and values of arguments to the resulting
7686 * handle consumed by the cleanup; and {@code B}/{@code b}, those of arguments to the resulting handle discarded by
7687 * the cleanup.
7688 * {@snippet lang="java" :
7689 * V target(A..., B...);
7690 * V cleanup(Throwable, V, A...);
7691 * V adapter(A... a, B... b) {
7692 * V result = (zero value for V);
7693 * Throwable throwable = null;
7694 * try {
7695 * result = target(a..., b...);
7696 * } catch (Throwable t) {
7697 * throwable = t;
7698 * throw t;
7699 * } finally {
7700 * result = cleanup(throwable, result, a...);
7701 * }
7702 * return result;
7703 * }
7704 * }
7705 * <p>
7706 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
7707 * be modified by execution of the target, and so are passed unchanged
7708 * from the caller to the cleanup, if it is invoked.
7709 * <p>
7710 * The target and cleanup must return the same type, even if the cleanup
7711 * always throws.
7712 * To create such a throwing cleanup, compose the cleanup logic
7713 * with {@link #throwException throwException},
7714 * in order to create a method handle of the correct return type.
7715 * <p>
7716 * Note that {@code tryFinally} never converts exceptions into normal returns.
7717 * In rare cases where exceptions must be converted in that way, first wrap
7718 * the target with {@link #catchException(MethodHandle, Class, MethodHandle)}
7719 * to capture an outgoing exception, and then wrap with {@code tryFinally}.
7720 * <p>
7721 * It is recommended that the first parameter type of {@code cleanup} be
7722 * declared {@code Throwable} rather than a narrower subtype. This ensures
7723 * {@code cleanup} will always be invoked with whatever exception that
7724 * {@code target} throws. Declaring a narrower type may result in a
7725 * {@code ClassCastException} being thrown by the {@code try-finally}
7726 * handle if the type of the exception thrown by {@code target} is not
7727 * assignable to the first parameter type of {@code cleanup}. Note that
7728 * various exception types of {@code VirtualMachineError},
7729 * {@code LinkageError}, and {@code RuntimeException} can in principle be
7730 * thrown by almost any kind of Java code, and a finally clause that
7731 * catches (say) only {@code IOException} would mask any of the others
7732 * behind a {@code ClassCastException}.
7733 *
7734 * @param target the handle whose execution is to be wrapped in a {@code try} block.
7735 * @param cleanup the handle that is invoked in the finally block.
7736 *
7737 * @return a method handle embodying the {@code try-finally} block composed of the two arguments.
7738 * @throws NullPointerException if any argument is null
7739 * @throws IllegalArgumentException if {@code cleanup} does not accept
7740 * the required leading arguments, or if the method handle types do
7741 * not match in their return types and their
7742 * corresponding trailing parameters
7743 *
7744 * @see MethodHandles#catchException(MethodHandle, Class, MethodHandle)
7745 * @since 9
7746 */
7747 public static MethodHandle tryFinally(MethodHandle target, MethodHandle cleanup) {
7748 Class<?>[] targetParamTypes = target.type().ptypes();
7749 Class<?> rtype = target.type().returnType();
7750
7751 tryFinallyChecks(target, cleanup);
7752
7753 // Match parameter lists: if the cleanup has a shorter parameter list than the target, add ignored arguments.
7754 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
7755 // target parameter list.
7756 cleanup = dropArgumentsToMatch(cleanup, (rtype == void.class ? 1 : 2), targetParamTypes, 0, false);
7757
7758 // Ensure that the intrinsic type checks the instance thrown by the
7759 // target against the first parameter of cleanup
7760 cleanup = cleanup.asType(cleanup.type().changeParameterType(0, Throwable.class));
7761
7762 // Use asFixedArity() to avoid unnecessary boxing of last argument for VarargsCollector case.
7763 return MethodHandleImpl.makeTryFinally(target.asFixedArity(), cleanup.asFixedArity(), rtype, targetParamTypes);
7764 }
7765
7766 private static void tryFinallyChecks(MethodHandle target, MethodHandle cleanup) {
7767 Class<?> rtype = target.type().returnType();
7768 if (rtype != cleanup.type().returnType()) {
7769 throw misMatchedTypes("target and return types", cleanup.type().returnType(), rtype);
7770 }
7771 MethodType cleanupType = cleanup.type();
7772 if (!Throwable.class.isAssignableFrom(cleanupType.parameterType(0))) {
7773 throw misMatchedTypes("cleanup first argument and Throwable", cleanup.type(), Throwable.class);
7774 }
7775 if (rtype != void.class && cleanupType.parameterType(1) != rtype) {
7776 throw misMatchedTypes("cleanup second argument and target return type", cleanup.type(), rtype);
7777 }
7778 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
7779 // target parameter list.
7780 int cleanupArgIndex = rtype == void.class ? 1 : 2;
7781 if (!cleanupType.effectivelyIdenticalParameters(cleanupArgIndex, target.type().parameterList())) {
7782 throw misMatchedTypes("cleanup parameters after (Throwable,result) and target parameter list prefix",
7783 cleanup.type(), target.type());
7784 }
7785 }
7786
7787 /**
7788 * Creates a table switch method handle, which can be used to switch over a set of target
7789 * method handles, based on a given target index, called selector.
7790 * <p>
7791 * For a selector value of {@code n}, where {@code n} falls in the range {@code [0, N)},
7792 * and where {@code N} is the number of target method handles, the table switch method
7793 * handle will invoke the n-th target method handle from the list of target method handles.
7794 * <p>
7795 * For a selector value that does not fall in the range {@code [0, N)}, the table switch
7796 * method handle will invoke the given fallback method handle.
7797 * <p>
7798 * All method handles passed to this method must have the same type, with the additional
7799 * requirement that the leading parameter be of type {@code int}. The leading parameter
7800 * represents the selector.
7801 * <p>
7802 * Any trailing parameters present in the type will appear on the returned table switch
7803 * method handle as well. Any arguments assigned to these parameters will be forwarded,
7804 * together with the selector value, to the selected method handle when invoking it.
7805 *
7806 * @apiNote Example:
7807 * The cases each drop the {@code selector} value they are given, and take an additional
7808 * {@code String} argument, which is concatenated (using {@link String#concat(String)})
7809 * to a specific constant label string for each case:
7810 * {@snippet lang="java" :
7811 * MethodHandles.Lookup lookup = MethodHandles.lookup();
7812 * MethodHandle caseMh = lookup.findVirtual(String.class, "concat",
7813 * MethodType.methodType(String.class, String.class));
7814 * caseMh = MethodHandles.dropArguments(caseMh, 0, int.class);
7815 *
7816 * MethodHandle caseDefault = MethodHandles.insertArguments(caseMh, 1, "default: ");
7817 * MethodHandle case0 = MethodHandles.insertArguments(caseMh, 1, "case 0: ");
7818 * MethodHandle case1 = MethodHandles.insertArguments(caseMh, 1, "case 1: ");
7819 *
7820 * MethodHandle mhSwitch = MethodHandles.tableSwitch(
7821 * caseDefault,
7822 * case0,
7823 * case1
7824 * );
7825 *
7826 * assertEquals("default: data", (String) mhSwitch.invokeExact(-1, "data"));
7827 * assertEquals("case 0: data", (String) mhSwitch.invokeExact(0, "data"));
7828 * assertEquals("case 1: data", (String) mhSwitch.invokeExact(1, "data"));
7829 * assertEquals("default: data", (String) mhSwitch.invokeExact(2, "data"));
7830 * }
7831 *
7832 * @param fallback the fallback method handle that is called when the selector is not
7833 * within the range {@code [0, N)}.
7834 * @param targets array of target method handles.
7835 * @return the table switch method handle.
7836 * @throws NullPointerException if {@code fallback}, the {@code targets} array, or any
7837 * any of the elements of the {@code targets} array are
7838 * {@code null}.
7839 * @throws IllegalArgumentException if the {@code targets} array is empty, if the leading
7840 * parameter of the fallback handle or any of the target
7841 * handles is not {@code int}, or if the types of
7842 * the fallback handle and all of target handles are
7843 * not the same.
7844 */
7845 public static MethodHandle tableSwitch(MethodHandle fallback, MethodHandle... targets) {
7846 Objects.requireNonNull(fallback);
7847 Objects.requireNonNull(targets);
7848 targets = targets.clone();
7849 MethodType type = tableSwitchChecks(fallback, targets);
7850 return MethodHandleImpl.makeTableSwitch(type, fallback, targets);
7851 }
7852
7853 private static MethodType tableSwitchChecks(MethodHandle defaultCase, MethodHandle[] caseActions) {
7854 if (caseActions.length == 0)
7855 throw new IllegalArgumentException("Not enough cases: " + Arrays.toString(caseActions));
7856
7857 MethodType expectedType = defaultCase.type();
7858
7859 if (!(expectedType.parameterCount() >= 1) || expectedType.parameterType(0) != int.class)
7860 throw new IllegalArgumentException(
7861 "Case actions must have int as leading parameter: " + Arrays.toString(caseActions));
7862
7863 for (MethodHandle mh : caseActions) {
7864 Objects.requireNonNull(mh);
7865 if (mh.type() != expectedType)
7866 throw new IllegalArgumentException(
7867 "Case actions must have the same type: " + Arrays.toString(caseActions));
7868 }
7869
7870 return expectedType;
7871 }
7872
7873 /**
7874 * Creates a var handle object, which can be used to dereference a {@linkplain java.lang.foreign.MemorySegment memory segment}
7875 * by viewing its contents as a sequence of the provided value layout.
7876 *
7877 * <p>The provided layout specifies the {@linkplain ValueLayout#carrier() carrier type},
7878 * the {@linkplain ValueLayout#byteSize() byte size},
7879 * the {@linkplain ValueLayout#byteAlignment() byte alignment} and the {@linkplain ValueLayout#order() byte order}
7880 * associated with the returned var handle.
7881 *
7882 * <p>The returned var handle's type is {@code carrier} and the list of coordinate types is
7883 * {@code (MemorySegment, long)}, where the {@code long} coordinate type corresponds to byte offset into
7884 * a given memory segment. The returned var handle accesses bytes at an offset in a given
7885 * memory segment, composing bytes to or from a value of the type {@code carrier} according to the given endianness;
7886 * the alignment constraint (in bytes) for the resulting var handle is given by {@code alignmentBytes}.
7887 *
7888 * <p>As an example, consider the memory layout expressed by a {@link GroupLayout} instance constructed as follows:
7889 * {@snippet lang="java" :
7890 * GroupLayout seq = java.lang.foreign.MemoryLayout.structLayout(
7891 * MemoryLayout.paddingLayout(32),
7892 * ValueLayout.JAVA_INT.withOrder(ByteOrder.BIG_ENDIAN).withName("value")
7893 * );
7894 * }
7895 * To access the member layout named {@code value}, we can construct a memory segment view var handle as follows:
7896 * {@snippet lang="java" :
7897 * VarHandle handle = MethodHandles.memorySegmentViewVarHandle(ValueLayout.JAVA_INT.withOrder(ByteOrder.BIG_ENDIAN)); //(MemorySegment, long) -> int
7898 * handle = MethodHandles.insertCoordinates(handle, 1, 4); //(MemorySegment) -> int
7899 * }
7900 *
7901 * @apiNote The resulting var handle features certain <i>access mode restrictions</i>,
7902 * which are common to all memory segment view var handles. A memory segment view var handle is associated
7903 * with an access size {@code S} and an alignment constraint {@code B}
7904 * (both expressed in bytes). We say that a memory access operation is <em>fully aligned</em> if it occurs
7905 * at a memory address {@code A} which is compatible with both alignment constraints {@code S} and {@code B}.
7906 * If access is fully aligned then following access modes are supported and are
7907 * guaranteed to support atomic access:
7908 * <ul>
7909 * <li>read write access modes for all {@code T}, with the exception of
7910 * access modes {@code get} and {@code set} for {@code long} and
7911 * {@code double} on 32-bit platforms.
7912 * <li>atomic update access modes for {@code int}, {@code long},
7913 * {@code float}, {@code double} or {@link MemorySegment}.
7914 * (Future major platform releases of the JDK may support additional
7915 * types for certain currently unsupported access modes.)
7916 * <li>numeric atomic update access modes for {@code int}, {@code long} and {@link MemorySegment}.
7917 * (Future major platform releases of the JDK may support additional
7918 * numeric types for certain currently unsupported access modes.)
7919 * <li>bitwise atomic update access modes for {@code int}, {@code long} and {@link MemorySegment}.
7920 * (Future major platform releases of the JDK may support additional
7921 * numeric types for certain currently unsupported access modes.)
7922 * </ul>
7923 *
7924 * If {@code T} is {@code float}, {@code double} or {@link MemorySegment} then atomic
7925 * update access modes compare values using their bitwise representation
7926 * (see {@link Float#floatToRawIntBits},
7927 * {@link Double#doubleToRawLongBits} and {@link MemorySegment#address()}, respectively).
7928 * <p>
7929 * Alternatively, a memory access operation is <em>partially aligned</em> if it occurs at a memory address {@code A}
7930 * which is only compatible with the alignment constraint {@code B}; in such cases, access for anything other than the
7931 * {@code get} and {@code set} access modes will result in an {@code IllegalStateException}. If access is partially aligned,
7932 * atomic access is only guaranteed with respect to the largest power of two that divides the GCD of {@code A} and {@code S}.
7933 * <p>
7934 * In all other cases, we say that a memory access operation is <em>misaligned</em>; in such cases an
7935 * {@code IllegalStateException} is thrown, irrespective of the access mode being used.
7936 * <p>
7937 * Finally, if {@code T} is {@code MemorySegment} all write access modes throw {@link IllegalArgumentException}
7938 * unless the value to be written is a {@linkplain MemorySegment#isNative() native} memory segment.
7939 *
7940 * @param layout the value layout for which a memory access handle is to be obtained.
7941 * @return the new memory segment view var handle.
7942 * @throws IllegalArgumentException if an illegal carrier type is used, or if {@code alignmentBytes} is not a power of two.
7943 * @throws NullPointerException if {@code layout} is {@code null}.
7944 * @see MemoryLayout#varHandle(MemoryLayout.PathElement...)
7945 * @since 19
7946 */
7947 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN)
7948 public static VarHandle memorySegmentViewVarHandle(ValueLayout layout) {
7949 Objects.requireNonNull(layout);
7950 return Utils.makeSegmentViewVarHandle(layout);
7951 }
7952
7953 /**
7954 * Adapts a target var handle by pre-processing incoming and outgoing values using a pair of filter functions.
7955 * <p>
7956 * When calling e.g. {@link VarHandle#set(Object...)} on the resulting var handle, the incoming value (of type {@code T}, where
7957 * {@code T} is the <em>last</em> parameter type of the first filter function) is processed using the first filter and then passed
7958 * to the target var handle.
7959 * Conversely, when calling e.g. {@link VarHandle#get(Object...)} on the resulting var handle, the return value obtained from
7960 * the target var handle (of type {@code T}, where {@code T} is the <em>last</em> parameter type of the second filter function)
7961 * is processed using the second filter and returned to the caller. More advanced access mode types, such as
7962 * {@link VarHandle.AccessMode#COMPARE_AND_EXCHANGE} might apply both filters at the same time.
7963 * <p>
7964 * For the boxing and unboxing filters to be well-formed, their types must be of the form {@code (A... , S) -> T} and
7965 * {@code (A... , T) -> S}, respectively, where {@code T} is the type of the target var handle. If this is the case,
7966 * the resulting var handle will have type {@code S} and will feature the additional coordinates {@code A...} (which
7967 * will be appended to the coordinates of the target var handle).
7968 * <p>
7969 * If the boxing and unboxing filters throw any checked exceptions when invoked, the resulting var handle will
7970 * throw an {@link IllegalStateException}.
7971 * <p>
7972 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
7973 * atomic access guarantees as those featured by the target var handle.
7974 *
7975 * @param target the target var handle
7976 * @param filterToTarget a filter to convert some type {@code S} into the type of {@code target}
7977 * @param filterFromTarget a filter to convert the type of {@code target} to some type {@code S}
7978 * @return an adapter var handle which accepts a new type, performing the provided boxing/unboxing conversions.
7979 * @throws IllegalArgumentException if {@code filterFromTarget} and {@code filterToTarget} are not well-formed, that is, they have types
7980 * other than {@code (A... , S) -> T} and {@code (A... , T) -> S}, respectively, where {@code T} is the type of the target var handle,
7981 * or if it's determined that either {@code filterFromTarget} or {@code filterToTarget} throws any checked exceptions.
7982 * @throws NullPointerException if any of the arguments is {@code null}.
7983 * @since 19
7984 */
7985 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN)
7986 public static VarHandle filterValue(VarHandle target, MethodHandle filterToTarget, MethodHandle filterFromTarget) {
7987 return VarHandles.filterValue(target, filterToTarget, filterFromTarget);
7988 }
7989
7990 /**
7991 * Adapts a target var handle by pre-processing incoming coordinate values using unary filter functions.
7992 * <p>
7993 * When calling e.g. {@link VarHandle#get(Object...)} on the resulting var handle, the incoming coordinate values
7994 * starting at position {@code pos} (of type {@code C1, C2 ... Cn}, where {@code C1, C2 ... Cn} are the return types
7995 * of the unary filter functions) are transformed into new values (of type {@code S1, S2 ... Sn}, where {@code S1, S2 ... Sn} are the
7996 * parameter types of the unary filter functions), and then passed (along with any coordinate that was left unaltered
7997 * by the adaptation) to the target var handle.
7998 * <p>
7999 * For the coordinate filters to be well-formed, their types must be of the form {@code S1 -> T1, S2 -> T1 ... Sn -> Tn},
8000 * where {@code T1, T2 ... Tn} are the coordinate types starting at position {@code pos} of the target var handle.
8001 * <p>
8002 * If any of the filters throws a checked exception when invoked, the resulting var handle will
8003 * throw an {@link IllegalStateException}.
8004 * <p>
8005 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
8006 * atomic access guarantees as those featured by the target var handle.
8007 *
8008 * @param target the target var handle
8009 * @param pos the position of the first coordinate to be transformed
8010 * @param filters the unary functions which are used to transform coordinates starting at position {@code pos}
8011 * @return an adapter var handle which accepts new coordinate types, applying the provided transformation
8012 * to the new coordinate values.
8013 * @throws IllegalArgumentException if the handles in {@code filters} are not well-formed, that is, they have types
8014 * other than {@code S1 -> T1, S2 -> T2, ... Sn -> Tn} where {@code T1, T2 ... Tn} are the coordinate types starting
8015 * at position {@code pos} of the target var handle, if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive,
8016 * or if more filters are provided than the actual number of coordinate types available starting at {@code pos},
8017 * or if it's determined that any of the filters throws any checked exceptions.
8018 * @throws NullPointerException if any of the arguments is {@code null} or {@code filters} contains {@code null}.
8019 * @since 19
8020 */
8021 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN)
8022 public static VarHandle filterCoordinates(VarHandle target, int pos, MethodHandle... filters) {
8023 return VarHandles.filterCoordinates(target, pos, filters);
8024 }
8025
8026 /**
8027 * Provides a target var handle with one or more <em>bound coordinates</em>
8028 * in advance of the var handle's invocation. As a consequence, the resulting var handle will feature less
8029 * coordinate types than the target var handle.
8030 * <p>
8031 * When calling e.g. {@link VarHandle#get(Object...)} on the resulting var handle, incoming coordinate values
8032 * are joined with bound coordinate values, and then passed to the target var handle.
8033 * <p>
8034 * For the bound coordinates to be well-formed, their types must be {@code T1, T2 ... Tn },
8035 * where {@code T1, T2 ... Tn} are the coordinate types starting at position {@code pos} of the target var handle.
8036 * <p>
8037 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
8038 * atomic access guarantees as those featured by the target var handle.
8039 *
8040 * @param target the var handle to invoke after the bound coordinates are inserted
8041 * @param pos the position of the first coordinate to be inserted
8042 * @param values the series of bound coordinates to insert
8043 * @return an adapter var handle which inserts additional coordinates,
8044 * before calling the target var handle
8045 * @throws IllegalArgumentException if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive,
8046 * or if more values are provided than the actual number of coordinate types available starting at {@code pos}.
8047 * @throws ClassCastException if the bound coordinates in {@code values} are not well-formed, that is, they have types
8048 * other than {@code T1, T2 ... Tn }, where {@code T1, T2 ... Tn} are the coordinate types starting at position {@code pos}
8049 * of the target var handle.
8050 * @throws NullPointerException if any of the arguments is {@code null} or {@code values} contains {@code null}.
8051 * @since 19
8052 */
8053 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN)
8054 public static VarHandle insertCoordinates(VarHandle target, int pos, Object... values) {
8055 return VarHandles.insertCoordinates(target, pos, values);
8056 }
8057
8058 /**
8059 * Provides a var handle which adapts the coordinate values of the target var handle, by re-arranging them
8060 * so that the new coordinates match the provided ones.
8061 * <p>
8062 * The given array controls the reordering.
8063 * Call {@code #I} the number of incoming coordinates (the value
8064 * {@code newCoordinates.size()}), and call {@code #O} the number
8065 * of outgoing coordinates (the number of coordinates associated with the target var handle).
8066 * Then the length of the reordering array must be {@code #O},
8067 * and each element must be a non-negative number less than {@code #I}.
8068 * For every {@code N} less than {@code #O}, the {@code N}-th
8069 * outgoing coordinate will be taken from the {@code I}-th incoming
8070 * coordinate, where {@code I} is {@code reorder[N]}.
8071 * <p>
8072 * No coordinate value conversions are applied.
8073 * The type of each incoming coordinate, as determined by {@code newCoordinates},
8074 * must be identical to the type of the corresponding outgoing coordinate
8075 * in the target var handle.
8076 * <p>
8077 * The reordering array need not specify an actual permutation.
8078 * An incoming coordinate will be duplicated if its index appears
8079 * more than once in the array, and an incoming coordinate will be dropped
8080 * if its index does not appear in the array.
8081 * <p>
8082 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
8083 * atomic access guarantees as those featured by the target var handle.
8084 * @param target the var handle to invoke after the coordinates have been reordered
8085 * @param newCoordinates the new coordinate types
8086 * @param reorder an index array which controls the reordering
8087 * @return an adapter var handle which re-arranges the incoming coordinate values,
8088 * before calling the target var handle
8089 * @throws IllegalArgumentException if the index array length is not equal to
8090 * the number of coordinates of the target var handle, or if any index array element is not a valid index for
8091 * a coordinate of {@code newCoordinates}, or if two corresponding coordinate types in
8092 * the target var handle and in {@code newCoordinates} are not identical.
8093 * @throws NullPointerException if any of the arguments is {@code null} or {@code newCoordinates} contains {@code null}.
8094 * @since 19
8095 */
8096 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN)
8097 public static VarHandle permuteCoordinates(VarHandle target, List<Class<?>> newCoordinates, int... reorder) {
8098 return VarHandles.permuteCoordinates(target, newCoordinates, reorder);
8099 }
8100
8101 /**
8102 * Adapts a target var handle by pre-processing
8103 * a sub-sequence of its coordinate values with a filter (a method handle).
8104 * The pre-processed coordinates are replaced by the result (if any) of the
8105 * filter function and the target var handle is then called on the modified (usually shortened)
8106 * coordinate list.
8107 * <p>
8108 * If {@code R} is the return type of the filter (which cannot be void), the target var handle must accept a value of
8109 * type {@code R} as its coordinate in position {@code pos}, preceded and/or followed by
8110 * any coordinate not passed to the filter.
8111 * No coordinates are reordered, and the result returned from the filter
8112 * replaces (in order) the whole subsequence of coordinates originally
8113 * passed to the adapter.
8114 * <p>
8115 * The argument types (if any) of the filter
8116 * replace zero or one coordinate types of the target var handle, at position {@code pos},
8117 * in the resulting adapted var handle.
8118 * The return type of the filter must be identical to the
8119 * coordinate type of the target var handle at position {@code pos}, and that target var handle
8120 * coordinate is supplied by the return value of the filter.
8121 * <p>
8122 * If any of the filters throws a checked exception when invoked, the resulting var handle will
8123 * throw an {@link IllegalStateException}.
8124 * <p>
8125 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
8126 * atomic access guarantees as those featured by the target var handle.
8127 *
8128 * @param target the var handle to invoke after the coordinates have been filtered
8129 * @param pos the position of the coordinate to be filtered
8130 * @param filter the filter method handle
8131 * @return an adapter var handle which filters the incoming coordinate values,
8132 * before calling the target var handle
8133 * @throws IllegalArgumentException if the return type of {@code filter}
8134 * is void, or it is not the same as the {@code pos} coordinate of the target var handle,
8135 * if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive,
8136 * if the resulting var handle's type would have <a href="MethodHandle.html#maxarity">too many coordinates</a>,
8137 * or if it's determined that {@code filter} throws any checked exceptions.
8138 * @throws NullPointerException if any of the arguments is {@code null}.
8139 * @since 19
8140 */
8141 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN)
8142 public static VarHandle collectCoordinates(VarHandle target, int pos, MethodHandle filter) {
8143 return VarHandles.collectCoordinates(target, pos, filter);
8144 }
8145
8146 /**
8147 * Returns a var handle which will discard some dummy coordinates before delegating to the
8148 * target var handle. As a consequence, the resulting var handle will feature more
8149 * coordinate types than the target var handle.
8150 * <p>
8151 * The {@code pos} argument may range between zero and <i>N</i>, where <i>N</i> is the arity of the
8152 * target var handle's coordinate types. If {@code pos} is zero, the dummy coordinates will precede
8153 * the target's real arguments; if {@code pos} is <i>N</i> they will come after.
8154 * <p>
8155 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
8156 * atomic access guarantees as those featured by the target var handle.
8157 *
8158 * @param target the var handle to invoke after the dummy coordinates are dropped
8159 * @param pos position of the first coordinate to drop (zero for the leftmost)
8160 * @param valueTypes the type(s) of the coordinate(s) to drop
8161 * @return an adapter var handle which drops some dummy coordinates,
8162 * before calling the target var handle
8163 * @throws IllegalArgumentException if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive.
8164 * @throws NullPointerException if any of the arguments is {@code null} or {@code valueTypes} contains {@code null}.
8165 * @since 19
8166 */
8167 @PreviewFeature(feature=PreviewFeature.Feature.FOREIGN)
8168 public static VarHandle dropCoordinates(VarHandle target, int pos, Class<?>... valueTypes) {
8169 return VarHandles.dropCoordinates(target, pos, valueTypes);
8170 }
8171 }