1 /*
2 * Copyright (c) 2008, 2024, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package java.lang.invoke;
27
28 import jdk.internal.access.SharedSecrets;
29 import jdk.internal.misc.Unsafe;
30 import jdk.internal.misc.VM;
31 import jdk.internal.reflect.CallerSensitive;
32 import jdk.internal.reflect.CallerSensitiveAdapter;
33 import jdk.internal.reflect.Reflection;
34 import jdk.internal.util.ClassFileDumper;
35 import jdk.internal.vm.annotation.ForceInline;
36 import sun.invoke.util.ValueConversions;
37 import sun.invoke.util.VerifyAccess;
38 import sun.invoke.util.Wrapper;
39 import sun.reflect.misc.ReflectUtil;
40 import sun.security.util.SecurityConstants;
41
42 import java.lang.classfile.ClassModel;
43 import java.lang.constant.ConstantDescs;
44 import java.lang.invoke.LambdaForm.BasicType;
45 import java.lang.invoke.MethodHandleImpl.Intrinsic;
46 import java.lang.reflect.Constructor;
47 import java.lang.reflect.Field;
48 import java.lang.reflect.Member;
49 import java.lang.reflect.Method;
50 import java.lang.reflect.Modifier;
51 import java.nio.ByteOrder;
52 import java.security.ProtectionDomain;
53 import java.util.ArrayList;
54 import java.util.Arrays;
55 import java.util.BitSet;
56 import java.util.Comparator;
57 import java.util.Iterator;
58 import java.util.List;
59 import java.util.Objects;
60 import java.util.Set;
61 import java.util.concurrent.ConcurrentHashMap;
62 import java.util.stream.Stream;
63
64 import static java.lang.classfile.ClassFile.*;
65 import static java.lang.invoke.LambdaForm.BasicType.V_TYPE;
66 import static java.lang.invoke.MethodHandleNatives.Constants.*;
67 import static java.lang.invoke.MethodHandleStatics.UNSAFE;
68 import static java.lang.invoke.MethodHandleStatics.newIllegalArgumentException;
69 import static java.lang.invoke.MethodHandleStatics.newInternalError;
70 import static java.lang.invoke.MethodType.methodType;
71
72 /**
73 * This class consists exclusively of static methods that operate on or return
74 * method handles. They fall into several categories:
75 * <ul>
76 * <li>Lookup methods which help create method handles for methods and fields.
77 * <li>Combinator methods, which combine or transform pre-existing method handles into new ones.
78 * <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns.
79 * </ul>
80 * A lookup, combinator, or factory method will fail and throw an
81 * {@code IllegalArgumentException} if the created method handle's type
82 * would have <a href="MethodHandle.html#maxarity">too many parameters</a>.
83 *
84 * @author John Rose, JSR 292 EG
85 * @since 1.7
86 */
87 public class MethodHandles {
88
89 private MethodHandles() { } // do not instantiate
90
91 static final MemberName.Factory IMPL_NAMES = MemberName.getFactory();
92
93 // See IMPL_LOOKUP below.
94
95 //--- Method handle creation from ordinary methods.
96
97 /**
98 * Returns a {@link Lookup lookup object} with
99 * full capabilities to emulate all supported bytecode behaviors of the caller.
100 * These capabilities include {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access} to the caller.
101 * Factory methods on the lookup object can create
102 * <a href="MethodHandleInfo.html#directmh">direct method handles</a>
103 * for any member that the caller has access to via bytecodes,
104 * including protected and private fields and methods.
105 * This lookup object is created by the original lookup class
106 * and has the {@link Lookup#ORIGINAL ORIGINAL} bit set.
107 * This lookup object is a <em>capability</em> which may be delegated to trusted agents.
108 * Do not store it in place where untrusted code can access it.
109 * <p>
110 * This method is caller sensitive, which means that it may return different
111 * values to different callers.
112 * In cases where {@code MethodHandles.lookup} is called from a context where
113 * there is no caller frame on the stack (e.g. when called directly
114 * from a JNI attached thread), {@code IllegalCallerException} is thrown.
115 * To obtain a {@link Lookup lookup object} in such a context, use an auxiliary class that will
116 * implicitly be identified as the caller, or use {@link MethodHandles#publicLookup()}
117 * to obtain a low-privileged lookup instead.
118 * @return a lookup object for the caller of this method, with
119 * {@linkplain Lookup#ORIGINAL original} and
120 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access}.
121 * @throws IllegalCallerException if there is no caller frame on the stack.
122 */
123 @CallerSensitive
124 @ForceInline // to ensure Reflection.getCallerClass optimization
125 public static Lookup lookup() {
126 final Class<?> c = Reflection.getCallerClass();
127 if (c == null) {
128 throw new IllegalCallerException("no caller frame");
129 }
130 return new Lookup(c);
131 }
132
133 /**
134 * This lookup method is the alternate implementation of
135 * the lookup method with a leading caller class argument which is
136 * non-caller-sensitive. This method is only invoked by reflection
137 * and method handle.
138 */
139 @CallerSensitiveAdapter
140 private static Lookup lookup(Class<?> caller) {
141 if (caller.getClassLoader() == null) {
142 throw newInternalError("calling lookup() reflectively is not supported: "+caller);
143 }
144 return new Lookup(caller);
145 }
146
147 /**
148 * Returns a {@link Lookup lookup object} which is trusted minimally.
149 * The lookup has the {@code UNCONDITIONAL} mode.
150 * It can only be used to create method handles to public members of
151 * public classes in packages that are exported unconditionally.
152 * <p>
153 * As a matter of pure convention, the {@linkplain Lookup#lookupClass() lookup class}
154 * of this lookup object will be {@link java.lang.Object}.
155 *
156 * @apiNote The use of Object is conventional, and because the lookup modes are
157 * limited, there is no special access provided to the internals of Object, its package
158 * or its module. This public lookup object or other lookup object with
159 * {@code UNCONDITIONAL} mode assumes readability. Consequently, the lookup class
160 * is not used to determine the lookup context.
161 *
162 * <p style="font-size:smaller;">
163 * <em>Discussion:</em>
164 * The lookup class can be changed to any other class {@code C} using an expression of the form
165 * {@link Lookup#in publicLookup().in(C.class)}.
166 * A public lookup object is always subject to
167 * <a href="MethodHandles.Lookup.html#secmgr">security manager checks</a>.
168 * Also, it cannot access
169 * <a href="MethodHandles.Lookup.html#callsens">caller sensitive methods</a>.
170 * @return a lookup object which is trusted minimally
171 */
172 public static Lookup publicLookup() {
173 return Lookup.PUBLIC_LOOKUP;
174 }
175
176 /**
177 * Returns a {@link Lookup lookup} object on a target class to emulate all supported
178 * bytecode behaviors, including <a href="MethodHandles.Lookup.html#privacc">private access</a>.
179 * The returned lookup object can provide access to classes in modules and packages,
180 * and members of those classes, outside the normal rules of Java access control,
181 * instead conforming to the more permissive rules for modular <em>deep reflection</em>.
182 * <p>
183 * A caller, specified as a {@code Lookup} object, in module {@code M1} is
184 * allowed to do deep reflection on module {@code M2} and package of the target class
185 * if and only if all of the following conditions are {@code true}:
186 * <ul>
187 * <li>If there is a security manager, its {@code checkPermission} method is
188 * called to check {@code ReflectPermission("suppressAccessChecks")} and
189 * that must return normally.
190 * <li>The caller lookup object must have {@linkplain Lookup#hasFullPrivilegeAccess()
191 * full privilege access}. Specifically:
192 * <ul>
193 * <li>The caller lookup object must have the {@link Lookup#MODULE MODULE} lookup mode.
194 * (This is because otherwise there would be no way to ensure the original lookup
195 * creator was a member of any particular module, and so any subsequent checks
196 * for readability and qualified exports would become ineffective.)
197 * <li>The caller lookup object must have {@link Lookup#PRIVATE PRIVATE} access.
198 * (This is because an application intending to share intra-module access
199 * using {@link Lookup#MODULE MODULE} alone will inadvertently also share
200 * deep reflection to its own module.)
201 * </ul>
202 * <li>The target class must be a proper class, not a primitive or array class.
203 * (Thus, {@code M2} is well-defined.)
204 * <li>If the caller module {@code M1} differs from
205 * the target module {@code M2} then both of the following must be true:
206 * <ul>
207 * <li>{@code M1} {@link Module#canRead reads} {@code M2}.</li>
208 * <li>{@code M2} {@link Module#isOpen(String,Module) opens} the package
209 * containing the target class to at least {@code M1}.</li>
210 * </ul>
211 * </ul>
212 * <p>
213 * If any of the above checks is violated, this method fails with an
214 * exception.
215 * <p>
216 * Otherwise, if {@code M1} and {@code M2} are the same module, this method
217 * returns a {@code Lookup} on {@code targetClass} with
218 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access}
219 * with {@code null} previous lookup class.
220 * <p>
221 * Otherwise, {@code M1} and {@code M2} are two different modules. This method
222 * returns a {@code Lookup} on {@code targetClass} that records
223 * the lookup class of the caller as the new previous lookup class with
224 * {@code PRIVATE} access but no {@code MODULE} access.
225 * <p>
226 * The resulting {@code Lookup} object has no {@code ORIGINAL} access.
227 *
228 * @apiNote The {@code Lookup} object returned by this method is allowed to
229 * {@linkplain Lookup#defineClass(byte[]) define classes} in the runtime package
230 * of {@code targetClass}. Extreme caution should be taken when opening a package
231 * to another module as such defined classes have the same full privilege
232 * access as other members in {@code targetClass}'s module.
233 *
234 * @param targetClass the target class
235 * @param caller the caller lookup object
236 * @return a lookup object for the target class, with private access
237 * @throws IllegalArgumentException if {@code targetClass} is a primitive type or void or array class
238 * @throws NullPointerException if {@code targetClass} or {@code caller} is {@code null}
239 * @throws SecurityException if denied by the security manager
240 * @throws IllegalAccessException if any of the other access checks specified above fails
241 * @since 9
242 * @see Lookup#dropLookupMode
243 * @see <a href="MethodHandles.Lookup.html#cross-module-lookup">Cross-module lookups</a>
244 */
245 public static Lookup privateLookupIn(Class<?> targetClass, Lookup caller) throws IllegalAccessException {
246 if (caller.allowedModes == Lookup.TRUSTED) {
247 return new Lookup(targetClass);
248 }
249
250 @SuppressWarnings("removal")
251 SecurityManager sm = System.getSecurityManager();
252 if (sm != null) sm.checkPermission(SecurityConstants.ACCESS_PERMISSION);
253 if (targetClass.isPrimitive())
254 throw new IllegalArgumentException(targetClass + " is a primitive class");
255 if (targetClass.isArray())
256 throw new IllegalArgumentException(targetClass + " is an array class");
257 // Ensure that we can reason accurately about private and module access.
258 int requireAccess = Lookup.PRIVATE|Lookup.MODULE;
259 if ((caller.lookupModes() & requireAccess) != requireAccess)
260 throw new IllegalAccessException("caller does not have PRIVATE and MODULE lookup mode");
261
262 // previous lookup class is never set if it has MODULE access
263 assert caller.previousLookupClass() == null;
264
265 Class<?> callerClass = caller.lookupClass();
266 Module callerModule = callerClass.getModule(); // M1
267 Module targetModule = targetClass.getModule(); // M2
268 Class<?> newPreviousClass = null;
269 int newModes = Lookup.FULL_POWER_MODES & ~Lookup.ORIGINAL;
270
271 if (targetModule != callerModule) {
272 if (!callerModule.canRead(targetModule))
273 throw new IllegalAccessException(callerModule + " does not read " + targetModule);
274 if (targetModule.isNamed()) {
275 String pn = targetClass.getPackageName();
276 assert !pn.isEmpty() : "unnamed package cannot be in named module";
277 if (!targetModule.isOpen(pn, callerModule))
278 throw new IllegalAccessException(targetModule + " does not open " + pn + " to " + callerModule);
279 }
280
281 // M2 != M1, set previous lookup class to M1 and drop MODULE access
282 newPreviousClass = callerClass;
283 newModes &= ~Lookup.MODULE;
284 }
285 return Lookup.newLookup(targetClass, newPreviousClass, newModes);
286 }
287
288 /**
289 * Returns the <em>class data</em> associated with the lookup class
290 * of the given {@code caller} lookup object, or {@code null}.
291 *
292 * <p> A hidden class with class data can be created by calling
293 * {@link Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...)
294 * Lookup::defineHiddenClassWithClassData}.
295 * This method will cause the static class initializer of the lookup
296 * class of the given {@code caller} lookup object be executed if
297 * it has not been initialized.
298 *
299 * <p> A hidden class created by {@link Lookup#defineHiddenClass(byte[], boolean, Lookup.ClassOption...)
300 * Lookup::defineHiddenClass} and non-hidden classes have no class data.
301 * {@code null} is returned if this method is called on the lookup object
302 * on these classes.
303 *
304 * <p> The {@linkplain Lookup#lookupModes() lookup modes} for this lookup
305 * must have {@linkplain Lookup#ORIGINAL original access}
306 * in order to retrieve the class data.
307 *
308 * @apiNote
309 * This method can be called as a bootstrap method for a dynamically computed
310 * constant. A framework can create a hidden class with class data, for
311 * example that can be {@code Class} or {@code MethodHandle} object.
312 * The class data is accessible only to the lookup object
313 * created by the original caller but inaccessible to other members
314 * in the same nest. If a framework passes security sensitive objects
315 * to a hidden class via class data, it is recommended to load the value
316 * of class data as a dynamically computed constant instead of storing
317 * the class data in private static field(s) which are accessible to
318 * other nestmates.
319 *
320 * @param <T> the type to cast the class data object to
321 * @param caller the lookup context describing the class performing the
322 * operation (normally stacked by the JVM)
323 * @param name must be {@link ConstantDescs#DEFAULT_NAME}
324 * ({@code "_"})
325 * @param type the type of the class data
326 * @return the value of the class data if present in the lookup class;
327 * otherwise {@code null}
328 * @throws IllegalArgumentException if name is not {@code "_"}
329 * @throws IllegalAccessException if the lookup context does not have
330 * {@linkplain Lookup#ORIGINAL original} access
331 * @throws ClassCastException if the class data cannot be converted to
332 * the given {@code type}
333 * @throws NullPointerException if {@code caller} or {@code type} argument
334 * is {@code null}
335 * @see Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...)
336 * @see MethodHandles#classDataAt(Lookup, String, Class, int)
337 * @since 16
338 * @jvms 5.5 Initialization
339 */
340 public static <T> T classData(Lookup caller, String name, Class<T> type) throws IllegalAccessException {
341 Objects.requireNonNull(caller);
342 Objects.requireNonNull(type);
343 if (!ConstantDescs.DEFAULT_NAME.equals(name)) {
344 throw new IllegalArgumentException("name must be \"_\": " + name);
345 }
346
347 if ((caller.lookupModes() & Lookup.ORIGINAL) != Lookup.ORIGINAL) {
348 throw new IllegalAccessException(caller + " does not have ORIGINAL access");
349 }
350
351 Object classdata = classData(caller.lookupClass());
352 if (classdata == null) return null;
353
354 try {
355 return BootstrapMethodInvoker.widenAndCast(classdata, type);
356 } catch (RuntimeException|Error e) {
357 throw e; // let CCE and other runtime exceptions through
358 } catch (Throwable e) {
359 throw new InternalError(e);
360 }
361 }
362
363 /*
364 * Returns the class data set by the VM in the Class::classData field.
365 *
366 * This is also invoked by LambdaForms as it cannot use condy via
367 * MethodHandles::classData due to bootstrapping issue.
368 */
369 static Object classData(Class<?> c) {
370 UNSAFE.ensureClassInitialized(c);
371 return SharedSecrets.getJavaLangAccess().classData(c);
372 }
373
374 /**
375 * Returns the element at the specified index in the
376 * {@linkplain #classData(Lookup, String, Class) class data},
377 * if the class data associated with the lookup class
378 * of the given {@code caller} lookup object is a {@code List}.
379 * If the class data is not present in this lookup class, this method
380 * returns {@code null}.
381 *
382 * <p> A hidden class with class data can be created by calling
383 * {@link Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...)
384 * Lookup::defineHiddenClassWithClassData}.
385 * This method will cause the static class initializer of the lookup
386 * class of the given {@code caller} lookup object be executed if
387 * it has not been initialized.
388 *
389 * <p> A hidden class created by {@link Lookup#defineHiddenClass(byte[], boolean, Lookup.ClassOption...)
390 * Lookup::defineHiddenClass} and non-hidden classes have no class data.
391 * {@code null} is returned if this method is called on the lookup object
392 * on these classes.
393 *
394 * <p> The {@linkplain Lookup#lookupModes() lookup modes} for this lookup
395 * must have {@linkplain Lookup#ORIGINAL original access}
396 * in order to retrieve the class data.
397 *
398 * @apiNote
399 * This method can be called as a bootstrap method for a dynamically computed
400 * constant. A framework can create a hidden class with class data, for
401 * example that can be {@code List.of(o1, o2, o3....)} containing more than
402 * one object and use this method to load one element at a specific index.
403 * The class data is accessible only to the lookup object
404 * created by the original caller but inaccessible to other members
405 * in the same nest. If a framework passes security sensitive objects
406 * to a hidden class via class data, it is recommended to load the value
407 * of class data as a dynamically computed constant instead of storing
408 * the class data in private static field(s) which are accessible to other
409 * nestmates.
410 *
411 * @param <T> the type to cast the result object to
412 * @param caller the lookup context describing the class performing the
413 * operation (normally stacked by the JVM)
414 * @param name must be {@link java.lang.constant.ConstantDescs#DEFAULT_NAME}
415 * ({@code "_"})
416 * @param type the type of the element at the given index in the class data
417 * @param index index of the element in the class data
418 * @return the element at the given index in the class data
419 * if the class data is present; otherwise {@code null}
420 * @throws IllegalArgumentException if name is not {@code "_"}
421 * @throws IllegalAccessException if the lookup context does not have
422 * {@linkplain Lookup#ORIGINAL original} access
423 * @throws ClassCastException if the class data cannot be converted to {@code List}
424 * or the element at the specified index cannot be converted to the given type
425 * @throws IndexOutOfBoundsException if the index is out of range
426 * @throws NullPointerException if {@code caller} or {@code type} argument is
427 * {@code null}; or if unboxing operation fails because
428 * the element at the given index is {@code null}
429 *
430 * @since 16
431 * @see #classData(Lookup, String, Class)
432 * @see Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...)
433 */
434 public static <T> T classDataAt(Lookup caller, String name, Class<T> type, int index)
435 throws IllegalAccessException
436 {
437 @SuppressWarnings("unchecked")
438 List<Object> classdata = (List<Object>)classData(caller, name, List.class);
439 if (classdata == null) return null;
440
441 try {
442 Object element = classdata.get(index);
443 return BootstrapMethodInvoker.widenAndCast(element, type);
444 } catch (RuntimeException|Error e) {
445 throw e; // let specified exceptions and other runtime exceptions/errors through
446 } catch (Throwable e) {
447 throw new InternalError(e);
448 }
449 }
450
451 /**
452 * Performs an unchecked "crack" of a
453 * <a href="MethodHandleInfo.html#directmh">direct method handle</a>.
454 * The result is as if the user had obtained a lookup object capable enough
455 * to crack the target method handle, called
456 * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect}
457 * on the target to obtain its symbolic reference, and then called
458 * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs}
459 * to resolve the symbolic reference to a member.
460 * <p>
461 * If there is a security manager, its {@code checkPermission} method
462 * is called with a {@code ReflectPermission("suppressAccessChecks")} permission.
463 * @param <T> the desired type of the result, either {@link Member} or a subtype
464 * @param target a direct method handle to crack into symbolic reference components
465 * @param expected a class object representing the desired result type {@code T}
466 * @return a reference to the method, constructor, or field object
467 * @throws SecurityException if the caller is not privileged to call {@code setAccessible}
468 * @throws NullPointerException if either argument is {@code null}
469 * @throws IllegalArgumentException if the target is not a direct method handle
470 * @throws ClassCastException if the member is not of the expected type
471 * @since 1.8
472 */
473 public static <T extends Member> T reflectAs(Class<T> expected, MethodHandle target) {
474 @SuppressWarnings("removal")
475 SecurityManager smgr = System.getSecurityManager();
476 if (smgr != null) smgr.checkPermission(SecurityConstants.ACCESS_PERMISSION);
477 Lookup lookup = Lookup.IMPL_LOOKUP; // use maximally privileged lookup
478 return lookup.revealDirect(target).reflectAs(expected, lookup);
479 }
480
481 /**
482 * A <em>lookup object</em> is a factory for creating method handles,
483 * when the creation requires access checking.
484 * Method handles do not perform
485 * access checks when they are called, but rather when they are created.
486 * Therefore, method handle access
487 * restrictions must be enforced when a method handle is created.
488 * The caller class against which those restrictions are enforced
489 * is known as the {@linkplain #lookupClass() lookup class}.
490 * <p>
491 * A lookup class which needs to create method handles will call
492 * {@link MethodHandles#lookup() MethodHandles.lookup} to create a factory for itself.
493 * When the {@code Lookup} factory object is created, the identity of the lookup class is
494 * determined, and securely stored in the {@code Lookup} object.
495 * The lookup class (or its delegates) may then use factory methods
496 * on the {@code Lookup} object to create method handles for access-checked members.
497 * This includes all methods, constructors, and fields which are allowed to the lookup class,
498 * even private ones.
499 *
500 * <h2><a id="lookups"></a>Lookup Factory Methods</h2>
501 * The factory methods on a {@code Lookup} object correspond to all major
502 * use cases for methods, constructors, and fields.
503 * Each method handle created by a factory method is the functional
504 * equivalent of a particular <em>bytecode behavior</em>.
505 * (Bytecode behaviors are described in section {@jvms 5.4.3.5} of
506 * the Java Virtual Machine Specification.)
507 * Here is a summary of the correspondence between these factory methods and
508 * the behavior of the resulting method handles:
509 * <table class="striped">
510 * <caption style="display:none">lookup method behaviors</caption>
511 * <thead>
512 * <tr>
513 * <th scope="col"><a id="equiv"></a>lookup expression</th>
514 * <th scope="col">member</th>
515 * <th scope="col">bytecode behavior</th>
516 * </tr>
517 * </thead>
518 * <tbody>
519 * <tr>
520 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</th>
521 * <td>{@code FT f;}</td><td>{@code (T) this.f;}</td>
522 * </tr>
523 * <tr>
524 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</th>
525 * <td>{@code static}<br>{@code FT f;}</td><td>{@code (FT) C.f;}</td>
526 * </tr>
527 * <tr>
528 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</th>
529 * <td>{@code FT f;}</td><td>{@code this.f = x;}</td>
530 * </tr>
531 * <tr>
532 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</th>
533 * <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td>
534 * </tr>
535 * <tr>
536 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</th>
537 * <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>
538 * </tr>
539 * <tr>
540 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</th>
541 * <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td>
542 * </tr>
543 * <tr>
544 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</th>
545 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
546 * </tr>
547 * <tr>
548 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</th>
549 * <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td>
550 * </tr>
551 * <tr>
552 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</th>
553 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td>
554 * </tr>
555 * <tr>
556 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</th>
557 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, arg);}</td>
558 * </tr>
559 * <tr>
560 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</th>
561 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
562 * </tr>
563 * <tr>
564 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</th>
565 * <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td>
566 * </tr>
567 * <tr>
568 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSpecial lookup.unreflectSpecial(aMethod,this.class)}</th>
569 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
570 * </tr>
571 * <tr>
572 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findClass lookup.findClass("C")}</th>
573 * <td>{@code class C { ... }}</td><td>{@code C.class;}</td>
574 * </tr>
575 * </tbody>
576 * </table>
577 *
578 * Here, the type {@code C} is the class or interface being searched for a member,
579 * documented as a parameter named {@code refc} in the lookup methods.
580 * The method type {@code MT} is composed from the return type {@code T}
581 * and the sequence of argument types {@code A*}.
582 * The constructor also has a sequence of argument types {@code A*} and
583 * is deemed to return the newly-created object of type {@code C}.
584 * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}.
585 * The formal parameter {@code this} stands for the self-reference of type {@code C};
586 * if it is present, it is always the leading argument to the method handle invocation.
587 * (In the case of some {@code protected} members, {@code this} may be
588 * restricted in type to the lookup class; see below.)
589 * The name {@code arg} stands for all the other method handle arguments.
590 * In the code examples for the Core Reflection API, the name {@code thisOrNull}
591 * stands for a null reference if the accessed method or field is static,
592 * and {@code this} otherwise.
593 * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand
594 * for reflective objects corresponding to the given members declared in type {@code C}.
595 * <p>
596 * The bytecode behavior for a {@code findClass} operation is a load of a constant class,
597 * as if by {@code ldc CONSTANT_Class}.
598 * The behavior is represented, not as a method handle, but directly as a {@code Class} constant.
599 * <p>
600 * In cases where the given member is of variable arity (i.e., a method or constructor)
601 * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}.
602 * In all other cases, the returned method handle will be of fixed arity.
603 * <p style="font-size:smaller;">
604 * <em>Discussion:</em>
605 * The equivalence between looked-up method handles and underlying
606 * class members and bytecode behaviors
607 * can break down in a few ways:
608 * <ul style="font-size:smaller;">
609 * <li>If {@code C} is not symbolically accessible from the lookup class's loader,
610 * the lookup can still succeed, even when there is no equivalent
611 * Java expression or bytecoded constant.
612 * <li>Likewise, if {@code T} or {@code MT}
613 * is not symbolically accessible from the lookup class's loader,
614 * the lookup can still succeed.
615 * For example, lookups for {@code MethodHandle.invokeExact} and
616 * {@code MethodHandle.invoke} will always succeed, regardless of requested type.
617 * <li>If there is a security manager installed, it can forbid the lookup
618 * on various grounds (<a href="MethodHandles.Lookup.html#secmgr">see below</a>).
619 * By contrast, the {@code ldc} instruction on a {@code CONSTANT_MethodHandle}
620 * constant is not subject to security manager checks.
621 * <li>If the looked-up method has a
622 * <a href="MethodHandle.html#maxarity">very large arity</a>,
623 * the method handle creation may fail with an
624 * {@code IllegalArgumentException}, due to the method handle type having
625 * <a href="MethodHandle.html#maxarity">too many parameters.</a>
626 * </ul>
627 *
628 * <h2><a id="access"></a>Access checking</h2>
629 * Access checks are applied in the factory methods of {@code Lookup},
630 * when a method handle is created.
631 * This is a key difference from the Core Reflection API, since
632 * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
633 * performs access checking against every caller, on every call.
634 * <p>
635 * All access checks start from a {@code Lookup} object, which
636 * compares its recorded lookup class against all requests to
637 * create method handles.
638 * A single {@code Lookup} object can be used to create any number
639 * of access-checked method handles, all checked against a single
640 * lookup class.
641 * <p>
642 * A {@code Lookup} object can be shared with other trusted code,
643 * such as a metaobject protocol.
644 * A shared {@code Lookup} object delegates the capability
645 * to create method handles on private members of the lookup class.
646 * Even if privileged code uses the {@code Lookup} object,
647 * the access checking is confined to the privileges of the
648 * original lookup class.
649 * <p>
650 * A lookup can fail, because
651 * the containing class is not accessible to the lookup class, or
652 * because the desired class member is missing, or because the
653 * desired class member is not accessible to the lookup class, or
654 * because the lookup object is not trusted enough to access the member.
655 * In the case of a field setter function on a {@code final} field,
656 * finality enforcement is treated as a kind of access control,
657 * and the lookup will fail, except in special cases of
658 * {@link Lookup#unreflectSetter Lookup.unreflectSetter}.
659 * In any of these cases, a {@code ReflectiveOperationException} will be
660 * thrown from the attempted lookup. The exact class will be one of
661 * the following:
662 * <ul>
663 * <li>NoSuchMethodException — if a method is requested but does not exist
664 * <li>NoSuchFieldException — if a field is requested but does not exist
665 * <li>IllegalAccessException — if the member exists but an access check fails
666 * </ul>
667 * <p>
668 * In general, the conditions under which a method handle may be
669 * looked up for a method {@code M} are no more restrictive than the conditions
670 * under which the lookup class could have compiled, verified, and resolved a call to {@code M}.
671 * Where the JVM would raise exceptions like {@code NoSuchMethodError},
672 * a method handle lookup will generally raise a corresponding
673 * checked exception, such as {@code NoSuchMethodException}.
674 * And the effect of invoking the method handle resulting from the lookup
675 * is <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a>
676 * to executing the compiled, verified, and resolved call to {@code M}.
677 * The same point is true of fields and constructors.
678 * <p style="font-size:smaller;">
679 * <em>Discussion:</em>
680 * Access checks only apply to named and reflected methods,
681 * constructors, and fields.
682 * Other method handle creation methods, such as
683 * {@link MethodHandle#asType MethodHandle.asType},
684 * do not require any access checks, and are used
685 * independently of any {@code Lookup} object.
686 * <p>
687 * If the desired member is {@code protected}, the usual JVM rules apply,
688 * including the requirement that the lookup class must either be in the
689 * same package as the desired member, or must inherit that member.
690 * (See the Java Virtual Machine Specification, sections {@jvms
691 * 4.9.2}, {@jvms 5.4.3.5}, and {@jvms 6.4}.)
692 * In addition, if the desired member is a non-static field or method
693 * in a different package, the resulting method handle may only be applied
694 * to objects of the lookup class or one of its subclasses.
695 * This requirement is enforced by narrowing the type of the leading
696 * {@code this} parameter from {@code C}
697 * (which will necessarily be a superclass of the lookup class)
698 * to the lookup class itself.
699 * <p>
700 * The JVM imposes a similar requirement on {@code invokespecial} instruction,
701 * that the receiver argument must match both the resolved method <em>and</em>
702 * the current class. Again, this requirement is enforced by narrowing the
703 * type of the leading parameter to the resulting method handle.
704 * (See the Java Virtual Machine Specification, section {@jvms 4.10.1.9}.)
705 * <p>
706 * The JVM represents constructors and static initializer blocks as internal methods
707 * with special names ({@value ConstantDescs#INIT_NAME} and {@value
708 * ConstantDescs#CLASS_INIT_NAME}).
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 produce 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 * <p>
872 * The {@code Lookup} object returned by {@code privateLookupIn} is allowed to
873 * {@linkplain Lookup#defineClass(byte[]) define classes} in the runtime package
874 * of {@code T}. Extreme caution should be taken when opening a package
875 * to another module as such defined classes have the same full privilege
876 * access as other members in {@code M2}.
877 *
878 * <h2><a id="module-access-check"></a>Cross-module access checks</h2>
879 *
880 * A {@code Lookup} with {@link #PUBLIC} or with {@link #UNCONDITIONAL} mode
881 * allows cross-module access. The access checking is performed with respect
882 * to both the lookup class and the previous lookup class if present.
883 * <p>
884 * A {@code Lookup} with {@link #UNCONDITIONAL} mode can access public type
885 * in all modules when the type is in a package that is {@linkplain Module#isExported(String)
886 * exported unconditionally}.
887 * <p>
888 * If a {@code Lookup} on {@code LC} in {@code M1} has no previous lookup class,
889 * the lookup with {@link #PUBLIC} mode can access all public types in modules
890 * that are readable to {@code M1} and the type is in a package that is exported
891 * at least to {@code M1}.
892 * <p>
893 * If a {@code Lookup} on {@code LC} in {@code M1} has a previous lookup class
894 * {@code PLC} on {@code M0}, the lookup with {@link #PUBLIC} mode can access
895 * the intersection of all public types that are accessible to {@code M1}
896 * with all public types that are accessible to {@code M0}. {@code M0}
897 * reads {@code M1} and hence the set of accessible types includes:
898 *
899 * <ul>
900 * <li>unconditional-exported packages from {@code M1}</li>
901 * <li>unconditional-exported packages from {@code M0} if {@code M1} reads {@code M0}</li>
902 * <li>
903 * unconditional-exported packages from a third module {@code M2}if both {@code M0}
904 * and {@code M1} read {@code M2}
905 * </li>
906 * <li>qualified-exported packages from {@code M1} to {@code M0}</li>
907 * <li>qualified-exported packages from {@code M0} to {@code M1} if {@code M1} reads {@code M0}</li>
908 * <li>
909 * qualified-exported packages from a third module {@code M2} to both {@code M0} and
910 * {@code M1} if both {@code M0} and {@code M1} read {@code M2}
911 * </li>
912 * </ul>
913 *
914 * <h2><a id="access-modes"></a>Access modes</h2>
915 *
916 * The table below shows the access modes of a {@code Lookup} produced by
917 * any of the following factory or transformation methods:
918 * <ul>
919 * <li>{@link #lookup() MethodHandles::lookup}</li>
920 * <li>{@link #publicLookup() MethodHandles::publicLookup}</li>
921 * <li>{@link #privateLookupIn(Class, Lookup) MethodHandles::privateLookupIn}</li>
922 * <li>{@link Lookup#in Lookup::in}</li>
923 * <li>{@link Lookup#dropLookupMode(int) Lookup::dropLookupMode}</li>
924 * </ul>
925 *
926 * <table class="striped">
927 * <caption style="display:none">
928 * Access mode summary
929 * </caption>
930 * <thead>
931 * <tr>
932 * <th scope="col">Lookup object</th>
933 * <th style="text-align:center">original</th>
934 * <th style="text-align:center">protected</th>
935 * <th style="text-align:center">private</th>
936 * <th style="text-align:center">package</th>
937 * <th style="text-align:center">module</th>
938 * <th style="text-align:center">public</th>
939 * </tr>
940 * </thead>
941 * <tbody>
942 * <tr>
943 * <th scope="row" style="text-align:left">{@code CL = MethodHandles.lookup()} in {@code C}</th>
944 * <td style="text-align:center">ORI</td>
945 * <td style="text-align:center">PRO</td>
946 * <td style="text-align:center">PRI</td>
947 * <td style="text-align:center">PAC</td>
948 * <td style="text-align:center">MOD</td>
949 * <td style="text-align:center">1R</td>
950 * </tr>
951 * <tr>
952 * <th scope="row" style="text-align:left">{@code CL.in(C1)} same package</th>
953 * <td></td>
954 * <td></td>
955 * <td></td>
956 * <td style="text-align:center">PAC</td>
957 * <td style="text-align:center">MOD</td>
958 * <td style="text-align:center">1R</td>
959 * </tr>
960 * <tr>
961 * <th scope="row" style="text-align:left">{@code CL.in(C1)} same module</th>
962 * <td></td>
963 * <td></td>
964 * <td></td>
965 * <td></td>
966 * <td style="text-align:center">MOD</td>
967 * <td style="text-align:center">1R</td>
968 * </tr>
969 * <tr>
970 * <th scope="row" style="text-align:left">{@code CL.in(D)} different module</th>
971 * <td></td>
972 * <td></td>
973 * <td></td>
974 * <td></td>
975 * <td></td>
976 * <td style="text-align:center">2R</td>
977 * </tr>
978 * <tr>
979 * <th scope="row" style="text-align:left">{@code CL.in(D).in(C)} hop back to module</th>
980 * <td></td>
981 * <td></td>
982 * <td></td>
983 * <td></td>
984 * <td></td>
985 * <td style="text-align:center">2R</td>
986 * </tr>
987 * <tr>
988 * <th scope="row" style="text-align:left">{@code PRI1 = privateLookupIn(C1,CL)}</th>
989 * <td></td>
990 * <td style="text-align:center">PRO</td>
991 * <td style="text-align:center">PRI</td>
992 * <td style="text-align:center">PAC</td>
993 * <td style="text-align:center">MOD</td>
994 * <td style="text-align:center">1R</td>
995 * </tr>
996 * <tr>
997 * <th scope="row" style="text-align:left">{@code PRI1a = privateLookupIn(C,PRI1)}</th>
998 * <td></td>
999 * <td style="text-align:center">PRO</td>
1000 * <td style="text-align:center">PRI</td>
1001 * <td style="text-align:center">PAC</td>
1002 * <td style="text-align:center">MOD</td>
1003 * <td style="text-align:center">1R</td>
1004 * </tr>
1005 * <tr>
1006 * <th scope="row" style="text-align:left">{@code PRI1.in(C1)} same package</th>
1007 * <td></td>
1008 * <td></td>
1009 * <td></td>
1010 * <td style="text-align:center">PAC</td>
1011 * <td style="text-align:center">MOD</td>
1012 * <td style="text-align:center">1R</td>
1013 * </tr>
1014 * <tr>
1015 * <th scope="row" style="text-align:left">{@code PRI1.in(C1)} different package</th>
1016 * <td></td>
1017 * <td></td>
1018 * <td></td>
1019 * <td></td>
1020 * <td style="text-align:center">MOD</td>
1021 * <td style="text-align:center">1R</td>
1022 * </tr>
1023 * <tr>
1024 * <th scope="row" style="text-align:left">{@code PRI1.in(D)} different module</th>
1025 * <td></td>
1026 * <td></td>
1027 * <td></td>
1028 * <td></td>
1029 * <td></td>
1030 * <td style="text-align:center">2R</td>
1031 * </tr>
1032 * <tr>
1033 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PROTECTED)}</th>
1034 * <td></td>
1035 * <td></td>
1036 * <td style="text-align:center">PRI</td>
1037 * <td style="text-align:center">PAC</td>
1038 * <td style="text-align:center">MOD</td>
1039 * <td style="text-align:center">1R</td>
1040 * </tr>
1041 * <tr>
1042 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PRIVATE)}</th>
1043 * <td></td>
1044 * <td></td>
1045 * <td></td>
1046 * <td style="text-align:center">PAC</td>
1047 * <td style="text-align:center">MOD</td>
1048 * <td style="text-align:center">1R</td>
1049 * </tr>
1050 * <tr>
1051 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PACKAGE)}</th>
1052 * <td></td>
1053 * <td></td>
1054 * <td></td>
1055 * <td></td>
1056 * <td style="text-align:center">MOD</td>
1057 * <td style="text-align:center">1R</td>
1058 * </tr>
1059 * <tr>
1060 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(MODULE)}</th>
1061 * <td></td>
1062 * <td></td>
1063 * <td></td>
1064 * <td></td>
1065 * <td></td>
1066 * <td style="text-align:center">1R</td>
1067 * </tr>
1068 * <tr>
1069 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PUBLIC)}</th>
1070 * <td></td>
1071 * <td></td>
1072 * <td></td>
1073 * <td></td>
1074 * <td></td>
1075 * <td style="text-align:center">none</td>
1076 * <tr>
1077 * <th scope="row" style="text-align:left">{@code PRI2 = privateLookupIn(D,CL)}</th>
1078 * <td></td>
1079 * <td style="text-align:center">PRO</td>
1080 * <td style="text-align:center">PRI</td>
1081 * <td style="text-align:center">PAC</td>
1082 * <td></td>
1083 * <td style="text-align:center">2R</td>
1084 * </tr>
1085 * <tr>
1086 * <th scope="row" style="text-align:left">{@code privateLookupIn(D,PRI1)}</th>
1087 * <td></td>
1088 * <td style="text-align:center">PRO</td>
1089 * <td style="text-align:center">PRI</td>
1090 * <td style="text-align:center">PAC</td>
1091 * <td></td>
1092 * <td style="text-align:center">2R</td>
1093 * </tr>
1094 * <tr>
1095 * <th scope="row" style="text-align:left">{@code privateLookupIn(C,PRI2)} fails</th>
1096 * <td></td>
1097 * <td></td>
1098 * <td></td>
1099 * <td></td>
1100 * <td></td>
1101 * <td style="text-align:center">IAE</td>
1102 * </tr>
1103 * <tr>
1104 * <th scope="row" style="text-align:left">{@code PRI2.in(D2)} same package</th>
1105 * <td></td>
1106 * <td></td>
1107 * <td></td>
1108 * <td style="text-align:center">PAC</td>
1109 * <td></td>
1110 * <td style="text-align:center">2R</td>
1111 * </tr>
1112 * <tr>
1113 * <th scope="row" style="text-align:left">{@code PRI2.in(D2)} different package</th>
1114 * <td></td>
1115 * <td></td>
1116 * <td></td>
1117 * <td></td>
1118 * <td></td>
1119 * <td style="text-align:center">2R</td>
1120 * </tr>
1121 * <tr>
1122 * <th scope="row" style="text-align:left">{@code PRI2.in(C1)} hop back to module</th>
1123 * <td></td>
1124 * <td></td>
1125 * <td></td>
1126 * <td></td>
1127 * <td></td>
1128 * <td style="text-align:center">2R</td>
1129 * </tr>
1130 * <tr>
1131 * <th scope="row" style="text-align:left">{@code PRI2.in(E)} hop to third module</th>
1132 * <td></td>
1133 * <td></td>
1134 * <td></td>
1135 * <td></td>
1136 * <td></td>
1137 * <td style="text-align:center">none</td>
1138 * </tr>
1139 * <tr>
1140 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PROTECTED)}</th>
1141 * <td></td>
1142 * <td></td>
1143 * <td style="text-align:center">PRI</td>
1144 * <td style="text-align:center">PAC</td>
1145 * <td></td>
1146 * <td style="text-align:center">2R</td>
1147 * </tr>
1148 * <tr>
1149 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PRIVATE)}</th>
1150 * <td></td>
1151 * <td></td>
1152 * <td></td>
1153 * <td style="text-align:center">PAC</td>
1154 * <td></td>
1155 * <td style="text-align:center">2R</td>
1156 * </tr>
1157 * <tr>
1158 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PACKAGE)}</th>
1159 * <td></td>
1160 * <td></td>
1161 * <td></td>
1162 * <td></td>
1163 * <td></td>
1164 * <td style="text-align:center">2R</td>
1165 * </tr>
1166 * <tr>
1167 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(MODULE)}</th>
1168 * <td></td>
1169 * <td></td>
1170 * <td></td>
1171 * <td></td>
1172 * <td></td>
1173 * <td style="text-align:center">2R</td>
1174 * </tr>
1175 * <tr>
1176 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PUBLIC)}</th>
1177 * <td></td>
1178 * <td></td>
1179 * <td></td>
1180 * <td></td>
1181 * <td></td>
1182 * <td style="text-align:center">none</td>
1183 * </tr>
1184 * <tr>
1185 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PROTECTED)}</th>
1186 * <td></td>
1187 * <td></td>
1188 * <td style="text-align:center">PRI</td>
1189 * <td style="text-align:center">PAC</td>
1190 * <td style="text-align:center">MOD</td>
1191 * <td style="text-align:center">1R</td>
1192 * </tr>
1193 * <tr>
1194 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PRIVATE)}</th>
1195 * <td></td>
1196 * <td></td>
1197 * <td></td>
1198 * <td style="text-align:center">PAC</td>
1199 * <td style="text-align:center">MOD</td>
1200 * <td style="text-align:center">1R</td>
1201 * </tr>
1202 * <tr>
1203 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PACKAGE)}</th>
1204 * <td></td>
1205 * <td></td>
1206 * <td></td>
1207 * <td></td>
1208 * <td style="text-align:center">MOD</td>
1209 * <td style="text-align:center">1R</td>
1210 * </tr>
1211 * <tr>
1212 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(MODULE)}</th>
1213 * <td></td>
1214 * <td></td>
1215 * <td></td>
1216 * <td></td>
1217 * <td></td>
1218 * <td style="text-align:center">1R</td>
1219 * </tr>
1220 * <tr>
1221 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PUBLIC)}</th>
1222 * <td></td>
1223 * <td></td>
1224 * <td></td>
1225 * <td></td>
1226 * <td></td>
1227 * <td style="text-align:center">none</td>
1228 * </tr>
1229 * <tr>
1230 * <th scope="row" style="text-align:left">{@code PUB = publicLookup()}</th>
1231 * <td></td>
1232 * <td></td>
1233 * <td></td>
1234 * <td></td>
1235 * <td></td>
1236 * <td style="text-align:center">U</td>
1237 * </tr>
1238 * <tr>
1239 * <th scope="row" style="text-align:left">{@code PUB.in(D)} different module</th>
1240 * <td></td>
1241 * <td></td>
1242 * <td></td>
1243 * <td></td>
1244 * <td></td>
1245 * <td style="text-align:center">U</td>
1246 * </tr>
1247 * <tr>
1248 * <th scope="row" style="text-align:left">{@code PUB.in(D).in(E)} third module</th>
1249 * <td></td>
1250 * <td></td>
1251 * <td></td>
1252 * <td></td>
1253 * <td></td>
1254 * <td style="text-align:center">U</td>
1255 * </tr>
1256 * <tr>
1257 * <th scope="row" style="text-align:left">{@code PUB.dropLookupMode(UNCONDITIONAL)}</th>
1258 * <td></td>
1259 * <td></td>
1260 * <td></td>
1261 * <td></td>
1262 * <td></td>
1263 * <td style="text-align:center">none</td>
1264 * </tr>
1265 * <tr>
1266 * <th scope="row" style="text-align:left">{@code privateLookupIn(C1,PUB)} fails</th>
1267 * <td></td>
1268 * <td></td>
1269 * <td></td>
1270 * <td></td>
1271 * <td></td>
1272 * <td style="text-align:center">IAE</td>
1273 * </tr>
1274 * <tr>
1275 * <th scope="row" style="text-align:left">{@code ANY.in(X)}, for inaccessible {@code X}</th>
1276 * <td></td>
1277 * <td></td>
1278 * <td></td>
1279 * <td></td>
1280 * <td></td>
1281 * <td style="text-align:center">none</td>
1282 * </tr>
1283 * </tbody>
1284 * </table>
1285 *
1286 * <p>
1287 * Notes:
1288 * <ul>
1289 * <li>Class {@code C} and class {@code C1} are in module {@code M1},
1290 * but {@code D} and {@code D2} are in module {@code M2}, and {@code E}
1291 * is in module {@code M3}. {@code X} stands for class which is inaccessible
1292 * to the lookup. {@code ANY} stands for any of the example lookups.</li>
1293 * <li>{@code ORI} indicates {@link #ORIGINAL} bit set,
1294 * {@code PRO} indicates {@link #PROTECTED} bit set,
1295 * {@code PRI} indicates {@link #PRIVATE} bit set,
1296 * {@code PAC} indicates {@link #PACKAGE} bit set,
1297 * {@code MOD} indicates {@link #MODULE} bit set,
1298 * {@code 1R} and {@code 2R} indicate {@link #PUBLIC} bit set,
1299 * {@code U} indicates {@link #UNCONDITIONAL} bit set,
1300 * {@code IAE} indicates {@code IllegalAccessException} thrown.</li>
1301 * <li>Public access comes in three kinds:
1302 * <ul>
1303 * <li>unconditional ({@code U}): the lookup assumes readability.
1304 * The lookup has {@code null} previous lookup class.
1305 * <li>one-module-reads ({@code 1R}): the module access checking is
1306 * performed with respect to the lookup class. The lookup has {@code null}
1307 * previous lookup class.
1308 * <li>two-module-reads ({@code 2R}): the module access checking is
1309 * performed with respect to the lookup class and the previous lookup class.
1310 * The lookup has a non-null previous lookup class which is in a
1311 * different module from the current lookup class.
1312 * </ul>
1313 * <li>Any attempt to reach a third module loses all access.</li>
1314 * <li>If a target class {@code X} is not accessible to {@code Lookup::in}
1315 * all access modes are dropped.</li>
1316 * </ul>
1317 *
1318 * <h2><a id="secmgr"></a>Security manager interactions</h2>
1319 * Although bytecode instructions can only refer to classes in
1320 * a related class loader, this API can search for methods in any
1321 * class, as long as a reference to its {@code Class} object is
1322 * available. Such cross-loader references are also possible with the
1323 * Core Reflection API, and are impossible to bytecode instructions
1324 * such as {@code invokestatic} or {@code getfield}.
1325 * There is a {@linkplain java.lang.SecurityManager security manager API}
1326 * to allow applications to check such cross-loader references.
1327 * These checks apply to both the {@code MethodHandles.Lookup} API
1328 * and the Core Reflection API
1329 * (as found on {@link java.lang.Class Class}).
1330 * <p>
1331 * If a security manager is present, member and class lookups are subject to
1332 * additional checks.
1333 * From one to three calls are made to the security manager.
1334 * Any of these calls can refuse access by throwing a
1335 * {@link java.lang.SecurityException SecurityException}.
1336 * Define {@code smgr} as the security manager,
1337 * {@code lookc} as the lookup class of the current lookup object,
1338 * {@code refc} as the containing class in which the member
1339 * is being sought, and {@code defc} as the class in which the
1340 * member is actually defined.
1341 * (If a class or other type is being accessed,
1342 * the {@code refc} and {@code defc} values are the class itself.)
1343 * The value {@code lookc} is defined as <em>not present</em>
1344 * if the current lookup object does not have
1345 * {@linkplain #hasFullPrivilegeAccess() full privilege access}.
1346 * The calls are made according to the following rules:
1347 * <ul>
1348 * <li><b>Step 1:</b>
1349 * If {@code lookc} is not present, or if its class loader is not
1350 * the same as or an ancestor of the class loader of {@code refc},
1351 * then {@link SecurityManager#checkPackageAccess
1352 * smgr.checkPackageAccess(refcPkg)} is called,
1353 * where {@code refcPkg} is the package of {@code refc}.
1354 * <li><b>Step 2a:</b>
1355 * If the retrieved member is not public and
1356 * {@code lookc} is not present, then
1357 * {@link SecurityManager#checkPermission smgr.checkPermission}
1358 * with {@code RuntimePermission("accessDeclaredMembers")} is called.
1359 * <li><b>Step 2b:</b>
1360 * If the retrieved class has a {@code null} class loader,
1361 * and {@code lookc} is not present, then
1362 * {@link SecurityManager#checkPermission smgr.checkPermission}
1363 * with {@code RuntimePermission("getClassLoader")} is called.
1364 * <li><b>Step 3:</b>
1365 * If the retrieved member is not public,
1366 * and if {@code lookc} is not present,
1367 * and if {@code defc} and {@code refc} are different,
1368 * then {@link SecurityManager#checkPackageAccess
1369 * smgr.checkPackageAccess(defcPkg)} is called,
1370 * where {@code defcPkg} is the package of {@code defc}.
1371 * </ul>
1372 * Security checks are performed after other access checks have passed.
1373 * Therefore, the above rules presuppose a member or class that is public,
1374 * or else that is being accessed from a lookup class that has
1375 * rights to access the member or class.
1376 * <p>
1377 * If a security manager is present and the current lookup object does not have
1378 * {@linkplain #hasFullPrivilegeAccess() full privilege access}, then
1379 * {@link #defineClass(byte[]) defineClass},
1380 * {@link #defineHiddenClass(byte[], boolean, ClassOption...) defineHiddenClass},
1381 * {@link #defineHiddenClassWithClassData(byte[], Object, boolean, ClassOption...)
1382 * defineHiddenClassWithClassData}
1383 * calls {@link SecurityManager#checkPermission smgr.checkPermission}
1384 * with {@code RuntimePermission("defineClass")}.
1385 *
1386 * <h2><a id="callsens"></a>Caller sensitive methods</h2>
1387 * A small number of Java methods have a special property called caller sensitivity.
1388 * A <em>caller-sensitive</em> method can behave differently depending on the
1389 * identity of its immediate caller.
1390 * <p>
1391 * If a method handle for a caller-sensitive method is requested,
1392 * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> apply,
1393 * but they take account of the lookup class in a special way.
1394 * The resulting method handle behaves as if it were called
1395 * from an instruction contained in the lookup class,
1396 * so that the caller-sensitive method detects the lookup class.
1397 * (By contrast, the invoker of the method handle is disregarded.)
1398 * Thus, in the case of caller-sensitive methods,
1399 * different lookup classes may give rise to
1400 * differently behaving method handles.
1401 * <p>
1402 * In cases where the lookup object is
1403 * {@link MethodHandles#publicLookup() publicLookup()},
1404 * or some other lookup object without the
1405 * {@linkplain #ORIGINAL original access},
1406 * the lookup class is disregarded.
1407 * In such cases, no caller-sensitive method handle can be created,
1408 * access is forbidden, and the lookup fails with an
1409 * {@code IllegalAccessException}.
1410 * <p style="font-size:smaller;">
1411 * <em>Discussion:</em>
1412 * For example, the caller-sensitive method
1413 * {@link java.lang.Class#forName(String) Class.forName(x)}
1414 * can return varying classes or throw varying exceptions,
1415 * depending on the class loader of the class that calls it.
1416 * A public lookup of {@code Class.forName} will fail, because
1417 * there is no reasonable way to determine its bytecode behavior.
1418 * <p style="font-size:smaller;">
1419 * If an application caches method handles for broad sharing,
1420 * it should use {@code publicLookup()} to create them.
1421 * If there is a lookup of {@code Class.forName}, it will fail,
1422 * and the application must take appropriate action in that case.
1423 * It may be that a later lookup, perhaps during the invocation of a
1424 * bootstrap method, can incorporate the specific identity
1425 * of the caller, making the method accessible.
1426 * <p style="font-size:smaller;">
1427 * The function {@code MethodHandles.lookup} is caller sensitive
1428 * so that there can be a secure foundation for lookups.
1429 * Nearly all other methods in the JSR 292 API rely on lookup
1430 * objects to check access requests.
1431 */
1432 public static final
1433 class Lookup {
1434 /** The class on behalf of whom the lookup is being performed. */
1435 private final Class<?> lookupClass;
1436
1437 /** previous lookup class */
1438 private final Class<?> prevLookupClass;
1439
1440 /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */
1441 private final int allowedModes;
1442
1443 static {
1444 Reflection.registerFieldsToFilter(Lookup.class, Set.of("lookupClass", "allowedModes"));
1445 }
1446
1447 /** A single-bit mask representing {@code public} access,
1448 * which may contribute to the result of {@link #lookupModes lookupModes}.
1449 * The value, {@code 0x01}, happens to be the same as the value of the
1450 * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.
1451 * <p>
1452 * A {@code Lookup} with this lookup mode performs cross-module access check
1453 * with respect to the {@linkplain #lookupClass() lookup class} and
1454 * {@linkplain #previousLookupClass() previous lookup class} if present.
1455 */
1456 public static final int PUBLIC = Modifier.PUBLIC;
1457
1458 /** A single-bit mask representing {@code private} access,
1459 * which may contribute to the result of {@link #lookupModes lookupModes}.
1460 * The value, {@code 0x02}, happens to be the same as the value of the
1461 * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.
1462 */
1463 public static final int PRIVATE = Modifier.PRIVATE;
1464
1465 /** A single-bit mask representing {@code protected} access,
1466 * which may contribute to the result of {@link #lookupModes lookupModes}.
1467 * The value, {@code 0x04}, happens to be the same as the value of the
1468 * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.
1469 */
1470 public static final int PROTECTED = Modifier.PROTECTED;
1471
1472 /** A single-bit mask representing {@code package} access (default access),
1473 * which may contribute to the result of {@link #lookupModes lookupModes}.
1474 * The value is {@code 0x08}, which does not correspond meaningfully to
1475 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1476 */
1477 public static final int PACKAGE = Modifier.STATIC;
1478
1479 /** A single-bit mask representing {@code module} access,
1480 * which may contribute to the result of {@link #lookupModes lookupModes}.
1481 * The value is {@code 0x10}, which does not correspond meaningfully to
1482 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1483 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup}
1484 * with this lookup mode can access all public types in the module of the
1485 * lookup class and public types in packages exported by other modules
1486 * to the module of the lookup class.
1487 * <p>
1488 * If this lookup mode is set, the {@linkplain #previousLookupClass()
1489 * previous lookup class} is always {@code null}.
1490 *
1491 * @since 9
1492 */
1493 public static final int MODULE = PACKAGE << 1;
1494
1495 /** A single-bit mask representing {@code unconditional} access
1496 * which may contribute to the result of {@link #lookupModes lookupModes}.
1497 * The value is {@code 0x20}, which does not correspond meaningfully to
1498 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1499 * A {@code Lookup} with this lookup mode assumes {@linkplain
1500 * java.lang.Module#canRead(java.lang.Module) readability}.
1501 * This lookup mode can access all public members of public types
1502 * of all modules when the type is in a package that is {@link
1503 * java.lang.Module#isExported(String) exported unconditionally}.
1504 *
1505 * <p>
1506 * If this lookup mode is set, the {@linkplain #previousLookupClass()
1507 * previous lookup class} is always {@code null}.
1508 *
1509 * @since 9
1510 * @see #publicLookup()
1511 */
1512 public static final int UNCONDITIONAL = PACKAGE << 2;
1513
1514 /** A single-bit mask representing {@code original} access
1515 * which may contribute to the result of {@link #lookupModes lookupModes}.
1516 * The value is {@code 0x40}, which does not correspond meaningfully to
1517 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1518 *
1519 * <p>
1520 * If this lookup mode is set, the {@code Lookup} object must be
1521 * created by the original lookup class by calling
1522 * {@link MethodHandles#lookup()} method or by a bootstrap method
1523 * invoked by the VM. The {@code Lookup} object with this lookup
1524 * mode has {@linkplain #hasFullPrivilegeAccess() full privilege access}.
1525 *
1526 * @since 16
1527 */
1528 public static final int ORIGINAL = PACKAGE << 3;
1529
1530 private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE | MODULE | UNCONDITIONAL | ORIGINAL);
1531 private static final int FULL_POWER_MODES = (ALL_MODES & ~UNCONDITIONAL); // with original access
1532 private static final int TRUSTED = -1;
1533
1534 /*
1535 * Adjust PUBLIC => PUBLIC|MODULE|ORIGINAL|UNCONDITIONAL
1536 * Adjust 0 => PACKAGE
1537 */
1538 private static int fixmods(int mods) {
1539 mods &= (ALL_MODES - PACKAGE - MODULE - ORIGINAL - UNCONDITIONAL);
1540 if (Modifier.isPublic(mods))
1541 mods |= UNCONDITIONAL;
1542 return (mods != 0) ? mods : PACKAGE;
1543 }
1544
1545 /** Tells which class is performing the lookup. It is this class against
1546 * which checks are performed for visibility and access permissions.
1547 * <p>
1548 * If this lookup object has a {@linkplain #previousLookupClass() previous lookup class},
1549 * access checks are performed against both the lookup class and the previous lookup class.
1550 * <p>
1551 * The class implies a maximum level of access permission,
1552 * but the permissions may be additionally limited by the bitmask
1553 * {@link #lookupModes lookupModes}, which controls whether non-public members
1554 * can be accessed.
1555 * @return the lookup class, on behalf of which this lookup object finds members
1556 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1557 */
1558 public Class<?> lookupClass() {
1559 return lookupClass;
1560 }
1561
1562 /** Reports a lookup class in another module that this lookup object
1563 * was previously teleported from, or {@code null}.
1564 * <p>
1565 * A {@code Lookup} object produced by the factory methods, such as the
1566 * {@link #lookup() lookup()} and {@link #publicLookup() publicLookup()} method,
1567 * has {@code null} previous lookup class.
1568 * A {@code Lookup} object has a non-null previous lookup class
1569 * when this lookup was teleported from an old lookup class
1570 * in one module to a new lookup class in another module.
1571 *
1572 * @return the lookup class in another module that this lookup object was
1573 * previously teleported from, or {@code null}
1574 * @since 14
1575 * @see #in(Class)
1576 * @see MethodHandles#privateLookupIn(Class, Lookup)
1577 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1578 */
1579 public Class<?> previousLookupClass() {
1580 return prevLookupClass;
1581 }
1582
1583 // This is just for calling out to MethodHandleImpl.
1584 private Class<?> lookupClassOrNull() {
1585 return (allowedModes == TRUSTED) ? null : lookupClass;
1586 }
1587
1588 /** Tells which access-protection classes of members this lookup object can produce.
1589 * The result is a bit-mask of the bits
1590 * {@linkplain #PUBLIC PUBLIC (0x01)},
1591 * {@linkplain #PRIVATE PRIVATE (0x02)},
1592 * {@linkplain #PROTECTED PROTECTED (0x04)},
1593 * {@linkplain #PACKAGE PACKAGE (0x08)},
1594 * {@linkplain #MODULE MODULE (0x10)},
1595 * {@linkplain #UNCONDITIONAL UNCONDITIONAL (0x20)},
1596 * and {@linkplain #ORIGINAL ORIGINAL (0x40)}.
1597 * <p>
1598 * A freshly-created lookup object
1599 * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class} has
1600 * all possible bits set, except {@code UNCONDITIONAL}.
1601 * A lookup object on a new lookup class
1602 * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object}
1603 * may have some mode bits set to zero.
1604 * Mode bits can also be
1605 * {@linkplain java.lang.invoke.MethodHandles.Lookup#dropLookupMode directly cleared}.
1606 * Once cleared, mode bits cannot be restored from the downgraded lookup object.
1607 * The purpose of this is to restrict access via the new lookup object,
1608 * so that it can access only names which can be reached by the original
1609 * lookup object, and also by the new lookup class.
1610 * @return the lookup modes, which limit the kinds of access performed by this lookup object
1611 * @see #in
1612 * @see #dropLookupMode
1613 */
1614 public int lookupModes() {
1615 return allowedModes & ALL_MODES;
1616 }
1617
1618 /** Embody the current class (the lookupClass) as a lookup class
1619 * for method handle creation.
1620 * Must be called by from a method in this package,
1621 * which in turn is called by a method not in this package.
1622 */
1623 Lookup(Class<?> lookupClass) {
1624 this(lookupClass, null, FULL_POWER_MODES);
1625 }
1626
1627 private Lookup(Class<?> lookupClass, Class<?> prevLookupClass, int allowedModes) {
1628 assert prevLookupClass == null || ((allowedModes & MODULE) == 0
1629 && prevLookupClass.getModule() != lookupClass.getModule());
1630 assert !lookupClass.isArray() && !lookupClass.isPrimitive();
1631 this.lookupClass = lookupClass;
1632 this.prevLookupClass = prevLookupClass;
1633 this.allowedModes = allowedModes;
1634 }
1635
1636 private static Lookup newLookup(Class<?> lookupClass, Class<?> prevLookupClass, int allowedModes) {
1637 // make sure we haven't accidentally picked up a privileged class:
1638 checkUnprivilegedlookupClass(lookupClass);
1639 return new Lookup(lookupClass, prevLookupClass, allowedModes);
1640 }
1641
1642 /**
1643 * Creates a lookup on the specified new lookup class.
1644 * The resulting object will report the specified
1645 * class as its own {@link #lookupClass() lookupClass}.
1646 *
1647 * <p>
1648 * However, the resulting {@code Lookup} object is guaranteed
1649 * to have no more access capabilities than the original.
1650 * In particular, access capabilities can be lost as follows:<ul>
1651 * <li>If the new lookup class is different from the old lookup class,
1652 * i.e. {@link #ORIGINAL ORIGINAL} access is lost.
1653 * <li>If the new lookup class is in a different module from the old one,
1654 * i.e. {@link #MODULE MODULE} access is lost.
1655 * <li>If the new lookup class is in a different package
1656 * than the old one, protected and default (package) members will not be accessible,
1657 * i.e. {@link #PROTECTED PROTECTED} and {@link #PACKAGE PACKAGE} access are lost.
1658 * <li>If the new lookup class is not within the same package member
1659 * as the old one, private members will not be accessible, and protected members
1660 * will not be accessible by virtue of inheritance,
1661 * i.e. {@link #PRIVATE PRIVATE} access is lost.
1662 * (Protected members may continue to be accessible because of package sharing.)
1663 * <li>If the new lookup class is not
1664 * {@linkplain #accessClass(Class) accessible} to this lookup,
1665 * then no members, not even public members, will be accessible
1666 * i.e. all access modes are lost.
1667 * <li>If the new lookup class, the old lookup class and the previous lookup class
1668 * are all in different modules i.e. teleporting to a third module,
1669 * all access modes are lost.
1670 * </ul>
1671 * <p>
1672 * The new previous lookup class is chosen as follows:
1673 * <ul>
1674 * <li>If the new lookup object has {@link #UNCONDITIONAL UNCONDITIONAL} bit,
1675 * the new previous lookup class is {@code null}.
1676 * <li>If the new lookup class is in the same module as the old lookup class,
1677 * the new previous lookup class is the old previous lookup class.
1678 * <li>If the new lookup class is in a different module from the old lookup class,
1679 * the new previous lookup class is the old lookup class.
1680 *</ul>
1681 * <p>
1682 * The resulting lookup's capabilities for loading classes
1683 * (used during {@link #findClass} invocations)
1684 * are determined by the lookup class' loader,
1685 * which may change due to this operation.
1686 *
1687 * @param requestedLookupClass the desired lookup class for the new lookup object
1688 * @return a lookup object which reports the desired lookup class, or the same object
1689 * if there is no change
1690 * @throws IllegalArgumentException if {@code requestedLookupClass} is a primitive type or void or array class
1691 * @throws NullPointerException if the argument is null
1692 *
1693 * @see #accessClass(Class)
1694 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1695 */
1696 public Lookup in(Class<?> requestedLookupClass) {
1697 Objects.requireNonNull(requestedLookupClass);
1698 if (requestedLookupClass.isPrimitive())
1699 throw new IllegalArgumentException(requestedLookupClass + " is a primitive class");
1700 if (requestedLookupClass.isArray())
1701 throw new IllegalArgumentException(requestedLookupClass + " is an array class");
1702
1703 if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all
1704 return new Lookup(requestedLookupClass, null, FULL_POWER_MODES);
1705 if (requestedLookupClass == this.lookupClass)
1706 return this; // keep same capabilities
1707 int newModes = (allowedModes & FULL_POWER_MODES) & ~ORIGINAL;
1708 Module fromModule = this.lookupClass.getModule();
1709 Module targetModule = requestedLookupClass.getModule();
1710 Class<?> plc = this.previousLookupClass();
1711 if ((this.allowedModes & UNCONDITIONAL) != 0) {
1712 assert plc == null;
1713 newModes = UNCONDITIONAL;
1714 } else if (fromModule != targetModule) {
1715 if (plc != null && !VerifyAccess.isSameModule(plc, requestedLookupClass)) {
1716 // allow hopping back and forth between fromModule and plc's module
1717 // but not the third module
1718 newModes = 0;
1719 }
1720 // drop MODULE access
1721 newModes &= ~(MODULE|PACKAGE|PRIVATE|PROTECTED);
1722 // teleport from this lookup class
1723 plc = this.lookupClass;
1724 }
1725 if ((newModes & PACKAGE) != 0
1726 && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {
1727 newModes &= ~(PACKAGE|PRIVATE|PROTECTED);
1728 }
1729 // Allow nestmate lookups to be created without special privilege:
1730 if ((newModes & PRIVATE) != 0
1731 && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {
1732 newModes &= ~(PRIVATE|PROTECTED);
1733 }
1734 if ((newModes & (PUBLIC|UNCONDITIONAL)) != 0
1735 && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, this.prevLookupClass, allowedModes)) {
1736 // The requested class it not accessible from the lookup class.
1737 // No permissions.
1738 newModes = 0;
1739 }
1740 return newLookup(requestedLookupClass, plc, newModes);
1741 }
1742
1743 /**
1744 * Creates a lookup on the same lookup class which this lookup object
1745 * finds members, but with a lookup mode that has lost the given lookup mode.
1746 * The lookup mode to drop is one of {@link #PUBLIC PUBLIC}, {@link #MODULE
1747 * MODULE}, {@link #PACKAGE PACKAGE}, {@link #PROTECTED PROTECTED},
1748 * {@link #PRIVATE PRIVATE}, {@link #ORIGINAL ORIGINAL}, or
1749 * {@link #UNCONDITIONAL UNCONDITIONAL}.
1750 *
1751 * <p> If this lookup is a {@linkplain MethodHandles#publicLookup() public lookup},
1752 * this lookup has {@code UNCONDITIONAL} mode set and it has no other mode set.
1753 * When dropping {@code UNCONDITIONAL} on a public lookup then the resulting
1754 * lookup has no access.
1755 *
1756 * <p> If this lookup is not a public lookup, then the following applies
1757 * regardless of its {@linkplain #lookupModes() lookup modes}.
1758 * {@link #PROTECTED PROTECTED} and {@link #ORIGINAL ORIGINAL} are always
1759 * dropped and so the resulting lookup mode will never have these access
1760 * capabilities. When dropping {@code PACKAGE}
1761 * then the resulting lookup will not have {@code PACKAGE} or {@code PRIVATE}
1762 * access. When dropping {@code MODULE} then the resulting lookup will not
1763 * have {@code MODULE}, {@code PACKAGE}, or {@code PRIVATE} access.
1764 * When dropping {@code PUBLIC} then the resulting lookup has no access.
1765 *
1766 * @apiNote
1767 * A lookup with {@code PACKAGE} but not {@code PRIVATE} mode can safely
1768 * delegate non-public access within the package of the lookup class without
1769 * conferring <a href="MethodHandles.Lookup.html#privacc">private access</a>.
1770 * A lookup with {@code MODULE} but not
1771 * {@code PACKAGE} mode can safely delegate {@code PUBLIC} access within
1772 * the module of the lookup class without conferring package access.
1773 * A lookup with a {@linkplain #previousLookupClass() previous lookup class}
1774 * (and {@code PUBLIC} but not {@code MODULE} mode) can safely delegate access
1775 * to public classes accessible to both the module of the lookup class
1776 * and the module of the previous lookup class.
1777 *
1778 * @param modeToDrop the lookup mode to drop
1779 * @return a lookup object which lacks the indicated mode, or the same object if there is no change
1780 * @throws IllegalArgumentException if {@code modeToDrop} is not one of {@code PUBLIC},
1781 * {@code MODULE}, {@code PACKAGE}, {@code PROTECTED}, {@code PRIVATE}, {@code ORIGINAL}
1782 * or {@code UNCONDITIONAL}
1783 * @see MethodHandles#privateLookupIn
1784 * @since 9
1785 */
1786 public Lookup dropLookupMode(int modeToDrop) {
1787 int oldModes = lookupModes();
1788 int newModes = oldModes & ~(modeToDrop | PROTECTED | ORIGINAL);
1789 switch (modeToDrop) {
1790 case PUBLIC: newModes &= ~(FULL_POWER_MODES); break;
1791 case MODULE: newModes &= ~(PACKAGE | PRIVATE); break;
1792 case PACKAGE: newModes &= ~(PRIVATE); break;
1793 case PROTECTED:
1794 case PRIVATE:
1795 case ORIGINAL:
1796 case UNCONDITIONAL: break;
1797 default: throw new IllegalArgumentException(modeToDrop + " is not a valid mode to drop");
1798 }
1799 if (newModes == oldModes) return this; // return self if no change
1800 return newLookup(lookupClass(), previousLookupClass(), newModes);
1801 }
1802
1803 /**
1804 * Creates and links a class or interface from {@code bytes}
1805 * with the same class loader and in the same runtime package and
1806 * {@linkplain java.security.ProtectionDomain protection domain} as this lookup's
1807 * {@linkplain #lookupClass() lookup class} as if calling
1808 * {@link ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain)
1809 * ClassLoader::defineClass}.
1810 *
1811 * <p> The {@linkplain #lookupModes() lookup modes} for this lookup must include
1812 * {@link #PACKAGE PACKAGE} access as default (package) members will be
1813 * accessible to the class. The {@code PACKAGE} lookup mode serves to authenticate
1814 * that the lookup object was created by a caller in the runtime package (or derived
1815 * from a lookup originally created by suitably privileged code to a target class in
1816 * the runtime package). </p>
1817 *
1818 * <p> The {@code bytes} parameter is the class bytes of a valid class file (as defined
1819 * by the <em>The Java Virtual Machine Specification</em>) with a class name in the
1820 * same package as the lookup class. </p>
1821 *
1822 * <p> This method does not run the class initializer. The class initializer may
1823 * run at a later time, as detailed in section 12.4 of the <em>The Java Language
1824 * Specification</em>. </p>
1825 *
1826 * <p> If there is a security manager and this lookup does not have {@linkplain
1827 * #hasFullPrivilegeAccess() full privilege access}, its {@code checkPermission} method
1828 * is first called to check {@code RuntimePermission("defineClass")}. </p>
1829 *
1830 * @param bytes the class bytes
1831 * @return the {@code Class} object for the class
1832 * @throws IllegalAccessException if this lookup does not have {@code PACKAGE} access
1833 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure
1834 * @throws IllegalArgumentException if {@code bytes} denotes a class in a different package
1835 * than the lookup class or {@code bytes} is not a class or interface
1836 * ({@code ACC_MODULE} flag is set in the value of the {@code access_flags} item)
1837 * @throws VerifyError if the newly created class cannot be verified
1838 * @throws LinkageError if the newly created class cannot be linked for any other reason
1839 * @throws SecurityException if a security manager is present and it
1840 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1841 * @throws NullPointerException if {@code bytes} is {@code null}
1842 * @since 9
1843 * @see MethodHandles#privateLookupIn
1844 * @see Lookup#dropLookupMode
1845 * @see ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain)
1846 */
1847 public Class<?> defineClass(byte[] bytes) throws IllegalAccessException {
1848 ensureDefineClassPermission();
1849 if ((lookupModes() & PACKAGE) == 0)
1850 throw new IllegalAccessException("Lookup does not have PACKAGE access");
1851 return makeClassDefiner(bytes.clone()).defineClass(false);
1852 }
1853
1854 private void ensureDefineClassPermission() {
1855 if (allowedModes == TRUSTED) return;
1856
1857 if (!hasFullPrivilegeAccess()) {
1858 @SuppressWarnings("removal")
1859 SecurityManager sm = System.getSecurityManager();
1860 if (sm != null)
1861 sm.checkPermission(new RuntimePermission("defineClass"));
1862 }
1863 }
1864
1865 /**
1866 * The set of class options that specify whether a hidden class created by
1867 * {@link Lookup#defineHiddenClass(byte[], boolean, ClassOption...)
1868 * Lookup::defineHiddenClass} method is dynamically added as a new member
1869 * to the nest of a lookup class and/or whether a hidden class has
1870 * a strong relationship with the class loader marked as its defining loader.
1871 *
1872 * @since 15
1873 */
1874 public enum ClassOption {
1875 /**
1876 * Specifies that a hidden class be added to {@linkplain Class#getNestHost nest}
1877 * of a lookup class as a nestmate.
1878 *
1879 * <p> A hidden nestmate class has access to the private members of all
1880 * classes and interfaces in the same nest.
1881 *
1882 * @see Class#getNestHost()
1883 */
1884 NESTMATE(NESTMATE_CLASS),
1885
1886 /**
1887 * Specifies that a hidden class has a <em>strong</em>
1888 * relationship with the class loader marked as its defining loader,
1889 * as a normal class or interface has with its own defining loader.
1890 * This means that the hidden class may be unloaded if and only if
1891 * its defining loader is not reachable and thus may be reclaimed
1892 * by a garbage collector (JLS {@jls 12.7}).
1893 *
1894 * <p> By default, a hidden class or interface may be unloaded
1895 * even if the class loader that is marked as its defining loader is
1896 * <a href="../ref/package-summary.html#reachability">reachable</a>.
1897
1898 *
1899 * @jls 12.7 Unloading of Classes and Interfaces
1900 */
1901 STRONG(STRONG_LOADER_LINK);
1902
1903 /* the flag value is used by VM at define class time */
1904 private final int flag;
1905 ClassOption(int flag) {
1906 this.flag = flag;
1907 }
1908
1909 static int optionsToFlag(Set<ClassOption> options) {
1910 int flags = 0;
1911 for (ClassOption cp : options) {
1912 flags |= cp.flag;
1913 }
1914 return flags;
1915 }
1916 }
1917
1918 /**
1919 * Creates a <em>hidden</em> class or interface from {@code bytes},
1920 * returning a {@code Lookup} on the newly created class or interface.
1921 *
1922 * <p> Ordinarily, a class or interface {@code C} is created by a class loader,
1923 * which either defines {@code C} directly or delegates to another class loader.
1924 * A class loader defines {@code C} directly by invoking
1925 * {@link ClassLoader#defineClass(String, byte[], int, int, ProtectionDomain)
1926 * ClassLoader::defineClass}, which causes the Java Virtual Machine
1927 * to derive {@code C} from a purported representation in {@code class} file format.
1928 * In situations where use of a class loader is undesirable, a class or interface
1929 * {@code C} can be created by this method instead. This method is capable of
1930 * defining {@code C}, and thereby creating it, without invoking
1931 * {@code ClassLoader::defineClass}.
1932 * Instead, this method defines {@code C} as if by arranging for
1933 * the Java Virtual Machine to derive a nonarray class or interface {@code C}
1934 * from a purported representation in {@code class} file format
1935 * using the following rules:
1936 *
1937 * <ol>
1938 * <li> The {@linkplain #lookupModes() lookup modes} for this {@code Lookup}
1939 * must include {@linkplain #hasFullPrivilegeAccess() full privilege} access.
1940 * This level of access is needed to create {@code C} in the module
1941 * of the lookup class of this {@code Lookup}.</li>
1942 *
1943 * <li> The purported representation in {@code bytes} must be a {@code ClassFile}
1944 * structure (JVMS {@jvms 4.1}) of a supported major and minor version.
1945 * The major and minor version may differ from the {@code class} file version
1946 * of the lookup class of this {@code Lookup}.</li>
1947 *
1948 * <li> The value of {@code this_class} must be a valid index in the
1949 * {@code constant_pool} table, and the entry at that index must be a valid
1950 * {@code CONSTANT_Class_info} structure. Let {@code N} be the binary name
1951 * encoded in internal form that is specified by this structure. {@code N} must
1952 * denote a class or interface in the same package as the lookup class.</li>
1953 *
1954 * <li> Let {@code CN} be the string {@code N + "." + <suffix>},
1955 * where {@code <suffix>} is an unqualified name.
1956 *
1957 * <p> Let {@code newBytes} be the {@code ClassFile} structure given by
1958 * {@code bytes} with an additional entry in the {@code constant_pool} table,
1959 * indicating a {@code CONSTANT_Utf8_info} structure for {@code CN}, and
1960 * where the {@code CONSTANT_Class_info} structure indicated by {@code this_class}
1961 * refers to the new {@code CONSTANT_Utf8_info} structure.
1962 *
1963 * <p> Let {@code L} be the defining class loader of the lookup class of this {@code Lookup}.
1964 *
1965 * <p> {@code C} is derived with name {@code CN}, class loader {@code L}, and
1966 * purported representation {@code newBytes} as if by the rules of JVMS {@jvms 5.3.5},
1967 * with the following adjustments:
1968 * <ul>
1969 * <li> The constant indicated by {@code this_class} is permitted to specify a name
1970 * that includes a single {@code "."} character, even though this is not a valid
1971 * binary class or interface name in internal form.</li>
1972 *
1973 * <li> The Java Virtual Machine marks {@code L} as the defining class loader of {@code C},
1974 * but no class loader is recorded as an initiating class loader of {@code C}.</li>
1975 *
1976 * <li> {@code C} is considered to have the same runtime
1977 * {@linkplain Class#getPackage() package}, {@linkplain Class#getModule() module}
1978 * and {@linkplain java.security.ProtectionDomain protection domain}
1979 * as the lookup class of this {@code Lookup}.
1980 * <li> Let {@code GN} be the binary name obtained by taking {@code N}
1981 * (a binary name encoded in internal form) and replacing ASCII forward slashes with
1982 * ASCII periods. For the instance of {@link java.lang.Class} representing {@code C}:
1983 * <ul>
1984 * <li> {@link Class#getName()} returns the string {@code GN + "/" + <suffix>},
1985 * even though this is not a valid binary class or interface name.</li>
1986 * <li> {@link Class#descriptorString()} returns the string
1987 * {@code "L" + N + "." + <suffix> + ";"},
1988 * even though this is not a valid type descriptor name.</li>
1989 * <li> {@link Class#describeConstable()} returns an empty optional as {@code C}
1990 * cannot be described in {@linkplain java.lang.constant.ClassDesc nominal form}.</li>
1991 * </ul>
1992 * </ul>
1993 * </li>
1994 * </ol>
1995 *
1996 * <p> After {@code C} is derived, it is linked by the Java Virtual Machine.
1997 * Linkage occurs as specified in JVMS {@jvms 5.4.3}, with the following adjustments:
1998 * <ul>
1999 * <li> During verification, whenever it is necessary to load the class named
2000 * {@code CN}, the attempt succeeds, producing class {@code C}. No request is
2001 * made of any class loader.</li>
2002 *
2003 * <li> On any attempt to resolve the entry in the run-time constant pool indicated
2004 * by {@code this_class}, the symbolic reference is considered to be resolved to
2005 * {@code C} and resolution always succeeds immediately.</li>
2006 * </ul>
2007 *
2008 * <p> If the {@code initialize} parameter is {@code true},
2009 * then {@code C} is initialized by the Java Virtual Machine.
2010 *
2011 * <p> The newly created class or interface {@code C} serves as the
2012 * {@linkplain #lookupClass() lookup class} of the {@code Lookup} object
2013 * returned by this method. {@code C} is <em>hidden</em> in the sense that
2014 * no other class or interface can refer to {@code C} via a constant pool entry.
2015 * That is, a hidden class or interface cannot be named as a supertype, a field type,
2016 * a method parameter type, or a method return type by any other class.
2017 * This is because a hidden class or interface does not have a binary name, so
2018 * there is no internal form available to record in any class's constant pool.
2019 * A hidden class or interface is not discoverable by {@link Class#forName(String, boolean, ClassLoader)},
2020 * {@link ClassLoader#loadClass(String, boolean)}, or {@link #findClass(String)}, and
2021 * is not {@linkplain java.instrument/java.lang.instrument.Instrumentation#isModifiableClass(Class)
2022 * modifiable} by Java agents or tool agents using the <a href="{@docRoot}/../specs/jvmti.html">
2023 * JVM Tool Interface</a>.
2024 *
2025 * <p> A class or interface created by
2026 * {@linkplain ClassLoader#defineClass(String, byte[], int, int, ProtectionDomain)
2027 * a class loader} has a strong relationship with that class loader.
2028 * That is, every {@code Class} object contains a reference to the {@code ClassLoader}
2029 * that {@linkplain Class#getClassLoader() defined it}.
2030 * This means that a class created by a class loader may be unloaded if and
2031 * only if its defining loader is not reachable and thus may be reclaimed
2032 * by a garbage collector (JLS {@jls 12.7}).
2033 *
2034 * By default, however, a hidden class or interface may be unloaded even if
2035 * the class loader that is marked as its defining loader is
2036 * <a href="../ref/package-summary.html#reachability">reachable</a>.
2037 * This behavior is useful when a hidden class or interface serves multiple
2038 * classes defined by arbitrary class loaders. In other cases, a hidden
2039 * class or interface may be linked to a single class (or a small number of classes)
2040 * with the same defining loader as the hidden class or interface.
2041 * In such cases, where the hidden class or interface must be coterminous
2042 * with a normal class or interface, the {@link ClassOption#STRONG STRONG}
2043 * option may be passed in {@code options}.
2044 * This arranges for a hidden class to have the same strong relationship
2045 * with the class loader marked as its defining loader,
2046 * as a normal class or interface has with its own defining loader.
2047 *
2048 * If {@code STRONG} is not used, then the invoker of {@code defineHiddenClass}
2049 * may still prevent a hidden class or interface from being
2050 * unloaded by ensuring that the {@code Class} object is reachable.
2051 *
2052 * <p> The unloading characteristics are set for each hidden class when it is
2053 * defined, and cannot be changed later. An advantage of allowing hidden classes
2054 * to be unloaded independently of the class loader marked as their defining loader
2055 * is that a very large number of hidden classes may be created by an application.
2056 * In contrast, if {@code STRONG} is used, then the JVM may run out of memory,
2057 * just as if normal classes were created by class loaders.
2058 *
2059 * <p> Classes and interfaces in a nest are allowed to have mutual access to
2060 * their private members. The nest relationship is determined by
2061 * the {@code NestHost} attribute (JVMS {@jvms 4.7.28}) and
2062 * the {@code NestMembers} attribute (JVMS {@jvms 4.7.29}) in a {@code class} file.
2063 * By default, a hidden class belongs to a nest consisting only of itself
2064 * because a hidden class has no binary name.
2065 * The {@link ClassOption#NESTMATE NESTMATE} option can be passed in {@code options}
2066 * to create a hidden class or interface {@code C} as a member of a nest.
2067 * The nest to which {@code C} belongs is not based on any {@code NestHost} attribute
2068 * in the {@code ClassFile} structure from which {@code C} was derived.
2069 * Instead, the following rules determine the nest host of {@code C}:
2070 * <ul>
2071 * <li>If the nest host of the lookup class of this {@code Lookup} has previously
2072 * been determined, then let {@code H} be the nest host of the lookup class.
2073 * Otherwise, the nest host of the lookup class is determined using the
2074 * algorithm in JVMS {@jvms 5.4.4}, yielding {@code H}.</li>
2075 * <li>The nest host of {@code C} is determined to be {@code H},
2076 * the nest host of the lookup class.</li>
2077 * </ul>
2078 *
2079 * <p> A hidden class or interface may be serializable, but this requires a custom
2080 * serialization mechanism in order to ensure that instances are properly serialized
2081 * and deserialized. The default serialization mechanism supports only classes and
2082 * interfaces that are discoverable by their class name.
2083 *
2084 * @param bytes the bytes that make up the class data,
2085 * in the format of a valid {@code class} file as defined by
2086 * <cite>The Java Virtual Machine Specification</cite>.
2087 * @param initialize if {@code true} the class will be initialized.
2088 * @param options {@linkplain ClassOption class options}
2089 * @return the {@code Lookup} object on the hidden class,
2090 * with {@linkplain #ORIGINAL original} and
2091 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege} access
2092 *
2093 * @throws IllegalAccessException if this {@code Lookup} does not have
2094 * {@linkplain #hasFullPrivilegeAccess() full privilege} access
2095 * @throws SecurityException if a security manager is present and it
2096 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2097 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure
2098 * @throws UnsupportedClassVersionError if {@code bytes} is not of a supported major or minor version
2099 * @throws IllegalArgumentException if {@code bytes} denotes a class in a different package
2100 * than the lookup class or {@code bytes} is not a class or interface
2101 * ({@code ACC_MODULE} flag is set in the value of the {@code access_flags} item)
2102 * @throws IncompatibleClassChangeError if the class or interface named as
2103 * the direct superclass of {@code C} is in fact an interface, or if any of the classes
2104 * or interfaces named as direct superinterfaces of {@code C} are not in fact interfaces
2105 * @throws ClassCircularityError if any of the superclasses or superinterfaces of
2106 * {@code C} is {@code C} itself
2107 * @throws VerifyError if the newly created class cannot be verified
2108 * @throws LinkageError if the newly created class cannot be linked for any other reason
2109 * @throws NullPointerException if any parameter is {@code null}
2110 *
2111 * @since 15
2112 * @see Class#isHidden()
2113 * @jvms 4.2.1 Binary Class and Interface Names
2114 * @jvms 4.2.2 Unqualified Names
2115 * @jvms 4.7.28 The {@code NestHost} Attribute
2116 * @jvms 4.7.29 The {@code NestMembers} Attribute
2117 * @jvms 5.4.3.1 Class and Interface Resolution
2118 * @jvms 5.4.4 Access Control
2119 * @jvms 5.3.5 Deriving a {@code Class} from a {@code class} File Representation
2120 * @jvms 5.4 Linking
2121 * @jvms 5.5 Initialization
2122 * @jls 12.7 Unloading of Classes and Interfaces
2123 */
2124 @SuppressWarnings("doclint:reference") // cross-module links
2125 public Lookup defineHiddenClass(byte[] bytes, boolean initialize, ClassOption... options)
2126 throws IllegalAccessException
2127 {
2128 Objects.requireNonNull(bytes);
2129 Objects.requireNonNull(options);
2130
2131 ensureDefineClassPermission();
2132 if (!hasFullPrivilegeAccess()) {
2133 throw new IllegalAccessException(this + " does not have full privilege access");
2134 }
2135
2136 return makeHiddenClassDefiner(bytes.clone(), Set.of(options), false).defineClassAsLookup(initialize);
2137 }
2138
2139 /**
2140 * Creates a <em>hidden</em> class or interface from {@code bytes} with associated
2141 * {@linkplain MethodHandles#classData(Lookup, String, Class) class data},
2142 * returning a {@code Lookup} on the newly created class or interface.
2143 *
2144 * <p> This method is equivalent to calling
2145 * {@link #defineHiddenClass(byte[], boolean, ClassOption...) defineHiddenClass(bytes, initialize, options)}
2146 * as if the hidden class is injected with a private static final <i>unnamed</i>
2147 * field which is initialized with the given {@code classData} at
2148 * the first instruction of the class initializer.
2149 * The newly created class is linked by the Java Virtual Machine.
2150 *
2151 * <p> The {@link MethodHandles#classData(Lookup, String, Class) MethodHandles::classData}
2152 * and {@link MethodHandles#classDataAt(Lookup, String, Class, int) MethodHandles::classDataAt}
2153 * methods can be used to retrieve the {@code classData}.
2154 *
2155 * @apiNote
2156 * A framework can create a hidden class with class data with one or more
2157 * objects and load the class data as dynamically-computed constant(s)
2158 * via a bootstrap method. {@link MethodHandles#classData(Lookup, String, Class)
2159 * Class data} is accessible only to the lookup object created by the newly
2160 * defined hidden class but inaccessible to other members in the same nest
2161 * (unlike private static fields that are accessible to nestmates).
2162 * Care should be taken w.r.t. mutability for example when passing
2163 * an array or other mutable structure through the class data.
2164 * Changing any value stored in the class data at runtime may lead to
2165 * unpredictable behavior.
2166 * If the class data is a {@code List}, it is good practice to make it
2167 * unmodifiable for example via {@link List#of List::of}.
2168 *
2169 * @param bytes the class bytes
2170 * @param classData pre-initialized class data
2171 * @param initialize if {@code true} the class will be initialized.
2172 * @param options {@linkplain ClassOption class options}
2173 * @return the {@code Lookup} object on the hidden class,
2174 * with {@linkplain #ORIGINAL original} and
2175 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege} access
2176 *
2177 * @throws IllegalAccessException if this {@code Lookup} does not have
2178 * {@linkplain #hasFullPrivilegeAccess() full privilege} access
2179 * @throws SecurityException if a security manager is present and it
2180 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2181 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure
2182 * @throws UnsupportedClassVersionError if {@code bytes} is not of a supported major or minor version
2183 * @throws IllegalArgumentException if {@code bytes} denotes a class in a different package
2184 * than the lookup class or {@code bytes} is not a class or interface
2185 * ({@code ACC_MODULE} flag is set in the value of the {@code access_flags} item)
2186 * @throws IncompatibleClassChangeError if the class or interface named as
2187 * the direct superclass of {@code C} is in fact an interface, or if any of the classes
2188 * or interfaces named as direct superinterfaces of {@code C} are not in fact interfaces
2189 * @throws ClassCircularityError if any of the superclasses or superinterfaces of
2190 * {@code C} is {@code C} itself
2191 * @throws VerifyError if the newly created class cannot be verified
2192 * @throws LinkageError if the newly created class cannot be linked for any other reason
2193 * @throws NullPointerException if any parameter is {@code null}
2194 *
2195 * @since 16
2196 * @see Lookup#defineHiddenClass(byte[], boolean, ClassOption...)
2197 * @see Class#isHidden()
2198 * @see MethodHandles#classData(Lookup, String, Class)
2199 * @see MethodHandles#classDataAt(Lookup, String, Class, int)
2200 * @jvms 4.2.1 Binary Class and Interface Names
2201 * @jvms 4.2.2 Unqualified Names
2202 * @jvms 4.7.28 The {@code NestHost} Attribute
2203 * @jvms 4.7.29 The {@code NestMembers} Attribute
2204 * @jvms 5.4.3.1 Class and Interface Resolution
2205 * @jvms 5.4.4 Access Control
2206 * @jvms 5.3.5 Deriving a {@code Class} from a {@code class} File Representation
2207 * @jvms 5.4 Linking
2208 * @jvms 5.5 Initialization
2209 * @jls 12.7 Unloading of Classes and Interface
2210 */
2211 public Lookup defineHiddenClassWithClassData(byte[] bytes, Object classData, boolean initialize, ClassOption... options)
2212 throws IllegalAccessException
2213 {
2214 Objects.requireNonNull(bytes);
2215 Objects.requireNonNull(classData);
2216 Objects.requireNonNull(options);
2217
2218 ensureDefineClassPermission();
2219 if (!hasFullPrivilegeAccess()) {
2220 throw new IllegalAccessException(this + " does not have full privilege access");
2221 }
2222
2223 return makeHiddenClassDefiner(bytes.clone(), Set.of(options), false)
2224 .defineClassAsLookup(initialize, classData);
2225 }
2226
2227 // A default dumper for writing class files passed to Lookup::defineClass
2228 // and Lookup::defineHiddenClass to disk for debugging purposes. To enable,
2229 // set -Djdk.invoke.MethodHandle.dumpHiddenClassFiles or
2230 // -Djdk.invoke.MethodHandle.dumpHiddenClassFiles=true
2231 //
2232 // This default dumper does not dump hidden classes defined by LambdaMetafactory
2233 // and LambdaForms and method handle internals. They are dumped via
2234 // different ClassFileDumpers.
2235 private static ClassFileDumper defaultDumper() {
2236 return DEFAULT_DUMPER;
2237 }
2238
2239 private static final ClassFileDumper DEFAULT_DUMPER = ClassFileDumper.getInstance(
2240 "jdk.invoke.MethodHandle.dumpClassFiles", "DUMP_CLASS_FILES");
2241
2242 static class ClassFile {
2243 final String name; // internal name
2244 final int accessFlags;
2245 final byte[] bytes;
2246 ClassFile(String name, int accessFlags, byte[] bytes) {
2247 this.name = name;
2248 this.accessFlags = accessFlags;
2249 this.bytes = bytes;
2250 }
2251
2252 static ClassFile newInstanceNoCheck(String name, byte[] bytes) {
2253 return new ClassFile(name, 0, bytes);
2254 }
2255
2256 /**
2257 * This method checks the class file version and the structure of `this_class`.
2258 * and checks if the bytes is a class or interface (ACC_MODULE flag not set)
2259 * that is in the named package.
2260 *
2261 * @throws IllegalArgumentException if ACC_MODULE flag is set in access flags
2262 * or the class is not in the given package name.
2263 */
2264 static ClassFile newInstance(byte[] bytes, String pkgName) {
2265 var cf = readClassFile(bytes);
2266
2267 // check if it's in the named package
2268 int index = cf.name.lastIndexOf('/');
2269 String pn = (index == -1) ? "" : cf.name.substring(0, index).replace('/', '.');
2270 if (!pn.equals(pkgName)) {
2271 throw newIllegalArgumentException(cf.name + " not in same package as lookup class");
2272 }
2273 return cf;
2274 }
2275
2276 private static ClassFile readClassFile(byte[] bytes) {
2277 int magic = readInt(bytes, 0);
2278 if (magic != 0xCAFEBABE) {
2279 throw new ClassFormatError("Incompatible magic value: " + magic);
2280 }
2281 int minor = readUnsignedShort(bytes, 4);
2282 int major = readUnsignedShort(bytes, 6);
2283 if (!VM.isSupportedClassFileVersion(major, minor)) {
2284 throw new UnsupportedClassVersionError("Unsupported class file version " + major + "." + minor);
2285 }
2286
2287 String name;
2288 int accessFlags;
2289 try {
2290 ClassModel cm = java.lang.classfile.ClassFile.of().parse(bytes);
2291 name = cm.thisClass().asInternalName();
2292 accessFlags = cm.flags().flagsMask();
2293 } catch (IllegalArgumentException e) {
2294 ClassFormatError cfe = new ClassFormatError();
2295 cfe.initCause(e);
2296 throw cfe;
2297 }
2298 // must be a class or interface
2299 if ((accessFlags & ACC_MODULE) != 0) {
2300 throw newIllegalArgumentException("Not a class or interface: ACC_MODULE flag is set");
2301 }
2302 return new ClassFile(name, accessFlags, bytes);
2303 }
2304
2305 private static int readInt(byte[] bytes, int offset) {
2306 if ((offset+4) > bytes.length) {
2307 throw new ClassFormatError("Invalid ClassFile structure");
2308 }
2309 return ((bytes[offset] & 0xFF) << 24)
2310 | ((bytes[offset + 1] & 0xFF) << 16)
2311 | ((bytes[offset + 2] & 0xFF) << 8)
2312 | (bytes[offset + 3] & 0xFF);
2313 }
2314
2315 private static int readUnsignedShort(byte[] bytes, int offset) {
2316 if ((offset+2) > bytes.length) {
2317 throw new ClassFormatError("Invalid ClassFile structure");
2318 }
2319 return ((bytes[offset] & 0xFF) << 8) | (bytes[offset + 1] & 0xFF);
2320 }
2321 }
2322
2323 /*
2324 * Returns a ClassDefiner that creates a {@code Class} object of a normal class
2325 * from the given bytes.
2326 *
2327 * Caller should make a defensive copy of the arguments if needed
2328 * before calling this factory method.
2329 *
2330 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or
2331 * {@code bytes} denotes a class in a different package than the lookup class
2332 */
2333 private ClassDefiner makeClassDefiner(byte[] bytes) {
2334 ClassFile cf = ClassFile.newInstance(bytes, lookupClass().getPackageName());
2335 return new ClassDefiner(this, cf, STRONG_LOADER_LINK, defaultDumper());
2336 }
2337
2338 /**
2339 * Returns a ClassDefiner that creates a {@code Class} object of a normal class
2340 * from the given bytes. No package name check on the given bytes.
2341 *
2342 * @param name internal name
2343 * @param bytes class bytes
2344 * @param dumper dumper to write the given bytes to the dumper's output directory
2345 * @return ClassDefiner that defines a normal class of the given bytes.
2346 */
2347 ClassDefiner makeClassDefiner(String name, byte[] bytes, ClassFileDumper dumper) {
2348 // skip package name validation
2349 ClassFile cf = ClassFile.newInstanceNoCheck(name, bytes);
2350 return new ClassDefiner(this, cf, STRONG_LOADER_LINK, dumper);
2351 }
2352
2353 /**
2354 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2355 * from the given bytes. The name must be in the same package as the lookup class.
2356 *
2357 * Caller should make a defensive copy of the arguments if needed
2358 * before calling this factory method.
2359 *
2360 * @param bytes class bytes
2361 * @param dumper dumper to write the given bytes to the dumper's output directory
2362 * @return ClassDefiner that defines a hidden class of the given bytes.
2363 *
2364 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or
2365 * {@code bytes} denotes a class in a different package than the lookup class
2366 */
2367 ClassDefiner makeHiddenClassDefiner(byte[] bytes, ClassFileDumper dumper) {
2368 ClassFile cf = ClassFile.newInstance(bytes, lookupClass().getPackageName());
2369 return makeHiddenClassDefiner(cf, Set.of(), false, dumper);
2370 }
2371
2372 /**
2373 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2374 * from the given bytes and options.
2375 * The name must be in the same package as the lookup class.
2376 *
2377 * Caller should make a defensive copy of the arguments if needed
2378 * before calling this factory method.
2379 *
2380 * @param bytes class bytes
2381 * @param options class options
2382 * @param accessVmAnnotations true to give the hidden class access to VM annotations
2383 * @return ClassDefiner that defines a hidden class of the given bytes and options
2384 *
2385 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or
2386 * {@code bytes} denotes a class in a different package than the lookup class
2387 */
2388 private ClassDefiner makeHiddenClassDefiner(byte[] bytes,
2389 Set<ClassOption> options,
2390 boolean accessVmAnnotations) {
2391 ClassFile cf = ClassFile.newInstance(bytes, lookupClass().getPackageName());
2392 return makeHiddenClassDefiner(cf, options, accessVmAnnotations, defaultDumper());
2393 }
2394
2395 /**
2396 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2397 * from the given bytes and the given options. No package name check on the given bytes.
2398 *
2399 * @param name internal name that specifies the prefix of the hidden class
2400 * @param bytes class bytes
2401 * @param options class options
2402 * @param dumper dumper to write the given bytes to the dumper's output directory
2403 * @return ClassDefiner that defines a hidden class of the given bytes and options.
2404 */
2405 ClassDefiner makeHiddenClassDefiner(String name, byte[] bytes, Set<ClassOption> options, ClassFileDumper dumper) {
2406 Objects.requireNonNull(dumper);
2407 // skip name and access flags validation
2408 return makeHiddenClassDefiner(ClassFile.newInstanceNoCheck(name, bytes), options, false, dumper);
2409 }
2410
2411 /**
2412 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2413 * from the given class file and options.
2414 *
2415 * @param cf ClassFile
2416 * @param options class options
2417 * @param accessVmAnnotations true to give the hidden class access to VM annotations
2418 * @param dumper dumper to write the given bytes to the dumper's output directory
2419 */
2420 private ClassDefiner makeHiddenClassDefiner(ClassFile cf,
2421 Set<ClassOption> options,
2422 boolean accessVmAnnotations,
2423 ClassFileDumper dumper) {
2424 int flags = HIDDEN_CLASS | ClassOption.optionsToFlag(options);
2425 if (accessVmAnnotations | VM.isSystemDomainLoader(lookupClass.getClassLoader())) {
2426 // jdk.internal.vm.annotations are permitted for classes
2427 // defined to boot loader and platform loader
2428 flags |= ACCESS_VM_ANNOTATIONS;
2429 }
2430
2431 return new ClassDefiner(this, cf, flags, dumper);
2432 }
2433
2434 static class ClassDefiner {
2435 private final Lookup lookup;
2436 private final String name; // internal name
2437 private final byte[] bytes;
2438 private final int classFlags;
2439 private final ClassFileDumper dumper;
2440
2441 private ClassDefiner(Lookup lookup, ClassFile cf, int flags, ClassFileDumper dumper) {
2442 assert ((flags & HIDDEN_CLASS) != 0 || (flags & STRONG_LOADER_LINK) == STRONG_LOADER_LINK);
2443 this.lookup = lookup;
2444 this.bytes = cf.bytes;
2445 this.name = cf.name;
2446 this.classFlags = flags;
2447 this.dumper = dumper;
2448 }
2449
2450 String internalName() {
2451 return name;
2452 }
2453
2454 Class<?> defineClass(boolean initialize) {
2455 return defineClass(initialize, null);
2456 }
2457
2458 Lookup defineClassAsLookup(boolean initialize) {
2459 Class<?> c = defineClass(initialize, null);
2460 return new Lookup(c, null, FULL_POWER_MODES);
2461 }
2462
2463 /**
2464 * Defines the class of the given bytes and the given classData.
2465 * If {@code initialize} parameter is true, then the class will be initialized.
2466 *
2467 * @param initialize true if the class to be initialized
2468 * @param classData classData or null
2469 * @return the class
2470 *
2471 * @throws LinkageError linkage error
2472 */
2473 Class<?> defineClass(boolean initialize, Object classData) {
2474 Class<?> lookupClass = lookup.lookupClass();
2475 ClassLoader loader = lookupClass.getClassLoader();
2476 ProtectionDomain pd = (loader != null) ? lookup.lookupClassProtectionDomain() : null;
2477 Class<?> c = null;
2478 try {
2479 c = SharedSecrets.getJavaLangAccess()
2480 .defineClass(loader, lookupClass, name, bytes, pd, initialize, classFlags, classData);
2481 assert !isNestmate() || c.getNestHost() == lookupClass.getNestHost();
2482 return c;
2483 } finally {
2484 // dump the classfile for debugging
2485 if (dumper.isEnabled()) {
2486 String name = internalName();
2487 if (c != null) {
2488 dumper.dumpClass(name, c, bytes);
2489 } else {
2490 dumper.dumpFailedClass(name, bytes);
2491 }
2492 }
2493 }
2494 }
2495
2496 /**
2497 * Defines the class of the given bytes and the given classData.
2498 * If {@code initialize} parameter is true, then the class will be initialized.
2499 *
2500 * @param initialize true if the class to be initialized
2501 * @param classData classData or null
2502 * @return a Lookup for the defined class
2503 *
2504 * @throws LinkageError linkage error
2505 */
2506 Lookup defineClassAsLookup(boolean initialize, Object classData) {
2507 Class<?> c = defineClass(initialize, classData);
2508 return new Lookup(c, null, FULL_POWER_MODES);
2509 }
2510
2511 private boolean isNestmate() {
2512 return (classFlags & NESTMATE_CLASS) != 0;
2513 }
2514 }
2515
2516 private ProtectionDomain lookupClassProtectionDomain() {
2517 ProtectionDomain pd = cachedProtectionDomain;
2518 if (pd == null) {
2519 cachedProtectionDomain = pd = SharedSecrets.getJavaLangAccess().protectionDomain(lookupClass);
2520 }
2521 return pd;
2522 }
2523
2524 // cached protection domain
2525 private volatile ProtectionDomain cachedProtectionDomain;
2526
2527 // Make sure outer class is initialized first.
2528 static { IMPL_NAMES.getClass(); }
2529
2530 /** Package-private version of lookup which is trusted. */
2531 static final Lookup IMPL_LOOKUP = new Lookup(Object.class, null, TRUSTED);
2532
2533 /** Version of lookup which is trusted minimally.
2534 * It can only be used to create method handles to publicly accessible
2535 * members in packages that are exported unconditionally.
2536 */
2537 static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, null, UNCONDITIONAL);
2538
2539 private static void checkUnprivilegedlookupClass(Class<?> lookupClass) {
2540 String name = lookupClass.getName();
2541 if (name.startsWith("java.lang.invoke."))
2542 throw newIllegalArgumentException("illegal lookupClass: "+lookupClass);
2543 }
2544
2545 /**
2546 * Displays the name of the class from which lookups are to be made,
2547 * followed by "/" and the name of the {@linkplain #previousLookupClass()
2548 * previous lookup class} if present.
2549 * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)
2550 * If there are restrictions on the access permitted to this lookup,
2551 * this is indicated by adding a suffix to the class name, consisting
2552 * of a slash and a keyword. The keyword represents the strongest
2553 * allowed access, and is chosen as follows:
2554 * <ul>
2555 * <li>If no access is allowed, the suffix is "/noaccess".
2556 * <li>If only unconditional access is allowed, the suffix is "/publicLookup".
2557 * <li>If only public access to types in exported packages is allowed, the suffix is "/public".
2558 * <li>If only public and module access are allowed, the suffix is "/module".
2559 * <li>If public and package access are allowed, the suffix is "/package".
2560 * <li>If public, package, and private access are allowed, the suffix is "/private".
2561 * </ul>
2562 * If none of the above cases apply, it is the case that
2563 * {@linkplain #hasFullPrivilegeAccess() full privilege access}
2564 * (public, module, package, private, and protected) is allowed.
2565 * In this case, no suffix is added.
2566 * This is true only of an object obtained originally from
2567 * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
2568 * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
2569 * always have restricted access, and will display a suffix.
2570 * <p>
2571 * (It may seem strange that protected access should be
2572 * stronger than private access. Viewed independently from
2573 * package access, protected access is the first to be lost,
2574 * because it requires a direct subclass relationship between
2575 * caller and callee.)
2576 * @see #in
2577 */
2578 @Override
2579 public String toString() {
2580 String cname = lookupClass.getName();
2581 if (prevLookupClass != null)
2582 cname += "/" + prevLookupClass.getName();
2583 switch (allowedModes) {
2584 case 0: // no privileges
2585 return cname + "/noaccess";
2586 case UNCONDITIONAL:
2587 return cname + "/publicLookup";
2588 case PUBLIC:
2589 return cname + "/public";
2590 case PUBLIC|MODULE:
2591 return cname + "/module";
2592 case PUBLIC|PACKAGE:
2593 case PUBLIC|MODULE|PACKAGE:
2594 return cname + "/package";
2595 case PUBLIC|PACKAGE|PRIVATE:
2596 case PUBLIC|MODULE|PACKAGE|PRIVATE:
2597 return cname + "/private";
2598 case PUBLIC|PACKAGE|PRIVATE|PROTECTED:
2599 case PUBLIC|MODULE|PACKAGE|PRIVATE|PROTECTED:
2600 case FULL_POWER_MODES:
2601 return cname;
2602 case TRUSTED:
2603 return "/trusted"; // internal only; not exported
2604 default: // Should not happen, but it's a bitfield...
2605 cname = cname + "/" + Integer.toHexString(allowedModes);
2606 assert(false) : cname;
2607 return cname;
2608 }
2609 }
2610
2611 /**
2612 * Produces a method handle for a static method.
2613 * The type of the method handle will be that of the method.
2614 * (Since static methods do not take receivers, there is no
2615 * additional receiver argument inserted into the method handle type,
2616 * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)
2617 * The method and all its argument types must be accessible to the lookup object.
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 * If the returned method handle is invoked, the method's class will
2624 * be initialized, if it has not already been initialized.
2625 * <p><b>Example:</b>
2626 * {@snippet lang="java" :
2627 import static java.lang.invoke.MethodHandles.*;
2628 import static java.lang.invoke.MethodType.*;
2629 ...
2630 MethodHandle MH_asList = publicLookup().findStatic(Arrays.class,
2631 "asList", methodType(List.class, Object[].class));
2632 assertEquals("[x, y]", MH_asList.invoke("x", "y").toString());
2633 * }
2634 * @param refc the class from which the method is accessed
2635 * @param name the name of the method
2636 * @param type the type of the method
2637 * @return the desired method handle
2638 * @throws NoSuchMethodException if the method does not exist
2639 * @throws IllegalAccessException if access checking fails,
2640 * or if the method is not {@code static},
2641 * or if the method's variable arity modifier bit
2642 * is set and {@code asVarargsCollector} fails
2643 * @throws SecurityException if a security manager is present and it
2644 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2645 * @throws NullPointerException if any argument is null
2646 */
2647 public MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2648 MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type);
2649 return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerLookup(method));
2650 }
2651
2652 /**
2653 * Produces a method handle for a virtual method.
2654 * The type of the method handle will be that of the method,
2655 * with the receiver type (usually {@code refc}) prepended.
2656 * The method and all its argument types must be accessible to the lookup object.
2657 * <p>
2658 * When called, the handle will treat the first argument as a receiver
2659 * and, for non-private methods, dispatch on the receiver's type to determine which method
2660 * implementation to enter.
2661 * For private methods the named method in {@code refc} will be invoked on the receiver.
2662 * (The dispatching action is identical with that performed by an
2663 * {@code invokevirtual} or {@code invokeinterface} instruction.)
2664 * <p>
2665 * The first argument will be of type {@code refc} if the lookup
2666 * class has full privileges to access the member. Otherwise
2667 * the member must be {@code protected} and the first argument
2668 * will be restricted in type to the lookup class.
2669 * <p>
2670 * The returned method handle will have
2671 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2672 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2673 * <p>
2674 * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual}
2675 * instructions and method handles produced by {@code findVirtual},
2676 * if the class is {@code MethodHandle} and the name string is
2677 * {@code invokeExact} or {@code invoke}, the resulting
2678 * method handle is equivalent to one produced by
2679 * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or
2680 * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}
2681 * with the same {@code type} argument.
2682 * <p>
2683 * If the class is {@code VarHandle} and the name string corresponds to
2684 * the name of a signature-polymorphic access mode method, the resulting
2685 * method handle is equivalent to one produced by
2686 * {@link java.lang.invoke.MethodHandles#varHandleInvoker} with
2687 * the access mode corresponding to the name string and with the same
2688 * {@code type} arguments.
2689 * <p>
2690 * <b>Example:</b>
2691 * {@snippet lang="java" :
2692 import static java.lang.invoke.MethodHandles.*;
2693 import static java.lang.invoke.MethodType.*;
2694 ...
2695 MethodHandle MH_concat = publicLookup().findVirtual(String.class,
2696 "concat", methodType(String.class, String.class));
2697 MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class,
2698 "hashCode", methodType(int.class));
2699 MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class,
2700 "hashCode", methodType(int.class));
2701 assertEquals("xy", (String) MH_concat.invokeExact("x", "y"));
2702 assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy"));
2703 assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy"));
2704 // interface method:
2705 MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class,
2706 "subSequence", methodType(CharSequence.class, int.class, int.class));
2707 assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString());
2708 // constructor "internal method" must be accessed differently:
2709 MethodType MT_newString = methodType(void.class); //()V for new String()
2710 try { assertEquals("impossible", lookup()
2711 .findVirtual(String.class, "<init>", MT_newString));
2712 } catch (NoSuchMethodException ex) { } // OK
2713 MethodHandle MH_newString = publicLookup()
2714 .findConstructor(String.class, MT_newString);
2715 assertEquals("", (String) MH_newString.invokeExact());
2716 * }
2717 *
2718 * @param refc the class or interface from which the method is accessed
2719 * @param name the name of the method
2720 * @param type the type of the method, with the receiver argument omitted
2721 * @return the desired method handle
2722 * @throws NoSuchMethodException if the method does not exist
2723 * @throws IllegalAccessException if access checking fails,
2724 * or if the method is {@code static},
2725 * or if the method's variable arity modifier bit
2726 * is set and {@code asVarargsCollector} fails
2727 * @throws SecurityException if a security manager is present and it
2728 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2729 * @throws NullPointerException if any argument is null
2730 */
2731 public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2732 if (refc == MethodHandle.class) {
2733 MethodHandle mh = findVirtualForMH(name, type);
2734 if (mh != null) return mh;
2735 } else if (refc == VarHandle.class) {
2736 MethodHandle mh = findVirtualForVH(name, type);
2737 if (mh != null) return mh;
2738 }
2739 byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual);
2740 MemberName method = resolveOrFail(refKind, refc, name, type);
2741 return getDirectMethod(refKind, refc, method, findBoundCallerLookup(method));
2742 }
2743 private MethodHandle findVirtualForMH(String name, MethodType type) {
2744 // these names require special lookups because of the implicit MethodType argument
2745 if ("invoke".equals(name))
2746 return invoker(type);
2747 if ("invokeExact".equals(name))
2748 return exactInvoker(type);
2749 assert(!MemberName.isMethodHandleInvokeName(name));
2750 return null;
2751 }
2752 private MethodHandle findVirtualForVH(String name, MethodType type) {
2753 try {
2754 return varHandleInvoker(VarHandle.AccessMode.valueFromMethodName(name), type);
2755 } catch (IllegalArgumentException e) {
2756 return null;
2757 }
2758 }
2759
2760 /**
2761 * Produces a method handle which creates an object and initializes it, using
2762 * the constructor of the specified type.
2763 * The parameter types of the method handle will be those of the constructor,
2764 * while the return type will be a reference to the constructor's class.
2765 * The constructor and all its argument types must be accessible to the lookup object.
2766 * <p>
2767 * The requested type must have a return type of {@code void}.
2768 * (This is consistent with the JVM's treatment of constructor type descriptors.)
2769 * <p>
2770 * The returned method handle will have
2771 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2772 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
2773 * <p>
2774 * If the returned method handle is invoked, the constructor's class will
2775 * be initialized, if it has not already been initialized.
2776 * <p><b>Example:</b>
2777 * {@snippet lang="java" :
2778 import static java.lang.invoke.MethodHandles.*;
2779 import static java.lang.invoke.MethodType.*;
2780 ...
2781 MethodHandle MH_newArrayList = publicLookup().findConstructor(
2782 ArrayList.class, methodType(void.class, Collection.class));
2783 Collection orig = Arrays.asList("x", "y");
2784 Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig);
2785 assert(orig != copy);
2786 assertEquals(orig, copy);
2787 // a variable-arity constructor:
2788 MethodHandle MH_newProcessBuilder = publicLookup().findConstructor(
2789 ProcessBuilder.class, methodType(void.class, String[].class));
2790 ProcessBuilder pb = (ProcessBuilder)
2791 MH_newProcessBuilder.invoke("x", "y", "z");
2792 assertEquals("[x, y, z]", pb.command().toString());
2793 * }
2794 *
2795 *
2796 * @param refc the class or interface from which the method is accessed
2797 * @param type the type of the method, with the receiver argument omitted, and a void return type
2798 * @return the desired method handle
2799 * @throws NoSuchMethodException if the constructor does not exist
2800 * @throws IllegalAccessException if access checking fails
2801 * or if the method's variable arity modifier bit
2802 * is set and {@code asVarargsCollector} fails
2803 * @throws SecurityException if a security manager is present and it
2804 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2805 * @throws NullPointerException if any argument is null
2806 */
2807 public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2808 if (refc.isArray()) {
2809 throw new NoSuchMethodException("no constructor for array class: " + refc.getName());
2810 }
2811 if (type.returnType() != void.class) {
2812 throw new NoSuchMethodException("Constructors must have void return type: " + refc.getName());
2813 }
2814 String name = ConstantDescs.INIT_NAME;
2815 MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type);
2816 return getDirectConstructor(refc, ctor);
2817 }
2818
2819 /**
2820 * Looks up a class by name from the lookup context defined by this {@code Lookup} object,
2821 * <a href="MethodHandles.Lookup.html#equiv">as if resolved</a> by an {@code ldc} instruction.
2822 * Such a resolution, as specified in JVMS {@jvms 5.4.3.1}, attempts to locate and load the class,
2823 * and then determines whether the class is accessible to this lookup object.
2824 * <p>
2825 * For a class or an interface, the name is the {@linkplain ClassLoader##binary-name binary name}.
2826 * For an array class of {@code n} dimensions, the name begins with {@code n} occurrences
2827 * of {@code '['} and followed by the element type as encoded in the
2828 * {@linkplain Class##nameFormat table} specified in {@link Class#getName}.
2829 * <p>
2830 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class},
2831 * its class loader, and the {@linkplain #lookupModes() lookup modes}.
2832 *
2833 * @param targetName the {@linkplain ClassLoader##binary-name binary name} of the class
2834 * or the string representing an array class
2835 * @return the requested class.
2836 * @throws SecurityException if a security manager is present and it
2837 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2838 * @throws LinkageError if the linkage fails
2839 * @throws ClassNotFoundException if the class cannot be loaded by the lookup class' loader.
2840 * @throws IllegalAccessException if the class is not accessible, using the allowed access
2841 * modes.
2842 * @throws NullPointerException if {@code targetName} is null
2843 * @since 9
2844 * @jvms 5.4.3.1 Class and Interface Resolution
2845 */
2846 public Class<?> findClass(String targetName) throws ClassNotFoundException, IllegalAccessException {
2847 Class<?> targetClass = Class.forName(targetName, false, lookupClass.getClassLoader());
2848 return accessClass(targetClass);
2849 }
2850
2851 /**
2852 * Ensures that {@code targetClass} has been initialized. The class
2853 * to be initialized must be {@linkplain #accessClass accessible}
2854 * to this {@code Lookup} object. This method causes {@code targetClass}
2855 * to be initialized if it has not been already initialized,
2856 * as specified in JVMS {@jvms 5.5}.
2857 *
2858 * <p>
2859 * This method returns when {@code targetClass} is fully initialized, or
2860 * when {@code targetClass} is being initialized by the current thread.
2861 *
2862 * @param <T> the type of the class to be initialized
2863 * @param targetClass the class to be initialized
2864 * @return {@code targetClass} that has been initialized, or that is being
2865 * initialized by the current thread.
2866 *
2867 * @throws IllegalArgumentException if {@code targetClass} is a primitive type or {@code void}
2868 * or array class
2869 * @throws IllegalAccessException if {@code targetClass} is not
2870 * {@linkplain #accessClass accessible} to this lookup
2871 * @throws ExceptionInInitializerError if the class initialization provoked
2872 * by this method fails
2873 * @throws SecurityException if a security manager is present and it
2874 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2875 * @since 15
2876 * @jvms 5.5 Initialization
2877 */
2878 public <T> Class<T> ensureInitialized(Class<T> targetClass) throws IllegalAccessException {
2879 if (targetClass.isPrimitive())
2880 throw new IllegalArgumentException(targetClass + " is a primitive class");
2881 if (targetClass.isArray())
2882 throw new IllegalArgumentException(targetClass + " is an array class");
2883
2884 if (!VerifyAccess.isClassAccessible(targetClass, lookupClass, prevLookupClass, allowedModes)) {
2885 throw makeAccessException(targetClass);
2886 }
2887 checkSecurityManager(targetClass);
2888
2889 // ensure class initialization
2890 Unsafe.getUnsafe().ensureClassInitialized(targetClass);
2891 return targetClass;
2892 }
2893
2894 /*
2895 * Returns IllegalAccessException due to access violation to the given targetClass.
2896 *
2897 * This method is called by {@link Lookup#accessClass} and {@link Lookup#ensureInitialized}
2898 * which verifies access to a class rather a member.
2899 */
2900 private IllegalAccessException makeAccessException(Class<?> targetClass) {
2901 String message = "access violation: "+ targetClass;
2902 if (this == MethodHandles.publicLookup()) {
2903 message += ", from public Lookup";
2904 } else {
2905 Module m = lookupClass().getModule();
2906 message += ", from " + lookupClass() + " (" + m + ")";
2907 if (prevLookupClass != null) {
2908 message += ", previous lookup " +
2909 prevLookupClass.getName() + " (" + prevLookupClass.getModule() + ")";
2910 }
2911 }
2912 return new IllegalAccessException(message);
2913 }
2914
2915 /**
2916 * Determines if a class can be accessed from the lookup context defined by
2917 * this {@code Lookup} object. The static initializer of the class is not run.
2918 * If {@code targetClass} is an array class, {@code targetClass} is accessible
2919 * if the element type of the array class is accessible. Otherwise,
2920 * {@code targetClass} is determined as accessible as follows.
2921 *
2922 * <p>
2923 * If {@code targetClass} is in the same module as the lookup class,
2924 * the lookup class is {@code LC} in module {@code M1} and
2925 * the previous lookup class is in module {@code M0} or
2926 * {@code null} if not present,
2927 * {@code targetClass} is accessible if and only if one of the following is true:
2928 * <ul>
2929 * <li>If this lookup has {@link #PRIVATE} access, {@code targetClass} is
2930 * {@code LC} or other class in the same nest of {@code LC}.</li>
2931 * <li>If this lookup has {@link #PACKAGE} access, {@code targetClass} is
2932 * in the same runtime package of {@code LC}.</li>
2933 * <li>If this lookup has {@link #MODULE} access, {@code targetClass} is
2934 * a public type in {@code M1}.</li>
2935 * <li>If this lookup has {@link #PUBLIC} access, {@code targetClass} is
2936 * a public type in a package exported by {@code M1} to at least {@code M0}
2937 * if the previous lookup class is present; otherwise, {@code targetClass}
2938 * is a public type in a package exported by {@code M1} unconditionally.</li>
2939 * </ul>
2940 *
2941 * <p>
2942 * Otherwise, if this lookup has {@link #UNCONDITIONAL} access, this lookup
2943 * can access public types in all modules when the type is in a package
2944 * that is exported unconditionally.
2945 * <p>
2946 * Otherwise, {@code targetClass} is in a different module from {@code lookupClass},
2947 * and if this lookup does not have {@code PUBLIC} access, {@code lookupClass}
2948 * is inaccessible.
2949 * <p>
2950 * Otherwise, if this lookup has no {@linkplain #previousLookupClass() previous lookup class},
2951 * {@code M1} is the module containing {@code lookupClass} and
2952 * {@code M2} is the module containing {@code targetClass},
2953 * then {@code targetClass} is accessible if and only if
2954 * <ul>
2955 * <li>{@code M1} reads {@code M2}, and
2956 * <li>{@code targetClass} is public and in a package exported by
2957 * {@code M2} at least to {@code M1}.
2958 * </ul>
2959 * <p>
2960 * Otherwise, if this lookup has a {@linkplain #previousLookupClass() previous lookup class},
2961 * {@code M1} and {@code M2} are as before, and {@code M0} is the module
2962 * containing the previous lookup class, then {@code targetClass} is accessible
2963 * if and only if one of the following is true:
2964 * <ul>
2965 * <li>{@code targetClass} is in {@code M0} and {@code M1}
2966 * {@linkplain Module#reads reads} {@code M0} and the type is
2967 * in a package that is exported to at least {@code M1}.
2968 * <li>{@code targetClass} is in {@code M1} and {@code M0}
2969 * {@linkplain Module#reads reads} {@code M1} and the type is
2970 * in a package that is exported to at least {@code M0}.
2971 * <li>{@code targetClass} is in a third module {@code M2} and both {@code M0}
2972 * and {@code M1} reads {@code M2} and the type is in a package
2973 * that is exported to at least both {@code M0} and {@code M2}.
2974 * </ul>
2975 * <p>
2976 * Otherwise, {@code targetClass} is not accessible.
2977 *
2978 * @param <T> the type of the class to be access-checked
2979 * @param targetClass the class to be access-checked
2980 * @return {@code targetClass} that has been access-checked
2981 * @throws IllegalAccessException if the class is not accessible from the lookup class
2982 * and previous lookup class, if present, using the allowed access modes.
2983 * @throws SecurityException if a security manager is present and it
2984 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2985 * @throws NullPointerException if {@code targetClass} is {@code null}
2986 * @since 9
2987 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
2988 */
2989 public <T> Class<T> accessClass(Class<T> targetClass) throws IllegalAccessException {
2990 if (!isClassAccessible(targetClass)) {
2991 throw makeAccessException(targetClass);
2992 }
2993 checkSecurityManager(targetClass);
2994 return targetClass;
2995 }
2996
2997 /**
2998 * Produces an early-bound method handle for a virtual method.
2999 * It will bypass checks for overriding methods on the receiver,
3000 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
3001 * instruction from within the explicitly specified {@code specialCaller}.
3002 * The type of the method handle will be that of the method,
3003 * with a suitably restricted receiver type prepended.
3004 * (The receiver type will be {@code specialCaller} or a subtype.)
3005 * The method and all its argument types must be accessible
3006 * to the lookup object.
3007 * <p>
3008 * Before method resolution,
3009 * if the explicitly specified caller class is not identical with the
3010 * lookup class, or if this lookup object does not have
3011 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
3012 * privileges, the access fails.
3013 * <p>
3014 * The returned method handle will have
3015 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3016 * the method's variable arity modifier bit ({@code 0x0080}) is set.
3017 * <p style="font-size:smaller;">
3018 * <em>(Note: JVM internal methods named {@value ConstantDescs#INIT_NAME}
3019 * are not visible to this API,
3020 * even though the {@code invokespecial} instruction can refer to them
3021 * in special circumstances. Use {@link #findConstructor findConstructor}
3022 * to access instance initialization methods in a safe manner.)</em>
3023 * <p><b>Example:</b>
3024 * {@snippet lang="java" :
3025 import static java.lang.invoke.MethodHandles.*;
3026 import static java.lang.invoke.MethodType.*;
3027 ...
3028 static class Listie extends ArrayList {
3029 public String toString() { return "[wee Listie]"; }
3030 static Lookup lookup() { return MethodHandles.lookup(); }
3031 }
3032 ...
3033 // no access to constructor via invokeSpecial:
3034 MethodHandle MH_newListie = Listie.lookup()
3035 .findConstructor(Listie.class, methodType(void.class));
3036 Listie l = (Listie) MH_newListie.invokeExact();
3037 try { assertEquals("impossible", Listie.lookup().findSpecial(
3038 Listie.class, "<init>", methodType(void.class), Listie.class));
3039 } catch (NoSuchMethodException ex) { } // OK
3040 // access to super and self methods via invokeSpecial:
3041 MethodHandle MH_super = Listie.lookup().findSpecial(
3042 ArrayList.class, "toString" , methodType(String.class), Listie.class);
3043 MethodHandle MH_this = Listie.lookup().findSpecial(
3044 Listie.class, "toString" , methodType(String.class), Listie.class);
3045 MethodHandle MH_duper = Listie.lookup().findSpecial(
3046 Object.class, "toString" , methodType(String.class), Listie.class);
3047 assertEquals("[]", (String) MH_super.invokeExact(l));
3048 assertEquals(""+l, (String) MH_this.invokeExact(l));
3049 assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method
3050 try { assertEquals("inaccessible", Listie.lookup().findSpecial(
3051 String.class, "toString", methodType(String.class), Listie.class));
3052 } catch (IllegalAccessException ex) { } // OK
3053 Listie subl = new Listie() { public String toString() { return "[subclass]"; } };
3054 assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method
3055 * }
3056 *
3057 * @param refc the class or interface from which the method is accessed
3058 * @param name the name of the method (which must not be "<init>")
3059 * @param type the type of the method, with the receiver argument omitted
3060 * @param specialCaller the proposed calling class to perform the {@code invokespecial}
3061 * @return the desired method handle
3062 * @throws NoSuchMethodException if the method does not exist
3063 * @throws IllegalAccessException if access checking fails,
3064 * or if the method is {@code static},
3065 * or if the method's variable arity modifier bit
3066 * is set and {@code asVarargsCollector} fails
3067 * @throws SecurityException if a security manager is present and it
3068 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3069 * @throws NullPointerException if any argument is null
3070 */
3071 public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,
3072 Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
3073 checkSpecialCaller(specialCaller, refc);
3074 Lookup specialLookup = this.in(specialCaller);
3075 MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type);
3076 return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerLookup(method));
3077 }
3078
3079 /**
3080 * Produces a method handle giving read access to a non-static field.
3081 * The type of the method handle will have a return type of the field's
3082 * value type.
3083 * The method handle's single argument will be the instance containing
3084 * the field.
3085 * Access checking is performed immediately on behalf of the lookup class.
3086 * @param refc the class or interface from which the method is accessed
3087 * @param name the field's name
3088 * @param type the field's type
3089 * @return a method handle which can load values from the field
3090 * @throws NoSuchFieldException if the field does not exist
3091 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
3092 * @throws SecurityException if a security manager is present and it
3093 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3094 * @throws NullPointerException if any argument is null
3095 * @see #findVarHandle(Class, String, Class)
3096 */
3097 public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3098 MemberName field = resolveOrFail(REF_getField, refc, name, type);
3099 return getDirectField(REF_getField, refc, field);
3100 }
3101
3102 /**
3103 * Produces a method handle giving write access to a non-static field.
3104 * The type of the method handle will have a void return type.
3105 * The method handle will take two arguments, the instance containing
3106 * the field, and the value to be stored.
3107 * The second argument will be of the field's value type.
3108 * Access checking is performed immediately on behalf of the lookup class.
3109 * @param refc the class or interface from which the method is accessed
3110 * @param name the field's name
3111 * @param type the field's type
3112 * @return a method handle which can store values into the field
3113 * @throws NoSuchFieldException if the field does not exist
3114 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
3115 * or {@code final}
3116 * @throws SecurityException if a security manager is present and it
3117 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3118 * @throws NullPointerException if any argument is null
3119 * @see #findVarHandle(Class, String, Class)
3120 */
3121 public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3122 MemberName field = resolveOrFail(REF_putField, refc, name, type);
3123 return getDirectField(REF_putField, refc, field);
3124 }
3125
3126 /**
3127 * Produces a VarHandle giving access to a non-static field {@code name}
3128 * of type {@code type} declared in a class of type {@code recv}.
3129 * The VarHandle's variable type is {@code type} and it has one
3130 * coordinate type, {@code recv}.
3131 * <p>
3132 * Access checking is performed immediately on behalf of the lookup
3133 * class.
3134 * <p>
3135 * Certain access modes of the returned VarHandle are unsupported under
3136 * the following conditions:
3137 * <ul>
3138 * <li>if the field is declared {@code final}, then the write, atomic
3139 * update, numeric atomic update, and bitwise atomic update access
3140 * modes are unsupported.
3141 * <li>if the field type is anything other than {@code byte},
3142 * {@code short}, {@code char}, {@code int}, {@code long},
3143 * {@code float}, or {@code double} then numeric atomic update
3144 * access modes are unsupported.
3145 * <li>if the field type is anything other than {@code boolean},
3146 * {@code byte}, {@code short}, {@code char}, {@code int} or
3147 * {@code long} then bitwise atomic update access modes are
3148 * unsupported.
3149 * </ul>
3150 * <p>
3151 * If the field is declared {@code volatile} then the returned VarHandle
3152 * will override access to the field (effectively ignore the
3153 * {@code volatile} declaration) in accordance to its specified
3154 * access modes.
3155 * <p>
3156 * If the field type is {@code float} or {@code double} then numeric
3157 * and atomic update access modes compare values using their bitwise
3158 * representation (see {@link Float#floatToRawIntBits} and
3159 * {@link Double#doubleToRawLongBits}, respectively).
3160 * @apiNote
3161 * Bitwise comparison of {@code float} values or {@code double} values,
3162 * as performed by the numeric and atomic update access modes, differ
3163 * from the primitive {@code ==} operator and the {@link Float#equals}
3164 * and {@link Double#equals} methods, specifically with respect to
3165 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
3166 * Care should be taken when performing a compare and set or a compare
3167 * and exchange operation with such values since the operation may
3168 * unexpectedly fail.
3169 * There are many possible NaN values that are considered to be
3170 * {@code NaN} in Java, although no IEEE 754 floating-point operation
3171 * provided by Java can distinguish between them. Operation failure can
3172 * occur if the expected or witness value is a NaN value and it is
3173 * transformed (perhaps in a platform specific manner) into another NaN
3174 * value, and thus has a different bitwise representation (see
3175 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
3176 * details).
3177 * The values {@code -0.0} and {@code +0.0} have different bitwise
3178 * representations but are considered equal when using the primitive
3179 * {@code ==} operator. Operation failure can occur if, for example, a
3180 * numeric algorithm computes an expected value to be say {@code -0.0}
3181 * and previously computed the witness value to be say {@code +0.0}.
3182 * @param recv the receiver class, of type {@code R}, that declares the
3183 * non-static field
3184 * @param name the field's name
3185 * @param type the field's type, of type {@code T}
3186 * @return a VarHandle giving access to non-static fields.
3187 * @throws NoSuchFieldException if the field does not exist
3188 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
3189 * @throws SecurityException if a security manager is present and it
3190 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3191 * @throws NullPointerException if any argument is null
3192 * @since 9
3193 */
3194 public VarHandle findVarHandle(Class<?> recv, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3195 MemberName getField = resolveOrFail(REF_getField, recv, name, type);
3196 MemberName putField = resolveOrFail(REF_putField, recv, name, type);
3197 return getFieldVarHandle(REF_getField, REF_putField, recv, getField, putField);
3198 }
3199
3200 /**
3201 * Produces a method handle giving read access to a static field.
3202 * The type of the method handle will have a return type of the field's
3203 * value type.
3204 * The method handle will take no arguments.
3205 * Access checking is performed immediately on behalf of the lookup class.
3206 * <p>
3207 * If the returned method handle is invoked, the field's class will
3208 * be initialized, if it has not already been initialized.
3209 * @param refc the class or interface from which the method is accessed
3210 * @param name the field's name
3211 * @param type the field's type
3212 * @return a method handle which can load values from the field
3213 * @throws NoSuchFieldException if the field does not exist
3214 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
3215 * @throws SecurityException if a security manager is present and it
3216 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3217 * @throws NullPointerException if any argument is null
3218 */
3219 public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3220 MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
3221 return getDirectField(REF_getStatic, refc, field);
3222 }
3223
3224 /**
3225 * Produces a method handle giving write access to a static field.
3226 * The type of the method handle will have a void return type.
3227 * The method handle will take a single
3228 * argument, of the field's value type, the value to be stored.
3229 * Access checking is performed immediately on behalf of the lookup class.
3230 * <p>
3231 * If the returned method handle is invoked, the field's class will
3232 * be initialized, if it has not already been initialized.
3233 * @param refc the class or interface from which the method is accessed
3234 * @param name the field's name
3235 * @param type the field's type
3236 * @return a method handle which can store values into the field
3237 * @throws NoSuchFieldException if the field does not exist
3238 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
3239 * or is {@code final}
3240 * @throws SecurityException if a security manager is present and it
3241 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3242 * @throws NullPointerException if any argument is null
3243 */
3244 public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3245 MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
3246 return getDirectField(REF_putStatic, refc, field);
3247 }
3248
3249 /**
3250 * Produces a VarHandle giving access to a static field {@code name} of
3251 * type {@code type} declared in a class of type {@code decl}.
3252 * The VarHandle's variable type is {@code type} and it has no
3253 * coordinate types.
3254 * <p>
3255 * Access checking is performed immediately on behalf of the lookup
3256 * class.
3257 * <p>
3258 * If the returned VarHandle is operated on, the declaring class will be
3259 * initialized, if it has not already been initialized.
3260 * <p>
3261 * Certain access modes of the returned VarHandle are unsupported under
3262 * the following conditions:
3263 * <ul>
3264 * <li>if the field is declared {@code final}, then the write, atomic
3265 * update, numeric atomic update, and bitwise atomic update access
3266 * modes are unsupported.
3267 * <li>if the field type is anything other than {@code byte},
3268 * {@code short}, {@code char}, {@code int}, {@code long},
3269 * {@code float}, or {@code double}, then numeric atomic update
3270 * access modes are unsupported.
3271 * <li>if the field type is anything other than {@code boolean},
3272 * {@code byte}, {@code short}, {@code char}, {@code int} or
3273 * {@code long} then bitwise atomic update access modes are
3274 * unsupported.
3275 * </ul>
3276 * <p>
3277 * If the field is declared {@code volatile} then the returned VarHandle
3278 * will override access to the field (effectively ignore the
3279 * {@code volatile} declaration) in accordance to its specified
3280 * access modes.
3281 * <p>
3282 * If the field type is {@code float} or {@code double} then numeric
3283 * and atomic update access modes compare values using their bitwise
3284 * representation (see {@link Float#floatToRawIntBits} and
3285 * {@link Double#doubleToRawLongBits}, respectively).
3286 * @apiNote
3287 * Bitwise comparison of {@code float} values or {@code double} values,
3288 * as performed by the numeric and atomic update access modes, differ
3289 * from the primitive {@code ==} operator and the {@link Float#equals}
3290 * and {@link Double#equals} methods, specifically with respect to
3291 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
3292 * Care should be taken when performing a compare and set or a compare
3293 * and exchange operation with such values since the operation may
3294 * unexpectedly fail.
3295 * There are many possible NaN values that are considered to be
3296 * {@code NaN} in Java, although no IEEE 754 floating-point operation
3297 * provided by Java can distinguish between them. Operation failure can
3298 * occur if the expected or witness value is a NaN value and it is
3299 * transformed (perhaps in a platform specific manner) into another NaN
3300 * value, and thus has a different bitwise representation (see
3301 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
3302 * details).
3303 * The values {@code -0.0} and {@code +0.0} have different bitwise
3304 * representations but are considered equal when using the primitive
3305 * {@code ==} operator. Operation failure can occur if, for example, a
3306 * numeric algorithm computes an expected value to be say {@code -0.0}
3307 * and previously computed the witness value to be say {@code +0.0}.
3308 * @param decl the class that declares the static field
3309 * @param name the field's name
3310 * @param type the field's type, of type {@code T}
3311 * @return a VarHandle giving access to a static field
3312 * @throws NoSuchFieldException if the field does not exist
3313 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
3314 * @throws SecurityException if a security manager is present and it
3315 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3316 * @throws NullPointerException if any argument is null
3317 * @since 9
3318 */
3319 public VarHandle findStaticVarHandle(Class<?> decl, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3320 MemberName getField = resolveOrFail(REF_getStatic, decl, name, type);
3321 MemberName putField = resolveOrFail(REF_putStatic, decl, name, type);
3322 return getFieldVarHandle(REF_getStatic, REF_putStatic, decl, getField, putField);
3323 }
3324
3325 /**
3326 * Produces an early-bound method handle for a non-static method.
3327 * The receiver must have a supertype {@code defc} in which a method
3328 * of the given name and type is accessible to the lookup class.
3329 * The method and all its argument types must be accessible to the lookup object.
3330 * The type of the method handle will be that of the method,
3331 * without any insertion of an additional receiver parameter.
3332 * The given receiver will be bound into the method handle,
3333 * so that every call to the method handle will invoke the
3334 * requested method on the given receiver.
3335 * <p>
3336 * The returned method handle will have
3337 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3338 * the method's variable arity modifier bit ({@code 0x0080}) is set
3339 * <em>and</em> the trailing array argument is not the only argument.
3340 * (If the trailing array argument is the only argument,
3341 * the given receiver value will be bound to it.)
3342 * <p>
3343 * This is almost equivalent to the following code, with some differences noted below:
3344 * {@snippet lang="java" :
3345 import static java.lang.invoke.MethodHandles.*;
3346 import static java.lang.invoke.MethodType.*;
3347 ...
3348 MethodHandle mh0 = lookup().findVirtual(defc, name, type);
3349 MethodHandle mh1 = mh0.bindTo(receiver);
3350 mh1 = mh1.withVarargs(mh0.isVarargsCollector());
3351 return mh1;
3352 * }
3353 * where {@code defc} is either {@code receiver.getClass()} or a super
3354 * type of that class, in which the requested method is accessible
3355 * to the lookup class.
3356 * (Unlike {@code bind}, {@code bindTo} does not preserve variable arity.
3357 * Also, {@code bindTo} may throw a {@code ClassCastException} in instances where {@code bind} would
3358 * throw an {@code IllegalAccessException}, as in the case where the member is {@code protected} and
3359 * the receiver is restricted by {@code findVirtual} to the lookup class.)
3360 * @param receiver the object from which the method is accessed
3361 * @param name the name of the method
3362 * @param type the type of the method, with the receiver argument omitted
3363 * @return the desired method handle
3364 * @throws NoSuchMethodException if the method does not exist
3365 * @throws IllegalAccessException if access checking fails
3366 * or if the method's variable arity modifier bit
3367 * is set and {@code asVarargsCollector} fails
3368 * @throws SecurityException if a security manager is present and it
3369 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3370 * @throws NullPointerException if any argument is null
3371 * @see MethodHandle#bindTo
3372 * @see #findVirtual
3373 */
3374 public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
3375 Class<? extends Object> refc = receiver.getClass(); // may get NPE
3376 MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
3377 MethodHandle mh = getDirectMethodNoRestrictInvokeSpecial(refc, method, findBoundCallerLookup(method));
3378 if (!mh.type().leadingReferenceParameter().isAssignableFrom(receiver.getClass())) {
3379 throw new IllegalAccessException("The restricted defining class " +
3380 mh.type().leadingReferenceParameter().getName() +
3381 " is not assignable from receiver class " +
3382 receiver.getClass().getName());
3383 }
3384 return mh.bindArgumentL(0, receiver).setVarargs(method);
3385 }
3386
3387 /**
3388 * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
3389 * to <i>m</i>, if the lookup class has permission.
3390 * If <i>m</i> is non-static, the receiver argument is treated as an initial argument.
3391 * If <i>m</i> is virtual, overriding is respected on every call.
3392 * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped.
3393 * The type of the method handle will be that of the method,
3394 * with the receiver type prepended (but only if it is non-static).
3395 * If the method's {@code accessible} flag is not set,
3396 * access checking is performed immediately on behalf of the lookup class.
3397 * If <i>m</i> is not public, do not share the resulting handle with untrusted parties.
3398 * <p>
3399 * The returned method handle will have
3400 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3401 * the method's variable arity modifier bit ({@code 0x0080}) is set.
3402 * <p>
3403 * If <i>m</i> is static, and
3404 * if the returned method handle is invoked, the method's class will
3405 * be initialized, if it has not already been initialized.
3406 * @param m the reflected method
3407 * @return a method handle which can invoke the reflected method
3408 * @throws IllegalAccessException if access checking fails
3409 * or if the method's variable arity modifier bit
3410 * is set and {@code asVarargsCollector} fails
3411 * @throws NullPointerException if the argument is null
3412 */
3413 public MethodHandle unreflect(Method m) throws IllegalAccessException {
3414 if (m.getDeclaringClass() == MethodHandle.class) {
3415 MethodHandle mh = unreflectForMH(m);
3416 if (mh != null) return mh;
3417 }
3418 if (m.getDeclaringClass() == VarHandle.class) {
3419 MethodHandle mh = unreflectForVH(m);
3420 if (mh != null) return mh;
3421 }
3422 MemberName method = new MemberName(m);
3423 byte refKind = method.getReferenceKind();
3424 if (refKind == REF_invokeSpecial)
3425 refKind = REF_invokeVirtual;
3426 assert(method.isMethod());
3427 @SuppressWarnings("deprecation")
3428 Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
3429 return lookup.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method, findBoundCallerLookup(method));
3430 }
3431 private MethodHandle unreflectForMH(Method m) {
3432 // these names require special lookups because they throw UnsupportedOperationException
3433 if (MemberName.isMethodHandleInvokeName(m.getName()))
3434 return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m));
3435 return null;
3436 }
3437 private MethodHandle unreflectForVH(Method m) {
3438 // these names require special lookups because they throw UnsupportedOperationException
3439 if (MemberName.isVarHandleMethodInvokeName(m.getName()))
3440 return MethodHandleImpl.fakeVarHandleInvoke(new MemberName(m));
3441 return null;
3442 }
3443
3444 /**
3445 * Produces a method handle for a reflected method.
3446 * It will bypass checks for overriding methods on the receiver,
3447 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
3448 * instruction from within the explicitly specified {@code specialCaller}.
3449 * The type of the method handle will be that of the method,
3450 * with a suitably restricted receiver type prepended.
3451 * (The receiver type will be {@code specialCaller} or a subtype.)
3452 * If the method's {@code accessible} flag is not set,
3453 * access checking is performed immediately on behalf of the lookup class,
3454 * as if {@code invokespecial} instruction were being linked.
3455 * <p>
3456 * Before method resolution,
3457 * if the explicitly specified caller class is not identical with the
3458 * lookup class, or if this lookup object does not have
3459 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
3460 * privileges, the access fails.
3461 * <p>
3462 * The returned method handle will have
3463 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3464 * the method's variable arity modifier bit ({@code 0x0080}) is set.
3465 * @param m the reflected method
3466 * @param specialCaller the class nominally calling the method
3467 * @return a method handle which can invoke the reflected method
3468 * @throws IllegalAccessException if access checking fails,
3469 * or if the method is {@code static},
3470 * or if the method's variable arity modifier bit
3471 * is set and {@code asVarargsCollector} fails
3472 * @throws NullPointerException if any argument is null
3473 */
3474 public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException {
3475 checkSpecialCaller(specialCaller, m.getDeclaringClass());
3476 Lookup specialLookup = this.in(specialCaller);
3477 MemberName method = new MemberName(m, true);
3478 assert(method.isMethod());
3479 // ignore m.isAccessible: this is a new kind of access
3480 return specialLookup.getDirectMethodNoSecurityManager(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerLookup(method));
3481 }
3482
3483 /**
3484 * Produces a method handle for a reflected constructor.
3485 * The type of the method handle will be that of the constructor,
3486 * with the return type changed to the declaring class.
3487 * The method handle will perform a {@code newInstance} operation,
3488 * creating a new instance of the constructor's class on the
3489 * arguments passed to the method handle.
3490 * <p>
3491 * If the constructor's {@code accessible} flag is not set,
3492 * access checking is performed immediately on behalf of the lookup class.
3493 * <p>
3494 * The returned method handle will have
3495 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3496 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
3497 * <p>
3498 * If the returned method handle is invoked, the constructor's class will
3499 * be initialized, if it has not already been initialized.
3500 * @param c the reflected constructor
3501 * @return a method handle which can invoke the reflected constructor
3502 * @throws IllegalAccessException if access checking fails
3503 * or if the method's variable arity modifier bit
3504 * is set and {@code asVarargsCollector} fails
3505 * @throws NullPointerException if the argument is null
3506 */
3507 public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException {
3508 MemberName ctor = new MemberName(c);
3509 assert(ctor.isConstructor());
3510 @SuppressWarnings("deprecation")
3511 Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
3512 return lookup.getDirectConstructorNoSecurityManager(ctor.getDeclaringClass(), ctor);
3513 }
3514
3515 /*
3516 * Produces a method handle that is capable of creating instances of the given class
3517 * and instantiated by the given constructor. No security manager check.
3518 *
3519 * This method should only be used by ReflectionFactory::newConstructorForSerialization.
3520 */
3521 /* package-private */ MethodHandle serializableConstructor(Class<?> decl, Constructor<?> c) throws IllegalAccessException {
3522 MemberName ctor = new MemberName(c);
3523 assert(ctor.isConstructor() && constructorInSuperclass(decl, c));
3524 checkAccess(REF_newInvokeSpecial, decl, ctor);
3525 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
3526 return DirectMethodHandle.makeAllocator(decl, ctor).setVarargs(ctor);
3527 }
3528
3529 private static boolean constructorInSuperclass(Class<?> decl, Constructor<?> ctor) {
3530 if (decl == ctor.getDeclaringClass())
3531 return true;
3532
3533 Class<?> cl = decl;
3534 while ((cl = cl.getSuperclass()) != null) {
3535 if (cl == ctor.getDeclaringClass()) {
3536 return true;
3537 }
3538 }
3539 return false;
3540 }
3541
3542 /**
3543 * Produces a method handle giving read access to a reflected field.
3544 * The type of the method handle will have a return type of the field's
3545 * value type.
3546 * If the field is {@code static}, the method handle will take no arguments.
3547 * Otherwise, its single argument will be the instance containing
3548 * the field.
3549 * If the {@code Field} object's {@code accessible} flag is not set,
3550 * access checking is performed immediately on behalf of the lookup class.
3551 * <p>
3552 * If the field is static, and
3553 * if the returned method handle is invoked, the field's class will
3554 * be initialized, if it has not already been initialized.
3555 * @param f the reflected field
3556 * @return a method handle which can load values from the reflected field
3557 * @throws IllegalAccessException if access checking fails
3558 * @throws NullPointerException if the argument is null
3559 */
3560 public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
3561 return unreflectField(f, false);
3562 }
3563
3564 /**
3565 * Produces a method handle giving write access to a reflected field.
3566 * The type of the method handle will have a void return type.
3567 * If the field is {@code static}, the method handle will take a single
3568 * argument, of the field's value type, the value to be stored.
3569 * Otherwise, the two arguments will be the instance containing
3570 * the field, and the value to be stored.
3571 * If the {@code Field} object's {@code accessible} flag is not set,
3572 * access checking is performed immediately on behalf of the lookup class.
3573 * <p>
3574 * If the field is {@code final}, write access will not be
3575 * allowed and access checking will fail, except under certain
3576 * narrow circumstances documented for {@link Field#set Field.set}.
3577 * A method handle is returned only if a corresponding call to
3578 * the {@code Field} object's {@code set} method could return
3579 * normally. In particular, fields which are both {@code static}
3580 * and {@code final} may never be set.
3581 * <p>
3582 * If the field is {@code static}, and
3583 * if the returned method handle is invoked, the field's class will
3584 * be initialized, if it has not already been initialized.
3585 * @param f the reflected field
3586 * @return a method handle which can store values into the reflected field
3587 * @throws IllegalAccessException if access checking fails,
3588 * or if the field is {@code final} and write access
3589 * is not enabled on the {@code Field} object
3590 * @throws NullPointerException if the argument is null
3591 */
3592 public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
3593 return unreflectField(f, true);
3594 }
3595
3596 private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
3597 MemberName field = new MemberName(f, isSetter);
3598 if (isSetter && field.isFinal()) {
3599 if (field.isTrustedFinalField()) {
3600 String msg = field.isStatic() ? "static final field has no write access"
3601 : "final field has no write access";
3602 throw field.makeAccessException(msg, this);
3603 }
3604 }
3605 assert(isSetter
3606 ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
3607 : MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
3608 @SuppressWarnings("deprecation")
3609 Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
3610 return lookup.getDirectFieldNoSecurityManager(field.getReferenceKind(), f.getDeclaringClass(), field);
3611 }
3612
3613 /**
3614 * Produces a VarHandle giving access to a reflected field {@code f}
3615 * of type {@code T} declared in a class of type {@code R}.
3616 * The VarHandle's variable type is {@code T}.
3617 * If the field is non-static the VarHandle has one coordinate type,
3618 * {@code R}. Otherwise, the field is static, and the VarHandle has no
3619 * coordinate types.
3620 * <p>
3621 * Access checking is performed immediately on behalf of the lookup
3622 * class, regardless of the value of the field's {@code accessible}
3623 * flag.
3624 * <p>
3625 * If the field is static, and if the returned VarHandle is operated
3626 * on, the field's declaring class will be initialized, if it has not
3627 * already been initialized.
3628 * <p>
3629 * Certain access modes of the returned VarHandle are unsupported under
3630 * the following conditions:
3631 * <ul>
3632 * <li>if the field is declared {@code final}, then the write, atomic
3633 * update, numeric atomic update, and bitwise atomic update access
3634 * modes are unsupported.
3635 * <li>if the field type is anything other than {@code byte},
3636 * {@code short}, {@code char}, {@code int}, {@code long},
3637 * {@code float}, or {@code double} then numeric atomic update
3638 * access modes are unsupported.
3639 * <li>if the field type is anything other than {@code boolean},
3640 * {@code byte}, {@code short}, {@code char}, {@code int} or
3641 * {@code long} then bitwise atomic update access modes are
3642 * unsupported.
3643 * </ul>
3644 * <p>
3645 * If the field is declared {@code volatile} then the returned VarHandle
3646 * will override access to the field (effectively ignore the
3647 * {@code volatile} declaration) in accordance to its specified
3648 * access modes.
3649 * <p>
3650 * If the field type is {@code float} or {@code double} then numeric
3651 * and atomic update access modes compare values using their bitwise
3652 * representation (see {@link Float#floatToRawIntBits} and
3653 * {@link Double#doubleToRawLongBits}, respectively).
3654 * @apiNote
3655 * Bitwise comparison of {@code float} values or {@code double} values,
3656 * as performed by the numeric and atomic update access modes, differ
3657 * from the primitive {@code ==} operator and the {@link Float#equals}
3658 * and {@link Double#equals} methods, specifically with respect to
3659 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
3660 * Care should be taken when performing a compare and set or a compare
3661 * and exchange operation with such values since the operation may
3662 * unexpectedly fail.
3663 * There are many possible NaN values that are considered to be
3664 * {@code NaN} in Java, although no IEEE 754 floating-point operation
3665 * provided by Java can distinguish between them. Operation failure can
3666 * occur if the expected or witness value is a NaN value and it is
3667 * transformed (perhaps in a platform specific manner) into another NaN
3668 * value, and thus has a different bitwise representation (see
3669 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
3670 * details).
3671 * The values {@code -0.0} and {@code +0.0} have different bitwise
3672 * representations but are considered equal when using the primitive
3673 * {@code ==} operator. Operation failure can occur if, for example, a
3674 * numeric algorithm computes an expected value to be say {@code -0.0}
3675 * and previously computed the witness value to be say {@code +0.0}.
3676 * @param f the reflected field, with a field of type {@code T}, and
3677 * a declaring class of type {@code R}
3678 * @return a VarHandle giving access to non-static fields or a static
3679 * field
3680 * @throws IllegalAccessException if access checking fails
3681 * @throws NullPointerException if the argument is null
3682 * @since 9
3683 */
3684 public VarHandle unreflectVarHandle(Field f) throws IllegalAccessException {
3685 MemberName getField = new MemberName(f, false);
3686 MemberName putField = new MemberName(f, true);
3687 return getFieldVarHandleNoSecurityManager(getField.getReferenceKind(), putField.getReferenceKind(),
3688 f.getDeclaringClass(), getField, putField);
3689 }
3690
3691 /**
3692 * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
3693 * created by this lookup object or a similar one.
3694 * Security and access checks are performed to ensure that this lookup object
3695 * is capable of reproducing the target method handle.
3696 * This means that the cracking may fail if target is a direct method handle
3697 * but was created by an unrelated lookup object.
3698 * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a>
3699 * and was created by a lookup object for a different class.
3700 * @param target a direct method handle to crack into symbolic reference components
3701 * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object
3702 * @throws SecurityException if a security manager is present and it
3703 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3704 * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails
3705 * @throws NullPointerException if the target is {@code null}
3706 * @see MethodHandleInfo
3707 * @since 1.8
3708 */
3709 public MethodHandleInfo revealDirect(MethodHandle target) {
3710 if (!target.isCrackable()) {
3711 throw newIllegalArgumentException("not a direct method handle");
3712 }
3713 MemberName member = target.internalMemberName();
3714 Class<?> defc = member.getDeclaringClass();
3715 byte refKind = member.getReferenceKind();
3716 assert(MethodHandleNatives.refKindIsValid(refKind));
3717 if (refKind == REF_invokeSpecial && !target.isInvokeSpecial())
3718 // Devirtualized method invocation is usually formally virtual.
3719 // To avoid creating extra MemberName objects for this common case,
3720 // we encode this extra degree of freedom using MH.isInvokeSpecial.
3721 refKind = REF_invokeVirtual;
3722 if (refKind == REF_invokeVirtual && defc.isInterface())
3723 // Symbolic reference is through interface but resolves to Object method (toString, etc.)
3724 refKind = REF_invokeInterface;
3725 // Check SM permissions and member access before cracking.
3726 try {
3727 checkAccess(refKind, defc, member);
3728 checkSecurityManager(defc, member);
3729 } catch (IllegalAccessException ex) {
3730 throw new IllegalArgumentException(ex);
3731 }
3732 if (allowedModes != TRUSTED && member.isCallerSensitive()) {
3733 Class<?> callerClass = target.internalCallerClass();
3734 if ((lookupModes() & ORIGINAL) == 0 || callerClass != lookupClass())
3735 throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass);
3736 }
3737 // Produce the handle to the results.
3738 return new InfoFromMemberName(this, member, refKind);
3739 }
3740
3741 //--- Helper methods, all package-private.
3742
3743 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3744 checkSymbolicClass(refc); // do this before attempting to resolve
3745 Objects.requireNonNull(name);
3746 Objects.requireNonNull(type);
3747 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), allowedModes,
3748 NoSuchFieldException.class);
3749 }
3750
3751 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
3752 checkSymbolicClass(refc); // do this before attempting to resolve
3753 Objects.requireNonNull(type);
3754 checkMethodName(refKind, name); // implicit null-check of name
3755 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), allowedModes,
3756 NoSuchMethodException.class);
3757 }
3758
3759 MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException {
3760 checkSymbolicClass(member.getDeclaringClass()); // do this before attempting to resolve
3761 Objects.requireNonNull(member.getName());
3762 Objects.requireNonNull(member.getType());
3763 return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(), allowedModes,
3764 ReflectiveOperationException.class);
3765 }
3766
3767 MemberName resolveOrNull(byte refKind, MemberName member) {
3768 // do this before attempting to resolve
3769 if (!isClassAccessible(member.getDeclaringClass())) {
3770 return null;
3771 }
3772 Objects.requireNonNull(member.getName());
3773 Objects.requireNonNull(member.getType());
3774 return IMPL_NAMES.resolveOrNull(refKind, member, lookupClassOrNull(), allowedModes);
3775 }
3776
3777 MemberName resolveOrNull(byte refKind, Class<?> refc, String name, MethodType type) {
3778 // do this before attempting to resolve
3779 if (!isClassAccessible(refc)) {
3780 return null;
3781 }
3782 Objects.requireNonNull(type);
3783 // implicit null-check of name
3784 if (name.startsWith("<") && refKind != REF_newInvokeSpecial) {
3785 return null;
3786 }
3787 return IMPL_NAMES.resolveOrNull(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), allowedModes);
3788 }
3789
3790 void checkSymbolicClass(Class<?> refc) throws IllegalAccessException {
3791 if (!isClassAccessible(refc)) {
3792 throw new MemberName(refc).makeAccessException("symbolic reference class is not accessible", this);
3793 }
3794 }
3795
3796 boolean isClassAccessible(Class<?> refc) {
3797 Objects.requireNonNull(refc);
3798 Class<?> caller = lookupClassOrNull();
3799 Class<?> type = refc;
3800 while (type.isArray()) {
3801 type = type.getComponentType();
3802 }
3803 return caller == null || VerifyAccess.isClassAccessible(type, caller, prevLookupClass, allowedModes);
3804 }
3805
3806 /** Check name for an illegal leading "<" character. */
3807 void checkMethodName(byte refKind, String name) throws NoSuchMethodException {
3808 if (name.startsWith("<") && refKind != REF_newInvokeSpecial)
3809 throw new NoSuchMethodException("illegal method name: "+name);
3810 }
3811
3812 /**
3813 * Find my trustable caller class if m is a caller sensitive method.
3814 * If this lookup object has original full privilege access, then the caller class is the lookupClass.
3815 * Otherwise, if m is caller-sensitive, throw IllegalAccessException.
3816 */
3817 Lookup findBoundCallerLookup(MemberName m) throws IllegalAccessException {
3818 if (MethodHandleNatives.isCallerSensitive(m) && (lookupModes() & ORIGINAL) == 0) {
3819 // Only lookups with full privilege access are allowed to resolve caller-sensitive methods
3820 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
3821 }
3822 return this;
3823 }
3824
3825 /**
3826 * Returns {@code true} if this lookup has {@code PRIVATE} and {@code MODULE} access.
3827 * @return {@code true} if this lookup has {@code PRIVATE} and {@code MODULE} access.
3828 *
3829 * @deprecated This method was originally designed to test {@code PRIVATE} access
3830 * that implies full privilege access but {@code MODULE} access has since become
3831 * independent of {@code PRIVATE} access. It is recommended to call
3832 * {@link #hasFullPrivilegeAccess()} instead.
3833 * @since 9
3834 */
3835 @Deprecated(since="14")
3836 public boolean hasPrivateAccess() {
3837 return hasFullPrivilegeAccess();
3838 }
3839
3840 /**
3841 * Returns {@code true} if this lookup has <em>full privilege access</em>,
3842 * i.e. {@code PRIVATE} and {@code MODULE} access.
3843 * A {@code Lookup} object must have full privilege access in order to
3844 * access all members that are allowed to the
3845 * {@linkplain #lookupClass() lookup class}.
3846 *
3847 * @return {@code true} if this lookup has full privilege access.
3848 * @since 14
3849 * @see <a href="MethodHandles.Lookup.html#privacc">private and module access</a>
3850 */
3851 public boolean hasFullPrivilegeAccess() {
3852 return (allowedModes & (PRIVATE|MODULE)) == (PRIVATE|MODULE);
3853 }
3854
3855 /**
3856 * Perform steps 1 and 2b <a href="MethodHandles.Lookup.html#secmgr">access checks</a>
3857 * for ensureInitialized, findClass or accessClass.
3858 */
3859 void checkSecurityManager(Class<?> refc) {
3860 if (allowedModes == TRUSTED) return;
3861
3862 @SuppressWarnings("removal")
3863 SecurityManager smgr = System.getSecurityManager();
3864 if (smgr == null) return;
3865
3866 // Step 1:
3867 boolean fullPrivilegeLookup = hasFullPrivilegeAccess();
3868 if (!fullPrivilegeLookup ||
3869 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
3870 ReflectUtil.checkPackageAccess(refc);
3871 }
3872
3873 // Step 2b:
3874 if (!fullPrivilegeLookup) {
3875 smgr.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
3876 }
3877 }
3878
3879 /**
3880 * Perform steps 1, 2a and 3 <a href="MethodHandles.Lookup.html#secmgr">access checks</a>.
3881 * Determines a trustable caller class to compare with refc, the symbolic reference class.
3882 * If this lookup object has full privilege access except original access,
3883 * then the caller class is the lookupClass.
3884 *
3885 * Lookup object created by {@link MethodHandles#privateLookupIn(Class, Lookup)}
3886 * from the same module skips the security permission check.
3887 */
3888 void checkSecurityManager(Class<?> refc, MemberName m) {
3889 Objects.requireNonNull(refc);
3890 Objects.requireNonNull(m);
3891
3892 if (allowedModes == TRUSTED) return;
3893
3894 @SuppressWarnings("removal")
3895 SecurityManager smgr = System.getSecurityManager();
3896 if (smgr == null) return;
3897
3898 // Step 1:
3899 boolean fullPrivilegeLookup = hasFullPrivilegeAccess();
3900 if (!fullPrivilegeLookup ||
3901 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
3902 ReflectUtil.checkPackageAccess(refc);
3903 }
3904
3905 // Step 2a:
3906 if (m.isPublic()) return;
3907 if (!fullPrivilegeLookup) {
3908 smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION);
3909 }
3910
3911 // Step 3:
3912 Class<?> defc = m.getDeclaringClass();
3913 if (!fullPrivilegeLookup && defc != refc) {
3914 ReflectUtil.checkPackageAccess(defc);
3915 }
3916 }
3917
3918 void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
3919 boolean wantStatic = (refKind == REF_invokeStatic);
3920 String message;
3921 if (m.isConstructor())
3922 message = "expected a method, not a constructor";
3923 else if (!m.isMethod())
3924 message = "expected a method";
3925 else if (wantStatic != m.isStatic())
3926 message = wantStatic ? "expected a static method" : "expected a non-static method";
3927 else
3928 { checkAccess(refKind, refc, m); return; }
3929 throw m.makeAccessException(message, this);
3930 }
3931
3932 void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
3933 boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
3934 String message;
3935 if (wantStatic != m.isStatic())
3936 message = wantStatic ? "expected a static field" : "expected a non-static field";
3937 else
3938 { checkAccess(refKind, refc, m); return; }
3939 throw m.makeAccessException(message, this);
3940 }
3941
3942 private boolean isArrayClone(byte refKind, Class<?> refc, MemberName m) {
3943 return Modifier.isProtected(m.getModifiers()) &&
3944 refKind == REF_invokeVirtual &&
3945 m.getDeclaringClass() == Object.class &&
3946 m.getName().equals("clone") &&
3947 refc.isArray();
3948 }
3949
3950 /** Check public/protected/private bits on the symbolic reference class and its member. */
3951 void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
3952 assert(m.referenceKindIsConsistentWith(refKind) &&
3953 MethodHandleNatives.refKindIsValid(refKind) &&
3954 (MethodHandleNatives.refKindIsField(refKind) == m.isField()));
3955 int allowedModes = this.allowedModes;
3956 if (allowedModes == TRUSTED) return;
3957 int mods = m.getModifiers();
3958 if (isArrayClone(refKind, refc, m)) {
3959 // The JVM does this hack also.
3960 // (See ClassVerifier::verify_invoke_instructions
3961 // and LinkResolver::check_method_accessability.)
3962 // Because the JVM does not allow separate methods on array types,
3963 // there is no separate method for int[].clone.
3964 // All arrays simply inherit Object.clone.
3965 // But for access checking logic, we make Object.clone
3966 // (normally protected) appear to be public.
3967 // Later on, when the DirectMethodHandle is created,
3968 // its leading argument will be restricted to the
3969 // requested array type.
3970 // N.B. The return type is not adjusted, because
3971 // that is *not* the bytecode behavior.
3972 mods ^= Modifier.PROTECTED | Modifier.PUBLIC;
3973 }
3974 if (Modifier.isProtected(mods) && refKind == REF_newInvokeSpecial) {
3975 // cannot "new" a protected ctor in a different package
3976 mods ^= Modifier.PROTECTED;
3977 }
3978 if (Modifier.isFinal(mods) &&
3979 MethodHandleNatives.refKindIsSetter(refKind))
3980 throw m.makeAccessException("unexpected set of a final field", this);
3981 int requestedModes = fixmods(mods); // adjust 0 => PACKAGE
3982 if ((requestedModes & allowedModes) != 0) {
3983 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
3984 mods, lookupClass(), previousLookupClass(), allowedModes))
3985 return;
3986 } else {
3987 // Protected members can also be checked as if they were package-private.
3988 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
3989 && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
3990 return;
3991 }
3992 throw m.makeAccessException(accessFailedMessage(refc, m), this);
3993 }
3994
3995 String accessFailedMessage(Class<?> refc, MemberName m) {
3996 Class<?> defc = m.getDeclaringClass();
3997 int mods = m.getModifiers();
3998 // check the class first:
3999 boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
4000 (defc == refc ||
4001 Modifier.isPublic(refc.getModifiers())));
4002 if (!classOK && (allowedModes & PACKAGE) != 0) {
4003 // ignore previous lookup class to check if default package access
4004 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), null, FULL_POWER_MODES) &&
4005 (defc == refc ||
4006 VerifyAccess.isClassAccessible(refc, lookupClass(), null, FULL_POWER_MODES)));
4007 }
4008 if (!classOK)
4009 return "class is not public";
4010 if (Modifier.isPublic(mods))
4011 return "access to public member failed"; // (how?, module not readable?)
4012 if (Modifier.isPrivate(mods))
4013 return "member is private";
4014 if (Modifier.isProtected(mods))
4015 return "member is protected";
4016 return "member is private to package";
4017 }
4018
4019 private void checkSpecialCaller(Class<?> specialCaller, Class<?> refc) throws IllegalAccessException {
4020 int allowedModes = this.allowedModes;
4021 if (allowedModes == TRUSTED) return;
4022 if ((lookupModes() & PRIVATE) == 0
4023 || (specialCaller != lookupClass()
4024 // ensure non-abstract methods in superinterfaces can be special-invoked
4025 && !(refc != null && refc.isInterface() && refc.isAssignableFrom(specialCaller))))
4026 throw new MemberName(specialCaller).
4027 makeAccessException("no private access for invokespecial", this);
4028 }
4029
4030 private boolean restrictProtectedReceiver(MemberName method) {
4031 // The accessing class only has the right to use a protected member
4032 // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc.
4033 if (!method.isProtected() || method.isStatic()
4034 || allowedModes == TRUSTED
4035 || method.getDeclaringClass() == lookupClass()
4036 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass()))
4037 return false;
4038 return true;
4039 }
4040 private MethodHandle restrictReceiver(MemberName method, DirectMethodHandle mh, Class<?> caller) throws IllegalAccessException {
4041 assert(!method.isStatic());
4042 // receiver type of mh is too wide; narrow to caller
4043 if (!method.getDeclaringClass().isAssignableFrom(caller)) {
4044 throw method.makeAccessException("caller class must be a subclass below the method", caller);
4045 }
4046 MethodType rawType = mh.type();
4047 if (caller.isAssignableFrom(rawType.parameterType(0))) return mh; // no need to restrict; already narrow
4048 MethodType narrowType = rawType.changeParameterType(0, caller);
4049 assert(!mh.isVarargsCollector()); // viewAsType will lose varargs-ness
4050 assert(mh.viewAsTypeChecks(narrowType, true));
4051 return mh.copyWith(narrowType, mh.form);
4052 }
4053
4054 /** Check access and get the requested method. */
4055 private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException {
4056 final boolean doRestrict = true;
4057 final boolean checkSecurity = true;
4058 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerLookup);
4059 }
4060 /** Check access and get the requested method, for invokespecial with no restriction on the application of narrowing rules. */
4061 private MethodHandle getDirectMethodNoRestrictInvokeSpecial(Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException {
4062 final boolean doRestrict = false;
4063 final boolean checkSecurity = true;
4064 return getDirectMethodCommon(REF_invokeSpecial, refc, method, checkSecurity, doRestrict, callerLookup);
4065 }
4066 /** Check access and get the requested method, eliding security manager checks. */
4067 private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException {
4068 final boolean doRestrict = true;
4069 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
4070 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerLookup);
4071 }
4072 /** Common code for all methods; do not call directly except from immediately above. */
4073 private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method,
4074 boolean checkSecurity,
4075 boolean doRestrict,
4076 Lookup boundCaller) throws IllegalAccessException {
4077 checkMethod(refKind, refc, method);
4078 // Optionally check with the security manager; this isn't needed for unreflect* calls.
4079 if (checkSecurity)
4080 checkSecurityManager(refc, method);
4081 assert(!method.isMethodHandleInvoke());
4082 if (refKind == REF_invokeSpecial &&
4083 refc != lookupClass() &&
4084 !refc.isInterface() && !lookupClass().isInterface() &&
4085 refc != lookupClass().getSuperclass() &&
4086 refc.isAssignableFrom(lookupClass())) {
4087 assert(!method.getName().equals(ConstantDescs.INIT_NAME)); // not this code path
4088
4089 // Per JVMS 6.5, desc. of invokespecial instruction:
4090 // If the method is in a superclass of the LC,
4091 // and if our original search was above LC.super,
4092 // repeat the search (symbolic lookup) from LC.super
4093 // and continue with the direct superclass of that class,
4094 // and so forth, until a match is found or no further superclasses exist.
4095 // FIXME: MemberName.resolve should handle this instead.
4096 Class<?> refcAsSuper = lookupClass();
4097 MemberName m2;
4098 do {
4099 refcAsSuper = refcAsSuper.getSuperclass();
4100 m2 = new MemberName(refcAsSuper,
4101 method.getName(),
4102 method.getMethodType(),
4103 REF_invokeSpecial);
4104 m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull(), allowedModes);
4105 } while (m2 == null && // no method is found yet
4106 refc != refcAsSuper); // search up to refc
4107 if (m2 == null) throw new InternalError(method.toString());
4108 method = m2;
4109 refc = refcAsSuper;
4110 // redo basic checks
4111 checkMethod(refKind, refc, method);
4112 }
4113 DirectMethodHandle dmh = DirectMethodHandle.make(refKind, refc, method, lookupClass());
4114 MethodHandle mh = dmh;
4115 // Optionally narrow the receiver argument to lookupClass using restrictReceiver.
4116 if ((doRestrict && refKind == REF_invokeSpecial) ||
4117 (MethodHandleNatives.refKindHasReceiver(refKind) &&
4118 restrictProtectedReceiver(method) &&
4119 // All arrays simply inherit the protected Object.clone method.
4120 // The leading argument is already restricted to the requested
4121 // array type (not the lookup class).
4122 !isArrayClone(refKind, refc, method))) {
4123 mh = restrictReceiver(method, dmh, lookupClass());
4124 }
4125 mh = maybeBindCaller(method, mh, boundCaller);
4126 mh = mh.setVarargs(method);
4127 return mh;
4128 }
4129 private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh, Lookup boundCaller)
4130 throws IllegalAccessException {
4131 if (boundCaller.allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method))
4132 return mh;
4133
4134 // boundCaller must have full privilege access.
4135 // It should have been checked by findBoundCallerLookup. Safe to check this again.
4136 if ((boundCaller.lookupModes() & ORIGINAL) == 0)
4137 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
4138
4139 assert boundCaller.hasFullPrivilegeAccess();
4140
4141 MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, boundCaller.lookupClass);
4142 // Note: caller will apply varargs after this step happens.
4143 return cbmh;
4144 }
4145
4146 /** Check access and get the requested field. */
4147 private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
4148 final boolean checkSecurity = true;
4149 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
4150 }
4151 /** Check access and get the requested field, eliding security manager checks. */
4152 private MethodHandle getDirectFieldNoSecurityManager(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
4153 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
4154 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
4155 }
4156 /** Common code for all fields; do not call directly except from immediately above. */
4157 private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field,
4158 boolean checkSecurity) throws IllegalAccessException {
4159 checkField(refKind, refc, field);
4160 // Optionally check with the security manager; this isn't needed for unreflect* calls.
4161 if (checkSecurity)
4162 checkSecurityManager(refc, field);
4163 DirectMethodHandle dmh = DirectMethodHandle.make(refc, field);
4164 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) &&
4165 restrictProtectedReceiver(field));
4166 if (doRestrict)
4167 return restrictReceiver(field, dmh, lookupClass());
4168 return dmh;
4169 }
4170 private VarHandle getFieldVarHandle(byte getRefKind, byte putRefKind,
4171 Class<?> refc, MemberName getField, MemberName putField)
4172 throws IllegalAccessException {
4173 final boolean checkSecurity = true;
4174 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
4175 }
4176 private VarHandle getFieldVarHandleNoSecurityManager(byte getRefKind, byte putRefKind,
4177 Class<?> refc, MemberName getField, MemberName putField)
4178 throws IllegalAccessException {
4179 final boolean checkSecurity = false;
4180 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
4181 }
4182 private VarHandle getFieldVarHandleCommon(byte getRefKind, byte putRefKind,
4183 Class<?> refc, MemberName getField, MemberName putField,
4184 boolean checkSecurity) throws IllegalAccessException {
4185 assert getField.isStatic() == putField.isStatic();
4186 assert getField.isGetter() && putField.isSetter();
4187 assert MethodHandleNatives.refKindIsStatic(getRefKind) == MethodHandleNatives.refKindIsStatic(putRefKind);
4188 assert MethodHandleNatives.refKindIsGetter(getRefKind) && MethodHandleNatives.refKindIsSetter(putRefKind);
4189
4190 checkField(getRefKind, refc, getField);
4191 if (checkSecurity)
4192 checkSecurityManager(refc, getField);
4193
4194 if (!putField.isFinal()) {
4195 // A VarHandle does not support updates to final fields, any
4196 // such VarHandle to a final field will be read-only and
4197 // therefore the following write-based accessibility checks are
4198 // only required for non-final fields
4199 checkField(putRefKind, refc, putField);
4200 if (checkSecurity)
4201 checkSecurityManager(refc, putField);
4202 }
4203
4204 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(getRefKind) &&
4205 restrictProtectedReceiver(getField));
4206 if (doRestrict) {
4207 assert !getField.isStatic();
4208 // receiver type of VarHandle is too wide; narrow to caller
4209 if (!getField.getDeclaringClass().isAssignableFrom(lookupClass())) {
4210 throw getField.makeAccessException("caller class must be a subclass below the method", lookupClass());
4211 }
4212 refc = lookupClass();
4213 }
4214 return VarHandles.makeFieldHandle(getField, refc,
4215 this.allowedModes == TRUSTED && !getField.isTrustedFinalField());
4216 }
4217 /** Check access and get the requested constructor. */
4218 private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException {
4219 final boolean checkSecurity = true;
4220 return getDirectConstructorCommon(refc, ctor, checkSecurity);
4221 }
4222 /** Check access and get the requested constructor, eliding security manager checks. */
4223 private MethodHandle getDirectConstructorNoSecurityManager(Class<?> refc, MemberName ctor) throws IllegalAccessException {
4224 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
4225 return getDirectConstructorCommon(refc, ctor, checkSecurity);
4226 }
4227 /** Common code for all constructors; do not call directly except from immediately above. */
4228 private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor,
4229 boolean checkSecurity) throws IllegalAccessException {
4230 assert(ctor.isConstructor());
4231 checkAccess(REF_newInvokeSpecial, refc, ctor);
4232 // Optionally check with the security manager; this isn't needed for unreflect* calls.
4233 if (checkSecurity)
4234 checkSecurityManager(refc, ctor);
4235 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
4236 return DirectMethodHandle.make(ctor).setVarargs(ctor);
4237 }
4238
4239 /** Hook called from the JVM (via MethodHandleNatives) to link MH constants:
4240 */
4241 /*non-public*/
4242 MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type)
4243 throws ReflectiveOperationException {
4244 if (!(type instanceof Class || type instanceof MethodType))
4245 throw new InternalError("unresolved MemberName");
4246 MemberName member = new MemberName(refKind, defc, name, type);
4247 MethodHandle mh = LOOKASIDE_TABLE.get(member);
4248 if (mh != null) {
4249 checkSymbolicClass(defc);
4250 return mh;
4251 }
4252 if (defc == MethodHandle.class && refKind == REF_invokeVirtual) {
4253 // Treat MethodHandle.invoke and invokeExact specially.
4254 mh = findVirtualForMH(member.getName(), member.getMethodType());
4255 if (mh != null) {
4256 return mh;
4257 }
4258 } else if (defc == VarHandle.class && refKind == REF_invokeVirtual) {
4259 // Treat signature-polymorphic methods on VarHandle specially.
4260 mh = findVirtualForVH(member.getName(), member.getMethodType());
4261 if (mh != null) {
4262 return mh;
4263 }
4264 }
4265 MemberName resolved = resolveOrFail(refKind, member);
4266 mh = getDirectMethodForConstant(refKind, defc, resolved);
4267 if (mh instanceof DirectMethodHandle dmh
4268 && canBeCached(refKind, defc, resolved)) {
4269 MemberName key = mh.internalMemberName();
4270 if (key != null) {
4271 key = key.asNormalOriginal();
4272 }
4273 if (member.equals(key)) { // better safe than sorry
4274 LOOKASIDE_TABLE.put(key, dmh);
4275 }
4276 }
4277 return mh;
4278 }
4279 private boolean canBeCached(byte refKind, Class<?> defc, MemberName member) {
4280 if (refKind == REF_invokeSpecial) {
4281 return false;
4282 }
4283 if (!Modifier.isPublic(defc.getModifiers()) ||
4284 !Modifier.isPublic(member.getDeclaringClass().getModifiers()) ||
4285 !member.isPublic() ||
4286 member.isCallerSensitive()) {
4287 return false;
4288 }
4289 ClassLoader loader = defc.getClassLoader();
4290 if (loader != null) {
4291 ClassLoader sysl = ClassLoader.getSystemClassLoader();
4292 boolean found = false;
4293 while (sysl != null) {
4294 if (loader == sysl) { found = true; break; }
4295 sysl = sysl.getParent();
4296 }
4297 if (!found) {
4298 return false;
4299 }
4300 }
4301 try {
4302 MemberName resolved2 = publicLookup().resolveOrNull(refKind,
4303 new MemberName(refKind, defc, member.getName(), member.getType()));
4304 if (resolved2 == null) {
4305 return false;
4306 }
4307 checkSecurityManager(defc, resolved2);
4308 } catch (SecurityException ex) {
4309 return false;
4310 }
4311 return true;
4312 }
4313 private MethodHandle getDirectMethodForConstant(byte refKind, Class<?> defc, MemberName member)
4314 throws ReflectiveOperationException {
4315 if (MethodHandleNatives.refKindIsField(refKind)) {
4316 return getDirectFieldNoSecurityManager(refKind, defc, member);
4317 } else if (MethodHandleNatives.refKindIsMethod(refKind)) {
4318 return getDirectMethodNoSecurityManager(refKind, defc, member, findBoundCallerLookup(member));
4319 } else if (refKind == REF_newInvokeSpecial) {
4320 return getDirectConstructorNoSecurityManager(defc, member);
4321 }
4322 // oops
4323 throw newIllegalArgumentException("bad MethodHandle constant #"+member);
4324 }
4325
4326 static ConcurrentHashMap<MemberName, DirectMethodHandle> LOOKASIDE_TABLE = new ConcurrentHashMap<>();
4327 }
4328
4329 /**
4330 * Produces a method handle constructing arrays of a desired type,
4331 * as if by the {@code anewarray} bytecode.
4332 * The return type of the method handle will be the array type.
4333 * The type of its sole argument will be {@code int}, which specifies the size of the array.
4334 *
4335 * <p> If the returned method handle is invoked with a negative
4336 * array size, a {@code NegativeArraySizeException} will be thrown.
4337 *
4338 * @param arrayClass an array type
4339 * @return a method handle which can create arrays of the given type
4340 * @throws NullPointerException if the argument is {@code null}
4341 * @throws IllegalArgumentException if {@code arrayClass} is not an array type
4342 * @see java.lang.reflect.Array#newInstance(Class, int)
4343 * @jvms 6.5 {@code anewarray} Instruction
4344 * @since 9
4345 */
4346 public static MethodHandle arrayConstructor(Class<?> arrayClass) throws IllegalArgumentException {
4347 if (!arrayClass.isArray()) {
4348 throw newIllegalArgumentException("not an array class: " + arrayClass.getName());
4349 }
4350 MethodHandle ani = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_Array_newInstance).
4351 bindTo(arrayClass.getComponentType());
4352 return ani.asType(ani.type().changeReturnType(arrayClass));
4353 }
4354
4355 /**
4356 * Produces a method handle returning the length of an array,
4357 * as if by the {@code arraylength} bytecode.
4358 * The type of the method handle will have {@code int} as return type,
4359 * and its sole argument will be the array type.
4360 *
4361 * <p> If the returned method handle is invoked with a {@code null}
4362 * array reference, a {@code NullPointerException} will be thrown.
4363 *
4364 * @param arrayClass an array type
4365 * @return a method handle which can retrieve the length of an array of the given array type
4366 * @throws NullPointerException if the argument is {@code null}
4367 * @throws IllegalArgumentException if arrayClass is not an array type
4368 * @jvms 6.5 {@code arraylength} Instruction
4369 * @since 9
4370 */
4371 public static MethodHandle arrayLength(Class<?> arrayClass) throws IllegalArgumentException {
4372 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.LENGTH);
4373 }
4374
4375 /**
4376 * Produces a method handle giving read access to elements of an array,
4377 * as if by the {@code aaload} bytecode.
4378 * The type of the method handle will have a return type of the array's
4379 * element type. Its first argument will be the array type,
4380 * and the second will be {@code int}.
4381 *
4382 * <p> When the returned method handle is invoked,
4383 * the array reference and array index are checked.
4384 * A {@code NullPointerException} will be thrown if the array reference
4385 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
4386 * thrown if the index is negative or if it is greater than or equal to
4387 * the length of the array.
4388 *
4389 * @param arrayClass an array type
4390 * @return a method handle which can load values from the given array type
4391 * @throws NullPointerException if the argument is null
4392 * @throws IllegalArgumentException if arrayClass is not an array type
4393 * @jvms 6.5 {@code aaload} Instruction
4394 */
4395 public static MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException {
4396 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.GET);
4397 }
4398
4399 /**
4400 * Produces a method handle giving write access to elements of an array,
4401 * as if by the {@code astore} bytecode.
4402 * The type of the method handle will have a void return type.
4403 * Its last argument will be the array's element type.
4404 * The first and second arguments will be the array type and int.
4405 *
4406 * <p> When the returned method handle is invoked,
4407 * the array reference and array index are checked.
4408 * A {@code NullPointerException} will be thrown if the array reference
4409 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
4410 * thrown if the index is negative or if it is greater than or equal to
4411 * the length of the array.
4412 *
4413 * @param arrayClass the class of an array
4414 * @return a method handle which can store values into the array type
4415 * @throws NullPointerException if the argument is null
4416 * @throws IllegalArgumentException if arrayClass is not an array type
4417 * @jvms 6.5 {@code aastore} Instruction
4418 */
4419 public static MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException {
4420 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.SET);
4421 }
4422
4423 /**
4424 * Produces a VarHandle giving access to elements of an array of type
4425 * {@code arrayClass}. The VarHandle's variable type is the component type
4426 * of {@code arrayClass} and the list of coordinate types is
4427 * {@code (arrayClass, int)}, where the {@code int} coordinate type
4428 * corresponds to an argument that is an index into an array.
4429 * <p>
4430 * Certain access modes of the returned VarHandle are unsupported under
4431 * the following conditions:
4432 * <ul>
4433 * <li>if the component type is anything other than {@code byte},
4434 * {@code short}, {@code char}, {@code int}, {@code long},
4435 * {@code float}, or {@code double} then numeric atomic update access
4436 * modes are unsupported.
4437 * <li>if the component type is anything other than {@code boolean},
4438 * {@code byte}, {@code short}, {@code char}, {@code int} or
4439 * {@code long} then bitwise atomic update access modes are
4440 * unsupported.
4441 * </ul>
4442 * <p>
4443 * If the component type is {@code float} or {@code double} then numeric
4444 * and atomic update access modes compare values using their bitwise
4445 * representation (see {@link Float#floatToRawIntBits} and
4446 * {@link Double#doubleToRawLongBits}, respectively).
4447 *
4448 * <p> When the returned {@code VarHandle} is invoked,
4449 * the array reference and array index are checked.
4450 * A {@code NullPointerException} will be thrown if the array reference
4451 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
4452 * thrown if the index is negative or if it is greater than or equal to
4453 * the length of the array.
4454 *
4455 * @apiNote
4456 * Bitwise comparison of {@code float} values or {@code double} values,
4457 * as performed by the numeric and atomic update access modes, differ
4458 * from the primitive {@code ==} operator and the {@link Float#equals}
4459 * and {@link Double#equals} methods, specifically with respect to
4460 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
4461 * Care should be taken when performing a compare and set or a compare
4462 * and exchange operation with such values since the operation may
4463 * unexpectedly fail.
4464 * There are many possible NaN values that are considered to be
4465 * {@code NaN} in Java, although no IEEE 754 floating-point operation
4466 * provided by Java can distinguish between them. Operation failure can
4467 * occur if the expected or witness value is a NaN value and it is
4468 * transformed (perhaps in a platform specific manner) into another NaN
4469 * value, and thus has a different bitwise representation (see
4470 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
4471 * details).
4472 * The values {@code -0.0} and {@code +0.0} have different bitwise
4473 * representations but are considered equal when using the primitive
4474 * {@code ==} operator. Operation failure can occur if, for example, a
4475 * numeric algorithm computes an expected value to be say {@code -0.0}
4476 * and previously computed the witness value to be say {@code +0.0}.
4477 * @param arrayClass the class of an array, of type {@code T[]}
4478 * @return a VarHandle giving access to elements of an array
4479 * @throws NullPointerException if the arrayClass is null
4480 * @throws IllegalArgumentException if arrayClass is not an array type
4481 * @since 9
4482 */
4483 public static VarHandle arrayElementVarHandle(Class<?> arrayClass) throws IllegalArgumentException {
4484 return VarHandles.makeArrayElementHandle(arrayClass);
4485 }
4486
4487 /**
4488 * Produces a VarHandle giving access to elements of a {@code byte[]} array
4489 * viewed as if it were a different primitive array type, such as
4490 * {@code int[]} or {@code long[]}.
4491 * The VarHandle's variable type is the component type of
4492 * {@code viewArrayClass} and the list of coordinate types is
4493 * {@code (byte[], int)}, where the {@code int} coordinate type
4494 * corresponds to an argument that is an index into a {@code byte[]} array.
4495 * The returned VarHandle accesses bytes at an index in a {@code byte[]}
4496 * array, composing bytes to or from a value of the component type of
4497 * {@code viewArrayClass} according to the given endianness.
4498 * <p>
4499 * The supported component types (variables types) are {@code short},
4500 * {@code char}, {@code int}, {@code long}, {@code float} and
4501 * {@code double}.
4502 * <p>
4503 * Access of bytes at a given index will result in an
4504 * {@code ArrayIndexOutOfBoundsException} if the index is less than {@code 0}
4505 * or greater than the {@code byte[]} array length minus the size (in bytes)
4506 * of {@code T}.
4507 * <p>
4508 * Only plain {@linkplain VarHandle.AccessMode#GET get} and {@linkplain VarHandle.AccessMode#SET set}
4509 * access modes are supported by the returned var handle. For all other access modes, an
4510 * {@link UnsupportedOperationException} will be thrown.
4511 *
4512 * @apiNote if access modes other than plain access are required, clients should
4513 * consider using off-heap memory through
4514 * {@linkplain java.nio.ByteBuffer#allocateDirect(int) direct byte buffers} or
4515 * off-heap {@linkplain java.lang.foreign.MemorySegment memory segments},
4516 * or memory segments backed by a
4517 * {@linkplain java.lang.foreign.MemorySegment#ofArray(long[]) {@code long[]}},
4518 * for which stronger alignment guarantees can be made.
4519 *
4520 * @param viewArrayClass the view array class, with a component type of
4521 * type {@code T}
4522 * @param byteOrder the endianness of the view array elements, as
4523 * stored in the underlying {@code byte} array
4524 * @return a VarHandle giving access to elements of a {@code byte[]} array
4525 * viewed as if elements corresponding to the components type of the view
4526 * array class
4527 * @throws NullPointerException if viewArrayClass or byteOrder is null
4528 * @throws IllegalArgumentException if viewArrayClass is not an array type
4529 * @throws UnsupportedOperationException if the component type of
4530 * viewArrayClass is not supported as a variable type
4531 * @since 9
4532 */
4533 public static VarHandle byteArrayViewVarHandle(Class<?> viewArrayClass,
4534 ByteOrder byteOrder) throws IllegalArgumentException {
4535 Objects.requireNonNull(byteOrder);
4536 return VarHandles.byteArrayViewHandle(viewArrayClass,
4537 byteOrder == ByteOrder.BIG_ENDIAN);
4538 }
4539
4540 /**
4541 * Produces a VarHandle giving access to elements of a {@code ByteBuffer}
4542 * viewed as if it were an array of elements of a different primitive
4543 * component type to that of {@code byte}, such as {@code int[]} or
4544 * {@code long[]}.
4545 * The VarHandle's variable type is the component type of
4546 * {@code viewArrayClass} and the list of coordinate types is
4547 * {@code (ByteBuffer, int)}, where the {@code int} coordinate type
4548 * corresponds to an argument that is an index into a {@code byte[]} array.
4549 * The returned VarHandle accesses bytes at an index in a
4550 * {@code ByteBuffer}, composing bytes to or from a value of the component
4551 * type of {@code viewArrayClass} according to the given endianness.
4552 * <p>
4553 * The supported component types (variables types) are {@code short},
4554 * {@code char}, {@code int}, {@code long}, {@code float} and
4555 * {@code double}.
4556 * <p>
4557 * Access will result in a {@code ReadOnlyBufferException} for anything
4558 * other than the read access modes if the {@code ByteBuffer} is read-only.
4559 * <p>
4560 * Access of bytes at a given index will result in an
4561 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
4562 * or greater than the {@code ByteBuffer} limit minus the size (in bytes) of
4563 * {@code T}.
4564 * <p>
4565 * For heap byte buffers, access is always unaligned. As a result, only the plain
4566 * {@linkplain VarHandle.AccessMode#GET get}
4567 * and {@linkplain VarHandle.AccessMode#SET set} access modes are supported by the
4568 * returned var handle. For all other access modes, an {@link IllegalStateException}
4569 * will be thrown.
4570 * <p>
4571 * For direct buffers only, access of bytes at an index may be aligned or misaligned for {@code T},
4572 * with respect to the underlying memory address, {@code A} say, associated
4573 * with the {@code ByteBuffer} and index.
4574 * If access is misaligned then access for anything other than the
4575 * {@code get} and {@code set} access modes will result in an
4576 * {@code IllegalStateException}. In such cases atomic access is only
4577 * guaranteed with respect to the largest power of two that divides the GCD
4578 * of {@code A} and the size (in bytes) of {@code T}.
4579 * If access is aligned then following access modes are supported and are
4580 * guaranteed to support atomic access:
4581 * <ul>
4582 * <li>read write access modes for all {@code T}, with the exception of
4583 * access modes {@code get} and {@code set} for {@code long} and
4584 * {@code double} on 32-bit platforms.
4585 * <li>atomic update access modes for {@code int}, {@code long},
4586 * {@code float} or {@code double}.
4587 * (Future major platform releases of the JDK may support additional
4588 * types for certain currently unsupported access modes.)
4589 * <li>numeric atomic update access modes for {@code int} and {@code long}.
4590 * (Future major platform releases of the JDK may support additional
4591 * numeric types for certain currently unsupported access modes.)
4592 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
4593 * (Future major platform releases of the JDK may support additional
4594 * numeric types for certain currently unsupported access modes.)
4595 * </ul>
4596 * <p>
4597 * Misaligned access, and therefore atomicity guarantees, may be determined
4598 * for a {@code ByteBuffer}, {@code bb} (direct or otherwise), an
4599 * {@code index}, {@code T} and its corresponding boxed type,
4600 * {@code T_BOX}, as follows:
4601 * <pre>{@code
4602 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
4603 * ByteBuffer bb = ...
4604 * int misalignedAtIndex = bb.alignmentOffset(index, sizeOfT);
4605 * boolean isMisaligned = misalignedAtIndex != 0;
4606 * }</pre>
4607 * <p>
4608 * If the variable type is {@code float} or {@code double} then atomic
4609 * update access modes compare values using their bitwise representation
4610 * (see {@link Float#floatToRawIntBits} and
4611 * {@link Double#doubleToRawLongBits}, respectively).
4612 * @param viewArrayClass the view array class, with a component type of
4613 * type {@code T}
4614 * @param byteOrder the endianness of the view array elements, as
4615 * stored in the underlying {@code ByteBuffer} (Note this overrides the
4616 * endianness of a {@code ByteBuffer})
4617 * @return a VarHandle giving access to elements of a {@code ByteBuffer}
4618 * viewed as if elements corresponding to the components type of the view
4619 * array class
4620 * @throws NullPointerException if viewArrayClass or byteOrder is null
4621 * @throws IllegalArgumentException if viewArrayClass is not an array type
4622 * @throws UnsupportedOperationException if the component type of
4623 * viewArrayClass is not supported as a variable type
4624 * @since 9
4625 */
4626 public static VarHandle byteBufferViewVarHandle(Class<?> viewArrayClass,
4627 ByteOrder byteOrder) throws IllegalArgumentException {
4628 Objects.requireNonNull(byteOrder);
4629 return VarHandles.makeByteBufferViewHandle(viewArrayClass,
4630 byteOrder == ByteOrder.BIG_ENDIAN);
4631 }
4632
4633
4634 //--- method handle invocation (reflective style)
4635
4636 /**
4637 * Produces a method handle which will invoke any method handle of the
4638 * given {@code type}, with a given number of trailing arguments replaced by
4639 * a single trailing {@code Object[]} array.
4640 * The resulting invoker will be a method handle with the following
4641 * arguments:
4642 * <ul>
4643 * <li>a single {@code MethodHandle} target
4644 * <li>zero or more leading values (counted by {@code leadingArgCount})
4645 * <li>an {@code Object[]} array containing trailing arguments
4646 * </ul>
4647 * <p>
4648 * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
4649 * the indicated {@code type}.
4650 * That is, if the target is exactly of the given {@code type}, it will behave
4651 * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
4652 * is used to convert the target to the required {@code type}.
4653 * <p>
4654 * The type of the returned invoker will not be the given {@code type}, but rather
4655 * will have all parameters except the first {@code leadingArgCount}
4656 * replaced by a single array of type {@code Object[]}, which will be
4657 * the final parameter.
4658 * <p>
4659 * Before invoking its target, the invoker will spread the final array, apply
4660 * reference casts as necessary, and unbox and widen primitive arguments.
4661 * If, when the invoker is called, the supplied array argument does
4662 * not have the correct number of elements, the invoker will throw
4663 * an {@link IllegalArgumentException} instead of invoking the target.
4664 * <p>
4665 * This method is equivalent to the following code (though it may be more efficient):
4666 * {@snippet lang="java" :
4667 MethodHandle invoker = MethodHandles.invoker(type);
4668 int spreadArgCount = type.parameterCount() - leadingArgCount;
4669 invoker = invoker.asSpreader(Object[].class, spreadArgCount);
4670 return invoker;
4671 * }
4672 * This method throws no reflective or security exceptions.
4673 * @param type the desired target type
4674 * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
4675 * @return a method handle suitable for invoking any method handle of the given type
4676 * @throws NullPointerException if {@code type} is null
4677 * @throws IllegalArgumentException if {@code leadingArgCount} is not in
4678 * the range from 0 to {@code type.parameterCount()} inclusive,
4679 * or if the resulting method handle's type would have
4680 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4681 */
4682 public static MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
4683 if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
4684 throw newIllegalArgumentException("bad argument count", leadingArgCount);
4685 type = type.asSpreaderType(Object[].class, leadingArgCount, type.parameterCount() - leadingArgCount);
4686 return type.invokers().spreadInvoker(leadingArgCount);
4687 }
4688
4689 /**
4690 * Produces a special <em>invoker method handle</em> which can be used to
4691 * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
4692 * The resulting invoker will have a type which is
4693 * exactly equal to the desired type, except that it will accept
4694 * an additional leading argument of type {@code MethodHandle}.
4695 * <p>
4696 * This method is equivalent to the following code (though it may be more efficient):
4697 * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)}
4698 *
4699 * <p style="font-size:smaller;">
4700 * <em>Discussion:</em>
4701 * Invoker method handles can be useful when working with variable method handles
4702 * of unknown types.
4703 * For example, to emulate an {@code invokeExact} call to a variable method
4704 * handle {@code M}, extract its type {@code T},
4705 * look up the invoker method {@code X} for {@code T},
4706 * and call the invoker method, as {@code X.invoke(T, A...)}.
4707 * (It would not work to call {@code X.invokeExact}, since the type {@code T}
4708 * is unknown.)
4709 * If spreading, collecting, or other argument transformations are required,
4710 * they can be applied once to the invoker {@code X} and reused on many {@code M}
4711 * method handle values, as long as they are compatible with the type of {@code X}.
4712 * <p style="font-size:smaller;">
4713 * <em>(Note: The invoker method is not available via the Core Reflection API.
4714 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
4715 * on the declared {@code invokeExact} or {@code invoke} method will raise an
4716 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
4717 * <p>
4718 * This method throws no reflective or security exceptions.
4719 * @param type the desired target type
4720 * @return a method handle suitable for invoking any method handle of the given type
4721 * @throws IllegalArgumentException if the resulting method handle's type would have
4722 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4723 */
4724 public static MethodHandle exactInvoker(MethodType type) {
4725 return type.invokers().exactInvoker();
4726 }
4727
4728 /**
4729 * Produces a special <em>invoker method handle</em> which can be used to
4730 * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
4731 * The resulting invoker will have a type which is
4732 * exactly equal to the desired type, except that it will accept
4733 * an additional leading argument of type {@code MethodHandle}.
4734 * <p>
4735 * Before invoking its target, if the target differs from the expected type,
4736 * the invoker will apply reference casts as
4737 * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
4738 * Similarly, the return value will be converted as necessary.
4739 * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
4740 * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
4741 * <p>
4742 * This method is equivalent to the following code (though it may be more efficient):
4743 * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)}
4744 * <p style="font-size:smaller;">
4745 * <em>Discussion:</em>
4746 * A {@linkplain MethodType#genericMethodType general method type} is one which
4747 * mentions only {@code Object} arguments and return values.
4748 * An invoker for such a type is capable of calling any method handle
4749 * of the same arity as the general type.
4750 * <p style="font-size:smaller;">
4751 * <em>(Note: The invoker method is not available via the Core Reflection API.
4752 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
4753 * on the declared {@code invokeExact} or {@code invoke} method will raise an
4754 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
4755 * <p>
4756 * This method throws no reflective or security exceptions.
4757 * @param type the desired target type
4758 * @return a method handle suitable for invoking any method handle convertible to the given type
4759 * @throws IllegalArgumentException if the resulting method handle's type would have
4760 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4761 */
4762 public static MethodHandle invoker(MethodType type) {
4763 return type.invokers().genericInvoker();
4764 }
4765
4766 /**
4767 * Produces a special <em>invoker method handle</em> which can be used to
4768 * invoke a signature-polymorphic access mode method on any VarHandle whose
4769 * associated access mode type is compatible with the given type.
4770 * The resulting invoker will have a type which is exactly equal to the
4771 * desired given type, except that it will accept an additional leading
4772 * argument of type {@code VarHandle}.
4773 *
4774 * @param accessMode the VarHandle access mode
4775 * @param type the desired target type
4776 * @return a method handle suitable for invoking an access mode method of
4777 * any VarHandle whose access mode type is of the given type.
4778 * @since 9
4779 */
4780 public static MethodHandle varHandleExactInvoker(VarHandle.AccessMode accessMode, MethodType type) {
4781 return type.invokers().varHandleMethodExactInvoker(accessMode);
4782 }
4783
4784 /**
4785 * Produces a special <em>invoker method handle</em> which can be used to
4786 * invoke a signature-polymorphic access mode method on any VarHandle whose
4787 * associated access mode type is compatible with the given type.
4788 * The resulting invoker will have a type which is exactly equal to the
4789 * desired given type, except that it will accept an additional leading
4790 * argument of type {@code VarHandle}.
4791 * <p>
4792 * Before invoking its target, if the access mode type differs from the
4793 * desired given type, the invoker will apply reference casts as necessary
4794 * and box, unbox, or widen primitive values, as if by
4795 * {@link MethodHandle#asType asType}. Similarly, the return value will be
4796 * converted as necessary.
4797 * <p>
4798 * This method is equivalent to the following code (though it may be more
4799 * efficient): {@code publicLookup().findVirtual(VarHandle.class, accessMode.name(), type)}
4800 *
4801 * @param accessMode the VarHandle access mode
4802 * @param type the desired target type
4803 * @return a method handle suitable for invoking an access mode method of
4804 * any VarHandle whose access mode type is convertible to the given
4805 * type.
4806 * @since 9
4807 */
4808 public static MethodHandle varHandleInvoker(VarHandle.AccessMode accessMode, MethodType type) {
4809 return type.invokers().varHandleMethodInvoker(accessMode);
4810 }
4811
4812 /*non-public*/
4813 static MethodHandle basicInvoker(MethodType type) {
4814 return type.invokers().basicInvoker();
4815 }
4816
4817 //--- method handle modification (creation from other method handles)
4818
4819 /**
4820 * Produces a method handle which adapts the type of the
4821 * given method handle to a new type by pairwise argument and return type conversion.
4822 * The original type and new type must have the same number of arguments.
4823 * The resulting method handle is guaranteed to report a type
4824 * which is equal to the desired new type.
4825 * <p>
4826 * If the original type and new type are equal, returns target.
4827 * <p>
4828 * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
4829 * and some additional conversions are also applied if those conversions fail.
4830 * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied
4831 * if possible, before or instead of any conversions done by {@code asType}:
4832 * <ul>
4833 * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type,
4834 * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast.
4835 * (This treatment of interfaces follows the usage of the bytecode verifier.)
4836 * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive,
4837 * the boolean is converted to a byte value, 1 for true, 0 for false.
4838 * (This treatment follows the usage of the bytecode verifier.)
4839 * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive,
4840 * <em>T0</em> is converted to byte via Java casting conversion (JLS {@jls 5.5}),
4841 * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}.
4842 * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean,
4843 * then a Java casting conversion (JLS {@jls 5.5}) is applied.
4844 * (Specifically, <em>T0</em> will convert to <em>T1</em> by
4845 * widening and/or narrowing.)
4846 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
4847 * conversion will be applied at runtime, possibly followed
4848 * by a Java casting conversion (JLS {@jls 5.5}) on the primitive value,
4849 * possibly followed by a conversion from byte to boolean by testing
4850 * the low-order bit.
4851 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive,
4852 * and if the reference is null at runtime, a zero value is introduced.
4853 * </ul>
4854 * @param target the method handle to invoke after arguments are retyped
4855 * @param newType the expected type of the new method handle
4856 * @return a method handle which delegates to the target after performing
4857 * any necessary argument conversions, and arranges for any
4858 * necessary return value conversions
4859 * @throws NullPointerException if either argument is null
4860 * @throws WrongMethodTypeException if the conversion cannot be made
4861 * @see MethodHandle#asType
4862 */
4863 public static MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
4864 explicitCastArgumentsChecks(target, newType);
4865 // use the asTypeCache when possible:
4866 MethodType oldType = target.type();
4867 if (oldType == newType) return target;
4868 if (oldType.explicitCastEquivalentToAsType(newType)) {
4869 return target.asFixedArity().asType(newType);
4870 }
4871 return MethodHandleImpl.makePairwiseConvert(target, newType, false);
4872 }
4873
4874 private static void explicitCastArgumentsChecks(MethodHandle target, MethodType newType) {
4875 if (target.type().parameterCount() != newType.parameterCount()) {
4876 throw new WrongMethodTypeException("cannot explicitly cast " + target + " to " + newType);
4877 }
4878 }
4879
4880 /**
4881 * Produces a method handle which adapts the calling sequence of the
4882 * given method handle to a new type, by reordering the arguments.
4883 * The resulting method handle is guaranteed to report a type
4884 * which is equal to the desired new type.
4885 * <p>
4886 * The given array controls the reordering.
4887 * Call {@code #I} the number of incoming parameters (the value
4888 * {@code newType.parameterCount()}, and call {@code #O} the number
4889 * of outgoing parameters (the value {@code target.type().parameterCount()}).
4890 * Then the length of the reordering array must be {@code #O},
4891 * and each element must be a non-negative number less than {@code #I}.
4892 * For every {@code N} less than {@code #O}, the {@code N}-th
4893 * outgoing argument will be taken from the {@code I}-th incoming
4894 * argument, where {@code I} is {@code reorder[N]}.
4895 * <p>
4896 * No argument or return value conversions are applied.
4897 * The type of each incoming argument, as determined by {@code newType},
4898 * must be identical to the type of the corresponding outgoing parameter
4899 * or parameters in the target method handle.
4900 * The return type of {@code newType} must be identical to the return
4901 * type of the original target.
4902 * <p>
4903 * The reordering array need not specify an actual permutation.
4904 * An incoming argument will be duplicated if its index appears
4905 * more than once in the array, and an incoming argument will be dropped
4906 * if its index does not appear in the array.
4907 * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
4908 * incoming arguments which are not mentioned in the reordering array
4909 * may be of any type, as determined only by {@code newType}.
4910 * {@snippet lang="java" :
4911 import static java.lang.invoke.MethodHandles.*;
4912 import static java.lang.invoke.MethodType.*;
4913 ...
4914 MethodType intfn1 = methodType(int.class, int.class);
4915 MethodType intfn2 = methodType(int.class, int.class, int.class);
4916 MethodHandle sub = ... (int x, int y) -> (x-y) ...;
4917 assert(sub.type().equals(intfn2));
4918 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
4919 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
4920 assert((int)rsub.invokeExact(1, 100) == 99);
4921 MethodHandle add = ... (int x, int y) -> (x+y) ...;
4922 assert(add.type().equals(intfn2));
4923 MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
4924 assert(twice.type().equals(intfn1));
4925 assert((int)twice.invokeExact(21) == 42);
4926 * }
4927 * <p>
4928 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4929 * variable-arity method handle}, even if the original target method handle was.
4930 * @param target the method handle to invoke after arguments are reordered
4931 * @param newType the expected type of the new method handle
4932 * @param reorder an index array which controls the reordering
4933 * @return a method handle which delegates to the target after it
4934 * drops unused arguments and moves and/or duplicates the other arguments
4935 * @throws NullPointerException if any argument is null
4936 * @throws IllegalArgumentException if the index array length is not equal to
4937 * the arity of the target, or if any index array element
4938 * not a valid index for a parameter of {@code newType},
4939 * or if two corresponding parameter types in
4940 * {@code target.type()} and {@code newType} are not identical,
4941 */
4942 public static MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
4943 reorder = reorder.clone(); // get a private copy
4944 MethodType oldType = target.type();
4945 permuteArgumentChecks(reorder, newType, oldType);
4946 // first detect dropped arguments and handle them separately
4947 int[] originalReorder = reorder;
4948 BoundMethodHandle result = target.rebind();
4949 LambdaForm form = result.form;
4950 int newArity = newType.parameterCount();
4951 // Normalize the reordering into a real permutation,
4952 // by removing duplicates and adding dropped elements.
4953 // This somewhat improves lambda form caching, as well
4954 // as simplifying the transform by breaking it up into steps.
4955 for (int ddIdx; (ddIdx = findFirstDupOrDrop(reorder, newArity)) != 0; ) {
4956 if (ddIdx > 0) {
4957 // We found a duplicated entry at reorder[ddIdx].
4958 // Example: (x,y,z)->asList(x,y,z)
4959 // permuted by [1*,0,1] => (a0,a1)=>asList(a1,a0,a1)
4960 // permuted by [0,1,0*] => (a0,a1)=>asList(a0,a1,a0)
4961 // The starred element corresponds to the argument
4962 // deleted by the dupArgumentForm transform.
4963 int srcPos = ddIdx, dstPos = srcPos, dupVal = reorder[srcPos];
4964 boolean killFirst = false;
4965 for (int val; (val = reorder[--dstPos]) != dupVal; ) {
4966 // Set killFirst if the dup is larger than an intervening position.
4967 // This will remove at least one inversion from the permutation.
4968 if (dupVal > val) killFirst = true;
4969 }
4970 if (!killFirst) {
4971 srcPos = dstPos;
4972 dstPos = ddIdx;
4973 }
4974 form = form.editor().dupArgumentForm(1 + srcPos, 1 + dstPos);
4975 assert (reorder[srcPos] == reorder[dstPos]);
4976 oldType = oldType.dropParameterTypes(dstPos, dstPos + 1);
4977 // contract the reordering by removing the element at dstPos
4978 int tailPos = dstPos + 1;
4979 System.arraycopy(reorder, tailPos, reorder, dstPos, reorder.length - tailPos);
4980 reorder = Arrays.copyOf(reorder, reorder.length - 1);
4981 } else {
4982 int dropVal = ~ddIdx, insPos = 0;
4983 while (insPos < reorder.length && reorder[insPos] < dropVal) {
4984 // Find first element of reorder larger than dropVal.
4985 // This is where we will insert the dropVal.
4986 insPos += 1;
4987 }
4988 Class<?> ptype = newType.parameterType(dropVal);
4989 form = form.editor().addArgumentForm(1 + insPos, BasicType.basicType(ptype));
4990 oldType = oldType.insertParameterTypes(insPos, ptype);
4991 // expand the reordering by inserting an element at insPos
4992 int tailPos = insPos + 1;
4993 reorder = Arrays.copyOf(reorder, reorder.length + 1);
4994 System.arraycopy(reorder, insPos, reorder, tailPos, reorder.length - tailPos);
4995 reorder[insPos] = dropVal;
4996 }
4997 assert (permuteArgumentChecks(reorder, newType, oldType));
4998 }
4999 assert (reorder.length == newArity); // a perfect permutation
5000 // Note: This may cache too many distinct LFs. Consider backing off to varargs code.
5001 form = form.editor().permuteArgumentsForm(1, reorder);
5002 if (newType == result.type() && form == result.internalForm())
5003 return result;
5004 return result.copyWith(newType, form);
5005 }
5006
5007 /**
5008 * Return an indication of any duplicate or omission in reorder.
5009 * If the reorder contains a duplicate entry, return the index of the second occurrence.
5010 * Otherwise, return ~(n), for the first n in [0..newArity-1] that is not present in reorder.
5011 * Otherwise, return zero.
5012 * If an element not in [0..newArity-1] is encountered, return reorder.length.
5013 */
5014 private static int findFirstDupOrDrop(int[] reorder, int newArity) {
5015 final int BIT_LIMIT = 63; // max number of bits in bit mask
5016 if (newArity < BIT_LIMIT) {
5017 long mask = 0;
5018 for (int i = 0; i < reorder.length; i++) {
5019 int arg = reorder[i];
5020 if (arg >= newArity) {
5021 return reorder.length;
5022 }
5023 long bit = 1L << arg;
5024 if ((mask & bit) != 0) {
5025 return i; // >0 indicates a dup
5026 }
5027 mask |= bit;
5028 }
5029 if (mask == (1L << newArity) - 1) {
5030 assert(Long.numberOfTrailingZeros(Long.lowestOneBit(~mask)) == newArity);
5031 return 0;
5032 }
5033 // find first zero
5034 long zeroBit = Long.lowestOneBit(~mask);
5035 int zeroPos = Long.numberOfTrailingZeros(zeroBit);
5036 assert(zeroPos <= newArity);
5037 if (zeroPos == newArity) {
5038 return 0;
5039 }
5040 return ~zeroPos;
5041 } else {
5042 // same algorithm, different bit set
5043 BitSet mask = new BitSet(newArity);
5044 for (int i = 0; i < reorder.length; i++) {
5045 int arg = reorder[i];
5046 if (arg >= newArity) {
5047 return reorder.length;
5048 }
5049 if (mask.get(arg)) {
5050 return i; // >0 indicates a dup
5051 }
5052 mask.set(arg);
5053 }
5054 int zeroPos = mask.nextClearBit(0);
5055 assert(zeroPos <= newArity);
5056 if (zeroPos == newArity) {
5057 return 0;
5058 }
5059 return ~zeroPos;
5060 }
5061 }
5062
5063 static boolean permuteArgumentChecks(int[] reorder, MethodType newType, MethodType oldType) {
5064 if (newType.returnType() != oldType.returnType())
5065 throw newIllegalArgumentException("return types do not match",
5066 oldType, newType);
5067 if (reorder.length != oldType.parameterCount())
5068 throw newIllegalArgumentException("old type parameter count and reorder array length do not match",
5069 oldType, Arrays.toString(reorder));
5070
5071 int limit = newType.parameterCount();
5072 for (int j = 0; j < reorder.length; j++) {
5073 int i = reorder[j];
5074 if (i < 0 || i >= limit) {
5075 throw newIllegalArgumentException("index is out of bounds for new type",
5076 i, newType);
5077 }
5078 Class<?> src = newType.parameterType(i);
5079 Class<?> dst = oldType.parameterType(j);
5080 if (src != dst)
5081 throw newIllegalArgumentException("parameter types do not match after reorder",
5082 oldType, newType);
5083 }
5084 return true;
5085 }
5086
5087 /**
5088 * Produces a method handle of the requested return type which returns the given
5089 * constant value every time it is invoked.
5090 * <p>
5091 * Before the method handle is returned, the passed-in value is converted to the requested type.
5092 * If the requested type is primitive, widening primitive conversions are attempted,
5093 * else reference conversions are attempted.
5094 * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
5095 * @param type the return type of the desired method handle
5096 * @param value the value to return
5097 * @return a method handle of the given return type and no arguments, which always returns the given value
5098 * @throws NullPointerException if the {@code type} argument is null
5099 * @throws ClassCastException if the value cannot be converted to the required return type
5100 * @throws IllegalArgumentException if the given type is {@code void.class}
5101 */
5102 public static MethodHandle constant(Class<?> type, Object value) {
5103 if (type.isPrimitive()) {
5104 if (type == void.class)
5105 throw newIllegalArgumentException("void type");
5106 Wrapper w = Wrapper.forPrimitiveType(type);
5107 value = w.convert(value, type);
5108 if (w.zero().equals(value))
5109 return zero(w, type);
5110 return insertArguments(identity(type), 0, value);
5111 } else {
5112 if (value == null)
5113 return zero(Wrapper.OBJECT, type);
5114 return identity(type).bindTo(value);
5115 }
5116 }
5117
5118 /**
5119 * Produces a method handle which returns its sole argument when invoked.
5120 * @param type the type of the sole parameter and return value of the desired method handle
5121 * @return a unary method handle which accepts and returns the given type
5122 * @throws NullPointerException if the argument is null
5123 * @throws IllegalArgumentException if the given type is {@code void.class}
5124 */
5125 public static MethodHandle identity(Class<?> type) {
5126 Wrapper btw = (type.isPrimitive() ? Wrapper.forPrimitiveType(type) : Wrapper.OBJECT);
5127 int pos = btw.ordinal();
5128 MethodHandle ident = IDENTITY_MHS[pos];
5129 if (ident == null) {
5130 ident = setCachedMethodHandle(IDENTITY_MHS, pos, makeIdentity(btw.primitiveType()));
5131 }
5132 if (ident.type().returnType() == type)
5133 return ident;
5134 // something like identity(Foo.class); do not bother to intern these
5135 assert (btw == Wrapper.OBJECT);
5136 return makeIdentity(type);
5137 }
5138
5139 /**
5140 * Produces a constant method handle of the requested return type which
5141 * returns the default value for that type every time it is invoked.
5142 * The resulting constant method handle will have no side effects.
5143 * <p>The returned method handle is equivalent to {@code empty(methodType(type))}.
5144 * It is also equivalent to {@code explicitCastArguments(constant(Object.class, null), methodType(type))},
5145 * since {@code explicitCastArguments} converts {@code null} to default values.
5146 * @param type the expected return type of the desired method handle
5147 * @return a constant method handle that takes no arguments
5148 * and returns the default value of the given type (or void, if the type is void)
5149 * @throws NullPointerException if the argument is null
5150 * @see MethodHandles#constant
5151 * @see MethodHandles#empty
5152 * @see MethodHandles#explicitCastArguments
5153 * @since 9
5154 */
5155 public static MethodHandle zero(Class<?> type) {
5156 Objects.requireNonNull(type);
5157 return type.isPrimitive() ? zero(Wrapper.forPrimitiveType(type), type) : zero(Wrapper.OBJECT, type);
5158 }
5159
5160 private static MethodHandle identityOrVoid(Class<?> type) {
5161 return type == void.class ? zero(type) : identity(type);
5162 }
5163
5164 /**
5165 * Produces a method handle of the requested type which ignores any arguments, does nothing,
5166 * and returns a suitable default depending on the return type.
5167 * That is, it returns a zero primitive value, a {@code null}, or {@code void}.
5168 * <p>The returned method handle is equivalent to
5169 * {@code dropArguments(zero(type.returnType()), 0, type.parameterList())}.
5170 *
5171 * @apiNote Given a predicate and target, a useful "if-then" construct can be produced as
5172 * {@code guardWithTest(pred, target, empty(target.type())}.
5173 * @param type the type of the desired method handle
5174 * @return a constant method handle of the given type, which returns a default value of the given return type
5175 * @throws NullPointerException if the argument is null
5176 * @see MethodHandles#zero
5177 * @see MethodHandles#constant
5178 * @since 9
5179 */
5180 public static MethodHandle empty(MethodType type) {
5181 Objects.requireNonNull(type);
5182 return dropArgumentsTrusted(zero(type.returnType()), 0, type.ptypes());
5183 }
5184
5185 private static final MethodHandle[] IDENTITY_MHS = new MethodHandle[Wrapper.COUNT];
5186 private static MethodHandle makeIdentity(Class<?> ptype) {
5187 MethodType mtype = methodType(ptype, ptype);
5188 LambdaForm lform = LambdaForm.identityForm(BasicType.basicType(ptype));
5189 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.IDENTITY);
5190 }
5191
5192 private static MethodHandle zero(Wrapper btw, Class<?> rtype) {
5193 int pos = btw.ordinal();
5194 MethodHandle zero = ZERO_MHS[pos];
5195 if (zero == null) {
5196 zero = setCachedMethodHandle(ZERO_MHS, pos, makeZero(btw.primitiveType()));
5197 }
5198 if (zero.type().returnType() == rtype)
5199 return zero;
5200 assert(btw == Wrapper.OBJECT);
5201 return makeZero(rtype);
5202 }
5203 private static final MethodHandle[] ZERO_MHS = new MethodHandle[Wrapper.COUNT];
5204 private static MethodHandle makeZero(Class<?> rtype) {
5205 MethodType mtype = methodType(rtype);
5206 LambdaForm lform = LambdaForm.zeroForm(BasicType.basicType(rtype));
5207 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.ZERO);
5208 }
5209
5210 private static synchronized MethodHandle setCachedMethodHandle(MethodHandle[] cache, int pos, MethodHandle value) {
5211 // Simulate a CAS, to avoid racy duplication of results.
5212 MethodHandle prev = cache[pos];
5213 if (prev != null) return prev;
5214 return cache[pos] = value;
5215 }
5216
5217 /**
5218 * Provides a target method handle with one or more <em>bound arguments</em>
5219 * in advance of the method handle's invocation.
5220 * The formal parameters to the target corresponding to the bound
5221 * arguments are called <em>bound parameters</em>.
5222 * Returns a new method handle which saves away the bound arguments.
5223 * When it is invoked, it receives arguments for any non-bound parameters,
5224 * binds the saved arguments to their corresponding parameters,
5225 * and calls the original target.
5226 * <p>
5227 * The type of the new method handle will drop the types for the bound
5228 * parameters from the original target type, since the new method handle
5229 * will no longer require those arguments to be supplied by its callers.
5230 * <p>
5231 * Each given argument object must match the corresponding bound parameter type.
5232 * If a bound parameter type is a primitive, the argument object
5233 * must be a wrapper, and will be unboxed to produce the primitive value.
5234 * <p>
5235 * The {@code pos} argument selects which parameters are to be bound.
5236 * It may range between zero and <i>N-L</i> (inclusively),
5237 * where <i>N</i> is the arity of the target method handle
5238 * and <i>L</i> is the length of the values array.
5239 * <p>
5240 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5241 * variable-arity method handle}, even if the original target method handle was.
5242 * @param target the method handle to invoke after the argument is inserted
5243 * @param pos where to insert the argument (zero for the first)
5244 * @param values the series of arguments to insert
5245 * @return a method handle which inserts an additional argument,
5246 * before calling the original method handle
5247 * @throws NullPointerException if the target or the {@code values} array is null
5248 * @throws IllegalArgumentException if {@code pos} is less than {@code 0} or greater than
5249 * {@code N - L} where {@code N} is the arity of the target method handle and {@code L}
5250 * is the length of the values array.
5251 * @throws ClassCastException if an argument does not match the corresponding bound parameter
5252 * type.
5253 * @see MethodHandle#bindTo
5254 */
5255 public static MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
5256 int insCount = values.length;
5257 Class<?>[] ptypes = insertArgumentsChecks(target, insCount, pos);
5258 if (insCount == 0) return target;
5259 BoundMethodHandle result = target.rebind();
5260 for (int i = 0; i < insCount; i++) {
5261 Object value = values[i];
5262 Class<?> ptype = ptypes[pos+i];
5263 if (ptype.isPrimitive()) {
5264 result = insertArgumentPrimitive(result, pos, ptype, value);
5265 } else {
5266 value = ptype.cast(value); // throw CCE if needed
5267 result = result.bindArgumentL(pos, value);
5268 }
5269 }
5270 return result;
5271 }
5272
5273 private static BoundMethodHandle insertArgumentPrimitive(BoundMethodHandle result, int pos,
5274 Class<?> ptype, Object value) {
5275 Wrapper w = Wrapper.forPrimitiveType(ptype);
5276 // perform unboxing and/or primitive conversion
5277 value = w.convert(value, ptype);
5278 return switch (w) {
5279 case INT -> result.bindArgumentI(pos, (int) value);
5280 case LONG -> result.bindArgumentJ(pos, (long) value);
5281 case FLOAT -> result.bindArgumentF(pos, (float) value);
5282 case DOUBLE -> result.bindArgumentD(pos, (double) value);
5283 default -> result.bindArgumentI(pos, ValueConversions.widenSubword(value));
5284 };
5285 }
5286
5287 private static Class<?>[] insertArgumentsChecks(MethodHandle target, int insCount, int pos) throws RuntimeException {
5288 MethodType oldType = target.type();
5289 int outargs = oldType.parameterCount();
5290 int inargs = outargs - insCount;
5291 if (inargs < 0)
5292 throw newIllegalArgumentException("too many values to insert");
5293 if (pos < 0 || pos > inargs)
5294 throw newIllegalArgumentException("no argument type to append");
5295 return oldType.ptypes();
5296 }
5297
5298 /**
5299 * Produces a method handle which will discard some dummy arguments
5300 * before calling some other specified <i>target</i> method handle.
5301 * The type of the new method handle will be the same as the target's type,
5302 * except it will also include the dummy argument types,
5303 * at some given position.
5304 * <p>
5305 * The {@code pos} argument may range between zero and <i>N</i>,
5306 * where <i>N</i> is the arity of the target.
5307 * If {@code pos} is zero, the dummy arguments will precede
5308 * the target's real arguments; if {@code pos} is <i>N</i>
5309 * they will come after.
5310 * <p>
5311 * <b>Example:</b>
5312 * {@snippet lang="java" :
5313 import static java.lang.invoke.MethodHandles.*;
5314 import static java.lang.invoke.MethodType.*;
5315 ...
5316 MethodHandle cat = lookup().findVirtual(String.class,
5317 "concat", methodType(String.class, String.class));
5318 assertEquals("xy", (String) cat.invokeExact("x", "y"));
5319 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
5320 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
5321 assertEquals(bigType, d0.type());
5322 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
5323 * }
5324 * <p>
5325 * This method is also equivalent to the following code:
5326 * <blockquote><pre>
5327 * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))}
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} list 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 too many parameters
5339 */
5340 public static MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) {
5341 return dropArgumentsTrusted(target, pos, valueTypes.toArray(new Class<?>[0]).clone());
5342 }
5343
5344 static MethodHandle dropArgumentsTrusted(MethodHandle target, int pos, Class<?>[] valueTypes) {
5345 MethodType oldType = target.type(); // get NPE
5346 int dropped = dropArgumentChecks(oldType, pos, valueTypes);
5347 MethodType newType = oldType.insertParameterTypes(pos, valueTypes);
5348 if (dropped == 0) return target;
5349 BoundMethodHandle result = target.rebind();
5350 LambdaForm lform = result.form;
5351 int insertFormArg = 1 + pos;
5352 for (Class<?> ptype : valueTypes) {
5353 lform = lform.editor().addArgumentForm(insertFormArg++, BasicType.basicType(ptype));
5354 }
5355 result = result.copyWith(newType, lform);
5356 return result;
5357 }
5358
5359 private static int dropArgumentChecks(MethodType oldType, int pos, Class<?>[] valueTypes) {
5360 int dropped = valueTypes.length;
5361 MethodType.checkSlotCount(dropped);
5362 int outargs = oldType.parameterCount();
5363 int inargs = outargs + dropped;
5364 if (pos < 0 || pos > outargs)
5365 throw newIllegalArgumentException("no argument type to remove"
5366 + Arrays.asList(oldType, pos, valueTypes, inargs, outargs)
5367 );
5368 return dropped;
5369 }
5370
5371 /**
5372 * Produces a method handle which will discard some dummy arguments
5373 * before calling some other specified <i>target</i> method handle.
5374 * The type of the new method handle will be the same as the target's type,
5375 * except it will also include the dummy argument types,
5376 * at some given position.
5377 * <p>
5378 * The {@code pos} argument may range between zero and <i>N</i>,
5379 * where <i>N</i> is the arity of the target.
5380 * If {@code pos} is zero, the dummy arguments will precede
5381 * the target's real arguments; if {@code pos} is <i>N</i>
5382 * they will come after.
5383 * @apiNote
5384 * {@snippet lang="java" :
5385 import static java.lang.invoke.MethodHandles.*;
5386 import static java.lang.invoke.MethodType.*;
5387 ...
5388 MethodHandle cat = lookup().findVirtual(String.class,
5389 "concat", methodType(String.class, String.class));
5390 assertEquals("xy", (String) cat.invokeExact("x", "y"));
5391 MethodHandle d0 = dropArguments(cat, 0, String.class);
5392 assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
5393 MethodHandle d1 = dropArguments(cat, 1, String.class);
5394 assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
5395 MethodHandle d2 = dropArguments(cat, 2, String.class);
5396 assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
5397 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
5398 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
5399 * }
5400 * <p>
5401 * This method is also equivalent to the following code:
5402 * <blockquote><pre>
5403 * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))}
5404 * </pre></blockquote>
5405 * @param target the method handle to invoke after the arguments are dropped
5406 * @param pos position of first argument to drop (zero for the leftmost)
5407 * @param valueTypes the type(s) of the argument(s) to drop
5408 * @return a method handle which drops arguments of the given types,
5409 * before calling the original method handle
5410 * @throws NullPointerException if the target is null,
5411 * or if the {@code valueTypes} array or any of its elements is null
5412 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
5413 * or if {@code pos} is negative or greater than the arity of the target,
5414 * or if the new method handle's type would have
5415 * <a href="MethodHandle.html#maxarity">too many parameters</a>
5416 */
5417 public static MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
5418 return dropArgumentsTrusted(target, pos, valueTypes.clone());
5419 }
5420
5421 /* Convenience overloads for trusting internal low-arity call-sites */
5422 static MethodHandle dropArguments(MethodHandle target, int pos, Class<?> valueType1) {
5423 return dropArgumentsTrusted(target, pos, new Class<?>[] { valueType1 });
5424 }
5425 static MethodHandle dropArguments(MethodHandle target, int pos, Class<?> valueType1, Class<?> valueType2) {
5426 return dropArgumentsTrusted(target, pos, new Class<?>[] { valueType1, valueType2 });
5427 }
5428
5429 // private version which allows caller some freedom with error handling
5430 private static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, Class<?>[] newTypes, int pos,
5431 boolean nullOnFailure) {
5432 Class<?>[] oldTypes = target.type().ptypes();
5433 int match = oldTypes.length;
5434 if (skip != 0) {
5435 if (skip < 0 || skip > match) {
5436 throw newIllegalArgumentException("illegal skip", skip, target);
5437 }
5438 oldTypes = Arrays.copyOfRange(oldTypes, skip, match);
5439 match -= skip;
5440 }
5441 Class<?>[] addTypes = newTypes;
5442 int add = addTypes.length;
5443 if (pos != 0) {
5444 if (pos < 0 || pos > add) {
5445 throw newIllegalArgumentException("illegal pos", pos, Arrays.toString(newTypes));
5446 }
5447 addTypes = Arrays.copyOfRange(addTypes, pos, add);
5448 add -= pos;
5449 assert(addTypes.length == add);
5450 }
5451 // Do not add types which already match the existing arguments.
5452 if (match > add || !Arrays.equals(oldTypes, 0, oldTypes.length, addTypes, 0, match)) {
5453 if (nullOnFailure) {
5454 return null;
5455 }
5456 throw newIllegalArgumentException("argument lists do not match",
5457 Arrays.toString(oldTypes), Arrays.toString(newTypes));
5458 }
5459 addTypes = Arrays.copyOfRange(addTypes, match, add);
5460 add -= match;
5461 assert(addTypes.length == add);
5462 // newTypes: ( P*[pos], M*[match], A*[add] )
5463 // target: ( S*[skip], M*[match] )
5464 MethodHandle adapter = target;
5465 if (add > 0) {
5466 adapter = dropArgumentsTrusted(adapter, skip+ match, addTypes);
5467 }
5468 // adapter: (S*[skip], M*[match], A*[add] )
5469 if (pos > 0) {
5470 adapter = dropArgumentsTrusted(adapter, skip, Arrays.copyOfRange(newTypes, 0, pos));
5471 }
5472 // adapter: (S*[skip], P*[pos], M*[match], A*[add] )
5473 return adapter;
5474 }
5475
5476 /**
5477 * Adapts a target method handle to match the given parameter type list. If necessary, adds dummy arguments. Some
5478 * leading parameters can be skipped before matching begins. The remaining types in the {@code target}'s parameter
5479 * type list must be a sub-list of the {@code newTypes} type list at the starting position {@code pos}. The
5480 * resulting handle will have the target handle's parameter type list, with any non-matching parameter types (before
5481 * or after the matching sub-list) inserted in corresponding positions of the target's original parameters, as if by
5482 * {@link #dropArguments(MethodHandle, int, Class[])}.
5483 * <p>
5484 * The resulting handle will have the same return type as the target handle.
5485 * <p>
5486 * In more formal terms, assume these two type lists:<ul>
5487 * <li>The target handle has the parameter type list {@code S..., M...}, with as many types in {@code S} as
5488 * indicated by {@code skip}. The {@code M} types are those that are supposed to match part of the given type list,
5489 * {@code newTypes}.
5490 * <li>The {@code newTypes} list contains types {@code P..., M..., A...}, with as many types in {@code P} as
5491 * indicated by {@code pos}. The {@code M} types are precisely those that the {@code M} types in the target handle's
5492 * parameter type list are supposed to match. The types in {@code A} are additional types found after the matching
5493 * sub-list.
5494 * </ul>
5495 * Given these assumptions, the result of an invocation of {@code dropArgumentsToMatch} will have the parameter type
5496 * list {@code S..., P..., M..., A...}, with the {@code P} and {@code A} types inserted as if by
5497 * {@link #dropArguments(MethodHandle, int, Class[])}.
5498 *
5499 * @apiNote
5500 * Two method handles whose argument lists are "effectively identical" (i.e., identical in a common prefix) may be
5501 * mutually converted to a common type by two calls to {@code dropArgumentsToMatch}, as follows:
5502 * {@snippet lang="java" :
5503 import static java.lang.invoke.MethodHandles.*;
5504 import static java.lang.invoke.MethodType.*;
5505 ...
5506 ...
5507 MethodHandle h0 = constant(boolean.class, true);
5508 MethodHandle h1 = lookup().findVirtual(String.class, "concat", methodType(String.class, String.class));
5509 MethodType bigType = h1.type().insertParameterTypes(1, String.class, int.class);
5510 MethodHandle h2 = dropArguments(h1, 0, bigType.parameterList());
5511 if (h1.type().parameterCount() < h2.type().parameterCount())
5512 h1 = dropArgumentsToMatch(h1, 0, h2.type().parameterList(), 0); // lengthen h1
5513 else
5514 h2 = dropArgumentsToMatch(h2, 0, h1.type().parameterList(), 0); // lengthen h2
5515 MethodHandle h3 = guardWithTest(h0, h1, h2);
5516 assertEquals("xy", h3.invoke("x", "y", 1, "a", "b", "c"));
5517 * }
5518 * @param target the method handle to adapt
5519 * @param skip number of targets parameters to disregard (they will be unchanged)
5520 * @param newTypes the list of types to match {@code target}'s parameter type list to
5521 * @param pos place in {@code newTypes} where the non-skipped target parameters must occur
5522 * @return a possibly adapted method handle
5523 * @throws NullPointerException if either argument is null
5524 * @throws IllegalArgumentException if any element of {@code newTypes} is {@code void.class},
5525 * or if {@code skip} is negative or greater than the arity of the target,
5526 * or if {@code pos} is negative or greater than the newTypes list size,
5527 * or if {@code newTypes} does not contain the {@code target}'s non-skipped parameter types at position
5528 * {@code pos}.
5529 * @since 9
5530 */
5531 public static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos) {
5532 Objects.requireNonNull(target);
5533 Objects.requireNonNull(newTypes);
5534 return dropArgumentsToMatch(target, skip, newTypes.toArray(new Class<?>[0]).clone(), pos, false);
5535 }
5536
5537 /**
5538 * Drop the return value of the target handle (if any).
5539 * The returned method handle will have a {@code void} return type.
5540 *
5541 * @param target the method handle to adapt
5542 * @return a possibly adapted method handle
5543 * @throws NullPointerException if {@code target} is null
5544 * @since 16
5545 */
5546 public static MethodHandle dropReturn(MethodHandle target) {
5547 Objects.requireNonNull(target);
5548 MethodType oldType = target.type();
5549 Class<?> oldReturnType = oldType.returnType();
5550 if (oldReturnType == void.class)
5551 return target;
5552 MethodType newType = oldType.changeReturnType(void.class);
5553 BoundMethodHandle result = target.rebind();
5554 LambdaForm lform = result.editor().filterReturnForm(V_TYPE, true);
5555 result = result.copyWith(newType, lform);
5556 return result;
5557 }
5558
5559 /**
5560 * Adapts a target method handle by pre-processing
5561 * one or more of its arguments, each with its own unary filter function,
5562 * and then calling the target with each pre-processed argument
5563 * replaced by the result of its corresponding filter function.
5564 * <p>
5565 * The pre-processing is performed by one or more method handles,
5566 * specified in the elements of the {@code filters} array.
5567 * The first element of the filter array corresponds to the {@code pos}
5568 * argument of the target, and so on in sequence.
5569 * The filter functions are invoked in left to right order.
5570 * <p>
5571 * Null arguments in the array are treated as identity functions,
5572 * and the corresponding arguments left unchanged.
5573 * (If there are no non-null elements in the array, the original target is returned.)
5574 * Each filter is applied to the corresponding argument of the adapter.
5575 * <p>
5576 * If a filter {@code F} applies to the {@code N}th argument of
5577 * the target, then {@code F} must be a method handle which
5578 * takes exactly one argument. The type of {@code F}'s sole argument
5579 * replaces the corresponding argument type of the target
5580 * in the resulting adapted method handle.
5581 * The return type of {@code F} must be identical to the corresponding
5582 * parameter type of the target.
5583 * <p>
5584 * It is an error if there are elements of {@code filters}
5585 * (null or not)
5586 * which do not correspond to argument positions in the target.
5587 * <p><b>Example:</b>
5588 * {@snippet lang="java" :
5589 import static java.lang.invoke.MethodHandles.*;
5590 import static java.lang.invoke.MethodType.*;
5591 ...
5592 MethodHandle cat = lookup().findVirtual(String.class,
5593 "concat", methodType(String.class, String.class));
5594 MethodHandle upcase = lookup().findVirtual(String.class,
5595 "toUpperCase", methodType(String.class));
5596 assertEquals("xy", (String) cat.invokeExact("x", "y"));
5597 MethodHandle f0 = filterArguments(cat, 0, upcase);
5598 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
5599 MethodHandle f1 = filterArguments(cat, 1, upcase);
5600 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
5601 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
5602 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
5603 * }
5604 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
5605 * denotes the return type of both the {@code target} and resulting adapter.
5606 * {@code P}/{@code p} and {@code B}/{@code b} represent the types and values
5607 * of the parameters and arguments that precede and follow the filter position
5608 * {@code pos}, respectively. {@code A[i]}/{@code a[i]} stand for the types and
5609 * values of the filtered parameters and arguments; they also represent the
5610 * return types of the {@code filter[i]} handles. The latter accept arguments
5611 * {@code v[i]} of type {@code V[i]}, which also appear in the signature of
5612 * the resulting adapter.
5613 * {@snippet lang="java" :
5614 * T target(P... p, A[i]... a[i], B... b);
5615 * A[i] filter[i](V[i]);
5616 * T adapter(P... p, V[i]... v[i], B... b) {
5617 * return target(p..., filter[i](v[i])..., b...);
5618 * }
5619 * }
5620 * <p>
5621 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5622 * variable-arity method handle}, even if the original target method handle was.
5623 *
5624 * @param target the method handle to invoke after arguments are filtered
5625 * @param pos the position of the first argument to filter
5626 * @param filters method handles to call initially on filtered arguments
5627 * @return method handle which incorporates the specified argument filtering logic
5628 * @throws NullPointerException if the target is null
5629 * or if the {@code filters} array is null
5630 * @throws IllegalArgumentException if a non-null element of {@code filters}
5631 * does not match a corresponding argument type of target as described above,
5632 * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()},
5633 * or if the resulting method handle's type would have
5634 * <a href="MethodHandle.html#maxarity">too many parameters</a>
5635 */
5636 public static MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
5637 // In method types arguments start at index 0, while the LF
5638 // editor have the MH receiver at position 0 - adjust appropriately.
5639 final int MH_RECEIVER_OFFSET = 1;
5640 filterArgumentsCheckArity(target, pos, filters);
5641 MethodHandle adapter = target;
5642
5643 // keep track of currently matched filters, as to optimize repeated filters
5644 int index = 0;
5645 int[] positions = new int[filters.length];
5646 MethodHandle filter = null;
5647
5648 // process filters in reverse order so that the invocation of
5649 // the resulting adapter will invoke the filters in left-to-right order
5650 for (int i = filters.length - 1; i >= 0; --i) {
5651 MethodHandle newFilter = filters[i];
5652 if (newFilter == null) continue; // ignore null elements of filters
5653
5654 // flush changes on update
5655 if (filter != newFilter) {
5656 if (filter != null) {
5657 if (index > 1) {
5658 adapter = filterRepeatedArgument(adapter, filter, Arrays.copyOf(positions, index));
5659 } else {
5660 adapter = filterArgument(adapter, positions[0] - 1, filter);
5661 }
5662 }
5663 filter = newFilter;
5664 index = 0;
5665 }
5666
5667 filterArgumentChecks(target, pos + i, newFilter);
5668 positions[index++] = pos + i + MH_RECEIVER_OFFSET;
5669 }
5670 if (index > 1) {
5671 adapter = filterRepeatedArgument(adapter, filter, Arrays.copyOf(positions, index));
5672 } else if (index == 1) {
5673 adapter = filterArgument(adapter, positions[0] - 1, filter);
5674 }
5675 return adapter;
5676 }
5677
5678 private static MethodHandle filterRepeatedArgument(MethodHandle adapter, MethodHandle filter, int[] positions) {
5679 MethodType targetType = adapter.type();
5680 MethodType filterType = filter.type();
5681 BoundMethodHandle result = adapter.rebind();
5682 Class<?> newParamType = filterType.parameterType(0);
5683
5684 Class<?>[] ptypes = targetType.ptypes().clone();
5685 for (int pos : positions) {
5686 ptypes[pos - 1] = newParamType;
5687 }
5688 MethodType newType = MethodType.methodType(targetType.rtype(), ptypes, true);
5689
5690 LambdaForm lform = result.editor().filterRepeatedArgumentForm(BasicType.basicType(newParamType), positions);
5691 return result.copyWithExtendL(newType, lform, filter);
5692 }
5693
5694 /*non-public*/
5695 static MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
5696 filterArgumentChecks(target, pos, filter);
5697 MethodType targetType = target.type();
5698 MethodType filterType = filter.type();
5699 BoundMethodHandle result = target.rebind();
5700 Class<?> newParamType = filterType.parameterType(0);
5701 LambdaForm lform = result.editor().filterArgumentForm(1 + pos, BasicType.basicType(newParamType));
5702 MethodType newType = targetType.changeParameterType(pos, newParamType);
5703 result = result.copyWithExtendL(newType, lform, filter);
5704 return result;
5705 }
5706
5707 private static void filterArgumentsCheckArity(MethodHandle target, int pos, MethodHandle[] filters) {
5708 MethodType targetType = target.type();
5709 int maxPos = targetType.parameterCount();
5710 if (pos + filters.length > maxPos)
5711 throw newIllegalArgumentException("too many filters");
5712 }
5713
5714 private static void filterArgumentChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
5715 MethodType targetType = target.type();
5716 MethodType filterType = filter.type();
5717 if (filterType.parameterCount() != 1
5718 || filterType.returnType() != targetType.parameterType(pos))
5719 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
5720 }
5721
5722 /**
5723 * Adapts a target method handle by pre-processing
5724 * a sub-sequence of its arguments with a filter (another method handle).
5725 * The pre-processed arguments are replaced by the result (if any) of the
5726 * filter function.
5727 * The target is then called on the modified (usually shortened) argument list.
5728 * <p>
5729 * If the filter returns a value, the target must accept that value as
5730 * its argument in position {@code pos}, preceded and/or followed by
5731 * any arguments not passed to the filter.
5732 * If the filter returns void, the target must accept all arguments
5733 * not passed to the filter.
5734 * No arguments are reordered, and a result returned from the filter
5735 * replaces (in order) the whole subsequence of arguments originally
5736 * passed to the adapter.
5737 * <p>
5738 * The argument types (if any) of the filter
5739 * replace zero or one argument types of the target, at position {@code pos},
5740 * in the resulting adapted method handle.
5741 * The return type of the filter (if any) must be identical to the
5742 * argument type of the target at position {@code pos}, and that target argument
5743 * is supplied by the return value of the filter.
5744 * <p>
5745 * In all cases, {@code pos} must be greater than or equal to zero, and
5746 * {@code pos} must also be less than or equal to the target's arity.
5747 * <p><b>Example:</b>
5748 * {@snippet lang="java" :
5749 import static java.lang.invoke.MethodHandles.*;
5750 import static java.lang.invoke.MethodType.*;
5751 ...
5752 MethodHandle deepToString = publicLookup()
5753 .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
5754
5755 MethodHandle ts1 = deepToString.asCollector(String[].class, 1);
5756 assertEquals("[strange]", (String) ts1.invokeExact("strange"));
5757
5758 MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
5759 assertEquals("[up, down]", (String) ts2.invokeExact("up", "down"));
5760
5761 MethodHandle ts3 = deepToString.asCollector(String[].class, 3);
5762 MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2);
5763 assertEquals("[top, [up, down], strange]",
5764 (String) ts3_ts2.invokeExact("top", "up", "down", "strange"));
5765
5766 MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1);
5767 assertEquals("[top, [up, down], [strange]]",
5768 (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange"));
5769
5770 MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3);
5771 assertEquals("[top, [[up, down, strange], charm], bottom]",
5772 (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom"));
5773 * }
5774 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
5775 * represents the return type of the {@code target} and resulting adapter.
5776 * {@code V}/{@code v} stand for the return type and value of the
5777 * {@code filter}, which are also found in the signature and arguments of
5778 * the {@code target}, respectively, unless {@code V} is {@code void}.
5779 * {@code A}/{@code a} and {@code C}/{@code c} represent the parameter types
5780 * and values preceding and following the collection position, {@code pos},
5781 * in the {@code target}'s signature. They also turn up in the resulting
5782 * adapter's signature and arguments, where they surround
5783 * {@code B}/{@code b}, which represent the parameter types and arguments
5784 * to the {@code filter} (if any).
5785 * {@snippet lang="java" :
5786 * T target(A...,V,C...);
5787 * V filter(B...);
5788 * T adapter(A... a,B... b,C... c) {
5789 * V v = filter(b...);
5790 * return target(a...,v,c...);
5791 * }
5792 * // and if the filter has no arguments:
5793 * T target2(A...,V,C...);
5794 * V filter2();
5795 * T adapter2(A... a,C... c) {
5796 * V v = filter2();
5797 * return target2(a...,v,c...);
5798 * }
5799 * // and if the filter has a void return:
5800 * T target3(A...,C...);
5801 * void filter3(B...);
5802 * T adapter3(A... a,B... b,C... c) {
5803 * filter3(b...);
5804 * return target3(a...,c...);
5805 * }
5806 * }
5807 * <p>
5808 * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to
5809 * one which first "folds" the affected arguments, and then drops them, in separate
5810 * steps as follows:
5811 * {@snippet lang="java" :
5812 * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2
5813 * mh = MethodHandles.foldArguments(mh, coll); //step 1
5814 * }
5815 * If the target method handle consumes no arguments besides than the result
5816 * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)}
5817 * is equivalent to {@code filterReturnValue(coll, mh)}.
5818 * If the filter method handle {@code coll} consumes one argument and produces
5819 * a non-void result, then {@code collectArguments(mh, N, coll)}
5820 * is equivalent to {@code filterArguments(mh, N, coll)}.
5821 * Other equivalences are possible but would require argument permutation.
5822 * <p>
5823 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5824 * variable-arity method handle}, even if the original target method handle was.
5825 *
5826 * @param target the method handle to invoke after filtering the subsequence of arguments
5827 * @param pos the position of the first adapter argument to pass to the filter,
5828 * and/or the target argument which receives the result of the filter
5829 * @param filter method handle to call on the subsequence of arguments
5830 * @return method handle which incorporates the specified argument subsequence filtering logic
5831 * @throws NullPointerException if either argument is null
5832 * @throws IllegalArgumentException if the return type of {@code filter}
5833 * is non-void and is not the same as the {@code pos} argument of the target,
5834 * or if {@code pos} is not between 0 and the target's arity, inclusive,
5835 * or if the resulting method handle's type would have
5836 * <a href="MethodHandle.html#maxarity">too many parameters</a>
5837 * @see MethodHandles#foldArguments
5838 * @see MethodHandles#filterArguments
5839 * @see MethodHandles#filterReturnValue
5840 */
5841 public static MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) {
5842 MethodType newType = collectArgumentsChecks(target, pos, filter);
5843 MethodType collectorType = filter.type();
5844 BoundMethodHandle result = target.rebind();
5845 LambdaForm lform = result.editor().collectArgumentsForm(1 + pos, collectorType.basicType());
5846 return result.copyWithExtendL(newType, lform, filter);
5847 }
5848
5849 private static MethodType collectArgumentsChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
5850 MethodType targetType = target.type();
5851 MethodType filterType = filter.type();
5852 Class<?> rtype = filterType.returnType();
5853 Class<?>[] filterArgs = filterType.ptypes();
5854 if (pos < 0 || (rtype == void.class && pos > targetType.parameterCount()) ||
5855 (rtype != void.class && pos >= targetType.parameterCount())) {
5856 throw newIllegalArgumentException("position is out of range for target", target, pos);
5857 }
5858 if (rtype == void.class) {
5859 return targetType.insertParameterTypes(pos, filterArgs);
5860 }
5861 if (rtype != targetType.parameterType(pos)) {
5862 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
5863 }
5864 return targetType.dropParameterTypes(pos, pos + 1).insertParameterTypes(pos, filterArgs);
5865 }
5866
5867 /**
5868 * Adapts a target method handle by post-processing
5869 * its return value (if any) with a filter (another method handle).
5870 * The result of the filter is returned from the adapter.
5871 * <p>
5872 * If the target returns a value, the filter must accept that value as
5873 * its only argument.
5874 * If the target returns void, the filter must accept no arguments.
5875 * <p>
5876 * The return type of the filter
5877 * replaces the return type of the target
5878 * in the resulting adapted method handle.
5879 * The argument type of the filter (if any) must be identical to the
5880 * return type of the target.
5881 * <p><b>Example:</b>
5882 * {@snippet lang="java" :
5883 import static java.lang.invoke.MethodHandles.*;
5884 import static java.lang.invoke.MethodType.*;
5885 ...
5886 MethodHandle cat = lookup().findVirtual(String.class,
5887 "concat", methodType(String.class, String.class));
5888 MethodHandle length = lookup().findVirtual(String.class,
5889 "length", methodType(int.class));
5890 System.out.println((String) cat.invokeExact("x", "y")); // xy
5891 MethodHandle f0 = filterReturnValue(cat, length);
5892 System.out.println((int) f0.invokeExact("x", "y")); // 2
5893 * }
5894 * <p>Here is pseudocode for the resulting adapter. In the code,
5895 * {@code T}/{@code t} represent the result type and value of the
5896 * {@code target}; {@code V}, the result type of the {@code filter}; and
5897 * {@code A}/{@code a}, the types and values of the parameters and arguments
5898 * of the {@code target} as well as the resulting adapter.
5899 * {@snippet lang="java" :
5900 * T target(A...);
5901 * V filter(T);
5902 * V adapter(A... a) {
5903 * T t = target(a...);
5904 * return filter(t);
5905 * }
5906 * // and if the target has a void return:
5907 * void target2(A...);
5908 * V filter2();
5909 * V adapter2(A... a) {
5910 * target2(a...);
5911 * return filter2();
5912 * }
5913 * // and if the filter has a void return:
5914 * T target3(A...);
5915 * void filter3(V);
5916 * void adapter3(A... a) {
5917 * T t = target3(a...);
5918 * filter3(t);
5919 * }
5920 * }
5921 * <p>
5922 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5923 * variable-arity method handle}, even if the original target method handle was.
5924 * @param target the method handle to invoke before filtering the return value
5925 * @param filter method handle to call on the return value
5926 * @return method handle which incorporates the specified return value filtering logic
5927 * @throws NullPointerException if either argument is null
5928 * @throws IllegalArgumentException if the argument list of {@code filter}
5929 * does not match the return type of target as described above
5930 */
5931 public static MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
5932 MethodType targetType = target.type();
5933 MethodType filterType = filter.type();
5934 filterReturnValueChecks(targetType, filterType);
5935 BoundMethodHandle result = target.rebind();
5936 BasicType rtype = BasicType.basicType(filterType.returnType());
5937 LambdaForm lform = result.editor().filterReturnForm(rtype, false);
5938 MethodType newType = targetType.changeReturnType(filterType.returnType());
5939 result = result.copyWithExtendL(newType, lform, filter);
5940 return result;
5941 }
5942
5943 private static void filterReturnValueChecks(MethodType targetType, MethodType filterType) throws RuntimeException {
5944 Class<?> rtype = targetType.returnType();
5945 int filterValues = filterType.parameterCount();
5946 if (filterValues == 0
5947 ? (rtype != void.class)
5948 : (rtype != filterType.parameterType(0) || filterValues != 1))
5949 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
5950 }
5951
5952 /**
5953 * Filter the return value of a target method handle with a filter function. The filter function is
5954 * applied to the return value of the original handle; if the filter specifies more than one parameters,
5955 * then any remaining parameter is appended to the adapter handle. In other words, the adaptation works
5956 * as follows:
5957 * {@snippet lang="java" :
5958 * T target(A...)
5959 * V filter(B... , T)
5960 * V adapter(A... a, B... b) {
5961 * T t = target(a...);
5962 * return filter(b..., t);
5963 * }
5964 * }
5965 * <p>
5966 * If the filter handle is a unary function, then this method behaves like {@link #filterReturnValue(MethodHandle, MethodHandle)}.
5967 *
5968 * @param target the target method handle
5969 * @param filter the filter method handle
5970 * @return the adapter method handle
5971 */
5972 /* package */ static MethodHandle collectReturnValue(MethodHandle target, MethodHandle filter) {
5973 MethodType targetType = target.type();
5974 MethodType filterType = filter.type();
5975 BoundMethodHandle result = target.rebind();
5976 LambdaForm lform = result.editor().collectReturnValueForm(filterType.basicType());
5977 MethodType newType = targetType.changeReturnType(filterType.returnType());
5978 if (filterType.parameterCount() > 1) {
5979 for (int i = 0 ; i < filterType.parameterCount() - 1 ; i++) {
5980 newType = newType.appendParameterTypes(filterType.parameterType(i));
5981 }
5982 }
5983 result = result.copyWithExtendL(newType, lform, filter);
5984 return result;
5985 }
5986
5987 /**
5988 * Adapts a target method handle by pre-processing
5989 * some of its arguments, and then calling the target with
5990 * the result of the pre-processing, inserted into the original
5991 * sequence of arguments.
5992 * <p>
5993 * The pre-processing is performed by {@code combiner}, a second method handle.
5994 * Of the arguments passed to the adapter, the first {@code N} arguments
5995 * are copied to the combiner, which is then called.
5996 * (Here, {@code N} is defined as the parameter count of the combiner.)
5997 * After this, control passes to the target, with any result
5998 * from the combiner inserted before the original {@code N} incoming
5999 * arguments.
6000 * <p>
6001 * If the combiner returns a value, the first parameter type of the target
6002 * must be identical with the return type of the combiner, and the next
6003 * {@code N} parameter types of the target must exactly match the parameters
6004 * of the combiner.
6005 * <p>
6006 * If the combiner has a void return, no result will be inserted,
6007 * and the first {@code N} parameter types of the target
6008 * must exactly match the parameters of the combiner.
6009 * <p>
6010 * The resulting adapter is the same type as the target, except that the
6011 * first parameter type is dropped,
6012 * if it corresponds to the result of the combiner.
6013 * <p>
6014 * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
6015 * that either the combiner or the target does not wish to receive.
6016 * If some of the incoming arguments are destined only for the combiner,
6017 * consider using {@link MethodHandle#asCollector asCollector} instead, since those
6018 * arguments will not need to be live on the stack on entry to the
6019 * target.)
6020 * <p><b>Example:</b>
6021 * {@snippet lang="java" :
6022 import static java.lang.invoke.MethodHandles.*;
6023 import static java.lang.invoke.MethodType.*;
6024 ...
6025 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
6026 "println", methodType(void.class, String.class))
6027 .bindTo(System.out);
6028 MethodHandle cat = lookup().findVirtual(String.class,
6029 "concat", methodType(String.class, String.class));
6030 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
6031 MethodHandle catTrace = foldArguments(cat, trace);
6032 // also prints "boo":
6033 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
6034 * }
6035 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
6036 * represents the result type of the {@code target} and resulting adapter.
6037 * {@code V}/{@code v} represent the type and value of the parameter and argument
6038 * of {@code target} that precedes the folding position; {@code V} also is
6039 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
6040 * types and values of the {@code N} parameters and arguments at the folding
6041 * position. {@code B}/{@code b} represent the types and values of the
6042 * {@code target} parameters and arguments that follow the folded parameters
6043 * and arguments.
6044 * {@snippet lang="java" :
6045 * // there are N arguments in A...
6046 * T target(V, A[N]..., B...);
6047 * V combiner(A...);
6048 * T adapter(A... a, B... b) {
6049 * V v = combiner(a...);
6050 * return target(v, a..., b...);
6051 * }
6052 * // and if the combiner has a void return:
6053 * T target2(A[N]..., B...);
6054 * void combiner2(A...);
6055 * T adapter2(A... a, B... b) {
6056 * combiner2(a...);
6057 * return target2(a..., b...);
6058 * }
6059 * }
6060 * <p>
6061 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
6062 * variable-arity method handle}, even if the original target method handle was.
6063 * @param target the method handle to invoke after arguments are combined
6064 * @param combiner method handle to call initially on the incoming arguments
6065 * @return method handle which incorporates the specified argument folding logic
6066 * @throws NullPointerException if either argument is null
6067 * @throws IllegalArgumentException if {@code combiner}'s return type
6068 * is non-void and not the same as the first argument type of
6069 * the target, or if the initial {@code N} argument types
6070 * of the target
6071 * (skipping one matching the {@code combiner}'s return type)
6072 * are not identical with the argument types of {@code combiner}
6073 */
6074 public static MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
6075 return foldArguments(target, 0, combiner);
6076 }
6077
6078 /**
6079 * Adapts a target method handle by pre-processing some of its arguments, starting at a given position, and then
6080 * calling the target with the result of the pre-processing, inserted into the original sequence of arguments just
6081 * before the folded arguments.
6082 * <p>
6083 * This method is closely related to {@link #foldArguments(MethodHandle, MethodHandle)}, but allows to control the
6084 * position in the parameter list at which folding takes place. The argument controlling this, {@code pos}, is a
6085 * zero-based index. The aforementioned method {@link #foldArguments(MethodHandle, MethodHandle)} assumes position
6086 * 0.
6087 *
6088 * @apiNote Example:
6089 * {@snippet lang="java" :
6090 import static java.lang.invoke.MethodHandles.*;
6091 import static java.lang.invoke.MethodType.*;
6092 ...
6093 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
6094 "println", methodType(void.class, String.class))
6095 .bindTo(System.out);
6096 MethodHandle cat = lookup().findVirtual(String.class,
6097 "concat", methodType(String.class, String.class));
6098 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
6099 MethodHandle catTrace = foldArguments(cat, 1, trace);
6100 // also prints "jum":
6101 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
6102 * }
6103 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
6104 * represents the result type of the {@code target} and resulting adapter.
6105 * {@code V}/{@code v} represent the type and value of the parameter and argument
6106 * of {@code target} that precedes the folding position; {@code V} also is
6107 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
6108 * types and values of the {@code N} parameters and arguments at the folding
6109 * position. {@code Z}/{@code z} and {@code B}/{@code b} represent the types
6110 * and values of the {@code target} parameters and arguments that precede and
6111 * follow the folded parameters and arguments starting at {@code pos},
6112 * respectively.
6113 * {@snippet lang="java" :
6114 * // there are N arguments in A...
6115 * T target(Z..., V, A[N]..., B...);
6116 * V combiner(A...);
6117 * T adapter(Z... z, A... a, B... b) {
6118 * V v = combiner(a...);
6119 * return target(z..., v, a..., b...);
6120 * }
6121 * // and if the combiner has a void return:
6122 * T target2(Z..., A[N]..., B...);
6123 * void combiner2(A...);
6124 * T adapter2(Z... z, A... a, B... b) {
6125 * combiner2(a...);
6126 * return target2(z..., a..., b...);
6127 * }
6128 * }
6129 * <p>
6130 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
6131 * variable-arity method handle}, even if the original target method handle was.
6132 *
6133 * @param target the method handle to invoke after arguments are combined
6134 * @param pos the position at which to start folding and at which to insert the folding result; if this is {@code
6135 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
6136 * @param combiner method handle to call initially on the incoming arguments
6137 * @return method handle which incorporates the specified argument folding logic
6138 * @throws NullPointerException if either argument is null
6139 * @throws IllegalArgumentException if either of the following two conditions holds:
6140 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
6141 * {@code pos} of the target signature;
6142 * (2) the {@code N} argument types at position {@code pos} of the target signature (skipping one matching
6143 * the {@code combiner}'s return type) are not identical with the argument types of {@code combiner}.
6144 *
6145 * @see #foldArguments(MethodHandle, MethodHandle)
6146 * @since 9
6147 */
6148 public static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner) {
6149 MethodType targetType = target.type();
6150 MethodType combinerType = combiner.type();
6151 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType);
6152 BoundMethodHandle result = target.rebind();
6153 boolean dropResult = rtype == void.class;
6154 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType());
6155 MethodType newType = targetType;
6156 if (!dropResult) {
6157 newType = newType.dropParameterTypes(pos, pos + 1);
6158 }
6159 result = result.copyWithExtendL(newType, lform, combiner);
6160 return result;
6161 }
6162
6163 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType) {
6164 int foldArgs = combinerType.parameterCount();
6165 Class<?> rtype = combinerType.returnType();
6166 int foldVals = rtype == void.class ? 0 : 1;
6167 int afterInsertPos = foldPos + foldVals;
6168 boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
6169 if (ok) {
6170 for (int i = 0; i < foldArgs; i++) {
6171 if (combinerType.parameterType(i) != targetType.parameterType(i + afterInsertPos)) {
6172 ok = false;
6173 break;
6174 }
6175 }
6176 }
6177 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos))
6178 ok = false;
6179 if (!ok)
6180 throw misMatchedTypes("target and combiner types", targetType, combinerType);
6181 return rtype;
6182 }
6183
6184 /**
6185 * Adapts a target method handle by pre-processing some of its arguments, then calling the target with the result
6186 * of the pre-processing replacing the argument at the given position.
6187 *
6188 * @param target the method handle to invoke after arguments are combined
6189 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code
6190 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
6191 * @param combiner method handle to call initially on the incoming arguments
6192 * @param argPositions indexes of the target to pick arguments sent to the combiner from
6193 * @return method handle which incorporates the specified argument folding logic
6194 * @throws NullPointerException if either argument is null
6195 * @throws IllegalArgumentException if either of the following two conditions holds:
6196 * (1) {@code combiner}'s return type is not the same as the argument type at position
6197 * {@code pos} of the target signature;
6198 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature are
6199 * not identical with the argument types of {@code combiner}.
6200 */
6201 /*non-public*/
6202 static MethodHandle filterArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
6203 return argumentsWithCombiner(true, target, position, combiner, argPositions);
6204 }
6205
6206 /**
6207 * Adapts a target method handle by pre-processing some of its arguments, calling the target with the result of
6208 * the pre-processing inserted into the original sequence of arguments at the given position.
6209 *
6210 * @param target the method handle to invoke after arguments are combined
6211 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code
6212 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
6213 * @param combiner method handle to call initially on the incoming arguments
6214 * @param argPositions indexes of the target to pick arguments sent to the combiner from
6215 * @return method handle which incorporates the specified argument folding logic
6216 * @throws NullPointerException if either argument is null
6217 * @throws IllegalArgumentException if either of the following two conditions holds:
6218 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
6219 * {@code pos} of the target signature;
6220 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature
6221 * (skipping {@code position} where the {@code combiner}'s return will be folded in) are not identical
6222 * with the argument types of {@code combiner}.
6223 */
6224 /*non-public*/
6225 static MethodHandle foldArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
6226 return argumentsWithCombiner(false, target, position, combiner, argPositions);
6227 }
6228
6229 private static MethodHandle argumentsWithCombiner(boolean filter, MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
6230 MethodType targetType = target.type();
6231 MethodType combinerType = combiner.type();
6232 Class<?> rtype = argumentsWithCombinerChecks(position, filter, targetType, combinerType, argPositions);
6233 BoundMethodHandle result = target.rebind();
6234
6235 MethodType newType = targetType;
6236 LambdaForm lform;
6237 if (filter) {
6238 lform = result.editor().filterArgumentsForm(1 + position, combinerType.basicType(), argPositions);
6239 } else {
6240 boolean dropResult = rtype == void.class;
6241 lform = result.editor().foldArgumentsForm(1 + position, dropResult, combinerType.basicType(), argPositions);
6242 if (!dropResult) {
6243 newType = newType.dropParameterTypes(position, position + 1);
6244 }
6245 }
6246 result = result.copyWithExtendL(newType, lform, combiner);
6247 return result;
6248 }
6249
6250 private static Class<?> argumentsWithCombinerChecks(int position, boolean filter, MethodType targetType, MethodType combinerType, int ... argPos) {
6251 int combinerArgs = combinerType.parameterCount();
6252 if (argPos.length != combinerArgs) {
6253 throw newIllegalArgumentException("combiner and argument map must be equal size", combinerType, argPos.length);
6254 }
6255 Class<?> rtype = combinerType.returnType();
6256
6257 for (int i = 0; i < combinerArgs; i++) {
6258 int arg = argPos[i];
6259 if (arg < 0 || arg > targetType.parameterCount()) {
6260 throw newIllegalArgumentException("arg outside of target parameterRange", targetType, arg);
6261 }
6262 if (combinerType.parameterType(i) != targetType.parameterType(arg)) {
6263 throw newIllegalArgumentException("target argument type at position " + arg
6264 + " must match combiner argument type at index " + i + ": " + targetType
6265 + " -> " + combinerType + ", map: " + Arrays.toString(argPos));
6266 }
6267 }
6268 if (filter && combinerType.returnType() != targetType.parameterType(position)) {
6269 throw misMatchedTypes("target and combiner types", targetType, combinerType);
6270 }
6271 return rtype;
6272 }
6273
6274 /**
6275 * Makes a method handle which adapts a target method handle,
6276 * by guarding it with a test, a boolean-valued method handle.
6277 * If the guard fails, a fallback handle is called instead.
6278 * All three method handles must have the same corresponding
6279 * argument and return types, except that the return type
6280 * of the test must be boolean, and the test is allowed
6281 * to have fewer arguments than the other two method handles.
6282 * <p>
6283 * Here is pseudocode for the resulting adapter. In the code, {@code T}
6284 * represents the uniform result type of the three involved handles;
6285 * {@code A}/{@code a}, the types and values of the {@code target}
6286 * parameters and arguments that are consumed by the {@code test}; and
6287 * {@code B}/{@code b}, those types and values of the {@code target}
6288 * parameters and arguments that are not consumed by the {@code test}.
6289 * {@snippet lang="java" :
6290 * boolean test(A...);
6291 * T target(A...,B...);
6292 * T fallback(A...,B...);
6293 * T adapter(A... a,B... b) {
6294 * if (test(a...))
6295 * return target(a..., b...);
6296 * else
6297 * return fallback(a..., b...);
6298 * }
6299 * }
6300 * Note that the test arguments ({@code a...} in the pseudocode) cannot
6301 * be modified by execution of the test, and so are passed unchanged
6302 * from the caller to the target or fallback as appropriate.
6303 * @param test method handle used for test, must return boolean
6304 * @param target method handle to call if test passes
6305 * @param fallback method handle to call if test fails
6306 * @return method handle which incorporates the specified if/then/else logic
6307 * @throws NullPointerException if any argument is null
6308 * @throws IllegalArgumentException if {@code test} does not return boolean,
6309 * or if all three method types do not match (with the return
6310 * type of {@code test} changed to match that of the target).
6311 */
6312 public static MethodHandle guardWithTest(MethodHandle test,
6313 MethodHandle target,
6314 MethodHandle fallback) {
6315 MethodType gtype = test.type();
6316 MethodType ttype = target.type();
6317 MethodType ftype = fallback.type();
6318 if (!ttype.equals(ftype))
6319 throw misMatchedTypes("target and fallback types", ttype, ftype);
6320 if (gtype.returnType() != boolean.class)
6321 throw newIllegalArgumentException("guard type is not a predicate "+gtype);
6322
6323 test = dropArgumentsToMatch(test, 0, ttype.ptypes(), 0, true);
6324 if (test == null) {
6325 throw misMatchedTypes("target and test types", ttype, gtype);
6326 }
6327 return MethodHandleImpl.makeGuardWithTest(test, target, fallback);
6328 }
6329
6330 static <T> RuntimeException misMatchedTypes(String what, T t1, T t2) {
6331 return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
6332 }
6333
6334 /**
6335 * Makes a method handle which adapts a target method handle,
6336 * by running it inside an exception handler.
6337 * If the target returns normally, the adapter returns that value.
6338 * If an exception matching the specified type is thrown, the fallback
6339 * handle is called instead on the exception, plus the original arguments.
6340 * <p>
6341 * The target and handler must have the same corresponding
6342 * argument and return types, except that handler may omit trailing arguments
6343 * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
6344 * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
6345 * <p>
6346 * Here is pseudocode for the resulting adapter. In the code, {@code T}
6347 * represents the return type of the {@code target} and {@code handler},
6348 * and correspondingly that of the resulting adapter; {@code A}/{@code a},
6349 * the types and values of arguments to the resulting handle consumed by
6350 * {@code handler}; and {@code B}/{@code b}, those of arguments to the
6351 * resulting handle discarded by {@code handler}.
6352 * {@snippet lang="java" :
6353 * T target(A..., B...);
6354 * T handler(ExType, A...);
6355 * T adapter(A... a, B... b) {
6356 * try {
6357 * return target(a..., b...);
6358 * } catch (ExType ex) {
6359 * return handler(ex, a...);
6360 * }
6361 * }
6362 * }
6363 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
6364 * be modified by execution of the target, and so are passed unchanged
6365 * from the caller to the handler, if the handler is invoked.
6366 * <p>
6367 * The target and handler must return the same type, even if the handler
6368 * always throws. (This might happen, for instance, because the handler
6369 * is simulating a {@code finally} clause).
6370 * To create such a throwing handler, compose the handler creation logic
6371 * with {@link #throwException throwException},
6372 * in order to create a method handle of the correct return type.
6373 * @param target method handle to call
6374 * @param exType the type of exception which the handler will catch
6375 * @param handler method handle to call if a matching exception is thrown
6376 * @return method handle which incorporates the specified try/catch logic
6377 * @throws NullPointerException if any argument is null
6378 * @throws IllegalArgumentException if {@code handler} does not accept
6379 * the given exception type, or if the method handle types do
6380 * not match in their return types and their
6381 * corresponding parameters
6382 * @see MethodHandles#tryFinally(MethodHandle, MethodHandle)
6383 */
6384 public static MethodHandle catchException(MethodHandle target,
6385 Class<? extends Throwable> exType,
6386 MethodHandle handler) {
6387 MethodType ttype = target.type();
6388 MethodType htype = handler.type();
6389 if (!Throwable.class.isAssignableFrom(exType))
6390 throw new ClassCastException(exType.getName());
6391 if (htype.parameterCount() < 1 ||
6392 !htype.parameterType(0).isAssignableFrom(exType))
6393 throw newIllegalArgumentException("handler does not accept exception type "+exType);
6394 if (htype.returnType() != ttype.returnType())
6395 throw misMatchedTypes("target and handler return types", ttype, htype);
6396 handler = dropArgumentsToMatch(handler, 1, ttype.ptypes(), 0, true);
6397 if (handler == null) {
6398 throw misMatchedTypes("target and handler types", ttype, htype);
6399 }
6400 return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
6401 }
6402
6403 /**
6404 * Produces a method handle which will throw exceptions of the given {@code exType}.
6405 * The method handle will accept a single argument of {@code exType},
6406 * and immediately throw it as an exception.
6407 * The method type will nominally specify a return of {@code returnType}.
6408 * The return type may be anything convenient: It doesn't matter to the
6409 * method handle's behavior, since it will never return normally.
6410 * @param returnType the return type of the desired method handle
6411 * @param exType the parameter type of the desired method handle
6412 * @return method handle which can throw the given exceptions
6413 * @throws NullPointerException if either argument is null
6414 */
6415 public static MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) {
6416 if (!Throwable.class.isAssignableFrom(exType))
6417 throw new ClassCastException(exType.getName());
6418 return MethodHandleImpl.throwException(methodType(returnType, exType));
6419 }
6420
6421 /**
6422 * Constructs a method handle representing a loop with several loop variables that are updated and checked upon each
6423 * iteration. Upon termination of the loop due to one of the predicates, a corresponding finalizer is run and
6424 * delivers the loop's result, which is the return value of the resulting handle.
6425 * <p>
6426 * Intuitively, every loop is formed by one or more "clauses", each specifying a local <em>iteration variable</em> and/or a loop
6427 * exit. Each iteration of the loop executes each clause in order. A clause can optionally update its iteration
6428 * variable; it can also optionally perform a test and conditional loop exit. In order to express this logic in
6429 * terms of method handles, each clause will specify up to four independent actions:<ul>
6430 * <li><em>init:</em> Before the loop executes, the initialization of an iteration variable {@code v} of type {@code V}.
6431 * <li><em>step:</em> When a clause executes, an update step for the iteration variable {@code v}.
6432 * <li><em>pred:</em> When a clause executes, a predicate execution to test for loop exit.
6433 * <li><em>fini:</em> If a clause causes a loop exit, a finalizer execution to compute the loop's return value.
6434 * </ul>
6435 * The full sequence of all iteration variable types, in clause order, will be notated as {@code (V...)}.
6436 * The values themselves will be {@code (v...)}. When we speak of "parameter lists", we will usually
6437 * be referring to types, but in some contexts (describing execution) the lists will be of actual values.
6438 * <p>
6439 * Some of these clause parts may be omitted according to certain rules, and useful default behavior is provided in
6440 * this case. See below for a detailed description.
6441 * <p>
6442 * <em>Parameters optional everywhere:</em>
6443 * Each clause function is allowed but not required to accept a parameter for each iteration variable {@code v}.
6444 * As an exception, the init functions cannot take any {@code v} parameters,
6445 * because those values are not yet computed when the init functions are executed.
6446 * Any clause function may neglect to take any trailing subsequence of parameters it is entitled to take.
6447 * In fact, any clause function may take no arguments at all.
6448 * <p>
6449 * <em>Loop parameters:</em>
6450 * A clause function may take all the iteration variable values it is entitled to, in which case
6451 * it may also take more trailing parameters. Such extra values are called <em>loop parameters</em>,
6452 * with their types and values notated as {@code (A...)} and {@code (a...)}.
6453 * These become the parameters of the resulting loop handle, to be supplied whenever the loop is executed.
6454 * (Since init functions do not accept iteration variables {@code v}, any parameter to an
6455 * init function is automatically a loop parameter {@code a}.)
6456 * As with iteration variables, clause functions are allowed but not required to accept loop parameters.
6457 * These loop parameters act as loop-invariant values visible across the whole loop.
6458 * <p>
6459 * <em>Parameters visible everywhere:</em>
6460 * Each non-init clause function is permitted to observe the entire loop state, because it can be passed the full
6461 * list {@code (v... a...)} of current iteration variable values and incoming loop parameters.
6462 * The init functions can observe initial pre-loop state, in the form {@code (a...)}.
6463 * Most clause functions will not need all of this information, but they will be formally connected to it
6464 * as if by {@link #dropArguments}.
6465 * <a id="astar"></a>
6466 * More specifically, we shall use the notation {@code (V*)} to express an arbitrary prefix of a full
6467 * sequence {@code (V...)} (and likewise for {@code (v*)}, {@code (A*)}, {@code (a*)}).
6468 * In that notation, the general form of an init function parameter list
6469 * is {@code (A*)}, and the general form of a non-init function parameter list is {@code (V*)} or {@code (V... A*)}.
6470 * <p>
6471 * <em>Checking clause structure:</em>
6472 * Given a set of clauses, there is a number of checks and adjustments performed to connect all the parts of the
6473 * loop. They are spelled out in detail in the steps below. In these steps, every occurrence of the word "must"
6474 * corresponds to a place where {@link IllegalArgumentException} will be thrown if the required constraint is not
6475 * met by the inputs to the loop combinator.
6476 * <p>
6477 * <em>Effectively identical sequences:</em>
6478 * <a id="effid"></a>
6479 * A parameter list {@code A} is defined to be <em>effectively identical</em> to another parameter list {@code B}
6480 * if {@code A} and {@code B} are identical, or if {@code A} is shorter and is identical with a proper prefix of {@code B}.
6481 * When speaking of an unordered set of parameter lists, we say they the set is "effectively identical"
6482 * as a whole if the set contains a longest list, and all members of the set are effectively identical to
6483 * that longest list.
6484 * For example, any set of type sequences of the form {@code (V*)} is effectively identical,
6485 * and the same is true if more sequences of the form {@code (V... A*)} are added.
6486 * <p>
6487 * <em>Step 0: Determine clause structure.</em><ol type="a">
6488 * <li>The clause array (of type {@code MethodHandle[][]}) must be non-{@code null} and contain at least one element.
6489 * <li>The clause array may not contain {@code null}s or sub-arrays longer than four elements.
6490 * <li>Clauses shorter than four elements are treated as if they were padded by {@code null} elements to length
6491 * four. Padding takes place by appending elements to the array.
6492 * <li>Clauses with all {@code null}s are disregarded.
6493 * <li>Each clause is treated as a four-tuple of functions, called "init", "step", "pred", and "fini".
6494 * </ol>
6495 * <p>
6496 * <em>Step 1A: Determine iteration variable types {@code (V...)}.</em><ol type="a">
6497 * <li>The iteration variable type for each clause is determined using the clause's init and step return types.
6498 * <li>If both functions are omitted, there is no iteration variable for the corresponding clause ({@code void} is
6499 * used as the type to indicate that). If one of them is omitted, the other's return type defines the clause's
6500 * iteration variable type. If both are given, the common return type (they must be identical) defines the clause's
6501 * iteration variable type.
6502 * <li>Form the list of return types (in clause order), omitting all occurrences of {@code void}.
6503 * <li>This list of types is called the "iteration variable types" ({@code (V...)}).
6504 * </ol>
6505 * <p>
6506 * <em>Step 1B: Determine loop parameters {@code (A...)}.</em><ul>
6507 * <li>Examine and collect init function parameter lists (which are of the form {@code (A*)}).
6508 * <li>Examine and collect the suffixes of the step, pred, and fini parameter lists, after removing the iteration variable types.
6509 * (They must have the form {@code (V... A*)}; collect the {@code (A*)} parts only.)
6510 * <li>Do not collect suffixes from step, pred, and fini parameter lists that do not begin with all the iteration variable types.
6511 * (These types will be checked in step 2, along with all the clause function types.)
6512 * <li>Omitted clause functions are ignored. (Equivalently, they are deemed to have empty parameter lists.)
6513 * <li>All of the collected parameter lists must be effectively identical.
6514 * <li>The longest parameter list (which is necessarily unique) is called the "external parameter list" ({@code (A...)}).
6515 * <li>If there is no such parameter list, the external parameter list is taken to be the empty sequence.
6516 * <li>The combined list consisting of iteration variable types followed by the external parameter types is called
6517 * the "internal parameter list".
6518 * </ul>
6519 * <p>
6520 * <em>Step 1C: Determine loop return type.</em><ol type="a">
6521 * <li>Examine fini function return types, disregarding omitted fini functions.
6522 * <li>If there are no fini functions, the loop return type is {@code void}.
6523 * <li>Otherwise, the common return type {@code R} of the fini functions (their return types must be identical) defines the loop return
6524 * type.
6525 * </ol>
6526 * <p>
6527 * <em>Step 1D: Check other types.</em><ol type="a">
6528 * <li>There must be at least one non-omitted pred function.
6529 * <li>Every non-omitted pred function must have a {@code boolean} return type.
6530 * </ol>
6531 * <p>
6532 * <em>Step 2: Determine parameter lists.</em><ol type="a">
6533 * <li>The parameter list for the resulting loop handle will be the external parameter list {@code (A...)}.
6534 * <li>The parameter list for init functions will be adjusted to the external parameter list.
6535 * (Note that their parameter lists are already effectively identical to this list.)
6536 * <li>The parameter list for every non-omitted, non-init (step, pred, and fini) function must be
6537 * effectively identical to the internal parameter list {@code (V... A...)}.
6538 * </ol>
6539 * <p>
6540 * <em>Step 3: Fill in omitted functions.</em><ol type="a">
6541 * <li>If an init function is omitted, use a {@linkplain #empty default value} for the clause's iteration variable
6542 * type.
6543 * <li>If a step function is omitted, use an {@linkplain #identity identity function} of the clause's iteration
6544 * variable type; insert dropped argument parameters before the identity function parameter for the non-{@code void}
6545 * iteration variables of preceding clauses. (This will turn the loop variable into a local loop invariant.)
6546 * <li>If a pred function is omitted, use a constant {@code true} function. (This will keep the loop going, as far
6547 * as this clause is concerned. Note that in such cases the corresponding fini function is unreachable.)
6548 * <li>If a fini function is omitted, use a {@linkplain #empty default value} for the
6549 * loop return type.
6550 * </ol>
6551 * <p>
6552 * <em>Step 4: Fill in missing parameter types.</em><ol type="a">
6553 * <li>At this point, every init function parameter list is effectively identical to the external parameter list {@code (A...)},
6554 * but some lists may be shorter. For every init function with a short parameter list, pad out the end of the list.
6555 * <li>At this point, every non-init function parameter list is effectively identical to the internal parameter
6556 * list {@code (V... A...)}, but some lists may be shorter. For every non-init function with a short parameter list,
6557 * pad out the end of the list.
6558 * <li>Argument lists are padded out by {@linkplain #dropArgumentsToMatch(MethodHandle, int, List, int) dropping unused trailing arguments}.
6559 * </ol>
6560 * <p>
6561 * <em>Final observations.</em><ol type="a">
6562 * <li>After these steps, all clauses have been adjusted by supplying omitted functions and arguments.
6563 * <li>All init functions have a common parameter type list {@code (A...)}, which the final loop handle will also have.
6564 * <li>All fini functions have a common return type {@code R}, which the final loop handle will also have.
6565 * <li>All non-init functions have a common parameter type list {@code (V... A...)}, of
6566 * (non-{@code void}) iteration variables {@code V} followed by loop parameters.
6567 * <li>Each pair of init and step functions agrees in their return type {@code V}.
6568 * <li>Each non-init function will be able to observe the current values {@code (v...)} of all iteration variables.
6569 * <li>Every function will be able to observe the incoming values {@code (a...)} of all loop parameters.
6570 * </ol>
6571 * <p>
6572 * <em>Example.</em> As a consequence of step 1A above, the {@code loop} combinator has the following property:
6573 * <ul>
6574 * <li>Given {@code N} clauses {@code Cn = {null, Sn, Pn}} with {@code n = 1..N}.
6575 * <li>Suppose predicate handles {@code Pn} are either {@code null} or have no parameters.
6576 * (Only one {@code Pn} has to be non-{@code null}.)
6577 * <li>Suppose step handles {@code Sn} have signatures {@code (B1..BX)Rn}, for some constant {@code X>=N}.
6578 * <li>Suppose {@code Q} is the count of non-void types {@code Rn}, and {@code (V1...VQ)} is the sequence of those types.
6579 * <li>It must be that {@code Vn == Bn} for {@code n = 1..min(X,Q)}.
6580 * <li>The parameter types {@code Vn} will be interpreted as loop-local state elements {@code (V...)}.
6581 * <li>Any remaining types {@code BQ+1..BX} (if {@code Q<X}) will determine
6582 * the resulting loop handle's parameter types {@code (A...)}.
6583 * </ul>
6584 * In this example, the loop handle parameters {@code (A...)} were derived from the step functions,
6585 * which is natural if most of the loop computation happens in the steps. For some loops,
6586 * the burden of computation might be heaviest in the pred functions, and so the pred functions
6587 * might need to accept the loop parameter values. For loops with complex exit logic, the fini
6588 * functions might need to accept loop parameters, and likewise for loops with complex entry logic,
6589 * where the init functions will need the extra parameters. For such reasons, the rules for
6590 * determining these parameters are as symmetric as possible, across all clause parts.
6591 * In general, the loop parameters function as common invariant values across the whole
6592 * loop, while the iteration variables function as common variant values, or (if there is
6593 * no step function) as internal loop invariant temporaries.
6594 * <p>
6595 * <em>Loop execution.</em><ol type="a">
6596 * <li>When the loop is called, the loop input values are saved in locals, to be passed to
6597 * every clause function. These locals are loop invariant.
6598 * <li>Each init function is executed in clause order (passing the external arguments {@code (a...)})
6599 * and the non-{@code void} values are saved (as the iteration variables {@code (v...)}) into locals.
6600 * These locals will be loop varying (unless their steps behave as identity functions, as noted above).
6601 * <li>All function executions (except init functions) will be passed the internal parameter list, consisting of
6602 * the non-{@code void} iteration values {@code (v...)} (in clause order) and then the loop inputs {@code (a...)}
6603 * (in argument order).
6604 * <li>The step and pred functions are then executed, in clause order (step before pred), until a pred function
6605 * returns {@code false}.
6606 * <li>The non-{@code void} result from a step function call is used to update the corresponding value in the
6607 * sequence {@code (v...)} of loop variables.
6608 * The updated value is immediately visible to all subsequent function calls.
6609 * <li>If a pred function returns {@code false}, the corresponding fini function is called, and the resulting value
6610 * (of type {@code R}) is returned from the loop as a whole.
6611 * <li>If all the pred functions always return true, no fini function is ever invoked, and the loop cannot exit
6612 * except by throwing an exception.
6613 * </ol>
6614 * <p>
6615 * <em>Usage tips.</em>
6616 * <ul>
6617 * <li>Although each step function will receive the current values of <em>all</em> the loop variables,
6618 * sometimes a step function only needs to observe the current value of its own variable.
6619 * In that case, the step function may need to explicitly {@linkplain #dropArguments drop all preceding loop variables}.
6620 * This will require mentioning their types, in an expression like {@code dropArguments(step, 0, V0.class, ...)}.
6621 * <li>Loop variables are not required to vary; they can be loop invariant. A clause can create
6622 * a loop invariant by a suitable init function with no step, pred, or fini function. This may be
6623 * useful to "wire" an incoming loop argument into the step or pred function of an adjacent loop variable.
6624 * <li>If some of the clause functions are virtual methods on an instance, the instance
6625 * itself can be conveniently placed in an initial invariant loop "variable", using an initial clause
6626 * like {@code new MethodHandle[]{identity(ObjType.class)}}. In that case, the instance reference
6627 * will be the first iteration variable value, and it will be easy to use virtual
6628 * methods as clause parts, since all of them will take a leading instance reference matching that value.
6629 * </ul>
6630 * <p>
6631 * Here is pseudocode for the resulting loop handle. As above, {@code V} and {@code v} represent the types
6632 * and values of loop variables; {@code A} and {@code a} represent arguments passed to the whole loop;
6633 * and {@code R} is the common result type of all finalizers as well as of the resulting loop.
6634 * {@snippet lang="java" :
6635 * V... init...(A...);
6636 * boolean pred...(V..., A...);
6637 * V... step...(V..., A...);
6638 * R fini...(V..., A...);
6639 * R loop(A... a) {
6640 * V... v... = init...(a...);
6641 * for (;;) {
6642 * for ((v, p, s, f) in (v..., pred..., step..., fini...)) {
6643 * v = s(v..., a...);
6644 * if (!p(v..., a...)) {
6645 * return f(v..., a...);
6646 * }
6647 * }
6648 * }
6649 * }
6650 * }
6651 * Note that the parameter type lists {@code (V...)} and {@code (A...)} have been expanded
6652 * to their full length, even though individual clause functions may neglect to take them all.
6653 * As noted above, missing parameters are filled in as if by {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}.
6654 *
6655 * @apiNote Example:
6656 * {@snippet lang="java" :
6657 * // iterative implementation of the factorial function as a loop handle
6658 * static int one(int k) { return 1; }
6659 * static int inc(int i, int acc, int k) { return i + 1; }
6660 * static int mult(int i, int acc, int k) { return i * acc; }
6661 * static boolean pred(int i, int acc, int k) { return i < k; }
6662 * static int fin(int i, int acc, int k) { return acc; }
6663 * // assume MH_one, MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
6664 * // null initializer for counter, should initialize to 0
6665 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
6666 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
6667 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
6668 * assertEquals(120, loop.invoke(5));
6669 * }
6670 * The same example, dropping arguments and using combinators:
6671 * {@snippet lang="java" :
6672 * // simplified implementation of the factorial function as a loop handle
6673 * static int inc(int i) { return i + 1; } // drop acc, k
6674 * static int mult(int i, int acc) { return i * acc; } //drop k
6675 * static boolean cmp(int i, int k) { return i < k; }
6676 * // assume MH_inc, MH_mult, and MH_cmp are handles to the above methods
6677 * // null initializer for counter, should initialize to 0
6678 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
6679 * MethodHandle MH_pred = MethodHandles.dropArguments(MH_cmp, 1, int.class); // drop acc
6680 * MethodHandle MH_fin = MethodHandles.dropArguments(MethodHandles.identity(int.class), 0, int.class); // drop i
6681 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
6682 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
6683 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
6684 * assertEquals(720, loop.invoke(6));
6685 * }
6686 * A similar example, using a helper object to hold a loop parameter:
6687 * {@snippet lang="java" :
6688 * // instance-based implementation of the factorial function as a loop handle
6689 * static class FacLoop {
6690 * final int k;
6691 * FacLoop(int k) { this.k = k; }
6692 * int inc(int i) { return i + 1; }
6693 * int mult(int i, int acc) { return i * acc; }
6694 * boolean pred(int i) { return i < k; }
6695 * int fin(int i, int acc) { return acc; }
6696 * }
6697 * // assume MH_FacLoop is a handle to the constructor
6698 * // assume MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
6699 * // null initializer for counter, should initialize to 0
6700 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
6701 * MethodHandle[] instanceClause = new MethodHandle[]{MH_FacLoop};
6702 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
6703 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
6704 * MethodHandle loop = MethodHandles.loop(instanceClause, counterClause, accumulatorClause);
6705 * assertEquals(5040, loop.invoke(7));
6706 * }
6707 *
6708 * @param clauses an array of arrays (4-tuples) of {@link MethodHandle}s adhering to the rules described above.
6709 *
6710 * @return a method handle embodying the looping behavior as defined by the arguments.
6711 *
6712 * @throws IllegalArgumentException in case any of the constraints described above is violated.
6713 *
6714 * @see MethodHandles#whileLoop(MethodHandle, MethodHandle, MethodHandle)
6715 * @see MethodHandles#doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
6716 * @see MethodHandles#countedLoop(MethodHandle, MethodHandle, MethodHandle)
6717 * @see MethodHandles#iteratedLoop(MethodHandle, MethodHandle, MethodHandle)
6718 * @since 9
6719 */
6720 public static MethodHandle loop(MethodHandle[]... clauses) {
6721 // Step 0: determine clause structure.
6722 loopChecks0(clauses);
6723
6724 List<MethodHandle> init = new ArrayList<>();
6725 List<MethodHandle> step = new ArrayList<>();
6726 List<MethodHandle> pred = new ArrayList<>();
6727 List<MethodHandle> fini = new ArrayList<>();
6728
6729 Stream.of(clauses).filter(c -> Stream.of(c).anyMatch(Objects::nonNull)).forEach(clause -> {
6730 init.add(clause[0]); // all clauses have at least length 1
6731 step.add(clause.length <= 1 ? null : clause[1]);
6732 pred.add(clause.length <= 2 ? null : clause[2]);
6733 fini.add(clause.length <= 3 ? null : clause[3]);
6734 });
6735
6736 assert Stream.of(init, step, pred, fini).map(List::size).distinct().count() == 1;
6737 final int nclauses = init.size();
6738
6739 // Step 1A: determine iteration variables (V...).
6740 final List<Class<?>> iterationVariableTypes = new ArrayList<>();
6741 for (int i = 0; i < nclauses; ++i) {
6742 MethodHandle in = init.get(i);
6743 MethodHandle st = step.get(i);
6744 if (in == null && st == null) {
6745 iterationVariableTypes.add(void.class);
6746 } else if (in != null && st != null) {
6747 loopChecks1a(i, in, st);
6748 iterationVariableTypes.add(in.type().returnType());
6749 } else {
6750 iterationVariableTypes.add(in == null ? st.type().returnType() : in.type().returnType());
6751 }
6752 }
6753 final List<Class<?>> commonPrefix = iterationVariableTypes.stream().filter(t -> t != void.class).toList();
6754
6755 // Step 1B: determine loop parameters (A...).
6756 final List<Class<?>> commonSuffix = buildCommonSuffix(init, step, pred, fini, commonPrefix.size());
6757 loopChecks1b(init, commonSuffix);
6758
6759 // Step 1C: determine loop return type.
6760 // Step 1D: check other types.
6761 // local variable required here; see JDK-8223553
6762 Stream<Class<?>> cstream = fini.stream().filter(Objects::nonNull).map(MethodHandle::type)
6763 .map(MethodType::returnType);
6764 final Class<?> loopReturnType = cstream.findFirst().orElse(void.class);
6765 loopChecks1cd(pred, fini, loopReturnType);
6766
6767 // Step 2: determine parameter lists.
6768 final List<Class<?>> commonParameterSequence = new ArrayList<>(commonPrefix);
6769 commonParameterSequence.addAll(commonSuffix);
6770 loopChecks2(step, pred, fini, commonParameterSequence);
6771 // Step 3: fill in omitted functions.
6772 for (int i = 0; i < nclauses; ++i) {
6773 Class<?> t = iterationVariableTypes.get(i);
6774 if (init.get(i) == null) {
6775 init.set(i, empty(methodType(t, commonSuffix)));
6776 }
6777 if (step.get(i) == null) {
6778 step.set(i, dropArgumentsToMatch(identityOrVoid(t), 0, commonParameterSequence, i));
6779 }
6780 if (pred.get(i) == null) {
6781 pred.set(i, dropArguments(constant(boolean.class, true), 0, commonParameterSequence));
6782 }
6783 if (fini.get(i) == null) {
6784 fini.set(i, empty(methodType(t, commonParameterSequence)));
6785 }
6786 }
6787
6788 // Step 4: fill in missing parameter types.
6789 // Also convert all handles to fixed-arity handles.
6790 List<MethodHandle> finit = fixArities(fillParameterTypes(init, commonSuffix));
6791 List<MethodHandle> fstep = fixArities(fillParameterTypes(step, commonParameterSequence));
6792 List<MethodHandle> fpred = fixArities(fillParameterTypes(pred, commonParameterSequence));
6793 List<MethodHandle> ffini = fixArities(fillParameterTypes(fini, commonParameterSequence));
6794
6795 assert finit.stream().map(MethodHandle::type).map(MethodType::parameterList).
6796 allMatch(pl -> pl.equals(commonSuffix));
6797 assert Stream.of(fstep, fpred, ffini).flatMap(List::stream).map(MethodHandle::type).map(MethodType::parameterList).
6798 allMatch(pl -> pl.equals(commonParameterSequence));
6799
6800 return MethodHandleImpl.makeLoop(loopReturnType, commonSuffix, finit, fstep, fpred, ffini);
6801 }
6802
6803 private static void loopChecks0(MethodHandle[][] clauses) {
6804 if (clauses == null || clauses.length == 0) {
6805 throw newIllegalArgumentException("null or no clauses passed");
6806 }
6807 if (Stream.of(clauses).anyMatch(Objects::isNull)) {
6808 throw newIllegalArgumentException("null clauses are not allowed");
6809 }
6810 if (Stream.of(clauses).anyMatch(c -> c.length > 4)) {
6811 throw newIllegalArgumentException("All loop clauses must be represented as MethodHandle arrays with at most 4 elements.");
6812 }
6813 }
6814
6815 private static void loopChecks1a(int i, MethodHandle in, MethodHandle st) {
6816 if (in.type().returnType() != st.type().returnType()) {
6817 throw misMatchedTypes("clause " + i + ": init and step return types", in.type().returnType(),
6818 st.type().returnType());
6819 }
6820 }
6821
6822 private static List<Class<?>> longestParameterList(Stream<MethodHandle> mhs, int skipSize) {
6823 return mhs.filter(Objects::nonNull)
6824 // take only those that can contribute to a common suffix because they are longer than the prefix
6825 .map(MethodHandle::type)
6826 .filter(t -> t.parameterCount() > skipSize)
6827 .max(Comparator.comparingInt(MethodType::parameterCount))
6828 .map(methodType -> List.of(Arrays.copyOfRange(methodType.ptypes(), skipSize, methodType.parameterCount())))
6829 .orElse(List.of());
6830 }
6831
6832 private static List<Class<?>> buildCommonSuffix(List<MethodHandle> init, List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, int cpSize) {
6833 final List<Class<?>> longest1 = longestParameterList(Stream.of(step, pred, fini).flatMap(List::stream), cpSize);
6834 final List<Class<?>> longest2 = longestParameterList(init.stream(), 0);
6835 return longest1.size() >= longest2.size() ? longest1 : longest2;
6836 }
6837
6838 private static void loopChecks1b(List<MethodHandle> init, List<Class<?>> commonSuffix) {
6839 if (init.stream().filter(Objects::nonNull).map(MethodHandle::type).
6840 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonSuffix))) {
6841 throw newIllegalArgumentException("found non-effectively identical init parameter type lists: " + init +
6842 " (common suffix: " + commonSuffix + ")");
6843 }
6844 }
6845
6846 private static void loopChecks1cd(List<MethodHandle> pred, List<MethodHandle> fini, Class<?> loopReturnType) {
6847 if (fini.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
6848 anyMatch(t -> t != loopReturnType)) {
6849 throw newIllegalArgumentException("found non-identical finalizer return types: " + fini + " (return type: " +
6850 loopReturnType + ")");
6851 }
6852
6853 if (pred.stream().noneMatch(Objects::nonNull)) {
6854 throw newIllegalArgumentException("no predicate found", pred);
6855 }
6856 if (pred.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
6857 anyMatch(t -> t != boolean.class)) {
6858 throw newIllegalArgumentException("predicates must have boolean return type", pred);
6859 }
6860 }
6861
6862 private static void loopChecks2(List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, List<Class<?>> commonParameterSequence) {
6863 if (Stream.of(step, pred, fini).flatMap(List::stream).filter(Objects::nonNull).map(MethodHandle::type).
6864 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonParameterSequence))) {
6865 throw newIllegalArgumentException("found non-effectively identical parameter type lists:\nstep: " + step +
6866 "\npred: " + pred + "\nfini: " + fini + " (common parameter sequence: " + commonParameterSequence + ")");
6867 }
6868 }
6869
6870 private static List<MethodHandle> fillParameterTypes(List<MethodHandle> hs, final List<Class<?>> targetParams) {
6871 return hs.stream().map(h -> {
6872 int pc = h.type().parameterCount();
6873 int tpsize = targetParams.size();
6874 return pc < tpsize ? dropArguments(h, pc, targetParams.subList(pc, tpsize)) : h;
6875 }).toList();
6876 }
6877
6878 private static List<MethodHandle> fixArities(List<MethodHandle> hs) {
6879 return hs.stream().map(MethodHandle::asFixedArity).toList();
6880 }
6881
6882 /**
6883 * Constructs a {@code while} loop from an initializer, a body, and a predicate.
6884 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
6885 * <p>
6886 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
6887 * method will, in each iteration, first evaluate the predicate and then execute its body (if the predicate
6888 * evaluates to {@code true}).
6889 * The loop will terminate once the predicate evaluates to {@code false} (the body will not be executed in this case).
6890 * <p>
6891 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
6892 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
6893 * and updated with the value returned from its invocation. The result of loop execution will be
6894 * the final value of the additional loop-local variable (if present).
6895 * <p>
6896 * The following rules hold for these argument handles:<ul>
6897 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
6898 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
6899 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
6900 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
6901 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
6902 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
6903 * It will constrain the parameter lists of the other loop parts.
6904 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
6905 * list {@code (A...)} is called the <em>external parameter list</em>.
6906 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
6907 * additional state variable of the loop.
6908 * The body must both accept and return a value of this type {@code V}.
6909 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
6910 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
6911 * <a href="MethodHandles.html#effid">effectively identical</a>
6912 * to the external parameter list {@code (A...)}.
6913 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
6914 * {@linkplain #empty default value}.
6915 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
6916 * Its parameter list (either empty or of the form {@code (V A*)}) must be
6917 * effectively identical to the internal parameter list.
6918 * </ul>
6919 * <p>
6920 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
6921 * <li>The loop handle's result type is the result type {@code V} of the body.
6922 * <li>The loop handle's parameter types are the types {@code (A...)},
6923 * from the external parameter list.
6924 * </ul>
6925 * <p>
6926 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
6927 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
6928 * passed to the loop.
6929 * {@snippet lang="java" :
6930 * V init(A...);
6931 * boolean pred(V, A...);
6932 * V body(V, A...);
6933 * V whileLoop(A... a...) {
6934 * V v = init(a...);
6935 * while (pred(v, a...)) {
6936 * v = body(v, a...);
6937 * }
6938 * return v;
6939 * }
6940 * }
6941 *
6942 * @apiNote Example:
6943 * {@snippet lang="java" :
6944 * // implement the zip function for lists as a loop handle
6945 * static List<String> initZip(Iterator<String> a, Iterator<String> b) { return new ArrayList<>(); }
6946 * static boolean zipPred(List<String> zip, Iterator<String> a, Iterator<String> b) { return a.hasNext() && b.hasNext(); }
6947 * static List<String> zipStep(List<String> zip, Iterator<String> a, Iterator<String> b) {
6948 * zip.add(a.next());
6949 * zip.add(b.next());
6950 * return zip;
6951 * }
6952 * // assume MH_initZip, MH_zipPred, and MH_zipStep are handles to the above methods
6953 * MethodHandle loop = MethodHandles.whileLoop(MH_initZip, MH_zipPred, MH_zipStep);
6954 * List<String> a = Arrays.asList("a", "b", "c", "d");
6955 * List<String> b = Arrays.asList("e", "f", "g", "h");
6956 * List<String> zipped = Arrays.asList("a", "e", "b", "f", "c", "g", "d", "h");
6957 * assertEquals(zipped, (List<String>) loop.invoke(a.iterator(), b.iterator()));
6958 * }
6959 *
6960 *
6961 * @apiNote The implementation of this method can be expressed as follows:
6962 * {@snippet lang="java" :
6963 * MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
6964 * MethodHandle fini = (body.type().returnType() == void.class
6965 * ? null : identity(body.type().returnType()));
6966 * MethodHandle[]
6967 * checkExit = { null, null, pred, fini },
6968 * varBody = { init, body };
6969 * return loop(checkExit, varBody);
6970 * }
6971 * }
6972 *
6973 * @param init optional initializer, providing the initial value of the loop variable.
6974 * May be {@code null}, implying a default initial value. See above for other constraints.
6975 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
6976 * above for other constraints.
6977 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
6978 * See above for other constraints.
6979 *
6980 * @return a method handle implementing the {@code while} loop as described by the arguments.
6981 * @throws IllegalArgumentException if the rules for the arguments are violated.
6982 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
6983 *
6984 * @see #loop(MethodHandle[][])
6985 * @see #doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
6986 * @since 9
6987 */
6988 public static MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
6989 whileLoopChecks(init, pred, body);
6990 MethodHandle fini = identityOrVoid(body.type().returnType());
6991 MethodHandle[] checkExit = { null, null, pred, fini };
6992 MethodHandle[] varBody = { init, body };
6993 return loop(checkExit, varBody);
6994 }
6995
6996 /**
6997 * Constructs a {@code do-while} loop from an initializer, a body, and a predicate.
6998 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
6999 * <p>
7000 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
7001 * method will, in each iteration, first execute its body and then evaluate the predicate.
7002 * The loop will terminate once the predicate evaluates to {@code false} after an execution of the body.
7003 * <p>
7004 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
7005 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
7006 * and updated with the value returned from its invocation. The result of loop execution will be
7007 * the final value of the additional loop-local variable (if present).
7008 * <p>
7009 * The following rules hold for these argument handles:<ul>
7010 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
7011 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
7012 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
7013 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
7014 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
7015 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
7016 * It will constrain the parameter lists of the other loop parts.
7017 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
7018 * list {@code (A...)} is called the <em>external parameter list</em>.
7019 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
7020 * additional state variable of the loop.
7021 * The body must both accept and return a value of this type {@code V}.
7022 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
7023 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
7024 * <a href="MethodHandles.html#effid">effectively identical</a>
7025 * to the external parameter list {@code (A...)}.
7026 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
7027 * {@linkplain #empty default value}.
7028 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
7029 * Its parameter list (either empty or of the form {@code (V A*)}) must be
7030 * effectively identical to the internal parameter list.
7031 * </ul>
7032 * <p>
7033 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
7034 * <li>The loop handle's result type is the result type {@code V} of the body.
7035 * <li>The loop handle's parameter types are the types {@code (A...)},
7036 * from the external parameter list.
7037 * </ul>
7038 * <p>
7039 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
7040 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
7041 * passed to the loop.
7042 * {@snippet lang="java" :
7043 * V init(A...);
7044 * boolean pred(V, A...);
7045 * V body(V, A...);
7046 * V doWhileLoop(A... a...) {
7047 * V v = init(a...);
7048 * do {
7049 * v = body(v, a...);
7050 * } while (pred(v, a...));
7051 * return v;
7052 * }
7053 * }
7054 *
7055 * @apiNote Example:
7056 * {@snippet lang="java" :
7057 * // int i = 0; while (i < limit) { ++i; } return i; => limit
7058 * static int zero(int limit) { return 0; }
7059 * static int step(int i, int limit) { return i + 1; }
7060 * static boolean pred(int i, int limit) { return i < limit; }
7061 * // assume MH_zero, MH_step, and MH_pred are handles to the above methods
7062 * MethodHandle loop = MethodHandles.doWhileLoop(MH_zero, MH_step, MH_pred);
7063 * assertEquals(23, loop.invoke(23));
7064 * }
7065 *
7066 *
7067 * @apiNote The implementation of this method can be expressed as follows:
7068 * {@snippet lang="java" :
7069 * MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
7070 * MethodHandle fini = (body.type().returnType() == void.class
7071 * ? null : identity(body.type().returnType()));
7072 * MethodHandle[] clause = { init, body, pred, fini };
7073 * return loop(clause);
7074 * }
7075 * }
7076 *
7077 * @param init optional initializer, providing the initial value of the loop variable.
7078 * May be {@code null}, implying a default initial value. See above for other constraints.
7079 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
7080 * See above for other constraints.
7081 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
7082 * above for other constraints.
7083 *
7084 * @return a method handle implementing the {@code while} loop as described by the arguments.
7085 * @throws IllegalArgumentException if the rules for the arguments are violated.
7086 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
7087 *
7088 * @see #loop(MethodHandle[][])
7089 * @see #whileLoop(MethodHandle, MethodHandle, MethodHandle)
7090 * @since 9
7091 */
7092 public static MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
7093 whileLoopChecks(init, pred, body);
7094 MethodHandle fini = identityOrVoid(body.type().returnType());
7095 MethodHandle[] clause = {init, body, pred, fini };
7096 return loop(clause);
7097 }
7098
7099 private static void whileLoopChecks(MethodHandle init, MethodHandle pred, MethodHandle body) {
7100 Objects.requireNonNull(pred);
7101 Objects.requireNonNull(body);
7102 MethodType bodyType = body.type();
7103 Class<?> returnType = bodyType.returnType();
7104 List<Class<?>> innerList = bodyType.parameterList();
7105 List<Class<?>> outerList = innerList;
7106 if (returnType == void.class) {
7107 // OK
7108 } else if (innerList.isEmpty() || innerList.get(0) != returnType) {
7109 // leading V argument missing => error
7110 MethodType expected = bodyType.insertParameterTypes(0, returnType);
7111 throw misMatchedTypes("body function", bodyType, expected);
7112 } else {
7113 outerList = innerList.subList(1, innerList.size());
7114 }
7115 MethodType predType = pred.type();
7116 if (predType.returnType() != boolean.class ||
7117 !predType.effectivelyIdenticalParameters(0, innerList)) {
7118 throw misMatchedTypes("loop predicate", predType, methodType(boolean.class, innerList));
7119 }
7120 if (init != null) {
7121 MethodType initType = init.type();
7122 if (initType.returnType() != returnType ||
7123 !initType.effectivelyIdenticalParameters(0, outerList)) {
7124 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
7125 }
7126 }
7127 }
7128
7129 /**
7130 * Constructs a loop that runs a given number of iterations.
7131 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
7132 * <p>
7133 * The number of iterations is determined by the {@code iterations} handle evaluation result.
7134 * The loop counter {@code i} is an extra loop iteration variable of type {@code int}.
7135 * It will be initialized to 0 and incremented by 1 in each iteration.
7136 * <p>
7137 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
7138 * of that type is also present. This variable is initialized using the optional {@code init} handle,
7139 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
7140 * <p>
7141 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
7142 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
7143 * iteration variable.
7144 * The result of the loop handle execution will be the final {@code V} value of that variable
7145 * (or {@code void} if there is no {@code V} variable).
7146 * <p>
7147 * The following rules hold for the argument handles:<ul>
7148 * <li>The {@code iterations} handle must not be {@code null}, and must return
7149 * the type {@code int}, referred to here as {@code I} in parameter type lists.
7150 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
7151 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
7152 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
7153 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
7154 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
7155 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
7156 * of types called the <em>internal parameter list</em>.
7157 * It will constrain the parameter lists of the other loop parts.
7158 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
7159 * with no additional {@code A} types, then the internal parameter list is extended by
7160 * the argument types {@code A...} of the {@code iterations} handle.
7161 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
7162 * list {@code (A...)} is called the <em>external parameter list</em>.
7163 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
7164 * additional state variable of the loop.
7165 * The body must both accept a leading parameter and return a value of this type {@code V}.
7166 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
7167 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
7168 * <a href="MethodHandles.html#effid">effectively identical</a>
7169 * to the external parameter list {@code (A...)}.
7170 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
7171 * {@linkplain #empty default value}.
7172 * <li>The parameter list of {@code iterations} (of some form {@code (A*)}) must be
7173 * effectively identical to the external parameter list {@code (A...)}.
7174 * </ul>
7175 * <p>
7176 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
7177 * <li>The loop handle's result type is the result type {@code V} of the body.
7178 * <li>The loop handle's parameter types are the types {@code (A...)},
7179 * from the external parameter list.
7180 * </ul>
7181 * <p>
7182 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
7183 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
7184 * arguments passed to the loop.
7185 * {@snippet lang="java" :
7186 * int iterations(A...);
7187 * V init(A...);
7188 * V body(V, int, A...);
7189 * V countedLoop(A... a...) {
7190 * int end = iterations(a...);
7191 * V v = init(a...);
7192 * for (int i = 0; i < end; ++i) {
7193 * v = body(v, i, a...);
7194 * }
7195 * return v;
7196 * }
7197 * }
7198 *
7199 * @apiNote Example with a fully conformant body method:
7200 * {@snippet lang="java" :
7201 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
7202 * // => a variation on a well known theme
7203 * static String step(String v, int counter, String init) { return "na " + v; }
7204 * // assume MH_step is a handle to the method above
7205 * MethodHandle fit13 = MethodHandles.constant(int.class, 13);
7206 * MethodHandle start = MethodHandles.identity(String.class);
7207 * MethodHandle loop = MethodHandles.countedLoop(fit13, start, MH_step);
7208 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("Lambdaman!"));
7209 * }
7210 *
7211 * @apiNote Example with the simplest possible body method type,
7212 * and passing the number of iterations to the loop invocation:
7213 * {@snippet lang="java" :
7214 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
7215 * // => a variation on a well known theme
7216 * static String step(String v, int counter ) { return "na " + v; }
7217 * // assume MH_step is a handle to the method above
7218 * MethodHandle count = MethodHandles.dropArguments(MethodHandles.identity(int.class), 1, String.class);
7219 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class);
7220 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i) -> "na " + v
7221 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "Lambdaman!"));
7222 * }
7223 *
7224 * @apiNote Example that treats the number of iterations, string to append to, and string to append
7225 * as loop parameters:
7226 * {@snippet lang="java" :
7227 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
7228 * // => a variation on a well known theme
7229 * static String step(String v, int counter, int iterations_, String pre, String start_) { return pre + " " + v; }
7230 * // assume MH_step is a handle to the method above
7231 * MethodHandle count = MethodHandles.identity(int.class);
7232 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class, String.class);
7233 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i, _, pre, _) -> pre + " " + v
7234 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "na", "Lambdaman!"));
7235 * }
7236 *
7237 * @apiNote Example that illustrates the usage of {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}
7238 * to enforce a loop type:
7239 * {@snippet lang="java" :
7240 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
7241 * // => a variation on a well known theme
7242 * static String step(String v, int counter, String pre) { return pre + " " + v; }
7243 * // assume MH_step is a handle to the method above
7244 * MethodType loopType = methodType(String.class, String.class, int.class, String.class);
7245 * MethodHandle count = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(int.class), 0, loopType.parameterList(), 1);
7246 * MethodHandle start = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(String.class), 0, loopType.parameterList(), 2);
7247 * MethodHandle body = MethodHandles.dropArgumentsToMatch(MH_step, 2, loopType.parameterList(), 0);
7248 * MethodHandle loop = MethodHandles.countedLoop(count, start, body); // (v, i, pre, _, _) -> pre + " " + v
7249 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("na", 13, "Lambdaman!"));
7250 * }
7251 *
7252 * @apiNote The implementation of this method can be expressed as follows:
7253 * {@snippet lang="java" :
7254 * MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
7255 * return countedLoop(empty(iterations.type()), iterations, init, body);
7256 * }
7257 * }
7258 *
7259 * @param iterations a non-{@code null} handle to return the number of iterations this loop should run. The handle's
7260 * result type must be {@code int}. See above for other constraints.
7261 * @param init optional initializer, providing the initial value of the loop variable.
7262 * May be {@code null}, implying a default initial value. See above for other constraints.
7263 * @param body body of the loop, which may not be {@code null}.
7264 * It controls the loop parameters and result type in the standard case (see above for details).
7265 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
7266 * and may accept any number of additional types.
7267 * See above for other constraints.
7268 *
7269 * @return a method handle representing the loop.
7270 * @throws NullPointerException if either of the {@code iterations} or {@code body} handles is {@code null}.
7271 * @throws IllegalArgumentException if any argument violates the rules formulated above.
7272 *
7273 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle, MethodHandle)
7274 * @since 9
7275 */
7276 public static MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
7277 return countedLoop(empty(iterations.type()), iterations, init, body);
7278 }
7279
7280 /**
7281 * Constructs a loop that counts over a range of numbers.
7282 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
7283 * <p>
7284 * The loop counter {@code i} is a loop iteration variable of type {@code int}.
7285 * The {@code start} and {@code end} handles determine the start (inclusive) and end (exclusive)
7286 * values of the loop counter.
7287 * The loop counter will be initialized to the {@code int} value returned from the evaluation of the
7288 * {@code start} handle and run to the value returned from {@code end} (exclusively) with a step width of 1.
7289 * <p>
7290 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
7291 * of that type is also present. This variable is initialized using the optional {@code init} handle,
7292 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
7293 * <p>
7294 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
7295 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
7296 * iteration variable.
7297 * The result of the loop handle execution will be the final {@code V} value of that variable
7298 * (or {@code void} if there is no {@code V} variable).
7299 * <p>
7300 * The following rules hold for the argument handles:<ul>
7301 * <li>The {@code start} and {@code end} handles must not be {@code null}, and must both return
7302 * the common type {@code int}, referred to here as {@code I} in parameter type lists.
7303 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
7304 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
7305 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
7306 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
7307 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
7308 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
7309 * of types called the <em>internal parameter list</em>.
7310 * It will constrain the parameter lists of the other loop parts.
7311 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
7312 * with no additional {@code A} types, then the internal parameter list is extended by
7313 * the argument types {@code A...} of the {@code end} handle.
7314 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
7315 * list {@code (A...)} is called the <em>external parameter list</em>.
7316 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
7317 * additional state variable of the loop.
7318 * The body must both accept a leading parameter and return a value of this type {@code V}.
7319 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
7320 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
7321 * <a href="MethodHandles.html#effid">effectively identical</a>
7322 * to the external parameter list {@code (A...)}.
7323 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
7324 * {@linkplain #empty default value}.
7325 * <li>The parameter list of {@code start} (of some form {@code (A*)}) must be
7326 * effectively identical to the external parameter list {@code (A...)}.
7327 * <li>Likewise, the parameter list of {@code end} must be effectively identical
7328 * to the external parameter list.
7329 * </ul>
7330 * <p>
7331 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
7332 * <li>The loop handle's result type is the result type {@code V} of the body.
7333 * <li>The loop handle's parameter types are the types {@code (A...)},
7334 * from the external parameter list.
7335 * </ul>
7336 * <p>
7337 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
7338 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
7339 * arguments passed to the loop.
7340 * {@snippet lang="java" :
7341 * int start(A...);
7342 * int end(A...);
7343 * V init(A...);
7344 * V body(V, int, A...);
7345 * V countedLoop(A... a...) {
7346 * int e = end(a...);
7347 * int s = start(a...);
7348 * V v = init(a...);
7349 * for (int i = s; i < e; ++i) {
7350 * v = body(v, i, a...);
7351 * }
7352 * return v;
7353 * }
7354 * }
7355 *
7356 * @apiNote The implementation of this method can be expressed as follows:
7357 * {@snippet lang="java" :
7358 * MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
7359 * MethodHandle returnVar = dropArguments(identity(init.type().returnType()), 0, int.class, int.class);
7360 * // assume MH_increment and MH_predicate are handles to implementation-internal methods with
7361 * // the following semantics:
7362 * // MH_increment: (int limit, int counter) -> counter + 1
7363 * // MH_predicate: (int limit, int counter) -> counter < limit
7364 * Class<?> counterType = start.type().returnType(); // int
7365 * Class<?> returnType = body.type().returnType();
7366 * MethodHandle incr = MH_increment, pred = MH_predicate, retv = null;
7367 * if (returnType != void.class) { // ignore the V variable
7368 * incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
7369 * pred = dropArguments(pred, 1, returnType); // ditto
7370 * retv = dropArguments(identity(returnType), 0, counterType); // ignore limit
7371 * }
7372 * body = dropArguments(body, 0, counterType); // ignore the limit variable
7373 * MethodHandle[]
7374 * loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
7375 * bodyClause = { init, body }, // v = init(); v = body(v, i)
7376 * indexVar = { start, incr }; // i = start(); i = i + 1
7377 * return loop(loopLimit, bodyClause, indexVar);
7378 * }
7379 * }
7380 *
7381 * @param start a non-{@code null} handle to return the start value of the loop counter, which must be {@code int}.
7382 * See above for other constraints.
7383 * @param end a non-{@code null} handle to return the end value of the loop counter (the loop will run to
7384 * {@code end-1}). The result type must be {@code int}. See above for other constraints.
7385 * @param init optional initializer, providing the initial value of the loop variable.
7386 * May be {@code null}, implying a default initial value. See above for other constraints.
7387 * @param body body of the loop, which may not be {@code null}.
7388 * It controls the loop parameters and result type in the standard case (see above for details).
7389 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
7390 * and may accept any number of additional types.
7391 * See above for other constraints.
7392 *
7393 * @return a method handle representing the loop.
7394 * @throws NullPointerException if any of the {@code start}, {@code end}, or {@code body} handles is {@code null}.
7395 * @throws IllegalArgumentException if any argument violates the rules formulated above.
7396 *
7397 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle)
7398 * @since 9
7399 */
7400 public static MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
7401 countedLoopChecks(start, end, init, body);
7402 Class<?> counterType = start.type().returnType(); // int, but who's counting?
7403 Class<?> limitType = end.type().returnType(); // yes, int again
7404 Class<?> returnType = body.type().returnType();
7405 MethodHandle incr = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopStep);
7406 MethodHandle pred = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopPred);
7407 MethodHandle retv = null;
7408 if (returnType != void.class) {
7409 incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
7410 pred = dropArguments(pred, 1, returnType); // ditto
7411 retv = dropArguments(identity(returnType), 0, counterType);
7412 }
7413 body = dropArguments(body, 0, counterType); // ignore the limit variable
7414 MethodHandle[]
7415 loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
7416 bodyClause = { init, body }, // v = init(); v = body(v, i)
7417 indexVar = { start, incr }; // i = start(); i = i + 1
7418 return loop(loopLimit, bodyClause, indexVar);
7419 }
7420
7421 private static void countedLoopChecks(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
7422 Objects.requireNonNull(start);
7423 Objects.requireNonNull(end);
7424 Objects.requireNonNull(body);
7425 Class<?> counterType = start.type().returnType();
7426 if (counterType != int.class) {
7427 MethodType expected = start.type().changeReturnType(int.class);
7428 throw misMatchedTypes("start function", start.type(), expected);
7429 } else if (end.type().returnType() != counterType) {
7430 MethodType expected = end.type().changeReturnType(counterType);
7431 throw misMatchedTypes("end function", end.type(), expected);
7432 }
7433 MethodType bodyType = body.type();
7434 Class<?> returnType = bodyType.returnType();
7435 List<Class<?>> innerList = bodyType.parameterList();
7436 // strip leading V value if present
7437 int vsize = (returnType == void.class ? 0 : 1);
7438 if (vsize != 0 && (innerList.isEmpty() || innerList.get(0) != returnType)) {
7439 // argument list has no "V" => error
7440 MethodType expected = bodyType.insertParameterTypes(0, returnType);
7441 throw misMatchedTypes("body function", bodyType, expected);
7442 } else if (innerList.size() <= vsize || innerList.get(vsize) != counterType) {
7443 // missing I type => error
7444 MethodType expected = bodyType.insertParameterTypes(vsize, counterType);
7445 throw misMatchedTypes("body function", bodyType, expected);
7446 }
7447 List<Class<?>> outerList = innerList.subList(vsize + 1, innerList.size());
7448 if (outerList.isEmpty()) {
7449 // special case; take lists from end handle
7450 outerList = end.type().parameterList();
7451 innerList = bodyType.insertParameterTypes(vsize + 1, outerList).parameterList();
7452 }
7453 MethodType expected = methodType(counterType, outerList);
7454 if (!start.type().effectivelyIdenticalParameters(0, outerList)) {
7455 throw misMatchedTypes("start parameter types", start.type(), expected);
7456 }
7457 if (end.type() != start.type() &&
7458 !end.type().effectivelyIdenticalParameters(0, outerList)) {
7459 throw misMatchedTypes("end parameter types", end.type(), expected);
7460 }
7461 if (init != null) {
7462 MethodType initType = init.type();
7463 if (initType.returnType() != returnType ||
7464 !initType.effectivelyIdenticalParameters(0, outerList)) {
7465 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
7466 }
7467 }
7468 }
7469
7470 /**
7471 * Constructs a loop that ranges over the values produced by an {@code Iterator<T>}.
7472 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
7473 * <p>
7474 * The iterator itself will be determined by the evaluation of the {@code iterator} handle.
7475 * Each value it produces will be stored in a loop iteration variable of type {@code T}.
7476 * <p>
7477 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
7478 * of that type is also present. This variable is initialized using the optional {@code init} handle,
7479 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
7480 * <p>
7481 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
7482 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
7483 * iteration variable.
7484 * The result of the loop handle execution will be the final {@code V} value of that variable
7485 * (or {@code void} if there is no {@code V} variable).
7486 * <p>
7487 * The following rules hold for the argument handles:<ul>
7488 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
7489 * {@code (V T A...)V}, where {@code V} is non-{@code void}, or else {@code (T A...)void}.
7490 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
7491 * and we will write {@code (V T A...)V} with the understanding that a {@code void} type {@code V}
7492 * is quietly dropped from the parameter list, leaving {@code (T A...)V}.)
7493 * <li>The parameter list {@code (V T A...)} of the body contributes to a list
7494 * of types called the <em>internal parameter list</em>.
7495 * It will constrain the parameter lists of the other loop parts.
7496 * <li>As a special case, if the body contributes only {@code V} and {@code T} types,
7497 * with no additional {@code A} types, then the internal parameter list is extended by
7498 * the argument types {@code A...} of the {@code iterator} handle; if it is {@code null} the
7499 * single type {@code Iterable} is added and constitutes the {@code A...} list.
7500 * <li>If the iteration variable types {@code (V T)} are dropped from the internal parameter list, the resulting shorter
7501 * list {@code (A...)} is called the <em>external parameter list</em>.
7502 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
7503 * additional state variable of the loop.
7504 * The body must both accept a leading parameter and return a value of this type {@code V}.
7505 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
7506 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
7507 * <a href="MethodHandles.html#effid">effectively identical</a>
7508 * to the external parameter list {@code (A...)}.
7509 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
7510 * {@linkplain #empty default value}.
7511 * <li>If the {@code iterator} handle is non-{@code null}, it must have the return
7512 * type {@code java.util.Iterator} or a subtype thereof.
7513 * The iterator it produces when the loop is executed will be assumed
7514 * to yield values which can be converted to type {@code T}.
7515 * <li>The parameter list of an {@code iterator} that is non-{@code null} (of some form {@code (A*)}) must be
7516 * effectively identical to the external parameter list {@code (A...)}.
7517 * <li>If {@code iterator} is {@code null} it defaults to a method handle which behaves
7518 * like {@link java.lang.Iterable#iterator()}. In that case, the internal parameter list
7519 * {@code (V T A...)} must have at least one {@code A} type, and the default iterator
7520 * handle parameter is adjusted to accept the leading {@code A} type, as if by
7521 * the {@link MethodHandle#asType asType} conversion method.
7522 * The leading {@code A} type must be {@code Iterable} or a subtype thereof.
7523 * This conversion step, done at loop construction time, must not throw a {@code WrongMethodTypeException}.
7524 * </ul>
7525 * <p>
7526 * The type {@code T} may be either a primitive or reference.
7527 * Since type {@code Iterator<T>} is erased in the method handle representation to the raw type {@code Iterator},
7528 * the {@code iteratedLoop} combinator adjusts the leading argument type for {@code body} to {@code Object}
7529 * as if by the {@link MethodHandle#asType asType} conversion method.
7530 * Therefore, if an iterator of the wrong type appears as the loop is executed, runtime exceptions may occur
7531 * as the result of dynamic conversions performed by {@link MethodHandle#asType(MethodType)}.
7532 * <p>
7533 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
7534 * <li>The loop handle's result type is the result type {@code V} of the body.
7535 * <li>The loop handle's parameter types are the types {@code (A...)},
7536 * from the external parameter list.
7537 * </ul>
7538 * <p>
7539 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
7540 * the loop variable as well as the result type of the loop; {@code T}/{@code t}, that of the elements of the
7541 * structure the loop iterates over, and {@code A...}/{@code a...} represent arguments passed to the loop.
7542 * {@snippet lang="java" :
7543 * Iterator<T> iterator(A...); // defaults to Iterable::iterator
7544 * V init(A...);
7545 * V body(V,T,A...);
7546 * V iteratedLoop(A... a...) {
7547 * Iterator<T> it = iterator(a...);
7548 * V v = init(a...);
7549 * while (it.hasNext()) {
7550 * T t = it.next();
7551 * v = body(v, t, a...);
7552 * }
7553 * return v;
7554 * }
7555 * }
7556 *
7557 * @apiNote Example:
7558 * {@snippet lang="java" :
7559 * // get an iterator from a list
7560 * static List<String> reverseStep(List<String> r, String e) {
7561 * r.add(0, e);
7562 * return r;
7563 * }
7564 * static List<String> newArrayList() { return new ArrayList<>(); }
7565 * // assume MH_reverseStep and MH_newArrayList are handles to the above methods
7566 * MethodHandle loop = MethodHandles.iteratedLoop(null, MH_newArrayList, MH_reverseStep);
7567 * List<String> list = Arrays.asList("a", "b", "c", "d", "e");
7568 * List<String> reversedList = Arrays.asList("e", "d", "c", "b", "a");
7569 * assertEquals(reversedList, (List<String>) loop.invoke(list));
7570 * }
7571 *
7572 * @apiNote The implementation of this method can be expressed approximately as follows:
7573 * {@snippet lang="java" :
7574 * MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
7575 * // assume MH_next, MH_hasNext, MH_startIter are handles to methods of Iterator/Iterable
7576 * Class<?> returnType = body.type().returnType();
7577 * Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
7578 * MethodHandle nextVal = MH_next.asType(MH_next.type().changeReturnType(ttype));
7579 * MethodHandle retv = null, step = body, startIter = iterator;
7580 * if (returnType != void.class) {
7581 * // the simple thing first: in (I V A...), drop the I to get V
7582 * retv = dropArguments(identity(returnType), 0, Iterator.class);
7583 * // body type signature (V T A...), internal loop types (I V A...)
7584 * step = swapArguments(body, 0, 1); // swap V <-> T
7585 * }
7586 * if (startIter == null) startIter = MH_getIter;
7587 * MethodHandle[]
7588 * iterVar = { startIter, null, MH_hasNext, retv }, // it = iterator; while (it.hasNext())
7589 * bodyClause = { init, filterArguments(step, 0, nextVal) }; // v = body(v, t, a)
7590 * return loop(iterVar, bodyClause);
7591 * }
7592 * }
7593 *
7594 * @param iterator an optional handle to return the iterator to start the loop.
7595 * If non-{@code null}, the handle must return {@link java.util.Iterator} or a subtype.
7596 * See above for other constraints.
7597 * @param init optional initializer, providing the initial value of the loop variable.
7598 * May be {@code null}, implying a default initial value. See above for other constraints.
7599 * @param body body of the loop, which may not be {@code null}.
7600 * It controls the loop parameters and result type in the standard case (see above for details).
7601 * It must accept its own return type (if non-void) plus a {@code T} parameter (for the iterated values),
7602 * and may accept any number of additional types.
7603 * See above for other constraints.
7604 *
7605 * @return a method handle embodying the iteration loop functionality.
7606 * @throws NullPointerException if the {@code body} handle is {@code null}.
7607 * @throws IllegalArgumentException if any argument violates the above requirements.
7608 *
7609 * @since 9
7610 */
7611 public static MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
7612 Class<?> iterableType = iteratedLoopChecks(iterator, init, body);
7613 Class<?> returnType = body.type().returnType();
7614 MethodHandle hasNext = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iteratePred);
7615 MethodHandle nextRaw = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iterateNext);
7616 MethodHandle startIter;
7617 MethodHandle nextVal;
7618 {
7619 MethodType iteratorType;
7620 if (iterator == null) {
7621 // derive argument type from body, if available, else use Iterable
7622 startIter = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_initIterator);
7623 iteratorType = startIter.type().changeParameterType(0, iterableType);
7624 } else {
7625 // force return type to the internal iterator class
7626 iteratorType = iterator.type().changeReturnType(Iterator.class);
7627 startIter = iterator;
7628 }
7629 Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
7630 MethodType nextValType = nextRaw.type().changeReturnType(ttype);
7631
7632 // perform the asType transforms under an exception transformer, as per spec.:
7633 try {
7634 startIter = startIter.asType(iteratorType);
7635 nextVal = nextRaw.asType(nextValType);
7636 } catch (WrongMethodTypeException ex) {
7637 throw new IllegalArgumentException(ex);
7638 }
7639 }
7640
7641 MethodHandle retv = null, step = body;
7642 if (returnType != void.class) {
7643 // the simple thing first: in (I V A...), drop the I to get V
7644 retv = dropArguments(identity(returnType), 0, Iterator.class);
7645 // body type signature (V T A...), internal loop types (I V A...)
7646 step = swapArguments(body, 0, 1); // swap V <-> T
7647 }
7648
7649 MethodHandle[]
7650 iterVar = { startIter, null, hasNext, retv },
7651 bodyClause = { init, filterArgument(step, 0, nextVal) };
7652 return loop(iterVar, bodyClause);
7653 }
7654
7655 private static Class<?> iteratedLoopChecks(MethodHandle iterator, MethodHandle init, MethodHandle body) {
7656 Objects.requireNonNull(body);
7657 MethodType bodyType = body.type();
7658 Class<?> returnType = bodyType.returnType();
7659 List<Class<?>> internalParamList = bodyType.parameterList();
7660 // strip leading V value if present
7661 int vsize = (returnType == void.class ? 0 : 1);
7662 if (vsize != 0 && (internalParamList.isEmpty() || internalParamList.get(0) != returnType)) {
7663 // argument list has no "V" => error
7664 MethodType expected = bodyType.insertParameterTypes(0, returnType);
7665 throw misMatchedTypes("body function", bodyType, expected);
7666 } else if (internalParamList.size() <= vsize) {
7667 // missing T type => error
7668 MethodType expected = bodyType.insertParameterTypes(vsize, Object.class);
7669 throw misMatchedTypes("body function", bodyType, expected);
7670 }
7671 List<Class<?>> externalParamList = internalParamList.subList(vsize + 1, internalParamList.size());
7672 Class<?> iterableType = null;
7673 if (iterator != null) {
7674 // special case; if the body handle only declares V and T then
7675 // the external parameter list is obtained from iterator handle
7676 if (externalParamList.isEmpty()) {
7677 externalParamList = iterator.type().parameterList();
7678 }
7679 MethodType itype = iterator.type();
7680 if (!Iterator.class.isAssignableFrom(itype.returnType())) {
7681 throw newIllegalArgumentException("iteratedLoop first argument must have Iterator return type");
7682 }
7683 if (!itype.effectivelyIdenticalParameters(0, externalParamList)) {
7684 MethodType expected = methodType(itype.returnType(), externalParamList);
7685 throw misMatchedTypes("iterator parameters", itype, expected);
7686 }
7687 } else {
7688 if (externalParamList.isEmpty()) {
7689 // special case; if the iterator handle is null and the body handle
7690 // only declares V and T then the external parameter list consists
7691 // of Iterable
7692 externalParamList = List.of(Iterable.class);
7693 iterableType = Iterable.class;
7694 } else {
7695 // special case; if the iterator handle is null and the external
7696 // parameter list is not empty then the first parameter must be
7697 // assignable to Iterable
7698 iterableType = externalParamList.get(0);
7699 if (!Iterable.class.isAssignableFrom(iterableType)) {
7700 throw newIllegalArgumentException(
7701 "inferred first loop argument must inherit from Iterable: " + iterableType);
7702 }
7703 }
7704 }
7705 if (init != null) {
7706 MethodType initType = init.type();
7707 if (initType.returnType() != returnType ||
7708 !initType.effectivelyIdenticalParameters(0, externalParamList)) {
7709 throw misMatchedTypes("loop initializer", initType, methodType(returnType, externalParamList));
7710 }
7711 }
7712 return iterableType; // help the caller a bit
7713 }
7714
7715 /*non-public*/
7716 static MethodHandle swapArguments(MethodHandle mh, int i, int j) {
7717 // there should be a better way to uncross my wires
7718 int arity = mh.type().parameterCount();
7719 int[] order = new int[arity];
7720 for (int k = 0; k < arity; k++) order[k] = k;
7721 order[i] = j; order[j] = i;
7722 Class<?>[] types = mh.type().parameterArray();
7723 Class<?> ti = types[i]; types[i] = types[j]; types[j] = ti;
7724 MethodType swapType = methodType(mh.type().returnType(), types);
7725 return permuteArguments(mh, swapType, order);
7726 }
7727
7728 /**
7729 * Makes a method handle that adapts a {@code target} method handle by wrapping it in a {@code try-finally} block.
7730 * Another method handle, {@code cleanup}, represents the functionality of the {@code finally} block. Any exception
7731 * thrown during the execution of the {@code target} handle will be passed to the {@code cleanup} handle. The
7732 * exception will be rethrown, unless {@code cleanup} handle throws an exception first. The
7733 * value returned from the {@code cleanup} handle's execution will be the result of the execution of the
7734 * {@code try-finally} handle.
7735 * <p>
7736 * The {@code cleanup} handle will be passed one or two additional leading arguments.
7737 * The first is the exception thrown during the
7738 * execution of the {@code target} handle, or {@code null} if no exception was thrown.
7739 * The second is the result of the execution of the {@code target} handle, or, if it throws an exception,
7740 * a {@code null}, zero, or {@code false} value of the required type is supplied as a placeholder.
7741 * The second argument is not present if the {@code target} handle has a {@code void} return type.
7742 * (Note that, except for argument type conversions, combinators represent {@code void} values in parameter lists
7743 * by omitting the corresponding paradoxical arguments, not by inserting {@code null} or zero values.)
7744 * <p>
7745 * The {@code target} and {@code cleanup} handles must have the same corresponding argument and return types, except
7746 * that the {@code cleanup} handle may omit trailing arguments. Also, the {@code cleanup} handle must have one or
7747 * two extra leading parameters:<ul>
7748 * <li>a {@code Throwable}, which will carry the exception thrown by the {@code target} handle (if any); and
7749 * <li>a parameter of the same type as the return type of both {@code target} and {@code cleanup}, which will carry
7750 * the result from the execution of the {@code target} handle.
7751 * This parameter is not present if the {@code target} returns {@code void}.
7752 * </ul>
7753 * <p>
7754 * The pseudocode for the resulting adapter looks as follows. In the code, {@code V} represents the result type of
7755 * the {@code try/finally} construct; {@code A}/{@code a}, the types and values of arguments to the resulting
7756 * handle consumed by the cleanup; and {@code B}/{@code b}, those of arguments to the resulting handle discarded by
7757 * the cleanup.
7758 * {@snippet lang="java" :
7759 * V target(A..., B...);
7760 * V cleanup(Throwable, V, A...);
7761 * V adapter(A... a, B... b) {
7762 * V result = (zero value for V);
7763 * Throwable throwable = null;
7764 * try {
7765 * result = target(a..., b...);
7766 * } catch (Throwable t) {
7767 * throwable = t;
7768 * throw t;
7769 * } finally {
7770 * result = cleanup(throwable, result, a...);
7771 * }
7772 * return result;
7773 * }
7774 * }
7775 * <p>
7776 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
7777 * be modified by execution of the target, and so are passed unchanged
7778 * from the caller to the cleanup, if it is invoked.
7779 * <p>
7780 * The target and cleanup must return the same type, even if the cleanup
7781 * always throws.
7782 * To create such a throwing cleanup, compose the cleanup logic
7783 * with {@link #throwException throwException},
7784 * in order to create a method handle of the correct return type.
7785 * <p>
7786 * Note that {@code tryFinally} never converts exceptions into normal returns.
7787 * In rare cases where exceptions must be converted in that way, first wrap
7788 * the target with {@link #catchException(MethodHandle, Class, MethodHandle)}
7789 * to capture an outgoing exception, and then wrap with {@code tryFinally}.
7790 * <p>
7791 * It is recommended that the first parameter type of {@code cleanup} be
7792 * declared {@code Throwable} rather than a narrower subtype. This ensures
7793 * {@code cleanup} will always be invoked with whatever exception that
7794 * {@code target} throws. Declaring a narrower type may result in a
7795 * {@code ClassCastException} being thrown by the {@code try-finally}
7796 * handle if the type of the exception thrown by {@code target} is not
7797 * assignable to the first parameter type of {@code cleanup}. Note that
7798 * various exception types of {@code VirtualMachineError},
7799 * {@code LinkageError}, and {@code RuntimeException} can in principle be
7800 * thrown by almost any kind of Java code, and a finally clause that
7801 * catches (say) only {@code IOException} would mask any of the others
7802 * behind a {@code ClassCastException}.
7803 *
7804 * @param target the handle whose execution is to be wrapped in a {@code try} block.
7805 * @param cleanup the handle that is invoked in the finally block.
7806 *
7807 * @return a method handle embodying the {@code try-finally} block composed of the two arguments.
7808 * @throws NullPointerException if any argument is null
7809 * @throws IllegalArgumentException if {@code cleanup} does not accept
7810 * the required leading arguments, or if the method handle types do
7811 * not match in their return types and their
7812 * corresponding trailing parameters
7813 *
7814 * @see MethodHandles#catchException(MethodHandle, Class, MethodHandle)
7815 * @since 9
7816 */
7817 public static MethodHandle tryFinally(MethodHandle target, MethodHandle cleanup) {
7818 Class<?>[] targetParamTypes = target.type().ptypes();
7819 Class<?> rtype = target.type().returnType();
7820
7821 tryFinallyChecks(target, cleanup);
7822
7823 // Match parameter lists: if the cleanup has a shorter parameter list than the target, add ignored arguments.
7824 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
7825 // target parameter list.
7826 cleanup = dropArgumentsToMatch(cleanup, (rtype == void.class ? 1 : 2), targetParamTypes, 0, false);
7827
7828 // Ensure that the intrinsic type checks the instance thrown by the
7829 // target against the first parameter of cleanup
7830 cleanup = cleanup.asType(cleanup.type().changeParameterType(0, Throwable.class));
7831
7832 // Use asFixedArity() to avoid unnecessary boxing of last argument for VarargsCollector case.
7833 return MethodHandleImpl.makeTryFinally(target.asFixedArity(), cleanup.asFixedArity(), rtype, targetParamTypes);
7834 }
7835
7836 private static void tryFinallyChecks(MethodHandle target, MethodHandle cleanup) {
7837 Class<?> rtype = target.type().returnType();
7838 if (rtype != cleanup.type().returnType()) {
7839 throw misMatchedTypes("target and return types", cleanup.type().returnType(), rtype);
7840 }
7841 MethodType cleanupType = cleanup.type();
7842 if (!Throwable.class.isAssignableFrom(cleanupType.parameterType(0))) {
7843 throw misMatchedTypes("cleanup first argument and Throwable", cleanup.type(), Throwable.class);
7844 }
7845 if (rtype != void.class && cleanupType.parameterType(1) != rtype) {
7846 throw misMatchedTypes("cleanup second argument and target return type", cleanup.type(), rtype);
7847 }
7848 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
7849 // target parameter list.
7850 int cleanupArgIndex = rtype == void.class ? 1 : 2;
7851 if (!cleanupType.effectivelyIdenticalParameters(cleanupArgIndex, target.type().parameterList())) {
7852 throw misMatchedTypes("cleanup parameters after (Throwable,result) and target parameter list prefix",
7853 cleanup.type(), target.type());
7854 }
7855 }
7856
7857 /**
7858 * Creates a table switch method handle, which can be used to switch over a set of target
7859 * method handles, based on a given target index, called selector.
7860 * <p>
7861 * For a selector value of {@code n}, where {@code n} falls in the range {@code [0, N)},
7862 * and where {@code N} is the number of target method handles, the table switch method
7863 * handle will invoke the n-th target method handle from the list of target method handles.
7864 * <p>
7865 * For a selector value that does not fall in the range {@code [0, N)}, the table switch
7866 * method handle will invoke the given fallback method handle.
7867 * <p>
7868 * All method handles passed to this method must have the same type, with the additional
7869 * requirement that the leading parameter be of type {@code int}. The leading parameter
7870 * represents the selector.
7871 * <p>
7872 * Any trailing parameters present in the type will appear on the returned table switch
7873 * method handle as well. Any arguments assigned to these parameters will be forwarded,
7874 * together with the selector value, to the selected method handle when invoking it.
7875 *
7876 * @apiNote Example:
7877 * The cases each drop the {@code selector} value they are given, and take an additional
7878 * {@code String} argument, which is concatenated (using {@link String#concat(String)})
7879 * to a specific constant label string for each case:
7880 * {@snippet lang="java" :
7881 * MethodHandles.Lookup lookup = MethodHandles.lookup();
7882 * MethodHandle caseMh = lookup.findVirtual(String.class, "concat",
7883 * MethodType.methodType(String.class, String.class));
7884 * caseMh = MethodHandles.dropArguments(caseMh, 0, int.class);
7885 *
7886 * MethodHandle caseDefault = MethodHandles.insertArguments(caseMh, 1, "default: ");
7887 * MethodHandle case0 = MethodHandles.insertArguments(caseMh, 1, "case 0: ");
7888 * MethodHandle case1 = MethodHandles.insertArguments(caseMh, 1, "case 1: ");
7889 *
7890 * MethodHandle mhSwitch = MethodHandles.tableSwitch(
7891 * caseDefault,
7892 * case0,
7893 * case1
7894 * );
7895 *
7896 * assertEquals("default: data", (String) mhSwitch.invokeExact(-1, "data"));
7897 * assertEquals("case 0: data", (String) mhSwitch.invokeExact(0, "data"));
7898 * assertEquals("case 1: data", (String) mhSwitch.invokeExact(1, "data"));
7899 * assertEquals("default: data", (String) mhSwitch.invokeExact(2, "data"));
7900 * }
7901 *
7902 * @param fallback the fallback method handle that is called when the selector is not
7903 * within the range {@code [0, N)}.
7904 * @param targets array of target method handles.
7905 * @return the table switch method handle.
7906 * @throws NullPointerException if {@code fallback}, the {@code targets} array, or any
7907 * any of the elements of the {@code targets} array are
7908 * {@code null}.
7909 * @throws IllegalArgumentException if the {@code targets} array is empty, if the leading
7910 * parameter of the fallback handle or any of the target
7911 * handles is not {@code int}, or if the types of
7912 * the fallback handle and all of target handles are
7913 * not the same.
7914 *
7915 * @since 17
7916 */
7917 public static MethodHandle tableSwitch(MethodHandle fallback, MethodHandle... targets) {
7918 Objects.requireNonNull(fallback);
7919 Objects.requireNonNull(targets);
7920 targets = targets.clone();
7921 MethodType type = tableSwitchChecks(fallback, targets);
7922 return MethodHandleImpl.makeTableSwitch(type, fallback, targets);
7923 }
7924
7925 private static MethodType tableSwitchChecks(MethodHandle defaultCase, MethodHandle[] caseActions) {
7926 if (caseActions.length == 0)
7927 throw new IllegalArgumentException("Not enough cases: " + Arrays.toString(caseActions));
7928
7929 MethodType expectedType = defaultCase.type();
7930
7931 if (!(expectedType.parameterCount() >= 1) || expectedType.parameterType(0) != int.class)
7932 throw new IllegalArgumentException(
7933 "Case actions must have int as leading parameter: " + Arrays.toString(caseActions));
7934
7935 for (MethodHandle mh : caseActions) {
7936 Objects.requireNonNull(mh);
7937 if (mh.type() != expectedType)
7938 throw new IllegalArgumentException(
7939 "Case actions must have the same type: " + Arrays.toString(caseActions));
7940 }
7941
7942 return expectedType;
7943 }
7944
7945 /**
7946 * Adapts a target var handle by pre-processing incoming and outgoing values using a pair of filter functions.
7947 * <p>
7948 * When calling e.g. {@link VarHandle#set(Object...)} on the resulting var handle, the incoming value (of type {@code T}, where
7949 * {@code T} is the <em>last</em> parameter type of the first filter function) is processed using the first filter and then passed
7950 * to the target var handle.
7951 * Conversely, when calling e.g. {@link VarHandle#get(Object...)} on the resulting var handle, the return value obtained from
7952 * the target var handle (of type {@code T}, where {@code T} is the <em>last</em> parameter type of the second filter function)
7953 * is processed using the second filter and returned to the caller. More advanced access mode types, such as
7954 * {@link VarHandle.AccessMode#COMPARE_AND_EXCHANGE} might apply both filters at the same time.
7955 * <p>
7956 * For the boxing and unboxing filters to be well-formed, their types must be of the form {@code (A... , S) -> T} and
7957 * {@code (A... , T) -> S}, respectively, where {@code T} is the type of the target var handle. If this is the case,
7958 * the resulting var handle will have type {@code S} and will feature the additional coordinates {@code A...} (which
7959 * will be appended to the coordinates of the target var handle).
7960 * <p>
7961 * If the boxing and unboxing filters throw any checked exceptions when invoked, the resulting var handle will
7962 * throw an {@link IllegalStateException}.
7963 * <p>
7964 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
7965 * atomic access guarantees as those featured by the target var handle.
7966 *
7967 * @param target the target var handle
7968 * @param filterToTarget a filter to convert some type {@code S} into the type of {@code target}
7969 * @param filterFromTarget a filter to convert the type of {@code target} to some type {@code S}
7970 * @return an adapter var handle which accepts a new type, performing the provided boxing/unboxing conversions.
7971 * @throws IllegalArgumentException if {@code filterFromTarget} and {@code filterToTarget} are not well-formed, that is, they have types
7972 * other than {@code (A... , S) -> T} and {@code (A... , T) -> S}, respectively, where {@code T} is the type of the target var handle,
7973 * or if it's determined that either {@code filterFromTarget} or {@code filterToTarget} throws any checked exceptions.
7974 * @throws NullPointerException if any of the arguments is {@code null}.
7975 * @since 22
7976 */
7977 public static VarHandle filterValue(VarHandle target, MethodHandle filterToTarget, MethodHandle filterFromTarget) {
7978 return VarHandles.filterValue(target, filterToTarget, filterFromTarget);
7979 }
7980
7981 /**
7982 * Adapts a target var handle by pre-processing incoming coordinate values using unary filter functions.
7983 * <p>
7984 * When calling e.g. {@link VarHandle#get(Object...)} on the resulting var handle, the incoming coordinate values
7985 * starting at position {@code pos} (of type {@code C1, C2 ... Cn}, where {@code C1, C2 ... Cn} are the return types
7986 * of the unary filter functions) are transformed into new values (of type {@code S1, S2 ... Sn}, where {@code S1, S2 ... Sn} are the
7987 * parameter types of the unary filter functions), and then passed (along with any coordinate that was left unaltered
7988 * by the adaptation) to the target var handle.
7989 * <p>
7990 * For the coordinate filters to be well-formed, their types must be of the form {@code S1 -> T1, S2 -> T1 ... Sn -> Tn},
7991 * where {@code T1, T2 ... Tn} are the coordinate types starting at position {@code pos} of the target var handle.
7992 * <p>
7993 * If any of the filters throws a checked exception when invoked, the resulting var handle will
7994 * throw an {@link IllegalStateException}.
7995 * <p>
7996 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
7997 * atomic access guarantees as those featured by the target var handle.
7998 *
7999 * @param target the target var handle
8000 * @param pos the position of the first coordinate to be transformed
8001 * @param filters the unary functions which are used to transform coordinates starting at position {@code pos}
8002 * @return an adapter var handle which accepts new coordinate types, applying the provided transformation
8003 * to the new coordinate values.
8004 * @throws IllegalArgumentException if the handles in {@code filters} are not well-formed, that is, they have types
8005 * other than {@code S1 -> T1, S2 -> T2, ... Sn -> Tn} where {@code T1, T2 ... Tn} are the coordinate types starting
8006 * at position {@code pos} of the target var handle, if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive,
8007 * or if more filters are provided than the actual number of coordinate types available starting at {@code pos},
8008 * or if it's determined that any of the filters throws any checked exceptions.
8009 * @throws NullPointerException if any of the arguments is {@code null} or {@code filters} contains {@code null}.
8010 * @since 22
8011 */
8012 public static VarHandle filterCoordinates(VarHandle target, int pos, MethodHandle... filters) {
8013 return VarHandles.filterCoordinates(target, pos, filters);
8014 }
8015
8016 /**
8017 * Provides a target var handle with one or more <em>bound coordinates</em>
8018 * in advance of the var handle's invocation. As a consequence, the resulting var handle will feature less
8019 * coordinate types than the target var handle.
8020 * <p>
8021 * When calling e.g. {@link VarHandle#get(Object...)} on the resulting var handle, incoming coordinate values
8022 * are joined with bound coordinate values, and then passed to the target var handle.
8023 * <p>
8024 * For the bound coordinates to be well-formed, their types must be {@code T1, T2 ... Tn },
8025 * where {@code T1, T2 ... Tn} are the coordinate types starting at position {@code pos} of the target var handle.
8026 * <p>
8027 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
8028 * atomic access guarantees as those featured by the target var handle.
8029 *
8030 * @param target the var handle to invoke after the bound coordinates are inserted
8031 * @param pos the position of the first coordinate to be inserted
8032 * @param values the series of bound coordinates to insert
8033 * @return an adapter var handle which inserts additional coordinates,
8034 * before calling the target var handle
8035 * @throws IllegalArgumentException if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive,
8036 * or if more values are provided than the actual number of coordinate types available starting at {@code pos}.
8037 * @throws ClassCastException if the bound coordinates in {@code values} are not well-formed, that is, they have types
8038 * other than {@code T1, T2 ... Tn }, where {@code T1, T2 ... Tn} are the coordinate types starting at position {@code pos}
8039 * of the target var handle.
8040 * @throws NullPointerException if any of the arguments is {@code null} or {@code values} contains {@code null}.
8041 * @since 22
8042 */
8043 public static VarHandle insertCoordinates(VarHandle target, int pos, Object... values) {
8044 return VarHandles.insertCoordinates(target, pos, values);
8045 }
8046
8047 /**
8048 * Provides a var handle which adapts the coordinate values of the target var handle, by re-arranging them
8049 * so that the new coordinates match the provided ones.
8050 * <p>
8051 * The given array controls the reordering.
8052 * Call {@code #I} the number of incoming coordinates (the value
8053 * {@code newCoordinates.size()}), and call {@code #O} the number
8054 * of outgoing coordinates (the number of coordinates associated with the target var handle).
8055 * Then the length of the reordering array must be {@code #O},
8056 * and each element must be a non-negative number less than {@code #I}.
8057 * For every {@code N} less than {@code #O}, the {@code N}-th
8058 * outgoing coordinate will be taken from the {@code I}-th incoming
8059 * coordinate, where {@code I} is {@code reorder[N]}.
8060 * <p>
8061 * No coordinate value conversions are applied.
8062 * The type of each incoming coordinate, as determined by {@code newCoordinates},
8063 * must be identical to the type of the corresponding outgoing coordinate
8064 * in the target var handle.
8065 * <p>
8066 * The reordering array need not specify an actual permutation.
8067 * An incoming coordinate will be duplicated if its index appears
8068 * more than once in the array, and an incoming coordinate will be dropped
8069 * if its index does not appear in the array.
8070 * <p>
8071 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
8072 * atomic access guarantees as those featured by the target var handle.
8073 * @param target the var handle to invoke after the coordinates have been reordered
8074 * @param newCoordinates the new coordinate types
8075 * @param reorder an index array which controls the reordering
8076 * @return an adapter var handle which re-arranges the incoming coordinate values,
8077 * before calling the target var handle
8078 * @throws IllegalArgumentException if the index array length is not equal to
8079 * the number of coordinates of the target var handle, or if any index array element is not a valid index for
8080 * a coordinate of {@code newCoordinates}, or if two corresponding coordinate types in
8081 * the target var handle and in {@code newCoordinates} are not identical.
8082 * @throws NullPointerException if any of the arguments is {@code null} or {@code newCoordinates} contains {@code null}.
8083 * @since 22
8084 */
8085 public static VarHandle permuteCoordinates(VarHandle target, List<Class<?>> newCoordinates, int... reorder) {
8086 return VarHandles.permuteCoordinates(target, newCoordinates, reorder);
8087 }
8088
8089 /**
8090 * Adapts a target var handle by pre-processing
8091 * a sub-sequence of its coordinate values with a filter (a method handle).
8092 * The pre-processed coordinates are replaced by the result (if any) of the
8093 * filter function and the target var handle is then called on the modified (usually shortened)
8094 * coordinate list.
8095 * <p>
8096 * If {@code R} is the return type of the filter, then:
8097 * <ul>
8098 * <li>if {@code R} <em>is not</em> {@code void}, the target var handle must have a coordinate of type {@code R} in
8099 * position {@code pos}. The parameter types of the filter will replace the coordinate type at position {@code pos}
8100 * of the target var handle. When the returned var handle is invoked, it will be as if the filter is invoked first,
8101 * and its result is passed in place of the coordinate at position {@code pos} in a downstream invocation of the
8102 * target var handle.</li>
8103 * <li> if {@code R} <em>is</em> {@code void}, the parameter types (if any) of the filter will be inserted in the
8104 * coordinate type list of the target var handle at position {@code pos}. In this case, when the returned var handle
8105 * is invoked, the filter essentially acts as a side effect, consuming some of the coordinate values, before a
8106 * downstream invocation of the target var handle.</li>
8107 * </ul>
8108 * <p>
8109 * If any of the filters throws a checked exception when invoked, the resulting var handle will
8110 * throw an {@link IllegalStateException}.
8111 * <p>
8112 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
8113 * atomic access guarantees as those featured by the target var handle.
8114 *
8115 * @param target the var handle to invoke after the coordinates have been filtered
8116 * @param pos the position in the coordinate list of the target var handle where the filter is to be inserted
8117 * @param filter the filter method handle
8118 * @return an adapter var handle which filters the incoming coordinate values,
8119 * before calling the target var handle
8120 * @throws IllegalArgumentException if the return type of {@code filter}
8121 * is not void, and it is not the same as the {@code pos} coordinate of the target var handle,
8122 * if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive,
8123 * if the resulting var handle's type would have <a href="MethodHandle.html#maxarity">too many coordinates</a>,
8124 * or if it's determined that {@code filter} throws any checked exceptions.
8125 * @throws NullPointerException if any of the arguments is {@code null}.
8126 * @since 22
8127 */
8128 public static VarHandle collectCoordinates(VarHandle target, int pos, MethodHandle filter) {
8129 return VarHandles.collectCoordinates(target, pos, filter);
8130 }
8131
8132 /**
8133 * Returns a var handle which will discard some dummy coordinates before delegating to the
8134 * target var handle. As a consequence, the resulting var handle will feature more
8135 * coordinate types than the target var handle.
8136 * <p>
8137 * The {@code pos} argument may range between zero and <i>N</i>, where <i>N</i> is the arity of the
8138 * target var handle's coordinate types. If {@code pos} is zero, the dummy coordinates will precede
8139 * the target's real arguments; if {@code pos} is <i>N</i> they will come after.
8140 * <p>
8141 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
8142 * atomic access guarantees as those featured by the target var handle.
8143 *
8144 * @param target the var handle to invoke after the dummy coordinates are dropped
8145 * @param pos position of the first coordinate to drop (zero for the leftmost)
8146 * @param valueTypes the type(s) of the coordinate(s) to drop
8147 * @return an adapter var handle which drops some dummy coordinates,
8148 * before calling the target var handle
8149 * @throws IllegalArgumentException if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive.
8150 * @throws NullPointerException if any of the arguments is {@code null} or {@code valueTypes} contains {@code null}.
8151 * @since 22
8152 */
8153 public static VarHandle dropCoordinates(VarHandle target, int pos, Class<?>... valueTypes) {
8154 return VarHandles.dropCoordinates(target, pos, valueTypes);
8155 }
8156 }