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.ClassFile;
43 import java.lang.classfile.ClassModel;
44 import java.lang.constant.ClassDesc;
45 import java.lang.constant.ConstantDescs;
46 import java.lang.invoke.LambdaForm.BasicType;
47 import java.lang.invoke.MethodHandleImpl.Intrinsic;
48 import java.lang.reflect.Constructor;
49 import java.lang.reflect.Field;
50 import java.lang.reflect.Member;
51 import java.lang.reflect.Method;
52 import java.lang.reflect.Modifier;
53 import java.nio.ByteOrder;
54 import java.security.ProtectionDomain;
55 import java.util.ArrayList;
56 import java.util.Arrays;
57 import java.util.BitSet;
58 import java.util.Comparator;
59 import java.util.Iterator;
60 import java.util.List;
61 import java.util.Objects;
62 import java.util.Set;
63 import java.util.concurrent.ConcurrentHashMap;
64 import java.util.stream.Stream;
65
66 import static java.lang.classfile.ClassFile.*;
67 import static java.lang.invoke.LambdaForm.BasicType.V_TYPE;
68 import static java.lang.invoke.MethodHandleNatives.Constants.*;
69 import static java.lang.invoke.MethodHandleStatics.UNSAFE;
70 import static java.lang.invoke.MethodHandleStatics.newIllegalArgumentException;
71 import static java.lang.invoke.MethodHandleStatics.newInternalError;
72 import static java.lang.invoke.MethodType.methodType;
73
74 /**
75 * This class consists exclusively of static methods that operate on or return
76 * method handles. They fall into several categories:
77 * <ul>
78 * <li>Lookup methods which help create method handles for methods and fields.
79 * <li>Combinator methods, which combine or transform pre-existing method handles into new ones.
80 * <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns.
81 * </ul>
82 * A lookup, combinator, or factory method will fail and throw an
83 * {@code IllegalArgumentException} if the created method handle's type
84 * would have <a href="MethodHandle.html#maxarity">too many parameters</a>.
85 *
86 * @author John Rose, JSR 292 EG
87 * @since 1.7
88 */
89 public class MethodHandles {
90
91 private MethodHandles() { } // do not instantiate
92
93 static final MemberName.Factory IMPL_NAMES = MemberName.getFactory();
94
95 // See IMPL_LOOKUP below.
96
97 //--- Method handle creation from ordinary methods.
98
99 /**
100 * Returns a {@link Lookup lookup object} with
101 * full capabilities to emulate all supported bytecode behaviors of the caller.
102 * These capabilities include {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access} to the caller.
103 * Factory methods on the lookup object can create
104 * <a href="MethodHandleInfo.html#directmh">direct method handles</a>
105 * for any member that the caller has access to via bytecodes,
106 * including protected and private fields and methods.
107 * This lookup object is created by the original lookup class
108 * and has the {@link Lookup#ORIGINAL ORIGINAL} bit set.
109 * This lookup object is a <em>capability</em> which may be delegated to trusted agents.
110 * Do not store it in place where untrusted code can access it.
111 * <p>
112 * This method is caller sensitive, which means that it may return different
113 * values to different callers.
114 * In cases where {@code MethodHandles.lookup} is called from a context where
115 * there is no caller frame on the stack (e.g. when called directly
116 * from a JNI attached thread), {@code IllegalCallerException} is thrown.
117 * To obtain a {@link Lookup lookup object} in such a context, use an auxiliary class that will
118 * implicitly be identified as the caller, or use {@link MethodHandles#publicLookup()}
119 * to obtain a low-privileged lookup instead.
120 * @return a lookup object for the caller of this method, with
121 * {@linkplain Lookup#ORIGINAL original} and
122 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access}.
123 * @throws IllegalCallerException if there is no caller frame on the stack.
124 */
125 @CallerSensitive
126 @ForceInline // to ensure Reflection.getCallerClass optimization
127 public static Lookup lookup() {
128 final Class<?> c = Reflection.getCallerClass();
129 if (c == null) {
130 throw new IllegalCallerException("no caller frame");
131 }
132 return new Lookup(c);
133 }
134
135 /**
136 * This lookup method is the alternate implementation of
137 * the lookup method with a leading caller class argument which is
138 * non-caller-sensitive. This method is only invoked by reflection
139 * and method handle.
140 */
141 @CallerSensitiveAdapter
142 private static Lookup lookup(Class<?> caller) {
143 if (caller.getClassLoader() == null) {
144 throw newInternalError("calling lookup() reflectively is not supported: "+caller);
145 }
146 return new Lookup(caller);
147 }
148
149 /**
150 * Returns a {@link Lookup lookup object} which is trusted minimally.
151 * The lookup has the {@code UNCONDITIONAL} mode.
152 * It can only be used to create method handles to public members of
153 * public classes in packages that are exported unconditionally.
154 * <p>
155 * As a matter of pure convention, the {@linkplain Lookup#lookupClass() lookup class}
156 * of this lookup object will be {@link java.lang.Object}.
157 *
158 * @apiNote The use of Object is conventional, and because the lookup modes are
159 * limited, there is no special access provided to the internals of Object, its package
160 * or its module. This public lookup object or other lookup object with
161 * {@code UNCONDITIONAL} mode assumes readability. Consequently, the lookup class
162 * is not used to determine the lookup context.
163 *
164 * <p style="font-size:smaller;">
165 * <em>Discussion:</em>
166 * The lookup class can be changed to any other class {@code C} using an expression of the form
167 * {@link Lookup#in publicLookup().in(C.class)}.
168 * A public lookup object is always subject to
169 * <a href="MethodHandles.Lookup.html#secmgr">security manager checks</a>.
170 * Also, it cannot access
171 * <a href="MethodHandles.Lookup.html#callsens">caller sensitive methods</a>.
172 * @return a lookup object which is trusted minimally
173 */
174 public static Lookup publicLookup() {
175 return Lookup.PUBLIC_LOOKUP;
176 }
177
178 /**
179 * Returns a {@link Lookup lookup} object on a target class to emulate all supported
180 * bytecode behaviors, including <a href="MethodHandles.Lookup.html#privacc">private access</a>.
181 * The returned lookup object can provide access to classes in modules and packages,
182 * and members of those classes, outside the normal rules of Java access control,
183 * instead conforming to the more permissive rules for modular <em>deep reflection</em>.
184 * <p>
185 * A caller, specified as a {@code Lookup} object, in module {@code M1} is
186 * allowed to do deep reflection on module {@code M2} and package of the target class
187 * if and only if all of the following conditions are {@code true}:
188 * <ul>
189 * <li>If there is a security manager, its {@code checkPermission} method is
190 * called to check {@code ReflectPermission("suppressAccessChecks")} and
191 * that must return normally.
192 * <li>The caller lookup object must have {@linkplain Lookup#hasFullPrivilegeAccess()
193 * full privilege access}. Specifically:
194 * <ul>
195 * <li>The caller lookup object must have the {@link Lookup#MODULE MODULE} lookup mode.
196 * (This is because otherwise there would be no way to ensure the original lookup
197 * creator was a member of any particular module, and so any subsequent checks
198 * for readability and qualified exports would become ineffective.)
199 * <li>The caller lookup object must have {@link Lookup#PRIVATE PRIVATE} access.
200 * (This is because an application intending to share intra-module access
201 * using {@link Lookup#MODULE MODULE} alone will inadvertently also share
202 * deep reflection to its own module.)
203 * </ul>
204 * <li>The target class must be a proper class, not a primitive or array class.
205 * (Thus, {@code M2} is well-defined.)
206 * <li>If the caller module {@code M1} differs from
207 * the target module {@code M2} then both of the following must be true:
208 * <ul>
209 * <li>{@code M1} {@link Module#canRead reads} {@code M2}.</li>
210 * <li>{@code M2} {@link Module#isOpen(String,Module) opens} the package
211 * containing the target class to at least {@code M1}.</li>
212 * </ul>
213 * </ul>
214 * <p>
215 * If any of the above checks is violated, this method fails with an
216 * exception.
217 * <p>
218 * Otherwise, if {@code M1} and {@code M2} are the same module, this method
219 * returns a {@code Lookup} on {@code targetClass} with
220 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege access}
221 * with {@code null} previous lookup class.
222 * <p>
223 * Otherwise, {@code M1} and {@code M2} are two different modules. This method
224 * returns a {@code Lookup} on {@code targetClass} that records
225 * the lookup class of the caller as the new previous lookup class with
226 * {@code PRIVATE} access but no {@code MODULE} access.
227 * <p>
228 * The resulting {@code Lookup} object has no {@code ORIGINAL} access.
229 *
230 * @apiNote The {@code Lookup} object returned by this method is allowed to
231 * {@linkplain Lookup#defineClass(byte[]) define classes} in the runtime package
232 * of {@code targetClass}. Extreme caution should be taken when opening a package
233 * to another module as such defined classes have the same full privilege
234 * access as other members in {@code targetClass}'s module.
235 *
236 * @param targetClass the target class
237 * @param caller the caller lookup object
238 * @return a lookup object for the target class, with private access
239 * @throws IllegalArgumentException if {@code targetClass} is a primitive type or void or array class
240 * @throws NullPointerException if {@code targetClass} or {@code caller} is {@code null}
241 * @throws SecurityException if denied by the security manager
242 * @throws IllegalAccessException if any of the other access checks specified above fails
243 * @since 9
244 * @see Lookup#dropLookupMode
245 * @see <a href="MethodHandles.Lookup.html#cross-module-lookup">Cross-module lookups</a>
246 */
247 public static Lookup privateLookupIn(Class<?> targetClass, Lookup caller) throws IllegalAccessException {
248 if (caller.allowedModes == Lookup.TRUSTED) {
249 return new Lookup(targetClass);
250 }
251
252 @SuppressWarnings("removal")
253 SecurityManager sm = System.getSecurityManager();
254 if (sm != null) sm.checkPermission(SecurityConstants.ACCESS_PERMISSION);
255 if (targetClass.isPrimitive())
256 throw new IllegalArgumentException(targetClass + " is a primitive class");
257 if (targetClass.isArray())
258 throw new IllegalArgumentException(targetClass + " is an array class");
259 // Ensure that we can reason accurately about private and module access.
260 int requireAccess = Lookup.PRIVATE|Lookup.MODULE;
261 if ((caller.lookupModes() & requireAccess) != requireAccess)
262 throw new IllegalAccessException("caller does not have PRIVATE and MODULE lookup mode");
263
264 // previous lookup class is never set if it has MODULE access
265 assert caller.previousLookupClass() == null;
266
267 Class<?> callerClass = caller.lookupClass();
268 Module callerModule = callerClass.getModule(); // M1
269 Module targetModule = targetClass.getModule(); // M2
270 Class<?> newPreviousClass = null;
271 int newModes = Lookup.FULL_POWER_MODES & ~Lookup.ORIGINAL;
272
273 if (targetModule != callerModule) {
274 if (!callerModule.canRead(targetModule))
275 throw new IllegalAccessException(callerModule + " does not read " + targetModule);
276 if (targetModule.isNamed()) {
277 String pn = targetClass.getPackageName();
278 assert !pn.isEmpty() : "unnamed package cannot be in named module";
279 if (!targetModule.isOpen(pn, callerModule))
280 throw new IllegalAccessException(targetModule + " does not open " + pn + " to " + callerModule);
281 }
282
283 // M2 != M1, set previous lookup class to M1 and drop MODULE access
284 newPreviousClass = callerClass;
285 newModes &= ~Lookup.MODULE;
286 }
287 return Lookup.newLookup(targetClass, newPreviousClass, newModes);
288 }
289
290 /**
291 * Returns the <em>class data</em> associated with the lookup class
292 * of the given {@code caller} lookup object, or {@code null}.
293 *
294 * <p> A hidden class with class data can be created by calling
295 * {@link Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...)
296 * Lookup::defineHiddenClassWithClassData}.
297 * This method will cause the static class initializer of the lookup
298 * class of the given {@code caller} lookup object be executed if
299 * it has not been initialized.
300 *
301 * <p> A hidden class created by {@link Lookup#defineHiddenClass(byte[], boolean, Lookup.ClassOption...)
302 * Lookup::defineHiddenClass} and non-hidden classes have no class data.
303 * {@code null} is returned if this method is called on the lookup object
304 * on these classes.
305 *
306 * <p> The {@linkplain Lookup#lookupModes() lookup modes} for this lookup
307 * must have {@linkplain Lookup#ORIGINAL original access}
308 * in order to retrieve the class data.
309 *
310 * @apiNote
311 * This method can be called as a bootstrap method for a dynamically computed
312 * constant. A framework can create a hidden class with class data, for
313 * example that can be {@code Class} or {@code MethodHandle} object.
314 * The class data is accessible only to the lookup object
315 * created by the original caller but inaccessible to other members
316 * in the same nest. If a framework passes security sensitive objects
317 * to a hidden class via class data, it is recommended to load the value
318 * of class data as a dynamically computed constant instead of storing
319 * the class data in private static field(s) which are accessible to
320 * other nestmates.
321 *
322 * @param <T> the type to cast the class data object to
323 * @param caller the lookup context describing the class performing the
324 * operation (normally stacked by the JVM)
325 * @param name must be {@link ConstantDescs#DEFAULT_NAME}
326 * ({@code "_"})
327 * @param type the type of the class data
328 * @return the value of the class data if present in the lookup class;
329 * otherwise {@code null}
330 * @throws IllegalArgumentException if name is not {@code "_"}
331 * @throws IllegalAccessException if the lookup context does not have
332 * {@linkplain Lookup#ORIGINAL original} access
333 * @throws ClassCastException if the class data cannot be converted to
334 * the given {@code type}
335 * @throws NullPointerException if {@code caller} or {@code type} argument
336 * is {@code null}
337 * @see Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...)
338 * @see MethodHandles#classDataAt(Lookup, String, Class, int)
339 * @since 16
340 * @jvms 5.5 Initialization
341 */
342 public static <T> T classData(Lookup caller, String name, Class<T> type) throws IllegalAccessException {
343 Objects.requireNonNull(caller);
344 Objects.requireNonNull(type);
345 if (!ConstantDescs.DEFAULT_NAME.equals(name)) {
346 throw new IllegalArgumentException("name must be \"_\": " + name);
347 }
348
349 if ((caller.lookupModes() & Lookup.ORIGINAL) != Lookup.ORIGINAL) {
350 throw new IllegalAccessException(caller + " does not have ORIGINAL access");
351 }
352
353 Object classdata = classData(caller.lookupClass());
354 if (classdata == null) return null;
355
356 try {
357 return BootstrapMethodInvoker.widenAndCast(classdata, type);
358 } catch (RuntimeException|Error e) {
359 throw e; // let CCE and other runtime exceptions through
360 } catch (Throwable e) {
361 throw new InternalError(e);
362 }
363 }
364
365 /*
366 * Returns the class data set by the VM in the Class::classData field.
367 *
368 * This is also invoked by LambdaForms as it cannot use condy via
369 * MethodHandles::classData due to bootstrapping issue.
370 */
371 static Object classData(Class<?> c) {
372 UNSAFE.ensureClassInitialized(c);
373 return SharedSecrets.getJavaLangAccess().classData(c);
374 }
375
376 /**
377 * Returns the element at the specified index in the
378 * {@linkplain #classData(Lookup, String, Class) class data},
379 * if the class data associated with the lookup class
380 * of the given {@code caller} lookup object is a {@code List}.
381 * If the class data is not present in this lookup class, this method
382 * returns {@code null}.
383 *
384 * <p> A hidden class with class data can be created by calling
385 * {@link Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...)
386 * Lookup::defineHiddenClassWithClassData}.
387 * This method will cause the static class initializer of the lookup
388 * class of the given {@code caller} lookup object be executed if
389 * it has not been initialized.
390 *
391 * <p> A hidden class created by {@link Lookup#defineHiddenClass(byte[], boolean, Lookup.ClassOption...)
392 * Lookup::defineHiddenClass} and non-hidden classes have no class data.
393 * {@code null} is returned if this method is called on the lookup object
394 * on these classes.
395 *
396 * <p> The {@linkplain Lookup#lookupModes() lookup modes} for this lookup
397 * must have {@linkplain Lookup#ORIGINAL original access}
398 * in order to retrieve the class data.
399 *
400 * @apiNote
401 * This method can be called as a bootstrap method for a dynamically computed
402 * constant. A framework can create a hidden class with class data, for
403 * example that can be {@code List.of(o1, o2, o3....)} containing more than
404 * one object and use this method to load one element at a specific index.
405 * The class data is accessible only to the lookup object
406 * created by the original caller but inaccessible to other members
407 * in the same nest. If a framework passes security sensitive objects
408 * to a hidden class via class data, it is recommended to load the value
409 * of class data as a dynamically computed constant instead of storing
410 * the class data in private static field(s) which are accessible to other
411 * nestmates.
412 *
413 * @param <T> the type to cast the result object to
414 * @param caller the lookup context describing the class performing the
415 * operation (normally stacked by the JVM)
416 * @param name must be {@link java.lang.constant.ConstantDescs#DEFAULT_NAME}
417 * ({@code "_"})
418 * @param type the type of the element at the given index in the class data
419 * @param index index of the element in the class data
420 * @return the element at the given index in the class data
421 * if the class data is present; otherwise {@code null}
422 * @throws IllegalArgumentException if name is not {@code "_"}
423 * @throws IllegalAccessException if the lookup context does not have
424 * {@linkplain Lookup#ORIGINAL original} access
425 * @throws ClassCastException if the class data cannot be converted to {@code List}
426 * or the element at the specified index cannot be converted to the given type
427 * @throws IndexOutOfBoundsException if the index is out of range
428 * @throws NullPointerException if {@code caller} or {@code type} argument is
429 * {@code null}; or if unboxing operation fails because
430 * the element at the given index is {@code null}
431 *
432 * @since 16
433 * @see #classData(Lookup, String, Class)
434 * @see Lookup#defineHiddenClassWithClassData(byte[], Object, boolean, Lookup.ClassOption...)
435 */
436 public static <T> T classDataAt(Lookup caller, String name, Class<T> type, int index)
437 throws IllegalAccessException
438 {
439 @SuppressWarnings("unchecked")
440 List<Object> classdata = (List<Object>)classData(caller, name, List.class);
441 if (classdata == null) return null;
442
443 try {
444 Object element = classdata.get(index);
445 return BootstrapMethodInvoker.widenAndCast(element, type);
446 } catch (RuntimeException|Error e) {
447 throw e; // let specified exceptions and other runtime exceptions/errors through
448 } catch (Throwable e) {
449 throw new InternalError(e);
450 }
451 }
452
453 /**
454 * Performs an unchecked "crack" of a
455 * <a href="MethodHandleInfo.html#directmh">direct method handle</a>.
456 * The result is as if the user had obtained a lookup object capable enough
457 * to crack the target method handle, called
458 * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect}
459 * on the target to obtain its symbolic reference, and then called
460 * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs}
461 * to resolve the symbolic reference to a member.
462 * <p>
463 * If there is a security manager, its {@code checkPermission} method
464 * is called with a {@code ReflectPermission("suppressAccessChecks")} permission.
465 * @param <T> the desired type of the result, either {@link Member} or a subtype
466 * @param expected a class object representing the desired result type {@code T}
467 * @param target a direct method handle to crack into symbolic reference components
468 * @return a reference to the method, constructor, or field object
469 * @throws SecurityException if the caller is not privileged to call {@code setAccessible}
470 * @throws NullPointerException if either argument is {@code null}
471 * @throws IllegalArgumentException if the target is not a direct method handle
472 * @throws ClassCastException if the member is not of the expected type
473 * @since 1.8
474 */
475 public static <T extends Member> T reflectAs(Class<T> expected, MethodHandle target) {
476 @SuppressWarnings("removal")
477 SecurityManager smgr = System.getSecurityManager();
478 if (smgr != null) smgr.checkPermission(SecurityConstants.ACCESS_PERMISSION);
479 Lookup lookup = Lookup.IMPL_LOOKUP; // use maximally privileged lookup
480 return lookup.revealDirect(target).reflectAs(expected, lookup);
481 }
482
483 /**
484 * A <em>lookup object</em> is a factory for creating method handles,
485 * when the creation requires access checking.
486 * Method handles do not perform
487 * access checks when they are called, but rather when they are created.
488 * Therefore, method handle access
489 * restrictions must be enforced when a method handle is created.
490 * The caller class against which those restrictions are enforced
491 * is known as the {@linkplain #lookupClass() lookup class}.
492 * <p>
493 * A lookup class which needs to create method handles will call
494 * {@link MethodHandles#lookup() MethodHandles.lookup} to create a factory for itself.
495 * When the {@code Lookup} factory object is created, the identity of the lookup class is
496 * determined, and securely stored in the {@code Lookup} object.
497 * The lookup class (or its delegates) may then use factory methods
498 * on the {@code Lookup} object to create method handles for access-checked members.
499 * This includes all methods, constructors, and fields which are allowed to the lookup class,
500 * even private ones.
501 *
502 * <h2><a id="lookups"></a>Lookup Factory Methods</h2>
503 * The factory methods on a {@code Lookup} object correspond to all major
504 * use cases for methods, constructors, and fields.
505 * Each method handle created by a factory method is the functional
506 * equivalent of a particular <em>bytecode behavior</em>.
507 * (Bytecode behaviors are described in section {@jvms 5.4.3.5} of
508 * the Java Virtual Machine Specification.)
509 * Here is a summary of the correspondence between these factory methods and
510 * the behavior of the resulting method handles:
511 * <table class="striped">
512 * <caption style="display:none">lookup method behaviors</caption>
513 * <thead>
514 * <tr>
515 * <th scope="col"><a id="equiv"></a>lookup expression</th>
516 * <th scope="col">member</th>
517 * <th scope="col">bytecode behavior</th>
518 * </tr>
519 * </thead>
520 * <tbody>
521 * <tr>
522 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</th>
523 * <td>{@code FT f;}</td><td>{@code (T) this.f;}</td>
524 * </tr>
525 * <tr>
526 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</th>
527 * <td>{@code static}<br>{@code FT f;}</td><td>{@code (FT) C.f;}</td>
528 * </tr>
529 * <tr>
530 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</th>
531 * <td>{@code FT f;}</td><td>{@code this.f = x;}</td>
532 * </tr>
533 * <tr>
534 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</th>
535 * <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td>
536 * </tr>
537 * <tr>
538 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</th>
539 * <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>
540 * </tr>
541 * <tr>
542 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</th>
543 * <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td>
544 * </tr>
545 * <tr>
546 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</th>
547 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
548 * </tr>
549 * <tr>
550 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</th>
551 * <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td>
552 * </tr>
553 * <tr>
554 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</th>
555 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td>
556 * </tr>
557 * <tr>
558 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</th>
559 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, arg);}</td>
560 * </tr>
561 * <tr>
562 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</th>
563 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
564 * </tr>
565 * <tr>
566 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</th>
567 * <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td>
568 * </tr>
569 * <tr>
570 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSpecial lookup.unreflectSpecial(aMethod,this.class)}</th>
571 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
572 * </tr>
573 * <tr>
574 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findClass lookup.findClass("C")}</th>
575 * <td>{@code class C { ... }}</td><td>{@code C.class;}</td>
576 * </tr>
577 * </tbody>
578 * </table>
579 *
580 * Here, the type {@code C} is the class or interface being searched for a member,
581 * documented as a parameter named {@code refc} in the lookup methods.
582 * The method type {@code MT} is composed from the return type {@code T}
583 * and the sequence of argument types {@code A*}.
584 * The constructor also has a sequence of argument types {@code A*} and
585 * is deemed to return the newly-created object of type {@code C}.
586 * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}.
587 * The formal parameter {@code this} stands for the self-reference of type {@code C};
588 * if it is present, it is always the leading argument to the method handle invocation.
589 * (In the case of some {@code protected} members, {@code this} may be
590 * restricted in type to the lookup class; see below.)
591 * The name {@code arg} stands for all the other method handle arguments.
592 * In the code examples for the Core Reflection API, the name {@code thisOrNull}
593 * stands for a null reference if the accessed method or field is static,
594 * and {@code this} otherwise.
595 * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand
596 * for reflective objects corresponding to the given members declared in type {@code C}.
597 * <p>
598 * The bytecode behavior for a {@code findClass} operation is a load of a constant class,
599 * as if by {@code ldc CONSTANT_Class}.
600 * The behavior is represented, not as a method handle, but directly as a {@code Class} constant.
601 * <p>
602 * In cases where the given member is of variable arity (i.e., a method or constructor)
603 * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}.
604 * In all other cases, the returned method handle will be of fixed arity.
605 * <p style="font-size:smaller;">
606 * <em>Discussion:</em>
607 * The equivalence between looked-up method handles and underlying
608 * class members and bytecode behaviors
609 * can break down in a few ways:
610 * <ul style="font-size:smaller;">
611 * <li>If {@code C} is not symbolically accessible from the lookup class's loader,
612 * the lookup can still succeed, even when there is no equivalent
613 * Java expression or bytecoded constant.
614 * <li>Likewise, if {@code T} or {@code MT}
615 * is not symbolically accessible from the lookup class's loader,
616 * the lookup can still succeed.
617 * For example, lookups for {@code MethodHandle.invokeExact} and
618 * {@code MethodHandle.invoke} will always succeed, regardless of requested type.
619 * <li>If there is a security manager installed, it can forbid the lookup
620 * on various grounds (<a href="MethodHandles.Lookup.html#secmgr">see below</a>).
621 * By contrast, the {@code ldc} instruction on a {@code CONSTANT_MethodHandle}
622 * constant is not subject to security manager checks.
623 * <li>If the looked-up method has a
624 * <a href="MethodHandle.html#maxarity">very large arity</a>,
625 * the method handle creation may fail with an
626 * {@code IllegalArgumentException}, due to the method handle type having
627 * <a href="MethodHandle.html#maxarity">too many parameters.</a>
628 * </ul>
629 *
630 * <h2><a id="access"></a>Access checking</h2>
631 * Access checks are applied in the factory methods of {@code Lookup},
632 * when a method handle is created.
633 * This is a key difference from the Core Reflection API, since
634 * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
635 * performs access checking against every caller, on every call.
636 * <p>
637 * All access checks start from a {@code Lookup} object, which
638 * compares its recorded lookup class against all requests to
639 * create method handles.
640 * A single {@code Lookup} object can be used to create any number
641 * of access-checked method handles, all checked against a single
642 * lookup class.
643 * <p>
644 * A {@code Lookup} object can be shared with other trusted code,
645 * such as a metaobject protocol.
646 * A shared {@code Lookup} object delegates the capability
647 * to create method handles on private members of the lookup class.
648 * Even if privileged code uses the {@code Lookup} object,
649 * the access checking is confined to the privileges of the
650 * original lookup class.
651 * <p>
652 * A lookup can fail, because
653 * the containing class is not accessible to the lookup class, or
654 * because the desired class member is missing, or because the
655 * desired class member is not accessible to the lookup class, or
656 * because the lookup object is not trusted enough to access the member.
657 * In the case of a field setter function on a {@code final} field,
658 * finality enforcement is treated as a kind of access control,
659 * and the lookup will fail, except in special cases of
660 * {@link Lookup#unreflectSetter Lookup.unreflectSetter}.
661 * In any of these cases, a {@code ReflectiveOperationException} will be
662 * thrown from the attempted lookup. The exact class will be one of
663 * the following:
664 * <ul>
665 * <li>NoSuchMethodException — if a method is requested but does not exist
666 * <li>NoSuchFieldException — if a field is requested but does not exist
667 * <li>IllegalAccessException — if the member exists but an access check fails
668 * </ul>
669 * <p>
670 * In general, the conditions under which a method handle may be
671 * looked up for a method {@code M} are no more restrictive than the conditions
672 * under which the lookup class could have compiled, verified, and resolved a call to {@code M}.
673 * Where the JVM would raise exceptions like {@code NoSuchMethodError},
674 * a method handle lookup will generally raise a corresponding
675 * checked exception, such as {@code NoSuchMethodException}.
676 * And the effect of invoking the method handle resulting from the lookup
677 * is <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a>
678 * to executing the compiled, verified, and resolved call to {@code M}.
679 * The same point is true of fields and constructors.
680 * <p style="font-size:smaller;">
681 * <em>Discussion:</em>
682 * Access checks only apply to named and reflected methods,
683 * constructors, and fields.
684 * Other method handle creation methods, such as
685 * {@link MethodHandle#asType MethodHandle.asType},
686 * do not require any access checks, and are used
687 * independently of any {@code Lookup} object.
688 * <p>
689 * If the desired member is {@code protected}, the usual JVM rules apply,
690 * including the requirement that the lookup class must either be in the
691 * same package as the desired member, or must inherit that member.
692 * (See the Java Virtual Machine Specification, sections {@jvms
693 * 4.9.2}, {@jvms 5.4.3.5}, and {@jvms 6.4}.)
694 * In addition, if the desired member is a non-static field or method
695 * in a different package, the resulting method handle may only be applied
696 * to objects of the lookup class or one of its subclasses.
697 * This requirement is enforced by narrowing the type of the leading
698 * {@code this} parameter from {@code C}
699 * (which will necessarily be a superclass of the lookup class)
700 * to the lookup class itself.
701 * <p>
702 * The JVM imposes a similar requirement on {@code invokespecial} instruction,
703 * that the receiver argument must match both the resolved method <em>and</em>
704 * the current class. Again, this requirement is enforced by narrowing the
705 * type of the leading parameter to the resulting method handle.
706 * (See the Java Virtual Machine Specification, section {@jvms 4.10.1.9}.)
707 * <p>
708 * The JVM represents constructors and static initializer blocks as internal methods
709 * with special names ({@value ConstantDescs#INIT_NAME} and {@value
710 * ConstantDescs#CLASS_INIT_NAME}).
711 * The internal syntax of invocation instructions allows them to refer to such internal
712 * methods as if they were normal methods, but the JVM bytecode verifier rejects them.
713 * A lookup of such an internal method will produce a {@code NoSuchMethodException}.
714 * <p>
715 * If the relationship between nested types is expressed directly through the
716 * {@code NestHost} and {@code NestMembers} attributes
717 * (see the Java Virtual Machine Specification, sections {@jvms
718 * 4.7.28} and {@jvms 4.7.29}),
719 * then the associated {@code Lookup} object provides direct access to
720 * the lookup class and all of its nestmates
721 * (see {@link java.lang.Class#getNestHost Class.getNestHost}).
722 * Otherwise, access between nested classes is obtained by the Java compiler creating
723 * a wrapper method to access a private method of another class in the same nest.
724 * For example, a nested class {@code C.D}
725 * can access private members within other related classes such as
726 * {@code C}, {@code C.D.E}, or {@code C.B},
727 * but the Java compiler may need to generate wrapper methods in
728 * those related classes. In such cases, a {@code Lookup} object on
729 * {@code C.E} would be unable to access those private members.
730 * A workaround for this limitation is the {@link Lookup#in Lookup.in} method,
731 * which can transform a lookup on {@code C.E} into one on any of those other
732 * classes, without special elevation of privilege.
733 * <p>
734 * The accesses permitted to a given lookup object may be limited,
735 * according to its set of {@link #lookupModes lookupModes},
736 * to a subset of members normally accessible to the lookup class.
737 * For example, the {@link MethodHandles#publicLookup publicLookup}
738 * method produces a lookup object which is only allowed to access
739 * public members in public classes of exported packages.
740 * The caller sensitive method {@link MethodHandles#lookup lookup}
741 * produces a lookup object with full capabilities relative to
742 * its caller class, to emulate all supported bytecode behaviors.
743 * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object
744 * with fewer access modes than the original lookup object.
745 *
746 * <p style="font-size:smaller;">
747 * <a id="privacc"></a>
748 * <em>Discussion of private and module access:</em>
749 * We say that a lookup has <em>private access</em>
750 * if its {@linkplain #lookupModes lookup modes}
751 * include the possibility of accessing {@code private} members
752 * (which includes the private members of nestmates).
753 * As documented in the relevant methods elsewhere,
754 * only lookups with private access possess the following capabilities:
755 * <ul style="font-size:smaller;">
756 * <li>access private fields, methods, and constructors of the lookup class and its nestmates
757 * <li>create method handles which {@link Lookup#findSpecial emulate invokespecial} instructions
758 * <li>avoid <a href="MethodHandles.Lookup.html#secmgr">package access checks</a>
759 * for classes accessible to the lookup class
760 * <li>create {@link Lookup#in delegated lookup objects} which have private access to other classes
761 * within the same package member
762 * </ul>
763 * <p style="font-size:smaller;">
764 * Similarly, a lookup with module access ensures that the original lookup creator was
765 * a member in the same module as the lookup class.
766 * <p style="font-size:smaller;">
767 * Private and module access are independently determined modes; a lookup may have
768 * either or both or neither. A lookup which possesses both access modes is said to
769 * possess {@linkplain #hasFullPrivilegeAccess() full privilege access}.
770 * <p style="font-size:smaller;">
771 * A lookup with <em>original access</em> ensures that this lookup is created by
772 * the original lookup class and the bootstrap method invoked by the VM.
773 * Such a lookup with original access also has private and module access
774 * which has the following additional capability:
775 * <ul style="font-size:smaller;">
776 * <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> methods,
777 * such as {@code Class.forName}
778 * <li>obtain the {@linkplain MethodHandles#classData(Lookup, String, Class)
779 * class data} associated with the lookup class</li>
780 * </ul>
781 * <p style="font-size:smaller;">
782 * Each of these permissions is a consequence of the fact that a lookup object
783 * with private access can be securely traced back to an originating class,
784 * whose <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> and Java language access permissions
785 * can be reliably determined and emulated by method handles.
786 *
787 * <h2><a id="cross-module-lookup"></a>Cross-module lookups</h2>
788 * When a lookup class in one module {@code M1} accesses a class in another module
789 * {@code M2}, extra access checking is performed beyond the access mode bits.
790 * A {@code Lookup} with {@link #PUBLIC} mode and a lookup class in {@code M1}
791 * can access public types in {@code M2} when {@code M2} is readable to {@code M1}
792 * and when the type is in a package of {@code M2} that is exported to
793 * at least {@code M1}.
794 * <p>
795 * A {@code Lookup} on {@code C} can also <em>teleport</em> to a target class
796 * via {@link #in(Class) Lookup.in} and {@link MethodHandles#privateLookupIn(Class, Lookup)
797 * MethodHandles.privateLookupIn} methods.
798 * Teleporting across modules will always record the original lookup class as
799 * the <em>{@linkplain #previousLookupClass() previous lookup class}</em>
800 * and drops {@link Lookup#MODULE MODULE} access.
801 * If the target class is in the same module as the lookup class {@code C},
802 * then the target class becomes the new lookup class
803 * and there is no change to the previous lookup class.
804 * If the target class is in a different module from {@code M1} ({@code C}'s module),
805 * {@code C} becomes the new previous lookup class
806 * and the target class becomes the new lookup class.
807 * In that case, if there was already a previous lookup class in {@code M0},
808 * and it differs from {@code M1} and {@code M2}, then the resulting lookup
809 * drops all privileges.
810 * For example,
811 * {@snippet lang="java" :
812 * Lookup lookup = MethodHandles.lookup(); // in class C
813 * Lookup lookup2 = lookup.in(D.class);
814 * MethodHandle mh = lookup2.findStatic(E.class, "m", MT);
815 * }
816 * <p>
817 * The {@link #lookup()} factory method produces a {@code Lookup} object
818 * with {@code null} previous lookup class.
819 * {@link Lookup#in lookup.in(D.class)} transforms the {@code lookup} on class {@code C}
820 * to class {@code D} without elevation of privileges.
821 * If {@code C} and {@code D} are in the same module,
822 * {@code lookup2} records {@code D} as the new lookup class and keeps the
823 * same previous lookup class as the original {@code lookup}, or
824 * {@code null} if not present.
825 * <p>
826 * When a {@code Lookup} teleports from a class
827 * in one nest to another nest, {@code PRIVATE} access is dropped.
828 * When a {@code Lookup} teleports from a class in one package to
829 * another package, {@code PACKAGE} access is dropped.
830 * When a {@code Lookup} teleports from a class in one module to another module,
831 * {@code MODULE} access is dropped.
832 * Teleporting across modules drops the ability to access non-exported classes
833 * in both the module of the new lookup class and the module of the old lookup class
834 * and the resulting {@code Lookup} remains only {@code PUBLIC} access.
835 * A {@code Lookup} can teleport back and forth to a class in the module of
836 * the lookup class and the module of the previous class lookup.
837 * Teleporting across modules can only decrease access but cannot increase it.
838 * Teleporting to some third module drops all accesses.
839 * <p>
840 * In the above example, if {@code C} and {@code D} are in different modules,
841 * {@code lookup2} records {@code D} as its lookup class and
842 * {@code C} as its previous lookup class and {@code lookup2} has only
843 * {@code PUBLIC} access. {@code lookup2} can teleport to other class in
844 * {@code C}'s module and {@code D}'s module.
845 * If class {@code E} is in a third module, {@code lookup2.in(E.class)} creates
846 * a {@code Lookup} on {@code E} with no access and {@code lookup2}'s lookup
847 * class {@code D} is recorded as its previous lookup class.
848 * <p>
849 * Teleporting across modules restricts access to the public types that
850 * both the lookup class and the previous lookup class can equally access
851 * (see below).
852 * <p>
853 * {@link MethodHandles#privateLookupIn(Class, Lookup) MethodHandles.privateLookupIn(T.class, lookup)}
854 * can be used to teleport a {@code lookup} from class {@code C} to class {@code T}
855 * and produce a new {@code Lookup} with <a href="#privacc">private access</a>
856 * if the lookup class is allowed to do <em>deep reflection</em> on {@code T}.
857 * The {@code lookup} must have {@link #MODULE} and {@link #PRIVATE} access
858 * to call {@code privateLookupIn}.
859 * A {@code lookup} on {@code C} in module {@code M1} is allowed to do deep reflection
860 * on all classes in {@code M1}. If {@code T} is in {@code M1}, {@code privateLookupIn}
861 * produces a new {@code Lookup} on {@code T} with full capabilities.
862 * A {@code lookup} on {@code C} is also allowed
863 * to do deep reflection on {@code T} in another module {@code M2} if
864 * {@code M1} reads {@code M2} and {@code M2} {@link Module#isOpen(String,Module) opens}
865 * the package containing {@code T} to at least {@code M1}.
866 * {@code T} becomes the new lookup class and {@code C} becomes the new previous
867 * lookup class and {@code MODULE} access is dropped from the resulting {@code Lookup}.
868 * The resulting {@code Lookup} can be used to do member lookup or teleport
869 * to another lookup class by calling {@link #in Lookup::in}. But
870 * it cannot be used to obtain another private {@code Lookup} by calling
871 * {@link MethodHandles#privateLookupIn(Class, Lookup) privateLookupIn}
872 * because it has no {@code MODULE} access.
873 * <p>
874 * The {@code Lookup} object returned by {@code privateLookupIn} is allowed to
875 * {@linkplain Lookup#defineClass(byte[]) define classes} in the runtime package
876 * of {@code T}. Extreme caution should be taken when opening a package
877 * to another module as such defined classes have the same full privilege
878 * access as other members in {@code M2}.
879 *
880 * <h2><a id="module-access-check"></a>Cross-module access checks</h2>
881 *
882 * A {@code Lookup} with {@link #PUBLIC} or with {@link #UNCONDITIONAL} mode
883 * allows cross-module access. The access checking is performed with respect
884 * to both the lookup class and the previous lookup class if present.
885 * <p>
886 * A {@code Lookup} with {@link #UNCONDITIONAL} mode can access public type
887 * in all modules when the type is in a package that is {@linkplain Module#isExported(String)
888 * exported unconditionally}.
889 * <p>
890 * If a {@code Lookup} on {@code LC} in {@code M1} has no previous lookup class,
891 * the lookup with {@link #PUBLIC} mode can access all public types in modules
892 * that are readable to {@code M1} and the type is in a package that is exported
893 * at least to {@code M1}.
894 * <p>
895 * If a {@code Lookup} on {@code LC} in {@code M1} has a previous lookup class
896 * {@code PLC} on {@code M0}, the lookup with {@link #PUBLIC} mode can access
897 * the intersection of all public types that are accessible to {@code M1}
898 * with all public types that are accessible to {@code M0}. {@code M0}
899 * reads {@code M1} and hence the set of accessible types includes:
900 *
901 * <ul>
902 * <li>unconditional-exported packages from {@code M1}</li>
903 * <li>unconditional-exported packages from {@code M0} if {@code M1} reads {@code M0}</li>
904 * <li>
905 * unconditional-exported packages from a third module {@code M2}if both {@code M0}
906 * and {@code M1} read {@code M2}
907 * </li>
908 * <li>qualified-exported packages from {@code M1} to {@code M0}</li>
909 * <li>qualified-exported packages from {@code M0} to {@code M1} if {@code M1} reads {@code M0}</li>
910 * <li>
911 * qualified-exported packages from a third module {@code M2} to both {@code M0} and
912 * {@code M1} if both {@code M0} and {@code M1} read {@code M2}
913 * </li>
914 * </ul>
915 *
916 * <h2><a id="access-modes"></a>Access modes</h2>
917 *
918 * The table below shows the access modes of a {@code Lookup} produced by
919 * any of the following factory or transformation methods:
920 * <ul>
921 * <li>{@link #lookup() MethodHandles::lookup}</li>
922 * <li>{@link #publicLookup() MethodHandles::publicLookup}</li>
923 * <li>{@link #privateLookupIn(Class, Lookup) MethodHandles::privateLookupIn}</li>
924 * <li>{@link Lookup#in Lookup::in}</li>
925 * <li>{@link Lookup#dropLookupMode(int) Lookup::dropLookupMode}</li>
926 * </ul>
927 *
928 * <table class="striped">
929 * <caption style="display:none">
930 * Access mode summary
931 * </caption>
932 * <thead>
933 * <tr>
934 * <th scope="col">Lookup object</th>
935 * <th style="text-align:center">original</th>
936 * <th style="text-align:center">protected</th>
937 * <th style="text-align:center">private</th>
938 * <th style="text-align:center">package</th>
939 * <th style="text-align:center">module</th>
940 * <th style="text-align:center">public</th>
941 * </tr>
942 * </thead>
943 * <tbody>
944 * <tr>
945 * <th scope="row" style="text-align:left">{@code CL = MethodHandles.lookup()} in {@code C}</th>
946 * <td style="text-align:center">ORI</td>
947 * <td style="text-align:center">PRO</td>
948 * <td style="text-align:center">PRI</td>
949 * <td style="text-align:center">PAC</td>
950 * <td style="text-align:center">MOD</td>
951 * <td style="text-align:center">1R</td>
952 * </tr>
953 * <tr>
954 * <th scope="row" style="text-align:left">{@code CL.in(C1)} same package</th>
955 * <td></td>
956 * <td></td>
957 * <td></td>
958 * <td style="text-align:center">PAC</td>
959 * <td style="text-align:center">MOD</td>
960 * <td style="text-align:center">1R</td>
961 * </tr>
962 * <tr>
963 * <th scope="row" style="text-align:left">{@code CL.in(C1)} same module</th>
964 * <td></td>
965 * <td></td>
966 * <td></td>
967 * <td></td>
968 * <td style="text-align:center">MOD</td>
969 * <td style="text-align:center">1R</td>
970 * </tr>
971 * <tr>
972 * <th scope="row" style="text-align:left">{@code CL.in(D)} different module</th>
973 * <td></td>
974 * <td></td>
975 * <td></td>
976 * <td></td>
977 * <td></td>
978 * <td style="text-align:center">2R</td>
979 * </tr>
980 * <tr>
981 * <th scope="row" style="text-align:left">{@code CL.in(D).in(C)} hop back to module</th>
982 * <td></td>
983 * <td></td>
984 * <td></td>
985 * <td></td>
986 * <td></td>
987 * <td style="text-align:center">2R</td>
988 * </tr>
989 * <tr>
990 * <th scope="row" style="text-align:left">{@code PRI1 = privateLookupIn(C1,CL)}</th>
991 * <td></td>
992 * <td style="text-align:center">PRO</td>
993 * <td style="text-align:center">PRI</td>
994 * <td style="text-align:center">PAC</td>
995 * <td style="text-align:center">MOD</td>
996 * <td style="text-align:center">1R</td>
997 * </tr>
998 * <tr>
999 * <th scope="row" style="text-align:left">{@code PRI1a = privateLookupIn(C,PRI1)}</th>
1000 * <td></td>
1001 * <td style="text-align:center">PRO</td>
1002 * <td style="text-align:center">PRI</td>
1003 * <td style="text-align:center">PAC</td>
1004 * <td style="text-align:center">MOD</td>
1005 * <td style="text-align:center">1R</td>
1006 * </tr>
1007 * <tr>
1008 * <th scope="row" style="text-align:left">{@code PRI1.in(C1)} same package</th>
1009 * <td></td>
1010 * <td></td>
1011 * <td></td>
1012 * <td style="text-align:center">PAC</td>
1013 * <td style="text-align:center">MOD</td>
1014 * <td style="text-align:center">1R</td>
1015 * </tr>
1016 * <tr>
1017 * <th scope="row" style="text-align:left">{@code PRI1.in(C1)} different package</th>
1018 * <td></td>
1019 * <td></td>
1020 * <td></td>
1021 * <td></td>
1022 * <td style="text-align:center">MOD</td>
1023 * <td style="text-align:center">1R</td>
1024 * </tr>
1025 * <tr>
1026 * <th scope="row" style="text-align:left">{@code PRI1.in(D)} different module</th>
1027 * <td></td>
1028 * <td></td>
1029 * <td></td>
1030 * <td></td>
1031 * <td></td>
1032 * <td style="text-align:center">2R</td>
1033 * </tr>
1034 * <tr>
1035 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PROTECTED)}</th>
1036 * <td></td>
1037 * <td></td>
1038 * <td style="text-align:center">PRI</td>
1039 * <td style="text-align:center">PAC</td>
1040 * <td style="text-align:center">MOD</td>
1041 * <td style="text-align:center">1R</td>
1042 * </tr>
1043 * <tr>
1044 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PRIVATE)}</th>
1045 * <td></td>
1046 * <td></td>
1047 * <td></td>
1048 * <td style="text-align:center">PAC</td>
1049 * <td style="text-align:center">MOD</td>
1050 * <td style="text-align:center">1R</td>
1051 * </tr>
1052 * <tr>
1053 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PACKAGE)}</th>
1054 * <td></td>
1055 * <td></td>
1056 * <td></td>
1057 * <td></td>
1058 * <td style="text-align:center">MOD</td>
1059 * <td style="text-align:center">1R</td>
1060 * </tr>
1061 * <tr>
1062 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(MODULE)}</th>
1063 * <td></td>
1064 * <td></td>
1065 * <td></td>
1066 * <td></td>
1067 * <td></td>
1068 * <td style="text-align:center">1R</td>
1069 * </tr>
1070 * <tr>
1071 * <th scope="row" style="text-align:left">{@code PRI1.dropLookupMode(PUBLIC)}</th>
1072 * <td></td>
1073 * <td></td>
1074 * <td></td>
1075 * <td></td>
1076 * <td></td>
1077 * <td style="text-align:center">none</td>
1078 * <tr>
1079 * <th scope="row" style="text-align:left">{@code PRI2 = privateLookupIn(D,CL)}</th>
1080 * <td></td>
1081 * <td style="text-align:center">PRO</td>
1082 * <td style="text-align:center">PRI</td>
1083 * <td style="text-align:center">PAC</td>
1084 * <td></td>
1085 * <td style="text-align:center">2R</td>
1086 * </tr>
1087 * <tr>
1088 * <th scope="row" style="text-align:left">{@code privateLookupIn(D,PRI1)}</th>
1089 * <td></td>
1090 * <td style="text-align:center">PRO</td>
1091 * <td style="text-align:center">PRI</td>
1092 * <td style="text-align:center">PAC</td>
1093 * <td></td>
1094 * <td style="text-align:center">2R</td>
1095 * </tr>
1096 * <tr>
1097 * <th scope="row" style="text-align:left">{@code privateLookupIn(C,PRI2)} fails</th>
1098 * <td></td>
1099 * <td></td>
1100 * <td></td>
1101 * <td></td>
1102 * <td></td>
1103 * <td style="text-align:center">IAE</td>
1104 * </tr>
1105 * <tr>
1106 * <th scope="row" style="text-align:left">{@code PRI2.in(D2)} same package</th>
1107 * <td></td>
1108 * <td></td>
1109 * <td></td>
1110 * <td style="text-align:center">PAC</td>
1111 * <td></td>
1112 * <td style="text-align:center">2R</td>
1113 * </tr>
1114 * <tr>
1115 * <th scope="row" style="text-align:left">{@code PRI2.in(D2)} different package</th>
1116 * <td></td>
1117 * <td></td>
1118 * <td></td>
1119 * <td></td>
1120 * <td></td>
1121 * <td style="text-align:center">2R</td>
1122 * </tr>
1123 * <tr>
1124 * <th scope="row" style="text-align:left">{@code PRI2.in(C1)} hop back to module</th>
1125 * <td></td>
1126 * <td></td>
1127 * <td></td>
1128 * <td></td>
1129 * <td></td>
1130 * <td style="text-align:center">2R</td>
1131 * </tr>
1132 * <tr>
1133 * <th scope="row" style="text-align:left">{@code PRI2.in(E)} hop to third module</th>
1134 * <td></td>
1135 * <td></td>
1136 * <td></td>
1137 * <td></td>
1138 * <td></td>
1139 * <td style="text-align:center">none</td>
1140 * </tr>
1141 * <tr>
1142 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PROTECTED)}</th>
1143 * <td></td>
1144 * <td></td>
1145 * <td style="text-align:center">PRI</td>
1146 * <td style="text-align:center">PAC</td>
1147 * <td></td>
1148 * <td style="text-align:center">2R</td>
1149 * </tr>
1150 * <tr>
1151 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PRIVATE)}</th>
1152 * <td></td>
1153 * <td></td>
1154 * <td></td>
1155 * <td style="text-align:center">PAC</td>
1156 * <td></td>
1157 * <td style="text-align:center">2R</td>
1158 * </tr>
1159 * <tr>
1160 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PACKAGE)}</th>
1161 * <td></td>
1162 * <td></td>
1163 * <td></td>
1164 * <td></td>
1165 * <td></td>
1166 * <td style="text-align:center">2R</td>
1167 * </tr>
1168 * <tr>
1169 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(MODULE)}</th>
1170 * <td></td>
1171 * <td></td>
1172 * <td></td>
1173 * <td></td>
1174 * <td></td>
1175 * <td style="text-align:center">2R</td>
1176 * </tr>
1177 * <tr>
1178 * <th scope="row" style="text-align:left">{@code PRI2.dropLookupMode(PUBLIC)}</th>
1179 * <td></td>
1180 * <td></td>
1181 * <td></td>
1182 * <td></td>
1183 * <td></td>
1184 * <td style="text-align:center">none</td>
1185 * </tr>
1186 * <tr>
1187 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PROTECTED)}</th>
1188 * <td></td>
1189 * <td></td>
1190 * <td style="text-align:center">PRI</td>
1191 * <td style="text-align:center">PAC</td>
1192 * <td style="text-align:center">MOD</td>
1193 * <td style="text-align:center">1R</td>
1194 * </tr>
1195 * <tr>
1196 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PRIVATE)}</th>
1197 * <td></td>
1198 * <td></td>
1199 * <td></td>
1200 * <td style="text-align:center">PAC</td>
1201 * <td style="text-align:center">MOD</td>
1202 * <td style="text-align:center">1R</td>
1203 * </tr>
1204 * <tr>
1205 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PACKAGE)}</th>
1206 * <td></td>
1207 * <td></td>
1208 * <td></td>
1209 * <td></td>
1210 * <td style="text-align:center">MOD</td>
1211 * <td style="text-align:center">1R</td>
1212 * </tr>
1213 * <tr>
1214 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(MODULE)}</th>
1215 * <td></td>
1216 * <td></td>
1217 * <td></td>
1218 * <td></td>
1219 * <td></td>
1220 * <td style="text-align:center">1R</td>
1221 * </tr>
1222 * <tr>
1223 * <th scope="row" style="text-align:left">{@code CL.dropLookupMode(PUBLIC)}</th>
1224 * <td></td>
1225 * <td></td>
1226 * <td></td>
1227 * <td></td>
1228 * <td></td>
1229 * <td style="text-align:center">none</td>
1230 * </tr>
1231 * <tr>
1232 * <th scope="row" style="text-align:left">{@code PUB = publicLookup()}</th>
1233 * <td></td>
1234 * <td></td>
1235 * <td></td>
1236 * <td></td>
1237 * <td></td>
1238 * <td style="text-align:center">U</td>
1239 * </tr>
1240 * <tr>
1241 * <th scope="row" style="text-align:left">{@code PUB.in(D)} different module</th>
1242 * <td></td>
1243 * <td></td>
1244 * <td></td>
1245 * <td></td>
1246 * <td></td>
1247 * <td style="text-align:center">U</td>
1248 * </tr>
1249 * <tr>
1250 * <th scope="row" style="text-align:left">{@code PUB.in(D).in(E)} third module</th>
1251 * <td></td>
1252 * <td></td>
1253 * <td></td>
1254 * <td></td>
1255 * <td></td>
1256 * <td style="text-align:center">U</td>
1257 * </tr>
1258 * <tr>
1259 * <th scope="row" style="text-align:left">{@code PUB.dropLookupMode(UNCONDITIONAL)}</th>
1260 * <td></td>
1261 * <td></td>
1262 * <td></td>
1263 * <td></td>
1264 * <td></td>
1265 * <td style="text-align:center">none</td>
1266 * </tr>
1267 * <tr>
1268 * <th scope="row" style="text-align:left">{@code privateLookupIn(C1,PUB)} fails</th>
1269 * <td></td>
1270 * <td></td>
1271 * <td></td>
1272 * <td></td>
1273 * <td></td>
1274 * <td style="text-align:center">IAE</td>
1275 * </tr>
1276 * <tr>
1277 * <th scope="row" style="text-align:left">{@code ANY.in(X)}, for inaccessible {@code X}</th>
1278 * <td></td>
1279 * <td></td>
1280 * <td></td>
1281 * <td></td>
1282 * <td></td>
1283 * <td style="text-align:center">none</td>
1284 * </tr>
1285 * </tbody>
1286 * </table>
1287 *
1288 * <p>
1289 * Notes:
1290 * <ul>
1291 * <li>Class {@code C} and class {@code C1} are in module {@code M1},
1292 * but {@code D} and {@code D2} are in module {@code M2}, and {@code E}
1293 * is in module {@code M3}. {@code X} stands for class which is inaccessible
1294 * to the lookup. {@code ANY} stands for any of the example lookups.</li>
1295 * <li>{@code ORI} indicates {@link #ORIGINAL} bit set,
1296 * {@code PRO} indicates {@link #PROTECTED} bit set,
1297 * {@code PRI} indicates {@link #PRIVATE} bit set,
1298 * {@code PAC} indicates {@link #PACKAGE} bit set,
1299 * {@code MOD} indicates {@link #MODULE} bit set,
1300 * {@code 1R} and {@code 2R} indicate {@link #PUBLIC} bit set,
1301 * {@code U} indicates {@link #UNCONDITIONAL} bit set,
1302 * {@code IAE} indicates {@code IllegalAccessException} thrown.</li>
1303 * <li>Public access comes in three kinds:
1304 * <ul>
1305 * <li>unconditional ({@code U}): the lookup assumes readability.
1306 * The lookup has {@code null} previous lookup class.
1307 * <li>one-module-reads ({@code 1R}): the module access checking is
1308 * performed with respect to the lookup class. The lookup has {@code null}
1309 * previous lookup class.
1310 * <li>two-module-reads ({@code 2R}): the module access checking is
1311 * performed with respect to the lookup class and the previous lookup class.
1312 * The lookup has a non-null previous lookup class which is in a
1313 * different module from the current lookup class.
1314 * </ul>
1315 * <li>Any attempt to reach a third module loses all access.</li>
1316 * <li>If a target class {@code X} is not accessible to {@code Lookup::in}
1317 * all access modes are dropped.</li>
1318 * </ul>
1319 *
1320 * <h2><a id="secmgr"></a>Security manager interactions</h2>
1321 * Although bytecode instructions can only refer to classes in
1322 * a related class loader, this API can search for methods in any
1323 * class, as long as a reference to its {@code Class} object is
1324 * available. Such cross-loader references are also possible with the
1325 * Core Reflection API, and are impossible to bytecode instructions
1326 * such as {@code invokestatic} or {@code getfield}.
1327 * There is a {@linkplain java.lang.SecurityManager security manager API}
1328 * to allow applications to check such cross-loader references.
1329 * These checks apply to both the {@code MethodHandles.Lookup} API
1330 * and the Core Reflection API
1331 * (as found on {@link java.lang.Class Class}).
1332 * <p>
1333 * If a security manager is present, member and class lookups are subject to
1334 * additional checks.
1335 * From one to three calls are made to the security manager.
1336 * Any of these calls can refuse access by throwing a
1337 * {@link java.lang.SecurityException SecurityException}.
1338 * Define {@code smgr} as the security manager,
1339 * {@code lookc} as the lookup class of the current lookup object,
1340 * {@code refc} as the containing class in which the member
1341 * is being sought, and {@code defc} as the class in which the
1342 * member is actually defined.
1343 * (If a class or other type is being accessed,
1344 * the {@code refc} and {@code defc} values are the class itself.)
1345 * The value {@code lookc} is defined as <em>not present</em>
1346 * if the current lookup object does not have
1347 * {@linkplain #hasFullPrivilegeAccess() full privilege access}.
1348 * The calls are made according to the following rules:
1349 * <ul>
1350 * <li><b>Step 1:</b>
1351 * If {@code lookc} is not present, or if its class loader is not
1352 * the same as or an ancestor of the class loader of {@code refc},
1353 * then {@link SecurityManager#checkPackageAccess
1354 * smgr.checkPackageAccess(refcPkg)} is called,
1355 * where {@code refcPkg} is the package of {@code refc}.
1356 * <li><b>Step 2a:</b>
1357 * If the retrieved member is not public and
1358 * {@code lookc} is not present, then
1359 * {@link SecurityManager#checkPermission smgr.checkPermission}
1360 * with {@code RuntimePermission("accessDeclaredMembers")} is called.
1361 * <li><b>Step 2b:</b>
1362 * If the retrieved class has a {@code null} class loader,
1363 * and {@code lookc} is not present, then
1364 * {@link SecurityManager#checkPermission smgr.checkPermission}
1365 * with {@code RuntimePermission("getClassLoader")} is called.
1366 * <li><b>Step 3:</b>
1367 * If the retrieved member is not public,
1368 * and if {@code lookc} is not present,
1369 * and if {@code defc} and {@code refc} are different,
1370 * then {@link SecurityManager#checkPackageAccess
1371 * smgr.checkPackageAccess(defcPkg)} is called,
1372 * where {@code defcPkg} is the package of {@code defc}.
1373 * </ul>
1374 * Security checks are performed after other access checks have passed.
1375 * Therefore, the above rules presuppose a member or class that is public,
1376 * or else that is being accessed from a lookup class that has
1377 * rights to access the member or class.
1378 * <p>
1379 * If a security manager is present and the current lookup object does not have
1380 * {@linkplain #hasFullPrivilegeAccess() full privilege access}, then
1381 * {@link #defineClass(byte[]) defineClass},
1382 * {@link #defineHiddenClass(byte[], boolean, ClassOption...) defineHiddenClass},
1383 * {@link #defineHiddenClassWithClassData(byte[], Object, boolean, ClassOption...)
1384 * defineHiddenClassWithClassData}
1385 * calls {@link SecurityManager#checkPermission smgr.checkPermission}
1386 * with {@code RuntimePermission("defineClass")}.
1387 *
1388 * <h2><a id="callsens"></a>Caller sensitive methods</h2>
1389 * A small number of Java methods have a special property called caller sensitivity.
1390 * A <em>caller-sensitive</em> method can behave differently depending on the
1391 * identity of its immediate caller.
1392 * <p>
1393 * If a method handle for a caller-sensitive method is requested,
1394 * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> apply,
1395 * but they take account of the lookup class in a special way.
1396 * The resulting method handle behaves as if it were called
1397 * from an instruction contained in the lookup class,
1398 * so that the caller-sensitive method detects the lookup class.
1399 * (By contrast, the invoker of the method handle is disregarded.)
1400 * Thus, in the case of caller-sensitive methods,
1401 * different lookup classes may give rise to
1402 * differently behaving method handles.
1403 * <p>
1404 * In cases where the lookup object is
1405 * {@link MethodHandles#publicLookup() publicLookup()},
1406 * or some other lookup object without the
1407 * {@linkplain #ORIGINAL original access},
1408 * the lookup class is disregarded.
1409 * In such cases, no caller-sensitive method handle can be created,
1410 * access is forbidden, and the lookup fails with an
1411 * {@code IllegalAccessException}.
1412 * <p style="font-size:smaller;">
1413 * <em>Discussion:</em>
1414 * For example, the caller-sensitive method
1415 * {@link java.lang.Class#forName(String) Class.forName(x)}
1416 * can return varying classes or throw varying exceptions,
1417 * depending on the class loader of the class that calls it.
1418 * A public lookup of {@code Class.forName} will fail, because
1419 * there is no reasonable way to determine its bytecode behavior.
1420 * <p style="font-size:smaller;">
1421 * If an application caches method handles for broad sharing,
1422 * it should use {@code publicLookup()} to create them.
1423 * If there is a lookup of {@code Class.forName}, it will fail,
1424 * and the application must take appropriate action in that case.
1425 * It may be that a later lookup, perhaps during the invocation of a
1426 * bootstrap method, can incorporate the specific identity
1427 * of the caller, making the method accessible.
1428 * <p style="font-size:smaller;">
1429 * The function {@code MethodHandles.lookup} is caller sensitive
1430 * so that there can be a secure foundation for lookups.
1431 * Nearly all other methods in the JSR 292 API rely on lookup
1432 * objects to check access requests.
1433 */
1434 public static final
1435 class Lookup {
1436 /** The class on behalf of whom the lookup is being performed. */
1437 private final Class<?> lookupClass;
1438
1439 /** previous lookup class */
1440 private final Class<?> prevLookupClass;
1441
1442 /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */
1443 private final int allowedModes;
1444
1445 static {
1446 Reflection.registerFieldsToFilter(Lookup.class, Set.of("lookupClass", "allowedModes"));
1447 }
1448
1449 /** A single-bit mask representing {@code public} access,
1450 * which may contribute to the result of {@link #lookupModes lookupModes}.
1451 * The value, {@code 0x01}, happens to be the same as the value of the
1452 * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.
1453 * <p>
1454 * A {@code Lookup} with this lookup mode performs cross-module access check
1455 * with respect to the {@linkplain #lookupClass() lookup class} and
1456 * {@linkplain #previousLookupClass() previous lookup class} if present.
1457 */
1458 public static final int PUBLIC = Modifier.PUBLIC;
1459
1460 /** A single-bit mask representing {@code private} access,
1461 * which may contribute to the result of {@link #lookupModes lookupModes}.
1462 * The value, {@code 0x02}, happens to be the same as the value of the
1463 * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.
1464 */
1465 public static final int PRIVATE = Modifier.PRIVATE;
1466
1467 /** A single-bit mask representing {@code protected} access,
1468 * which may contribute to the result of {@link #lookupModes lookupModes}.
1469 * The value, {@code 0x04}, happens to be the same as the value of the
1470 * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.
1471 */
1472 public static final int PROTECTED = Modifier.PROTECTED;
1473
1474 /** A single-bit mask representing {@code package} access (default access),
1475 * which may contribute to the result of {@link #lookupModes lookupModes}.
1476 * The value is {@code 0x08}, which does not correspond meaningfully to
1477 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1478 */
1479 public static final int PACKAGE = Modifier.STATIC;
1480
1481 /** A single-bit mask representing {@code module} access,
1482 * which may contribute to the result of {@link #lookupModes lookupModes}.
1483 * The value is {@code 0x10}, which does not correspond meaningfully to
1484 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1485 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup}
1486 * with this lookup mode can access all public types in the module of the
1487 * lookup class and public types in packages exported by other modules
1488 * to the module of the lookup class.
1489 * <p>
1490 * If this lookup mode is set, the {@linkplain #previousLookupClass()
1491 * previous lookup class} is always {@code null}.
1492 *
1493 * @since 9
1494 */
1495 public static final int MODULE = PACKAGE << 1;
1496
1497 /** A single-bit mask representing {@code unconditional} access
1498 * which may contribute to the result of {@link #lookupModes lookupModes}.
1499 * The value is {@code 0x20}, which does not correspond meaningfully to
1500 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1501 * A {@code Lookup} with this lookup mode assumes {@linkplain
1502 * java.lang.Module#canRead(java.lang.Module) readability}.
1503 * This lookup mode can access all public members of public types
1504 * of all modules when the type is in a package that is {@link
1505 * java.lang.Module#isExported(String) exported unconditionally}.
1506 *
1507 * <p>
1508 * If this lookup mode is set, the {@linkplain #previousLookupClass()
1509 * previous lookup class} is always {@code null}.
1510 *
1511 * @since 9
1512 * @see #publicLookup()
1513 */
1514 public static final int UNCONDITIONAL = PACKAGE << 2;
1515
1516 /** A single-bit mask representing {@code original} access
1517 * which may contribute to the result of {@link #lookupModes lookupModes}.
1518 * The value is {@code 0x40}, which does not correspond meaningfully to
1519 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
1520 *
1521 * <p>
1522 * If this lookup mode is set, the {@code Lookup} object must be
1523 * created by the original lookup class by calling
1524 * {@link MethodHandles#lookup()} method or by a bootstrap method
1525 * invoked by the VM. The {@code Lookup} object with this lookup
1526 * mode has {@linkplain #hasFullPrivilegeAccess() full privilege access}.
1527 *
1528 * @since 16
1529 */
1530 public static final int ORIGINAL = PACKAGE << 3;
1531
1532 private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE | MODULE | UNCONDITIONAL | ORIGINAL);
1533 private static final int FULL_POWER_MODES = (ALL_MODES & ~UNCONDITIONAL); // with original access
1534 private static final int TRUSTED = -1;
1535
1536 /*
1537 * Adjust PUBLIC => PUBLIC|MODULE|ORIGINAL|UNCONDITIONAL
1538 * Adjust 0 => PACKAGE
1539 */
1540 private static int fixmods(int mods) {
1541 mods &= (ALL_MODES - PACKAGE - MODULE - ORIGINAL - UNCONDITIONAL);
1542 if (Modifier.isPublic(mods))
1543 mods |= UNCONDITIONAL;
1544 return (mods != 0) ? mods : PACKAGE;
1545 }
1546
1547 /** Tells which class is performing the lookup. It is this class against
1548 * which checks are performed for visibility and access permissions.
1549 * <p>
1550 * If this lookup object has a {@linkplain #previousLookupClass() previous lookup class},
1551 * access checks are performed against both the lookup class and the previous lookup class.
1552 * <p>
1553 * The class implies a maximum level of access permission,
1554 * but the permissions may be additionally limited by the bitmask
1555 * {@link #lookupModes lookupModes}, which controls whether non-public members
1556 * can be accessed.
1557 * @return the lookup class, on behalf of which this lookup object finds members
1558 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1559 */
1560 public Class<?> lookupClass() {
1561 return lookupClass;
1562 }
1563
1564 /** Reports a lookup class in another module that this lookup object
1565 * was previously teleported from, or {@code null}.
1566 * <p>
1567 * A {@code Lookup} object produced by the factory methods, such as the
1568 * {@link #lookup() lookup()} and {@link #publicLookup() publicLookup()} method,
1569 * has {@code null} previous lookup class.
1570 * A {@code Lookup} object has a non-null previous lookup class
1571 * when this lookup was teleported from an old lookup class
1572 * in one module to a new lookup class in another module.
1573 *
1574 * @return the lookup class in another module that this lookup object was
1575 * previously teleported from, or {@code null}
1576 * @since 14
1577 * @see #in(Class)
1578 * @see MethodHandles#privateLookupIn(Class, Lookup)
1579 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1580 */
1581 public Class<?> previousLookupClass() {
1582 return prevLookupClass;
1583 }
1584
1585 // This is just for calling out to MethodHandleImpl.
1586 private Class<?> lookupClassOrNull() {
1587 return (allowedModes == TRUSTED) ? null : lookupClass;
1588 }
1589
1590 /** Tells which access-protection classes of members this lookup object can produce.
1591 * The result is a bit-mask of the bits
1592 * {@linkplain #PUBLIC PUBLIC (0x01)},
1593 * {@linkplain #PRIVATE PRIVATE (0x02)},
1594 * {@linkplain #PROTECTED PROTECTED (0x04)},
1595 * {@linkplain #PACKAGE PACKAGE (0x08)},
1596 * {@linkplain #MODULE MODULE (0x10)},
1597 * {@linkplain #UNCONDITIONAL UNCONDITIONAL (0x20)},
1598 * and {@linkplain #ORIGINAL ORIGINAL (0x40)}.
1599 * <p>
1600 * A freshly-created lookup object
1601 * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class} has
1602 * all possible bits set, except {@code UNCONDITIONAL}.
1603 * A lookup object on a new lookup class
1604 * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object}
1605 * may have some mode bits set to zero.
1606 * Mode bits can also be
1607 * {@linkplain java.lang.invoke.MethodHandles.Lookup#dropLookupMode directly cleared}.
1608 * Once cleared, mode bits cannot be restored from the downgraded lookup object.
1609 * The purpose of this is to restrict access via the new lookup object,
1610 * so that it can access only names which can be reached by the original
1611 * lookup object, and also by the new lookup class.
1612 * @return the lookup modes, which limit the kinds of access performed by this lookup object
1613 * @see #in
1614 * @see #dropLookupMode
1615 */
1616 public int lookupModes() {
1617 return allowedModes & ALL_MODES;
1618 }
1619
1620 /** Embody the current class (the lookupClass) as a lookup class
1621 * for method handle creation.
1622 * Must be called by from a method in this package,
1623 * which in turn is called by a method not in this package.
1624 */
1625 Lookup(Class<?> lookupClass) {
1626 this(lookupClass, null, FULL_POWER_MODES);
1627 }
1628
1629 private Lookup(Class<?> lookupClass, Class<?> prevLookupClass, int allowedModes) {
1630 assert prevLookupClass == null || ((allowedModes & MODULE) == 0
1631 && prevLookupClass.getModule() != lookupClass.getModule());
1632 assert !lookupClass.isArray() && !lookupClass.isPrimitive();
1633 this.lookupClass = lookupClass;
1634 this.prevLookupClass = prevLookupClass;
1635 this.allowedModes = allowedModes;
1636 }
1637
1638 private static Lookup newLookup(Class<?> lookupClass, Class<?> prevLookupClass, int allowedModes) {
1639 // make sure we haven't accidentally picked up a privileged class:
1640 checkUnprivilegedlookupClass(lookupClass);
1641 return new Lookup(lookupClass, prevLookupClass, allowedModes);
1642 }
1643
1644 /**
1645 * Creates a lookup on the specified new lookup class.
1646 * The resulting object will report the specified
1647 * class as its own {@link #lookupClass() lookupClass}.
1648 *
1649 * <p>
1650 * However, the resulting {@code Lookup} object is guaranteed
1651 * to have no more access capabilities than the original.
1652 * In particular, access capabilities can be lost as follows:<ul>
1653 * <li>If the new lookup class is different from the old lookup class,
1654 * i.e. {@link #ORIGINAL ORIGINAL} access is lost.
1655 * <li>If the new lookup class is in a different module from the old one,
1656 * i.e. {@link #MODULE MODULE} access is lost.
1657 * <li>If the new lookup class is in a different package
1658 * than the old one, protected and default (package) members will not be accessible,
1659 * i.e. {@link #PROTECTED PROTECTED} and {@link #PACKAGE PACKAGE} access are lost.
1660 * <li>If the new lookup class is not within the same package member
1661 * as the old one, private members will not be accessible, and protected members
1662 * will not be accessible by virtue of inheritance,
1663 * i.e. {@link #PRIVATE PRIVATE} access is lost.
1664 * (Protected members may continue to be accessible because of package sharing.)
1665 * <li>If the new lookup class is not
1666 * {@linkplain #accessClass(Class) accessible} to this lookup,
1667 * then no members, not even public members, will be accessible
1668 * i.e. all access modes are lost.
1669 * <li>If the new lookup class, the old lookup class and the previous lookup class
1670 * are all in different modules i.e. teleporting to a third module,
1671 * all access modes are lost.
1672 * </ul>
1673 * <p>
1674 * The new previous lookup class is chosen as follows:
1675 * <ul>
1676 * <li>If the new lookup object has {@link #UNCONDITIONAL UNCONDITIONAL} bit,
1677 * the new previous lookup class is {@code null}.
1678 * <li>If the new lookup class is in the same module as the old lookup class,
1679 * the new previous lookup class is the old previous lookup class.
1680 * <li>If the new lookup class is in a different module from the old lookup class,
1681 * the new previous lookup class is the old lookup class.
1682 *</ul>
1683 * <p>
1684 * The resulting lookup's capabilities for loading classes
1685 * (used during {@link #findClass} invocations)
1686 * are determined by the lookup class' loader,
1687 * which may change due to this operation.
1688 *
1689 * @param requestedLookupClass the desired lookup class for the new lookup object
1690 * @return a lookup object which reports the desired lookup class, or the same object
1691 * if there is no change
1692 * @throws IllegalArgumentException if {@code requestedLookupClass} is a primitive type or void or array class
1693 * @throws NullPointerException if the argument is null
1694 *
1695 * @see #accessClass(Class)
1696 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
1697 */
1698 public Lookup in(Class<?> requestedLookupClass) {
1699 Objects.requireNonNull(requestedLookupClass);
1700 if (requestedLookupClass.isPrimitive())
1701 throw new IllegalArgumentException(requestedLookupClass + " is a primitive class");
1702 if (requestedLookupClass.isArray())
1703 throw new IllegalArgumentException(requestedLookupClass + " is an array class");
1704
1705 if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all
1706 return new Lookup(requestedLookupClass, null, FULL_POWER_MODES);
1707 if (requestedLookupClass == this.lookupClass)
1708 return this; // keep same capabilities
1709 int newModes = (allowedModes & FULL_POWER_MODES) & ~ORIGINAL;
1710 Module fromModule = this.lookupClass.getModule();
1711 Module targetModule = requestedLookupClass.getModule();
1712 Class<?> plc = this.previousLookupClass();
1713 if ((this.allowedModes & UNCONDITIONAL) != 0) {
1714 assert plc == null;
1715 newModes = UNCONDITIONAL;
1716 } else if (fromModule != targetModule) {
1717 if (plc != null && !VerifyAccess.isSameModule(plc, requestedLookupClass)) {
1718 // allow hopping back and forth between fromModule and plc's module
1719 // but not the third module
1720 newModes = 0;
1721 }
1722 // drop MODULE access
1723 newModes &= ~(MODULE|PACKAGE|PRIVATE|PROTECTED);
1724 // teleport from this lookup class
1725 plc = this.lookupClass;
1726 }
1727 if ((newModes & PACKAGE) != 0
1728 && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {
1729 newModes &= ~(PACKAGE|PRIVATE|PROTECTED);
1730 }
1731 // Allow nestmate lookups to be created without special privilege:
1732 if ((newModes & PRIVATE) != 0
1733 && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {
1734 newModes &= ~(PRIVATE|PROTECTED);
1735 }
1736 if ((newModes & (PUBLIC|UNCONDITIONAL)) != 0
1737 && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, this.prevLookupClass, allowedModes)) {
1738 // The requested class it not accessible from the lookup class.
1739 // No permissions.
1740 newModes = 0;
1741 }
1742 return newLookup(requestedLookupClass, plc, newModes);
1743 }
1744
1745 /**
1746 * Creates a lookup on the same lookup class which this lookup object
1747 * finds members, but with a lookup mode that has lost the given lookup mode.
1748 * The lookup mode to drop is one of {@link #PUBLIC PUBLIC}, {@link #MODULE
1749 * MODULE}, {@link #PACKAGE PACKAGE}, {@link #PROTECTED PROTECTED},
1750 * {@link #PRIVATE PRIVATE}, {@link #ORIGINAL ORIGINAL}, or
1751 * {@link #UNCONDITIONAL UNCONDITIONAL}.
1752 *
1753 * <p> If this lookup is a {@linkplain MethodHandles#publicLookup() public lookup},
1754 * this lookup has {@code UNCONDITIONAL} mode set and it has no other mode set.
1755 * When dropping {@code UNCONDITIONAL} on a public lookup then the resulting
1756 * lookup has no access.
1757 *
1758 * <p> If this lookup is not a public lookup, then the following applies
1759 * regardless of its {@linkplain #lookupModes() lookup modes}.
1760 * {@link #PROTECTED PROTECTED} and {@link #ORIGINAL ORIGINAL} are always
1761 * dropped and so the resulting lookup mode will never have these access
1762 * capabilities. When dropping {@code PACKAGE}
1763 * then the resulting lookup will not have {@code PACKAGE} or {@code PRIVATE}
1764 * access. When dropping {@code MODULE} then the resulting lookup will not
1765 * have {@code MODULE}, {@code PACKAGE}, or {@code PRIVATE} access.
1766 * When dropping {@code PUBLIC} then the resulting lookup has no access.
1767 *
1768 * @apiNote
1769 * A lookup with {@code PACKAGE} but not {@code PRIVATE} mode can safely
1770 * delegate non-public access within the package of the lookup class without
1771 * conferring <a href="MethodHandles.Lookup.html#privacc">private access</a>.
1772 * A lookup with {@code MODULE} but not
1773 * {@code PACKAGE} mode can safely delegate {@code PUBLIC} access within
1774 * the module of the lookup class without conferring package access.
1775 * A lookup with a {@linkplain #previousLookupClass() previous lookup class}
1776 * (and {@code PUBLIC} but not {@code MODULE} mode) can safely delegate access
1777 * to public classes accessible to both the module of the lookup class
1778 * and the module of the previous lookup class.
1779 *
1780 * @param modeToDrop the lookup mode to drop
1781 * @return a lookup object which lacks the indicated mode, or the same object if there is no change
1782 * @throws IllegalArgumentException if {@code modeToDrop} is not one of {@code PUBLIC},
1783 * {@code MODULE}, {@code PACKAGE}, {@code PROTECTED}, {@code PRIVATE}, {@code ORIGINAL}
1784 * or {@code UNCONDITIONAL}
1785 * @see MethodHandles#privateLookupIn
1786 * @since 9
1787 */
1788 public Lookup dropLookupMode(int modeToDrop) {
1789 int oldModes = lookupModes();
1790 int newModes = oldModes & ~(modeToDrop | PROTECTED | ORIGINAL);
1791 switch (modeToDrop) {
1792 case PUBLIC: newModes &= ~(FULL_POWER_MODES); break;
1793 case MODULE: newModes &= ~(PACKAGE | PRIVATE); break;
1794 case PACKAGE: newModes &= ~(PRIVATE); break;
1795 case PROTECTED:
1796 case PRIVATE:
1797 case ORIGINAL:
1798 case UNCONDITIONAL: break;
1799 default: throw new IllegalArgumentException(modeToDrop + " is not a valid mode to drop");
1800 }
1801 if (newModes == oldModes) return this; // return self if no change
1802 return newLookup(lookupClass(), previousLookupClass(), newModes);
1803 }
1804
1805 /**
1806 * Creates and links a class or interface from {@code bytes}
1807 * with the same class loader and in the same runtime package and
1808 * {@linkplain java.security.ProtectionDomain protection domain} as this lookup's
1809 * {@linkplain #lookupClass() lookup class} as if calling
1810 * {@link ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain)
1811 * ClassLoader::defineClass}.
1812 *
1813 * <p> The {@linkplain #lookupModes() lookup modes} for this lookup must include
1814 * {@link #PACKAGE PACKAGE} access as default (package) members will be
1815 * accessible to the class. The {@code PACKAGE} lookup mode serves to authenticate
1816 * that the lookup object was created by a caller in the runtime package (or derived
1817 * from a lookup originally created by suitably privileged code to a target class in
1818 * the runtime package). </p>
1819 *
1820 * <p> The {@code bytes} parameter is the class bytes of a valid class file (as defined
1821 * by the <em>The Java Virtual Machine Specification</em>) with a class name in the
1822 * same package as the lookup class. </p>
1823 *
1824 * <p> This method does not run the class initializer. The class initializer may
1825 * run at a later time, as detailed in section 12.4 of the <em>The Java Language
1826 * Specification</em>. </p>
1827 *
1828 * <p> If there is a security manager and this lookup does not have {@linkplain
1829 * #hasFullPrivilegeAccess() full privilege access}, its {@code checkPermission} method
1830 * is first called to check {@code RuntimePermission("defineClass")}. </p>
1831 *
1832 * @param bytes the class bytes
1833 * @return the {@code Class} object for the class
1834 * @throws IllegalAccessException if this lookup does not have {@code PACKAGE} access
1835 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure
1836 * @throws IllegalArgumentException if {@code bytes} denotes a class in a different package
1837 * than the lookup class or {@code bytes} is not a class or interface
1838 * ({@code ACC_MODULE} flag is set in the value of the {@code access_flags} item)
1839 * @throws VerifyError if the newly created class cannot be verified
1840 * @throws LinkageError if the newly created class cannot be linked for any other reason
1841 * @throws SecurityException if a security manager is present and it
1842 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1843 * @throws NullPointerException if {@code bytes} is {@code null}
1844 * @since 9
1845 * @see MethodHandles#privateLookupIn
1846 * @see Lookup#dropLookupMode
1847 * @see ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain)
1848 */
1849 public Class<?> defineClass(byte[] bytes) throws IllegalAccessException {
1850 ensureDefineClassPermission();
1851 if ((lookupModes() & PACKAGE) == 0)
1852 throw new IllegalAccessException("Lookup does not have PACKAGE access");
1853 return makeClassDefiner(bytes.clone()).defineClass(false);
1854 }
1855
1856 private void ensureDefineClassPermission() {
1857 if (allowedModes == TRUSTED) return;
1858
1859 if (!hasFullPrivilegeAccess()) {
1860 @SuppressWarnings("removal")
1861 SecurityManager sm = System.getSecurityManager();
1862 if (sm != null)
1863 sm.checkPermission(new RuntimePermission("defineClass"));
1864 }
1865 }
1866
1867 /**
1868 * The set of class options that specify whether a hidden class created by
1869 * {@link Lookup#defineHiddenClass(byte[], boolean, ClassOption...)
1870 * Lookup::defineHiddenClass} method is dynamically added as a new member
1871 * to the nest of a lookup class and/or whether a hidden class has
1872 * a strong relationship with the class loader marked as its defining loader.
1873 *
1874 * @since 15
1875 */
1876 public enum ClassOption {
1877 /**
1878 * Specifies that a hidden class be added to {@linkplain Class#getNestHost nest}
1879 * of a lookup class as a nestmate.
1880 *
1881 * <p> A hidden nestmate class has access to the private members of all
1882 * classes and interfaces in the same nest.
1883 *
1884 * @see Class#getNestHost()
1885 */
1886 NESTMATE(NESTMATE_CLASS),
1887
1888 /**
1889 * Specifies that a hidden class has a <em>strong</em>
1890 * relationship with the class loader marked as its defining loader,
1891 * as a normal class or interface has with its own defining loader.
1892 * This means that the hidden class may be unloaded if and only if
1893 * its defining loader is not reachable and thus may be reclaimed
1894 * by a garbage collector (JLS {@jls 12.7}).
1895 *
1896 * <p> By default, a hidden class or interface may be unloaded
1897 * even if the class loader that is marked as its defining loader is
1898 * <a href="../ref/package-summary.html#reachability">reachable</a>.
1899
1900 *
1901 * @jls 12.7 Unloading of Classes and Interfaces
1902 */
1903 STRONG(STRONG_LOADER_LINK);
1904
1905 /* the flag value is used by VM at define class time */
1906 private final int flag;
1907 ClassOption(int flag) {
1908 this.flag = flag;
1909 }
1910
1911 static int optionsToFlag(ClassOption[] options) {
1912 int flags = 0;
1913 for (ClassOption cp : options) {
1914 if ((flags & cp.flag) != 0) {
1915 throw new IllegalArgumentException("Duplicate ClassOption " + cp);
1916 }
1917 flags |= cp.flag;
1918 }
1919 return flags;
1920 }
1921 }
1922
1923 /**
1924 * Creates a <em>hidden</em> class or interface from {@code bytes},
1925 * returning a {@code Lookup} on the newly created class or interface.
1926 *
1927 * <p> Ordinarily, a class or interface {@code C} is created by a class loader,
1928 * which either defines {@code C} directly or delegates to another class loader.
1929 * A class loader defines {@code C} directly by invoking
1930 * {@link ClassLoader#defineClass(String, byte[], int, int, ProtectionDomain)
1931 * ClassLoader::defineClass}, which causes the Java Virtual Machine
1932 * to derive {@code C} from a purported representation in {@code class} file format.
1933 * In situations where use of a class loader is undesirable, a class or interface
1934 * {@code C} can be created by this method instead. This method is capable of
1935 * defining {@code C}, and thereby creating it, without invoking
1936 * {@code ClassLoader::defineClass}.
1937 * Instead, this method defines {@code C} as if by arranging for
1938 * the Java Virtual Machine to derive a nonarray class or interface {@code C}
1939 * from a purported representation in {@code class} file format
1940 * using the following rules:
1941 *
1942 * <ol>
1943 * <li> The {@linkplain #lookupModes() lookup modes} for this {@code Lookup}
1944 * must include {@linkplain #hasFullPrivilegeAccess() full privilege} access.
1945 * This level of access is needed to create {@code C} in the module
1946 * of the lookup class of this {@code Lookup}.</li>
1947 *
1948 * <li> The purported representation in {@code bytes} must be a {@code ClassFile}
1949 * structure (JVMS {@jvms 4.1}) of a supported major and minor version.
1950 * The major and minor version may differ from the {@code class} file version
1951 * of the lookup class of this {@code Lookup}.</li>
1952 *
1953 * <li> The value of {@code this_class} must be a valid index in the
1954 * {@code constant_pool} table, and the entry at that index must be a valid
1955 * {@code CONSTANT_Class_info} structure. Let {@code N} be the binary name
1956 * encoded in internal form that is specified by this structure. {@code N} must
1957 * denote a class or interface in the same package as the lookup class.</li>
1958 *
1959 * <li> Let {@code CN} be the string {@code N + "." + <suffix>},
1960 * where {@code <suffix>} is an unqualified name.
1961 *
1962 * <p> Let {@code newBytes} be the {@code ClassFile} structure given by
1963 * {@code bytes} with an additional entry in the {@code constant_pool} table,
1964 * indicating a {@code CONSTANT_Utf8_info} structure for {@code CN}, and
1965 * where the {@code CONSTANT_Class_info} structure indicated by {@code this_class}
1966 * refers to the new {@code CONSTANT_Utf8_info} structure.
1967 *
1968 * <p> Let {@code L} be the defining class loader of the lookup class of this {@code Lookup}.
1969 *
1970 * <p> {@code C} is derived with name {@code CN}, class loader {@code L}, and
1971 * purported representation {@code newBytes} as if by the rules of JVMS {@jvms 5.3.5},
1972 * with the following adjustments:
1973 * <ul>
1974 * <li> The constant indicated by {@code this_class} is permitted to specify a name
1975 * that includes a single {@code "."} character, even though this is not a valid
1976 * binary class or interface name in internal form.</li>
1977 *
1978 * <li> The Java Virtual Machine marks {@code L} as the defining class loader of {@code C},
1979 * but no class loader is recorded as an initiating class loader of {@code C}.</li>
1980 *
1981 * <li> {@code C} is considered to have the same runtime
1982 * {@linkplain Class#getPackage() package}, {@linkplain Class#getModule() module}
1983 * and {@linkplain java.security.ProtectionDomain protection domain}
1984 * as the lookup class of this {@code Lookup}.
1985 * <li> Let {@code GN} be the binary name obtained by taking {@code N}
1986 * (a binary name encoded in internal form) and replacing ASCII forward slashes with
1987 * ASCII periods. For the instance of {@link java.lang.Class} representing {@code C}:
1988 * <ul>
1989 * <li> {@link Class#getName()} returns the string {@code GN + "/" + <suffix>},
1990 * even though this is not a valid binary class or interface name.</li>
1991 * <li> {@link Class#descriptorString()} returns the string
1992 * {@code "L" + N + "." + <suffix> + ";"},
1993 * even though this is not a valid type descriptor name.</li>
1994 * <li> {@link Class#describeConstable()} returns an empty optional as {@code C}
1995 * cannot be described in {@linkplain java.lang.constant.ClassDesc nominal form}.</li>
1996 * </ul>
1997 * </ul>
1998 * </li>
1999 * </ol>
2000 *
2001 * <p> After {@code C} is derived, it is linked by the Java Virtual Machine.
2002 * Linkage occurs as specified in JVMS {@jvms 5.4.3}, with the following adjustments:
2003 * <ul>
2004 * <li> During verification, whenever it is necessary to load the class named
2005 * {@code CN}, the attempt succeeds, producing class {@code C}. No request is
2006 * made of any class loader.</li>
2007 *
2008 * <li> On any attempt to resolve the entry in the run-time constant pool indicated
2009 * by {@code this_class}, the symbolic reference is considered to be resolved to
2010 * {@code C} and resolution always succeeds immediately.</li>
2011 * </ul>
2012 *
2013 * <p> If the {@code initialize} parameter is {@code true},
2014 * then {@code C} is initialized by the Java Virtual Machine.
2015 *
2016 * <p> The newly created class or interface {@code C} serves as the
2017 * {@linkplain #lookupClass() lookup class} of the {@code Lookup} object
2018 * returned by this method. {@code C} is <em>hidden</em> in the sense that
2019 * no other class or interface can refer to {@code C} via a constant pool entry.
2020 * That is, a hidden class or interface cannot be named as a supertype, a field type,
2021 * a method parameter type, or a method return type by any other class.
2022 * This is because a hidden class or interface does not have a binary name, so
2023 * there is no internal form available to record in any class's constant pool.
2024 * A hidden class or interface is not discoverable by {@link Class#forName(String, boolean, ClassLoader)},
2025 * {@link ClassLoader#loadClass(String, boolean)}, or {@link #findClass(String)}, and
2026 * is not {@linkplain java.instrument/java.lang.instrument.Instrumentation#isModifiableClass(Class)
2027 * modifiable} by Java agents or tool agents using the <a href="{@docRoot}/../specs/jvmti.html">
2028 * JVM Tool Interface</a>.
2029 *
2030 * <p> A class or interface created by
2031 * {@linkplain ClassLoader#defineClass(String, byte[], int, int, ProtectionDomain)
2032 * a class loader} has a strong relationship with that class loader.
2033 * That is, every {@code Class} object contains a reference to the {@code ClassLoader}
2034 * that {@linkplain Class#getClassLoader() defined it}.
2035 * This means that a class created by a class loader may be unloaded if and
2036 * only if its defining loader is not reachable and thus may be reclaimed
2037 * by a garbage collector (JLS {@jls 12.7}).
2038 *
2039 * By default, however, a hidden class or interface may be unloaded even if
2040 * the class loader that is marked as its defining loader is
2041 * <a href="../ref/package-summary.html#reachability">reachable</a>.
2042 * This behavior is useful when a hidden class or interface serves multiple
2043 * classes defined by arbitrary class loaders. In other cases, a hidden
2044 * class or interface may be linked to a single class (or a small number of classes)
2045 * with the same defining loader as the hidden class or interface.
2046 * In such cases, where the hidden class or interface must be coterminous
2047 * with a normal class or interface, the {@link ClassOption#STRONG STRONG}
2048 * option may be passed in {@code options}.
2049 * This arranges for a hidden class to have the same strong relationship
2050 * with the class loader marked as its defining loader,
2051 * as a normal class or interface has with its own defining loader.
2052 *
2053 * If {@code STRONG} is not used, then the invoker of {@code defineHiddenClass}
2054 * may still prevent a hidden class or interface from being
2055 * unloaded by ensuring that the {@code Class} object is reachable.
2056 *
2057 * <p> The unloading characteristics are set for each hidden class when it is
2058 * defined, and cannot be changed later. An advantage of allowing hidden classes
2059 * to be unloaded independently of the class loader marked as their defining loader
2060 * is that a very large number of hidden classes may be created by an application.
2061 * In contrast, if {@code STRONG} is used, then the JVM may run out of memory,
2062 * just as if normal classes were created by class loaders.
2063 *
2064 * <p> Classes and interfaces in a nest are allowed to have mutual access to
2065 * their private members. The nest relationship is determined by
2066 * the {@code NestHost} attribute (JVMS {@jvms 4.7.28}) and
2067 * the {@code NestMembers} attribute (JVMS {@jvms 4.7.29}) in a {@code class} file.
2068 * By default, a hidden class belongs to a nest consisting only of itself
2069 * because a hidden class has no binary name.
2070 * The {@link ClassOption#NESTMATE NESTMATE} option can be passed in {@code options}
2071 * to create a hidden class or interface {@code C} as a member of a nest.
2072 * The nest to which {@code C} belongs is not based on any {@code NestHost} attribute
2073 * in the {@code ClassFile} structure from which {@code C} was derived.
2074 * Instead, the following rules determine the nest host of {@code C}:
2075 * <ul>
2076 * <li>If the nest host of the lookup class of this {@code Lookup} has previously
2077 * been determined, then let {@code H} be the nest host of the lookup class.
2078 * Otherwise, the nest host of the lookup class is determined using the
2079 * algorithm in JVMS {@jvms 5.4.4}, yielding {@code H}.</li>
2080 * <li>The nest host of {@code C} is determined to be {@code H},
2081 * the nest host of the lookup class.</li>
2082 * </ul>
2083 *
2084 * <p> A hidden class or interface may be serializable, but this requires a custom
2085 * serialization mechanism in order to ensure that instances are properly serialized
2086 * and deserialized. The default serialization mechanism supports only classes and
2087 * interfaces that are discoverable by their class name.
2088 *
2089 * @param bytes the bytes that make up the class data,
2090 * in the format of a valid {@code class} file as defined by
2091 * <cite>The Java Virtual Machine Specification</cite>.
2092 * @param initialize if {@code true} the class will be initialized.
2093 * @param options {@linkplain ClassOption class options}
2094 * @return the {@code Lookup} object on the hidden class,
2095 * with {@linkplain #ORIGINAL original} and
2096 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege} access
2097 *
2098 * @throws IllegalAccessException if this {@code Lookup} does not have
2099 * {@linkplain #hasFullPrivilegeAccess() full privilege} access
2100 * @throws SecurityException if a security manager is present and it
2101 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2102 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure
2103 * @throws UnsupportedClassVersionError if {@code bytes} is not of a supported major or minor version
2104 * @throws IllegalArgumentException if {@code bytes} denotes a class in a different package
2105 * than the lookup class or {@code bytes} is not a class or interface
2106 * ({@code ACC_MODULE} flag is set in the value of the {@code access_flags} item)
2107 * @throws IncompatibleClassChangeError if the class or interface named as
2108 * the direct superclass of {@code C} is in fact an interface, or if any of the classes
2109 * or interfaces named as direct superinterfaces of {@code C} are not in fact interfaces
2110 * @throws ClassCircularityError if any of the superclasses or superinterfaces of
2111 * {@code C} is {@code C} itself
2112 * @throws VerifyError if the newly created class cannot be verified
2113 * @throws LinkageError if the newly created class cannot be linked for any other reason
2114 * @throws NullPointerException if any parameter is {@code null}
2115 *
2116 * @since 15
2117 * @see Class#isHidden()
2118 * @jvms 4.2.1 Binary Class and Interface Names
2119 * @jvms 4.2.2 Unqualified Names
2120 * @jvms 4.7.28 The {@code NestHost} Attribute
2121 * @jvms 4.7.29 The {@code NestMembers} Attribute
2122 * @jvms 5.4.3.1 Class and Interface Resolution
2123 * @jvms 5.4.4 Access Control
2124 * @jvms 5.3.5 Deriving a {@code Class} from a {@code class} File Representation
2125 * @jvms 5.4 Linking
2126 * @jvms 5.5 Initialization
2127 * @jls 12.7 Unloading of Classes and Interfaces
2128 */
2129 @SuppressWarnings("doclint:reference") // cross-module links
2130 public Lookup defineHiddenClass(byte[] bytes, boolean initialize, ClassOption... options)
2131 throws IllegalAccessException
2132 {
2133 Objects.requireNonNull(bytes);
2134 int flags = ClassOption.optionsToFlag(options);
2135 ensureDefineClassPermission();
2136 if (!hasFullPrivilegeAccess()) {
2137 throw new IllegalAccessException(this + " does not have full privilege access");
2138 }
2139
2140 return makeHiddenClassDefiner(bytes.clone(), false, flags).defineClassAsLookup(initialize);
2141 }
2142
2143 /**
2144 * Creates a <em>hidden</em> class or interface from {@code bytes} with associated
2145 * {@linkplain MethodHandles#classData(Lookup, String, Class) class data},
2146 * returning a {@code Lookup} on the newly created class or interface.
2147 *
2148 * <p> This method is equivalent to calling
2149 * {@link #defineHiddenClass(byte[], boolean, ClassOption...) defineHiddenClass(bytes, initialize, options)}
2150 * as if the hidden class is injected with a private static final <i>unnamed</i>
2151 * field which is initialized with the given {@code classData} at
2152 * the first instruction of the class initializer.
2153 * The newly created class is linked by the Java Virtual Machine.
2154 *
2155 * <p> The {@link MethodHandles#classData(Lookup, String, Class) MethodHandles::classData}
2156 * and {@link MethodHandles#classDataAt(Lookup, String, Class, int) MethodHandles::classDataAt}
2157 * methods can be used to retrieve the {@code classData}.
2158 *
2159 * @apiNote
2160 * A framework can create a hidden class with class data with one or more
2161 * objects and load the class data as dynamically-computed constant(s)
2162 * via a bootstrap method. {@link MethodHandles#classData(Lookup, String, Class)
2163 * Class data} is accessible only to the lookup object created by the newly
2164 * defined hidden class but inaccessible to other members in the same nest
2165 * (unlike private static fields that are accessible to nestmates).
2166 * Care should be taken w.r.t. mutability for example when passing
2167 * an array or other mutable structure through the class data.
2168 * Changing any value stored in the class data at runtime may lead to
2169 * unpredictable behavior.
2170 * If the class data is a {@code List}, it is good practice to make it
2171 * unmodifiable for example via {@link List#of List::of}.
2172 *
2173 * @param bytes the class bytes
2174 * @param classData pre-initialized class data
2175 * @param initialize if {@code true} the class will be initialized.
2176 * @param options {@linkplain ClassOption class options}
2177 * @return the {@code Lookup} object on the hidden class,
2178 * with {@linkplain #ORIGINAL original} and
2179 * {@linkplain Lookup#hasFullPrivilegeAccess() full privilege} access
2180 *
2181 * @throws IllegalAccessException if this {@code Lookup} does not have
2182 * {@linkplain #hasFullPrivilegeAccess() full privilege} access
2183 * @throws SecurityException if a security manager is present and it
2184 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2185 * @throws ClassFormatError if {@code bytes} is not a {@code ClassFile} structure
2186 * @throws UnsupportedClassVersionError if {@code bytes} is not of a supported major or minor version
2187 * @throws IllegalArgumentException if {@code bytes} denotes a class in a different package
2188 * than the lookup class or {@code bytes} is not a class or interface
2189 * ({@code ACC_MODULE} flag is set in the value of the {@code access_flags} item)
2190 * @throws IncompatibleClassChangeError if the class or interface named as
2191 * the direct superclass of {@code C} is in fact an interface, or if any of the classes
2192 * or interfaces named as direct superinterfaces of {@code C} are not in fact interfaces
2193 * @throws ClassCircularityError if any of the superclasses or superinterfaces of
2194 * {@code C} is {@code C} itself
2195 * @throws VerifyError if the newly created class cannot be verified
2196 * @throws LinkageError if the newly created class cannot be linked for any other reason
2197 * @throws NullPointerException if any parameter is {@code null}
2198 *
2199 * @since 16
2200 * @see Lookup#defineHiddenClass(byte[], boolean, ClassOption...)
2201 * @see Class#isHidden()
2202 * @see MethodHandles#classData(Lookup, String, Class)
2203 * @see MethodHandles#classDataAt(Lookup, String, Class, int)
2204 * @jvms 4.2.1 Binary Class and Interface Names
2205 * @jvms 4.2.2 Unqualified Names
2206 * @jvms 4.7.28 The {@code NestHost} Attribute
2207 * @jvms 4.7.29 The {@code NestMembers} Attribute
2208 * @jvms 5.4.3.1 Class and Interface Resolution
2209 * @jvms 5.4.4 Access Control
2210 * @jvms 5.3.5 Deriving a {@code Class} from a {@code class} File Representation
2211 * @jvms 5.4 Linking
2212 * @jvms 5.5 Initialization
2213 * @jls 12.7 Unloading of Classes and Interfaces
2214 */
2215 public Lookup defineHiddenClassWithClassData(byte[] bytes, Object classData, boolean initialize, ClassOption... options)
2216 throws IllegalAccessException
2217 {
2218 Objects.requireNonNull(bytes);
2219 Objects.requireNonNull(classData);
2220
2221 int flags = ClassOption.optionsToFlag(options);
2222
2223 ensureDefineClassPermission();
2224 if (!hasFullPrivilegeAccess()) {
2225 throw new IllegalAccessException(this + " does not have full privilege access");
2226 }
2227
2228 return makeHiddenClassDefiner(bytes.clone(), false, flags)
2229 .defineClassAsLookup(initialize, classData);
2230 }
2231
2232 // A default dumper for writing class files passed to Lookup::defineClass
2233 // and Lookup::defineHiddenClass to disk for debugging purposes. To enable,
2234 // set -Djdk.invoke.MethodHandle.dumpHiddenClassFiles or
2235 // -Djdk.invoke.MethodHandle.dumpHiddenClassFiles=true
2236 //
2237 // This default dumper does not dump hidden classes defined by LambdaMetafactory
2238 // and LambdaForms and method handle internals. They are dumped via
2239 // different ClassFileDumpers.
2240 private static ClassFileDumper defaultDumper() {
2241 return DEFAULT_DUMPER;
2242 }
2243
2244 private static final ClassFileDumper DEFAULT_DUMPER = ClassFileDumper.getInstance(
2245 "jdk.invoke.MethodHandle.dumpClassFiles", "DUMP_CLASS_FILES");
2246
2247 /**
2248 * This method checks the class file version and the structure of `this_class`.
2249 * and checks if the bytes is a class or interface (ACC_MODULE flag not set)
2250 * that is in the named package.
2251 *
2252 * @throws IllegalArgumentException if ACC_MODULE flag is set in access flags
2253 * or the class is not in the given package name.
2254 */
2255 static String validateAndFindInternalName(byte[] bytes, String pkgName) {
2256 int magic = readInt(bytes, 0);
2257 if (magic != ClassFile.MAGIC_NUMBER) {
2258 throw new ClassFormatError("Incompatible magic value: " + magic);
2259 }
2260 // We have to read major and minor this way as ClassFile API throws IAE
2261 // yet we want distinct ClassFormatError and UnsupportedClassVersionError
2262 int minor = readUnsignedShort(bytes, 4);
2263 int major = readUnsignedShort(bytes, 6);
2264
2265 if (!VM.isSupportedClassFileVersion(major, minor)) {
2266 throw new UnsupportedClassVersionError("Unsupported class file version " + major + "." + minor);
2267 }
2268
2269 String name;
2270 ClassDesc sym;
2271 int accessFlags;
2272 try {
2273 ClassModel cm = ClassFile.of().parse(bytes);
2274 var thisClass = cm.thisClass();
2275 name = thisClass.asInternalName();
2276 sym = thisClass.asSymbol();
2277 accessFlags = cm.flags().flagsMask();
2278 } catch (IllegalArgumentException e) {
2279 ClassFormatError cfe = new ClassFormatError();
2280 cfe.initCause(e);
2281 throw cfe;
2282 }
2283 // must be a class or interface
2284 if ((accessFlags & ACC_MODULE) != 0) {
2285 throw newIllegalArgumentException("Not a class or interface: ACC_MODULE flag is set");
2286 }
2287
2288 String pn = sym.packageName();
2289 if (!pn.equals(pkgName)) {
2290 throw newIllegalArgumentException(name + " not in same package as lookup class");
2291 }
2292
2293 return name;
2294 }
2295
2296 private static int readInt(byte[] bytes, int offset) {
2297 if ((offset + 4) > bytes.length) {
2298 throw new ClassFormatError("Invalid ClassFile structure");
2299 }
2300 return ((bytes[offset] & 0xFF) << 24)
2301 | ((bytes[offset + 1] & 0xFF) << 16)
2302 | ((bytes[offset + 2] & 0xFF) << 8)
2303 | (bytes[offset + 3] & 0xFF);
2304 }
2305
2306 private static int readUnsignedShort(byte[] bytes, int offset) {
2307 if ((offset+2) > bytes.length) {
2308 throw new ClassFormatError("Invalid ClassFile structure");
2309 }
2310 return ((bytes[offset] & 0xFF) << 8) | (bytes[offset + 1] & 0xFF);
2311 }
2312
2313 /*
2314 * Returns a ClassDefiner that creates a {@code Class} object of a normal class
2315 * from the given bytes.
2316 *
2317 * Caller should make a defensive copy of the arguments if needed
2318 * before calling this factory method.
2319 *
2320 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or
2321 * {@code bytes} denotes a class in a different package than the lookup class
2322 */
2323 private ClassDefiner makeClassDefiner(byte[] bytes) {
2324 var internalName = validateAndFindInternalName(bytes, lookupClass().getPackageName());
2325 return new ClassDefiner(this, internalName, bytes, STRONG_LOADER_LINK, defaultDumper());
2326 }
2327
2328 /**
2329 * Returns a ClassDefiner that creates a {@code Class} object of a normal class
2330 * from the given bytes. No package name check on the given bytes.
2331 *
2332 * @param internalName internal name
2333 * @param bytes class bytes
2334 * @param dumper dumper to write the given bytes to the dumper's output directory
2335 * @return ClassDefiner that defines a normal class of the given bytes.
2336 */
2337 ClassDefiner makeClassDefiner(String internalName, byte[] bytes, ClassFileDumper dumper) {
2338 // skip package name validation
2339 return new ClassDefiner(this, internalName, bytes, STRONG_LOADER_LINK, dumper);
2340 }
2341
2342 /**
2343 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2344 * from the given bytes. The name must be in the same package as the lookup class.
2345 *
2346 * Caller should make a defensive copy of the arguments if needed
2347 * before calling this factory method.
2348 *
2349 * @param bytes class bytes
2350 * @param dumper dumper to write the given bytes to the dumper's output directory
2351 * @return ClassDefiner that defines a hidden class of the given bytes.
2352 *
2353 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or
2354 * {@code bytes} denotes a class in a different package than the lookup class
2355 */
2356 ClassDefiner makeHiddenClassDefiner(byte[] bytes, ClassFileDumper dumper) {
2357 var internalName = validateAndFindInternalName(bytes, lookupClass().getPackageName());
2358 return makeHiddenClassDefiner(internalName, bytes, false, dumper, 0);
2359 }
2360
2361 /**
2362 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2363 * from the given bytes and options.
2364 * The name must be in the same package as the lookup class.
2365 *
2366 * Caller should make a defensive copy of the arguments if needed
2367 * before calling this factory method.
2368 *
2369 * @param bytes class bytes
2370 * @param flags class option flag mask
2371 * @param accessVmAnnotations true to give the hidden class access to VM annotations
2372 * @return ClassDefiner that defines a hidden class of the given bytes and options
2373 *
2374 * @throws IllegalArgumentException if {@code bytes} is not a class or interface or
2375 * {@code bytes} denotes a class in a different package than the lookup class
2376 */
2377 private ClassDefiner makeHiddenClassDefiner(byte[] bytes,
2378 boolean accessVmAnnotations,
2379 int flags) {
2380 var internalName = validateAndFindInternalName(bytes, lookupClass().getPackageName());
2381 return makeHiddenClassDefiner(internalName, bytes, accessVmAnnotations, defaultDumper(), flags);
2382 }
2383
2384 /**
2385 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2386 * from the given bytes and the given options. No package name check on the given bytes.
2387 *
2388 * @param internalName internal name that specifies the prefix of the hidden class
2389 * @param bytes class bytes
2390 * @param dumper dumper to write the given bytes to the dumper's output directory
2391 * @return ClassDefiner that defines a hidden class of the given bytes and options.
2392 */
2393 ClassDefiner makeHiddenClassDefiner(String internalName, byte[] bytes, ClassFileDumper dumper) {
2394 Objects.requireNonNull(dumper);
2395 // skip name and access flags validation
2396 return makeHiddenClassDefiner(internalName, bytes, false, dumper, 0);
2397 }
2398
2399 /**
2400 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2401 * from the given bytes and the given options. No package name check on the given bytes.
2402 *
2403 * @param internalName internal name that specifies the prefix of the hidden class
2404 * @param bytes class bytes
2405 * @param flags class options flag mask
2406 * @param dumper dumper to write the given bytes to the dumper's output directory
2407 * @return ClassDefiner that defines a hidden class of the given bytes and options.
2408 */
2409 ClassDefiner makeHiddenClassDefiner(String internalName, byte[] bytes, ClassFileDumper dumper, int flags) {
2410 Objects.requireNonNull(dumper);
2411 // skip name and access flags validation
2412 return makeHiddenClassDefiner(internalName, bytes, false, dumper, flags);
2413 }
2414
2415 /**
2416 * Returns a ClassDefiner that creates a {@code Class} object of a hidden class
2417 * from the given class file and options.
2418 *
2419 * @param internalName internal name
2420 * @param bytes Class byte array
2421 * @param flags class option flag mask
2422 * @param accessVmAnnotations true to give the hidden class access to VM annotations
2423 * @param dumper dumper to write the given bytes to the dumper's output directory
2424 */
2425 private ClassDefiner makeHiddenClassDefiner(String internalName,
2426 byte[] bytes,
2427 boolean accessVmAnnotations,
2428 ClassFileDumper dumper,
2429 int flags) {
2430 flags |= HIDDEN_CLASS;
2431 if (accessVmAnnotations | VM.isSystemDomainLoader(lookupClass.getClassLoader())) {
2432 // jdk.internal.vm.annotations are permitted for classes
2433 // defined to boot loader and platform loader
2434 flags |= ACCESS_VM_ANNOTATIONS;
2435 }
2436
2437 return new ClassDefiner(this, internalName, bytes, flags, dumper);
2438 }
2439
2440 record ClassDefiner(Lookup lookup, String internalName, byte[] bytes, int classFlags, ClassFileDumper dumper) {
2441 ClassDefiner {
2442 assert ((classFlags & HIDDEN_CLASS) != 0 || (classFlags & STRONG_LOADER_LINK) == STRONG_LOADER_LINK);
2443 }
2444
2445 Class<?> defineClass(boolean initialize) {
2446 return defineClass(initialize, null);
2447 }
2448
2449 Lookup defineClassAsLookup(boolean initialize) {
2450 Class<?> c = defineClass(initialize, null);
2451 return new Lookup(c, null, FULL_POWER_MODES);
2452 }
2453
2454 /**
2455 * Defines the class of the given bytes and the given classData.
2456 * If {@code initialize} parameter is true, then the class will be initialized.
2457 *
2458 * @param initialize true if the class to be initialized
2459 * @param classData classData or null
2460 * @return the class
2461 *
2462 * @throws LinkageError linkage error
2463 */
2464 Class<?> defineClass(boolean initialize, Object classData) {
2465 Class<?> lookupClass = lookup.lookupClass();
2466 ClassLoader loader = lookupClass.getClassLoader();
2467 ProtectionDomain pd = (loader != null) ? lookup.lookupClassProtectionDomain() : null;
2468 Class<?> c = null;
2469 try {
2470 c = SharedSecrets.getJavaLangAccess()
2471 .defineClass(loader, lookupClass, internalName, bytes, pd, initialize, classFlags, classData);
2472 assert !isNestmate() || c.getNestHost() == lookupClass.getNestHost();
2473 return c;
2474 } finally {
2475 // dump the classfile for debugging
2476 if (dumper.isEnabled()) {
2477 String name = internalName();
2478 if (c != null) {
2479 dumper.dumpClass(name, c, bytes);
2480 } else {
2481 dumper.dumpFailedClass(name, bytes);
2482 }
2483 }
2484 }
2485 }
2486
2487 /**
2488 * Defines the class of the given bytes and the given classData.
2489 * If {@code initialize} parameter is true, then the class will be initialized.
2490 *
2491 * @param initialize true if the class to be initialized
2492 * @param classData classData or null
2493 * @return a Lookup for the defined class
2494 *
2495 * @throws LinkageError linkage error
2496 */
2497 Lookup defineClassAsLookup(boolean initialize, Object classData) {
2498 Class<?> c = defineClass(initialize, classData);
2499 return new Lookup(c, null, FULL_POWER_MODES);
2500 }
2501
2502 private boolean isNestmate() {
2503 return (classFlags & NESTMATE_CLASS) != 0;
2504 }
2505 }
2506
2507 private ProtectionDomain lookupClassProtectionDomain() {
2508 ProtectionDomain pd = cachedProtectionDomain;
2509 if (pd == null) {
2510 cachedProtectionDomain = pd = SharedSecrets.getJavaLangAccess().protectionDomain(lookupClass);
2511 }
2512 return pd;
2513 }
2514
2515 // cached protection domain
2516 private volatile ProtectionDomain cachedProtectionDomain;
2517
2518 // Make sure outer class is initialized first.
2519 static { IMPL_NAMES.getClass(); }
2520
2521 /** Package-private version of lookup which is trusted. */
2522 static final Lookup IMPL_LOOKUP = new Lookup(Object.class, null, TRUSTED);
2523
2524 /** Version of lookup which is trusted minimally.
2525 * It can only be used to create method handles to publicly accessible
2526 * members in packages that are exported unconditionally.
2527 */
2528 static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, null, UNCONDITIONAL);
2529
2530 private static void checkUnprivilegedlookupClass(Class<?> lookupClass) {
2531 String name = lookupClass.getName();
2532 if (name.startsWith("java.lang.invoke."))
2533 throw newIllegalArgumentException("illegal lookupClass: "+lookupClass);
2534 }
2535
2536 /**
2537 * Displays the name of the class from which lookups are to be made,
2538 * followed by "/" and the name of the {@linkplain #previousLookupClass()
2539 * previous lookup class} if present.
2540 * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)
2541 * If there are restrictions on the access permitted to this lookup,
2542 * this is indicated by adding a suffix to the class name, consisting
2543 * of a slash and a keyword. The keyword represents the strongest
2544 * allowed access, and is chosen as follows:
2545 * <ul>
2546 * <li>If no access is allowed, the suffix is "/noaccess".
2547 * <li>If only unconditional access is allowed, the suffix is "/publicLookup".
2548 * <li>If only public access to types in exported packages is allowed, the suffix is "/public".
2549 * <li>If only public and module access are allowed, the suffix is "/module".
2550 * <li>If public and package access are allowed, the suffix is "/package".
2551 * <li>If public, package, and private access are allowed, the suffix is "/private".
2552 * </ul>
2553 * If none of the above cases apply, it is the case that
2554 * {@linkplain #hasFullPrivilegeAccess() full privilege access}
2555 * (public, module, package, private, and protected) is allowed.
2556 * In this case, no suffix is added.
2557 * This is true only of an object obtained originally from
2558 * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
2559 * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
2560 * always have restricted access, and will display a suffix.
2561 * <p>
2562 * (It may seem strange that protected access should be
2563 * stronger than private access. Viewed independently from
2564 * package access, protected access is the first to be lost,
2565 * because it requires a direct subclass relationship between
2566 * caller and callee.)
2567 * @see #in
2568 */
2569 @Override
2570 public String toString() {
2571 String cname = lookupClass.getName();
2572 if (prevLookupClass != null)
2573 cname += "/" + prevLookupClass.getName();
2574 switch (allowedModes) {
2575 case 0: // no privileges
2576 return cname + "/noaccess";
2577 case UNCONDITIONAL:
2578 return cname + "/publicLookup";
2579 case PUBLIC:
2580 return cname + "/public";
2581 case PUBLIC|MODULE:
2582 return cname + "/module";
2583 case PUBLIC|PACKAGE:
2584 case PUBLIC|MODULE|PACKAGE:
2585 return cname + "/package";
2586 case PUBLIC|PACKAGE|PRIVATE:
2587 case PUBLIC|MODULE|PACKAGE|PRIVATE:
2588 return cname + "/private";
2589 case PUBLIC|PACKAGE|PRIVATE|PROTECTED:
2590 case PUBLIC|MODULE|PACKAGE|PRIVATE|PROTECTED:
2591 case FULL_POWER_MODES:
2592 return cname;
2593 case TRUSTED:
2594 return "/trusted"; // internal only; not exported
2595 default: // Should not happen, but it's a bitfield...
2596 cname = cname + "/" + Integer.toHexString(allowedModes);
2597 assert(false) : cname;
2598 return cname;
2599 }
2600 }
2601
2602 /**
2603 * Produces a method handle for a static method.
2604 * The type of the method handle will be that of the method.
2605 * (Since static methods do not take receivers, there is no
2606 * additional receiver argument inserted into the method handle type,
2607 * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)
2608 * The method and all its argument types must be accessible to the lookup object.
2609 * <p>
2610 * The returned method handle will have
2611 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2612 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2613 * <p>
2614 * If the returned method handle is invoked, the method's class will
2615 * be initialized, if it has not already been initialized.
2616 * <p><b>Example:</b>
2617 * {@snippet lang="java" :
2618 import static java.lang.invoke.MethodHandles.*;
2619 import static java.lang.invoke.MethodType.*;
2620 ...
2621 MethodHandle MH_asList = publicLookup().findStatic(Arrays.class,
2622 "asList", methodType(List.class, Object[].class));
2623 assertEquals("[x, y]", MH_asList.invoke("x", "y").toString());
2624 * }
2625 * @param refc the class from which the method is accessed
2626 * @param name the name of the method
2627 * @param type the type of the method
2628 * @return the desired method handle
2629 * @throws NoSuchMethodException if the method does not exist
2630 * @throws IllegalAccessException if access checking fails,
2631 * or if the method is not {@code static},
2632 * or if the method's variable arity modifier bit
2633 * is set and {@code asVarargsCollector} fails
2634 * @throws SecurityException if a security manager is present and it
2635 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2636 * @throws NullPointerException if any argument is null
2637 */
2638 public MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2639 MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type);
2640 return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerLookup(method));
2641 }
2642
2643 /**
2644 * Produces a method handle for a virtual method.
2645 * The type of the method handle will be that of the method,
2646 * with the receiver type (usually {@code refc}) prepended.
2647 * The method and all its argument types must be accessible to the lookup object.
2648 * <p>
2649 * When called, the handle will treat the first argument as a receiver
2650 * and, for non-private methods, dispatch on the receiver's type to determine which method
2651 * implementation to enter.
2652 * For private methods the named method in {@code refc} will be invoked on the receiver.
2653 * (The dispatching action is identical with that performed by an
2654 * {@code invokevirtual} or {@code invokeinterface} instruction.)
2655 * <p>
2656 * The first argument will be of type {@code refc} if the lookup
2657 * class has full privileges to access the member. Otherwise
2658 * the member must be {@code protected} and the first argument
2659 * will be restricted in type to the lookup class.
2660 * <p>
2661 * The returned method handle will have
2662 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2663 * the method's variable arity modifier bit ({@code 0x0080}) is set.
2664 * <p>
2665 * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual}
2666 * instructions and method handles produced by {@code findVirtual},
2667 * if the class is {@code MethodHandle} and the name string is
2668 * {@code invokeExact} or {@code invoke}, the resulting
2669 * method handle is equivalent to one produced by
2670 * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or
2671 * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}
2672 * with the same {@code type} argument.
2673 * <p>
2674 * If the class is {@code VarHandle} and the name string corresponds to
2675 * the name of a signature-polymorphic access mode method, the resulting
2676 * method handle is equivalent to one produced by
2677 * {@link java.lang.invoke.MethodHandles#varHandleInvoker} with
2678 * the access mode corresponding to the name string and with the same
2679 * {@code type} arguments.
2680 * <p>
2681 * <b>Example:</b>
2682 * {@snippet lang="java" :
2683 import static java.lang.invoke.MethodHandles.*;
2684 import static java.lang.invoke.MethodType.*;
2685 ...
2686 MethodHandle MH_concat = publicLookup().findVirtual(String.class,
2687 "concat", methodType(String.class, String.class));
2688 MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class,
2689 "hashCode", methodType(int.class));
2690 MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class,
2691 "hashCode", methodType(int.class));
2692 assertEquals("xy", (String) MH_concat.invokeExact("x", "y"));
2693 assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy"));
2694 assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy"));
2695 // interface method:
2696 MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class,
2697 "subSequence", methodType(CharSequence.class, int.class, int.class));
2698 assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString());
2699 // constructor "internal method" must be accessed differently:
2700 MethodType MT_newString = methodType(void.class); //()V for new String()
2701 try { assertEquals("impossible", lookup()
2702 .findVirtual(String.class, "<init>", MT_newString));
2703 } catch (NoSuchMethodException ex) { } // OK
2704 MethodHandle MH_newString = publicLookup()
2705 .findConstructor(String.class, MT_newString);
2706 assertEquals("", (String) MH_newString.invokeExact());
2707 * }
2708 *
2709 * @param refc the class or interface from which the method is accessed
2710 * @param name the name of the method
2711 * @param type the type of the method, with the receiver argument omitted
2712 * @return the desired method handle
2713 * @throws NoSuchMethodException if the method does not exist
2714 * @throws IllegalAccessException if access checking fails,
2715 * or if the method is {@code static},
2716 * or if the method's variable arity modifier bit
2717 * is set and {@code asVarargsCollector} fails
2718 * @throws SecurityException if a security manager is present and it
2719 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2720 * @throws NullPointerException if any argument is null
2721 */
2722 public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2723 if (refc == MethodHandle.class) {
2724 MethodHandle mh = findVirtualForMH(name, type);
2725 if (mh != null) return mh;
2726 } else if (refc == VarHandle.class) {
2727 MethodHandle mh = findVirtualForVH(name, type);
2728 if (mh != null) return mh;
2729 }
2730 byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual);
2731 MemberName method = resolveOrFail(refKind, refc, name, type);
2732 return getDirectMethod(refKind, refc, method, findBoundCallerLookup(method));
2733 }
2734 private MethodHandle findVirtualForMH(String name, MethodType type) {
2735 // these names require special lookups because of the implicit MethodType argument
2736 if ("invoke".equals(name))
2737 return invoker(type);
2738 if ("invokeExact".equals(name))
2739 return exactInvoker(type);
2740 assert(!MemberName.isMethodHandleInvokeName(name));
2741 return null;
2742 }
2743 private MethodHandle findVirtualForVH(String name, MethodType type) {
2744 try {
2745 return varHandleInvoker(VarHandle.AccessMode.valueFromMethodName(name), type);
2746 } catch (IllegalArgumentException e) {
2747 return null;
2748 }
2749 }
2750
2751 /**
2752 * Produces a method handle which creates an object and initializes it, using
2753 * the constructor of the specified type.
2754 * The parameter types of the method handle will be those of the constructor,
2755 * while the return type will be a reference to the constructor's class.
2756 * The constructor and all its argument types must be accessible to the lookup object.
2757 * <p>
2758 * The requested type must have a return type of {@code void}.
2759 * (This is consistent with the JVM's treatment of constructor type descriptors.)
2760 * <p>
2761 * The returned method handle will have
2762 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
2763 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
2764 * <p>
2765 * If the returned method handle is invoked, the constructor's class will
2766 * be initialized, if it has not already been initialized.
2767 * <p><b>Example:</b>
2768 * {@snippet lang="java" :
2769 import static java.lang.invoke.MethodHandles.*;
2770 import static java.lang.invoke.MethodType.*;
2771 ...
2772 MethodHandle MH_newArrayList = publicLookup().findConstructor(
2773 ArrayList.class, methodType(void.class, Collection.class));
2774 Collection orig = Arrays.asList("x", "y");
2775 Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig);
2776 assert(orig != copy);
2777 assertEquals(orig, copy);
2778 // a variable-arity constructor:
2779 MethodHandle MH_newProcessBuilder = publicLookup().findConstructor(
2780 ProcessBuilder.class, methodType(void.class, String[].class));
2781 ProcessBuilder pb = (ProcessBuilder)
2782 MH_newProcessBuilder.invoke("x", "y", "z");
2783 assertEquals("[x, y, z]", pb.command().toString());
2784 * }
2785 *
2786 *
2787 * @param refc the class or interface from which the method is accessed
2788 * @param type the type of the method, with the receiver argument omitted, and a void return type
2789 * @return the desired method handle
2790 * @throws NoSuchMethodException if the constructor does not exist
2791 * @throws IllegalAccessException if access checking fails
2792 * or if the method's variable arity modifier bit
2793 * is set and {@code asVarargsCollector} fails
2794 * @throws SecurityException if a security manager is present and it
2795 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2796 * @throws NullPointerException if any argument is null
2797 */
2798 public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2799 if (refc.isArray()) {
2800 throw new NoSuchMethodException("no constructor for array class: " + refc.getName());
2801 }
2802 if (type.returnType() != void.class) {
2803 throw new NoSuchMethodException("Constructors must have void return type: " + refc.getName());
2804 }
2805 String name = ConstantDescs.INIT_NAME;
2806 MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type);
2807 return getDirectConstructor(refc, ctor);
2808 }
2809
2810 /**
2811 * Looks up a class by name from the lookup context defined by this {@code Lookup} object,
2812 * <a href="MethodHandles.Lookup.html#equiv">as if resolved</a> by an {@code ldc} instruction.
2813 * Such a resolution, as specified in JVMS {@jvms 5.4.3.1}, attempts to locate and load the class,
2814 * and then determines whether the class is accessible to this lookup object.
2815 * <p>
2816 * For a class or an interface, the name is the {@linkplain ClassLoader##binary-name binary name}.
2817 * For an array class of {@code n} dimensions, the name begins with {@code n} occurrences
2818 * of {@code '['} and followed by the element type as encoded in the
2819 * {@linkplain Class##nameFormat table} specified in {@link Class#getName}.
2820 * <p>
2821 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class},
2822 * its class loader, and the {@linkplain #lookupModes() lookup modes}.
2823 *
2824 * @param targetName the {@linkplain ClassLoader##binary-name binary name} of the class
2825 * or the string representing an array class
2826 * @return the requested class.
2827 * @throws SecurityException if a security manager is present and it
2828 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2829 * @throws LinkageError if the linkage fails
2830 * @throws ClassNotFoundException if the class cannot be loaded by the lookup class' loader.
2831 * @throws IllegalAccessException if the class is not accessible, using the allowed access
2832 * modes.
2833 * @throws NullPointerException if {@code targetName} is null
2834 * @since 9
2835 * @jvms 5.4.3.1 Class and Interface Resolution
2836 */
2837 public Class<?> findClass(String targetName) throws ClassNotFoundException, IllegalAccessException {
2838 Class<?> targetClass = Class.forName(targetName, false, lookupClass.getClassLoader());
2839 return accessClass(targetClass);
2840 }
2841
2842 /**
2843 * Ensures that {@code targetClass} has been initialized. The class
2844 * to be initialized must be {@linkplain #accessClass accessible}
2845 * to this {@code Lookup} object. This method causes {@code targetClass}
2846 * to be initialized if it has not been already initialized,
2847 * as specified in JVMS {@jvms 5.5}.
2848 *
2849 * <p>
2850 * This method returns when {@code targetClass} is fully initialized, or
2851 * when {@code targetClass} is being initialized by the current thread.
2852 *
2853 * @param <T> the type of the class to be initialized
2854 * @param targetClass the class to be initialized
2855 * @return {@code targetClass} that has been initialized, or that is being
2856 * initialized by the current thread.
2857 *
2858 * @throws IllegalArgumentException if {@code targetClass} is a primitive type or {@code void}
2859 * or array class
2860 * @throws IllegalAccessException if {@code targetClass} is not
2861 * {@linkplain #accessClass accessible} to this lookup
2862 * @throws ExceptionInInitializerError if the class initialization provoked
2863 * by this method fails
2864 * @throws SecurityException if a security manager is present and it
2865 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2866 * @since 15
2867 * @jvms 5.5 Initialization
2868 */
2869 public <T> Class<T> ensureInitialized(Class<T> targetClass) throws IllegalAccessException {
2870 if (targetClass.isPrimitive())
2871 throw new IllegalArgumentException(targetClass + " is a primitive class");
2872 if (targetClass.isArray())
2873 throw new IllegalArgumentException(targetClass + " is an array class");
2874
2875 if (!VerifyAccess.isClassAccessible(targetClass, lookupClass, prevLookupClass, allowedModes)) {
2876 throw makeAccessException(targetClass);
2877 }
2878 checkSecurityManager(targetClass);
2879
2880 // ensure class initialization
2881 Unsafe.getUnsafe().ensureClassInitialized(targetClass);
2882 return targetClass;
2883 }
2884
2885 /*
2886 * Returns IllegalAccessException due to access violation to the given targetClass.
2887 *
2888 * This method is called by {@link Lookup#accessClass} and {@link Lookup#ensureInitialized}
2889 * which verifies access to a class rather a member.
2890 */
2891 private IllegalAccessException makeAccessException(Class<?> targetClass) {
2892 String message = "access violation: "+ targetClass;
2893 if (this == MethodHandles.publicLookup()) {
2894 message += ", from public Lookup";
2895 } else {
2896 Module m = lookupClass().getModule();
2897 message += ", from " + lookupClass() + " (" + m + ")";
2898 if (prevLookupClass != null) {
2899 message += ", previous lookup " +
2900 prevLookupClass.getName() + " (" + prevLookupClass.getModule() + ")";
2901 }
2902 }
2903 return new IllegalAccessException(message);
2904 }
2905
2906 /**
2907 * Determines if a class can be accessed from the lookup context defined by
2908 * this {@code Lookup} object. The static initializer of the class is not run.
2909 * If {@code targetClass} is an array class, {@code targetClass} is accessible
2910 * if the element type of the array class is accessible. Otherwise,
2911 * {@code targetClass} is determined as accessible as follows.
2912 *
2913 * <p>
2914 * If {@code targetClass} is in the same module as the lookup class,
2915 * the lookup class is {@code LC} in module {@code M1} and
2916 * the previous lookup class is in module {@code M0} or
2917 * {@code null} if not present,
2918 * {@code targetClass} is accessible if and only if one of the following is true:
2919 * <ul>
2920 * <li>If this lookup has {@link #PRIVATE} access, {@code targetClass} is
2921 * {@code LC} or other class in the same nest of {@code LC}.</li>
2922 * <li>If this lookup has {@link #PACKAGE} access, {@code targetClass} is
2923 * in the same runtime package of {@code LC}.</li>
2924 * <li>If this lookup has {@link #MODULE} access, {@code targetClass} is
2925 * a public type in {@code M1}.</li>
2926 * <li>If this lookup has {@link #PUBLIC} access, {@code targetClass} is
2927 * a public type in a package exported by {@code M1} to at least {@code M0}
2928 * if the previous lookup class is present; otherwise, {@code targetClass}
2929 * is a public type in a package exported by {@code M1} unconditionally.</li>
2930 * </ul>
2931 *
2932 * <p>
2933 * Otherwise, if this lookup has {@link #UNCONDITIONAL} access, this lookup
2934 * can access public types in all modules when the type is in a package
2935 * that is exported unconditionally.
2936 * <p>
2937 * Otherwise, {@code targetClass} is in a different module from {@code lookupClass},
2938 * and if this lookup does not have {@code PUBLIC} access, {@code lookupClass}
2939 * is inaccessible.
2940 * <p>
2941 * Otherwise, if this lookup has no {@linkplain #previousLookupClass() previous lookup class},
2942 * {@code M1} is the module containing {@code lookupClass} and
2943 * {@code M2} is the module containing {@code targetClass},
2944 * then {@code targetClass} is accessible if and only if
2945 * <ul>
2946 * <li>{@code M1} reads {@code M2}, and
2947 * <li>{@code targetClass} is public and in a package exported by
2948 * {@code M2} at least to {@code M1}.
2949 * </ul>
2950 * <p>
2951 * Otherwise, if this lookup has a {@linkplain #previousLookupClass() previous lookup class},
2952 * {@code M1} and {@code M2} are as before, and {@code M0} is the module
2953 * containing the previous lookup class, then {@code targetClass} is accessible
2954 * if and only if one of the following is true:
2955 * <ul>
2956 * <li>{@code targetClass} is in {@code M0} and {@code M1}
2957 * {@linkplain Module#reads reads} {@code M0} and the type is
2958 * in a package that is exported to at least {@code M1}.
2959 * <li>{@code targetClass} is in {@code M1} and {@code M0}
2960 * {@linkplain Module#reads reads} {@code M1} and the type is
2961 * in a package that is exported to at least {@code M0}.
2962 * <li>{@code targetClass} is in a third module {@code M2} and both {@code M0}
2963 * and {@code M1} reads {@code M2} and the type is in a package
2964 * that is exported to at least both {@code M0} and {@code M2}.
2965 * </ul>
2966 * <p>
2967 * Otherwise, {@code targetClass} is not accessible.
2968 *
2969 * @param <T> the type of the class to be access-checked
2970 * @param targetClass the class to be access-checked
2971 * @return {@code targetClass} that has been access-checked
2972 * @throws IllegalAccessException if the class is not accessible from the lookup class
2973 * and previous lookup class, if present, using the allowed access modes.
2974 * @throws SecurityException if a security manager is present and it
2975 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
2976 * @throws NullPointerException if {@code targetClass} is {@code null}
2977 * @since 9
2978 * @see <a href="#cross-module-lookup">Cross-module lookups</a>
2979 */
2980 public <T> Class<T> accessClass(Class<T> targetClass) throws IllegalAccessException {
2981 if (!isClassAccessible(targetClass)) {
2982 throw makeAccessException(targetClass);
2983 }
2984 checkSecurityManager(targetClass);
2985 return targetClass;
2986 }
2987
2988 /**
2989 * Produces an early-bound method handle for a virtual method.
2990 * It will bypass checks for overriding methods on the receiver,
2991 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
2992 * instruction from within the explicitly specified {@code specialCaller}.
2993 * The type of the method handle will be that of the method,
2994 * with a suitably restricted receiver type prepended.
2995 * (The receiver type will be {@code specialCaller} or a subtype.)
2996 * The method and all its argument types must be accessible
2997 * to the lookup object.
2998 * <p>
2999 * Before method resolution,
3000 * if the explicitly specified caller class is not identical with the
3001 * lookup class, or if this lookup object does not have
3002 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
3003 * privileges, the access fails.
3004 * <p>
3005 * The returned method handle will have
3006 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3007 * the method's variable arity modifier bit ({@code 0x0080}) is set.
3008 * <p style="font-size:smaller;">
3009 * <em>(Note: JVM internal methods named {@value ConstantDescs#INIT_NAME}
3010 * are not visible to this API,
3011 * even though the {@code invokespecial} instruction can refer to them
3012 * in special circumstances. Use {@link #findConstructor findConstructor}
3013 * to access instance initialization methods in a safe manner.)</em>
3014 * <p><b>Example:</b>
3015 * {@snippet lang="java" :
3016 import static java.lang.invoke.MethodHandles.*;
3017 import static java.lang.invoke.MethodType.*;
3018 ...
3019 static class Listie extends ArrayList {
3020 public String toString() { return "[wee Listie]"; }
3021 static Lookup lookup() { return MethodHandles.lookup(); }
3022 }
3023 ...
3024 // no access to constructor via invokeSpecial:
3025 MethodHandle MH_newListie = Listie.lookup()
3026 .findConstructor(Listie.class, methodType(void.class));
3027 Listie l = (Listie) MH_newListie.invokeExact();
3028 try { assertEquals("impossible", Listie.lookup().findSpecial(
3029 Listie.class, "<init>", methodType(void.class), Listie.class));
3030 } catch (NoSuchMethodException ex) { } // OK
3031 // access to super and self methods via invokeSpecial:
3032 MethodHandle MH_super = Listie.lookup().findSpecial(
3033 ArrayList.class, "toString" , methodType(String.class), Listie.class);
3034 MethodHandle MH_this = Listie.lookup().findSpecial(
3035 Listie.class, "toString" , methodType(String.class), Listie.class);
3036 MethodHandle MH_duper = Listie.lookup().findSpecial(
3037 Object.class, "toString" , methodType(String.class), Listie.class);
3038 assertEquals("[]", (String) MH_super.invokeExact(l));
3039 assertEquals(""+l, (String) MH_this.invokeExact(l));
3040 assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method
3041 try { assertEquals("inaccessible", Listie.lookup().findSpecial(
3042 String.class, "toString", methodType(String.class), Listie.class));
3043 } catch (IllegalAccessException ex) { } // OK
3044 Listie subl = new Listie() { public String toString() { return "[subclass]"; } };
3045 assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method
3046 * }
3047 *
3048 * @param refc the class or interface from which the method is accessed
3049 * @param name the name of the method (which must not be "<init>")
3050 * @param type the type of the method, with the receiver argument omitted
3051 * @param specialCaller the proposed calling class to perform the {@code invokespecial}
3052 * @return the desired method handle
3053 * @throws NoSuchMethodException if the method does not exist
3054 * @throws IllegalAccessException if access checking fails,
3055 * or if the method is {@code static},
3056 * or if the method's variable arity modifier bit
3057 * is set and {@code asVarargsCollector} fails
3058 * @throws SecurityException if a security manager is present and it
3059 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3060 * @throws NullPointerException if any argument is null
3061 */
3062 public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,
3063 Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
3064 checkSpecialCaller(specialCaller, refc);
3065 Lookup specialLookup = this.in(specialCaller);
3066 MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type);
3067 return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerLookup(method));
3068 }
3069
3070 /**
3071 * Produces a method handle giving read access to a non-static field.
3072 * The type of the method handle will have a return type of the field's
3073 * value type.
3074 * The method handle's single argument will be the instance containing
3075 * the field.
3076 * Access checking is performed immediately on behalf of the lookup class.
3077 * @param refc the class or interface from which the method is accessed
3078 * @param name the field's name
3079 * @param type the field's type
3080 * @return a method handle which can load values from the field
3081 * @throws NoSuchFieldException if the field does not exist
3082 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
3083 * @throws SecurityException if a security manager is present and it
3084 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3085 * @throws NullPointerException if any argument is null
3086 * @see #findVarHandle(Class, String, Class)
3087 */
3088 public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3089 MemberName field = resolveOrFail(REF_getField, refc, name, type);
3090 return getDirectField(REF_getField, refc, field);
3091 }
3092
3093 /**
3094 * Produces a method handle giving write access to a non-static field.
3095 * The type of the method handle will have a void return type.
3096 * The method handle will take two arguments, the instance containing
3097 * the field, and the value to be stored.
3098 * The second argument will be of the field's value type.
3099 * Access checking is performed immediately on behalf of the lookup class.
3100 * @param refc the class or interface from which the method is accessed
3101 * @param name the field's name
3102 * @param type the field's type
3103 * @return a method handle which can store values into the field
3104 * @throws NoSuchFieldException if the field does not exist
3105 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
3106 * or {@code final}
3107 * @throws SecurityException if a security manager is present and it
3108 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3109 * @throws NullPointerException if any argument is null
3110 * @see #findVarHandle(Class, String, Class)
3111 */
3112 public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3113 MemberName field = resolveOrFail(REF_putField, refc, name, type);
3114 return getDirectField(REF_putField, refc, field);
3115 }
3116
3117 /**
3118 * Produces a VarHandle giving access to a non-static field {@code name}
3119 * of type {@code type} declared in a class of type {@code recv}.
3120 * The VarHandle's variable type is {@code type} and it has one
3121 * coordinate type, {@code recv}.
3122 * <p>
3123 * Access checking is performed immediately on behalf of the lookup
3124 * class.
3125 * <p>
3126 * Certain access modes of the returned VarHandle are unsupported under
3127 * the following conditions:
3128 * <ul>
3129 * <li>if the field is declared {@code final}, then the write, atomic
3130 * update, numeric atomic update, and bitwise atomic update access
3131 * modes are unsupported.
3132 * <li>if the field type is anything other than {@code byte},
3133 * {@code short}, {@code char}, {@code int}, {@code long},
3134 * {@code float}, or {@code double} then numeric atomic update
3135 * access modes are unsupported.
3136 * <li>if the field type is anything other than {@code boolean},
3137 * {@code byte}, {@code short}, {@code char}, {@code int} or
3138 * {@code long} then bitwise atomic update access modes are
3139 * unsupported.
3140 * </ul>
3141 * <p>
3142 * If the field is declared {@code volatile} then the returned VarHandle
3143 * will override access to the field (effectively ignore the
3144 * {@code volatile} declaration) in accordance to its specified
3145 * access modes.
3146 * <p>
3147 * If the field type is {@code float} or {@code double} then numeric
3148 * and atomic update access modes compare values using their bitwise
3149 * representation (see {@link Float#floatToRawIntBits} and
3150 * {@link Double#doubleToRawLongBits}, respectively).
3151 * @apiNote
3152 * Bitwise comparison of {@code float} values or {@code double} values,
3153 * as performed by the numeric and atomic update access modes, differ
3154 * from the primitive {@code ==} operator and the {@link Float#equals}
3155 * and {@link Double#equals} methods, specifically with respect to
3156 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
3157 * Care should be taken when performing a compare and set or a compare
3158 * and exchange operation with such values since the operation may
3159 * unexpectedly fail.
3160 * There are many possible NaN values that are considered to be
3161 * {@code NaN} in Java, although no IEEE 754 floating-point operation
3162 * provided by Java can distinguish between them. Operation failure can
3163 * occur if the expected or witness value is a NaN value and it is
3164 * transformed (perhaps in a platform specific manner) into another NaN
3165 * value, and thus has a different bitwise representation (see
3166 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
3167 * details).
3168 * The values {@code -0.0} and {@code +0.0} have different bitwise
3169 * representations but are considered equal when using the primitive
3170 * {@code ==} operator. Operation failure can occur if, for example, a
3171 * numeric algorithm computes an expected value to be say {@code -0.0}
3172 * and previously computed the witness value to be say {@code +0.0}.
3173 * @param recv the receiver class, of type {@code R}, that declares the
3174 * non-static field
3175 * @param name the field's name
3176 * @param type the field's type, of type {@code T}
3177 * @return a VarHandle giving access to non-static fields.
3178 * @throws NoSuchFieldException if the field does not exist
3179 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
3180 * @throws SecurityException if a security manager is present and it
3181 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3182 * @throws NullPointerException if any argument is null
3183 * @since 9
3184 */
3185 public VarHandle findVarHandle(Class<?> recv, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3186 MemberName getField = resolveOrFail(REF_getField, recv, name, type);
3187 MemberName putField = resolveOrFail(REF_putField, recv, name, type);
3188 return getFieldVarHandle(REF_getField, REF_putField, recv, getField, putField);
3189 }
3190
3191 /**
3192 * Produces a method handle giving read access to a static field.
3193 * The type of the method handle will have a return type of the field's
3194 * value type.
3195 * The method handle will take no arguments.
3196 * Access checking is performed immediately on behalf of the lookup class.
3197 * <p>
3198 * If the returned method handle is invoked, the field's class will
3199 * be initialized, if it has not already been initialized.
3200 * @param refc the class or interface from which the method is accessed
3201 * @param name the field's name
3202 * @param type the field's type
3203 * @return a method handle which can load values from the field
3204 * @throws NoSuchFieldException if the field does not exist
3205 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
3206 * @throws SecurityException if a security manager is present and it
3207 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3208 * @throws NullPointerException if any argument is null
3209 */
3210 public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3211 MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
3212 return getDirectField(REF_getStatic, refc, field);
3213 }
3214
3215 /**
3216 * Produces a method handle giving write access to a static field.
3217 * The type of the method handle will have a void return type.
3218 * The method handle will take a single
3219 * argument, of the field's value type, the value to be stored.
3220 * Access checking is performed immediately on behalf of the lookup class.
3221 * <p>
3222 * If the returned method handle is invoked, the field's class will
3223 * be initialized, if it has not already been initialized.
3224 * @param refc the class or interface from which the method is accessed
3225 * @param name the field's name
3226 * @param type the field's type
3227 * @return a method handle which can store values into the field
3228 * @throws NoSuchFieldException if the field does not exist
3229 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
3230 * or is {@code final}
3231 * @throws SecurityException if a security manager is present and it
3232 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3233 * @throws NullPointerException if any argument is null
3234 */
3235 public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3236 MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
3237 return getDirectField(REF_putStatic, refc, field);
3238 }
3239
3240 /**
3241 * Produces a VarHandle giving access to a static field {@code name} of
3242 * type {@code type} declared in a class of type {@code decl}.
3243 * The VarHandle's variable type is {@code type} and it has no
3244 * coordinate types.
3245 * <p>
3246 * Access checking is performed immediately on behalf of the lookup
3247 * class.
3248 * <p>
3249 * If the returned VarHandle is operated on, the declaring class will be
3250 * initialized, if it has not already been initialized.
3251 * <p>
3252 * Certain access modes of the returned VarHandle are unsupported under
3253 * the following conditions:
3254 * <ul>
3255 * <li>if the field is declared {@code final}, then the write, atomic
3256 * update, numeric atomic update, and bitwise atomic update access
3257 * modes are unsupported.
3258 * <li>if the field type is anything other than {@code byte},
3259 * {@code short}, {@code char}, {@code int}, {@code long},
3260 * {@code float}, or {@code double}, then numeric atomic update
3261 * access modes are unsupported.
3262 * <li>if the field type is anything other than {@code boolean},
3263 * {@code byte}, {@code short}, {@code char}, {@code int} or
3264 * {@code long} then bitwise atomic update access modes are
3265 * unsupported.
3266 * </ul>
3267 * <p>
3268 * If the field is declared {@code volatile} then the returned VarHandle
3269 * will override access to the field (effectively ignore the
3270 * {@code volatile} declaration) in accordance to its specified
3271 * access modes.
3272 * <p>
3273 * If the field type is {@code float} or {@code double} then numeric
3274 * and atomic update access modes compare values using their bitwise
3275 * representation (see {@link Float#floatToRawIntBits} and
3276 * {@link Double#doubleToRawLongBits}, respectively).
3277 * @apiNote
3278 * Bitwise comparison of {@code float} values or {@code double} values,
3279 * as performed by the numeric and atomic update access modes, differ
3280 * from the primitive {@code ==} operator and the {@link Float#equals}
3281 * and {@link Double#equals} methods, specifically with respect to
3282 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
3283 * Care should be taken when performing a compare and set or a compare
3284 * and exchange operation with such values since the operation may
3285 * unexpectedly fail.
3286 * There are many possible NaN values that are considered to be
3287 * {@code NaN} in Java, although no IEEE 754 floating-point operation
3288 * provided by Java can distinguish between them. Operation failure can
3289 * occur if the expected or witness value is a NaN value and it is
3290 * transformed (perhaps in a platform specific manner) into another NaN
3291 * value, and thus has a different bitwise representation (see
3292 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
3293 * details).
3294 * The values {@code -0.0} and {@code +0.0} have different bitwise
3295 * representations but are considered equal when using the primitive
3296 * {@code ==} operator. Operation failure can occur if, for example, a
3297 * numeric algorithm computes an expected value to be say {@code -0.0}
3298 * and previously computed the witness value to be say {@code +0.0}.
3299 * @param decl the class that declares the static field
3300 * @param name the field's name
3301 * @param type the field's type, of type {@code T}
3302 * @return a VarHandle giving access to a static field
3303 * @throws NoSuchFieldException if the field does not exist
3304 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
3305 * @throws SecurityException if a security manager is present and it
3306 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3307 * @throws NullPointerException if any argument is null
3308 * @since 9
3309 */
3310 public VarHandle findStaticVarHandle(Class<?> decl, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3311 MemberName getField = resolveOrFail(REF_getStatic, decl, name, type);
3312 MemberName putField = resolveOrFail(REF_putStatic, decl, name, type);
3313 return getFieldVarHandle(REF_getStatic, REF_putStatic, decl, getField, putField);
3314 }
3315
3316 /**
3317 * Produces an early-bound method handle for a non-static method.
3318 * The receiver must have a supertype {@code defc} in which a method
3319 * of the given name and type is accessible to the lookup class.
3320 * The method and all its argument types must be accessible to the lookup object.
3321 * The type of the method handle will be that of the method,
3322 * without any insertion of an additional receiver parameter.
3323 * The given receiver will be bound into the method handle,
3324 * so that every call to the method handle will invoke the
3325 * requested method on the given receiver.
3326 * <p>
3327 * The returned method handle will have
3328 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3329 * the method's variable arity modifier bit ({@code 0x0080}) is set
3330 * <em>and</em> the trailing array argument is not the only argument.
3331 * (If the trailing array argument is the only argument,
3332 * the given receiver value will be bound to it.)
3333 * <p>
3334 * This is almost equivalent to the following code, with some differences noted below:
3335 * {@snippet lang="java" :
3336 import static java.lang.invoke.MethodHandles.*;
3337 import static java.lang.invoke.MethodType.*;
3338 ...
3339 MethodHandle mh0 = lookup().findVirtual(defc, name, type);
3340 MethodHandle mh1 = mh0.bindTo(receiver);
3341 mh1 = mh1.withVarargs(mh0.isVarargsCollector());
3342 return mh1;
3343 * }
3344 * where {@code defc} is either {@code receiver.getClass()} or a super
3345 * type of that class, in which the requested method is accessible
3346 * to the lookup class.
3347 * (Unlike {@code bind}, {@code bindTo} does not preserve variable arity.
3348 * Also, {@code bindTo} may throw a {@code ClassCastException} in instances where {@code bind} would
3349 * throw an {@code IllegalAccessException}, as in the case where the member is {@code protected} and
3350 * the receiver is restricted by {@code findVirtual} to the lookup class.)
3351 * @param receiver the object from which the method is accessed
3352 * @param name the name of the method
3353 * @param type the type of the method, with the receiver argument omitted
3354 * @return the desired method handle
3355 * @throws NoSuchMethodException if the method does not exist
3356 * @throws IllegalAccessException if access checking fails
3357 * or if the method's variable arity modifier bit
3358 * is set and {@code asVarargsCollector} fails
3359 * @throws SecurityException if a security manager is present and it
3360 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3361 * @throws NullPointerException if any argument is null
3362 * @see MethodHandle#bindTo
3363 * @see #findVirtual
3364 */
3365 public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
3366 Class<? extends Object> refc = receiver.getClass(); // may get NPE
3367 MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
3368 MethodHandle mh = getDirectMethodNoRestrictInvokeSpecial(refc, method, findBoundCallerLookup(method));
3369 if (!mh.type().leadingReferenceParameter().isAssignableFrom(receiver.getClass())) {
3370 throw new IllegalAccessException("The restricted defining class " +
3371 mh.type().leadingReferenceParameter().getName() +
3372 " is not assignable from receiver class " +
3373 receiver.getClass().getName());
3374 }
3375 return mh.bindArgumentL(0, receiver).setVarargs(method);
3376 }
3377
3378 /**
3379 * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
3380 * to <i>m</i>, if the lookup class has permission.
3381 * If <i>m</i> is non-static, the receiver argument is treated as an initial argument.
3382 * If <i>m</i> is virtual, overriding is respected on every call.
3383 * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped.
3384 * The type of the method handle will be that of the method,
3385 * with the receiver type prepended (but only if it is non-static).
3386 * If the method's {@code accessible} flag is not set,
3387 * access checking is performed immediately on behalf of the lookup class.
3388 * If <i>m</i> is not public, do not share the resulting handle with untrusted parties.
3389 * <p>
3390 * The returned method handle will have
3391 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3392 * the method's variable arity modifier bit ({@code 0x0080}) is set.
3393 * <p>
3394 * If <i>m</i> is static, and
3395 * if the returned method handle is invoked, the method's class will
3396 * be initialized, if it has not already been initialized.
3397 * @param m the reflected method
3398 * @return a method handle which can invoke the reflected method
3399 * @throws IllegalAccessException if access checking fails
3400 * or if the method's variable arity modifier bit
3401 * is set and {@code asVarargsCollector} fails
3402 * @throws NullPointerException if the argument is null
3403 */
3404 public MethodHandle unreflect(Method m) throws IllegalAccessException {
3405 if (m.getDeclaringClass() == MethodHandle.class) {
3406 MethodHandle mh = unreflectForMH(m);
3407 if (mh != null) return mh;
3408 }
3409 if (m.getDeclaringClass() == VarHandle.class) {
3410 MethodHandle mh = unreflectForVH(m);
3411 if (mh != null) return mh;
3412 }
3413 MemberName method = new MemberName(m);
3414 byte refKind = method.getReferenceKind();
3415 if (refKind == REF_invokeSpecial)
3416 refKind = REF_invokeVirtual;
3417 assert(method.isMethod());
3418 @SuppressWarnings("deprecation")
3419 Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
3420 return lookup.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method, findBoundCallerLookup(method));
3421 }
3422 private MethodHandle unreflectForMH(Method m) {
3423 // these names require special lookups because they throw UnsupportedOperationException
3424 if (MemberName.isMethodHandleInvokeName(m.getName()))
3425 return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m));
3426 return null;
3427 }
3428 private MethodHandle unreflectForVH(Method m) {
3429 // these names require special lookups because they throw UnsupportedOperationException
3430 if (MemberName.isVarHandleMethodInvokeName(m.getName()))
3431 return MethodHandleImpl.fakeVarHandleInvoke(new MemberName(m));
3432 return null;
3433 }
3434
3435 /**
3436 * Produces a method handle for a reflected method.
3437 * It will bypass checks for overriding methods on the receiver,
3438 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
3439 * instruction from within the explicitly specified {@code specialCaller}.
3440 * The type of the method handle will be that of the method,
3441 * with a suitably restricted receiver type prepended.
3442 * (The receiver type will be {@code specialCaller} or a subtype.)
3443 * If the method's {@code accessible} flag is not set,
3444 * access checking is performed immediately on behalf of the lookup class,
3445 * as if {@code invokespecial} instruction were being linked.
3446 * <p>
3447 * Before method resolution,
3448 * if the explicitly specified caller class is not identical with the
3449 * lookup class, or if this lookup object does not have
3450 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
3451 * privileges, the access fails.
3452 * <p>
3453 * The returned method handle will have
3454 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3455 * the method's variable arity modifier bit ({@code 0x0080}) is set.
3456 * @param m the reflected method
3457 * @param specialCaller the class nominally calling the method
3458 * @return a method handle which can invoke the reflected method
3459 * @throws IllegalAccessException if access checking fails,
3460 * or if the method is {@code static},
3461 * or if the method's variable arity modifier bit
3462 * is set and {@code asVarargsCollector} fails
3463 * @throws NullPointerException if any argument is null
3464 */
3465 public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException {
3466 checkSpecialCaller(specialCaller, m.getDeclaringClass());
3467 Lookup specialLookup = this.in(specialCaller);
3468 MemberName method = new MemberName(m, true);
3469 assert(method.isMethod());
3470 // ignore m.isAccessible: this is a new kind of access
3471 return specialLookup.getDirectMethodNoSecurityManager(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerLookup(method));
3472 }
3473
3474 /**
3475 * Produces a method handle for a reflected constructor.
3476 * The type of the method handle will be that of the constructor,
3477 * with the return type changed to the declaring class.
3478 * The method handle will perform a {@code newInstance} operation,
3479 * creating a new instance of the constructor's class on the
3480 * arguments passed to the method handle.
3481 * <p>
3482 * If the constructor's {@code accessible} flag is not set,
3483 * access checking is performed immediately on behalf of the lookup class.
3484 * <p>
3485 * The returned method handle will have
3486 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
3487 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
3488 * <p>
3489 * If the returned method handle is invoked, the constructor's class will
3490 * be initialized, if it has not already been initialized.
3491 * @param c the reflected constructor
3492 * @return a method handle which can invoke the reflected constructor
3493 * @throws IllegalAccessException if access checking fails
3494 * or if the method's variable arity modifier bit
3495 * is set and {@code asVarargsCollector} fails
3496 * @throws NullPointerException if the argument is null
3497 */
3498 public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException {
3499 MemberName ctor = new MemberName(c);
3500 assert(ctor.isConstructor());
3501 @SuppressWarnings("deprecation")
3502 Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
3503 return lookup.getDirectConstructorNoSecurityManager(ctor.getDeclaringClass(), ctor);
3504 }
3505
3506 /*
3507 * Produces a method handle that is capable of creating instances of the given class
3508 * and instantiated by the given constructor. No security manager check.
3509 *
3510 * This method should only be used by ReflectionFactory::newConstructorForSerialization.
3511 */
3512 /* package-private */ MethodHandle serializableConstructor(Class<?> decl, Constructor<?> c) throws IllegalAccessException {
3513 MemberName ctor = new MemberName(c);
3514 assert(ctor.isConstructor() && constructorInSuperclass(decl, c));
3515 checkAccess(REF_newInvokeSpecial, decl, ctor);
3516 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
3517 return DirectMethodHandle.makeAllocator(decl, ctor).setVarargs(ctor);
3518 }
3519
3520 private static boolean constructorInSuperclass(Class<?> decl, Constructor<?> ctor) {
3521 if (decl == ctor.getDeclaringClass())
3522 return true;
3523
3524 Class<?> cl = decl;
3525 while ((cl = cl.getSuperclass()) != null) {
3526 if (cl == ctor.getDeclaringClass()) {
3527 return true;
3528 }
3529 }
3530 return false;
3531 }
3532
3533 /**
3534 * Produces a method handle giving read access to a reflected field.
3535 * The type of the method handle will have a return type of the field's
3536 * value type.
3537 * If the field is {@code static}, the method handle will take no arguments.
3538 * Otherwise, its single argument will be the instance containing
3539 * the field.
3540 * If the {@code Field} object's {@code accessible} flag is not set,
3541 * access checking is performed immediately on behalf of the lookup class.
3542 * <p>
3543 * If the field is static, and
3544 * if the returned method handle is invoked, the field's class will
3545 * be initialized, if it has not already been initialized.
3546 * @param f the reflected field
3547 * @return a method handle which can load values from the reflected field
3548 * @throws IllegalAccessException if access checking fails
3549 * @throws NullPointerException if the argument is null
3550 */
3551 public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
3552 return unreflectField(f, false);
3553 }
3554
3555 /**
3556 * Produces a method handle giving write access to a reflected field.
3557 * The type of the method handle will have a void return type.
3558 * If the field is {@code static}, the method handle will take a single
3559 * argument, of the field's value type, the value to be stored.
3560 * Otherwise, the two arguments will be the instance containing
3561 * the field, and the value to be stored.
3562 * If the {@code Field} object's {@code accessible} flag is not set,
3563 * access checking is performed immediately on behalf of the lookup class.
3564 * <p>
3565 * If the field is {@code final}, write access will not be
3566 * allowed and access checking will fail, except under certain
3567 * narrow circumstances documented for {@link Field#set Field.set}.
3568 * A method handle is returned only if a corresponding call to
3569 * the {@code Field} object's {@code set} method could return
3570 * normally. In particular, fields which are both {@code static}
3571 * and {@code final} may never be set.
3572 * <p>
3573 * If the field is {@code static}, and
3574 * if the returned method handle is invoked, the field's class will
3575 * be initialized, if it has not already been initialized.
3576 * @param f the reflected field
3577 * @return a method handle which can store values into the reflected field
3578 * @throws IllegalAccessException if access checking fails,
3579 * or if the field is {@code final} and write access
3580 * is not enabled on the {@code Field} object
3581 * @throws NullPointerException if the argument is null
3582 */
3583 public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
3584 return unreflectField(f, true);
3585 }
3586
3587 private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
3588 MemberName field = new MemberName(f, isSetter);
3589 if (isSetter && field.isFinal()) {
3590 if (field.isTrustedFinalField()) {
3591 String msg = field.isStatic() ? "static final field has no write access"
3592 : "final field has no write access";
3593 throw field.makeAccessException(msg, this);
3594 }
3595 }
3596 assert(isSetter
3597 ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
3598 : MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
3599 @SuppressWarnings("deprecation")
3600 Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
3601 return lookup.getDirectFieldNoSecurityManager(field.getReferenceKind(), f.getDeclaringClass(), field);
3602 }
3603
3604 /**
3605 * Produces a VarHandle giving access to a reflected field {@code f}
3606 * of type {@code T} declared in a class of type {@code R}.
3607 * The VarHandle's variable type is {@code T}.
3608 * If the field is non-static the VarHandle has one coordinate type,
3609 * {@code R}. Otherwise, the field is static, and the VarHandle has no
3610 * coordinate types.
3611 * <p>
3612 * Access checking is performed immediately on behalf of the lookup
3613 * class, regardless of the value of the field's {@code accessible}
3614 * flag.
3615 * <p>
3616 * If the field is static, and if the returned VarHandle is operated
3617 * on, the field's declaring class will be initialized, if it has not
3618 * already been initialized.
3619 * <p>
3620 * Certain access modes of the returned VarHandle are unsupported under
3621 * the following conditions:
3622 * <ul>
3623 * <li>if the field is declared {@code final}, then the write, atomic
3624 * update, numeric atomic update, and bitwise atomic update access
3625 * modes are unsupported.
3626 * <li>if the field type is anything other than {@code byte},
3627 * {@code short}, {@code char}, {@code int}, {@code long},
3628 * {@code float}, or {@code double} then numeric atomic update
3629 * access modes are unsupported.
3630 * <li>if the field type is anything other than {@code boolean},
3631 * {@code byte}, {@code short}, {@code char}, {@code int} or
3632 * {@code long} then bitwise atomic update access modes are
3633 * unsupported.
3634 * </ul>
3635 * <p>
3636 * If the field is declared {@code volatile} then the returned VarHandle
3637 * will override access to the field (effectively ignore the
3638 * {@code volatile} declaration) in accordance to its specified
3639 * access modes.
3640 * <p>
3641 * If the field type is {@code float} or {@code double} then numeric
3642 * and atomic update access modes compare values using their bitwise
3643 * representation (see {@link Float#floatToRawIntBits} and
3644 * {@link Double#doubleToRawLongBits}, respectively).
3645 * @apiNote
3646 * Bitwise comparison of {@code float} values or {@code double} values,
3647 * as performed by the numeric and atomic update access modes, differ
3648 * from the primitive {@code ==} operator and the {@link Float#equals}
3649 * and {@link Double#equals} methods, specifically with respect to
3650 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
3651 * Care should be taken when performing a compare and set or a compare
3652 * and exchange operation with such values since the operation may
3653 * unexpectedly fail.
3654 * There are many possible NaN values that are considered to be
3655 * {@code NaN} in Java, although no IEEE 754 floating-point operation
3656 * provided by Java can distinguish between them. Operation failure can
3657 * occur if the expected or witness value is a NaN value and it is
3658 * transformed (perhaps in a platform specific manner) into another NaN
3659 * value, and thus has a different bitwise representation (see
3660 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
3661 * details).
3662 * The values {@code -0.0} and {@code +0.0} have different bitwise
3663 * representations but are considered equal when using the primitive
3664 * {@code ==} operator. Operation failure can occur if, for example, a
3665 * numeric algorithm computes an expected value to be say {@code -0.0}
3666 * and previously computed the witness value to be say {@code +0.0}.
3667 * @param f the reflected field, with a field of type {@code T}, and
3668 * a declaring class of type {@code R}
3669 * @return a VarHandle giving access to non-static fields or a static
3670 * field
3671 * @throws IllegalAccessException if access checking fails
3672 * @throws NullPointerException if the argument is null
3673 * @since 9
3674 */
3675 public VarHandle unreflectVarHandle(Field f) throws IllegalAccessException {
3676 MemberName getField = new MemberName(f, false);
3677 MemberName putField = new MemberName(f, true);
3678 return getFieldVarHandleNoSecurityManager(getField.getReferenceKind(), putField.getReferenceKind(),
3679 f.getDeclaringClass(), getField, putField);
3680 }
3681
3682 /**
3683 * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
3684 * created by this lookup object or a similar one.
3685 * Security and access checks are performed to ensure that this lookup object
3686 * is capable of reproducing the target method handle.
3687 * This means that the cracking may fail if target is a direct method handle
3688 * but was created by an unrelated lookup object.
3689 * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a>
3690 * and was created by a lookup object for a different class.
3691 * @param target a direct method handle to crack into symbolic reference components
3692 * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object
3693 * @throws SecurityException if a security manager is present and it
3694 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
3695 * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails
3696 * @throws NullPointerException if the target is {@code null}
3697 * @see MethodHandleInfo
3698 * @since 1.8
3699 */
3700 public MethodHandleInfo revealDirect(MethodHandle target) {
3701 if (!target.isCrackable()) {
3702 throw newIllegalArgumentException("not a direct method handle");
3703 }
3704 MemberName member = target.internalMemberName();
3705 Class<?> defc = member.getDeclaringClass();
3706 byte refKind = member.getReferenceKind();
3707 assert(MethodHandleNatives.refKindIsValid(refKind));
3708 if (refKind == REF_invokeSpecial && !target.isInvokeSpecial())
3709 // Devirtualized method invocation is usually formally virtual.
3710 // To avoid creating extra MemberName objects for this common case,
3711 // we encode this extra degree of freedom using MH.isInvokeSpecial.
3712 refKind = REF_invokeVirtual;
3713 if (refKind == REF_invokeVirtual && defc.isInterface())
3714 // Symbolic reference is through interface but resolves to Object method (toString, etc.)
3715 refKind = REF_invokeInterface;
3716 // Check SM permissions and member access before cracking.
3717 try {
3718 checkAccess(refKind, defc, member);
3719 checkSecurityManager(defc, member);
3720 } catch (IllegalAccessException ex) {
3721 throw new IllegalArgumentException(ex);
3722 }
3723 if (allowedModes != TRUSTED && member.isCallerSensitive()) {
3724 Class<?> callerClass = target.internalCallerClass();
3725 if ((lookupModes() & ORIGINAL) == 0 || callerClass != lookupClass())
3726 throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass);
3727 }
3728 // Produce the handle to the results.
3729 return new InfoFromMemberName(this, member, refKind);
3730 }
3731
3732 //--- Helper methods, all package-private.
3733
3734 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
3735 checkSymbolicClass(refc); // do this before attempting to resolve
3736 Objects.requireNonNull(name);
3737 Objects.requireNonNull(type);
3738 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), allowedModes,
3739 NoSuchFieldException.class);
3740 }
3741
3742 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
3743 checkSymbolicClass(refc); // do this before attempting to resolve
3744 Objects.requireNonNull(type);
3745 checkMethodName(refKind, name); // implicit null-check of name
3746 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), allowedModes,
3747 NoSuchMethodException.class);
3748 }
3749
3750 MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException {
3751 checkSymbolicClass(member.getDeclaringClass()); // do this before attempting to resolve
3752 Objects.requireNonNull(member.getName());
3753 Objects.requireNonNull(member.getType());
3754 return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(), allowedModes,
3755 ReflectiveOperationException.class);
3756 }
3757
3758 MemberName resolveOrNull(byte refKind, MemberName member) {
3759 // do this before attempting to resolve
3760 if (!isClassAccessible(member.getDeclaringClass())) {
3761 return null;
3762 }
3763 Objects.requireNonNull(member.getName());
3764 Objects.requireNonNull(member.getType());
3765 return IMPL_NAMES.resolveOrNull(refKind, member, lookupClassOrNull(), allowedModes);
3766 }
3767
3768 MemberName resolveOrNull(byte refKind, Class<?> refc, String name, MethodType type) {
3769 // do this before attempting to resolve
3770 if (!isClassAccessible(refc)) {
3771 return null;
3772 }
3773 Objects.requireNonNull(type);
3774 // implicit null-check of name
3775 if (name.startsWith("<") && refKind != REF_newInvokeSpecial) {
3776 return null;
3777 }
3778 return IMPL_NAMES.resolveOrNull(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), allowedModes);
3779 }
3780
3781 void checkSymbolicClass(Class<?> refc) throws IllegalAccessException {
3782 if (!isClassAccessible(refc)) {
3783 throw new MemberName(refc).makeAccessException("symbolic reference class is not accessible", this);
3784 }
3785 }
3786
3787 boolean isClassAccessible(Class<?> refc) {
3788 Objects.requireNonNull(refc);
3789 Class<?> caller = lookupClassOrNull();
3790 Class<?> type = refc;
3791 while (type.isArray()) {
3792 type = type.getComponentType();
3793 }
3794 return caller == null || VerifyAccess.isClassAccessible(type, caller, prevLookupClass, allowedModes);
3795 }
3796
3797 /** Check name for an illegal leading "<" character. */
3798 void checkMethodName(byte refKind, String name) throws NoSuchMethodException {
3799 if (name.startsWith("<") && refKind != REF_newInvokeSpecial)
3800 throw new NoSuchMethodException("illegal method name: "+name);
3801 }
3802
3803 /**
3804 * Find my trustable caller class if m is a caller sensitive method.
3805 * If this lookup object has original full privilege access, then the caller class is the lookupClass.
3806 * Otherwise, if m is caller-sensitive, throw IllegalAccessException.
3807 */
3808 Lookup findBoundCallerLookup(MemberName m) throws IllegalAccessException {
3809 if (MethodHandleNatives.isCallerSensitive(m) && (lookupModes() & ORIGINAL) == 0) {
3810 // Only lookups with full privilege access are allowed to resolve caller-sensitive methods
3811 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
3812 }
3813 return this;
3814 }
3815
3816 /**
3817 * Returns {@code true} if this lookup has {@code PRIVATE} and {@code MODULE} access.
3818 * @return {@code true} if this lookup has {@code PRIVATE} and {@code MODULE} access.
3819 *
3820 * @deprecated This method was originally designed to test {@code PRIVATE} access
3821 * that implies full privilege access but {@code MODULE} access has since become
3822 * independent of {@code PRIVATE} access. It is recommended to call
3823 * {@link #hasFullPrivilegeAccess()} instead.
3824 * @since 9
3825 */
3826 @Deprecated(since="14")
3827 public boolean hasPrivateAccess() {
3828 return hasFullPrivilegeAccess();
3829 }
3830
3831 /**
3832 * Returns {@code true} if this lookup has <em>full privilege access</em>,
3833 * i.e. {@code PRIVATE} and {@code MODULE} access.
3834 * A {@code Lookup} object must have full privilege access in order to
3835 * access all members that are allowed to the
3836 * {@linkplain #lookupClass() lookup class}.
3837 *
3838 * @return {@code true} if this lookup has full privilege access.
3839 * @since 14
3840 * @see <a href="MethodHandles.Lookup.html#privacc">private and module access</a>
3841 */
3842 public boolean hasFullPrivilegeAccess() {
3843 return (allowedModes & (PRIVATE|MODULE)) == (PRIVATE|MODULE);
3844 }
3845
3846 /**
3847 * Perform steps 1 and 2b <a href="MethodHandles.Lookup.html#secmgr">access checks</a>
3848 * for ensureInitialized, findClass or accessClass.
3849 */
3850 void checkSecurityManager(Class<?> refc) {
3851 if (allowedModes == TRUSTED) return;
3852
3853 @SuppressWarnings("removal")
3854 SecurityManager smgr = System.getSecurityManager();
3855 if (smgr == null) return;
3856
3857 // Step 1:
3858 boolean fullPrivilegeLookup = hasFullPrivilegeAccess();
3859 if (!fullPrivilegeLookup ||
3860 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
3861 ReflectUtil.checkPackageAccess(refc);
3862 }
3863
3864 // Step 2b:
3865 if (!fullPrivilegeLookup) {
3866 smgr.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
3867 }
3868 }
3869
3870 /**
3871 * Perform steps 1, 2a and 3 <a href="MethodHandles.Lookup.html#secmgr">access checks</a>.
3872 * Determines a trustable caller class to compare with refc, the symbolic reference class.
3873 * If this lookup object has full privilege access except original access,
3874 * then the caller class is the lookupClass.
3875 *
3876 * Lookup object created by {@link MethodHandles#privateLookupIn(Class, Lookup)}
3877 * from the same module skips the security permission check.
3878 */
3879 void checkSecurityManager(Class<?> refc, MemberName m) {
3880 Objects.requireNonNull(refc);
3881 Objects.requireNonNull(m);
3882
3883 if (allowedModes == TRUSTED) return;
3884
3885 @SuppressWarnings("removal")
3886 SecurityManager smgr = System.getSecurityManager();
3887 if (smgr == null) return;
3888
3889 // Step 1:
3890 boolean fullPrivilegeLookup = hasFullPrivilegeAccess();
3891 if (!fullPrivilegeLookup ||
3892 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
3893 ReflectUtil.checkPackageAccess(refc);
3894 }
3895
3896 // Step 2a:
3897 if (m.isPublic()) return;
3898 if (!fullPrivilegeLookup) {
3899 smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION);
3900 }
3901
3902 // Step 3:
3903 Class<?> defc = m.getDeclaringClass();
3904 if (!fullPrivilegeLookup && defc != refc) {
3905 ReflectUtil.checkPackageAccess(defc);
3906 }
3907 }
3908
3909 void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
3910 boolean wantStatic = (refKind == REF_invokeStatic);
3911 String message;
3912 if (m.isConstructor())
3913 message = "expected a method, not a constructor";
3914 else if (!m.isMethod())
3915 message = "expected a method";
3916 else if (wantStatic != m.isStatic())
3917 message = wantStatic ? "expected a static method" : "expected a non-static method";
3918 else
3919 { checkAccess(refKind, refc, m); return; }
3920 throw m.makeAccessException(message, this);
3921 }
3922
3923 void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
3924 boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
3925 String message;
3926 if (wantStatic != m.isStatic())
3927 message = wantStatic ? "expected a static field" : "expected a non-static field";
3928 else
3929 { checkAccess(refKind, refc, m); return; }
3930 throw m.makeAccessException(message, this);
3931 }
3932
3933 private boolean isArrayClone(byte refKind, Class<?> refc, MemberName m) {
3934 return Modifier.isProtected(m.getModifiers()) &&
3935 refKind == REF_invokeVirtual &&
3936 m.getDeclaringClass() == Object.class &&
3937 m.getName().equals("clone") &&
3938 refc.isArray();
3939 }
3940
3941 /** Check public/protected/private bits on the symbolic reference class and its member. */
3942 void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
3943 assert(m.referenceKindIsConsistentWith(refKind) &&
3944 MethodHandleNatives.refKindIsValid(refKind) &&
3945 (MethodHandleNatives.refKindIsField(refKind) == m.isField()));
3946 int allowedModes = this.allowedModes;
3947 if (allowedModes == TRUSTED) return;
3948 int mods = m.getModifiers();
3949 if (isArrayClone(refKind, refc, m)) {
3950 // The JVM does this hack also.
3951 // (See ClassVerifier::verify_invoke_instructions
3952 // and LinkResolver::check_method_accessability.)
3953 // Because the JVM does not allow separate methods on array types,
3954 // there is no separate method for int[].clone.
3955 // All arrays simply inherit Object.clone.
3956 // But for access checking logic, we make Object.clone
3957 // (normally protected) appear to be public.
3958 // Later on, when the DirectMethodHandle is created,
3959 // its leading argument will be restricted to the
3960 // requested array type.
3961 // N.B. The return type is not adjusted, because
3962 // that is *not* the bytecode behavior.
3963 mods ^= Modifier.PROTECTED | Modifier.PUBLIC;
3964 }
3965 if (Modifier.isProtected(mods) && refKind == REF_newInvokeSpecial) {
3966 // cannot "new" a protected ctor in a different package
3967 mods ^= Modifier.PROTECTED;
3968 }
3969 if (Modifier.isFinal(mods) &&
3970 MethodHandleNatives.refKindIsSetter(refKind))
3971 throw m.makeAccessException("unexpected set of a final field", this);
3972 int requestedModes = fixmods(mods); // adjust 0 => PACKAGE
3973 if ((requestedModes & allowedModes) != 0) {
3974 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
3975 mods, lookupClass(), previousLookupClass(), allowedModes))
3976 return;
3977 } else {
3978 // Protected members can also be checked as if they were package-private.
3979 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
3980 && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
3981 return;
3982 }
3983 throw m.makeAccessException(accessFailedMessage(refc, m), this);
3984 }
3985
3986 String accessFailedMessage(Class<?> refc, MemberName m) {
3987 Class<?> defc = m.getDeclaringClass();
3988 int mods = m.getModifiers();
3989 // check the class first:
3990 boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
3991 (defc == refc ||
3992 Modifier.isPublic(refc.getModifiers())));
3993 if (!classOK && (allowedModes & PACKAGE) != 0) {
3994 // ignore previous lookup class to check if default package access
3995 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), null, FULL_POWER_MODES) &&
3996 (defc == refc ||
3997 VerifyAccess.isClassAccessible(refc, lookupClass(), null, FULL_POWER_MODES)));
3998 }
3999 if (!classOK)
4000 return "class is not public";
4001 if (Modifier.isPublic(mods))
4002 return "access to public member failed"; // (how?, module not readable?)
4003 if (Modifier.isPrivate(mods))
4004 return "member is private";
4005 if (Modifier.isProtected(mods))
4006 return "member is protected";
4007 return "member is private to package";
4008 }
4009
4010 private void checkSpecialCaller(Class<?> specialCaller, Class<?> refc) throws IllegalAccessException {
4011 int allowedModes = this.allowedModes;
4012 if (allowedModes == TRUSTED) return;
4013 if ((lookupModes() & PRIVATE) == 0
4014 || (specialCaller != lookupClass()
4015 // ensure non-abstract methods in superinterfaces can be special-invoked
4016 && !(refc != null && refc.isInterface() && refc.isAssignableFrom(specialCaller))))
4017 throw new MemberName(specialCaller).
4018 makeAccessException("no private access for invokespecial", this);
4019 }
4020
4021 private boolean restrictProtectedReceiver(MemberName method) {
4022 // The accessing class only has the right to use a protected member
4023 // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc.
4024 if (!method.isProtected() || method.isStatic()
4025 || allowedModes == TRUSTED
4026 || method.getDeclaringClass() == lookupClass()
4027 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass()))
4028 return false;
4029 return true;
4030 }
4031 private MethodHandle restrictReceiver(MemberName method, DirectMethodHandle mh, Class<?> caller) throws IllegalAccessException {
4032 assert(!method.isStatic());
4033 // receiver type of mh is too wide; narrow to caller
4034 if (!method.getDeclaringClass().isAssignableFrom(caller)) {
4035 throw method.makeAccessException("caller class must be a subclass below the method", caller);
4036 }
4037 MethodType rawType = mh.type();
4038 if (caller.isAssignableFrom(rawType.parameterType(0))) return mh; // no need to restrict; already narrow
4039 MethodType narrowType = rawType.changeParameterType(0, caller);
4040 assert(!mh.isVarargsCollector()); // viewAsType will lose varargs-ness
4041 assert(mh.viewAsTypeChecks(narrowType, true));
4042 return mh.copyWith(narrowType, mh.form);
4043 }
4044
4045 /** Check access and get the requested method. */
4046 private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException {
4047 final boolean doRestrict = true;
4048 final boolean checkSecurity = true;
4049 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerLookup);
4050 }
4051 /** Check access and get the requested method, for invokespecial with no restriction on the application of narrowing rules. */
4052 private MethodHandle getDirectMethodNoRestrictInvokeSpecial(Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException {
4053 final boolean doRestrict = false;
4054 final boolean checkSecurity = true;
4055 return getDirectMethodCommon(REF_invokeSpecial, refc, method, checkSecurity, doRestrict, callerLookup);
4056 }
4057 /** Check access and get the requested method, eliding security manager checks. */
4058 private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class<?> refc, MemberName method, Lookup callerLookup) throws IllegalAccessException {
4059 final boolean doRestrict = true;
4060 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
4061 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerLookup);
4062 }
4063 /** Common code for all methods; do not call directly except from immediately above. */
4064 private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method,
4065 boolean checkSecurity,
4066 boolean doRestrict,
4067 Lookup boundCaller) throws IllegalAccessException {
4068 checkMethod(refKind, refc, method);
4069 // Optionally check with the security manager; this isn't needed for unreflect* calls.
4070 if (checkSecurity)
4071 checkSecurityManager(refc, method);
4072 assert(!method.isMethodHandleInvoke());
4073 if (refKind == REF_invokeSpecial &&
4074 refc != lookupClass() &&
4075 !refc.isInterface() && !lookupClass().isInterface() &&
4076 refc != lookupClass().getSuperclass() &&
4077 refc.isAssignableFrom(lookupClass())) {
4078 assert(!method.getName().equals(ConstantDescs.INIT_NAME)); // not this code path
4079
4080 // Per JVMS 6.5, desc. of invokespecial instruction:
4081 // If the method is in a superclass of the LC,
4082 // and if our original search was above LC.super,
4083 // repeat the search (symbolic lookup) from LC.super
4084 // and continue with the direct superclass of that class,
4085 // and so forth, until a match is found or no further superclasses exist.
4086 // FIXME: MemberName.resolve should handle this instead.
4087 Class<?> refcAsSuper = lookupClass();
4088 MemberName m2;
4089 do {
4090 refcAsSuper = refcAsSuper.getSuperclass();
4091 m2 = new MemberName(refcAsSuper,
4092 method.getName(),
4093 method.getMethodType(),
4094 REF_invokeSpecial);
4095 m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull(), allowedModes);
4096 } while (m2 == null && // no method is found yet
4097 refc != refcAsSuper); // search up to refc
4098 if (m2 == null) throw new InternalError(method.toString());
4099 method = m2;
4100 refc = refcAsSuper;
4101 // redo basic checks
4102 checkMethod(refKind, refc, method);
4103 }
4104 DirectMethodHandle dmh = DirectMethodHandle.make(refKind, refc, method, lookupClass());
4105 MethodHandle mh = dmh;
4106 // Optionally narrow the receiver argument to lookupClass using restrictReceiver.
4107 if ((doRestrict && refKind == REF_invokeSpecial) ||
4108 (MethodHandleNatives.refKindHasReceiver(refKind) &&
4109 restrictProtectedReceiver(method) &&
4110 // All arrays simply inherit the protected Object.clone method.
4111 // The leading argument is already restricted to the requested
4112 // array type (not the lookup class).
4113 !isArrayClone(refKind, refc, method))) {
4114 mh = restrictReceiver(method, dmh, lookupClass());
4115 }
4116 mh = maybeBindCaller(method, mh, boundCaller);
4117 mh = mh.setVarargs(method);
4118 return mh;
4119 }
4120 private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh, Lookup boundCaller)
4121 throws IllegalAccessException {
4122 if (boundCaller.allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method))
4123 return mh;
4124
4125 // boundCaller must have full privilege access.
4126 // It should have been checked by findBoundCallerLookup. Safe to check this again.
4127 if ((boundCaller.lookupModes() & ORIGINAL) == 0)
4128 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
4129
4130 assert boundCaller.hasFullPrivilegeAccess();
4131
4132 MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, boundCaller.lookupClass);
4133 // Note: caller will apply varargs after this step happens.
4134 return cbmh;
4135 }
4136
4137 /** Check access and get the requested field. */
4138 private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
4139 final boolean checkSecurity = true;
4140 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
4141 }
4142 /** Check access and get the requested field, eliding security manager checks. */
4143 private MethodHandle getDirectFieldNoSecurityManager(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
4144 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
4145 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
4146 }
4147 /** Common code for all fields; do not call directly except from immediately above. */
4148 private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field,
4149 boolean checkSecurity) throws IllegalAccessException {
4150 checkField(refKind, refc, field);
4151 // Optionally check with the security manager; this isn't needed for unreflect* calls.
4152 if (checkSecurity)
4153 checkSecurityManager(refc, field);
4154 DirectMethodHandle dmh = DirectMethodHandle.make(refc, field);
4155 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) &&
4156 restrictProtectedReceiver(field));
4157 if (doRestrict)
4158 return restrictReceiver(field, dmh, lookupClass());
4159 return dmh;
4160 }
4161 private VarHandle getFieldVarHandle(byte getRefKind, byte putRefKind,
4162 Class<?> refc, MemberName getField, MemberName putField)
4163 throws IllegalAccessException {
4164 final boolean checkSecurity = true;
4165 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
4166 }
4167 private VarHandle getFieldVarHandleNoSecurityManager(byte getRefKind, byte putRefKind,
4168 Class<?> refc, MemberName getField, MemberName putField)
4169 throws IllegalAccessException {
4170 final boolean checkSecurity = false;
4171 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
4172 }
4173 private VarHandle getFieldVarHandleCommon(byte getRefKind, byte putRefKind,
4174 Class<?> refc, MemberName getField, MemberName putField,
4175 boolean checkSecurity) throws IllegalAccessException {
4176 assert getField.isStatic() == putField.isStatic();
4177 assert getField.isGetter() && putField.isSetter();
4178 assert MethodHandleNatives.refKindIsStatic(getRefKind) == MethodHandleNatives.refKindIsStatic(putRefKind);
4179 assert MethodHandleNatives.refKindIsGetter(getRefKind) && MethodHandleNatives.refKindIsSetter(putRefKind);
4180
4181 checkField(getRefKind, refc, getField);
4182 if (checkSecurity)
4183 checkSecurityManager(refc, getField);
4184
4185 if (!putField.isFinal()) {
4186 // A VarHandle does not support updates to final fields, any
4187 // such VarHandle to a final field will be read-only and
4188 // therefore the following write-based accessibility checks are
4189 // only required for non-final fields
4190 checkField(putRefKind, refc, putField);
4191 if (checkSecurity)
4192 checkSecurityManager(refc, putField);
4193 }
4194
4195 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(getRefKind) &&
4196 restrictProtectedReceiver(getField));
4197 if (doRestrict) {
4198 assert !getField.isStatic();
4199 // receiver type of VarHandle is too wide; narrow to caller
4200 if (!getField.getDeclaringClass().isAssignableFrom(lookupClass())) {
4201 throw getField.makeAccessException("caller class must be a subclass below the method", lookupClass());
4202 }
4203 refc = lookupClass();
4204 }
4205 return VarHandles.makeFieldHandle(getField, refc,
4206 this.allowedModes == TRUSTED && !getField.isTrustedFinalField());
4207 }
4208 /** Check access and get the requested constructor. */
4209 private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException {
4210 final boolean checkSecurity = true;
4211 return getDirectConstructorCommon(refc, ctor, checkSecurity);
4212 }
4213 /** Check access and get the requested constructor, eliding security manager checks. */
4214 private MethodHandle getDirectConstructorNoSecurityManager(Class<?> refc, MemberName ctor) throws IllegalAccessException {
4215 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
4216 return getDirectConstructorCommon(refc, ctor, checkSecurity);
4217 }
4218 /** Common code for all constructors; do not call directly except from immediately above. */
4219 private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor,
4220 boolean checkSecurity) throws IllegalAccessException {
4221 assert(ctor.isConstructor());
4222 checkAccess(REF_newInvokeSpecial, refc, ctor);
4223 // Optionally check with the security manager; this isn't needed for unreflect* calls.
4224 if (checkSecurity)
4225 checkSecurityManager(refc, ctor);
4226 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
4227 return DirectMethodHandle.make(ctor).setVarargs(ctor);
4228 }
4229
4230 /** Hook called from the JVM (via MethodHandleNatives) to link MH constants:
4231 */
4232 /*non-public*/
4233 MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type)
4234 throws ReflectiveOperationException {
4235 if (!(type instanceof Class || type instanceof MethodType))
4236 throw new InternalError("unresolved MemberName");
4237 MemberName member = new MemberName(refKind, defc, name, type);
4238 MethodHandle mh = LOOKASIDE_TABLE.get(member);
4239 if (mh != null) {
4240 checkSymbolicClass(defc);
4241 return mh;
4242 }
4243 if (defc == MethodHandle.class && refKind == REF_invokeVirtual) {
4244 // Treat MethodHandle.invoke and invokeExact specially.
4245 mh = findVirtualForMH(member.getName(), member.getMethodType());
4246 if (mh != null) {
4247 return mh;
4248 }
4249 } else if (defc == VarHandle.class && refKind == REF_invokeVirtual) {
4250 // Treat signature-polymorphic methods on VarHandle specially.
4251 mh = findVirtualForVH(member.getName(), member.getMethodType());
4252 if (mh != null) {
4253 return mh;
4254 }
4255 }
4256 MemberName resolved = resolveOrFail(refKind, member);
4257 mh = getDirectMethodForConstant(refKind, defc, resolved);
4258 if (mh instanceof DirectMethodHandle dmh
4259 && canBeCached(refKind, defc, resolved)) {
4260 MemberName key = mh.internalMemberName();
4261 if (key != null) {
4262 key = key.asNormalOriginal();
4263 }
4264 if (member.equals(key)) { // better safe than sorry
4265 LOOKASIDE_TABLE.put(key, dmh);
4266 }
4267 }
4268 return mh;
4269 }
4270 private boolean canBeCached(byte refKind, Class<?> defc, MemberName member) {
4271 if (refKind == REF_invokeSpecial) {
4272 return false;
4273 }
4274 if (!Modifier.isPublic(defc.getModifiers()) ||
4275 !Modifier.isPublic(member.getDeclaringClass().getModifiers()) ||
4276 !member.isPublic() ||
4277 member.isCallerSensitive()) {
4278 return false;
4279 }
4280 ClassLoader loader = defc.getClassLoader();
4281 if (loader != null) {
4282 ClassLoader sysl = ClassLoader.getSystemClassLoader();
4283 boolean found = false;
4284 while (sysl != null) {
4285 if (loader == sysl) { found = true; break; }
4286 sysl = sysl.getParent();
4287 }
4288 if (!found) {
4289 return false;
4290 }
4291 }
4292 try {
4293 MemberName resolved2 = publicLookup().resolveOrNull(refKind,
4294 new MemberName(refKind, defc, member.getName(), member.getType()));
4295 if (resolved2 == null) {
4296 return false;
4297 }
4298 checkSecurityManager(defc, resolved2);
4299 } catch (SecurityException ex) {
4300 return false;
4301 }
4302 return true;
4303 }
4304 private MethodHandle getDirectMethodForConstant(byte refKind, Class<?> defc, MemberName member)
4305 throws ReflectiveOperationException {
4306 if (MethodHandleNatives.refKindIsField(refKind)) {
4307 return getDirectFieldNoSecurityManager(refKind, defc, member);
4308 } else if (MethodHandleNatives.refKindIsMethod(refKind)) {
4309 return getDirectMethodNoSecurityManager(refKind, defc, member, findBoundCallerLookup(member));
4310 } else if (refKind == REF_newInvokeSpecial) {
4311 return getDirectConstructorNoSecurityManager(defc, member);
4312 }
4313 // oops
4314 throw newIllegalArgumentException("bad MethodHandle constant #"+member);
4315 }
4316
4317 static ConcurrentHashMap<MemberName, DirectMethodHandle> LOOKASIDE_TABLE = new ConcurrentHashMap<>();
4318 }
4319
4320 /**
4321 * Produces a method handle constructing arrays of a desired type,
4322 * as if by the {@code anewarray} bytecode.
4323 * The return type of the method handle will be the array type.
4324 * The type of its sole argument will be {@code int}, which specifies the size of the array.
4325 *
4326 * <p> If the returned method handle is invoked with a negative
4327 * array size, a {@code NegativeArraySizeException} will be thrown.
4328 *
4329 * @param arrayClass an array type
4330 * @return a method handle which can create arrays of the given type
4331 * @throws NullPointerException if the argument is {@code null}
4332 * @throws IllegalArgumentException if {@code arrayClass} is not an array type
4333 * @see java.lang.reflect.Array#newInstance(Class, int)
4334 * @jvms 6.5 {@code anewarray} Instruction
4335 * @since 9
4336 */
4337 public static MethodHandle arrayConstructor(Class<?> arrayClass) throws IllegalArgumentException {
4338 if (!arrayClass.isArray()) {
4339 throw newIllegalArgumentException("not an array class: " + arrayClass.getName());
4340 }
4341 MethodHandle ani = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_Array_newInstance).
4342 bindTo(arrayClass.getComponentType());
4343 return ani.asType(ani.type().changeReturnType(arrayClass));
4344 }
4345
4346 /**
4347 * Produces a method handle returning the length of an array,
4348 * as if by the {@code arraylength} bytecode.
4349 * The type of the method handle will have {@code int} as return type,
4350 * and its sole argument will be the array type.
4351 *
4352 * <p> If the returned method handle is invoked with a {@code null}
4353 * array reference, a {@code NullPointerException} will be thrown.
4354 *
4355 * @param arrayClass an array type
4356 * @return a method handle which can retrieve the length of an array of the given array type
4357 * @throws NullPointerException if the argument is {@code null}
4358 * @throws IllegalArgumentException if arrayClass is not an array type
4359 * @jvms 6.5 {@code arraylength} Instruction
4360 * @since 9
4361 */
4362 public static MethodHandle arrayLength(Class<?> arrayClass) throws IllegalArgumentException {
4363 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.LENGTH);
4364 }
4365
4366 /**
4367 * Produces a method handle giving read access to elements of an array,
4368 * as if by the {@code aaload} bytecode.
4369 * The type of the method handle will have a return type of the array's
4370 * element type. Its first argument will be the array type,
4371 * and the second will be {@code int}.
4372 *
4373 * <p> When the returned method handle is invoked,
4374 * the array reference and array index are checked.
4375 * A {@code NullPointerException} will be thrown if the array reference
4376 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
4377 * thrown if the index is negative or if it is greater than or equal to
4378 * the length of the array.
4379 *
4380 * @param arrayClass an array type
4381 * @return a method handle which can load values from the given array type
4382 * @throws NullPointerException if the argument is null
4383 * @throws IllegalArgumentException if arrayClass is not an array type
4384 * @jvms 6.5 {@code aaload} Instruction
4385 */
4386 public static MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException {
4387 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.GET);
4388 }
4389
4390 /**
4391 * Produces a method handle giving write access to elements of an array,
4392 * as if by the {@code astore} bytecode.
4393 * The type of the method handle will have a void return type.
4394 * Its last argument will be the array's element type.
4395 * The first and second arguments will be the array type and int.
4396 *
4397 * <p> When the returned method handle is invoked,
4398 * the array reference and array index are checked.
4399 * A {@code NullPointerException} will be thrown if the array reference
4400 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
4401 * thrown if the index is negative or if it is greater than or equal to
4402 * the length of the array.
4403 *
4404 * @param arrayClass the class of an array
4405 * @return a method handle which can store values into the array type
4406 * @throws NullPointerException if the argument is null
4407 * @throws IllegalArgumentException if arrayClass is not an array type
4408 * @jvms 6.5 {@code aastore} Instruction
4409 */
4410 public static MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException {
4411 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.SET);
4412 }
4413
4414 /**
4415 * Produces a VarHandle giving access to elements of an array of type
4416 * {@code arrayClass}. The VarHandle's variable type is the component type
4417 * of {@code arrayClass} and the list of coordinate types is
4418 * {@code (arrayClass, int)}, where the {@code int} coordinate type
4419 * corresponds to an argument that is an index into an array.
4420 * <p>
4421 * Certain access modes of the returned VarHandle are unsupported under
4422 * the following conditions:
4423 * <ul>
4424 * <li>if the component type is anything other than {@code byte},
4425 * {@code short}, {@code char}, {@code int}, {@code long},
4426 * {@code float}, or {@code double} then numeric atomic update access
4427 * modes are unsupported.
4428 * <li>if the component type is anything other than {@code boolean},
4429 * {@code byte}, {@code short}, {@code char}, {@code int} or
4430 * {@code long} then bitwise atomic update access modes are
4431 * unsupported.
4432 * </ul>
4433 * <p>
4434 * If the component type is {@code float} or {@code double} then numeric
4435 * and atomic update access modes compare values using their bitwise
4436 * representation (see {@link Float#floatToRawIntBits} and
4437 * {@link Double#doubleToRawLongBits}, respectively).
4438 *
4439 * <p> When the returned {@code VarHandle} is invoked,
4440 * the array reference and array index are checked.
4441 * A {@code NullPointerException} will be thrown if the array reference
4442 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
4443 * thrown if the index is negative or if it is greater than or equal to
4444 * the length of the array.
4445 *
4446 * @apiNote
4447 * Bitwise comparison of {@code float} values or {@code double} values,
4448 * as performed by the numeric and atomic update access modes, differ
4449 * from the primitive {@code ==} operator and the {@link Float#equals}
4450 * and {@link Double#equals} methods, specifically with respect to
4451 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
4452 * Care should be taken when performing a compare and set or a compare
4453 * and exchange operation with such values since the operation may
4454 * unexpectedly fail.
4455 * There are many possible NaN values that are considered to be
4456 * {@code NaN} in Java, although no IEEE 754 floating-point operation
4457 * provided by Java can distinguish between them. Operation failure can
4458 * occur if the expected or witness value is a NaN value and it is
4459 * transformed (perhaps in a platform specific manner) into another NaN
4460 * value, and thus has a different bitwise representation (see
4461 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
4462 * details).
4463 * The values {@code -0.0} and {@code +0.0} have different bitwise
4464 * representations but are considered equal when using the primitive
4465 * {@code ==} operator. Operation failure can occur if, for example, a
4466 * numeric algorithm computes an expected value to be say {@code -0.0}
4467 * and previously computed the witness value to be say {@code +0.0}.
4468 * @param arrayClass the class of an array, of type {@code T[]}
4469 * @return a VarHandle giving access to elements of an array
4470 * @throws NullPointerException if the arrayClass is null
4471 * @throws IllegalArgumentException if arrayClass is not an array type
4472 * @since 9
4473 */
4474 public static VarHandle arrayElementVarHandle(Class<?> arrayClass) throws IllegalArgumentException {
4475 return VarHandles.makeArrayElementHandle(arrayClass);
4476 }
4477
4478 /**
4479 * Produces a VarHandle giving access to elements of a {@code byte[]} array
4480 * viewed as if it were a different primitive array type, such as
4481 * {@code int[]} or {@code long[]}.
4482 * The VarHandle's variable type is the component type of
4483 * {@code viewArrayClass} and the list of coordinate types is
4484 * {@code (byte[], int)}, where the {@code int} coordinate type
4485 * corresponds to an argument that is an index into a {@code byte[]} array.
4486 * The returned VarHandle accesses bytes at an index in a {@code byte[]}
4487 * array, composing bytes to or from a value of the component type of
4488 * {@code viewArrayClass} according to the given endianness.
4489 * <p>
4490 * The supported component types (variables types) are {@code short},
4491 * {@code char}, {@code int}, {@code long}, {@code float} and
4492 * {@code double}.
4493 * <p>
4494 * Access of bytes at a given index will result in an
4495 * {@code ArrayIndexOutOfBoundsException} if the index is less than {@code 0}
4496 * or greater than the {@code byte[]} array length minus the size (in bytes)
4497 * of {@code T}.
4498 * <p>
4499 * Only plain {@linkplain VarHandle.AccessMode#GET get} and {@linkplain VarHandle.AccessMode#SET set}
4500 * access modes are supported by the returned var handle. For all other access modes, an
4501 * {@link UnsupportedOperationException} will be thrown.
4502 *
4503 * @apiNote if access modes other than plain access are required, clients should
4504 * consider using off-heap memory through
4505 * {@linkplain java.nio.ByteBuffer#allocateDirect(int) direct byte buffers} or
4506 * off-heap {@linkplain java.lang.foreign.MemorySegment memory segments},
4507 * or memory segments backed by a
4508 * {@linkplain java.lang.foreign.MemorySegment#ofArray(long[]) {@code long[]}},
4509 * for which stronger alignment guarantees can be made.
4510 *
4511 * @param viewArrayClass the view array class, with a component type of
4512 * type {@code T}
4513 * @param byteOrder the endianness of the view array elements, as
4514 * stored in the underlying {@code byte} array
4515 * @return a VarHandle giving access to elements of a {@code byte[]} array
4516 * viewed as if elements corresponding to the components type of the view
4517 * array class
4518 * @throws NullPointerException if viewArrayClass or byteOrder is null
4519 * @throws IllegalArgumentException if viewArrayClass is not an array type
4520 * @throws UnsupportedOperationException if the component type of
4521 * viewArrayClass is not supported as a variable type
4522 * @since 9
4523 */
4524 public static VarHandle byteArrayViewVarHandle(Class<?> viewArrayClass,
4525 ByteOrder byteOrder) throws IllegalArgumentException {
4526 Objects.requireNonNull(byteOrder);
4527 return VarHandles.byteArrayViewHandle(viewArrayClass,
4528 byteOrder == ByteOrder.BIG_ENDIAN);
4529 }
4530
4531 /**
4532 * Produces a VarHandle giving access to elements of a {@code ByteBuffer}
4533 * viewed as if it were an array of elements of a different primitive
4534 * component type to that of {@code byte}, such as {@code int[]} or
4535 * {@code long[]}.
4536 * The VarHandle's variable type is the component type of
4537 * {@code viewArrayClass} and the list of coordinate types is
4538 * {@code (ByteBuffer, int)}, where the {@code int} coordinate type
4539 * corresponds to an argument that is an index into a {@code byte[]} array.
4540 * The returned VarHandle accesses bytes at an index in a
4541 * {@code ByteBuffer}, composing bytes to or from a value of the component
4542 * type of {@code viewArrayClass} according to the given endianness.
4543 * <p>
4544 * The supported component types (variables types) are {@code short},
4545 * {@code char}, {@code int}, {@code long}, {@code float} and
4546 * {@code double}.
4547 * <p>
4548 * Access will result in a {@code ReadOnlyBufferException} for anything
4549 * other than the read access modes if the {@code ByteBuffer} is read-only.
4550 * <p>
4551 * Access of bytes at a given index will result in an
4552 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
4553 * or greater than the {@code ByteBuffer} limit minus the size (in bytes) of
4554 * {@code T}.
4555 * <p>
4556 * For heap byte buffers, access is always unaligned. As a result, only the plain
4557 * {@linkplain VarHandle.AccessMode#GET get}
4558 * and {@linkplain VarHandle.AccessMode#SET set} access modes are supported by the
4559 * returned var handle. For all other access modes, an {@link IllegalStateException}
4560 * will be thrown.
4561 * <p>
4562 * For direct buffers only, access of bytes at an index may be aligned or misaligned for {@code T},
4563 * with respect to the underlying memory address, {@code A} say, associated
4564 * with the {@code ByteBuffer} and index.
4565 * If access is misaligned then access for anything other than the
4566 * {@code get} and {@code set} access modes will result in an
4567 * {@code IllegalStateException}. In such cases atomic access is only
4568 * guaranteed with respect to the largest power of two that divides the GCD
4569 * of {@code A} and the size (in bytes) of {@code T}.
4570 * If access is aligned then following access modes are supported and are
4571 * guaranteed to support atomic access:
4572 * <ul>
4573 * <li>read write access modes for all {@code T}, with the exception of
4574 * access modes {@code get} and {@code set} for {@code long} and
4575 * {@code double} on 32-bit platforms.
4576 * <li>atomic update access modes for {@code int}, {@code long},
4577 * {@code float} or {@code double}.
4578 * (Future major platform releases of the JDK may support additional
4579 * types for certain currently unsupported access modes.)
4580 * <li>numeric atomic update access modes for {@code int} and {@code long}.
4581 * (Future major platform releases of the JDK may support additional
4582 * numeric types for certain currently unsupported access modes.)
4583 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
4584 * (Future major platform releases of the JDK may support additional
4585 * numeric types for certain currently unsupported access modes.)
4586 * </ul>
4587 * <p>
4588 * Misaligned access, and therefore atomicity guarantees, may be determined
4589 * for a {@code ByteBuffer}, {@code bb} (direct or otherwise), an
4590 * {@code index}, {@code T} and its corresponding boxed type,
4591 * {@code T_BOX}, as follows:
4592 * <pre>{@code
4593 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
4594 * ByteBuffer bb = ...
4595 * int misalignedAtIndex = bb.alignmentOffset(index, sizeOfT);
4596 * boolean isMisaligned = misalignedAtIndex != 0;
4597 * }</pre>
4598 * <p>
4599 * If the variable type is {@code float} or {@code double} then atomic
4600 * update access modes compare values using their bitwise representation
4601 * (see {@link Float#floatToRawIntBits} and
4602 * {@link Double#doubleToRawLongBits}, respectively).
4603 * @param viewArrayClass the view array class, with a component type of
4604 * type {@code T}
4605 * @param byteOrder the endianness of the view array elements, as
4606 * stored in the underlying {@code ByteBuffer} (Note this overrides the
4607 * endianness of a {@code ByteBuffer})
4608 * @return a VarHandle giving access to elements of a {@code ByteBuffer}
4609 * viewed as if elements corresponding to the components type of the view
4610 * array class
4611 * @throws NullPointerException if viewArrayClass or byteOrder is null
4612 * @throws IllegalArgumentException if viewArrayClass is not an array type
4613 * @throws UnsupportedOperationException if the component type of
4614 * viewArrayClass is not supported as a variable type
4615 * @since 9
4616 */
4617 public static VarHandle byteBufferViewVarHandle(Class<?> viewArrayClass,
4618 ByteOrder byteOrder) throws IllegalArgumentException {
4619 Objects.requireNonNull(byteOrder);
4620 return VarHandles.makeByteBufferViewHandle(viewArrayClass,
4621 byteOrder == ByteOrder.BIG_ENDIAN);
4622 }
4623
4624
4625 //--- method handle invocation (reflective style)
4626
4627 /**
4628 * Produces a method handle which will invoke any method handle of the
4629 * given {@code type}, with a given number of trailing arguments replaced by
4630 * a single trailing {@code Object[]} array.
4631 * The resulting invoker will be a method handle with the following
4632 * arguments:
4633 * <ul>
4634 * <li>a single {@code MethodHandle} target
4635 * <li>zero or more leading values (counted by {@code leadingArgCount})
4636 * <li>an {@code Object[]} array containing trailing arguments
4637 * </ul>
4638 * <p>
4639 * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
4640 * the indicated {@code type}.
4641 * That is, if the target is exactly of the given {@code type}, it will behave
4642 * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
4643 * is used to convert the target to the required {@code type}.
4644 * <p>
4645 * The type of the returned invoker will not be the given {@code type}, but rather
4646 * will have all parameters except the first {@code leadingArgCount}
4647 * replaced by a single array of type {@code Object[]}, which will be
4648 * the final parameter.
4649 * <p>
4650 * Before invoking its target, the invoker will spread the final array, apply
4651 * reference casts as necessary, and unbox and widen primitive arguments.
4652 * If, when the invoker is called, the supplied array argument does
4653 * not have the correct number of elements, the invoker will throw
4654 * an {@link IllegalArgumentException} instead of invoking the target.
4655 * <p>
4656 * This method is equivalent to the following code (though it may be more efficient):
4657 * {@snippet lang="java" :
4658 MethodHandle invoker = MethodHandles.invoker(type);
4659 int spreadArgCount = type.parameterCount() - leadingArgCount;
4660 invoker = invoker.asSpreader(Object[].class, spreadArgCount);
4661 return invoker;
4662 * }
4663 * This method throws no reflective or security exceptions.
4664 * @param type the desired target type
4665 * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
4666 * @return a method handle suitable for invoking any method handle of the given type
4667 * @throws NullPointerException if {@code type} is null
4668 * @throws IllegalArgumentException if {@code leadingArgCount} is not in
4669 * the range from 0 to {@code type.parameterCount()} inclusive,
4670 * or if the resulting method handle's type would have
4671 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4672 */
4673 public static MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
4674 if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
4675 throw newIllegalArgumentException("bad argument count", leadingArgCount);
4676 type = type.asSpreaderType(Object[].class, leadingArgCount, type.parameterCount() - leadingArgCount);
4677 return type.invokers().spreadInvoker(leadingArgCount);
4678 }
4679
4680 /**
4681 * Produces a special <em>invoker method handle</em> which can be used to
4682 * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
4683 * The resulting invoker will have a type which is
4684 * exactly equal to the desired type, except that it will accept
4685 * an additional leading argument of type {@code MethodHandle}.
4686 * <p>
4687 * This method is equivalent to the following code (though it may be more efficient):
4688 * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)}
4689 *
4690 * <p style="font-size:smaller;">
4691 * <em>Discussion:</em>
4692 * Invoker method handles can be useful when working with variable method handles
4693 * of unknown types.
4694 * For example, to emulate an {@code invokeExact} call to a variable method
4695 * handle {@code M}, extract its type {@code T},
4696 * look up the invoker method {@code X} for {@code T},
4697 * and call the invoker method, as {@code X.invoke(T, A...)}.
4698 * (It would not work to call {@code X.invokeExact}, since the type {@code T}
4699 * is unknown.)
4700 * If spreading, collecting, or other argument transformations are required,
4701 * they can be applied once to the invoker {@code X} and reused on many {@code M}
4702 * method handle values, as long as they are compatible with the type of {@code X}.
4703 * <p style="font-size:smaller;">
4704 * <em>(Note: The invoker method is not available via the Core Reflection API.
4705 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
4706 * on the declared {@code invokeExact} or {@code invoke} method will raise an
4707 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
4708 * <p>
4709 * This method throws no reflective or security exceptions.
4710 * @param type the desired target type
4711 * @return a method handle suitable for invoking any method handle of the given type
4712 * @throws IllegalArgumentException if the resulting method handle's type would have
4713 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4714 */
4715 public static MethodHandle exactInvoker(MethodType type) {
4716 return type.invokers().exactInvoker();
4717 }
4718
4719 /**
4720 * Produces a special <em>invoker method handle</em> which can be used to
4721 * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
4722 * The resulting invoker will have a type which is
4723 * exactly equal to the desired type, except that it will accept
4724 * an additional leading argument of type {@code MethodHandle}.
4725 * <p>
4726 * Before invoking its target, if the target differs from the expected type,
4727 * the invoker will apply reference casts as
4728 * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
4729 * Similarly, the return value will be converted as necessary.
4730 * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
4731 * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
4732 * <p>
4733 * This method is equivalent to the following code (though it may be more efficient):
4734 * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)}
4735 * <p style="font-size:smaller;">
4736 * <em>Discussion:</em>
4737 * A {@linkplain MethodType#genericMethodType general method type} is one which
4738 * mentions only {@code Object} arguments and return values.
4739 * An invoker for such a type is capable of calling any method handle
4740 * of the same arity as the general type.
4741 * <p style="font-size:smaller;">
4742 * <em>(Note: The invoker method is not available via the Core Reflection API.
4743 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
4744 * on the declared {@code invokeExact} or {@code invoke} method will raise an
4745 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
4746 * <p>
4747 * This method throws no reflective or security exceptions.
4748 * @param type the desired target type
4749 * @return a method handle suitable for invoking any method handle convertible to the given type
4750 * @throws IllegalArgumentException if the resulting method handle's type would have
4751 * <a href="MethodHandle.html#maxarity">too many parameters</a>
4752 */
4753 public static MethodHandle invoker(MethodType type) {
4754 return type.invokers().genericInvoker();
4755 }
4756
4757 /**
4758 * Produces a special <em>invoker method handle</em> which can be used to
4759 * invoke a signature-polymorphic access mode method on any VarHandle whose
4760 * associated access mode type is compatible with the given type.
4761 * The resulting invoker will have a type which is exactly equal to the
4762 * desired given type, except that it will accept an additional leading
4763 * argument of type {@code VarHandle}.
4764 *
4765 * @param accessMode the VarHandle access mode
4766 * @param type the desired target type
4767 * @return a method handle suitable for invoking an access mode method of
4768 * any VarHandle whose access mode type is of the given type.
4769 * @since 9
4770 */
4771 public static MethodHandle varHandleExactInvoker(VarHandle.AccessMode accessMode, MethodType type) {
4772 return type.invokers().varHandleMethodExactInvoker(accessMode);
4773 }
4774
4775 /**
4776 * Produces a special <em>invoker method handle</em> which can be used to
4777 * invoke a signature-polymorphic access mode method on any VarHandle whose
4778 * associated access mode type is compatible with the given type.
4779 * The resulting invoker will have a type which is exactly equal to the
4780 * desired given type, except that it will accept an additional leading
4781 * argument of type {@code VarHandle}.
4782 * <p>
4783 * Before invoking its target, if the access mode type differs from the
4784 * desired given type, the invoker will apply reference casts as necessary
4785 * and box, unbox, or widen primitive values, as if by
4786 * {@link MethodHandle#asType asType}. Similarly, the return value will be
4787 * converted as necessary.
4788 * <p>
4789 * This method is equivalent to the following code (though it may be more
4790 * efficient): {@code publicLookup().findVirtual(VarHandle.class, accessMode.name(), type)}
4791 *
4792 * @param accessMode the VarHandle access mode
4793 * @param type the desired target type
4794 * @return a method handle suitable for invoking an access mode method of
4795 * any VarHandle whose access mode type is convertible to the given
4796 * type.
4797 * @since 9
4798 */
4799 public static MethodHandle varHandleInvoker(VarHandle.AccessMode accessMode, MethodType type) {
4800 return type.invokers().varHandleMethodInvoker(accessMode);
4801 }
4802
4803 /*non-public*/
4804 static MethodHandle basicInvoker(MethodType type) {
4805 return type.invokers().basicInvoker();
4806 }
4807
4808 //--- method handle modification (creation from other method handles)
4809
4810 /**
4811 * Produces a method handle which adapts the type of the
4812 * given method handle to a new type by pairwise argument and return type conversion.
4813 * The original type and new type must have the same number of arguments.
4814 * The resulting method handle is guaranteed to report a type
4815 * which is equal to the desired new type.
4816 * <p>
4817 * If the original type and new type are equal, returns target.
4818 * <p>
4819 * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
4820 * and some additional conversions are also applied if those conversions fail.
4821 * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied
4822 * if possible, before or instead of any conversions done by {@code asType}:
4823 * <ul>
4824 * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type,
4825 * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast.
4826 * (This treatment of interfaces follows the usage of the bytecode verifier.)
4827 * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive,
4828 * the boolean is converted to a byte value, 1 for true, 0 for false.
4829 * (This treatment follows the usage of the bytecode verifier.)
4830 * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive,
4831 * <em>T0</em> is converted to byte via Java casting conversion (JLS {@jls 5.5}),
4832 * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}.
4833 * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean,
4834 * then a Java casting conversion (JLS {@jls 5.5}) is applied.
4835 * (Specifically, <em>T0</em> will convert to <em>T1</em> by
4836 * widening and/or narrowing.)
4837 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
4838 * conversion will be applied at runtime, possibly followed
4839 * by a Java casting conversion (JLS {@jls 5.5}) on the primitive value,
4840 * possibly followed by a conversion from byte to boolean by testing
4841 * the low-order bit.
4842 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive,
4843 * and if the reference is null at runtime, a zero value is introduced.
4844 * </ul>
4845 * @param target the method handle to invoke after arguments are retyped
4846 * @param newType the expected type of the new method handle
4847 * @return a method handle which delegates to the target after performing
4848 * any necessary argument conversions, and arranges for any
4849 * necessary return value conversions
4850 * @throws NullPointerException if either argument is null
4851 * @throws WrongMethodTypeException if the conversion cannot be made
4852 * @see MethodHandle#asType
4853 */
4854 public static MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
4855 explicitCastArgumentsChecks(target, newType);
4856 // use the asTypeCache when possible:
4857 MethodType oldType = target.type();
4858 if (oldType == newType) return target;
4859 if (oldType.explicitCastEquivalentToAsType(newType)) {
4860 return target.asFixedArity().asType(newType);
4861 }
4862 return MethodHandleImpl.makePairwiseConvert(target, newType, false);
4863 }
4864
4865 private static void explicitCastArgumentsChecks(MethodHandle target, MethodType newType) {
4866 if (target.type().parameterCount() != newType.parameterCount()) {
4867 throw new WrongMethodTypeException("cannot explicitly cast " + target + " to " + newType);
4868 }
4869 }
4870
4871 /**
4872 * Produces a method handle which adapts the calling sequence of the
4873 * given method handle to a new type, by reordering the arguments.
4874 * The resulting method handle is guaranteed to report a type
4875 * which is equal to the desired new type.
4876 * <p>
4877 * The given array controls the reordering.
4878 * Call {@code #I} the number of incoming parameters (the value
4879 * {@code newType.parameterCount()}, and call {@code #O} the number
4880 * of outgoing parameters (the value {@code target.type().parameterCount()}).
4881 * Then the length of the reordering array must be {@code #O},
4882 * and each element must be a non-negative number less than {@code #I}.
4883 * For every {@code N} less than {@code #O}, the {@code N}-th
4884 * outgoing argument will be taken from the {@code I}-th incoming
4885 * argument, where {@code I} is {@code reorder[N]}.
4886 * <p>
4887 * No argument or return value conversions are applied.
4888 * The type of each incoming argument, as determined by {@code newType},
4889 * must be identical to the type of the corresponding outgoing parameter
4890 * or parameters in the target method handle.
4891 * The return type of {@code newType} must be identical to the return
4892 * type of the original target.
4893 * <p>
4894 * The reordering array need not specify an actual permutation.
4895 * An incoming argument will be duplicated if its index appears
4896 * more than once in the array, and an incoming argument will be dropped
4897 * if its index does not appear in the array.
4898 * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
4899 * incoming arguments which are not mentioned in the reordering array
4900 * may be of any type, as determined only by {@code newType}.
4901 * {@snippet lang="java" :
4902 import static java.lang.invoke.MethodHandles.*;
4903 import static java.lang.invoke.MethodType.*;
4904 ...
4905 MethodType intfn1 = methodType(int.class, int.class);
4906 MethodType intfn2 = methodType(int.class, int.class, int.class);
4907 MethodHandle sub = ... (int x, int y) -> (x-y) ...;
4908 assert(sub.type().equals(intfn2));
4909 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
4910 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
4911 assert((int)rsub.invokeExact(1, 100) == 99);
4912 MethodHandle add = ... (int x, int y) -> (x+y) ...;
4913 assert(add.type().equals(intfn2));
4914 MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
4915 assert(twice.type().equals(intfn1));
4916 assert((int)twice.invokeExact(21) == 42);
4917 * }
4918 * <p>
4919 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4920 * variable-arity method handle}, even if the original target method handle was.
4921 * @param target the method handle to invoke after arguments are reordered
4922 * @param newType the expected type of the new method handle
4923 * @param reorder an index array which controls the reordering
4924 * @return a method handle which delegates to the target after it
4925 * drops unused arguments and moves and/or duplicates the other arguments
4926 * @throws NullPointerException if any argument is null
4927 * @throws IllegalArgumentException if the index array length is not equal to
4928 * the arity of the target, or if any index array element
4929 * not a valid index for a parameter of {@code newType},
4930 * or if two corresponding parameter types in
4931 * {@code target.type()} and {@code newType} are not identical,
4932 */
4933 public static MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
4934 reorder = reorder.clone(); // get a private copy
4935 MethodType oldType = target.type();
4936 permuteArgumentChecks(reorder, newType, oldType);
4937 // first detect dropped arguments and handle them separately
4938 int[] originalReorder = reorder;
4939 BoundMethodHandle result = target.rebind();
4940 LambdaForm form = result.form;
4941 int newArity = newType.parameterCount();
4942 // Normalize the reordering into a real permutation,
4943 // by removing duplicates and adding dropped elements.
4944 // This somewhat improves lambda form caching, as well
4945 // as simplifying the transform by breaking it up into steps.
4946 for (int ddIdx; (ddIdx = findFirstDupOrDrop(reorder, newArity)) != 0; ) {
4947 if (ddIdx > 0) {
4948 // We found a duplicated entry at reorder[ddIdx].
4949 // Example: (x,y,z)->asList(x,y,z)
4950 // permuted by [1*,0,1] => (a0,a1)=>asList(a1,a0,a1)
4951 // permuted by [0,1,0*] => (a0,a1)=>asList(a0,a1,a0)
4952 // The starred element corresponds to the argument
4953 // deleted by the dupArgumentForm transform.
4954 int srcPos = ddIdx, dstPos = srcPos, dupVal = reorder[srcPos];
4955 boolean killFirst = false;
4956 for (int val; (val = reorder[--dstPos]) != dupVal; ) {
4957 // Set killFirst if the dup is larger than an intervening position.
4958 // This will remove at least one inversion from the permutation.
4959 if (dupVal > val) killFirst = true;
4960 }
4961 if (!killFirst) {
4962 srcPos = dstPos;
4963 dstPos = ddIdx;
4964 }
4965 form = form.editor().dupArgumentForm(1 + srcPos, 1 + dstPos);
4966 assert (reorder[srcPos] == reorder[dstPos]);
4967 oldType = oldType.dropParameterTypes(dstPos, dstPos + 1);
4968 // contract the reordering by removing the element at dstPos
4969 int tailPos = dstPos + 1;
4970 System.arraycopy(reorder, tailPos, reorder, dstPos, reorder.length - tailPos);
4971 reorder = Arrays.copyOf(reorder, reorder.length - 1);
4972 } else {
4973 int dropVal = ~ddIdx, insPos = 0;
4974 while (insPos < reorder.length && reorder[insPos] < dropVal) {
4975 // Find first element of reorder larger than dropVal.
4976 // This is where we will insert the dropVal.
4977 insPos += 1;
4978 }
4979 Class<?> ptype = newType.parameterType(dropVal);
4980 form = form.editor().addArgumentForm(1 + insPos, BasicType.basicType(ptype));
4981 oldType = oldType.insertParameterTypes(insPos, ptype);
4982 // expand the reordering by inserting an element at insPos
4983 int tailPos = insPos + 1;
4984 reorder = Arrays.copyOf(reorder, reorder.length + 1);
4985 System.arraycopy(reorder, insPos, reorder, tailPos, reorder.length - tailPos);
4986 reorder[insPos] = dropVal;
4987 }
4988 assert (permuteArgumentChecks(reorder, newType, oldType));
4989 }
4990 assert (reorder.length == newArity); // a perfect permutation
4991 // Note: This may cache too many distinct LFs. Consider backing off to varargs code.
4992 form = form.editor().permuteArgumentsForm(1, reorder);
4993 if (newType == result.type() && form == result.internalForm())
4994 return result;
4995 return result.copyWith(newType, form);
4996 }
4997
4998 /**
4999 * Return an indication of any duplicate or omission in reorder.
5000 * If the reorder contains a duplicate entry, return the index of the second occurrence.
5001 * Otherwise, return ~(n), for the first n in [0..newArity-1] that is not present in reorder.
5002 * Otherwise, return zero.
5003 * If an element not in [0..newArity-1] is encountered, return reorder.length.
5004 */
5005 private static int findFirstDupOrDrop(int[] reorder, int newArity) {
5006 final int BIT_LIMIT = 63; // max number of bits in bit mask
5007 if (newArity < BIT_LIMIT) {
5008 long mask = 0;
5009 for (int i = 0; i < reorder.length; i++) {
5010 int arg = reorder[i];
5011 if (arg >= newArity) {
5012 return reorder.length;
5013 }
5014 long bit = 1L << arg;
5015 if ((mask & bit) != 0) {
5016 return i; // >0 indicates a dup
5017 }
5018 mask |= bit;
5019 }
5020 if (mask == (1L << newArity) - 1) {
5021 assert(Long.numberOfTrailingZeros(Long.lowestOneBit(~mask)) == newArity);
5022 return 0;
5023 }
5024 // find first zero
5025 long zeroBit = Long.lowestOneBit(~mask);
5026 int zeroPos = Long.numberOfTrailingZeros(zeroBit);
5027 assert(zeroPos <= newArity);
5028 if (zeroPos == newArity) {
5029 return 0;
5030 }
5031 return ~zeroPos;
5032 } else {
5033 // same algorithm, different bit set
5034 BitSet mask = new BitSet(newArity);
5035 for (int i = 0; i < reorder.length; i++) {
5036 int arg = reorder[i];
5037 if (arg >= newArity) {
5038 return reorder.length;
5039 }
5040 if (mask.get(arg)) {
5041 return i; // >0 indicates a dup
5042 }
5043 mask.set(arg);
5044 }
5045 int zeroPos = mask.nextClearBit(0);
5046 assert(zeroPos <= newArity);
5047 if (zeroPos == newArity) {
5048 return 0;
5049 }
5050 return ~zeroPos;
5051 }
5052 }
5053
5054 static boolean permuteArgumentChecks(int[] reorder, MethodType newType, MethodType oldType) {
5055 if (newType.returnType() != oldType.returnType())
5056 throw newIllegalArgumentException("return types do not match",
5057 oldType, newType);
5058 if (reorder.length != oldType.parameterCount())
5059 throw newIllegalArgumentException("old type parameter count and reorder array length do not match",
5060 oldType, Arrays.toString(reorder));
5061
5062 int limit = newType.parameterCount();
5063 for (int j = 0; j < reorder.length; j++) {
5064 int i = reorder[j];
5065 if (i < 0 || i >= limit) {
5066 throw newIllegalArgumentException("index is out of bounds for new type",
5067 i, newType);
5068 }
5069 Class<?> src = newType.parameterType(i);
5070 Class<?> dst = oldType.parameterType(j);
5071 if (src != dst)
5072 throw newIllegalArgumentException("parameter types do not match after reorder",
5073 oldType, newType);
5074 }
5075 return true;
5076 }
5077
5078 /**
5079 * Produces a method handle of the requested return type which returns the given
5080 * constant value every time it is invoked.
5081 * <p>
5082 * Before the method handle is returned, the passed-in value is converted to the requested type.
5083 * If the requested type is primitive, widening primitive conversions are attempted,
5084 * else reference conversions are attempted.
5085 * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
5086 * @param type the return type of the desired method handle
5087 * @param value the value to return
5088 * @return a method handle of the given return type and no arguments, which always returns the given value
5089 * @throws NullPointerException if the {@code type} argument is null
5090 * @throws ClassCastException if the value cannot be converted to the required return type
5091 * @throws IllegalArgumentException if the given type is {@code void.class}
5092 */
5093 public static MethodHandle constant(Class<?> type, Object value) {
5094 if (type.isPrimitive()) {
5095 if (type == void.class)
5096 throw newIllegalArgumentException("void type");
5097 Wrapper w = Wrapper.forPrimitiveType(type);
5098 value = w.convert(value, type);
5099 if (w.zero().equals(value))
5100 return zero(w, type);
5101 return insertArguments(identity(type), 0, value);
5102 } else {
5103 if (value == null)
5104 return zero(Wrapper.OBJECT, type);
5105 return identity(type).bindTo(value);
5106 }
5107 }
5108
5109 /**
5110 * Produces a method handle which returns its sole argument when invoked.
5111 * @param type the type of the sole parameter and return value of the desired method handle
5112 * @return a unary method handle which accepts and returns the given type
5113 * @throws NullPointerException if the argument is null
5114 * @throws IllegalArgumentException if the given type is {@code void.class}
5115 */
5116 public static MethodHandle identity(Class<?> type) {
5117 Wrapper btw = (type.isPrimitive() ? Wrapper.forPrimitiveType(type) : Wrapper.OBJECT);
5118 int pos = btw.ordinal();
5119 MethodHandle ident = IDENTITY_MHS[pos];
5120 if (ident == null) {
5121 ident = setCachedMethodHandle(IDENTITY_MHS, pos, makeIdentity(btw.primitiveType()));
5122 }
5123 if (ident.type().returnType() == type)
5124 return ident;
5125 // something like identity(Foo.class); do not bother to intern these
5126 assert (btw == Wrapper.OBJECT);
5127 return makeIdentity(type);
5128 }
5129
5130 /**
5131 * Produces a constant method handle of the requested return type which
5132 * returns the default value for that type every time it is invoked.
5133 * The resulting constant method handle will have no side effects.
5134 * <p>The returned method handle is equivalent to {@code empty(methodType(type))}.
5135 * It is also equivalent to {@code explicitCastArguments(constant(Object.class, null), methodType(type))},
5136 * since {@code explicitCastArguments} converts {@code null} to default values.
5137 * @param type the expected return type of the desired method handle
5138 * @return a constant method handle that takes no arguments
5139 * and returns the default value of the given type (or void, if the type is void)
5140 * @throws NullPointerException if the argument is null
5141 * @see MethodHandles#constant
5142 * @see MethodHandles#empty
5143 * @see MethodHandles#explicitCastArguments
5144 * @since 9
5145 */
5146 public static MethodHandle zero(Class<?> type) {
5147 Objects.requireNonNull(type);
5148 return type.isPrimitive() ? zero(Wrapper.forPrimitiveType(type), type) : zero(Wrapper.OBJECT, type);
5149 }
5150
5151 private static MethodHandle identityOrVoid(Class<?> type) {
5152 return type == void.class ? zero(type) : identity(type);
5153 }
5154
5155 /**
5156 * Produces a method handle of the requested type which ignores any arguments, does nothing,
5157 * and returns a suitable default depending on the return type.
5158 * That is, it returns a zero primitive value, a {@code null}, or {@code void}.
5159 * <p>The returned method handle is equivalent to
5160 * {@code dropArguments(zero(type.returnType()), 0, type.parameterList())}.
5161 *
5162 * @apiNote Given a predicate and target, a useful "if-then" construct can be produced as
5163 * {@code guardWithTest(pred, target, empty(target.type())}.
5164 * @param type the type of the desired method handle
5165 * @return a constant method handle of the given type, which returns a default value of the given return type
5166 * @throws NullPointerException if the argument is null
5167 * @see MethodHandles#zero
5168 * @see MethodHandles#constant
5169 * @since 9
5170 */
5171 public static MethodHandle empty(MethodType type) {
5172 Objects.requireNonNull(type);
5173 return dropArgumentsTrusted(zero(type.returnType()), 0, type.ptypes());
5174 }
5175
5176 private static final MethodHandle[] IDENTITY_MHS = new MethodHandle[Wrapper.COUNT];
5177 private static MethodHandle makeIdentity(Class<?> ptype) {
5178 MethodType mtype = methodType(ptype, ptype);
5179 LambdaForm lform = LambdaForm.identityForm(BasicType.basicType(ptype));
5180 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.IDENTITY);
5181 }
5182
5183 private static MethodHandle zero(Wrapper btw, Class<?> rtype) {
5184 int pos = btw.ordinal();
5185 MethodHandle zero = ZERO_MHS[pos];
5186 if (zero == null) {
5187 zero = setCachedMethodHandle(ZERO_MHS, pos, makeZero(btw.primitiveType()));
5188 }
5189 if (zero.type().returnType() == rtype)
5190 return zero;
5191 assert(btw == Wrapper.OBJECT);
5192 return makeZero(rtype);
5193 }
5194 private static final MethodHandle[] ZERO_MHS = new MethodHandle[Wrapper.COUNT];
5195 private static MethodHandle makeZero(Class<?> rtype) {
5196 MethodType mtype = methodType(rtype);
5197 LambdaForm lform = LambdaForm.zeroForm(BasicType.basicType(rtype));
5198 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.ZERO);
5199 }
5200
5201 private static synchronized MethodHandle setCachedMethodHandle(MethodHandle[] cache, int pos, MethodHandle value) {
5202 // Simulate a CAS, to avoid racy duplication of results.
5203 MethodHandle prev = cache[pos];
5204 if (prev != null) return prev;
5205 return cache[pos] = value;
5206 }
5207
5208 /**
5209 * Provides a target method handle with one or more <em>bound arguments</em>
5210 * in advance of the method handle's invocation.
5211 * The formal parameters to the target corresponding to the bound
5212 * arguments are called <em>bound parameters</em>.
5213 * Returns a new method handle which saves away the bound arguments.
5214 * When it is invoked, it receives arguments for any non-bound parameters,
5215 * binds the saved arguments to their corresponding parameters,
5216 * and calls the original target.
5217 * <p>
5218 * The type of the new method handle will drop the types for the bound
5219 * parameters from the original target type, since the new method handle
5220 * will no longer require those arguments to be supplied by its callers.
5221 * <p>
5222 * Each given argument object must match the corresponding bound parameter type.
5223 * If a bound parameter type is a primitive, the argument object
5224 * must be a wrapper, and will be unboxed to produce the primitive value.
5225 * <p>
5226 * The {@code pos} argument selects which parameters are to be bound.
5227 * It may range between zero and <i>N-L</i> (inclusively),
5228 * where <i>N</i> is the arity of the target method handle
5229 * and <i>L</i> is the length of the values array.
5230 * <p>
5231 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5232 * variable-arity method handle}, even if the original target method handle was.
5233 * @param target the method handle to invoke after the argument is inserted
5234 * @param pos where to insert the argument (zero for the first)
5235 * @param values the series of arguments to insert
5236 * @return a method handle which inserts an additional argument,
5237 * before calling the original method handle
5238 * @throws NullPointerException if the target or the {@code values} array is null
5239 * @throws IllegalArgumentException if {@code pos} is less than {@code 0} or greater than
5240 * {@code N - L} where {@code N} is the arity of the target method handle and {@code L}
5241 * is the length of the values array.
5242 * @throws ClassCastException if an argument does not match the corresponding bound parameter
5243 * type.
5244 * @see MethodHandle#bindTo
5245 */
5246 public static MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
5247 int insCount = values.length;
5248 Class<?>[] ptypes = insertArgumentsChecks(target, insCount, pos);
5249 if (insCount == 0) return target;
5250 BoundMethodHandle result = target.rebind();
5251 for (int i = 0; i < insCount; i++) {
5252 Object value = values[i];
5253 Class<?> ptype = ptypes[pos+i];
5254 if (ptype.isPrimitive()) {
5255 result = insertArgumentPrimitive(result, pos, ptype, value);
5256 } else {
5257 value = ptype.cast(value); // throw CCE if needed
5258 result = result.bindArgumentL(pos, value);
5259 }
5260 }
5261 return result;
5262 }
5263
5264 private static BoundMethodHandle insertArgumentPrimitive(BoundMethodHandle result, int pos,
5265 Class<?> ptype, Object value) {
5266 Wrapper w = Wrapper.forPrimitiveType(ptype);
5267 // perform unboxing and/or primitive conversion
5268 value = w.convert(value, ptype);
5269 return switch (w) {
5270 case INT -> result.bindArgumentI(pos, (int) value);
5271 case LONG -> result.bindArgumentJ(pos, (long) value);
5272 case FLOAT -> result.bindArgumentF(pos, (float) value);
5273 case DOUBLE -> result.bindArgumentD(pos, (double) value);
5274 default -> result.bindArgumentI(pos, ValueConversions.widenSubword(value));
5275 };
5276 }
5277
5278 private static Class<?>[] insertArgumentsChecks(MethodHandle target, int insCount, int pos) throws RuntimeException {
5279 MethodType oldType = target.type();
5280 int outargs = oldType.parameterCount();
5281 int inargs = outargs - insCount;
5282 if (inargs < 0)
5283 throw newIllegalArgumentException("too many values to insert");
5284 if (pos < 0 || pos > inargs)
5285 throw newIllegalArgumentException("no argument type to append");
5286 return oldType.ptypes();
5287 }
5288
5289 /**
5290 * Produces a method handle which will discard some dummy arguments
5291 * before calling some other specified <i>target</i> method handle.
5292 * The type of the new method handle will be the same as the target's type,
5293 * except it will also include the dummy argument types,
5294 * at some given position.
5295 * <p>
5296 * The {@code pos} argument may range between zero and <i>N</i>,
5297 * where <i>N</i> is the arity of the target.
5298 * If {@code pos} is zero, the dummy arguments will precede
5299 * the target's real arguments; if {@code pos} is <i>N</i>
5300 * they will come after.
5301 * <p>
5302 * <b>Example:</b>
5303 * {@snippet lang="java" :
5304 import static java.lang.invoke.MethodHandles.*;
5305 import static java.lang.invoke.MethodType.*;
5306 ...
5307 MethodHandle cat = lookup().findVirtual(String.class,
5308 "concat", methodType(String.class, String.class));
5309 assertEquals("xy", (String) cat.invokeExact("x", "y"));
5310 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
5311 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
5312 assertEquals(bigType, d0.type());
5313 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
5314 * }
5315 * <p>
5316 * This method is also equivalent to the following code:
5317 * <blockquote><pre>
5318 * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))}
5319 * </pre></blockquote>
5320 * @param target the method handle to invoke after the arguments are dropped
5321 * @param pos position of first argument to drop (zero for the leftmost)
5322 * @param valueTypes the type(s) of the argument(s) to drop
5323 * @return a method handle which drops arguments of the given types,
5324 * before calling the original method handle
5325 * @throws NullPointerException if the target is null,
5326 * or if the {@code valueTypes} list or any of its elements is null
5327 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
5328 * or if {@code pos} is negative or greater than the arity of the target,
5329 * or if the new method handle's type would have too many parameters
5330 */
5331 public static MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) {
5332 return dropArgumentsTrusted(target, pos, valueTypes.toArray(new Class<?>[0]).clone());
5333 }
5334
5335 static MethodHandle dropArgumentsTrusted(MethodHandle target, int pos, Class<?>[] valueTypes) {
5336 MethodType oldType = target.type(); // get NPE
5337 int dropped = dropArgumentChecks(oldType, pos, valueTypes);
5338 MethodType newType = oldType.insertParameterTypes(pos, valueTypes);
5339 if (dropped == 0) return target;
5340 BoundMethodHandle result = target.rebind();
5341 LambdaForm lform = result.form;
5342 int insertFormArg = 1 + pos;
5343 for (Class<?> ptype : valueTypes) {
5344 lform = lform.editor().addArgumentForm(insertFormArg++, BasicType.basicType(ptype));
5345 }
5346 result = result.copyWith(newType, lform);
5347 return result;
5348 }
5349
5350 private static int dropArgumentChecks(MethodType oldType, int pos, Class<?>[] valueTypes) {
5351 int dropped = valueTypes.length;
5352 MethodType.checkSlotCount(dropped);
5353 int outargs = oldType.parameterCount();
5354 int inargs = outargs + dropped;
5355 if (pos < 0 || pos > outargs)
5356 throw newIllegalArgumentException("no argument type to remove"
5357 + Arrays.asList(oldType, pos, valueTypes, inargs, outargs)
5358 );
5359 return dropped;
5360 }
5361
5362 /**
5363 * Produces a method handle which will discard some dummy arguments
5364 * before calling some other specified <i>target</i> method handle.
5365 * The type of the new method handle will be the same as the target's type,
5366 * except it will also include the dummy argument types,
5367 * at some given position.
5368 * <p>
5369 * The {@code pos} argument may range between zero and <i>N</i>,
5370 * where <i>N</i> is the arity of the target.
5371 * If {@code pos} is zero, the dummy arguments will precede
5372 * the target's real arguments; if {@code pos} is <i>N</i>
5373 * they will come after.
5374 * @apiNote
5375 * {@snippet lang="java" :
5376 import static java.lang.invoke.MethodHandles.*;
5377 import static java.lang.invoke.MethodType.*;
5378 ...
5379 MethodHandle cat = lookup().findVirtual(String.class,
5380 "concat", methodType(String.class, String.class));
5381 assertEquals("xy", (String) cat.invokeExact("x", "y"));
5382 MethodHandle d0 = dropArguments(cat, 0, String.class);
5383 assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
5384 MethodHandle d1 = dropArguments(cat, 1, String.class);
5385 assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
5386 MethodHandle d2 = dropArguments(cat, 2, String.class);
5387 assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
5388 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
5389 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
5390 * }
5391 * <p>
5392 * This method is also equivalent to the following code:
5393 * <blockquote><pre>
5394 * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))}
5395 * </pre></blockquote>
5396 * @param target the method handle to invoke after the arguments are dropped
5397 * @param pos position of first argument to drop (zero for the leftmost)
5398 * @param valueTypes the type(s) of the argument(s) to drop
5399 * @return a method handle which drops arguments of the given types,
5400 * before calling the original method handle
5401 * @throws NullPointerException if the target is null,
5402 * or if the {@code valueTypes} array or any of its elements is null
5403 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
5404 * or if {@code pos} is negative or greater than the arity of the target,
5405 * or if the new method handle's type would have
5406 * <a href="MethodHandle.html#maxarity">too many parameters</a>
5407 */
5408 public static MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
5409 return dropArgumentsTrusted(target, pos, valueTypes.clone());
5410 }
5411
5412 /* Convenience overloads for trusting internal low-arity call-sites */
5413 static MethodHandle dropArguments(MethodHandle target, int pos, Class<?> valueType1) {
5414 return dropArgumentsTrusted(target, pos, new Class<?>[] { valueType1 });
5415 }
5416 static MethodHandle dropArguments(MethodHandle target, int pos, Class<?> valueType1, Class<?> valueType2) {
5417 return dropArgumentsTrusted(target, pos, new Class<?>[] { valueType1, valueType2 });
5418 }
5419
5420 // private version which allows caller some freedom with error handling
5421 private static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, Class<?>[] newTypes, int pos,
5422 boolean nullOnFailure) {
5423 Class<?>[] oldTypes = target.type().ptypes();
5424 int match = oldTypes.length;
5425 if (skip != 0) {
5426 if (skip < 0 || skip > match) {
5427 throw newIllegalArgumentException("illegal skip", skip, target);
5428 }
5429 oldTypes = Arrays.copyOfRange(oldTypes, skip, match);
5430 match -= skip;
5431 }
5432 Class<?>[] addTypes = newTypes;
5433 int add = addTypes.length;
5434 if (pos != 0) {
5435 if (pos < 0 || pos > add) {
5436 throw newIllegalArgumentException("illegal pos", pos, Arrays.toString(newTypes));
5437 }
5438 addTypes = Arrays.copyOfRange(addTypes, pos, add);
5439 add -= pos;
5440 assert(addTypes.length == add);
5441 }
5442 // Do not add types which already match the existing arguments.
5443 if (match > add || !Arrays.equals(oldTypes, 0, oldTypes.length, addTypes, 0, match)) {
5444 if (nullOnFailure) {
5445 return null;
5446 }
5447 throw newIllegalArgumentException("argument lists do not match",
5448 Arrays.toString(oldTypes), Arrays.toString(newTypes));
5449 }
5450 addTypes = Arrays.copyOfRange(addTypes, match, add);
5451 add -= match;
5452 assert(addTypes.length == add);
5453 // newTypes: ( P*[pos], M*[match], A*[add] )
5454 // target: ( S*[skip], M*[match] )
5455 MethodHandle adapter = target;
5456 if (add > 0) {
5457 adapter = dropArgumentsTrusted(adapter, skip+ match, addTypes);
5458 }
5459 // adapter: (S*[skip], M*[match], A*[add] )
5460 if (pos > 0) {
5461 adapter = dropArgumentsTrusted(adapter, skip, Arrays.copyOfRange(newTypes, 0, pos));
5462 }
5463 // adapter: (S*[skip], P*[pos], M*[match], A*[add] )
5464 return adapter;
5465 }
5466
5467 /**
5468 * Adapts a target method handle to match the given parameter type list. If necessary, adds dummy arguments. Some
5469 * leading parameters can be skipped before matching begins. The remaining types in the {@code target}'s parameter
5470 * type list must be a sub-list of the {@code newTypes} type list at the starting position {@code pos}. The
5471 * resulting handle will have the target handle's parameter type list, with any non-matching parameter types (before
5472 * or after the matching sub-list) inserted in corresponding positions of the target's original parameters, as if by
5473 * {@link #dropArguments(MethodHandle, int, Class[])}.
5474 * <p>
5475 * The resulting handle will have the same return type as the target handle.
5476 * <p>
5477 * In more formal terms, assume these two type lists:<ul>
5478 * <li>The target handle has the parameter type list {@code S..., M...}, with as many types in {@code S} as
5479 * indicated by {@code skip}. The {@code M} types are those that are supposed to match part of the given type list,
5480 * {@code newTypes}.
5481 * <li>The {@code newTypes} list contains types {@code P..., M..., A...}, with as many types in {@code P} as
5482 * indicated by {@code pos}. The {@code M} types are precisely those that the {@code M} types in the target handle's
5483 * parameter type list are supposed to match. The types in {@code A} are additional types found after the matching
5484 * sub-list.
5485 * </ul>
5486 * Given these assumptions, the result of an invocation of {@code dropArgumentsToMatch} will have the parameter type
5487 * list {@code S..., P..., M..., A...}, with the {@code P} and {@code A} types inserted as if by
5488 * {@link #dropArguments(MethodHandle, int, Class[])}.
5489 *
5490 * @apiNote
5491 * Two method handles whose argument lists are "effectively identical" (i.e., identical in a common prefix) may be
5492 * mutually converted to a common type by two calls to {@code dropArgumentsToMatch}, as follows:
5493 * {@snippet lang="java" :
5494 import static java.lang.invoke.MethodHandles.*;
5495 import static java.lang.invoke.MethodType.*;
5496 ...
5497 ...
5498 MethodHandle h0 = constant(boolean.class, true);
5499 MethodHandle h1 = lookup().findVirtual(String.class, "concat", methodType(String.class, String.class));
5500 MethodType bigType = h1.type().insertParameterTypes(1, String.class, int.class);
5501 MethodHandle h2 = dropArguments(h1, 0, bigType.parameterList());
5502 if (h1.type().parameterCount() < h2.type().parameterCount())
5503 h1 = dropArgumentsToMatch(h1, 0, h2.type().parameterList(), 0); // lengthen h1
5504 else
5505 h2 = dropArgumentsToMatch(h2, 0, h1.type().parameterList(), 0); // lengthen h2
5506 MethodHandle h3 = guardWithTest(h0, h1, h2);
5507 assertEquals("xy", h3.invoke("x", "y", 1, "a", "b", "c"));
5508 * }
5509 * @param target the method handle to adapt
5510 * @param skip number of targets parameters to disregard (they will be unchanged)
5511 * @param newTypes the list of types to match {@code target}'s parameter type list to
5512 * @param pos place in {@code newTypes} where the non-skipped target parameters must occur
5513 * @return a possibly adapted method handle
5514 * @throws NullPointerException if either argument is null
5515 * @throws IllegalArgumentException if any element of {@code newTypes} is {@code void.class},
5516 * or if {@code skip} is negative or greater than the arity of the target,
5517 * or if {@code pos} is negative or greater than the newTypes list size,
5518 * or if {@code newTypes} does not contain the {@code target}'s non-skipped parameter types at position
5519 * {@code pos}.
5520 * @since 9
5521 */
5522 public static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos) {
5523 Objects.requireNonNull(target);
5524 Objects.requireNonNull(newTypes);
5525 return dropArgumentsToMatch(target, skip, newTypes.toArray(new Class<?>[0]).clone(), pos, false);
5526 }
5527
5528 /**
5529 * Drop the return value of the target handle (if any).
5530 * The returned method handle will have a {@code void} return type.
5531 *
5532 * @param target the method handle to adapt
5533 * @return a possibly adapted method handle
5534 * @throws NullPointerException if {@code target} is null
5535 * @since 16
5536 */
5537 public static MethodHandle dropReturn(MethodHandle target) {
5538 Objects.requireNonNull(target);
5539 MethodType oldType = target.type();
5540 Class<?> oldReturnType = oldType.returnType();
5541 if (oldReturnType == void.class)
5542 return target;
5543 MethodType newType = oldType.changeReturnType(void.class);
5544 BoundMethodHandle result = target.rebind();
5545 LambdaForm lform = result.editor().filterReturnForm(V_TYPE, true);
5546 result = result.copyWith(newType, lform);
5547 return result;
5548 }
5549
5550 /**
5551 * Adapts a target method handle by pre-processing
5552 * one or more of its arguments, each with its own unary filter function,
5553 * and then calling the target with each pre-processed argument
5554 * replaced by the result of its corresponding filter function.
5555 * <p>
5556 * The pre-processing is performed by one or more method handles,
5557 * specified in the elements of the {@code filters} array.
5558 * The first element of the filter array corresponds to the {@code pos}
5559 * argument of the target, and so on in sequence.
5560 * The filter functions are invoked in left to right order.
5561 * <p>
5562 * Null arguments in the array are treated as identity functions,
5563 * and the corresponding arguments left unchanged.
5564 * (If there are no non-null elements in the array, the original target is returned.)
5565 * Each filter is applied to the corresponding argument of the adapter.
5566 * <p>
5567 * If a filter {@code F} applies to the {@code N}th argument of
5568 * the target, then {@code F} must be a method handle which
5569 * takes exactly one argument. The type of {@code F}'s sole argument
5570 * replaces the corresponding argument type of the target
5571 * in the resulting adapted method handle.
5572 * The return type of {@code F} must be identical to the corresponding
5573 * parameter type of the target.
5574 * <p>
5575 * It is an error if there are elements of {@code filters}
5576 * (null or not)
5577 * which do not correspond to argument positions in the target.
5578 * <p><b>Example:</b>
5579 * {@snippet lang="java" :
5580 import static java.lang.invoke.MethodHandles.*;
5581 import static java.lang.invoke.MethodType.*;
5582 ...
5583 MethodHandle cat = lookup().findVirtual(String.class,
5584 "concat", methodType(String.class, String.class));
5585 MethodHandle upcase = lookup().findVirtual(String.class,
5586 "toUpperCase", methodType(String.class));
5587 assertEquals("xy", (String) cat.invokeExact("x", "y"));
5588 MethodHandle f0 = filterArguments(cat, 0, upcase);
5589 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
5590 MethodHandle f1 = filterArguments(cat, 1, upcase);
5591 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
5592 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
5593 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
5594 * }
5595 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
5596 * denotes the return type of both the {@code target} and resulting adapter.
5597 * {@code P}/{@code p} and {@code B}/{@code b} represent the types and values
5598 * of the parameters and arguments that precede and follow the filter position
5599 * {@code pos}, respectively. {@code A[i]}/{@code a[i]} stand for the types and
5600 * values of the filtered parameters and arguments; they also represent the
5601 * return types of the {@code filter[i]} handles. The latter accept arguments
5602 * {@code v[i]} of type {@code V[i]}, which also appear in the signature of
5603 * the resulting adapter.
5604 * {@snippet lang="java" :
5605 * T target(P... p, A[i]... a[i], B... b);
5606 * A[i] filter[i](V[i]);
5607 * T adapter(P... p, V[i]... v[i], B... b) {
5608 * return target(p..., filter[i](v[i])..., b...);
5609 * }
5610 * }
5611 * <p>
5612 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5613 * variable-arity method handle}, even if the original target method handle was.
5614 *
5615 * @param target the method handle to invoke after arguments are filtered
5616 * @param pos the position of the first argument to filter
5617 * @param filters method handles to call initially on filtered arguments
5618 * @return method handle which incorporates the specified argument filtering logic
5619 * @throws NullPointerException if the target is null
5620 * or if the {@code filters} array is null
5621 * @throws IllegalArgumentException if a non-null element of {@code filters}
5622 * does not match a corresponding argument type of target as described above,
5623 * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()},
5624 * or if the resulting method handle's type would have
5625 * <a href="MethodHandle.html#maxarity">too many parameters</a>
5626 */
5627 public static MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
5628 // In method types arguments start at index 0, while the LF
5629 // editor have the MH receiver at position 0 - adjust appropriately.
5630 final int MH_RECEIVER_OFFSET = 1;
5631 filterArgumentsCheckArity(target, pos, filters);
5632 MethodHandle adapter = target;
5633
5634 // keep track of currently matched filters, as to optimize repeated filters
5635 int index = 0;
5636 int[] positions = new int[filters.length];
5637 MethodHandle filter = null;
5638
5639 // process filters in reverse order so that the invocation of
5640 // the resulting adapter will invoke the filters in left-to-right order
5641 for (int i = filters.length - 1; i >= 0; --i) {
5642 MethodHandle newFilter = filters[i];
5643 if (newFilter == null) continue; // ignore null elements of filters
5644
5645 // flush changes on update
5646 if (filter != newFilter) {
5647 if (filter != null) {
5648 if (index > 1) {
5649 adapter = filterRepeatedArgument(adapter, filter, Arrays.copyOf(positions, index));
5650 } else {
5651 adapter = filterArgument(adapter, positions[0] - 1, filter);
5652 }
5653 }
5654 filter = newFilter;
5655 index = 0;
5656 }
5657
5658 filterArgumentChecks(target, pos + i, newFilter);
5659 positions[index++] = pos + i + MH_RECEIVER_OFFSET;
5660 }
5661 if (index > 1) {
5662 adapter = filterRepeatedArgument(adapter, filter, Arrays.copyOf(positions, index));
5663 } else if (index == 1) {
5664 adapter = filterArgument(adapter, positions[0] - 1, filter);
5665 }
5666 return adapter;
5667 }
5668
5669 private static MethodHandle filterRepeatedArgument(MethodHandle adapter, MethodHandle filter, int[] positions) {
5670 MethodType targetType = adapter.type();
5671 MethodType filterType = filter.type();
5672 BoundMethodHandle result = adapter.rebind();
5673 Class<?> newParamType = filterType.parameterType(0);
5674
5675 Class<?>[] ptypes = targetType.ptypes().clone();
5676 for (int pos : positions) {
5677 ptypes[pos - 1] = newParamType;
5678 }
5679 MethodType newType = MethodType.methodType(targetType.rtype(), ptypes, true);
5680
5681 LambdaForm lform = result.editor().filterRepeatedArgumentForm(BasicType.basicType(newParamType), positions);
5682 return result.copyWithExtendL(newType, lform, filter);
5683 }
5684
5685 /*non-public*/
5686 static MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
5687 filterArgumentChecks(target, pos, filter);
5688 MethodType targetType = target.type();
5689 MethodType filterType = filter.type();
5690 BoundMethodHandle result = target.rebind();
5691 Class<?> newParamType = filterType.parameterType(0);
5692 LambdaForm lform = result.editor().filterArgumentForm(1 + pos, BasicType.basicType(newParamType));
5693 MethodType newType = targetType.changeParameterType(pos, newParamType);
5694 result = result.copyWithExtendL(newType, lform, filter);
5695 return result;
5696 }
5697
5698 private static void filterArgumentsCheckArity(MethodHandle target, int pos, MethodHandle[] filters) {
5699 MethodType targetType = target.type();
5700 int maxPos = targetType.parameterCount();
5701 if (pos + filters.length > maxPos)
5702 throw newIllegalArgumentException("too many filters");
5703 }
5704
5705 private static void filterArgumentChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
5706 MethodType targetType = target.type();
5707 MethodType filterType = filter.type();
5708 if (filterType.parameterCount() != 1
5709 || filterType.returnType() != targetType.parameterType(pos))
5710 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
5711 }
5712
5713 /**
5714 * Adapts a target method handle by pre-processing
5715 * a sub-sequence of its arguments with a filter (another method handle).
5716 * The pre-processed arguments are replaced by the result (if any) of the
5717 * filter function.
5718 * The target is then called on the modified (usually shortened) argument list.
5719 * <p>
5720 * If the filter returns a value, the target must accept that value as
5721 * its argument in position {@code pos}, preceded and/or followed by
5722 * any arguments not passed to the filter.
5723 * If the filter returns void, the target must accept all arguments
5724 * not passed to the filter.
5725 * No arguments are reordered, and a result returned from the filter
5726 * replaces (in order) the whole subsequence of arguments originally
5727 * passed to the adapter.
5728 * <p>
5729 * The argument types (if any) of the filter
5730 * replace zero or one argument types of the target, at position {@code pos},
5731 * in the resulting adapted method handle.
5732 * The return type of the filter (if any) must be identical to the
5733 * argument type of the target at position {@code pos}, and that target argument
5734 * is supplied by the return value of the filter.
5735 * <p>
5736 * In all cases, {@code pos} must be greater than or equal to zero, and
5737 * {@code pos} must also be less than or equal to the target's arity.
5738 * <p><b>Example:</b>
5739 * {@snippet lang="java" :
5740 import static java.lang.invoke.MethodHandles.*;
5741 import static java.lang.invoke.MethodType.*;
5742 ...
5743 MethodHandle deepToString = publicLookup()
5744 .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
5745
5746 MethodHandle ts1 = deepToString.asCollector(String[].class, 1);
5747 assertEquals("[strange]", (String) ts1.invokeExact("strange"));
5748
5749 MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
5750 assertEquals("[up, down]", (String) ts2.invokeExact("up", "down"));
5751
5752 MethodHandle ts3 = deepToString.asCollector(String[].class, 3);
5753 MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2);
5754 assertEquals("[top, [up, down], strange]",
5755 (String) ts3_ts2.invokeExact("top", "up", "down", "strange"));
5756
5757 MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1);
5758 assertEquals("[top, [up, down], [strange]]",
5759 (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange"));
5760
5761 MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3);
5762 assertEquals("[top, [[up, down, strange], charm], bottom]",
5763 (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom"));
5764 * }
5765 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
5766 * represents the return type of the {@code target} and resulting adapter.
5767 * {@code V}/{@code v} stand for the return type and value of the
5768 * {@code filter}, which are also found in the signature and arguments of
5769 * the {@code target}, respectively, unless {@code V} is {@code void}.
5770 * {@code A}/{@code a} and {@code C}/{@code c} represent the parameter types
5771 * and values preceding and following the collection position, {@code pos},
5772 * in the {@code target}'s signature. They also turn up in the resulting
5773 * adapter's signature and arguments, where they surround
5774 * {@code B}/{@code b}, which represent the parameter types and arguments
5775 * to the {@code filter} (if any).
5776 * {@snippet lang="java" :
5777 * T target(A...,V,C...);
5778 * V filter(B...);
5779 * T adapter(A... a,B... b,C... c) {
5780 * V v = filter(b...);
5781 * return target(a...,v,c...);
5782 * }
5783 * // and if the filter has no arguments:
5784 * T target2(A...,V,C...);
5785 * V filter2();
5786 * T adapter2(A... a,C... c) {
5787 * V v = filter2();
5788 * return target2(a...,v,c...);
5789 * }
5790 * // and if the filter has a void return:
5791 * T target3(A...,C...);
5792 * void filter3(B...);
5793 * T adapter3(A... a,B... b,C... c) {
5794 * filter3(b...);
5795 * return target3(a...,c...);
5796 * }
5797 * }
5798 * <p>
5799 * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to
5800 * one which first "folds" the affected arguments, and then drops them, in separate
5801 * steps as follows:
5802 * {@snippet lang="java" :
5803 * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2
5804 * mh = MethodHandles.foldArguments(mh, coll); //step 1
5805 * }
5806 * If the target method handle consumes no arguments besides than the result
5807 * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)}
5808 * is equivalent to {@code filterReturnValue(coll, mh)}.
5809 * If the filter method handle {@code coll} consumes one argument and produces
5810 * a non-void result, then {@code collectArguments(mh, N, coll)}
5811 * is equivalent to {@code filterArguments(mh, N, coll)}.
5812 * Other equivalences are possible but would require argument permutation.
5813 * <p>
5814 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5815 * variable-arity method handle}, even if the original target method handle was.
5816 *
5817 * @param target the method handle to invoke after filtering the subsequence of arguments
5818 * @param pos the position of the first adapter argument to pass to the filter,
5819 * and/or the target argument which receives the result of the filter
5820 * @param filter method handle to call on the subsequence of arguments
5821 * @return method handle which incorporates the specified argument subsequence filtering logic
5822 * @throws NullPointerException if either argument is null
5823 * @throws IllegalArgumentException if the return type of {@code filter}
5824 * is non-void and is not the same as the {@code pos} argument of the target,
5825 * or if {@code pos} is not between 0 and the target's arity, inclusive,
5826 * or if the resulting method handle's type would have
5827 * <a href="MethodHandle.html#maxarity">too many parameters</a>
5828 * @see MethodHandles#foldArguments
5829 * @see MethodHandles#filterArguments
5830 * @see MethodHandles#filterReturnValue
5831 */
5832 public static MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) {
5833 MethodType newType = collectArgumentsChecks(target, pos, filter);
5834 MethodType collectorType = filter.type();
5835 BoundMethodHandle result = target.rebind();
5836 LambdaForm lform = result.editor().collectArgumentsForm(1 + pos, collectorType.basicType());
5837 return result.copyWithExtendL(newType, lform, filter);
5838 }
5839
5840 private static MethodType collectArgumentsChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
5841 MethodType targetType = target.type();
5842 MethodType filterType = filter.type();
5843 Class<?> rtype = filterType.returnType();
5844 Class<?>[] filterArgs = filterType.ptypes();
5845 if (pos < 0 || (rtype == void.class && pos > targetType.parameterCount()) ||
5846 (rtype != void.class && pos >= targetType.parameterCount())) {
5847 throw newIllegalArgumentException("position is out of range for target", target, pos);
5848 }
5849 if (rtype == void.class) {
5850 return targetType.insertParameterTypes(pos, filterArgs);
5851 }
5852 if (rtype != targetType.parameterType(pos)) {
5853 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
5854 }
5855 return targetType.dropParameterTypes(pos, pos + 1).insertParameterTypes(pos, filterArgs);
5856 }
5857
5858 /**
5859 * Adapts a target method handle by post-processing
5860 * its return value (if any) with a filter (another method handle).
5861 * The result of the filter is returned from the adapter.
5862 * <p>
5863 * If the target returns a value, the filter must accept that value as
5864 * its only argument.
5865 * If the target returns void, the filter must accept no arguments.
5866 * <p>
5867 * The return type of the filter
5868 * replaces the return type of the target
5869 * in the resulting adapted method handle.
5870 * The argument type of the filter (if any) must be identical to the
5871 * return type of the target.
5872 * <p><b>Example:</b>
5873 * {@snippet lang="java" :
5874 import static java.lang.invoke.MethodHandles.*;
5875 import static java.lang.invoke.MethodType.*;
5876 ...
5877 MethodHandle cat = lookup().findVirtual(String.class,
5878 "concat", methodType(String.class, String.class));
5879 MethodHandle length = lookup().findVirtual(String.class,
5880 "length", methodType(int.class));
5881 System.out.println((String) cat.invokeExact("x", "y")); // xy
5882 MethodHandle f0 = filterReturnValue(cat, length);
5883 System.out.println((int) f0.invokeExact("x", "y")); // 2
5884 * }
5885 * <p>Here is pseudocode for the resulting adapter. In the code,
5886 * {@code T}/{@code t} represent the result type and value of the
5887 * {@code target}; {@code V}, the result type of the {@code filter}; and
5888 * {@code A}/{@code a}, the types and values of the parameters and arguments
5889 * of the {@code target} as well as the resulting adapter.
5890 * {@snippet lang="java" :
5891 * T target(A...);
5892 * V filter(T);
5893 * V adapter(A... a) {
5894 * T t = target(a...);
5895 * return filter(t);
5896 * }
5897 * // and if the target has a void return:
5898 * void target2(A...);
5899 * V filter2();
5900 * V adapter2(A... a) {
5901 * target2(a...);
5902 * return filter2();
5903 * }
5904 * // and if the filter has a void return:
5905 * T target3(A...);
5906 * void filter3(V);
5907 * void adapter3(A... a) {
5908 * T t = target3(a...);
5909 * filter3(t);
5910 * }
5911 * }
5912 * <p>
5913 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
5914 * variable-arity method handle}, even if the original target method handle was.
5915 * @param target the method handle to invoke before filtering the return value
5916 * @param filter method handle to call on the return value
5917 * @return method handle which incorporates the specified return value filtering logic
5918 * @throws NullPointerException if either argument is null
5919 * @throws IllegalArgumentException if the argument list of {@code filter}
5920 * does not match the return type of target as described above
5921 */
5922 public static MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
5923 MethodType targetType = target.type();
5924 MethodType filterType = filter.type();
5925 filterReturnValueChecks(targetType, filterType);
5926 BoundMethodHandle result = target.rebind();
5927 BasicType rtype = BasicType.basicType(filterType.returnType());
5928 LambdaForm lform = result.editor().filterReturnForm(rtype, false);
5929 MethodType newType = targetType.changeReturnType(filterType.returnType());
5930 result = result.copyWithExtendL(newType, lform, filter);
5931 return result;
5932 }
5933
5934 private static void filterReturnValueChecks(MethodType targetType, MethodType filterType) throws RuntimeException {
5935 Class<?> rtype = targetType.returnType();
5936 int filterValues = filterType.parameterCount();
5937 if (filterValues == 0
5938 ? (rtype != void.class)
5939 : (rtype != filterType.parameterType(0) || filterValues != 1))
5940 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
5941 }
5942
5943 /**
5944 * Filter the return value of a target method handle with a filter function. The filter function is
5945 * applied to the return value of the original handle; if the filter specifies more than one parameters,
5946 * then any remaining parameter is appended to the adapter handle. In other words, the adaptation works
5947 * as follows:
5948 * {@snippet lang="java" :
5949 * T target(A...)
5950 * V filter(B... , T)
5951 * V adapter(A... a, B... b) {
5952 * T t = target(a...);
5953 * return filter(b..., t);
5954 * }
5955 * }
5956 * <p>
5957 * If the filter handle is a unary function, then this method behaves like {@link #filterReturnValue(MethodHandle, MethodHandle)}.
5958 *
5959 * @param target the target method handle
5960 * @param filter the filter method handle
5961 * @return the adapter method handle
5962 */
5963 /* package */ static MethodHandle collectReturnValue(MethodHandle target, MethodHandle filter) {
5964 MethodType targetType = target.type();
5965 MethodType filterType = filter.type();
5966 BoundMethodHandle result = target.rebind();
5967 LambdaForm lform = result.editor().collectReturnValueForm(filterType.basicType());
5968 MethodType newType = targetType.changeReturnType(filterType.returnType());
5969 if (filterType.parameterCount() > 1) {
5970 for (int i = 0 ; i < filterType.parameterCount() - 1 ; i++) {
5971 newType = newType.appendParameterTypes(filterType.parameterType(i));
5972 }
5973 }
5974 result = result.copyWithExtendL(newType, lform, filter);
5975 return result;
5976 }
5977
5978 /**
5979 * Adapts a target method handle by pre-processing
5980 * some of its arguments, and then calling the target with
5981 * the result of the pre-processing, inserted into the original
5982 * sequence of arguments.
5983 * <p>
5984 * The pre-processing is performed by {@code combiner}, a second method handle.
5985 * Of the arguments passed to the adapter, the first {@code N} arguments
5986 * are copied to the combiner, which is then called.
5987 * (Here, {@code N} is defined as the parameter count of the combiner.)
5988 * After this, control passes to the target, with any result
5989 * from the combiner inserted before the original {@code N} incoming
5990 * arguments.
5991 * <p>
5992 * If the combiner returns a value, the first parameter type of the target
5993 * must be identical with the return type of the combiner, and the next
5994 * {@code N} parameter types of the target must exactly match the parameters
5995 * of the combiner.
5996 * <p>
5997 * If the combiner has a void return, no result will be inserted,
5998 * and the first {@code N} parameter types of the target
5999 * must exactly match the parameters of the combiner.
6000 * <p>
6001 * The resulting adapter is the same type as the target, except that the
6002 * first parameter type is dropped,
6003 * if it corresponds to the result of the combiner.
6004 * <p>
6005 * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
6006 * that either the combiner or the target does not wish to receive.
6007 * If some of the incoming arguments are destined only for the combiner,
6008 * consider using {@link MethodHandle#asCollector asCollector} instead, since those
6009 * arguments will not need to be live on the stack on entry to the
6010 * target.)
6011 * <p><b>Example:</b>
6012 * {@snippet lang="java" :
6013 import static java.lang.invoke.MethodHandles.*;
6014 import static java.lang.invoke.MethodType.*;
6015 ...
6016 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
6017 "println", methodType(void.class, String.class))
6018 .bindTo(System.out);
6019 MethodHandle cat = lookup().findVirtual(String.class,
6020 "concat", methodType(String.class, String.class));
6021 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
6022 MethodHandle catTrace = foldArguments(cat, trace);
6023 // also prints "boo":
6024 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
6025 * }
6026 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
6027 * represents the result type of the {@code target} and resulting adapter.
6028 * {@code V}/{@code v} represent the type and value of the parameter and argument
6029 * of {@code target} that precedes the folding position; {@code V} also is
6030 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
6031 * types and values of the {@code N} parameters and arguments at the folding
6032 * position. {@code B}/{@code b} represent the types and values of the
6033 * {@code target} parameters and arguments that follow the folded parameters
6034 * and arguments.
6035 * {@snippet lang="java" :
6036 * // there are N arguments in A...
6037 * T target(V, A[N]..., B...);
6038 * V combiner(A...);
6039 * T adapter(A... a, B... b) {
6040 * V v = combiner(a...);
6041 * return target(v, a..., b...);
6042 * }
6043 * // and if the combiner has a void return:
6044 * T target2(A[N]..., B...);
6045 * void combiner2(A...);
6046 * T adapter2(A... a, B... b) {
6047 * combiner2(a...);
6048 * return target2(a..., b...);
6049 * }
6050 * }
6051 * <p>
6052 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
6053 * variable-arity method handle}, even if the original target method handle was.
6054 * @param target the method handle to invoke after arguments are combined
6055 * @param combiner method handle to call initially on the incoming arguments
6056 * @return method handle which incorporates the specified argument folding logic
6057 * @throws NullPointerException if either argument is null
6058 * @throws IllegalArgumentException if {@code combiner}'s return type
6059 * is non-void and not the same as the first argument type of
6060 * the target, or if the initial {@code N} argument types
6061 * of the target
6062 * (skipping one matching the {@code combiner}'s return type)
6063 * are not identical with the argument types of {@code combiner}
6064 */
6065 public static MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
6066 return foldArguments(target, 0, combiner);
6067 }
6068
6069 /**
6070 * Adapts a target method handle by pre-processing some of its arguments, starting at a given position, and then
6071 * calling the target with the result of the pre-processing, inserted into the original sequence of arguments just
6072 * before the folded arguments.
6073 * <p>
6074 * This method is closely related to {@link #foldArguments(MethodHandle, MethodHandle)}, but allows to control the
6075 * position in the parameter list at which folding takes place. The argument controlling this, {@code pos}, is a
6076 * zero-based index. The aforementioned method {@link #foldArguments(MethodHandle, MethodHandle)} assumes position
6077 * 0.
6078 *
6079 * @apiNote Example:
6080 * {@snippet lang="java" :
6081 import static java.lang.invoke.MethodHandles.*;
6082 import static java.lang.invoke.MethodType.*;
6083 ...
6084 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
6085 "println", methodType(void.class, String.class))
6086 .bindTo(System.out);
6087 MethodHandle cat = lookup().findVirtual(String.class,
6088 "concat", methodType(String.class, String.class));
6089 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
6090 MethodHandle catTrace = foldArguments(cat, 1, trace);
6091 // also prints "jum":
6092 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
6093 * }
6094 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
6095 * represents the result type of the {@code target} and resulting adapter.
6096 * {@code V}/{@code v} represent the type and value of the parameter and argument
6097 * of {@code target} that precedes the folding position; {@code V} also is
6098 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
6099 * types and values of the {@code N} parameters and arguments at the folding
6100 * position. {@code Z}/{@code z} and {@code B}/{@code b} represent the types
6101 * and values of the {@code target} parameters and arguments that precede and
6102 * follow the folded parameters and arguments starting at {@code pos},
6103 * respectively.
6104 * {@snippet lang="java" :
6105 * // there are N arguments in A...
6106 * T target(Z..., V, A[N]..., B...);
6107 * V combiner(A...);
6108 * T adapter(Z... z, A... a, B... b) {
6109 * V v = combiner(a...);
6110 * return target(z..., v, a..., b...);
6111 * }
6112 * // and if the combiner has a void return:
6113 * T target2(Z..., A[N]..., B...);
6114 * void combiner2(A...);
6115 * T adapter2(Z... z, A... a, B... b) {
6116 * combiner2(a...);
6117 * return target2(z..., a..., b...);
6118 * }
6119 * }
6120 * <p>
6121 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
6122 * variable-arity method handle}, even if the original target method handle was.
6123 *
6124 * @param target the method handle to invoke after arguments are combined
6125 * @param pos the position at which to start folding and at which to insert the folding result; if this is {@code
6126 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
6127 * @param combiner method handle to call initially on the incoming arguments
6128 * @return method handle which incorporates the specified argument folding logic
6129 * @throws NullPointerException if either argument is null
6130 * @throws IllegalArgumentException if either of the following two conditions holds:
6131 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
6132 * {@code pos} of the target signature;
6133 * (2) the {@code N} argument types at position {@code pos} of the target signature (skipping one matching
6134 * the {@code combiner}'s return type) are not identical with the argument types of {@code combiner}.
6135 *
6136 * @see #foldArguments(MethodHandle, MethodHandle)
6137 * @since 9
6138 */
6139 public static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner) {
6140 MethodType targetType = target.type();
6141 MethodType combinerType = combiner.type();
6142 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType);
6143 BoundMethodHandle result = target.rebind();
6144 boolean dropResult = rtype == void.class;
6145 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType());
6146 MethodType newType = targetType;
6147 if (!dropResult) {
6148 newType = newType.dropParameterTypes(pos, pos + 1);
6149 }
6150 result = result.copyWithExtendL(newType, lform, combiner);
6151 return result;
6152 }
6153
6154 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType) {
6155 int foldArgs = combinerType.parameterCount();
6156 Class<?> rtype = combinerType.returnType();
6157 int foldVals = rtype == void.class ? 0 : 1;
6158 int afterInsertPos = foldPos + foldVals;
6159 boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
6160 if (ok) {
6161 for (int i = 0; i < foldArgs; i++) {
6162 if (combinerType.parameterType(i) != targetType.parameterType(i + afterInsertPos)) {
6163 ok = false;
6164 break;
6165 }
6166 }
6167 }
6168 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos))
6169 ok = false;
6170 if (!ok)
6171 throw misMatchedTypes("target and combiner types", targetType, combinerType);
6172 return rtype;
6173 }
6174
6175 /**
6176 * Adapts a target method handle by pre-processing some of its arguments, then calling the target with the result
6177 * of the pre-processing replacing the argument at the given position.
6178 *
6179 * @param target the method handle to invoke after arguments are combined
6180 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code
6181 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
6182 * @param combiner method handle to call initially on the incoming arguments
6183 * @param argPositions indexes of the target to pick arguments sent to the combiner from
6184 * @return method handle which incorporates the specified argument folding logic
6185 * @throws NullPointerException if either argument is null
6186 * @throws IllegalArgumentException if either of the following two conditions holds:
6187 * (1) {@code combiner}'s return type is not the same as the argument type at position
6188 * {@code pos} of the target signature;
6189 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature are
6190 * not identical with the argument types of {@code combiner}.
6191 */
6192 /*non-public*/
6193 static MethodHandle filterArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
6194 return argumentsWithCombiner(true, target, position, combiner, argPositions);
6195 }
6196
6197 /**
6198 * Adapts a target method handle by pre-processing some of its arguments, calling the target with the result of
6199 * the pre-processing inserted into the original sequence of arguments at the given position.
6200 *
6201 * @param target the method handle to invoke after arguments are combined
6202 * @param position the position at which to start folding and at which to insert the folding result; if this is {@code
6203 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
6204 * @param combiner method handle to call initially on the incoming arguments
6205 * @param argPositions indexes of the target to pick arguments sent to the combiner from
6206 * @return method handle which incorporates the specified argument folding logic
6207 * @throws NullPointerException if either argument is null
6208 * @throws IllegalArgumentException if either of the following two conditions holds:
6209 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
6210 * {@code pos} of the target signature;
6211 * (2) the {@code N} argument types at positions {@code argPositions[1...N]} of the target signature
6212 * (skipping {@code position} where the {@code combiner}'s return will be folded in) are not identical
6213 * with the argument types of {@code combiner}.
6214 */
6215 /*non-public*/
6216 static MethodHandle foldArgumentsWithCombiner(MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
6217 return argumentsWithCombiner(false, target, position, combiner, argPositions);
6218 }
6219
6220 private static MethodHandle argumentsWithCombiner(boolean filter, MethodHandle target, int position, MethodHandle combiner, int ... argPositions) {
6221 MethodType targetType = target.type();
6222 MethodType combinerType = combiner.type();
6223 Class<?> rtype = argumentsWithCombinerChecks(position, filter, targetType, combinerType, argPositions);
6224 BoundMethodHandle result = target.rebind();
6225
6226 MethodType newType = targetType;
6227 LambdaForm lform;
6228 if (filter) {
6229 lform = result.editor().filterArgumentsForm(1 + position, combinerType.basicType(), argPositions);
6230 } else {
6231 boolean dropResult = rtype == void.class;
6232 lform = result.editor().foldArgumentsForm(1 + position, dropResult, combinerType.basicType(), argPositions);
6233 if (!dropResult) {
6234 newType = newType.dropParameterTypes(position, position + 1);
6235 }
6236 }
6237 result = result.copyWithExtendL(newType, lform, combiner);
6238 return result;
6239 }
6240
6241 private static Class<?> argumentsWithCombinerChecks(int position, boolean filter, MethodType targetType, MethodType combinerType, int ... argPos) {
6242 int combinerArgs = combinerType.parameterCount();
6243 if (argPos.length != combinerArgs) {
6244 throw newIllegalArgumentException("combiner and argument map must be equal size", combinerType, argPos.length);
6245 }
6246 Class<?> rtype = combinerType.returnType();
6247
6248 for (int i = 0; i < combinerArgs; i++) {
6249 int arg = argPos[i];
6250 if (arg < 0 || arg > targetType.parameterCount()) {
6251 throw newIllegalArgumentException("arg outside of target parameterRange", targetType, arg);
6252 }
6253 if (combinerType.parameterType(i) != targetType.parameterType(arg)) {
6254 throw newIllegalArgumentException("target argument type at position " + arg
6255 + " must match combiner argument type at index " + i + ": " + targetType
6256 + " -> " + combinerType + ", map: " + Arrays.toString(argPos));
6257 }
6258 }
6259 if (filter && combinerType.returnType() != targetType.parameterType(position)) {
6260 throw misMatchedTypes("target and combiner types", targetType, combinerType);
6261 }
6262 return rtype;
6263 }
6264
6265 /**
6266 * Makes a method handle which adapts a target method handle,
6267 * by guarding it with a test, a boolean-valued method handle.
6268 * If the guard fails, a fallback handle is called instead.
6269 * All three method handles must have the same corresponding
6270 * argument and return types, except that the return type
6271 * of the test must be boolean, and the test is allowed
6272 * to have fewer arguments than the other two method handles.
6273 * <p>
6274 * Here is pseudocode for the resulting adapter. In the code, {@code T}
6275 * represents the uniform result type of the three involved handles;
6276 * {@code A}/{@code a}, the types and values of the {@code target}
6277 * parameters and arguments that are consumed by the {@code test}; and
6278 * {@code B}/{@code b}, those types and values of the {@code target}
6279 * parameters and arguments that are not consumed by the {@code test}.
6280 * {@snippet lang="java" :
6281 * boolean test(A...);
6282 * T target(A...,B...);
6283 * T fallback(A...,B...);
6284 * T adapter(A... a,B... b) {
6285 * if (test(a...))
6286 * return target(a..., b...);
6287 * else
6288 * return fallback(a..., b...);
6289 * }
6290 * }
6291 * Note that the test arguments ({@code a...} in the pseudocode) cannot
6292 * be modified by execution of the test, and so are passed unchanged
6293 * from the caller to the target or fallback as appropriate.
6294 * @param test method handle used for test, must return boolean
6295 * @param target method handle to call if test passes
6296 * @param fallback method handle to call if test fails
6297 * @return method handle which incorporates the specified if/then/else logic
6298 * @throws NullPointerException if any argument is null
6299 * @throws IllegalArgumentException if {@code test} does not return boolean,
6300 * or if all three method types do not match (with the return
6301 * type of {@code test} changed to match that of the target).
6302 */
6303 public static MethodHandle guardWithTest(MethodHandle test,
6304 MethodHandle target,
6305 MethodHandle fallback) {
6306 MethodType gtype = test.type();
6307 MethodType ttype = target.type();
6308 MethodType ftype = fallback.type();
6309 if (!ttype.equals(ftype))
6310 throw misMatchedTypes("target and fallback types", ttype, ftype);
6311 if (gtype.returnType() != boolean.class)
6312 throw newIllegalArgumentException("guard type is not a predicate "+gtype);
6313
6314 test = dropArgumentsToMatch(test, 0, ttype.ptypes(), 0, true);
6315 if (test == null) {
6316 throw misMatchedTypes("target and test types", ttype, gtype);
6317 }
6318 return MethodHandleImpl.makeGuardWithTest(test, target, fallback);
6319 }
6320
6321 static <T> RuntimeException misMatchedTypes(String what, T t1, T t2) {
6322 return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
6323 }
6324
6325 /**
6326 * Makes a method handle which adapts a target method handle,
6327 * by running it inside an exception handler.
6328 * If the target returns normally, the adapter returns that value.
6329 * If an exception matching the specified type is thrown, the fallback
6330 * handle is called instead on the exception, plus the original arguments.
6331 * <p>
6332 * The target and handler must have the same corresponding
6333 * argument and return types, except that handler may omit trailing arguments
6334 * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
6335 * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
6336 * <p>
6337 * Here is pseudocode for the resulting adapter. In the code, {@code T}
6338 * represents the return type of the {@code target} and {@code handler},
6339 * and correspondingly that of the resulting adapter; {@code A}/{@code a},
6340 * the types and values of arguments to the resulting handle consumed by
6341 * {@code handler}; and {@code B}/{@code b}, those of arguments to the
6342 * resulting handle discarded by {@code handler}.
6343 * {@snippet lang="java" :
6344 * T target(A..., B...);
6345 * T handler(ExType, A...);
6346 * T adapter(A... a, B... b) {
6347 * try {
6348 * return target(a..., b...);
6349 * } catch (ExType ex) {
6350 * return handler(ex, a...);
6351 * }
6352 * }
6353 * }
6354 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
6355 * be modified by execution of the target, and so are passed unchanged
6356 * from the caller to the handler, if the handler is invoked.
6357 * <p>
6358 * The target and handler must return the same type, even if the handler
6359 * always throws. (This might happen, for instance, because the handler
6360 * is simulating a {@code finally} clause).
6361 * To create such a throwing handler, compose the handler creation logic
6362 * with {@link #throwException throwException},
6363 * in order to create a method handle of the correct return type.
6364 * @param target method handle to call
6365 * @param exType the type of exception which the handler will catch
6366 * @param handler method handle to call if a matching exception is thrown
6367 * @return method handle which incorporates the specified try/catch logic
6368 * @throws NullPointerException if any argument is null
6369 * @throws IllegalArgumentException if {@code handler} does not accept
6370 * the given exception type, or if the method handle types do
6371 * not match in their return types and their
6372 * corresponding parameters
6373 * @see MethodHandles#tryFinally(MethodHandle, MethodHandle)
6374 */
6375 public static MethodHandle catchException(MethodHandle target,
6376 Class<? extends Throwable> exType,
6377 MethodHandle handler) {
6378 MethodType ttype = target.type();
6379 MethodType htype = handler.type();
6380 if (!Throwable.class.isAssignableFrom(exType))
6381 throw new ClassCastException(exType.getName());
6382 if (htype.parameterCount() < 1 ||
6383 !htype.parameterType(0).isAssignableFrom(exType))
6384 throw newIllegalArgumentException("handler does not accept exception type "+exType);
6385 if (htype.returnType() != ttype.returnType())
6386 throw misMatchedTypes("target and handler return types", ttype, htype);
6387 handler = dropArgumentsToMatch(handler, 1, ttype.ptypes(), 0, true);
6388 if (handler == null) {
6389 throw misMatchedTypes("target and handler types", ttype, htype);
6390 }
6391 return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
6392 }
6393
6394 /**
6395 * Produces a method handle which will throw exceptions of the given {@code exType}.
6396 * The method handle will accept a single argument of {@code exType},
6397 * and immediately throw it as an exception.
6398 * The method type will nominally specify a return of {@code returnType}.
6399 * The return type may be anything convenient: It doesn't matter to the
6400 * method handle's behavior, since it will never return normally.
6401 * @param returnType the return type of the desired method handle
6402 * @param exType the parameter type of the desired method handle
6403 * @return method handle which can throw the given exceptions
6404 * @throws NullPointerException if either argument is null
6405 */
6406 public static MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) {
6407 if (!Throwable.class.isAssignableFrom(exType))
6408 throw new ClassCastException(exType.getName());
6409 return MethodHandleImpl.throwException(methodType(returnType, exType));
6410 }
6411
6412 /**
6413 * Constructs a method handle representing a loop with several loop variables that are updated and checked upon each
6414 * iteration. Upon termination of the loop due to one of the predicates, a corresponding finalizer is run and
6415 * delivers the loop's result, which is the return value of the resulting handle.
6416 * <p>
6417 * Intuitively, every loop is formed by one or more "clauses", each specifying a local <em>iteration variable</em> and/or a loop
6418 * exit. Each iteration of the loop executes each clause in order. A clause can optionally update its iteration
6419 * variable; it can also optionally perform a test and conditional loop exit. In order to express this logic in
6420 * terms of method handles, each clause will specify up to four independent actions:<ul>
6421 * <li><em>init:</em> Before the loop executes, the initialization of an iteration variable {@code v} of type {@code V}.
6422 * <li><em>step:</em> When a clause executes, an update step for the iteration variable {@code v}.
6423 * <li><em>pred:</em> When a clause executes, a predicate execution to test for loop exit.
6424 * <li><em>fini:</em> If a clause causes a loop exit, a finalizer execution to compute the loop's return value.
6425 * </ul>
6426 * The full sequence of all iteration variable types, in clause order, will be notated as {@code (V...)}.
6427 * The values themselves will be {@code (v...)}. When we speak of "parameter lists", we will usually
6428 * be referring to types, but in some contexts (describing execution) the lists will be of actual values.
6429 * <p>
6430 * Some of these clause parts may be omitted according to certain rules, and useful default behavior is provided in
6431 * this case. See below for a detailed description.
6432 * <p>
6433 * <em>Parameters optional everywhere:</em>
6434 * Each clause function is allowed but not required to accept a parameter for each iteration variable {@code v}.
6435 * As an exception, the init functions cannot take any {@code v} parameters,
6436 * because those values are not yet computed when the init functions are executed.
6437 * Any clause function may neglect to take any trailing subsequence of parameters it is entitled to take.
6438 * In fact, any clause function may take no arguments at all.
6439 * <p>
6440 * <em>Loop parameters:</em>
6441 * A clause function may take all the iteration variable values it is entitled to, in which case
6442 * it may also take more trailing parameters. Such extra values are called <em>loop parameters</em>,
6443 * with their types and values notated as {@code (A...)} and {@code (a...)}.
6444 * These become the parameters of the resulting loop handle, to be supplied whenever the loop is executed.
6445 * (Since init functions do not accept iteration variables {@code v}, any parameter to an
6446 * init function is automatically a loop parameter {@code a}.)
6447 * As with iteration variables, clause functions are allowed but not required to accept loop parameters.
6448 * These loop parameters act as loop-invariant values visible across the whole loop.
6449 * <p>
6450 * <em>Parameters visible everywhere:</em>
6451 * Each non-init clause function is permitted to observe the entire loop state, because it can be passed the full
6452 * list {@code (v... a...)} of current iteration variable values and incoming loop parameters.
6453 * The init functions can observe initial pre-loop state, in the form {@code (a...)}.
6454 * Most clause functions will not need all of this information, but they will be formally connected to it
6455 * as if by {@link #dropArguments}.
6456 * <a id="astar"></a>
6457 * More specifically, we shall use the notation {@code (V*)} to express an arbitrary prefix of a full
6458 * sequence {@code (V...)} (and likewise for {@code (v*)}, {@code (A*)}, {@code (a*)}).
6459 * In that notation, the general form of an init function parameter list
6460 * is {@code (A*)}, and the general form of a non-init function parameter list is {@code (V*)} or {@code (V... A*)}.
6461 * <p>
6462 * <em>Checking clause structure:</em>
6463 * Given a set of clauses, there is a number of checks and adjustments performed to connect all the parts of the
6464 * loop. They are spelled out in detail in the steps below. In these steps, every occurrence of the word "must"
6465 * corresponds to a place where {@link IllegalArgumentException} will be thrown if the required constraint is not
6466 * met by the inputs to the loop combinator.
6467 * <p>
6468 * <em>Effectively identical sequences:</em>
6469 * <a id="effid"></a>
6470 * A parameter list {@code A} is defined to be <em>effectively identical</em> to another parameter list {@code B}
6471 * if {@code A} and {@code B} are identical, or if {@code A} is shorter and is identical with a proper prefix of {@code B}.
6472 * When speaking of an unordered set of parameter lists, we say they the set is "effectively identical"
6473 * as a whole if the set contains a longest list, and all members of the set are effectively identical to
6474 * that longest list.
6475 * For example, any set of type sequences of the form {@code (V*)} is effectively identical,
6476 * and the same is true if more sequences of the form {@code (V... A*)} are added.
6477 * <p>
6478 * <em>Step 0: Determine clause structure.</em><ol type="a">
6479 * <li>The clause array (of type {@code MethodHandle[][]}) must be non-{@code null} and contain at least one element.
6480 * <li>The clause array may not contain {@code null}s or sub-arrays longer than four elements.
6481 * <li>Clauses shorter than four elements are treated as if they were padded by {@code null} elements to length
6482 * four. Padding takes place by appending elements to the array.
6483 * <li>Clauses with all {@code null}s are disregarded.
6484 * <li>Each clause is treated as a four-tuple of functions, called "init", "step", "pred", and "fini".
6485 * </ol>
6486 * <p>
6487 * <em>Step 1A: Determine iteration variable types {@code (V...)}.</em><ol type="a">
6488 * <li>The iteration variable type for each clause is determined using the clause's init and step return types.
6489 * <li>If both functions are omitted, there is no iteration variable for the corresponding clause ({@code void} is
6490 * used as the type to indicate that). If one of them is omitted, the other's return type defines the clause's
6491 * iteration variable type. If both are given, the common return type (they must be identical) defines the clause's
6492 * iteration variable type.
6493 * <li>Form the list of return types (in clause order), omitting all occurrences of {@code void}.
6494 * <li>This list of types is called the "iteration variable types" ({@code (V...)}).
6495 * </ol>
6496 * <p>
6497 * <em>Step 1B: Determine loop parameters {@code (A...)}.</em><ul>
6498 * <li>Examine and collect init function parameter lists (which are of the form {@code (A*)}).
6499 * <li>Examine and collect the suffixes of the step, pred, and fini parameter lists, after removing the iteration variable types.
6500 * (They must have the form {@code (V... A*)}; collect the {@code (A*)} parts only.)
6501 * <li>Do not collect suffixes from step, pred, and fini parameter lists that do not begin with all the iteration variable types.
6502 * (These types will be checked in step 2, along with all the clause function types.)
6503 * <li>Omitted clause functions are ignored. (Equivalently, they are deemed to have empty parameter lists.)
6504 * <li>All of the collected parameter lists must be effectively identical.
6505 * <li>The longest parameter list (which is necessarily unique) is called the "external parameter list" ({@code (A...)}).
6506 * <li>If there is no such parameter list, the external parameter list is taken to be the empty sequence.
6507 * <li>The combined list consisting of iteration variable types followed by the external parameter types is called
6508 * the "internal parameter list".
6509 * </ul>
6510 * <p>
6511 * <em>Step 1C: Determine loop return type.</em><ol type="a">
6512 * <li>Examine fini function return types, disregarding omitted fini functions.
6513 * <li>If there are no fini functions, the loop return type is {@code void}.
6514 * <li>Otherwise, the common return type {@code R} of the fini functions (their return types must be identical) defines the loop return
6515 * type.
6516 * </ol>
6517 * <p>
6518 * <em>Step 1D: Check other types.</em><ol type="a">
6519 * <li>There must be at least one non-omitted pred function.
6520 * <li>Every non-omitted pred function must have a {@code boolean} return type.
6521 * </ol>
6522 * <p>
6523 * <em>Step 2: Determine parameter lists.</em><ol type="a">
6524 * <li>The parameter list for the resulting loop handle will be the external parameter list {@code (A...)}.
6525 * <li>The parameter list for init functions will be adjusted to the external parameter list.
6526 * (Note that their parameter lists are already effectively identical to this list.)
6527 * <li>The parameter list for every non-omitted, non-init (step, pred, and fini) function must be
6528 * effectively identical to the internal parameter list {@code (V... A...)}.
6529 * </ol>
6530 * <p>
6531 * <em>Step 3: Fill in omitted functions.</em><ol type="a">
6532 * <li>If an init function is omitted, use a {@linkplain #empty default value} for the clause's iteration variable
6533 * type.
6534 * <li>If a step function is omitted, use an {@linkplain #identity identity function} of the clause's iteration
6535 * variable type; insert dropped argument parameters before the identity function parameter for the non-{@code void}
6536 * iteration variables of preceding clauses. (This will turn the loop variable into a local loop invariant.)
6537 * <li>If a pred function is omitted, use a constant {@code true} function. (This will keep the loop going, as far
6538 * as this clause is concerned. Note that in such cases the corresponding fini function is unreachable.)
6539 * <li>If a fini function is omitted, use a {@linkplain #empty default value} for the
6540 * loop return type.
6541 * </ol>
6542 * <p>
6543 * <em>Step 4: Fill in missing parameter types.</em><ol type="a">
6544 * <li>At this point, every init function parameter list is effectively identical to the external parameter list {@code (A...)},
6545 * but some lists may be shorter. For every init function with a short parameter list, pad out the end of the list.
6546 * <li>At this point, every non-init function parameter list is effectively identical to the internal parameter
6547 * list {@code (V... A...)}, but some lists may be shorter. For every non-init function with a short parameter list,
6548 * pad out the end of the list.
6549 * <li>Argument lists are padded out by {@linkplain #dropArgumentsToMatch(MethodHandle, int, List, int) dropping unused trailing arguments}.
6550 * </ol>
6551 * <p>
6552 * <em>Final observations.</em><ol type="a">
6553 * <li>After these steps, all clauses have been adjusted by supplying omitted functions and arguments.
6554 * <li>All init functions have a common parameter type list {@code (A...)}, which the final loop handle will also have.
6555 * <li>All fini functions have a common return type {@code R}, which the final loop handle will also have.
6556 * <li>All non-init functions have a common parameter type list {@code (V... A...)}, of
6557 * (non-{@code void}) iteration variables {@code V} followed by loop parameters.
6558 * <li>Each pair of init and step functions agrees in their return type {@code V}.
6559 * <li>Each non-init function will be able to observe the current values {@code (v...)} of all iteration variables.
6560 * <li>Every function will be able to observe the incoming values {@code (a...)} of all loop parameters.
6561 * </ol>
6562 * <p>
6563 * <em>Example.</em> As a consequence of step 1A above, the {@code loop} combinator has the following property:
6564 * <ul>
6565 * <li>Given {@code N} clauses {@code Cn = {null, Sn, Pn}} with {@code n = 1..N}.
6566 * <li>Suppose predicate handles {@code Pn} are either {@code null} or have no parameters.
6567 * (Only one {@code Pn} has to be non-{@code null}.)
6568 * <li>Suppose step handles {@code Sn} have signatures {@code (B1..BX)Rn}, for some constant {@code X>=N}.
6569 * <li>Suppose {@code Q} is the count of non-void types {@code Rn}, and {@code (V1...VQ)} is the sequence of those types.
6570 * <li>It must be that {@code Vn == Bn} for {@code n = 1..min(X,Q)}.
6571 * <li>The parameter types {@code Vn} will be interpreted as loop-local state elements {@code (V...)}.
6572 * <li>Any remaining types {@code BQ+1..BX} (if {@code Q<X}) will determine
6573 * the resulting loop handle's parameter types {@code (A...)}.
6574 * </ul>
6575 * In this example, the loop handle parameters {@code (A...)} were derived from the step functions,
6576 * which is natural if most of the loop computation happens in the steps. For some loops,
6577 * the burden of computation might be heaviest in the pred functions, and so the pred functions
6578 * might need to accept the loop parameter values. For loops with complex exit logic, the fini
6579 * functions might need to accept loop parameters, and likewise for loops with complex entry logic,
6580 * where the init functions will need the extra parameters. For such reasons, the rules for
6581 * determining these parameters are as symmetric as possible, across all clause parts.
6582 * In general, the loop parameters function as common invariant values across the whole
6583 * loop, while the iteration variables function as common variant values, or (if there is
6584 * no step function) as internal loop invariant temporaries.
6585 * <p>
6586 * <em>Loop execution.</em><ol type="a">
6587 * <li>When the loop is called, the loop input values are saved in locals, to be passed to
6588 * every clause function. These locals are loop invariant.
6589 * <li>Each init function is executed in clause order (passing the external arguments {@code (a...)})
6590 * and the non-{@code void} values are saved (as the iteration variables {@code (v...)}) into locals.
6591 * These locals will be loop varying (unless their steps behave as identity functions, as noted above).
6592 * <li>All function executions (except init functions) will be passed the internal parameter list, consisting of
6593 * the non-{@code void} iteration values {@code (v...)} (in clause order) and then the loop inputs {@code (a...)}
6594 * (in argument order).
6595 * <li>The step and pred functions are then executed, in clause order (step before pred), until a pred function
6596 * returns {@code false}.
6597 * <li>The non-{@code void} result from a step function call is used to update the corresponding value in the
6598 * sequence {@code (v...)} of loop variables.
6599 * The updated value is immediately visible to all subsequent function calls.
6600 * <li>If a pred function returns {@code false}, the corresponding fini function is called, and the resulting value
6601 * (of type {@code R}) is returned from the loop as a whole.
6602 * <li>If all the pred functions always return true, no fini function is ever invoked, and the loop cannot exit
6603 * except by throwing an exception.
6604 * </ol>
6605 * <p>
6606 * <em>Usage tips.</em>
6607 * <ul>
6608 * <li>Although each step function will receive the current values of <em>all</em> the loop variables,
6609 * sometimes a step function only needs to observe the current value of its own variable.
6610 * In that case, the step function may need to explicitly {@linkplain #dropArguments drop all preceding loop variables}.
6611 * This will require mentioning their types, in an expression like {@code dropArguments(step, 0, V0.class, ...)}.
6612 * <li>Loop variables are not required to vary; they can be loop invariant. A clause can create
6613 * a loop invariant by a suitable init function with no step, pred, or fini function. This may be
6614 * useful to "wire" an incoming loop argument into the step or pred function of an adjacent loop variable.
6615 * <li>If some of the clause functions are virtual methods on an instance, the instance
6616 * itself can be conveniently placed in an initial invariant loop "variable", using an initial clause
6617 * like {@code new MethodHandle[]{identity(ObjType.class)}}. In that case, the instance reference
6618 * will be the first iteration variable value, and it will be easy to use virtual
6619 * methods as clause parts, since all of them will take a leading instance reference matching that value.
6620 * </ul>
6621 * <p>
6622 * Here is pseudocode for the resulting loop handle. As above, {@code V} and {@code v} represent the types
6623 * and values of loop variables; {@code A} and {@code a} represent arguments passed to the whole loop;
6624 * and {@code R} is the common result type of all finalizers as well as of the resulting loop.
6625 * {@snippet lang="java" :
6626 * V... init...(A...);
6627 * boolean pred...(V..., A...);
6628 * V... step...(V..., A...);
6629 * R fini...(V..., A...);
6630 * R loop(A... a) {
6631 * V... v... = init...(a...);
6632 * for (;;) {
6633 * for ((v, p, s, f) in (v..., pred..., step..., fini...)) {
6634 * v = s(v..., a...);
6635 * if (!p(v..., a...)) {
6636 * return f(v..., a...);
6637 * }
6638 * }
6639 * }
6640 * }
6641 * }
6642 * Note that the parameter type lists {@code (V...)} and {@code (A...)} have been expanded
6643 * to their full length, even though individual clause functions may neglect to take them all.
6644 * As noted above, missing parameters are filled in as if by {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}.
6645 *
6646 * @apiNote Example:
6647 * {@snippet lang="java" :
6648 * // iterative implementation of the factorial function as a loop handle
6649 * static int one(int k) { return 1; }
6650 * static int inc(int i, int acc, int k) { return i + 1; }
6651 * static int mult(int i, int acc, int k) { return i * acc; }
6652 * static boolean pred(int i, int acc, int k) { return i < k; }
6653 * static int fin(int i, int acc, int k) { return acc; }
6654 * // assume MH_one, MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
6655 * // null initializer for counter, should initialize to 0
6656 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
6657 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
6658 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
6659 * assertEquals(120, loop.invoke(5));
6660 * }
6661 * The same example, dropping arguments and using combinators:
6662 * {@snippet lang="java" :
6663 * // simplified implementation of the factorial function as a loop handle
6664 * static int inc(int i) { return i + 1; } // drop acc, k
6665 * static int mult(int i, int acc) { return i * acc; } //drop k
6666 * static boolean cmp(int i, int k) { return i < k; }
6667 * // assume MH_inc, MH_mult, and MH_cmp are handles to the above methods
6668 * // null initializer for counter, should initialize to 0
6669 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
6670 * MethodHandle MH_pred = MethodHandles.dropArguments(MH_cmp, 1, int.class); // drop acc
6671 * MethodHandle MH_fin = MethodHandles.dropArguments(MethodHandles.identity(int.class), 0, int.class); // drop i
6672 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
6673 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
6674 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
6675 * assertEquals(720, loop.invoke(6));
6676 * }
6677 * A similar example, using a helper object to hold a loop parameter:
6678 * {@snippet lang="java" :
6679 * // instance-based implementation of the factorial function as a loop handle
6680 * static class FacLoop {
6681 * final int k;
6682 * FacLoop(int k) { this.k = k; }
6683 * int inc(int i) { return i + 1; }
6684 * int mult(int i, int acc) { return i * acc; }
6685 * boolean pred(int i) { return i < k; }
6686 * int fin(int i, int acc) { return acc; }
6687 * }
6688 * // assume MH_FacLoop is a handle to the constructor
6689 * // assume MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
6690 * // null initializer for counter, should initialize to 0
6691 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
6692 * MethodHandle[] instanceClause = new MethodHandle[]{MH_FacLoop};
6693 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
6694 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
6695 * MethodHandle loop = MethodHandles.loop(instanceClause, counterClause, accumulatorClause);
6696 * assertEquals(5040, loop.invoke(7));
6697 * }
6698 *
6699 * @param clauses an array of arrays (4-tuples) of {@link MethodHandle}s adhering to the rules described above.
6700 *
6701 * @return a method handle embodying the looping behavior as defined by the arguments.
6702 *
6703 * @throws IllegalArgumentException in case any of the constraints described above is violated.
6704 *
6705 * @see MethodHandles#whileLoop(MethodHandle, MethodHandle, MethodHandle)
6706 * @see MethodHandles#doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
6707 * @see MethodHandles#countedLoop(MethodHandle, MethodHandle, MethodHandle)
6708 * @see MethodHandles#iteratedLoop(MethodHandle, MethodHandle, MethodHandle)
6709 * @since 9
6710 */
6711 public static MethodHandle loop(MethodHandle[]... clauses) {
6712 // Step 0: determine clause structure.
6713 loopChecks0(clauses);
6714
6715 List<MethodHandle> init = new ArrayList<>();
6716 List<MethodHandle> step = new ArrayList<>();
6717 List<MethodHandle> pred = new ArrayList<>();
6718 List<MethodHandle> fini = new ArrayList<>();
6719
6720 Stream.of(clauses).filter(c -> Stream.of(c).anyMatch(Objects::nonNull)).forEach(clause -> {
6721 init.add(clause[0]); // all clauses have at least length 1
6722 step.add(clause.length <= 1 ? null : clause[1]);
6723 pred.add(clause.length <= 2 ? null : clause[2]);
6724 fini.add(clause.length <= 3 ? null : clause[3]);
6725 });
6726
6727 assert Stream.of(init, step, pred, fini).map(List::size).distinct().count() == 1;
6728 final int nclauses = init.size();
6729
6730 // Step 1A: determine iteration variables (V...).
6731 final List<Class<?>> iterationVariableTypes = new ArrayList<>();
6732 for (int i = 0; i < nclauses; ++i) {
6733 MethodHandle in = init.get(i);
6734 MethodHandle st = step.get(i);
6735 if (in == null && st == null) {
6736 iterationVariableTypes.add(void.class);
6737 } else if (in != null && st != null) {
6738 loopChecks1a(i, in, st);
6739 iterationVariableTypes.add(in.type().returnType());
6740 } else {
6741 iterationVariableTypes.add(in == null ? st.type().returnType() : in.type().returnType());
6742 }
6743 }
6744 final List<Class<?>> commonPrefix = iterationVariableTypes.stream().filter(t -> t != void.class).toList();
6745
6746 // Step 1B: determine loop parameters (A...).
6747 final List<Class<?>> commonSuffix = buildCommonSuffix(init, step, pred, fini, commonPrefix.size());
6748 loopChecks1b(init, commonSuffix);
6749
6750 // Step 1C: determine loop return type.
6751 // Step 1D: check other types.
6752 // local variable required here; see JDK-8223553
6753 Stream<Class<?>> cstream = fini.stream().filter(Objects::nonNull).map(MethodHandle::type)
6754 .map(MethodType::returnType);
6755 final Class<?> loopReturnType = cstream.findFirst().orElse(void.class);
6756 loopChecks1cd(pred, fini, loopReturnType);
6757
6758 // Step 2: determine parameter lists.
6759 final List<Class<?>> commonParameterSequence = new ArrayList<>(commonPrefix);
6760 commonParameterSequence.addAll(commonSuffix);
6761 loopChecks2(step, pred, fini, commonParameterSequence);
6762 // Step 3: fill in omitted functions.
6763 for (int i = 0; i < nclauses; ++i) {
6764 Class<?> t = iterationVariableTypes.get(i);
6765 if (init.get(i) == null) {
6766 init.set(i, empty(methodType(t, commonSuffix)));
6767 }
6768 if (step.get(i) == null) {
6769 step.set(i, dropArgumentsToMatch(identityOrVoid(t), 0, commonParameterSequence, i));
6770 }
6771 if (pred.get(i) == null) {
6772 pred.set(i, dropArguments(constant(boolean.class, true), 0, commonParameterSequence));
6773 }
6774 if (fini.get(i) == null) {
6775 fini.set(i, empty(methodType(t, commonParameterSequence)));
6776 }
6777 }
6778
6779 // Step 4: fill in missing parameter types.
6780 // Also convert all handles to fixed-arity handles.
6781 List<MethodHandle> finit = fixArities(fillParameterTypes(init, commonSuffix));
6782 List<MethodHandle> fstep = fixArities(fillParameterTypes(step, commonParameterSequence));
6783 List<MethodHandle> fpred = fixArities(fillParameterTypes(pred, commonParameterSequence));
6784 List<MethodHandle> ffini = fixArities(fillParameterTypes(fini, commonParameterSequence));
6785
6786 assert finit.stream().map(MethodHandle::type).map(MethodType::parameterList).
6787 allMatch(pl -> pl.equals(commonSuffix));
6788 assert Stream.of(fstep, fpred, ffini).flatMap(List::stream).map(MethodHandle::type).map(MethodType::parameterList).
6789 allMatch(pl -> pl.equals(commonParameterSequence));
6790
6791 return MethodHandleImpl.makeLoop(loopReturnType, commonSuffix, finit, fstep, fpred, ffini);
6792 }
6793
6794 private static void loopChecks0(MethodHandle[][] clauses) {
6795 if (clauses == null || clauses.length == 0) {
6796 throw newIllegalArgumentException("null or no clauses passed");
6797 }
6798 if (Stream.of(clauses).anyMatch(Objects::isNull)) {
6799 throw newIllegalArgumentException("null clauses are not allowed");
6800 }
6801 if (Stream.of(clauses).anyMatch(c -> c.length > 4)) {
6802 throw newIllegalArgumentException("All loop clauses must be represented as MethodHandle arrays with at most 4 elements.");
6803 }
6804 }
6805
6806 private static void loopChecks1a(int i, MethodHandle in, MethodHandle st) {
6807 if (in.type().returnType() != st.type().returnType()) {
6808 throw misMatchedTypes("clause " + i + ": init and step return types", in.type().returnType(),
6809 st.type().returnType());
6810 }
6811 }
6812
6813 private static List<Class<?>> longestParameterList(Stream<MethodHandle> mhs, int skipSize) {
6814 return mhs.filter(Objects::nonNull)
6815 // take only those that can contribute to a common suffix because they are longer than the prefix
6816 .map(MethodHandle::type)
6817 .filter(t -> t.parameterCount() > skipSize)
6818 .max(Comparator.comparingInt(MethodType::parameterCount))
6819 .map(methodType -> List.of(Arrays.copyOfRange(methodType.ptypes(), skipSize, methodType.parameterCount())))
6820 .orElse(List.of());
6821 }
6822
6823 private static List<Class<?>> buildCommonSuffix(List<MethodHandle> init, List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, int cpSize) {
6824 final List<Class<?>> longest1 = longestParameterList(Stream.of(step, pred, fini).flatMap(List::stream), cpSize);
6825 final List<Class<?>> longest2 = longestParameterList(init.stream(), 0);
6826 return longest1.size() >= longest2.size() ? longest1 : longest2;
6827 }
6828
6829 private static void loopChecks1b(List<MethodHandle> init, List<Class<?>> commonSuffix) {
6830 if (init.stream().filter(Objects::nonNull).map(MethodHandle::type).
6831 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonSuffix))) {
6832 throw newIllegalArgumentException("found non-effectively identical init parameter type lists: " + init +
6833 " (common suffix: " + commonSuffix + ")");
6834 }
6835 }
6836
6837 private static void loopChecks1cd(List<MethodHandle> pred, List<MethodHandle> fini, Class<?> loopReturnType) {
6838 if (fini.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
6839 anyMatch(t -> t != loopReturnType)) {
6840 throw newIllegalArgumentException("found non-identical finalizer return types: " + fini + " (return type: " +
6841 loopReturnType + ")");
6842 }
6843
6844 if (pred.stream().noneMatch(Objects::nonNull)) {
6845 throw newIllegalArgumentException("no predicate found", pred);
6846 }
6847 if (pred.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
6848 anyMatch(t -> t != boolean.class)) {
6849 throw newIllegalArgumentException("predicates must have boolean return type", pred);
6850 }
6851 }
6852
6853 private static void loopChecks2(List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, List<Class<?>> commonParameterSequence) {
6854 if (Stream.of(step, pred, fini).flatMap(List::stream).filter(Objects::nonNull).map(MethodHandle::type).
6855 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonParameterSequence))) {
6856 throw newIllegalArgumentException("found non-effectively identical parameter type lists:\nstep: " + step +
6857 "\npred: " + pred + "\nfini: " + fini + " (common parameter sequence: " + commonParameterSequence + ")");
6858 }
6859 }
6860
6861 private static List<MethodHandle> fillParameterTypes(List<MethodHandle> hs, final List<Class<?>> targetParams) {
6862 return hs.stream().map(h -> {
6863 int pc = h.type().parameterCount();
6864 int tpsize = targetParams.size();
6865 return pc < tpsize ? dropArguments(h, pc, targetParams.subList(pc, tpsize)) : h;
6866 }).toList();
6867 }
6868
6869 private static List<MethodHandle> fixArities(List<MethodHandle> hs) {
6870 return hs.stream().map(MethodHandle::asFixedArity).toList();
6871 }
6872
6873 /**
6874 * Constructs a {@code while} loop from an initializer, a body, and a predicate.
6875 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
6876 * <p>
6877 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
6878 * method will, in each iteration, first evaluate the predicate and then execute its body (if the predicate
6879 * evaluates to {@code true}).
6880 * The loop will terminate once the predicate evaluates to {@code false} (the body will not be executed in this case).
6881 * <p>
6882 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
6883 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
6884 * and updated with the value returned from its invocation. The result of loop execution will be
6885 * the final value of the additional loop-local variable (if present).
6886 * <p>
6887 * The following rules hold for these argument handles:<ul>
6888 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
6889 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
6890 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
6891 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
6892 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
6893 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
6894 * It will constrain the parameter lists of the other loop parts.
6895 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
6896 * list {@code (A...)} is called the <em>external parameter list</em>.
6897 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
6898 * additional state variable of the loop.
6899 * The body must both accept and return a value of this type {@code V}.
6900 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
6901 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
6902 * <a href="MethodHandles.html#effid">effectively identical</a>
6903 * to the external parameter list {@code (A...)}.
6904 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
6905 * {@linkplain #empty default value}.
6906 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
6907 * Its parameter list (either empty or of the form {@code (V A*)}) must be
6908 * effectively identical to the internal parameter list.
6909 * </ul>
6910 * <p>
6911 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
6912 * <li>The loop handle's result type is the result type {@code V} of the body.
6913 * <li>The loop handle's parameter types are the types {@code (A...)},
6914 * from the external parameter list.
6915 * </ul>
6916 * <p>
6917 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
6918 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
6919 * passed to the loop.
6920 * {@snippet lang="java" :
6921 * V init(A...);
6922 * boolean pred(V, A...);
6923 * V body(V, A...);
6924 * V whileLoop(A... a...) {
6925 * V v = init(a...);
6926 * while (pred(v, a...)) {
6927 * v = body(v, a...);
6928 * }
6929 * return v;
6930 * }
6931 * }
6932 *
6933 * @apiNote Example:
6934 * {@snippet lang="java" :
6935 * // implement the zip function for lists as a loop handle
6936 * static List<String> initZip(Iterator<String> a, Iterator<String> b) { return new ArrayList<>(); }
6937 * static boolean zipPred(List<String> zip, Iterator<String> a, Iterator<String> b) { return a.hasNext() && b.hasNext(); }
6938 * static List<String> zipStep(List<String> zip, Iterator<String> a, Iterator<String> b) {
6939 * zip.add(a.next());
6940 * zip.add(b.next());
6941 * return zip;
6942 * }
6943 * // assume MH_initZip, MH_zipPred, and MH_zipStep are handles to the above methods
6944 * MethodHandle loop = MethodHandles.whileLoop(MH_initZip, MH_zipPred, MH_zipStep);
6945 * List<String> a = Arrays.asList("a", "b", "c", "d");
6946 * List<String> b = Arrays.asList("e", "f", "g", "h");
6947 * List<String> zipped = Arrays.asList("a", "e", "b", "f", "c", "g", "d", "h");
6948 * assertEquals(zipped, (List<String>) loop.invoke(a.iterator(), b.iterator()));
6949 * }
6950 *
6951 *
6952 * @apiNote The implementation of this method can be expressed as follows:
6953 * {@snippet lang="java" :
6954 * MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
6955 * MethodHandle fini = (body.type().returnType() == void.class
6956 * ? null : identity(body.type().returnType()));
6957 * MethodHandle[]
6958 * checkExit = { null, null, pred, fini },
6959 * varBody = { init, body };
6960 * return loop(checkExit, varBody);
6961 * }
6962 * }
6963 *
6964 * @param init optional initializer, providing the initial value of the loop variable.
6965 * May be {@code null}, implying a default initial value. See above for other constraints.
6966 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
6967 * above for other constraints.
6968 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
6969 * See above for other constraints.
6970 *
6971 * @return a method handle implementing the {@code while} loop as described by the arguments.
6972 * @throws IllegalArgumentException if the rules for the arguments are violated.
6973 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
6974 *
6975 * @see #loop(MethodHandle[][])
6976 * @see #doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
6977 * @since 9
6978 */
6979 public static MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
6980 whileLoopChecks(init, pred, body);
6981 MethodHandle fini = identityOrVoid(body.type().returnType());
6982 MethodHandle[] checkExit = { null, null, pred, fini };
6983 MethodHandle[] varBody = { init, body };
6984 return loop(checkExit, varBody);
6985 }
6986
6987 /**
6988 * Constructs a {@code do-while} loop from an initializer, a body, and a predicate.
6989 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
6990 * <p>
6991 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
6992 * method will, in each iteration, first execute its body and then evaluate the predicate.
6993 * The loop will terminate once the predicate evaluates to {@code false} after an execution of the body.
6994 * <p>
6995 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
6996 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
6997 * and updated with the value returned from its invocation. The result of loop execution will be
6998 * the final value of the additional loop-local variable (if present).
6999 * <p>
7000 * The following rules hold for these argument handles:<ul>
7001 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
7002 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
7003 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
7004 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
7005 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
7006 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
7007 * It will constrain the parameter lists of the other loop parts.
7008 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
7009 * list {@code (A...)} is called the <em>external parameter list</em>.
7010 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
7011 * additional state variable of the loop.
7012 * The body must both accept and return a value of this type {@code V}.
7013 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
7014 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
7015 * <a href="MethodHandles.html#effid">effectively identical</a>
7016 * to the external parameter list {@code (A...)}.
7017 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
7018 * {@linkplain #empty default value}.
7019 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
7020 * Its parameter list (either empty or of the form {@code (V A*)}) must be
7021 * effectively identical to the internal parameter list.
7022 * </ul>
7023 * <p>
7024 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
7025 * <li>The loop handle's result type is the result type {@code V} of the body.
7026 * <li>The loop handle's parameter types are the types {@code (A...)},
7027 * from the external parameter list.
7028 * </ul>
7029 * <p>
7030 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
7031 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
7032 * passed to the loop.
7033 * {@snippet lang="java" :
7034 * V init(A...);
7035 * boolean pred(V, A...);
7036 * V body(V, A...);
7037 * V doWhileLoop(A... a...) {
7038 * V v = init(a...);
7039 * do {
7040 * v = body(v, a...);
7041 * } while (pred(v, a...));
7042 * return v;
7043 * }
7044 * }
7045 *
7046 * @apiNote Example:
7047 * {@snippet lang="java" :
7048 * // int i = 0; while (i < limit) { ++i; } return i; => limit
7049 * static int zero(int limit) { return 0; }
7050 * static int step(int i, int limit) { return i + 1; }
7051 * static boolean pred(int i, int limit) { return i < limit; }
7052 * // assume MH_zero, MH_step, and MH_pred are handles to the above methods
7053 * MethodHandle loop = MethodHandles.doWhileLoop(MH_zero, MH_step, MH_pred);
7054 * assertEquals(23, loop.invoke(23));
7055 * }
7056 *
7057 *
7058 * @apiNote The implementation of this method can be expressed as follows:
7059 * {@snippet lang="java" :
7060 * MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
7061 * MethodHandle fini = (body.type().returnType() == void.class
7062 * ? null : identity(body.type().returnType()));
7063 * MethodHandle[] clause = { init, body, pred, fini };
7064 * return loop(clause);
7065 * }
7066 * }
7067 *
7068 * @param init optional initializer, providing the initial value of the loop variable.
7069 * May be {@code null}, implying a default initial value. See above for other constraints.
7070 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
7071 * See above for other constraints.
7072 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
7073 * above for other constraints.
7074 *
7075 * @return a method handle implementing the {@code while} loop as described by the arguments.
7076 * @throws IllegalArgumentException if the rules for the arguments are violated.
7077 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
7078 *
7079 * @see #loop(MethodHandle[][])
7080 * @see #whileLoop(MethodHandle, MethodHandle, MethodHandle)
7081 * @since 9
7082 */
7083 public static MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
7084 whileLoopChecks(init, pred, body);
7085 MethodHandle fini = identityOrVoid(body.type().returnType());
7086 MethodHandle[] clause = {init, body, pred, fini };
7087 return loop(clause);
7088 }
7089
7090 private static void whileLoopChecks(MethodHandle init, MethodHandle pred, MethodHandle body) {
7091 Objects.requireNonNull(pred);
7092 Objects.requireNonNull(body);
7093 MethodType bodyType = body.type();
7094 Class<?> returnType = bodyType.returnType();
7095 List<Class<?>> innerList = bodyType.parameterList();
7096 List<Class<?>> outerList = innerList;
7097 if (returnType == void.class) {
7098 // OK
7099 } else if (innerList.isEmpty() || innerList.get(0) != returnType) {
7100 // leading V argument missing => error
7101 MethodType expected = bodyType.insertParameterTypes(0, returnType);
7102 throw misMatchedTypes("body function", bodyType, expected);
7103 } else {
7104 outerList = innerList.subList(1, innerList.size());
7105 }
7106 MethodType predType = pred.type();
7107 if (predType.returnType() != boolean.class ||
7108 !predType.effectivelyIdenticalParameters(0, innerList)) {
7109 throw misMatchedTypes("loop predicate", predType, methodType(boolean.class, innerList));
7110 }
7111 if (init != null) {
7112 MethodType initType = init.type();
7113 if (initType.returnType() != returnType ||
7114 !initType.effectivelyIdenticalParameters(0, outerList)) {
7115 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
7116 }
7117 }
7118 }
7119
7120 /**
7121 * Constructs a loop that runs a given number of iterations.
7122 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
7123 * <p>
7124 * The number of iterations is determined by the {@code iterations} handle evaluation result.
7125 * The loop counter {@code i} is an extra loop iteration variable of type {@code int}.
7126 * It will be initialized to 0 and incremented by 1 in each iteration.
7127 * <p>
7128 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
7129 * of that type is also present. This variable is initialized using the optional {@code init} handle,
7130 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
7131 * <p>
7132 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
7133 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
7134 * iteration variable.
7135 * The result of the loop handle execution will be the final {@code V} value of that variable
7136 * (or {@code void} if there is no {@code V} variable).
7137 * <p>
7138 * The following rules hold for the argument handles:<ul>
7139 * <li>The {@code iterations} handle must not be {@code null}, and must return
7140 * the type {@code int}, referred to here as {@code I} in parameter type lists.
7141 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
7142 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
7143 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
7144 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
7145 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
7146 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
7147 * of types called the <em>internal parameter list</em>.
7148 * It will constrain the parameter lists of the other loop parts.
7149 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
7150 * with no additional {@code A} types, then the internal parameter list is extended by
7151 * the argument types {@code A...} of the {@code iterations} handle.
7152 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
7153 * list {@code (A...)} is called the <em>external parameter list</em>.
7154 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
7155 * additional state variable of the loop.
7156 * The body must both accept a leading parameter and return a value of this type {@code V}.
7157 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
7158 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
7159 * <a href="MethodHandles.html#effid">effectively identical</a>
7160 * to the external parameter list {@code (A...)}.
7161 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
7162 * {@linkplain #empty default value}.
7163 * <li>The parameter list of {@code iterations} (of some form {@code (A*)}) must be
7164 * effectively identical to the external parameter list {@code (A...)}.
7165 * </ul>
7166 * <p>
7167 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
7168 * <li>The loop handle's result type is the result type {@code V} of the body.
7169 * <li>The loop handle's parameter types are the types {@code (A...)},
7170 * from the external parameter list.
7171 * </ul>
7172 * <p>
7173 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
7174 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
7175 * arguments passed to the loop.
7176 * {@snippet lang="java" :
7177 * int iterations(A...);
7178 * V init(A...);
7179 * V body(V, int, A...);
7180 * V countedLoop(A... a...) {
7181 * int end = iterations(a...);
7182 * V v = init(a...);
7183 * for (int i = 0; i < end; ++i) {
7184 * v = body(v, i, a...);
7185 * }
7186 * return v;
7187 * }
7188 * }
7189 *
7190 * @apiNote Example with a fully conformant body method:
7191 * {@snippet lang="java" :
7192 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
7193 * // => a variation on a well known theme
7194 * static String step(String v, int counter, String init) { return "na " + v; }
7195 * // assume MH_step is a handle to the method above
7196 * MethodHandle fit13 = MethodHandles.constant(int.class, 13);
7197 * MethodHandle start = MethodHandles.identity(String.class);
7198 * MethodHandle loop = MethodHandles.countedLoop(fit13, start, MH_step);
7199 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("Lambdaman!"));
7200 * }
7201 *
7202 * @apiNote Example with the simplest possible body method type,
7203 * and passing the number of iterations to the loop invocation:
7204 * {@snippet lang="java" :
7205 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
7206 * // => a variation on a well known theme
7207 * static String step(String v, int counter ) { return "na " + v; }
7208 * // assume MH_step is a handle to the method above
7209 * MethodHandle count = MethodHandles.dropArguments(MethodHandles.identity(int.class), 1, String.class);
7210 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class);
7211 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i) -> "na " + v
7212 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "Lambdaman!"));
7213 * }
7214 *
7215 * @apiNote Example that treats the number of iterations, string to append to, and string to append
7216 * as loop parameters:
7217 * {@snippet lang="java" :
7218 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
7219 * // => a variation on a well known theme
7220 * static String step(String v, int counter, int iterations_, String pre, String start_) { return pre + " " + v; }
7221 * // assume MH_step is a handle to the method above
7222 * MethodHandle count = MethodHandles.identity(int.class);
7223 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class, String.class);
7224 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i, _, pre, _) -> pre + " " + v
7225 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "na", "Lambdaman!"));
7226 * }
7227 *
7228 * @apiNote Example that illustrates the usage of {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}
7229 * to enforce a loop type:
7230 * {@snippet lang="java" :
7231 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
7232 * // => a variation on a well known theme
7233 * static String step(String v, int counter, String pre) { return pre + " " + v; }
7234 * // assume MH_step is a handle to the method above
7235 * MethodType loopType = methodType(String.class, String.class, int.class, String.class);
7236 * MethodHandle count = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(int.class), 0, loopType.parameterList(), 1);
7237 * MethodHandle start = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(String.class), 0, loopType.parameterList(), 2);
7238 * MethodHandle body = MethodHandles.dropArgumentsToMatch(MH_step, 2, loopType.parameterList(), 0);
7239 * MethodHandle loop = MethodHandles.countedLoop(count, start, body); // (v, i, pre, _, _) -> pre + " " + v
7240 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("na", 13, "Lambdaman!"));
7241 * }
7242 *
7243 * @apiNote The implementation of this method can be expressed as follows:
7244 * {@snippet lang="java" :
7245 * MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
7246 * return countedLoop(empty(iterations.type()), iterations, init, body);
7247 * }
7248 * }
7249 *
7250 * @param iterations a non-{@code null} handle to return the number of iterations this loop should run. The handle's
7251 * result type must be {@code int}. See above for other constraints.
7252 * @param init optional initializer, providing the initial value of the loop variable.
7253 * May be {@code null}, implying a default initial value. See above for other constraints.
7254 * @param body body of the loop, which may not be {@code null}.
7255 * It controls the loop parameters and result type in the standard case (see above for details).
7256 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
7257 * and may accept any number of additional types.
7258 * See above for other constraints.
7259 *
7260 * @return a method handle representing the loop.
7261 * @throws NullPointerException if either of the {@code iterations} or {@code body} handles is {@code null}.
7262 * @throws IllegalArgumentException if any argument violates the rules formulated above.
7263 *
7264 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle, MethodHandle)
7265 * @since 9
7266 */
7267 public static MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
7268 return countedLoop(empty(iterations.type()), iterations, init, body);
7269 }
7270
7271 /**
7272 * Constructs a loop that counts over a range of numbers.
7273 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
7274 * <p>
7275 * The loop counter {@code i} is a loop iteration variable of type {@code int}.
7276 * The {@code start} and {@code end} handles determine the start (inclusive) and end (exclusive)
7277 * values of the loop counter.
7278 * The loop counter will be initialized to the {@code int} value returned from the evaluation of the
7279 * {@code start} handle and run to the value returned from {@code end} (exclusively) with a step width of 1.
7280 * <p>
7281 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
7282 * of that type is also present. This variable is initialized using the optional {@code init} handle,
7283 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
7284 * <p>
7285 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
7286 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
7287 * iteration variable.
7288 * The result of the loop handle execution will be the final {@code V} value of that variable
7289 * (or {@code void} if there is no {@code V} variable).
7290 * <p>
7291 * The following rules hold for the argument handles:<ul>
7292 * <li>The {@code start} and {@code end} handles must not be {@code null}, and must both return
7293 * the common type {@code int}, referred to here as {@code I} in parameter type lists.
7294 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
7295 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
7296 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
7297 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
7298 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
7299 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
7300 * of types called the <em>internal parameter list</em>.
7301 * It will constrain the parameter lists of the other loop parts.
7302 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
7303 * with no additional {@code A} types, then the internal parameter list is extended by
7304 * the argument types {@code A...} of the {@code end} handle.
7305 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
7306 * list {@code (A...)} is called the <em>external parameter list</em>.
7307 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
7308 * additional state variable of the loop.
7309 * The body must both accept a leading parameter and return a value of this type {@code V}.
7310 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
7311 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
7312 * <a href="MethodHandles.html#effid">effectively identical</a>
7313 * to the external parameter list {@code (A...)}.
7314 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
7315 * {@linkplain #empty default value}.
7316 * <li>The parameter list of {@code start} (of some form {@code (A*)}) must be
7317 * effectively identical to the external parameter list {@code (A...)}.
7318 * <li>Likewise, the parameter list of {@code end} must be effectively identical
7319 * to the external parameter list.
7320 * </ul>
7321 * <p>
7322 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
7323 * <li>The loop handle's result type is the result type {@code V} of the body.
7324 * <li>The loop handle's parameter types are the types {@code (A...)},
7325 * from the external parameter list.
7326 * </ul>
7327 * <p>
7328 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
7329 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
7330 * arguments passed to the loop.
7331 * {@snippet lang="java" :
7332 * int start(A...);
7333 * int end(A...);
7334 * V init(A...);
7335 * V body(V, int, A...);
7336 * V countedLoop(A... a...) {
7337 * int e = end(a...);
7338 * int s = start(a...);
7339 * V v = init(a...);
7340 * for (int i = s; i < e; ++i) {
7341 * v = body(v, i, a...);
7342 * }
7343 * return v;
7344 * }
7345 * }
7346 *
7347 * @apiNote The implementation of this method can be expressed as follows:
7348 * {@snippet lang="java" :
7349 * MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
7350 * MethodHandle returnVar = dropArguments(identity(init.type().returnType()), 0, int.class, int.class);
7351 * // assume MH_increment and MH_predicate are handles to implementation-internal methods with
7352 * // the following semantics:
7353 * // MH_increment: (int limit, int counter) -> counter + 1
7354 * // MH_predicate: (int limit, int counter) -> counter < limit
7355 * Class<?> counterType = start.type().returnType(); // int
7356 * Class<?> returnType = body.type().returnType();
7357 * MethodHandle incr = MH_increment, pred = MH_predicate, retv = null;
7358 * if (returnType != void.class) { // ignore the V variable
7359 * incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
7360 * pred = dropArguments(pred, 1, returnType); // ditto
7361 * retv = dropArguments(identity(returnType), 0, counterType); // ignore limit
7362 * }
7363 * body = dropArguments(body, 0, counterType); // ignore the limit variable
7364 * MethodHandle[]
7365 * loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
7366 * bodyClause = { init, body }, // v = init(); v = body(v, i)
7367 * indexVar = { start, incr }; // i = start(); i = i + 1
7368 * return loop(loopLimit, bodyClause, indexVar);
7369 * }
7370 * }
7371 *
7372 * @param start a non-{@code null} handle to return the start value of the loop counter, which must be {@code int}.
7373 * See above for other constraints.
7374 * @param end a non-{@code null} handle to return the end value of the loop counter (the loop will run to
7375 * {@code end-1}). The result type must be {@code int}. See above for other constraints.
7376 * @param init optional initializer, providing the initial value of the loop variable.
7377 * May be {@code null}, implying a default initial value. See above for other constraints.
7378 * @param body body of the loop, which may not be {@code null}.
7379 * It controls the loop parameters and result type in the standard case (see above for details).
7380 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
7381 * and may accept any number of additional types.
7382 * See above for other constraints.
7383 *
7384 * @return a method handle representing the loop.
7385 * @throws NullPointerException if any of the {@code start}, {@code end}, or {@code body} handles is {@code null}.
7386 * @throws IllegalArgumentException if any argument violates the rules formulated above.
7387 *
7388 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle)
7389 * @since 9
7390 */
7391 public static MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
7392 countedLoopChecks(start, end, init, body);
7393 Class<?> counterType = start.type().returnType(); // int, but who's counting?
7394 Class<?> limitType = end.type().returnType(); // yes, int again
7395 Class<?> returnType = body.type().returnType();
7396 MethodHandle incr = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopStep);
7397 MethodHandle pred = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopPred);
7398 MethodHandle retv = null;
7399 if (returnType != void.class) {
7400 incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
7401 pred = dropArguments(pred, 1, returnType); // ditto
7402 retv = dropArguments(identity(returnType), 0, counterType);
7403 }
7404 body = dropArguments(body, 0, counterType); // ignore the limit variable
7405 MethodHandle[]
7406 loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
7407 bodyClause = { init, body }, // v = init(); v = body(v, i)
7408 indexVar = { start, incr }; // i = start(); i = i + 1
7409 return loop(loopLimit, bodyClause, indexVar);
7410 }
7411
7412 private static void countedLoopChecks(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
7413 Objects.requireNonNull(start);
7414 Objects.requireNonNull(end);
7415 Objects.requireNonNull(body);
7416 Class<?> counterType = start.type().returnType();
7417 if (counterType != int.class) {
7418 MethodType expected = start.type().changeReturnType(int.class);
7419 throw misMatchedTypes("start function", start.type(), expected);
7420 } else if (end.type().returnType() != counterType) {
7421 MethodType expected = end.type().changeReturnType(counterType);
7422 throw misMatchedTypes("end function", end.type(), expected);
7423 }
7424 MethodType bodyType = body.type();
7425 Class<?> returnType = bodyType.returnType();
7426 List<Class<?>> innerList = bodyType.parameterList();
7427 // strip leading V value if present
7428 int vsize = (returnType == void.class ? 0 : 1);
7429 if (vsize != 0 && (innerList.isEmpty() || innerList.get(0) != returnType)) {
7430 // argument list has no "V" => error
7431 MethodType expected = bodyType.insertParameterTypes(0, returnType);
7432 throw misMatchedTypes("body function", bodyType, expected);
7433 } else if (innerList.size() <= vsize || innerList.get(vsize) != counterType) {
7434 // missing I type => error
7435 MethodType expected = bodyType.insertParameterTypes(vsize, counterType);
7436 throw misMatchedTypes("body function", bodyType, expected);
7437 }
7438 List<Class<?>> outerList = innerList.subList(vsize + 1, innerList.size());
7439 if (outerList.isEmpty()) {
7440 // special case; take lists from end handle
7441 outerList = end.type().parameterList();
7442 innerList = bodyType.insertParameterTypes(vsize + 1, outerList).parameterList();
7443 }
7444 MethodType expected = methodType(counterType, outerList);
7445 if (!start.type().effectivelyIdenticalParameters(0, outerList)) {
7446 throw misMatchedTypes("start parameter types", start.type(), expected);
7447 }
7448 if (end.type() != start.type() &&
7449 !end.type().effectivelyIdenticalParameters(0, outerList)) {
7450 throw misMatchedTypes("end parameter types", end.type(), expected);
7451 }
7452 if (init != null) {
7453 MethodType initType = init.type();
7454 if (initType.returnType() != returnType ||
7455 !initType.effectivelyIdenticalParameters(0, outerList)) {
7456 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
7457 }
7458 }
7459 }
7460
7461 /**
7462 * Constructs a loop that ranges over the values produced by an {@code Iterator<T>}.
7463 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
7464 * <p>
7465 * The iterator itself will be determined by the evaluation of the {@code iterator} handle.
7466 * Each value it produces will be stored in a loop iteration variable of type {@code T}.
7467 * <p>
7468 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
7469 * of that type is also present. This variable is initialized using the optional {@code init} handle,
7470 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
7471 * <p>
7472 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
7473 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
7474 * iteration variable.
7475 * The result of the loop handle execution will be the final {@code V} value of that variable
7476 * (or {@code void} if there is no {@code V} variable).
7477 * <p>
7478 * The following rules hold for the argument handles:<ul>
7479 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
7480 * {@code (V T A...)V}, where {@code V} is non-{@code void}, or else {@code (T A...)void}.
7481 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
7482 * and we will write {@code (V T A...)V} with the understanding that a {@code void} type {@code V}
7483 * is quietly dropped from the parameter list, leaving {@code (T A...)V}.)
7484 * <li>The parameter list {@code (V T A...)} of the body contributes to a list
7485 * of types called the <em>internal parameter list</em>.
7486 * It will constrain the parameter lists of the other loop parts.
7487 * <li>As a special case, if the body contributes only {@code V} and {@code T} types,
7488 * with no additional {@code A} types, then the internal parameter list is extended by
7489 * the argument types {@code A...} of the {@code iterator} handle; if it is {@code null} the
7490 * single type {@code Iterable} is added and constitutes the {@code A...} list.
7491 * <li>If the iteration variable types {@code (V T)} are dropped from the internal parameter list, the resulting shorter
7492 * list {@code (A...)} is called the <em>external parameter list</em>.
7493 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
7494 * additional state variable of the loop.
7495 * The body must both accept a leading parameter and return a value of this type {@code V}.
7496 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
7497 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
7498 * <a href="MethodHandles.html#effid">effectively identical</a>
7499 * to the external parameter list {@code (A...)}.
7500 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
7501 * {@linkplain #empty default value}.
7502 * <li>If the {@code iterator} handle is non-{@code null}, it must have the return
7503 * type {@code java.util.Iterator} or a subtype thereof.
7504 * The iterator it produces when the loop is executed will be assumed
7505 * to yield values which can be converted to type {@code T}.
7506 * <li>The parameter list of an {@code iterator} that is non-{@code null} (of some form {@code (A*)}) must be
7507 * effectively identical to the external parameter list {@code (A...)}.
7508 * <li>If {@code iterator} is {@code null} it defaults to a method handle which behaves
7509 * like {@link java.lang.Iterable#iterator()}. In that case, the internal parameter list
7510 * {@code (V T A...)} must have at least one {@code A} type, and the default iterator
7511 * handle parameter is adjusted to accept the leading {@code A} type, as if by
7512 * the {@link MethodHandle#asType asType} conversion method.
7513 * The leading {@code A} type must be {@code Iterable} or a subtype thereof.
7514 * This conversion step, done at loop construction time, must not throw a {@code WrongMethodTypeException}.
7515 * </ul>
7516 * <p>
7517 * The type {@code T} may be either a primitive or reference.
7518 * Since type {@code Iterator<T>} is erased in the method handle representation to the raw type {@code Iterator},
7519 * the {@code iteratedLoop} combinator adjusts the leading argument type for {@code body} to {@code Object}
7520 * as if by the {@link MethodHandle#asType asType} conversion method.
7521 * Therefore, if an iterator of the wrong type appears as the loop is executed, runtime exceptions may occur
7522 * as the result of dynamic conversions performed by {@link MethodHandle#asType(MethodType)}.
7523 * <p>
7524 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
7525 * <li>The loop handle's result type is the result type {@code V} of the body.
7526 * <li>The loop handle's parameter types are the types {@code (A...)},
7527 * from the external parameter list.
7528 * </ul>
7529 * <p>
7530 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
7531 * the loop variable as well as the result type of the loop; {@code T}/{@code t}, that of the elements of the
7532 * structure the loop iterates over, and {@code A...}/{@code a...} represent arguments passed to the loop.
7533 * {@snippet lang="java" :
7534 * Iterator<T> iterator(A...); // defaults to Iterable::iterator
7535 * V init(A...);
7536 * V body(V,T,A...);
7537 * V iteratedLoop(A... a...) {
7538 * Iterator<T> it = iterator(a...);
7539 * V v = init(a...);
7540 * while (it.hasNext()) {
7541 * T t = it.next();
7542 * v = body(v, t, a...);
7543 * }
7544 * return v;
7545 * }
7546 * }
7547 *
7548 * @apiNote Example:
7549 * {@snippet lang="java" :
7550 * // get an iterator from a list
7551 * static List<String> reverseStep(List<String> r, String e) {
7552 * r.add(0, e);
7553 * return r;
7554 * }
7555 * static List<String> newArrayList() { return new ArrayList<>(); }
7556 * // assume MH_reverseStep and MH_newArrayList are handles to the above methods
7557 * MethodHandle loop = MethodHandles.iteratedLoop(null, MH_newArrayList, MH_reverseStep);
7558 * List<String> list = Arrays.asList("a", "b", "c", "d", "e");
7559 * List<String> reversedList = Arrays.asList("e", "d", "c", "b", "a");
7560 * assertEquals(reversedList, (List<String>) loop.invoke(list));
7561 * }
7562 *
7563 * @apiNote The implementation of this method can be expressed approximately as follows:
7564 * {@snippet lang="java" :
7565 * MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
7566 * // assume MH_next, MH_hasNext, MH_startIter are handles to methods of Iterator/Iterable
7567 * Class<?> returnType = body.type().returnType();
7568 * Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
7569 * MethodHandle nextVal = MH_next.asType(MH_next.type().changeReturnType(ttype));
7570 * MethodHandle retv = null, step = body, startIter = iterator;
7571 * if (returnType != void.class) {
7572 * // the simple thing first: in (I V A...), drop the I to get V
7573 * retv = dropArguments(identity(returnType), 0, Iterator.class);
7574 * // body type signature (V T A...), internal loop types (I V A...)
7575 * step = swapArguments(body, 0, 1); // swap V <-> T
7576 * }
7577 * if (startIter == null) startIter = MH_getIter;
7578 * MethodHandle[]
7579 * iterVar = { startIter, null, MH_hasNext, retv }, // it = iterator; while (it.hasNext())
7580 * bodyClause = { init, filterArguments(step, 0, nextVal) }; // v = body(v, t, a)
7581 * return loop(iterVar, bodyClause);
7582 * }
7583 * }
7584 *
7585 * @param iterator an optional handle to return the iterator to start the loop.
7586 * If non-{@code null}, the handle must return {@link java.util.Iterator} or a subtype.
7587 * See above for other constraints.
7588 * @param init optional initializer, providing the initial value of the loop variable.
7589 * May be {@code null}, implying a default initial value. See above for other constraints.
7590 * @param body body of the loop, which may not be {@code null}.
7591 * It controls the loop parameters and result type in the standard case (see above for details).
7592 * It must accept its own return type (if non-void) plus a {@code T} parameter (for the iterated values),
7593 * and may accept any number of additional types.
7594 * See above for other constraints.
7595 *
7596 * @return a method handle embodying the iteration loop functionality.
7597 * @throws NullPointerException if the {@code body} handle is {@code null}.
7598 * @throws IllegalArgumentException if any argument violates the above requirements.
7599 *
7600 * @since 9
7601 */
7602 public static MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
7603 Class<?> iterableType = iteratedLoopChecks(iterator, init, body);
7604 Class<?> returnType = body.type().returnType();
7605 MethodHandle hasNext = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iteratePred);
7606 MethodHandle nextRaw = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iterateNext);
7607 MethodHandle startIter;
7608 MethodHandle nextVal;
7609 {
7610 MethodType iteratorType;
7611 if (iterator == null) {
7612 // derive argument type from body, if available, else use Iterable
7613 startIter = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_initIterator);
7614 iteratorType = startIter.type().changeParameterType(0, iterableType);
7615 } else {
7616 // force return type to the internal iterator class
7617 iteratorType = iterator.type().changeReturnType(Iterator.class);
7618 startIter = iterator;
7619 }
7620 Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
7621 MethodType nextValType = nextRaw.type().changeReturnType(ttype);
7622
7623 // perform the asType transforms under an exception transformer, as per spec.:
7624 try {
7625 startIter = startIter.asType(iteratorType);
7626 nextVal = nextRaw.asType(nextValType);
7627 } catch (WrongMethodTypeException ex) {
7628 throw new IllegalArgumentException(ex);
7629 }
7630 }
7631
7632 MethodHandle retv = null, step = body;
7633 if (returnType != void.class) {
7634 // the simple thing first: in (I V A...), drop the I to get V
7635 retv = dropArguments(identity(returnType), 0, Iterator.class);
7636 // body type signature (V T A...), internal loop types (I V A...)
7637 step = swapArguments(body, 0, 1); // swap V <-> T
7638 }
7639
7640 MethodHandle[]
7641 iterVar = { startIter, null, hasNext, retv },
7642 bodyClause = { init, filterArgument(step, 0, nextVal) };
7643 return loop(iterVar, bodyClause);
7644 }
7645
7646 private static Class<?> iteratedLoopChecks(MethodHandle iterator, MethodHandle init, MethodHandle body) {
7647 Objects.requireNonNull(body);
7648 MethodType bodyType = body.type();
7649 Class<?> returnType = bodyType.returnType();
7650 List<Class<?>> internalParamList = bodyType.parameterList();
7651 // strip leading V value if present
7652 int vsize = (returnType == void.class ? 0 : 1);
7653 if (vsize != 0 && (internalParamList.isEmpty() || internalParamList.get(0) != returnType)) {
7654 // argument list has no "V" => error
7655 MethodType expected = bodyType.insertParameterTypes(0, returnType);
7656 throw misMatchedTypes("body function", bodyType, expected);
7657 } else if (internalParamList.size() <= vsize) {
7658 // missing T type => error
7659 MethodType expected = bodyType.insertParameterTypes(vsize, Object.class);
7660 throw misMatchedTypes("body function", bodyType, expected);
7661 }
7662 List<Class<?>> externalParamList = internalParamList.subList(vsize + 1, internalParamList.size());
7663 Class<?> iterableType = null;
7664 if (iterator != null) {
7665 // special case; if the body handle only declares V and T then
7666 // the external parameter list is obtained from iterator handle
7667 if (externalParamList.isEmpty()) {
7668 externalParamList = iterator.type().parameterList();
7669 }
7670 MethodType itype = iterator.type();
7671 if (!Iterator.class.isAssignableFrom(itype.returnType())) {
7672 throw newIllegalArgumentException("iteratedLoop first argument must have Iterator return type");
7673 }
7674 if (!itype.effectivelyIdenticalParameters(0, externalParamList)) {
7675 MethodType expected = methodType(itype.returnType(), externalParamList);
7676 throw misMatchedTypes("iterator parameters", itype, expected);
7677 }
7678 } else {
7679 if (externalParamList.isEmpty()) {
7680 // special case; if the iterator handle is null and the body handle
7681 // only declares V and T then the external parameter list consists
7682 // of Iterable
7683 externalParamList = List.of(Iterable.class);
7684 iterableType = Iterable.class;
7685 } else {
7686 // special case; if the iterator handle is null and the external
7687 // parameter list is not empty then the first parameter must be
7688 // assignable to Iterable
7689 iterableType = externalParamList.get(0);
7690 if (!Iterable.class.isAssignableFrom(iterableType)) {
7691 throw newIllegalArgumentException(
7692 "inferred first loop argument must inherit from Iterable: " + iterableType);
7693 }
7694 }
7695 }
7696 if (init != null) {
7697 MethodType initType = init.type();
7698 if (initType.returnType() != returnType ||
7699 !initType.effectivelyIdenticalParameters(0, externalParamList)) {
7700 throw misMatchedTypes("loop initializer", initType, methodType(returnType, externalParamList));
7701 }
7702 }
7703 return iterableType; // help the caller a bit
7704 }
7705
7706 /*non-public*/
7707 static MethodHandle swapArguments(MethodHandle mh, int i, int j) {
7708 // there should be a better way to uncross my wires
7709 int arity = mh.type().parameterCount();
7710 int[] order = new int[arity];
7711 for (int k = 0; k < arity; k++) order[k] = k;
7712 order[i] = j; order[j] = i;
7713 Class<?>[] types = mh.type().parameterArray();
7714 Class<?> ti = types[i]; types[i] = types[j]; types[j] = ti;
7715 MethodType swapType = methodType(mh.type().returnType(), types);
7716 return permuteArguments(mh, swapType, order);
7717 }
7718
7719 /**
7720 * Makes a method handle that adapts a {@code target} method handle by wrapping it in a {@code try-finally} block.
7721 * Another method handle, {@code cleanup}, represents the functionality of the {@code finally} block. Any exception
7722 * thrown during the execution of the {@code target} handle will be passed to the {@code cleanup} handle. The
7723 * exception will be rethrown, unless {@code cleanup} handle throws an exception first. The
7724 * value returned from the {@code cleanup} handle's execution will be the result of the execution of the
7725 * {@code try-finally} handle.
7726 * <p>
7727 * The {@code cleanup} handle will be passed one or two additional leading arguments.
7728 * The first is the exception thrown during the
7729 * execution of the {@code target} handle, or {@code null} if no exception was thrown.
7730 * The second is the result of the execution of the {@code target} handle, or, if it throws an exception,
7731 * a {@code null}, zero, or {@code false} value of the required type is supplied as a placeholder.
7732 * The second argument is not present if the {@code target} handle has a {@code void} return type.
7733 * (Note that, except for argument type conversions, combinators represent {@code void} values in parameter lists
7734 * by omitting the corresponding paradoxical arguments, not by inserting {@code null} or zero values.)
7735 * <p>
7736 * The {@code target} and {@code cleanup} handles must have the same corresponding argument and return types, except
7737 * that the {@code cleanup} handle may omit trailing arguments. Also, the {@code cleanup} handle must have one or
7738 * two extra leading parameters:<ul>
7739 * <li>a {@code Throwable}, which will carry the exception thrown by the {@code target} handle (if any); and
7740 * <li>a parameter of the same type as the return type of both {@code target} and {@code cleanup}, which will carry
7741 * the result from the execution of the {@code target} handle.
7742 * This parameter is not present if the {@code target} returns {@code void}.
7743 * </ul>
7744 * <p>
7745 * The pseudocode for the resulting adapter looks as follows. In the code, {@code V} represents the result type of
7746 * the {@code try/finally} construct; {@code A}/{@code a}, the types and values of arguments to the resulting
7747 * handle consumed by the cleanup; and {@code B}/{@code b}, those of arguments to the resulting handle discarded by
7748 * the cleanup.
7749 * {@snippet lang="java" :
7750 * V target(A..., B...);
7751 * V cleanup(Throwable, V, A...);
7752 * V adapter(A... a, B... b) {
7753 * V result = (zero value for V);
7754 * Throwable throwable = null;
7755 * try {
7756 * result = target(a..., b...);
7757 * } catch (Throwable t) {
7758 * throwable = t;
7759 * throw t;
7760 * } finally {
7761 * result = cleanup(throwable, result, a...);
7762 * }
7763 * return result;
7764 * }
7765 * }
7766 * <p>
7767 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
7768 * be modified by execution of the target, and so are passed unchanged
7769 * from the caller to the cleanup, if it is invoked.
7770 * <p>
7771 * The target and cleanup must return the same type, even if the cleanup
7772 * always throws.
7773 * To create such a throwing cleanup, compose the cleanup logic
7774 * with {@link #throwException throwException},
7775 * in order to create a method handle of the correct return type.
7776 * <p>
7777 * Note that {@code tryFinally} never converts exceptions into normal returns.
7778 * In rare cases where exceptions must be converted in that way, first wrap
7779 * the target with {@link #catchException(MethodHandle, Class, MethodHandle)}
7780 * to capture an outgoing exception, and then wrap with {@code tryFinally}.
7781 * <p>
7782 * It is recommended that the first parameter type of {@code cleanup} be
7783 * declared {@code Throwable} rather than a narrower subtype. This ensures
7784 * {@code cleanup} will always be invoked with whatever exception that
7785 * {@code target} throws. Declaring a narrower type may result in a
7786 * {@code ClassCastException} being thrown by the {@code try-finally}
7787 * handle if the type of the exception thrown by {@code target} is not
7788 * assignable to the first parameter type of {@code cleanup}. Note that
7789 * various exception types of {@code VirtualMachineError},
7790 * {@code LinkageError}, and {@code RuntimeException} can in principle be
7791 * thrown by almost any kind of Java code, and a finally clause that
7792 * catches (say) only {@code IOException} would mask any of the others
7793 * behind a {@code ClassCastException}.
7794 *
7795 * @param target the handle whose execution is to be wrapped in a {@code try} block.
7796 * @param cleanup the handle that is invoked in the finally block.
7797 *
7798 * @return a method handle embodying the {@code try-finally} block composed of the two arguments.
7799 * @throws NullPointerException if any argument is null
7800 * @throws IllegalArgumentException if {@code cleanup} does not accept
7801 * the required leading arguments, or if the method handle types do
7802 * not match in their return types and their
7803 * corresponding trailing parameters
7804 *
7805 * @see MethodHandles#catchException(MethodHandle, Class, MethodHandle)
7806 * @since 9
7807 */
7808 public static MethodHandle tryFinally(MethodHandle target, MethodHandle cleanup) {
7809 Class<?>[] targetParamTypes = target.type().ptypes();
7810 Class<?> rtype = target.type().returnType();
7811
7812 tryFinallyChecks(target, cleanup);
7813
7814 // Match parameter lists: if the cleanup has a shorter parameter list than the target, add ignored arguments.
7815 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
7816 // target parameter list.
7817 cleanup = dropArgumentsToMatch(cleanup, (rtype == void.class ? 1 : 2), targetParamTypes, 0, false);
7818
7819 // Ensure that the intrinsic type checks the instance thrown by the
7820 // target against the first parameter of cleanup
7821 cleanup = cleanup.asType(cleanup.type().changeParameterType(0, Throwable.class));
7822
7823 // Use asFixedArity() to avoid unnecessary boxing of last argument for VarargsCollector case.
7824 return MethodHandleImpl.makeTryFinally(target.asFixedArity(), cleanup.asFixedArity(), rtype, targetParamTypes);
7825 }
7826
7827 private static void tryFinallyChecks(MethodHandle target, MethodHandle cleanup) {
7828 Class<?> rtype = target.type().returnType();
7829 if (rtype != cleanup.type().returnType()) {
7830 throw misMatchedTypes("target and return types", cleanup.type().returnType(), rtype);
7831 }
7832 MethodType cleanupType = cleanup.type();
7833 if (!Throwable.class.isAssignableFrom(cleanupType.parameterType(0))) {
7834 throw misMatchedTypes("cleanup first argument and Throwable", cleanup.type(), Throwable.class);
7835 }
7836 if (rtype != void.class && cleanupType.parameterType(1) != rtype) {
7837 throw misMatchedTypes("cleanup second argument and target return type", cleanup.type(), rtype);
7838 }
7839 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
7840 // target parameter list.
7841 int cleanupArgIndex = rtype == void.class ? 1 : 2;
7842 if (!cleanupType.effectivelyIdenticalParameters(cleanupArgIndex, target.type().parameterList())) {
7843 throw misMatchedTypes("cleanup parameters after (Throwable,result) and target parameter list prefix",
7844 cleanup.type(), target.type());
7845 }
7846 }
7847
7848 /**
7849 * Creates a table switch method handle, which can be used to switch over a set of target
7850 * method handles, based on a given target index, called selector.
7851 * <p>
7852 * For a selector value of {@code n}, where {@code n} falls in the range {@code [0, N)},
7853 * and where {@code N} is the number of target method handles, the table switch method
7854 * handle will invoke the n-th target method handle from the list of target method handles.
7855 * <p>
7856 * For a selector value that does not fall in the range {@code [0, N)}, the table switch
7857 * method handle will invoke the given fallback method handle.
7858 * <p>
7859 * All method handles passed to this method must have the same type, with the additional
7860 * requirement that the leading parameter be of type {@code int}. The leading parameter
7861 * represents the selector.
7862 * <p>
7863 * Any trailing parameters present in the type will appear on the returned table switch
7864 * method handle as well. Any arguments assigned to these parameters will be forwarded,
7865 * together with the selector value, to the selected method handle when invoking it.
7866 *
7867 * @apiNote Example:
7868 * The cases each drop the {@code selector} value they are given, and take an additional
7869 * {@code String} argument, which is concatenated (using {@link String#concat(String)})
7870 * to a specific constant label string for each case:
7871 * {@snippet lang="java" :
7872 * MethodHandles.Lookup lookup = MethodHandles.lookup();
7873 * MethodHandle caseMh = lookup.findVirtual(String.class, "concat",
7874 * MethodType.methodType(String.class, String.class));
7875 * caseMh = MethodHandles.dropArguments(caseMh, 0, int.class);
7876 *
7877 * MethodHandle caseDefault = MethodHandles.insertArguments(caseMh, 1, "default: ");
7878 * MethodHandle case0 = MethodHandles.insertArguments(caseMh, 1, "case 0: ");
7879 * MethodHandle case1 = MethodHandles.insertArguments(caseMh, 1, "case 1: ");
7880 *
7881 * MethodHandle mhSwitch = MethodHandles.tableSwitch(
7882 * caseDefault,
7883 * case0,
7884 * case1
7885 * );
7886 *
7887 * assertEquals("default: data", (String) mhSwitch.invokeExact(-1, "data"));
7888 * assertEquals("case 0: data", (String) mhSwitch.invokeExact(0, "data"));
7889 * assertEquals("case 1: data", (String) mhSwitch.invokeExact(1, "data"));
7890 * assertEquals("default: data", (String) mhSwitch.invokeExact(2, "data"));
7891 * }
7892 *
7893 * @param fallback the fallback method handle that is called when the selector is not
7894 * within the range {@code [0, N)}.
7895 * @param targets array of target method handles.
7896 * @return the table switch method handle.
7897 * @throws NullPointerException if {@code fallback}, the {@code targets} array, or any
7898 * any of the elements of the {@code targets} array are
7899 * {@code null}.
7900 * @throws IllegalArgumentException if the {@code targets} array is empty, if the leading
7901 * parameter of the fallback handle or any of the target
7902 * handles is not {@code int}, or if the types of
7903 * the fallback handle and all of target handles are
7904 * not the same.
7905 *
7906 * @since 17
7907 */
7908 public static MethodHandle tableSwitch(MethodHandle fallback, MethodHandle... targets) {
7909 Objects.requireNonNull(fallback);
7910 Objects.requireNonNull(targets);
7911 targets = targets.clone();
7912 MethodType type = tableSwitchChecks(fallback, targets);
7913 return MethodHandleImpl.makeTableSwitch(type, fallback, targets);
7914 }
7915
7916 private static MethodType tableSwitchChecks(MethodHandle defaultCase, MethodHandle[] caseActions) {
7917 if (caseActions.length == 0)
7918 throw new IllegalArgumentException("Not enough cases: " + Arrays.toString(caseActions));
7919
7920 MethodType expectedType = defaultCase.type();
7921
7922 if (!(expectedType.parameterCount() >= 1) || expectedType.parameterType(0) != int.class)
7923 throw new IllegalArgumentException(
7924 "Case actions must have int as leading parameter: " + Arrays.toString(caseActions));
7925
7926 for (MethodHandle mh : caseActions) {
7927 Objects.requireNonNull(mh);
7928 if (mh.type() != expectedType)
7929 throw new IllegalArgumentException(
7930 "Case actions must have the same type: " + Arrays.toString(caseActions));
7931 }
7932
7933 return expectedType;
7934 }
7935
7936 /**
7937 * Adapts a target var handle by pre-processing incoming and outgoing values using a pair of filter functions.
7938 * <p>
7939 * When calling e.g. {@link VarHandle#set(Object...)} on the resulting var handle, the incoming value (of type {@code T}, where
7940 * {@code T} is the <em>last</em> parameter type of the first filter function) is processed using the first filter and then passed
7941 * to the target var handle.
7942 * Conversely, when calling e.g. {@link VarHandle#get(Object...)} on the resulting var handle, the return value obtained from
7943 * the target var handle (of type {@code T}, where {@code T} is the <em>last</em> parameter type of the second filter function)
7944 * is processed using the second filter and returned to the caller. More advanced access mode types, such as
7945 * {@link VarHandle.AccessMode#COMPARE_AND_EXCHANGE} might apply both filters at the same time.
7946 * <p>
7947 * For the boxing and unboxing filters to be well-formed, their types must be of the form {@code (A... , S) -> T} and
7948 * {@code (A... , T) -> S}, respectively, where {@code T} is the type of the target var handle. If this is the case,
7949 * the resulting var handle will have type {@code S} and will feature the additional coordinates {@code A...} (which
7950 * will be appended to the coordinates of the target var handle).
7951 * <p>
7952 * If the boxing and unboxing filters throw any checked exceptions when invoked, the resulting var handle will
7953 * throw an {@link IllegalStateException}.
7954 * <p>
7955 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
7956 * atomic access guarantees as those featured by the target var handle.
7957 *
7958 * @param target the target var handle
7959 * @param filterToTarget a filter to convert some type {@code S} into the type of {@code target}
7960 * @param filterFromTarget a filter to convert the type of {@code target} to some type {@code S}
7961 * @return an adapter var handle which accepts a new type, performing the provided boxing/unboxing conversions.
7962 * @throws IllegalArgumentException if {@code filterFromTarget} and {@code filterToTarget} are not well-formed, that is, they have types
7963 * other than {@code (A... , S) -> T} and {@code (A... , T) -> S}, respectively, where {@code T} is the type of the target var handle,
7964 * or if it's determined that either {@code filterFromTarget} or {@code filterToTarget} throws any checked exceptions.
7965 * @throws NullPointerException if any of the arguments is {@code null}.
7966 * @since 22
7967 */
7968 public static VarHandle filterValue(VarHandle target, MethodHandle filterToTarget, MethodHandle filterFromTarget) {
7969 return VarHandles.filterValue(target, filterToTarget, filterFromTarget);
7970 }
7971
7972 /**
7973 * Adapts a target var handle by pre-processing incoming coordinate values using unary filter functions.
7974 * <p>
7975 * When calling e.g. {@link VarHandle#get(Object...)} on the resulting var handle, the incoming coordinate values
7976 * starting at position {@code pos} (of type {@code C1, C2 ... Cn}, where {@code C1, C2 ... Cn} are the return types
7977 * of the unary filter functions) are transformed into new values (of type {@code S1, S2 ... Sn}, where {@code S1, S2 ... Sn} are the
7978 * parameter types of the unary filter functions), and then passed (along with any coordinate that was left unaltered
7979 * by the adaptation) to the target var handle.
7980 * <p>
7981 * For the coordinate filters to be well-formed, their types must be of the form {@code S1 -> T1, S2 -> T1 ... Sn -> Tn},
7982 * where {@code T1, T2 ... Tn} are the coordinate types starting at position {@code pos} of the target var handle.
7983 * <p>
7984 * If any of the filters throws a checked exception when invoked, the resulting var handle will
7985 * throw an {@link IllegalStateException}.
7986 * <p>
7987 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
7988 * atomic access guarantees as those featured by the target var handle.
7989 *
7990 * @param target the target var handle
7991 * @param pos the position of the first coordinate to be transformed
7992 * @param filters the unary functions which are used to transform coordinates starting at position {@code pos}
7993 * @return an adapter var handle which accepts new coordinate types, applying the provided transformation
7994 * to the new coordinate values.
7995 * @throws IllegalArgumentException if the handles in {@code filters} are not well-formed, that is, they have types
7996 * other than {@code S1 -> T1, S2 -> T2, ... Sn -> Tn} where {@code T1, T2 ... Tn} are the coordinate types starting
7997 * at position {@code pos} of the target var handle, if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive,
7998 * or if more filters are provided than the actual number of coordinate types available starting at {@code pos},
7999 * or if it's determined that any of the filters throws any checked exceptions.
8000 * @throws NullPointerException if any of the arguments is {@code null} or {@code filters} contains {@code null}.
8001 * @since 22
8002 */
8003 public static VarHandle filterCoordinates(VarHandle target, int pos, MethodHandle... filters) {
8004 return VarHandles.filterCoordinates(target, pos, filters);
8005 }
8006
8007 /**
8008 * Provides a target var handle with one or more <em>bound coordinates</em>
8009 * in advance of the var handle's invocation. As a consequence, the resulting var handle will feature less
8010 * coordinate types than the target var handle.
8011 * <p>
8012 * When calling e.g. {@link VarHandle#get(Object...)} on the resulting var handle, incoming coordinate values
8013 * are joined with bound coordinate values, and then passed to the target var handle.
8014 * <p>
8015 * For the bound coordinates to be well-formed, their types must be {@code T1, T2 ... Tn },
8016 * where {@code T1, T2 ... Tn} are the coordinate types starting at position {@code pos} of the target var handle.
8017 * <p>
8018 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
8019 * atomic access guarantees as those featured by the target var handle.
8020 *
8021 * @param target the var handle to invoke after the bound coordinates are inserted
8022 * @param pos the position of the first coordinate to be inserted
8023 * @param values the series of bound coordinates to insert
8024 * @return an adapter var handle which inserts additional coordinates,
8025 * before calling the target var handle
8026 * @throws IllegalArgumentException if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive,
8027 * or if more values are provided than the actual number of coordinate types available starting at {@code pos}.
8028 * @throws ClassCastException if the bound coordinates in {@code values} are not well-formed, that is, they have types
8029 * other than {@code T1, T2 ... Tn }, where {@code T1, T2 ... Tn} are the coordinate types starting at position {@code pos}
8030 * of the target var handle.
8031 * @throws NullPointerException if any of the arguments is {@code null} or {@code values} contains {@code null}.
8032 * @since 22
8033 */
8034 public static VarHandle insertCoordinates(VarHandle target, int pos, Object... values) {
8035 return VarHandles.insertCoordinates(target, pos, values);
8036 }
8037
8038 /**
8039 * Provides a var handle which adapts the coordinate values of the target var handle, by re-arranging them
8040 * so that the new coordinates match the provided ones.
8041 * <p>
8042 * The given array controls the reordering.
8043 * Call {@code #I} the number of incoming coordinates (the value
8044 * {@code newCoordinates.size()}), and call {@code #O} the number
8045 * of outgoing coordinates (the number of coordinates associated with the target var handle).
8046 * Then the length of the reordering array must be {@code #O},
8047 * and each element must be a non-negative number less than {@code #I}.
8048 * For every {@code N} less than {@code #O}, the {@code N}-th
8049 * outgoing coordinate will be taken from the {@code I}-th incoming
8050 * coordinate, where {@code I} is {@code reorder[N]}.
8051 * <p>
8052 * No coordinate value conversions are applied.
8053 * The type of each incoming coordinate, as determined by {@code newCoordinates},
8054 * must be identical to the type of the corresponding outgoing coordinate
8055 * in the target var handle.
8056 * <p>
8057 * The reordering array need not specify an actual permutation.
8058 * An incoming coordinate will be duplicated if its index appears
8059 * more than once in the array, and an incoming coordinate will be dropped
8060 * if its index does not appear in the array.
8061 * <p>
8062 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
8063 * atomic access guarantees as those featured by the target var handle.
8064 * @param target the var handle to invoke after the coordinates have been reordered
8065 * @param newCoordinates the new coordinate types
8066 * @param reorder an index array which controls the reordering
8067 * @return an adapter var handle which re-arranges the incoming coordinate values,
8068 * before calling the target var handle
8069 * @throws IllegalArgumentException if the index array length is not equal to
8070 * the number of coordinates of the target var handle, or if any index array element is not a valid index for
8071 * a coordinate of {@code newCoordinates}, or if two corresponding coordinate types in
8072 * the target var handle and in {@code newCoordinates} are not identical.
8073 * @throws NullPointerException if any of the arguments is {@code null} or {@code newCoordinates} contains {@code null}.
8074 * @since 22
8075 */
8076 public static VarHandle permuteCoordinates(VarHandle target, List<Class<?>> newCoordinates, int... reorder) {
8077 return VarHandles.permuteCoordinates(target, newCoordinates, reorder);
8078 }
8079
8080 /**
8081 * Adapts a target var handle by pre-processing
8082 * a sub-sequence of its coordinate values with a filter (a method handle).
8083 * The pre-processed coordinates are replaced by the result (if any) of the
8084 * filter function and the target var handle is then called on the modified (usually shortened)
8085 * coordinate list.
8086 * <p>
8087 * If {@code R} is the return type of the filter, then:
8088 * <ul>
8089 * <li>if {@code R} <em>is not</em> {@code void}, the target var handle must have a coordinate of type {@code R} in
8090 * position {@code pos}. The parameter types of the filter will replace the coordinate type at position {@code pos}
8091 * of the target var handle. When the returned var handle is invoked, it will be as if the filter is invoked first,
8092 * and its result is passed in place of the coordinate at position {@code pos} in a downstream invocation of the
8093 * target var handle.</li>
8094 * <li> if {@code R} <em>is</em> {@code void}, the parameter types (if any) of the filter will be inserted in the
8095 * coordinate type list of the target var handle at position {@code pos}. In this case, when the returned var handle
8096 * is invoked, the filter essentially acts as a side effect, consuming some of the coordinate values, before a
8097 * downstream invocation of the target var handle.</li>
8098 * </ul>
8099 * <p>
8100 * If any of the filters throws a checked exception when invoked, the resulting var handle will
8101 * throw an {@link IllegalStateException}.
8102 * <p>
8103 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
8104 * atomic access guarantees as those featured by the target var handle.
8105 *
8106 * @param target the var handle to invoke after the coordinates have been filtered
8107 * @param pos the position in the coordinate list of the target var handle where the filter is to be inserted
8108 * @param filter the filter method handle
8109 * @return an adapter var handle which filters the incoming coordinate values,
8110 * before calling the target var handle
8111 * @throws IllegalArgumentException if the return type of {@code filter}
8112 * is not void, and it is not the same as the {@code pos} coordinate of the target var handle,
8113 * if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive,
8114 * if the resulting var handle's type would have <a href="MethodHandle.html#maxarity">too many coordinates</a>,
8115 * or if it's determined that {@code filter} throws any checked exceptions.
8116 * @throws NullPointerException if any of the arguments is {@code null}.
8117 * @since 22
8118 */
8119 public static VarHandle collectCoordinates(VarHandle target, int pos, MethodHandle filter) {
8120 return VarHandles.collectCoordinates(target, pos, filter);
8121 }
8122
8123 /**
8124 * Returns a var handle which will discard some dummy coordinates before delegating to the
8125 * target var handle. As a consequence, the resulting var handle will feature more
8126 * coordinate types than the target var handle.
8127 * <p>
8128 * The {@code pos} argument may range between zero and <i>N</i>, where <i>N</i> is the arity of the
8129 * target var handle's coordinate types. If {@code pos} is zero, the dummy coordinates will precede
8130 * the target's real arguments; if {@code pos} is <i>N</i> they will come after.
8131 * <p>
8132 * The resulting var handle will feature the same access modes (see {@link VarHandle.AccessMode}) and
8133 * atomic access guarantees as those featured by the target var handle.
8134 *
8135 * @param target the var handle to invoke after the dummy coordinates are dropped
8136 * @param pos position of the first coordinate to drop (zero for the leftmost)
8137 * @param valueTypes the type(s) of the coordinate(s) to drop
8138 * @return an adapter var handle which drops some dummy coordinates,
8139 * before calling the target var handle
8140 * @throws IllegalArgumentException if {@code pos} is not between 0 and the target var handle coordinate arity, inclusive.
8141 * @throws NullPointerException if any of the arguments is {@code null} or {@code valueTypes} contains {@code null}.
8142 * @since 22
8143 */
8144 public static VarHandle dropCoordinates(VarHandle target, int pos, Class<?>... valueTypes) {
8145 return VarHandles.dropCoordinates(target, pos, valueTypes);
8146 }
8147 }