1 /*
2 * Copyright (c) 2008, 2016, 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.org.objectweb.asm.ClassWriter;
29 import jdk.internal.org.objectweb.asm.Opcodes;
30 import jdk.internal.reflect.CallerSensitive;
31 import jdk.internal.reflect.Reflection;
32 import sun.invoke.util.ValueConversions;
33 import sun.invoke.util.VerifyAccess;
34 import sun.invoke.util.Wrapper;
35 import sun.reflect.misc.ReflectUtil;
36 import sun.security.util.SecurityConstants;
37
38 import java.lang.invoke.LambdaForm.BasicType;
39 import java.lang.reflect.Constructor;
40 import java.lang.reflect.Field;
41 import java.lang.reflect.Member;
42 import java.lang.reflect.Method;
43 import java.lang.reflect.Modifier;
44 import java.lang.reflect.ReflectPermission;
45 import java.nio.ByteOrder;
46 import java.security.AccessController;
47 import java.security.PrivilegedAction;
48 import java.util.ArrayList;
49 import java.util.Arrays;
50 import java.util.BitSet;
51 import java.util.Iterator;
52 import java.util.List;
53 import java.util.Objects;
54 import java.util.concurrent.ConcurrentHashMap;
55 import java.util.stream.Collectors;
56 import java.util.stream.Stream;
57
58 import static java.lang.invoke.MethodHandleImpl.Intrinsic;
59 import static java.lang.invoke.MethodHandleNatives.Constants.*;
60 import static java.lang.invoke.MethodHandleStatics.newIllegalArgumentException;
61 import static java.lang.invoke.MethodType.methodType;
62
63 /**
64 * This class consists exclusively of static methods that operate on or return
65 * method handles. They fall into several categories:
66 * <ul>
67 * <li>Lookup methods which help create method handles for methods and fields.
68 * <li>Combinator methods, which combine or transform pre-existing method handles into new ones.
69 * <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns.
70 * </ul>
71 *
72 * @author John Rose, JSR 292 EG
73 * @since 1.7
74 */
75 public class MethodHandles {
76
77 private MethodHandles() { } // do not instantiate
78
79 private static final MemberName.Factory IMPL_NAMES = MemberName.getFactory();
80
81 // See IMPL_LOOKUP below.
82
83 //// Method handle creation from ordinary methods.
84
85 /**
86 * Returns a {@link Lookup lookup object} with
87 * full capabilities to emulate all supported bytecode behaviors of the caller.
88 * These capabilities include <a href="MethodHandles.Lookup.html#privacc">private access</a> to the caller.
89 * Factory methods on the lookup object can create
90 * <a href="MethodHandleInfo.html#directmh">direct method handles</a>
91 * for any member that the caller has access to via bytecodes,
92 * including protected and private fields and methods.
93 * This lookup object is a <em>capability</em> which may be delegated to trusted agents.
94 * Do not store it in place where untrusted code can access it.
95 * <p>
96 * This method is caller sensitive, which means that it may return different
97 * values to different callers.
98 * <p>
99 * For any given caller class {@code C}, the lookup object returned by this call
100 * has equivalent capabilities to any lookup object
101 * supplied by the JVM to the bootstrap method of an
102 * <a href="package-summary.html#indyinsn">invokedynamic instruction</a>
103 * executing in the same caller class {@code C}.
104 * @return a lookup object for the caller of this method, with private access
105 */
106 @CallerSensitive
107 public static Lookup lookup() {
108 return new Lookup(Reflection.getCallerClass());
109 }
110
111 /**
112 * Returns a {@link Lookup lookup object} which is trusted minimally.
113 * It can only be used to create method handles to public members in
114 * public classes in packages that are exported unconditionally.
115 * <p>
116 * For now, the {@linkplain Lookup#lookupClass lookup class} of this lookup
117 * object is in an unnamed module.
118 * Consequently, the lookup context of this lookup object will be the bootstrap
119 * class loader, which means it cannot find user classes.
120 *
121 * <p style="font-size:smaller;">
122 * <em>Discussion:</em>
123 * The lookup class can be changed to any other class {@code C} using an expression of the form
124 * {@link Lookup#in publicLookup().in(C.class)}.
125 * but may change the lookup context by virtue of changing the class loader.
126 * A public lookup object is always subject to
127 * <a href="MethodHandles.Lookup.html#secmgr">security manager checks</a>.
128 * Also, it cannot access
129 * <a href="MethodHandles.Lookup.html#callsens">caller sensitive methods</a>.
130 * @return a lookup object which is trusted minimally
131 */
132 public static Lookup publicLookup() {
133 // During VM startup then only classes in the java.base module can be
134 // loaded and linked. This is because java.base exports aren't setup until
135 // the module system is initialized, hence types in the unnamed module
136 // (or any named module) can't link to java/lang/Object.
137 if (!jdk.internal.misc.VM.isModuleSystemInited()) {
138 return new Lookup(Object.class, Lookup.PUBLIC);
139 } else {
140 return LookupHelper.PUBLIC_LOOKUP;
141 }
142 }
143
144 /**
145 * Performs an unchecked "crack" of a
146 * <a href="MethodHandleInfo.html#directmh">direct method handle</a>.
147 * The result is as if the user had obtained a lookup object capable enough
148 * to crack the target method handle, called
149 * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect}
150 * on the target to obtain its symbolic reference, and then called
151 * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs}
152 * to resolve the symbolic reference to a member.
153 * <p>
154 * If there is a security manager, its {@code checkPermission} method
155 * is called with a {@code ReflectPermission("suppressAccessChecks")} permission.
156 * @param <T> the desired type of the result, either {@link Member} or a subtype
157 * @param target a direct method handle to crack into symbolic reference components
158 * @param expected a class object representing the desired result type {@code T}
159 * @return a reference to the method, constructor, or field object
160 * @exception SecurityException if the caller is not privileged to call {@code setAccessible}
161 * @exception NullPointerException if either argument is {@code null}
162 * @exception IllegalArgumentException if the target is not a direct method handle
163 * @exception ClassCastException if the member is not of the expected type
164 * @since 1.8
165 */
166 public static <T extends Member> T
167 reflectAs(Class<T> expected, MethodHandle target) {
168 SecurityManager smgr = System.getSecurityManager();
169 if (smgr != null) smgr.checkPermission(ACCESS_PERMISSION);
170 Lookup lookup = Lookup.IMPL_LOOKUP; // use maximally privileged lookup
171 return lookup.revealDirect(target).reflectAs(expected, lookup);
172 }
173 // Copied from AccessibleObject, as used by Method.setAccessible, etc.:
174 private static final java.security.Permission ACCESS_PERMISSION =
175 new ReflectPermission("suppressAccessChecks");
176
177 /**
178 * A <em>lookup object</em> is a factory for creating method handles,
179 * when the creation requires access checking.
180 * Method handles do not perform
181 * access checks when they are called, but rather when they are created.
182 * Therefore, method handle access
183 * restrictions must be enforced when a method handle is created.
184 * The caller class against which those restrictions are enforced
185 * is known as the {@linkplain #lookupClass lookup class}.
186 * <p>
187 * A lookup class which needs to create method handles will call
188 * {@link MethodHandles#lookup MethodHandles.lookup} to create a factory for itself.
189 * When the {@code Lookup} factory object is created, the identity of the lookup class is
190 * determined, and securely stored in the {@code Lookup} object.
191 * The lookup class (or its delegates) may then use factory methods
192 * on the {@code Lookup} object to create method handles for access-checked members.
193 * This includes all methods, constructors, and fields which are allowed to the lookup class,
194 * even private ones.
195 *
196 * <h1><a name="lookups"></a>Lookup Factory Methods</h1>
197 * The factory methods on a {@code Lookup} object correspond to all major
198 * use cases for methods, constructors, and fields.
199 * Each method handle created by a factory method is the functional
200 * equivalent of a particular <em>bytecode behavior</em>.
201 * (Bytecode behaviors are described in section 5.4.3.5 of the Java Virtual Machine Specification.)
202 * Here is a summary of the correspondence between these factory methods and
203 * the behavior of the resulting method handles:
204 * <table border=1 cellpadding=5 summary="lookup method behaviors">
205 * <tr>
206 * <th><a name="equiv"></a>lookup expression</th>
207 * <th>member</th>
208 * <th>bytecode behavior</th>
209 * </tr>
210 * <tr>
211 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</td>
212 * <td>{@code FT f;}</td><td>{@code (T) this.f;}</td>
213 * </tr>
214 * <tr>
215 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</td>
216 * <td>{@code static}<br>{@code FT f;}</td><td>{@code (T) C.f;}</td>
217 * </tr>
218 * <tr>
219 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</td>
220 * <td>{@code FT f;}</td><td>{@code this.f = x;}</td>
221 * </tr>
222 * <tr>
223 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</td>
224 * <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td>
225 * </tr>
226 * <tr>
227 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</td>
228 * <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>
229 * </tr>
230 * <tr>
231 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</td>
232 * <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td>
233 * </tr>
234 * <tr>
235 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</td>
236 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
237 * </tr>
238 * <tr>
239 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</td>
240 * <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td>
241 * </tr>
242 * <tr>
243 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</td>
244 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td>
245 * </tr>
246 * <tr>
247 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</td>
248 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, arg);}</td>
249 * </tr>
250 * <tr>
251 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</td>
252 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
253 * </tr>
254 * <tr>
255 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</td>
256 * <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td>
257 * </tr>
258 * <tr>
259 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</td>
260 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
261 * </tr>
262 * <tr>
263 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findClass lookup.findClass("C")}</td>
264 * <td>{@code class C { ... }}</td><td>{@code C.class;}</td>
265 * </tr>
266 * </table>
267 *
268 * Here, the type {@code C} is the class or interface being searched for a member,
269 * documented as a parameter named {@code refc} in the lookup methods.
270 * The method type {@code MT} is composed from the return type {@code T}
271 * and the sequence of argument types {@code A*}.
272 * The constructor also has a sequence of argument types {@code A*} and
273 * is deemed to return the newly-created object of type {@code C}.
274 * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}.
275 * The formal parameter {@code this} stands for the self-reference of type {@code C};
276 * if it is present, it is always the leading argument to the method handle invocation.
277 * (In the case of some {@code protected} members, {@code this} may be
278 * restricted in type to the lookup class; see below.)
279 * The name {@code arg} stands for all the other method handle arguments.
280 * In the code examples for the Core Reflection API, the name {@code thisOrNull}
281 * stands for a null reference if the accessed method or field is static,
282 * and {@code this} otherwise.
283 * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand
284 * for reflective objects corresponding to the given members.
285 * <p>
286 * The bytecode behavior for a {@code findClass} operation is a load of a constant class,
287 * as if by {@code ldc CONSTANT_Class}.
288 * The behavior is represented, not as a method handle, but directly as a {@code Class} constant.
289 * <p>
290 * In cases where the given member is of variable arity (i.e., a method or constructor)
291 * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}.
292 * In all other cases, the returned method handle will be of fixed arity.
293 * <p style="font-size:smaller;">
294 * <em>Discussion:</em>
295 * The equivalence between looked-up method handles and underlying
296 * class members and bytecode behaviors
297 * can break down in a few ways:
298 * <ul style="font-size:smaller;">
299 * <li>If {@code C} is not symbolically accessible from the lookup class's loader,
300 * the lookup can still succeed, even when there is no equivalent
301 * Java expression or bytecoded constant.
302 * <li>Likewise, if {@code T} or {@code MT}
303 * is not symbolically accessible from the lookup class's loader,
304 * the lookup can still succeed.
305 * For example, lookups for {@code MethodHandle.invokeExact} and
306 * {@code MethodHandle.invoke} will always succeed, regardless of requested type.
307 * <li>If there is a security manager installed, it can forbid the lookup
308 * on various grounds (<a href="MethodHandles.Lookup.html#secmgr">see below</a>).
309 * By contrast, the {@code ldc} instruction on a {@code CONSTANT_MethodHandle}
310 * constant is not subject to security manager checks.
311 * <li>If the looked-up method has a
312 * <a href="MethodHandle.html#maxarity">very large arity</a>,
313 * the method handle creation may fail, due to the method handle
314 * type having too many parameters.
315 * </ul>
316 *
317 * <h1><a name="access"></a>Access checking</h1>
318 * Access checks are applied in the factory methods of {@code Lookup},
319 * when a method handle is created.
320 * This is a key difference from the Core Reflection API, since
321 * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
322 * performs access checking against every caller, on every call.
323 * <p>
324 * All access checks start from a {@code Lookup} object, which
325 * compares its recorded lookup class against all requests to
326 * create method handles.
327 * A single {@code Lookup} object can be used to create any number
328 * of access-checked method handles, all checked against a single
329 * lookup class.
330 * <p>
331 * A {@code Lookup} object can be shared with other trusted code,
332 * such as a metaobject protocol.
333 * A shared {@code Lookup} object delegates the capability
334 * to create method handles on private members of the lookup class.
335 * Even if privileged code uses the {@code Lookup} object,
336 * the access checking is confined to the privileges of the
337 * original lookup class.
338 * <p>
339 * A lookup can fail, because
340 * the containing class is not accessible to the lookup class, or
341 * because the desired class member is missing, or because the
342 * desired class member is not accessible to the lookup class, or
343 * because the lookup object is not trusted enough to access the member.
344 * In any of these cases, a {@code ReflectiveOperationException} will be
345 * thrown from the attempted lookup. The exact class will be one of
346 * the following:
347 * <ul>
348 * <li>NoSuchMethodException — if a method is requested but does not exist
349 * <li>NoSuchFieldException — if a field is requested but does not exist
350 * <li>IllegalAccessException — if the member exists but an access check fails
351 * </ul>
352 * <p>
353 * In general, the conditions under which a method handle may be
354 * looked up for a method {@code M} are no more restrictive than the conditions
355 * under which the lookup class could have compiled, verified, and resolved a call to {@code M}.
356 * Where the JVM would raise exceptions like {@code NoSuchMethodError},
357 * a method handle lookup will generally raise a corresponding
358 * checked exception, such as {@code NoSuchMethodException}.
359 * And the effect of invoking the method handle resulting from the lookup
360 * is <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a>
361 * to executing the compiled, verified, and resolved call to {@code M}.
362 * The same point is true of fields and constructors.
363 * <p style="font-size:smaller;">
364 * <em>Discussion:</em>
365 * Access checks only apply to named and reflected methods,
366 * constructors, and fields.
367 * Other method handle creation methods, such as
368 * {@link MethodHandle#asType MethodHandle.asType},
369 * do not require any access checks, and are used
370 * independently of any {@code Lookup} object.
371 * <p>
372 * If the desired member is {@code protected}, the usual JVM rules apply,
373 * including the requirement that the lookup class must be either be in the
374 * same package as the desired member, or must inherit that member.
375 * (See the Java Virtual Machine Specification, sections 4.9.2, 5.4.3.5, and 6.4.)
376 * In addition, if the desired member is a non-static field or method
377 * in a different package, the resulting method handle may only be applied
378 * to objects of the lookup class or one of its subclasses.
379 * This requirement is enforced by narrowing the type of the leading
380 * {@code this} parameter from {@code C}
381 * (which will necessarily be a superclass of the lookup class)
382 * to the lookup class itself.
383 * <p>
384 * The JVM imposes a similar requirement on {@code invokespecial} instruction,
385 * that the receiver argument must match both the resolved method <em>and</em>
386 * the current class. Again, this requirement is enforced by narrowing the
387 * type of the leading parameter to the resulting method handle.
388 * (See the Java Virtual Machine Specification, section 4.10.1.9.)
389 * <p>
390 * The JVM represents constructors and static initializer blocks as internal methods
391 * with special names ({@code "<init>"} and {@code "<clinit>"}).
392 * The internal syntax of invocation instructions allows them to refer to such internal
393 * methods as if they were normal methods, but the JVM bytecode verifier rejects them.
394 * A lookup of such an internal method will produce a {@code NoSuchMethodException}.
395 * <p>
396 * In some cases, access between nested classes is obtained by the Java compiler by creating
397 * an wrapper method to access a private method of another class
398 * in the same top-level declaration.
399 * For example, a nested class {@code C.D}
400 * can access private members within other related classes such as
401 * {@code C}, {@code C.D.E}, or {@code C.B},
402 * but the Java compiler may need to generate wrapper methods in
403 * those related classes. In such cases, a {@code Lookup} object on
404 * {@code C.E} would be unable to those private members.
405 * A workaround for this limitation is the {@link Lookup#in Lookup.in} method,
406 * which can transform a lookup on {@code C.E} into one on any of those other
407 * classes, without special elevation of privilege.
408 * <p>
409 * The accesses permitted to a given lookup object may be limited,
410 * according to its set of {@link #lookupModes lookupModes},
411 * to a subset of members normally accessible to the lookup class.
412 * For example, the {@link MethodHandles#publicLookup publicLookup}
413 * method produces a lookup object which is only allowed to access
414 * public members in public classes of exported packages.
415 * The caller sensitive method {@link MethodHandles#lookup lookup}
416 * produces a lookup object with full capabilities relative to
417 * its caller class, to emulate all supported bytecode behaviors.
418 * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object
419 * with fewer access modes than the original lookup object.
420 *
421 * <p style="font-size:smaller;">
422 * <a name="privacc"></a>
423 * <em>Discussion of private access:</em>
424 * We say that a lookup has <em>private access</em>
425 * if its {@linkplain #lookupModes lookup modes}
426 * include the possibility of accessing {@code private} members.
427 * As documented in the relevant methods elsewhere,
428 * only lookups with private access possess the following capabilities:
429 * <ul style="font-size:smaller;">
430 * <li>access private fields, methods, and constructors of the lookup class
431 * <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> methods,
432 * such as {@code Class.forName}
433 * <li>create method handles which {@link Lookup#findSpecial emulate invokespecial} instructions
434 * <li>avoid <a href="MethodHandles.Lookup.html#secmgr">package access checks</a>
435 * for classes accessible to the lookup class
436 * <li>create {@link Lookup#in delegated lookup objects} which have private access to other classes
437 * within the same package member
438 * </ul>
439 * <p style="font-size:smaller;">
440 * Each of these permissions is a consequence of the fact that a lookup object
441 * with private access can be securely traced back to an originating class,
442 * whose <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> and Java language access permissions
443 * can be reliably determined and emulated by method handles.
444 *
445 * <h1><a name="secmgr"></a>Security manager interactions</h1>
446 * Although bytecode instructions can only refer to classes in
447 * a related class loader, this API can search for methods in any
448 * class, as long as a reference to its {@code Class} object is
449 * available. Such cross-loader references are also possible with the
450 * Core Reflection API, and are impossible to bytecode instructions
451 * such as {@code invokestatic} or {@code getfield}.
452 * There is a {@linkplain java.lang.SecurityManager security manager API}
453 * to allow applications to check such cross-loader references.
454 * These checks apply to both the {@code MethodHandles.Lookup} API
455 * and the Core Reflection API
456 * (as found on {@link java.lang.Class Class}).
457 * <p>
458 * If a security manager is present, member and class lookups are subject to
459 * additional checks.
460 * From one to three calls are made to the security manager.
461 * Any of these calls can refuse access by throwing a
462 * {@link java.lang.SecurityException SecurityException}.
463 * Define {@code smgr} as the security manager,
464 * {@code lookc} as the lookup class of the current lookup object,
465 * {@code refc} as the containing class in which the member
466 * is being sought, and {@code defc} as the class in which the
467 * member is actually defined.
468 * (If a class or other type is being accessed,
469 * the {@code refc} and {@code defc} values are the class itself.)
470 * The value {@code lookc} is defined as <em>not present</em>
471 * if the current lookup object does not have
472 * <a href="MethodHandles.Lookup.html#privacc">private access</a>.
473 * The calls are made according to the following rules:
474 * <ul>
475 * <li><b>Step 1:</b>
476 * If {@code lookc} is not present, or if its class loader is not
477 * the same as or an ancestor of the class loader of {@code refc},
478 * then {@link SecurityManager#checkPackageAccess
479 * smgr.checkPackageAccess(refcPkg)} is called,
480 * where {@code refcPkg} is the package of {@code refc}.
481 * <li><b>Step 2a:</b>
482 * If the retrieved member is not public and
483 * {@code lookc} is not present, then
484 * {@link SecurityManager#checkPermission smgr.checkPermission}
485 * with {@code RuntimePermission("accessDeclaredMembers")} is called.
486 * <li><b>Step 2b:</b>
487 * If the retrieved class has a {@code null} class loader,
488 * and {@code lookc} is not present, then
489 * {@link SecurityManager#checkPermission smgr.checkPermission}
490 * with {@code RuntimePermission("getClassLoader")} is called.
491 * <li><b>Step 3:</b>
492 * If the retrieved member is not public,
493 * and if {@code lookc} is not present,
494 * and if {@code defc} and {@code refc} are different,
495 * then {@link SecurityManager#checkPackageAccess
496 * smgr.checkPackageAccess(defcPkg)} is called,
497 * where {@code defcPkg} is the package of {@code defc}.
498 * </ul>
499 * Security checks are performed after other access checks have passed.
500 * Therefore, the above rules presuppose a member or class that is public,
501 * or else that is being accessed from a lookup class that has
502 * rights to access the member or class.
503 *
504 * <h1><a name="callsens"></a>Caller sensitive methods</h1>
505 * A small number of Java methods have a special property called caller sensitivity.
506 * A <em>caller-sensitive</em> method can behave differently depending on the
507 * identity of its immediate caller.
508 * <p>
509 * If a method handle for a caller-sensitive method is requested,
510 * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> apply,
511 * but they take account of the lookup class in a special way.
512 * The resulting method handle behaves as if it were called
513 * from an instruction contained in the lookup class,
514 * so that the caller-sensitive method detects the lookup class.
515 * (By contrast, the invoker of the method handle is disregarded.)
516 * Thus, in the case of caller-sensitive methods,
517 * different lookup classes may give rise to
518 * differently behaving method handles.
519 * <p>
520 * In cases where the lookup object is
521 * {@link MethodHandles#publicLookup() publicLookup()},
522 * or some other lookup object without
523 * <a href="MethodHandles.Lookup.html#privacc">private access</a>,
524 * the lookup class is disregarded.
525 * In such cases, no caller-sensitive method handle can be created,
526 * access is forbidden, and the lookup fails with an
527 * {@code IllegalAccessException}.
528 * <p style="font-size:smaller;">
529 * <em>Discussion:</em>
530 * For example, the caller-sensitive method
531 * {@link java.lang.Class#forName(String) Class.forName(x)}
532 * can return varying classes or throw varying exceptions,
533 * depending on the class loader of the class that calls it.
534 * A public lookup of {@code Class.forName} will fail, because
535 * there is no reasonable way to determine its bytecode behavior.
536 * <p style="font-size:smaller;">
537 * If an application caches method handles for broad sharing,
538 * it should use {@code publicLookup()} to create them.
539 * If there is a lookup of {@code Class.forName}, it will fail,
540 * and the application must take appropriate action in that case.
541 * It may be that a later lookup, perhaps during the invocation of a
542 * bootstrap method, can incorporate the specific identity
543 * of the caller, making the method accessible.
544 * <p style="font-size:smaller;">
545 * The function {@code MethodHandles.lookup} is caller sensitive
546 * so that there can be a secure foundation for lookups.
547 * Nearly all other methods in the JSR 292 API rely on lookup
548 * objects to check access requests.
549 */
550 public static final
551 class Lookup {
552 /** The class on behalf of whom the lookup is being performed. */
553 private final Class<?> lookupClass;
554
555 /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */
556 private final int allowedModes;
557
558 /** A single-bit mask representing {@code public} access,
559 * which may contribute to the result of {@link #lookupModes lookupModes}.
560 * The value, {@code 0x01}, happens to be the same as the value of the
561 * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.
562 */
563 public static final int PUBLIC = Modifier.PUBLIC;
564
565 /** A single-bit mask representing {@code private} access,
566 * which may contribute to the result of {@link #lookupModes lookupModes}.
567 * The value, {@code 0x02}, happens to be the same as the value of the
568 * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.
569 */
570 public static final int PRIVATE = Modifier.PRIVATE;
571
572 /** A single-bit mask representing {@code protected} access,
573 * which may contribute to the result of {@link #lookupModes lookupModes}.
574 * The value, {@code 0x04}, happens to be the same as the value of the
575 * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.
576 */
577 public static final int PROTECTED = Modifier.PROTECTED;
578
579 /** A single-bit mask representing {@code package} access (default access),
580 * which may contribute to the result of {@link #lookupModes lookupModes}.
581 * The value is {@code 0x08}, which does not correspond meaningfully to
582 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
583 */
584 public static final int PACKAGE = Modifier.STATIC;
585
586 /** A single-bit mask representing {@code module} access (default access),
587 * which may contribute to the result of {@link #lookupModes lookupModes}.
588 * The value is {@code 0x10}, which does not correspond meaningfully to
589 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
590 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup}
591 * with this lookup mode can access all public types in the module of the
592 * lookup class and public types in packages exported by other modules
593 * to the module of the lookup class.
594 * @since 9
595 */
596 public static final int MODULE = PACKAGE << 1;
597
598 private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE | MODULE);
599 private static final int TRUSTED = -1;
600
601 private static int fixmods(int mods) {
602 mods &= (ALL_MODES - PACKAGE - MODULE);
603 return (mods != 0) ? mods : (PACKAGE | MODULE);
604 }
605
606 /** Tells which class is performing the lookup. It is this class against
607 * which checks are performed for visibility and access permissions.
608 * <p>
609 * The class implies a maximum level of access permission,
610 * but the permissions may be additionally limited by the bitmask
611 * {@link #lookupModes lookupModes}, which controls whether non-public members
612 * can be accessed.
613 * @return the lookup class, on behalf of which this lookup object finds members
614 */
615 public Class<?> lookupClass() {
616 return lookupClass;
617 }
618
619 // This is just for calling out to MethodHandleImpl.
620 private Class<?> lookupClassOrNull() {
621 return (allowedModes == TRUSTED) ? null : lookupClass;
622 }
623
624 /** Tells which access-protection classes of members this lookup object can produce.
625 * The result is a bit-mask of the bits
626 * {@linkplain #PUBLIC PUBLIC (0x01)},
627 * {@linkplain #PRIVATE PRIVATE (0x02)},
628 * {@linkplain #PROTECTED PROTECTED (0x04)},
629 * {@linkplain #PACKAGE PACKAGE (0x08)},
630 * and {@linkplain #MODULE MODULE (0x10)}.
631 * <p>
632 * A freshly-created lookup object
633 * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class}
634 * has all possible bits set, since the caller class can access all its own members,
635 * all public types in the caller's module, and all public types in packages exported
636 * by other modules to the caller's module.
637 * A lookup object on a new lookup class
638 * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object}
639 * may have some mode bits set to zero.
640 * The purpose of this is to restrict access via the new lookup object,
641 * so that it can access only names which can be reached by the original
642 * lookup object, and also by the new lookup class.
643 * @return the lookup modes, which limit the kinds of access performed by this lookup object
644 */
645 public int lookupModes() {
646 return allowedModes & ALL_MODES;
647 }
648
649 /** Embody the current class (the lookupClass) as a lookup class
650 * for method handle creation.
651 * Must be called by from a method in this package,
652 * which in turn is called by a method not in this package.
653 */
654 Lookup(Class<?> lookupClass) {
655 this(lookupClass, ALL_MODES);
656 // make sure we haven't accidentally picked up a privileged class:
657 checkUnprivilegedlookupClass(lookupClass, ALL_MODES);
658 }
659
660 private Lookup(Class<?> lookupClass, int allowedModes) {
661 this.lookupClass = lookupClass;
662 this.allowedModes = allowedModes;
663 }
664
665 /**
666 * Creates a lookup on the specified new lookup class.
667 * The resulting object will report the specified
668 * class as its own {@link #lookupClass lookupClass}.
669 * <p>
670 * However, the resulting {@code Lookup} object is guaranteed
671 * to have no more access capabilities than the original.
672 * In particular, access capabilities can be lost as follows:<ul>
673 * <li>If the lookup class for this {@code Lookup} is not in a named module,
674 * and the new lookup class is in a named module {@code M}, then no members in
675 * {@code M}'s non-exported packages will be accessible.
676 * <li>If the lookup for this {@code Lookup} is in a named module, and the
677 * new lookup class is in a different module {@code M}, then no members, not even
678 * public members in {@code M}'s exported packages, will be accessible.
679 * <li>If the new lookup class differs from the old one,
680 * protected members will not be accessible by virtue of inheritance.
681 * (Protected members may continue to be accessible because of package sharing.)
682 * <li>If the new lookup class is in a different package
683 * than the old one, protected and default (package) members will not be accessible.
684 * <li>If the new lookup class is not within the same package member
685 * as the old one, private members will not be accessible.
686 * <li>If the new lookup class is not accessible to the old lookup class,
687 * then no members, not even public members, will be accessible.
688 * (In all other cases, public members will continue to be accessible.)
689 * </ul>
690 * <p>
691 * The resulting lookup's capabilities for loading classes
692 * (used during {@link #findClass} invocations)
693 * are determined by the lookup class' loader,
694 * which may change due to this operation.
695 *
696 * @param requestedLookupClass the desired lookup class for the new lookup object
697 * @return a lookup object which reports the desired lookup class
698 * @throws NullPointerException if the argument is null
699 */
700 public Lookup in(Class<?> requestedLookupClass) {
701 Objects.requireNonNull(requestedLookupClass);
702 if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all
703 return new Lookup(requestedLookupClass, ALL_MODES);
704 if (requestedLookupClass == this.lookupClass)
705 return this; // keep same capabilities
706
707 int newModes = (allowedModes & (ALL_MODES & ~PROTECTED));
708 if (!VerifyAccess.isSameModule(this.lookupClass, requestedLookupClass)) {
709 // Allowed to teleport from an unnamed to a named module but resulting
710 // Lookup has no access to module private members
711 if (this.lookupClass.getModule().isNamed()) {
712 newModes = 0;
713 } else {
714 newModes &= ~MODULE;
715 }
716 }
717 if ((newModes & PACKAGE) != 0
718 && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {
719 newModes &= ~(PACKAGE|PRIVATE);
720 }
721 // Allow nestmate lookups to be created without special privilege:
722 if ((newModes & PRIVATE) != 0
723 && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {
724 newModes &= ~PRIVATE;
725 }
726 if ((newModes & PUBLIC) != 0
727 && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, allowedModes)) {
728 // The requested class it not accessible from the lookup class.
729 // No permissions.
730 newModes = 0;
731 }
732
733 checkUnprivilegedlookupClass(requestedLookupClass, newModes);
734 return new Lookup(requestedLookupClass, newModes);
735 }
736
737 // Make sure outer class is initialized first.
738 static { IMPL_NAMES.getClass(); }
739
740 /** Package-private version of lookup which is trusted. */
741 static final Lookup IMPL_LOOKUP = new Lookup(Object.class, TRUSTED);
742
743 private static void checkUnprivilegedlookupClass(Class<?> lookupClass, int allowedModes) {
744 String name = lookupClass.getName();
745 if (name.startsWith("java.lang.invoke."))
746 throw newIllegalArgumentException("illegal lookupClass: "+lookupClass);
747
748 // For caller-sensitive MethodHandles.lookup() disallow lookup from
749 // restricted packages. This a fragile and blunt approach.
750 // TODO replace with a more formal and less fragile mechanism
751 // that does not bluntly restrict classes under packages within
752 // java.base from looking up MethodHandles or VarHandles.
753 if (allowedModes == ALL_MODES && lookupClass.getClassLoader() == null) {
754 if ((name.startsWith("java.") && !name.startsWith("java.util.concurrent.")) ||
755 (name.startsWith("sun.") && !name.startsWith("sun.invoke."))) {
756 throw newIllegalArgumentException("illegal lookupClass: " + lookupClass);
757 }
758 }
759 }
760
761 /**
762 * Displays the name of the class from which lookups are to be made.
763 * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)
764 * If there are restrictions on the access permitted to this lookup,
765 * this is indicated by adding a suffix to the class name, consisting
766 * of a slash and a keyword. The keyword represents the strongest
767 * allowed access, and is chosen as follows:
768 * <ul>
769 * <li>If no access is allowed, the suffix is "/noaccess".
770 * <li>If only public access to types in exported packages is allowed, the suffix is "/public".
771 * <li>If only public and module access are allowed, the suffix is "/module".
772 * <li>If only public, module and package access are allowed, the suffix is "/package".
773 * <li>If only public, module, package, and private access are allowed, the suffix is "/private".
774 * </ul>
775 * If none of the above cases apply, it is the case that full
776 * access (public, module, package, private, and protected) is allowed.
777 * In this case, no suffix is added.
778 * This is true only of an object obtained originally from
779 * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
780 * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
781 * always have restricted access, and will display a suffix.
782 * <p>
783 * (It may seem strange that protected access should be
784 * stronger than private access. Viewed independently from
785 * package access, protected access is the first to be lost,
786 * because it requires a direct subclass relationship between
787 * caller and callee.)
788 * @see #in
789 */
790 @Override
791 public String toString() {
792 String cname = lookupClass.getName();
793 switch (allowedModes) {
794 case 0: // no privileges
795 return cname + "/noaccess";
796 case PUBLIC:
797 return cname + "/public";
798 case PUBLIC|MODULE:
799 return cname + "/module";
800 case PUBLIC|MODULE|PACKAGE:
801 return cname + "/package";
802 case ALL_MODES & ~PROTECTED:
803 return cname + "/private";
804 case ALL_MODES:
805 return cname;
806 case TRUSTED:
807 return "/trusted"; // internal only; not exported
808 default: // Should not happen, but it's a bitfield...
809 cname = cname + "/" + Integer.toHexString(allowedModes);
810 assert(false) : cname;
811 return cname;
812 }
813 }
814
815 /**
816 * Produces a method handle for a static method.
817 * The type of the method handle will be that of the method.
818 * (Since static methods do not take receivers, there is no
819 * additional receiver argument inserted into the method handle type,
820 * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)
821 * The method and all its argument types must be accessible to the lookup object.
822 * <p>
823 * The returned method handle will have
824 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
825 * the method's variable arity modifier bit ({@code 0x0080}) is set.
826 * <p>
827 * If the returned method handle is invoked, the method's class will
828 * be initialized, if it has not already been initialized.
829 * <p><b>Example:</b>
830 * <blockquote><pre>{@code
831 import static java.lang.invoke.MethodHandles.*;
832 import static java.lang.invoke.MethodType.*;
833 ...
834 MethodHandle MH_asList = publicLookup().findStatic(Arrays.class,
835 "asList", methodType(List.class, Object[].class));
836 assertEquals("[x, y]", MH_asList.invoke("x", "y").toString());
837 * }</pre></blockquote>
838 * @param refc the class from which the method is accessed
839 * @param name the name of the method
840 * @param type the type of the method
841 * @return the desired method handle
842 * @throws NoSuchMethodException if the method does not exist
843 * @throws IllegalAccessException if access checking fails,
844 * or if the method is not {@code static},
845 * or if the method's variable arity modifier bit
846 * is set and {@code asVarargsCollector} fails
847 * @exception SecurityException if a security manager is present and it
848 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
849 * @throws NullPointerException if any argument is null
850 */
851 public
852 MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
853 MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type);
854 return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerClass(method));
855 }
856
857 /**
858 * Produces a method handle for a virtual method.
859 * The type of the method handle will be that of the method,
860 * with the receiver type (usually {@code refc}) prepended.
861 * The method and all its argument types must be accessible to the lookup object.
862 * <p>
863 * When called, the handle will treat the first argument as a receiver
864 * and dispatch on the receiver's type to determine which method
865 * implementation to enter.
866 * (The dispatching action is identical with that performed by an
867 * {@code invokevirtual} or {@code invokeinterface} instruction.)
868 * <p>
869 * The first argument will be of type {@code refc} if the lookup
870 * class has full privileges to access the member. Otherwise
871 * the member must be {@code protected} and the first argument
872 * will be restricted in type to the lookup class.
873 * <p>
874 * The returned method handle will have
875 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
876 * the method's variable arity modifier bit ({@code 0x0080}) is set.
877 * <p>
878 * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual}
879 * instructions and method handles produced by {@code findVirtual},
880 * if the class is {@code MethodHandle} and the name string is
881 * {@code invokeExact} or {@code invoke}, the resulting
882 * method handle is equivalent to one produced by
883 * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or
884 * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}
885 * with the same {@code type} argument.
886 * <p>
887 * If the class is {@code VarHandle} and the name string corresponds to
888 * the name of a signature-polymorphic access mode method, the resulting
889 * method handle is equivalent to one produced by
890 * {@link java.lang.invoke.MethodHandles#varHandleInvoker} with
891 * the access mode corresponding to the name string and with the same
892 * {@code type} arguments.
893 * <p>
894 * <b>Example:</b>
895 * <blockquote><pre>{@code
896 import static java.lang.invoke.MethodHandles.*;
897 import static java.lang.invoke.MethodType.*;
898 ...
899 MethodHandle MH_concat = publicLookup().findVirtual(String.class,
900 "concat", methodType(String.class, String.class));
901 MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class,
902 "hashCode", methodType(int.class));
903 MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class,
904 "hashCode", methodType(int.class));
905 assertEquals("xy", (String) MH_concat.invokeExact("x", "y"));
906 assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy"));
907 assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy"));
908 // interface method:
909 MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class,
910 "subSequence", methodType(CharSequence.class, int.class, int.class));
911 assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString());
912 // constructor "internal method" must be accessed differently:
913 MethodType MT_newString = methodType(void.class); //()V for new String()
914 try { assertEquals("impossible", lookup()
915 .findVirtual(String.class, "<init>", MT_newString));
916 } catch (NoSuchMethodException ex) { } // OK
917 MethodHandle MH_newString = publicLookup()
918 .findConstructor(String.class, MT_newString);
919 assertEquals("", (String) MH_newString.invokeExact());
920 * }</pre></blockquote>
921 *
922 * @param refc the class or interface from which the method is accessed
923 * @param name the name of the method
924 * @param type the type of the method, with the receiver argument omitted
925 * @return the desired method handle
926 * @throws NoSuchMethodException if the method does not exist
927 * @throws IllegalAccessException if access checking fails,
928 * or if the method is {@code static},
929 * or if the method is {@code private} method of interface,
930 * or if the method's variable arity modifier bit
931 * is set and {@code asVarargsCollector} fails
932 * @exception SecurityException if a security manager is present and it
933 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
934 * @throws NullPointerException if any argument is null
935 */
936 public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
937 if (refc == MethodHandle.class) {
938 MethodHandle mh = findVirtualForMH(name, type);
939 if (mh != null) return mh;
940 } else if (refc == VarHandle.class) {
941 MethodHandle mh = findVirtualForVH(name, type);
942 if (mh != null) return mh;
943 }
944 byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual);
945 MemberName method = resolveOrFail(refKind, refc, name, type);
946 return getDirectMethod(refKind, refc, method, findBoundCallerClass(method));
947 }
948 private MethodHandle findVirtualForMH(String name, MethodType type) {
949 // these names require special lookups because of the implicit MethodType argument
950 if ("invoke".equals(name))
951 return invoker(type);
952 if ("invokeExact".equals(name))
953 return exactInvoker(type);
954 if ("invokeBasic".equals(name))
955 return basicInvoker(type);
956 assert(!MemberName.isMethodHandleInvokeName(name));
957 return null;
958 }
959 private MethodHandle findVirtualForVH(String name, MethodType type) {
960 try {
961 return varHandleInvoker(VarHandle.AccessMode.valueFromMethodName(name), type);
962 } catch (IllegalArgumentException e) {
963 return null;
964 }
965 }
966
967 /**
968 * Produces a method handle which creates an object and initializes it, using
969 * the constructor of the specified type.
970 * The parameter types of the method handle will be those of the constructor,
971 * while the return type will be a reference to the constructor's class.
972 * The constructor and all its argument types must be accessible to the lookup object.
973 * <p>
974 * The requested type must have a return type of {@code void}.
975 * (This is consistent with the JVM's treatment of constructor type descriptors.)
976 * <p>
977 * The returned method handle will have
978 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
979 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
980 * <p>
981 * If the returned method handle is invoked, the constructor's class will
982 * be initialized, if it has not already been initialized.
983 * <p><b>Example:</b>
984 * <blockquote><pre>{@code
985 import static java.lang.invoke.MethodHandles.*;
986 import static java.lang.invoke.MethodType.*;
987 ...
988 MethodHandle MH_newArrayList = publicLookup().findConstructor(
989 ArrayList.class, methodType(void.class, Collection.class));
990 Collection orig = Arrays.asList("x", "y");
991 Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig);
992 assert(orig != copy);
993 assertEquals(orig, copy);
994 // a variable-arity constructor:
995 MethodHandle MH_newProcessBuilder = publicLookup().findConstructor(
996 ProcessBuilder.class, methodType(void.class, String[].class));
997 ProcessBuilder pb = (ProcessBuilder)
998 MH_newProcessBuilder.invoke("x", "y", "z");
999 assertEquals("[x, y, z]", pb.command().toString());
1000 * }</pre></blockquote>
1001 * @param refc the class or interface from which the method is accessed
1002 * @param type the type of the method, with the receiver argument omitted, and a void return type
1003 * @return the desired method handle
1004 * @throws NoSuchMethodException if the constructor does not exist
1005 * @throws IllegalAccessException if access checking fails
1006 * or if the method's variable arity modifier bit
1007 * is set and {@code asVarargsCollector} fails
1008 * @exception SecurityException if a security manager is present and it
1009 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1010 * @throws NullPointerException if any argument is null
1011 */
1012 public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1013 String name = "<init>";
1014 MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type);
1015 return getDirectConstructor(refc, ctor);
1016 }
1017
1018 /**
1019 * Looks up a class by name from the lookup context defined by this {@code Lookup} object. The static
1020 * initializer of the class is not run.
1021 * <p>
1022 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class}, its class
1023 * loader, and the {@linkplain #lookupModes() lookup modes}. In particular, the method first attempts to
1024 * load the requested class, and then determines whether the class is accessible to this lookup object.
1025 *
1026 * @param targetName the fully qualified name of the class to be looked up.
1027 * @return the requested class.
1028 * @exception SecurityException if a security manager is present and it
1029 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1030 * @throws LinkageError if the linkage fails
1031 * @throws ClassNotFoundException if the class cannot be loaded by the lookup class' loader.
1032 * @throws IllegalAccessException if the class is not accessible, using the allowed access
1033 * modes.
1034 * @exception SecurityException if a security manager is present and it
1035 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1036 * @since 9
1037 */
1038 public Class<?> findClass(String targetName) throws ClassNotFoundException, IllegalAccessException {
1039 Class<?> targetClass = Class.forName(targetName, false, lookupClass.getClassLoader());
1040 return accessClass(targetClass);
1041 }
1042
1043 /**
1044 * Determines if a class can be accessed from the lookup context defined by this {@code Lookup} object. The
1045 * static initializer of the class is not run.
1046 * <p>
1047 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class} and the
1048 * {@linkplain #lookupModes() lookup modes}.
1049 *
1050 * @param targetClass the class to be access-checked
1051 *
1052 * @return the class that has been access-checked
1053 *
1054 * @throws IllegalAccessException if the class is not accessible from the lookup class, using the allowed access
1055 * modes.
1056 * @exception SecurityException if a security manager is present and it
1057 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1058 * @since 9
1059 */
1060 public Class<?> accessClass(Class<?> targetClass) throws IllegalAccessException {
1061 if (!VerifyAccess.isClassAccessible(targetClass, lookupClass, allowedModes)) {
1062 throw new MemberName(targetClass).makeAccessException("access violation", this);
1063 }
1064 checkSecurityManager(targetClass, null);
1065 return targetClass;
1066 }
1067
1068 /**
1069 * Produces an early-bound method handle for a virtual method.
1070 * It will bypass checks for overriding methods on the receiver,
1071 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
1072 * instruction from within the explicitly specified {@code specialCaller}.
1073 * The type of the method handle will be that of the method,
1074 * with a suitably restricted receiver type prepended.
1075 * (The receiver type will be {@code specialCaller} or a subtype.)
1076 * The method and all its argument types must be accessible
1077 * to the lookup object.
1078 * <p>
1079 * Before method resolution,
1080 * if the explicitly specified caller class is not identical with the
1081 * lookup class, or if this lookup object does not have
1082 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
1083 * privileges, the access fails.
1084 * <p>
1085 * The returned method handle will have
1086 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1087 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1088 * <p style="font-size:smaller;">
1089 * <em>(Note: JVM internal methods named {@code "<init>"} are not visible to this API,
1090 * even though the {@code invokespecial} instruction can refer to them
1091 * in special circumstances. Use {@link #findConstructor findConstructor}
1092 * to access instance initialization methods in a safe manner.)</em>
1093 * <p><b>Example:</b>
1094 * <blockquote><pre>{@code
1095 import static java.lang.invoke.MethodHandles.*;
1096 import static java.lang.invoke.MethodType.*;
1097 ...
1098 static class Listie extends ArrayList {
1099 public String toString() { return "[wee Listie]"; }
1100 static Lookup lookup() { return MethodHandles.lookup(); }
1101 }
1102 ...
1103 // no access to constructor via invokeSpecial:
1104 MethodHandle MH_newListie = Listie.lookup()
1105 .findConstructor(Listie.class, methodType(void.class));
1106 Listie l = (Listie) MH_newListie.invokeExact();
1107 try { assertEquals("impossible", Listie.lookup().findSpecial(
1108 Listie.class, "<init>", methodType(void.class), Listie.class));
1109 } catch (NoSuchMethodException ex) { } // OK
1110 // access to super and self methods via invokeSpecial:
1111 MethodHandle MH_super = Listie.lookup().findSpecial(
1112 ArrayList.class, "toString" , methodType(String.class), Listie.class);
1113 MethodHandle MH_this = Listie.lookup().findSpecial(
1114 Listie.class, "toString" , methodType(String.class), Listie.class);
1115 MethodHandle MH_duper = Listie.lookup().findSpecial(
1116 Object.class, "toString" , methodType(String.class), Listie.class);
1117 assertEquals("[]", (String) MH_super.invokeExact(l));
1118 assertEquals(""+l, (String) MH_this.invokeExact(l));
1119 assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method
1120 try { assertEquals("inaccessible", Listie.lookup().findSpecial(
1121 String.class, "toString", methodType(String.class), Listie.class));
1122 } catch (IllegalAccessException ex) { } // OK
1123 Listie subl = new Listie() { public String toString() { return "[subclass]"; } };
1124 assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method
1125 * }</pre></blockquote>
1126 *
1127 * @param refc the class or interface from which the method is accessed
1128 * @param name the name of the method (which must not be "<init>")
1129 * @param type the type of the method, with the receiver argument omitted
1130 * @param specialCaller the proposed calling class to perform the {@code invokespecial}
1131 * @return the desired method handle
1132 * @throws NoSuchMethodException if the method does not exist
1133 * @throws IllegalAccessException if access checking fails,
1134 * or if the method is {@code static},
1135 * or if the method's variable arity modifier bit
1136 * is set and {@code asVarargsCollector} fails
1137 * @exception SecurityException if a security manager is present and it
1138 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1139 * @throws NullPointerException if any argument is null
1140 */
1141 public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,
1142 Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
1143 checkSpecialCaller(specialCaller, refc);
1144 Lookup specialLookup = this.in(specialCaller);
1145 MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type);
1146 return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerClass(method));
1147 }
1148
1149 /**
1150 * Produces a method handle giving read access to a non-static field.
1151 * The type of the method handle will have a return type of the field's
1152 * value type.
1153 * The method handle's single argument will be the instance containing
1154 * the field.
1155 * Access checking is performed immediately on behalf of the lookup class.
1156 * @param refc the class or interface from which the method is accessed
1157 * @param name the field's name
1158 * @param type the field's type
1159 * @return a method handle which can load values from the field
1160 * @throws NoSuchFieldException if the field does not exist
1161 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1162 * @exception SecurityException if a security manager is present and it
1163 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1164 * @throws NullPointerException if any argument is null
1165 * @see #findVarHandle(Class, String, Class)
1166 */
1167 public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1168 MemberName field = resolveOrFail(REF_getField, refc, name, type);
1169 return getDirectField(REF_getField, refc, field);
1170 }
1171
1172 /**
1173 * Produces a method handle giving write access to a non-static field.
1174 * The type of the method handle will have a void return type.
1175 * The method handle will take two arguments, the instance containing
1176 * the field, and the value to be stored.
1177 * The second argument will be of the field's value type.
1178 * Access checking is performed immediately on behalf of the lookup class.
1179 * @param refc the class or interface from which the method is accessed
1180 * @param name the field's name
1181 * @param type the field's type
1182 * @return a method handle which can store values into the field
1183 * @throws NoSuchFieldException if the field does not exist
1184 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1185 * @exception SecurityException if a security manager is present and it
1186 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1187 * @throws NullPointerException if any argument is null
1188 * @see #findVarHandle(Class, String, Class)
1189 */
1190 public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1191 MemberName field = resolveOrFail(REF_putField, refc, name, type);
1192 return getDirectField(REF_putField, refc, field);
1193 }
1194
1195 /**
1196 * Produces a VarHandle giving access to non-static fields of type
1197 * {@code T} declared by a receiver class of type {@code R}, supporting
1198 * shape {@code (R : T)}.
1199 * <p>
1200 * Access checking is performed immediately on behalf of the lookup
1201 * class.
1202 * <p>
1203 * Certain access modes of the returned VarHandle are unsupported under
1204 * the following conditions:
1205 * <ul>
1206 * <li>if the field is declared {@code final}, then the write, atomic
1207 * update, and numeric atomic update access modes are unsupported.
1208 * <li>if the field type is anything other than {@code int},
1209 * {@code long} or a reference type, then atomic update access modes
1210 * are unsupported. (Future major platform releases of the JDK may
1211 * support additional types for certain currently unsupported access
1212 * modes.)
1213 * <li>if the field type is anything other than {@code int} or
1214 * {@code long}, then numeric atomic update access modes are
1215 * unsupported. (Future major platform releases of the JDK may
1216 * support additional numeric types for certain currently
1217 * unsupported access modes.)
1218 * </ul>
1219 * <p>
1220 * If the field is declared {@code volatile} then the returned VarHandle
1221 * will override access to the field (effectively ignore the
1222 * {@code volatile} declaration) in accordance to it's specified
1223 * access modes.
1224 * @param recv the receiver class, of type {@code R}, that declares the
1225 * non-static field
1226 * @param name the field's name
1227 * @param type the field's type, of type {@code T}
1228 * @return a VarHandle giving access to non-static fields.
1229 * @throws NoSuchFieldException if the field does not exist
1230 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1231 * @exception SecurityException if a security manager is present and it
1232 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1233 * @throws NullPointerException if any argument is null
1234 * @since 9
1235 */
1236 public VarHandle findVarHandle(Class<?> recv, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1237 MemberName getField = resolveOrFail(REF_getField, recv, name, type);
1238 MemberName putField = resolveOrFail(REF_putField, recv, name, type);
1239 return getFieldVarHandle(REF_getField, REF_putField, recv, getField, putField);
1240 }
1241
1242 /**
1243 * Produces a method handle giving read access to a static field.
1244 * The type of the method handle will have a return type of the field's
1245 * value type.
1246 * The method handle will take no arguments.
1247 * Access checking is performed immediately on behalf of the lookup class.
1248 * <p>
1249 * If the returned method handle is invoked, the field's class will
1250 * be initialized, if it has not already been initialized.
1251 * @param refc the class or interface from which the method is accessed
1252 * @param name the field's name
1253 * @param type the field's type
1254 * @return a method handle which can load values from the field
1255 * @throws NoSuchFieldException if the field does not exist
1256 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1257 * @exception SecurityException if a security manager is present and it
1258 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1259 * @throws NullPointerException if any argument is null
1260 */
1261 public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1262 MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
1263 return getDirectField(REF_getStatic, refc, field);
1264 }
1265
1266 /**
1267 * Produces a method handle giving write access to a static field.
1268 * The type of the method handle will have a void return type.
1269 * The method handle will take a single
1270 * argument, of the field's value type, the value to be stored.
1271 * Access checking is performed immediately on behalf of the lookup class.
1272 * <p>
1273 * If the returned method handle is invoked, the field's class will
1274 * be initialized, if it has not already been initialized.
1275 * @param refc the class or interface from which the method is accessed
1276 * @param name the field's name
1277 * @param type the field's type
1278 * @return a method handle which can store values into the field
1279 * @throws NoSuchFieldException if the field does not exist
1280 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1281 * @exception SecurityException if a security manager is present and it
1282 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1283 * @throws NullPointerException if any argument is null
1284 */
1285 public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1286 MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
1287 return getDirectField(REF_putStatic, refc, field);
1288 }
1289
1290 /**
1291 * Produces a VarHandle giving access to a static field of type
1292 * {@code T} declared by a given declaring class, supporting shape
1293 * {@code ((empty) : T)}.
1294 * <p>
1295 * Access checking is performed immediately on behalf of the lookup
1296 * class.
1297 * <p>
1298 * If the returned VarHandle is operated on, the declaring class will be
1299 * initialized, if it has not already been initialized.
1300 * <p>
1301 * Certain access modes of the returned VarHandle are unsupported under
1302 * the following conditions:
1303 * <ul>
1304 * <li>if the field is declared {@code final}, then the write, atomic
1305 * update, and numeric atomic update access modes are unsupported.
1306 * <li>if the field type is anything other than {@code int},
1307 * {@code long} or a reference type, then atomic update access modes
1308 * are unsupported. (Future major platform releases of the JDK may
1309 * support additional types for certain currently unsupported access
1310 * modes.)
1311 * <li>if the field type is anything other than {@code int} or
1312 * {@code long}, then numeric atomic update access modes are
1313 * unsupported. (Future major platform releases of the JDK may
1314 * support additional numeric types for certain currently
1315 * unsupported access modes.)
1316 * </ul>
1317 * <p>
1318 * If the field is declared {@code volatile} then the returned VarHandle
1319 * will override access to the field (effectively ignore the
1320 * {@code volatile} declaration) in accordance to it's specified
1321 * access modes.
1322 * @param decl the class that declares the static field
1323 * @param name the field's name
1324 * @param type the field's type, of type {@code T}
1325 * @return a VarHandle giving access to a static field
1326 * @throws NoSuchFieldException if the field does not exist
1327 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1328 * @exception SecurityException if a security manager is present and it
1329 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1330 * @throws NullPointerException if any argument is null
1331 * @since 9
1332 */
1333 public VarHandle findStaticVarHandle(Class<?> decl, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1334 MemberName getField = resolveOrFail(REF_getStatic, decl, name, type);
1335 MemberName putField = resolveOrFail(REF_putStatic, decl, name, type);
1336 return getFieldVarHandle(REF_getStatic, REF_putStatic, decl, getField, putField);
1337 }
1338
1339 /**
1340 * Produces an early-bound method handle for a non-static method.
1341 * The receiver must have a supertype {@code defc} in which a method
1342 * of the given name and type is accessible to the lookup class.
1343 * The method and all its argument types must be accessible to the lookup object.
1344 * The type of the method handle will be that of the method,
1345 * without any insertion of an additional receiver parameter.
1346 * The given receiver will be bound into the method handle,
1347 * so that every call to the method handle will invoke the
1348 * requested method on the given receiver.
1349 * <p>
1350 * The returned method handle will have
1351 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1352 * the method's variable arity modifier bit ({@code 0x0080}) is set
1353 * <em>and</em> the trailing array argument is not the only argument.
1354 * (If the trailing array argument is the only argument,
1355 * the given receiver value will be bound to it.)
1356 * <p>
1357 * This is equivalent to the following code:
1358 * <blockquote><pre>{@code
1359 import static java.lang.invoke.MethodHandles.*;
1360 import static java.lang.invoke.MethodType.*;
1361 ...
1362 MethodHandle mh0 = lookup().findVirtual(defc, name, type);
1363 MethodHandle mh1 = mh0.bindTo(receiver);
1364 mh1 = mh1.withVarargs(mh0.isVarargsCollector());
1365 return mh1;
1366 * }</pre></blockquote>
1367 * where {@code defc} is either {@code receiver.getClass()} or a super
1368 * type of that class, in which the requested method is accessible
1369 * to the lookup class.
1370 * (Note that {@code bindTo} does not preserve variable arity.)
1371 * @param receiver the object from which the method is accessed
1372 * @param name the name of the method
1373 * @param type the type of the method, with the receiver argument omitted
1374 * @return the desired method handle
1375 * @throws NoSuchMethodException if the method does not exist
1376 * @throws IllegalAccessException if access checking fails
1377 * or if the method's variable arity modifier bit
1378 * is set and {@code asVarargsCollector} fails
1379 * @exception SecurityException if a security manager is present and it
1380 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1381 * @throws NullPointerException if any argument is null
1382 * @see MethodHandle#bindTo
1383 * @see #findVirtual
1384 */
1385 public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1386 Class<? extends Object> refc = receiver.getClass(); // may get NPE
1387 MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
1388 MethodHandle mh = getDirectMethodNoRestrict(REF_invokeSpecial, refc, method, findBoundCallerClass(method));
1389 return mh.bindArgumentL(0, receiver).setVarargs(method);
1390 }
1391
1392 /**
1393 * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
1394 * to <i>m</i>, if the lookup class has permission.
1395 * If <i>m</i> is non-static, the receiver argument is treated as an initial argument.
1396 * If <i>m</i> is virtual, overriding is respected on every call.
1397 * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped.
1398 * The type of the method handle will be that of the method,
1399 * with the receiver type prepended (but only if it is non-static).
1400 * If the method's {@code accessible} flag is not set,
1401 * access checking is performed immediately on behalf of the lookup class.
1402 * If <i>m</i> is not public, do not share the resulting handle with untrusted parties.
1403 * <p>
1404 * The returned method handle will have
1405 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1406 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1407 * <p>
1408 * If <i>m</i> is static, and
1409 * if the returned method handle is invoked, the method's class will
1410 * be initialized, if it has not already been initialized.
1411 * @param m the reflected method
1412 * @return a method handle which can invoke the reflected method
1413 * @throws IllegalAccessException if access checking fails
1414 * or if the method's variable arity modifier bit
1415 * is set and {@code asVarargsCollector} fails
1416 * @throws NullPointerException if the argument is null
1417 */
1418 public MethodHandle unreflect(Method m) throws IllegalAccessException {
1419 if (m.getDeclaringClass() == MethodHandle.class) {
1420 MethodHandle mh = unreflectForMH(m);
1421 if (mh != null) return mh;
1422 }
1423 if (m.getDeclaringClass() == VarHandle.class) {
1424 MethodHandle mh = unreflectForVH(m);
1425 if (mh != null) return mh;
1426 }
1427 MemberName method = new MemberName(m);
1428 byte refKind = method.getReferenceKind();
1429 if (refKind == REF_invokeSpecial)
1430 refKind = REF_invokeVirtual;
1431 assert(method.isMethod());
1432 Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
1433 return lookup.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method, findBoundCallerClass(method));
1434 }
1435 private MethodHandle unreflectForMH(Method m) {
1436 // these names require special lookups because they throw UnsupportedOperationException
1437 if (MemberName.isMethodHandleInvokeName(m.getName()))
1438 return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m));
1439 return null;
1440 }
1441 private MethodHandle unreflectForVH(Method m) {
1442 // these names require special lookups because they throw UnsupportedOperationException
1443 if (MemberName.isVarHandleMethodInvokeName(m.getName()))
1444 return MethodHandleImpl.fakeVarHandleInvoke(new MemberName(m));
1445 return null;
1446 }
1447
1448 /**
1449 * Produces a method handle for a reflected method.
1450 * It will bypass checks for overriding methods on the receiver,
1451 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
1452 * instruction from within the explicitly specified {@code specialCaller}.
1453 * The type of the method handle will be that of the method,
1454 * with a suitably restricted receiver type prepended.
1455 * (The receiver type will be {@code specialCaller} or a subtype.)
1456 * If the method's {@code accessible} flag is not set,
1457 * access checking is performed immediately on behalf of the lookup class,
1458 * as if {@code invokespecial} instruction were being linked.
1459 * <p>
1460 * Before method resolution,
1461 * if the explicitly specified caller class is not identical with the
1462 * lookup class, or if this lookup object does not have
1463 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
1464 * privileges, the access fails.
1465 * <p>
1466 * The returned method handle will have
1467 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1468 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1469 * @param m the reflected method
1470 * @param specialCaller the class nominally calling the method
1471 * @return a method handle which can invoke the reflected method
1472 * @throws IllegalAccessException if access checking fails,
1473 * or if the method is {@code static},
1474 * or if the method's variable arity modifier bit
1475 * is set and {@code asVarargsCollector} fails
1476 * @throws NullPointerException if any argument is null
1477 */
1478 public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException {
1479 checkSpecialCaller(specialCaller, null);
1480 Lookup specialLookup = this.in(specialCaller);
1481 MemberName method = new MemberName(m, true);
1482 assert(method.isMethod());
1483 // ignore m.isAccessible: this is a new kind of access
1484 return specialLookup.getDirectMethodNoSecurityManager(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerClass(method));
1485 }
1486
1487 /**
1488 * Produces a method handle for a reflected constructor.
1489 * The type of the method handle will be that of the constructor,
1490 * with the return type changed to the declaring class.
1491 * The method handle will perform a {@code newInstance} operation,
1492 * creating a new instance of the constructor's class on the
1493 * arguments passed to the method handle.
1494 * <p>
1495 * If the constructor's {@code accessible} flag is not set,
1496 * access checking is performed immediately on behalf of the lookup class.
1497 * <p>
1498 * The returned method handle will have
1499 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1500 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
1501 * <p>
1502 * If the returned method handle is invoked, the constructor's class will
1503 * be initialized, if it has not already been initialized.
1504 * @param c the reflected constructor
1505 * @return a method handle which can invoke the reflected constructor
1506 * @throws IllegalAccessException if access checking fails
1507 * or if the method's variable arity modifier bit
1508 * is set and {@code asVarargsCollector} fails
1509 * @throws NullPointerException if the argument is null
1510 */
1511 public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException {
1512 MemberName ctor = new MemberName(c);
1513 assert(ctor.isConstructor());
1514 Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
1515 return lookup.getDirectConstructorNoSecurityManager(ctor.getDeclaringClass(), ctor);
1516 }
1517
1518 /**
1519 * Produces a method handle giving read access to a reflected field.
1520 * The type of the method handle will have a return type of the field's
1521 * value type.
1522 * If the field is static, the method handle will take no arguments.
1523 * Otherwise, its single argument will be the instance containing
1524 * the field.
1525 * If the field's {@code accessible} flag is not set,
1526 * access checking is performed immediately on behalf of the lookup class.
1527 * <p>
1528 * If the field is static, and
1529 * if the returned method handle is invoked, the field's class will
1530 * be initialized, if it has not already been initialized.
1531 * @param f the reflected field
1532 * @return a method handle which can load values from the reflected field
1533 * @throws IllegalAccessException if access checking fails
1534 * @throws NullPointerException if the argument is null
1535 */
1536 public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
1537 return unreflectField(f, false);
1538 }
1539 private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
1540 MemberName field = new MemberName(f, isSetter);
1541 assert(isSetter
1542 ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
1543 : MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
1544 Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
1545 return lookup.getDirectFieldNoSecurityManager(field.getReferenceKind(), f.getDeclaringClass(), field);
1546 }
1547
1548 /**
1549 * Produces a method handle giving write access to a reflected field.
1550 * The type of the method handle will have a void return type.
1551 * If the field is static, the method handle will take a single
1552 * argument, of the field's value type, the value to be stored.
1553 * Otherwise, the two arguments will be the instance containing
1554 * the field, and the value to be stored.
1555 * If the field's {@code accessible} flag is not set,
1556 * access checking is performed immediately on behalf of the lookup class.
1557 * <p>
1558 * If the field is static, and
1559 * if the returned method handle is invoked, the field's class will
1560 * be initialized, if it has not already been initialized.
1561 * @param f the reflected field
1562 * @return a method handle which can store values into the reflected field
1563 * @throws IllegalAccessException if access checking fails
1564 * @throws NullPointerException if the argument is null
1565 */
1566 public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
1567 return unreflectField(f, true);
1568 }
1569
1570 /**
1571 * Produces a VarHandle that accesses fields of type {@code T} declared
1572 * by a class of type {@code R}, as described by the given reflected
1573 * field.
1574 * If the field is non-static the VarHandle supports a shape of
1575 * {@code (R : T)}, otherwise supports a shape of {@code ((empty) : T)}.
1576 * <p>
1577 * Access checking is performed immediately on behalf of the lookup
1578 * class, regardless of the value of the field's {@code accessible}
1579 * flag.
1580 * <p>
1581 * If the field is static, and if the returned VarHandle is operated
1582 * on, the field's declaring class will be initialized, if it has not
1583 * already been initialized.
1584 * <p>
1585 * Certain access modes of the returned VarHandle are unsupported under
1586 * the following conditions:
1587 * <ul>
1588 * <li>if the field is declared {@code final}, then the write, atomic
1589 * update, and numeric atomic update access modes are unsupported.
1590 * <li>if the field type is anything other than {@code int},
1591 * {@code long} or a reference type, then atomic update access modes
1592 * are unsupported. (Future major platform releases of the JDK may
1593 * support additional types for certain currently unsupported access
1594 * modes.)
1595 * <li>if the field type is anything other than {@code int} or
1596 * {@code long}, then numeric atomic update access modes are
1597 * unsupported. (Future major platform releases of the JDK may
1598 * support additional numeric types for certain currently
1599 * unsupported access modes.)
1600 * </ul>
1601 * <p>
1602 * If the field is declared {@code volatile} then the returned VarHandle
1603 * will override access to the field (effectively ignore the
1604 * {@code volatile} declaration) in accordance to it's specified
1605 * access modes.
1606 * @param f the reflected field, with a field of type {@code T}, and
1607 * a declaring class of type {@code R}
1608 * @return a VarHandle giving access to non-static fields or a static
1609 * field
1610 * @throws IllegalAccessException if access checking fails
1611 * @throws NullPointerException if the argument is null
1612 * @since 9
1613 */
1614 public VarHandle unreflectVarHandle(Field f) throws IllegalAccessException {
1615 MemberName getField = new MemberName(f, false);
1616 MemberName putField = new MemberName(f, true);
1617 return getFieldVarHandleNoSecurityManager(getField.getReferenceKind(), putField.getReferenceKind(),
1618 f.getDeclaringClass(), getField, putField);
1619 }
1620
1621 /**
1622 * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
1623 * created by this lookup object or a similar one.
1624 * Security and access checks are performed to ensure that this lookup object
1625 * is capable of reproducing the target method handle.
1626 * This means that the cracking may fail if target is a direct method handle
1627 * but was created by an unrelated lookup object.
1628 * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a>
1629 * and was created by a lookup object for a different class.
1630 * @param target a direct method handle to crack into symbolic reference components
1631 * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object
1632 * @exception SecurityException if a security manager is present and it
1633 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1634 * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails
1635 * @exception NullPointerException if the target is {@code null}
1636 * @see MethodHandleInfo
1637 * @since 1.8
1638 */
1639 public MethodHandleInfo revealDirect(MethodHandle target) {
1640 MemberName member = target.internalMemberName();
1641 if (member == null || (!member.isResolved() &&
1642 !member.isMethodHandleInvoke() &&
1643 !member.isVarHandleMethodInvoke()))
1644 throw newIllegalArgumentException("not a direct method handle");
1645 Class<?> defc = member.getDeclaringClass();
1646 byte refKind = member.getReferenceKind();
1647 assert(MethodHandleNatives.refKindIsValid(refKind));
1648 if (refKind == REF_invokeSpecial && !target.isInvokeSpecial())
1649 // Devirtualized method invocation is usually formally virtual.
1650 // To avoid creating extra MemberName objects for this common case,
1651 // we encode this extra degree of freedom using MH.isInvokeSpecial.
1652 refKind = REF_invokeVirtual;
1653 if (refKind == REF_invokeVirtual && defc.isInterface())
1654 // Symbolic reference is through interface but resolves to Object method (toString, etc.)
1655 refKind = REF_invokeInterface;
1656 // Check SM permissions and member access before cracking.
1657 try {
1658 checkAccess(refKind, defc, member);
1659 checkSecurityManager(defc, member);
1660 } catch (IllegalAccessException ex) {
1661 throw new IllegalArgumentException(ex);
1662 }
1663 if (allowedModes != TRUSTED && member.isCallerSensitive()) {
1664 Class<?> callerClass = target.internalCallerClass();
1665 if (!hasPrivateAccess() || callerClass != lookupClass())
1666 throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass);
1667 }
1668 // Produce the handle to the results.
1669 return new InfoFromMemberName(this, member, refKind);
1670 }
1671
1672 /// Helper methods, all package-private.
1673
1674 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1675 checkSymbolicClass(refc); // do this before attempting to resolve
1676 Objects.requireNonNull(name);
1677 Objects.requireNonNull(type);
1678 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
1679 NoSuchFieldException.class);
1680 }
1681
1682 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1683 checkSymbolicClass(refc); // do this before attempting to resolve
1684 Objects.requireNonNull(name);
1685 Objects.requireNonNull(type);
1686 checkMethodName(refKind, name); // NPE check on name
1687 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
1688 NoSuchMethodException.class);
1689 }
1690
1691 MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException {
1692 checkSymbolicClass(member.getDeclaringClass()); // do this before attempting to resolve
1693 Objects.requireNonNull(member.getName());
1694 Objects.requireNonNull(member.getType());
1695 return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(),
1696 ReflectiveOperationException.class);
1697 }
1698
1699 void checkSymbolicClass(Class<?> refc) throws IllegalAccessException {
1700 Objects.requireNonNull(refc);
1701 Class<?> caller = lookupClassOrNull();
1702 if (caller != null && !VerifyAccess.isClassAccessible(refc, caller, allowedModes))
1703 throw new MemberName(refc).makeAccessException("symbolic reference class is not accessible", this);
1704 }
1705
1706 /** Check name for an illegal leading "<" character. */
1707 void checkMethodName(byte refKind, String name) throws NoSuchMethodException {
1708 if (name.startsWith("<") && refKind != REF_newInvokeSpecial)
1709 throw new NoSuchMethodException("illegal method name: "+name);
1710 }
1711
1712
1713 /**
1714 * Find my trustable caller class if m is a caller sensitive method.
1715 * If this lookup object has private access, then the caller class is the lookupClass.
1716 * Otherwise, if m is caller-sensitive, throw IllegalAccessException.
1717 */
1718 Class<?> findBoundCallerClass(MemberName m) throws IllegalAccessException {
1719 Class<?> callerClass = null;
1720 if (MethodHandleNatives.isCallerSensitive(m)) {
1721 // Only lookups with private access are allowed to resolve caller-sensitive methods
1722 if (hasPrivateAccess()) {
1723 callerClass = lookupClass;
1724 } else {
1725 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
1726 }
1727 }
1728 return callerClass;
1729 }
1730
1731 private boolean hasPrivateAccess() {
1732 return (allowedModes & PRIVATE) != 0;
1733 }
1734
1735 /**
1736 * Perform necessary <a href="MethodHandles.Lookup.html#secmgr">access checks</a>.
1737 * Determines a trustable caller class to compare with refc, the symbolic reference class.
1738 * If this lookup object has private access, then the caller class is the lookupClass.
1739 */
1740 void checkSecurityManager(Class<?> refc, MemberName m) {
1741 SecurityManager smgr = System.getSecurityManager();
1742 if (smgr == null) return;
1743 if (allowedModes == TRUSTED) return;
1744
1745 // Step 1:
1746 boolean fullPowerLookup = hasPrivateAccess();
1747 if (!fullPowerLookup ||
1748 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
1749 ReflectUtil.checkPackageAccess(refc);
1750 }
1751
1752 if (m == null) { // findClass or accessClass
1753 // Step 2b:
1754 if (!fullPowerLookup) {
1755 smgr.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
1756 }
1757 return;
1758 }
1759
1760 // Step 2a:
1761 if (m.isPublic()) return;
1762 if (!fullPowerLookup) {
1763 smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION);
1764 }
1765
1766 // Step 3:
1767 Class<?> defc = m.getDeclaringClass();
1768 if (!fullPowerLookup && defc != refc) {
1769 ReflectUtil.checkPackageAccess(defc);
1770 }
1771 }
1772
1773 void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
1774 boolean wantStatic = (refKind == REF_invokeStatic);
1775 String message;
1776 if (m.isConstructor())
1777 message = "expected a method, not a constructor";
1778 else if (!m.isMethod())
1779 message = "expected a method";
1780 else if (wantStatic != m.isStatic())
1781 message = wantStatic ? "expected a static method" : "expected a non-static method";
1782 else
1783 { checkAccess(refKind, refc, m); return; }
1784 throw m.makeAccessException(message, this);
1785 }
1786
1787 void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
1788 boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
1789 String message;
1790 if (wantStatic != m.isStatic())
1791 message = wantStatic ? "expected a static field" : "expected a non-static field";
1792 else
1793 { checkAccess(refKind, refc, m); return; }
1794 throw m.makeAccessException(message, this);
1795 }
1796
1797 /** Check public/protected/private bits on the symbolic reference class and its member. */
1798 void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
1799 assert(m.referenceKindIsConsistentWith(refKind) &&
1800 MethodHandleNatives.refKindIsValid(refKind) &&
1801 (MethodHandleNatives.refKindIsField(refKind) == m.isField()));
1802 int allowedModes = this.allowedModes;
1803 if (allowedModes == TRUSTED) return;
1804 int mods = m.getModifiers();
1805 if (Modifier.isProtected(mods) &&
1806 refKind == REF_invokeVirtual &&
1807 m.getDeclaringClass() == Object.class &&
1808 m.getName().equals("clone") &&
1809 refc.isArray()) {
1810 // The JVM does this hack also.
1811 // (See ClassVerifier::verify_invoke_instructions
1812 // and LinkResolver::check_method_accessability.)
1813 // Because the JVM does not allow separate methods on array types,
1814 // there is no separate method for int[].clone.
1815 // All arrays simply inherit Object.clone.
1816 // But for access checking logic, we make Object.clone
1817 // (normally protected) appear to be public.
1818 // Later on, when the DirectMethodHandle is created,
1819 // its leading argument will be restricted to the
1820 // requested array type.
1821 // N.B. The return type is not adjusted, because
1822 // that is *not* the bytecode behavior.
1823 mods ^= Modifier.PROTECTED | Modifier.PUBLIC;
1824 }
1825 if (Modifier.isProtected(mods) && refKind == REF_newInvokeSpecial) {
1826 // cannot "new" a protected ctor in a different package
1827 mods ^= Modifier.PROTECTED;
1828 }
1829 if (Modifier.isFinal(mods) &&
1830 MethodHandleNatives.refKindIsSetter(refKind))
1831 throw m.makeAccessException("unexpected set of a final field", this);
1832 int requestedModes = fixmods(mods); // adjust 0 => PACKAGE
1833 if ((requestedModes & allowedModes) != 0) {
1834 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
1835 mods, lookupClass(), allowedModes))
1836 return;
1837 } else {
1838 // Protected members can also be checked as if they were package-private.
1839 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
1840 && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
1841 return;
1842 }
1843 throw m.makeAccessException(accessFailedMessage(refc, m), this);
1844 }
1845
1846 String accessFailedMessage(Class<?> refc, MemberName m) {
1847 Class<?> defc = m.getDeclaringClass();
1848 int mods = m.getModifiers();
1849 // check the class first:
1850 boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
1851 (defc == refc ||
1852 Modifier.isPublic(refc.getModifiers())));
1853 if (!classOK && (allowedModes & PACKAGE) != 0) {
1854 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), ALL_MODES) &&
1855 (defc == refc ||
1856 VerifyAccess.isClassAccessible(refc, lookupClass(), ALL_MODES)));
1857 }
1858 if (!classOK)
1859 return "class is not public";
1860 if (Modifier.isPublic(mods))
1861 return "access to public member failed"; // (how?, module not readable?)
1862 if (Modifier.isPrivate(mods))
1863 return "member is private";
1864 if (Modifier.isProtected(mods))
1865 return "member is protected";
1866 return "member is private to package";
1867 }
1868
1869 private static final boolean ALLOW_NESTMATE_ACCESS = false;
1870
1871 private void checkSpecialCaller(Class<?> specialCaller, Class<?> refc) throws IllegalAccessException {
1872 int allowedModes = this.allowedModes;
1873 if (allowedModes == TRUSTED) return;
1874 if (!hasPrivateAccess()
1875 || (specialCaller != lookupClass()
1876 // ensure non-abstract methods in superinterfaces can be special-invoked
1877 && !(refc != null && refc.isInterface() && refc.isAssignableFrom(specialCaller))
1878 && !(ALLOW_NESTMATE_ACCESS &&
1879 VerifyAccess.isSamePackageMember(specialCaller, lookupClass()))))
1880 throw new MemberName(specialCaller).
1881 makeAccessException("no private access for invokespecial", this);
1882 }
1883
1884 private boolean restrictProtectedReceiver(MemberName method) {
1885 // The accessing class only has the right to use a protected member
1886 // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc.
1887 if (!method.isProtected() || method.isStatic()
1888 || allowedModes == TRUSTED
1889 || method.getDeclaringClass() == lookupClass()
1890 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass())
1891 || (ALLOW_NESTMATE_ACCESS &&
1892 VerifyAccess.isSamePackageMember(method.getDeclaringClass(), lookupClass())))
1893 return false;
1894 return true;
1895 }
1896 private MethodHandle restrictReceiver(MemberName method, DirectMethodHandle mh, Class<?> caller) throws IllegalAccessException {
1897 assert(!method.isStatic());
1898 // receiver type of mh is too wide; narrow to caller
1899 if (!method.getDeclaringClass().isAssignableFrom(caller)) {
1900 throw method.makeAccessException("caller class must be a subclass below the method", caller);
1901 }
1902 MethodType rawType = mh.type();
1903 if (rawType.parameterType(0) == caller) return mh;
1904 MethodType narrowType = rawType.changeParameterType(0, caller);
1905 assert(!mh.isVarargsCollector()); // viewAsType will lose varargs-ness
1906 assert(mh.viewAsTypeChecks(narrowType, true));
1907 return mh.copyWith(narrowType, mh.form);
1908 }
1909
1910 /** Check access and get the requested method. */
1911 private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
1912 final boolean doRestrict = true;
1913 final boolean checkSecurity = true;
1914 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
1915 }
1916 /** Check access and get the requested method, eliding receiver narrowing rules. */
1917 private MethodHandle getDirectMethodNoRestrict(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
1918 final boolean doRestrict = false;
1919 final boolean checkSecurity = true;
1920 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
1921 }
1922 /** Check access and get the requested method, eliding security manager checks. */
1923 private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
1924 final boolean doRestrict = true;
1925 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
1926 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
1927 }
1928 /** Common code for all methods; do not call directly except from immediately above. */
1929 private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method,
1930 boolean checkSecurity,
1931 boolean doRestrict, Class<?> callerClass) throws IllegalAccessException {
1932 checkMethod(refKind, refc, method);
1933 // Optionally check with the security manager; this isn't needed for unreflect* calls.
1934 if (checkSecurity)
1935 checkSecurityManager(refc, method);
1936 assert(!method.isMethodHandleInvoke());
1937
1938 if (refKind == REF_invokeSpecial &&
1939 refc != lookupClass() &&
1940 !refc.isInterface() &&
1941 refc != lookupClass().getSuperclass() &&
1942 refc.isAssignableFrom(lookupClass())) {
1943 assert(!method.getName().equals("<init>")); // not this code path
1944 // Per JVMS 6.5, desc. of invokespecial instruction:
1945 // If the method is in a superclass of the LC,
1946 // and if our original search was above LC.super,
1947 // repeat the search (symbolic lookup) from LC.super
1948 // and continue with the direct superclass of that class,
1949 // and so forth, until a match is found or no further superclasses exist.
1950 // FIXME: MemberName.resolve should handle this instead.
1951 Class<?> refcAsSuper = lookupClass();
1952 MemberName m2;
1953 do {
1954 refcAsSuper = refcAsSuper.getSuperclass();
1955 m2 = new MemberName(refcAsSuper,
1956 method.getName(),
1957 method.getMethodType(),
1958 REF_invokeSpecial);
1959 m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull());
1960 } while (m2 == null && // no method is found yet
1961 refc != refcAsSuper); // search up to refc
1962 if (m2 == null) throw new InternalError(method.toString());
1963 method = m2;
1964 refc = refcAsSuper;
1965 // redo basic checks
1966 checkMethod(refKind, refc, method);
1967 }
1968
1969 DirectMethodHandle dmh = DirectMethodHandle.make(refKind, refc, method);
1970 MethodHandle mh = dmh;
1971 // Optionally narrow the receiver argument to refc using restrictReceiver.
1972 if (doRestrict &&
1973 (refKind == REF_invokeSpecial ||
1974 (MethodHandleNatives.refKindHasReceiver(refKind) &&
1975 restrictProtectedReceiver(method)))) {
1976 mh = restrictReceiver(method, dmh, lookupClass());
1977 }
1978 mh = maybeBindCaller(method, mh, callerClass);
1979 mh = mh.setVarargs(method);
1980 return mh;
1981 }
1982 private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh,
1983 Class<?> callerClass)
1984 throws IllegalAccessException {
1985 if (allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method))
1986 return mh;
1987 Class<?> hostClass = lookupClass;
1988 if (!hasPrivateAccess()) // caller must have private access
1989 hostClass = callerClass; // callerClass came from a security manager style stack walk
1990 MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, hostClass);
1991 // Note: caller will apply varargs after this step happens.
1992 return cbmh;
1993 }
1994 /** Check access and get the requested field. */
1995 private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
1996 final boolean checkSecurity = true;
1997 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
1998 }
1999 /** Check access and get the requested field, eliding security manager checks. */
2000 private MethodHandle getDirectFieldNoSecurityManager(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
2001 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
2002 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
2003 }
2004 /** Common code for all fields; do not call directly except from immediately above. */
2005 private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field,
2006 boolean checkSecurity) throws IllegalAccessException {
2007 checkField(refKind, refc, field);
2008 // Optionally check with the security manager; this isn't needed for unreflect* calls.
2009 if (checkSecurity)
2010 checkSecurityManager(refc, field);
2011 DirectMethodHandle dmh = DirectMethodHandle.make(refc, field);
2012 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) &&
2013 restrictProtectedReceiver(field));
2014 if (doRestrict)
2015 return restrictReceiver(field, dmh, lookupClass());
2016 return dmh;
2017 }
2018 private VarHandle getFieldVarHandle(byte getRefKind, byte putRefKind,
2019 Class<?> refc, MemberName getField, MemberName putField)
2020 throws IllegalAccessException {
2021 final boolean checkSecurity = true;
2022 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
2023 }
2024 private VarHandle getFieldVarHandleNoSecurityManager(byte getRefKind, byte putRefKind,
2025 Class<?> refc, MemberName getField, MemberName putField)
2026 throws IllegalAccessException {
2027 final boolean checkSecurity = false;
2028 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
2029 }
2030 private VarHandle getFieldVarHandleCommon(byte getRefKind, byte putRefKind,
2031 Class<?> refc, MemberName getField, MemberName putField,
2032 boolean checkSecurity) throws IllegalAccessException {
2033 assert getField.isStatic() == putField.isStatic();
2034 assert getField.isGetter() && putField.isSetter();
2035 assert MethodHandleNatives.refKindIsStatic(getRefKind) == MethodHandleNatives.refKindIsStatic(putRefKind);
2036 assert MethodHandleNatives.refKindIsGetter(getRefKind) && MethodHandleNatives.refKindIsSetter(putRefKind);
2037
2038 checkField(getRefKind, refc, getField);
2039 if (checkSecurity)
2040 checkSecurityManager(refc, getField);
2041
2042 if (!putField.isFinal()) {
2043 // A VarHandle does not support updates to final fields, any
2044 // such VarHandle to a final field will be read-only and
2045 // therefore the following write-based accessibility checks are
2046 // only required for non-final fields
2047 checkField(putRefKind, refc, putField);
2048 if (checkSecurity)
2049 checkSecurityManager(refc, putField);
2050 }
2051
2052 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(getRefKind) &&
2053 restrictProtectedReceiver(getField));
2054 if (doRestrict) {
2055 assert !getField.isStatic();
2056 // receiver type of VarHandle is too wide; narrow to caller
2057 if (!getField.getDeclaringClass().isAssignableFrom(lookupClass())) {
2058 throw getField.makeAccessException("caller class must be a subclass below the method", lookupClass());
2059 }
2060 refc = lookupClass();
2061 }
2062 return VarHandles.makeFieldHandle(getField, refc, getField.getFieldType(), this.allowedModes == TRUSTED);
2063 }
2064 /** Check access and get the requested constructor. */
2065 private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException {
2066 final boolean checkSecurity = true;
2067 return getDirectConstructorCommon(refc, ctor, checkSecurity);
2068 }
2069 /** Check access and get the requested constructor, eliding security manager checks. */
2070 private MethodHandle getDirectConstructorNoSecurityManager(Class<?> refc, MemberName ctor) throws IllegalAccessException {
2071 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
2072 return getDirectConstructorCommon(refc, ctor, checkSecurity);
2073 }
2074 /** Common code for all constructors; do not call directly except from immediately above. */
2075 private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor,
2076 boolean checkSecurity) throws IllegalAccessException {
2077 assert(ctor.isConstructor());
2078 checkAccess(REF_newInvokeSpecial, refc, ctor);
2079 // Optionally check with the security manager; this isn't needed for unreflect* calls.
2080 if (checkSecurity)
2081 checkSecurityManager(refc, ctor);
2082 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
2083 return DirectMethodHandle.make(ctor).setVarargs(ctor);
2084 }
2085
2086 /** Hook called from the JVM (via MethodHandleNatives) to link MH constants:
2087 */
2088 /*non-public*/
2089 MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type) throws ReflectiveOperationException {
2090 if (!(type instanceof Class || type instanceof MethodType))
2091 throw new InternalError("unresolved MemberName");
2092 MemberName member = new MemberName(refKind, defc, name, type);
2093 MethodHandle mh = LOOKASIDE_TABLE.get(member);
2094 if (mh != null) {
2095 checkSymbolicClass(defc);
2096 return mh;
2097 }
2098 // Treat MethodHandle.invoke and invokeExact specially.
2099 if (defc == MethodHandle.class && refKind == REF_invokeVirtual) {
2100 mh = findVirtualForMH(member.getName(), member.getMethodType());
2101 if (mh != null) {
2102 return mh;
2103 }
2104 }
2105 MemberName resolved = resolveOrFail(refKind, member);
2106 mh = getDirectMethodForConstant(refKind, defc, resolved);
2107 if (mh instanceof DirectMethodHandle
2108 && canBeCached(refKind, defc, resolved)) {
2109 MemberName key = mh.internalMemberName();
2110 if (key != null) {
2111 key = key.asNormalOriginal();
2112 }
2113 if (member.equals(key)) { // better safe than sorry
2114 LOOKASIDE_TABLE.put(key, (DirectMethodHandle) mh);
2115 }
2116 }
2117 return mh;
2118 }
2119 private
2120 boolean canBeCached(byte refKind, Class<?> defc, MemberName member) {
2121 if (refKind == REF_invokeSpecial) {
2122 return false;
2123 }
2124 if (!Modifier.isPublic(defc.getModifiers()) ||
2125 !Modifier.isPublic(member.getDeclaringClass().getModifiers()) ||
2126 !member.isPublic() ||
2127 member.isCallerSensitive()) {
2128 return false;
2129 }
2130 ClassLoader loader = defc.getClassLoader();
2131 if (!jdk.internal.misc.VM.isSystemDomainLoader(loader)) {
2132 ClassLoader sysl = ClassLoader.getSystemClassLoader();
2133 boolean found = false;
2134 while (sysl != null) {
2135 if (loader == sysl) { found = true; break; }
2136 sysl = sysl.getParent();
2137 }
2138 if (!found) {
2139 return false;
2140 }
2141 }
2142 try {
2143 MemberName resolved2 = publicLookup().resolveOrFail(refKind,
2144 new MemberName(refKind, defc, member.getName(), member.getType()));
2145 checkSecurityManager(defc, resolved2);
2146 } catch (ReflectiveOperationException | SecurityException ex) {
2147 return false;
2148 }
2149 return true;
2150 }
2151 private
2152 MethodHandle getDirectMethodForConstant(byte refKind, Class<?> defc, MemberName member)
2153 throws ReflectiveOperationException {
2154 if (MethodHandleNatives.refKindIsField(refKind)) {
2155 return getDirectFieldNoSecurityManager(refKind, defc, member);
2156 } else if (MethodHandleNatives.refKindIsMethod(refKind)) {
2157 return getDirectMethodNoSecurityManager(refKind, defc, member, lookupClass);
2158 } else if (refKind == REF_newInvokeSpecial) {
2159 return getDirectConstructorNoSecurityManager(defc, member);
2160 }
2161 // oops
2162 throw newIllegalArgumentException("bad MethodHandle constant #"+member);
2163 }
2164
2165 static ConcurrentHashMap<MemberName, DirectMethodHandle> LOOKASIDE_TABLE = new ConcurrentHashMap<>();
2166 }
2167
2168 /**
2169 * Helper class used to lazily create PUBLIC_LOOKUP with a lookup class
2170 * in an <em>unnamed module</em>.
2171 *
2172 * @see Lookup#publicLookup
2173 */
2174 private static class LookupHelper {
2175 private static final String UNNAMED = "Unnamed";
2176 private static final String OBJECT = "java/lang/Object";
2177
2178 private static Class<?> createClass() {
2179 try {
2180 ClassWriter cw = new ClassWriter(0);
2181 cw.visit(Opcodes.V1_8,
2182 Opcodes.ACC_FINAL + Opcodes.ACC_SUPER,
2183 UNNAMED,
2184 null,
2185 OBJECT,
2186 null);
2187 cw.visitSource(UNNAMED, null);
2188 cw.visitEnd();
2189 byte[] bytes = cw.toByteArray();
2190 ClassLoader loader = new ClassLoader(null) {
2191 @Override
2192 protected Class<?> findClass(String cn) throws ClassNotFoundException {
2193 if (cn.equals(UNNAMED))
2194 return super.defineClass(UNNAMED, bytes, 0, bytes.length);
2195 throw new ClassNotFoundException(cn);
2196 }
2197 };
2198 return loader.loadClass(UNNAMED);
2199 } catch (Exception e) {
2200 throw new InternalError(e);
2201 }
2202 }
2203
2204 private static final Class<?> PUBLIC_LOOKUP_CLASS;
2205 static {
2206 PrivilegedAction<Class<?>> pa = new PrivilegedAction<Class<?>>() {
2207 public Class<?> run() {
2208 return createClass();
2209 }
2210 };
2211 PUBLIC_LOOKUP_CLASS = AccessController.doPrivileged(pa);
2212 }
2213
2214 /**
2215 * Lookup that is trusted minimally. It can only be used to create
2216 * method handles to publicly accessible members in exported packages.
2217 *
2218 * @see MethodHandles#publicLookup
2219 */
2220 static final Lookup PUBLIC_LOOKUP = new Lookup(PUBLIC_LOOKUP_CLASS, Lookup.PUBLIC);
2221 }
2222
2223 /**
2224 * Produces a method handle giving read access to elements of an array.
2225 * The type of the method handle will have a return type of the array's
2226 * element type. Its first argument will be the array type,
2227 * and the second will be {@code int}.
2228 * @param arrayClass an array type
2229 * @return a method handle which can load values from the given array type
2230 * @throws NullPointerException if the argument is null
2231 * @throws IllegalArgumentException if arrayClass is not an array type
2232 */
2233 public static
2234 MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException {
2235 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, false);
2236 }
2237
2238 /**
2239 * Produces a method handle giving write access to elements of an array.
2240 * The type of the method handle will have a void return type.
2241 * Its last argument will be the array's element type.
2242 * The first and second arguments will be the array type and int.
2243 * @param arrayClass the class of an array
2244 * @return a method handle which can store values into the array type
2245 * @throws NullPointerException if the argument is null
2246 * @throws IllegalArgumentException if arrayClass is not an array type
2247 */
2248 public static
2249 MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException {
2250 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, true);
2251 }
2252
2253 /**
2254 *
2255 * Produces a VarHandle giving access to elements of an array type
2256 * {@code T[]}, supporting shape {@code (T[], int : T)}.
2257 * <p>
2258 * Certain access modes of the returned VarHandle are unsupported under
2259 * the following conditions:
2260 * <ul>
2261 * <li>if the component type is anything other than {@code int},
2262 * {@code long} or a reference type, then atomic update access modes
2263 * are unsupported. (Future major platform releases of the JDK may
2264 * support additional types for certain currently unsupported access
2265 * modes.)
2266 * <li>if the component type is anything other than {@code int} or
2267 * {@code long}, then numeric atomic update access modes are
2268 * unsupported. (Future major platform releases of the JDK may
2269 * support additional numeric types for certain currently
2270 * unsupported access modes.)
2271 * </ul>
2272 * @param arrayClass the class of an array, of type {@code T[]}
2273 * @return a VarHandle giving access to elements of an array
2274 * @throws NullPointerException if the arrayClass is null
2275 * @throws IllegalArgumentException if arrayClass is not an array type
2276 * @since 9
2277 */
2278 public static
2279 VarHandle arrayElementVarHandle(Class<?> arrayClass) throws IllegalArgumentException {
2280 return VarHandles.makeArrayElementHandle(arrayClass);
2281 }
2282
2283 /**
2284 * Produces a VarHandle giving access to elements of a {@code byte[]} array
2285 * viewed as if it were a different primitive array type, such as
2286 * {@code int[]} or {@code long[]}. The shape of the resulting VarHandle is
2287 * {@code (byte[], int : T)}, where the {@code int} coordinate type
2288 * corresponds to an argument that is an index in a {@code byte[]} array,
2289 * and {@code T} is the component type of the given view array class. The
2290 * returned VarHandle accesses bytes at an index in a {@code byte[]} array,
2291 * composing bytes to or from a value of {@code T} according to the given
2292 * endianness.
2293 * <p>
2294 * The supported component types (variables types) are {@code short},
2295 * {@code char}, {@code int}, {@code long}, {@code float} and
2296 * {@code double}.
2297 * <p>
2298 * Access of bytes at a given index will result in an
2299 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
2300 * or greater than the {@code byte[]} array length minus the size (in bytes)
2301 * of {@code T}.
2302 * <p>
2303 * Access of bytes at an index may be aligned or misaligned for {@code T},
2304 * with respect to the underlying memory address, {@code A} say, associated
2305 * with the array and index.
2306 * If access is misaligned then access for anything other than the
2307 * {@code get} and {@code set} access modes will result in an
2308 * {@code IllegalStateException}. In such cases atomic access is only
2309 * guaranteed with respect to the largest power of two that divides the GCD
2310 * of {@code A} and the size (in bytes) of {@code T}.
2311 * If access is aligned then following access modes are supported and are
2312 * guaranteed to support atomic access:
2313 * <ul>
2314 * <li>read write access modes for all {@code T};
2315 * <li>atomic update access modes for {@code int}, {@code long},
2316 * {@code float} or {@code double}.
2317 * (Future major platform releases of the JDK may support additional
2318 * types for certain currently unsupported access modes.)
2319 * <li>numeric atomic update access modes for {@code int} and {@code long}.
2320 * (Future major platform releases of the JDK may support additional
2321 * numeric types for certain currently unsupported access modes.)
2322 * </ul>
2323 * <p>
2324 * Misaligned access, and therefore atomicity guarantees, may be determined
2325 * for {@code byte[]} arrays without operating on a specific array. Given
2326 * an {@code index}, {@code T} and it's corresponding boxed type,
2327 * {@code T_BOX}, misalignment may be determined as follows:
2328 * <pre>{@code
2329 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
2330 * int misalignedAtZeroIndex = ByteBuffer.wrap(new byte[0]).
2331 * alignmentOffset(0, sizeOfT);
2332 * int misalignedAtIndex = (misalignedAtZeroIndex + index) % sizeOfT;
2333 * boolean isMisaligned = misalignedAtIndex != 0;
2334 * }</pre>
2335 *
2336 * @implNote
2337 * The variable types {@code float} and {@code double} are supported as if
2338 * by transformation to and access with the variable types {@code int} and
2339 * {@code long} respectively. For example, the transformation of a
2340 * {@code double} value to a long value is performed as if using
2341 * {@link Double#doubleToRawLongBits(double)}, and the reverse
2342 * transformation is performed as if using
2343 * {@link Double#longBitsToDouble(long)}.
2344 *
2345 * @param viewArrayClass the view array class, with a component type of
2346 * type {@code T}
2347 * @param byteOrder the endianness of the view array elements, as
2348 * stored in the underlying {@code byte} array
2349 * @return a VarHandle giving access to elements of a {@code byte[]} array
2350 * viewed as if elements corresponding to the components type of the view
2351 * array class
2352 * @throws NullPointerException if viewArrayClass or byteOrder is null
2353 * @throws IllegalArgumentException if viewArrayClass is not an array type
2354 * @throws UnsupportedOperationException if the component type of
2355 * viewArrayClass is not supported as a variable type
2356 * @since 9
2357 */
2358 public static
2359 VarHandle byteArrayViewVarHandle(Class<?> viewArrayClass,
2360 ByteOrder byteOrder) throws IllegalArgumentException {
2361 Objects.requireNonNull(byteOrder);
2362 return VarHandles.byteArrayViewHandle(viewArrayClass,
2363 byteOrder == ByteOrder.BIG_ENDIAN);
2364 }
2365
2366 /**
2367 * Produces a VarHandle giving access to elements of a {@code ByteBuffer}
2368 * viewed as if it were an array of elements of a different primitive
2369 * component type to that of {@code byte}, such as {@code int[]} or
2370 * {@code long[]}. The shape of the resulting VarHandle is
2371 * {@code (ByteBuffer, int : T)}, where the {@code int} coordinate type
2372 * corresponds to an argument that is an index in a {@code ByteBuffer}, and
2373 * {@code T} is the component type of the given view array class. The
2374 * returned VarHandle accesses bytes at an index in a {@code ByteBuffer},
2375 * composing bytes to or from a value of {@code T} according to the given
2376 * endianness.
2377 * <p>
2378 * The supported component types (variables types) are {@code short},
2379 * {@code char}, {@code int}, {@code long}, {@code float} and
2380 * {@code double}.
2381 * <p>
2382 * Access will result in a {@code ReadOnlyBufferException} for anything
2383 * other than the read access modes if the {@code ByteBuffer} is read-only.
2384 * <p>
2385 * Access of bytes at a given index will result in an
2386 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
2387 * or greater than the {@code ByteBuffer} limit minus the size (in bytes) of
2388 * {@code T}.
2389 * <p>
2390 * Access of bytes at an index may be aligned or misaligned for {@code T},
2391 * with respect to the underlying memory address, {@code A} say, associated
2392 * with the {@code ByteBuffer} and index.
2393 * If access is misaligned then access for anything other than the
2394 * {@code get} and {@code set} access modes will result in an
2395 * {@code IllegalStateException}. In such cases atomic access is only
2396 * guaranteed with respect to the largest power of two that divides the GCD
2397 * of {@code A} and the size (in bytes) of {@code T}.
2398 * If access is aligned then following access modes are supported and are
2399 * guaranteed to support atomic access:
2400 * <ul>
2401 * <li>read write access modes for all {@code T};
2402 * <li>atomic update access modes for {@code int}, {@code long},
2403 * {@code float} or {@code double}.
2404 * (Future major platform releases of the JDK may support additional
2405 * types for certain currently unsupported access modes.)
2406 * <li>numeric atomic update access modes for {@code int} and {@code long}.
2407 * (Future major platform releases of the JDK may support additional
2408 * numeric types for certain currently unsupported access modes.)
2409 * </ul>
2410 * <p>
2411 * Misaligned access, and therefore atomicity guarantees, may be determined
2412 * for a {@code ByteBuffer}, {@code bb} (direct or otherwise), an
2413 * {@code index}, {@code T} and it's corresponding boxed type,
2414 * {@code T_BOX}, as follows:
2415 * <pre>{@code
2416 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
2417 * ByteBuffer bb = ...
2418 * int misalignedAtIndex = bb.alignmentOffset(index, sizeOfT);
2419 * boolean isMisaligned = misalignedAtIndex != 0;
2420 * }</pre>
2421 *
2422 * @implNote
2423 * The variable types {@code float} and {@code double} are supported as if
2424 * by transformation to and access with the variable types {@code int} and
2425 * {@code long} respectively. For example, the transformation of a
2426 * {@code double} value to a long value is performed as if using
2427 * {@link Double#doubleToRawLongBits(double)}, and the reverse
2428 * transformation is performed as if using
2429 * {@link Double#longBitsToDouble(long)}.
2430 *
2431 * @param viewArrayClass the view array class, with a component type of
2432 * type {@code T}
2433 * @param byteOrder the endianness of the view array elements, as
2434 * stored in the underlying {@code ByteBuffer} (Note this overrides the
2435 * endianness of a {@code ByteBuffer})
2436 * @return a VarHandle giving access to elements of a {@code ByteBuffer}
2437 * viewed as if elements corresponding to the components type of the view
2438 * array class
2439 * @throws NullPointerException if viewArrayClass or byteOrder is null
2440 * @throws IllegalArgumentException if viewArrayClass is not an array type
2441 * @throws UnsupportedOperationException if the component type of
2442 * viewArrayClass is not supported as a variable type
2443 * @since 9
2444 */
2445 public static
2446 VarHandle byteBufferViewVarHandle(Class<?> viewArrayClass,
2447 ByteOrder byteOrder) throws IllegalArgumentException {
2448 Objects.requireNonNull(byteOrder);
2449 return VarHandles.makeByteBufferViewHandle(viewArrayClass,
2450 byteOrder == ByteOrder.BIG_ENDIAN);
2451 }
2452
2453
2454 /// method handle invocation (reflective style)
2455
2456 /**
2457 * Produces a method handle which will invoke any method handle of the
2458 * given {@code type}, with a given number of trailing arguments replaced by
2459 * a single trailing {@code Object[]} array.
2460 * The resulting invoker will be a method handle with the following
2461 * arguments:
2462 * <ul>
2463 * <li>a single {@code MethodHandle} target
2464 * <li>zero or more leading values (counted by {@code leadingArgCount})
2465 * <li>an {@code Object[]} array containing trailing arguments
2466 * </ul>
2467 * <p>
2468 * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
2469 * the indicated {@code type}.
2470 * That is, if the target is exactly of the given {@code type}, it will behave
2471 * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
2472 * is used to convert the target to the required {@code type}.
2473 * <p>
2474 * The type of the returned invoker will not be the given {@code type}, but rather
2475 * will have all parameters except the first {@code leadingArgCount}
2476 * replaced by a single array of type {@code Object[]}, which will be
2477 * the final parameter.
2478 * <p>
2479 * Before invoking its target, the invoker will spread the final array, apply
2480 * reference casts as necessary, and unbox and widen primitive arguments.
2481 * If, when the invoker is called, the supplied array argument does
2482 * not have the correct number of elements, the invoker will throw
2483 * an {@link IllegalArgumentException} instead of invoking the target.
2484 * <p>
2485 * This method is equivalent to the following code (though it may be more efficient):
2486 * <blockquote><pre>{@code
2487 MethodHandle invoker = MethodHandles.invoker(type);
2488 int spreadArgCount = type.parameterCount() - leadingArgCount;
2489 invoker = invoker.asSpreader(Object[].class, spreadArgCount);
2490 return invoker;
2491 * }</pre></blockquote>
2492 * This method throws no reflective or security exceptions.
2493 * @param type the desired target type
2494 * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
2495 * @return a method handle suitable for invoking any method handle of the given type
2496 * @throws NullPointerException if {@code type} is null
2497 * @throws IllegalArgumentException if {@code leadingArgCount} is not in
2498 * the range from 0 to {@code type.parameterCount()} inclusive,
2499 * or if the resulting method handle's type would have
2500 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2501 */
2502 public static
2503 MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
2504 if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
2505 throw newIllegalArgumentException("bad argument count", leadingArgCount);
2506 type = type.asSpreaderType(Object[].class, leadingArgCount, type.parameterCount() - leadingArgCount);
2507 return type.invokers().spreadInvoker(leadingArgCount);
2508 }
2509
2510 /**
2511 * Produces a special <em>invoker method handle</em> which can be used to
2512 * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
2513 * The resulting invoker will have a type which is
2514 * exactly equal to the desired type, except that it will accept
2515 * an additional leading argument of type {@code MethodHandle}.
2516 * <p>
2517 * This method is equivalent to the following code (though it may be more efficient):
2518 * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)}
2519 *
2520 * <p style="font-size:smaller;">
2521 * <em>Discussion:</em>
2522 * Invoker method handles can be useful when working with variable method handles
2523 * of unknown types.
2524 * For example, to emulate an {@code invokeExact} call to a variable method
2525 * handle {@code M}, extract its type {@code T},
2526 * look up the invoker method {@code X} for {@code T},
2527 * and call the invoker method, as {@code X.invoke(T, A...)}.
2528 * (It would not work to call {@code X.invokeExact}, since the type {@code T}
2529 * is unknown.)
2530 * If spreading, collecting, or other argument transformations are required,
2531 * they can be applied once to the invoker {@code X} and reused on many {@code M}
2532 * method handle values, as long as they are compatible with the type of {@code X}.
2533 * <p style="font-size:smaller;">
2534 * <em>(Note: The invoker method is not available via the Core Reflection API.
2535 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
2536 * on the declared {@code invokeExact} or {@code invoke} method will raise an
2537 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
2538 * <p>
2539 * This method throws no reflective or security exceptions.
2540 * @param type the desired target type
2541 * @return a method handle suitable for invoking any method handle of the given type
2542 * @throws IllegalArgumentException if the resulting method handle's type would have
2543 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2544 */
2545 public static
2546 MethodHandle exactInvoker(MethodType type) {
2547 return type.invokers().exactInvoker();
2548 }
2549
2550 /**
2551 * Produces a special <em>invoker method handle</em> which can be used to
2552 * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
2553 * The resulting invoker will have a type which is
2554 * exactly equal to the desired type, except that it will accept
2555 * an additional leading argument of type {@code MethodHandle}.
2556 * <p>
2557 * Before invoking its target, if the target differs from the expected type,
2558 * the invoker will apply reference casts as
2559 * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
2560 * Similarly, the return value will be converted as necessary.
2561 * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
2562 * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
2563 * <p>
2564 * This method is equivalent to the following code (though it may be more efficient):
2565 * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)}
2566 * <p style="font-size:smaller;">
2567 * <em>Discussion:</em>
2568 * A {@linkplain MethodType#genericMethodType general method type} is one which
2569 * mentions only {@code Object} arguments and return values.
2570 * An invoker for such a type is capable of calling any method handle
2571 * of the same arity as the general type.
2572 * <p style="font-size:smaller;">
2573 * <em>(Note: The invoker method is not available via the Core Reflection API.
2574 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
2575 * on the declared {@code invokeExact} or {@code invoke} method will raise an
2576 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
2577 * <p>
2578 * This method throws no reflective or security exceptions.
2579 * @param type the desired target type
2580 * @return a method handle suitable for invoking any method handle convertible to the given type
2581 * @throws IllegalArgumentException if the resulting method handle's type would have
2582 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2583 */
2584 public static
2585 MethodHandle invoker(MethodType type) {
2586 return type.invokers().genericInvoker();
2587 }
2588
2589 /**
2590 * Produces a special <em>invoker method handle</em> which can be used to
2591 * invoke a signature-polymorphic access mode method on any VarHandle whose
2592 * associated access mode type is compatible with the given type.
2593 * The resulting invoker will have a type which is exactly equal to the
2594 * desired given type, except that it will accept an additional leading
2595 * argument of type {@code VarHandle}.
2596 *
2597 * @param accessMode the VarHandle access mode
2598 * @param type the desired target type
2599 * @return a method handle suitable for invoking an access mode method of
2600 * any VarHandle whose access mode type is of the given type.
2601 * @since 9
2602 */
2603 static public
2604 MethodHandle varHandleExactInvoker(VarHandle.AccessMode accessMode, MethodType type) {
2605 return type.invokers().varHandleMethodExactInvoker(accessMode);
2606 }
2607
2608 /**
2609 * Produces a special <em>invoker method handle</em> which can be used to
2610 * invoke a signature-polymorphic access mode method on any VarHandle whose
2611 * associated access mode type is compatible with the given type.
2612 * The resulting invoker will have a type which is exactly equal to the
2613 * desired given type, except that it will accept an additional leading
2614 * argument of type {@code VarHandle}.
2615 * <p>
2616 * Before invoking its target, if the access mode type differs from the
2617 * desired given type, the invoker will apply reference casts as necessary
2618 * and box, unbox, or widen primitive values, as if by
2619 * {@link MethodHandle#asType asType}. Similarly, the return value will be
2620 * converted as necessary.
2621 * <p>
2622 * This method is equivalent to the following code (though it may be more
2623 * efficient): {@code publicLookup().findVirtual(VarHandle.class, accessMode.name(), type)}
2624 *
2625 * @param accessMode the VarHandle access mode
2626 * @param type the desired target type
2627 * @return a method handle suitable for invoking an access mode method of
2628 * any VarHandle whose access mode type is convertible to the given
2629 * type.
2630 * @since 9
2631 */
2632 static public
2633 MethodHandle varHandleInvoker(VarHandle.AccessMode accessMode, MethodType type) {
2634 return type.invokers().varHandleMethodInvoker(accessMode);
2635 }
2636
2637 static /*non-public*/
2638 MethodHandle basicInvoker(MethodType type) {
2639 return type.invokers().basicInvoker();
2640 }
2641
2642 /// method handle modification (creation from other method handles)
2643
2644 /**
2645 * Produces a method handle which adapts the type of the
2646 * given method handle to a new type by pairwise argument and return type conversion.
2647 * The original type and new type must have the same number of arguments.
2648 * The resulting method handle is guaranteed to report a type
2649 * which is equal to the desired new type.
2650 * <p>
2651 * If the original type and new type are equal, returns target.
2652 * <p>
2653 * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
2654 * and some additional conversions are also applied if those conversions fail.
2655 * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied
2656 * if possible, before or instead of any conversions done by {@code asType}:
2657 * <ul>
2658 * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type,
2659 * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast.
2660 * (This treatment of interfaces follows the usage of the bytecode verifier.)
2661 * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive,
2662 * the boolean is converted to a byte value, 1 for true, 0 for false.
2663 * (This treatment follows the usage of the bytecode verifier.)
2664 * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive,
2665 * <em>T0</em> is converted to byte via Java casting conversion (JLS 5.5),
2666 * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}.
2667 * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean,
2668 * then a Java casting conversion (JLS 5.5) is applied.
2669 * (Specifically, <em>T0</em> will convert to <em>T1</em> by
2670 * widening and/or narrowing.)
2671 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
2672 * conversion will be applied at runtime, possibly followed
2673 * by a Java casting conversion (JLS 5.5) on the primitive value,
2674 * possibly followed by a conversion from byte to boolean by testing
2675 * the low-order bit.
2676 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive,
2677 * and if the reference is null at runtime, a zero value is introduced.
2678 * </ul>
2679 * @param target the method handle to invoke after arguments are retyped
2680 * @param newType the expected type of the new method handle
2681 * @return a method handle which delegates to the target after performing
2682 * any necessary argument conversions, and arranges for any
2683 * necessary return value conversions
2684 * @throws NullPointerException if either argument is null
2685 * @throws WrongMethodTypeException if the conversion cannot be made
2686 * @see MethodHandle#asType
2687 */
2688 public static
2689 MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
2690 explicitCastArgumentsChecks(target, newType);
2691 // use the asTypeCache when possible:
2692 MethodType oldType = target.type();
2693 if (oldType == newType) return target;
2694 if (oldType.explicitCastEquivalentToAsType(newType)) {
2695 return target.asFixedArity().asType(newType);
2696 }
2697 return MethodHandleImpl.makePairwiseConvert(target, newType, false);
2698 }
2699
2700 private static void explicitCastArgumentsChecks(MethodHandle target, MethodType newType) {
2701 if (target.type().parameterCount() != newType.parameterCount()) {
2702 throw new WrongMethodTypeException("cannot explicitly cast " + target + " to " + newType);
2703 }
2704 }
2705
2706 /**
2707 * Produces a method handle which adapts the calling sequence of the
2708 * given method handle to a new type, by reordering the arguments.
2709 * The resulting method handle is guaranteed to report a type
2710 * which is equal to the desired new type.
2711 * <p>
2712 * The given array controls the reordering.
2713 * Call {@code #I} the number of incoming parameters (the value
2714 * {@code newType.parameterCount()}, and call {@code #O} the number
2715 * of outgoing parameters (the value {@code target.type().parameterCount()}).
2716 * Then the length of the reordering array must be {@code #O},
2717 * and each element must be a non-negative number less than {@code #I}.
2718 * For every {@code N} less than {@code #O}, the {@code N}-th
2719 * outgoing argument will be taken from the {@code I}-th incoming
2720 * argument, where {@code I} is {@code reorder[N]}.
2721 * <p>
2722 * No argument or return value conversions are applied.
2723 * The type of each incoming argument, as determined by {@code newType},
2724 * must be identical to the type of the corresponding outgoing parameter
2725 * or parameters in the target method handle.
2726 * The return type of {@code newType} must be identical to the return
2727 * type of the original target.
2728 * <p>
2729 * The reordering array need not specify an actual permutation.
2730 * An incoming argument will be duplicated if its index appears
2731 * more than once in the array, and an incoming argument will be dropped
2732 * if its index does not appear in the array.
2733 * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
2734 * incoming arguments which are not mentioned in the reordering array
2735 * may be of any type, as determined only by {@code newType}.
2736 * <blockquote><pre>{@code
2737 import static java.lang.invoke.MethodHandles.*;
2738 import static java.lang.invoke.MethodType.*;
2739 ...
2740 MethodType intfn1 = methodType(int.class, int.class);
2741 MethodType intfn2 = methodType(int.class, int.class, int.class);
2742 MethodHandle sub = ... (int x, int y) -> (x-y) ...;
2743 assert(sub.type().equals(intfn2));
2744 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
2745 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
2746 assert((int)rsub.invokeExact(1, 100) == 99);
2747 MethodHandle add = ... (int x, int y) -> (x+y) ...;
2748 assert(add.type().equals(intfn2));
2749 MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
2750 assert(twice.type().equals(intfn1));
2751 assert((int)twice.invokeExact(21) == 42);
2752 * }</pre></blockquote>
2753 * <p>
2754 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
2755 * variable-arity method handle}, even if the original target method handle was.
2756 * @param target the method handle to invoke after arguments are reordered
2757 * @param newType the expected type of the new method handle
2758 * @param reorder an index array which controls the reordering
2759 * @return a method handle which delegates to the target after it
2760 * drops unused arguments and moves and/or duplicates the other arguments
2761 * @throws NullPointerException if any argument is null
2762 * @throws IllegalArgumentException if the index array length is not equal to
2763 * the arity of the target, or if any index array element
2764 * not a valid index for a parameter of {@code newType},
2765 * or if two corresponding parameter types in
2766 * {@code target.type()} and {@code newType} are not identical,
2767 */
2768 public static
2769 MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
2770 reorder = reorder.clone(); // get a private copy
2771 MethodType oldType = target.type();
2772 permuteArgumentChecks(reorder, newType, oldType);
2773 // first detect dropped arguments and handle them separately
2774 int[] originalReorder = reorder;
2775 BoundMethodHandle result = target.rebind();
2776 LambdaForm form = result.form;
2777 int newArity = newType.parameterCount();
2778 // Normalize the reordering into a real permutation,
2779 // by removing duplicates and adding dropped elements.
2780 // This somewhat improves lambda form caching, as well
2781 // as simplifying the transform by breaking it up into steps.
2782 for (int ddIdx; (ddIdx = findFirstDupOrDrop(reorder, newArity)) != 0; ) {
2783 if (ddIdx > 0) {
2784 // We found a duplicated entry at reorder[ddIdx].
2785 // Example: (x,y,z)->asList(x,y,z)
2786 // permuted by [1*,0,1] => (a0,a1)=>asList(a1,a0,a1)
2787 // permuted by [0,1,0*] => (a0,a1)=>asList(a0,a1,a0)
2788 // The starred element corresponds to the argument
2789 // deleted by the dupArgumentForm transform.
2790 int srcPos = ddIdx, dstPos = srcPos, dupVal = reorder[srcPos];
2791 boolean killFirst = false;
2792 for (int val; (val = reorder[--dstPos]) != dupVal; ) {
2793 // Set killFirst if the dup is larger than an intervening position.
2794 // This will remove at least one inversion from the permutation.
2795 if (dupVal > val) killFirst = true;
2796 }
2797 if (!killFirst) {
2798 srcPos = dstPos;
2799 dstPos = ddIdx;
2800 }
2801 form = form.editor().dupArgumentForm(1 + srcPos, 1 + dstPos);
2802 assert (reorder[srcPos] == reorder[dstPos]);
2803 oldType = oldType.dropParameterTypes(dstPos, dstPos + 1);
2804 // contract the reordering by removing the element at dstPos
2805 int tailPos = dstPos + 1;
2806 System.arraycopy(reorder, tailPos, reorder, dstPos, reorder.length - tailPos);
2807 reorder = Arrays.copyOf(reorder, reorder.length - 1);
2808 } else {
2809 int dropVal = ~ddIdx, insPos = 0;
2810 while (insPos < reorder.length && reorder[insPos] < dropVal) {
2811 // Find first element of reorder larger than dropVal.
2812 // This is where we will insert the dropVal.
2813 insPos += 1;
2814 }
2815 Class<?> ptype = newType.parameterType(dropVal);
2816 form = form.editor().addArgumentForm(1 + insPos, BasicType.basicType(ptype));
2817 oldType = oldType.insertParameterTypes(insPos, ptype);
2818 // expand the reordering by inserting an element at insPos
2819 int tailPos = insPos + 1;
2820 reorder = Arrays.copyOf(reorder, reorder.length + 1);
2821 System.arraycopy(reorder, insPos, reorder, tailPos, reorder.length - tailPos);
2822 reorder[insPos] = dropVal;
2823 }
2824 assert (permuteArgumentChecks(reorder, newType, oldType));
2825 }
2826 assert (reorder.length == newArity); // a perfect permutation
2827 // Note: This may cache too many distinct LFs. Consider backing off to varargs code.
2828 form = form.editor().permuteArgumentsForm(1, reorder);
2829 if (newType == result.type() && form == result.internalForm())
2830 return result;
2831 return result.copyWith(newType, form);
2832 }
2833
2834 /**
2835 * Return an indication of any duplicate or omission in reorder.
2836 * If the reorder contains a duplicate entry, return the index of the second occurrence.
2837 * Otherwise, return ~(n), for the first n in [0..newArity-1] that is not present in reorder.
2838 * Otherwise, return zero.
2839 * If an element not in [0..newArity-1] is encountered, return reorder.length.
2840 */
2841 private static int findFirstDupOrDrop(int[] reorder, int newArity) {
2842 final int BIT_LIMIT = 63; // max number of bits in bit mask
2843 if (newArity < BIT_LIMIT) {
2844 long mask = 0;
2845 for (int i = 0; i < reorder.length; i++) {
2846 int arg = reorder[i];
2847 if (arg >= newArity) {
2848 return reorder.length;
2849 }
2850 long bit = 1L << arg;
2851 if ((mask & bit) != 0) {
2852 return i; // >0 indicates a dup
2853 }
2854 mask |= bit;
2855 }
2856 if (mask == (1L << newArity) - 1) {
2857 assert(Long.numberOfTrailingZeros(Long.lowestOneBit(~mask)) == newArity);
2858 return 0;
2859 }
2860 // find first zero
2861 long zeroBit = Long.lowestOneBit(~mask);
2862 int zeroPos = Long.numberOfTrailingZeros(zeroBit);
2863 assert(zeroPos <= newArity);
2864 if (zeroPos == newArity) {
2865 return 0;
2866 }
2867 return ~zeroPos;
2868 } else {
2869 // same algorithm, different bit set
2870 BitSet mask = new BitSet(newArity);
2871 for (int i = 0; i < reorder.length; i++) {
2872 int arg = reorder[i];
2873 if (arg >= newArity) {
2874 return reorder.length;
2875 }
2876 if (mask.get(arg)) {
2877 return i; // >0 indicates a dup
2878 }
2879 mask.set(arg);
2880 }
2881 int zeroPos = mask.nextClearBit(0);
2882 assert(zeroPos <= newArity);
2883 if (zeroPos == newArity) {
2884 return 0;
2885 }
2886 return ~zeroPos;
2887 }
2888 }
2889
2890 private static boolean permuteArgumentChecks(int[] reorder, MethodType newType, MethodType oldType) {
2891 if (newType.returnType() != oldType.returnType())
2892 throw newIllegalArgumentException("return types do not match",
2893 oldType, newType);
2894 if (reorder.length == oldType.parameterCount()) {
2895 int limit = newType.parameterCount();
2896 boolean bad = false;
2897 for (int j = 0; j < reorder.length; j++) {
2898 int i = reorder[j];
2899 if (i < 0 || i >= limit) {
2900 bad = true; break;
2901 }
2902 Class<?> src = newType.parameterType(i);
2903 Class<?> dst = oldType.parameterType(j);
2904 if (src != dst)
2905 throw newIllegalArgumentException("parameter types do not match after reorder",
2906 oldType, newType);
2907 }
2908 if (!bad) return true;
2909 }
2910 throw newIllegalArgumentException("bad reorder array: "+Arrays.toString(reorder));
2911 }
2912
2913 /**
2914 * Produces a method handle of the requested return type which returns the given
2915 * constant value every time it is invoked.
2916 * <p>
2917 * Before the method handle is returned, the passed-in value is converted to the requested type.
2918 * If the requested type is primitive, widening primitive conversions are attempted,
2919 * else reference conversions are attempted.
2920 * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
2921 * @param type the return type of the desired method handle
2922 * @param value the value to return
2923 * @return a method handle of the given return type and no arguments, which always returns the given value
2924 * @throws NullPointerException if the {@code type} argument is null
2925 * @throws ClassCastException if the value cannot be converted to the required return type
2926 * @throws IllegalArgumentException if the given type is {@code void.class}
2927 */
2928 public static
2929 MethodHandle constant(Class<?> type, Object value) {
2930 if (type.isPrimitive()) {
2931 if (type == void.class)
2932 throw newIllegalArgumentException("void type");
2933 Wrapper w = Wrapper.forPrimitiveType(type);
2934 value = w.convert(value, type);
2935 if (w.zero().equals(value))
2936 return zero(w, type);
2937 return insertArguments(identity(type), 0, value);
2938 } else {
2939 if (value == null)
2940 return zero(Wrapper.OBJECT, type);
2941 return identity(type).bindTo(value);
2942 }
2943 }
2944
2945 /**
2946 * Produces a method handle which returns its sole argument when invoked.
2947 * @param type the type of the sole parameter and return value of the desired method handle
2948 * @return a unary method handle which accepts and returns the given type
2949 * @throws NullPointerException if the argument is null
2950 * @throws IllegalArgumentException if the given type is {@code void.class}
2951 */
2952 public static
2953 MethodHandle identity(Class<?> type) {
2954 Wrapper btw = (type.isPrimitive() ? Wrapper.forPrimitiveType(type) : Wrapper.OBJECT);
2955 int pos = btw.ordinal();
2956 MethodHandle ident = IDENTITY_MHS[pos];
2957 if (ident == null) {
2958 ident = setCachedMethodHandle(IDENTITY_MHS, pos, makeIdentity(btw.primitiveType()));
2959 }
2960 if (ident.type().returnType() == type)
2961 return ident;
2962 // something like identity(Foo.class); do not bother to intern these
2963 assert (btw == Wrapper.OBJECT);
2964 return makeIdentity(type);
2965 }
2966
2967 /**
2968 * Produces a constant method handle of the requested return type which
2969 * returns the default value for that type every time it is invoked.
2970 * The resulting constant method handle will have no side effects.
2971 * <p>The returned method handle is equivalent to {@code empty(methodType(type))}.
2972 * It is also equivalent to {@code explicitCastArguments(constant(Object.class, null), methodType(type))},
2973 * since {@code explicitCastArguments} converts {@code null} to default values.
2974 * @param type the expected return type of the desired method handle
2975 * @return a constant method handle that takes no arguments
2976 * and returns the default value of the given type (or void, if the type is void)
2977 * @throws NullPointerException if the argument is null
2978 * @see MethodHandles#constant
2979 * @see MethodHandles#empty
2980 * @since 9
2981 */
2982 public static MethodHandle zero(Class<?> type) {
2983 Objects.requireNonNull(type);
2984 return type.isPrimitive() ? zero(Wrapper.forPrimitiveType(type), type) : zero(Wrapper.OBJECT, type);
2985 }
2986
2987 private static MethodHandle identityOrVoid(Class<?> type) {
2988 return type == void.class ? zero(type) : identity(type);
2989 }
2990
2991 /**
2992 * Produces a method handle of the requested type which ignores any arguments, does nothing,
2993 * and returns a suitable default depending on the return type.
2994 * That is, it returns a zero primitive value, a {@code null}, or {@code void}.
2995 * <p>The returned method handle is equivalent to
2996 * {@code dropArguments(zero(type.returnType()), 0, type.parameterList())}.
2997 * <p>
2998 * @apiNote Given a predicate and target, a useful "if-then" construct can be produced as
2999 * {@code guardWithTest(pred, target, empty(target.type())}.
3000 * @param type the type of the desired method handle
3001 * @return a constant method handle of the given type, which returns a default value of the given return type
3002 * @throws NullPointerException if the argument is null
3003 * @see MethodHandles#zero
3004 * @see MethodHandles#constant
3005 * @since 9
3006 */
3007 public static MethodHandle empty(MethodType type) {
3008 Objects.requireNonNull(type);
3009 return dropArguments(zero(type.returnType()), 0, type.parameterList());
3010 }
3011
3012 private static final MethodHandle[] IDENTITY_MHS = new MethodHandle[Wrapper.values().length];
3013 private static MethodHandle makeIdentity(Class<?> ptype) {
3014 MethodType mtype = methodType(ptype, ptype);
3015 LambdaForm lform = LambdaForm.identityForm(BasicType.basicType(ptype));
3016 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.IDENTITY);
3017 }
3018
3019 private static MethodHandle zero(Wrapper btw, Class<?> rtype) {
3020 int pos = btw.ordinal();
3021 MethodHandle zero = ZERO_MHS[pos];
3022 if (zero == null) {
3023 zero = setCachedMethodHandle(ZERO_MHS, pos, makeZero(btw.primitiveType()));
3024 }
3025 if (zero.type().returnType() == rtype)
3026 return zero;
3027 assert(btw == Wrapper.OBJECT);
3028 return makeZero(rtype);
3029 }
3030 private static final MethodHandle[] ZERO_MHS = new MethodHandle[Wrapper.values().length];
3031 private static MethodHandle makeZero(Class<?> rtype) {
3032 MethodType mtype = methodType(rtype);
3033 LambdaForm lform = LambdaForm.zeroForm(BasicType.basicType(rtype));
3034 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.ZERO);
3035 }
3036
3037 private static synchronized MethodHandle setCachedMethodHandle(MethodHandle[] cache, int pos, MethodHandle value) {
3038 // Simulate a CAS, to avoid racy duplication of results.
3039 MethodHandle prev = cache[pos];
3040 if (prev != null) return prev;
3041 return cache[pos] = value;
3042 }
3043
3044 /**
3045 * Provides a target method handle with one or more <em>bound arguments</em>
3046 * in advance of the method handle's invocation.
3047 * The formal parameters to the target corresponding to the bound
3048 * arguments are called <em>bound parameters</em>.
3049 * Returns a new method handle which saves away the bound arguments.
3050 * When it is invoked, it receives arguments for any non-bound parameters,
3051 * binds the saved arguments to their corresponding parameters,
3052 * and calls the original target.
3053 * <p>
3054 * The type of the new method handle will drop the types for the bound
3055 * parameters from the original target type, since the new method handle
3056 * will no longer require those arguments to be supplied by its callers.
3057 * <p>
3058 * Each given argument object must match the corresponding bound parameter type.
3059 * If a bound parameter type is a primitive, the argument object
3060 * must be a wrapper, and will be unboxed to produce the primitive value.
3061 * <p>
3062 * The {@code pos} argument selects which parameters are to be bound.
3063 * It may range between zero and <i>N-L</i> (inclusively),
3064 * where <i>N</i> is the arity of the target method handle
3065 * and <i>L</i> is the length of the values array.
3066 * <p>
3067 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3068 * variable-arity method handle}, even if the original target method handle was.
3069 * @param target the method handle to invoke after the argument is inserted
3070 * @param pos where to insert the argument (zero for the first)
3071 * @param values the series of arguments to insert
3072 * @return a method handle which inserts an additional argument,
3073 * before calling the original method handle
3074 * @throws NullPointerException if the target or the {@code values} array is null
3075 * @see MethodHandle#bindTo
3076 */
3077 public static
3078 MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
3079 int insCount = values.length;
3080 Class<?>[] ptypes = insertArgumentsChecks(target, insCount, pos);
3081 if (insCount == 0) return target;
3082 BoundMethodHandle result = target.rebind();
3083 for (int i = 0; i < insCount; i++) {
3084 Object value = values[i];
3085 Class<?> ptype = ptypes[pos+i];
3086 if (ptype.isPrimitive()) {
3087 result = insertArgumentPrimitive(result, pos, ptype, value);
3088 } else {
3089 value = ptype.cast(value); // throw CCE if needed
3090 result = result.bindArgumentL(pos, value);
3091 }
3092 }
3093 return result;
3094 }
3095
3096 private static BoundMethodHandle insertArgumentPrimitive(BoundMethodHandle result, int pos,
3097 Class<?> ptype, Object value) {
3098 Wrapper w = Wrapper.forPrimitiveType(ptype);
3099 // perform unboxing and/or primitive conversion
3100 value = w.convert(value, ptype);
3101 switch (w) {
3102 case INT: return result.bindArgumentI(pos, (int)value);
3103 case LONG: return result.bindArgumentJ(pos, (long)value);
3104 case FLOAT: return result.bindArgumentF(pos, (float)value);
3105 case DOUBLE: return result.bindArgumentD(pos, (double)value);
3106 default: return result.bindArgumentI(pos, ValueConversions.widenSubword(value));
3107 }
3108 }
3109
3110 private static Class<?>[] insertArgumentsChecks(MethodHandle target, int insCount, int pos) throws RuntimeException {
3111 MethodType oldType = target.type();
3112 int outargs = oldType.parameterCount();
3113 int inargs = outargs - insCount;
3114 if (inargs < 0)
3115 throw newIllegalArgumentException("too many values to insert");
3116 if (pos < 0 || pos > inargs)
3117 throw newIllegalArgumentException("no argument type to append");
3118 return oldType.ptypes();
3119 }
3120
3121 /**
3122 * Produces a method handle which will discard some dummy arguments
3123 * before calling some other specified <i>target</i> method handle.
3124 * The type of the new method handle will be the same as the target's type,
3125 * except it will also include the dummy argument types,
3126 * at some given position.
3127 * <p>
3128 * The {@code pos} argument may range between zero and <i>N</i>,
3129 * where <i>N</i> is the arity of the target.
3130 * If {@code pos} is zero, the dummy arguments will precede
3131 * the target's real arguments; if {@code pos} is <i>N</i>
3132 * they will come after.
3133 * <p>
3134 * <b>Example:</b>
3135 * <blockquote><pre>{@code
3136 import static java.lang.invoke.MethodHandles.*;
3137 import static java.lang.invoke.MethodType.*;
3138 ...
3139 MethodHandle cat = lookup().findVirtual(String.class,
3140 "concat", methodType(String.class, String.class));
3141 assertEquals("xy", (String) cat.invokeExact("x", "y"));
3142 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
3143 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
3144 assertEquals(bigType, d0.type());
3145 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
3146 * }</pre></blockquote>
3147 * <p>
3148 * This method is also equivalent to the following code:
3149 * <blockquote><pre>
3150 * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))}
3151 * </pre></blockquote>
3152 * @param target the method handle to invoke after the arguments are dropped
3153 * @param valueTypes the type(s) of the argument(s) to drop
3154 * @param pos position of first argument to drop (zero for the leftmost)
3155 * @return a method handle which drops arguments of the given types,
3156 * before calling the original method handle
3157 * @throws NullPointerException if the target is null,
3158 * or if the {@code valueTypes} list or any of its elements is null
3159 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
3160 * or if {@code pos} is negative or greater than the arity of the target,
3161 * or if the new method handle's type would have too many parameters
3162 */
3163 public static
3164 MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) {
3165 MethodType oldType = target.type(); // get NPE
3166 int dropped = dropArgumentChecks(oldType, pos, valueTypes);
3167 MethodType newType = oldType.insertParameterTypes(pos, valueTypes);
3168 if (dropped == 0) return target;
3169 BoundMethodHandle result = target.rebind();
3170 LambdaForm lform = result.form;
3171 int insertFormArg = 1 + pos;
3172 for (Class<?> ptype : valueTypes) {
3173 lform = lform.editor().addArgumentForm(insertFormArg++, BasicType.basicType(ptype));
3174 }
3175 result = result.copyWith(newType, lform);
3176 return result;
3177 }
3178
3179 private static int dropArgumentChecks(MethodType oldType, int pos, List<Class<?>> valueTypes) {
3180 int dropped = valueTypes.size();
3181 MethodType.checkSlotCount(dropped);
3182 int outargs = oldType.parameterCount();
3183 int inargs = outargs + dropped;
3184 if (pos < 0 || pos > outargs)
3185 throw newIllegalArgumentException("no argument type to remove"
3186 + Arrays.asList(oldType, pos, valueTypes, inargs, outargs)
3187 );
3188 return dropped;
3189 }
3190
3191 /**
3192 * Produces a method handle which will discard some dummy arguments
3193 * before calling some other specified <i>target</i> method handle.
3194 * The type of the new method handle will be the same as the target's type,
3195 * except it will also include the dummy argument types,
3196 * at some given position.
3197 * <p>
3198 * The {@code pos} argument may range between zero and <i>N</i>,
3199 * where <i>N</i> is the arity of the target.
3200 * If {@code pos} is zero, the dummy arguments will precede
3201 * the target's real arguments; if {@code pos} is <i>N</i>
3202 * they will come after.
3203 * @apiNote
3204 * <blockquote><pre>{@code
3205 import static java.lang.invoke.MethodHandles.*;
3206 import static java.lang.invoke.MethodType.*;
3207 ...
3208 MethodHandle cat = lookup().findVirtual(String.class,
3209 "concat", methodType(String.class, String.class));
3210 assertEquals("xy", (String) cat.invokeExact("x", "y"));
3211 MethodHandle d0 = dropArguments(cat, 0, String.class);
3212 assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
3213 MethodHandle d1 = dropArguments(cat, 1, String.class);
3214 assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
3215 MethodHandle d2 = dropArguments(cat, 2, String.class);
3216 assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
3217 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
3218 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
3219 * }</pre></blockquote>
3220 * <p>
3221 * This method is also equivalent to the following code:
3222 * <blockquote><pre>
3223 * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))}
3224 * </pre></blockquote>
3225 * @param target the method handle to invoke after the arguments are dropped
3226 * @param valueTypes the type(s) of the argument(s) to drop
3227 * @param pos position of first argument to drop (zero for the leftmost)
3228 * @return a method handle which drops arguments of the given types,
3229 * before calling the original method handle
3230 * @throws NullPointerException if the target is null,
3231 * or if the {@code valueTypes} array or any of its elements is null
3232 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
3233 * or if {@code pos} is negative or greater than the arity of the target,
3234 * or if the new method handle's type would have
3235 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3236 */
3237 public static
3238 MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
3239 return dropArguments(target, pos, Arrays.asList(valueTypes));
3240 }
3241
3242 // private version which allows caller some freedom with error handling
3243 private static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos,
3244 boolean nullOnFailure) {
3245 List<Class<?>> oldTypes = target.type().parameterList();
3246 int match = oldTypes.size();
3247 if (skip != 0) {
3248 if (skip < 0 || skip > match) {
3249 throw newIllegalArgumentException("illegal skip", skip, target);
3250 }
3251 oldTypes = oldTypes.subList(skip, match);
3252 match -= skip;
3253 }
3254 List<Class<?>> addTypes = newTypes;
3255 int add = addTypes.size();
3256 if (pos != 0) {
3257 if (pos < 0 || pos > add) {
3258 throw newIllegalArgumentException("illegal pos", pos, newTypes);
3259 }
3260 addTypes = addTypes.subList(pos, add);
3261 add -= pos; assert(addTypes.size() == add);
3262 }
3263 // Do not add types which already match the existing arguments.
3264 if (match > add || !oldTypes.equals(addTypes.subList(0, match))) {
3265 if (nullOnFailure) {
3266 return null;
3267 }
3268 throw newIllegalArgumentException("argument lists do not match", oldTypes, newTypes);
3269 }
3270 addTypes = addTypes.subList(match, add);
3271 add -= match; assert(addTypes.size() == add);
3272 // newTypes: ( P*[pos], M*[match], A*[add] )
3273 // target: ( S*[skip], M*[match] )
3274 MethodHandle adapter = target;
3275 if (add > 0) {
3276 adapter = dropArguments(adapter, skip+ match, addTypes);
3277 }
3278 // adapter: (S*[skip], M*[match], A*[add] )
3279 if (pos > 0) {
3280 adapter = dropArguments(adapter, skip, newTypes.subList(0, pos));
3281 }
3282 // adapter: (S*[skip], P*[pos], M*[match], A*[add] )
3283 return adapter;
3284 }
3285
3286 /**
3287 * Adapts a target method handle to match the given parameter type list, if necessary, by adding dummy arguments.
3288 * Some leading parameters are first skipped; they will be left unchanged and are otherwise ignored.
3289 * The remaining types in the target's parameter type list must be contained as a sub-list of the given type list,
3290 * at the given position.
3291 * Any non-matching parameter types (before or after the matching sub-list) are inserted in corresponding
3292 * positions of the target method handle's parameters, as if by {@link #dropArguments}.
3293 * (More precisely, elements in the new list before {@code pos} are inserted into the target list at {@code skip},
3294 * while elements in the new list after the match beginning at {@code pos} are inserted at the end of the
3295 * target list.)
3296 * The target's return type will be unchanged.
3297 * @apiNote
3298 * Two method handles whose argument lists are "effectively identical" (i.e., identical
3299 * in a common prefix) may be mutually converted to a common type
3300 * by two calls to {@code dropArgumentsToMatch}, as follows:
3301 * <blockquote><pre>{@code
3302 import static java.lang.invoke.MethodHandles.*;
3303 import static java.lang.invoke.MethodType.*;
3304 ...
3305 ...
3306 MethodHandle h0 = constant(boolean.class, true);
3307 MethodHandle h1 = lookup().findVirtual(String.class, "concat", methodType(String.class, String.class));
3308 MethodType bigType = h1.type().insertParameterTypes(1, String.class, int.class);
3309 MethodHandle h2 = dropArguments(h1, 0, bigType.parameterList());
3310 if (h1.type().parameterCount() < h2.type().parameterCount())
3311 h1 = dropArgumentsToMatch(h1, 0, h2.type().parameterList(), 0); // lengthen h1
3312 else
3313 h2 = dropArgumentsToMatch(h2, 0, h1.type().parameterList(), 0); // lengthen h2
3314 MethodHandle h3 = guardWithTest(h0, h1, h2);
3315 assertEquals("xy", h3.invoke("x", "y", 1, "a", "b", "c"));
3316 * }</pre></blockquote>
3317 * @param target the method handle to adapt
3318 * @param skip number of targets parameters to disregard (they will be unchanged)
3319 * @param newTypes the desired argument list of the method handle
3320 * @param pos place in {@code newTypes} where the non-skipped target parameters must occur
3321 * @return a possibly adapted method handle
3322 * @throws NullPointerException if either argument is null
3323 * @throws IllegalArgumentException
3324 * if either index is out of range in its corresponding list, or
3325 * if the non-skipped target parameter types match the new types at {@code pos}
3326 * @since 9
3327 */
3328 public static
3329 MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos) {
3330 Objects.requireNonNull(target);
3331 Objects.requireNonNull(newTypes);
3332 return dropArgumentsToMatch(target, skip, newTypes, pos, false);
3333 }
3334
3335 /**
3336 * Adapts a target method handle by pre-processing
3337 * one or more of its arguments, each with its own unary filter function,
3338 * and then calling the target with each pre-processed argument
3339 * replaced by the result of its corresponding filter function.
3340 * <p>
3341 * The pre-processing is performed by one or more method handles,
3342 * specified in the elements of the {@code filters} array.
3343 * The first element of the filter array corresponds to the {@code pos}
3344 * argument of the target, and so on in sequence.
3345 * <p>
3346 * Null arguments in the array are treated as identity functions,
3347 * and the corresponding arguments left unchanged.
3348 * (If there are no non-null elements in the array, the original target is returned.)
3349 * Each filter is applied to the corresponding argument of the adapter.
3350 * <p>
3351 * If a filter {@code F} applies to the {@code N}th argument of
3352 * the target, then {@code F} must be a method handle which
3353 * takes exactly one argument. The type of {@code F}'s sole argument
3354 * replaces the corresponding argument type of the target
3355 * in the resulting adapted method handle.
3356 * The return type of {@code F} must be identical to the corresponding
3357 * parameter type of the target.
3358 * <p>
3359 * It is an error if there are elements of {@code filters}
3360 * (null or not)
3361 * which do not correspond to argument positions in the target.
3362 * <p><b>Example:</b>
3363 * <blockquote><pre>{@code
3364 import static java.lang.invoke.MethodHandles.*;
3365 import static java.lang.invoke.MethodType.*;
3366 ...
3367 MethodHandle cat = lookup().findVirtual(String.class,
3368 "concat", methodType(String.class, String.class));
3369 MethodHandle upcase = lookup().findVirtual(String.class,
3370 "toUpperCase", methodType(String.class));
3371 assertEquals("xy", (String) cat.invokeExact("x", "y"));
3372 MethodHandle f0 = filterArguments(cat, 0, upcase);
3373 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
3374 MethodHandle f1 = filterArguments(cat, 1, upcase);
3375 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
3376 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
3377 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
3378 * }</pre></blockquote>
3379 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
3380 * denotes the return type of both the {@code target} and resulting adapter.
3381 * {@code P}/{@code p} and {@code B}/{@code b} represent the types and values
3382 * of the parameters and arguments that precede and follow the filter position
3383 * {@code pos}, respectively. {@code A[i]}/{@code a[i]} stand for the types and
3384 * values of the filtered parameters and arguments; they also represent the
3385 * return types of the {@code filter[i]} handles. The latter accept arguments
3386 * {@code v[i]} of type {@code V[i]}, which also appear in the signature of
3387 * the resulting adapter.
3388 * <blockquote><pre>{@code
3389 * T target(P... p, A[i]... a[i], B... b);
3390 * A[i] filter[i](V[i]);
3391 * T adapter(P... p, V[i]... v[i], B... b) {
3392 * return target(p..., filter[i](v[i])..., b...);
3393 * }
3394 * }</pre></blockquote>
3395 * <p>
3396 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3397 * variable-arity method handle}, even if the original target method handle was.
3398 *
3399 * @param target the method handle to invoke after arguments are filtered
3400 * @param pos the position of the first argument to filter
3401 * @param filters method handles to call initially on filtered arguments
3402 * @return method handle which incorporates the specified argument filtering logic
3403 * @throws NullPointerException if the target is null
3404 * or if the {@code filters} array is null
3405 * @throws IllegalArgumentException if a non-null element of {@code filters}
3406 * does not match a corresponding argument type of target as described above,
3407 * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()},
3408 * or if the resulting method handle's type would have
3409 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3410 */
3411 public static
3412 MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
3413 filterArgumentsCheckArity(target, pos, filters);
3414 MethodHandle adapter = target;
3415 int curPos = pos-1; // pre-incremented
3416 for (MethodHandle filter : filters) {
3417 curPos += 1;
3418 if (filter == null) continue; // ignore null elements of filters
3419 adapter = filterArgument(adapter, curPos, filter);
3420 }
3421 return adapter;
3422 }
3423
3424 /*non-public*/ static
3425 MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
3426 filterArgumentChecks(target, pos, filter);
3427 MethodType targetType = target.type();
3428 MethodType filterType = filter.type();
3429 BoundMethodHandle result = target.rebind();
3430 Class<?> newParamType = filterType.parameterType(0);
3431 LambdaForm lform = result.editor().filterArgumentForm(1 + pos, BasicType.basicType(newParamType));
3432 MethodType newType = targetType.changeParameterType(pos, newParamType);
3433 result = result.copyWithExtendL(newType, lform, filter);
3434 return result;
3435 }
3436
3437 private static void filterArgumentsCheckArity(MethodHandle target, int pos, MethodHandle[] filters) {
3438 MethodType targetType = target.type();
3439 int maxPos = targetType.parameterCount();
3440 if (pos + filters.length > maxPos)
3441 throw newIllegalArgumentException("too many filters");
3442 }
3443
3444 private static void filterArgumentChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
3445 MethodType targetType = target.type();
3446 MethodType filterType = filter.type();
3447 if (filterType.parameterCount() != 1
3448 || filterType.returnType() != targetType.parameterType(pos))
3449 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
3450 }
3451
3452 /**
3453 * Adapts a target method handle by pre-processing
3454 * a sub-sequence of its arguments with a filter (another method handle).
3455 * The pre-processed arguments are replaced by the result (if any) of the
3456 * filter function.
3457 * The target is then called on the modified (usually shortened) argument list.
3458 * <p>
3459 * If the filter returns a value, the target must accept that value as
3460 * its argument in position {@code pos}, preceded and/or followed by
3461 * any arguments not passed to the filter.
3462 * If the filter returns void, the target must accept all arguments
3463 * not passed to the filter.
3464 * No arguments are reordered, and a result returned from the filter
3465 * replaces (in order) the whole subsequence of arguments originally
3466 * passed to the adapter.
3467 * <p>
3468 * The argument types (if any) of the filter
3469 * replace zero or one argument types of the target, at position {@code pos},
3470 * in the resulting adapted method handle.
3471 * The return type of the filter (if any) must be identical to the
3472 * argument type of the target at position {@code pos}, and that target argument
3473 * is supplied by the return value of the filter.
3474 * <p>
3475 * In all cases, {@code pos} must be greater than or equal to zero, and
3476 * {@code pos} must also be less than or equal to the target's arity.
3477 * <p><b>Example:</b>
3478 * <blockquote><pre>{@code
3479 import static java.lang.invoke.MethodHandles.*;
3480 import static java.lang.invoke.MethodType.*;
3481 ...
3482 MethodHandle deepToString = publicLookup()
3483 .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
3484
3485 MethodHandle ts1 = deepToString.asCollector(String[].class, 1);
3486 assertEquals("[strange]", (String) ts1.invokeExact("strange"));
3487
3488 MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
3489 assertEquals("[up, down]", (String) ts2.invokeExact("up", "down"));
3490
3491 MethodHandle ts3 = deepToString.asCollector(String[].class, 3);
3492 MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2);
3493 assertEquals("[top, [up, down], strange]",
3494 (String) ts3_ts2.invokeExact("top", "up", "down", "strange"));
3495
3496 MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1);
3497 assertEquals("[top, [up, down], [strange]]",
3498 (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange"));
3499
3500 MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3);
3501 assertEquals("[top, [[up, down, strange], charm], bottom]",
3502 (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom"));
3503 * }</pre></blockquote>
3504 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
3505 * represents the return type of the {@code target} and resulting adapter.
3506 * {@code V}/{@code v} stand for the return type and value of the
3507 * {@code filter}, which are also found in the signature and arguments of
3508 * the {@code target}, respectively, unless {@code V} is {@code void}.
3509 * {@code A}/{@code a} and {@code C}/{@code c} represent the parameter types
3510 * and values preceding and following the collection position, {@code pos},
3511 * in the {@code target}'s signature. They also turn up in the resulting
3512 * adapter's signature and arguments, where they surround
3513 * {@code B}/{@code b}, which represent the parameter types and arguments
3514 * to the {@code filter} (if any).
3515 * <blockquote><pre>{@code
3516 * T target(A...,V,C...);
3517 * V filter(B...);
3518 * T adapter(A... a,B... b,C... c) {
3519 * V v = filter(b...);
3520 * return target(a...,v,c...);
3521 * }
3522 * // and if the filter has no arguments:
3523 * T target2(A...,V,C...);
3524 * V filter2();
3525 * T adapter2(A... a,C... c) {
3526 * V v = filter2();
3527 * return target2(a...,v,c...);
3528 * }
3529 * // and if the filter has a void return:
3530 * T target3(A...,C...);
3531 * void filter3(B...);
3532 * T adapter3(A... a,B... b,C... c) {
3533 * filter3(b...);
3534 * return target3(a...,c...);
3535 * }
3536 * }</pre></blockquote>
3537 * <p>
3538 * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to
3539 * one which first "folds" the affected arguments, and then drops them, in separate
3540 * steps as follows:
3541 * <blockquote><pre>{@code
3542 * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2
3543 * mh = MethodHandles.foldArguments(mh, coll); //step 1
3544 * }</pre></blockquote>
3545 * If the target method handle consumes no arguments besides than the result
3546 * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)}
3547 * is equivalent to {@code filterReturnValue(coll, mh)}.
3548 * If the filter method handle {@code coll} consumes one argument and produces
3549 * a non-void result, then {@code collectArguments(mh, N, coll)}
3550 * is equivalent to {@code filterArguments(mh, N, coll)}.
3551 * Other equivalences are possible but would require argument permutation.
3552 * <p>
3553 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3554 * variable-arity method handle}, even if the original target method handle was.
3555 *
3556 * @param target the method handle to invoke after filtering the subsequence of arguments
3557 * @param pos the position of the first adapter argument to pass to the filter,
3558 * and/or the target argument which receives the result of the filter
3559 * @param filter method handle to call on the subsequence of arguments
3560 * @return method handle which incorporates the specified argument subsequence filtering logic
3561 * @throws NullPointerException if either argument is null
3562 * @throws IllegalArgumentException if the return type of {@code filter}
3563 * is non-void and is not the same as the {@code pos} argument of the target,
3564 * or if {@code pos} is not between 0 and the target's arity, inclusive,
3565 * or if the resulting method handle's type would have
3566 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3567 * @see MethodHandles#foldArguments
3568 * @see MethodHandles#filterArguments
3569 * @see MethodHandles#filterReturnValue
3570 */
3571 public static
3572 MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) {
3573 MethodType newType = collectArgumentsChecks(target, pos, filter);
3574 MethodType collectorType = filter.type();
3575 BoundMethodHandle result = target.rebind();
3576 LambdaForm lform;
3577 if (collectorType.returnType().isArray() && filter.intrinsicName() == Intrinsic.NEW_ARRAY) {
3578 lform = result.editor().collectArgumentArrayForm(1 + pos, filter);
3579 if (lform != null) {
3580 return result.copyWith(newType, lform);
3581 }
3582 }
3583 lform = result.editor().collectArgumentsForm(1 + pos, collectorType.basicType());
3584 return result.copyWithExtendL(newType, lform, filter);
3585 }
3586
3587 private static MethodType collectArgumentsChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
3588 MethodType targetType = target.type();
3589 MethodType filterType = filter.type();
3590 Class<?> rtype = filterType.returnType();
3591 List<Class<?>> filterArgs = filterType.parameterList();
3592 if (rtype == void.class) {
3593 return targetType.insertParameterTypes(pos, filterArgs);
3594 }
3595 if (rtype != targetType.parameterType(pos)) {
3596 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
3597 }
3598 return targetType.dropParameterTypes(pos, pos+1).insertParameterTypes(pos, filterArgs);
3599 }
3600
3601 /**
3602 * Adapts a target method handle by post-processing
3603 * its return value (if any) with a filter (another method handle).
3604 * The result of the filter is returned from the adapter.
3605 * <p>
3606 * If the target returns a value, the filter must accept that value as
3607 * its only argument.
3608 * If the target returns void, the filter must accept no arguments.
3609 * <p>
3610 * The return type of the filter
3611 * replaces the return type of the target
3612 * in the resulting adapted method handle.
3613 * The argument type of the filter (if any) must be identical to the
3614 * return type of the target.
3615 * <p><b>Example:</b>
3616 * <blockquote><pre>{@code
3617 import static java.lang.invoke.MethodHandles.*;
3618 import static java.lang.invoke.MethodType.*;
3619 ...
3620 MethodHandle cat = lookup().findVirtual(String.class,
3621 "concat", methodType(String.class, String.class));
3622 MethodHandle length = lookup().findVirtual(String.class,
3623 "length", methodType(int.class));
3624 System.out.println((String) cat.invokeExact("x", "y")); // xy
3625 MethodHandle f0 = filterReturnValue(cat, length);
3626 System.out.println((int) f0.invokeExact("x", "y")); // 2
3627 * }</pre></blockquote>
3628 * <p>Here is pseudocode for the resulting adapter. In the code,
3629 * {@code T}/{@code t} represent the result type and value of the
3630 * {@code target}; {@code V}, the result type of the {@code filter}; and
3631 * {@code A}/{@code a}, the types and values of the parameters and arguments
3632 * of the {@code target} as well as the resulting adapter.
3633 * <blockquote><pre>{@code
3634 * T target(A...);
3635 * V filter(T);
3636 * V adapter(A... a) {
3637 * T t = target(a...);
3638 * return filter(t);
3639 * }
3640 * // and if the target has a void return:
3641 * void target2(A...);
3642 * V filter2();
3643 * V adapter2(A... a) {
3644 * target2(a...);
3645 * return filter2();
3646 * }
3647 * // and if the filter has a void return:
3648 * T target3(A...);
3649 * void filter3(V);
3650 * void adapter3(A... a) {
3651 * T t = target3(a...);
3652 * filter3(t);
3653 * }
3654 * }</pre></blockquote>
3655 * <p>
3656 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3657 * variable-arity method handle}, even if the original target method handle was.
3658 * @param target the method handle to invoke before filtering the return value
3659 * @param filter method handle to call on the return value
3660 * @return method handle which incorporates the specified return value filtering logic
3661 * @throws NullPointerException if either argument is null
3662 * @throws IllegalArgumentException if the argument list of {@code filter}
3663 * does not match the return type of target as described above
3664 */
3665 public static
3666 MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
3667 MethodType targetType = target.type();
3668 MethodType filterType = filter.type();
3669 filterReturnValueChecks(targetType, filterType);
3670 BoundMethodHandle result = target.rebind();
3671 BasicType rtype = BasicType.basicType(filterType.returnType());
3672 LambdaForm lform = result.editor().filterReturnForm(rtype, false);
3673 MethodType newType = targetType.changeReturnType(filterType.returnType());
3674 result = result.copyWithExtendL(newType, lform, filter);
3675 return result;
3676 }
3677
3678 private static void filterReturnValueChecks(MethodType targetType, MethodType filterType) throws RuntimeException {
3679 Class<?> rtype = targetType.returnType();
3680 int filterValues = filterType.parameterCount();
3681 if (filterValues == 0
3682 ? (rtype != void.class)
3683 : (rtype != filterType.parameterType(0)))
3684 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
3685 }
3686
3687 /**
3688 * Adapts a target method handle by pre-processing
3689 * some of its arguments, and then calling the target with
3690 * the result of the pre-processing, inserted into the original
3691 * sequence of arguments.
3692 * <p>
3693 * The pre-processing is performed by {@code combiner}, a second method handle.
3694 * Of the arguments passed to the adapter, the first {@code N} arguments
3695 * are copied to the combiner, which is then called.
3696 * (Here, {@code N} is defined as the parameter count of the combiner.)
3697 * After this, control passes to the target, with any result
3698 * from the combiner inserted before the original {@code N} incoming
3699 * arguments.
3700 * <p>
3701 * If the combiner returns a value, the first parameter type of the target
3702 * must be identical with the return type of the combiner, and the next
3703 * {@code N} parameter types of the target must exactly match the parameters
3704 * of the combiner.
3705 * <p>
3706 * If the combiner has a void return, no result will be inserted,
3707 * and the first {@code N} parameter types of the target
3708 * must exactly match the parameters of the combiner.
3709 * <p>
3710 * The resulting adapter is the same type as the target, except that the
3711 * first parameter type is dropped,
3712 * if it corresponds to the result of the combiner.
3713 * <p>
3714 * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
3715 * that either the combiner or the target does not wish to receive.
3716 * If some of the incoming arguments are destined only for the combiner,
3717 * consider using {@link MethodHandle#asCollector asCollector} instead, since those
3718 * arguments will not need to be live on the stack on entry to the
3719 * target.)
3720 * <p><b>Example:</b>
3721 * <blockquote><pre>{@code
3722 import static java.lang.invoke.MethodHandles.*;
3723 import static java.lang.invoke.MethodType.*;
3724 ...
3725 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
3726 "println", methodType(void.class, String.class))
3727 .bindTo(System.out);
3728 MethodHandle cat = lookup().findVirtual(String.class,
3729 "concat", methodType(String.class, String.class));
3730 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
3731 MethodHandle catTrace = foldArguments(cat, trace);
3732 // also prints "boo":
3733 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
3734 * }</pre></blockquote>
3735 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
3736 * represents the result type of the {@code target} and resulting adapter.
3737 * {@code V}/{@code v} represent the type and value of the parameter and argument
3738 * of {@code target} that precedes the folding position; {@code V} also is
3739 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
3740 * types and values of the {@code N} parameters and arguments at the folding
3741 * position. {@code B}/{@code b} represent the types and values of the
3742 * {@code target} parameters and arguments that follow the folded parameters
3743 * and arguments.
3744 * <blockquote><pre>{@code
3745 * // there are N arguments in A...
3746 * T target(V, A[N]..., B...);
3747 * V combiner(A...);
3748 * T adapter(A... a, B... b) {
3749 * V v = combiner(a...);
3750 * return target(v, a..., b...);
3751 * }
3752 * // and if the combiner has a void return:
3753 * T target2(A[N]..., B...);
3754 * void combiner2(A...);
3755 * T adapter2(A... a, B... b) {
3756 * combiner2(a...);
3757 * return target2(a..., b...);
3758 * }
3759 * }</pre></blockquote>
3760 * <p>
3761 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3762 * variable-arity method handle}, even if the original target method handle was.
3763 * @param target the method handle to invoke after arguments are combined
3764 * @param combiner method handle to call initially on the incoming arguments
3765 * @return method handle which incorporates the specified argument folding logic
3766 * @throws NullPointerException if either argument is null
3767 * @throws IllegalArgumentException if {@code combiner}'s return type
3768 * is non-void and not the same as the first argument type of
3769 * the target, or if the initial {@code N} argument types
3770 * of the target
3771 * (skipping one matching the {@code combiner}'s return type)
3772 * are not identical with the argument types of {@code combiner}
3773 */
3774 public static
3775 MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
3776 return foldArguments(target, 0, combiner);
3777 }
3778
3779 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType) {
3780 int foldArgs = combinerType.parameterCount();
3781 Class<?> rtype = combinerType.returnType();
3782 int foldVals = rtype == void.class ? 0 : 1;
3783 int afterInsertPos = foldPos + foldVals;
3784 boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
3785 if (ok && !(combinerType.parameterList()
3786 .equals(targetType.parameterList().subList(afterInsertPos,
3787 afterInsertPos + foldArgs))))
3788 ok = false;
3789 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos))
3790 ok = false;
3791 if (!ok)
3792 throw misMatchedTypes("target and combiner types", targetType, combinerType);
3793 return rtype;
3794 }
3795
3796 /**
3797 * Makes a method handle which adapts a target method handle,
3798 * by guarding it with a test, a boolean-valued method handle.
3799 * If the guard fails, a fallback handle is called instead.
3800 * All three method handles must have the same corresponding
3801 * argument and return types, except that the return type
3802 * of the test must be boolean, and the test is allowed
3803 * to have fewer arguments than the other two method handles.
3804 * <p>
3805 * Here is pseudocode for the resulting adapter. In the code, {@code T}
3806 * represents the uniform result type of the three involved handles;
3807 * {@code A}/{@code a}, the types and values of the {@code target}
3808 * parameters and arguments that are consumed by the {@code test}; and
3809 * {@code B}/{@code b}, those types and values of the {@code target}
3810 * parameters and arguments that are not consumed by the {@code test}.
3811 * <blockquote><pre>{@code
3812 * boolean test(A...);
3813 * T target(A...,B...);
3814 * T fallback(A...,B...);
3815 * T adapter(A... a,B... b) {
3816 * if (test(a...))
3817 * return target(a..., b...);
3818 * else
3819 * return fallback(a..., b...);
3820 * }
3821 * }</pre></blockquote>
3822 * Note that the test arguments ({@code a...} in the pseudocode) cannot
3823 * be modified by execution of the test, and so are passed unchanged
3824 * from the caller to the target or fallback as appropriate.
3825 * @param test method handle used for test, must return boolean
3826 * @param target method handle to call if test passes
3827 * @param fallback method handle to call if test fails
3828 * @return method handle which incorporates the specified if/then/else logic
3829 * @throws NullPointerException if any argument is null
3830 * @throws IllegalArgumentException if {@code test} does not return boolean,
3831 * or if all three method types do not match (with the return
3832 * type of {@code test} changed to match that of the target).
3833 */
3834 public static
3835 MethodHandle guardWithTest(MethodHandle test,
3836 MethodHandle target,
3837 MethodHandle fallback) {
3838 MethodType gtype = test.type();
3839 MethodType ttype = target.type();
3840 MethodType ftype = fallback.type();
3841 if (!ttype.equals(ftype))
3842 throw misMatchedTypes("target and fallback types", ttype, ftype);
3843 if (gtype.returnType() != boolean.class)
3844 throw newIllegalArgumentException("guard type is not a predicate "+gtype);
3845 List<Class<?>> targs = ttype.parameterList();
3846 test = dropArgumentsToMatch(test, 0, targs, 0, true);
3847 if (test == null) {
3848 throw misMatchedTypes("target and test types", ttype, gtype);
3849 }
3850 return MethodHandleImpl.makeGuardWithTest(test, target, fallback);
3851 }
3852
3853 static <T> RuntimeException misMatchedTypes(String what, T t1, T t2) {
3854 return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
3855 }
3856
3857 /**
3858 * Makes a method handle which adapts a target method handle,
3859 * by running it inside an exception handler.
3860 * If the target returns normally, the adapter returns that value.
3861 * If an exception matching the specified type is thrown, the fallback
3862 * handle is called instead on the exception, plus the original arguments.
3863 * <p>
3864 * The target and handler must have the same corresponding
3865 * argument and return types, except that handler may omit trailing arguments
3866 * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
3867 * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
3868 * <p>
3869 * Here is pseudocode for the resulting adapter. In the code, {@code T}
3870 * represents the return type of the {@code target} and {@code handler},
3871 * and correspondingly that of the resulting adapter; {@code A}/{@code a},
3872 * the types and values of arguments to the resulting handle consumed by
3873 * {@code handler}; and {@code B}/{@code b}, those of arguments to the
3874 * resulting handle discarded by {@code handler}.
3875 * <blockquote><pre>{@code
3876 * T target(A..., B...);
3877 * T handler(ExType, A...);
3878 * T adapter(A... a, B... b) {
3879 * try {
3880 * return target(a..., b...);
3881 * } catch (ExType ex) {
3882 * return handler(ex, a...);
3883 * }
3884 * }
3885 * }</pre></blockquote>
3886 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
3887 * be modified by execution of the target, and so are passed unchanged
3888 * from the caller to the handler, if the handler is invoked.
3889 * <p>
3890 * The target and handler must return the same type, even if the handler
3891 * always throws. (This might happen, for instance, because the handler
3892 * is simulating a {@code finally} clause).
3893 * To create such a throwing handler, compose the handler creation logic
3894 * with {@link #throwException throwException},
3895 * in order to create a method handle of the correct return type.
3896 * @param target method handle to call
3897 * @param exType the type of exception which the handler will catch
3898 * @param handler method handle to call if a matching exception is thrown
3899 * @return method handle which incorporates the specified try/catch logic
3900 * @throws NullPointerException if any argument is null
3901 * @throws IllegalArgumentException if {@code handler} does not accept
3902 * the given exception type, or if the method handle types do
3903 * not match in their return types and their
3904 * corresponding parameters
3905 * @see MethodHandles#tryFinally(MethodHandle, MethodHandle)
3906 */
3907 public static
3908 MethodHandle catchException(MethodHandle target,
3909 Class<? extends Throwable> exType,
3910 MethodHandle handler) {
3911 MethodType ttype = target.type();
3912 MethodType htype = handler.type();
3913 if (!Throwable.class.isAssignableFrom(exType))
3914 throw new ClassCastException(exType.getName());
3915 if (htype.parameterCount() < 1 ||
3916 !htype.parameterType(0).isAssignableFrom(exType))
3917 throw newIllegalArgumentException("handler does not accept exception type "+exType);
3918 if (htype.returnType() != ttype.returnType())
3919 throw misMatchedTypes("target and handler return types", ttype, htype);
3920 handler = dropArgumentsToMatch(handler, 1, ttype.parameterList(), 0, true);
3921 if (handler == null) {
3922 throw misMatchedTypes("target and handler types", ttype, htype);
3923 }
3924 return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
3925 }
3926
3927 /**
3928 * Produces a method handle which will throw exceptions of the given {@code exType}.
3929 * The method handle will accept a single argument of {@code exType},
3930 * and immediately throw it as an exception.
3931 * The method type will nominally specify a return of {@code returnType}.
3932 * The return type may be anything convenient: It doesn't matter to the
3933 * method handle's behavior, since it will never return normally.
3934 * @param returnType the return type of the desired method handle
3935 * @param exType the parameter type of the desired method handle
3936 * @return method handle which can throw the given exceptions
3937 * @throws NullPointerException if either argument is null
3938 */
3939 public static
3940 MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) {
3941 if (!Throwable.class.isAssignableFrom(exType))
3942 throw new ClassCastException(exType.getName());
3943 return MethodHandleImpl.throwException(methodType(returnType, exType));
3944 }
3945
3946 /**
3947 * Constructs a method handle representing a loop with several loop variables that are updated and checked upon each
3948 * iteration. Upon termination of the loop due to one of the predicates, a corresponding finalizer is run and
3949 * delivers the loop's result, which is the return value of the resulting handle.
3950 * <p>
3951 * Intuitively, every loop is formed by one or more "clauses", each specifying a local iteration value and/or a loop
3952 * exit. Each iteration of the loop executes each clause in order. A clause can optionally update its iteration
3953 * variable; it can also optionally perform a test and conditional loop exit. In order to express this logic in
3954 * terms of method handles, each clause will determine four actions:<ul>
3955 * <li>Before the loop executes, the initialization of an iteration variable or loop invariant local.
3956 * <li>When a clause executes, an update step for the iteration variable.
3957 * <li>When a clause executes, a predicate execution to test for loop exit.
3958 * <li>If a clause causes a loop exit, a finalizer execution to compute the loop's return value.
3959 * </ul>
3960 * <p>
3961 * Some of these clause parts may be omitted according to certain rules, and useful default behavior is provided in
3962 * this case. See below for a detailed description.
3963 * <p>
3964 * Each clause function, with the exception of clause initializers, is able to observe the entire loop state,
3965 * because it will be passed <em>all</em> current iteration variable values, as well as all incoming loop
3966 * parameters. Most clause functions will not need all of this information, but they will be formally connected as
3967 * if by {@link #dropArguments}.
3968 * <p>
3969 * Given a set of clauses, there is a number of checks and adjustments performed to connect all the parts of the
3970 * loop. They are spelled out in detail in the steps below. In these steps, every occurrence of the word "must"
3971 * corresponds to a place where {@link IllegalArgumentException} may be thrown if the required constraint is not met
3972 * by the inputs to the loop combinator. The term "effectively identical", applied to parameter type lists, means
3973 * that they must be identical, or else one list must be a proper prefix of the other.
3974 * <p>
3975 * <em>Step 0: Determine clause structure.</em><ol type="a">
3976 * <li>The clause array (of type {@code MethodHandle[][]} must be non-{@code null} and contain at least one element.
3977 * <li>The clause array may not contain {@code null}s or sub-arrays longer than four elements.
3978 * <li>Clauses shorter than four elements are treated as if they were padded by {@code null} elements to length
3979 * four. Padding takes place by appending elements to the array.
3980 * <li>Clauses with all {@code null}s are disregarded.
3981 * <li>Each clause is treated as a four-tuple of functions, called "init", "step", "pred", and "fini".
3982 * </ol>
3983 * <p>
3984 * <em>Step 1A: Determine iteration variables.</em><ol type="a">
3985 * <li>Examine init and step function return types, pairwise, to determine each clause's iteration variable type.
3986 * <li>If both functions are omitted, use {@code void}; else if one is omitted, use the other's return type; else
3987 * use the common return type (they must be identical).
3988 * <li>Form the list of return types (in clause order), omitting all occurrences of {@code void}.
3989 * <li>This list of types is called the "common prefix".
3990 * </ol>
3991 * <p>
3992 * <em>Step 1B: Determine loop parameters.</em><ul>
3993 * <li><b>If at least one init function is given,</b><ol type="a">
3994 * <li>Examine init function parameter lists.
3995 * <li>Omitted init functions are deemed to have {@code null} parameter lists.
3996 * <li>All init function parameter lists must be effectively identical.
3997 * <li>The longest parameter list (which is necessarily unique) is called the "common suffix".
3998 * </ol>
3999 * <li><b>If no init function is given,</b><ol type="a">
4000 * <li>Examine the suffixes of the step, pred, and fini parameter lists, after removing the "common prefix".
4001 * <li>The longest of these suffixes is taken as the "common suffix".
4002 * </ol></ul>
4003 * <p>
4004 * <em>Step 1C: Determine loop return type.</em><ol type="a">
4005 * <li>Examine fini function return types, disregarding omitted fini functions.
4006 * <li>If there are no fini functions, use {@code void} as the loop return type.
4007 * <li>Otherwise, use the common return type of the fini functions; they must all be identical.
4008 * </ol>
4009 * <p>
4010 * <em>Step 1D: Check other types.</em><ol type="a">
4011 * <li>There must be at least one non-omitted pred function.
4012 * <li>Every non-omitted pred function must have a {@code boolean} return type.
4013 * </ol>
4014 * <p>
4015 * <em>Step 2: Determine parameter lists.</em><ol type="a">
4016 * <li>The parameter list for the resulting loop handle will be the "common suffix".
4017 * <li>The parameter list for init functions will be adjusted to the "common suffix". (Note that their parameter
4018 * lists are already effectively identical to the common suffix.)
4019 * <li>The parameter list for non-init (step, pred, and fini) functions will be adjusted to the common prefix
4020 * followed by the common suffix, called the "common parameter sequence".
4021 * <li>Every non-init, non-omitted function parameter list must be effectively identical to the common parameter
4022 * sequence.
4023 * </ol>
4024 * <p>
4025 * <em>Step 3: Fill in omitted functions.</em><ol type="a">
4026 * <li>If an init function is omitted, use a {@linkplain #constant constant function} of the appropriate
4027 * {@code null}/zero/{@code false}/{@code void} type. (For this purpose, a constant {@code void} is simply a
4028 * function which does nothing and returns {@code void}; it can be obtained from another constant function by
4029 * {@linkplain MethodHandle#asType type conversion}.)
4030 * <li>If a step function is omitted, use an {@linkplain #identity identity function} of the clause's iteration
4031 * variable type; insert dropped argument parameters before the identity function parameter for the non-{@code void}
4032 * iteration variables of preceding clauses. (This will turn the loop variable into a local loop invariant.)
4033 * <li>If a pred function is omitted, the corresponding fini function must also be omitted.
4034 * <li>If a pred function is omitted, use a constant {@code true} function. (This will keep the loop going, as far
4035 * as this clause is concerned.)
4036 * <li>If a fini function is omitted, use a constant {@code null}/zero/{@code false}/{@code void} function of the
4037 * loop return type.
4038 * </ol>
4039 * <p>
4040 * <em>Step 4: Fill in missing parameter types.</em><ol type="a">
4041 * <li>At this point, every init function parameter list is effectively identical to the common suffix, but some
4042 * lists may be shorter. For every init function with a short parameter list, pad out the end of the list by
4043 * {@linkplain #dropArguments dropping arguments}.
4044 * <li>At this point, every non-init function parameter list is effectively identical to the common parameter
4045 * sequence, but some lists may be shorter. For every non-init function with a short parameter list, pad out the end
4046 * of the list by {@linkplain #dropArguments dropping arguments}.
4047 * </ol>
4048 * <p>
4049 * <em>Final observations.</em><ol type="a">
4050 * <li>After these steps, all clauses have been adjusted by supplying omitted functions and arguments.
4051 * <li>All init functions have a common parameter type list, which the final loop handle will also have.
4052 * <li>All fini functions have a common return type, which the final loop handle will also have.
4053 * <li>All non-init functions have a common parameter type list, which is the common parameter sequence, of
4054 * (non-{@code void}) iteration variables followed by loop parameters.
4055 * <li>Each pair of init and step functions agrees in their return types.
4056 * <li>Each non-init function will be able to observe the current values of all iteration variables, by means of the
4057 * common prefix.
4058 * </ol>
4059 * <p>
4060 * <em>Loop execution.</em><ol type="a">
4061 * <li>When the loop is called, the loop input values are saved in locals, to be passed (as the common suffix) to
4062 * every clause function. These locals are loop invariant.
4063 * <li>Each init function is executed in clause order (passing the common suffix) and the non-{@code void} values
4064 * are saved (as the common prefix) into locals. These locals are loop varying (unless their steps are identity
4065 * functions, as noted above).
4066 * <li>All function executions (except init functions) will be passed the common parameter sequence, consisting of
4067 * the non-{@code void} iteration values (in clause order) and then the loop inputs (in argument order).
4068 * <li>The step and pred functions are then executed, in clause order (step before pred), until a pred function
4069 * returns {@code false}.
4070 * <li>The non-{@code void} result from a step function call is used to update the corresponding loop variable. The
4071 * updated value is immediately visible to all subsequent function calls.
4072 * <li>If a pred function returns {@code false}, the corresponding fini function is called, and the resulting value
4073 * is returned from the loop as a whole.
4074 * </ol>
4075 * <p>
4076 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the types / values
4077 * of loop variables; {@code A}/{@code a}, those of arguments passed to the resulting loop; and {@code R}, the
4078 * result types of finalizers as well as of the resulting loop.
4079 * <blockquote><pre>{@code
4080 * V... init...(A...);
4081 * boolean pred...(V..., A...);
4082 * V... step...(V..., A...);
4083 * R fini...(V..., A...);
4084 * R loop(A... a) {
4085 * V... v... = init...(a...);
4086 * for (;;) {
4087 * for ((v, p, s, f) in (v..., pred..., step..., fini...)) {
4088 * v = s(v..., a...);
4089 * if (!p(v..., a...)) {
4090 * return f(v..., a...);
4091 * }
4092 * }
4093 * }
4094 * }
4095 * }</pre></blockquote>
4096 * <p>
4097 * @apiNote Example:
4098 * <blockquote><pre>{@code
4099 * // iterative implementation of the factorial function as a loop handle
4100 * static int one(int k) { return 1; }
4101 * static int inc(int i, int acc, int k) { return i + 1; }
4102 * static int mult(int i, int acc, int k) { return i * acc; }
4103 * static boolean pred(int i, int acc, int k) { return i < k; }
4104 * static int fin(int i, int acc, int k) { return acc; }
4105 * // assume MH_one, MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
4106 * // null initializer for counter, should initialize to 0
4107 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
4108 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
4109 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
4110 * assertEquals(120, loop.invoke(5));
4111 * }</pre></blockquote>
4112 *
4113 * @param clauses an array of arrays (4-tuples) of {@link MethodHandle}s adhering to the rules described above.
4114 *
4115 * @return a method handle embodying the looping behavior as defined by the arguments.
4116 *
4117 * @throws IllegalArgumentException in case any of the constraints described above is violated.
4118 *
4119 * @see MethodHandles#whileLoop(MethodHandle, MethodHandle, MethodHandle)
4120 * @see MethodHandles#doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
4121 * @see MethodHandles#countedLoop(MethodHandle, MethodHandle, MethodHandle)
4122 * @see MethodHandles#iteratedLoop(MethodHandle, MethodHandle, MethodHandle)
4123 * @since 9
4124 */
4125 public static MethodHandle loop(MethodHandle[]... clauses) {
4126 // Step 0: determine clause structure.
4127 checkLoop0(clauses);
4128
4129 List<MethodHandle> init = new ArrayList<>();
4130 List<MethodHandle> step = new ArrayList<>();
4131 List<MethodHandle> pred = new ArrayList<>();
4132 List<MethodHandle> fini = new ArrayList<>();
4133
4134 Stream.of(clauses).filter(c -> Stream.of(c).anyMatch(Objects::nonNull)).forEach(clause -> {
4135 init.add(clause[0]); // all clauses have at least length 1
4136 step.add(clause.length <= 1 ? null : clause[1]);
4137 pred.add(clause.length <= 2 ? null : clause[2]);
4138 fini.add(clause.length <= 3 ? null : clause[3]);
4139 });
4140
4141 assert Stream.of(init, step, pred, fini).map(List::size).distinct().count() == 1;
4142 final int nclauses = init.size();
4143
4144 // Step 1A: determine iteration variables.
4145 final List<Class<?>> iterationVariableTypes = new ArrayList<>();
4146 for (int i = 0; i < nclauses; ++i) {
4147 MethodHandle in = init.get(i);
4148 MethodHandle st = step.get(i);
4149 if (in == null && st == null) {
4150 iterationVariableTypes.add(void.class);
4151 } else if (in != null && st != null) {
4152 checkLoop1a(i, in, st);
4153 iterationVariableTypes.add(in.type().returnType());
4154 } else {
4155 iterationVariableTypes.add(in == null ? st.type().returnType() : in.type().returnType());
4156 }
4157 }
4158 final List<Class<?>> commonPrefix = iterationVariableTypes.stream().filter(t -> t != void.class).
4159 collect(Collectors.toList());
4160
4161 // Step 1B: determine loop parameters.
4162 final List<Class<?>> commonSuffix = buildCommonSuffix(init, step, pred, fini, commonPrefix.size());
4163 checkLoop1b(init, commonSuffix);
4164
4165 // Step 1C: determine loop return type.
4166 // Step 1D: check other types.
4167 final Class<?> loopReturnType = fini.stream().filter(Objects::nonNull).map(MethodHandle::type).
4168 map(MethodType::returnType).findFirst().orElse(void.class);
4169 checkLoop1cd(pred, fini, loopReturnType);
4170
4171 // Step 2: determine parameter lists.
4172 final List<Class<?>> commonParameterSequence = new ArrayList<>(commonPrefix);
4173 commonParameterSequence.addAll(commonSuffix);
4174 checkLoop2(step, pred, fini, commonParameterSequence);
4175
4176 // Step 3: fill in omitted functions.
4177 for (int i = 0; i < nclauses; ++i) {
4178 Class<?> t = iterationVariableTypes.get(i);
4179 if (init.get(i) == null) {
4180 init.set(i, empty(methodType(t, commonSuffix)));
4181 }
4182 if (step.get(i) == null) {
4183 step.set(i, dropArgumentsToMatch(identityOrVoid(t), 0, commonParameterSequence, i));
4184 }
4185 if (pred.get(i) == null) {
4186 pred.set(i, dropArguments(constant(boolean.class, true), 0, commonParameterSequence));
4187 }
4188 if (fini.get(i) == null) {
4189 fini.set(i, empty(methodType(t, commonParameterSequence)));
4190 }
4191 }
4192
4193 // Step 4: fill in missing parameter types.
4194 List<MethodHandle> finit = fillParameterTypes(init, commonSuffix);
4195 List<MethodHandle> fstep = fillParameterTypes(step, commonParameterSequence);
4196 List<MethodHandle> fpred = fillParameterTypes(pred, commonParameterSequence);
4197 List<MethodHandle> ffini = fillParameterTypes(fini, commonParameterSequence);
4198
4199 assert finit.stream().map(MethodHandle::type).map(MethodType::parameterList).
4200 allMatch(pl -> pl.equals(commonSuffix));
4201 assert Stream.of(fstep, fpred, ffini).flatMap(List::stream).map(MethodHandle::type).map(MethodType::parameterList).
4202 allMatch(pl -> pl.equals(commonParameterSequence));
4203
4204 return MethodHandleImpl.makeLoop(loopReturnType, commonSuffix, commonPrefix, finit, fstep, fpred, ffini);
4205 }
4206
4207 private static List<MethodHandle> fillParameterTypes(List<MethodHandle> hs, final List<Class<?>> targetParams) {
4208 return hs.stream().map(h -> {
4209 int pc = h.type().parameterCount();
4210 int tpsize = targetParams.size();
4211 return pc < tpsize ? dropArguments(h, pc, targetParams.subList(pc, tpsize)) : h;
4212 }).collect(Collectors.toList());
4213 }
4214
4215 /**
4216 * Constructs a {@code while} loop from an initializer, a body, and a predicate. This is a convenience wrapper for
4217 * the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
4218 * <p>
4219 * The loop handle's result type is the same as the sole loop variable's, i.e., the result type of {@code init}.
4220 * The parameter type list of {@code init} also determines that of the resulting handle. The {@code pred} handle
4221 * must have an additional leading parameter of the same type as {@code init}'s result, and so must the {@code
4222 * body}. These constraints follow directly from those described for the {@linkplain MethodHandles#loop(MethodHandle[][])
4223 * generic loop combinator}.
4224 * <p>
4225 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
4226 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
4227 * passed to the loop.
4228 * <blockquote><pre>{@code
4229 * V init(A);
4230 * boolean pred(V, A);
4231 * V body(V, A);
4232 * V whileLoop(A a) {
4233 * V v = init(a);
4234 * while (pred(v, a)) {
4235 * v = body(v, a);
4236 * }
4237 * return v;
4238 * }
4239 * }</pre></blockquote>
4240 * <p>
4241 * @apiNote Example:
4242 * <blockquote><pre>{@code
4243 * // implement the zip function for lists as a loop handle
4244 * static List<String> initZip(Iterator<String> a, Iterator<String> b) { return new ArrayList<>(); }
4245 * static boolean zipPred(List<String> zip, Iterator<String> a, Iterator<String> b) { return a.hasNext() && b.hasNext(); }
4246 * static List<String> zipStep(List<String> zip, Iterator<String> a, Iterator<String> b) {
4247 * zip.add(a.next());
4248 * zip.add(b.next());
4249 * return zip;
4250 * }
4251 * // assume MH_initZip, MH_zipPred, and MH_zipStep are handles to the above methods
4252 * MethodHandle loop = MethodHandles.whileLoop(MH_initZip, MH_zipPred, MH_zipStep);
4253 * List<String> a = Arrays.asList("a", "b", "c", "d");
4254 * List<String> b = Arrays.asList("e", "f", "g", "h");
4255 * List<String> zipped = Arrays.asList("a", "e", "b", "f", "c", "g", "d", "h");
4256 * assertEquals(zipped, (List<String>) loop.invoke(a.iterator(), b.iterator()));
4257 * }</pre></blockquote>
4258 *
4259 * <p>
4260 * @implSpec The implementation of this method is equivalent to:
4261 * <blockquote><pre>{@code
4262 * MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
4263 * MethodHandle[]
4264 * checkExit = {null, null, pred, identity(init.type().returnType())},
4265 * varBody = {init, body};
4266 * return loop(checkExit, varBody);
4267 * }
4268 * }</pre></blockquote>
4269 *
4270 * @param init initializer: it should provide the initial value of the loop variable. This controls the loop's
4271 * result type. Passing {@code null} or a {@code void} init function will make the loop's result type
4272 * {@code void}.
4273 * @param pred condition for the loop, which may not be {@code null}.
4274 * @param body body of the loop, which may not be {@code null}.
4275 *
4276 * @return the value of the loop variable as the loop terminates.
4277 * @throws IllegalArgumentException if any argument has a type inconsistent with the loop structure
4278 *
4279 * @see MethodHandles#loop(MethodHandle[][])
4280 * @since 9
4281 */
4282 public static MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
4283 MethodHandle fin = init == null || init.type().returnType() == void.class ? zero(void.class) :
4284 identity(init.type().returnType());
4285 MethodHandle[] checkExit = {null, null, pred, fin};
4286 MethodHandle[] varBody = {init, body};
4287 return loop(checkExit, varBody);
4288 }
4289
4290 /**
4291 * Constructs a {@code do-while} loop from an initializer, a body, and a predicate. This is a convenience wrapper
4292 * for the {@linkplain MethodHandles#loop(MethodHandle[][]) generic loop combinator}.
4293 * <p>
4294 * The loop handle's result type is the same as the sole loop variable's, i.e., the result type of {@code init}.
4295 * The parameter type list of {@code init} also determines that of the resulting handle. The {@code pred} handle
4296 * must have an additional leading parameter of the same type as {@code init}'s result, and so must the {@code
4297 * body}. These constraints follow directly from those described for the {@linkplain MethodHandles#loop(MethodHandle[][])
4298 * generic loop combinator}.
4299 * <p>
4300 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
4301 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
4302 * passed to the loop.
4303 * <blockquote><pre>{@code
4304 * V init(A);
4305 * boolean pred(V, A);
4306 * V body(V, A);
4307 * V doWhileLoop(A a) {
4308 * V v = init(a);
4309 * do {
4310 * v = body(v, a);
4311 * } while (pred(v, a));
4312 * return v;
4313 * }
4314 * }</pre></blockquote>
4315 * <p>
4316 * @apiNote Example:
4317 * <blockquote><pre>{@code
4318 * // int i = 0; while (i < limit) { ++i; } return i; => limit
4319 * static int zero(int limit) { return 0; }
4320 * static int step(int i, int limit) { return i + 1; }
4321 * static boolean pred(int i, int limit) { return i < limit; }
4322 * // assume MH_zero, MH_step, and MH_pred are handles to the above methods
4323 * MethodHandle loop = MethodHandles.doWhileLoop(MH_zero, MH_step, MH_pred);
4324 * assertEquals(23, loop.invoke(23));
4325 * }</pre></blockquote>
4326 *
4327 * <p>
4328 * @implSpec The implementation of this method is equivalent to:
4329 * <blockquote><pre>{@code
4330 * MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
4331 * MethodHandle[] clause = { init, body, pred, identity(init.type().returnType()) };
4332 * return loop(clause);
4333 * }
4334 * }</pre></blockquote>
4335 *
4336 *
4337 * @param init initializer: it should provide the initial value of the loop variable. This controls the loop's
4338 * result type. Passing {@code null} or a {@code void} init function will make the loop's result type
4339 * {@code void}.
4340 * @param pred condition for the loop, which may not be {@code null}.
4341 * @param body body of the loop, which may not be {@code null}.
4342 *
4343 * @return the value of the loop variable as the loop terminates.
4344 * @throws IllegalArgumentException if any argument has a type inconsistent with the loop structure
4345 *
4346 * @see MethodHandles#loop(MethodHandle[][])
4347 * @since 9
4348 */
4349 public static MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
4350 MethodHandle fin = init == null || init.type().returnType() == void.class ? zero(void.class) :
4351 identity(init.type().returnType());
4352 MethodHandle[] clause = {init, body, pred, fin};
4353 return loop(clause);
4354 }
4355
4356 /**
4357 * Constructs a loop that runs a given number of iterations. The loop counter is an {@code int} initialized from the
4358 * {@code iterations} handle evaluation result. The counter is passed to the {@code body} function, so that must
4359 * accept an initial {@code int} argument. The result of the loop execution is the final value of the additional
4360 * local state. This is a convenience wrapper for the {@linkplain MethodHandles#loop(MethodHandle[][]) generic loop
4361 * combinator}.
4362 * <p>
4363 * The result type and parameter type list of {@code init} determine those of the resulting handle. The {@code
4364 * iterations} handle must accept the same parameter types as {@code init} but return an {@code int}. The {@code
4365 * body} handle must accept the same parameter types as well, preceded by an {@code int} parameter for the counter,
4366 * and a parameter of the same type as {@code init}'s result. These constraints follow directly from those described
4367 * for the {@linkplain MethodHandles#loop(MethodHandle[][]) generic loop combinator}.
4368 * <p>
4369 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
4370 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
4371 * passed to the loop.
4372 * <blockquote><pre>{@code
4373 * int iterations(A);
4374 * V init(A);
4375 * V body(int, V, A);
4376 * V countedLoop(A a) {
4377 * int end = iterations(a);
4378 * V v = init(a);
4379 * for (int i = 0; i < end; ++i) {
4380 * v = body(i, v, a);
4381 * }
4382 * return v;
4383 * }
4384 * }</pre></blockquote>
4385 * <p>
4386 * @apiNote Example:
4387 * <blockquote><pre>{@code
4388 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
4389 * // => a variation on a well known theme
4390 * static String start(String arg) { return arg; }
4391 * static String step(int counter, String v, String arg) { return "na " + v; }
4392 * // assume MH_start and MH_step are handles to the two methods above
4393 * MethodHandle fit13 = MethodHandles.constant(int.class, 13);
4394 * MethodHandle loop = MethodHandles.countedLoop(fit13, MH_start, MH_step);
4395 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("Lambdaman!"));
4396 * }</pre></blockquote>
4397 *
4398 * <p>
4399 * @implSpec The implementation of this method is equivalent to:
4400 * <blockquote><pre>{@code
4401 * MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
4402 * return countedLoop(null, iterations, init, body); // null => constant zero
4403 * }
4404 * }</pre></blockquote>
4405 *
4406 * @param iterations a handle to return the number of iterations this loop should run.
4407 * @param init initializer for additional loop state. This determines the loop's result type.
4408 * Passing {@code null} or a {@code void} init function will make the loop's result type
4409 * {@code void}.
4410 * @param body the body of the loop, which must not be {@code null}.
4411 * It must accept an initial {@code int} parameter (for the counter), and then any
4412 * additional loop-local variable plus loop parameters.
4413 *
4414 * @return a method handle representing the loop.
4415 * @throws IllegalArgumentException if any argument has a type inconsistent with the loop structure
4416 *
4417 * @since 9
4418 */
4419 public static MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
4420 return countedLoop(null, iterations, init, body);
4421 }
4422
4423 /**
4424 * Constructs a loop that counts over a range of numbers. The loop counter is an {@code int} that will be
4425 * initialized to the {@code int} value returned from the evaluation of the {@code start} handle and run to the
4426 * value returned from {@code end} (exclusively) with a step width of 1. The counter value is passed to the {@code
4427 * body} function in each iteration; it has to accept an initial {@code int} parameter
4428 * for that. The result of the loop execution is the final value of the additional local state
4429 * obtained by running {@code init}.
4430 * This is a
4431 * convenience wrapper for the {@linkplain MethodHandles#loop(MethodHandle[][]) generic loop combinator}.
4432 * <p>
4433 * The constraints for the {@code init} and {@code body} handles are the same as for {@link
4434 * #countedLoop(MethodHandle, MethodHandle, MethodHandle)}. Additionally, the {@code start} and {@code end} handles
4435 * must return an {@code int} and accept the same parameters as {@code init}.
4436 * <p>
4437 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
4438 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
4439 * passed to the loop.
4440 * <blockquote><pre>{@code
4441 * int start(A);
4442 * int end(A);
4443 * V init(A);
4444 * V body(int, V, A);
4445 * V countedLoop(A a) {
4446 * int s = start(a);
4447 * int e = end(a);
4448 * V v = init(a);
4449 * for (int i = s; i < e; ++i) {
4450 * v = body(i, v, a);
4451 * }
4452 * return v;
4453 * }
4454 * }</pre></blockquote>
4455 *
4456 * <p>
4457 * @implSpec The implementation of this method is equivalent to:
4458 * <blockquote><pre>{@code
4459 * MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
4460 * MethodHandle returnVar = dropArguments(identity(init.type().returnType()), 0, int.class, int.class);
4461 * // assume MH_increment and MH_lessThan are handles to x+1 and x<y of type int,
4462 * // assume MH_decrement is a handle to x-1 of type int
4463 * MethodHandle[]
4464 * indexVar = {start, MH_increment}, // i = start; i = i+1
4465 * loopLimit = {end, null, MH_lessThan, returnVar }, // i<end
4466 * bodyClause = {init,
4467 * filterArgument(dropArguments(body, 1, int.class), 0, MH_decrement}; // v = body(i-1, v)
4468 * return loop(indexVar, loopLimit, bodyClause);
4469 * }
4470 * }</pre></blockquote>
4471 *
4472 * @param start a handle to return the start value of the loop counter.
4473 * If it is {@code null}, a constant zero is assumed.
4474 * @param end a non-{@code null} handle to return the end value of the loop counter (the loop will run to {@code end-1}).
4475 * @param init initializer for additional loop state. This determines the loop's result type.
4476 * Passing {@code null} or a {@code void} init function will make the loop's result type
4477 * {@code void}.
4478 * @param body the body of the loop, which must not be {@code null}.
4479 * It must accept an initial {@code int} parameter (for the counter), and then any
4480 * additional loop-local variable plus loop parameters.
4481 *
4482 * @return a method handle representing the loop.
4483 * @throws IllegalArgumentException if any argument has a type inconsistent with the loop structure
4484 *
4485 * @since 9
4486 */
4487 public static MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
4488 Class<?> resultType;
4489 MethodHandle actualInit;
4490 if (init == null) {
4491 resultType = body == null ? void.class : body.type().returnType();
4492 actualInit = empty(methodType(resultType));
4493 } else {
4494 resultType = init.type().returnType();
4495 actualInit = init;
4496 }
4497 MethodHandle defaultResultHandle = resultType == void.class ? zero(void.class) : identity(resultType);
4498 MethodHandle actualBody = body == null ? dropArguments(defaultResultHandle, 0, int.class) : body;
4499 MethodHandle returnVar = dropArguments(defaultResultHandle, 0, int.class, int.class);
4500 MethodHandle actualEnd = end == null ? constant(int.class, 0) : end;
4501 MethodHandle[] indexVar = {start, MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopStep)};
4502 MethodHandle[] loopLimit = {actualEnd, null,
4503 MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopPred), returnVar};
4504 MethodHandle[] bodyClause = {actualInit,
4505 filterArgument(dropArguments(actualBody, 1, int.class), 0,
4506 MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_decrementCounter))};
4507 return loop(indexVar, loopLimit, bodyClause);
4508 }
4509
4510 /**
4511 * Constructs a loop that ranges over the elements produced by an {@code Iterator<T>}.
4512 * The iterator will be produced by the evaluation of the {@code iterator} handle.
4513 * This handle must have {@link java.util.Iterator} as its return type.
4514 * If this handle is passed as {@code null} the method {@link Iterable#iterator} will be used instead,
4515 * and will be applied to a leading argument of the loop handle.
4516 * Each value produced by the iterator is passed to the {@code body}, which must accept an initial {@code T} parameter.
4517 * The result of the loop execution is the final value of the additional local state
4518 * obtained by running {@code init}.
4519 * <p>
4520 * This is a convenience wrapper for the
4521 * {@linkplain MethodHandles#loop(MethodHandle[][]) generic loop combinator}, and the constraints imposed on the {@code body}
4522 * handle follow directly from those described for the latter.
4523 * <p>
4524 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
4525 * the loop variable as well as the result type of the loop; {@code T}/{@code t}, that of the elements of the
4526 * structure the loop iterates over, and {@code A}/{@code a}, that of the argument passed to the loop.
4527 * <blockquote><pre>{@code
4528 * Iterator<T> iterator(A); // defaults to Iterable::iterator
4529 * V init(A);
4530 * V body(T,V,A);
4531 * V iteratedLoop(A a) {
4532 * Iterator<T> it = iterator(a);
4533 * V v = init(a);
4534 * for (T t : it) {
4535 * v = body(t, v, a);
4536 * }
4537 * return v;
4538 * }
4539 * }</pre></blockquote>
4540 * <p>
4541 * The type {@code T} may be either a primitive or reference.
4542 * Since type {@code Iterator<T>} is erased in the method handle representation to the raw type
4543 * {@code Iterator}, the {@code iteratedLoop} combinator adjusts the leading argument type for {@code body}
4544 * to {@code Object} as if by the {@link MethodHandle#asType asType} conversion method.
4545 * Therefore, if an iterator of the wrong type appears as the loop is executed,
4546 * runtime exceptions may occur as the result of dynamic conversions performed by {@code asType}.
4547 * <p>
4548 * @apiNote Example:
4549 * <blockquote><pre>{@code
4550 * // reverse a list
4551 * static List<String> reverseStep(String e, List<String> r, List<String> l) {
4552 * r.add(0, e);
4553 * return r;
4554 * }
4555 * static List<String> newArrayList(List<String> l) { return new ArrayList<>(); }
4556 * // assume MH_reverseStep, MH_newArrayList are handles to the above methods
4557 * MethodHandle loop = MethodHandles.iteratedLoop(null, MH_newArrayList, MH_reverseStep);
4558 * List<String> list = Arrays.asList("a", "b", "c", "d", "e");
4559 * List<String> reversedList = Arrays.asList("e", "d", "c", "b", "a");
4560 * assertEquals(reversedList, (List<String>) loop.invoke(list));
4561 * }</pre></blockquote>
4562 * <p>
4563 * @implSpec The implementation of this method is equivalent to (excluding error handling):
4564 * <blockquote><pre>{@code
4565 * MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
4566 * // assume MH_next and MH_hasNext are handles to methods of Iterator
4567 * Class<?> itype = iterator.type().returnType();
4568 * Class<?> ttype = body.type().parameterType(0);
4569 * MethodHandle returnVar = dropArguments(identity(init.type().returnType()), 0, itype);
4570 * MethodHandle nextVal = MH_next.asType(MH_next.type().changeReturnType(ttype));
4571 * MethodHandle[]
4572 * iterVar = {iterator, null, MH_hasNext, returnVar}, // it = iterator(); while (it.hasNext)
4573 * bodyClause = {init, filterArgument(body, 0, nextVal)}; // v = body(t, v, a);
4574 * return loop(iterVar, bodyClause);
4575 * }
4576 * }</pre></blockquote>
4577 *
4578 * @param iterator a handle to return the iterator to start the loop.
4579 * The handle must have {@link java.util.Iterator} as its return type.
4580 * Passing {@code null} will make the loop call {@link Iterable#iterator()} on the first
4581 * incoming value.
4582 * @param init initializer for additional loop state. This determines the loop's result type.
4583 * Passing {@code null} or a {@code void} init function will make the loop's result type
4584 * {@code void}.
4585 * @param body the body of the loop, which must not be {@code null}.
4586 * It must accept an initial {@code T} parameter (for the iterated values), and then any
4587 * additional loop-local variable plus loop parameters.
4588 *
4589 * @return a method handle embodying the iteration loop functionality.
4590 * @throws IllegalArgumentException if any argument has a type inconsistent with the loop structure
4591 *
4592 * @since 9
4593 */
4594 public static MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
4595 checkIteratedLoop(iterator, body);
4596 Class<?> resultType = init == null ?
4597 body == null ? void.class : body.type().returnType() :
4598 init.type().returnType();
4599 boolean voidResult = resultType == void.class;
4600
4601 MethodHandle initIterator;
4602 if (iterator == null) {
4603 MethodHandle initit = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_initIterator);
4604 initIterator = initit.asType(initit.type().changeParameterType(0,
4605 body.type().parameterType(voidResult ? 1 : 2)));
4606 } else {
4607 initIterator = iterator.asType(iterator.type().changeReturnType(Iterator.class));
4608 }
4609
4610 Class<?> ttype = body.type().parameterType(0);
4611
4612 MethodHandle returnVar =
4613 dropArguments(voidResult ? zero(void.class) : identity(resultType), 0, Iterator.class);
4614 MethodHandle initnx = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iterateNext);
4615 MethodHandle nextVal = initnx.asType(initnx.type().changeReturnType(ttype));
4616
4617 MethodHandle[] iterVar = {initIterator, null, MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iteratePred),
4618 returnVar};
4619 MethodHandle[] bodyClause = {init, filterArgument(body, 0, nextVal)};
4620
4621 return loop(iterVar, bodyClause);
4622 }
4623
4624 /**
4625 * Makes a method handle that adapts a {@code target} method handle by wrapping it in a {@code try-finally} block.
4626 * Another method handle, {@code cleanup}, represents the functionality of the {@code finally} block. Any exception
4627 * thrown during the execution of the {@code target} handle will be passed to the {@code cleanup} handle. The
4628 * exception will be rethrown, unless {@code cleanup} handle throws an exception first. The
4629 * value returned from the {@code cleanup} handle's execution will be the result of the execution of the
4630 * {@code try-finally} handle.
4631 * <p>
4632 * The {@code cleanup} handle will be passed one or two additional leading arguments.
4633 * The first is the exception thrown during the
4634 * execution of the {@code target} handle, or {@code null} if no exception was thrown.
4635 * The second is the result of the execution of the {@code target} handle, or, if it throws an exception,
4636 * a {@code null}, zero, or {@code false} value of the required type is supplied as a placeholder.
4637 * The second argument is not present if the {@code target} handle has a {@code void} return type.
4638 * (Note that, except for argument type conversions, combinators represent {@code void} values in parameter lists
4639 * by omitting the corresponding paradoxical arguments, not by inserting {@code null} or zero values.)
4640 * <p>
4641 * The {@code target} and {@code cleanup} handles must have the same corresponding argument and return types, except
4642 * that the {@code cleanup} handle may omit trailing arguments. Also, the {@code cleanup} handle must have one or
4643 * two extra leading parameters:<ul>
4644 * <li>a {@code Throwable}, which will carry the exception thrown by the {@code target} handle (if any); and
4645 * <li>a parameter of the same type as the return type of both {@code target} and {@code cleanup}, which will carry
4646 * the result from the execution of the {@code target} handle.
4647 * This parameter is not present if the {@code target} returns {@code void}.
4648 * </ul>
4649 * <p>
4650 * The pseudocode for the resulting adapter looks as follows. In the code, {@code V} represents the result type of
4651 * the {@code try/finally} construct; {@code A}/{@code a}, the types and values of arguments to the resulting
4652 * handle consumed by the cleanup; and {@code B}/{@code b}, those of arguments to the resulting handle discarded by
4653 * the cleanup.
4654 * <blockquote><pre>{@code
4655 * V target(A..., B...);
4656 * V cleanup(Throwable, V, A...);
4657 * V adapter(A... a, B... b) {
4658 * V result = (zero value for V);
4659 * Throwable throwable = null;
4660 * try {
4661 * result = target(a..., b...);
4662 * } catch (Throwable t) {
4663 * throwable = t;
4664 * throw t;
4665 * } finally {
4666 * result = cleanup(throwable, result, a...);
4667 * }
4668 * return result;
4669 * }
4670 * }</pre></blockquote>
4671 * <p>
4672 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
4673 * be modified by execution of the target, and so are passed unchanged
4674 * from the caller to the cleanup, if it is invoked.
4675 * <p>
4676 * The target and cleanup must return the same type, even if the cleanup
4677 * always throws.
4678 * To create such a throwing cleanup, compose the cleanup logic
4679 * with {@link #throwException throwException},
4680 * in order to create a method handle of the correct return type.
4681 * <p>
4682 * Note that {@code tryFinally} never converts exceptions into normal returns.
4683 * In rare cases where exceptions must be converted in that way, first wrap
4684 * the target with {@link #catchException(MethodHandle, Class, MethodHandle)}
4685 * to capture an outgoing exception, and then wrap with {@code tryFinally}.
4686 *
4687 * @param target the handle whose execution is to be wrapped in a {@code try} block.
4688 * @param cleanup the handle that is invoked in the finally block.
4689 *
4690 * @return a method handle embodying the {@code try-finally} block composed of the two arguments.
4691 * @throws NullPointerException if any argument is null
4692 * @throws IllegalArgumentException if {@code cleanup} does not accept
4693 * the required leading arguments, or if the method handle types do
4694 * not match in their return types and their
4695 * corresponding trailing parameters
4696 *
4697 * @see MethodHandles#catchException(MethodHandle, Class, MethodHandle)
4698 * @since 9
4699 */
4700 public static MethodHandle tryFinally(MethodHandle target, MethodHandle cleanup) {
4701 List<Class<?>> targetParamTypes = target.type().parameterList();
4702 List<Class<?>> cleanupParamTypes = cleanup.type().parameterList();
4703 Class<?> rtype = target.type().returnType();
4704
4705 checkTryFinally(target, cleanup);
4706
4707 // Match parameter lists: if the cleanup has a shorter parameter list than the target, add ignored arguments.
4708 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
4709 // target parameter list.
4710 cleanup = dropArgumentsToMatch(cleanup, (rtype == void.class ? 1 : 2), targetParamTypes, 0);
4711 MethodHandle aTarget = target.asSpreader(Object[].class, target.type().parameterCount());
4712 MethodHandle aCleanup = cleanup.asSpreader(Object[].class, targetParamTypes.size());
4713
4714 return MethodHandleImpl.makeTryFinally(aTarget, aCleanup, rtype, targetParamTypes);
4715 }
4716
4717 /**
4718 * Adapts a target method handle by pre-processing some of its arguments, starting at a given position, and then
4719 * calling the target with the result of the pre-processing, inserted into the original sequence of arguments just
4720 * before the folded arguments.
4721 * <p>
4722 * This method is closely related to {@link #foldArguments(MethodHandle, MethodHandle)}, but allows to control the
4723 * position in the parameter list at which folding takes place. The argument controlling this, {@code pos}, is a
4724 * zero-based index. The aforementioned method {@link #foldArguments(MethodHandle, MethodHandle)} assumes position
4725 * 0.
4726 * <p>
4727 * @apiNote Example:
4728 * <blockquote><pre>{@code
4729 import static java.lang.invoke.MethodHandles.*;
4730 import static java.lang.invoke.MethodType.*;
4731 ...
4732 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
4733 "println", methodType(void.class, String.class))
4734 .bindTo(System.out);
4735 MethodHandle cat = lookup().findVirtual(String.class,
4736 "concat", methodType(String.class, String.class));
4737 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
4738 MethodHandle catTrace = foldArguments(cat, 1, trace);
4739 // also prints "jum":
4740 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
4741 * }</pre></blockquote>
4742 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
4743 * represents the result type of the {@code target} and resulting adapter.
4744 * {@code V}/{@code v} represent the type and value of the parameter and argument
4745 * of {@code target} that precedes the folding position; {@code V} also is
4746 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
4747 * types and values of the {@code N} parameters and arguments at the folding
4748 * position. {@code Z}/{@code z} and {@code B}/{@code b} represent the types
4749 * and values of the {@code target} parameters and arguments that precede and
4750 * follow the folded parameters and arguments starting at {@code pos},
4751 * respectively.
4752 * <blockquote><pre>{@code
4753 * // there are N arguments in A...
4754 * T target(Z..., V, A[N]..., B...);
4755 * V combiner(A...);
4756 * T adapter(Z... z, A... a, B... b) {
4757 * V v = combiner(a...);
4758 * return target(z..., v, a..., b...);
4759 * }
4760 * // and if the combiner has a void return:
4761 * T target2(Z..., A[N]..., B...);
4762 * void combiner2(A...);
4763 * T adapter2(Z... z, A... a, B... b) {
4764 * combiner2(a...);
4765 * return target2(z..., a..., b...);
4766 * }
4767 * }</pre></blockquote>
4768 * <p>
4769 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4770 * variable-arity method handle}, even if the original target method handle was.
4771 *
4772 * @param target the method handle to invoke after arguments are combined
4773 * @param pos the position at which to start folding and at which to insert the folding result; if this is {@code
4774 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
4775 * @param combiner method handle to call initially on the incoming arguments
4776 * @return method handle which incorporates the specified argument folding logic
4777 * @throws NullPointerException if either argument is null
4778 * @throws IllegalArgumentException if {@code combiner}'s return type
4779 * is non-void and not the same as the argument type at position {@code pos} of
4780 * the target signature, or if the {@code N} argument types at position {@code pos}
4781 * of the target signature
4782 * (skipping one matching the {@code combiner}'s return type)
4783 * are not identical with the argument types of {@code combiner}
4784 *
4785 * @see #foldArguments(MethodHandle, MethodHandle)
4786 * @since 9
4787 */
4788 public static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner) {
4789 MethodType targetType = target.type();
4790 MethodType combinerType = combiner.type();
4791 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType);
4792 BoundMethodHandle result = target.rebind();
4793 boolean dropResult = rtype == void.class;
4794 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType());
4795 MethodType newType = targetType;
4796 if (!dropResult) {
4797 newType = newType.dropParameterTypes(pos, pos + 1);
4798 }
4799 result = result.copyWithExtendL(newType, lform, combiner);
4800 return result;
4801 }
4802
4803
4804 private static void checkLoop0(MethodHandle[][] clauses) {
4805 if (clauses == null || clauses.length == 0) {
4806 throw newIllegalArgumentException("null or no clauses passed");
4807 }
4808 if (Stream.of(clauses).anyMatch(Objects::isNull)) {
4809 throw newIllegalArgumentException("null clauses are not allowed");
4810 }
4811 if (Stream.of(clauses).anyMatch(c -> c.length > 4)) {
4812 throw newIllegalArgumentException("All loop clauses must be represented as MethodHandle arrays with at most 4 elements.");
4813 }
4814 }
4815
4816 private static void checkLoop1a(int i, MethodHandle in, MethodHandle st) {
4817 if (in.type().returnType() != st.type().returnType()) {
4818 throw misMatchedTypes("clause " + i + ": init and step return types", in.type().returnType(),
4819 st.type().returnType());
4820 }
4821 }
4822
4823 private static List<Class<?>> buildCommonSuffix(List<MethodHandle> init, List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, int cpSize) {
4824 final List<Class<?>> empty = List.of();
4825 final List<MethodHandle> nonNullInits = init.stream().filter(Objects::nonNull).collect(Collectors.toList());
4826 if (nonNullInits.isEmpty()) {
4827 final List<Class<?>> longest = Stream.of(step, pred, fini).flatMap(List::stream).filter(Objects::nonNull).
4828 // take only those that can contribute to a common suffix because they are longer than the prefix
4829 map(MethodHandle::type).filter(t -> t.parameterCount() > cpSize).map(MethodType::parameterList).
4830 reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
4831 return longest.size() == 0 ? empty : longest.subList(cpSize, longest.size());
4832 } else {
4833 return nonNullInits.stream().map(MethodHandle::type).map(MethodType::parameterList).
4834 reduce((p, q) -> p.size() >= q.size() ? p : q).get();
4835 }
4836 }
4837
4838 private static void checkLoop1b(List<MethodHandle> init, List<Class<?>> commonSuffix) {
4839 if (init.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::parameterList).
4840 anyMatch(pl -> !pl.equals(commonSuffix.subList(0, pl.size())))) {
4841 throw newIllegalArgumentException("found non-effectively identical init parameter type lists: " + init +
4842 " (common suffix: " + commonSuffix + ")");
4843 }
4844 }
4845
4846 private static void checkLoop1cd(List<MethodHandle> pred, List<MethodHandle> fini, Class<?> loopReturnType) {
4847 if (fini.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
4848 anyMatch(t -> t != loopReturnType)) {
4849 throw newIllegalArgumentException("found non-identical finalizer return types: " + fini + " (return type: " +
4850 loopReturnType + ")");
4851 }
4852
4853 if (!pred.stream().filter(Objects::nonNull).findFirst().isPresent()) {
4854 throw newIllegalArgumentException("no predicate found", pred);
4855 }
4856 if (pred.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
4857 anyMatch(t -> t != boolean.class)) {
4858 throw newIllegalArgumentException("predicates must have boolean return type", pred);
4859 }
4860 }
4861
4862 private static void checkLoop2(List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, List<Class<?>> commonParameterSequence) {
4863 final int cpSize = commonParameterSequence.size();
4864 if (Stream.of(step, pred, fini).flatMap(List::stream).filter(Objects::nonNull).map(MethodHandle::type).
4865 map(MethodType::parameterList).
4866 anyMatch(pl -> pl.size() > cpSize || !pl.equals(commonParameterSequence.subList(0, pl.size())))) {
4867 throw newIllegalArgumentException("found non-effectively identical parameter type lists:\nstep: " + step +
4868 "\npred: " + pred + "\nfini: " + fini + " (common parameter sequence: " + commonParameterSequence + ")");
4869 }
4870 }
4871
4872 private static void checkIteratedLoop(MethodHandle iterator, MethodHandle body) {
4873 if (null != iterator && !Iterator.class.isAssignableFrom(iterator.type().returnType())) {
4874 throw newIllegalArgumentException("iteratedLoop first argument must have Iterator return type");
4875 }
4876 if (null == body) {
4877 throw newIllegalArgumentException("iterated loop body must not be null");
4878 }
4879 }
4880
4881 private static void checkTryFinally(MethodHandle target, MethodHandle cleanup) {
4882 Class<?> rtype = target.type().returnType();
4883 if (rtype != cleanup.type().returnType()) {
4884 throw misMatchedTypes("target and return types", cleanup.type().returnType(), rtype);
4885 }
4886 List<Class<?>> cleanupParamTypes = cleanup.type().parameterList();
4887 if (!Throwable.class.isAssignableFrom(cleanupParamTypes.get(0))) {
4888 throw misMatchedTypes("cleanup first argument and Throwable", cleanup.type(), Throwable.class);
4889 }
4890 if (rtype != void.class && cleanupParamTypes.get(1) != rtype) {
4891 throw misMatchedTypes("cleanup second argument and target return type", cleanup.type(), rtype);
4892 }
4893 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
4894 // target parameter list.
4895 int cleanupArgIndex = rtype == void.class ? 1 : 2;
4896 List<Class<?>> cleanupArgSuffix = cleanupParamTypes.subList(cleanupArgIndex, cleanupParamTypes.size());
4897 List<Class<?>> targetParamTypes = target.type().parameterList();
4898 if (targetParamTypes.size() < cleanupArgSuffix.size() ||
4899 !cleanupArgSuffix.equals(targetParamTypes.subList(0, cleanupParamTypes.size() - cleanupArgIndex))) {
4900 throw misMatchedTypes("cleanup parameters after (Throwable,result) and target parameter list prefix",
4901 cleanup.type(), target.type());
4902 }
4903 }
4904
4905 }