1 /*
2 * Copyright (c) 2008, 2017, 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.misc.SharedSecrets;
29 import jdk.internal.module.IllegalAccessLogger;
30 import jdk.internal.org.objectweb.asm.ClassReader;
31 import jdk.internal.reflect.CallerSensitive;
32 import jdk.internal.reflect.Reflection;
33 import jdk.internal.vm.annotation.ForceInline;
34 import sun.invoke.util.ValueConversions;
35 import sun.invoke.util.VerifyAccess;
36 import sun.invoke.util.Wrapper;
37 import sun.reflect.misc.ReflectUtil;
38 import sun.security.util.SecurityConstants;
39
40 import java.lang.invoke.LambdaForm.BasicType;
41 import java.lang.reflect.Constructor;
42 import java.lang.reflect.Field;
43 import java.lang.reflect.Member;
44 import java.lang.reflect.Method;
45 import java.lang.reflect.Modifier;
46 import java.lang.reflect.ReflectPermission;
47 import java.nio.ByteOrder;
48 import java.security.AccessController;
49 import java.security.PrivilegedAction;
50 import java.security.ProtectionDomain;
51 import java.util.ArrayList;
52 import java.util.Arrays;
53 import java.util.BitSet;
54 import java.util.Iterator;
55 import java.util.List;
56 import java.util.Objects;
57 import java.util.concurrent.ConcurrentHashMap;
58 import java.util.stream.Collectors;
59 import java.util.stream.Stream;
60
61 import static java.lang.invoke.MethodHandleImpl.Intrinsic;
62 import static java.lang.invoke.MethodHandleNatives.Constants.*;
63 import static java.lang.invoke.MethodHandleStatics.newIllegalArgumentException;
64 import static java.lang.invoke.MethodType.methodType;
65
66 /**
67 * This class consists exclusively of static methods that operate on or return
68 * method handles. They fall into several categories:
69 * <ul>
70 * <li>Lookup methods which help create method handles for methods and fields.
71 * <li>Combinator methods, which combine or transform pre-existing method handles into new ones.
72 * <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns.
73 * </ul>
74 *
75 * @author John Rose, JSR 292 EG
76 * @since 1.7
77 */
78 public class MethodHandles {
79
80 private MethodHandles() { } // do not instantiate
81
82 static final MemberName.Factory IMPL_NAMES = MemberName.getFactory();
83
84 // See IMPL_LOOKUP below.
85
86 //// Method handle creation from ordinary methods.
87
88 /**
89 * Returns a {@link Lookup lookup object} with
90 * full capabilities to emulate all supported bytecode behaviors of the caller.
91 * These capabilities include <a href="MethodHandles.Lookup.html#privacc">private access</a> to the caller.
92 * Factory methods on the lookup object can create
93 * <a href="MethodHandleInfo.html#directmh">direct method handles</a>
94 * for any member that the caller has access to via bytecodes,
95 * including protected and private fields and methods.
96 * This lookup object is a <em>capability</em> which may be delegated to trusted agents.
97 * Do not store it in place where untrusted code can access it.
98 * <p>
99 * This method is caller sensitive, which means that it may return different
100 * values to different callers.
101 * @return a lookup object for the caller of this method, with private access
102 */
103 @CallerSensitive
104 @ForceInline // to ensure Reflection.getCallerClass optimization
105 public static Lookup lookup() {
106 return new Lookup(Reflection.getCallerClass());
107 }
108
109 /**
110 * This reflected$lookup method is the alternate implementation of
111 * the lookup method when being invoked by reflection.
112 */
113 @CallerSensitive
114 private static Lookup reflected$lookup() {
115 Class<?> caller = Reflection.getCallerClass();
116 if (caller.getClassLoader() == null) {
117 throw newIllegalArgumentException("illegal lookupClass: "+caller);
118 }
119 return new Lookup(caller);
120 }
121
122 /**
123 * Returns a {@link Lookup lookup object} which is trusted minimally.
124 * The lookup has the {@code PUBLIC} and {@code UNCONDITIONAL} modes.
125 * It can only be used to create method handles to public members of
126 * public classes in packages that are exported unconditionally.
127 * <p>
128 * As a matter of pure convention, the {@linkplain Lookup#lookupClass() lookup class}
129 * of this lookup object will be {@link java.lang.Object}.
130 *
131 * @apiNote The use of Object is conventional, and because the lookup modes are
132 * limited, there is no special access provided to the internals of Object, its package
133 * or its module. Consequently, the lookup context of this lookup object will be the
134 * bootstrap class loader, which means it cannot find user classes.
135 *
136 * <p style="font-size:smaller;">
137 * <em>Discussion:</em>
138 * The lookup class can be changed to any other class {@code C} using an expression of the form
139 * {@link Lookup#in publicLookup().in(C.class)}.
140 * but may change the lookup context by virtue of changing the class loader.
141 * A public lookup object is always subject to
142 * <a href="MethodHandles.Lookup.html#secmgr">security manager checks</a>.
143 * Also, it cannot access
144 * <a href="MethodHandles.Lookup.html#callsens">caller sensitive methods</a>.
145 * @return a lookup object which is trusted minimally
146 *
147 * @revised 9
148 * @spec JPMS
149 */
150 public static Lookup publicLookup() {
151 return Lookup.PUBLIC_LOOKUP;
152 }
153
154 /**
155 * Returns a {@link Lookup lookup object} with full capabilities to emulate all
156 * supported bytecode behaviors, including <a href="MethodHandles.Lookup.html#privacc">
157 * private access</a>, on a target class.
158 * This method checks that a caller, specified as a {@code Lookup} object, is allowed to
159 * do <em>deep reflection</em> on the target class. If {@code m1} is the module containing
160 * the {@link Lookup#lookupClass() lookup class}, and {@code m2} is the module containing
161 * the target class, then this check ensures that
162 * <ul>
163 * <li>{@code m1} {@link Module#canRead reads} {@code m2}.</li>
164 * <li>{@code m2} {@link Module#isOpen(String,Module) opens} the package containing
165 * the target class to at least {@code m1}.</li>
166 * <li>The lookup has the {@link Lookup#MODULE MODULE} lookup mode.</li>
167 * </ul>
168 * <p>
169 * If there is a security manager, its {@code checkPermission} method is called to
170 * check {@code ReflectPermission("suppressAccessChecks")}.
171 * @apiNote The {@code MODULE} lookup mode serves to authenticate that the lookup object
172 * was created by code in the caller module (or derived from a lookup object originally
173 * created by the caller). A lookup object with the {@code MODULE} lookup mode can be
174 * shared with trusted parties without giving away {@code PRIVATE} and {@code PACKAGE}
175 * access to the caller.
176 * @param targetClass the target class
177 * @param lookup the caller lookup object
178 * @return a lookup object for the target class, with private access
179 * @throws IllegalArgumentException if {@code targetClass} is a primitve type or array class
180 * @throws NullPointerException if {@code targetClass} or {@code caller} is {@code null}
181 * @throws IllegalAccessException if the access check specified above fails
182 * @throws SecurityException if denied by the security manager
183 * @since 9
184 * @spec JPMS
185 * @see Lookup#dropLookupMode
186 */
187 public static Lookup privateLookupIn(Class<?> targetClass, Lookup lookup) throws IllegalAccessException {
188 SecurityManager sm = System.getSecurityManager();
189 if (sm != null) sm.checkPermission(ACCESS_PERMISSION);
190 if (targetClass.isPrimitive())
191 throw new IllegalArgumentException(targetClass + " is a primitive class");
192 if (targetClass.isArray())
193 throw new IllegalArgumentException(targetClass + " is an array class");
194 Module targetModule = targetClass.getModule();
195 Module callerModule = lookup.lookupClass().getModule();
196 if (!callerModule.canRead(targetModule))
197 throw new IllegalAccessException(callerModule + " does not read " + targetModule);
198 if (targetModule.isNamed()) {
199 String pn = targetClass.getPackageName();
200 assert pn.length() > 0 : "unnamed package cannot be in named module";
201 if (!targetModule.isOpen(pn, callerModule))
202 throw new IllegalAccessException(targetModule + " does not open " + pn + " to " + callerModule);
203 }
204 if ((lookup.lookupModes() & Lookup.MODULE) == 0)
205 throw new IllegalAccessException("lookup does not have MODULE lookup mode");
206 if (!callerModule.isNamed() && targetModule.isNamed()) {
207 IllegalAccessLogger logger = IllegalAccessLogger.illegalAccessLogger();
208 if (logger != null) {
209 logger.logIfOpenedForIllegalAccess(lookup, targetClass);
210 }
211 }
212 return new Lookup(targetClass);
213 }
214
215 /**
216 * Performs an unchecked "crack" of a
217 * <a href="MethodHandleInfo.html#directmh">direct method handle</a>.
218 * The result is as if the user had obtained a lookup object capable enough
219 * to crack the target method handle, called
220 * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect}
221 * on the target to obtain its symbolic reference, and then called
222 * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs}
223 * to resolve the symbolic reference to a member.
224 * <p>
225 * If there is a security manager, its {@code checkPermission} method
226 * is called with a {@code ReflectPermission("suppressAccessChecks")} permission.
227 * @param <T> the desired type of the result, either {@link Member} or a subtype
228 * @param target a direct method handle to crack into symbolic reference components
229 * @param expected a class object representing the desired result type {@code T}
230 * @return a reference to the method, constructor, or field object
231 * @exception SecurityException if the caller is not privileged to call {@code setAccessible}
232 * @exception NullPointerException if either argument is {@code null}
233 * @exception IllegalArgumentException if the target is not a direct method handle
234 * @exception ClassCastException if the member is not of the expected type
235 * @since 1.8
236 */
237 public static <T extends Member> T
238 reflectAs(Class<T> expected, MethodHandle target) {
239 SecurityManager smgr = System.getSecurityManager();
240 if (smgr != null) smgr.checkPermission(ACCESS_PERMISSION);
241 Lookup lookup = Lookup.IMPL_LOOKUP; // use maximally privileged lookup
242 return lookup.revealDirect(target).reflectAs(expected, lookup);
243 }
244 // Copied from AccessibleObject, as used by Method.setAccessible, etc.:
245 private static final java.security.Permission ACCESS_PERMISSION =
246 new ReflectPermission("suppressAccessChecks");
247
248 /**
249 * A <em>lookup object</em> is a factory for creating method handles,
250 * when the creation requires access checking.
251 * Method handles do not perform
252 * access checks when they are called, but rather when they are created.
253 * Therefore, method handle access
254 * restrictions must be enforced when a method handle is created.
255 * The caller class against which those restrictions are enforced
256 * is known as the {@linkplain #lookupClass() lookup class}.
257 * <p>
258 * A lookup class which needs to create method handles will call
259 * {@link MethodHandles#lookup() MethodHandles.lookup} to create a factory for itself.
260 * When the {@code Lookup} factory object is created, the identity of the lookup class is
261 * determined, and securely stored in the {@code Lookup} object.
262 * The lookup class (or its delegates) may then use factory methods
263 * on the {@code Lookup} object to create method handles for access-checked members.
264 * This includes all methods, constructors, and fields which are allowed to the lookup class,
265 * even private ones.
266 *
267 * <h1><a id="lookups"></a>Lookup Factory Methods</h1>
268 * The factory methods on a {@code Lookup} object correspond to all major
269 * use cases for methods, constructors, and fields.
270 * Each method handle created by a factory method is the functional
271 * equivalent of a particular <em>bytecode behavior</em>.
272 * (Bytecode behaviors are described in section 5.4.3.5 of the Java Virtual Machine Specification.)
273 * Here is a summary of the correspondence between these factory methods and
274 * the behavior of the resulting method handles:
275 * <table class="striped">
276 * <caption style="display:none">lookup method behaviors</caption>
277 * <thead>
278 * <tr>
279 * <th scope="col"><a id="equiv"></a>lookup expression</th>
280 * <th scope="col">member</th>
281 * <th scope="col">bytecode behavior</th>
282 * </tr>
283 * </thead>
284 * <tbody>
285 * <tr>
286 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</th>
287 * <td>{@code FT f;}</td><td>{@code (T) this.f;}</td>
288 * </tr>
289 * <tr>
290 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</th>
291 * <td>{@code static}<br>{@code FT f;}</td><td>{@code (T) C.f;}</td>
292 * </tr>
293 * <tr>
294 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</th>
295 * <td>{@code FT f;}</td><td>{@code this.f = x;}</td>
296 * </tr>
297 * <tr>
298 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</th>
299 * <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td>
300 * </tr>
301 * <tr>
302 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</th>
303 * <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>
304 * </tr>
305 * <tr>
306 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</th>
307 * <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td>
308 * </tr>
309 * <tr>
310 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</th>
311 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
312 * </tr>
313 * <tr>
314 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</th>
315 * <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td>
316 * </tr>
317 * <tr>
318 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</th>
319 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td>
320 * </tr>
321 * <tr>
322 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</th>
323 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, arg);}</td>
324 * </tr>
325 * <tr>
326 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</th>
327 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
328 * </tr>
329 * <tr>
330 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</th>
331 * <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td>
332 * </tr>
333 * <tr>
334 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</th>
335 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
336 * </tr>
337 * <tr>
338 * <th scope="row">{@link java.lang.invoke.MethodHandles.Lookup#findClass lookup.findClass("C")}</th>
339 * <td>{@code class C { ... }}</td><td>{@code C.class;}</td>
340 * </tr>
341 * </tbody>
342 * </table>
343 *
344 * Here, the type {@code C} is the class or interface being searched for a member,
345 * documented as a parameter named {@code refc} in the lookup methods.
346 * The method type {@code MT} is composed from the return type {@code T}
347 * and the sequence of argument types {@code A*}.
348 * The constructor also has a sequence of argument types {@code A*} and
349 * is deemed to return the newly-created object of type {@code C}.
350 * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}.
351 * The formal parameter {@code this} stands for the self-reference of type {@code C};
352 * if it is present, it is always the leading argument to the method handle invocation.
353 * (In the case of some {@code protected} members, {@code this} may be
354 * restricted in type to the lookup class; see below.)
355 * The name {@code arg} stands for all the other method handle arguments.
356 * In the code examples for the Core Reflection API, the name {@code thisOrNull}
357 * stands for a null reference if the accessed method or field is static,
358 * and {@code this} otherwise.
359 * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand
360 * for reflective objects corresponding to the given members.
361 * <p>
362 * The bytecode behavior for a {@code findClass} operation is a load of a constant class,
363 * as if by {@code ldc CONSTANT_Class}.
364 * The behavior is represented, not as a method handle, but directly as a {@code Class} constant.
365 * <p>
366 * In cases where the given member is of variable arity (i.e., a method or constructor)
367 * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}.
368 * In all other cases, the returned method handle will be of fixed arity.
369 * <p style="font-size:smaller;">
370 * <em>Discussion:</em>
371 * The equivalence between looked-up method handles and underlying
372 * class members and bytecode behaviors
373 * can break down in a few ways:
374 * <ul style="font-size:smaller;">
375 * <li>If {@code C} is not symbolically accessible from the lookup class's loader,
376 * the lookup can still succeed, even when there is no equivalent
377 * Java expression or bytecoded constant.
378 * <li>Likewise, if {@code T} or {@code MT}
379 * is not symbolically accessible from the lookup class's loader,
380 * the lookup can still succeed.
381 * For example, lookups for {@code MethodHandle.invokeExact} and
382 * {@code MethodHandle.invoke} will always succeed, regardless of requested type.
383 * <li>If there is a security manager installed, it can forbid the lookup
384 * on various grounds (<a href="MethodHandles.Lookup.html#secmgr">see below</a>).
385 * By contrast, the {@code ldc} instruction on a {@code CONSTANT_MethodHandle}
386 * constant is not subject to security manager checks.
387 * <li>If the looked-up method has a
388 * <a href="MethodHandle.html#maxarity">very large arity</a>,
389 * the method handle creation may fail, due to the method handle
390 * type having too many parameters.
391 * </ul>
392 *
393 * <h1><a id="access"></a>Access checking</h1>
394 * Access checks are applied in the factory methods of {@code Lookup},
395 * when a method handle is created.
396 * This is a key difference from the Core Reflection API, since
397 * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
398 * performs access checking against every caller, on every call.
399 * <p>
400 * All access checks start from a {@code Lookup} object, which
401 * compares its recorded lookup class against all requests to
402 * create method handles.
403 * A single {@code Lookup} object can be used to create any number
404 * of access-checked method handles, all checked against a single
405 * lookup class.
406 * <p>
407 * A {@code Lookup} object can be shared with other trusted code,
408 * such as a metaobject protocol.
409 * A shared {@code Lookup} object delegates the capability
410 * to create method handles on private members of the lookup class.
411 * Even if privileged code uses the {@code Lookup} object,
412 * the access checking is confined to the privileges of the
413 * original lookup class.
414 * <p>
415 * A lookup can fail, because
416 * the containing class is not accessible to the lookup class, or
417 * because the desired class member is missing, or because the
418 * desired class member is not accessible to the lookup class, or
419 * because the lookup object is not trusted enough to access the member.
420 * In any of these cases, a {@code ReflectiveOperationException} will be
421 * thrown from the attempted lookup. The exact class will be one of
422 * the following:
423 * <ul>
424 * <li>NoSuchMethodException — if a method is requested but does not exist
425 * <li>NoSuchFieldException — if a field is requested but does not exist
426 * <li>IllegalAccessException — if the member exists but an access check fails
427 * </ul>
428 * <p>
429 * In general, the conditions under which a method handle may be
430 * looked up for a method {@code M} are no more restrictive than the conditions
431 * under which the lookup class could have compiled, verified, and resolved a call to {@code M}.
432 * Where the JVM would raise exceptions like {@code NoSuchMethodError},
433 * a method handle lookup will generally raise a corresponding
434 * checked exception, such as {@code NoSuchMethodException}.
435 * And the effect of invoking the method handle resulting from the lookup
436 * is <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a>
437 * to executing the compiled, verified, and resolved call to {@code M}.
438 * The same point is true of fields and constructors.
439 * <p style="font-size:smaller;">
440 * <em>Discussion:</em>
441 * Access checks only apply to named and reflected methods,
442 * constructors, and fields.
443 * Other method handle creation methods, such as
444 * {@link MethodHandle#asType MethodHandle.asType},
445 * do not require any access checks, and are used
446 * independently of any {@code Lookup} object.
447 * <p>
448 * If the desired member is {@code protected}, the usual JVM rules apply,
449 * including the requirement that the lookup class must be either be in the
450 * same package as the desired member, or must inherit that member.
451 * (See the Java Virtual Machine Specification, sections 4.9.2, 5.4.3.5, and 6.4.)
452 * In addition, if the desired member is a non-static field or method
453 * in a different package, the resulting method handle may only be applied
454 * to objects of the lookup class or one of its subclasses.
455 * This requirement is enforced by narrowing the type of the leading
456 * {@code this} parameter from {@code C}
457 * (which will necessarily be a superclass of the lookup class)
458 * to the lookup class itself.
459 * <p>
460 * The JVM imposes a similar requirement on {@code invokespecial} instruction,
461 * that the receiver argument must match both the resolved method <em>and</em>
462 * the current class. Again, this requirement is enforced by narrowing the
463 * type of the leading parameter to the resulting method handle.
464 * (See the Java Virtual Machine Specification, section 4.10.1.9.)
465 * <p>
466 * The JVM represents constructors and static initializer blocks as internal methods
467 * with special names ({@code "<init>"} and {@code "<clinit>"}).
468 * The internal syntax of invocation instructions allows them to refer to such internal
469 * methods as if they were normal methods, but the JVM bytecode verifier rejects them.
470 * A lookup of such an internal method will produce a {@code NoSuchMethodException}.
471 * <p>
472 * In some cases, access between nested classes is obtained by the Java compiler by creating
473 * an wrapper method to access a private method of another class
474 * in the same top-level declaration.
475 * For example, a nested class {@code C.D}
476 * can access private members within other related classes such as
477 * {@code C}, {@code C.D.E}, or {@code C.B},
478 * but the Java compiler may need to generate wrapper methods in
479 * those related classes. In such cases, a {@code Lookup} object on
480 * {@code C.E} would be unable to those private members.
481 * A workaround for this limitation is the {@link Lookup#in Lookup.in} method,
482 * which can transform a lookup on {@code C.E} into one on any of those other
483 * classes, without special elevation of privilege.
484 * <p>
485 * The accesses permitted to a given lookup object may be limited,
486 * according to its set of {@link #lookupModes lookupModes},
487 * to a subset of members normally accessible to the lookup class.
488 * For example, the {@link MethodHandles#publicLookup publicLookup}
489 * method produces a lookup object which is only allowed to access
490 * public members in public classes of exported packages.
491 * The caller sensitive method {@link MethodHandles#lookup lookup}
492 * produces a lookup object with full capabilities relative to
493 * its caller class, to emulate all supported bytecode behaviors.
494 * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object
495 * with fewer access modes than the original lookup object.
496 *
497 * <p style="font-size:smaller;">
498 * <a id="privacc"></a>
499 * <em>Discussion of private access:</em>
500 * We say that a lookup has <em>private access</em>
501 * if its {@linkplain #lookupModes lookup modes}
502 * include the possibility of accessing {@code private} members.
503 * As documented in the relevant methods elsewhere,
504 * only lookups with private access possess the following capabilities:
505 * <ul style="font-size:smaller;">
506 * <li>access private fields, methods, and constructors of the lookup class
507 * <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> methods,
508 * such as {@code Class.forName}
509 * <li>create method handles which {@link Lookup#findSpecial emulate invokespecial} instructions
510 * <li>avoid <a href="MethodHandles.Lookup.html#secmgr">package access checks</a>
511 * for classes accessible to the lookup class
512 * <li>create {@link Lookup#in delegated lookup objects} which have private access to other classes
513 * within the same package member
514 * </ul>
515 * <p style="font-size:smaller;">
516 * Each of these permissions is a consequence of the fact that a lookup object
517 * with private access can be securely traced back to an originating class,
518 * whose <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> and Java language access permissions
519 * can be reliably determined and emulated by method handles.
520 *
521 * <h1><a id="secmgr"></a>Security manager interactions</h1>
522 * Although bytecode instructions can only refer to classes in
523 * a related class loader, this API can search for methods in any
524 * class, as long as a reference to its {@code Class} object is
525 * available. Such cross-loader references are also possible with the
526 * Core Reflection API, and are impossible to bytecode instructions
527 * such as {@code invokestatic} or {@code getfield}.
528 * There is a {@linkplain java.lang.SecurityManager security manager API}
529 * to allow applications to check such cross-loader references.
530 * These checks apply to both the {@code MethodHandles.Lookup} API
531 * and the Core Reflection API
532 * (as found on {@link java.lang.Class Class}).
533 * <p>
534 * If a security manager is present, member and class lookups are subject to
535 * additional checks.
536 * From one to three calls are made to the security manager.
537 * Any of these calls can refuse access by throwing a
538 * {@link java.lang.SecurityException SecurityException}.
539 * Define {@code smgr} as the security manager,
540 * {@code lookc} as the lookup class of the current lookup object,
541 * {@code refc} as the containing class in which the member
542 * is being sought, and {@code defc} as the class in which the
543 * member is actually defined.
544 * (If a class or other type is being accessed,
545 * the {@code refc} and {@code defc} values are the class itself.)
546 * The value {@code lookc} is defined as <em>not present</em>
547 * if the current lookup object does not have
548 * <a href="MethodHandles.Lookup.html#privacc">private access</a>.
549 * The calls are made according to the following rules:
550 * <ul>
551 * <li><b>Step 1:</b>
552 * If {@code lookc} is not present, or if its class loader is not
553 * the same as or an ancestor of the class loader of {@code refc},
554 * then {@link SecurityManager#checkPackageAccess
555 * smgr.checkPackageAccess(refcPkg)} is called,
556 * where {@code refcPkg} is the package of {@code refc}.
557 * <li><b>Step 2a:</b>
558 * If the retrieved member is not public and
559 * {@code lookc} is not present, then
560 * {@link SecurityManager#checkPermission smgr.checkPermission}
561 * with {@code RuntimePermission("accessDeclaredMembers")} is called.
562 * <li><b>Step 2b:</b>
563 * If the retrieved class has a {@code null} class loader,
564 * and {@code lookc} is not present, then
565 * {@link SecurityManager#checkPermission smgr.checkPermission}
566 * with {@code RuntimePermission("getClassLoader")} is called.
567 * <li><b>Step 3:</b>
568 * If the retrieved member is not public,
569 * and if {@code lookc} is not present,
570 * and if {@code defc} and {@code refc} are different,
571 * then {@link SecurityManager#checkPackageAccess
572 * smgr.checkPackageAccess(defcPkg)} is called,
573 * where {@code defcPkg} is the package of {@code defc}.
574 * </ul>
575 * Security checks are performed after other access checks have passed.
576 * Therefore, the above rules presuppose a member or class that is public,
577 * or else that is being accessed from a lookup class that has
578 * rights to access the member or class.
579 *
580 * <h1><a id="callsens"></a>Caller sensitive methods</h1>
581 * A small number of Java methods have a special property called caller sensitivity.
582 * A <em>caller-sensitive</em> method can behave differently depending on the
583 * identity of its immediate caller.
584 * <p>
585 * If a method handle for a caller-sensitive method is requested,
586 * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> apply,
587 * but they take account of the lookup class in a special way.
588 * The resulting method handle behaves as if it were called
589 * from an instruction contained in the lookup class,
590 * so that the caller-sensitive method detects the lookup class.
591 * (By contrast, the invoker of the method handle is disregarded.)
592 * Thus, in the case of caller-sensitive methods,
593 * different lookup classes may give rise to
594 * differently behaving method handles.
595 * <p>
596 * In cases where the lookup object is
597 * {@link MethodHandles#publicLookup() publicLookup()},
598 * or some other lookup object without
599 * <a href="MethodHandles.Lookup.html#privacc">private access</a>,
600 * the lookup class is disregarded.
601 * In such cases, no caller-sensitive method handle can be created,
602 * access is forbidden, and the lookup fails with an
603 * {@code IllegalAccessException}.
604 * <p style="font-size:smaller;">
605 * <em>Discussion:</em>
606 * For example, the caller-sensitive method
607 * {@link java.lang.Class#forName(String) Class.forName(x)}
608 * can return varying classes or throw varying exceptions,
609 * depending on the class loader of the class that calls it.
610 * A public lookup of {@code Class.forName} will fail, because
611 * there is no reasonable way to determine its bytecode behavior.
612 * <p style="font-size:smaller;">
613 * If an application caches method handles for broad sharing,
614 * it should use {@code publicLookup()} to create them.
615 * If there is a lookup of {@code Class.forName}, it will fail,
616 * and the application must take appropriate action in that case.
617 * It may be that a later lookup, perhaps during the invocation of a
618 * bootstrap method, can incorporate the specific identity
619 * of the caller, making the method accessible.
620 * <p style="font-size:smaller;">
621 * The function {@code MethodHandles.lookup} is caller sensitive
622 * so that there can be a secure foundation for lookups.
623 * Nearly all other methods in the JSR 292 API rely on lookup
624 * objects to check access requests.
625 *
626 * @revised 9
627 */
628 public static final
629 class Lookup {
630 /** The class on behalf of whom the lookup is being performed. */
631 private final Class<?> lookupClass;
632
633 /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */
634 private final int allowedModes;
635
636 /** A single-bit mask representing {@code public} access,
637 * which may contribute to the result of {@link #lookupModes lookupModes}.
638 * The value, {@code 0x01}, happens to be the same as the value of the
639 * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.
640 */
641 public static final int PUBLIC = Modifier.PUBLIC;
642
643 /** A single-bit mask representing {@code private} access,
644 * which may contribute to the result of {@link #lookupModes lookupModes}.
645 * The value, {@code 0x02}, happens to be the same as the value of the
646 * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.
647 */
648 public static final int PRIVATE = Modifier.PRIVATE;
649
650 /** A single-bit mask representing {@code protected} access,
651 * which may contribute to the result of {@link #lookupModes lookupModes}.
652 * The value, {@code 0x04}, happens to be the same as the value of the
653 * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.
654 */
655 public static final int PROTECTED = Modifier.PROTECTED;
656
657 /** A single-bit mask representing {@code package} access (default access),
658 * which may contribute to the result of {@link #lookupModes lookupModes}.
659 * The value is {@code 0x08}, which does not correspond meaningfully to
660 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
661 */
662 public static final int PACKAGE = Modifier.STATIC;
663
664 /** A single-bit mask representing {@code module} access (default access),
665 * which may contribute to the result of {@link #lookupModes lookupModes}.
666 * The value is {@code 0x10}, which does not correspond meaningfully to
667 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
668 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup}
669 * with this lookup mode can access all public types in the module of the
670 * lookup class and public types in packages exported by other modules
671 * to the module of the lookup class.
672 * @since 9
673 * @spec JPMS
674 */
675 public static final int MODULE = PACKAGE << 1;
676
677 /** A single-bit mask representing {@code unconditional} access
678 * which may contribute to the result of {@link #lookupModes lookupModes}.
679 * The value is {@code 0x20}, which does not correspond meaningfully to
680 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
681 * A {@code Lookup} with this lookup mode assumes {@linkplain
682 * java.lang.Module#canRead(java.lang.Module) readability}.
683 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup}
684 * with this lookup mode can access all public members of public types
685 * of all modules where the type is in a package that is {@link
686 * java.lang.Module#isExported(String) exported unconditionally}.
687 * @since 9
688 * @spec JPMS
689 * @see #publicLookup()
690 */
691 public static final int UNCONDITIONAL = PACKAGE << 2;
692
693 private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE | MODULE | UNCONDITIONAL);
694 private static final int FULL_POWER_MODES = (ALL_MODES & ~UNCONDITIONAL);
695 private static final int TRUSTED = -1;
696
697 private static int fixmods(int mods) {
698 mods &= (ALL_MODES - PACKAGE - MODULE - UNCONDITIONAL);
699 return (mods != 0) ? mods : (PACKAGE | MODULE | UNCONDITIONAL);
700 }
701
702 /** Tells which class is performing the lookup. It is this class against
703 * which checks are performed for visibility and access permissions.
704 * <p>
705 * The class implies a maximum level of access permission,
706 * but the permissions may be additionally limited by the bitmask
707 * {@link #lookupModes lookupModes}, which controls whether non-public members
708 * can be accessed.
709 * @return the lookup class, on behalf of which this lookup object finds members
710 */
711 public Class<?> lookupClass() {
712 return lookupClass;
713 }
714
715 // This is just for calling out to MethodHandleImpl.
716 private Class<?> lookupClassOrNull() {
717 return (allowedModes == TRUSTED) ? null : lookupClass;
718 }
719
720 /** Tells which access-protection classes of members this lookup object can produce.
721 * The result is a bit-mask of the bits
722 * {@linkplain #PUBLIC PUBLIC (0x01)},
723 * {@linkplain #PRIVATE PRIVATE (0x02)},
724 * {@linkplain #PROTECTED PROTECTED (0x04)},
725 * {@linkplain #PACKAGE PACKAGE (0x08)},
726 * {@linkplain #MODULE MODULE (0x10)},
727 * and {@linkplain #UNCONDITIONAL UNCONDITIONAL (0x20)}.
728 * <p>
729 * A freshly-created lookup object
730 * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class} has
731 * all possible bits set, except {@code UNCONDITIONAL}. The lookup can be used to
732 * access all members of the caller's class, all public types in the caller's module,
733 * and all public types in packages exported by other modules to the caller's module.
734 * A lookup object on a new lookup class
735 * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object}
736 * may have some mode bits set to zero.
737 * Mode bits can also be
738 * {@linkplain java.lang.invoke.MethodHandles.Lookup#dropLookupMode directly cleared}.
739 * Once cleared, mode bits cannot be restored from the downgraded lookup object.
740 * The purpose of this is to restrict access via the new lookup object,
741 * so that it can access only names which can be reached by the original
742 * lookup object, and also by the new lookup class.
743 * @return the lookup modes, which limit the kinds of access performed by this lookup object
744 * @see #in
745 * @see #dropLookupMode
746 *
747 * @revised 9
748 * @spec JPMS
749 */
750 public int lookupModes() {
751 return allowedModes & ALL_MODES;
752 }
753
754 /** Embody the current class (the lookupClass) as a lookup class
755 * for method handle creation.
756 * Must be called by from a method in this package,
757 * which in turn is called by a method not in this package.
758 */
759 Lookup(Class<?> lookupClass) {
760 this(lookupClass, FULL_POWER_MODES);
761 // make sure we haven't accidentally picked up a privileged class:
762 checkUnprivilegedlookupClass(lookupClass);
763 }
764
765 private Lookup(Class<?> lookupClass, int allowedModes) {
766 this.lookupClass = lookupClass;
767 this.allowedModes = allowedModes;
768 }
769
770 /**
771 * Creates a lookup on the specified new lookup class.
772 * The resulting object will report the specified
773 * class as its own {@link #lookupClass() lookupClass}.
774 * <p>
775 * However, the resulting {@code Lookup} object is guaranteed
776 * to have no more access capabilities than the original.
777 * In particular, access capabilities can be lost as follows:<ul>
778 * <li>If the old lookup class is in a {@link Module#isNamed() named} module, and
779 * the new lookup class is in a different module {@code M}, then no members, not
780 * even public members in {@code M}'s exported packages, will be accessible.
781 * The exception to this is when this lookup is {@link #publicLookup()
782 * publicLookup}, in which case {@code PUBLIC} access is not lost.
783 * <li>If the old lookup class is in an unnamed module, and the new lookup class
784 * is a different module then {@link #MODULE MODULE} access is lost.
785 * <li>If the new lookup class differs from the old one then {@code UNCONDITIONAL} is lost.
786 * <li>If the new lookup class is in a different package
787 * than the old one, protected and default (package) members will not be accessible.
788 * <li>If the new lookup class is not within the same package member
789 * as the old one, private members will not be accessible, and protected members
790 * will not be accessible by virtue of inheritance.
791 * (Protected members may continue to be accessible because of package sharing.)
792 * <li>If the new lookup class is not accessible to the old lookup class,
793 * then no members, not even public members, will be accessible.
794 * (In all other cases, public members will continue to be accessible.)
795 * </ul>
796 * <p>
797 * The resulting lookup's capabilities for loading classes
798 * (used during {@link #findClass} invocations)
799 * are determined by the lookup class' loader,
800 * which may change due to this operation.
801 *
802 * @param requestedLookupClass the desired lookup class for the new lookup object
803 * @return a lookup object which reports the desired lookup class, or the same object
804 * if there is no change
805 * @throws NullPointerException if the argument is null
806 *
807 * @revised 9
808 * @spec JPMS
809 */
810 public Lookup in(Class<?> requestedLookupClass) {
811 Objects.requireNonNull(requestedLookupClass);
812 if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all
813 return new Lookup(requestedLookupClass, FULL_POWER_MODES);
814 if (requestedLookupClass == this.lookupClass)
815 return this; // keep same capabilities
816 int newModes = (allowedModes & FULL_POWER_MODES);
817 if (!VerifyAccess.isSameModule(this.lookupClass, requestedLookupClass)) {
818 // Need to drop all access when teleporting from a named module to another
819 // module. The exception is publicLookup where PUBLIC is not lost.
820 if (this.lookupClass.getModule().isNamed()
821 && (this.allowedModes & UNCONDITIONAL) == 0)
822 newModes = 0;
823 else
824 newModes &= ~(MODULE|PACKAGE|PRIVATE|PROTECTED);
825 }
826 if ((newModes & PACKAGE) != 0
827 && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {
828 newModes &= ~(PACKAGE|PRIVATE|PROTECTED);
829 }
830 // Allow nestmate lookups to be created without special privilege:
831 if ((newModes & PRIVATE) != 0
832 && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {
833 newModes &= ~(PRIVATE|PROTECTED);
834 }
835 if ((newModes & PUBLIC) != 0
836 && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, allowedModes)) {
837 // The requested class it not accessible from the lookup class.
838 // No permissions.
839 newModes = 0;
840 }
841
842 checkUnprivilegedlookupClass(requestedLookupClass);
843 return new Lookup(requestedLookupClass, newModes);
844 }
845
846
847 /**
848 * Creates a lookup on the same lookup class which this lookup object
849 * finds members, but with a lookup mode that has lost the given lookup mode.
850 * The lookup mode to drop is one of {@link #PUBLIC PUBLIC}, {@link #MODULE
851 * MODULE}, {@link #PACKAGE PACKAGE}, {@link #PROTECTED PROTECTED} or {@link #PRIVATE PRIVATE}.
852 * {@link #PROTECTED PROTECTED} and {@link #UNCONDITIONAL UNCONDITIONAL} are always
853 * dropped and so the resulting lookup mode will never have these access capabilities.
854 * When dropping {@code PACKAGE} then the resulting lookup will not have {@code PACKAGE}
855 * or {@code PRIVATE} access. When dropping {@code MODULE} then the resulting lookup will
856 * not have {@code MODULE}, {@code PACKAGE}, or {@code PRIVATE} access. If {@code PUBLIC}
857 * is dropped then the resulting lookup has no access.
858 * @param modeToDrop the lookup mode to drop
859 * @return a lookup object which lacks the indicated mode, or the same object if there is no change
860 * @throws IllegalArgumentException if {@code modeToDrop} is not one of {@code PUBLIC},
861 * {@code MODULE}, {@code PACKAGE}, {@code PROTECTED}, {@code PRIVATE} or {@code UNCONDITIONAL}
862 * @see MethodHandles#privateLookupIn
863 * @since 9
864 */
865 public Lookup dropLookupMode(int modeToDrop) {
866 int oldModes = lookupModes();
867 int newModes = oldModes & ~(modeToDrop | PROTECTED | UNCONDITIONAL);
868 switch (modeToDrop) {
869 case PUBLIC: newModes &= ~(ALL_MODES); break;
870 case MODULE: newModes &= ~(PACKAGE | PRIVATE); break;
871 case PACKAGE: newModes &= ~(PRIVATE); break;
872 case PROTECTED:
873 case PRIVATE:
874 case UNCONDITIONAL: break;
875 default: throw new IllegalArgumentException(modeToDrop + " is not a valid mode to drop");
876 }
877 if (newModes == oldModes) return this; // return self if no change
878 return new Lookup(lookupClass(), newModes);
879 }
880
881 /**
882 * Defines a class to the same class loader and in the same runtime package and
883 * {@linkplain java.security.ProtectionDomain protection domain} as this lookup's
884 * {@linkplain #lookupClass() lookup class}.
885 *
886 * <p> The {@linkplain #lookupModes() lookup modes} for this lookup must include
887 * {@link #PACKAGE PACKAGE} access as default (package) members will be
888 * accessible to the class. The {@code PACKAGE} lookup mode serves to authenticate
889 * that the lookup object was created by a caller in the runtime package (or derived
890 * from a lookup originally created by suitably privileged code to a target class in
891 * the runtime package). </p>
892 *
893 * <p> The {@code bytes} parameter is the class bytes of a valid class file (as defined
894 * by the <em>The Java Virtual Machine Specification</em>) with a class name in the
895 * same package as the lookup class. </p>
896 *
897 * <p> This method does not run the class initializer. The class initializer may
898 * run at a later time, as detailed in section 12.4 of the <em>The Java Language
899 * Specification</em>. </p>
900 *
901 * <p> If there is a security manager, its {@code checkPermission} method is first called
902 * to check {@code RuntimePermission("defineClass")}. </p>
903 *
904 * @param bytes the class bytes
905 * @return the {@code Class} object for the class
906 * @throws IllegalArgumentException the bytes are for a class in a different package
907 * to the lookup class
908 * @throws IllegalAccessException if this lookup does not have {@code PACKAGE} access
909 * @throws LinkageError if the class is malformed ({@code ClassFormatError}), cannot be
910 * verified ({@code VerifyError}), is already defined, or another linkage error occurs
911 * @throws SecurityException if denied by the security manager
912 * @throws NullPointerException if {@code bytes} is {@code null}
913 * @since 9
914 * @spec JPMS
915 * @see Lookup#privateLookupIn
916 * @see Lookup#dropLookupMode
917 * @see ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain)
918 */
919 public Class<?> defineClass(byte[] bytes) throws IllegalAccessException {
920 SecurityManager sm = System.getSecurityManager();
921 if (sm != null)
922 sm.checkPermission(new RuntimePermission("defineClass"));
923 if ((lookupModes() & PACKAGE) == 0)
924 throw new IllegalAccessException("Lookup does not have PACKAGE access");
925 assert (lookupModes() & (MODULE|PUBLIC)) != 0;
926
927 // parse class bytes to get class name (in internal form)
928 bytes = bytes.clone();
929 String name;
930 try {
931 ClassReader reader = new ClassReader(bytes);
932 name = reader.getClassName();
933 } catch (RuntimeException e) {
934 // ASM exceptions are poorly specified
935 ClassFormatError cfe = new ClassFormatError();
936 cfe.initCause(e);
937 throw cfe;
938 }
939
940 // get package and class name in binary form
941 String cn, pn;
942 int index = name.lastIndexOf('/');
943 if (index == -1) {
944 cn = name;
945 pn = "";
946 } else {
947 cn = name.replace('/', '.');
948 pn = cn.substring(0, index);
949 }
950 if (!pn.equals(lookupClass.getPackageName())) {
951 throw new IllegalArgumentException("Class not in same package as lookup class");
952 }
953
954 // invoke the class loader's defineClass method
955 ClassLoader loader = lookupClass.getClassLoader();
956 ProtectionDomain pd = (loader != null) ? lookupClassProtectionDomain() : null;
957 String source = "__Lookup_defineClass__";
958 Class<?> clazz = SharedSecrets.getJavaLangAccess().defineClass(loader, cn, bytes, pd, source);
959 assert clazz.getClassLoader() == lookupClass.getClassLoader()
960 && clazz.getPackageName().equals(lookupClass.getPackageName())
961 && protectionDomain(clazz) == lookupClassProtectionDomain();
962 return clazz;
963 }
964
965 private ProtectionDomain lookupClassProtectionDomain() {
966 ProtectionDomain pd = cachedProtectionDomain;
967 if (pd == null) {
968 cachedProtectionDomain = pd = protectionDomain(lookupClass);
969 }
970 return pd;
971 }
972
973 private ProtectionDomain protectionDomain(Class<?> clazz) {
974 PrivilegedAction<ProtectionDomain> pa = clazz::getProtectionDomain;
975 return AccessController.doPrivileged(pa);
976 }
977
978 // cached protection domain
979 private volatile ProtectionDomain cachedProtectionDomain;
980
981
982 // Make sure outer class is initialized first.
983 static { IMPL_NAMES.getClass(); }
984
985 /** Package-private version of lookup which is trusted. */
986 static final Lookup IMPL_LOOKUP = new Lookup(Object.class, TRUSTED);
987
988 /** Version of lookup which is trusted minimally.
989 * It can only be used to create method handles to publicly accessible
990 * members in packages that are exported unconditionally.
991 */
992 static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, (PUBLIC|UNCONDITIONAL));
993
994 private static void checkUnprivilegedlookupClass(Class<?> lookupClass) {
995 String name = lookupClass.getName();
996 if (name.startsWith("java.lang.invoke."))
997 throw newIllegalArgumentException("illegal lookupClass: "+lookupClass);
998 }
999
1000 /**
1001 * Displays the name of the class from which lookups are to be made.
1002 * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)
1003 * If there are restrictions on the access permitted to this lookup,
1004 * this is indicated by adding a suffix to the class name, consisting
1005 * of a slash and a keyword. The keyword represents the strongest
1006 * allowed access, and is chosen as follows:
1007 * <ul>
1008 * <li>If no access is allowed, the suffix is "/noaccess".
1009 * <li>If only public access to types in exported packages is allowed, the suffix is "/public".
1010 * <li>If only public access and unconditional access are allowed, the suffix is "/publicLookup".
1011 * <li>If only public and module access are allowed, the suffix is "/module".
1012 * <li>If only public, module and package access are allowed, the suffix is "/package".
1013 * <li>If only public, module, package, and private access are allowed, the suffix is "/private".
1014 * </ul>
1015 * If none of the above cases apply, it is the case that full
1016 * access (public, module, package, private, and protected) is allowed.
1017 * In this case, no suffix is added.
1018 * This is true only of an object obtained originally from
1019 * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
1020 * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
1021 * always have restricted access, and will display a suffix.
1022 * <p>
1023 * (It may seem strange that protected access should be
1024 * stronger than private access. Viewed independently from
1025 * package access, protected access is the first to be lost,
1026 * because it requires a direct subclass relationship between
1027 * caller and callee.)
1028 * @see #in
1029 *
1030 * @revised 9
1031 * @spec JPMS
1032 */
1033 @Override
1034 public String toString() {
1035 String cname = lookupClass.getName();
1036 switch (allowedModes) {
1037 case 0: // no privileges
1038 return cname + "/noaccess";
1039 case PUBLIC:
1040 return cname + "/public";
1041 case PUBLIC|UNCONDITIONAL:
1042 return cname + "/publicLookup";
1043 case PUBLIC|MODULE:
1044 return cname + "/module";
1045 case PUBLIC|MODULE|PACKAGE:
1046 return cname + "/package";
1047 case FULL_POWER_MODES & ~PROTECTED:
1048 return cname + "/private";
1049 case FULL_POWER_MODES:
1050 return cname;
1051 case TRUSTED:
1052 return "/trusted"; // internal only; not exported
1053 default: // Should not happen, but it's a bitfield...
1054 cname = cname + "/" + Integer.toHexString(allowedModes);
1055 assert(false) : cname;
1056 return cname;
1057 }
1058 }
1059
1060 /**
1061 * Produces a method handle for a static method.
1062 * The type of the method handle will be that of the method.
1063 * (Since static methods do not take receivers, there is no
1064 * additional receiver argument inserted into the method handle type,
1065 * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)
1066 * The method and all its argument types must be accessible to the lookup object.
1067 * <p>
1068 * The returned method handle will have
1069 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1070 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1071 * <p>
1072 * If the returned method handle is invoked, the method's class will
1073 * be initialized, if it has not already been initialized.
1074 * <p><b>Example:</b>
1075 * <blockquote><pre>{@code
1076 import static java.lang.invoke.MethodHandles.*;
1077 import static java.lang.invoke.MethodType.*;
1078 ...
1079 MethodHandle MH_asList = publicLookup().findStatic(Arrays.class,
1080 "asList", methodType(List.class, Object[].class));
1081 assertEquals("[x, y]", MH_asList.invoke("x", "y").toString());
1082 * }</pre></blockquote>
1083 * @param refc the class from which the method is accessed
1084 * @param name the name of the method
1085 * @param type the type of the method
1086 * @return the desired method handle
1087 * @throws NoSuchMethodException if the method does not exist
1088 * @throws IllegalAccessException if access checking fails,
1089 * or if the method is not {@code static},
1090 * or if the method's variable arity modifier bit
1091 * is set and {@code asVarargsCollector} fails
1092 * @exception SecurityException if a security manager is present and it
1093 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1094 * @throws NullPointerException if any argument is null
1095 */
1096 public
1097 MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1098 MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type);
1099 return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerClass(method));
1100 }
1101
1102 /**
1103 * Produces a method handle for a virtual method.
1104 * The type of the method handle will be that of the method,
1105 * with the receiver type (usually {@code refc}) prepended.
1106 * The method and all its argument types must be accessible to the lookup object.
1107 * <p>
1108 * When called, the handle will treat the first argument as a receiver
1109 * and dispatch on the receiver's type to determine which method
1110 * implementation to enter.
1111 * (The dispatching action is identical with that performed by an
1112 * {@code invokevirtual} or {@code invokeinterface} instruction.)
1113 * <p>
1114 * The first argument will be of type {@code refc} if the lookup
1115 * class has full privileges to access the member. Otherwise
1116 * the member must be {@code protected} and the first argument
1117 * will be restricted in type to the lookup class.
1118 * <p>
1119 * The returned method handle will have
1120 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1121 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1122 * <p>
1123 * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual}
1124 * instructions and method handles produced by {@code findVirtual},
1125 * if the class is {@code MethodHandle} and the name string is
1126 * {@code invokeExact} or {@code invoke}, the resulting
1127 * method handle is equivalent to one produced by
1128 * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or
1129 * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}
1130 * with the same {@code type} argument.
1131 * <p>
1132 * If the class is {@code VarHandle} and the name string corresponds to
1133 * the name of a signature-polymorphic access mode method, the resulting
1134 * method handle is equivalent to one produced by
1135 * {@link java.lang.invoke.MethodHandles#varHandleInvoker} with
1136 * the access mode corresponding to the name string and with the same
1137 * {@code type} arguments.
1138 * <p>
1139 * <b>Example:</b>
1140 * <blockquote><pre>{@code
1141 import static java.lang.invoke.MethodHandles.*;
1142 import static java.lang.invoke.MethodType.*;
1143 ...
1144 MethodHandle MH_concat = publicLookup().findVirtual(String.class,
1145 "concat", methodType(String.class, String.class));
1146 MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class,
1147 "hashCode", methodType(int.class));
1148 MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class,
1149 "hashCode", methodType(int.class));
1150 assertEquals("xy", (String) MH_concat.invokeExact("x", "y"));
1151 assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy"));
1152 assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy"));
1153 // interface method:
1154 MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class,
1155 "subSequence", methodType(CharSequence.class, int.class, int.class));
1156 assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString());
1157 // constructor "internal method" must be accessed differently:
1158 MethodType MT_newString = methodType(void.class); //()V for new String()
1159 try { assertEquals("impossible", lookup()
1160 .findVirtual(String.class, "<init>", MT_newString));
1161 } catch (NoSuchMethodException ex) { } // OK
1162 MethodHandle MH_newString = publicLookup()
1163 .findConstructor(String.class, MT_newString);
1164 assertEquals("", (String) MH_newString.invokeExact());
1165 * }</pre></blockquote>
1166 *
1167 * @param refc the class or interface from which the method is accessed
1168 * @param name the name of the method
1169 * @param type the type of the method, with the receiver argument omitted
1170 * @return the desired method handle
1171 * @throws NoSuchMethodException if the method does not exist
1172 * @throws IllegalAccessException if access checking fails,
1173 * or if the method is {@code static},
1174 * or if the method is {@code private} method of interface,
1175 * or if the method's variable arity modifier bit
1176 * is set and {@code asVarargsCollector} fails
1177 * @exception SecurityException if a security manager is present and it
1178 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1179 * @throws NullPointerException if any argument is null
1180 */
1181 public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1182 if (refc == MethodHandle.class) {
1183 MethodHandle mh = findVirtualForMH(name, type);
1184 if (mh != null) return mh;
1185 } else if (refc == VarHandle.class) {
1186 MethodHandle mh = findVirtualForVH(name, type);
1187 if (mh != null) return mh;
1188 }
1189 byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual);
1190 MemberName method = resolveOrFail(refKind, refc, name, type);
1191 return getDirectMethod(refKind, refc, method, findBoundCallerClass(method));
1192 }
1193 private MethodHandle findVirtualForMH(String name, MethodType type) {
1194 // these names require special lookups because of the implicit MethodType argument
1195 if ("invoke".equals(name))
1196 return invoker(type);
1197 if ("invokeExact".equals(name))
1198 return exactInvoker(type);
1199 assert(!MemberName.isMethodHandleInvokeName(name));
1200 return null;
1201 }
1202 private MethodHandle findVirtualForVH(String name, MethodType type) {
1203 try {
1204 return varHandleInvoker(VarHandle.AccessMode.valueFromMethodName(name), type);
1205 } catch (IllegalArgumentException e) {
1206 return null;
1207 }
1208 }
1209
1210 /**
1211 * Produces a method handle which creates an object and initializes it, using
1212 * the constructor of the specified type.
1213 * The parameter types of the method handle will be those of the constructor,
1214 * while the return type will be a reference to the constructor's class.
1215 * The constructor and all its argument types must be accessible to the lookup object.
1216 * <p>
1217 * The requested type must have a return type of {@code void}.
1218 * (This is consistent with the JVM's treatment of constructor type descriptors.)
1219 * <p>
1220 * The returned method handle will have
1221 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1222 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
1223 * <p>
1224 * If the returned method handle is invoked, the constructor's class will
1225 * be initialized, if it has not already been initialized.
1226 * <p><b>Example:</b>
1227 * <blockquote><pre>{@code
1228 import static java.lang.invoke.MethodHandles.*;
1229 import static java.lang.invoke.MethodType.*;
1230 ...
1231 MethodHandle MH_newArrayList = publicLookup().findConstructor(
1232 ArrayList.class, methodType(void.class, Collection.class));
1233 Collection orig = Arrays.asList("x", "y");
1234 Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig);
1235 assert(orig != copy);
1236 assertEquals(orig, copy);
1237 // a variable-arity constructor:
1238 MethodHandle MH_newProcessBuilder = publicLookup().findConstructor(
1239 ProcessBuilder.class, methodType(void.class, String[].class));
1240 ProcessBuilder pb = (ProcessBuilder)
1241 MH_newProcessBuilder.invoke("x", "y", "z");
1242 assertEquals("[x, y, z]", pb.command().toString());
1243 * }</pre></blockquote>
1244 * @param refc the class or interface from which the method is accessed
1245 * @param type the type of the method, with the receiver argument omitted, and a void return type
1246 * @return the desired method handle
1247 * @throws NoSuchMethodException if the constructor does not exist
1248 * @throws IllegalAccessException if access checking fails
1249 * or if the method's variable arity modifier bit
1250 * is set and {@code asVarargsCollector} fails
1251 * @exception SecurityException if a security manager is present and it
1252 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1253 * @throws NullPointerException if any argument is null
1254 */
1255 public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1256 if (refc.isArray()) {
1257 throw new NoSuchMethodException("no constructor for array class: " + refc.getName());
1258 }
1259 String name = "<init>";
1260 MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type);
1261 return getDirectConstructor(refc, ctor);
1262 }
1263
1264 /**
1265 * Looks up a class by name from the lookup context defined by this {@code Lookup} object. The static
1266 * initializer of the class is not run.
1267 * <p>
1268 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class}, its class
1269 * loader, and the {@linkplain #lookupModes() lookup modes}. In particular, the method first attempts to
1270 * load the requested class, and then determines whether the class is accessible to this lookup object.
1271 *
1272 * @param targetName the fully qualified name of the class to be looked up.
1273 * @return the requested class.
1274 * @exception SecurityException if a security manager is present and it
1275 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1276 * @throws LinkageError if the linkage fails
1277 * @throws ClassNotFoundException if the class cannot be loaded by the lookup class' loader.
1278 * @throws IllegalAccessException if the class is not accessible, using the allowed access
1279 * modes.
1280 * @exception SecurityException if a security manager is present and it
1281 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1282 * @since 9
1283 */
1284 public Class<?> findClass(String targetName) throws ClassNotFoundException, IllegalAccessException {
1285 Class<?> targetClass = Class.forName(targetName, false, lookupClass.getClassLoader());
1286 return accessClass(targetClass);
1287 }
1288
1289 /**
1290 * Determines if a class can be accessed from the lookup context defined by this {@code Lookup} object. The
1291 * static initializer of the class is not run.
1292 * <p>
1293 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class} and the
1294 * {@linkplain #lookupModes() lookup modes}.
1295 *
1296 * @param targetClass the class to be access-checked
1297 *
1298 * @return the class that has been access-checked
1299 *
1300 * @throws IllegalAccessException if the class is not accessible from the lookup class, using the allowed access
1301 * modes.
1302 * @exception SecurityException if a security manager is present and it
1303 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1304 * @since 9
1305 */
1306 public Class<?> accessClass(Class<?> targetClass) throws IllegalAccessException {
1307 if (!VerifyAccess.isClassAccessible(targetClass, lookupClass, allowedModes)) {
1308 throw new MemberName(targetClass).makeAccessException("access violation", this);
1309 }
1310 checkSecurityManager(targetClass, null);
1311 return targetClass;
1312 }
1313
1314 /**
1315 * Produces an early-bound method handle for a virtual method.
1316 * It will bypass checks for overriding methods on the receiver,
1317 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
1318 * instruction from within the explicitly specified {@code specialCaller}.
1319 * The type of the method handle will be that of the method,
1320 * with a suitably restricted receiver type prepended.
1321 * (The receiver type will be {@code specialCaller} or a subtype.)
1322 * The method and all its argument types must be accessible
1323 * to the lookup object.
1324 * <p>
1325 * Before method resolution,
1326 * if the explicitly specified caller class is not identical with the
1327 * lookup class, or if this lookup object does not have
1328 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
1329 * privileges, the access fails.
1330 * <p>
1331 * The returned method handle will have
1332 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1333 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1334 * <p style="font-size:smaller;">
1335 * <em>(Note: JVM internal methods named {@code "<init>"} are not visible to this API,
1336 * even though the {@code invokespecial} instruction can refer to them
1337 * in special circumstances. Use {@link #findConstructor findConstructor}
1338 * to access instance initialization methods in a safe manner.)</em>
1339 * <p><b>Example:</b>
1340 * <blockquote><pre>{@code
1341 import static java.lang.invoke.MethodHandles.*;
1342 import static java.lang.invoke.MethodType.*;
1343 ...
1344 static class Listie extends ArrayList {
1345 public String toString() { return "[wee Listie]"; }
1346 static Lookup lookup() { return MethodHandles.lookup(); }
1347 }
1348 ...
1349 // no access to constructor via invokeSpecial:
1350 MethodHandle MH_newListie = Listie.lookup()
1351 .findConstructor(Listie.class, methodType(void.class));
1352 Listie l = (Listie) MH_newListie.invokeExact();
1353 try { assertEquals("impossible", Listie.lookup().findSpecial(
1354 Listie.class, "<init>", methodType(void.class), Listie.class));
1355 } catch (NoSuchMethodException ex) { } // OK
1356 // access to super and self methods via invokeSpecial:
1357 MethodHandle MH_super = Listie.lookup().findSpecial(
1358 ArrayList.class, "toString" , methodType(String.class), Listie.class);
1359 MethodHandle MH_this = Listie.lookup().findSpecial(
1360 Listie.class, "toString" , methodType(String.class), Listie.class);
1361 MethodHandle MH_duper = Listie.lookup().findSpecial(
1362 Object.class, "toString" , methodType(String.class), Listie.class);
1363 assertEquals("[]", (String) MH_super.invokeExact(l));
1364 assertEquals(""+l, (String) MH_this.invokeExact(l));
1365 assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method
1366 try { assertEquals("inaccessible", Listie.lookup().findSpecial(
1367 String.class, "toString", methodType(String.class), Listie.class));
1368 } catch (IllegalAccessException ex) { } // OK
1369 Listie subl = new Listie() { public String toString() { return "[subclass]"; } };
1370 assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method
1371 * }</pre></blockquote>
1372 *
1373 * @param refc the class or interface from which the method is accessed
1374 * @param name the name of the method (which must not be "<init>")
1375 * @param type the type of the method, with the receiver argument omitted
1376 * @param specialCaller the proposed calling class to perform the {@code invokespecial}
1377 * @return the desired method handle
1378 * @throws NoSuchMethodException if the method does not exist
1379 * @throws IllegalAccessException if access checking fails,
1380 * or if the method is {@code static},
1381 * or if the method's variable arity modifier bit
1382 * is set and {@code asVarargsCollector} fails
1383 * @exception SecurityException if a security manager is present and it
1384 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1385 * @throws NullPointerException if any argument is null
1386 */
1387 public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,
1388 Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
1389 checkSpecialCaller(specialCaller, refc);
1390 Lookup specialLookup = this.in(specialCaller);
1391 MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type);
1392 return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerClass(method));
1393 }
1394
1395 /**
1396 * Produces a method handle giving read access to a non-static field.
1397 * The type of the method handle will have a return type of the field's
1398 * value type.
1399 * The method handle's single argument will be the instance containing
1400 * the field.
1401 * Access checking is performed immediately on behalf of the lookup class.
1402 * @param refc the class or interface from which the method is accessed
1403 * @param name the field's name
1404 * @param type the field's type
1405 * @return a method handle which can load values from the field
1406 * @throws NoSuchFieldException if the field does not exist
1407 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1408 * @exception SecurityException if a security manager is present and it
1409 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1410 * @throws NullPointerException if any argument is null
1411 * @see #findVarHandle(Class, String, Class)
1412 */
1413 public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1414 MemberName field = resolveOrFail(REF_getField, refc, name, type);
1415 return getDirectField(REF_getField, refc, field);
1416 }
1417
1418 /**
1419 * Produces a method handle giving write access to a non-static field.
1420 * The type of the method handle will have a void return type.
1421 * The method handle will take two arguments, the instance containing
1422 * the field, and the value to be stored.
1423 * The second argument will be of the field's value type.
1424 * Access checking is performed immediately on behalf of the lookup class.
1425 * @param refc the class or interface from which the method is accessed
1426 * @param name the field's name
1427 * @param type the field's type
1428 * @return a method handle which can store values into the field
1429 * @throws NoSuchFieldException if the field does not exist
1430 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1431 * @exception SecurityException if a security manager is present and it
1432 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1433 * @throws NullPointerException if any argument is null
1434 * @see #findVarHandle(Class, String, Class)
1435 */
1436 public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1437 MemberName field = resolveOrFail(REF_putField, refc, name, type);
1438 return getDirectField(REF_putField, refc, field);
1439 }
1440
1441 /**
1442 * Produces a VarHandle giving access to a non-static field {@code name}
1443 * of type {@code type} declared in a class of type {@code recv}.
1444 * The VarHandle's variable type is {@code type} and it has one
1445 * coordinate type, {@code recv}.
1446 * <p>
1447 * Access checking is performed immediately on behalf of the lookup
1448 * class.
1449 * <p>
1450 * Certain access modes of the returned VarHandle are unsupported under
1451 * the following conditions:
1452 * <ul>
1453 * <li>if the field is declared {@code final}, then the write, atomic
1454 * update, numeric atomic update, and bitwise atomic update access
1455 * modes are unsupported.
1456 * <li>if the field type is anything other than {@code byte},
1457 * {@code short}, {@code char}, {@code int}, {@code long},
1458 * {@code float}, or {@code double} then numeric atomic update
1459 * access modes are unsupported.
1460 * <li>if the field type is anything other than {@code boolean},
1461 * {@code byte}, {@code short}, {@code char}, {@code int} or
1462 * {@code long} then bitwise atomic update access modes are
1463 * unsupported.
1464 * </ul>
1465 * <p>
1466 * If the field is declared {@code volatile} then the returned VarHandle
1467 * will override access to the field (effectively ignore the
1468 * {@code volatile} declaration) in accordance to its specified
1469 * access modes.
1470 * <p>
1471 * If the field type is {@code float} or {@code double} then numeric
1472 * and atomic update access modes compare values using their bitwise
1473 * representation (see {@link Float#floatToRawIntBits} and
1474 * {@link Double#doubleToRawLongBits}, respectively).
1475 * @apiNote
1476 * Bitwise comparison of {@code float} values or {@code double} values,
1477 * as performed by the numeric and atomic update access modes, differ
1478 * from the primitive {@code ==} operator and the {@link Float#equals}
1479 * and {@link Double#equals} methods, specifically with respect to
1480 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
1481 * Care should be taken when performing a compare and set or a compare
1482 * and exchange operation with such values since the operation may
1483 * unexpectedly fail.
1484 * There are many possible NaN values that are considered to be
1485 * {@code NaN} in Java, although no IEEE 754 floating-point operation
1486 * provided by Java can distinguish between them. Operation failure can
1487 * occur if the expected or witness value is a NaN value and it is
1488 * transformed (perhaps in a platform specific manner) into another NaN
1489 * value, and thus has a different bitwise representation (see
1490 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
1491 * details).
1492 * The values {@code -0.0} and {@code +0.0} have different bitwise
1493 * representations but are considered equal when using the primitive
1494 * {@code ==} operator. Operation failure can occur if, for example, a
1495 * numeric algorithm computes an expected value to be say {@code -0.0}
1496 * and previously computed the witness value to be say {@code +0.0}.
1497 * @param recv the receiver class, of type {@code R}, that declares the
1498 * non-static field
1499 * @param name the field's name
1500 * @param type the field's type, of type {@code T}
1501 * @return a VarHandle giving access to non-static fields.
1502 * @throws NoSuchFieldException if the field does not exist
1503 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1504 * @exception SecurityException if a security manager is present and it
1505 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1506 * @throws NullPointerException if any argument is null
1507 * @since 9
1508 */
1509 public VarHandle findVarHandle(Class<?> recv, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1510 MemberName getField = resolveOrFail(REF_getField, recv, name, type);
1511 MemberName putField = resolveOrFail(REF_putField, recv, name, type);
1512 return getFieldVarHandle(REF_getField, REF_putField, recv, getField, putField);
1513 }
1514
1515 /**
1516 * Produces a method handle giving read access to a static field.
1517 * The type of the method handle will have a return type of the field's
1518 * value type.
1519 * The method handle will take no arguments.
1520 * Access checking is performed immediately on behalf of the lookup class.
1521 * <p>
1522 * If the returned method handle is invoked, the field's class will
1523 * be initialized, if it has not already been initialized.
1524 * @param refc the class or interface from which the method is accessed
1525 * @param name the field's name
1526 * @param type the field's type
1527 * @return a method handle which can load values from the field
1528 * @throws NoSuchFieldException if the field does not exist
1529 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1530 * @exception SecurityException if a security manager is present and it
1531 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1532 * @throws NullPointerException if any argument is null
1533 */
1534 public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1535 MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
1536 return getDirectField(REF_getStatic, refc, field);
1537 }
1538
1539 /**
1540 * Produces a method handle giving write access to a static field.
1541 * The type of the method handle will have a void return type.
1542 * The method handle will take a single
1543 * argument, of the field's value type, the value to be stored.
1544 * Access checking is performed immediately on behalf of the lookup class.
1545 * <p>
1546 * If the returned method handle is invoked, the field's class will
1547 * be initialized, if it has not already been initialized.
1548 * @param refc the class or interface from which the method is accessed
1549 * @param name the field's name
1550 * @param type the field's type
1551 * @return a method handle which can store values into the field
1552 * @throws NoSuchFieldException if the field does not exist
1553 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1554 * @exception SecurityException if a security manager is present and it
1555 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1556 * @throws NullPointerException if any argument is null
1557 */
1558 public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1559 MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
1560 return getDirectField(REF_putStatic, refc, field);
1561 }
1562
1563 /**
1564 * Produces a VarHandle giving access to a static field {@code name} of
1565 * type {@code type} declared in a class of type {@code decl}.
1566 * The VarHandle's variable type is {@code type} and it has no
1567 * coordinate types.
1568 * <p>
1569 * Access checking is performed immediately on behalf of the lookup
1570 * class.
1571 * <p>
1572 * If the returned VarHandle is operated on, the declaring class will be
1573 * initialized, if it has not already been initialized.
1574 * <p>
1575 * Certain access modes of the returned VarHandle are unsupported under
1576 * the following conditions:
1577 * <ul>
1578 * <li>if the field is declared {@code final}, then the write, atomic
1579 * update, numeric atomic update, and bitwise atomic update access
1580 * modes are unsupported.
1581 * <li>if the field type is anything other than {@code byte},
1582 * {@code short}, {@code char}, {@code int}, {@code long},
1583 * {@code float}, or {@code double}, then numeric atomic update
1584 * access modes are unsupported.
1585 * <li>if the field type is anything other than {@code boolean},
1586 * {@code byte}, {@code short}, {@code char}, {@code int} or
1587 * {@code long} then bitwise atomic update access modes are
1588 * unsupported.
1589 * </ul>
1590 * <p>
1591 * If the field is declared {@code volatile} then the returned VarHandle
1592 * will override access to the field (effectively ignore the
1593 * {@code volatile} declaration) in accordance to its specified
1594 * access modes.
1595 * <p>
1596 * If the field type is {@code float} or {@code double} then numeric
1597 * and atomic update access modes compare values using their bitwise
1598 * representation (see {@link Float#floatToRawIntBits} and
1599 * {@link Double#doubleToRawLongBits}, respectively).
1600 * @apiNote
1601 * Bitwise comparison of {@code float} values or {@code double} values,
1602 * as performed by the numeric and atomic update access modes, differ
1603 * from the primitive {@code ==} operator and the {@link Float#equals}
1604 * and {@link Double#equals} methods, specifically with respect to
1605 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
1606 * Care should be taken when performing a compare and set or a compare
1607 * and exchange operation with such values since the operation may
1608 * unexpectedly fail.
1609 * There are many possible NaN values that are considered to be
1610 * {@code NaN} in Java, although no IEEE 754 floating-point operation
1611 * provided by Java can distinguish between them. Operation failure can
1612 * occur if the expected or witness value is a NaN value and it is
1613 * transformed (perhaps in a platform specific manner) into another NaN
1614 * value, and thus has a different bitwise representation (see
1615 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
1616 * details).
1617 * The values {@code -0.0} and {@code +0.0} have different bitwise
1618 * representations but are considered equal when using the primitive
1619 * {@code ==} operator. Operation failure can occur if, for example, a
1620 * numeric algorithm computes an expected value to be say {@code -0.0}
1621 * and previously computed the witness value to be say {@code +0.0}.
1622 * @param decl the class that declares the static field
1623 * @param name the field's name
1624 * @param type the field's type, of type {@code T}
1625 * @return a VarHandle giving access to a static field
1626 * @throws NoSuchFieldException if the field does not exist
1627 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1628 * @exception SecurityException if a security manager is present and it
1629 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1630 * @throws NullPointerException if any argument is null
1631 * @since 9
1632 */
1633 public VarHandle findStaticVarHandle(Class<?> decl, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1634 MemberName getField = resolveOrFail(REF_getStatic, decl, name, type);
1635 MemberName putField = resolveOrFail(REF_putStatic, decl, name, type);
1636 return getFieldVarHandle(REF_getStatic, REF_putStatic, decl, getField, putField);
1637 }
1638
1639 /**
1640 * Produces an early-bound method handle for a non-static method.
1641 * The receiver must have a supertype {@code defc} in which a method
1642 * of the given name and type is accessible to the lookup class.
1643 * The method and all its argument types must be accessible to the lookup object.
1644 * The type of the method handle will be that of the method,
1645 * without any insertion of an additional receiver parameter.
1646 * The given receiver will be bound into the method handle,
1647 * so that every call to the method handle will invoke the
1648 * requested method on the given receiver.
1649 * <p>
1650 * The returned method handle will have
1651 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1652 * the method's variable arity modifier bit ({@code 0x0080}) is set
1653 * <em>and</em> the trailing array argument is not the only argument.
1654 * (If the trailing array argument is the only argument,
1655 * the given receiver value will be bound to it.)
1656 * <p>
1657 * This is almost equivalent to the following code, with some differences noted below:
1658 * <blockquote><pre>{@code
1659 import static java.lang.invoke.MethodHandles.*;
1660 import static java.lang.invoke.MethodType.*;
1661 ...
1662 MethodHandle mh0 = lookup().findVirtual(defc, name, type);
1663 MethodHandle mh1 = mh0.bindTo(receiver);
1664 mh1 = mh1.withVarargs(mh0.isVarargsCollector());
1665 return mh1;
1666 * }</pre></blockquote>
1667 * where {@code defc} is either {@code receiver.getClass()} or a super
1668 * type of that class, in which the requested method is accessible
1669 * to the lookup class.
1670 * (Unlike {@code bind}, {@code bindTo} does not preserve variable arity.
1671 * Also, {@code bindTo} may throw a {@code ClassCastException} in instances where {@code bind} would
1672 * throw an {@code IllegalAccessException}, as in the case where the member is {@code protected} and
1673 * the receiver is restricted by {@code findVirtual} to the lookup class.)
1674 * @param receiver the object from which the method is accessed
1675 * @param name the name of the method
1676 * @param type the type of the method, with the receiver argument omitted
1677 * @return the desired method handle
1678 * @throws NoSuchMethodException if the method does not exist
1679 * @throws IllegalAccessException if access checking fails
1680 * or if the method's variable arity modifier bit
1681 * is set and {@code asVarargsCollector} fails
1682 * @exception SecurityException if a security manager is present and it
1683 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1684 * @throws NullPointerException if any argument is null
1685 * @see MethodHandle#bindTo
1686 * @see #findVirtual
1687 */
1688 public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1689 Class<? extends Object> refc = receiver.getClass(); // may get NPE
1690 MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
1691 MethodHandle mh = getDirectMethodNoRestrictInvokeSpecial(refc, method, findBoundCallerClass(method));
1692 if (!mh.type().leadingReferenceParameter().isAssignableFrom(receiver.getClass())) {
1693 throw new IllegalAccessException("The restricted defining class " +
1694 mh.type().leadingReferenceParameter().getName() +
1695 " is not assignable from receiver class " +
1696 receiver.getClass().getName());
1697 }
1698 return mh.bindArgumentL(0, receiver).setVarargs(method);
1699 }
1700
1701 /**
1702 * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
1703 * to <i>m</i>, if the lookup class has permission.
1704 * If <i>m</i> is non-static, the receiver argument is treated as an initial argument.
1705 * If <i>m</i> is virtual, overriding is respected on every call.
1706 * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped.
1707 * The type of the method handle will be that of the method,
1708 * with the receiver type prepended (but only if it is non-static).
1709 * If the method's {@code accessible} flag is not set,
1710 * access checking is performed immediately on behalf of the lookup class.
1711 * If <i>m</i> is not public, do not share the resulting handle with untrusted parties.
1712 * <p>
1713 * The returned method handle will have
1714 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1715 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1716 * <p>
1717 * If <i>m</i> is static, and
1718 * if the returned method handle is invoked, the method's class will
1719 * be initialized, if it has not already been initialized.
1720 * @param m the reflected method
1721 * @return a method handle which can invoke the reflected method
1722 * @throws IllegalAccessException if access checking fails
1723 * or if the method's variable arity modifier bit
1724 * is set and {@code asVarargsCollector} fails
1725 * @throws NullPointerException if the argument is null
1726 */
1727 public MethodHandle unreflect(Method m) throws IllegalAccessException {
1728 if (m.getDeclaringClass() == MethodHandle.class) {
1729 MethodHandle mh = unreflectForMH(m);
1730 if (mh != null) return mh;
1731 }
1732 if (m.getDeclaringClass() == VarHandle.class) {
1733 MethodHandle mh = unreflectForVH(m);
1734 if (mh != null) return mh;
1735 }
1736 MemberName method = new MemberName(m);
1737 byte refKind = method.getReferenceKind();
1738 if (refKind == REF_invokeSpecial)
1739 refKind = REF_invokeVirtual;
1740 assert(method.isMethod());
1741 @SuppressWarnings("deprecation")
1742 Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
1743 return lookup.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method, findBoundCallerClass(method));
1744 }
1745 private MethodHandle unreflectForMH(Method m) {
1746 // these names require special lookups because they throw UnsupportedOperationException
1747 if (MemberName.isMethodHandleInvokeName(m.getName()))
1748 return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m));
1749 return null;
1750 }
1751 private MethodHandle unreflectForVH(Method m) {
1752 // these names require special lookups because they throw UnsupportedOperationException
1753 if (MemberName.isVarHandleMethodInvokeName(m.getName()))
1754 return MethodHandleImpl.fakeVarHandleInvoke(new MemberName(m));
1755 return null;
1756 }
1757
1758 /**
1759 * Produces a method handle for a reflected method.
1760 * It will bypass checks for overriding methods on the receiver,
1761 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
1762 * instruction from within the explicitly specified {@code specialCaller}.
1763 * The type of the method handle will be that of the method,
1764 * with a suitably restricted receiver type prepended.
1765 * (The receiver type will be {@code specialCaller} or a subtype.)
1766 * If the method's {@code accessible} flag is not set,
1767 * access checking is performed immediately on behalf of the lookup class,
1768 * as if {@code invokespecial} instruction were being linked.
1769 * <p>
1770 * Before method resolution,
1771 * if the explicitly specified caller class is not identical with the
1772 * lookup class, or if this lookup object does not have
1773 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
1774 * privileges, the access fails.
1775 * <p>
1776 * The returned method handle will have
1777 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1778 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1779 * @param m the reflected method
1780 * @param specialCaller the class nominally calling the method
1781 * @return a method handle which can invoke the reflected method
1782 * @throws IllegalAccessException if access checking fails,
1783 * or if the method is {@code static},
1784 * or if the method's variable arity modifier bit
1785 * is set and {@code asVarargsCollector} fails
1786 * @throws NullPointerException if any argument is null
1787 */
1788 public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException {
1789 checkSpecialCaller(specialCaller, null);
1790 Lookup specialLookup = this.in(specialCaller);
1791 MemberName method = new MemberName(m, true);
1792 assert(method.isMethod());
1793 // ignore m.isAccessible: this is a new kind of access
1794 return specialLookup.getDirectMethodNoSecurityManager(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerClass(method));
1795 }
1796
1797 /**
1798 * Produces a method handle for a reflected constructor.
1799 * The type of the method handle will be that of the constructor,
1800 * with the return type changed to the declaring class.
1801 * The method handle will perform a {@code newInstance} operation,
1802 * creating a new instance of the constructor's class on the
1803 * arguments passed to the method handle.
1804 * <p>
1805 * If the constructor's {@code accessible} flag is not set,
1806 * access checking is performed immediately on behalf of the lookup class.
1807 * <p>
1808 * The returned method handle will have
1809 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1810 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
1811 * <p>
1812 * If the returned method handle is invoked, the constructor's class will
1813 * be initialized, if it has not already been initialized.
1814 * @param c the reflected constructor
1815 * @return a method handle which can invoke the reflected constructor
1816 * @throws IllegalAccessException if access checking fails
1817 * or if the method's variable arity modifier bit
1818 * is set and {@code asVarargsCollector} fails
1819 * @throws NullPointerException if the argument is null
1820 */
1821 public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException {
1822 MemberName ctor = new MemberName(c);
1823 assert(ctor.isConstructor());
1824 @SuppressWarnings("deprecation")
1825 Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
1826 return lookup.getDirectConstructorNoSecurityManager(ctor.getDeclaringClass(), ctor);
1827 }
1828
1829 /**
1830 * Produces a method handle giving read access to a reflected field.
1831 * The type of the method handle will have a return type of the field's
1832 * value type.
1833 * If the field is static, the method handle will take no arguments.
1834 * Otherwise, its single argument will be the instance containing
1835 * the field.
1836 * If the field's {@code accessible} flag is not set,
1837 * access checking is performed immediately on behalf of the lookup class.
1838 * <p>
1839 * If the field is static, and
1840 * if the returned method handle is invoked, the field's class will
1841 * be initialized, if it has not already been initialized.
1842 * @param f the reflected field
1843 * @return a method handle which can load values from the reflected field
1844 * @throws IllegalAccessException if access checking fails
1845 * @throws NullPointerException if the argument is null
1846 */
1847 public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
1848 return unreflectField(f, false);
1849 }
1850 private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
1851 MemberName field = new MemberName(f, isSetter);
1852 assert(isSetter
1853 ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
1854 : MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
1855 @SuppressWarnings("deprecation")
1856 Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
1857 return lookup.getDirectFieldNoSecurityManager(field.getReferenceKind(), f.getDeclaringClass(), field);
1858 }
1859
1860 /**
1861 * Produces a method handle giving write access to a reflected field.
1862 * The type of the method handle will have a void return type.
1863 * If the field is static, the method handle will take a single
1864 * argument, of the field's value type, the value to be stored.
1865 * Otherwise, the two arguments will be the instance containing
1866 * the field, and the value to be stored.
1867 * If the field's {@code accessible} flag is not set,
1868 * access checking is performed immediately on behalf of the lookup class.
1869 * <p>
1870 * If the field is static, and
1871 * if the returned method handle is invoked, the field's class will
1872 * be initialized, if it has not already been initialized.
1873 * @param f the reflected field
1874 * @return a method handle which can store values into the reflected field
1875 * @throws IllegalAccessException if access checking fails
1876 * @throws NullPointerException if the argument is null
1877 */
1878 public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
1879 return unreflectField(f, true);
1880 }
1881
1882 /**
1883 * Produces a VarHandle giving access to a reflected field {@code f}
1884 * of type {@code T} declared in a class of type {@code R}.
1885 * The VarHandle's variable type is {@code T}.
1886 * If the field is non-static the VarHandle has one coordinate type,
1887 * {@code R}. Otherwise, the field is static, and the VarHandle has no
1888 * coordinate types.
1889 * <p>
1890 * Access checking is performed immediately on behalf of the lookup
1891 * class, regardless of the value of the field's {@code accessible}
1892 * flag.
1893 * <p>
1894 * If the field is static, and if the returned VarHandle is operated
1895 * on, the field's declaring class will be initialized, if it has not
1896 * already been initialized.
1897 * <p>
1898 * Certain access modes of the returned VarHandle are unsupported under
1899 * the following conditions:
1900 * <ul>
1901 * <li>if the field is declared {@code final}, then the write, atomic
1902 * update, numeric atomic update, and bitwise atomic update access
1903 * modes are unsupported.
1904 * <li>if the field type is anything other than {@code byte},
1905 * {@code short}, {@code char}, {@code int}, {@code long},
1906 * {@code float}, or {@code double} then numeric atomic update
1907 * access modes are unsupported.
1908 * <li>if the field type is anything other than {@code boolean},
1909 * {@code byte}, {@code short}, {@code char}, {@code int} or
1910 * {@code long} then bitwise atomic update access modes are
1911 * unsupported.
1912 * </ul>
1913 * <p>
1914 * If the field is declared {@code volatile} then the returned VarHandle
1915 * will override access to the field (effectively ignore the
1916 * {@code volatile} declaration) in accordance to its specified
1917 * access modes.
1918 * <p>
1919 * If the field type is {@code float} or {@code double} then numeric
1920 * and atomic update access modes compare values using their bitwise
1921 * representation (see {@link Float#floatToRawIntBits} and
1922 * {@link Double#doubleToRawLongBits}, respectively).
1923 * @apiNote
1924 * Bitwise comparison of {@code float} values or {@code double} values,
1925 * as performed by the numeric and atomic update access modes, differ
1926 * from the primitive {@code ==} operator and the {@link Float#equals}
1927 * and {@link Double#equals} methods, specifically with respect to
1928 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
1929 * Care should be taken when performing a compare and set or a compare
1930 * and exchange operation with such values since the operation may
1931 * unexpectedly fail.
1932 * There are many possible NaN values that are considered to be
1933 * {@code NaN} in Java, although no IEEE 754 floating-point operation
1934 * provided by Java can distinguish between them. Operation failure can
1935 * occur if the expected or witness value is a NaN value and it is
1936 * transformed (perhaps in a platform specific manner) into another NaN
1937 * value, and thus has a different bitwise representation (see
1938 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
1939 * details).
1940 * The values {@code -0.0} and {@code +0.0} have different bitwise
1941 * representations but are considered equal when using the primitive
1942 * {@code ==} operator. Operation failure can occur if, for example, a
1943 * numeric algorithm computes an expected value to be say {@code -0.0}
1944 * and previously computed the witness value to be say {@code +0.0}.
1945 * @param f the reflected field, with a field of type {@code T}, and
1946 * a declaring class of type {@code R}
1947 * @return a VarHandle giving access to non-static fields or a static
1948 * field
1949 * @throws IllegalAccessException if access checking fails
1950 * @throws NullPointerException if the argument is null
1951 * @since 9
1952 */
1953 public VarHandle unreflectVarHandle(Field f) throws IllegalAccessException {
1954 MemberName getField = new MemberName(f, false);
1955 MemberName putField = new MemberName(f, true);
1956 return getFieldVarHandleNoSecurityManager(getField.getReferenceKind(), putField.getReferenceKind(),
1957 f.getDeclaringClass(), getField, putField);
1958 }
1959
1960 /**
1961 * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
1962 * created by this lookup object or a similar one.
1963 * Security and access checks are performed to ensure that this lookup object
1964 * is capable of reproducing the target method handle.
1965 * This means that the cracking may fail if target is a direct method handle
1966 * but was created by an unrelated lookup object.
1967 * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a>
1968 * and was created by a lookup object for a different class.
1969 * @param target a direct method handle to crack into symbolic reference components
1970 * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object
1971 * @exception SecurityException if a security manager is present and it
1972 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1973 * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails
1974 * @exception NullPointerException if the target is {@code null}
1975 * @see MethodHandleInfo
1976 * @since 1.8
1977 */
1978 public MethodHandleInfo revealDirect(MethodHandle target) {
1979 MemberName member = target.internalMemberName();
1980 if (member == null || (!member.isResolved() &&
1981 !member.isMethodHandleInvoke() &&
1982 !member.isVarHandleMethodInvoke()))
1983 throw newIllegalArgumentException("not a direct method handle");
1984 Class<?> defc = member.getDeclaringClass();
1985 byte refKind = member.getReferenceKind();
1986 assert(MethodHandleNatives.refKindIsValid(refKind));
1987 if (refKind == REF_invokeSpecial && !target.isInvokeSpecial())
1988 // Devirtualized method invocation is usually formally virtual.
1989 // To avoid creating extra MemberName objects for this common case,
1990 // we encode this extra degree of freedom using MH.isInvokeSpecial.
1991 refKind = REF_invokeVirtual;
1992 if (refKind == REF_invokeVirtual && defc.isInterface())
1993 // Symbolic reference is through interface but resolves to Object method (toString, etc.)
1994 refKind = REF_invokeInterface;
1995 // Check SM permissions and member access before cracking.
1996 try {
1997 checkAccess(refKind, defc, member);
1998 checkSecurityManager(defc, member);
1999 } catch (IllegalAccessException ex) {
2000 throw new IllegalArgumentException(ex);
2001 }
2002 if (allowedModes != TRUSTED && member.isCallerSensitive()) {
2003 Class<?> callerClass = target.internalCallerClass();
2004 if (!hasPrivateAccess() || callerClass != lookupClass())
2005 throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass);
2006 }
2007 // Produce the handle to the results.
2008 return new InfoFromMemberName(this, member, refKind);
2009 }
2010
2011 /// Helper methods, all package-private.
2012
2013 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2014 checkSymbolicClass(refc); // do this before attempting to resolve
2015 Objects.requireNonNull(name);
2016 Objects.requireNonNull(type);
2017 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
2018 NoSuchFieldException.class);
2019 }
2020
2021 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2022 checkSymbolicClass(refc); // do this before attempting to resolve
2023 Objects.requireNonNull(name);
2024 Objects.requireNonNull(type);
2025 checkMethodName(refKind, name); // NPE check on name
2026 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
2027 NoSuchMethodException.class);
2028 }
2029
2030 MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException {
2031 checkSymbolicClass(member.getDeclaringClass()); // do this before attempting to resolve
2032 Objects.requireNonNull(member.getName());
2033 Objects.requireNonNull(member.getType());
2034 return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(),
2035 ReflectiveOperationException.class);
2036 }
2037
2038 void checkSymbolicClass(Class<?> refc) throws IllegalAccessException {
2039 Objects.requireNonNull(refc);
2040 Class<?> caller = lookupClassOrNull();
2041 if (caller != null && !VerifyAccess.isClassAccessible(refc, caller, allowedModes))
2042 throw new MemberName(refc).makeAccessException("symbolic reference class is not accessible", this);
2043 }
2044
2045 /** Check name for an illegal leading "<" character. */
2046 void checkMethodName(byte refKind, String name) throws NoSuchMethodException {
2047 if (name.startsWith("<") && refKind != REF_newInvokeSpecial)
2048 throw new NoSuchMethodException("illegal method name: "+name);
2049 }
2050
2051
2052 /**
2053 * Find my trustable caller class if m is a caller sensitive method.
2054 * If this lookup object has private access, then the caller class is the lookupClass.
2055 * Otherwise, if m is caller-sensitive, throw IllegalAccessException.
2056 */
2057 Class<?> findBoundCallerClass(MemberName m) throws IllegalAccessException {
2058 Class<?> callerClass = null;
2059 if (MethodHandleNatives.isCallerSensitive(m)) {
2060 // Only lookups with private access are allowed to resolve caller-sensitive methods
2061 if (hasPrivateAccess()) {
2062 callerClass = lookupClass;
2063 } else {
2064 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
2065 }
2066 }
2067 return callerClass;
2068 }
2069
2070 /**
2071 * Returns {@code true} if this lookup has {@code PRIVATE} access.
2072 * @return {@code true} if this lookup has {@code PRIVATE} access.
2073 * @since 9
2074 */
2075 public boolean hasPrivateAccess() {
2076 return (allowedModes & PRIVATE) != 0;
2077 }
2078
2079 /**
2080 * Perform necessary <a href="MethodHandles.Lookup.html#secmgr">access checks</a>.
2081 * Determines a trustable caller class to compare with refc, the symbolic reference class.
2082 * If this lookup object has private access, then the caller class is the lookupClass.
2083 */
2084 void checkSecurityManager(Class<?> refc, MemberName m) {
2085 SecurityManager smgr = System.getSecurityManager();
2086 if (smgr == null) return;
2087 if (allowedModes == TRUSTED) return;
2088
2089 // Step 1:
2090 boolean fullPowerLookup = hasPrivateAccess();
2091 if (!fullPowerLookup ||
2092 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
2093 ReflectUtil.checkPackageAccess(refc);
2094 }
2095
2096 if (m == null) { // findClass or accessClass
2097 // Step 2b:
2098 if (!fullPowerLookup) {
2099 smgr.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
2100 }
2101 return;
2102 }
2103
2104 // Step 2a:
2105 if (m.isPublic()) return;
2106 if (!fullPowerLookup) {
2107 smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION);
2108 }
2109
2110 // Step 3:
2111 Class<?> defc = m.getDeclaringClass();
2112 if (!fullPowerLookup && defc != refc) {
2113 ReflectUtil.checkPackageAccess(defc);
2114 }
2115 }
2116
2117 void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
2118 boolean wantStatic = (refKind == REF_invokeStatic);
2119 String message;
2120 if (m.isConstructor())
2121 message = "expected a method, not a constructor";
2122 else if (!m.isMethod())
2123 message = "expected a method";
2124 else if (wantStatic != m.isStatic())
2125 message = wantStatic ? "expected a static method" : "expected a non-static method";
2126 else
2127 { checkAccess(refKind, refc, m); return; }
2128 throw m.makeAccessException(message, this);
2129 }
2130
2131 void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
2132 boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
2133 String message;
2134 if (wantStatic != m.isStatic())
2135 message = wantStatic ? "expected a static field" : "expected a non-static field";
2136 else
2137 { checkAccess(refKind, refc, m); return; }
2138 throw m.makeAccessException(message, this);
2139 }
2140
2141 /** Check public/protected/private bits on the symbolic reference class and its member. */
2142 void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
2143 assert(m.referenceKindIsConsistentWith(refKind) &&
2144 MethodHandleNatives.refKindIsValid(refKind) &&
2145 (MethodHandleNatives.refKindIsField(refKind) == m.isField()));
2146 int allowedModes = this.allowedModes;
2147 if (allowedModes == TRUSTED) return;
2148 int mods = m.getModifiers();
2149 if (Modifier.isProtected(mods) &&
2150 refKind == REF_invokeVirtual &&
2151 m.getDeclaringClass() == Object.class &&
2152 m.getName().equals("clone") &&
2153 refc.isArray()) {
2154 // The JVM does this hack also.
2155 // (See ClassVerifier::verify_invoke_instructions
2156 // and LinkResolver::check_method_accessability.)
2157 // Because the JVM does not allow separate methods on array types,
2158 // there is no separate method for int[].clone.
2159 // All arrays simply inherit Object.clone.
2160 // But for access checking logic, we make Object.clone
2161 // (normally protected) appear to be public.
2162 // Later on, when the DirectMethodHandle is created,
2163 // its leading argument will be restricted to the
2164 // requested array type.
2165 // N.B. The return type is not adjusted, because
2166 // that is *not* the bytecode behavior.
2167 mods ^= Modifier.PROTECTED | Modifier.PUBLIC;
2168 }
2169 if (Modifier.isProtected(mods) && refKind == REF_newInvokeSpecial) {
2170 // cannot "new" a protected ctor in a different package
2171 mods ^= Modifier.PROTECTED;
2172 }
2173 if (Modifier.isFinal(mods) &&
2174 MethodHandleNatives.refKindIsSetter(refKind))
2175 throw m.makeAccessException("unexpected set of a final field", this);
2176 int requestedModes = fixmods(mods); // adjust 0 => PACKAGE
2177 if ((requestedModes & allowedModes) != 0) {
2178 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
2179 mods, lookupClass(), allowedModes))
2180 return;
2181 } else {
2182 // Protected members can also be checked as if they were package-private.
2183 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
2184 && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
2185 return;
2186 }
2187 throw m.makeAccessException(accessFailedMessage(refc, m), this);
2188 }
2189
2190 String accessFailedMessage(Class<?> refc, MemberName m) {
2191 Class<?> defc = m.getDeclaringClass();
2192 int mods = m.getModifiers();
2193 // check the class first:
2194 boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
2195 (defc == refc ||
2196 Modifier.isPublic(refc.getModifiers())));
2197 if (!classOK && (allowedModes & PACKAGE) != 0) {
2198 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), FULL_POWER_MODES) &&
2199 (defc == refc ||
2200 VerifyAccess.isClassAccessible(refc, lookupClass(), FULL_POWER_MODES)));
2201 }
2202 if (!classOK)
2203 return "class is not public";
2204 if (Modifier.isPublic(mods))
2205 return "access to public member failed"; // (how?, module not readable?)
2206 if (Modifier.isPrivate(mods))
2207 return "member is private";
2208 if (Modifier.isProtected(mods))
2209 return "member is protected";
2210 return "member is private to package";
2211 }
2212
2213 private static final boolean ALLOW_NESTMATE_ACCESS = false;
2214
2215 private void checkSpecialCaller(Class<?> specialCaller, Class<?> refc) throws IllegalAccessException {
2216 int allowedModes = this.allowedModes;
2217 if (allowedModes == TRUSTED) return;
2218 if (!hasPrivateAccess()
2219 || (specialCaller != lookupClass()
2220 // ensure non-abstract methods in superinterfaces can be special-invoked
2221 && !(refc != null && refc.isInterface() && refc.isAssignableFrom(specialCaller))
2222 && !(ALLOW_NESTMATE_ACCESS &&
2223 VerifyAccess.isSamePackageMember(specialCaller, lookupClass()))))
2224 throw new MemberName(specialCaller).
2225 makeAccessException("no private access for invokespecial", this);
2226 }
2227
2228 private boolean restrictProtectedReceiver(MemberName method) {
2229 // The accessing class only has the right to use a protected member
2230 // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc.
2231 if (!method.isProtected() || method.isStatic()
2232 || allowedModes == TRUSTED
2233 || method.getDeclaringClass() == lookupClass()
2234 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass())
2235 || (ALLOW_NESTMATE_ACCESS &&
2236 VerifyAccess.isSamePackageMember(method.getDeclaringClass(), lookupClass())))
2237 return false;
2238 return true;
2239 }
2240 private MethodHandle restrictReceiver(MemberName method, DirectMethodHandle mh, Class<?> caller) throws IllegalAccessException {
2241 assert(!method.isStatic());
2242 // receiver type of mh is too wide; narrow to caller
2243 if (!method.getDeclaringClass().isAssignableFrom(caller)) {
2244 throw method.makeAccessException("caller class must be a subclass below the method", caller);
2245 }
2246 MethodType rawType = mh.type();
2247 if (caller.isAssignableFrom(rawType.parameterType(0))) return mh; // no need to restrict; already narrow
2248 MethodType narrowType = rawType.changeParameterType(0, caller);
2249 assert(!mh.isVarargsCollector()); // viewAsType will lose varargs-ness
2250 assert(mh.viewAsTypeChecks(narrowType, true));
2251 return mh.copyWith(narrowType, mh.form);
2252 }
2253
2254 /** Check access and get the requested method. */
2255 private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
2256 final boolean doRestrict = true;
2257 final boolean checkSecurity = true;
2258 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
2259 }
2260 /** Check access and get the requested method, for invokespecial with no restriction on the application of narrowing rules. */
2261 private MethodHandle getDirectMethodNoRestrictInvokeSpecial(Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
2262 final boolean doRestrict = false;
2263 final boolean checkSecurity = true;
2264 return getDirectMethodCommon(REF_invokeSpecial, refc, method, checkSecurity, doRestrict, callerClass);
2265 }
2266 /** Check access and get the requested method, eliding security manager checks. */
2267 private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
2268 final boolean doRestrict = true;
2269 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
2270 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
2271 }
2272 /** Common code for all methods; do not call directly except from immediately above. */
2273 private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method,
2274 boolean checkSecurity,
2275 boolean doRestrict, Class<?> callerClass) throws IllegalAccessException {
2276 checkMethod(refKind, refc, method);
2277 // Optionally check with the security manager; this isn't needed for unreflect* calls.
2278 if (checkSecurity)
2279 checkSecurityManager(refc, method);
2280 assert(!method.isMethodHandleInvoke());
2281
2282 if (refKind == REF_invokeSpecial &&
2283 refc != lookupClass() &&
2284 !refc.isInterface() &&
2285 refc != lookupClass().getSuperclass() &&
2286 refc.isAssignableFrom(lookupClass())) {
2287 assert(!method.getName().equals("<init>")); // not this code path
2288 // Per JVMS 6.5, desc. of invokespecial instruction:
2289 // If the method is in a superclass of the LC,
2290 // and if our original search was above LC.super,
2291 // repeat the search (symbolic lookup) from LC.super
2292 // and continue with the direct superclass of that class,
2293 // and so forth, until a match is found or no further superclasses exist.
2294 // FIXME: MemberName.resolve should handle this instead.
2295 Class<?> refcAsSuper = lookupClass();
2296 MemberName m2;
2297 do {
2298 refcAsSuper = refcAsSuper.getSuperclass();
2299 m2 = new MemberName(refcAsSuper,
2300 method.getName(),
2301 method.getMethodType(),
2302 REF_invokeSpecial);
2303 m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull());
2304 } while (m2 == null && // no method is found yet
2305 refc != refcAsSuper); // search up to refc
2306 if (m2 == null) throw new InternalError(method.toString());
2307 method = m2;
2308 refc = refcAsSuper;
2309 // redo basic checks
2310 checkMethod(refKind, refc, method);
2311 }
2312
2313 DirectMethodHandle dmh = DirectMethodHandle.make(refKind, refc, method);
2314 MethodHandle mh = dmh;
2315 // Optionally narrow the receiver argument to refc using restrictReceiver.
2316 if ((doRestrict && refKind == REF_invokeSpecial) ||
2317 (MethodHandleNatives.refKindHasReceiver(refKind) && restrictProtectedReceiver(method))) {
2318 mh = restrictReceiver(method, dmh, lookupClass());
2319 }
2320 mh = maybeBindCaller(method, mh, callerClass);
2321 mh = mh.setVarargs(method);
2322 return mh;
2323 }
2324 private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh,
2325 Class<?> callerClass)
2326 throws IllegalAccessException {
2327 if (allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method))
2328 return mh;
2329 Class<?> hostClass = lookupClass;
2330 if (!hasPrivateAccess()) // caller must have private access
2331 hostClass = callerClass; // callerClass came from a security manager style stack walk
2332 MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, hostClass);
2333 // Note: caller will apply varargs after this step happens.
2334 return cbmh;
2335 }
2336 /** Check access and get the requested field. */
2337 private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
2338 final boolean checkSecurity = true;
2339 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
2340 }
2341 /** Check access and get the requested field, eliding security manager checks. */
2342 private MethodHandle getDirectFieldNoSecurityManager(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
2343 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
2344 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
2345 }
2346 /** Common code for all fields; do not call directly except from immediately above. */
2347 private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field,
2348 boolean checkSecurity) throws IllegalAccessException {
2349 checkField(refKind, refc, field);
2350 // Optionally check with the security manager; this isn't needed for unreflect* calls.
2351 if (checkSecurity)
2352 checkSecurityManager(refc, field);
2353 DirectMethodHandle dmh = DirectMethodHandle.make(refc, field);
2354 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) &&
2355 restrictProtectedReceiver(field));
2356 if (doRestrict)
2357 return restrictReceiver(field, dmh, lookupClass());
2358 return dmh;
2359 }
2360 private VarHandle getFieldVarHandle(byte getRefKind, byte putRefKind,
2361 Class<?> refc, MemberName getField, MemberName putField)
2362 throws IllegalAccessException {
2363 final boolean checkSecurity = true;
2364 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
2365 }
2366 private VarHandle getFieldVarHandleNoSecurityManager(byte getRefKind, byte putRefKind,
2367 Class<?> refc, MemberName getField, MemberName putField)
2368 throws IllegalAccessException {
2369 final boolean checkSecurity = false;
2370 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
2371 }
2372 private VarHandle getFieldVarHandleCommon(byte getRefKind, byte putRefKind,
2373 Class<?> refc, MemberName getField, MemberName putField,
2374 boolean checkSecurity) throws IllegalAccessException {
2375 assert getField.isStatic() == putField.isStatic();
2376 assert getField.isGetter() && putField.isSetter();
2377 assert MethodHandleNatives.refKindIsStatic(getRefKind) == MethodHandleNatives.refKindIsStatic(putRefKind);
2378 assert MethodHandleNatives.refKindIsGetter(getRefKind) && MethodHandleNatives.refKindIsSetter(putRefKind);
2379
2380 checkField(getRefKind, refc, getField);
2381 if (checkSecurity)
2382 checkSecurityManager(refc, getField);
2383
2384 if (!putField.isFinal()) {
2385 // A VarHandle does not support updates to final fields, any
2386 // such VarHandle to a final field will be read-only and
2387 // therefore the following write-based accessibility checks are
2388 // only required for non-final fields
2389 checkField(putRefKind, refc, putField);
2390 if (checkSecurity)
2391 checkSecurityManager(refc, putField);
2392 }
2393
2394 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(getRefKind) &&
2395 restrictProtectedReceiver(getField));
2396 if (doRestrict) {
2397 assert !getField.isStatic();
2398 // receiver type of VarHandle is too wide; narrow to caller
2399 if (!getField.getDeclaringClass().isAssignableFrom(lookupClass())) {
2400 throw getField.makeAccessException("caller class must be a subclass below the method", lookupClass());
2401 }
2402 refc = lookupClass();
2403 }
2404 return VarHandles.makeFieldHandle(getField, refc, getField.getFieldType(), this.allowedModes == TRUSTED);
2405 }
2406 /** Check access and get the requested constructor. */
2407 private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException {
2408 final boolean checkSecurity = true;
2409 return getDirectConstructorCommon(refc, ctor, checkSecurity);
2410 }
2411 /** Check access and get the requested constructor, eliding security manager checks. */
2412 private MethodHandle getDirectConstructorNoSecurityManager(Class<?> refc, MemberName ctor) throws IllegalAccessException {
2413 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
2414 return getDirectConstructorCommon(refc, ctor, checkSecurity);
2415 }
2416 /** Common code for all constructors; do not call directly except from immediately above. */
2417 private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor,
2418 boolean checkSecurity) throws IllegalAccessException {
2419 assert(ctor.isConstructor());
2420 checkAccess(REF_newInvokeSpecial, refc, ctor);
2421 // Optionally check with the security manager; this isn't needed for unreflect* calls.
2422 if (checkSecurity)
2423 checkSecurityManager(refc, ctor);
2424 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
2425 return DirectMethodHandle.make(ctor).setVarargs(ctor);
2426 }
2427
2428 /** Hook called from the JVM (via MethodHandleNatives) to link MH constants:
2429 */
2430 /*non-public*/
2431 MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type) throws ReflectiveOperationException {
2432 if (!(type instanceof Class || type instanceof MethodType))
2433 throw new InternalError("unresolved MemberName");
2434 MemberName member = new MemberName(refKind, defc, name, type);
2435 MethodHandle mh = LOOKASIDE_TABLE.get(member);
2436 if (mh != null) {
2437 checkSymbolicClass(defc);
2438 return mh;
2439 }
2440 // Treat MethodHandle.invoke and invokeExact specially.
2441 if (defc == MethodHandle.class && refKind == REF_invokeVirtual) {
2442 mh = findVirtualForMH(member.getName(), member.getMethodType());
2443 if (mh != null) {
2444 return mh;
2445 }
2446 }
2447 MemberName resolved = resolveOrFail(refKind, member);
2448 mh = getDirectMethodForConstant(refKind, defc, resolved);
2449 if (mh instanceof DirectMethodHandle
2450 && canBeCached(refKind, defc, resolved)) {
2451 MemberName key = mh.internalMemberName();
2452 if (key != null) {
2453 key = key.asNormalOriginal();
2454 }
2455 if (member.equals(key)) { // better safe than sorry
2456 LOOKASIDE_TABLE.put(key, (DirectMethodHandle) mh);
2457 }
2458 }
2459 return mh;
2460 }
2461 private
2462 boolean canBeCached(byte refKind, Class<?> defc, MemberName member) {
2463 if (refKind == REF_invokeSpecial) {
2464 return false;
2465 }
2466 if (!Modifier.isPublic(defc.getModifiers()) ||
2467 !Modifier.isPublic(member.getDeclaringClass().getModifiers()) ||
2468 !member.isPublic() ||
2469 member.isCallerSensitive()) {
2470 return false;
2471 }
2472 ClassLoader loader = defc.getClassLoader();
2473 if (loader != null) {
2474 ClassLoader sysl = ClassLoader.getSystemClassLoader();
2475 boolean found = false;
2476 while (sysl != null) {
2477 if (loader == sysl) { found = true; break; }
2478 sysl = sysl.getParent();
2479 }
2480 if (!found) {
2481 return false;
2482 }
2483 }
2484 try {
2485 MemberName resolved2 = publicLookup().resolveOrFail(refKind,
2486 new MemberName(refKind, defc, member.getName(), member.getType()));
2487 checkSecurityManager(defc, resolved2);
2488 } catch (ReflectiveOperationException | SecurityException ex) {
2489 return false;
2490 }
2491 return true;
2492 }
2493 private
2494 MethodHandle getDirectMethodForConstant(byte refKind, Class<?> defc, MemberName member)
2495 throws ReflectiveOperationException {
2496 if (MethodHandleNatives.refKindIsField(refKind)) {
2497 return getDirectFieldNoSecurityManager(refKind, defc, member);
2498 } else if (MethodHandleNatives.refKindIsMethod(refKind)) {
2499 return getDirectMethodNoSecurityManager(refKind, defc, member, lookupClass);
2500 } else if (refKind == REF_newInvokeSpecial) {
2501 return getDirectConstructorNoSecurityManager(defc, member);
2502 }
2503 // oops
2504 throw newIllegalArgumentException("bad MethodHandle constant #"+member);
2505 }
2506
2507 static ConcurrentHashMap<MemberName, DirectMethodHandle> LOOKASIDE_TABLE = new ConcurrentHashMap<>();
2508 }
2509
2510 /**
2511 * Produces a method handle constructing arrays of a desired type,
2512 * as if by the {@code anewarray} bytecode.
2513 * The return type of the method handle will be the array type.
2514 * The type of its sole argument will be {@code int}, which specifies the size of the array.
2515 *
2516 * <p> If the returned method handle is invoked with a negative
2517 * array size, a {@code NegativeArraySizeException} will be thrown.
2518 *
2519 * @param arrayClass an array type
2520 * @return a method handle which can create arrays of the given type
2521 * @throws NullPointerException if the argument is {@code null}
2522 * @throws IllegalArgumentException if {@code arrayClass} is not an array type
2523 * @see java.lang.reflect.Array#newInstance(Class, int)
2524 * @jvms 6.5 {@code anewarray} Instruction
2525 * @since 9
2526 */
2527 public static
2528 MethodHandle arrayConstructor(Class<?> arrayClass) throws IllegalArgumentException {
2529 if (!arrayClass.isArray()) {
2530 throw newIllegalArgumentException("not an array class: " + arrayClass.getName());
2531 }
2532 MethodHandle ani = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_Array_newInstance).
2533 bindTo(arrayClass.getComponentType());
2534 return ani.asType(ani.type().changeReturnType(arrayClass));
2535 }
2536
2537 /**
2538 * Produces a method handle returning the length of an array,
2539 * as if by the {@code arraylength} bytecode.
2540 * The type of the method handle will have {@code int} as return type,
2541 * and its sole argument will be the array type.
2542 *
2543 * <p> If the returned method handle is invoked with a {@code null}
2544 * array reference, a {@code NullPointerException} will be thrown.
2545 *
2546 * @param arrayClass an array type
2547 * @return a method handle which can retrieve the length of an array of the given array type
2548 * @throws NullPointerException if the argument is {@code null}
2549 * @throws IllegalArgumentException if arrayClass is not an array type
2550 * @jvms 6.5 {@code arraylength} Instruction
2551 * @since 9
2552 */
2553 public static
2554 MethodHandle arrayLength(Class<?> arrayClass) throws IllegalArgumentException {
2555 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.LENGTH);
2556 }
2557
2558 /**
2559 * Produces a method handle giving read access to elements of an array,
2560 * as if by the {@code aaload} bytecode.
2561 * The type of the method handle will have a return type of the array's
2562 * element type. Its first argument will be the array type,
2563 * and the second will be {@code int}.
2564 *
2565 * <p> When the returned method handle is invoked,
2566 * the array reference and array index are checked.
2567 * A {@code NullPointerException} will be thrown if the array reference
2568 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
2569 * thrown if the index is negative or if it is greater than or equal to
2570 * the length of the array.
2571 *
2572 * @param arrayClass an array type
2573 * @return a method handle which can load values from the given array type
2574 * @throws NullPointerException if the argument is null
2575 * @throws IllegalArgumentException if arrayClass is not an array type
2576 * @jvms 6.5 {@code aaload} Instruction
2577 */
2578 public static
2579 MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException {
2580 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.GET);
2581 }
2582
2583 /**
2584 * Produces a method handle giving write access to elements of an array,
2585 * as if by the {@code astore} bytecode.
2586 * The type of the method handle will have a void return type.
2587 * Its last argument will be the array's element type.
2588 * The first and second arguments will be the array type and int.
2589 *
2590 * <p> When the returned method handle is invoked,
2591 * the array reference and array index are checked.
2592 * A {@code NullPointerException} will be thrown if the array reference
2593 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
2594 * thrown if the index is negative or if it is greater than or equal to
2595 * the length of the array.
2596 *
2597 * @param arrayClass the class of an array
2598 * @return a method handle which can store values into the array type
2599 * @throws NullPointerException if the argument is null
2600 * @throws IllegalArgumentException if arrayClass is not an array type
2601 * @jvms 6.5 {@code aastore} Instruction
2602 */
2603 public static
2604 MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException {
2605 if (arrayClass.isValue()) {
2606 throw new UnsupportedOperationException();
2607 }
2608 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.SET);
2609 }
2610
2611 /**
2612 * Produces a VarHandle giving access to elements of an array of type
2613 * {@code arrayClass}. The VarHandle's variable type is the component type
2614 * of {@code arrayClass} and the list of coordinate types is
2615 * {@code (arrayClass, int)}, where the {@code int} coordinate type
2616 * corresponds to an argument that is an index into an array.
2617 * <p>
2618 * Certain access modes of the returned VarHandle are unsupported under
2619 * the following conditions:
2620 * <ul>
2621 * <li>if the component type is anything other than {@code byte},
2622 * {@code short}, {@code char}, {@code int}, {@code long},
2623 * {@code float}, or {@code double} then numeric atomic update access
2624 * modes are unsupported.
2625 * <li>if the field type is anything other than {@code boolean},
2626 * {@code byte}, {@code short}, {@code char}, {@code int} or
2627 * {@code long} then bitwise atomic update access modes are
2628 * unsupported.
2629 * </ul>
2630 * <p>
2631 * If the component type is {@code float} or {@code double} then numeric
2632 * and atomic update access modes compare values using their bitwise
2633 * representation (see {@link Float#floatToRawIntBits} and
2634 * {@link Double#doubleToRawLongBits}, respectively).
2635 *
2636 * <p> When the returned {@code VarHandle} is invoked,
2637 * the array reference and array index are checked.
2638 * A {@code NullPointerException} will be thrown if the array reference
2639 * is {@code null} and an {@code ArrayIndexOutOfBoundsException} will be
2640 * thrown if the index is negative or if it is greater than or equal to
2641 * the length of the array.
2642 *
2643 * @apiNote
2644 * Bitwise comparison of {@code float} values or {@code double} values,
2645 * as performed by the numeric and atomic update access modes, differ
2646 * from the primitive {@code ==} operator and the {@link Float#equals}
2647 * and {@link Double#equals} methods, specifically with respect to
2648 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
2649 * Care should be taken when performing a compare and set or a compare
2650 * and exchange operation with such values since the operation may
2651 * unexpectedly fail.
2652 * There are many possible NaN values that are considered to be
2653 * {@code NaN} in Java, although no IEEE 754 floating-point operation
2654 * provided by Java can distinguish between them. Operation failure can
2655 * occur if the expected or witness value is a NaN value and it is
2656 * transformed (perhaps in a platform specific manner) into another NaN
2657 * value, and thus has a different bitwise representation (see
2658 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
2659 * details).
2660 * The values {@code -0.0} and {@code +0.0} have different bitwise
2661 * representations but are considered equal when using the primitive
2662 * {@code ==} operator. Operation failure can occur if, for example, a
2663 * numeric algorithm computes an expected value to be say {@code -0.0}
2664 * and previously computed the witness value to be say {@code +0.0}.
2665 * @param arrayClass the class of an array, of type {@code T[]}
2666 * @return a VarHandle giving access to elements of an array
2667 * @throws NullPointerException if the arrayClass is null
2668 * @throws IllegalArgumentException if arrayClass is not an array type
2669 * @since 9
2670 */
2671 public static
2672 VarHandle arrayElementVarHandle(Class<?> arrayClass) throws IllegalArgumentException {
2673 return VarHandles.makeArrayElementHandle(arrayClass);
2674 }
2675
2676 /**
2677 * Produces a VarHandle giving access to elements of a {@code byte[]} array
2678 * viewed as if it were a different primitive array type, such as
2679 * {@code int[]} or {@code long[]}.
2680 * The VarHandle's variable type is the component type of
2681 * {@code viewArrayClass} and the list of coordinate types is
2682 * {@code (byte[], int)}, where the {@code int} coordinate type
2683 * corresponds to an argument that is an index into a {@code byte[]} array.
2684 * The returned VarHandle accesses bytes at an index in a {@code byte[]}
2685 * array, composing bytes to or from a value of the component type of
2686 * {@code viewArrayClass} according to the given endianness.
2687 * <p>
2688 * The supported component types (variables types) are {@code short},
2689 * {@code char}, {@code int}, {@code long}, {@code float} and
2690 * {@code double}.
2691 * <p>
2692 * Access of bytes at a given index will result in an
2693 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
2694 * or greater than the {@code byte[]} array length minus the size (in bytes)
2695 * of {@code T}.
2696 * <p>
2697 * Access of bytes at an index may be aligned or misaligned for {@code T},
2698 * with respect to the underlying memory address, {@code A} say, associated
2699 * with the array and index.
2700 * If access is misaligned then access for anything other than the
2701 * {@code get} and {@code set} access modes will result in an
2702 * {@code IllegalStateException}. In such cases atomic access is only
2703 * guaranteed with respect to the largest power of two that divides the GCD
2704 * of {@code A} and the size (in bytes) of {@code T}.
2705 * If access is aligned then following access modes are supported and are
2706 * guaranteed to support atomic access:
2707 * <ul>
2708 * <li>read write access modes for all {@code T}, with the exception of
2709 * access modes {@code get} and {@code set} for {@code long} and
2710 * {@code double} on 32-bit platforms.
2711 * <li>atomic update access modes for {@code int}, {@code long},
2712 * {@code float} or {@code double}.
2713 * (Future major platform releases of the JDK may support additional
2714 * types for certain currently unsupported access modes.)
2715 * <li>numeric atomic update access modes for {@code int} and {@code long}.
2716 * (Future major platform releases of the JDK may support additional
2717 * numeric types for certain currently unsupported access modes.)
2718 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
2719 * (Future major platform releases of the JDK may support additional
2720 * numeric types for certain currently unsupported access modes.)
2721 * </ul>
2722 * <p>
2723 * Misaligned access, and therefore atomicity guarantees, may be determined
2724 * for {@code byte[]} arrays without operating on a specific array. Given
2725 * an {@code index}, {@code T} and it's corresponding boxed type,
2726 * {@code T_BOX}, misalignment may be determined as follows:
2727 * <pre>{@code
2728 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
2729 * int misalignedAtZeroIndex = ByteBuffer.wrap(new byte[0]).
2730 * alignmentOffset(0, sizeOfT);
2731 * int misalignedAtIndex = (misalignedAtZeroIndex + index) % sizeOfT;
2732 * boolean isMisaligned = misalignedAtIndex != 0;
2733 * }</pre>
2734 * <p>
2735 * If the variable type is {@code float} or {@code double} then atomic
2736 * update access modes compare values using their bitwise representation
2737 * (see {@link Float#floatToRawIntBits} and
2738 * {@link Double#doubleToRawLongBits}, respectively).
2739 * @param viewArrayClass the view array class, with a component type of
2740 * type {@code T}
2741 * @param byteOrder the endianness of the view array elements, as
2742 * stored in the underlying {@code byte} array
2743 * @return a VarHandle giving access to elements of a {@code byte[]} array
2744 * viewed as if elements corresponding to the components type of the view
2745 * array class
2746 * @throws NullPointerException if viewArrayClass or byteOrder is null
2747 * @throws IllegalArgumentException if viewArrayClass is not an array type
2748 * @throws UnsupportedOperationException if the component type of
2749 * viewArrayClass is not supported as a variable type
2750 * @since 9
2751 */
2752 public static
2753 VarHandle byteArrayViewVarHandle(Class<?> viewArrayClass,
2754 ByteOrder byteOrder) throws IllegalArgumentException {
2755 Objects.requireNonNull(byteOrder);
2756 return VarHandles.byteArrayViewHandle(viewArrayClass,
2757 byteOrder == ByteOrder.BIG_ENDIAN);
2758 }
2759
2760 /**
2761 * Produces a VarHandle giving access to elements of a {@code ByteBuffer}
2762 * viewed as if it were an array of elements of a different primitive
2763 * component type to that of {@code byte}, such as {@code int[]} or
2764 * {@code long[]}.
2765 * The VarHandle's variable type is the component type of
2766 * {@code viewArrayClass} and the list of coordinate types is
2767 * {@code (ByteBuffer, int)}, where the {@code int} coordinate type
2768 * corresponds to an argument that is an index into a {@code byte[]} array.
2769 * The returned VarHandle accesses bytes at an index in a
2770 * {@code ByteBuffer}, composing bytes to or from a value of the component
2771 * type of {@code viewArrayClass} according to the given endianness.
2772 * <p>
2773 * The supported component types (variables types) are {@code short},
2774 * {@code char}, {@code int}, {@code long}, {@code float} and
2775 * {@code double}.
2776 * <p>
2777 * Access will result in a {@code ReadOnlyBufferException} for anything
2778 * other than the read access modes if the {@code ByteBuffer} is read-only.
2779 * <p>
2780 * Access of bytes at a given index will result in an
2781 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
2782 * or greater than the {@code ByteBuffer} limit minus the size (in bytes) of
2783 * {@code T}.
2784 * <p>
2785 * Access of bytes at an index may be aligned or misaligned for {@code T},
2786 * with respect to the underlying memory address, {@code A} say, associated
2787 * with the {@code ByteBuffer} and index.
2788 * If access is misaligned then access for anything other than the
2789 * {@code get} and {@code set} access modes will result in an
2790 * {@code IllegalStateException}. In such cases atomic access is only
2791 * guaranteed with respect to the largest power of two that divides the GCD
2792 * of {@code A} and the size (in bytes) of {@code T}.
2793 * If access is aligned then following access modes are supported and are
2794 * guaranteed to support atomic access:
2795 * <ul>
2796 * <li>read write access modes for all {@code T}, with the exception of
2797 * access modes {@code get} and {@code set} for {@code long} and
2798 * {@code double} on 32-bit platforms.
2799 * <li>atomic update access modes for {@code int}, {@code long},
2800 * {@code float} or {@code double}.
2801 * (Future major platform releases of the JDK may support additional
2802 * types for certain currently unsupported access modes.)
2803 * <li>numeric atomic update access modes for {@code int} and {@code long}.
2804 * (Future major platform releases of the JDK may support additional
2805 * numeric types for certain currently unsupported access modes.)
2806 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
2807 * (Future major platform releases of the JDK may support additional
2808 * numeric types for certain currently unsupported access modes.)
2809 * </ul>
2810 * <p>
2811 * Misaligned access, and therefore atomicity guarantees, may be determined
2812 * for a {@code ByteBuffer}, {@code bb} (direct or otherwise), an
2813 * {@code index}, {@code T} and it's corresponding boxed type,
2814 * {@code T_BOX}, as follows:
2815 * <pre>{@code
2816 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
2817 * ByteBuffer bb = ...
2818 * int misalignedAtIndex = bb.alignmentOffset(index, sizeOfT);
2819 * boolean isMisaligned = misalignedAtIndex != 0;
2820 * }</pre>
2821 * <p>
2822 * If the variable type is {@code float} or {@code double} then atomic
2823 * update access modes compare values using their bitwise representation
2824 * (see {@link Float#floatToRawIntBits} and
2825 * {@link Double#doubleToRawLongBits}, respectively).
2826 * @param viewArrayClass the view array class, with a component type of
2827 * type {@code T}
2828 * @param byteOrder the endianness of the view array elements, as
2829 * stored in the underlying {@code ByteBuffer} (Note this overrides the
2830 * endianness of a {@code ByteBuffer})
2831 * @return a VarHandle giving access to elements of a {@code ByteBuffer}
2832 * viewed as if elements corresponding to the components type of the view
2833 * array class
2834 * @throws NullPointerException if viewArrayClass or byteOrder is null
2835 * @throws IllegalArgumentException if viewArrayClass is not an array type
2836 * @throws UnsupportedOperationException if the component type of
2837 * viewArrayClass is not supported as a variable type
2838 * @since 9
2839 */
2840 public static
2841 VarHandle byteBufferViewVarHandle(Class<?> viewArrayClass,
2842 ByteOrder byteOrder) throws IllegalArgumentException {
2843 Objects.requireNonNull(byteOrder);
2844 return VarHandles.makeByteBufferViewHandle(viewArrayClass,
2845 byteOrder == ByteOrder.BIG_ENDIAN);
2846 }
2847
2848
2849 /// method handle invocation (reflective style)
2850
2851 /**
2852 * Produces a method handle which will invoke any method handle of the
2853 * given {@code type}, with a given number of trailing arguments replaced by
2854 * a single trailing {@code Object[]} array.
2855 * The resulting invoker will be a method handle with the following
2856 * arguments:
2857 * <ul>
2858 * <li>a single {@code MethodHandle} target
2859 * <li>zero or more leading values (counted by {@code leadingArgCount})
2860 * <li>an {@code Object[]} array containing trailing arguments
2861 * </ul>
2862 * <p>
2863 * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
2864 * the indicated {@code type}.
2865 * That is, if the target is exactly of the given {@code type}, it will behave
2866 * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
2867 * is used to convert the target to the required {@code type}.
2868 * <p>
2869 * The type of the returned invoker will not be the given {@code type}, but rather
2870 * will have all parameters except the first {@code leadingArgCount}
2871 * replaced by a single array of type {@code Object[]}, which will be
2872 * the final parameter.
2873 * <p>
2874 * Before invoking its target, the invoker will spread the final array, apply
2875 * reference casts as necessary, and unbox and widen primitive arguments.
2876 * If, when the invoker is called, the supplied array argument does
2877 * not have the correct number of elements, the invoker will throw
2878 * an {@link IllegalArgumentException} instead of invoking the target.
2879 * <p>
2880 * This method is equivalent to the following code (though it may be more efficient):
2881 * <blockquote><pre>{@code
2882 MethodHandle invoker = MethodHandles.invoker(type);
2883 int spreadArgCount = type.parameterCount() - leadingArgCount;
2884 invoker = invoker.asSpreader(Object[].class, spreadArgCount);
2885 return invoker;
2886 * }</pre></blockquote>
2887 * This method throws no reflective or security exceptions.
2888 * @param type the desired target type
2889 * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
2890 * @return a method handle suitable for invoking any method handle of the given type
2891 * @throws NullPointerException if {@code type} is null
2892 * @throws IllegalArgumentException if {@code leadingArgCount} is not in
2893 * the range from 0 to {@code type.parameterCount()} inclusive,
2894 * or if the resulting method handle's type would have
2895 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2896 */
2897 public static
2898 MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
2899 if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
2900 throw newIllegalArgumentException("bad argument count", leadingArgCount);
2901 type = type.asSpreaderType(Object[].class, leadingArgCount, type.parameterCount() - leadingArgCount);
2902 return type.invokers().spreadInvoker(leadingArgCount);
2903 }
2904
2905 /**
2906 * Produces a special <em>invoker method handle</em> which can be used to
2907 * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
2908 * The resulting invoker will have a type which is
2909 * exactly equal to the desired type, except that it will accept
2910 * an additional leading argument of type {@code MethodHandle}.
2911 * <p>
2912 * This method is equivalent to the following code (though it may be more efficient):
2913 * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)}
2914 *
2915 * <p style="font-size:smaller;">
2916 * <em>Discussion:</em>
2917 * Invoker method handles can be useful when working with variable method handles
2918 * of unknown types.
2919 * For example, to emulate an {@code invokeExact} call to a variable method
2920 * handle {@code M}, extract its type {@code T},
2921 * look up the invoker method {@code X} for {@code T},
2922 * and call the invoker method, as {@code X.invoke(T, A...)}.
2923 * (It would not work to call {@code X.invokeExact}, since the type {@code T}
2924 * is unknown.)
2925 * If spreading, collecting, or other argument transformations are required,
2926 * they can be applied once to the invoker {@code X} and reused on many {@code M}
2927 * method handle values, as long as they are compatible with the type of {@code X}.
2928 * <p style="font-size:smaller;">
2929 * <em>(Note: The invoker method is not available via the Core Reflection API.
2930 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
2931 * on the declared {@code invokeExact} or {@code invoke} method will raise an
2932 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
2933 * <p>
2934 * This method throws no reflective or security exceptions.
2935 * @param type the desired target type
2936 * @return a method handle suitable for invoking any method handle of the given type
2937 * @throws IllegalArgumentException if the resulting method handle's type would have
2938 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2939 */
2940 public static
2941 MethodHandle exactInvoker(MethodType type) {
2942 return type.invokers().exactInvoker();
2943 }
2944
2945 /**
2946 * Produces a special <em>invoker method handle</em> which can be used to
2947 * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
2948 * The resulting invoker will have a type which is
2949 * exactly equal to the desired type, except that it will accept
2950 * an additional leading argument of type {@code MethodHandle}.
2951 * <p>
2952 * Before invoking its target, if the target differs from the expected type,
2953 * the invoker will apply reference casts as
2954 * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
2955 * Similarly, the return value will be converted as necessary.
2956 * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
2957 * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
2958 * <p>
2959 * This method is equivalent to the following code (though it may be more efficient):
2960 * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)}
2961 * <p style="font-size:smaller;">
2962 * <em>Discussion:</em>
2963 * A {@linkplain MethodType#genericMethodType general method type} is one which
2964 * mentions only {@code Object} arguments and return values.
2965 * An invoker for such a type is capable of calling any method handle
2966 * of the same arity as the general type.
2967 * <p style="font-size:smaller;">
2968 * <em>(Note: The invoker method is not available via the Core Reflection API.
2969 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
2970 * on the declared {@code invokeExact} or {@code invoke} method will raise an
2971 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
2972 * <p>
2973 * This method throws no reflective or security exceptions.
2974 * @param type the desired target type
2975 * @return a method handle suitable for invoking any method handle convertible to the given type
2976 * @throws IllegalArgumentException if the resulting method handle's type would have
2977 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2978 */
2979 public static
2980 MethodHandle invoker(MethodType type) {
2981 return type.invokers().genericInvoker();
2982 }
2983
2984 /**
2985 * Produces a special <em>invoker method handle</em> which can be used to
2986 * invoke a signature-polymorphic access mode method on any VarHandle whose
2987 * associated access mode type is compatible with the given type.
2988 * The resulting invoker will have a type which is exactly equal to the
2989 * desired given type, except that it will accept an additional leading
2990 * argument of type {@code VarHandle}.
2991 *
2992 * @param accessMode the VarHandle access mode
2993 * @param type the desired target type
2994 * @return a method handle suitable for invoking an access mode method of
2995 * any VarHandle whose access mode type is of the given type.
2996 * @since 9
2997 */
2998 static public
2999 MethodHandle varHandleExactInvoker(VarHandle.AccessMode accessMode, MethodType type) {
3000 return type.invokers().varHandleMethodExactInvoker(accessMode);
3001 }
3002
3003 /**
3004 * Produces a special <em>invoker method handle</em> which can be used to
3005 * invoke a signature-polymorphic access mode method on any VarHandle whose
3006 * associated access mode type is compatible with the given type.
3007 * The resulting invoker will have a type which is exactly equal to the
3008 * desired given type, except that it will accept an additional leading
3009 * argument of type {@code VarHandle}.
3010 * <p>
3011 * Before invoking its target, if the access mode type differs from the
3012 * desired given type, the invoker will apply reference casts as necessary
3013 * and box, unbox, or widen primitive values, as if by
3014 * {@link MethodHandle#asType asType}. Similarly, the return value will be
3015 * converted as necessary.
3016 * <p>
3017 * This method is equivalent to the following code (though it may be more
3018 * efficient): {@code publicLookup().findVirtual(VarHandle.class, accessMode.name(), type)}
3019 *
3020 * @param accessMode the VarHandle access mode
3021 * @param type the desired target type
3022 * @return a method handle suitable for invoking an access mode method of
3023 * any VarHandle whose access mode type is convertible to the given
3024 * type.
3025 * @since 9
3026 */
3027 static public
3028 MethodHandle varHandleInvoker(VarHandle.AccessMode accessMode, MethodType type) {
3029 return type.invokers().varHandleMethodInvoker(accessMode);
3030 }
3031
3032 static /*non-public*/
3033 MethodHandle basicInvoker(MethodType type) {
3034 return type.invokers().basicInvoker();
3035 }
3036
3037 /// method handle modification (creation from other method handles)
3038
3039 /**
3040 * Produces a method handle which adapts the type of the
3041 * given method handle to a new type by pairwise argument and return type conversion.
3042 * The original type and new type must have the same number of arguments.
3043 * The resulting method handle is guaranteed to report a type
3044 * which is equal to the desired new type.
3045 * <p>
3046 * If the original type and new type are equal, returns target.
3047 * <p>
3048 * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
3049 * and some additional conversions are also applied if those conversions fail.
3050 * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied
3051 * if possible, before or instead of any conversions done by {@code asType}:
3052 * <ul>
3053 * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type,
3054 * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast.
3055 * (This treatment of interfaces follows the usage of the bytecode verifier.)
3056 * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive,
3057 * the boolean is converted to a byte value, 1 for true, 0 for false.
3058 * (This treatment follows the usage of the bytecode verifier.)
3059 * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive,
3060 * <em>T0</em> is converted to byte via Java casting conversion (JLS 5.5),
3061 * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}.
3062 * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean,
3063 * then a Java casting conversion (JLS 5.5) is applied.
3064 * (Specifically, <em>T0</em> will convert to <em>T1</em> by
3065 * widening and/or narrowing.)
3066 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
3067 * conversion will be applied at runtime, possibly followed
3068 * by a Java casting conversion (JLS 5.5) on the primitive value,
3069 * possibly followed by a conversion from byte to boolean by testing
3070 * the low-order bit.
3071 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive,
3072 * and if the reference is null at runtime, a zero value is introduced.
3073 * </ul>
3074 * @param target the method handle to invoke after arguments are retyped
3075 * @param newType the expected type of the new method handle
3076 * @return a method handle which delegates to the target after performing
3077 * any necessary argument conversions, and arranges for any
3078 * necessary return value conversions
3079 * @throws NullPointerException if either argument is null
3080 * @throws WrongMethodTypeException if the conversion cannot be made
3081 * @see MethodHandle#asType
3082 */
3083 public static
3084 MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
3085 explicitCastArgumentsChecks(target, newType);
3086 // use the asTypeCache when possible:
3087 MethodType oldType = target.type();
3088 if (oldType == newType) return target;
3089 if (oldType.explicitCastEquivalentToAsType(newType)) {
3090 return target.asFixedArity().asType(newType);
3091 }
3092 return MethodHandleImpl.makePairwiseConvert(target, newType, false);
3093 }
3094
3095 private static void explicitCastArgumentsChecks(MethodHandle target, MethodType newType) {
3096 if (target.type().parameterCount() != newType.parameterCount()) {
3097 throw new WrongMethodTypeException("cannot explicitly cast " + target + " to " + newType);
3098 }
3099 }
3100
3101 /**
3102 * Produces a method handle which adapts the calling sequence of the
3103 * given method handle to a new type, by reordering the arguments.
3104 * The resulting method handle is guaranteed to report a type
3105 * which is equal to the desired new type.
3106 * <p>
3107 * The given array controls the reordering.
3108 * Call {@code #I} the number of incoming parameters (the value
3109 * {@code newType.parameterCount()}, and call {@code #O} the number
3110 * of outgoing parameters (the value {@code target.type().parameterCount()}).
3111 * Then the length of the reordering array must be {@code #O},
3112 * and each element must be a non-negative number less than {@code #I}.
3113 * For every {@code N} less than {@code #O}, the {@code N}-th
3114 * outgoing argument will be taken from the {@code I}-th incoming
3115 * argument, where {@code I} is {@code reorder[N]}.
3116 * <p>
3117 * No argument or return value conversions are applied.
3118 * The type of each incoming argument, as determined by {@code newType},
3119 * must be identical to the type of the corresponding outgoing parameter
3120 * or parameters in the target method handle.
3121 * The return type of {@code newType} must be identical to the return
3122 * type of the original target.
3123 * <p>
3124 * The reordering array need not specify an actual permutation.
3125 * An incoming argument will be duplicated if its index appears
3126 * more than once in the array, and an incoming argument will be dropped
3127 * if its index does not appear in the array.
3128 * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
3129 * incoming arguments which are not mentioned in the reordering array
3130 * may be of any type, as determined only by {@code newType}.
3131 * <blockquote><pre>{@code
3132 import static java.lang.invoke.MethodHandles.*;
3133 import static java.lang.invoke.MethodType.*;
3134 ...
3135 MethodType intfn1 = methodType(int.class, int.class);
3136 MethodType intfn2 = methodType(int.class, int.class, int.class);
3137 MethodHandle sub = ... (int x, int y) -> (x-y) ...;
3138 assert(sub.type().equals(intfn2));
3139 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
3140 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
3141 assert((int)rsub.invokeExact(1, 100) == 99);
3142 MethodHandle add = ... (int x, int y) -> (x+y) ...;
3143 assert(add.type().equals(intfn2));
3144 MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
3145 assert(twice.type().equals(intfn1));
3146 assert((int)twice.invokeExact(21) == 42);
3147 * }</pre></blockquote>
3148 * <p>
3149 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3150 * variable-arity method handle}, even if the original target method handle was.
3151 * @param target the method handle to invoke after arguments are reordered
3152 * @param newType the expected type of the new method handle
3153 * @param reorder an index array which controls the reordering
3154 * @return a method handle which delegates to the target after it
3155 * drops unused arguments and moves and/or duplicates the other arguments
3156 * @throws NullPointerException if any argument is null
3157 * @throws IllegalArgumentException if the index array length is not equal to
3158 * the arity of the target, or if any index array element
3159 * not a valid index for a parameter of {@code newType},
3160 * or if two corresponding parameter types in
3161 * {@code target.type()} and {@code newType} are not identical,
3162 */
3163 public static
3164 MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
3165 reorder = reorder.clone(); // get a private copy
3166 MethodType oldType = target.type();
3167 permuteArgumentChecks(reorder, newType, oldType);
3168 // first detect dropped arguments and handle them separately
3169 int[] originalReorder = reorder;
3170 BoundMethodHandle result = target.rebind();
3171 LambdaForm form = result.form;
3172 int newArity = newType.parameterCount();
3173 // Normalize the reordering into a real permutation,
3174 // by removing duplicates and adding dropped elements.
3175 // This somewhat improves lambda form caching, as well
3176 // as simplifying the transform by breaking it up into steps.
3177 for (int ddIdx; (ddIdx = findFirstDupOrDrop(reorder, newArity)) != 0; ) {
3178 if (ddIdx > 0) {
3179 // We found a duplicated entry at reorder[ddIdx].
3180 // Example: (x,y,z)->asList(x,y,z)
3181 // permuted by [1*,0,1] => (a0,a1)=>asList(a1,a0,a1)
3182 // permuted by [0,1,0*] => (a0,a1)=>asList(a0,a1,a0)
3183 // The starred element corresponds to the argument
3184 // deleted by the dupArgumentForm transform.
3185 int srcPos = ddIdx, dstPos = srcPos, dupVal = reorder[srcPos];
3186 boolean killFirst = false;
3187 for (int val; (val = reorder[--dstPos]) != dupVal; ) {
3188 // Set killFirst if the dup is larger than an intervening position.
3189 // This will remove at least one inversion from the permutation.
3190 if (dupVal > val) killFirst = true;
3191 }
3192 if (!killFirst) {
3193 srcPos = dstPos;
3194 dstPos = ddIdx;
3195 }
3196 form = form.editor().dupArgumentForm(1 + srcPos, 1 + dstPos);
3197 assert (reorder[srcPos] == reorder[dstPos]);
3198 oldType = oldType.dropParameterTypes(dstPos, dstPos + 1);
3199 // contract the reordering by removing the element at dstPos
3200 int tailPos = dstPos + 1;
3201 System.arraycopy(reorder, tailPos, reorder, dstPos, reorder.length - tailPos);
3202 reorder = Arrays.copyOf(reorder, reorder.length - 1);
3203 } else {
3204 int dropVal = ~ddIdx, insPos = 0;
3205 while (insPos < reorder.length && reorder[insPos] < dropVal) {
3206 // Find first element of reorder larger than dropVal.
3207 // This is where we will insert the dropVal.
3208 insPos += 1;
3209 }
3210 Class<?> ptype = newType.parameterType(dropVal);
3211 form = form.editor().addArgumentForm(1 + insPos, BasicType.basicType(ptype));
3212 oldType = oldType.insertParameterTypes(insPos, ptype);
3213 // expand the reordering by inserting an element at insPos
3214 int tailPos = insPos + 1;
3215 reorder = Arrays.copyOf(reorder, reorder.length + 1);
3216 System.arraycopy(reorder, insPos, reorder, tailPos, reorder.length - tailPos);
3217 reorder[insPos] = dropVal;
3218 }
3219 assert (permuteArgumentChecks(reorder, newType, oldType));
3220 }
3221 assert (reorder.length == newArity); // a perfect permutation
3222 // Note: This may cache too many distinct LFs. Consider backing off to varargs code.
3223 form = form.editor().permuteArgumentsForm(1, reorder);
3224 if (newType == result.type() && form == result.internalForm())
3225 return result;
3226 return result.copyWith(newType, form);
3227 }
3228
3229 /**
3230 * Return an indication of any duplicate or omission in reorder.
3231 * If the reorder contains a duplicate entry, return the index of the second occurrence.
3232 * Otherwise, return ~(n), for the first n in [0..newArity-1] that is not present in reorder.
3233 * Otherwise, return zero.
3234 * If an element not in [0..newArity-1] is encountered, return reorder.length.
3235 */
3236 private static int findFirstDupOrDrop(int[] reorder, int newArity) {
3237 final int BIT_LIMIT = 63; // max number of bits in bit mask
3238 if (newArity < BIT_LIMIT) {
3239 long mask = 0;
3240 for (int i = 0; i < reorder.length; i++) {
3241 int arg = reorder[i];
3242 if (arg >= newArity) {
3243 return reorder.length;
3244 }
3245 long bit = 1L << arg;
3246 if ((mask & bit) != 0) {
3247 return i; // >0 indicates a dup
3248 }
3249 mask |= bit;
3250 }
3251 if (mask == (1L << newArity) - 1) {
3252 assert(Long.numberOfTrailingZeros(Long.lowestOneBit(~mask)) == newArity);
3253 return 0;
3254 }
3255 // find first zero
3256 long zeroBit = Long.lowestOneBit(~mask);
3257 int zeroPos = Long.numberOfTrailingZeros(zeroBit);
3258 assert(zeroPos <= newArity);
3259 if (zeroPos == newArity) {
3260 return 0;
3261 }
3262 return ~zeroPos;
3263 } else {
3264 // same algorithm, different bit set
3265 BitSet mask = new BitSet(newArity);
3266 for (int i = 0; i < reorder.length; i++) {
3267 int arg = reorder[i];
3268 if (arg >= newArity) {
3269 return reorder.length;
3270 }
3271 if (mask.get(arg)) {
3272 return i; // >0 indicates a dup
3273 }
3274 mask.set(arg);
3275 }
3276 int zeroPos = mask.nextClearBit(0);
3277 assert(zeroPos <= newArity);
3278 if (zeroPos == newArity) {
3279 return 0;
3280 }
3281 return ~zeroPos;
3282 }
3283 }
3284
3285 private static boolean permuteArgumentChecks(int[] reorder, MethodType newType, MethodType oldType) {
3286 if (newType.returnType() != oldType.returnType())
3287 throw newIllegalArgumentException("return types do not match",
3288 oldType, newType);
3289 if (reorder.length == oldType.parameterCount()) {
3290 int limit = newType.parameterCount();
3291 boolean bad = false;
3292 for (int j = 0; j < reorder.length; j++) {
3293 int i = reorder[j];
3294 if (i < 0 || i >= limit) {
3295 bad = true; break;
3296 }
3297 Class<?> src = newType.parameterType(i);
3298 Class<?> dst = oldType.parameterType(j);
3299 if (src != dst)
3300 throw newIllegalArgumentException("parameter types do not match after reorder",
3301 oldType, newType);
3302 }
3303 if (!bad) return true;
3304 }
3305 throw newIllegalArgumentException("bad reorder array: "+Arrays.toString(reorder));
3306 }
3307
3308 /**
3309 * Produces a method handle of the requested return type which returns the given
3310 * constant value every time it is invoked.
3311 * <p>
3312 * Before the method handle is returned, the passed-in value is converted to the requested type.
3313 * If the requested type is primitive, widening primitive conversions are attempted,
3314 * else reference conversions are attempted.
3315 * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
3316 * @param type the return type of the desired method handle
3317 * @param value the value to return
3318 * @return a method handle of the given return type and no arguments, which always returns the given value
3319 * @throws NullPointerException if the {@code type} argument is null
3320 * @throws ClassCastException if the value cannot be converted to the required return type
3321 * @throws IllegalArgumentException if the given type is {@code void.class}
3322 */
3323 public static
3324 MethodHandle constant(Class<?> type, Object value) {
3325 if (type.isPrimitive()) {
3326 if (type == void.class)
3327 throw newIllegalArgumentException("void type");
3328 Wrapper w = Wrapper.forPrimitiveType(type);
3329 value = w.convert(value, type);
3330 if (w.zero().equals(value))
3331 return zero(w, type);
3332 return insertArguments(identity(type), 0, value);
3333 } else {
3334 if (value == null)
3335 return zero(Wrapper.OBJECT, type);
3336 return identity(type).bindTo(value);
3337 }
3338 }
3339
3340 /**
3341 * Produces a method handle which returns its sole argument when invoked.
3342 * @param type the type of the sole parameter and return value of the desired method handle
3343 * @return a unary method handle which accepts and returns the given type
3344 * @throws NullPointerException if the argument is null
3345 * @throws IllegalArgumentException if the given type is {@code void.class}
3346 */
3347 public static
3348 MethodHandle identity(Class<?> type) {
3349 Wrapper btw = (type.isPrimitive() ? Wrapper.forPrimitiveType(type) : Wrapper.OBJECT);
3350 int pos = btw.ordinal();
3351 MethodHandle ident = IDENTITY_MHS[pos];
3352 if (ident == null) {
3353 ident = setCachedMethodHandle(IDENTITY_MHS, pos, makeIdentity(btw.primitiveType()));
3354 }
3355 if (ident.type().returnType() == type)
3356 return ident;
3357 // something like identity(Foo.class); do not bother to intern these
3358 assert (btw == Wrapper.OBJECT);
3359 return makeIdentity(type);
3360 }
3361
3362 /**
3363 * Produces a constant method handle of the requested return type which
3364 * returns the default value for that type every time it is invoked.
3365 * The resulting constant method handle will have no side effects.
3366 * <p>The returned method handle is equivalent to {@code empty(methodType(type))}.
3367 * It is also equivalent to {@code explicitCastArguments(constant(Object.class, null), methodType(type))},
3368 * since {@code explicitCastArguments} converts {@code null} to default values.
3369 * @param type the expected return type of the desired method handle
3370 * @return a constant method handle that takes no arguments
3371 * and returns the default value of the given type (or void, if the type is void)
3372 * @throws NullPointerException if the argument is null
3373 * @see MethodHandles#constant
3374 * @see MethodHandles#empty
3375 * @see MethodHandles#explicitCastArguments
3376 * @since 9
3377 */
3378 public static MethodHandle zero(Class<?> type) {
3379 Objects.requireNonNull(type);
3380 if (type.isPrimitive()) {
3381 return zero(Wrapper.forPrimitiveType(type), type);
3382 } else if (type.isValue()) {
3383 throw new UnsupportedOperationException();
3384 } else {
3385 return zero(Wrapper.OBJECT, type);
3386 }
3387 }
3388
3389 private static MethodHandle identityOrVoid(Class<?> type) {
3390 return type == void.class ? zero(type) : identity(type);
3391 }
3392
3393 /**
3394 * Produces a method handle of the requested type which ignores any arguments, does nothing,
3395 * and returns a suitable default depending on the return type.
3396 * That is, it returns a zero primitive value, a {@code null}, or {@code void}.
3397 * <p>The returned method handle is equivalent to
3398 * {@code dropArguments(zero(type.returnType()), 0, type.parameterList())}.
3399 *
3400 * @apiNote Given a predicate and target, a useful "if-then" construct can be produced as
3401 * {@code guardWithTest(pred, target, empty(target.type())}.
3402 * @param type the type of the desired method handle
3403 * @return a constant method handle of the given type, which returns a default value of the given return type
3404 * @throws NullPointerException if the argument is null
3405 * @see MethodHandles#zero
3406 * @see MethodHandles#constant
3407 * @since 9
3408 */
3409 public static MethodHandle empty(MethodType type) {
3410 Objects.requireNonNull(type);
3411 return dropArguments(zero(type.returnType()), 0, type.parameterList());
3412 }
3413
3414 private static final MethodHandle[] IDENTITY_MHS = new MethodHandle[Wrapper.COUNT];
3415 private static MethodHandle makeIdentity(Class<?> ptype) {
3416 MethodType mtype = MethodType.methodType(ptype, ptype);
3417 LambdaForm lform = LambdaForm.identityForm(BasicType.basicType(ptype));
3418 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.IDENTITY);
3419 }
3420
3421 private static MethodHandle zero(Wrapper btw, Class<?> rtype) {
3422 int pos = btw.ordinal();
3423 MethodHandle zero = ZERO_MHS[pos];
3424 if (zero == null) {
3425 zero = setCachedMethodHandle(ZERO_MHS, pos, makeZero(btw.primitiveType()));
3426 }
3427 if (zero.type().returnType() == rtype)
3428 return zero;
3429 assert(btw == Wrapper.OBJECT);
3430 return makeZero(rtype);
3431 }
3432 private static final MethodHandle[] ZERO_MHS = new MethodHandle[Wrapper.COUNT];
3433 private static MethodHandle makeZero(Class<?> rtype) {
3434 MethodType mtype = methodType(rtype);
3435 LambdaForm lform = LambdaForm.zeroForm(BasicType.basicType(rtype));
3436 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.ZERO);
3437 }
3438
3439 private static synchronized MethodHandle setCachedMethodHandle(MethodHandle[] cache, int pos, MethodHandle value) {
3440 // Simulate a CAS, to avoid racy duplication of results.
3441 MethodHandle prev = cache[pos];
3442 if (prev != null) return prev;
3443 return cache[pos] = value;
3444 }
3445
3446 /**
3447 * Provides a target method handle with one or more <em>bound arguments</em>
3448 * in advance of the method handle's invocation.
3449 * The formal parameters to the target corresponding to the bound
3450 * arguments are called <em>bound parameters</em>.
3451 * Returns a new method handle which saves away the bound arguments.
3452 * When it is invoked, it receives arguments for any non-bound parameters,
3453 * binds the saved arguments to their corresponding parameters,
3454 * and calls the original target.
3455 * <p>
3456 * The type of the new method handle will drop the types for the bound
3457 * parameters from the original target type, since the new method handle
3458 * will no longer require those arguments to be supplied by its callers.
3459 * <p>
3460 * Each given argument object must match the corresponding bound parameter type.
3461 * If a bound parameter type is a primitive, the argument object
3462 * must be a wrapper, and will be unboxed to produce the primitive value.
3463 * <p>
3464 * The {@code pos} argument selects which parameters are to be bound.
3465 * It may range between zero and <i>N-L</i> (inclusively),
3466 * where <i>N</i> is the arity of the target method handle
3467 * and <i>L</i> is the length of the values array.
3468 * <p>
3469 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3470 * variable-arity method handle}, even if the original target method handle was.
3471 * @param target the method handle to invoke after the argument is inserted
3472 * @param pos where to insert the argument (zero for the first)
3473 * @param values the series of arguments to insert
3474 * @return a method handle which inserts an additional argument,
3475 * before calling the original method handle
3476 * @throws NullPointerException if the target or the {@code values} array is null
3477 * @see MethodHandle#bindTo
3478 */
3479 public static
3480 MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
3481 int insCount = values.length;
3482 Class<?>[] ptypes = insertArgumentsChecks(target, insCount, pos);
3483 if (insCount == 0) return target;
3484 BoundMethodHandle result = target.rebind();
3485 for (int i = 0; i < insCount; i++) {
3486 Object value = values[i];
3487 Class<?> ptype = ptypes[pos+i];
3488 if (ptype.isPrimitive()) {
3489 result = insertArgumentPrimitive(result, pos, ptype, value);
3490 } else {
3491 value = ptype.cast(value); // throw CCE if needed
3492 result = result.bindArgumentL(pos, value);
3493 }
3494 }
3495 return result;
3496 }
3497
3498 private static BoundMethodHandle insertArgumentPrimitive(BoundMethodHandle result, int pos,
3499 Class<?> ptype, Object value) {
3500 Wrapper w = Wrapper.forPrimitiveType(ptype);
3501 // perform unboxing and/or primitive conversion
3502 value = w.convert(value, ptype);
3503 switch (w) {
3504 case INT: return result.bindArgumentI(pos, (int)value);
3505 case LONG: return result.bindArgumentJ(pos, (long)value);
3506 case FLOAT: return result.bindArgumentF(pos, (float)value);
3507 case DOUBLE: return result.bindArgumentD(pos, (double)value);
3508 default: return result.bindArgumentI(pos, ValueConversions.widenSubword(value));
3509 }
3510 }
3511
3512 private static Class<?>[] insertArgumentsChecks(MethodHandle target, int insCount, int pos) throws RuntimeException {
3513 MethodType oldType = target.type();
3514 int outargs = oldType.parameterCount();
3515 int inargs = outargs - insCount;
3516 if (inargs < 0)
3517 throw newIllegalArgumentException("too many values to insert");
3518 if (pos < 0 || pos > inargs)
3519 throw newIllegalArgumentException("no argument type to append");
3520 return oldType.ptypes();
3521 }
3522
3523 /**
3524 * Produces a method handle which will discard some dummy arguments
3525 * before calling some other specified <i>target</i> method handle.
3526 * The type of the new method handle will be the same as the target's type,
3527 * except it will also include the dummy argument types,
3528 * at some given position.
3529 * <p>
3530 * The {@code pos} argument may range between zero and <i>N</i>,
3531 * where <i>N</i> is the arity of the target.
3532 * If {@code pos} is zero, the dummy arguments will precede
3533 * the target's real arguments; if {@code pos} is <i>N</i>
3534 * they will come after.
3535 * <p>
3536 * <b>Example:</b>
3537 * <blockquote><pre>{@code
3538 import static java.lang.invoke.MethodHandles.*;
3539 import static java.lang.invoke.MethodType.*;
3540 ...
3541 MethodHandle cat = lookup().findVirtual(String.class,
3542 "concat", methodType(String.class, String.class));
3543 assertEquals("xy", (String) cat.invokeExact("x", "y"));
3544 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
3545 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
3546 assertEquals(bigType, d0.type());
3547 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
3548 * }</pre></blockquote>
3549 * <p>
3550 * This method is also equivalent to the following code:
3551 * <blockquote><pre>
3552 * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))}
3553 * </pre></blockquote>
3554 * @param target the method handle to invoke after the arguments are dropped
3555 * @param valueTypes the type(s) of the argument(s) to drop
3556 * @param pos position of first argument to drop (zero for the leftmost)
3557 * @return a method handle which drops arguments of the given types,
3558 * before calling the original method handle
3559 * @throws NullPointerException if the target is null,
3560 * or if the {@code valueTypes} list or any of its elements is null
3561 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
3562 * or if {@code pos} is negative or greater than the arity of the target,
3563 * or if the new method handle's type would have too many parameters
3564 */
3565 public static
3566 MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) {
3567 return dropArguments0(target, pos, copyTypes(valueTypes.toArray()));
3568 }
3569
3570 private static List<Class<?>> copyTypes(Object[] array) {
3571 return Arrays.asList(Arrays.copyOf(array, array.length, Class[].class));
3572 }
3573
3574 private static
3575 MethodHandle dropArguments0(MethodHandle target, int pos, List<Class<?>> valueTypes) {
3576 MethodType oldType = target.type(); // get NPE
3577 int dropped = dropArgumentChecks(oldType, pos, valueTypes);
3578 MethodType newType = oldType.insertParameterTypes(pos, valueTypes);
3579 if (dropped == 0) return target;
3580 BoundMethodHandle result = target.rebind();
3581 LambdaForm lform = result.form;
3582 int insertFormArg = 1 + pos;
3583 for (Class<?> ptype : valueTypes) {
3584 lform = lform.editor().addArgumentForm(insertFormArg++, BasicType.basicType(ptype));
3585 }
3586 result = result.copyWith(newType, lform);
3587 return result;
3588 }
3589
3590 private static int dropArgumentChecks(MethodType oldType, int pos, List<Class<?>> valueTypes) {
3591 int dropped = valueTypes.size();
3592 MethodType.checkSlotCount(dropped);
3593 int outargs = oldType.parameterCount();
3594 int inargs = outargs + dropped;
3595 if (pos < 0 || pos > outargs)
3596 throw newIllegalArgumentException("no argument type to remove"
3597 + Arrays.asList(oldType, pos, valueTypes, inargs, outargs)
3598 );
3599 return dropped;
3600 }
3601
3602 /**
3603 * Produces a method handle which will discard some dummy arguments
3604 * before calling some other specified <i>target</i> method handle.
3605 * The type of the new method handle will be the same as the target's type,
3606 * except it will also include the dummy argument types,
3607 * at some given position.
3608 * <p>
3609 * The {@code pos} argument may range between zero and <i>N</i>,
3610 * where <i>N</i> is the arity of the target.
3611 * If {@code pos} is zero, the dummy arguments will precede
3612 * the target's real arguments; if {@code pos} is <i>N</i>
3613 * they will come after.
3614 * @apiNote
3615 * <blockquote><pre>{@code
3616 import static java.lang.invoke.MethodHandles.*;
3617 import static java.lang.invoke.MethodType.*;
3618 ...
3619 MethodHandle cat = lookup().findVirtual(String.class,
3620 "concat", methodType(String.class, String.class));
3621 assertEquals("xy", (String) cat.invokeExact("x", "y"));
3622 MethodHandle d0 = dropArguments(cat, 0, String.class);
3623 assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
3624 MethodHandle d1 = dropArguments(cat, 1, String.class);
3625 assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
3626 MethodHandle d2 = dropArguments(cat, 2, String.class);
3627 assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
3628 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
3629 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
3630 * }</pre></blockquote>
3631 * <p>
3632 * This method is also equivalent to the following code:
3633 * <blockquote><pre>
3634 * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))}
3635 * </pre></blockquote>
3636 * @param target the method handle to invoke after the arguments are dropped
3637 * @param valueTypes the type(s) of the argument(s) to drop
3638 * @param pos position of first argument to drop (zero for the leftmost)
3639 * @return a method handle which drops arguments of the given types,
3640 * before calling the original method handle
3641 * @throws NullPointerException if the target is null,
3642 * or if the {@code valueTypes} array or any of its elements is null
3643 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
3644 * or if {@code pos} is negative or greater than the arity of the target,
3645 * or if the new method handle's type would have
3646 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3647 */
3648 public static
3649 MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
3650 return dropArguments0(target, pos, copyTypes(valueTypes));
3651 }
3652
3653 // private version which allows caller some freedom with error handling
3654 private static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos,
3655 boolean nullOnFailure) {
3656 newTypes = copyTypes(newTypes.toArray());
3657 List<Class<?>> oldTypes = target.type().parameterList();
3658 int match = oldTypes.size();
3659 if (skip != 0) {
3660 if (skip < 0 || skip > match) {
3661 throw newIllegalArgumentException("illegal skip", skip, target);
3662 }
3663 oldTypes = oldTypes.subList(skip, match);
3664 match -= skip;
3665 }
3666 List<Class<?>> addTypes = newTypes;
3667 int add = addTypes.size();
3668 if (pos != 0) {
3669 if (pos < 0 || pos > add) {
3670 throw newIllegalArgumentException("illegal pos", pos, newTypes);
3671 }
3672 addTypes = addTypes.subList(pos, add);
3673 add -= pos;
3674 assert(addTypes.size() == add);
3675 }
3676 // Do not add types which already match the existing arguments.
3677 if (match > add || !oldTypes.equals(addTypes.subList(0, match))) {
3678 if (nullOnFailure) {
3679 return null;
3680 }
3681 throw newIllegalArgumentException("argument lists do not match", oldTypes, newTypes);
3682 }
3683 addTypes = addTypes.subList(match, add);
3684 add -= match;
3685 assert(addTypes.size() == add);
3686 // newTypes: ( P*[pos], M*[match], A*[add] )
3687 // target: ( S*[skip], M*[match] )
3688 MethodHandle adapter = target;
3689 if (add > 0) {
3690 adapter = dropArguments0(adapter, skip+ match, addTypes);
3691 }
3692 // adapter: (S*[skip], M*[match], A*[add] )
3693 if (pos > 0) {
3694 adapter = dropArguments0(adapter, skip, newTypes.subList(0, pos));
3695 }
3696 // adapter: (S*[skip], P*[pos], M*[match], A*[add] )
3697 return adapter;
3698 }
3699
3700 /**
3701 * Adapts a target method handle to match the given parameter type list. If necessary, adds dummy arguments. Some
3702 * leading parameters can be skipped before matching begins. The remaining types in the {@code target}'s parameter
3703 * type list must be a sub-list of the {@code newTypes} type list at the starting position {@code pos}. The
3704 * resulting handle will have the target handle's parameter type list, with any non-matching parameter types (before
3705 * or after the matching sub-list) inserted in corresponding positions of the target's original parameters, as if by
3706 * {@link #dropArguments(MethodHandle, int, Class[])}.
3707 * <p>
3708 * The resulting handle will have the same return type as the target handle.
3709 * <p>
3710 * In more formal terms, assume these two type lists:<ul>
3711 * <li>The target handle has the parameter type list {@code S..., M...}, with as many types in {@code S} as
3712 * indicated by {@code skip}. The {@code M} types are those that are supposed to match part of the given type list,
3713 * {@code newTypes}.
3714 * <li>The {@code newTypes} list contains types {@code P..., M..., A...}, with as many types in {@code P} as
3715 * indicated by {@code pos}. The {@code M} types are precisely those that the {@code M} types in the target handle's
3716 * parameter type list are supposed to match. The types in {@code A} are additional types found after the matching
3717 * sub-list.
3718 * </ul>
3719 * Given these assumptions, the result of an invocation of {@code dropArgumentsToMatch} will have the parameter type
3720 * list {@code S..., P..., M..., A...}, with the {@code P} and {@code A} types inserted as if by
3721 * {@link #dropArguments(MethodHandle, int, Class[])}.
3722 *
3723 * @apiNote
3724 * Two method handles whose argument lists are "effectively identical" (i.e., identical in a common prefix) may be
3725 * mutually converted to a common type by two calls to {@code dropArgumentsToMatch}, as follows:
3726 * <blockquote><pre>{@code
3727 import static java.lang.invoke.MethodHandles.*;
3728 import static java.lang.invoke.MethodType.*;
3729 ...
3730 ...
3731 MethodHandle h0 = constant(boolean.class, true);
3732 MethodHandle h1 = lookup().findVirtual(String.class, "concat", methodType(String.class, String.class));
3733 MethodType bigType = h1.type().insertParameterTypes(1, String.class, int.class);
3734 MethodHandle h2 = dropArguments(h1, 0, bigType.parameterList());
3735 if (h1.type().parameterCount() < h2.type().parameterCount())
3736 h1 = dropArgumentsToMatch(h1, 0, h2.type().parameterList(), 0); // lengthen h1
3737 else
3738 h2 = dropArgumentsToMatch(h2, 0, h1.type().parameterList(), 0); // lengthen h2
3739 MethodHandle h3 = guardWithTest(h0, h1, h2);
3740 assertEquals("xy", h3.invoke("x", "y", 1, "a", "b", "c"));
3741 * }</pre></blockquote>
3742 * @param target the method handle to adapt
3743 * @param skip number of targets parameters to disregard (they will be unchanged)
3744 * @param newTypes the list of types to match {@code target}'s parameter type list to
3745 * @param pos place in {@code newTypes} where the non-skipped target parameters must occur
3746 * @return a possibly adapted method handle
3747 * @throws NullPointerException if either argument is null
3748 * @throws IllegalArgumentException if any element of {@code newTypes} is {@code void.class},
3749 * or if {@code skip} is negative or greater than the arity of the target,
3750 * or if {@code pos} is negative or greater than the newTypes list size,
3751 * or if {@code newTypes} does not contain the {@code target}'s non-skipped parameter types at position
3752 * {@code pos}.
3753 * @since 9
3754 */
3755 public static
3756 MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos) {
3757 Objects.requireNonNull(target);
3758 Objects.requireNonNull(newTypes);
3759 return dropArgumentsToMatch(target, skip, newTypes, pos, false);
3760 }
3761
3762 /**
3763 * Adapts a target method handle by pre-processing
3764 * one or more of its arguments, each with its own unary filter function,
3765 * and then calling the target with each pre-processed argument
3766 * replaced by the result of its corresponding filter function.
3767 * <p>
3768 * The pre-processing is performed by one or more method handles,
3769 * specified in the elements of the {@code filters} array.
3770 * The first element of the filter array corresponds to the {@code pos}
3771 * argument of the target, and so on in sequence.
3772 * The filter functions are invoked in left to right order.
3773 * <p>
3774 * Null arguments in the array are treated as identity functions,
3775 * and the corresponding arguments left unchanged.
3776 * (If there are no non-null elements in the array, the original target is returned.)
3777 * Each filter is applied to the corresponding argument of the adapter.
3778 * <p>
3779 * If a filter {@code F} applies to the {@code N}th argument of
3780 * the target, then {@code F} must be a method handle which
3781 * takes exactly one argument. The type of {@code F}'s sole argument
3782 * replaces the corresponding argument type of the target
3783 * in the resulting adapted method handle.
3784 * The return type of {@code F} must be identical to the corresponding
3785 * parameter type of the target.
3786 * <p>
3787 * It is an error if there are elements of {@code filters}
3788 * (null or not)
3789 * which do not correspond to argument positions in the target.
3790 * <p><b>Example:</b>
3791 * <blockquote><pre>{@code
3792 import static java.lang.invoke.MethodHandles.*;
3793 import static java.lang.invoke.MethodType.*;
3794 ...
3795 MethodHandle cat = lookup().findVirtual(String.class,
3796 "concat", methodType(String.class, String.class));
3797 MethodHandle upcase = lookup().findVirtual(String.class,
3798 "toUpperCase", methodType(String.class));
3799 assertEquals("xy", (String) cat.invokeExact("x", "y"));
3800 MethodHandle f0 = filterArguments(cat, 0, upcase);
3801 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
3802 MethodHandle f1 = filterArguments(cat, 1, upcase);
3803 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
3804 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
3805 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
3806 * }</pre></blockquote>
3807 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
3808 * denotes the return type of both the {@code target} and resulting adapter.
3809 * {@code P}/{@code p} and {@code B}/{@code b} represent the types and values
3810 * of the parameters and arguments that precede and follow the filter position
3811 * {@code pos}, respectively. {@code A[i]}/{@code a[i]} stand for the types and
3812 * values of the filtered parameters and arguments; they also represent the
3813 * return types of the {@code filter[i]} handles. The latter accept arguments
3814 * {@code v[i]} of type {@code V[i]}, which also appear in the signature of
3815 * the resulting adapter.
3816 * <blockquote><pre>{@code
3817 * T target(P... p, A[i]... a[i], B... b);
3818 * A[i] filter[i](V[i]);
3819 * T adapter(P... p, V[i]... v[i], B... b) {
3820 * return target(p..., filter[i](v[i])..., b...);
3821 * }
3822 * }</pre></blockquote>
3823 * <p>
3824 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3825 * variable-arity method handle}, even if the original target method handle was.
3826 *
3827 * @param target the method handle to invoke after arguments are filtered
3828 * @param pos the position of the first argument to filter
3829 * @param filters method handles to call initially on filtered arguments
3830 * @return method handle which incorporates the specified argument filtering logic
3831 * @throws NullPointerException if the target is null
3832 * or if the {@code filters} array is null
3833 * @throws IllegalArgumentException if a non-null element of {@code filters}
3834 * does not match a corresponding argument type of target as described above,
3835 * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()},
3836 * or if the resulting method handle's type would have
3837 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3838 */
3839 public static
3840 MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
3841 filterArgumentsCheckArity(target, pos, filters);
3842 MethodHandle adapter = target;
3843 // process filters in reverse order so that the invocation of
3844 // the resulting adapter will invoke the filters in left-to-right order
3845 for (int i = filters.length - 1; i >= 0; --i) {
3846 MethodHandle filter = filters[i];
3847 if (filter == null) continue; // ignore null elements of filters
3848 adapter = filterArgument(adapter, pos + i, filter);
3849 }
3850 return adapter;
3851 }
3852
3853 /*non-public*/ static
3854 MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
3855 filterArgumentChecks(target, pos, filter);
3856 MethodType targetType = target.type();
3857 MethodType filterType = filter.type();
3858 BoundMethodHandle result = target.rebind();
3859 Class<?> newParamType = filterType.parameterType(0);
3860 LambdaForm lform = result.editor().filterArgumentForm(1 + pos, BasicType.basicType(newParamType));
3861 MethodType newType = targetType.changeParameterType(pos, newParamType);
3862 result = result.copyWithExtendL(newType, lform, filter);
3863 return result;
3864 }
3865
3866 private static void filterArgumentsCheckArity(MethodHandle target, int pos, MethodHandle[] filters) {
3867 MethodType targetType = target.type();
3868 int maxPos = targetType.parameterCount();
3869 if (pos + filters.length > maxPos)
3870 throw newIllegalArgumentException("too many filters");
3871 }
3872
3873 private static void filterArgumentChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
3874 MethodType targetType = target.type();
3875 MethodType filterType = filter.type();
3876 if (filterType.parameterCount() != 1
3877 || filterType.returnType() != targetType.parameterType(pos))
3878 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
3879 }
3880
3881 /**
3882 * Adapts a target method handle by pre-processing
3883 * a sub-sequence of its arguments with a filter (another method handle).
3884 * The pre-processed arguments are replaced by the result (if any) of the
3885 * filter function.
3886 * The target is then called on the modified (usually shortened) argument list.
3887 * <p>
3888 * If the filter returns a value, the target must accept that value as
3889 * its argument in position {@code pos}, preceded and/or followed by
3890 * any arguments not passed to the filter.
3891 * If the filter returns void, the target must accept all arguments
3892 * not passed to the filter.
3893 * No arguments are reordered, and a result returned from the filter
3894 * replaces (in order) the whole subsequence of arguments originally
3895 * passed to the adapter.
3896 * <p>
3897 * The argument types (if any) of the filter
3898 * replace zero or one argument types of the target, at position {@code pos},
3899 * in the resulting adapted method handle.
3900 * The return type of the filter (if any) must be identical to the
3901 * argument type of the target at position {@code pos}, and that target argument
3902 * is supplied by the return value of the filter.
3903 * <p>
3904 * In all cases, {@code pos} must be greater than or equal to zero, and
3905 * {@code pos} must also be less than or equal to the target's arity.
3906 * <p><b>Example:</b>
3907 * <blockquote><pre>{@code
3908 import static java.lang.invoke.MethodHandles.*;
3909 import static java.lang.invoke.MethodType.*;
3910 ...
3911 MethodHandle deepToString = publicLookup()
3912 .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
3913
3914 MethodHandle ts1 = deepToString.asCollector(String[].class, 1);
3915 assertEquals("[strange]", (String) ts1.invokeExact("strange"));
3916
3917 MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
3918 assertEquals("[up, down]", (String) ts2.invokeExact("up", "down"));
3919
3920 MethodHandle ts3 = deepToString.asCollector(String[].class, 3);
3921 MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2);
3922 assertEquals("[top, [up, down], strange]",
3923 (String) ts3_ts2.invokeExact("top", "up", "down", "strange"));
3924
3925 MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1);
3926 assertEquals("[top, [up, down], [strange]]",
3927 (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange"));
3928
3929 MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3);
3930 assertEquals("[top, [[up, down, strange], charm], bottom]",
3931 (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom"));
3932 * }</pre></blockquote>
3933 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
3934 * represents the return type of the {@code target} and resulting adapter.
3935 * {@code V}/{@code v} stand for the return type and value of the
3936 * {@code filter}, which are also found in the signature and arguments of
3937 * the {@code target}, respectively, unless {@code V} is {@code void}.
3938 * {@code A}/{@code a} and {@code C}/{@code c} represent the parameter types
3939 * and values preceding and following the collection position, {@code pos},
3940 * in the {@code target}'s signature. They also turn up in the resulting
3941 * adapter's signature and arguments, where they surround
3942 * {@code B}/{@code b}, which represent the parameter types and arguments
3943 * to the {@code filter} (if any).
3944 * <blockquote><pre>{@code
3945 * T target(A...,V,C...);
3946 * V filter(B...);
3947 * T adapter(A... a,B... b,C... c) {
3948 * V v = filter(b...);
3949 * return target(a...,v,c...);
3950 * }
3951 * // and if the filter has no arguments:
3952 * T target2(A...,V,C...);
3953 * V filter2();
3954 * T adapter2(A... a,C... c) {
3955 * V v = filter2();
3956 * return target2(a...,v,c...);
3957 * }
3958 * // and if the filter has a void return:
3959 * T target3(A...,C...);
3960 * void filter3(B...);
3961 * T adapter3(A... a,B... b,C... c) {
3962 * filter3(b...);
3963 * return target3(a...,c...);
3964 * }
3965 * }</pre></blockquote>
3966 * <p>
3967 * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to
3968 * one which first "folds" the affected arguments, and then drops them, in separate
3969 * steps as follows:
3970 * <blockquote><pre>{@code
3971 * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2
3972 * mh = MethodHandles.foldArguments(mh, coll); //step 1
3973 * }</pre></blockquote>
3974 * If the target method handle consumes no arguments besides than the result
3975 * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)}
3976 * is equivalent to {@code filterReturnValue(coll, mh)}.
3977 * If the filter method handle {@code coll} consumes one argument and produces
3978 * a non-void result, then {@code collectArguments(mh, N, coll)}
3979 * is equivalent to {@code filterArguments(mh, N, coll)}.
3980 * Other equivalences are possible but would require argument permutation.
3981 * <p>
3982 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3983 * variable-arity method handle}, even if the original target method handle was.
3984 *
3985 * @param target the method handle to invoke after filtering the subsequence of arguments
3986 * @param pos the position of the first adapter argument to pass to the filter,
3987 * and/or the target argument which receives the result of the filter
3988 * @param filter method handle to call on the subsequence of arguments
3989 * @return method handle which incorporates the specified argument subsequence filtering logic
3990 * @throws NullPointerException if either argument is null
3991 * @throws IllegalArgumentException if the return type of {@code filter}
3992 * is non-void and is not the same as the {@code pos} argument of the target,
3993 * or if {@code pos} is not between 0 and the target's arity, inclusive,
3994 * or if the resulting method handle's type would have
3995 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3996 * @see MethodHandles#foldArguments
3997 * @see MethodHandles#filterArguments
3998 * @see MethodHandles#filterReturnValue
3999 */
4000 public static
4001 MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) {
4002 MethodType newType = collectArgumentsChecks(target, pos, filter);
4003 MethodType collectorType = filter.type();
4004 BoundMethodHandle result = target.rebind();
4005 LambdaForm lform;
4006 if (collectorType.returnType().isArray() && filter.intrinsicName() == Intrinsic.NEW_ARRAY) {
4007 lform = result.editor().collectArgumentArrayForm(1 + pos, filter);
4008 if (lform != null) {
4009 return result.copyWith(newType, lform);
4010 }
4011 }
4012 lform = result.editor().collectArgumentsForm(1 + pos, collectorType.basicType());
4013 return result.copyWithExtendL(newType, lform, filter);
4014 }
4015
4016 private static MethodType collectArgumentsChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
4017 MethodType targetType = target.type();
4018 MethodType filterType = filter.type();
4019 Class<?> rtype = filterType.returnType();
4020 List<Class<?>> filterArgs = filterType.parameterList();
4021 if (rtype == void.class) {
4022 return targetType.insertParameterTypes(pos, filterArgs);
4023 }
4024 if (rtype != targetType.parameterType(pos)) {
4025 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
4026 }
4027 return targetType.dropParameterTypes(pos, pos+1).insertParameterTypes(pos, filterArgs);
4028 }
4029
4030 /**
4031 * Adapts a target method handle by post-processing
4032 * its return value (if any) with a filter (another method handle).
4033 * The result of the filter is returned from the adapter.
4034 * <p>
4035 * If the target returns a value, the filter must accept that value as
4036 * its only argument.
4037 * If the target returns void, the filter must accept no arguments.
4038 * <p>
4039 * The return type of the filter
4040 * replaces the return type of the target
4041 * in the resulting adapted method handle.
4042 * The argument type of the filter (if any) must be identical to the
4043 * return type of the target.
4044 * <p><b>Example:</b>
4045 * <blockquote><pre>{@code
4046 import static java.lang.invoke.MethodHandles.*;
4047 import static java.lang.invoke.MethodType.*;
4048 ...
4049 MethodHandle cat = lookup().findVirtual(String.class,
4050 "concat", methodType(String.class, String.class));
4051 MethodHandle length = lookup().findVirtual(String.class,
4052 "length", methodType(int.class));
4053 System.out.println((String) cat.invokeExact("x", "y")); // xy
4054 MethodHandle f0 = filterReturnValue(cat, length);
4055 System.out.println((int) f0.invokeExact("x", "y")); // 2
4056 * }</pre></blockquote>
4057 * <p>Here is pseudocode for the resulting adapter. In the code,
4058 * {@code T}/{@code t} represent the result type and value of the
4059 * {@code target}; {@code V}, the result type of the {@code filter}; and
4060 * {@code A}/{@code a}, the types and values of the parameters and arguments
4061 * of the {@code target} as well as the resulting adapter.
4062 * <blockquote><pre>{@code
4063 * T target(A...);
4064 * V filter(T);
4065 * V adapter(A... a) {
4066 * T t = target(a...);
4067 * return filter(t);
4068 * }
4069 * // and if the target has a void return:
4070 * void target2(A...);
4071 * V filter2();
4072 * V adapter2(A... a) {
4073 * target2(a...);
4074 * return filter2();
4075 * }
4076 * // and if the filter has a void return:
4077 * T target3(A...);
4078 * void filter3(V);
4079 * void adapter3(A... a) {
4080 * T t = target3(a...);
4081 * filter3(t);
4082 * }
4083 * }</pre></blockquote>
4084 * <p>
4085 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4086 * variable-arity method handle}, even if the original target method handle was.
4087 * @param target the method handle to invoke before filtering the return value
4088 * @param filter method handle to call on the return value
4089 * @return method handle which incorporates the specified return value filtering logic
4090 * @throws NullPointerException if either argument is null
4091 * @throws IllegalArgumentException if the argument list of {@code filter}
4092 * does not match the return type of target as described above
4093 */
4094 public static
4095 MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
4096 MethodType targetType = target.type();
4097 MethodType filterType = filter.type();
4098 filterReturnValueChecks(targetType, filterType);
4099 BoundMethodHandle result = target.rebind();
4100 BasicType rtype = BasicType.basicType(filterType.returnType());
4101 LambdaForm lform = result.editor().filterReturnForm(rtype, false);
4102 MethodType newType = targetType.changeReturnType(filterType.returnType());
4103 result = result.copyWithExtendL(newType, lform, filter);
4104 return result;
4105 }
4106
4107 private static void filterReturnValueChecks(MethodType targetType, MethodType filterType) throws RuntimeException {
4108 Class<?> rtype = targetType.returnType();
4109 int filterValues = filterType.parameterCount();
4110 if (filterValues == 0
4111 ? (rtype != void.class)
4112 : (rtype != filterType.parameterType(0) || filterValues != 1))
4113 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
4114 }
4115
4116 /**
4117 * Adapts a target method handle by pre-processing
4118 * some of its arguments, and then calling the target with
4119 * the result of the pre-processing, inserted into the original
4120 * sequence of arguments.
4121 * <p>
4122 * The pre-processing is performed by {@code combiner}, a second method handle.
4123 * Of the arguments passed to the adapter, the first {@code N} arguments
4124 * are copied to the combiner, which is then called.
4125 * (Here, {@code N} is defined as the parameter count of the combiner.)
4126 * After this, control passes to the target, with any result
4127 * from the combiner inserted before the original {@code N} incoming
4128 * arguments.
4129 * <p>
4130 * If the combiner returns a value, the first parameter type of the target
4131 * must be identical with the return type of the combiner, and the next
4132 * {@code N} parameter types of the target must exactly match the parameters
4133 * of the combiner.
4134 * <p>
4135 * If the combiner has a void return, no result will be inserted,
4136 * and the first {@code N} parameter types of the target
4137 * must exactly match the parameters of the combiner.
4138 * <p>
4139 * The resulting adapter is the same type as the target, except that the
4140 * first parameter type is dropped,
4141 * if it corresponds to the result of the combiner.
4142 * <p>
4143 * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
4144 * that either the combiner or the target does not wish to receive.
4145 * If some of the incoming arguments are destined only for the combiner,
4146 * consider using {@link MethodHandle#asCollector asCollector} instead, since those
4147 * arguments will not need to be live on the stack on entry to the
4148 * target.)
4149 * <p><b>Example:</b>
4150 * <blockquote><pre>{@code
4151 import static java.lang.invoke.MethodHandles.*;
4152 import static java.lang.invoke.MethodType.*;
4153 ...
4154 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
4155 "println", methodType(void.class, String.class))
4156 .bindTo(System.out);
4157 MethodHandle cat = lookup().findVirtual(String.class,
4158 "concat", methodType(String.class, String.class));
4159 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
4160 MethodHandle catTrace = foldArguments(cat, trace);
4161 // also prints "boo":
4162 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
4163 * }</pre></blockquote>
4164 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
4165 * represents the result type of the {@code target} and resulting adapter.
4166 * {@code V}/{@code v} represent the type and value of the parameter and argument
4167 * of {@code target} that precedes the folding position; {@code V} also is
4168 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
4169 * types and values of the {@code N} parameters and arguments at the folding
4170 * position. {@code B}/{@code b} represent the types and values of the
4171 * {@code target} parameters and arguments that follow the folded parameters
4172 * and arguments.
4173 * <blockquote><pre>{@code
4174 * // there are N arguments in A...
4175 * T target(V, A[N]..., B...);
4176 * V combiner(A...);
4177 * T adapter(A... a, B... b) {
4178 * V v = combiner(a...);
4179 * return target(v, a..., b...);
4180 * }
4181 * // and if the combiner has a void return:
4182 * T target2(A[N]..., B...);
4183 * void combiner2(A...);
4184 * T adapter2(A... a, B... b) {
4185 * combiner2(a...);
4186 * return target2(a..., b...);
4187 * }
4188 * }</pre></blockquote>
4189 * <p>
4190 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4191 * variable-arity method handle}, even if the original target method handle was.
4192 * @param target the method handle to invoke after arguments are combined
4193 * @param combiner method handle to call initially on the incoming arguments
4194 * @return method handle which incorporates the specified argument folding logic
4195 * @throws NullPointerException if either argument is null
4196 * @throws IllegalArgumentException if {@code combiner}'s return type
4197 * is non-void and not the same as the first argument type of
4198 * the target, or if the initial {@code N} argument types
4199 * of the target
4200 * (skipping one matching the {@code combiner}'s return type)
4201 * are not identical with the argument types of {@code combiner}
4202 */
4203 public static
4204 MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
4205 return foldArguments(target, 0, combiner);
4206 }
4207
4208 /**
4209 * Adapts a target method handle by pre-processing some of its arguments, starting at a given position, and then
4210 * calling the target with the result of the pre-processing, inserted into the original sequence of arguments just
4211 * before the folded arguments.
4212 * <p>
4213 * This method is closely related to {@link #foldArguments(MethodHandle, MethodHandle)}, but allows to control the
4214 * position in the parameter list at which folding takes place. The argument controlling this, {@code pos}, is a
4215 * zero-based index. The aforementioned method {@link #foldArguments(MethodHandle, MethodHandle)} assumes position
4216 * 0.
4217 *
4218 * @apiNote Example:
4219 * <blockquote><pre>{@code
4220 import static java.lang.invoke.MethodHandles.*;
4221 import static java.lang.invoke.MethodType.*;
4222 ...
4223 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
4224 "println", methodType(void.class, String.class))
4225 .bindTo(System.out);
4226 MethodHandle cat = lookup().findVirtual(String.class,
4227 "concat", methodType(String.class, String.class));
4228 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
4229 MethodHandle catTrace = foldArguments(cat, 1, trace);
4230 // also prints "jum":
4231 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
4232 * }</pre></blockquote>
4233 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
4234 * represents the result type of the {@code target} and resulting adapter.
4235 * {@code V}/{@code v} represent the type and value of the parameter and argument
4236 * of {@code target} that precedes the folding position; {@code V} also is
4237 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
4238 * types and values of the {@code N} parameters and arguments at the folding
4239 * position. {@code Z}/{@code z} and {@code B}/{@code b} represent the types
4240 * and values of the {@code target} parameters and arguments that precede and
4241 * follow the folded parameters and arguments starting at {@code pos},
4242 * respectively.
4243 * <blockquote><pre>{@code
4244 * // there are N arguments in A...
4245 * T target(Z..., V, A[N]..., B...);
4246 * V combiner(A...);
4247 * T adapter(Z... z, A... a, B... b) {
4248 * V v = combiner(a...);
4249 * return target(z..., v, a..., b...);
4250 * }
4251 * // and if the combiner has a void return:
4252 * T target2(Z..., A[N]..., B...);
4253 * void combiner2(A...);
4254 * T adapter2(Z... z, A... a, B... b) {
4255 * combiner2(a...);
4256 * return target2(z..., a..., b...);
4257 * }
4258 * }</pre></blockquote>
4259 * <p>
4260 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4261 * variable-arity method handle}, even if the original target method handle was.
4262 *
4263 * @param target the method handle to invoke after arguments are combined
4264 * @param pos the position at which to start folding and at which to insert the folding result; if this is {@code
4265 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
4266 * @param combiner method handle to call initially on the incoming arguments
4267 * @return method handle which incorporates the specified argument folding logic
4268 * @throws NullPointerException if either argument is null
4269 * @throws IllegalArgumentException if either of the following two conditions holds:
4270 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
4271 * {@code pos} of the target signature;
4272 * (2) the {@code N} argument types at position {@code pos} of the target signature (skipping one matching
4273 * the {@code combiner}'s return type) are not identical with the argument types of {@code combiner}.
4274 *
4275 * @see #foldArguments(MethodHandle, MethodHandle)
4276 * @since 9
4277 */
4278 public static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner) {
4279 MethodType targetType = target.type();
4280 MethodType combinerType = combiner.type();
4281 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType);
4282 BoundMethodHandle result = target.rebind();
4283 boolean dropResult = rtype == void.class;
4284 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType());
4285 MethodType newType = targetType;
4286 if (!dropResult) {
4287 newType = newType.dropParameterTypes(pos, pos + 1);
4288 }
4289 result = result.copyWithExtendL(newType, lform, combiner);
4290 return result;
4291 }
4292
4293 /**
4294 * As {@see foldArguments(MethodHandle, int, MethodHandle)}, but with the
4295 * added capability of selecting the arguments from the targets parameters
4296 * to call the combiner with. This allows us to avoid some simple cases of
4297 * permutations and padding the combiner with dropArguments to select the
4298 * right argument, which may ultimately produce fewer intermediaries.
4299 */
4300 static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner, int ... argPositions) {
4301 MethodType targetType = target.type();
4302 MethodType combinerType = combiner.type();
4303 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType, argPositions);
4304 BoundMethodHandle result = target.rebind();
4305 boolean dropResult = rtype == void.class;
4306 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType(), argPositions);
4307 MethodType newType = targetType;
4308 if (!dropResult) {
4309 newType = newType.dropParameterTypes(pos, pos + 1);
4310 }
4311 result = result.copyWithExtendL(newType, lform, combiner);
4312 return result;
4313 }
4314
4315 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType) {
4316 int foldArgs = combinerType.parameterCount();
4317 Class<?> rtype = combinerType.returnType();
4318 int foldVals = rtype == void.class ? 0 : 1;
4319 int afterInsertPos = foldPos + foldVals;
4320 boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
4321 if (ok) {
4322 for (int i = 0; i < foldArgs; i++) {
4323 if (combinerType.parameterType(i) != targetType.parameterType(i + afterInsertPos)) {
4324 ok = false;
4325 break;
4326 }
4327 }
4328 }
4329 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos))
4330 ok = false;
4331 if (!ok)
4332 throw misMatchedTypes("target and combiner types", targetType, combinerType);
4333 return rtype;
4334 }
4335
4336 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType, int ... argPos) {
4337 int foldArgs = combinerType.parameterCount();
4338 if (argPos.length != foldArgs) {
4339 throw newIllegalArgumentException("combiner and argument map must be equal size", combinerType, argPos.length);
4340 }
4341 Class<?> rtype = combinerType.returnType();
4342 int foldVals = rtype == void.class ? 0 : 1;
4343 boolean ok = true;
4344 for (int i = 0; i < foldArgs; i++) {
4345 int arg = argPos[i];
4346 if (arg < 0 || arg > targetType.parameterCount()) {
4347 throw newIllegalArgumentException("arg outside of target parameterRange", targetType, arg);
4348 }
4349 if (combinerType.parameterType(i) != targetType.parameterType(arg)) {
4350 throw newIllegalArgumentException("target argument type at position " + arg
4351 + " must match combiner argument type at index " + i + ": " + targetType
4352 + " -> " + combinerType + ", map: " + Arrays.toString(argPos));
4353 }
4354 }
4355 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos)) {
4356 ok = false;
4357 }
4358 if (!ok)
4359 throw misMatchedTypes("target and combiner types", targetType, combinerType);
4360 return rtype;
4361 }
4362
4363 /**
4364 * Makes a method handle which adapts a target method handle,
4365 * by guarding it with a test, a boolean-valued method handle.
4366 * If the guard fails, a fallback handle is called instead.
4367 * All three method handles must have the same corresponding
4368 * argument and return types, except that the return type
4369 * of the test must be boolean, and the test is allowed
4370 * to have fewer arguments than the other two method handles.
4371 * <p>
4372 * Here is pseudocode for the resulting adapter. In the code, {@code T}
4373 * represents the uniform result type of the three involved handles;
4374 * {@code A}/{@code a}, the types and values of the {@code target}
4375 * parameters and arguments that are consumed by the {@code test}; and
4376 * {@code B}/{@code b}, those types and values of the {@code target}
4377 * parameters and arguments that are not consumed by the {@code test}.
4378 * <blockquote><pre>{@code
4379 * boolean test(A...);
4380 * T target(A...,B...);
4381 * T fallback(A...,B...);
4382 * T adapter(A... a,B... b) {
4383 * if (test(a...))
4384 * return target(a..., b...);
4385 * else
4386 * return fallback(a..., b...);
4387 * }
4388 * }</pre></blockquote>
4389 * Note that the test arguments ({@code a...} in the pseudocode) cannot
4390 * be modified by execution of the test, and so are passed unchanged
4391 * from the caller to the target or fallback as appropriate.
4392 * @param test method handle used for test, must return boolean
4393 * @param target method handle to call if test passes
4394 * @param fallback method handle to call if test fails
4395 * @return method handle which incorporates the specified if/then/else logic
4396 * @throws NullPointerException if any argument is null
4397 * @throws IllegalArgumentException if {@code test} does not return boolean,
4398 * or if all three method types do not match (with the return
4399 * type of {@code test} changed to match that of the target).
4400 */
4401 public static
4402 MethodHandle guardWithTest(MethodHandle test,
4403 MethodHandle target,
4404 MethodHandle fallback) {
4405 MethodType gtype = test.type();
4406 MethodType ttype = target.type();
4407 MethodType ftype = fallback.type();
4408 if (!ttype.equals(ftype))
4409 throw misMatchedTypes("target and fallback types", ttype, ftype);
4410 if (gtype.returnType() != boolean.class)
4411 throw newIllegalArgumentException("guard type is not a predicate "+gtype);
4412 List<Class<?>> targs = ttype.parameterList();
4413 test = dropArgumentsToMatch(test, 0, targs, 0, true);
4414 if (test == null) {
4415 throw misMatchedTypes("target and test types", ttype, gtype);
4416 }
4417 return MethodHandleImpl.makeGuardWithTest(test, target, fallback);
4418 }
4419
4420 static <T> RuntimeException misMatchedTypes(String what, T t1, T t2) {
4421 return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
4422 }
4423
4424 /**
4425 * Makes a method handle which adapts a target method handle,
4426 * by running it inside an exception handler.
4427 * If the target returns normally, the adapter returns that value.
4428 * If an exception matching the specified type is thrown, the fallback
4429 * handle is called instead on the exception, plus the original arguments.
4430 * <p>
4431 * The target and handler must have the same corresponding
4432 * argument and return types, except that handler may omit trailing arguments
4433 * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
4434 * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
4435 * <p>
4436 * Here is pseudocode for the resulting adapter. In the code, {@code T}
4437 * represents the return type of the {@code target} and {@code handler},
4438 * and correspondingly that of the resulting adapter; {@code A}/{@code a},
4439 * the types and values of arguments to the resulting handle consumed by
4440 * {@code handler}; and {@code B}/{@code b}, those of arguments to the
4441 * resulting handle discarded by {@code handler}.
4442 * <blockquote><pre>{@code
4443 * T target(A..., B...);
4444 * T handler(ExType, A...);
4445 * T adapter(A... a, B... b) {
4446 * try {
4447 * return target(a..., b...);
4448 * } catch (ExType ex) {
4449 * return handler(ex, a...);
4450 * }
4451 * }
4452 * }</pre></blockquote>
4453 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
4454 * be modified by execution of the target, and so are passed unchanged
4455 * from the caller to the handler, if the handler is invoked.
4456 * <p>
4457 * The target and handler must return the same type, even if the handler
4458 * always throws. (This might happen, for instance, because the handler
4459 * is simulating a {@code finally} clause).
4460 * To create such a throwing handler, compose the handler creation logic
4461 * with {@link #throwException throwException},
4462 * in order to create a method handle of the correct return type.
4463 * @param target method handle to call
4464 * @param exType the type of exception which the handler will catch
4465 * @param handler method handle to call if a matching exception is thrown
4466 * @return method handle which incorporates the specified try/catch logic
4467 * @throws NullPointerException if any argument is null
4468 * @throws IllegalArgumentException if {@code handler} does not accept
4469 * the given exception type, or if the method handle types do
4470 * not match in their return types and their
4471 * corresponding parameters
4472 * @see MethodHandles#tryFinally(MethodHandle, MethodHandle)
4473 */
4474 public static
4475 MethodHandle catchException(MethodHandle target,
4476 Class<? extends Throwable> exType,
4477 MethodHandle handler) {
4478 MethodType ttype = target.type();
4479 MethodType htype = handler.type();
4480 if (!Throwable.class.isAssignableFrom(exType))
4481 throw new ClassCastException(exType.getName());
4482 if (htype.parameterCount() < 1 ||
4483 !htype.parameterType(0).isAssignableFrom(exType))
4484 throw newIllegalArgumentException("handler does not accept exception type "+exType);
4485 if (htype.returnType() != ttype.returnType())
4486 throw misMatchedTypes("target and handler return types", ttype, htype);
4487 handler = dropArgumentsToMatch(handler, 1, ttype.parameterList(), 0, true);
4488 if (handler == null) {
4489 throw misMatchedTypes("target and handler types", ttype, htype);
4490 }
4491 return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
4492 }
4493
4494 /**
4495 * Produces a method handle which will throw exceptions of the given {@code exType}.
4496 * The method handle will accept a single argument of {@code exType},
4497 * and immediately throw it as an exception.
4498 * The method type will nominally specify a return of {@code returnType}.
4499 * The return type may be anything convenient: It doesn't matter to the
4500 * method handle's behavior, since it will never return normally.
4501 * @param returnType the return type of the desired method handle
4502 * @param exType the parameter type of the desired method handle
4503 * @return method handle which can throw the given exceptions
4504 * @throws NullPointerException if either argument is null
4505 */
4506 public static
4507 MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) {
4508 if (!Throwable.class.isAssignableFrom(exType))
4509 throw new ClassCastException(exType.getName());
4510 return MethodHandleImpl.throwException(methodType(returnType, exType));
4511 }
4512
4513 /**
4514 * Constructs a method handle representing a loop with several loop variables that are updated and checked upon each
4515 * iteration. Upon termination of the loop due to one of the predicates, a corresponding finalizer is run and
4516 * delivers the loop's result, which is the return value of the resulting handle.
4517 * <p>
4518 * Intuitively, every loop is formed by one or more "clauses", each specifying a local <em>iteration variable</em> and/or a loop
4519 * exit. Each iteration of the loop executes each clause in order. A clause can optionally update its iteration
4520 * variable; it can also optionally perform a test and conditional loop exit. In order to express this logic in
4521 * terms of method handles, each clause will specify up to four independent actions:<ul>
4522 * <li><em>init:</em> Before the loop executes, the initialization of an iteration variable {@code v} of type {@code V}.
4523 * <li><em>step:</em> When a clause executes, an update step for the iteration variable {@code v}.
4524 * <li><em>pred:</em> When a clause executes, a predicate execution to test for loop exit.
4525 * <li><em>fini:</em> If a clause causes a loop exit, a finalizer execution to compute the loop's return value.
4526 * </ul>
4527 * The full sequence of all iteration variable types, in clause order, will be notated as {@code (V...)}.
4528 * The values themselves will be {@code (v...)}. When we speak of "parameter lists", we will usually
4529 * be referring to types, but in some contexts (describing execution) the lists will be of actual values.
4530 * <p>
4531 * Some of these clause parts may be omitted according to certain rules, and useful default behavior is provided in
4532 * this case. See below for a detailed description.
4533 * <p>
4534 * <em>Parameters optional everywhere:</em>
4535 * Each clause function is allowed but not required to accept a parameter for each iteration variable {@code v}.
4536 * As an exception, the init functions cannot take any {@code v} parameters,
4537 * because those values are not yet computed when the init functions are executed.
4538 * Any clause function may neglect to take any trailing subsequence of parameters it is entitled to take.
4539 * In fact, any clause function may take no arguments at all.
4540 * <p>
4541 * <em>Loop parameters:</em>
4542 * A clause function may take all the iteration variable values it is entitled to, in which case
4543 * it may also take more trailing parameters. Such extra values are called <em>loop parameters</em>,
4544 * with their types and values notated as {@code (A...)} and {@code (a...)}.
4545 * These become the parameters of the resulting loop handle, to be supplied whenever the loop is executed.
4546 * (Since init functions do not accept iteration variables {@code v}, any parameter to an
4547 * init function is automatically a loop parameter {@code a}.)
4548 * As with iteration variables, clause functions are allowed but not required to accept loop parameters.
4549 * These loop parameters act as loop-invariant values visible across the whole loop.
4550 * <p>
4551 * <em>Parameters visible everywhere:</em>
4552 * Each non-init clause function is permitted to observe the entire loop state, because it can be passed the full
4553 * list {@code (v... a...)} of current iteration variable values and incoming loop parameters.
4554 * The init functions can observe initial pre-loop state, in the form {@code (a...)}.
4555 * Most clause functions will not need all of this information, but they will be formally connected to it
4556 * as if by {@link #dropArguments}.
4557 * <a id="astar"></a>
4558 * More specifically, we shall use the notation {@code (V*)} to express an arbitrary prefix of a full
4559 * sequence {@code (V...)} (and likewise for {@code (v*)}, {@code (A*)}, {@code (a*)}).
4560 * In that notation, the general form of an init function parameter list
4561 * is {@code (A*)}, and the general form of a non-init function parameter list is {@code (V*)} or {@code (V... A*)}.
4562 * <p>
4563 * <em>Checking clause structure:</em>
4564 * Given a set of clauses, there is a number of checks and adjustments performed to connect all the parts of the
4565 * loop. They are spelled out in detail in the steps below. In these steps, every occurrence of the word "must"
4566 * corresponds to a place where {@link IllegalArgumentException} will be thrown if the required constraint is not
4567 * met by the inputs to the loop combinator.
4568 * <p>
4569 * <em>Effectively identical sequences:</em>
4570 * <a id="effid"></a>
4571 * A parameter list {@code A} is defined to be <em>effectively identical</em> to another parameter list {@code B}
4572 * if {@code A} and {@code B} are identical, or if {@code A} is shorter and is identical with a proper prefix of {@code B}.
4573 * When speaking of an unordered set of parameter lists, we say they the set is "effectively identical"
4574 * as a whole if the set contains a longest list, and all members of the set are effectively identical to
4575 * that longest list.
4576 * For example, any set of type sequences of the form {@code (V*)} is effectively identical,
4577 * and the same is true if more sequences of the form {@code (V... A*)} are added.
4578 * <p>
4579 * <em>Step 0: Determine clause structure.</em><ol type="a">
4580 * <li>The clause array (of type {@code MethodHandle[][]}) must be non-{@code null} and contain at least one element.
4581 * <li>The clause array may not contain {@code null}s or sub-arrays longer than four elements.
4582 * <li>Clauses shorter than four elements are treated as if they were padded by {@code null} elements to length
4583 * four. Padding takes place by appending elements to the array.
4584 * <li>Clauses with all {@code null}s are disregarded.
4585 * <li>Each clause is treated as a four-tuple of functions, called "init", "step", "pred", and "fini".
4586 * </ol>
4587 * <p>
4588 * <em>Step 1A: Determine iteration variable types {@code (V...)}.</em><ol type="a">
4589 * <li>The iteration variable type for each clause is determined using the clause's init and step return types.
4590 * <li>If both functions are omitted, there is no iteration variable for the corresponding clause ({@code void} is
4591 * used as the type to indicate that). If one of them is omitted, the other's return type defines the clause's
4592 * iteration variable type. If both are given, the common return type (they must be identical) defines the clause's
4593 * iteration variable type.
4594 * <li>Form the list of return types (in clause order), omitting all occurrences of {@code void}.
4595 * <li>This list of types is called the "iteration variable types" ({@code (V...)}).
4596 * </ol>
4597 * <p>
4598 * <em>Step 1B: Determine loop parameters {@code (A...)}.</em><ul>
4599 * <li>Examine and collect init function parameter lists (which are of the form {@code (A*)}).
4600 * <li>Examine and collect the suffixes of the step, pred, and fini parameter lists, after removing the iteration variable types.
4601 * (They must have the form {@code (V... A*)}; collect the {@code (A*)} parts only.)
4602 * <li>Do not collect suffixes from step, pred, and fini parameter lists that do not begin with all the iteration variable types.
4603 * (These types will checked in step 2, along with all the clause function types.)
4604 * <li>Omitted clause functions are ignored. (Equivalently, they are deemed to have empty parameter lists.)
4605 * <li>All of the collected parameter lists must be effectively identical.
4606 * <li>The longest parameter list (which is necessarily unique) is called the "external parameter list" ({@code (A...)}).
4607 * <li>If there is no such parameter list, the external parameter list is taken to be the empty sequence.
4608 * <li>The combined list consisting of iteration variable types followed by the external parameter types is called
4609 * the "internal parameter list".
4610 * </ul>
4611 * <p>
4612 * <em>Step 1C: Determine loop return type.</em><ol type="a">
4613 * <li>Examine fini function return types, disregarding omitted fini functions.
4614 * <li>If there are no fini functions, the loop return type is {@code void}.
4615 * <li>Otherwise, the common return type {@code R} of the fini functions (their return types must be identical) defines the loop return
4616 * type.
4617 * </ol>
4618 * <p>
4619 * <em>Step 1D: Check other types.</em><ol type="a">
4620 * <li>There must be at least one non-omitted pred function.
4621 * <li>Every non-omitted pred function must have a {@code boolean} return type.
4622 * </ol>
4623 * <p>
4624 * <em>Step 2: Determine parameter lists.</em><ol type="a">
4625 * <li>The parameter list for the resulting loop handle will be the external parameter list {@code (A...)}.
4626 * <li>The parameter list for init functions will be adjusted to the external parameter list.
4627 * (Note that their parameter lists are already effectively identical to this list.)
4628 * <li>The parameter list for every non-omitted, non-init (step, pred, and fini) function must be
4629 * effectively identical to the internal parameter list {@code (V... A...)}.
4630 * </ol>
4631 * <p>
4632 * <em>Step 3: Fill in omitted functions.</em><ol type="a">
4633 * <li>If an init function is omitted, use a {@linkplain #empty default value} for the clause's iteration variable
4634 * type.
4635 * <li>If a step function is omitted, use an {@linkplain #identity identity function} of the clause's iteration
4636 * variable type; insert dropped argument parameters before the identity function parameter for the non-{@code void}
4637 * iteration variables of preceding clauses. (This will turn the loop variable into a local loop invariant.)
4638 * <li>If a pred function is omitted, use a constant {@code true} function. (This will keep the loop going, as far
4639 * as this clause is concerned. Note that in such cases the corresponding fini function is unreachable.)
4640 * <li>If a fini function is omitted, use a {@linkplain #empty default value} for the
4641 * loop return type.
4642 * </ol>
4643 * <p>
4644 * <em>Step 4: Fill in missing parameter types.</em><ol type="a">
4645 * <li>At this point, every init function parameter list is effectively identical to the external parameter list {@code (A...)},
4646 * but some lists may be shorter. For every init function with a short parameter list, pad out the end of the list.
4647 * <li>At this point, every non-init function parameter list is effectively identical to the internal parameter
4648 * list {@code (V... A...)}, but some lists may be shorter. For every non-init function with a short parameter list,
4649 * pad out the end of the list.
4650 * <li>Argument lists are padded out by {@linkplain #dropArgumentsToMatch(MethodHandle, int, List, int) dropping unused trailing arguments}.
4651 * </ol>
4652 * <p>
4653 * <em>Final observations.</em><ol type="a">
4654 * <li>After these steps, all clauses have been adjusted by supplying omitted functions and arguments.
4655 * <li>All init functions have a common parameter type list {@code (A...)}, which the final loop handle will also have.
4656 * <li>All fini functions have a common return type {@code R}, which the final loop handle will also have.
4657 * <li>All non-init functions have a common parameter type list {@code (V... A...)}, of
4658 * (non-{@code void}) iteration variables {@code V} followed by loop parameters.
4659 * <li>Each pair of init and step functions agrees in their return type {@code V}.
4660 * <li>Each non-init function will be able to observe the current values {@code (v...)} of all iteration variables.
4661 * <li>Every function will be able to observe the incoming values {@code (a...)} of all loop parameters.
4662 * </ol>
4663 * <p>
4664 * <em>Example.</em> As a consequence of step 1A above, the {@code loop} combinator has the following property:
4665 * <ul>
4666 * <li>Given {@code N} clauses {@code Cn = {null, Sn, Pn}} with {@code n = 1..N}.
4667 * <li>Suppose predicate handles {@code Pn} are either {@code null} or have no parameters.
4668 * (Only one {@code Pn} has to be non-{@code null}.)
4669 * <li>Suppose step handles {@code Sn} have signatures {@code (B1..BX)Rn}, for some constant {@code X>=N}.
4670 * <li>Suppose {@code Q} is the count of non-void types {@code Rn}, and {@code (V1...VQ)} is the sequence of those types.
4671 * <li>It must be that {@code Vn == Bn} for {@code n = 1..min(X,Q)}.
4672 * <li>The parameter types {@code Vn} will be interpreted as loop-local state elements {@code (V...)}.
4673 * <li>Any remaining types {@code BQ+1..BX} (if {@code Q<X}) will determine
4674 * the resulting loop handle's parameter types {@code (A...)}.
4675 * </ul>
4676 * In this example, the loop handle parameters {@code (A...)} were derived from the step functions,
4677 * which is natural if most of the loop computation happens in the steps. For some loops,
4678 * the burden of computation might be heaviest in the pred functions, and so the pred functions
4679 * might need to accept the loop parameter values. For loops with complex exit logic, the fini
4680 * functions might need to accept loop parameters, and likewise for loops with complex entry logic,
4681 * where the init functions will need the extra parameters. For such reasons, the rules for
4682 * determining these parameters are as symmetric as possible, across all clause parts.
4683 * In general, the loop parameters function as common invariant values across the whole
4684 * loop, while the iteration variables function as common variant values, or (if there is
4685 * no step function) as internal loop invariant temporaries.
4686 * <p>
4687 * <em>Loop execution.</em><ol type="a">
4688 * <li>When the loop is called, the loop input values are saved in locals, to be passed to
4689 * every clause function. These locals are loop invariant.
4690 * <li>Each init function is executed in clause order (passing the external arguments {@code (a...)})
4691 * and the non-{@code void} values are saved (as the iteration variables {@code (v...)}) into locals.
4692 * These locals will be loop varying (unless their steps behave as identity functions, as noted above).
4693 * <li>All function executions (except init functions) will be passed the internal parameter list, consisting of
4694 * the non-{@code void} iteration values {@code (v...)} (in clause order) and then the loop inputs {@code (a...)}
4695 * (in argument order).
4696 * <li>The step and pred functions are then executed, in clause order (step before pred), until a pred function
4697 * returns {@code false}.
4698 * <li>The non-{@code void} result from a step function call is used to update the corresponding value in the
4699 * sequence {@code (v...)} of loop variables.
4700 * The updated value is immediately visible to all subsequent function calls.
4701 * <li>If a pred function returns {@code false}, the corresponding fini function is called, and the resulting value
4702 * (of type {@code R}) is returned from the loop as a whole.
4703 * <li>If all the pred functions always return true, no fini function is ever invoked, and the loop cannot exit
4704 * except by throwing an exception.
4705 * </ol>
4706 * <p>
4707 * <em>Usage tips.</em>
4708 * <ul>
4709 * <li>Although each step function will receive the current values of <em>all</em> the loop variables,
4710 * sometimes a step function only needs to observe the current value of its own variable.
4711 * In that case, the step function may need to explicitly {@linkplain #dropArguments drop all preceding loop variables}.
4712 * This will require mentioning their types, in an expression like {@code dropArguments(step, 0, V0.class, ...)}.
4713 * <li>Loop variables are not required to vary; they can be loop invariant. A clause can create
4714 * a loop invariant by a suitable init function with no step, pred, or fini function. This may be
4715 * useful to "wire" an incoming loop argument into the step or pred function of an adjacent loop variable.
4716 * <li>If some of the clause functions are virtual methods on an instance, the instance
4717 * itself can be conveniently placed in an initial invariant loop "variable", using an initial clause
4718 * like {@code new MethodHandle[]{identity(ObjType.class)}}. In that case, the instance reference
4719 * will be the first iteration variable value, and it will be easy to use virtual
4720 * methods as clause parts, since all of them will take a leading instance reference matching that value.
4721 * </ul>
4722 * <p>
4723 * Here is pseudocode for the resulting loop handle. As above, {@code V} and {@code v} represent the types
4724 * and values of loop variables; {@code A} and {@code a} represent arguments passed to the whole loop;
4725 * and {@code R} is the common result type of all finalizers as well as of the resulting loop.
4726 * <blockquote><pre>{@code
4727 * V... init...(A...);
4728 * boolean pred...(V..., A...);
4729 * V... step...(V..., A...);
4730 * R fini...(V..., A...);
4731 * R loop(A... a) {
4732 * V... v... = init...(a...);
4733 * for (;;) {
4734 * for ((v, p, s, f) in (v..., pred..., step..., fini...)) {
4735 * v = s(v..., a...);
4736 * if (!p(v..., a...)) {
4737 * return f(v..., a...);
4738 * }
4739 * }
4740 * }
4741 * }
4742 * }</pre></blockquote>
4743 * Note that the parameter type lists {@code (V...)} and {@code (A...)} have been expanded
4744 * to their full length, even though individual clause functions may neglect to take them all.
4745 * As noted above, missing parameters are filled in as if by {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}.
4746 *
4747 * @apiNote Example:
4748 * <blockquote><pre>{@code
4749 * // iterative implementation of the factorial function as a loop handle
4750 * static int one(int k) { return 1; }
4751 * static int inc(int i, int acc, int k) { return i + 1; }
4752 * static int mult(int i, int acc, int k) { return i * acc; }
4753 * static boolean pred(int i, int acc, int k) { return i < k; }
4754 * static int fin(int i, int acc, int k) { return acc; }
4755 * // assume MH_one, MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
4756 * // null initializer for counter, should initialize to 0
4757 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
4758 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
4759 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
4760 * assertEquals(120, loop.invoke(5));
4761 * }</pre></blockquote>
4762 * The same example, dropping arguments and using combinators:
4763 * <blockquote><pre>{@code
4764 * // simplified implementation of the factorial function as a loop handle
4765 * static int inc(int i) { return i + 1; } // drop acc, k
4766 * static int mult(int i, int acc) { return i * acc; } //drop k
4767 * static boolean cmp(int i, int k) { return i < k; }
4768 * // assume MH_inc, MH_mult, and MH_cmp are handles to the above methods
4769 * // null initializer for counter, should initialize to 0
4770 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
4771 * MethodHandle MH_pred = MethodHandles.dropArguments(MH_cmp, 1, int.class); // drop acc
4772 * MethodHandle MH_fin = MethodHandles.dropArguments(MethodHandles.identity(int.class), 0, int.class); // drop i
4773 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
4774 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
4775 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
4776 * assertEquals(720, loop.invoke(6));
4777 * }</pre></blockquote>
4778 * A similar example, using a helper object to hold a loop parameter:
4779 * <blockquote><pre>{@code
4780 * // instance-based implementation of the factorial function as a loop handle
4781 * static class FacLoop {
4782 * final int k;
4783 * FacLoop(int k) { this.k = k; }
4784 * int inc(int i) { return i + 1; }
4785 * int mult(int i, int acc) { return i * acc; }
4786 * boolean pred(int i) { return i < k; }
4787 * int fin(int i, int acc) { return acc; }
4788 * }
4789 * // assume MH_FacLoop is a handle to the constructor
4790 * // assume MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
4791 * // null initializer for counter, should initialize to 0
4792 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
4793 * MethodHandle[] instanceClause = new MethodHandle[]{MH_FacLoop};
4794 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
4795 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
4796 * MethodHandle loop = MethodHandles.loop(instanceClause, counterClause, accumulatorClause);
4797 * assertEquals(5040, loop.invoke(7));
4798 * }</pre></blockquote>
4799 *
4800 * @param clauses an array of arrays (4-tuples) of {@link MethodHandle}s adhering to the rules described above.
4801 *
4802 * @return a method handle embodying the looping behavior as defined by the arguments.
4803 *
4804 * @throws IllegalArgumentException in case any of the constraints described above is violated.
4805 *
4806 * @see MethodHandles#whileLoop(MethodHandle, MethodHandle, MethodHandle)
4807 * @see MethodHandles#doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
4808 * @see MethodHandles#countedLoop(MethodHandle, MethodHandle, MethodHandle)
4809 * @see MethodHandles#iteratedLoop(MethodHandle, MethodHandle, MethodHandle)
4810 * @since 9
4811 */
4812 public static MethodHandle loop(MethodHandle[]... clauses) {
4813 // Step 0: determine clause structure.
4814 loopChecks0(clauses);
4815
4816 List<MethodHandle> init = new ArrayList<>();
4817 List<MethodHandle> step = new ArrayList<>();
4818 List<MethodHandle> pred = new ArrayList<>();
4819 List<MethodHandle> fini = new ArrayList<>();
4820
4821 Stream.of(clauses).filter(c -> Stream.of(c).anyMatch(Objects::nonNull)).forEach(clause -> {
4822 init.add(clause[0]); // all clauses have at least length 1
4823 step.add(clause.length <= 1 ? null : clause[1]);
4824 pred.add(clause.length <= 2 ? null : clause[2]);
4825 fini.add(clause.length <= 3 ? null : clause[3]);
4826 });
4827
4828 assert Stream.of(init, step, pred, fini).map(List::size).distinct().count() == 1;
4829 final int nclauses = init.size();
4830
4831 // Step 1A: determine iteration variables (V...).
4832 final List<Class<?>> iterationVariableTypes = new ArrayList<>();
4833 for (int i = 0; i < nclauses; ++i) {
4834 MethodHandle in = init.get(i);
4835 MethodHandle st = step.get(i);
4836 if (in == null && st == null) {
4837 iterationVariableTypes.add(void.class);
4838 } else if (in != null && st != null) {
4839 loopChecks1a(i, in, st);
4840 iterationVariableTypes.add(in.type().returnType());
4841 } else {
4842 iterationVariableTypes.add(in == null ? st.type().returnType() : in.type().returnType());
4843 }
4844 }
4845 final List<Class<?>> commonPrefix = iterationVariableTypes.stream().filter(t -> t != void.class).
4846 collect(Collectors.toList());
4847
4848 // Step 1B: determine loop parameters (A...).
4849 final List<Class<?>> commonSuffix = buildCommonSuffix(init, step, pred, fini, commonPrefix.size());
4850 loopChecks1b(init, commonSuffix);
4851
4852 // Step 1C: determine loop return type.
4853 // Step 1D: check other types.
4854 final Class<?> loopReturnType = fini.stream().filter(Objects::nonNull).map(MethodHandle::type).
4855 map(MethodType::returnType).findFirst().orElse(void.class);
4856 loopChecks1cd(pred, fini, loopReturnType);
4857
4858 // Step 2: determine parameter lists.
4859 final List<Class<?>> commonParameterSequence = new ArrayList<>(commonPrefix);
4860 commonParameterSequence.addAll(commonSuffix);
4861 loopChecks2(step, pred, fini, commonParameterSequence);
4862
4863 // Step 3: fill in omitted functions.
4864 for (int i = 0; i < nclauses; ++i) {
4865 Class<?> t = iterationVariableTypes.get(i);
4866 if (init.get(i) == null) {
4867 init.set(i, empty(methodType(t, commonSuffix)));
4868 }
4869 if (step.get(i) == null) {
4870 step.set(i, dropArgumentsToMatch(identityOrVoid(t), 0, commonParameterSequence, i));
4871 }
4872 if (pred.get(i) == null) {
4873 pred.set(i, dropArguments0(constant(boolean.class, true), 0, commonParameterSequence));
4874 }
4875 if (fini.get(i) == null) {
4876 fini.set(i, empty(methodType(t, commonParameterSequence)));
4877 }
4878 }
4879
4880 // Step 4: fill in missing parameter types.
4881 // Also convert all handles to fixed-arity handles.
4882 List<MethodHandle> finit = fixArities(fillParameterTypes(init, commonSuffix));
4883 List<MethodHandle> fstep = fixArities(fillParameterTypes(step, commonParameterSequence));
4884 List<MethodHandle> fpred = fixArities(fillParameterTypes(pred, commonParameterSequence));
4885 List<MethodHandle> ffini = fixArities(fillParameterTypes(fini, commonParameterSequence));
4886
4887 assert finit.stream().map(MethodHandle::type).map(MethodType::parameterList).
4888 allMatch(pl -> pl.equals(commonSuffix));
4889 assert Stream.of(fstep, fpred, ffini).flatMap(List::stream).map(MethodHandle::type).map(MethodType::parameterList).
4890 allMatch(pl -> pl.equals(commonParameterSequence));
4891
4892 return MethodHandleImpl.makeLoop(loopReturnType, commonSuffix, finit, fstep, fpred, ffini);
4893 }
4894
4895 private static void loopChecks0(MethodHandle[][] clauses) {
4896 if (clauses == null || clauses.length == 0) {
4897 throw newIllegalArgumentException("null or no clauses passed");
4898 }
4899 if (Stream.of(clauses).anyMatch(Objects::isNull)) {
4900 throw newIllegalArgumentException("null clauses are not allowed");
4901 }
4902 if (Stream.of(clauses).anyMatch(c -> c.length > 4)) {
4903 throw newIllegalArgumentException("All loop clauses must be represented as MethodHandle arrays with at most 4 elements.");
4904 }
4905 }
4906
4907 private static void loopChecks1a(int i, MethodHandle in, MethodHandle st) {
4908 if (in.type().returnType() != st.type().returnType()) {
4909 throw misMatchedTypes("clause " + i + ": init and step return types", in.type().returnType(),
4910 st.type().returnType());
4911 }
4912 }
4913
4914 private static List<Class<?>> longestParameterList(Stream<MethodHandle> mhs, int skipSize) {
4915 final List<Class<?>> empty = List.of();
4916 final List<Class<?>> longest = mhs.filter(Objects::nonNull).
4917 // take only those that can contribute to a common suffix because they are longer than the prefix
4918 map(MethodHandle::type).
4919 filter(t -> t.parameterCount() > skipSize).
4920 map(MethodType::parameterList).
4921 reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
4922 return longest.size() == 0 ? empty : longest.subList(skipSize, longest.size());
4923 }
4924
4925 private static List<Class<?>> longestParameterList(List<List<Class<?>>> lists) {
4926 final List<Class<?>> empty = List.of();
4927 return lists.stream().reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
4928 }
4929
4930 private static List<Class<?>> buildCommonSuffix(List<MethodHandle> init, List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, int cpSize) {
4931 final List<Class<?>> longest1 = longestParameterList(Stream.of(step, pred, fini).flatMap(List::stream), cpSize);
4932 final List<Class<?>> longest2 = longestParameterList(init.stream(), 0);
4933 return longestParameterList(Arrays.asList(longest1, longest2));
4934 }
4935
4936 private static void loopChecks1b(List<MethodHandle> init, List<Class<?>> commonSuffix) {
4937 if (init.stream().filter(Objects::nonNull).map(MethodHandle::type).
4938 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonSuffix))) {
4939 throw newIllegalArgumentException("found non-effectively identical init parameter type lists: " + init +
4940 " (common suffix: " + commonSuffix + ")");
4941 }
4942 }
4943
4944 private static void loopChecks1cd(List<MethodHandle> pred, List<MethodHandle> fini, Class<?> loopReturnType) {
4945 if (fini.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
4946 anyMatch(t -> t != loopReturnType)) {
4947 throw newIllegalArgumentException("found non-identical finalizer return types: " + fini + " (return type: " +
4948 loopReturnType + ")");
4949 }
4950
4951 if (!pred.stream().filter(Objects::nonNull).findFirst().isPresent()) {
4952 throw newIllegalArgumentException("no predicate found", pred);
4953 }
4954 if (pred.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
4955 anyMatch(t -> t != boolean.class)) {
4956 throw newIllegalArgumentException("predicates must have boolean return type", pred);
4957 }
4958 }
4959
4960 private static void loopChecks2(List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, List<Class<?>> commonParameterSequence) {
4961 if (Stream.of(step, pred, fini).flatMap(List::stream).filter(Objects::nonNull).map(MethodHandle::type).
4962 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonParameterSequence))) {
4963 throw newIllegalArgumentException("found non-effectively identical parameter type lists:\nstep: " + step +
4964 "\npred: " + pred + "\nfini: " + fini + " (common parameter sequence: " + commonParameterSequence + ")");
4965 }
4966 }
4967
4968 private static List<MethodHandle> fillParameterTypes(List<MethodHandle> hs, final List<Class<?>> targetParams) {
4969 return hs.stream().map(h -> {
4970 int pc = h.type().parameterCount();
4971 int tpsize = targetParams.size();
4972 return pc < tpsize ? dropArguments0(h, pc, targetParams.subList(pc, tpsize)) : h;
4973 }).collect(Collectors.toList());
4974 }
4975
4976 private static List<MethodHandle> fixArities(List<MethodHandle> hs) {
4977 return hs.stream().map(MethodHandle::asFixedArity).collect(Collectors.toList());
4978 }
4979
4980 /**
4981 * Constructs a {@code while} loop from an initializer, a body, and a predicate.
4982 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
4983 * <p>
4984 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
4985 * method will, in each iteration, first evaluate the predicate and then execute its body (if the predicate
4986 * evaluates to {@code true}).
4987 * The loop will terminate once the predicate evaluates to {@code false} (the body will not be executed in this case).
4988 * <p>
4989 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
4990 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
4991 * and updated with the value returned from its invocation. The result of loop execution will be
4992 * the final value of the additional loop-local variable (if present).
4993 * <p>
4994 * The following rules hold for these argument handles:<ul>
4995 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
4996 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
4997 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
4998 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
4999 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
5000 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
5001 * It will constrain the parameter lists of the other loop parts.
5002 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
5003 * list {@code (A...)} is called the <em>external parameter list</em>.
5004 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5005 * additional state variable of the loop.
5006 * The body must both accept and return a value of this type {@code V}.
5007 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5008 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5009 * <a href="MethodHandles.html#effid">effectively identical</a>
5010 * to the external parameter list {@code (A...)}.
5011 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5012 * {@linkplain #empty default value}.
5013 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
5014 * Its parameter list (either empty or of the form {@code (V A*)}) must be
5015 * effectively identical to the internal parameter list.
5016 * </ul>
5017 * <p>
5018 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5019 * <li>The loop handle's result type is the result type {@code V} of the body.
5020 * <li>The loop handle's parameter types are the types {@code (A...)},
5021 * from the external parameter list.
5022 * </ul>
5023 * <p>
5024 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5025 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
5026 * passed to the loop.
5027 * <blockquote><pre>{@code
5028 * V init(A...);
5029 * boolean pred(V, A...);
5030 * V body(V, A...);
5031 * V whileLoop(A... a...) {
5032 * V v = init(a...);
5033 * while (pred(v, a...)) {
5034 * v = body(v, a...);
5035 * }
5036 * return v;
5037 * }
5038 * }</pre></blockquote>
5039 *
5040 * @apiNote Example:
5041 * <blockquote><pre>{@code
5042 * // implement the zip function for lists as a loop handle
5043 * static List<String> initZip(Iterator<String> a, Iterator<String> b) { return new ArrayList<>(); }
5044 * static boolean zipPred(List<String> zip, Iterator<String> a, Iterator<String> b) { return a.hasNext() && b.hasNext(); }
5045 * static List<String> zipStep(List<String> zip, Iterator<String> a, Iterator<String> b) {
5046 * zip.add(a.next());
5047 * zip.add(b.next());
5048 * return zip;
5049 * }
5050 * // assume MH_initZip, MH_zipPred, and MH_zipStep are handles to the above methods
5051 * MethodHandle loop = MethodHandles.whileLoop(MH_initZip, MH_zipPred, MH_zipStep);
5052 * List<String> a = Arrays.asList("a", "b", "c", "d");
5053 * List<String> b = Arrays.asList("e", "f", "g", "h");
5054 * List<String> zipped = Arrays.asList("a", "e", "b", "f", "c", "g", "d", "h");
5055 * assertEquals(zipped, (List<String>) loop.invoke(a.iterator(), b.iterator()));
5056 * }</pre></blockquote>
5057 *
5058 *
5059 * @apiNote The implementation of this method can be expressed as follows:
5060 * <blockquote><pre>{@code
5061 * MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
5062 * MethodHandle fini = (body.type().returnType() == void.class
5063 * ? null : identity(body.type().returnType()));
5064 * MethodHandle[]
5065 * checkExit = { null, null, pred, fini },
5066 * varBody = { init, body };
5067 * return loop(checkExit, varBody);
5068 * }
5069 * }</pre></blockquote>
5070 *
5071 * @param init optional initializer, providing the initial value of the loop variable.
5072 * May be {@code null}, implying a default initial value. See above for other constraints.
5073 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
5074 * above for other constraints.
5075 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
5076 * See above for other constraints.
5077 *
5078 * @return a method handle implementing the {@code while} loop as described by the arguments.
5079 * @throws IllegalArgumentException if the rules for the arguments are violated.
5080 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
5081 *
5082 * @see #loop(MethodHandle[][])
5083 * @see #doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
5084 * @since 9
5085 */
5086 public static MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
5087 whileLoopChecks(init, pred, body);
5088 MethodHandle fini = identityOrVoid(body.type().returnType());
5089 MethodHandle[] checkExit = { null, null, pred, fini };
5090 MethodHandle[] varBody = { init, body };
5091 return loop(checkExit, varBody);
5092 }
5093
5094 /**
5095 * Constructs a {@code do-while} loop from an initializer, a body, and a predicate.
5096 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5097 * <p>
5098 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
5099 * method will, in each iteration, first execute its body and then evaluate the predicate.
5100 * The loop will terminate once the predicate evaluates to {@code false} after an execution of the body.
5101 * <p>
5102 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
5103 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
5104 * and updated with the value returned from its invocation. The result of loop execution will be
5105 * the final value of the additional loop-local variable (if present).
5106 * <p>
5107 * The following rules hold for these argument handles:<ul>
5108 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5109 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
5110 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5111 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
5112 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
5113 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
5114 * It will constrain the parameter lists of the other loop parts.
5115 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
5116 * list {@code (A...)} is called the <em>external parameter list</em>.
5117 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5118 * additional state variable of the loop.
5119 * The body must both accept and return a value of this type {@code V}.
5120 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5121 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5122 * <a href="MethodHandles.html#effid">effectively identical</a>
5123 * to the external parameter list {@code (A...)}.
5124 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5125 * {@linkplain #empty default value}.
5126 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
5127 * Its parameter list (either empty or of the form {@code (V A*)}) must be
5128 * effectively identical to the internal parameter list.
5129 * </ul>
5130 * <p>
5131 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5132 * <li>The loop handle's result type is the result type {@code V} of the body.
5133 * <li>The loop handle's parameter types are the types {@code (A...)},
5134 * from the external parameter list.
5135 * </ul>
5136 * <p>
5137 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5138 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
5139 * passed to the loop.
5140 * <blockquote><pre>{@code
5141 * V init(A...);
5142 * boolean pred(V, A...);
5143 * V body(V, A...);
5144 * V doWhileLoop(A... a...) {
5145 * V v = init(a...);
5146 * do {
5147 * v = body(v, a...);
5148 * } while (pred(v, a...));
5149 * return v;
5150 * }
5151 * }</pre></blockquote>
5152 *
5153 * @apiNote Example:
5154 * <blockquote><pre>{@code
5155 * // int i = 0; while (i < limit) { ++i; } return i; => limit
5156 * static int zero(int limit) { return 0; }
5157 * static int step(int i, int limit) { return i + 1; }
5158 * static boolean pred(int i, int limit) { return i < limit; }
5159 * // assume MH_zero, MH_step, and MH_pred are handles to the above methods
5160 * MethodHandle loop = MethodHandles.doWhileLoop(MH_zero, MH_step, MH_pred);
5161 * assertEquals(23, loop.invoke(23));
5162 * }</pre></blockquote>
5163 *
5164 *
5165 * @apiNote The implementation of this method can be expressed as follows:
5166 * <blockquote><pre>{@code
5167 * MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
5168 * MethodHandle fini = (body.type().returnType() == void.class
5169 * ? null : identity(body.type().returnType()));
5170 * MethodHandle[] clause = { init, body, pred, fini };
5171 * return loop(clause);
5172 * }
5173 * }</pre></blockquote>
5174 *
5175 * @param init optional initializer, providing the initial value of the loop variable.
5176 * May be {@code null}, implying a default initial value. See above for other constraints.
5177 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
5178 * See above for other constraints.
5179 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
5180 * above for other constraints.
5181 *
5182 * @return a method handle implementing the {@code while} loop as described by the arguments.
5183 * @throws IllegalArgumentException if the rules for the arguments are violated.
5184 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
5185 *
5186 * @see #loop(MethodHandle[][])
5187 * @see #whileLoop(MethodHandle, MethodHandle, MethodHandle)
5188 * @since 9
5189 */
5190 public static MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
5191 whileLoopChecks(init, pred, body);
5192 MethodHandle fini = identityOrVoid(body.type().returnType());
5193 MethodHandle[] clause = {init, body, pred, fini };
5194 return loop(clause);
5195 }
5196
5197 private static void whileLoopChecks(MethodHandle init, MethodHandle pred, MethodHandle body) {
5198 Objects.requireNonNull(pred);
5199 Objects.requireNonNull(body);
5200 MethodType bodyType = body.type();
5201 Class<?> returnType = bodyType.returnType();
5202 List<Class<?>> innerList = bodyType.parameterList();
5203 List<Class<?>> outerList = innerList;
5204 if (returnType == void.class) {
5205 // OK
5206 } else if (innerList.size() == 0 || innerList.get(0) != returnType) {
5207 // leading V argument missing => error
5208 MethodType expected = bodyType.insertParameterTypes(0, returnType);
5209 throw misMatchedTypes("body function", bodyType, expected);
5210 } else {
5211 outerList = innerList.subList(1, innerList.size());
5212 }
5213 MethodType predType = pred.type();
5214 if (predType.returnType() != boolean.class ||
5215 !predType.effectivelyIdenticalParameters(0, innerList)) {
5216 throw misMatchedTypes("loop predicate", predType, methodType(boolean.class, innerList));
5217 }
5218 if (init != null) {
5219 MethodType initType = init.type();
5220 if (initType.returnType() != returnType ||
5221 !initType.effectivelyIdenticalParameters(0, outerList)) {
5222 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
5223 }
5224 }
5225 }
5226
5227 /**
5228 * Constructs a loop that runs a given number of iterations.
5229 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5230 * <p>
5231 * The number of iterations is determined by the {@code iterations} handle evaluation result.
5232 * The loop counter {@code i} is an extra loop iteration variable of type {@code int}.
5233 * It will be initialized to 0 and incremented by 1 in each iteration.
5234 * <p>
5235 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
5236 * of that type is also present. This variable is initialized using the optional {@code init} handle,
5237 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
5238 * <p>
5239 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
5240 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
5241 * iteration variable.
5242 * The result of the loop handle execution will be the final {@code V} value of that variable
5243 * (or {@code void} if there is no {@code V} variable).
5244 * <p>
5245 * The following rules hold for the argument handles:<ul>
5246 * <li>The {@code iterations} handle must not be {@code null}, and must return
5247 * the type {@code int}, referred to here as {@code I} in parameter type lists.
5248 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5249 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
5250 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5251 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
5252 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
5253 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
5254 * of types called the <em>internal parameter list</em>.
5255 * It will constrain the parameter lists of the other loop parts.
5256 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
5257 * with no additional {@code A} types, then the internal parameter list is extended by
5258 * the argument types {@code A...} of the {@code iterations} handle.
5259 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
5260 * list {@code (A...)} is called the <em>external parameter list</em>.
5261 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5262 * additional state variable of the loop.
5263 * The body must both accept a leading parameter and return a value of this type {@code V}.
5264 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5265 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5266 * <a href="MethodHandles.html#effid">effectively identical</a>
5267 * to the external parameter list {@code (A...)}.
5268 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5269 * {@linkplain #empty default value}.
5270 * <li>The parameter list of {@code iterations} (of some form {@code (A*)}) must be
5271 * effectively identical to the external parameter list {@code (A...)}.
5272 * </ul>
5273 * <p>
5274 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5275 * <li>The loop handle's result type is the result type {@code V} of the body.
5276 * <li>The loop handle's parameter types are the types {@code (A...)},
5277 * from the external parameter list.
5278 * </ul>
5279 * <p>
5280 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5281 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
5282 * arguments passed to the loop.
5283 * <blockquote><pre>{@code
5284 * int iterations(A...);
5285 * V init(A...);
5286 * V body(V, int, A...);
5287 * V countedLoop(A... a...) {
5288 * int end = iterations(a...);
5289 * V v = init(a...);
5290 * for (int i = 0; i < end; ++i) {
5291 * v = body(v, i, a...);
5292 * }
5293 * return v;
5294 * }
5295 * }</pre></blockquote>
5296 *
5297 * @apiNote Example with a fully conformant body method:
5298 * <blockquote><pre>{@code
5299 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
5300 * // => a variation on a well known theme
5301 * static String step(String v, int counter, String init) { return "na " + v; }
5302 * // assume MH_step is a handle to the method above
5303 * MethodHandle fit13 = MethodHandles.constant(int.class, 13);
5304 * MethodHandle start = MethodHandles.identity(String.class);
5305 * MethodHandle loop = MethodHandles.countedLoop(fit13, start, MH_step);
5306 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("Lambdaman!"));
5307 * }</pre></blockquote>
5308 *
5309 * @apiNote Example with the simplest possible body method type,
5310 * and passing the number of iterations to the loop invocation:
5311 * <blockquote><pre>{@code
5312 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
5313 * // => a variation on a well known theme
5314 * static String step(String v, int counter ) { return "na " + v; }
5315 * // assume MH_step is a handle to the method above
5316 * MethodHandle count = MethodHandles.dropArguments(MethodHandles.identity(int.class), 1, String.class);
5317 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class);
5318 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i) -> "na " + v
5319 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "Lambdaman!"));
5320 * }</pre></blockquote>
5321 *
5322 * @apiNote Example that treats the number of iterations, string to append to, and string to append
5323 * as loop parameters:
5324 * <blockquote><pre>{@code
5325 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
5326 * // => a variation on a well known theme
5327 * static String step(String v, int counter, int iterations_, String pre, String start_) { return pre + " " + v; }
5328 * // assume MH_step is a handle to the method above
5329 * MethodHandle count = MethodHandles.identity(int.class);
5330 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class, String.class);
5331 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i, _, pre, _) -> pre + " " + v
5332 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "na", "Lambdaman!"));
5333 * }</pre></blockquote>
5334 *
5335 * @apiNote Example that illustrates the usage of {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}
5336 * to enforce a loop type:
5337 * <blockquote><pre>{@code
5338 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
5339 * // => a variation on a well known theme
5340 * static String step(String v, int counter, String pre) { return pre + " " + v; }
5341 * // assume MH_step is a handle to the method above
5342 * MethodType loopType = methodType(String.class, String.class, int.class, String.class);
5343 * MethodHandle count = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(int.class), 0, loopType.parameterList(), 1);
5344 * MethodHandle start = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(String.class), 0, loopType.parameterList(), 2);
5345 * MethodHandle body = MethodHandles.dropArgumentsToMatch(MH_step, 2, loopType.parameterList(), 0);
5346 * MethodHandle loop = MethodHandles.countedLoop(count, start, body); // (v, i, pre, _, _) -> pre + " " + v
5347 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("na", 13, "Lambdaman!"));
5348 * }</pre></blockquote>
5349 *
5350 * @apiNote The implementation of this method can be expressed as follows:
5351 * <blockquote><pre>{@code
5352 * MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
5353 * return countedLoop(empty(iterations.type()), iterations, init, body);
5354 * }
5355 * }</pre></blockquote>
5356 *
5357 * @param iterations a non-{@code null} handle to return the number of iterations this loop should run. The handle's
5358 * result type must be {@code int}. See above for other constraints.
5359 * @param init optional initializer, providing the initial value of the loop variable.
5360 * May be {@code null}, implying a default initial value. See above for other constraints.
5361 * @param body body of the loop, which may not be {@code null}.
5362 * It controls the loop parameters and result type in the standard case (see above for details).
5363 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
5364 * and may accept any number of additional types.
5365 * See above for other constraints.
5366 *
5367 * @return a method handle representing the loop.
5368 * @throws NullPointerException if either of the {@code iterations} or {@code body} handles is {@code null}.
5369 * @throws IllegalArgumentException if any argument violates the rules formulated above.
5370 *
5371 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle, MethodHandle)
5372 * @since 9
5373 */
5374 public static MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
5375 return countedLoop(empty(iterations.type()), iterations, init, body);
5376 }
5377
5378 /**
5379 * Constructs a loop that counts over a range of numbers.
5380 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5381 * <p>
5382 * The loop counter {@code i} is a loop iteration variable of type {@code int}.
5383 * The {@code start} and {@code end} handles determine the start (inclusive) and end (exclusive)
5384 * values of the loop counter.
5385 * The loop counter will be initialized to the {@code int} value returned from the evaluation of the
5386 * {@code start} handle and run to the value returned from {@code end} (exclusively) with a step width of 1.
5387 * <p>
5388 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
5389 * of that type is also present. This variable is initialized using the optional {@code init} handle,
5390 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
5391 * <p>
5392 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
5393 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
5394 * iteration variable.
5395 * The result of the loop handle execution will be the final {@code V} value of that variable
5396 * (or {@code void} if there is no {@code V} variable).
5397 * <p>
5398 * The following rules hold for the argument handles:<ul>
5399 * <li>The {@code start} and {@code end} handles must not be {@code null}, and must both return
5400 * the common type {@code int}, referred to here as {@code I} in parameter type lists.
5401 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5402 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
5403 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5404 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
5405 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
5406 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
5407 * of types called the <em>internal parameter list</em>.
5408 * It will constrain the parameter lists of the other loop parts.
5409 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
5410 * with no additional {@code A} types, then the internal parameter list is extended by
5411 * the argument types {@code A...} of the {@code end} handle.
5412 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
5413 * list {@code (A...)} is called the <em>external parameter list</em>.
5414 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5415 * additional state variable of the loop.
5416 * The body must both accept a leading parameter and return a value of this type {@code V}.
5417 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5418 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5419 * <a href="MethodHandles.html#effid">effectively identical</a>
5420 * to the external parameter list {@code (A...)}.
5421 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5422 * {@linkplain #empty default value}.
5423 * <li>The parameter list of {@code start} (of some form {@code (A*)}) must be
5424 * effectively identical to the external parameter list {@code (A...)}.
5425 * <li>Likewise, the parameter list of {@code end} must be effectively identical
5426 * to the external parameter list.
5427 * </ul>
5428 * <p>
5429 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5430 * <li>The loop handle's result type is the result type {@code V} of the body.
5431 * <li>The loop handle's parameter types are the types {@code (A...)},
5432 * from the external parameter list.
5433 * </ul>
5434 * <p>
5435 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5436 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
5437 * arguments passed to the loop.
5438 * <blockquote><pre>{@code
5439 * int start(A...);
5440 * int end(A...);
5441 * V init(A...);
5442 * V body(V, int, A...);
5443 * V countedLoop(A... a...) {
5444 * int e = end(a...);
5445 * int s = start(a...);
5446 * V v = init(a...);
5447 * for (int i = s; i < e; ++i) {
5448 * v = body(v, i, a...);
5449 * }
5450 * return v;
5451 * }
5452 * }</pre></blockquote>
5453 *
5454 * @apiNote The implementation of this method can be expressed as follows:
5455 * <blockquote><pre>{@code
5456 * MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
5457 * MethodHandle returnVar = dropArguments(identity(init.type().returnType()), 0, int.class, int.class);
5458 * // assume MH_increment and MH_predicate are handles to implementation-internal methods with
5459 * // the following semantics:
5460 * // MH_increment: (int limit, int counter) -> counter + 1
5461 * // MH_predicate: (int limit, int counter) -> counter < limit
5462 * Class<?> counterType = start.type().returnType(); // int
5463 * Class<?> returnType = body.type().returnType();
5464 * MethodHandle incr = MH_increment, pred = MH_predicate, retv = null;
5465 * if (returnType != void.class) { // ignore the V variable
5466 * incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
5467 * pred = dropArguments(pred, 1, returnType); // ditto
5468 * retv = dropArguments(identity(returnType), 0, counterType); // ignore limit
5469 * }
5470 * body = dropArguments(body, 0, counterType); // ignore the limit variable
5471 * MethodHandle[]
5472 * loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
5473 * bodyClause = { init, body }, // v = init(); v = body(v, i)
5474 * indexVar = { start, incr }; // i = start(); i = i + 1
5475 * return loop(loopLimit, bodyClause, indexVar);
5476 * }
5477 * }</pre></blockquote>
5478 *
5479 * @param start a non-{@code null} handle to return the start value of the loop counter, which must be {@code int}.
5480 * See above for other constraints.
5481 * @param end a non-{@code null} handle to return the end value of the loop counter (the loop will run to
5482 * {@code end-1}). The result type must be {@code int}. See above for other constraints.
5483 * @param init optional initializer, providing the initial value of the loop variable.
5484 * May be {@code null}, implying a default initial value. See above for other constraints.
5485 * @param body body of the loop, which may not be {@code null}.
5486 * It controls the loop parameters and result type in the standard case (see above for details).
5487 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
5488 * and may accept any number of additional types.
5489 * See above for other constraints.
5490 *
5491 * @return a method handle representing the loop.
5492 * @throws NullPointerException if any of the {@code start}, {@code end}, or {@code body} handles is {@code null}.
5493 * @throws IllegalArgumentException if any argument violates the rules formulated above.
5494 *
5495 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle)
5496 * @since 9
5497 */
5498 public static MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
5499 countedLoopChecks(start, end, init, body);
5500 Class<?> counterType = start.type().returnType(); // int, but who's counting?
5501 Class<?> limitType = end.type().returnType(); // yes, int again
5502 Class<?> returnType = body.type().returnType();
5503 MethodHandle incr = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopStep);
5504 MethodHandle pred = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopPred);
5505 MethodHandle retv = null;
5506 if (returnType != void.class) {
5507 incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
5508 pred = dropArguments(pred, 1, returnType); // ditto
5509 retv = dropArguments(identity(returnType), 0, counterType);
5510 }
5511 body = dropArguments(body, 0, counterType); // ignore the limit variable
5512 MethodHandle[]
5513 loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
5514 bodyClause = { init, body }, // v = init(); v = body(v, i)
5515 indexVar = { start, incr }; // i = start(); i = i + 1
5516 return loop(loopLimit, bodyClause, indexVar);
5517 }
5518
5519 private static void countedLoopChecks(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
5520 Objects.requireNonNull(start);
5521 Objects.requireNonNull(end);
5522 Objects.requireNonNull(body);
5523 Class<?> counterType = start.type().returnType();
5524 if (counterType != int.class) {
5525 MethodType expected = start.type().changeReturnType(int.class);
5526 throw misMatchedTypes("start function", start.type(), expected);
5527 } else if (end.type().returnType() != counterType) {
5528 MethodType expected = end.type().changeReturnType(counterType);
5529 throw misMatchedTypes("end function", end.type(), expected);
5530 }
5531 MethodType bodyType = body.type();
5532 Class<?> returnType = bodyType.returnType();
5533 List<Class<?>> innerList = bodyType.parameterList();
5534 // strip leading V value if present
5535 int vsize = (returnType == void.class ? 0 : 1);
5536 if (vsize != 0 && (innerList.size() == 0 || innerList.get(0) != returnType)) {
5537 // argument list has no "V" => error
5538 MethodType expected = bodyType.insertParameterTypes(0, returnType);
5539 throw misMatchedTypes("body function", bodyType, expected);
5540 } else if (innerList.size() <= vsize || innerList.get(vsize) != counterType) {
5541 // missing I type => error
5542 MethodType expected = bodyType.insertParameterTypes(vsize, counterType);
5543 throw misMatchedTypes("body function", bodyType, expected);
5544 }
5545 List<Class<?>> outerList = innerList.subList(vsize + 1, innerList.size());
5546 if (outerList.isEmpty()) {
5547 // special case; take lists from end handle
5548 outerList = end.type().parameterList();
5549 innerList = bodyType.insertParameterTypes(vsize + 1, outerList).parameterList();
5550 }
5551 MethodType expected = methodType(counterType, outerList);
5552 if (!start.type().effectivelyIdenticalParameters(0, outerList)) {
5553 throw misMatchedTypes("start parameter types", start.type(), expected);
5554 }
5555 if (end.type() != start.type() &&
5556 !end.type().effectivelyIdenticalParameters(0, outerList)) {
5557 throw misMatchedTypes("end parameter types", end.type(), expected);
5558 }
5559 if (init != null) {
5560 MethodType initType = init.type();
5561 if (initType.returnType() != returnType ||
5562 !initType.effectivelyIdenticalParameters(0, outerList)) {
5563 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
5564 }
5565 }
5566 }
5567
5568 /**
5569 * Constructs a loop that ranges over the values produced by an {@code Iterator<T>}.
5570 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5571 * <p>
5572 * The iterator itself will be determined by the evaluation of the {@code iterator} handle.
5573 * Each value it produces will be stored in a loop iteration variable of type {@code T}.
5574 * <p>
5575 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
5576 * of that type is also present. This variable is initialized using the optional {@code init} handle,
5577 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
5578 * <p>
5579 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
5580 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
5581 * iteration variable.
5582 * The result of the loop handle execution will be the final {@code V} value of that variable
5583 * (or {@code void} if there is no {@code V} variable).
5584 * <p>
5585 * The following rules hold for the argument handles:<ul>
5586 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5587 * {@code (V T A...)V}, where {@code V} is non-{@code void}, or else {@code (T A...)void}.
5588 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5589 * and we will write {@code (V T A...)V} with the understanding that a {@code void} type {@code V}
5590 * is quietly dropped from the parameter list, leaving {@code (T A...)V}.)
5591 * <li>The parameter list {@code (V T A...)} of the body contributes to a list
5592 * of types called the <em>internal parameter list</em>.
5593 * It will constrain the parameter lists of the other loop parts.
5594 * <li>As a special case, if the body contributes only {@code V} and {@code T} types,
5595 * with no additional {@code A} types, then the internal parameter list is extended by
5596 * the argument types {@code A...} of the {@code iterator} handle; if it is {@code null} the
5597 * single type {@code Iterable} is added and constitutes the {@code A...} list.
5598 * <li>If the iteration variable types {@code (V T)} are dropped from the internal parameter list, the resulting shorter
5599 * list {@code (A...)} is called the <em>external parameter list</em>.
5600 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5601 * additional state variable of the loop.
5602 * The body must both accept a leading parameter and return a value of this type {@code V}.
5603 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5604 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5605 * <a href="MethodHandles.html#effid">effectively identical</a>
5606 * to the external parameter list {@code (A...)}.
5607 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5608 * {@linkplain #empty default value}.
5609 * <li>If the {@code iterator} handle is non-{@code null}, it must have the return
5610 * type {@code java.util.Iterator} or a subtype thereof.
5611 * The iterator it produces when the loop is executed will be assumed
5612 * to yield values which can be converted to type {@code T}.
5613 * <li>The parameter list of an {@code iterator} that is non-{@code null} (of some form {@code (A*)}) must be
5614 * effectively identical to the external parameter list {@code (A...)}.
5615 * <li>If {@code iterator} is {@code null} it defaults to a method handle which behaves
5616 * like {@link java.lang.Iterable#iterator()}. In that case, the internal parameter list
5617 * {@code (V T A...)} must have at least one {@code A} type, and the default iterator
5618 * handle parameter is adjusted to accept the leading {@code A} type, as if by
5619 * the {@link MethodHandle#asType asType} conversion method.
5620 * The leading {@code A} type must be {@code Iterable} or a subtype thereof.
5621 * This conversion step, done at loop construction time, must not throw a {@code WrongMethodTypeException}.
5622 * </ul>
5623 * <p>
5624 * The type {@code T} may be either a primitive or reference.
5625 * Since type {@code Iterator<T>} is erased in the method handle representation to the raw type {@code Iterator},
5626 * the {@code iteratedLoop} combinator adjusts the leading argument type for {@code body} to {@code Object}
5627 * as if by the {@link MethodHandle#asType asType} conversion method.
5628 * Therefore, if an iterator of the wrong type appears as the loop is executed, runtime exceptions may occur
5629 * as the result of dynamic conversions performed by {@link MethodHandle#asType(MethodType)}.
5630 * <p>
5631 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5632 * <li>The loop handle's result type is the result type {@code V} of the body.
5633 * <li>The loop handle's parameter types are the types {@code (A...)},
5634 * from the external parameter list.
5635 * </ul>
5636 * <p>
5637 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5638 * the loop variable as well as the result type of the loop; {@code T}/{@code t}, that of the elements of the
5639 * structure the loop iterates over, and {@code A...}/{@code a...} represent arguments passed to the loop.
5640 * <blockquote><pre>{@code
5641 * Iterator<T> iterator(A...); // defaults to Iterable::iterator
5642 * V init(A...);
5643 * V body(V,T,A...);
5644 * V iteratedLoop(A... a...) {
5645 * Iterator<T> it = iterator(a...);
5646 * V v = init(a...);
5647 * while (it.hasNext()) {
5648 * T t = it.next();
5649 * v = body(v, t, a...);
5650 * }
5651 * return v;
5652 * }
5653 * }</pre></blockquote>
5654 *
5655 * @apiNote Example:
5656 * <blockquote><pre>{@code
5657 * // get an iterator from a list
5658 * static List<String> reverseStep(List<String> r, String e) {
5659 * r.add(0, e);
5660 * return r;
5661 * }
5662 * static List<String> newArrayList() { return new ArrayList<>(); }
5663 * // assume MH_reverseStep and MH_newArrayList are handles to the above methods
5664 * MethodHandle loop = MethodHandles.iteratedLoop(null, MH_newArrayList, MH_reverseStep);
5665 * List<String> list = Arrays.asList("a", "b", "c", "d", "e");
5666 * List<String> reversedList = Arrays.asList("e", "d", "c", "b", "a");
5667 * assertEquals(reversedList, (List<String>) loop.invoke(list));
5668 * }</pre></blockquote>
5669 *
5670 * @apiNote The implementation of this method can be expressed approximately as follows:
5671 * <blockquote><pre>{@code
5672 * MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
5673 * // assume MH_next, MH_hasNext, MH_startIter are handles to methods of Iterator/Iterable
5674 * Class<?> returnType = body.type().returnType();
5675 * Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
5676 * MethodHandle nextVal = MH_next.asType(MH_next.type().changeReturnType(ttype));
5677 * MethodHandle retv = null, step = body, startIter = iterator;
5678 * if (returnType != void.class) {
5679 * // the simple thing first: in (I V A...), drop the I to get V
5680 * retv = dropArguments(identity(returnType), 0, Iterator.class);
5681 * // body type signature (V T A...), internal loop types (I V A...)
5682 * step = swapArguments(body, 0, 1); // swap V <-> T
5683 * }
5684 * if (startIter == null) startIter = MH_getIter;
5685 * MethodHandle[]
5686 * iterVar = { startIter, null, MH_hasNext, retv }, // it = iterator; while (it.hasNext())
5687 * bodyClause = { init, filterArguments(step, 0, nextVal) }; // v = body(v, t, a)
5688 * return loop(iterVar, bodyClause);
5689 * }
5690 * }</pre></blockquote>
5691 *
5692 * @param iterator an optional handle to return the iterator to start the loop.
5693 * If non-{@code null}, the handle must return {@link java.util.Iterator} or a subtype.
5694 * See above for other constraints.
5695 * @param init optional initializer, providing the initial value of the loop variable.
5696 * May be {@code null}, implying a default initial value. See above for other constraints.
5697 * @param body body of the loop, which may not be {@code null}.
5698 * It controls the loop parameters and result type in the standard case (see above for details).
5699 * It must accept its own return type (if non-void) plus a {@code T} parameter (for the iterated values),
5700 * and may accept any number of additional types.
5701 * See above for other constraints.
5702 *
5703 * @return a method handle embodying the iteration loop functionality.
5704 * @throws NullPointerException if the {@code body} handle is {@code null}.
5705 * @throws IllegalArgumentException if any argument violates the above requirements.
5706 *
5707 * @since 9
5708 */
5709 public static MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
5710 Class<?> iterableType = iteratedLoopChecks(iterator, init, body);
5711 Class<?> returnType = body.type().returnType();
5712 MethodHandle hasNext = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iteratePred);
5713 MethodHandle nextRaw = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iterateNext);
5714 MethodHandle startIter;
5715 MethodHandle nextVal;
5716 {
5717 MethodType iteratorType;
5718 if (iterator == null) {
5719 // derive argument type from body, if available, else use Iterable
5720 startIter = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_initIterator);
5721 iteratorType = startIter.type().changeParameterType(0, iterableType);
5722 } else {
5723 // force return type to the internal iterator class
5724 iteratorType = iterator.type().changeReturnType(Iterator.class);
5725 startIter = iterator;
5726 }
5727 Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
5728 MethodType nextValType = nextRaw.type().changeReturnType(ttype);
5729
5730 // perform the asType transforms under an exception transformer, as per spec.:
5731 try {
5732 startIter = startIter.asType(iteratorType);
5733 nextVal = nextRaw.asType(nextValType);
5734 } catch (WrongMethodTypeException ex) {
5735 throw new IllegalArgumentException(ex);
5736 }
5737 }
5738
5739 MethodHandle retv = null, step = body;
5740 if (returnType != void.class) {
5741 // the simple thing first: in (I V A...), drop the I to get V
5742 retv = dropArguments(identity(returnType), 0, Iterator.class);
5743 // body type signature (V T A...), internal loop types (I V A...)
5744 step = swapArguments(body, 0, 1); // swap V <-> T
5745 }
5746
5747 MethodHandle[]
5748 iterVar = { startIter, null, hasNext, retv },
5749 bodyClause = { init, filterArgument(step, 0, nextVal) };
5750 return loop(iterVar, bodyClause);
5751 }
5752
5753 private static Class<?> iteratedLoopChecks(MethodHandle iterator, MethodHandle init, MethodHandle body) {
5754 Objects.requireNonNull(body);
5755 MethodType bodyType = body.type();
5756 Class<?> returnType = bodyType.returnType();
5757 List<Class<?>> internalParamList = bodyType.parameterList();
5758 // strip leading V value if present
5759 int vsize = (returnType == void.class ? 0 : 1);
5760 if (vsize != 0 && (internalParamList.size() == 0 || internalParamList.get(0) != returnType)) {
5761 // argument list has no "V" => error
5762 MethodType expected = bodyType.insertParameterTypes(0, returnType);
5763 throw misMatchedTypes("body function", bodyType, expected);
5764 } else if (internalParamList.size() <= vsize) {
5765 // missing T type => error
5766 MethodType expected = bodyType.insertParameterTypes(vsize, Object.class);
5767 throw misMatchedTypes("body function", bodyType, expected);
5768 }
5769 List<Class<?>> externalParamList = internalParamList.subList(vsize + 1, internalParamList.size());
5770 Class<?> iterableType = null;
5771 if (iterator != null) {
5772 // special case; if the body handle only declares V and T then
5773 // the external parameter list is obtained from iterator handle
5774 if (externalParamList.isEmpty()) {
5775 externalParamList = iterator.type().parameterList();
5776 }
5777 MethodType itype = iterator.type();
5778 if (!Iterator.class.isAssignableFrom(itype.returnType())) {
5779 throw newIllegalArgumentException("iteratedLoop first argument must have Iterator return type");
5780 }
5781 if (!itype.effectivelyIdenticalParameters(0, externalParamList)) {
5782 MethodType expected = methodType(itype.returnType(), externalParamList);
5783 throw misMatchedTypes("iterator parameters", itype, expected);
5784 }
5785 } else {
5786 if (externalParamList.isEmpty()) {
5787 // special case; if the iterator handle is null and the body handle
5788 // only declares V and T then the external parameter list consists
5789 // of Iterable
5790 externalParamList = Arrays.asList(Iterable.class);
5791 iterableType = Iterable.class;
5792 } else {
5793 // special case; if the iterator handle is null and the external
5794 // parameter list is not empty then the first parameter must be
5795 // assignable to Iterable
5796 iterableType = externalParamList.get(0);
5797 if (!Iterable.class.isAssignableFrom(iterableType)) {
5798 throw newIllegalArgumentException(
5799 "inferred first loop argument must inherit from Iterable: " + iterableType);
5800 }
5801 }
5802 }
5803 if (init != null) {
5804 MethodType initType = init.type();
5805 if (initType.returnType() != returnType ||
5806 !initType.effectivelyIdenticalParameters(0, externalParamList)) {
5807 throw misMatchedTypes("loop initializer", initType, methodType(returnType, externalParamList));
5808 }
5809 }
5810 return iterableType; // help the caller a bit
5811 }
5812
5813 /*non-public*/ static MethodHandle swapArguments(MethodHandle mh, int i, int j) {
5814 // there should be a better way to uncross my wires
5815 int arity = mh.type().parameterCount();
5816 int[] order = new int[arity];
5817 for (int k = 0; k < arity; k++) order[k] = k;
5818 order[i] = j; order[j] = i;
5819 Class<?>[] types = mh.type().parameterArray();
5820 Class<?> ti = types[i]; types[i] = types[j]; types[j] = ti;
5821 MethodType swapType = methodType(mh.type().returnType(), types);
5822 return permuteArguments(mh, swapType, order);
5823 }
5824
5825 /**
5826 * Makes a method handle that adapts a {@code target} method handle by wrapping it in a {@code try-finally} block.
5827 * Another method handle, {@code cleanup}, represents the functionality of the {@code finally} block. Any exception
5828 * thrown during the execution of the {@code target} handle will be passed to the {@code cleanup} handle. The
5829 * exception will be rethrown, unless {@code cleanup} handle throws an exception first. The
5830 * value returned from the {@code cleanup} handle's execution will be the result of the execution of the
5831 * {@code try-finally} handle.
5832 * <p>
5833 * The {@code cleanup} handle will be passed one or two additional leading arguments.
5834 * The first is the exception thrown during the
5835 * execution of the {@code target} handle, or {@code null} if no exception was thrown.
5836 * The second is the result of the execution of the {@code target} handle, or, if it throws an exception,
5837 * a {@code null}, zero, or {@code false} value of the required type is supplied as a placeholder.
5838 * The second argument is not present if the {@code target} handle has a {@code void} return type.
5839 * (Note that, except for argument type conversions, combinators represent {@code void} values in parameter lists
5840 * by omitting the corresponding paradoxical arguments, not by inserting {@code null} or zero values.)
5841 * <p>
5842 * The {@code target} and {@code cleanup} handles must have the same corresponding argument and return types, except
5843 * that the {@code cleanup} handle may omit trailing arguments. Also, the {@code cleanup} handle must have one or
5844 * two extra leading parameters:<ul>
5845 * <li>a {@code Throwable}, which will carry the exception thrown by the {@code target} handle (if any); and
5846 * <li>a parameter of the same type as the return type of both {@code target} and {@code cleanup}, which will carry
5847 * the result from the execution of the {@code target} handle.
5848 * This parameter is not present if the {@code target} returns {@code void}.
5849 * </ul>
5850 * <p>
5851 * The pseudocode for the resulting adapter looks as follows. In the code, {@code V} represents the result type of
5852 * the {@code try/finally} construct; {@code A}/{@code a}, the types and values of arguments to the resulting
5853 * handle consumed by the cleanup; and {@code B}/{@code b}, those of arguments to the resulting handle discarded by
5854 * the cleanup.
5855 * <blockquote><pre>{@code
5856 * V target(A..., B...);
5857 * V cleanup(Throwable, V, A...);
5858 * V adapter(A... a, B... b) {
5859 * V result = (zero value for V);
5860 * Throwable throwable = null;
5861 * try {
5862 * result = target(a..., b...);
5863 * } catch (Throwable t) {
5864 * throwable = t;
5865 * throw t;
5866 * } finally {
5867 * result = cleanup(throwable, result, a...);
5868 * }
5869 * return result;
5870 * }
5871 * }</pre></blockquote>
5872 * <p>
5873 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
5874 * be modified by execution of the target, and so are passed unchanged
5875 * from the caller to the cleanup, if it is invoked.
5876 * <p>
5877 * The target and cleanup must return the same type, even if the cleanup
5878 * always throws.
5879 * To create such a throwing cleanup, compose the cleanup logic
5880 * with {@link #throwException throwException},
5881 * in order to create a method handle of the correct return type.
5882 * <p>
5883 * Note that {@code tryFinally} never converts exceptions into normal returns.
5884 * In rare cases where exceptions must be converted in that way, first wrap
5885 * the target with {@link #catchException(MethodHandle, Class, MethodHandle)}
5886 * to capture an outgoing exception, and then wrap with {@code tryFinally}.
5887 *
5888 * @param target the handle whose execution is to be wrapped in a {@code try} block.
5889 * @param cleanup the handle that is invoked in the finally block.
5890 *
5891 * @return a method handle embodying the {@code try-finally} block composed of the two arguments.
5892 * @throws NullPointerException if any argument is null
5893 * @throws IllegalArgumentException if {@code cleanup} does not accept
5894 * the required leading arguments, or if the method handle types do
5895 * not match in their return types and their
5896 * corresponding trailing parameters
5897 *
5898 * @see MethodHandles#catchException(MethodHandle, Class, MethodHandle)
5899 * @since 9
5900 */
5901 public static MethodHandle tryFinally(MethodHandle target, MethodHandle cleanup) {
5902 List<Class<?>> targetParamTypes = target.type().parameterList();
5903 List<Class<?>> cleanupParamTypes = cleanup.type().parameterList();
5904 Class<?> rtype = target.type().returnType();
5905
5906 tryFinallyChecks(target, cleanup);
5907
5908 // Match parameter lists: if the cleanup has a shorter parameter list than the target, add ignored arguments.
5909 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
5910 // target parameter list.
5911 cleanup = dropArgumentsToMatch(cleanup, (rtype == void.class ? 1 : 2), targetParamTypes, 0);
5912
5913 // Use asFixedArity() to avoid unnecessary boxing of last argument for VarargsCollector case.
5914 return MethodHandleImpl.makeTryFinally(target.asFixedArity(), cleanup.asFixedArity(), rtype, targetParamTypes);
5915 }
5916
5917 private static void tryFinallyChecks(MethodHandle target, MethodHandle cleanup) {
5918 Class<?> rtype = target.type().returnType();
5919 if (rtype != cleanup.type().returnType()) {
5920 throw misMatchedTypes("target and return types", cleanup.type().returnType(), rtype);
5921 }
5922 MethodType cleanupType = cleanup.type();
5923 if (!Throwable.class.isAssignableFrom(cleanupType.parameterType(0))) {
5924 throw misMatchedTypes("cleanup first argument and Throwable", cleanup.type(), Throwable.class);
5925 }
5926 if (rtype != void.class && cleanupType.parameterType(1) != rtype) {
5927 throw misMatchedTypes("cleanup second argument and target return type", cleanup.type(), rtype);
5928 }
5929 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
5930 // target parameter list.
5931 int cleanupArgIndex = rtype == void.class ? 1 : 2;
5932 if (!cleanupType.effectivelyIdenticalParameters(cleanupArgIndex, target.type().parameterList())) {
5933 throw misMatchedTypes("cleanup parameters after (Throwable,result) and target parameter list prefix",
5934 cleanup.type(), target.type());
5935 }
5936 }
5937
5938 }