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.experimental.value.ValueType;
29 import jdk.internal.misc.SharedSecrets;
30 import jdk.internal.module.IllegalAccessLogger;
31 import jdk.internal.org.objectweb.asm.ClassReader;
32 import jdk.internal.reflect.CallerSensitive;
33 import jdk.internal.reflect.Reflection;
34 import jdk.internal.vm.annotation.ForceInline;
35 import sun.invoke.util.ValueConversions;
36 import sun.invoke.util.VerifyAccess;
37 import sun.invoke.util.Wrapper;
38 import sun.reflect.misc.ReflectUtil;
39 import sun.security.util.SecurityConstants;
40 import valhalla.shady.MinimalValueTypes_1_0;
41
42 import java.lang.invoke.LambdaForm.BasicType;
43 import java.lang.reflect.Constructor;
44 import java.lang.reflect.Field;
45 import java.lang.reflect.Member;
46 import java.lang.reflect.Method;
47 import java.lang.reflect.Modifier;
48 import java.lang.reflect.ReflectPermission;
49 import java.nio.ByteOrder;
50 import java.security.AccessController;
51 import java.security.PrivilegedAction;
52 import java.security.ProtectionDomain;
53 import java.util.ArrayList;
54 import java.util.Arrays;
55 import java.util.BitSet;
56 import java.util.Iterator;
57 import java.util.List;
58 import java.util.Objects;
59 import java.util.*;
60 import java.util.concurrent.ConcurrentHashMap;
61 import java.util.stream.Collectors;
62 import java.util.stream.Stream;
63
64 import static java.lang.invoke.MethodHandleImpl.Intrinsic;
65 import static java.lang.invoke.MethodHandleNatives.Constants.*;
66 import static java.lang.invoke.MethodHandleStatics.newIllegalArgumentException;
67 import static java.lang.invoke.MethodType.methodType;
68
69 /**
70 * This class consists exclusively of static methods that operate on or return
71 * method handles. They fall into several categories:
72 * <ul>
73 * <li>Lookup methods which help create method handles for methods and fields.
74 * <li>Combinator methods, which combine or transform pre-existing method handles into new ones.
75 * <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns.
76 * </ul>
77 *
78 * @author John Rose, JSR 292 EG
79 * @since 1.7
80 */
81 public class MethodHandles {
82
83 private MethodHandles() { } // do not instantiate
84
85 static final MemberName.Factory IMPL_NAMES = MemberName.getFactory();
86
87 // See IMPL_LOOKUP below.
88
89 //// Method handle creation from ordinary methods.
90
91 /**
92 * Returns a {@link Lookup lookup object} with
93 * full capabilities to emulate all supported bytecode behaviors of the caller.
94 * These capabilities include <a href="MethodHandles.Lookup.html#privacc">private access</a> to the caller.
95 * Factory methods on the lookup object can create
96 * <a href="MethodHandleInfo.html#directmh">direct method handles</a>
97 * for any member that the caller has access to via bytecodes,
98 * including protected and private fields and methods.
99 * This lookup object is a <em>capability</em> which may be delegated to trusted agents.
100 * Do not store it in place where untrusted code can access it.
101 * <p>
102 * This method is caller sensitive, which means that it may return different
103 * values to different callers.
104 * <p>
105 * For any given caller class {@code C}, the lookup object returned by this call
106 * has equivalent capabilities to any lookup object
107 * supplied by the JVM to the bootstrap method of an
108 * <a href="package-summary.html#indyinsn">invokedynamic instruction</a>
109 * executing in the same caller class {@code C}.
110 * @return a lookup object for the caller of this method, with private access
111 */
112 @CallerSensitive
113 @ForceInline // to ensure Reflection.getCallerClass optimization
114 public static Lookup lookup() {
115 return new Lookup(Reflection.getCallerClass());
116 }
117
118 /**
119 * This reflected$lookup method is the alternate implementation of
120 * the lookup method when being invoked by reflection.
121 */
122 @CallerSensitive
123 private static Lookup reflected$lookup() {
124 Class<?> caller = Reflection.getCallerClass();
125 if (caller.getClassLoader() == null) {
126 throw newIllegalArgumentException("illegal lookupClass: "+caller);
127 }
128 return new Lookup(caller);
129 }
130
131 /**
132 * Returns a {@link Lookup lookup object} which is trusted minimally.
133 * The lookup has the {@code PUBLIC} and {@code UNCONDITIONAL} modes.
134 * It can only be used to create method handles to public members of
135 * public classes in packages that are exported unconditionally.
136 * <p>
137 * As a matter of pure convention, the {@linkplain Lookup#lookupClass lookup class}
138 * of this lookup object will be {@link java.lang.Object}.
139 *
140 * @apiNote The use of Object is conventional, and because the lookup modes are
141 * limited, there is no special access provided to the internals of Object, its package
142 * or its module. Consequently, the lookup context of this lookup object will be the
143 * bootstrap class loader, which means it cannot find user classes.
144 *
145 * <p style="font-size:smaller;">
146 * <em>Discussion:</em>
147 * The lookup class can be changed to any other class {@code C} using an expression of the form
148 * {@link Lookup#in publicLookup().in(C.class)}.
149 * but may change the lookup context by virtue of changing the class loader.
150 * A public lookup object is always subject to
151 * <a href="MethodHandles.Lookup.html#secmgr">security manager checks</a>.
152 * Also, it cannot access
153 * <a href="MethodHandles.Lookup.html#callsens">caller sensitive methods</a>.
154 * @return a lookup object which is trusted minimally
155 *
156 * @revised 9
157 * @spec JPMS
158 */
159 public static Lookup publicLookup() {
160 return Lookup.PUBLIC_LOOKUP;
161 }
162
163 /**
164 * Returns a {@link Lookup lookup object} with full capabilities to emulate all
165 * supported bytecode behaviors, including <a href="MethodHandles.Lookup.html#privacc">
166 * private access</a>, on a target class.
167 * This method checks that a caller, specified as a {@code Lookup} object, is allowed to
168 * do <em>deep reflection</em> on the target class. If {@code m1} is the module containing
169 * the {@link Lookup#lookupClass() lookup class}, and {@code m2} is the module containing
170 * the target class, then this check ensures that
171 * <ul>
172 * <li>{@code m1} {@link Module#canRead reads} {@code m2}.</li>
173 * <li>{@code m2} {@link Module#isOpen(String,Module) opens} the package containing
174 * the target class to at least {@code m1}.</li>
175 * <li>The lookup has the {@link Lookup#MODULE MODULE} lookup mode.</li>
176 * </ul>
177 * <p>
178 * If there is a security manager, its {@code checkPermission} method is called to
179 * check {@code ReflectPermission("suppressAccessChecks")}.
180 * @apiNote The {@code MODULE} lookup mode serves to authenticate that the lookup object
181 * was created by code in the caller module (or derived from a lookup object originally
182 * created by the caller). A lookup object with the {@code MODULE} lookup mode can be
183 * shared with trusted parties without giving away {@code PRIVATE} and {@code PACKAGE}
184 * access to the caller.
185 * @param targetClass the target class
186 * @param lookup the caller lookup object
187 * @return a lookup object for the target class, with private access
188 * @throws IllegalArgumentException if {@code targetClass} is a primitve type or array class
189 * @throws NullPointerException if {@code targetClass} or {@code caller} is {@code null}
190 * @throws IllegalAccessException if the access check specified above fails
191 * @throws SecurityException if denied by the security manager
192 * @since 9
193 * @spec JPMS
194 * @see Lookup#dropLookupMode
195 */
196 public static Lookup privateLookupIn(Class<?> targetClass, Lookup lookup) throws IllegalAccessException {
197 SecurityManager sm = System.getSecurityManager();
198 if (sm != null) sm.checkPermission(ACCESS_PERMISSION);
199 if (targetClass.isPrimitive())
200 throw new IllegalArgumentException(targetClass + " is a primitive class");
201 if (targetClass.isArray())
202 throw new IllegalArgumentException(targetClass + " is an array class");
203 Module targetModule = targetClass.getModule();
204 Module callerModule = lookup.lookupClass().getModule();
205 if (!callerModule.canRead(targetModule))
206 throw new IllegalAccessException(callerModule + " does not read " + targetModule);
207 if (targetModule.isNamed()) {
208 String pn = targetClass.getPackageName();
209 assert pn.length() > 0 : "unnamed package cannot be in named module";
210 if (!targetModule.isOpen(pn, callerModule))
211 throw new IllegalAccessException(targetModule + " does not open " + pn + " to " + callerModule);
212 }
213 if ((lookup.lookupModes() & Lookup.MODULE) == 0)
214 throw new IllegalAccessException("lookup does not have MODULE lookup mode");
215 if (!callerModule.isNamed() && targetModule.isNamed()) {
216 IllegalAccessLogger logger = IllegalAccessLogger.illegalAccessLogger();
217 if (logger != null) {
218 logger.logIfOpenedByBackdoor(lookup, targetClass);
219 }
220 }
221 return new Lookup(targetClass);
222 }
223
224 /**
225 * Performs an unchecked "crack" of a
226 * <a href="MethodHandleInfo.html#directmh">direct method handle</a>.
227 * The result is as if the user had obtained a lookup object capable enough
228 * to crack the target method handle, called
229 * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect}
230 * on the target to obtain its symbolic reference, and then called
231 * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs}
232 * to resolve the symbolic reference to a member.
233 * <p>
234 * If there is a security manager, its {@code checkPermission} method
235 * is called with a {@code ReflectPermission("suppressAccessChecks")} permission.
236 * @param <T> the desired type of the result, either {@link Member} or a subtype
237 * @param target a direct method handle to crack into symbolic reference components
238 * @param expected a class object representing the desired result type {@code T}
239 * @return a reference to the method, constructor, or field object
240 * @exception SecurityException if the caller is not privileged to call {@code setAccessible}
241 * @exception NullPointerException if either argument is {@code null}
242 * @exception IllegalArgumentException if the target is not a direct method handle
243 * @exception ClassCastException if the member is not of the expected type
244 * @since 1.8
245 */
246 public static <T extends Member> T
247 reflectAs(Class<T> expected, MethodHandle target) {
248 SecurityManager smgr = System.getSecurityManager();
249 if (smgr != null) smgr.checkPermission(ACCESS_PERMISSION);
250 Lookup lookup = Lookup.IMPL_LOOKUP; // use maximally privileged lookup
251 return lookup.revealDirect(target).reflectAs(expected, lookup);
252 }
253 // Copied from AccessibleObject, as used by Method.setAccessible, etc.:
254 private static final java.security.Permission ACCESS_PERMISSION =
255 new ReflectPermission("suppressAccessChecks");
256
257 /**
258 * A <em>lookup object</em> is a factory for creating method handles,
259 * when the creation requires access checking.
260 * Method handles do not perform
261 * access checks when they are called, but rather when they are created.
262 * Therefore, method handle access
263 * restrictions must be enforced when a method handle is created.
264 * The caller class against which those restrictions are enforced
265 * is known as the {@linkplain #lookupClass lookup class}.
266 * <p>
267 * A lookup class which needs to create method handles will call
268 * {@link MethodHandles#lookup MethodHandles.lookup} to create a factory for itself.
269 * When the {@code Lookup} factory object is created, the identity of the lookup class is
270 * determined, and securely stored in the {@code Lookup} object.
271 * The lookup class (or its delegates) may then use factory methods
272 * on the {@code Lookup} object to create method handles for access-checked members.
273 * This includes all methods, constructors, and fields which are allowed to the lookup class,
274 * even private ones.
275 *
276 * <h1><a id="lookups"></a>Lookup Factory Methods</h1>
277 * The factory methods on a {@code Lookup} object correspond to all major
278 * use cases for methods, constructors, and fields.
279 * Each method handle created by a factory method is the functional
280 * equivalent of a particular <em>bytecode behavior</em>.
281 * (Bytecode behaviors are described in section 5.4.3.5 of the Java Virtual Machine Specification.)
282 * Here is a summary of the correspondence between these factory methods and
283 * the behavior of the resulting method handles:
284 * <table border=1 cellpadding=5 summary="lookup method behaviors">
285 * <tr>
286 * <th><a id="equiv"></a>lookup expression</th>
287 * <th>member</th>
288 * <th>bytecode behavior</th>
289 * </tr>
290 * <tr>
291 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</td>
292 * <td>{@code FT f;}</td><td>{@code (T) this.f;}</td>
293 * </tr>
294 * <tr>
295 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</td>
296 * <td>{@code static}<br>{@code FT f;}</td><td>{@code (T) C.f;}</td>
297 * </tr>
298 * <tr>
299 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</td>
300 * <td>{@code FT f;}</td><td>{@code this.f = x;}</td>
301 * </tr>
302 * <tr>
303 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</td>
304 * <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td>
305 * </tr>
306 * <tr>
307 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</td>
308 * <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>
309 * </tr>
310 * <tr>
311 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</td>
312 * <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td>
313 * </tr>
314 * <tr>
315 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</td>
316 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
317 * </tr>
318 * <tr>
319 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</td>
320 * <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td>
321 * </tr>
322 * <tr>
323 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</td>
324 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td>
325 * </tr>
326 * <tr>
327 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</td>
328 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, arg);}</td>
329 * </tr>
330 * <tr>
331 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</td>
332 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
333 * </tr>
334 * <tr>
335 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</td>
336 * <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td>
337 * </tr>
338 * <tr>
339 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</td>
340 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
341 * </tr>
342 * <tr>
343 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findClass lookup.findClass("C")}</td>
344 * <td>{@code class C { ... }}</td><td>{@code C.class;}</td>
345 * </tr>
346 * </table>
347 *
348 * Here, the type {@code C} is the class or interface being searched for a member,
349 * documented as a parameter named {@code refc} in the lookup methods.
350 * The method type {@code MT} is composed from the return type {@code T}
351 * and the sequence of argument types {@code A*}.
352 * The constructor also has a sequence of argument types {@code A*} and
353 * is deemed to return the newly-created object of type {@code C}.
354 * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}.
355 * The formal parameter {@code this} stands for the self-reference of type {@code C};
356 * if it is present, it is always the leading argument to the method handle invocation.
357 * (In the case of some {@code protected} members, {@code this} may be
358 * restricted in type to the lookup class; see below.)
359 * The name {@code arg} stands for all the other method handle arguments.
360 * In the code examples for the Core Reflection API, the name {@code thisOrNull}
361 * stands for a null reference if the accessed method or field is static,
362 * and {@code this} otherwise.
363 * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand
364 * for reflective objects corresponding to the given members.
365 * <p>
366 * The bytecode behavior for a {@code findClass} operation is a load of a constant class,
367 * as if by {@code ldc CONSTANT_Class}.
368 * The behavior is represented, not as a method handle, but directly as a {@code Class} constant.
369 * <p>
370 * In cases where the given member is of variable arity (i.e., a method or constructor)
371 * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}.
372 * In all other cases, the returned method handle will be of fixed arity.
373 * <p style="font-size:smaller;">
374 * <em>Discussion:</em>
375 * The equivalence between looked-up method handles and underlying
376 * class members and bytecode behaviors
377 * can break down in a few ways:
378 * <ul style="font-size:smaller;">
379 * <li>If {@code C} is not symbolically accessible from the lookup class's loader,
380 * the lookup can still succeed, even when there is no equivalent
381 * Java expression or bytecoded constant.
382 * <li>Likewise, if {@code T} or {@code MT}
383 * is not symbolically accessible from the lookup class's loader,
384 * the lookup can still succeed.
385 * For example, lookups for {@code MethodHandle.invokeExact} and
386 * {@code MethodHandle.invoke} will always succeed, regardless of requested type.
387 * <li>If there is a security manager installed, it can forbid the lookup
388 * on various grounds (<a href="MethodHandles.Lookup.html#secmgr">see below</a>).
389 * By contrast, the {@code ldc} instruction on a {@code CONSTANT_MethodHandle}
390 * constant is not subject to security manager checks.
391 * <li>If the looked-up method has a
392 * <a href="MethodHandle.html#maxarity">very large arity</a>,
393 * the method handle creation may fail, due to the method handle
394 * type having too many parameters.
395 * </ul>
396 *
397 * <h1><a id="access"></a>Access checking</h1>
398 * Access checks are applied in the factory methods of {@code Lookup},
399 * when a method handle is created.
400 * This is a key difference from the Core Reflection API, since
401 * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
402 * performs access checking against every caller, on every call.
403 * <p>
404 * All access checks start from a {@code Lookup} object, which
405 * compares its recorded lookup class against all requests to
406 * create method handles.
407 * A single {@code Lookup} object can be used to create any number
408 * of access-checked method handles, all checked against a single
409 * lookup class.
410 * <p>
411 * A {@code Lookup} object can be shared with other trusted code,
412 * such as a metaobject protocol.
413 * A shared {@code Lookup} object delegates the capability
414 * to create method handles on private members of the lookup class.
415 * Even if privileged code uses the {@code Lookup} object,
416 * the access checking is confined to the privileges of the
417 * original lookup class.
418 * <p>
419 * A lookup can fail, because
420 * the containing class is not accessible to the lookup class, or
421 * because the desired class member is missing, or because the
422 * desired class member is not accessible to the lookup class, or
423 * because the lookup object is not trusted enough to access the member.
424 * In any of these cases, a {@code ReflectiveOperationException} will be
425 * thrown from the attempted lookup. The exact class will be one of
426 * the following:
427 * <ul>
428 * <li>NoSuchMethodException — if a method is requested but does not exist
429 * <li>NoSuchFieldException — if a field is requested but does not exist
430 * <li>IllegalAccessException — if the member exists but an access check fails
431 * </ul>
432 * <p>
433 * In general, the conditions under which a method handle may be
434 * looked up for a method {@code M} are no more restrictive than the conditions
435 * under which the lookup class could have compiled, verified, and resolved a call to {@code M}.
436 * Where the JVM would raise exceptions like {@code NoSuchMethodError},
437 * a method handle lookup will generally raise a corresponding
438 * checked exception, such as {@code NoSuchMethodException}.
439 * And the effect of invoking the method handle resulting from the lookup
440 * is <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a>
441 * to executing the compiled, verified, and resolved call to {@code M}.
442 * The same point is true of fields and constructors.
443 * <p style="font-size:smaller;">
444 * <em>Discussion:</em>
445 * Access checks only apply to named and reflected methods,
446 * constructors, and fields.
447 * Other method handle creation methods, such as
448 * {@link MethodHandle#asType MethodHandle.asType},
449 * do not require any access checks, and are used
450 * independently of any {@code Lookup} object.
451 * <p>
452 * If the desired member is {@code protected}, the usual JVM rules apply,
453 * including the requirement that the lookup class must be either be in the
454 * same package as the desired member, or must inherit that member.
455 * (See the Java Virtual Machine Specification, sections 4.9.2, 5.4.3.5, and 6.4.)
456 * In addition, if the desired member is a non-static field or method
457 * in a different package, the resulting method handle may only be applied
458 * to objects of the lookup class or one of its subclasses.
459 * This requirement is enforced by narrowing the type of the leading
460 * {@code this} parameter from {@code C}
461 * (which will necessarily be a superclass of the lookup class)
462 * to the lookup class itself.
463 * <p>
464 * The JVM imposes a similar requirement on {@code invokespecial} instruction,
465 * that the receiver argument must match both the resolved method <em>and</em>
466 * the current class. Again, this requirement is enforced by narrowing the
467 * type of the leading parameter to the resulting method handle.
468 * (See the Java Virtual Machine Specification, section 4.10.1.9.)
469 * <p>
470 * The JVM represents constructors and static initializer blocks as internal methods
471 * with special names ({@code "<init>"} and {@code "<clinit>"}).
472 * The internal syntax of invocation instructions allows them to refer to such internal
473 * methods as if they were normal methods, but the JVM bytecode verifier rejects them.
474 * A lookup of such an internal method will produce a {@code NoSuchMethodException}.
475 * <p>
476 * In some cases, access between nested classes is obtained by the Java compiler by creating
477 * an wrapper method to access a private method of another class
478 * in the same top-level declaration.
479 * For example, a nested class {@code C.D}
480 * can access private members within other related classes such as
481 * {@code C}, {@code C.D.E}, or {@code C.B},
482 * but the Java compiler may need to generate wrapper methods in
483 * those related classes. In such cases, a {@code Lookup} object on
484 * {@code C.E} would be unable to those private members.
485 * A workaround for this limitation is the {@link Lookup#in Lookup.in} method,
486 * which can transform a lookup on {@code C.E} into one on any of those other
487 * classes, without special elevation of privilege.
488 * <p>
489 * The accesses permitted to a given lookup object may be limited,
490 * according to its set of {@link #lookupModes lookupModes},
491 * to a subset of members normally accessible to the lookup class.
492 * For example, the {@link MethodHandles#publicLookup publicLookup}
493 * method produces a lookup object which is only allowed to access
494 * public members in public classes of exported packages.
495 * The caller sensitive method {@link MethodHandles#lookup lookup}
496 * produces a lookup object with full capabilities relative to
497 * its caller class, to emulate all supported bytecode behaviors.
498 * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object
499 * with fewer access modes than the original lookup object.
500 *
501 * <p style="font-size:smaller;">
502 * <a id="privacc"></a>
503 * <em>Discussion of private access:</em>
504 * We say that a lookup has <em>private access</em>
505 * if its {@linkplain #lookupModes lookup modes}
506 * include the possibility of accessing {@code private} members.
507 * As documented in the relevant methods elsewhere,
508 * only lookups with private access possess the following capabilities:
509 * <ul style="font-size:smaller;">
510 * <li>access private fields, methods, and constructors of the lookup class
511 * <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> methods,
512 * such as {@code Class.forName}
513 * <li>create method handles which {@link Lookup#findSpecial emulate invokespecial} instructions
514 * <li>avoid <a href="MethodHandles.Lookup.html#secmgr">package access checks</a>
515 * for classes accessible to the lookup class
516 * <li>create {@link Lookup#in delegated lookup objects} which have private access to other classes
517 * within the same package member
518 * </ul>
519 * <p style="font-size:smaller;">
520 * Each of these permissions is a consequence of the fact that a lookup object
521 * with private access can be securely traced back to an originating class,
522 * whose <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> and Java language access permissions
523 * can be reliably determined and emulated by method handles.
524 *
525 * <h1><a id="secmgr"></a>Security manager interactions</h1>
526 * Although bytecode instructions can only refer to classes in
527 * a related class loader, this API can search for methods in any
528 * class, as long as a reference to its {@code Class} object is
529 * available. Such cross-loader references are also possible with the
530 * Core Reflection API, and are impossible to bytecode instructions
531 * such as {@code invokestatic} or {@code getfield}.
532 * There is a {@linkplain java.lang.SecurityManager security manager API}
533 * to allow applications to check such cross-loader references.
534 * These checks apply to both the {@code MethodHandles.Lookup} API
535 * and the Core Reflection API
536 * (as found on {@link java.lang.Class Class}).
537 * <p>
538 * If a security manager is present, member and class lookups are subject to
539 * additional checks.
540 * From one to three calls are made to the security manager.
541 * Any of these calls can refuse access by throwing a
542 * {@link java.lang.SecurityException SecurityException}.
543 * Define {@code smgr} as the security manager,
544 * {@code lookc} as the lookup class of the current lookup object,
545 * {@code refc} as the containing class in which the member
546 * is being sought, and {@code defc} as the class in which the
547 * member is actually defined.
548 * (If a class or other type is being accessed,
549 * the {@code refc} and {@code defc} values are the class itself.)
550 * The value {@code lookc} is defined as <em>not present</em>
551 * if the current lookup object does not have
552 * <a href="MethodHandles.Lookup.html#privacc">private access</a>.
553 * The calls are made according to the following rules:
554 * <ul>
555 * <li><b>Step 1:</b>
556 * If {@code lookc} is not present, or if its class loader is not
557 * the same as or an ancestor of the class loader of {@code refc},
558 * then {@link SecurityManager#checkPackageAccess
559 * smgr.checkPackageAccess(refcPkg)} is called,
560 * where {@code refcPkg} is the package of {@code refc}.
561 * <li><b>Step 2a:</b>
562 * If the retrieved member is not public and
563 * {@code lookc} is not present, then
564 * {@link SecurityManager#checkPermission smgr.checkPermission}
565 * with {@code RuntimePermission("accessDeclaredMembers")} is called.
566 * <li><b>Step 2b:</b>
567 * If the retrieved class has a {@code null} class loader,
568 * and {@code lookc} is not present, then
569 * {@link SecurityManager#checkPermission smgr.checkPermission}
570 * with {@code RuntimePermission("getClassLoader")} is called.
571 * <li><b>Step 3:</b>
572 * If the retrieved member is not public,
573 * and if {@code lookc} is not present,
574 * and if {@code defc} and {@code refc} are different,
575 * then {@link SecurityManager#checkPackageAccess
576 * smgr.checkPackageAccess(defcPkg)} is called,
577 * where {@code defcPkg} is the package of {@code defc}.
578 * </ul>
579 * Security checks are performed after other access checks have passed.
580 * Therefore, the above rules presuppose a member or class that is public,
581 * or else that is being accessed from a lookup class that has
582 * rights to access the member or class.
583 *
584 * <h1><a id="callsens"></a>Caller sensitive methods</h1>
585 * A small number of Java methods have a special property called caller sensitivity.
586 * A <em>caller-sensitive</em> method can behave differently depending on the
587 * identity of its immediate caller.
588 * <p>
589 * If a method handle for a caller-sensitive method is requested,
590 * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> apply,
591 * but they take account of the lookup class in a special way.
592 * The resulting method handle behaves as if it were called
593 * from an instruction contained in the lookup class,
594 * so that the caller-sensitive method detects the lookup class.
595 * (By contrast, the invoker of the method handle is disregarded.)
596 * Thus, in the case of caller-sensitive methods,
597 * different lookup classes may give rise to
598 * differently behaving method handles.
599 * <p>
600 * In cases where the lookup object is
601 * {@link MethodHandles#publicLookup() publicLookup()},
602 * or some other lookup object without
603 * <a href="MethodHandles.Lookup.html#privacc">private access</a>,
604 * the lookup class is disregarded.
605 * In such cases, no caller-sensitive method handle can be created,
606 * access is forbidden, and the lookup fails with an
607 * {@code IllegalAccessException}.
608 * <p style="font-size:smaller;">
609 * <em>Discussion:</em>
610 * For example, the caller-sensitive method
611 * {@link java.lang.Class#forName(String) Class.forName(x)}
612 * can return varying classes or throw varying exceptions,
613 * depending on the class loader of the class that calls it.
614 * A public lookup of {@code Class.forName} will fail, because
615 * there is no reasonable way to determine its bytecode behavior.
616 * <p style="font-size:smaller;">
617 * If an application caches method handles for broad sharing,
618 * it should use {@code publicLookup()} to create them.
619 * If there is a lookup of {@code Class.forName}, it will fail,
620 * and the application must take appropriate action in that case.
621 * It may be that a later lookup, perhaps during the invocation of a
622 * bootstrap method, can incorporate the specific identity
623 * of the caller, making the method accessible.
624 * <p style="font-size:smaller;">
625 * The function {@code MethodHandles.lookup} is caller sensitive
626 * so that there can be a secure foundation for lookups.
627 * Nearly all other methods in the JSR 292 API rely on lookup
628 * objects to check access requests.
629 *
630 * @revised 9
631 */
632 public static final
633 class Lookup {
634 /** The class on behalf of whom the lookup is being performed. */
635 private final Class<?> lookupClass;
636
637 /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */
638 private final int allowedModes;
639
640 /** A single-bit mask representing {@code public} access,
641 * which may contribute to the result of {@link #lookupModes lookupModes}.
642 * The value, {@code 0x01}, happens to be the same as the value of the
643 * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.
644 */
645 public static final int PUBLIC = Modifier.PUBLIC;
646
647 /** A single-bit mask representing {@code private} access,
648 * which may contribute to the result of {@link #lookupModes lookupModes}.
649 * The value, {@code 0x02}, happens to be the same as the value of the
650 * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.
651 */
652 public static final int PRIVATE = Modifier.PRIVATE;
653
654 /** A single-bit mask representing {@code protected} access,
655 * which may contribute to the result of {@link #lookupModes lookupModes}.
656 * The value, {@code 0x04}, happens to be the same as the value of the
657 * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.
658 */
659 public static final int PROTECTED = Modifier.PROTECTED;
660
661 /** A single-bit mask representing {@code package} access (default access),
662 * which may contribute to the result of {@link #lookupModes lookupModes}.
663 * The value is {@code 0x08}, which does not correspond meaningfully to
664 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
665 */
666 public static final int PACKAGE = Modifier.STATIC;
667
668 /** A single-bit mask representing {@code module} access (default access),
669 * which may contribute to the result of {@link #lookupModes lookupModes}.
670 * The value is {@code 0x10}, which does not correspond meaningfully to
671 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
672 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup}
673 * with this lookup mode can access all public types in the module of the
674 * lookup class and public types in packages exported by other modules
675 * to the module of the lookup class.
676 * @since 9
677 * @spec JPMS
678 */
679 public static final int MODULE = PACKAGE << 1;
680
681 /** A single-bit mask representing {@code unconditional} access
682 * which may contribute to the result of {@link #lookupModes lookupModes}.
683 * The value is {@code 0x20}, which does not correspond meaningfully to
684 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
685 * A {@code Lookup} with this lookup mode assumes {@linkplain
686 * java.lang.Module#canRead(java.lang.Module) readability}.
687 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup}
688 * with this lookup mode can access all public members of public types
689 * of all modules where the type is in a package that is {@link
690 * java.lang.Module#isExported(String) exported unconditionally}.
691 * @since 9
692 * @spec JPMS
693 * @see #publicLookup()
694 */
695 public static final int UNCONDITIONAL = PACKAGE << 2;
696
697 private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE | MODULE | UNCONDITIONAL);
698 private static final int FULL_POWER_MODES = (ALL_MODES & ~UNCONDITIONAL);
699 private static final int TRUSTED = -1;
700
701 private static int fixmods(int mods) {
702 mods &= (ALL_MODES - PACKAGE - MODULE - UNCONDITIONAL);
703 return (mods != 0) ? mods : (PACKAGE | MODULE | UNCONDITIONAL);
704 }
705
706 /** Tells which class is performing the lookup. It is this class against
707 * which checks are performed for visibility and access permissions.
708 * <p>
709 * The class implies a maximum level of access permission,
710 * but the permissions may be additionally limited by the bitmask
711 * {@link #lookupModes lookupModes}, which controls whether non-public members
712 * can be accessed.
713 * @return the lookup class, on behalf of which this lookup object finds members
714 */
715 public Class<?> lookupClass() {
716 return lookupClass;
717 }
718
719 // This is just for calling out to MethodHandleImpl.
720 private Class<?> lookupClassOrNull() {
721 return (allowedModes == TRUSTED) ? null : lookupClass;
722 }
723
724 /** Tells which access-protection classes of members this lookup object can produce.
725 * The result is a bit-mask of the bits
726 * {@linkplain #PUBLIC PUBLIC (0x01)},
727 * {@linkplain #PRIVATE PRIVATE (0x02)},
728 * {@linkplain #PROTECTED PROTECTED (0x04)},
729 * {@linkplain #PACKAGE PACKAGE (0x08)},
730 * {@linkplain #MODULE MODULE (0x10)},
731 * and {@linkplain #UNCONDITIONAL UNCONDITIONAL (0x20)}.
732 * <p>
733 * A freshly-created lookup object
734 * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class} has
735 * all possible bits set, except {@code UNCONDITIONAL}. The lookup can be used to
736 * access all members of the caller's class, all public types in the caller's module,
737 * and all public types in packages exported by other modules to the caller's module.
738 * A lookup object on a new lookup class
739 * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object}
740 * may have some mode bits set to zero.
741 * Mode bits can also be
742 * {@linkplain java.lang.invoke.MethodHandles.Lookup#dropLookupMode directly cleared}.
743 * Once cleared, mode bits cannot be restored from the downgraded lookup object.
744 * The purpose of this is to restrict access via the new lookup object,
745 * so that it can access only names which can be reached by the original
746 * lookup object, and also by the new lookup class.
747 * @return the lookup modes, which limit the kinds of access performed by this lookup object
748 * @see #in
749 * @see #dropLookupMode
750 *
751 * @revised 9
752 * @spec JPMS
753 */
754 public int lookupModes() {
755 return allowedModes & ALL_MODES;
756 }
757
758 /** Embody the current class (the lookupClass) as a lookup class
759 * for method handle creation.
760 * Must be called by from a method in this package,
761 * which in turn is called by a method not in this package.
762 */
763 Lookup(Class<?> lookupClass) {
764 this(lookupClass, FULL_POWER_MODES);
765 // make sure we haven't accidentally picked up a privileged class:
766 checkUnprivilegedlookupClass(lookupClass);
767 }
768
769 private Lookup(Class<?> lookupClass, int allowedModes) {
770 this.lookupClass = lookupClass;
771 this.allowedModes = allowedModes;
772 }
773
774 /**
775 * Creates a lookup on the specified new lookup class.
776 * The resulting object will report the specified
777 * class as its own {@link #lookupClass lookupClass}.
778 * <p>
779 * However, the resulting {@code Lookup} object is guaranteed
780 * to have no more access capabilities than the original.
781 * In particular, access capabilities can be lost as follows:<ul>
782 * <li>If the old lookup class is in a {@link Module#isNamed() named} module, and
783 * the new lookup class is in a different module {@code M}, then no members, not
784 * even public members in {@code M}'s exported packages, will be accessible.
785 * The exception to this is when this lookup is {@link #publicLookup()
786 * publicLookup}, in which case {@code PUBLIC} access is not lost.
787 * <li>If the old lookup class is in an unnamed module, and the new lookup class
788 * is a different module then {@link #MODULE MODULE} access is lost.
789 * <li>If the new lookup class differs from the old one then {@code UNCONDITIONAL} is lost.
790 * <li>If the new lookup class is in a different package
791 * than the old one, protected and default (package) members will not be accessible.
792 * <li>If the new lookup class is not within the same package member
793 * as the old one, private members will not be accessible, and protected members
794 * will not be accessible by virtue of inheritance.
795 * (Protected members may continue to be accessible because of package sharing.)
796 * <li>If the new lookup class is not accessible to the old lookup class,
797 * then no members, not even public members, will be accessible.
798 * (In all other cases, public members will continue to be accessible.)
799 * </ul>
800 * <p>
801 * The resulting lookup's capabilities for loading classes
802 * (used during {@link #findClass} invocations)
803 * are determined by the lookup class' loader,
804 * which may change due to this operation.
805 *
806 * @param requestedLookupClass the desired lookup class for the new lookup object
807 * @return a lookup object which reports the desired lookup class, or the same object
808 * if there is no change
809 * @throws NullPointerException if the argument is null
810 *
811 * @revised 9
812 * @spec JPMS
813 */
814 public Lookup in(Class<?> requestedLookupClass) {
815 Objects.requireNonNull(requestedLookupClass);
816 if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all
817 return new Lookup(requestedLookupClass, FULL_POWER_MODES);
818 if (requestedLookupClass == this.lookupClass)
819 return this; // keep same capabilities
820 int newModes = (allowedModes & FULL_POWER_MODES);
821 if (!VerifyAccess.isSameModule(this.lookupClass, requestedLookupClass)) {
822 // Need to drop all access when teleporting from a named module to another
823 // module. The exception is publicLookup where PUBLIC is not lost.
824 if (this.lookupClass.getModule().isNamed()
825 && (this.allowedModes & UNCONDITIONAL) == 0)
826 newModes = 0;
827 else
828 newModes &= ~(MODULE|PACKAGE|PRIVATE|PROTECTED);
829 }
830 if ((newModes & PACKAGE) != 0
831 && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {
832 newModes &= ~(PACKAGE|PRIVATE|PROTECTED);
833 }
834 // Allow nestmate lookups to be created without special privilege:
835 if ((newModes & PRIVATE) != 0
836 && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {
837 newModes &= ~(PRIVATE|PROTECTED);
838 }
839 if ((newModes & PUBLIC) != 0
840 && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, allowedModes)) {
841 // The requested class it not accessible from the lookup class.
842 // No permissions.
843 newModes = 0;
844 }
845
846 checkUnprivilegedlookupClass(requestedLookupClass);
847 return new Lookup(requestedLookupClass, newModes);
848 }
849
850
851 /**
852 * Creates a lookup on the same lookup class which this lookup object
853 * finds members, but with a lookup mode that has lost the given lookup mode.
854 * The lookup mode to drop is one of {@link #PUBLIC PUBLIC}, {@link #MODULE
855 * MODULE}, {@link #PACKAGE PACKAGE}, {@link #PROTECTED PROTECTED} or {@link #PRIVATE PRIVATE}.
856 * {@link #PROTECTED PROTECTED} and {@link #UNCONDITIONAL UNCONDITIONAL} are always
857 * dropped and so the resulting lookup mode will never have these access capabilities.
858 * When dropping {@code PACKAGE} then the resulting lookup will not have {@code PACKAGE}
859 * or {@code PRIVATE} access. When dropping {@code MODULE} then the resulting lookup will
860 * not have {@code MODULE}, {@code PACKAGE}, or {@code PRIVATE} access. If {@code PUBLIC}
861 * is dropped then the resulting lookup has no access.
862 * @param modeToDrop the lookup mode to drop
863 * @return a lookup object which lacks the indicated mode, or the same object if there is no change
864 * @throws IllegalArgumentException if {@code modeToDrop} is not one of {@code PUBLIC},
865 * {@code MODULE}, {@code PACKAGE}, {@code PROTECTED}, {@code PRIVATE} or {@code UNCONDITIONAL}
866 * @see MethodHandles#privateLookupIn
867 * @since 9
868 */
869 public Lookup dropLookupMode(int modeToDrop) {
870 int oldModes = lookupModes();
871 int newModes = oldModes & ~(modeToDrop | PROTECTED | UNCONDITIONAL);
872 switch (modeToDrop) {
873 case PUBLIC: newModes &= ~(ALL_MODES); break;
874 case MODULE: newModes &= ~(PACKAGE | PRIVATE); break;
875 case PACKAGE: newModes &= ~(PRIVATE); break;
876 case PROTECTED:
877 case PRIVATE:
878 case UNCONDITIONAL: break;
879 default: throw new IllegalArgumentException(modeToDrop + " is not a valid mode to drop");
880 }
881 if (newModes == oldModes) return this; // return self if no change
882 return new Lookup(lookupClass(), newModes);
883 }
884
885 /**
886 * Defines a class to the same class loader and in the same runtime package and
887 * {@linkplain java.security.ProtectionDomain protection domain} as this lookup's
888 * {@linkplain #lookupClass() lookup class}.
889 *
890 * <p> The {@linkplain #lookupModes() lookup modes} for this lookup must include
891 * {@link #PACKAGE PACKAGE} access as default (package) members will be
892 * accessible to the class. The {@code PACKAGE} lookup mode serves to authenticate
893 * that the lookup object was created by a caller in the runtime package (or derived
894 * from a lookup originally created by suitably privileged code to a target class in
895 * the runtime package). </p>
896 *
897 * <p> The {@code bytes} parameter is the class bytes of a valid class file (as defined
898 * by the <em>The Java Virtual Machine Specification</em>) with a class name in the
899 * same package as the lookup class. </p>
900 *
901 * <p> This method does not run the class initializer. The class initializer may
902 * run at a later time, as detailed in section 12.4 of the <em>The Java Language
903 * Specification</em>. </p>
904 *
905 * <p> If there is a security manager, its {@code checkPermission} method is first called
906 * to check {@code RuntimePermission("defineClass")}. </p>
907 *
908 * @param bytes the class bytes
909 * @return the {@code Class} object for the class
910 * @throws IllegalArgumentException the bytes are for a class in a different package
911 * to the lookup class
912 * @throws IllegalAccessException if this lookup does not have {@code PACKAGE} access
913 * @throws LinkageError if the class is malformed ({@code ClassFormatError}), cannot be
914 * verified ({@code VerifyError}), is already defined, or another linkage error occurs
915 * @throws SecurityException if denied by the security manager
916 * @throws NullPointerException if {@code bytes} is {@code null}
917 * @since 9
918 * @spec JPMS
919 * @see Lookup#privateLookupIn
920 * @see Lookup#dropLookupMode
921 * @see ClassLoader#defineClass(String,byte[],int,int,ProtectionDomain)
922 */
923 public Class<?> defineClass(byte[] bytes) throws IllegalAccessException {
924 SecurityManager sm = System.getSecurityManager();
925 if (sm != null)
926 sm.checkPermission(new RuntimePermission("defineClass"));
927 if ((lookupModes() & PACKAGE) == 0)
928 throw new IllegalAccessException("Lookup does not have PACKAGE access");
929 assert (lookupModes() & (MODULE|PUBLIC)) != 0;
930
931 // parse class bytes to get class name (in internal form)
932 bytes = bytes.clone();
933 String name;
934 try {
935 ClassReader reader = new ClassReader(bytes);
936 name = reader.getClassName();
937 } catch (RuntimeException e) {
938 // ASM exceptions are poorly specified
939 ClassFormatError cfe = new ClassFormatError();
940 cfe.initCause(e);
941 throw cfe;
942 }
943
944 // get package and class name in binary form
945 String cn, pn;
946 int index = name.lastIndexOf('/');
947 if (index == -1) {
948 cn = name;
949 pn = "";
950 } else {
951 cn = name.replace('/', '.');
952 pn = cn.substring(0, index);
953 }
954 if (!pn.equals(lookupClass.getPackageName())) {
955 throw new IllegalArgumentException("Class not in same package as lookup class");
956 }
957
958 // invoke the class loader's defineClass method
959 ClassLoader loader = lookupClass.getClassLoader();
960 ProtectionDomain pd = (loader != null) ? lookupClassProtectionDomain() : null;
961 String source = "__Lookup_defineClass__";
962 Class<?> clazz = SharedSecrets.getJavaLangAccess().defineClass(loader, cn, bytes, pd, source);
963 assert clazz.getClassLoader() == lookupClass.getClassLoader()
964 && clazz.getPackageName().equals(lookupClass.getPackageName())
965 && protectionDomain(clazz) == lookupClassProtectionDomain();
966 return clazz;
967 }
968
969 private ProtectionDomain lookupClassProtectionDomain() {
970 ProtectionDomain pd = cachedProtectionDomain;
971 if (pd == null) {
972 cachedProtectionDomain = pd = protectionDomain(lookupClass);
973 }
974 return pd;
975 }
976
977 private ProtectionDomain protectionDomain(Class<?> clazz) {
978 PrivilegedAction<ProtectionDomain> pa = clazz::getProtectionDomain;
979 return AccessController.doPrivileged(pa);
980 }
981
982 // cached protection domain
983 private volatile ProtectionDomain cachedProtectionDomain;
984
985
986 // Make sure outer class is initialized first.
987 static { IMPL_NAMES.getClass(); }
988
989 /** Package-private version of lookup which is trusted. */
990 static final Lookup IMPL_LOOKUP = new Lookup(Object.class, TRUSTED);
991
992 /** Version of lookup which is trusted minimally.
993 * It can only be used to create method handles to publicly accessible
994 * members in packages that are exported unconditionally.
995 */
996 static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, (PUBLIC|UNCONDITIONAL));
997
998 private static void checkUnprivilegedlookupClass(Class<?> lookupClass) {
999 String name = lookupClass.getName();
1000 if (name.startsWith("java.lang.invoke."))
1001 throw newIllegalArgumentException("illegal lookupClass: "+lookupClass);
1002 }
1003
1004 /**
1005 * Displays the name of the class from which lookups are to be made.
1006 * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)
1007 * If there are restrictions on the access permitted to this lookup,
1008 * this is indicated by adding a suffix to the class name, consisting
1009 * of a slash and a keyword. The keyword represents the strongest
1010 * allowed access, and is chosen as follows:
1011 * <ul>
1012 * <li>If no access is allowed, the suffix is "/noaccess".
1013 * <li>If only public access to types in exported packages is allowed, the suffix is "/public".
1014 * <li>If only public access and unconditional access are allowed, the suffix is "/publicLookup".
1015 * <li>If only public and module access are allowed, the suffix is "/module".
1016 * <li>If only public, module and package access are allowed, the suffix is "/package".
1017 * <li>If only public, module, package, and private access are allowed, the suffix is "/private".
1018 * </ul>
1019 * If none of the above cases apply, it is the case that full
1020 * access (public, module, package, private, and protected) is allowed.
1021 * In this case, no suffix is added.
1022 * This is true only of an object obtained originally from
1023 * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
1024 * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
1025 * always have restricted access, and will display a suffix.
1026 * <p>
1027 * (It may seem strange that protected access should be
1028 * stronger than private access. Viewed independently from
1029 * package access, protected access is the first to be lost,
1030 * because it requires a direct subclass relationship between
1031 * caller and callee.)
1032 * @see #in
1033 *
1034 * @revised 9
1035 * @spec JPMS
1036 */
1037 @Override
1038 public String toString() {
1039 String cname = lookupClass.getName();
1040 switch (allowedModes) {
1041 case 0: // no privileges
1042 return cname + "/noaccess";
1043 case PUBLIC:
1044 return cname + "/public";
1045 case PUBLIC|UNCONDITIONAL:
1046 return cname + "/publicLookup";
1047 case PUBLIC|MODULE:
1048 return cname + "/module";
1049 case PUBLIC|MODULE|PACKAGE:
1050 return cname + "/package";
1051 case FULL_POWER_MODES & ~PROTECTED:
1052 return cname + "/private";
1053 case FULL_POWER_MODES:
1054 return cname;
1055 case TRUSTED:
1056 return "/trusted"; // internal only; not exported
1057 default: // Should not happen, but it's a bitfield...
1058 cname = cname + "/" + Integer.toHexString(allowedModes);
1059 assert(false) : cname;
1060 return cname;
1061 }
1062 }
1063
1064 /**
1065 * Produces a method handle for a static method.
1066 * The type of the method handle will be that of the method.
1067 * (Since static methods do not take receivers, there is no
1068 * additional receiver argument inserted into the method handle type,
1069 * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)
1070 * The method and all its argument types must be accessible to the lookup object.
1071 * <p>
1072 * The returned method handle will have
1073 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1074 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1075 * <p>
1076 * If the returned method handle is invoked, the method's class will
1077 * be initialized, if it has not already been initialized.
1078 * <p><b>Example:</b>
1079 * <blockquote><pre>{@code
1080 import static java.lang.invoke.MethodHandles.*;
1081 import static java.lang.invoke.MethodType.*;
1082 ...
1083 MethodHandle MH_asList = publicLookup().findStatic(Arrays.class,
1084 "asList", methodType(List.class, Object[].class));
1085 assertEquals("[x, y]", MH_asList.invoke("x", "y").toString());
1086 * }</pre></blockquote>
1087 * @param refc the class from which the method is accessed
1088 * @param name the name of the method
1089 * @param type the type of the method
1090 * @return the desired method handle
1091 * @throws NoSuchMethodException if the method does not exist
1092 * @throws IllegalAccessException if access checking fails,
1093 * or if the method is not {@code static},
1094 * or if the method's variable arity modifier bit
1095 * is set and {@code asVarargsCollector} fails
1096 * @exception SecurityException if a security manager is present and it
1097 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1098 * @throws NullPointerException if any argument is null
1099 */
1100 public
1101 MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1102 MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type);
1103 return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerClass(method));
1104 }
1105
1106 /**
1107 * Produces a method handle for a virtual method.
1108 * The type of the method handle will be that of the method,
1109 * with the receiver type (usually {@code refc}) prepended.
1110 * The method and all its argument types must be accessible to the lookup object.
1111 * <p>
1112 * When called, the handle will treat the first argument as a receiver
1113 * and dispatch on the receiver's type to determine which method
1114 * implementation to enter.
1115 * (The dispatching action is identical with that performed by an
1116 * {@code invokevirtual} or {@code invokeinterface} instruction.)
1117 * <p>
1118 * The first argument will be of type {@code refc} if the lookup
1119 * class has full privileges to access the member. Otherwise
1120 * the member must be {@code protected} and the first argument
1121 * will be restricted in type to the lookup class.
1122 * <p>
1123 * The returned method handle will have
1124 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1125 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1126 * <p>
1127 * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual}
1128 * instructions and method handles produced by {@code findVirtual},
1129 * if the class is {@code MethodHandle} and the name string is
1130 * {@code invokeExact} or {@code invoke}, the resulting
1131 * method handle is equivalent to one produced by
1132 * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or
1133 * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}
1134 * with the same {@code type} argument.
1135 * <p>
1136 * If the class is {@code VarHandle} and the name string corresponds to
1137 * the name of a signature-polymorphic access mode method, the resulting
1138 * method handle is equivalent to one produced by
1139 * {@link java.lang.invoke.MethodHandles#varHandleInvoker} with
1140 * the access mode corresponding to the name string and with the same
1141 * {@code type} arguments.
1142 * <p>
1143 * <b>Example:</b>
1144 * <blockquote><pre>{@code
1145 import static java.lang.invoke.MethodHandles.*;
1146 import static java.lang.invoke.MethodType.*;
1147 ...
1148 MethodHandle MH_concat = publicLookup().findVirtual(String.class,
1149 "concat", methodType(String.class, String.class));
1150 MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class,
1151 "hashCode", methodType(int.class));
1152 MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class,
1153 "hashCode", methodType(int.class));
1154 assertEquals("xy", (String) MH_concat.invokeExact("x", "y"));
1155 assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy"));
1156 assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy"));
1157 // interface method:
1158 MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class,
1159 "subSequence", methodType(CharSequence.class, int.class, int.class));
1160 assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString());
1161 // constructor "internal method" must be accessed differently:
1162 MethodType MT_newString = methodType(void.class); //()V for new String()
1163 try { assertEquals("impossible", lookup()
1164 .findVirtual(String.class, "<init>", MT_newString));
1165 } catch (NoSuchMethodException ex) { } // OK
1166 MethodHandle MH_newString = publicLookup()
1167 .findConstructor(String.class, MT_newString);
1168 assertEquals("", (String) MH_newString.invokeExact());
1169 * }</pre></blockquote>
1170 *
1171 * @param refc the class or interface from which the method is accessed
1172 * @param name the name of the method
1173 * @param type the type of the method, with the receiver argument omitted
1174 * @return the desired method handle
1175 * @throws NoSuchMethodException if the method does not exist
1176 * @throws IllegalAccessException if access checking fails,
1177 * or if the method is {@code static},
1178 * or if the method is {@code private} method of interface,
1179 * or if the method's variable arity modifier bit
1180 * is set and {@code asVarargsCollector} fails
1181 * @exception SecurityException if a security manager is present and it
1182 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1183 * @throws NullPointerException if any argument is null
1184 */
1185 public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1186 if (refc == MethodHandle.class) {
1187 MethodHandle mh = findVirtualForMH(name, type);
1188 if (mh != null) return mh;
1189 } else if (refc == VarHandle.class) {
1190 MethodHandle mh = findVirtualForVH(name, type);
1191 if (mh != null) return mh;
1192 }
1193 byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual);
1194 MemberName method = resolveOrFail(refKind, refc, name, type);
1195 return getDirectMethod(refKind, refc, method, findBoundCallerClass(method));
1196 }
1197 private MethodHandle findVirtualForMH(String name, MethodType type) {
1198 // these names require special lookups because of the implicit MethodType argument
1199 if ("invoke".equals(name))
1200 return invoker(type);
1201 if ("invokeExact".equals(name))
1202 return exactInvoker(type);
1203 assert(!MemberName.isMethodHandleInvokeName(name));
1204 return null;
1205 }
1206 private MethodHandle findVirtualForVH(String name, MethodType type) {
1207 try {
1208 return varHandleInvoker(VarHandle.AccessMode.valueFromMethodName(name), type);
1209 } catch (IllegalArgumentException e) {
1210 return null;
1211 }
1212 }
1213
1214 /**
1215 * Produces a method handle which creates an object and initializes it, using
1216 * the constructor of the specified type.
1217 * The parameter types of the method handle will be those of the constructor,
1218 * while the return type will be a reference to the constructor's class.
1219 * The constructor and all its argument types must be accessible to the lookup object.
1220 * <p>
1221 * The requested type must have a return type of {@code void}.
1222 * (This is consistent with the JVM's treatment of constructor type descriptors.)
1223 * <p>
1224 * The returned method handle will have
1225 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1226 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
1227 * <p>
1228 * If the returned method handle is invoked, the constructor's class will
1229 * be initialized, if it has not already been initialized.
1230 * <p><b>Example:</b>
1231 * <blockquote><pre>{@code
1232 import static java.lang.invoke.MethodHandles.*;
1233 import static java.lang.invoke.MethodType.*;
1234 ...
1235 MethodHandle MH_newArrayList = publicLookup().findConstructor(
1236 ArrayList.class, methodType(void.class, Collection.class));
1237 Collection orig = Arrays.asList("x", "y");
1238 Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig);
1239 assert(orig != copy);
1240 assertEquals(orig, copy);
1241 // a variable-arity constructor:
1242 MethodHandle MH_newProcessBuilder = publicLookup().findConstructor(
1243 ProcessBuilder.class, methodType(void.class, String[].class));
1244 ProcessBuilder pb = (ProcessBuilder)
1245 MH_newProcessBuilder.invoke("x", "y", "z");
1246 assertEquals("[x, y, z]", pb.command().toString());
1247 * }</pre></blockquote>
1248 * @param refc the class or interface from which the method is accessed
1249 * @param type the type of the method, with the receiver argument omitted, and a void return type
1250 * @return the desired method handle
1251 * @throws NoSuchMethodException if the constructor does not exist
1252 * @throws IllegalAccessException if access checking fails
1253 * or if the method's variable arity modifier bit
1254 * is set and {@code asVarargsCollector} fails
1255 * @exception SecurityException if a security manager is present and it
1256 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1257 * @throws NullPointerException if any argument is null
1258 */
1259 public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1260 if (refc.isArray()) {
1261 throw new NoSuchMethodException("no constructor for array class: " + refc.getName());
1262 }
1263 String name = "<init>";
1264 if (MinimalValueTypes_1_0.isValueType(refc)) {
1265 //shady: The findConstructor method of Lookup will expose all accessible constructors of the original
1266 //value-capable class, for both the Q-type and the legacy L-type. The return type of a method handle produced
1267 //by findConstructor will be identical with the lookup class, even if it is a Q-type.
1268 refc = MinimalValueTypes_1_0.getValueCapableClass(refc);
1269 }
1270 MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type);
1271 return getDirectConstructor(refc, ctor);
1272 }
1273
1274 /**
1275 * Looks up a class by name from the lookup context defined by this {@code Lookup} object. The static
1276 * initializer of the class is not run.
1277 * <p>
1278 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class}, its class
1279 * loader, and the {@linkplain #lookupModes() lookup modes}. In particular, the method first attempts to
1280 * load the requested class, and then determines whether the class is accessible to this lookup object.
1281 *
1282 * @param targetName the fully qualified name of the class to be looked up.
1283 * @return the requested class.
1284 * @exception SecurityException if a security manager is present and it
1285 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1286 * @throws LinkageError if the linkage fails
1287 * @throws ClassNotFoundException if the class cannot be loaded by the lookup class' loader.
1288 * @throws IllegalAccessException if the class is not accessible, using the allowed access
1289 * modes.
1290 * @exception SecurityException if a security manager is present and it
1291 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1292 * @since 9
1293 */
1294 public Class<?> findClass(String targetName) throws ClassNotFoundException, IllegalAccessException {
1295 Class<?> targetClass = Class.forName(targetName, false, lookupClass.getClassLoader());
1296 return accessClass(targetClass);
1297 }
1298
1299 /**
1300 * Determines if a class can be accessed from the lookup context defined by this {@code Lookup} object. The
1301 * static initializer of the class is not run.
1302 * <p>
1303 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class} and the
1304 * {@linkplain #lookupModes() lookup modes}.
1305 *
1306 * @param targetClass the class to be access-checked
1307 *
1308 * @return the class that has been access-checked
1309 *
1310 * @throws IllegalAccessException if the class is not accessible from the lookup class, using the allowed access
1311 * modes.
1312 * @exception SecurityException if a security manager is present and it
1313 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1314 * @since 9
1315 */
1316 public Class<?> accessClass(Class<?> targetClass) throws IllegalAccessException {
1317 if (!VerifyAccess.isClassAccessible(targetClass, lookupClass, allowedModes)) {
1318 throw new MemberName(targetClass).makeAccessException("access violation", this);
1319 }
1320 checkSecurityManager(targetClass, null);
1321 return targetClass;
1322 }
1323
1324 /**
1325 * Produces an early-bound method handle for a virtual method.
1326 * It will bypass checks for overriding methods on the receiver,
1327 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
1328 * instruction from within the explicitly specified {@code specialCaller}.
1329 * The type of the method handle will be that of the method,
1330 * with a suitably restricted receiver type prepended.
1331 * (The receiver type will be {@code specialCaller} or a subtype.)
1332 * The method and all its argument types must be accessible
1333 * to the lookup object.
1334 * <p>
1335 * Before method resolution,
1336 * if the explicitly specified caller class is not identical with the
1337 * lookup class, or if this lookup object does not have
1338 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
1339 * privileges, the access fails.
1340 * <p>
1341 * The returned method handle will have
1342 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1343 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1344 * <p style="font-size:smaller;">
1345 * <em>(Note: JVM internal methods named {@code "<init>"} are not visible to this API,
1346 * even though the {@code invokespecial} instruction can refer to them
1347 * in special circumstances. Use {@link #findConstructor findConstructor}
1348 * to access instance initialization methods in a safe manner.)</em>
1349 * <p><b>Example:</b>
1350 * <blockquote><pre>{@code
1351 import static java.lang.invoke.MethodHandles.*;
1352 import static java.lang.invoke.MethodType.*;
1353 ...
1354 static class Listie extends ArrayList {
1355 public String toString() { return "[wee Listie]"; }
1356 static Lookup lookup() { return MethodHandles.lookup(); }
1357 }
1358 ...
1359 // no access to constructor via invokeSpecial:
1360 MethodHandle MH_newListie = Listie.lookup()
1361 .findConstructor(Listie.class, methodType(void.class));
1362 Listie l = (Listie) MH_newListie.invokeExact();
1363 try { assertEquals("impossible", Listie.lookup().findSpecial(
1364 Listie.class, "<init>", methodType(void.class), Listie.class));
1365 } catch (NoSuchMethodException ex) { } // OK
1366 // access to super and self methods via invokeSpecial:
1367 MethodHandle MH_super = Listie.lookup().findSpecial(
1368 ArrayList.class, "toString" , methodType(String.class), Listie.class);
1369 MethodHandle MH_this = Listie.lookup().findSpecial(
1370 Listie.class, "toString" , methodType(String.class), Listie.class);
1371 MethodHandle MH_duper = Listie.lookup().findSpecial(
1372 Object.class, "toString" , methodType(String.class), Listie.class);
1373 assertEquals("[]", (String) MH_super.invokeExact(l));
1374 assertEquals(""+l, (String) MH_this.invokeExact(l));
1375 assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method
1376 try { assertEquals("inaccessible", Listie.lookup().findSpecial(
1377 String.class, "toString", methodType(String.class), Listie.class));
1378 } catch (IllegalAccessException ex) { } // OK
1379 Listie subl = new Listie() { public String toString() { return "[subclass]"; } };
1380 assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method
1381 * }</pre></blockquote>
1382 *
1383 * @param refc the class or interface from which the method is accessed
1384 * @param name the name of the method (which must not be "<init>")
1385 * @param type the type of the method, with the receiver argument omitted
1386 * @param specialCaller the proposed calling class to perform the {@code invokespecial}
1387 * @return the desired method handle
1388 * @throws NoSuchMethodException if the method does not exist
1389 * @throws IllegalAccessException if access checking fails,
1390 * or if the method is {@code static},
1391 * or if the method's variable arity modifier bit
1392 * is set and {@code asVarargsCollector} fails
1393 * @exception SecurityException if a security manager is present and it
1394 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1395 * @throws NullPointerException if any argument is null
1396 */
1397 public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,
1398 Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
1399 checkSpecialCaller(specialCaller, refc);
1400 Lookup specialLookup = this.in(specialCaller);
1401 MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type);
1402 return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerClass(method));
1403 }
1404
1405 /**
1406 * Produces a method handle giving read access to a non-static field.
1407 * The type of the method handle will have a return type of the field's
1408 * value type.
1409 * The method handle's single argument will be the instance containing
1410 * the field.
1411 * Access checking is performed immediately on behalf of the lookup class.
1412 * @param refc the class or interface from which the method is accessed
1413 * @param name the field's name
1414 * @param type the field's type
1415 * @return a method handle which can load values from the field
1416 * @throws NoSuchFieldException if the field does not exist
1417 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1418 * @exception SecurityException if a security manager is present and it
1419 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1420 * @throws NullPointerException if any argument is null
1421 * @see #findVarHandle(Class, String, Class)
1422 */
1423 public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1424 if (MinimalValueTypes_1_0.isValueType(refc)) {
1425 return ValueType.forClass(MinimalValueTypes_1_0.getValueCapableClass(refc)).findGetter(this, name, type);
1426 } else {
1427 MemberName field = resolveOrFail(REF_getField, refc, name, type);
1428 return getDirectField(REF_getField, refc, field);
1429 }
1430 }
1431
1432 /**
1433 * Produces a method handle giving write access to a non-static field.
1434 * The type of the method handle will have a void return type.
1435 * The method handle will take two arguments, the instance containing
1436 * the field, and the value to be stored.
1437 * The second argument will be of the field's value type.
1438 * Access checking is performed immediately on behalf of the lookup class.
1439 * @param refc the class or interface from which the method is accessed
1440 * @param name the field's name
1441 * @param type the field's type
1442 * @return a method handle which can store values into the field
1443 * @throws NoSuchFieldException if the field does not exist
1444 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1445 * @exception SecurityException if a security manager is present and it
1446 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1447 * @throws NullPointerException if any argument is null
1448 * @see #findVarHandle(Class, String, Class)
1449 */
1450 public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1451 MemberName field = resolveOrFail(REF_putField, refc, name, type);
1452 return getDirectField(REF_putField, refc, field);
1453 }
1454
1455 /**
1456 * Produces a VarHandle giving access to a non-static field {@code name}
1457 * of type {@code type} declared in a class of type {@code recv}.
1458 * The VarHandle's variable type is {@code type} and it has one
1459 * coordinate type, {@code recv}.
1460 * <p>
1461 * Access checking is performed immediately on behalf of the lookup
1462 * class.
1463 * <p>
1464 * Certain access modes of the returned VarHandle are unsupported under
1465 * the following conditions:
1466 * <ul>
1467 * <li>if the field is declared {@code final}, then the write, atomic
1468 * update, numeric atomic update, and bitwise atomic update access
1469 * modes are unsupported.
1470 * <li>if the field type is anything other than {@code byte},
1471 * {@code short}, {@code char}, {@code int}, {@code long},
1472 * {@code float}, or {@code double} then numeric atomic update
1473 * access modes are unsupported.
1474 * <li>if the field type is anything other than {@code boolean},
1475 * {@code byte}, {@code short}, {@code char}, {@code int} or
1476 * {@code long} then bitwise atomic update access modes are
1477 * unsupported.
1478 * </ul>
1479 * <p>
1480 * If the field is declared {@code volatile} then the returned VarHandle
1481 * will override access to the field (effectively ignore the
1482 * {@code volatile} declaration) in accordance to its specified
1483 * access modes.
1484 * <p>
1485 * If the field type is {@code float} or {@code double} then numeric
1486 * and atomic update access modes compare values using their bitwise
1487 * representation (see {@link Float#floatToRawIntBits} and
1488 * {@link Double#doubleToRawLongBits}, respectively).
1489 * @apiNote
1490 * Bitwise comparison of {@code float} values or {@code double} values,
1491 * as performed by the numeric and atomic update access modes, differ
1492 * from the primitive {@code ==} operator and the {@link Float#equals}
1493 * and {@link Double#equals} methods, specifically with respect to
1494 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
1495 * Care should be taken when performing a compare and set or a compare
1496 * and exchange operation with such values since the operation may
1497 * unexpectedly fail.
1498 * There are many possible NaN values that are considered to be
1499 * {@code NaN} in Java, although no IEEE 754 floating-point operation
1500 * provided by Java can distinguish between them. Operation failure can
1501 * occur if the expected or witness value is a NaN value and it is
1502 * transformed (perhaps in a platform specific manner) into another NaN
1503 * value, and thus has a different bitwise representation (see
1504 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
1505 * details).
1506 * The values {@code -0.0} and {@code +0.0} have different bitwise
1507 * representations but are considered equal when using the primitive
1508 * {@code ==} operator. Operation failure can occur if, for example, a
1509 * numeric algorithm computes an expected value to be say {@code -0.0}
1510 * and previously computed the witness value to be say {@code +0.0}.
1511 * @param recv the receiver class, of type {@code R}, that declares the
1512 * non-static field
1513 * @param name the field's name
1514 * @param type the field's type, of type {@code T}
1515 * @return a VarHandle giving access to non-static fields.
1516 * @throws NoSuchFieldException if the field does not exist
1517 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1518 * @exception SecurityException if a security manager is present and it
1519 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1520 * @throws NullPointerException if any argument is null
1521 * @since 9
1522 */
1523 public VarHandle findVarHandle(Class<?> recv, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1524 MemberName getField = resolveOrFail(REF_getField, recv, name, type);
1525 MemberName putField = resolveOrFail(REF_putField, recv, name, type);
1526 return getFieldVarHandle(REF_getField, REF_putField, recv, getField, putField);
1527 }
1528
1529 /**
1530 * Produces a method handle giving read access to a static field.
1531 * The type of the method handle will have a return type of the field's
1532 * value type.
1533 * The method handle will take no arguments.
1534 * Access checking is performed immediately on behalf of the lookup class.
1535 * <p>
1536 * If the returned method handle is invoked, the field's class will
1537 * be initialized, if it has not already been initialized.
1538 * @param refc the class or interface from which the method is accessed
1539 * @param name the field's name
1540 * @param type the field's type
1541 * @return a method handle which can load values from the field
1542 * @throws NoSuchFieldException if the field does not exist
1543 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1544 * @exception SecurityException if a security manager is present and it
1545 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1546 * @throws NullPointerException if any argument is null
1547 */
1548 public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1549 MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
1550 return getDirectField(REF_getStatic, refc, field);
1551 }
1552
1553 /**
1554 * Produces a method handle giving write access to a static field.
1555 * The type of the method handle will have a void return type.
1556 * The method handle will take a single
1557 * argument, of the field's value type, the value to be stored.
1558 * Access checking is performed immediately on behalf of the lookup class.
1559 * <p>
1560 * If the returned method handle is invoked, the field's class will
1561 * be initialized, if it has not already been initialized.
1562 * @param refc the class or interface from which the method is accessed
1563 * @param name the field's name
1564 * @param type the field's type
1565 * @return a method handle which can store values into the field
1566 * @throws NoSuchFieldException if the field does not exist
1567 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1568 * @exception SecurityException if a security manager is present and it
1569 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1570 * @throws NullPointerException if any argument is null
1571 */
1572 public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1573 MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
1574 return getDirectField(REF_putStatic, refc, field);
1575 }
1576
1577 /**
1578 * Produces a VarHandle giving access to a static field {@code name} of
1579 * type {@code type} declared in a class of type {@code decl}.
1580 * The VarHandle's variable type is {@code type} and it has no
1581 * coordinate types.
1582 * <p>
1583 * Access checking is performed immediately on behalf of the lookup
1584 * class.
1585 * <p>
1586 * If the returned VarHandle is operated on, the declaring class will be
1587 * initialized, if it has not already been initialized.
1588 * <p>
1589 * Certain access modes of the returned VarHandle are unsupported under
1590 * the following conditions:
1591 * <ul>
1592 * <li>if the field is declared {@code final}, then the write, atomic
1593 * update, numeric atomic update, and bitwise atomic update access
1594 * modes are unsupported.
1595 * <li>if the field type is anything other than {@code byte},
1596 * {@code short}, {@code char}, {@code int}, {@code long},
1597 * {@code float}, or {@code double}, then numeric atomic update
1598 * access modes are unsupported.
1599 * <li>if the field type is anything other than {@code boolean},
1600 * {@code byte}, {@code short}, {@code char}, {@code int} or
1601 * {@code long} then bitwise atomic update access modes are
1602 * unsupported.
1603 * </ul>
1604 * <p>
1605 * If the field is declared {@code volatile} then the returned VarHandle
1606 * will override access to the field (effectively ignore the
1607 * {@code volatile} declaration) in accordance to its specified
1608 * access modes.
1609 * <p>
1610 * If the field type is {@code float} or {@code double} then numeric
1611 * and atomic update access modes compare values using their bitwise
1612 * representation (see {@link Float#floatToRawIntBits} and
1613 * {@link Double#doubleToRawLongBits}, respectively).
1614 * @apiNote
1615 * Bitwise comparison of {@code float} values or {@code double} values,
1616 * as performed by the numeric and atomic update access modes, differ
1617 * from the primitive {@code ==} operator and the {@link Float#equals}
1618 * and {@link Double#equals} methods, specifically with respect to
1619 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
1620 * Care should be taken when performing a compare and set or a compare
1621 * and exchange operation with such values since the operation may
1622 * unexpectedly fail.
1623 * There are many possible NaN values that are considered to be
1624 * {@code NaN} in Java, although no IEEE 754 floating-point operation
1625 * provided by Java can distinguish between them. Operation failure can
1626 * occur if the expected or witness value is a NaN value and it is
1627 * transformed (perhaps in a platform specific manner) into another NaN
1628 * value, and thus has a different bitwise representation (see
1629 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
1630 * details).
1631 * The values {@code -0.0} and {@code +0.0} have different bitwise
1632 * representations but are considered equal when using the primitive
1633 * {@code ==} operator. Operation failure can occur if, for example, a
1634 * numeric algorithm computes an expected value to be say {@code -0.0}
1635 * and previously computed the witness value to be say {@code +0.0}.
1636 * @param decl the class that declares the static field
1637 * @param name the field's name
1638 * @param type the field's type, of type {@code T}
1639 * @return a VarHandle giving access to a static field
1640 * @throws NoSuchFieldException if the field does not exist
1641 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1642 * @exception SecurityException if a security manager is present and it
1643 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1644 * @throws NullPointerException if any argument is null
1645 * @since 9
1646 */
1647 public VarHandle findStaticVarHandle(Class<?> decl, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1648 MemberName getField = resolveOrFail(REF_getStatic, decl, name, type);
1649 MemberName putField = resolveOrFail(REF_putStatic, decl, name, type);
1650 return getFieldVarHandle(REF_getStatic, REF_putStatic, decl, getField, putField);
1651 }
1652
1653 /**
1654 * Produces an early-bound method handle for a non-static method.
1655 * The receiver must have a supertype {@code defc} in which a method
1656 * of the given name and type is accessible to the lookup class.
1657 * The method and all its argument types must be accessible to the lookup object.
1658 * The type of the method handle will be that of the method,
1659 * without any insertion of an additional receiver parameter.
1660 * The given receiver will be bound into the method handle,
1661 * so that every call to the method handle will invoke the
1662 * requested method on the given receiver.
1663 * <p>
1664 * The returned method handle will have
1665 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1666 * the method's variable arity modifier bit ({@code 0x0080}) is set
1667 * <em>and</em> the trailing array argument is not the only argument.
1668 * (If the trailing array argument is the only argument,
1669 * the given receiver value will be bound to it.)
1670 * <p>
1671 * This is almost equivalent to the following code, with some differences noted below:
1672 * <blockquote><pre>{@code
1673 import static java.lang.invoke.MethodHandles.*;
1674 import static java.lang.invoke.MethodType.*;
1675 ...
1676 MethodHandle mh0 = lookup().findVirtual(defc, name, type);
1677 MethodHandle mh1 = mh0.bindTo(receiver);
1678 mh1 = mh1.withVarargs(mh0.isVarargsCollector());
1679 return mh1;
1680 * }</pre></blockquote>
1681 * where {@code defc} is either {@code receiver.getClass()} or a super
1682 * type of that class, in which the requested method is accessible
1683 * to the lookup class.
1684 * (Unlike {@code bind}, {@code bindTo} does not preserve variable arity.
1685 * Also, {@code bindTo} may throw a {@code ClassCastException} in instances where {@code bind} would
1686 * throw a {@code IllegalAccessException}, as in the case where the member is {@code protected} and
1687 * the receiver is restricted by {@code findVirtual} to the lookup class)
1688 * @param receiver the object from which the method is accessed
1689 * @param name the name of the method
1690 * @param type the type of the method, with the receiver argument omitted
1691 * @return the desired method handle
1692 * @throws NoSuchMethodException if the method does not exist
1693 * @throws IllegalAccessException if access checking fails
1694 * or if the method's variable arity modifier bit
1695 * is set and {@code asVarargsCollector} fails
1696 * @exception SecurityException if a security manager is present and it
1697 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1698 * @throws NullPointerException if any argument is null
1699 * @see MethodHandle#bindTo
1700 * @see #findVirtual
1701 */
1702 public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1703 Class<? extends Object> refc = receiver.getClass(); // may get NPE
1704 MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
1705 MethodHandle mh = getDirectMethodNoRestrictInvokeSpecial(refc, method, findBoundCallerClass(method));
1706 if (!mh.type().leadingReferenceParameter().isAssignableFrom(receiver.getClass())) {
1707 throw new IllegalAccessException("The restricted defining class " +
1708 mh.type().leadingReferenceParameter().getName() +
1709 " is not assignable from receiver class " +
1710 receiver.getClass().getName());
1711 }
1712 return mh.bindArgumentL(0, receiver).setVarargs(method);
1713 }
1714
1715 /**
1716 * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
1717 * to <i>m</i>, if the lookup class has permission.
1718 * If <i>m</i> is non-static, the receiver argument is treated as an initial argument.
1719 * If <i>m</i> is virtual, overriding is respected on every call.
1720 * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped.
1721 * The type of the method handle will be that of the method,
1722 * with the receiver type prepended (but only if it is non-static).
1723 * If the method's {@code accessible} flag is not set,
1724 * access checking is performed immediately on behalf of the lookup class.
1725 * If <i>m</i> is not public, do not share the resulting handle with untrusted parties.
1726 * <p>
1727 * The returned method handle will have
1728 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1729 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1730 * <p>
1731 * If <i>m</i> is static, and
1732 * if the returned method handle is invoked, the method's class will
1733 * be initialized, if it has not already been initialized.
1734 * @param m the reflected method
1735 * @return a method handle which can invoke the reflected method
1736 * @throws IllegalAccessException if access checking fails
1737 * or if the method's variable arity modifier bit
1738 * is set and {@code asVarargsCollector} fails
1739 * @throws NullPointerException if the argument is null
1740 */
1741 public MethodHandle unreflect(Method m) throws IllegalAccessException {
1742 if (m.getDeclaringClass() == MethodHandle.class) {
1743 MethodHandle mh = unreflectForMH(m);
1744 if (mh != null) return mh;
1745 }
1746 if (m.getDeclaringClass() == VarHandle.class) {
1747 MethodHandle mh = unreflectForVH(m);
1748 if (mh != null) return mh;
1749 }
1750 MemberName method = new MemberName(m);
1751 byte refKind = method.getReferenceKind();
1752 if (refKind == REF_invokeSpecial)
1753 refKind = REF_invokeVirtual;
1754 assert(method.isMethod());
1755 @SuppressWarnings("deprecation")
1756 Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
1757 return lookup.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method, findBoundCallerClass(method));
1758 }
1759 private MethodHandle unreflectForMH(Method m) {
1760 // these names require special lookups because they throw UnsupportedOperationException
1761 if (MemberName.isMethodHandleInvokeName(m.getName()))
1762 return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m));
1763 return null;
1764 }
1765 private MethodHandle unreflectForVH(Method m) {
1766 // these names require special lookups because they throw UnsupportedOperationException
1767 if (MemberName.isVarHandleMethodInvokeName(m.getName()))
1768 return MethodHandleImpl.fakeVarHandleInvoke(new MemberName(m));
1769 return null;
1770 }
1771
1772 /**
1773 * Produces a method handle for a reflected method.
1774 * It will bypass checks for overriding methods on the receiver,
1775 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
1776 * instruction from within the explicitly specified {@code specialCaller}.
1777 * The type of the method handle will be that of the method,
1778 * with a suitably restricted receiver type prepended.
1779 * (The receiver type will be {@code specialCaller} or a subtype.)
1780 * If the method's {@code accessible} flag is not set,
1781 * access checking is performed immediately on behalf of the lookup class,
1782 * as if {@code invokespecial} instruction were being linked.
1783 * <p>
1784 * Before method resolution,
1785 * if the explicitly specified caller class is not identical with the
1786 * lookup class, or if this lookup object does not have
1787 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
1788 * privileges, the access fails.
1789 * <p>
1790 * The returned method handle will have
1791 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1792 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1793 * @param m the reflected method
1794 * @param specialCaller the class nominally calling the method
1795 * @return a method handle which can invoke the reflected method
1796 * @throws IllegalAccessException if access checking fails,
1797 * or if the method is {@code static},
1798 * or if the method's variable arity modifier bit
1799 * is set and {@code asVarargsCollector} fails
1800 * @throws NullPointerException if any argument is null
1801 */
1802 public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException {
1803 checkSpecialCaller(specialCaller, null);
1804 Lookup specialLookup = this.in(specialCaller);
1805 MemberName method = new MemberName(m, true);
1806 assert(method.isMethod());
1807 // ignore m.isAccessible: this is a new kind of access
1808 return specialLookup.getDirectMethodNoSecurityManager(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerClass(method));
1809 }
1810
1811 /**
1812 * Produces a method handle for a reflected constructor.
1813 * The type of the method handle will be that of the constructor,
1814 * with the return type changed to the declaring class.
1815 * The method handle will perform a {@code newInstance} operation,
1816 * creating a new instance of the constructor's class on the
1817 * arguments passed to the method handle.
1818 * <p>
1819 * If the constructor's {@code accessible} flag is not set,
1820 * access checking is performed immediately on behalf of the lookup class.
1821 * <p>
1822 * The returned method handle will have
1823 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1824 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
1825 * <p>
1826 * If the returned method handle is invoked, the constructor's class will
1827 * be initialized, if it has not already been initialized.
1828 * @param c the reflected constructor
1829 * @return a method handle which can invoke the reflected constructor
1830 * @throws IllegalAccessException if access checking fails
1831 * or if the method's variable arity modifier bit
1832 * is set and {@code asVarargsCollector} fails
1833 * @throws NullPointerException if the argument is null
1834 */
1835 public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException {
1836 MemberName ctor = new MemberName(c);
1837 assert(ctor.isConstructor());
1838 @SuppressWarnings("deprecation")
1839 Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
1840 return lookup.getDirectConstructorNoSecurityManager(ctor.getDeclaringClass(), ctor);
1841 }
1842
1843 /**
1844 * Produces a method handle giving read access to a reflected field.
1845 * The type of the method handle will have a return type of the field's
1846 * value type.
1847 * If the field is static, the method handle will take no arguments.
1848 * Otherwise, its single argument will be the instance containing
1849 * the field.
1850 * If the field's {@code accessible} flag is not set,
1851 * access checking is performed immediately on behalf of the lookup class.
1852 * <p>
1853 * If the field is static, and
1854 * if the returned method handle is invoked, the field's class will
1855 * be initialized, if it has not already been initialized.
1856 * @param f the reflected field
1857 * @return a method handle which can load values from the reflected field
1858 * @throws IllegalAccessException if access checking fails
1859 * @throws NullPointerException if the argument is null
1860 */
1861 public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
1862 return unreflectField(f, false);
1863 }
1864 private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
1865 MemberName field = new MemberName(f, isSetter);
1866 assert(isSetter
1867 ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
1868 : MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
1869 @SuppressWarnings("deprecation")
1870 Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
1871 return lookup.getDirectFieldNoSecurityManager(field.getReferenceKind(), f.getDeclaringClass(), field);
1872 }
1873
1874 /**
1875 * Produces a method handle giving write access to a reflected field.
1876 * The type of the method handle will have a void return type.
1877 * If the field is static, the method handle will take a single
1878 * argument, of the field's value type, the value to be stored.
1879 * Otherwise, the two arguments will be the instance containing
1880 * the field, and the value to be stored.
1881 * If the field's {@code accessible} flag is not set,
1882 * access checking is performed immediately on behalf of the lookup class.
1883 * <p>
1884 * If the field is static, and
1885 * if the returned method handle is invoked, the field's class will
1886 * be initialized, if it has not already been initialized.
1887 * @param f the reflected field
1888 * @return a method handle which can store values into the reflected field
1889 * @throws IllegalAccessException if access checking fails
1890 * @throws NullPointerException if the argument is null
1891 */
1892 public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
1893 return unreflectField(f, true);
1894 }
1895
1896 /**
1897 * Produces a VarHandle giving access to a reflected field {@code f}
1898 * of type {@code T} declared in a class of type {@code R}.
1899 * The VarHandle's variable type is {@code T}.
1900 * If the field is non-static the VarHandle has one coordinate type,
1901 * {@code R}. Otherwise, the field is static, and the VarHandle has no
1902 * coordinate types.
1903 * <p>
1904 * Access checking is performed immediately on behalf of the lookup
1905 * class, regardless of the value of the field's {@code accessible}
1906 * flag.
1907 * <p>
1908 * If the field is static, and if the returned VarHandle is operated
1909 * on, the field's declaring class will be initialized, if it has not
1910 * already been initialized.
1911 * <p>
1912 * Certain access modes of the returned VarHandle are unsupported under
1913 * the following conditions:
1914 * <ul>
1915 * <li>if the field is declared {@code final}, then the write, atomic
1916 * update, numeric atomic update, and bitwise atomic update access
1917 * modes are unsupported.
1918 * <li>if the field type is anything other than {@code byte},
1919 * {@code short}, {@code char}, {@code int}, {@code long},
1920 * {@code float}, or {@code double} then numeric atomic update
1921 * access modes are unsupported.
1922 * <li>if the field type is anything other than {@code boolean},
1923 * {@code byte}, {@code short}, {@code char}, {@code int} or
1924 * {@code long} then bitwise atomic update access modes are
1925 * unsupported.
1926 * </ul>
1927 * <p>
1928 * If the field is declared {@code volatile} then the returned VarHandle
1929 * will override access to the field (effectively ignore the
1930 * {@code volatile} declaration) in accordance to its specified
1931 * access modes.
1932 * <p>
1933 * If the field type is {@code float} or {@code double} then numeric
1934 * and atomic update access modes compare values using their bitwise
1935 * representation (see {@link Float#floatToRawIntBits} and
1936 * {@link Double#doubleToRawLongBits}, respectively).
1937 * @apiNote
1938 * Bitwise comparison of {@code float} values or {@code double} values,
1939 * as performed by the numeric and atomic update access modes, differ
1940 * from the primitive {@code ==} operator and the {@link Float#equals}
1941 * and {@link Double#equals} methods, specifically with respect to
1942 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
1943 * Care should be taken when performing a compare and set or a compare
1944 * and exchange operation with such values since the operation may
1945 * unexpectedly fail.
1946 * There are many possible NaN values that are considered to be
1947 * {@code NaN} in Java, although no IEEE 754 floating-point operation
1948 * provided by Java can distinguish between them. Operation failure can
1949 * occur if the expected or witness value is a NaN value and it is
1950 * transformed (perhaps in a platform specific manner) into another NaN
1951 * value, and thus has a different bitwise representation (see
1952 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
1953 * details).
1954 * The values {@code -0.0} and {@code +0.0} have different bitwise
1955 * representations but are considered equal when using the primitive
1956 * {@code ==} operator. Operation failure can occur if, for example, a
1957 * numeric algorithm computes an expected value to be say {@code -0.0}
1958 * and previously computed the witness value to be say {@code +0.0}.
1959 * @param f the reflected field, with a field of type {@code T}, and
1960 * a declaring class of type {@code R}
1961 * @return a VarHandle giving access to non-static fields or a static
1962 * field
1963 * @throws IllegalAccessException if access checking fails
1964 * @throws NullPointerException if the argument is null
1965 * @since 9
1966 */
1967 public VarHandle unreflectVarHandle(Field f) throws IllegalAccessException {
1968 MemberName getField = new MemberName(f, false);
1969 MemberName putField = new MemberName(f, true);
1970 return getFieldVarHandleNoSecurityManager(getField.getReferenceKind(), putField.getReferenceKind(),
1971 f.getDeclaringClass(), getField, putField);
1972 }
1973
1974 /**
1975 * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
1976 * created by this lookup object or a similar one.
1977 * Security and access checks are performed to ensure that this lookup object
1978 * is capable of reproducing the target method handle.
1979 * This means that the cracking may fail if target is a direct method handle
1980 * but was created by an unrelated lookup object.
1981 * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a>
1982 * and was created by a lookup object for a different class.
1983 * @param target a direct method handle to crack into symbolic reference components
1984 * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object
1985 * @exception SecurityException if a security manager is present and it
1986 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1987 * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails
1988 * @exception NullPointerException if the target is {@code null}
1989 * @see MethodHandleInfo
1990 * @since 1.8
1991 */
1992 public MethodHandleInfo revealDirect(MethodHandle target) {
1993 MemberName member = target.internalMemberName();
1994 if (member == null || (!member.isResolved() &&
1995 !member.isMethodHandleInvoke() &&
1996 !member.isVarHandleMethodInvoke()))
1997 throw newIllegalArgumentException("not a direct method handle");
1998 Class<?> defc = member.getDeclaringClass();
1999 byte refKind = member.getReferenceKind();
2000 assert(MethodHandleNatives.refKindIsValid(refKind));
2001 if (refKind == REF_invokeSpecial && !target.isInvokeSpecial())
2002 // Devirtualized method invocation is usually formally virtual.
2003 // To avoid creating extra MemberName objects for this common case,
2004 // we encode this extra degree of freedom using MH.isInvokeSpecial.
2005 refKind = REF_invokeVirtual;
2006 if (refKind == REF_invokeVirtual && defc.isInterface())
2007 // Symbolic reference is through interface but resolves to Object method (toString, etc.)
2008 refKind = REF_invokeInterface;
2009 // Check SM permissions and member access before cracking.
2010 try {
2011 checkAccess(refKind, defc, member);
2012 checkSecurityManager(defc, member);
2013 } catch (IllegalAccessException ex) {
2014 throw new IllegalArgumentException(ex);
2015 }
2016 if (allowedModes != TRUSTED && member.isCallerSensitive()) {
2017 Class<?> callerClass = target.internalCallerClass();
2018 if (!hasPrivateAccess() || callerClass != lookupClass())
2019 throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass);
2020 }
2021 // Produce the handle to the results.
2022 return new InfoFromMemberName(this, member, refKind);
2023 }
2024
2025 /// Helper methods, all package-private.
2026
2027 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
2028 checkSymbolicClass(refc); // do this before attempting to resolve
2029 Objects.requireNonNull(name);
2030 Objects.requireNonNull(type);
2031 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
2032 NoSuchFieldException.class);
2033 }
2034
2035 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
2036 checkSymbolicClass(refc); // do this before attempting to resolve
2037 Objects.requireNonNull(name);
2038 Objects.requireNonNull(type);
2039 checkMethodName(refKind, name); // NPE check on name
2040 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
2041 NoSuchMethodException.class);
2042 }
2043
2044 MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException {
2045 checkSymbolicClass(member.getDeclaringClass()); // do this before attempting to resolve
2046 Objects.requireNonNull(member.getName());
2047 Objects.requireNonNull(member.getType());
2048 return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(),
2049 ReflectiveOperationException.class);
2050 }
2051
2052 void checkSymbolicClass(Class<?> refc) throws IllegalAccessException {
2053 Objects.requireNonNull(refc);
2054 Class<?> caller = lookupClassOrNull();
2055 if (caller != null && !VerifyAccess.isClassAccessible(refc, caller, allowedModes))
2056 throw new MemberName(refc).makeAccessException("symbolic reference class is not accessible", this);
2057 }
2058
2059 /** Check name for an illegal leading "<" character. */
2060 void checkMethodName(byte refKind, String name) throws NoSuchMethodException {
2061 if (name.startsWith("<") && refKind != REF_newInvokeSpecial)
2062 throw new NoSuchMethodException("illegal method name: "+name);
2063 }
2064
2065
2066 /**
2067 * Find my trustable caller class if m is a caller sensitive method.
2068 * If this lookup object has private access, then the caller class is the lookupClass.
2069 * Otherwise, if m is caller-sensitive, throw IllegalAccessException.
2070 */
2071 Class<?> findBoundCallerClass(MemberName m) throws IllegalAccessException {
2072 Class<?> callerClass = null;
2073 if (MethodHandleNatives.isCallerSensitive(m)) {
2074 // Only lookups with private access are allowed to resolve caller-sensitive methods
2075 if (hasPrivateAccess()) {
2076 callerClass = lookupClass;
2077 } else {
2078 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
2079 }
2080 }
2081 return callerClass;
2082 }
2083
2084 /**
2085 * Returns {@code true} if this lookup has {@code PRIVATE} access.
2086 * @return {@code true} if this lookup has {@code PRIVATE} access.
2087 * @since 9
2088 */
2089 public boolean hasPrivateAccess() {
2090 return (allowedModes & PRIVATE) != 0;
2091 }
2092
2093 /**
2094 * Perform necessary <a href="MethodHandles.Lookup.html#secmgr">access checks</a>.
2095 * Determines a trustable caller class to compare with refc, the symbolic reference class.
2096 * If this lookup object has private access, then the caller class is the lookupClass.
2097 */
2098 void checkSecurityManager(Class<?> refc, MemberName m) {
2099 SecurityManager smgr = System.getSecurityManager();
2100 if (smgr == null) return;
2101 if (allowedModes == TRUSTED) return;
2102
2103 // Step 1:
2104 boolean fullPowerLookup = hasPrivateAccess();
2105 if (!fullPowerLookup ||
2106 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
2107 ReflectUtil.checkPackageAccess(refc);
2108 }
2109
2110 if (m == null) { // findClass or accessClass
2111 // Step 2b:
2112 if (!fullPowerLookup) {
2113 smgr.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
2114 }
2115 return;
2116 }
2117
2118 // Step 2a:
2119 if (m.isPublic()) return;
2120 if (!fullPowerLookup) {
2121 smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION);
2122 }
2123
2124 // Step 3:
2125 Class<?> defc = m.getDeclaringClass();
2126 if (!fullPowerLookup && defc != refc) {
2127 ReflectUtil.checkPackageAccess(defc);
2128 }
2129 }
2130
2131 void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
2132 boolean wantStatic = (refKind == REF_invokeStatic);
2133 String message;
2134 if (m.isConstructor())
2135 message = "expected a method, not a constructor";
2136 else if (!m.isMethod())
2137 message = "expected a method";
2138 else if (wantStatic != m.isStatic())
2139 message = wantStatic ? "expected a static method" : "expected a non-static method";
2140 else
2141 { checkAccess(refKind, refc, m); return; }
2142 throw m.makeAccessException(message, this);
2143 }
2144
2145 void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
2146 boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
2147 String message;
2148 if (wantStatic != m.isStatic())
2149 message = wantStatic ? "expected a static field" : "expected a non-static field";
2150 else
2151 { checkAccess(refKind, refc, m); return; }
2152 throw m.makeAccessException(message, this);
2153 }
2154
2155 /** Check public/protected/private bits on the symbolic reference class and its member. */
2156 void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
2157 assert(m.referenceKindIsConsistentWith(refKind) &&
2158 MethodHandleNatives.refKindIsValid(refKind) &&
2159 (MethodHandleNatives.refKindIsField(refKind) == m.isField()));
2160 int allowedModes = this.allowedModes;
2161 if (allowedModes == TRUSTED) return;
2162 int mods = m.getModifiers();
2163 if (Modifier.isProtected(mods) &&
2164 refKind == REF_invokeVirtual &&
2165 m.getDeclaringClass() == Object.class &&
2166 m.getName().equals("clone") &&
2167 refc.isArray()) {
2168 // The JVM does this hack also.
2169 // (See ClassVerifier::verify_invoke_instructions
2170 // and LinkResolver::check_method_accessability.)
2171 // Because the JVM does not allow separate methods on array types,
2172 // there is no separate method for int[].clone.
2173 // All arrays simply inherit Object.clone.
2174 // But for access checking logic, we make Object.clone
2175 // (normally protected) appear to be public.
2176 // Later on, when the DirectMethodHandle is created,
2177 // its leading argument will be restricted to the
2178 // requested array type.
2179 // N.B. The return type is not adjusted, because
2180 // that is *not* the bytecode behavior.
2181 mods ^= Modifier.PROTECTED | Modifier.PUBLIC;
2182 }
2183 if (Modifier.isProtected(mods) && refKind == REF_newInvokeSpecial) {
2184 // cannot "new" a protected ctor in a different package
2185 mods ^= Modifier.PROTECTED;
2186 }
2187 if (Modifier.isFinal(mods) &&
2188 MethodHandleNatives.refKindIsSetter(refKind))
2189 throw m.makeAccessException("unexpected set of a final field", this);
2190 int requestedModes = fixmods(mods); // adjust 0 => PACKAGE
2191 if ((requestedModes & allowedModes) != 0) {
2192 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
2193 mods, lookupClass(), allowedModes))
2194 return;
2195 } else {
2196 // Protected members can also be checked as if they were package-private.
2197 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
2198 && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
2199 return;
2200 }
2201 throw m.makeAccessException(accessFailedMessage(refc, m), this);
2202 }
2203
2204 String accessFailedMessage(Class<?> refc, MemberName m) {
2205 Class<?> defc = m.getDeclaringClass();
2206 int mods = m.getModifiers();
2207 // check the class first:
2208 boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
2209 (defc == refc ||
2210 Modifier.isPublic(refc.getModifiers())));
2211 if (!classOK && (allowedModes & PACKAGE) != 0) {
2212 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), FULL_POWER_MODES) &&
2213 (defc == refc ||
2214 VerifyAccess.isClassAccessible(refc, lookupClass(), FULL_POWER_MODES)));
2215 }
2216 if (!classOK)
2217 return "class is not public";
2218 if (Modifier.isPublic(mods))
2219 return "access to public member failed"; // (how?, module not readable?)
2220 if (Modifier.isPrivate(mods))
2221 return "member is private";
2222 if (Modifier.isProtected(mods))
2223 return "member is protected";
2224 return "member is private to package";
2225 }
2226
2227 private static final boolean ALLOW_NESTMATE_ACCESS = false;
2228
2229 private void checkSpecialCaller(Class<?> specialCaller, Class<?> refc) throws IllegalAccessException {
2230 int allowedModes = this.allowedModes;
2231 if (allowedModes == TRUSTED) return;
2232 if (!hasPrivateAccess()
2233 || (specialCaller != lookupClass()
2234 // ensure non-abstract methods in superinterfaces can be special-invoked
2235 && !(refc != null && refc.isInterface() && refc.isAssignableFrom(specialCaller))
2236 && !(ALLOW_NESTMATE_ACCESS &&
2237 VerifyAccess.isSamePackageMember(specialCaller, lookupClass()))))
2238 throw new MemberName(specialCaller).
2239 makeAccessException("no private access for invokespecial", this);
2240 }
2241
2242 private boolean restrictProtectedReceiver(MemberName method) {
2243 // The accessing class only has the right to use a protected member
2244 // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc.
2245 if (!method.isProtected() || method.isStatic()
2246 || allowedModes == TRUSTED
2247 || method.getDeclaringClass() == lookupClass()
2248 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass())
2249 || (ALLOW_NESTMATE_ACCESS &&
2250 VerifyAccess.isSamePackageMember(method.getDeclaringClass(), lookupClass())))
2251 return false;
2252 return true;
2253 }
2254 private MethodHandle restrictReceiver(MemberName method, DirectMethodHandle mh, Class<?> caller) throws IllegalAccessException {
2255 assert(!method.isStatic());
2256 // receiver type of mh is too wide; narrow to caller
2257 if (!method.getDeclaringClass().isAssignableFrom(caller)) {
2258 throw method.makeAccessException("caller class must be a subclass below the method", caller);
2259 }
2260 MethodType rawType = mh.type();
2261 if (caller.isAssignableFrom(rawType.parameterType(0))) return mh; // no need to restrict; already narrow
2262 MethodType narrowType = rawType.changeParameterType(0, caller);
2263 assert(!mh.isVarargsCollector()); // viewAsType will lose varargs-ness
2264 assert(mh.viewAsTypeChecks(narrowType, true));
2265 return mh.copyWith(narrowType, mh.form);
2266 }
2267
2268 /** Check access and get the requested method. */
2269 private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
2270 final boolean doRestrict = true;
2271 final boolean checkSecurity = true;
2272 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
2273 }
2274 /** Check access and get the requested method, for invokespecial with no restriction on the application of narrowing rules. */
2275 private MethodHandle getDirectMethodNoRestrictInvokeSpecial(Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
2276 final boolean doRestrict = false;
2277 final boolean checkSecurity = true;
2278 return getDirectMethodCommon(REF_invokeSpecial, refc, method, checkSecurity, doRestrict, callerClass);
2279 }
2280 /** Check access and get the requested method, eliding security manager checks. */
2281 private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
2282 final boolean doRestrict = true;
2283 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
2284 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
2285 }
2286 /** Common code for all methods; do not call directly except from immediately above. */
2287 private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method,
2288 boolean checkSecurity,
2289 boolean doRestrict, Class<?> callerClass) throws IllegalAccessException {
2290 checkMethod(refKind, refc, method);
2291 // Optionally check with the security manager; this isn't needed for unreflect* calls.
2292 if (checkSecurity)
2293 checkSecurityManager(refc, method);
2294 assert(!method.isMethodHandleInvoke());
2295
2296 if (refKind == REF_invokeSpecial &&
2297 refc != lookupClass() &&
2298 !refc.isInterface() &&
2299 refc != lookupClass().getSuperclass() &&
2300 refc.isAssignableFrom(lookupClass())) {
2301 assert(!method.getName().equals("<init>")); // not this code path
2302 // Per JVMS 6.5, desc. of invokespecial instruction:
2303 // If the method is in a superclass of the LC,
2304 // and if our original search was above LC.super,
2305 // repeat the search (symbolic lookup) from LC.super
2306 // and continue with the direct superclass of that class,
2307 // and so forth, until a match is found or no further superclasses exist.
2308 // FIXME: MemberName.resolve should handle this instead.
2309 Class<?> refcAsSuper = lookupClass();
2310 MemberName m2;
2311 do {
2312 refcAsSuper = refcAsSuper.getSuperclass();
2313 m2 = new MemberName(refcAsSuper,
2314 method.getName(),
2315 method.getMethodType(),
2316 REF_invokeSpecial);
2317 m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull());
2318 } while (m2 == null && // no method is found yet
2319 refc != refcAsSuper); // search up to refc
2320 if (m2 == null) throw new InternalError(method.toString());
2321 method = m2;
2322 refc = refcAsSuper;
2323 // redo basic checks
2324 checkMethod(refKind, refc, method);
2325 }
2326
2327 DirectMethodHandle dmh = DirectMethodHandle.make(refKind, refc, method);
2328 MethodHandle mh = dmh;
2329 // Optionally narrow the receiver argument to refc using restrictReceiver.
2330 if ((doRestrict && refKind == REF_invokeSpecial) ||
2331 (MethodHandleNatives.refKindHasReceiver(refKind) && restrictProtectedReceiver(method))) {
2332 mh = restrictReceiver(method, dmh, lookupClass());
2333 }
2334 mh = maybeBindCaller(method, mh, callerClass);
2335 mh = mh.setVarargs(method);
2336 return mh;
2337 }
2338 private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh,
2339 Class<?> callerClass)
2340 throws IllegalAccessException {
2341 if (allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method))
2342 return mh;
2343 Class<?> hostClass = lookupClass;
2344 if (!hasPrivateAccess()) // caller must have private access
2345 hostClass = callerClass; // callerClass came from a security manager style stack walk
2346 MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, hostClass);
2347 // Note: caller will apply varargs after this step happens.
2348 return cbmh;
2349 }
2350 /** Check access and get the requested field. */
2351 private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
2352 final boolean checkSecurity = true;
2353 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
2354 }
2355 /** Check access and get the requested field, eliding security manager checks. */
2356 private MethodHandle getDirectFieldNoSecurityManager(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
2357 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
2358 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
2359 }
2360 /** Common code for all fields; do not call directly except from immediately above. */
2361 private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field,
2362 boolean checkSecurity) throws IllegalAccessException {
2363 checkField(refKind, refc, field);
2364 // Optionally check with the security manager; this isn't needed for unreflect* calls.
2365 if (checkSecurity)
2366 checkSecurityManager(refc, field);
2367 DirectMethodHandle dmh = DirectMethodHandle.make(refc, field);
2368 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) &&
2369 restrictProtectedReceiver(field));
2370 if (doRestrict)
2371 return restrictReceiver(field, dmh, lookupClass());
2372 return dmh;
2373 }
2374 private VarHandle getFieldVarHandle(byte getRefKind, byte putRefKind,
2375 Class<?> refc, MemberName getField, MemberName putField)
2376 throws IllegalAccessException {
2377 final boolean checkSecurity = true;
2378 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
2379 }
2380 private VarHandle getFieldVarHandleNoSecurityManager(byte getRefKind, byte putRefKind,
2381 Class<?> refc, MemberName getField, MemberName putField)
2382 throws IllegalAccessException {
2383 final boolean checkSecurity = false;
2384 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
2385 }
2386 private VarHandle getFieldVarHandleCommon(byte getRefKind, byte putRefKind,
2387 Class<?> refc, MemberName getField, MemberName putField,
2388 boolean checkSecurity) throws IllegalAccessException {
2389 assert getField.isStatic() == putField.isStatic();
2390 assert getField.isGetter() && putField.isSetter();
2391 assert MethodHandleNatives.refKindIsStatic(getRefKind) == MethodHandleNatives.refKindIsStatic(putRefKind);
2392 assert MethodHandleNatives.refKindIsGetter(getRefKind) && MethodHandleNatives.refKindIsSetter(putRefKind);
2393
2394 checkField(getRefKind, refc, getField);
2395 if (checkSecurity)
2396 checkSecurityManager(refc, getField);
2397
2398 if (!putField.isFinal()) {
2399 // A VarHandle does not support updates to final fields, any
2400 // such VarHandle to a final field will be read-only and
2401 // therefore the following write-based accessibility checks are
2402 // only required for non-final fields
2403 checkField(putRefKind, refc, putField);
2404 if (checkSecurity)
2405 checkSecurityManager(refc, putField);
2406 }
2407
2408 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(getRefKind) &&
2409 restrictProtectedReceiver(getField));
2410 if (doRestrict) {
2411 assert !getField.isStatic();
2412 // receiver type of VarHandle is too wide; narrow to caller
2413 if (!getField.getDeclaringClass().isAssignableFrom(lookupClass())) {
2414 throw getField.makeAccessException("caller class must be a subclass below the method", lookupClass());
2415 }
2416 refc = lookupClass();
2417 }
2418 return VarHandles.makeFieldHandle(getField, refc, getField.getFieldType(), this.allowedModes == TRUSTED);
2419 }
2420 /** Check access and get the requested constructor. */
2421 private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException {
2422 final boolean checkSecurity = true;
2423 return getDirectConstructorCommon(refc, ctor, checkSecurity);
2424 }
2425 /** Check access and get the requested constructor, eliding security manager checks. */
2426 private MethodHandle getDirectConstructorNoSecurityManager(Class<?> refc, MemberName ctor) throws IllegalAccessException {
2427 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
2428 return getDirectConstructorCommon(refc, ctor, checkSecurity);
2429 }
2430 /** Common code for all constructors; do not call directly except from immediately above. */
2431 private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor,
2432 boolean checkSecurity) throws IllegalAccessException {
2433 assert(ctor.isConstructor());
2434 checkAccess(REF_newInvokeSpecial, refc, ctor);
2435 // Optionally check with the security manager; this isn't needed for unreflect* calls.
2436 if (checkSecurity)
2437 checkSecurityManager(refc, ctor);
2438 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
2439 return DirectMethodHandle.make(ctor).setVarargs(ctor);
2440 }
2441
2442 /** Hook called from the JVM (via MethodHandleNatives) to link MH constants:
2443 */
2444 /*non-public*/
2445 MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type) throws ReflectiveOperationException {
2446 if (!(type instanceof Class || type instanceof MethodType))
2447 throw new InternalError("unresolved MemberName");
2448 MemberName member = new MemberName(refKind, defc, name, type);
2449 MethodHandle mh = LOOKASIDE_TABLE.get(member);
2450 if (mh != null) {
2451 checkSymbolicClass(defc);
2452 return mh;
2453 }
2454 // Treat MethodHandle.invoke and invokeExact specially.
2455 if (defc == MethodHandle.class && refKind == REF_invokeVirtual) {
2456 mh = findVirtualForMH(member.getName(), member.getMethodType());
2457 if (mh != null) {
2458 return mh;
2459 }
2460 }
2461 MemberName resolved = resolveOrFail(refKind, member);
2462 mh = getDirectMethodForConstant(refKind, defc, resolved);
2463 if (mh instanceof DirectMethodHandle
2464 && canBeCached(refKind, defc, resolved)) {
2465 MemberName key = mh.internalMemberName();
2466 if (key != null) {
2467 key = key.asNormalOriginal();
2468 }
2469 if (member.equals(key)) { // better safe than sorry
2470 LOOKASIDE_TABLE.put(key, (DirectMethodHandle) mh);
2471 }
2472 }
2473 return mh;
2474 }
2475 private
2476 boolean canBeCached(byte refKind, Class<?> defc, MemberName member) {
2477 if (refKind == REF_invokeSpecial) {
2478 return false;
2479 }
2480 if (!Modifier.isPublic(defc.getModifiers()) ||
2481 !Modifier.isPublic(member.getDeclaringClass().getModifiers()) ||
2482 !member.isPublic() ||
2483 member.isCallerSensitive()) {
2484 return false;
2485 }
2486 ClassLoader loader = defc.getClassLoader();
2487 if (!jdk.internal.misc.VM.isSystemDomainLoader(loader)) {
2488 ClassLoader sysl = ClassLoader.getSystemClassLoader();
2489 boolean found = false;
2490 while (sysl != null) {
2491 if (loader == sysl) { found = true; break; }
2492 sysl = sysl.getParent();
2493 }
2494 if (!found) {
2495 return false;
2496 }
2497 }
2498 try {
2499 MemberName resolved2 = publicLookup().resolveOrFail(refKind,
2500 new MemberName(refKind, defc, member.getName(), member.getType()));
2501 checkSecurityManager(defc, resolved2);
2502 } catch (ReflectiveOperationException | SecurityException ex) {
2503 return false;
2504 }
2505 return true;
2506 }
2507 private
2508 MethodHandle getDirectMethodForConstant(byte refKind, Class<?> defc, MemberName member)
2509 throws ReflectiveOperationException {
2510 if (MethodHandleNatives.refKindIsField(refKind)) {
2511 return getDirectFieldNoSecurityManager(refKind, defc, member);
2512 } else if (MethodHandleNatives.refKindIsMethod(refKind)) {
2513 return getDirectMethodNoSecurityManager(refKind, defc, member, lookupClass);
2514 } else if (refKind == REF_newInvokeSpecial) {
2515 return getDirectConstructorNoSecurityManager(defc, member);
2516 }
2517 // oops
2518 throw newIllegalArgumentException("bad MethodHandle constant #"+member);
2519 }
2520
2521 static ConcurrentHashMap<MemberName, DirectMethodHandle> LOOKASIDE_TABLE = new ConcurrentHashMap<>();
2522 }
2523
2524 /**
2525 * Produces a method handle constructing arrays of a desired type.
2526 * The return type of the method handle will be the array type.
2527 * The type of its sole argument will be {@code int}, which specifies the size of the array.
2528 * @param arrayClass an array type
2529 * @return a method handle which can create arrays of the given type
2530 * @throws NullPointerException if the argument is {@code null}
2531 * @throws IllegalArgumentException if {@code arrayClass} is not an array type
2532 * @see java.lang.reflect.Array#newInstance(Class, int)
2533 * @since 9
2534 */
2535 public static
2536 MethodHandle arrayConstructor(Class<?> arrayClass) throws IllegalArgumentException {
2537 if (!arrayClass.isArray()) {
2538 throw newIllegalArgumentException("not an array class: " + arrayClass.getName());
2539 }
2540 ValueType<?> compValue = valueComponent(arrayClass);
2541 if (compValue != null) {
2542 return compValue.newArray();
2543 } else {
2544 MethodHandle ani = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_Array_newInstance).
2545 bindTo(arrayClass.getComponentType());
2546 return ani.asType(ani.type().changeReturnType(arrayClass));
2547 }
2548 }
2549
2550 /**
2551 * Produces a method handle returning the length of an array.
2552 * The type of the method handle will have {@code int} as return type,
2553 * and its sole argument will be the array type.
2554 * @param arrayClass an array type
2555 * @return a method handle which can retrieve the length of an array of the given array type
2556 * @throws NullPointerException if the argument is {@code null}
2557 * @throws IllegalArgumentException if arrayClass is not an array type
2558 * @since 9
2559 */
2560 public static
2561 MethodHandle arrayLength(Class<?> arrayClass) throws IllegalArgumentException {
2562 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.LENGTH);
2563 }
2564
2565 /**
2566 * Produces a method handle giving read access to elements of an array.
2567 * The type of the method handle will have a return type of the array's
2568 * element type. Its first argument will be the array type,
2569 * and the second will be {@code int}.
2570 * @param arrayClass an array type
2571 * @return a method handle which can load values from the given array type
2572 * @throws NullPointerException if the argument is null
2573 * @throws IllegalArgumentException if arrayClass is not an array type
2574 */
2575 public static
2576 MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException {
2577 ValueType<?> compValue = valueComponent(arrayClass);
2578 return (compValue != null) ?
2579 compValue.arrayGetter() :
2580 MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.GET);
2581 }
2582
2583 /**
2584 * Produces a method handle giving write access to elements of an array.
2585 * The type of the method handle will have a void return type.
2586 * Its last argument will be the array's element type.
2587 * The first and second arguments will be the array type and int.
2588 * @param arrayClass the class of an array
2589 * @return a method handle which can store values into the array type
2590 * @throws NullPointerException if the argument is null
2591 * @throws IllegalArgumentException if arrayClass is not an array type
2592 */
2593 public static
2594 MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException {
2595 ValueType<?> compValue = valueComponent(arrayClass);
2596 return (compValue != null) ?
2597 compValue.arraySetter() :
2598 MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.SET);
2599 }
2600
2601 @SuppressWarnings("unchecked")
2602 private static <Z> ValueType<Z> valueComponent(Class<Z> clazz) {
2603 Class<?> comp = clazz.getComponentType();
2604 if (MinimalValueTypes_1_0.isValueType(comp)) {
2605 return (ValueType<Z>)ValueType.forClass(MinimalValueTypes_1_0.getValueCapableClass(comp));
2606 } else {
2607 return null;
2608 }
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 * @apiNote
2636 * Bitwise comparison of {@code float} values or {@code double} values,
2637 * as performed by the numeric and atomic update access modes, differ
2638 * from the primitive {@code ==} operator and the {@link Float#equals}
2639 * and {@link Double#equals} methods, specifically with respect to
2640 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
2641 * Care should be taken when performing a compare and set or a compare
2642 * and exchange operation with such values since the operation may
2643 * unexpectedly fail.
2644 * There are many possible NaN values that are considered to be
2645 * {@code NaN} in Java, although no IEEE 754 floating-point operation
2646 * provided by Java can distinguish between them. Operation failure can
2647 * occur if the expected or witness value is a NaN value and it is
2648 * transformed (perhaps in a platform specific manner) into another NaN
2649 * value, and thus has a different bitwise representation (see
2650 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
2651 * details).
2652 * The values {@code -0.0} and {@code +0.0} have different bitwise
2653 * representations but are considered equal when using the primitive
2654 * {@code ==} operator. Operation failure can occur if, for example, a
2655 * numeric algorithm computes an expected value to be say {@code -0.0}
2656 * and previously computed the witness value to be say {@code +0.0}.
2657 * @param arrayClass the class of an array, of type {@code T[]}
2658 * @return a VarHandle giving access to elements of an array
2659 * @throws NullPointerException if the arrayClass is null
2660 * @throws IllegalArgumentException if arrayClass is not an array type
2661 * @since 9
2662 */
2663 public static
2664 VarHandle arrayElementVarHandle(Class<?> arrayClass) throws IllegalArgumentException {
2665 return VarHandles.makeArrayElementHandle(arrayClass);
2666 }
2667
2668 /**
2669 * Produces a VarHandle giving access to elements of a {@code byte[]} array
2670 * viewed as if it were a different primitive array type, such as
2671 * {@code int[]} or {@code long[]}.
2672 * The VarHandle's variable type is the component type of
2673 * {@code viewArrayClass} and the list of coordinate types is
2674 * {@code (byte[], int)}, where the {@code int} coordinate type
2675 * corresponds to an argument that is an index into a {@code byte[]} array.
2676 * The returned VarHandle accesses bytes at an index in a {@code byte[]}
2677 * array, composing bytes to or from a value of the component type of
2678 * {@code viewArrayClass} according to the given endianness.
2679 * <p>
2680 * The supported component types (variables types) are {@code short},
2681 * {@code char}, {@code int}, {@code long}, {@code float} and
2682 * {@code double}.
2683 * <p>
2684 * Access of bytes at a given index will result in an
2685 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
2686 * or greater than the {@code byte[]} array length minus the size (in bytes)
2687 * of {@code T}.
2688 * <p>
2689 * Access of bytes at an index may be aligned or misaligned for {@code T},
2690 * with respect to the underlying memory address, {@code A} say, associated
2691 * with the array and index.
2692 * If access is misaligned then access for anything other than the
2693 * {@code get} and {@code set} access modes will result in an
2694 * {@code IllegalStateException}. In such cases atomic access is only
2695 * guaranteed with respect to the largest power of two that divides the GCD
2696 * of {@code A} and the size (in bytes) of {@code T}.
2697 * If access is aligned then following access modes are supported and are
2698 * guaranteed to support atomic access:
2699 * <ul>
2700 * <li>read write access modes for all {@code T}, with the exception of
2701 * access modes {@code get} and {@code set} for {@code long} and
2702 * {@code double} on 32-bit platforms.
2703 * <li>atomic update access modes for {@code int}, {@code long},
2704 * {@code float} or {@code double}.
2705 * (Future major platform releases of the JDK may support additional
2706 * types for certain currently unsupported access modes.)
2707 * <li>numeric atomic update access modes for {@code int} and {@code long}.
2708 * (Future major platform releases of the JDK may support additional
2709 * numeric types for certain currently unsupported access modes.)
2710 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
2711 * (Future major platform releases of the JDK may support additional
2712 * numeric types for certain currently unsupported access modes.)
2713 * </ul>
2714 * <p>
2715 * Misaligned access, and therefore atomicity guarantees, may be determined
2716 * for {@code byte[]} arrays without operating on a specific array. Given
2717 * an {@code index}, {@code T} and it's corresponding boxed type,
2718 * {@code T_BOX}, misalignment may be determined as follows:
2719 * <pre>{@code
2720 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
2721 * int misalignedAtZeroIndex = ByteBuffer.wrap(new byte[0]).
2722 * alignmentOffset(0, sizeOfT);
2723 * int misalignedAtIndex = (misalignedAtZeroIndex + index) % sizeOfT;
2724 * boolean isMisaligned = misalignedAtIndex != 0;
2725 * }</pre>
2726 * <p>
2727 * If the variable type is {@code float} or {@code double} then atomic
2728 * update access modes compare values using their bitwise representation
2729 * (see {@link Float#floatToRawIntBits} and
2730 * {@link Double#doubleToRawLongBits}, respectively).
2731 * @param viewArrayClass the view array class, with a component type of
2732 * type {@code T}
2733 * @param byteOrder the endianness of the view array elements, as
2734 * stored in the underlying {@code byte} array
2735 * @return a VarHandle giving access to elements of a {@code byte[]} array
2736 * viewed as if elements corresponding to the components type of the view
2737 * array class
2738 * @throws NullPointerException if viewArrayClass or byteOrder is null
2739 * @throws IllegalArgumentException if viewArrayClass is not an array type
2740 * @throws UnsupportedOperationException if the component type of
2741 * viewArrayClass is not supported as a variable type
2742 * @since 9
2743 */
2744 public static
2745 VarHandle byteArrayViewVarHandle(Class<?> viewArrayClass,
2746 ByteOrder byteOrder) throws IllegalArgumentException {
2747 Objects.requireNonNull(byteOrder);
2748 return VarHandles.byteArrayViewHandle(viewArrayClass,
2749 byteOrder == ByteOrder.BIG_ENDIAN);
2750 }
2751
2752 /**
2753 * Produces a VarHandle giving access to elements of a {@code ByteBuffer}
2754 * viewed as if it were an array of elements of a different primitive
2755 * component type to that of {@code byte}, such as {@code int[]} or
2756 * {@code long[]}.
2757 * The VarHandle's variable type is the component type of
2758 * {@code viewArrayClass} and the list of coordinate types is
2759 * {@code (ByteBuffer, int)}, where the {@code int} coordinate type
2760 * corresponds to an argument that is an index into a {@code byte[]} array.
2761 * The returned VarHandle accesses bytes at an index in a
2762 * {@code ByteBuffer}, composing bytes to or from a value of the component
2763 * type of {@code viewArrayClass} according to the given endianness.
2764 * <p>
2765 * The supported component types (variables types) are {@code short},
2766 * {@code char}, {@code int}, {@code long}, {@code float} and
2767 * {@code double}.
2768 * <p>
2769 * Access will result in a {@code ReadOnlyBufferException} for anything
2770 * other than the read access modes if the {@code ByteBuffer} is read-only.
2771 * <p>
2772 * Access of bytes at a given index will result in an
2773 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
2774 * or greater than the {@code ByteBuffer} limit minus the size (in bytes) of
2775 * {@code T}.
2776 * <p>
2777 * Access of bytes at an index may be aligned or misaligned for {@code T},
2778 * with respect to the underlying memory address, {@code A} say, associated
2779 * with the {@code ByteBuffer} and index.
2780 * If access is misaligned then access for anything other than the
2781 * {@code get} and {@code set} access modes will result in an
2782 * {@code IllegalStateException}. In such cases atomic access is only
2783 * guaranteed with respect to the largest power of two that divides the GCD
2784 * of {@code A} and the size (in bytes) of {@code T}.
2785 * If access is aligned then following access modes are supported and are
2786 * guaranteed to support atomic access:
2787 * <ul>
2788 * <li>read write access modes for all {@code T}, with the exception of
2789 * access modes {@code get} and {@code set} for {@code long} and
2790 * {@code double} on 32-bit platforms.
2791 * <li>atomic update access modes for {@code int}, {@code long},
2792 * {@code float} or {@code double}.
2793 * (Future major platform releases of the JDK may support additional
2794 * types for certain currently unsupported access modes.)
2795 * <li>numeric atomic update access modes for {@code int} and {@code long}.
2796 * (Future major platform releases of the JDK may support additional
2797 * numeric types for certain currently unsupported access modes.)
2798 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
2799 * (Future major platform releases of the JDK may support additional
2800 * numeric types for certain currently unsupported access modes.)
2801 * </ul>
2802 * <p>
2803 * Misaligned access, and therefore atomicity guarantees, may be determined
2804 * for a {@code ByteBuffer}, {@code bb} (direct or otherwise), an
2805 * {@code index}, {@code T} and it's corresponding boxed type,
2806 * {@code T_BOX}, as follows:
2807 * <pre>{@code
2808 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
2809 * ByteBuffer bb = ...
2810 * int misalignedAtIndex = bb.alignmentOffset(index, sizeOfT);
2811 * boolean isMisaligned = misalignedAtIndex != 0;
2812 * }</pre>
2813 * <p>
2814 * If the variable type is {@code float} or {@code double} then atomic
2815 * update access modes compare values using their bitwise representation
2816 * (see {@link Float#floatToRawIntBits} and
2817 * {@link Double#doubleToRawLongBits}, respectively).
2818 * @param viewArrayClass the view array class, with a component type of
2819 * type {@code T}
2820 * @param byteOrder the endianness of the view array elements, as
2821 * stored in the underlying {@code ByteBuffer} (Note this overrides the
2822 * endianness of a {@code ByteBuffer})
2823 * @return a VarHandle giving access to elements of a {@code ByteBuffer}
2824 * viewed as if elements corresponding to the components type of the view
2825 * array class
2826 * @throws NullPointerException if viewArrayClass or byteOrder is null
2827 * @throws IllegalArgumentException if viewArrayClass is not an array type
2828 * @throws UnsupportedOperationException if the component type of
2829 * viewArrayClass is not supported as a variable type
2830 * @since 9
2831 */
2832 public static
2833 VarHandle byteBufferViewVarHandle(Class<?> viewArrayClass,
2834 ByteOrder byteOrder) throws IllegalArgumentException {
2835 Objects.requireNonNull(byteOrder);
2836 return VarHandles.makeByteBufferViewHandle(viewArrayClass,
2837 byteOrder == ByteOrder.BIG_ENDIAN);
2838 }
2839
2840
2841 /// method handle invocation (reflective style)
2842
2843 /**
2844 * Produces a method handle which will invoke any method handle of the
2845 * given {@code type}, with a given number of trailing arguments replaced by
2846 * a single trailing {@code Object[]} array.
2847 * The resulting invoker will be a method handle with the following
2848 * arguments:
2849 * <ul>
2850 * <li>a single {@code MethodHandle} target
2851 * <li>zero or more leading values (counted by {@code leadingArgCount})
2852 * <li>an {@code Object[]} array containing trailing arguments
2853 * </ul>
2854 * <p>
2855 * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
2856 * the indicated {@code type}.
2857 * That is, if the target is exactly of the given {@code type}, it will behave
2858 * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
2859 * is used to convert the target to the required {@code type}.
2860 * <p>
2861 * The type of the returned invoker will not be the given {@code type}, but rather
2862 * will have all parameters except the first {@code leadingArgCount}
2863 * replaced by a single array of type {@code Object[]}, which will be
2864 * the final parameter.
2865 * <p>
2866 * Before invoking its target, the invoker will spread the final array, apply
2867 * reference casts as necessary, and unbox and widen primitive arguments.
2868 * If, when the invoker is called, the supplied array argument does
2869 * not have the correct number of elements, the invoker will throw
2870 * an {@link IllegalArgumentException} instead of invoking the target.
2871 * <p>
2872 * This method is equivalent to the following code (though it may be more efficient):
2873 * <blockquote><pre>{@code
2874 MethodHandle invoker = MethodHandles.invoker(type);
2875 int spreadArgCount = type.parameterCount() - leadingArgCount;
2876 invoker = invoker.asSpreader(Object[].class, spreadArgCount);
2877 return invoker;
2878 * }</pre></blockquote>
2879 * This method throws no reflective or security exceptions.
2880 * @param type the desired target type
2881 * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
2882 * @return a method handle suitable for invoking any method handle of the given type
2883 * @throws NullPointerException if {@code type} is null
2884 * @throws IllegalArgumentException if {@code leadingArgCount} is not in
2885 * the range from 0 to {@code type.parameterCount()} inclusive,
2886 * or if the resulting method handle's type would have
2887 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2888 */
2889 public static
2890 MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
2891 if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
2892 throw newIllegalArgumentException("bad argument count", leadingArgCount);
2893 type = type.asSpreaderType(Object[].class, leadingArgCount, type.parameterCount() - leadingArgCount);
2894 return type.invokers().spreadInvoker(leadingArgCount);
2895 }
2896
2897 /**
2898 * Produces a special <em>invoker method handle</em> which can be used to
2899 * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
2900 * The resulting invoker will have a type which is
2901 * exactly equal to the desired type, except that it will accept
2902 * an additional leading argument of type {@code MethodHandle}.
2903 * <p>
2904 * This method is equivalent to the following code (though it may be more efficient):
2905 * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)}
2906 *
2907 * <p style="font-size:smaller;">
2908 * <em>Discussion:</em>
2909 * Invoker method handles can be useful when working with variable method handles
2910 * of unknown types.
2911 * For example, to emulate an {@code invokeExact} call to a variable method
2912 * handle {@code M}, extract its type {@code T},
2913 * look up the invoker method {@code X} for {@code T},
2914 * and call the invoker method, as {@code X.invoke(T, A...)}.
2915 * (It would not work to call {@code X.invokeExact}, since the type {@code T}
2916 * is unknown.)
2917 * If spreading, collecting, or other argument transformations are required,
2918 * they can be applied once to the invoker {@code X} and reused on many {@code M}
2919 * method handle values, as long as they are compatible with the type of {@code X}.
2920 * <p style="font-size:smaller;">
2921 * <em>(Note: The invoker method is not available via the Core Reflection API.
2922 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
2923 * on the declared {@code invokeExact} or {@code invoke} method will raise an
2924 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
2925 * <p>
2926 * This method throws no reflective or security exceptions.
2927 * @param type the desired target type
2928 * @return a method handle suitable for invoking any method handle of the given type
2929 * @throws IllegalArgumentException if the resulting method handle's type would have
2930 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2931 */
2932 public static
2933 MethodHandle exactInvoker(MethodType type) {
2934 return type.invokers().exactInvoker();
2935 }
2936
2937 /**
2938 * Produces a special <em>invoker method handle</em> which can be used to
2939 * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
2940 * The resulting invoker will have a type which is
2941 * exactly equal to the desired type, except that it will accept
2942 * an additional leading argument of type {@code MethodHandle}.
2943 * <p>
2944 * Before invoking its target, if the target differs from the expected type,
2945 * the invoker will apply reference casts as
2946 * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
2947 * Similarly, the return value will be converted as necessary.
2948 * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
2949 * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
2950 * <p>
2951 * This method is equivalent to the following code (though it may be more efficient):
2952 * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)}
2953 * <p style="font-size:smaller;">
2954 * <em>Discussion:</em>
2955 * A {@linkplain MethodType#genericMethodType general method type} is one which
2956 * mentions only {@code Object} arguments and return values.
2957 * An invoker for such a type is capable of calling any method handle
2958 * of the same arity as the general type.
2959 * <p style="font-size:smaller;">
2960 * <em>(Note: The invoker method is not available via the Core Reflection API.
2961 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
2962 * on the declared {@code invokeExact} or {@code invoke} method will raise an
2963 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
2964 * <p>
2965 * This method throws no reflective or security exceptions.
2966 * @param type the desired target type
2967 * @return a method handle suitable for invoking any method handle convertible to the given type
2968 * @throws IllegalArgumentException if the resulting method handle's type would have
2969 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2970 */
2971 public static
2972 MethodHandle invoker(MethodType type) {
2973 return type.invokers().genericInvoker();
2974 }
2975
2976 /**
2977 * Produces a special <em>invoker method handle</em> which can be used to
2978 * invoke a signature-polymorphic access mode method on any VarHandle whose
2979 * associated access mode type is compatible with the given type.
2980 * The resulting invoker will have a type which is exactly equal to the
2981 * desired given type, except that it will accept an additional leading
2982 * argument of type {@code VarHandle}.
2983 *
2984 * @param accessMode the VarHandle access mode
2985 * @param type the desired target type
2986 * @return a method handle suitable for invoking an access mode method of
2987 * any VarHandle whose access mode type is of the given type.
2988 * @since 9
2989 */
2990 static public
2991 MethodHandle varHandleExactInvoker(VarHandle.AccessMode accessMode, MethodType type) {
2992 return type.invokers().varHandleMethodExactInvoker(accessMode);
2993 }
2994
2995 /**
2996 * Produces a special <em>invoker method handle</em> which can be used to
2997 * invoke a signature-polymorphic access mode method on any VarHandle whose
2998 * associated access mode type is compatible with the given type.
2999 * The resulting invoker will have a type which is exactly equal to the
3000 * desired given type, except that it will accept an additional leading
3001 * argument of type {@code VarHandle}.
3002 * <p>
3003 * Before invoking its target, if the access mode type differs from the
3004 * desired given type, the invoker will apply reference casts as necessary
3005 * and box, unbox, or widen primitive values, as if by
3006 * {@link MethodHandle#asType asType}. Similarly, the return value will be
3007 * converted as necessary.
3008 * <p>
3009 * This method is equivalent to the following code (though it may be more
3010 * efficient): {@code publicLookup().findVirtual(VarHandle.class, accessMode.name(), type)}
3011 *
3012 * @param accessMode the VarHandle access mode
3013 * @param type the desired target type
3014 * @return a method handle suitable for invoking an access mode method of
3015 * any VarHandle whose access mode type is convertible to the given
3016 * type.
3017 * @since 9
3018 */
3019 static public
3020 MethodHandle varHandleInvoker(VarHandle.AccessMode accessMode, MethodType type) {
3021 return type.invokers().varHandleMethodInvoker(accessMode);
3022 }
3023
3024 static /*non-public*/
3025 MethodHandle basicInvoker(MethodType type) {
3026 return type.invokers().basicInvoker();
3027 }
3028
3029 /// method handle modification (creation from other method handles)
3030
3031 /**
3032 * Produces a method handle which adapts the type of the
3033 * given method handle to a new type by pairwise argument and return type conversion.
3034 * The original type and new type must have the same number of arguments.
3035 * The resulting method handle is guaranteed to report a type
3036 * which is equal to the desired new type.
3037 * <p>
3038 * If the original type and new type are equal, returns target.
3039 * <p>
3040 * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
3041 * and some additional conversions are also applied if those conversions fail.
3042 * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied
3043 * if possible, before or instead of any conversions done by {@code asType}:
3044 * <ul>
3045 * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type,
3046 * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast.
3047 * (This treatment of interfaces follows the usage of the bytecode verifier.)
3048 * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive,
3049 * the boolean is converted to a byte value, 1 for true, 0 for false.
3050 * (This treatment follows the usage of the bytecode verifier.)
3051 * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive,
3052 * <em>T0</em> is converted to byte via Java casting conversion (JLS 5.5),
3053 * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}.
3054 * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean,
3055 * then a Java casting conversion (JLS 5.5) is applied.
3056 * (Specifically, <em>T0</em> will convert to <em>T1</em> by
3057 * widening and/or narrowing.)
3058 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
3059 * conversion will be applied at runtime, possibly followed
3060 * by a Java casting conversion (JLS 5.5) on the primitive value,
3061 * possibly followed by a conversion from byte to boolean by testing
3062 * the low-order bit.
3063 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive,
3064 * and if the reference is null at runtime, a zero value is introduced.
3065 * </ul>
3066 * @param target the method handle to invoke after arguments are retyped
3067 * @param newType the expected type of the new method handle
3068 * @return a method handle which delegates to the target after performing
3069 * any necessary argument conversions, and arranges for any
3070 * necessary return value conversions
3071 * @throws NullPointerException if either argument is null
3072 * @throws WrongMethodTypeException if the conversion cannot be made
3073 * @see MethodHandle#asType
3074 */
3075 public static
3076 MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
3077 explicitCastArgumentsChecks(target, newType);
3078 // use the asTypeCache when possible:
3079 MethodType oldType = target.type();
3080 if (oldType == newType) return target;
3081 if (oldType.explicitCastEquivalentToAsType(newType)) {
3082 return target.asFixedArity().asType(newType);
3083 }
3084 return MethodHandleImpl.makePairwiseConvert(target, newType, false);
3085 }
3086
3087 private static void explicitCastArgumentsChecks(MethodHandle target, MethodType newType) {
3088 if (target.type().parameterCount() != newType.parameterCount()) {
3089 throw new WrongMethodTypeException("cannot explicitly cast " + target + " to " + newType);
3090 }
3091 }
3092
3093 /**
3094 * Produces a method handle which adapts the calling sequence of the
3095 * given method handle to a new type, by reordering the arguments.
3096 * The resulting method handle is guaranteed to report a type
3097 * which is equal to the desired new type.
3098 * <p>
3099 * The given array controls the reordering.
3100 * Call {@code #I} the number of incoming parameters (the value
3101 * {@code newType.parameterCount()}, and call {@code #O} the number
3102 * of outgoing parameters (the value {@code target.type().parameterCount()}).
3103 * Then the length of the reordering array must be {@code #O},
3104 * and each element must be a non-negative number less than {@code #I}.
3105 * For every {@code N} less than {@code #O}, the {@code N}-th
3106 * outgoing argument will be taken from the {@code I}-th incoming
3107 * argument, where {@code I} is {@code reorder[N]}.
3108 * <p>
3109 * No argument or return value conversions are applied.
3110 * The type of each incoming argument, as determined by {@code newType},
3111 * must be identical to the type of the corresponding outgoing parameter
3112 * or parameters in the target method handle.
3113 * The return type of {@code newType} must be identical to the return
3114 * type of the original target.
3115 * <p>
3116 * The reordering array need not specify an actual permutation.
3117 * An incoming argument will be duplicated if its index appears
3118 * more than once in the array, and an incoming argument will be dropped
3119 * if its index does not appear in the array.
3120 * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
3121 * incoming arguments which are not mentioned in the reordering array
3122 * may be of any type, as determined only by {@code newType}.
3123 * <blockquote><pre>{@code
3124 import static java.lang.invoke.MethodHandles.*;
3125 import static java.lang.invoke.MethodType.*;
3126 ...
3127 MethodType intfn1 = methodType(int.class, int.class);
3128 MethodType intfn2 = methodType(int.class, int.class, int.class);
3129 MethodHandle sub = ... (int x, int y) -> (x-y) ...;
3130 assert(sub.type().equals(intfn2));
3131 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
3132 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
3133 assert((int)rsub.invokeExact(1, 100) == 99);
3134 MethodHandle add = ... (int x, int y) -> (x+y) ...;
3135 assert(add.type().equals(intfn2));
3136 MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
3137 assert(twice.type().equals(intfn1));
3138 assert((int)twice.invokeExact(21) == 42);
3139 * }</pre></blockquote>
3140 * <p>
3141 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3142 * variable-arity method handle}, even if the original target method handle was.
3143 * @param target the method handle to invoke after arguments are reordered
3144 * @param newType the expected type of the new method handle
3145 * @param reorder an index array which controls the reordering
3146 * @return a method handle which delegates to the target after it
3147 * drops unused arguments and moves and/or duplicates the other arguments
3148 * @throws NullPointerException if any argument is null
3149 * @throws IllegalArgumentException if the index array length is not equal to
3150 * the arity of the target, or if any index array element
3151 * not a valid index for a parameter of {@code newType},
3152 * or if two corresponding parameter types in
3153 * {@code target.type()} and {@code newType} are not identical,
3154 */
3155 public static
3156 MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
3157 reorder = reorder.clone(); // get a private copy
3158 MethodType oldType = target.type();
3159 permuteArgumentChecks(reorder, newType, oldType);
3160 // first detect dropped arguments and handle them separately
3161 int[] originalReorder = reorder;
3162 BoundMethodHandle result = target.rebind();
3163 LambdaForm form = result.form;
3164 int newArity = newType.parameterCount();
3165 // Normalize the reordering into a real permutation,
3166 // by removing duplicates and adding dropped elements.
3167 // This somewhat improves lambda form caching, as well
3168 // as simplifying the transform by breaking it up into steps.
3169 for (int ddIdx; (ddIdx = findFirstDupOrDrop(reorder, newArity)) != 0; ) {
3170 if (ddIdx > 0) {
3171 // We found a duplicated entry at reorder[ddIdx].
3172 // Example: (x,y,z)->asList(x,y,z)
3173 // permuted by [1*,0,1] => (a0,a1)=>asList(a1,a0,a1)
3174 // permuted by [0,1,0*] => (a0,a1)=>asList(a0,a1,a0)
3175 // The starred element corresponds to the argument
3176 // deleted by the dupArgumentForm transform.
3177 int srcPos = ddIdx, dstPos = srcPos, dupVal = reorder[srcPos];
3178 boolean killFirst = false;
3179 for (int val; (val = reorder[--dstPos]) != dupVal; ) {
3180 // Set killFirst if the dup is larger than an intervening position.
3181 // This will remove at least one inversion from the permutation.
3182 if (dupVal > val) killFirst = true;
3183 }
3184 if (!killFirst) {
3185 srcPos = dstPos;
3186 dstPos = ddIdx;
3187 }
3188 form = form.editor().dupArgumentForm(1 + srcPos, 1 + dstPos);
3189 assert (reorder[srcPos] == reorder[dstPos]);
3190 oldType = oldType.dropParameterTypes(dstPos, dstPos + 1);
3191 // contract the reordering by removing the element at dstPos
3192 int tailPos = dstPos + 1;
3193 System.arraycopy(reorder, tailPos, reorder, dstPos, reorder.length - tailPos);
3194 reorder = Arrays.copyOf(reorder, reorder.length - 1);
3195 } else {
3196 int dropVal = ~ddIdx, insPos = 0;
3197 while (insPos < reorder.length && reorder[insPos] < dropVal) {
3198 // Find first element of reorder larger than dropVal.
3199 // This is where we will insert the dropVal.
3200 insPos += 1;
3201 }
3202 Class<?> ptype = newType.parameterType(dropVal);
3203 form = form.editor().addArgumentForm(1 + insPos, BasicType.basicType(ptype));
3204 oldType = oldType.insertParameterTypes(insPos, ptype);
3205 // expand the reordering by inserting an element at insPos
3206 int tailPos = insPos + 1;
3207 reorder = Arrays.copyOf(reorder, reorder.length + 1);
3208 System.arraycopy(reorder, insPos, reorder, tailPos, reorder.length - tailPos);
3209 reorder[insPos] = dropVal;
3210 }
3211 assert (permuteArgumentChecks(reorder, newType, oldType));
3212 }
3213 assert (reorder.length == newArity); // a perfect permutation
3214 // Note: This may cache too many distinct LFs. Consider backing off to varargs code.
3215 form = form.editor().permuteArgumentsForm(1, reorder);
3216 if (newType == result.type() && form == result.internalForm())
3217 return result;
3218 return result.copyWith(newType, form);
3219 }
3220
3221 /**
3222 * Return an indication of any duplicate or omission in reorder.
3223 * If the reorder contains a duplicate entry, return the index of the second occurrence.
3224 * Otherwise, return ~(n), for the first n in [0..newArity-1] that is not present in reorder.
3225 * Otherwise, return zero.
3226 * If an element not in [0..newArity-1] is encountered, return reorder.length.
3227 */
3228 private static int findFirstDupOrDrop(int[] reorder, int newArity) {
3229 final int BIT_LIMIT = 63; // max number of bits in bit mask
3230 if (newArity < BIT_LIMIT) {
3231 long mask = 0;
3232 for (int i = 0; i < reorder.length; i++) {
3233 int arg = reorder[i];
3234 if (arg >= newArity) {
3235 return reorder.length;
3236 }
3237 long bit = 1L << arg;
3238 if ((mask & bit) != 0) {
3239 return i; // >0 indicates a dup
3240 }
3241 mask |= bit;
3242 }
3243 if (mask == (1L << newArity) - 1) {
3244 assert(Long.numberOfTrailingZeros(Long.lowestOneBit(~mask)) == newArity);
3245 return 0;
3246 }
3247 // find first zero
3248 long zeroBit = Long.lowestOneBit(~mask);
3249 int zeroPos = Long.numberOfTrailingZeros(zeroBit);
3250 assert(zeroPos <= newArity);
3251 if (zeroPos == newArity) {
3252 return 0;
3253 }
3254 return ~zeroPos;
3255 } else {
3256 // same algorithm, different bit set
3257 BitSet mask = new BitSet(newArity);
3258 for (int i = 0; i < reorder.length; i++) {
3259 int arg = reorder[i];
3260 if (arg >= newArity) {
3261 return reorder.length;
3262 }
3263 if (mask.get(arg)) {
3264 return i; // >0 indicates a dup
3265 }
3266 mask.set(arg);
3267 }
3268 int zeroPos = mask.nextClearBit(0);
3269 assert(zeroPos <= newArity);
3270 if (zeroPos == newArity) {
3271 return 0;
3272 }
3273 return ~zeroPos;
3274 }
3275 }
3276
3277 private static boolean permuteArgumentChecks(int[] reorder, MethodType newType, MethodType oldType) {
3278 if (newType.returnType() != oldType.returnType())
3279 throw newIllegalArgumentException("return types do not match",
3280 oldType, newType);
3281 if (reorder.length == oldType.parameterCount()) {
3282 int limit = newType.parameterCount();
3283 boolean bad = false;
3284 for (int j = 0; j < reorder.length; j++) {
3285 int i = reorder[j];
3286 if (i < 0 || i >= limit) {
3287 bad = true; break;
3288 }
3289 Class<?> src = newType.parameterType(i);
3290 Class<?> dst = oldType.parameterType(j);
3291 if (src != dst)
3292 throw newIllegalArgumentException("parameter types do not match after reorder",
3293 oldType, newType);
3294 }
3295 if (!bad) return true;
3296 }
3297 throw newIllegalArgumentException("bad reorder array: "+Arrays.toString(reorder));
3298 }
3299
3300 /**
3301 * Produces a method handle of the requested return type which returns the given
3302 * constant value every time it is invoked.
3303 * <p>
3304 * Before the method handle is returned, the passed-in value is converted to the requested type.
3305 * If the requested type is primitive, widening primitive conversions are attempted,
3306 * else reference conversions are attempted.
3307 * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
3308 * @param type the return type of the desired method handle
3309 * @param value the value to return
3310 * @return a method handle of the given return type and no arguments, which always returns the given value
3311 * @throws NullPointerException if the {@code type} argument is null
3312 * @throws ClassCastException if the value cannot be converted to the required return type
3313 * @throws IllegalArgumentException if the given type is {@code void.class}
3314 */
3315 public static
3316 MethodHandle constant(Class<?> type, Object value) {
3317 if (type.isPrimitive()) {
3318 if (type == void.class)
3319 throw newIllegalArgumentException("void type");
3320 Wrapper w = Wrapper.forPrimitiveType(type);
3321 value = w.convert(value, type);
3322 if (w.zero().equals(value))
3323 return zero(w, type);
3324 return insertArguments(identity(type), 0, value);
3325 } else {
3326 if (value == null)
3327 return zero(Wrapper.OBJECT, type);
3328 return identity(type).bindTo(value);
3329 }
3330 }
3331
3332 /**
3333 * Produces a method handle which returns its sole argument when invoked.
3334 * @param type the type of the sole parameter and return value of the desired method handle
3335 * @return a unary method handle which accepts and returns the given type
3336 * @throws NullPointerException if the argument is null
3337 * @throws IllegalArgumentException if the given type is {@code void.class}
3338 */
3339 public static
3340 MethodHandle identity(Class<?> type) {
3341 Wrapper btw = (type.isPrimitive() ? Wrapper.forPrimitiveType(type) : Wrapper.OBJECT);
3342 int pos = btw.ordinal();
3343 MethodHandle ident = IDENTITY_MHS[pos];
3344 if (ident == null) {
3345 ident = setCachedMethodHandle(IDENTITY_MHS, pos, makeIdentity(btw.primitiveType()));
3346 }
3347 if (ident.type().returnType() == type)
3348 return ident;
3349 // something like identity(Foo.class); do not bother to intern these
3350 assert (btw == Wrapper.OBJECT);
3351 return makeIdentity(type);
3352 }
3353
3354 /**
3355 * Produces a constant method handle of the requested return type which
3356 * returns the default value for that type every time it is invoked.
3357 * The resulting constant method handle will have no side effects.
3358 * <p>The returned method handle is equivalent to {@code empty(methodType(type))}.
3359 * It is also equivalent to {@code explicitCastArguments(constant(Object.class, null), methodType(type))},
3360 * since {@code explicitCastArguments} converts {@code null} to default values.
3361 * @param type the expected return type of the desired method handle
3362 * @return a constant method handle that takes no arguments
3363 * and returns the default value of the given type (or void, if the type is void)
3364 * @throws NullPointerException if the argument is null
3365 * @see MethodHandles#constant
3366 * @see MethodHandles#empty
3367 * @see MethodHandles#explicitCastArguments
3368 * @since 9
3369 */
3370 public static MethodHandle zero(Class<?> type) {
3371 Objects.requireNonNull(type);
3372 if (type.isPrimitive()) {
3373 return zero(Wrapper.forPrimitiveType(type), type);
3374 } else if (MinimalValueTypes_1_0.isValueType(type)) {
3375 return ValueType.forClass(MinimalValueTypes_1_0.getValueCapableClass(type)).defaultValueConstant();
3376 } else {
3377 return zero(Wrapper.OBJECT, type);
3378 }
3379 }
3380
3381 private static MethodHandle identityOrVoid(Class<?> type) {
3382 return type == void.class ? zero(type) : identity(type);
3383 }
3384
3385 /**
3386 * Produces a method handle of the requested type which ignores any arguments, does nothing,
3387 * and returns a suitable default depending on the return type.
3388 * That is, it returns a zero primitive value, a {@code null}, or {@code void}.
3389 * <p>The returned method handle is equivalent to
3390 * {@code dropArguments(zero(type.returnType()), 0, type.parameterList())}.
3391 * <p>
3392 * @apiNote Given a predicate and target, a useful "if-then" construct can be produced as
3393 * {@code guardWithTest(pred, target, empty(target.type())}.
3394 * @param type the type of the desired method handle
3395 * @return a constant method handle of the given type, which returns a default value of the given return type
3396 * @throws NullPointerException if the argument is null
3397 * @see MethodHandles#zero
3398 * @see MethodHandles#constant
3399 * @since 9
3400 */
3401 public static MethodHandle empty(MethodType type) {
3402 Objects.requireNonNull(type);
3403 return dropArguments(zero(type.returnType()), 0, type.parameterList());
3404 }
3405
3406 private static final MethodHandle[] IDENTITY_MHS = new MethodHandle[Wrapper.COUNT];
3407 private static MethodHandle makeIdentity(Class<?> ptype) {
3408 if (!MinimalValueTypes_1_0.isValueType(ptype)) {
3409 MethodType mtype = MethodType.methodType(ptype, ptype);
3410 LambdaForm lform = LambdaForm.identityForm(BasicType.basicType(ptype));
3411 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.IDENTITY);
3412 } else {
3413 return ValueType.forClass(MinimalValueTypes_1_0.getValueCapableClass(ptype)).identity();
3414 }
3415 }
3416
3417 private static MethodHandle zero(Wrapper btw, Class<?> rtype) {
3418 int pos = btw.ordinal();
3419 MethodHandle zero = ZERO_MHS[pos];
3420 if (zero == null) {
3421 zero = setCachedMethodHandle(ZERO_MHS, pos, makeZero(btw.primitiveType()));
3422 }
3423 if (zero.type().returnType() == rtype)
3424 return zero;
3425 assert(btw == Wrapper.OBJECT);
3426 return makeZero(rtype);
3427 }
3428 private static final MethodHandle[] ZERO_MHS = new MethodHandle[Wrapper.COUNT];
3429 private static MethodHandle makeZero(Class<?> rtype) {
3430 MethodType mtype = methodType(rtype);
3431 LambdaForm lform = LambdaForm.zeroForm(BasicType.basicType(rtype));
3432 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.ZERO);
3433 }
3434
3435 private static synchronized MethodHandle setCachedMethodHandle(MethodHandle[] cache, int pos, MethodHandle value) {
3436 // Simulate a CAS, to avoid racy duplication of results.
3437 MethodHandle prev = cache[pos];
3438 if (prev != null) return prev;
3439 return cache[pos] = value;
3440 }
3441
3442 /**
3443 * Provides a target method handle with one or more <em>bound arguments</em>
3444 * in advance of the method handle's invocation.
3445 * The formal parameters to the target corresponding to the bound
3446 * arguments are called <em>bound parameters</em>.
3447 * Returns a new method handle which saves away the bound arguments.
3448 * When it is invoked, it receives arguments for any non-bound parameters,
3449 * binds the saved arguments to their corresponding parameters,
3450 * and calls the original target.
3451 * <p>
3452 * The type of the new method handle will drop the types for the bound
3453 * parameters from the original target type, since the new method handle
3454 * will no longer require those arguments to be supplied by its callers.
3455 * <p>
3456 * Each given argument object must match the corresponding bound parameter type.
3457 * If a bound parameter type is a primitive, the argument object
3458 * must be a wrapper, and will be unboxed to produce the primitive value.
3459 * <p>
3460 * The {@code pos} argument selects which parameters are to be bound.
3461 * It may range between zero and <i>N-L</i> (inclusively),
3462 * where <i>N</i> is the arity of the target method handle
3463 * and <i>L</i> is the length of the values array.
3464 * <p>
3465 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3466 * variable-arity method handle}, even if the original target method handle was.
3467 * @param target the method handle to invoke after the argument is inserted
3468 * @param pos where to insert the argument (zero for the first)
3469 * @param values the series of arguments to insert
3470 * @return a method handle which inserts an additional argument,
3471 * before calling the original method handle
3472 * @throws NullPointerException if the target or the {@code values} array is null
3473 * @see MethodHandle#bindTo
3474 */
3475 public static
3476 MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
3477 int insCount = values.length;
3478 Class<?>[] ptypes = insertArgumentsChecks(target, insCount, pos);
3479 if (insCount == 0) return target;
3480 BoundMethodHandle result = target.rebind();
3481 for (int i = 0; i < insCount; i++) {
3482 Object value = values[i];
3483 Class<?> ptype = ptypes[pos+i];
3484 if (ptype.isPrimitive()) {
3485 result = insertArgumentPrimitive(result, pos, ptype, value);
3486 } else {
3487 value = ptype.cast(value); // throw CCE if needed
3488 result = result.bindArgumentL(pos, value);
3489 }
3490 }
3491 return result;
3492 }
3493
3494 private static BoundMethodHandle insertArgumentPrimitive(BoundMethodHandle result, int pos,
3495 Class<?> ptype, Object value) {
3496 Wrapper w = Wrapper.forPrimitiveType(ptype);
3497 // perform unboxing and/or primitive conversion
3498 value = w.convert(value, ptype);
3499 switch (w) {
3500 case INT: return result.bindArgumentI(pos, (int)value);
3501 case LONG: return result.bindArgumentJ(pos, (long)value);
3502 case FLOAT: return result.bindArgumentF(pos, (float)value);
3503 case DOUBLE: return result.bindArgumentD(pos, (double)value);
3504 default: return result.bindArgumentI(pos, ValueConversions.widenSubword(value));
3505 }
3506 }
3507
3508 private static Class<?>[] insertArgumentsChecks(MethodHandle target, int insCount, int pos) throws RuntimeException {
3509 MethodType oldType = target.type();
3510 int outargs = oldType.parameterCount();
3511 int inargs = outargs - insCount;
3512 if (inargs < 0)
3513 throw newIllegalArgumentException("too many values to insert");
3514 if (pos < 0 || pos > inargs)
3515 throw newIllegalArgumentException("no argument type to append");
3516 return oldType.ptypes();
3517 }
3518
3519 /**
3520 * Produces a method handle which will discard some dummy arguments
3521 * before calling some other specified <i>target</i> method handle.
3522 * The type of the new method handle will be the same as the target's type,
3523 * except it will also include the dummy argument types,
3524 * at some given position.
3525 * <p>
3526 * The {@code pos} argument may range between zero and <i>N</i>,
3527 * where <i>N</i> is the arity of the target.
3528 * If {@code pos} is zero, the dummy arguments will precede
3529 * the target's real arguments; if {@code pos} is <i>N</i>
3530 * they will come after.
3531 * <p>
3532 * <b>Example:</b>
3533 * <blockquote><pre>{@code
3534 import static java.lang.invoke.MethodHandles.*;
3535 import static java.lang.invoke.MethodType.*;
3536 ...
3537 MethodHandle cat = lookup().findVirtual(String.class,
3538 "concat", methodType(String.class, String.class));
3539 assertEquals("xy", (String) cat.invokeExact("x", "y"));
3540 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
3541 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
3542 assertEquals(bigType, d0.type());
3543 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
3544 * }</pre></blockquote>
3545 * <p>
3546 * This method is also equivalent to the following code:
3547 * <blockquote><pre>
3548 * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))}
3549 * </pre></blockquote>
3550 * @param target the method handle to invoke after the arguments are dropped
3551 * @param valueTypes the type(s) of the argument(s) to drop
3552 * @param pos position of first argument to drop (zero for the leftmost)
3553 * @return a method handle which drops arguments of the given types,
3554 * before calling the original method handle
3555 * @throws NullPointerException if the target is null,
3556 * or if the {@code valueTypes} list or any of its elements is null
3557 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
3558 * or if {@code pos} is negative or greater than the arity of the target,
3559 * or if the new method handle's type would have too many parameters
3560 */
3561 public static
3562 MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) {
3563 return dropArguments0(target, pos, copyTypes(valueTypes.toArray()));
3564 }
3565
3566 private static List<Class<?>> copyTypes(Object[] array) {
3567 return Arrays.asList(Arrays.copyOf(array, array.length, Class[].class));
3568 }
3569
3570 private static
3571 MethodHandle dropArguments0(MethodHandle target, int pos, List<Class<?>> valueTypes) {
3572 MethodType oldType = target.type(); // get NPE
3573 int dropped = dropArgumentChecks(oldType, pos, valueTypes);
3574 MethodType newType = oldType.insertParameterTypes(pos, valueTypes);
3575 if (dropped == 0) return target;
3576 BoundMethodHandle result = target.rebind();
3577 LambdaForm lform = result.form;
3578 int insertFormArg = 1 + pos;
3579 for (Class<?> ptype : valueTypes) {
3580 lform = lform.editor().addArgumentForm(insertFormArg++, BasicType.basicType(ptype));
3581 }
3582 result = result.copyWith(newType, lform);
3583 return result;
3584 }
3585
3586 private static int dropArgumentChecks(MethodType oldType, int pos, List<Class<?>> valueTypes) {
3587 int dropped = valueTypes.size();
3588 MethodType.checkSlotCount(dropped);
3589 int outargs = oldType.parameterCount();
3590 int inargs = outargs + dropped;
3591 if (pos < 0 || pos > outargs)
3592 throw newIllegalArgumentException("no argument type to remove"
3593 + Arrays.asList(oldType, pos, valueTypes, inargs, outargs)
3594 );
3595 return dropped;
3596 }
3597
3598 /**
3599 * Produces a method handle which will discard some dummy arguments
3600 * before calling some other specified <i>target</i> method handle.
3601 * The type of the new method handle will be the same as the target's type,
3602 * except it will also include the dummy argument types,
3603 * at some given position.
3604 * <p>
3605 * The {@code pos} argument may range between zero and <i>N</i>,
3606 * where <i>N</i> is the arity of the target.
3607 * If {@code pos} is zero, the dummy arguments will precede
3608 * the target's real arguments; if {@code pos} is <i>N</i>
3609 * they will come after.
3610 * @apiNote
3611 * <blockquote><pre>{@code
3612 import static java.lang.invoke.MethodHandles.*;
3613 import static java.lang.invoke.MethodType.*;
3614 ...
3615 MethodHandle cat = lookup().findVirtual(String.class,
3616 "concat", methodType(String.class, String.class));
3617 assertEquals("xy", (String) cat.invokeExact("x", "y"));
3618 MethodHandle d0 = dropArguments(cat, 0, String.class);
3619 assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
3620 MethodHandle d1 = dropArguments(cat, 1, String.class);
3621 assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
3622 MethodHandle d2 = dropArguments(cat, 2, String.class);
3623 assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
3624 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
3625 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
3626 * }</pre></blockquote>
3627 * <p>
3628 * This method is also equivalent to the following code:
3629 * <blockquote><pre>
3630 * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))}
3631 * </pre></blockquote>
3632 * @param target the method handle to invoke after the arguments are dropped
3633 * @param valueTypes the type(s) of the argument(s) to drop
3634 * @param pos position of first argument to drop (zero for the leftmost)
3635 * @return a method handle which drops arguments of the given types,
3636 * before calling the original method handle
3637 * @throws NullPointerException if the target is null,
3638 * or if the {@code valueTypes} array or any of its elements is null
3639 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
3640 * or if {@code pos} is negative or greater than the arity of the target,
3641 * or if the new method handle's type would have
3642 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3643 */
3644 public static
3645 MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
3646 return dropArguments0(target, pos, copyTypes(valueTypes));
3647 }
3648
3649 // private version which allows caller some freedom with error handling
3650 private static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos,
3651 boolean nullOnFailure) {
3652 newTypes = copyTypes(newTypes.toArray());
3653 List<Class<?>> oldTypes = target.type().parameterList();
3654 int match = oldTypes.size();
3655 if (skip != 0) {
3656 if (skip < 0 || skip > match) {
3657 throw newIllegalArgumentException("illegal skip", skip, target);
3658 }
3659 oldTypes = oldTypes.subList(skip, match);
3660 match -= skip;
3661 }
3662 List<Class<?>> addTypes = newTypes;
3663 int add = addTypes.size();
3664 if (pos != 0) {
3665 if (pos < 0 || pos > add) {
3666 throw newIllegalArgumentException("illegal pos", pos, newTypes);
3667 }
3668 addTypes = addTypes.subList(pos, add);
3669 add -= pos;
3670 assert(addTypes.size() == add);
3671 }
3672 // Do not add types which already match the existing arguments.
3673 if (match > add || !oldTypes.equals(addTypes.subList(0, match))) {
3674 if (nullOnFailure) {
3675 return null;
3676 }
3677 throw newIllegalArgumentException("argument lists do not match", oldTypes, newTypes);
3678 }
3679 addTypes = addTypes.subList(match, add);
3680 add -= match;
3681 assert(addTypes.size() == add);
3682 // newTypes: ( P*[pos], M*[match], A*[add] )
3683 // target: ( S*[skip], M*[match] )
3684 MethodHandle adapter = target;
3685 if (add > 0) {
3686 adapter = dropArguments0(adapter, skip+ match, addTypes);
3687 }
3688 // adapter: (S*[skip], M*[match], A*[add] )
3689 if (pos > 0) {
3690 adapter = dropArguments0(adapter, skip, newTypes.subList(0, pos));
3691 }
3692 // adapter: (S*[skip], P*[pos], M*[match], A*[add] )
3693 return adapter;
3694 }
3695
3696 /**
3697 * Adapts a target method handle to match the given parameter type list. If necessary, adds dummy arguments. Some
3698 * leading parameters can be skipped before matching begins. The remaining types in the {@code target}'s parameter
3699 * type list must be a sub-list of the {@code newTypes} type list at the starting position {@code pos}. The
3700 * resulting handle will have the target handle's parameter type list, with any non-matching parameter types (before
3701 * or after the matching sub-list) inserted in corresponding positions of the target's original parameters, as if by
3702 * {@link #dropArguments(MethodHandle, int, Class[])}.
3703 * <p>
3704 * The resulting handle will have the same return type as the target handle.
3705 * <p>
3706 * In more formal terms, assume these two type lists:<ul>
3707 * <li>The target handle has the parameter type list {@code S..., M...}, with as many types in {@code S} as
3708 * indicated by {@code skip}. The {@code M} types are those that are supposed to match part of the given type list,
3709 * {@code newTypes}.
3710 * <li>The {@code newTypes} list contains types {@code P..., M..., A...}, with as many types in {@code P} as
3711 * indicated by {@code pos}. The {@code M} types are precisely those that the {@code M} types in the target handle's
3712 * parameter type list are supposed to match. The types in {@code A} are additional types found after the matching
3713 * sub-list.
3714 * </ul>
3715 * Given these assumptions, the result of an invocation of {@code dropArgumentsToMatch} will have the parameter type
3716 * list {@code S..., P..., M..., A...}, with the {@code P} and {@code A} types inserted as if by
3717 * {@link #dropArguments(MethodHandle, int, Class[])}.
3718 * <p>
3719 * @apiNote
3720 * Two method handles whose argument lists are "effectively identical" (i.e., identical in a common prefix) may be
3721 * mutually converted to a common type by two calls to {@code dropArgumentsToMatch}, as follows:
3722 * <blockquote><pre>{@code
3723 import static java.lang.invoke.MethodHandles.*;
3724 import static java.lang.invoke.MethodType.*;
3725 ...
3726 ...
3727 MethodHandle h0 = constant(boolean.class, true);
3728 MethodHandle h1 = lookup().findVirtual(String.class, "concat", methodType(String.class, String.class));
3729 MethodType bigType = h1.type().insertParameterTypes(1, String.class, int.class);
3730 MethodHandle h2 = dropArguments(h1, 0, bigType.parameterList());
3731 if (h1.type().parameterCount() < h2.type().parameterCount())
3732 h1 = dropArgumentsToMatch(h1, 0, h2.type().parameterList(), 0); // lengthen h1
3733 else
3734 h2 = dropArgumentsToMatch(h2, 0, h1.type().parameterList(), 0); // lengthen h2
3735 MethodHandle h3 = guardWithTest(h0, h1, h2);
3736 assertEquals("xy", h3.invoke("x", "y", 1, "a", "b", "c"));
3737 * }</pre></blockquote>
3738 * @param target the method handle to adapt
3739 * @param skip number of targets parameters to disregard (they will be unchanged)
3740 * @param newTypes the list of types to match {@code target}'s parameter type list to
3741 * @param pos place in {@code newTypes} where the non-skipped target parameters must occur
3742 * @return a possibly adapted method handle
3743 * @throws NullPointerException if either argument is null
3744 * @throws IllegalArgumentException if any element of {@code newTypes} is {@code void.class},
3745 * or if {@code skip} is negative or greater than the arity of the target,
3746 * or if {@code pos} is negative or greater than the newTypes list size,
3747 * or if {@code newTypes} does not contain the {@code target}'s non-skipped parameter types at position
3748 * {@code pos}.
3749 * @since 9
3750 */
3751 public static
3752 MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos) {
3753 Objects.requireNonNull(target);
3754 Objects.requireNonNull(newTypes);
3755 return dropArgumentsToMatch(target, skip, newTypes, pos, false);
3756 }
3757
3758 /**
3759 * Adapts a target method handle by pre-processing
3760 * one or more of its arguments, each with its own unary filter function,
3761 * and then calling the target with each pre-processed argument
3762 * replaced by the result of its corresponding filter function.
3763 * <p>
3764 * The pre-processing is performed by one or more method handles,
3765 * specified in the elements of the {@code filters} array.
3766 * The first element of the filter array corresponds to the {@code pos}
3767 * argument of the target, and so on in sequence.
3768 * <p>
3769 * Null arguments in the array are treated as identity functions,
3770 * and the corresponding arguments left unchanged.
3771 * (If there are no non-null elements in the array, the original target is returned.)
3772 * Each filter is applied to the corresponding argument of the adapter.
3773 * <p>
3774 * If a filter {@code F} applies to the {@code N}th argument of
3775 * the target, then {@code F} must be a method handle which
3776 * takes exactly one argument. The type of {@code F}'s sole argument
3777 * replaces the corresponding argument type of the target
3778 * in the resulting adapted method handle.
3779 * The return type of {@code F} must be identical to the corresponding
3780 * parameter type of the target.
3781 * <p>
3782 * It is an error if there are elements of {@code filters}
3783 * (null or not)
3784 * which do not correspond to argument positions in the target.
3785 * <p><b>Example:</b>
3786 * <blockquote><pre>{@code
3787 import static java.lang.invoke.MethodHandles.*;
3788 import static java.lang.invoke.MethodType.*;
3789 ...
3790 MethodHandle cat = lookup().findVirtual(String.class,
3791 "concat", methodType(String.class, String.class));
3792 MethodHandle upcase = lookup().findVirtual(String.class,
3793 "toUpperCase", methodType(String.class));
3794 assertEquals("xy", (String) cat.invokeExact("x", "y"));
3795 MethodHandle f0 = filterArguments(cat, 0, upcase);
3796 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
3797 MethodHandle f1 = filterArguments(cat, 1, upcase);
3798 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
3799 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
3800 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
3801 * }</pre></blockquote>
3802 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
3803 * denotes the return type of both the {@code target} and resulting adapter.
3804 * {@code P}/{@code p} and {@code B}/{@code b} represent the types and values
3805 * of the parameters and arguments that precede and follow the filter position
3806 * {@code pos}, respectively. {@code A[i]}/{@code a[i]} stand for the types and
3807 * values of the filtered parameters and arguments; they also represent the
3808 * return types of the {@code filter[i]} handles. The latter accept arguments
3809 * {@code v[i]} of type {@code V[i]}, which also appear in the signature of
3810 * the resulting adapter.
3811 * <blockquote><pre>{@code
3812 * T target(P... p, A[i]... a[i], B... b);
3813 * A[i] filter[i](V[i]);
3814 * T adapter(P... p, V[i]... v[i], B... b) {
3815 * return target(p..., filter[i](v[i])..., b...);
3816 * }
3817 * }</pre></blockquote>
3818 * <p>
3819 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3820 * variable-arity method handle}, even if the original target method handle was.
3821 *
3822 * @param target the method handle to invoke after arguments are filtered
3823 * @param pos the position of the first argument to filter
3824 * @param filters method handles to call initially on filtered arguments
3825 * @return method handle which incorporates the specified argument filtering logic
3826 * @throws NullPointerException if the target is null
3827 * or if the {@code filters} array is null
3828 * @throws IllegalArgumentException if a non-null element of {@code filters}
3829 * does not match a corresponding argument type of target as described above,
3830 * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()},
3831 * or if the resulting method handle's type would have
3832 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3833 */
3834 public static
3835 MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
3836 filterArgumentsCheckArity(target, pos, filters);
3837 MethodHandle adapter = target;
3838 int curPos = pos-1; // pre-incremented
3839 for (MethodHandle filter : filters) {
3840 curPos += 1;
3841 if (filter == null) continue; // ignore null elements of filters
3842 adapter = filterArgument(adapter, curPos, filter);
3843 }
3844 return adapter;
3845 }
3846
3847 /*non-public*/ static
3848 MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
3849 filterArgumentChecks(target, pos, filter);
3850 MethodType targetType = target.type();
3851 MethodType filterType = filter.type();
3852 BoundMethodHandle result = target.rebind();
3853 Class<?> newParamType = filterType.parameterType(0);
3854 LambdaForm lform = result.editor().filterArgumentForm(1 + pos, BasicType.basicType(newParamType));
3855 MethodType newType = targetType.changeParameterType(pos, newParamType);
3856 result = result.copyWithExtendL(newType, lform, filter);
3857 return result;
3858 }
3859
3860 private static void filterArgumentsCheckArity(MethodHandle target, int pos, MethodHandle[] filters) {
3861 MethodType targetType = target.type();
3862 int maxPos = targetType.parameterCount();
3863 if (pos + filters.length > maxPos)
3864 throw newIllegalArgumentException("too many filters");
3865 }
3866
3867 private static void filterArgumentChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
3868 MethodType targetType = target.type();
3869 MethodType filterType = filter.type();
3870 if (filterType.parameterCount() != 1
3871 || filterType.returnType() != targetType.parameterType(pos))
3872 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
3873 }
3874
3875 /**
3876 * Adapts a target method handle by pre-processing
3877 * a sub-sequence of its arguments with a filter (another method handle).
3878 * The pre-processed arguments are replaced by the result (if any) of the
3879 * filter function.
3880 * The target is then called on the modified (usually shortened) argument list.
3881 * <p>
3882 * If the filter returns a value, the target must accept that value as
3883 * its argument in position {@code pos}, preceded and/or followed by
3884 * any arguments not passed to the filter.
3885 * If the filter returns void, the target must accept all arguments
3886 * not passed to the filter.
3887 * No arguments are reordered, and a result returned from the filter
3888 * replaces (in order) the whole subsequence of arguments originally
3889 * passed to the adapter.
3890 * <p>
3891 * The argument types (if any) of the filter
3892 * replace zero or one argument types of the target, at position {@code pos},
3893 * in the resulting adapted method handle.
3894 * The return type of the filter (if any) must be identical to the
3895 * argument type of the target at position {@code pos}, and that target argument
3896 * is supplied by the return value of the filter.
3897 * <p>
3898 * In all cases, {@code pos} must be greater than or equal to zero, and
3899 * {@code pos} must also be less than or equal to the target's arity.
3900 * <p><b>Example:</b>
3901 * <blockquote><pre>{@code
3902 import static java.lang.invoke.MethodHandles.*;
3903 import static java.lang.invoke.MethodType.*;
3904 ...
3905 MethodHandle deepToString = publicLookup()
3906 .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
3907
3908 MethodHandle ts1 = deepToString.asCollector(String[].class, 1);
3909 assertEquals("[strange]", (String) ts1.invokeExact("strange"));
3910
3911 MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
3912 assertEquals("[up, down]", (String) ts2.invokeExact("up", "down"));
3913
3914 MethodHandle ts3 = deepToString.asCollector(String[].class, 3);
3915 MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2);
3916 assertEquals("[top, [up, down], strange]",
3917 (String) ts3_ts2.invokeExact("top", "up", "down", "strange"));
3918
3919 MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1);
3920 assertEquals("[top, [up, down], [strange]]",
3921 (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange"));
3922
3923 MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3);
3924 assertEquals("[top, [[up, down, strange], charm], bottom]",
3925 (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom"));
3926 * }</pre></blockquote>
3927 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
3928 * represents the return type of the {@code target} and resulting adapter.
3929 * {@code V}/{@code v} stand for the return type and value of the
3930 * {@code filter}, which are also found in the signature and arguments of
3931 * the {@code target}, respectively, unless {@code V} is {@code void}.
3932 * {@code A}/{@code a} and {@code C}/{@code c} represent the parameter types
3933 * and values preceding and following the collection position, {@code pos},
3934 * in the {@code target}'s signature. They also turn up in the resulting
3935 * adapter's signature and arguments, where they surround
3936 * {@code B}/{@code b}, which represent the parameter types and arguments
3937 * to the {@code filter} (if any).
3938 * <blockquote><pre>{@code
3939 * T target(A...,V,C...);
3940 * V filter(B...);
3941 * T adapter(A... a,B... b,C... c) {
3942 * V v = filter(b...);
3943 * return target(a...,v,c...);
3944 * }
3945 * // and if the filter has no arguments:
3946 * T target2(A...,V,C...);
3947 * V filter2();
3948 * T adapter2(A... a,C... c) {
3949 * V v = filter2();
3950 * return target2(a...,v,c...);
3951 * }
3952 * // and if the filter has a void return:
3953 * T target3(A...,C...);
3954 * void filter3(B...);
3955 * T adapter3(A... a,B... b,C... c) {
3956 * filter3(b...);
3957 * return target3(a...,c...);
3958 * }
3959 * }</pre></blockquote>
3960 * <p>
3961 * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to
3962 * one which first "folds" the affected arguments, and then drops them, in separate
3963 * steps as follows:
3964 * <blockquote><pre>{@code
3965 * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2
3966 * mh = MethodHandles.foldArguments(mh, coll); //step 1
3967 * }</pre></blockquote>
3968 * If the target method handle consumes no arguments besides than the result
3969 * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)}
3970 * is equivalent to {@code filterReturnValue(coll, mh)}.
3971 * If the filter method handle {@code coll} consumes one argument and produces
3972 * a non-void result, then {@code collectArguments(mh, N, coll)}
3973 * is equivalent to {@code filterArguments(mh, N, coll)}.
3974 * Other equivalences are possible but would require argument permutation.
3975 * <p>
3976 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3977 * variable-arity method handle}, even if the original target method handle was.
3978 *
3979 * @param target the method handle to invoke after filtering the subsequence of arguments
3980 * @param pos the position of the first adapter argument to pass to the filter,
3981 * and/or the target argument which receives the result of the filter
3982 * @param filter method handle to call on the subsequence of arguments
3983 * @return method handle which incorporates the specified argument subsequence filtering logic
3984 * @throws NullPointerException if either argument is null
3985 * @throws IllegalArgumentException if the return type of {@code filter}
3986 * is non-void and is not the same as the {@code pos} argument of the target,
3987 * or if {@code pos} is not between 0 and the target's arity, inclusive,
3988 * or if the resulting method handle's type would have
3989 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3990 * @see MethodHandles#foldArguments
3991 * @see MethodHandles#filterArguments
3992 * @see MethodHandles#filterReturnValue
3993 */
3994 public static
3995 MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) {
3996 MethodType newType = collectArgumentsChecks(target, pos, filter);
3997 MethodType collectorType = filter.type();
3998 BoundMethodHandle result = target.rebind();
3999 LambdaForm lform;
4000 if (collectorType.returnType().isArray() && filter.intrinsicName() == Intrinsic.NEW_ARRAY) {
4001 lform = result.editor().collectArgumentArrayForm(1 + pos, filter);
4002 if (lform != null) {
4003 return result.copyWith(newType, lform);
4004 }
4005 }
4006 lform = result.editor().collectArgumentsForm(1 + pos, collectorType.basicType());
4007 return result.copyWithExtendL(newType, lform, filter);
4008 }
4009
4010 private static MethodType collectArgumentsChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
4011 MethodType targetType = target.type();
4012 MethodType filterType = filter.type();
4013 Class<?> rtype = filterType.returnType();
4014 List<Class<?>> filterArgs = filterType.parameterList();
4015 if (rtype == void.class) {
4016 return targetType.insertParameterTypes(pos, filterArgs);
4017 }
4018 if (rtype != targetType.parameterType(pos)) {
4019 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
4020 }
4021 return targetType.dropParameterTypes(pos, pos+1).insertParameterTypes(pos, filterArgs);
4022 }
4023
4024 /**
4025 * Adapts a target method handle by post-processing
4026 * its return value (if any) with a filter (another method handle).
4027 * The result of the filter is returned from the adapter.
4028 * <p>
4029 * If the target returns a value, the filter must accept that value as
4030 * its only argument.
4031 * If the target returns void, the filter must accept no arguments.
4032 * <p>
4033 * The return type of the filter
4034 * replaces the return type of the target
4035 * in the resulting adapted method handle.
4036 * The argument type of the filter (if any) must be identical to the
4037 * return type of the target.
4038 * <p><b>Example:</b>
4039 * <blockquote><pre>{@code
4040 import static java.lang.invoke.MethodHandles.*;
4041 import static java.lang.invoke.MethodType.*;
4042 ...
4043 MethodHandle cat = lookup().findVirtual(String.class,
4044 "concat", methodType(String.class, String.class));
4045 MethodHandle length = lookup().findVirtual(String.class,
4046 "length", methodType(int.class));
4047 System.out.println((String) cat.invokeExact("x", "y")); // xy
4048 MethodHandle f0 = filterReturnValue(cat, length);
4049 System.out.println((int) f0.invokeExact("x", "y")); // 2
4050 * }</pre></blockquote>
4051 * <p>Here is pseudocode for the resulting adapter. In the code,
4052 * {@code T}/{@code t} represent the result type and value of the
4053 * {@code target}; {@code V}, the result type of the {@code filter}; and
4054 * {@code A}/{@code a}, the types and values of the parameters and arguments
4055 * of the {@code target} as well as the resulting adapter.
4056 * <blockquote><pre>{@code
4057 * T target(A...);
4058 * V filter(T);
4059 * V adapter(A... a) {
4060 * T t = target(a...);
4061 * return filter(t);
4062 * }
4063 * // and if the target has a void return:
4064 * void target2(A...);
4065 * V filter2();
4066 * V adapter2(A... a) {
4067 * target2(a...);
4068 * return filter2();
4069 * }
4070 * // and if the filter has a void return:
4071 * T target3(A...);
4072 * void filter3(V);
4073 * void adapter3(A... a) {
4074 * T t = target3(a...);
4075 * filter3(t);
4076 * }
4077 * }</pre></blockquote>
4078 * <p>
4079 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4080 * variable-arity method handle}, even if the original target method handle was.
4081 * @param target the method handle to invoke before filtering the return value
4082 * @param filter method handle to call on the return value
4083 * @return method handle which incorporates the specified return value filtering logic
4084 * @throws NullPointerException if either argument is null
4085 * @throws IllegalArgumentException if the argument list of {@code filter}
4086 * does not match the return type of target as described above
4087 */
4088 public static
4089 MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
4090 MethodType targetType = target.type();
4091 MethodType filterType = filter.type();
4092 filterReturnValueChecks(targetType, filterType);
4093 BoundMethodHandle result = target.rebind();
4094 BasicType rtype = BasicType.basicType(filterType.returnType());
4095 LambdaForm lform = result.editor().filterReturnForm(rtype, false);
4096 MethodType newType = targetType.changeReturnType(filterType.returnType());
4097 result = result.copyWithExtendL(newType, lform, filter);
4098 return result;
4099 }
4100
4101 private static void filterReturnValueChecks(MethodType targetType, MethodType filterType) throws RuntimeException {
4102 Class<?> rtype = targetType.returnType();
4103 int filterValues = filterType.parameterCount();
4104 if (filterValues == 0
4105 ? (rtype != void.class)
4106 : (rtype != filterType.parameterType(0) || filterValues != 1))
4107 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
4108 }
4109
4110 /**
4111 * Adapts a target method handle by pre-processing
4112 * some of its arguments, and then calling the target with
4113 * the result of the pre-processing, inserted into the original
4114 * sequence of arguments.
4115 * <p>
4116 * The pre-processing is performed by {@code combiner}, a second method handle.
4117 * Of the arguments passed to the adapter, the first {@code N} arguments
4118 * are copied to the combiner, which is then called.
4119 * (Here, {@code N} is defined as the parameter count of the combiner.)
4120 * After this, control passes to the target, with any result
4121 * from the combiner inserted before the original {@code N} incoming
4122 * arguments.
4123 * <p>
4124 * If the combiner returns a value, the first parameter type of the target
4125 * must be identical with the return type of the combiner, and the next
4126 * {@code N} parameter types of the target must exactly match the parameters
4127 * of the combiner.
4128 * <p>
4129 * If the combiner has a void return, no result will be inserted,
4130 * and the first {@code N} parameter types of the target
4131 * must exactly match the parameters of the combiner.
4132 * <p>
4133 * The resulting adapter is the same type as the target, except that the
4134 * first parameter type is dropped,
4135 * if it corresponds to the result of the combiner.
4136 * <p>
4137 * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
4138 * that either the combiner or the target does not wish to receive.
4139 * If some of the incoming arguments are destined only for the combiner,
4140 * consider using {@link MethodHandle#asCollector asCollector} instead, since those
4141 * arguments will not need to be live on the stack on entry to the
4142 * target.)
4143 * <p><b>Example:</b>
4144 * <blockquote><pre>{@code
4145 import static java.lang.invoke.MethodHandles.*;
4146 import static java.lang.invoke.MethodType.*;
4147 ...
4148 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
4149 "println", methodType(void.class, String.class))
4150 .bindTo(System.out);
4151 MethodHandle cat = lookup().findVirtual(String.class,
4152 "concat", methodType(String.class, String.class));
4153 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
4154 MethodHandle catTrace = foldArguments(cat, trace);
4155 // also prints "boo":
4156 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
4157 * }</pre></blockquote>
4158 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
4159 * represents the result type of the {@code target} and resulting adapter.
4160 * {@code V}/{@code v} represent the type and value of the parameter and argument
4161 * of {@code target} that precedes the folding position; {@code V} also is
4162 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
4163 * types and values of the {@code N} parameters and arguments at the folding
4164 * position. {@code B}/{@code b} represent the types and values of the
4165 * {@code target} parameters and arguments that follow the folded parameters
4166 * and arguments.
4167 * <blockquote><pre>{@code
4168 * // there are N arguments in A...
4169 * T target(V, A[N]..., B...);
4170 * V combiner(A...);
4171 * T adapter(A... a, B... b) {
4172 * V v = combiner(a...);
4173 * return target(v, a..., b...);
4174 * }
4175 * // and if the combiner has a void return:
4176 * T target2(A[N]..., B...);
4177 * void combiner2(A...);
4178 * T adapter2(A... a, B... b) {
4179 * combiner2(a...);
4180 * return target2(a..., b...);
4181 * }
4182 * }</pre></blockquote>
4183 * <p>
4184 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4185 * variable-arity method handle}, even if the original target method handle was.
4186 * @param target the method handle to invoke after arguments are combined
4187 * @param combiner method handle to call initially on the incoming arguments
4188 * @return method handle which incorporates the specified argument folding logic
4189 * @throws NullPointerException if either argument is null
4190 * @throws IllegalArgumentException if {@code combiner}'s return type
4191 * is non-void and not the same as the first argument type of
4192 * the target, or if the initial {@code N} argument types
4193 * of the target
4194 * (skipping one matching the {@code combiner}'s return type)
4195 * are not identical with the argument types of {@code combiner}
4196 */
4197 public static
4198 MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
4199 return foldArguments(target, 0, combiner);
4200 }
4201
4202 /**
4203 * Adapts a target method handle by pre-processing some of its arguments, starting at a given position, and then
4204 * calling the target with the result of the pre-processing, inserted into the original sequence of arguments just
4205 * before the folded arguments.
4206 * <p>
4207 * This method is closely related to {@link #foldArguments(MethodHandle, MethodHandle)}, but allows to control the
4208 * position in the parameter list at which folding takes place. The argument controlling this, {@code pos}, is a
4209 * zero-based index. The aforementioned method {@link #foldArguments(MethodHandle, MethodHandle)} assumes position
4210 * 0.
4211 * <p>
4212 * @apiNote Example:
4213 * <blockquote><pre>{@code
4214 import static java.lang.invoke.MethodHandles.*;
4215 import static java.lang.invoke.MethodType.*;
4216 ...
4217 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
4218 "println", methodType(void.class, String.class))
4219 .bindTo(System.out);
4220 MethodHandle cat = lookup().findVirtual(String.class,
4221 "concat", methodType(String.class, String.class));
4222 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
4223 MethodHandle catTrace = foldArguments(cat, 1, trace);
4224 // also prints "jum":
4225 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
4226 * }</pre></blockquote>
4227 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
4228 * represents the result type of the {@code target} and resulting adapter.
4229 * {@code V}/{@code v} represent the type and value of the parameter and argument
4230 * of {@code target} that precedes the folding position; {@code V} also is
4231 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
4232 * types and values of the {@code N} parameters and arguments at the folding
4233 * position. {@code Z}/{@code z} and {@code B}/{@code b} represent the types
4234 * and values of the {@code target} parameters and arguments that precede and
4235 * follow the folded parameters and arguments starting at {@code pos},
4236 * respectively.
4237 * <blockquote><pre>{@code
4238 * // there are N arguments in A...
4239 * T target(Z..., V, A[N]..., B...);
4240 * V combiner(A...);
4241 * T adapter(Z... z, A... a, B... b) {
4242 * V v = combiner(a...);
4243 * return target(z..., v, a..., b...);
4244 * }
4245 * // and if the combiner has a void return:
4246 * T target2(Z..., A[N]..., B...);
4247 * void combiner2(A...);
4248 * T adapter2(Z... z, A... a, B... b) {
4249 * combiner2(a...);
4250 * return target2(z..., a..., b...);
4251 * }
4252 * }</pre></blockquote>
4253 * <p>
4254 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4255 * variable-arity method handle}, even if the original target method handle was.
4256 *
4257 * @param target the method handle to invoke after arguments are combined
4258 * @param pos the position at which to start folding and at which to insert the folding result; if this is {@code
4259 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
4260 * @param combiner method handle to call initially on the incoming arguments
4261 * @return method handle which incorporates the specified argument folding logic
4262 * @throws NullPointerException if either argument is null
4263 * @throws IllegalArgumentException if either of the following two conditions holds:
4264 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
4265 * {@code pos} of the target signature;
4266 * (2) the {@code N} argument types at position {@code pos} of the target signature (skipping one matching
4267 * the {@code combiner}'s return type) are not identical with the argument types of {@code combiner}.
4268 *
4269 * @see #foldArguments(MethodHandle, MethodHandle)
4270 * @since 9
4271 */
4272 public static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner) {
4273 MethodType targetType = target.type();
4274 MethodType combinerType = combiner.type();
4275 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType);
4276 BoundMethodHandle result = target.rebind();
4277 boolean dropResult = rtype == void.class;
4278 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType());
4279 MethodType newType = targetType;
4280 if (!dropResult) {
4281 newType = newType.dropParameterTypes(pos, pos + 1);
4282 }
4283 result = result.copyWithExtendL(newType, lform, combiner);
4284 return result;
4285 }
4286
4287 /**
4288 * As {@see foldArguments(MethodHandle, int, MethodHandle)}, but with the
4289 * added capability of selecting the arguments from the targets parameters
4290 * to call the combiner with. This allows us to avoid some simple cases of
4291 * permutations and padding the combiner with dropArguments to select the
4292 * right argument, which may ultimately produce fewer intermediaries.
4293 */
4294 static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner, int ... argPositions) {
4295 MethodType targetType = target.type();
4296 MethodType combinerType = combiner.type();
4297 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType, argPositions);
4298 BoundMethodHandle result = target.rebind();
4299 boolean dropResult = rtype == void.class;
4300 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType(), argPositions);
4301 MethodType newType = targetType;
4302 if (!dropResult) {
4303 newType = newType.dropParameterTypes(pos, pos + 1);
4304 }
4305 result = result.copyWithExtendL(newType, lform, combiner);
4306 return result;
4307 }
4308
4309 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType) {
4310 int foldArgs = combinerType.parameterCount();
4311 Class<?> rtype = combinerType.returnType();
4312 int foldVals = rtype == void.class ? 0 : 1;
4313 int afterInsertPos = foldPos + foldVals;
4314 boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
4315 if (ok) {
4316 for (int i = 0; i < foldArgs; i++) {
4317 if (combinerType.parameterType(i) != targetType.parameterType(i + afterInsertPos)) {
4318 ok = false;
4319 break;
4320 }
4321 }
4322 }
4323 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos))
4324 ok = false;
4325 if (!ok)
4326 throw misMatchedTypes("target and combiner types", targetType, combinerType);
4327 return rtype;
4328 }
4329
4330 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType, int ... argPos) {
4331 int foldArgs = combinerType.parameterCount();
4332 if (argPos.length != foldArgs) {
4333 throw newIllegalArgumentException("combiner and argument map must be equal size", combinerType, argPos.length);
4334 }
4335 Class<?> rtype = combinerType.returnType();
4336 int foldVals = rtype == void.class ? 0 : 1;
4337 boolean ok = true;
4338 for (int i = 0; i < foldArgs; i++) {
4339 int arg = argPos[i];
4340 if (arg < 0 || arg > targetType.parameterCount()) {
4341 throw newIllegalArgumentException("arg outside of target parameterRange", targetType, arg);
4342 }
4343 if (combinerType.parameterType(i) != targetType.parameterType(arg)) {
4344 throw newIllegalArgumentException("target argument type at position " + arg
4345 + " must match combiner argument type at index " + i + ": " + targetType
4346 + " -> " + combinerType + ", map: " + Arrays.toString(argPos));
4347 }
4348 }
4349 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos)) {
4350 ok = false;
4351 }
4352 if (!ok)
4353 throw misMatchedTypes("target and combiner types", targetType, combinerType);
4354 return rtype;
4355 }
4356
4357 /**
4358 * Makes a method handle which adapts a target method handle,
4359 * by guarding it with a test, a boolean-valued method handle.
4360 * If the guard fails, a fallback handle is called instead.
4361 * All three method handles must have the same corresponding
4362 * argument and return types, except that the return type
4363 * of the test must be boolean, and the test is allowed
4364 * to have fewer arguments than the other two method handles.
4365 * <p>
4366 * Here is pseudocode for the resulting adapter. In the code, {@code T}
4367 * represents the uniform result type of the three involved handles;
4368 * {@code A}/{@code a}, the types and values of the {@code target}
4369 * parameters and arguments that are consumed by the {@code test}; and
4370 * {@code B}/{@code b}, those types and values of the {@code target}
4371 * parameters and arguments that are not consumed by the {@code test}.
4372 * <blockquote><pre>{@code
4373 * boolean test(A...);
4374 * T target(A...,B...);
4375 * T fallback(A...,B...);
4376 * T adapter(A... a,B... b) {
4377 * if (test(a...))
4378 * return target(a..., b...);
4379 * else
4380 * return fallback(a..., b...);
4381 * }
4382 * }</pre></blockquote>
4383 * Note that the test arguments ({@code a...} in the pseudocode) cannot
4384 * be modified by execution of the test, and so are passed unchanged
4385 * from the caller to the target or fallback as appropriate.
4386 * @param test method handle used for test, must return boolean
4387 * @param target method handle to call if test passes
4388 * @param fallback method handle to call if test fails
4389 * @return method handle which incorporates the specified if/then/else logic
4390 * @throws NullPointerException if any argument is null
4391 * @throws IllegalArgumentException if {@code test} does not return boolean,
4392 * or if all three method types do not match (with the return
4393 * type of {@code test} changed to match that of the target).
4394 */
4395 public static
4396 MethodHandle guardWithTest(MethodHandle test,
4397 MethodHandle target,
4398 MethodHandle fallback) {
4399 MethodType gtype = test.type();
4400 MethodType ttype = target.type();
4401 MethodType ftype = fallback.type();
4402 if (!ttype.equals(ftype))
4403 throw misMatchedTypes("target and fallback types", ttype, ftype);
4404 if (gtype.returnType() != boolean.class)
4405 throw newIllegalArgumentException("guard type is not a predicate "+gtype);
4406 List<Class<?>> targs = ttype.parameterList();
4407 test = dropArgumentsToMatch(test, 0, targs, 0, true);
4408 if (test == null) {
4409 throw misMatchedTypes("target and test types", ttype, gtype);
4410 }
4411 return MethodHandleImpl.makeGuardWithTest(test, target, fallback);
4412 }
4413
4414 static <T> RuntimeException misMatchedTypes(String what, T t1, T t2) {
4415 return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
4416 }
4417
4418 /**
4419 * Makes a method handle which adapts a target method handle,
4420 * by running it inside an exception handler.
4421 * If the target returns normally, the adapter returns that value.
4422 * If an exception matching the specified type is thrown, the fallback
4423 * handle is called instead on the exception, plus the original arguments.
4424 * <p>
4425 * The target and handler must have the same corresponding
4426 * argument and return types, except that handler may omit trailing arguments
4427 * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
4428 * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
4429 * <p>
4430 * Here is pseudocode for the resulting adapter. In the code, {@code T}
4431 * represents the return type of the {@code target} and {@code handler},
4432 * and correspondingly that of the resulting adapter; {@code A}/{@code a},
4433 * the types and values of arguments to the resulting handle consumed by
4434 * {@code handler}; and {@code B}/{@code b}, those of arguments to the
4435 * resulting handle discarded by {@code handler}.
4436 * <blockquote><pre>{@code
4437 * T target(A..., B...);
4438 * T handler(ExType, A...);
4439 * T adapter(A... a, B... b) {
4440 * try {
4441 * return target(a..., b...);
4442 * } catch (ExType ex) {
4443 * return handler(ex, a...);
4444 * }
4445 * }
4446 * }</pre></blockquote>
4447 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
4448 * be modified by execution of the target, and so are passed unchanged
4449 * from the caller to the handler, if the handler is invoked.
4450 * <p>
4451 * The target and handler must return the same type, even if the handler
4452 * always throws. (This might happen, for instance, because the handler
4453 * is simulating a {@code finally} clause).
4454 * To create such a throwing handler, compose the handler creation logic
4455 * with {@link #throwException throwException},
4456 * in order to create a method handle of the correct return type.
4457 * @param target method handle to call
4458 * @param exType the type of exception which the handler will catch
4459 * @param handler method handle to call if a matching exception is thrown
4460 * @return method handle which incorporates the specified try/catch logic
4461 * @throws NullPointerException if any argument is null
4462 * @throws IllegalArgumentException if {@code handler} does not accept
4463 * the given exception type, or if the method handle types do
4464 * not match in their return types and their
4465 * corresponding parameters
4466 * @see MethodHandles#tryFinally(MethodHandle, MethodHandle)
4467 */
4468 public static
4469 MethodHandle catchException(MethodHandle target,
4470 Class<? extends Throwable> exType,
4471 MethodHandle handler) {
4472 MethodType ttype = target.type();
4473 MethodType htype = handler.type();
4474 if (!Throwable.class.isAssignableFrom(exType))
4475 throw new ClassCastException(exType.getName());
4476 if (htype.parameterCount() < 1 ||
4477 !htype.parameterType(0).isAssignableFrom(exType))
4478 throw newIllegalArgumentException("handler does not accept exception type "+exType);
4479 if (htype.returnType() != ttype.returnType())
4480 throw misMatchedTypes("target and handler return types", ttype, htype);
4481 handler = dropArgumentsToMatch(handler, 1, ttype.parameterList(), 0, true);
4482 if (handler == null) {
4483 throw misMatchedTypes("target and handler types", ttype, htype);
4484 }
4485 return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
4486 }
4487
4488 /**
4489 * Produces a method handle which will throw exceptions of the given {@code exType}.
4490 * The method handle will accept a single argument of {@code exType},
4491 * and immediately throw it as an exception.
4492 * The method type will nominally specify a return of {@code returnType}.
4493 * The return type may be anything convenient: It doesn't matter to the
4494 * method handle's behavior, since it will never return normally.
4495 * @param returnType the return type of the desired method handle
4496 * @param exType the parameter type of the desired method handle
4497 * @return method handle which can throw the given exceptions
4498 * @throws NullPointerException if either argument is null
4499 */
4500 public static
4501 MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) {
4502 if (!Throwable.class.isAssignableFrom(exType))
4503 throw new ClassCastException(exType.getName());
4504 return MethodHandleImpl.throwException(methodType(returnType, exType));
4505 }
4506
4507 /**
4508 * Constructs a method handle representing a loop with several loop variables that are updated and checked upon each
4509 * iteration. Upon termination of the loop due to one of the predicates, a corresponding finalizer is run and
4510 * delivers the loop's result, which is the return value of the resulting handle.
4511 * <p>
4512 * Intuitively, every loop is formed by one or more "clauses", each specifying a local <em>iteration variable</em> and/or a loop
4513 * exit. Each iteration of the loop executes each clause in order. A clause can optionally update its iteration
4514 * variable; it can also optionally perform a test and conditional loop exit. In order to express this logic in
4515 * terms of method handles, each clause will specify up to four independent actions:<ul>
4516 * <li><em>init:</em> Before the loop executes, the initialization of an iteration variable {@code v} of type {@code V}.
4517 * <li><em>step:</em> When a clause executes, an update step for the iteration variable {@code v}.
4518 * <li><em>pred:</em> When a clause executes, a predicate execution to test for loop exit.
4519 * <li><em>fini:</em> If a clause causes a loop exit, a finalizer execution to compute the loop's return value.
4520 * </ul>
4521 * The full sequence of all iteration variable types, in clause order, will be notated as {@code (V...)}.
4522 * The values themselves will be {@code (v...)}. When we speak of "parameter lists", we will usually
4523 * be referring to types, but in some contexts (describing execution) the lists will be of actual values.
4524 * <p>
4525 * Some of these clause parts may be omitted according to certain rules, and useful default behavior is provided in
4526 * this case. See below for a detailed description.
4527 * <p>
4528 * <em>Parameters optional everywhere:</em>
4529 * Each clause function is allowed but not required to accept a parameter for each iteration variable {@code v}.
4530 * As an exception, the init functions cannot take any {@code v} parameters,
4531 * because those values are not yet computed when the init functions are executed.
4532 * Any clause function may neglect to take any trailing subsequence of parameters it is entitled to take.
4533 * In fact, any clause function may take no arguments at all.
4534 * <p>
4535 * <em>Loop parameters:</em>
4536 * A clause function may take all the iteration variable values it is entitled to, in which case
4537 * it may also take more trailing parameters. Such extra values are called <em>loop parameters</em>,
4538 * with their types and values notated as {@code (A...)} and {@code (a...)}.
4539 * These become the parameters of the resulting loop handle, to be supplied whenever the loop is executed.
4540 * (Since init functions do not accept iteration variables {@code v}, any parameter to an
4541 * init function is automatically a loop parameter {@code a}.)
4542 * As with iteration variables, clause functions are allowed but not required to accept loop parameters.
4543 * These loop parameters act as loop-invariant values visible across the whole loop.
4544 * <p>
4545 * <em>Parameters visible everywhere:</em>
4546 * Each non-init clause function is permitted to observe the entire loop state, because it can be passed the full
4547 * list {@code (v... a...)} of current iteration variable values and incoming loop parameters.
4548 * The init functions can observe initial pre-loop state, in the form {@code (a...)}.
4549 * Most clause functions will not need all of this information, but they will be formally connected to it
4550 * as if by {@link #dropArguments}.
4551 * <a id="astar"></a>
4552 * More specifically, we shall use the notation {@code (V*)} to express an arbitrary prefix of a full
4553 * sequence {@code (V...)} (and likewise for {@code (v*)}, {@code (A*)}, {@code (a*)}).
4554 * In that notation, the general form of an init function parameter list
4555 * is {@code (A*)}, and the general form of a non-init function parameter list is {@code (V*)} or {@code (V... A*)}.
4556 * <p>
4557 * <em>Checking clause structure:</em>
4558 * Given a set of clauses, there is a number of checks and adjustments performed to connect all the parts of the
4559 * loop. They are spelled out in detail in the steps below. In these steps, every occurrence of the word "must"
4560 * corresponds to a place where {@link IllegalArgumentException} will be thrown if the required constraint is not
4561 * met by the inputs to the loop combinator.
4562 * <p>
4563 * <em>Effectively identical sequences:</em>
4564 * <a id="effid"></a>
4565 * A parameter list {@code A} is defined to be <em>effectively identical</em> to another parameter list {@code B}
4566 * if {@code A} and {@code B} are identical, or if {@code A} is shorter and is identical with a proper prefix of {@code B}.
4567 * When speaking of an unordered set of parameter lists, we say they the set is "effectively identical"
4568 * as a whole if the set contains a longest list, and all members of the set are effectively identical to
4569 * that longest list.
4570 * For example, any set of type sequences of the form {@code (V*)} is effectively identical,
4571 * and the same is true if more sequences of the form {@code (V... A*)} are added.
4572 * <p>
4573 * <em>Step 0: Determine clause structure.</em><ol type="a">
4574 * <li>The clause array (of type {@code MethodHandle[][]}) must be non-{@code null} and contain at least one element.
4575 * <li>The clause array may not contain {@code null}s or sub-arrays longer than four elements.
4576 * <li>Clauses shorter than four elements are treated as if they were padded by {@code null} elements to length
4577 * four. Padding takes place by appending elements to the array.
4578 * <li>Clauses with all {@code null}s are disregarded.
4579 * <li>Each clause is treated as a four-tuple of functions, called "init", "step", "pred", and "fini".
4580 * </ol>
4581 * <p>
4582 * <em>Step 1A: Determine iteration variable types {@code (V...)}.</em><ol type="a">
4583 * <li>The iteration variable type for each clause is determined using the clause's init and step return types.
4584 * <li>If both functions are omitted, there is no iteration variable for the corresponding clause ({@code void} is
4585 * used as the type to indicate that). If one of them is omitted, the other's return type defines the clause's
4586 * iteration variable type. If both are given, the common return type (they must be identical) defines the clause's
4587 * iteration variable type.
4588 * <li>Form the list of return types (in clause order), omitting all occurrences of {@code void}.
4589 * <li>This list of types is called the "iteration variable types" ({@code (V...)}).
4590 * </ol>
4591 * <p>
4592 * <em>Step 1B: Determine loop parameters {@code (A...)}.</em><ul>
4593 * <li>Examine and collect init function parameter lists (which are of the form {@code (A*)}).
4594 * <li>Examine and collect the suffixes of the step, pred, and fini parameter lists, after removing the iteration variable types.
4595 * (They must have the form {@code (V... A*)}; collect the {@code (A*)} parts only.)
4596 * <li>Do not collect suffixes from step, pred, and fini parameter lists that do not begin with all the iteration variable types.
4597 * (These types will checked in step 2, along with all the clause function types.)
4598 * <li>Omitted clause functions are ignored. (Equivalently, they are deemed to have empty parameter lists.)
4599 * <li>All of the collected parameter lists must be effectively identical.
4600 * <li>The longest parameter list (which is necessarily unique) is called the "external parameter list" ({@code (A...)}).
4601 * <li>If there is no such parameter list, the external parameter list is taken to be the empty sequence.
4602 * <li>The combined list consisting of iteration variable types followed by the external parameter types is called
4603 * the "internal parameter list".
4604 * </ul>
4605 * <p>
4606 * <em>Step 1C: Determine loop return type.</em><ol type="a">
4607 * <li>Examine fini function return types, disregarding omitted fini functions.
4608 * <li>If there are no fini functions, the loop return type is {@code void}.
4609 * <li>Otherwise, the common return type {@code R} of the fini functions (their return types must be identical) defines the loop return
4610 * type.
4611 * </ol>
4612 * <p>
4613 * <em>Step 1D: Check other types.</em><ol type="a">
4614 * <li>There must be at least one non-omitted pred function.
4615 * <li>Every non-omitted pred function must have a {@code boolean} return type.
4616 * </ol>
4617 * <p>
4618 * <em>Step 2: Determine parameter lists.</em><ol type="a">
4619 * <li>The parameter list for the resulting loop handle will be the external parameter list {@code (A...)}.
4620 * <li>The parameter list for init functions will be adjusted to the external parameter list.
4621 * (Note that their parameter lists are already effectively identical to this list.)
4622 * <li>The parameter list for every non-omitted, non-init (step, pred, and fini) function must be
4623 * effectively identical to the internal parameter list {@code (V... A...)}.
4624 * </ol>
4625 * <p>
4626 * <em>Step 3: Fill in omitted functions.</em><ol type="a">
4627 * <li>If an init function is omitted, use a {@linkplain #empty default value} for the clause's iteration variable
4628 * type.
4629 * <li>If a step function is omitted, use an {@linkplain #identity identity function} of the clause's iteration
4630 * variable type; insert dropped argument parameters before the identity function parameter for the non-{@code void}
4631 * iteration variables of preceding clauses. (This will turn the loop variable into a local loop invariant.)
4632 * <li>If a pred function is omitted, use a constant {@code true} function. (This will keep the loop going, as far
4633 * as this clause is concerned. Note that in such cases the corresponding fini function is unreachable.)
4634 * <li>If a fini function is omitted, use a {@linkplain #empty default value} for the
4635 * loop return type.
4636 * </ol>
4637 * <p>
4638 * <em>Step 4: Fill in missing parameter types.</em><ol type="a">
4639 * <li>At this point, every init function parameter list is effectively identical to the external parameter list {@code (A...)},
4640 * but some lists may be shorter. For every init function with a short parameter list, pad out the end of the list.
4641 * <li>At this point, every non-init function parameter list is effectively identical to the internal parameter
4642 * list {@code (V... A...)}, but some lists may be shorter. For every non-init function with a short parameter list,
4643 * pad out the end of the list.
4644 * <li>Argument lists are padded out by {@linkplain #dropArgumentsToMatch dropping unused trailing arguments}.
4645 * </ol>
4646 * <p>
4647 * <em>Final observations.</em><ol type="a">
4648 * <li>After these steps, all clauses have been adjusted by supplying omitted functions and arguments.
4649 * <li>All init functions have a common parameter type list {@code (A...)}, which the final loop handle will also have.
4650 * <li>All fini functions have a common return type {@code R}, which the final loop handle will also have.
4651 * <li>All non-init functions have a common parameter type list {@code (V... A...)}, of
4652 * (non-{@code void}) iteration variables {@code V} followed by loop parameters.
4653 * <li>Each pair of init and step functions agrees in their return type {@code V}.
4654 * <li>Each non-init function will be able to observe the current values {@code (v...)} of all iteration variables.
4655 * <li>Every function will be able to observe the incoming values {@code (a...)} of all loop parameters.
4656 * </ol>
4657 * <p>
4658 * <em>Example.</em> As a consequence of step 1A above, the {@code loop} combinator has the following property:
4659 * <ul>
4660 * <li>Given {@code N} clauses {@code Cn = {null, Sn, Pn}} with {@code n = 1..N}.
4661 * <li>Suppose predicate handles {@code Pn} are either {@code null} or have no parameters.
4662 * (Only one {@code Pn} has to be non-{@code null}.)
4663 * <li>Suppose step handles {@code Sn} have signatures {@code (B1..BX)Rn}, for some constant {@code X>=N}.
4664 * <li>Suppose {@code Q} is the count of non-void types {@code Rn}, and {@code (V1...VQ)} is the sequence of those types.
4665 * <li>It must be that {@code Vn == Bn} for {@code n = 1..min(X,Q)}.
4666 * <li>The parameter types {@code Vn} will be interpreted as loop-local state elements {@code (V...)}.
4667 * <li>Any remaining types {@code BQ+1..BX} (if {@code Q<X}) will determine
4668 * the resulting loop handle's parameter types {@code (A...)}.
4669 * </ul>
4670 * In this example, the loop handle parameters {@code (A...)} were derived from the step functions,
4671 * which is natural if most of the loop computation happens in the steps. For some loops,
4672 * the burden of computation might be heaviest in the pred functions, and so the pred functions
4673 * might need to accept the loop parameter values. For loops with complex exit logic, the fini
4674 * functions might need to accept loop parameters, and likewise for loops with complex entry logic,
4675 * where the init functions will need the extra parameters. For such reasons, the rules for
4676 * determining these parameters are as symmetric as possible, across all clause parts.
4677 * In general, the loop parameters function as common invariant values across the whole
4678 * loop, while the iteration variables function as common variant values, or (if there is
4679 * no step function) as internal loop invariant temporaries.
4680 * <p>
4681 * <em>Loop execution.</em><ol type="a">
4682 * <li>When the loop is called, the loop input values are saved in locals, to be passed to
4683 * every clause function. These locals are loop invariant.
4684 * <li>Each init function is executed in clause order (passing the external arguments {@code (a...)})
4685 * and the non-{@code void} values are saved (as the iteration variables {@code (v...)}) into locals.
4686 * These locals will be loop varying (unless their steps behave as identity functions, as noted above).
4687 * <li>All function executions (except init functions) will be passed the internal parameter list, consisting of
4688 * the non-{@code void} iteration values {@code (v...)} (in clause order) and then the loop inputs {@code (a...)}
4689 * (in argument order).
4690 * <li>The step and pred functions are then executed, in clause order (step before pred), until a pred function
4691 * returns {@code false}.
4692 * <li>The non-{@code void} result from a step function call is used to update the corresponding value in the
4693 * sequence {@code (v...)} of loop variables.
4694 * The updated value is immediately visible to all subsequent function calls.
4695 * <li>If a pred function returns {@code false}, the corresponding fini function is called, and the resulting value
4696 * (of type {@code R}) is returned from the loop as a whole.
4697 * <li>If all the pred functions always return true, no fini function is ever invoked, and the loop cannot exit
4698 * except by throwing an exception.
4699 * </ol>
4700 * <p>
4701 * <em>Usage tips.</em>
4702 * <ul>
4703 * <li>Although each step function will receive the current values of <em>all</em> the loop variables,
4704 * sometimes a step function only needs to observe the current value of its own variable.
4705 * In that case, the step function may need to explicitly {@linkplain #dropArguments drop all preceding loop variables}.
4706 * This will require mentioning their types, in an expression like {@code dropArguments(step, 0, V0.class, ...)}.
4707 * <li>Loop variables are not required to vary; they can be loop invariant. A clause can create
4708 * a loop invariant by a suitable init function with no step, pred, or fini function. This may be
4709 * useful to "wire" an incoming loop argument into the step or pred function of an adjacent loop variable.
4710 * <li>If some of the clause functions are virtual methods on an instance, the instance
4711 * itself can be conveniently placed in an initial invariant loop "variable", using an initial clause
4712 * like {@code new MethodHandle[]{identity(ObjType.class)}}. In that case, the instance reference
4713 * will be the first iteration variable value, and it will be easy to use virtual
4714 * methods as clause parts, since all of them will take a leading instance reference matching that value.
4715 * </ul>
4716 * <p>
4717 * Here is pseudocode for the resulting loop handle. As above, {@code V} and {@code v} represent the types
4718 * and values of loop variables; {@code A} and {@code a} represent arguments passed to the whole loop;
4719 * and {@code R} is the common result type of all finalizers as well as of the resulting loop.
4720 * <blockquote><pre>{@code
4721 * V... init...(A...);
4722 * boolean pred...(V..., A...);
4723 * V... step...(V..., A...);
4724 * R fini...(V..., A...);
4725 * R loop(A... a) {
4726 * V... v... = init...(a...);
4727 * for (;;) {
4728 * for ((v, p, s, f) in (v..., pred..., step..., fini...)) {
4729 * v = s(v..., a...);
4730 * if (!p(v..., a...)) {
4731 * return f(v..., a...);
4732 * }
4733 * }
4734 * }
4735 * }
4736 * }</pre></blockquote>
4737 * Note that the parameter type lists {@code (V...)} and {@code (A...)} have been expanded
4738 * to their full length, even though individual clause functions may neglect to take them all.
4739 * As noted above, missing parameters are filled in as if by {@link #dropArgumentsToMatch}.
4740 * <p>
4741 * @apiNote Example:
4742 * <blockquote><pre>{@code
4743 * // iterative implementation of the factorial function as a loop handle
4744 * static int one(int k) { return 1; }
4745 * static int inc(int i, int acc, int k) { return i + 1; }
4746 * static int mult(int i, int acc, int k) { return i * acc; }
4747 * static boolean pred(int i, int acc, int k) { return i < k; }
4748 * static int fin(int i, int acc, int k) { return acc; }
4749 * // assume MH_one, MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
4750 * // null initializer for counter, should initialize to 0
4751 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
4752 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
4753 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
4754 * assertEquals(120, loop.invoke(5));
4755 * }</pre></blockquote>
4756 * The same example, dropping arguments and using combinators:
4757 * <blockquote><pre>{@code
4758 * // simplified implementation of the factorial function as a loop handle
4759 * static int inc(int i) { return i + 1; } // drop acc, k
4760 * static int mult(int i, int acc) { return i * acc; } //drop k
4761 * static boolean cmp(int i, int k) { return i < k; }
4762 * // assume MH_inc, MH_mult, and MH_cmp are handles to the above methods
4763 * // null initializer for counter, should initialize to 0
4764 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
4765 * MethodHandle MH_pred = MethodHandles.dropArguments(MH_cmp, 1, int.class); // drop acc
4766 * MethodHandle MH_fin = MethodHandles.dropArguments(MethodHandles.identity(int.class), 0, int.class); // drop i
4767 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
4768 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
4769 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
4770 * assertEquals(720, loop.invoke(6));
4771 * }</pre></blockquote>
4772 * A similar example, using a helper object to hold a loop parameter:
4773 * <blockquote><pre>{@code
4774 * // instance-based implementation of the factorial function as a loop handle
4775 * static class FacLoop {
4776 * final int k;
4777 * FacLoop(int k) { this.k = k; }
4778 * int inc(int i) { return i + 1; }
4779 * int mult(int i, int acc) { return i * acc; }
4780 * boolean pred(int i) { return i < k; }
4781 * int fin(int i, int acc) { return acc; }
4782 * }
4783 * // assume MH_FacLoop is a handle to the constructor
4784 * // assume MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
4785 * // null initializer for counter, should initialize to 0
4786 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
4787 * MethodHandle[] instanceClause = new MethodHandle[]{MH_FacLoop};
4788 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
4789 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
4790 * MethodHandle loop = MethodHandles.loop(instanceClause, counterClause, accumulatorClause);
4791 * assertEquals(5040, loop.invoke(7));
4792 * }</pre></blockquote>
4793 *
4794 * @param clauses an array of arrays (4-tuples) of {@link MethodHandle}s adhering to the rules described above.
4795 *
4796 * @return a method handle embodying the looping behavior as defined by the arguments.
4797 *
4798 * @throws IllegalArgumentException in case any of the constraints described above is violated.
4799 *
4800 * @see MethodHandles#whileLoop(MethodHandle, MethodHandle, MethodHandle)
4801 * @see MethodHandles#doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
4802 * @see MethodHandles#countedLoop(MethodHandle, MethodHandle, MethodHandle)
4803 * @see MethodHandles#iteratedLoop(MethodHandle, MethodHandle, MethodHandle)
4804 * @since 9
4805 */
4806 public static MethodHandle loop(MethodHandle[]... clauses) {
4807 // Step 0: determine clause structure.
4808 loopChecks0(clauses);
4809
4810 List<MethodHandle> init = new ArrayList<>();
4811 List<MethodHandle> step = new ArrayList<>();
4812 List<MethodHandle> pred = new ArrayList<>();
4813 List<MethodHandle> fini = new ArrayList<>();
4814
4815 Stream.of(clauses).filter(c -> Stream.of(c).anyMatch(Objects::nonNull)).forEach(clause -> {
4816 init.add(clause[0]); // all clauses have at least length 1
4817 step.add(clause.length <= 1 ? null : clause[1]);
4818 pred.add(clause.length <= 2 ? null : clause[2]);
4819 fini.add(clause.length <= 3 ? null : clause[3]);
4820 });
4821
4822 assert Stream.of(init, step, pred, fini).map(List::size).distinct().count() == 1;
4823 final int nclauses = init.size();
4824
4825 // Step 1A: determine iteration variables (V...).
4826 final List<Class<?>> iterationVariableTypes = new ArrayList<>();
4827 for (int i = 0; i < nclauses; ++i) {
4828 MethodHandle in = init.get(i);
4829 MethodHandle st = step.get(i);
4830 if (in == null && st == null) {
4831 iterationVariableTypes.add(void.class);
4832 } else if (in != null && st != null) {
4833 loopChecks1a(i, in, st);
4834 iterationVariableTypes.add(in.type().returnType());
4835 } else {
4836 iterationVariableTypes.add(in == null ? st.type().returnType() : in.type().returnType());
4837 }
4838 }
4839 final List<Class<?>> commonPrefix = iterationVariableTypes.stream().filter(t -> t != void.class).
4840 collect(Collectors.toList());
4841
4842 // Step 1B: determine loop parameters (A...).
4843 final List<Class<?>> commonSuffix = buildCommonSuffix(init, step, pred, fini, commonPrefix.size());
4844 loopChecks1b(init, commonSuffix);
4845
4846 // Step 1C: determine loop return type.
4847 // Step 1D: check other types.
4848 final Class<?> loopReturnType = fini.stream().filter(Objects::nonNull).map(MethodHandle::type).
4849 map(MethodType::returnType).findFirst().orElse(void.class);
4850 loopChecks1cd(pred, fini, loopReturnType);
4851
4852 // Step 2: determine parameter lists.
4853 final List<Class<?>> commonParameterSequence = new ArrayList<>(commonPrefix);
4854 commonParameterSequence.addAll(commonSuffix);
4855 loopChecks2(step, pred, fini, commonParameterSequence);
4856
4857 // Step 3: fill in omitted functions.
4858 for (int i = 0; i < nclauses; ++i) {
4859 Class<?> t = iterationVariableTypes.get(i);
4860 if (init.get(i) == null) {
4861 init.set(i, empty(methodType(t, commonSuffix)));
4862 }
4863 if (step.get(i) == null) {
4864 step.set(i, dropArgumentsToMatch(identityOrVoid(t), 0, commonParameterSequence, i));
4865 }
4866 if (pred.get(i) == null) {
4867 pred.set(i, dropArguments0(constant(boolean.class, true), 0, commonParameterSequence));
4868 }
4869 if (fini.get(i) == null) {
4870 fini.set(i, empty(methodType(t, commonParameterSequence)));
4871 }
4872 }
4873
4874 // Step 4: fill in missing parameter types.
4875 // Also convert all handles to fixed-arity handles.
4876 List<MethodHandle> finit = fixArities(fillParameterTypes(init, commonSuffix));
4877 List<MethodHandle> fstep = fixArities(fillParameterTypes(step, commonParameterSequence));
4878 List<MethodHandle> fpred = fixArities(fillParameterTypes(pred, commonParameterSequence));
4879 List<MethodHandle> ffini = fixArities(fillParameterTypes(fini, commonParameterSequence));
4880
4881 assert finit.stream().map(MethodHandle::type).map(MethodType::parameterList).
4882 allMatch(pl -> pl.equals(commonSuffix));
4883 assert Stream.of(fstep, fpred, ffini).flatMap(List::stream).map(MethodHandle::type).map(MethodType::parameterList).
4884 allMatch(pl -> pl.equals(commonParameterSequence));
4885
4886 return MethodHandleImpl.makeLoop(loopReturnType, commonSuffix, finit, fstep, fpred, ffini);
4887 }
4888
4889 private static void loopChecks0(MethodHandle[][] clauses) {
4890 if (clauses == null || clauses.length == 0) {
4891 throw newIllegalArgumentException("null or no clauses passed");
4892 }
4893 if (Stream.of(clauses).anyMatch(Objects::isNull)) {
4894 throw newIllegalArgumentException("null clauses are not allowed");
4895 }
4896 if (Stream.of(clauses).anyMatch(c -> c.length > 4)) {
4897 throw newIllegalArgumentException("All loop clauses must be represented as MethodHandle arrays with at most 4 elements.");
4898 }
4899 }
4900
4901 private static void loopChecks1a(int i, MethodHandle in, MethodHandle st) {
4902 if (in.type().returnType() != st.type().returnType()) {
4903 throw misMatchedTypes("clause " + i + ": init and step return types", in.type().returnType(),
4904 st.type().returnType());
4905 }
4906 }
4907
4908 private static List<Class<?>> longestParameterList(Stream<MethodHandle> mhs, int skipSize) {
4909 final List<Class<?>> empty = List.of();
4910 final List<Class<?>> longest = mhs.filter(Objects::nonNull).
4911 // take only those that can contribute to a common suffix because they are longer than the prefix
4912 map(MethodHandle::type).
4913 filter(t -> t.parameterCount() > skipSize).
4914 map(MethodType::parameterList).
4915 reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
4916 return longest.size() == 0 ? empty : longest.subList(skipSize, longest.size());
4917 }
4918
4919 private static List<Class<?>> longestParameterList(List<List<Class<?>>> lists) {
4920 final List<Class<?>> empty = List.of();
4921 return lists.stream().reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
4922 }
4923
4924 private static List<Class<?>> buildCommonSuffix(List<MethodHandle> init, List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, int cpSize) {
4925 final List<Class<?>> longest1 = longestParameterList(Stream.of(step, pred, fini).flatMap(List::stream), cpSize);
4926 final List<Class<?>> longest2 = longestParameterList(init.stream(), 0);
4927 return longestParameterList(Arrays.asList(longest1, longest2));
4928 }
4929
4930 private static void loopChecks1b(List<MethodHandle> init, List<Class<?>> commonSuffix) {
4931 if (init.stream().filter(Objects::nonNull).map(MethodHandle::type).
4932 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonSuffix))) {
4933 throw newIllegalArgumentException("found non-effectively identical init parameter type lists: " + init +
4934 " (common suffix: " + commonSuffix + ")");
4935 }
4936 }
4937
4938 private static void loopChecks1cd(List<MethodHandle> pred, List<MethodHandle> fini, Class<?> loopReturnType) {
4939 if (fini.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
4940 anyMatch(t -> t != loopReturnType)) {
4941 throw newIllegalArgumentException("found non-identical finalizer return types: " + fini + " (return type: " +
4942 loopReturnType + ")");
4943 }
4944
4945 if (!pred.stream().filter(Objects::nonNull).findFirst().isPresent()) {
4946 throw newIllegalArgumentException("no predicate found", pred);
4947 }
4948 if (pred.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
4949 anyMatch(t -> t != boolean.class)) {
4950 throw newIllegalArgumentException("predicates must have boolean return type", pred);
4951 }
4952 }
4953
4954 private static void loopChecks2(List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, List<Class<?>> commonParameterSequence) {
4955 if (Stream.of(step, pred, fini).flatMap(List::stream).filter(Objects::nonNull).map(MethodHandle::type).
4956 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonParameterSequence))) {
4957 throw newIllegalArgumentException("found non-effectively identical parameter type lists:\nstep: " + step +
4958 "\npred: " + pred + "\nfini: " + fini + " (common parameter sequence: " + commonParameterSequence + ")");
4959 }
4960 }
4961
4962 private static List<MethodHandle> fillParameterTypes(List<MethodHandle> hs, final List<Class<?>> targetParams) {
4963 return hs.stream().map(h -> {
4964 int pc = h.type().parameterCount();
4965 int tpsize = targetParams.size();
4966 return pc < tpsize ? dropArguments0(h, pc, targetParams.subList(pc, tpsize)) : h;
4967 }).collect(Collectors.toList());
4968 }
4969
4970 private static List<MethodHandle> fixArities(List<MethodHandle> hs) {
4971 return hs.stream().map(MethodHandle::asFixedArity).collect(Collectors.toList());
4972 }
4973
4974 /**
4975 * Constructs a {@code while} loop from an initializer, a body, and a predicate.
4976 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
4977 * <p>
4978 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
4979 * method will, in each iteration, first evaluate the predicate and then execute its body (if the predicate
4980 * evaluates to {@code true}).
4981 * The loop will terminate once the predicate evaluates to {@code false} (the body will not be executed in this case).
4982 * <p>
4983 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
4984 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
4985 * and updated with the value returned from its invocation. The result of loop execution will be
4986 * the final value of the additional loop-local variable (if present).
4987 * <p>
4988 * The following rules hold for these argument handles:<ul>
4989 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
4990 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
4991 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
4992 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
4993 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
4994 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
4995 * It will constrain the parameter lists of the other loop parts.
4996 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
4997 * list {@code (A...)} is called the <em>external parameter list</em>.
4998 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
4999 * additional state variable of the loop.
5000 * The body must both accept and return a value of this type {@code V}.
5001 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5002 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5003 * <a href="MethodHandles.html#effid">effectively identical</a>
5004 * to the external parameter list {@code (A...)}.
5005 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5006 * {@linkplain #empty default value}.
5007 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
5008 * Its parameter list (either empty or of the form {@code (V A*)}) must be
5009 * effectively identical to the internal parameter list.
5010 * </ul>
5011 * <p>
5012 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5013 * <li>The loop handle's result type is the result type {@code V} of the body.
5014 * <li>The loop handle's parameter types are the types {@code (A...)},
5015 * from the external parameter list.
5016 * </ul>
5017 * <p>
5018 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5019 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
5020 * passed to the loop.
5021 * <blockquote><pre>{@code
5022 * V init(A...);
5023 * boolean pred(V, A...);
5024 * V body(V, A...);
5025 * V whileLoop(A... a...) {
5026 * V v = init(a...);
5027 * while (pred(v, a...)) {
5028 * v = body(v, a...);
5029 * }
5030 * return v;
5031 * }
5032 * }</pre></blockquote>
5033 * <p>
5034 * @apiNote Example:
5035 * <blockquote><pre>{@code
5036 * // implement the zip function for lists as a loop handle
5037 * static List<String> initZip(Iterator<String> a, Iterator<String> b) { return new ArrayList<>(); }
5038 * static boolean zipPred(List<String> zip, Iterator<String> a, Iterator<String> b) { return a.hasNext() && b.hasNext(); }
5039 * static List<String> zipStep(List<String> zip, Iterator<String> a, Iterator<String> b) {
5040 * zip.add(a.next());
5041 * zip.add(b.next());
5042 * return zip;
5043 * }
5044 * // assume MH_initZip, MH_zipPred, and MH_zipStep are handles to the above methods
5045 * MethodHandle loop = MethodHandles.whileLoop(MH_initZip, MH_zipPred, MH_zipStep);
5046 * List<String> a = Arrays.asList("a", "b", "c", "d");
5047 * List<String> b = Arrays.asList("e", "f", "g", "h");
5048 * List<String> zipped = Arrays.asList("a", "e", "b", "f", "c", "g", "d", "h");
5049 * assertEquals(zipped, (List<String>) loop.invoke(a.iterator(), b.iterator()));
5050 * }</pre></blockquote>
5051 *
5052 * <p>
5053 * @apiNote The implementation of this method can be expressed as follows:
5054 * <blockquote><pre>{@code
5055 * MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
5056 * MethodHandle fini = (body.type().returnType() == void.class
5057 * ? null : identity(body.type().returnType()));
5058 * MethodHandle[]
5059 * checkExit = { null, null, pred, fini },
5060 * varBody = { init, body };
5061 * return loop(checkExit, varBody);
5062 * }
5063 * }</pre></blockquote>
5064 *
5065 * @param init optional initializer, providing the initial value of the loop variable.
5066 * May be {@code null}, implying a default initial value. See above for other constraints.
5067 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
5068 * above for other constraints.
5069 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
5070 * See above for other constraints.
5071 *
5072 * @return a method handle implementing the {@code while} loop as described by the arguments.
5073 * @throws IllegalArgumentException if the rules for the arguments are violated.
5074 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
5075 *
5076 * @see #loop(MethodHandle[][])
5077 * @see #doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
5078 * @since 9
5079 */
5080 public static MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
5081 whileLoopChecks(init, pred, body);
5082 MethodHandle fini = identityOrVoid(body.type().returnType());
5083 MethodHandle[] checkExit = { null, null, pred, fini };
5084 MethodHandle[] varBody = { init, body };
5085 return loop(checkExit, varBody);
5086 }
5087
5088 /**
5089 * Constructs a {@code do-while} loop from an initializer, a body, and a predicate.
5090 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5091 * <p>
5092 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
5093 * method will, in each iteration, first execute its body and then evaluate the predicate.
5094 * The loop will terminate once the predicate evaluates to {@code false} after an execution of the body.
5095 * <p>
5096 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
5097 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
5098 * and updated with the value returned from its invocation. The result of loop execution will be
5099 * the final value of the additional loop-local variable (if present).
5100 * <p>
5101 * The following rules hold for these argument handles:<ul>
5102 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5103 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
5104 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5105 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
5106 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
5107 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
5108 * It will constrain the parameter lists of the other loop parts.
5109 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
5110 * list {@code (A...)} is called the <em>external parameter list</em>.
5111 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5112 * additional state variable of the loop.
5113 * The body must both accept and return a value of this type {@code V}.
5114 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5115 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5116 * <a href="MethodHandles.html#effid">effectively identical</a>
5117 * to the external parameter list {@code (A...)}.
5118 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5119 * {@linkplain #empty default value}.
5120 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
5121 * Its parameter list (either empty or of the form {@code (V A*)}) must be
5122 * effectively identical to the internal parameter list.
5123 * </ul>
5124 * <p>
5125 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5126 * <li>The loop handle's result type is the result type {@code V} of the body.
5127 * <li>The loop handle's parameter types are the types {@code (A...)},
5128 * from the external parameter list.
5129 * </ul>
5130 * <p>
5131 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5132 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
5133 * passed to the loop.
5134 * <blockquote><pre>{@code
5135 * V init(A...);
5136 * boolean pred(V, A...);
5137 * V body(V, A...);
5138 * V doWhileLoop(A... a...) {
5139 * V v = init(a...);
5140 * do {
5141 * v = body(v, a...);
5142 * } while (pred(v, a...));
5143 * return v;
5144 * }
5145 * }</pre></blockquote>
5146 * <p>
5147 * @apiNote Example:
5148 * <blockquote><pre>{@code
5149 * // int i = 0; while (i < limit) { ++i; } return i; => limit
5150 * static int zero(int limit) { return 0; }
5151 * static int step(int i, int limit) { return i + 1; }
5152 * static boolean pred(int i, int limit) { return i < limit; }
5153 * // assume MH_zero, MH_step, and MH_pred are handles to the above methods
5154 * MethodHandle loop = MethodHandles.doWhileLoop(MH_zero, MH_step, MH_pred);
5155 * assertEquals(23, loop.invoke(23));
5156 * }</pre></blockquote>
5157 *
5158 * <p>
5159 * @apiNote The implementation of this method can be expressed as follows:
5160 * <blockquote><pre>{@code
5161 * MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
5162 * MethodHandle fini = (body.type().returnType() == void.class
5163 * ? null : identity(body.type().returnType()));
5164 * MethodHandle[] clause = { init, body, pred, fini };
5165 * return loop(clause);
5166 * }
5167 * }</pre></blockquote>
5168 *
5169 * @param init optional initializer, providing the initial value of the loop variable.
5170 * May be {@code null}, implying a default initial value. See above for other constraints.
5171 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
5172 * See above for other constraints.
5173 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
5174 * above for other constraints.
5175 *
5176 * @return a method handle implementing the {@code while} loop as described by the arguments.
5177 * @throws IllegalArgumentException if the rules for the arguments are violated.
5178 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
5179 *
5180 * @see #loop(MethodHandle[][])
5181 * @see #whileLoop(MethodHandle, MethodHandle, MethodHandle)
5182 * @since 9
5183 */
5184 public static MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
5185 whileLoopChecks(init, pred, body);
5186 MethodHandle fini = identityOrVoid(body.type().returnType());
5187 MethodHandle[] clause = {init, body, pred, fini };
5188 return loop(clause);
5189 }
5190
5191 private static void whileLoopChecks(MethodHandle init, MethodHandle pred, MethodHandle body) {
5192 Objects.requireNonNull(pred);
5193 Objects.requireNonNull(body);
5194 MethodType bodyType = body.type();
5195 Class<?> returnType = bodyType.returnType();
5196 List<Class<?>> innerList = bodyType.parameterList();
5197 List<Class<?>> outerList = innerList;
5198 if (returnType == void.class) {
5199 // OK
5200 } else if (innerList.size() == 0 || innerList.get(0) != returnType) {
5201 // leading V argument missing => error
5202 MethodType expected = bodyType.insertParameterTypes(0, returnType);
5203 throw misMatchedTypes("body function", bodyType, expected);
5204 } else {
5205 outerList = innerList.subList(1, innerList.size());
5206 }
5207 MethodType predType = pred.type();
5208 if (predType.returnType() != boolean.class ||
5209 !predType.effectivelyIdenticalParameters(0, innerList)) {
5210 throw misMatchedTypes("loop predicate", predType, methodType(boolean.class, innerList));
5211 }
5212 if (init != null) {
5213 MethodType initType = init.type();
5214 if (initType.returnType() != returnType ||
5215 !initType.effectivelyIdenticalParameters(0, outerList)) {
5216 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
5217 }
5218 }
5219 }
5220
5221 /**
5222 * Constructs a loop that runs a given number of iterations.
5223 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5224 * <p>
5225 * The number of iterations is determined by the {@code iterations} handle evaluation result.
5226 * The loop counter {@code i} is an extra loop iteration variable of type {@code int}.
5227 * It will be initialized to 0 and incremented by 1 in each iteration.
5228 * <p>
5229 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
5230 * of that type is also present. This variable is initialized using the optional {@code init} handle,
5231 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
5232 * <p>
5233 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
5234 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
5235 * iteration variable.
5236 * The result of the loop handle execution will be the final {@code V} value of that variable
5237 * (or {@code void} if there is no {@code V} variable).
5238 * <p>
5239 * The following rules hold for the argument handles:<ul>
5240 * <li>The {@code iterations} handle must not be {@code null}, and must return
5241 * the type {@code int}, referred to here as {@code I} in parameter type lists.
5242 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5243 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
5244 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5245 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
5246 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
5247 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
5248 * of types called the <em>internal parameter list</em>.
5249 * It will constrain the parameter lists of the other loop parts.
5250 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
5251 * with no additional {@code A} types, then the internal parameter list is extended by
5252 * the argument types {@code A...} of the {@code iterations} handle.
5253 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
5254 * list {@code (A...)} is called the <em>external parameter list</em>.
5255 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5256 * additional state variable of the loop.
5257 * The body must both accept a leading parameter and return a value of this type {@code V}.
5258 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5259 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5260 * <a href="MethodHandles.html#effid">effectively identical</a>
5261 * to the external parameter list {@code (A...)}.
5262 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5263 * {@linkplain #empty default value}.
5264 * <li>The parameter list of {@code iterations} (of some form {@code (A*)}) must be
5265 * effectively identical to the external parameter list {@code (A...)}.
5266 * </ul>
5267 * <p>
5268 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5269 * <li>The loop handle's result type is the result type {@code V} of the body.
5270 * <li>The loop handle's parameter types are the types {@code (A...)},
5271 * from the external parameter list.
5272 * </ul>
5273 * <p>
5274 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5275 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
5276 * arguments passed to the loop.
5277 * <blockquote><pre>{@code
5278 * int iterations(A...);
5279 * V init(A...);
5280 * V body(V, int, A...);
5281 * V countedLoop(A... a...) {
5282 * int end = iterations(a...);
5283 * V v = init(a...);
5284 * for (int i = 0; i < end; ++i) {
5285 * v = body(v, i, a...);
5286 * }
5287 * return v;
5288 * }
5289 * }</pre></blockquote>
5290 * <p>
5291 * @apiNote Example with a fully conformant body method:
5292 * <blockquote><pre>{@code
5293 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
5294 * // => a variation on a well known theme
5295 * static String step(String v, int counter, String init) { return "na " + v; }
5296 * // assume MH_step is a handle to the method above
5297 * MethodHandle fit13 = MethodHandles.constant(int.class, 13);
5298 * MethodHandle start = MethodHandles.identity(String.class);
5299 * MethodHandle loop = MethodHandles.countedLoop(fit13, start, MH_step);
5300 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("Lambdaman!"));
5301 * }</pre></blockquote>
5302 * <p>
5303 * @apiNote Example with the simplest possible body method type,
5304 * and passing the number of iterations to the loop invocation:
5305 * <blockquote><pre>{@code
5306 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
5307 * // => a variation on a well known theme
5308 * static String step(String v, int counter ) { return "na " + v; }
5309 * // assume MH_step is a handle to the method above
5310 * MethodHandle count = MethodHandles.dropArguments(MethodHandles.identity(int.class), 1, String.class);
5311 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class);
5312 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i) -> "na " + v
5313 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "Lambdaman!"));
5314 * }</pre></blockquote>
5315 * <p>
5316 * @apiNote Example that treats the number of iterations, string to append to, and string to append
5317 * as loop parameters:
5318 * <blockquote><pre>{@code
5319 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
5320 * // => a variation on a well known theme
5321 * static String step(String v, int counter, int iterations_, String pre, String start_) { return pre + " " + v; }
5322 * // assume MH_step is a handle to the method above
5323 * MethodHandle count = MethodHandles.identity(int.class);
5324 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class, String.class);
5325 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i, _, pre, _) -> pre + " " + v
5326 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "na", "Lambdaman!"));
5327 * }</pre></blockquote>
5328 * <p>
5329 * @apiNote Example that illustrates the usage of {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}
5330 * to enforce a loop type:
5331 * <blockquote><pre>{@code
5332 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
5333 * // => a variation on a well known theme
5334 * static String step(String v, int counter, String pre) { return pre + " " + v; }
5335 * // assume MH_step is a handle to the method above
5336 * MethodType loopType = methodType(String.class, String.class, int.class, String.class);
5337 * MethodHandle count = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(int.class), 0, loopType.parameterList(), 1);
5338 * MethodHandle start = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(String.class), 0, loopType.parameterList(), 2);
5339 * MethodHandle body = MethodHandles.dropArgumentsToMatch(MH_step, 2, loopType.parameterList(), 0);
5340 * MethodHandle loop = MethodHandles.countedLoop(count, start, body); // (v, i, pre, _, _) -> pre + " " + v
5341 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("na", 13, "Lambdaman!"));
5342 * }</pre></blockquote>
5343 * <p>
5344 * @apiNote The implementation of this method can be expressed as follows:
5345 * <blockquote><pre>{@code
5346 * MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
5347 * return countedLoop(empty(iterations.type()), iterations, init, body);
5348 * }
5349 * }</pre></blockquote>
5350 *
5351 * @param iterations a non-{@code null} handle to return the number of iterations this loop should run. The handle's
5352 * result type must be {@code int}. See above for other constraints.
5353 * @param init optional initializer, providing the initial value of the loop variable.
5354 * May be {@code null}, implying a default initial value. See above for other constraints.
5355 * @param body body of the loop, which may not be {@code null}.
5356 * It controls the loop parameters and result type in the standard case (see above for details).
5357 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
5358 * and may accept any number of additional types.
5359 * See above for other constraints.
5360 *
5361 * @return a method handle representing the loop.
5362 * @throws NullPointerException if either of the {@code iterations} or {@code body} handles is {@code null}.
5363 * @throws IllegalArgumentException if any argument violates the rules formulated above.
5364 *
5365 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle, MethodHandle)
5366 * @since 9
5367 */
5368 public static MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
5369 return countedLoop(empty(iterations.type()), iterations, init, body);
5370 }
5371
5372 /**
5373 * Constructs a loop that counts over a range of numbers.
5374 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5375 * <p>
5376 * The loop counter {@code i} is a loop iteration variable of type {@code int}.
5377 * The {@code start} and {@code end} handles determine the start (inclusive) and end (exclusive)
5378 * values of the loop counter.
5379 * The loop counter will be initialized to the {@code int} value returned from the evaluation of the
5380 * {@code start} handle and run to the value returned from {@code end} (exclusively) with a step width of 1.
5381 * <p>
5382 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
5383 * of that type is also present. This variable is initialized using the optional {@code init} handle,
5384 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
5385 * <p>
5386 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
5387 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
5388 * iteration variable.
5389 * The result of the loop handle execution will be the final {@code V} value of that variable
5390 * (or {@code void} if there is no {@code V} variable).
5391 * <p>
5392 * The following rules hold for the argument handles:<ul>
5393 * <li>The {@code start} and {@code end} handles must not be {@code null}, and must both return
5394 * the common type {@code int}, referred to here as {@code I} in parameter type lists.
5395 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5396 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
5397 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5398 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
5399 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
5400 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
5401 * of types called the <em>internal parameter list</em>.
5402 * It will constrain the parameter lists of the other loop parts.
5403 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
5404 * with no additional {@code A} types, then the internal parameter list is extended by
5405 * the argument types {@code A...} of the {@code end} handle.
5406 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
5407 * list {@code (A...)} is called the <em>external parameter list</em>.
5408 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5409 * additional state variable of the loop.
5410 * The body must both accept a leading parameter and return a value of this type {@code V}.
5411 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5412 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5413 * <a href="MethodHandles.html#effid">effectively identical</a>
5414 * to the external parameter list {@code (A...)}.
5415 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5416 * {@linkplain #empty default value}.
5417 * <li>The parameter list of {@code start} (of some form {@code (A*)}) must be
5418 * effectively identical to the external parameter list {@code (A...)}.
5419 * <li>Likewise, the parameter list of {@code end} must be effectively identical
5420 * to the external parameter list.
5421 * </ul>
5422 * <p>
5423 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5424 * <li>The loop handle's result type is the result type {@code V} of the body.
5425 * <li>The loop handle's parameter types are the types {@code (A...)},
5426 * from the external parameter list.
5427 * </ul>
5428 * <p>
5429 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5430 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
5431 * arguments passed to the loop.
5432 * <blockquote><pre>{@code
5433 * int start(A...);
5434 * int end(A...);
5435 * V init(A...);
5436 * V body(V, int, A...);
5437 * V countedLoop(A... a...) {
5438 * int e = end(a...);
5439 * int s = start(a...);
5440 * V v = init(a...);
5441 * for (int i = s; i < e; ++i) {
5442 * v = body(v, i, a...);
5443 * }
5444 * return v;
5445 * }
5446 * }</pre></blockquote>
5447 *
5448 * <p>
5449 * @apiNote The implementation of this method can be expressed as follows:
5450 * <blockquote><pre>{@code
5451 * MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
5452 * MethodHandle returnVar = dropArguments(identity(init.type().returnType()), 0, int.class, int.class);
5453 * // assume MH_increment and MH_predicate are handles to implementation-internal methods with
5454 * // the following semantics:
5455 * // MH_increment: (int limit, int counter) -> counter + 1
5456 * // MH_predicate: (int limit, int counter) -> counter < limit
5457 * Class<?> counterType = start.type().returnType(); // int
5458 * Class<?> returnType = body.type().returnType();
5459 * MethodHandle incr = MH_increment, pred = MH_predicate, retv = null;
5460 * if (returnType != void.class) { // ignore the V variable
5461 * incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
5462 * pred = dropArguments(pred, 1, returnType); // ditto
5463 * retv = dropArguments(identity(returnType), 0, counterType); // ignore limit
5464 * }
5465 * body = dropArguments(body, 0, counterType); // ignore the limit variable
5466 * MethodHandle[]
5467 * loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
5468 * bodyClause = { init, body }, // v = init(); v = body(v, i)
5469 * indexVar = { start, incr }; // i = start(); i = i + 1
5470 * return loop(loopLimit, bodyClause, indexVar);
5471 * }
5472 * }</pre></blockquote>
5473 *
5474 * @param start a non-{@code null} handle to return the start value of the loop counter, which must be {@code int}.
5475 * See above for other constraints.
5476 * @param end a non-{@code null} handle to return the end value of the loop counter (the loop will run to
5477 * {@code end-1}). The result type must be {@code int}. See above for other constraints.
5478 * @param init optional initializer, providing the initial value of the loop variable.
5479 * May be {@code null}, implying a default initial value. See above for other constraints.
5480 * @param body body of the loop, which may not be {@code null}.
5481 * It controls the loop parameters and result type in the standard case (see above for details).
5482 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
5483 * and may accept any number of additional types.
5484 * See above for other constraints.
5485 *
5486 * @return a method handle representing the loop.
5487 * @throws NullPointerException if any of the {@code start}, {@code end}, or {@code body} handles is {@code null}.
5488 * @throws IllegalArgumentException if any argument violates the rules formulated above.
5489 *
5490 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle)
5491 * @since 9
5492 */
5493 public static MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
5494 countedLoopChecks(start, end, init, body);
5495 Class<?> counterType = start.type().returnType(); // int, but who's counting?
5496 Class<?> limitType = end.type().returnType(); // yes, int again
5497 Class<?> returnType = body.type().returnType();
5498 MethodHandle incr = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopStep);
5499 MethodHandle pred = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopPred);
5500 MethodHandle retv = null;
5501 if (returnType != void.class) {
5502 incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
5503 pred = dropArguments(pred, 1, returnType); // ditto
5504 retv = dropArguments(identity(returnType), 0, counterType);
5505 }
5506 body = dropArguments(body, 0, counterType); // ignore the limit variable
5507 MethodHandle[]
5508 loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
5509 bodyClause = { init, body }, // v = init(); v = body(v, i)
5510 indexVar = { start, incr }; // i = start(); i = i + 1
5511 return loop(loopLimit, bodyClause, indexVar);
5512 }
5513
5514 private static void countedLoopChecks(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
5515 Objects.requireNonNull(start);
5516 Objects.requireNonNull(end);
5517 Objects.requireNonNull(body);
5518 Class<?> counterType = start.type().returnType();
5519 if (counterType != int.class) {
5520 MethodType expected = start.type().changeReturnType(int.class);
5521 throw misMatchedTypes("start function", start.type(), expected);
5522 } else if (end.type().returnType() != counterType) {
5523 MethodType expected = end.type().changeReturnType(counterType);
5524 throw misMatchedTypes("end function", end.type(), expected);
5525 }
5526 MethodType bodyType = body.type();
5527 Class<?> returnType = bodyType.returnType();
5528 List<Class<?>> innerList = bodyType.parameterList();
5529 // strip leading V value if present
5530 int vsize = (returnType == void.class ? 0 : 1);
5531 if (vsize != 0 && (innerList.size() == 0 || innerList.get(0) != returnType)) {
5532 // argument list has no "V" => error
5533 MethodType expected = bodyType.insertParameterTypes(0, returnType);
5534 throw misMatchedTypes("body function", bodyType, expected);
5535 } else if (innerList.size() <= vsize || innerList.get(vsize) != counterType) {
5536 // missing I type => error
5537 MethodType expected = bodyType.insertParameterTypes(vsize, counterType);
5538 throw misMatchedTypes("body function", bodyType, expected);
5539 }
5540 List<Class<?>> outerList = innerList.subList(vsize + 1, innerList.size());
5541 if (outerList.isEmpty()) {
5542 // special case; take lists from end handle
5543 outerList = end.type().parameterList();
5544 innerList = bodyType.insertParameterTypes(vsize + 1, outerList).parameterList();
5545 }
5546 MethodType expected = methodType(counterType, outerList);
5547 if (!start.type().effectivelyIdenticalParameters(0, outerList)) {
5548 throw misMatchedTypes("start parameter types", start.type(), expected);
5549 }
5550 if (end.type() != start.type() &&
5551 !end.type().effectivelyIdenticalParameters(0, outerList)) {
5552 throw misMatchedTypes("end parameter types", end.type(), expected);
5553 }
5554 if (init != null) {
5555 MethodType initType = init.type();
5556 if (initType.returnType() != returnType ||
5557 !initType.effectivelyIdenticalParameters(0, outerList)) {
5558 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
5559 }
5560 }
5561 }
5562
5563 /**
5564 * Constructs a loop that ranges over the values produced by an {@code Iterator<T>}.
5565 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5566 * <p>
5567 * The iterator itself will be determined by the evaluation of the {@code iterator} handle.
5568 * Each value it produces will be stored in a loop iteration variable of type {@code T}.
5569 * <p>
5570 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
5571 * of that type is also present. This variable is initialized using the optional {@code init} handle,
5572 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
5573 * <p>
5574 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
5575 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
5576 * iteration variable.
5577 * The result of the loop handle execution will be the final {@code V} value of that variable
5578 * (or {@code void} if there is no {@code V} variable).
5579 * <p>
5580 * The following rules hold for the argument handles:<ul>
5581 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5582 * {@code (V T A...)V}, where {@code V} is non-{@code void}, or else {@code (T A...)void}.
5583 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5584 * and we will write {@code (V T A...)V} with the understanding that a {@code void} type {@code V}
5585 * is quietly dropped from the parameter list, leaving {@code (T A...)V}.)
5586 * <li>The parameter list {@code (V T A...)} of the body contributes to a list
5587 * of types called the <em>internal parameter list</em>.
5588 * It will constrain the parameter lists of the other loop parts.
5589 * <li>As a special case, if the body contributes only {@code V} and {@code T} types,
5590 * with no additional {@code A} types, then the internal parameter list is extended by
5591 * the argument types {@code A...} of the {@code iterator} handle; if it is {@code null} the
5592 * single type {@code Iterable} is added and constitutes the {@code A...} list.
5593 * <li>If the iteration variable types {@code (V T)} are dropped from the internal parameter list, the resulting shorter
5594 * list {@code (A...)} is called the <em>external parameter list</em>.
5595 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5596 * additional state variable of the loop.
5597 * The body must both accept a leading parameter and return a value of this type {@code V}.
5598 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5599 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5600 * <a href="MethodHandles.html#effid">effectively identical</a>
5601 * to the external parameter list {@code (A...)}.
5602 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5603 * {@linkplain #empty default value}.
5604 * <li>If the {@code iterator} handle is non-{@code null}, it must have the return
5605 * type {@code java.util.Iterator} or a subtype thereof.
5606 * The iterator it produces when the loop is executed will be assumed
5607 * to yield values which can be converted to type {@code T}.
5608 * <li>The parameter list of an {@code iterator} that is non-{@code null} (of some form {@code (A*)}) must be
5609 * effectively identical to the external parameter list {@code (A...)}.
5610 * <li>If {@code iterator} is {@code null} it defaults to a method handle which behaves
5611 * like {@link java.lang.Iterable#iterator()}. In that case, the internal parameter list
5612 * {@code (V T A...)} must have at least one {@code A} type, and the default iterator
5613 * handle parameter is adjusted to accept the leading {@code A} type, as if by
5614 * the {@link MethodHandle#asType asType} conversion method.
5615 * The leading {@code A} type must be {@code Iterable} or a subtype thereof.
5616 * This conversion step, done at loop construction time, must not throw a {@code WrongMethodTypeException}.
5617 * </ul>
5618 * <p>
5619 * The type {@code T} may be either a primitive or reference.
5620 * Since type {@code Iterator<T>} is erased in the method handle representation to the raw type {@code Iterator},
5621 * the {@code iteratedLoop} combinator adjusts the leading argument type for {@code body} to {@code Object}
5622 * as if by the {@link MethodHandle#asType asType} conversion method.
5623 * Therefore, if an iterator of the wrong type appears as the loop is executed, runtime exceptions may occur
5624 * as the result of dynamic conversions performed by {@link MethodHandle#asType(MethodType)}.
5625 * <p>
5626 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5627 * <li>The loop handle's result type is the result type {@code V} of the body.
5628 * <li>The loop handle's parameter types are the types {@code (A...)},
5629 * from the external parameter list.
5630 * </ul>
5631 * <p>
5632 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5633 * the loop variable as well as the result type of the loop; {@code T}/{@code t}, that of the elements of the
5634 * structure the loop iterates over, and {@code A...}/{@code a...} represent arguments passed to the loop.
5635 * <blockquote><pre>{@code
5636 * Iterator<T> iterator(A...); // defaults to Iterable::iterator
5637 * V init(A...);
5638 * V body(V,T,A...);
5639 * V iteratedLoop(A... a...) {
5640 * Iterator<T> it = iterator(a...);
5641 * V v = init(a...);
5642 * while (it.hasNext()) {
5643 * T t = it.next();
5644 * v = body(v, t, a...);
5645 * }
5646 * return v;
5647 * }
5648 * }</pre></blockquote>
5649 * <p>
5650 * @apiNote Example:
5651 * <blockquote><pre>{@code
5652 * // get an iterator from a list
5653 * static List<String> reverseStep(List<String> r, String e) {
5654 * r.add(0, e);
5655 * return r;
5656 * }
5657 * static List<String> newArrayList() { return new ArrayList<>(); }
5658 * // assume MH_reverseStep and MH_newArrayList are handles to the above methods
5659 * MethodHandle loop = MethodHandles.iteratedLoop(null, MH_newArrayList, MH_reverseStep);
5660 * List<String> list = Arrays.asList("a", "b", "c", "d", "e");
5661 * List<String> reversedList = Arrays.asList("e", "d", "c", "b", "a");
5662 * assertEquals(reversedList, (List<String>) loop.invoke(list));
5663 * }</pre></blockquote>
5664 * <p>
5665 * @apiNote The implementation of this method can be expressed approximately as follows:
5666 * <blockquote><pre>{@code
5667 * MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
5668 * // assume MH_next, MH_hasNext, MH_startIter are handles to methods of Iterator/Iterable
5669 * Class<?> returnType = body.type().returnType();
5670 * Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
5671 * MethodHandle nextVal = MH_next.asType(MH_next.type().changeReturnType(ttype));
5672 * MethodHandle retv = null, step = body, startIter = iterator;
5673 * if (returnType != void.class) {
5674 * // the simple thing first: in (I V A...), drop the I to get V
5675 * retv = dropArguments(identity(returnType), 0, Iterator.class);
5676 * // body type signature (V T A...), internal loop types (I V A...)
5677 * step = swapArguments(body, 0, 1); // swap V <-> T
5678 * }
5679 * if (startIter == null) startIter = MH_getIter;
5680 * MethodHandle[]
5681 * iterVar = { startIter, null, MH_hasNext, retv }, // it = iterator; while (it.hasNext())
5682 * bodyClause = { init, filterArguments(step, 0, nextVal) }; // v = body(v, t, a)
5683 * return loop(iterVar, bodyClause);
5684 * }
5685 * }</pre></blockquote>
5686 *
5687 * @param iterator an optional handle to return the iterator to start the loop.
5688 * If non-{@code null}, the handle must return {@link java.util.Iterator} or a subtype.
5689 * See above for other constraints.
5690 * @param init optional initializer, providing the initial value of the loop variable.
5691 * May be {@code null}, implying a default initial value. See above for other constraints.
5692 * @param body body of the loop, which may not be {@code null}.
5693 * It controls the loop parameters and result type in the standard case (see above for details).
5694 * It must accept its own return type (if non-void) plus a {@code T} parameter (for the iterated values),
5695 * and may accept any number of additional types.
5696 * See above for other constraints.
5697 *
5698 * @return a method handle embodying the iteration loop functionality.
5699 * @throws NullPointerException if the {@code body} handle is {@code null}.
5700 * @throws IllegalArgumentException if any argument violates the above requirements.
5701 *
5702 * @since 9
5703 */
5704 public static MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
5705 Class<?> iterableType = iteratedLoopChecks(iterator, init, body);
5706 Class<?> returnType = body.type().returnType();
5707 MethodHandle hasNext = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iteratePred);
5708 MethodHandle nextRaw = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iterateNext);
5709 MethodHandle startIter;
5710 MethodHandle nextVal;
5711 {
5712 MethodType iteratorType;
5713 if (iterator == null) {
5714 // derive argument type from body, if available, else use Iterable
5715 startIter = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_initIterator);
5716 iteratorType = startIter.type().changeParameterType(0, iterableType);
5717 } else {
5718 // force return type to the internal iterator class
5719 iteratorType = iterator.type().changeReturnType(Iterator.class);
5720 startIter = iterator;
5721 }
5722 Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
5723 MethodType nextValType = nextRaw.type().changeReturnType(ttype);
5724
5725 // perform the asType transforms under an exception transformer, as per spec.:
5726 try {
5727 startIter = startIter.asType(iteratorType);
5728 nextVal = nextRaw.asType(nextValType);
5729 } catch (WrongMethodTypeException ex) {
5730 throw new IllegalArgumentException(ex);
5731 }
5732 }
5733
5734 MethodHandle retv = null, step = body;
5735 if (returnType != void.class) {
5736 // the simple thing first: in (I V A...), drop the I to get V
5737 retv = dropArguments(identity(returnType), 0, Iterator.class);
5738 // body type signature (V T A...), internal loop types (I V A...)
5739 step = swapArguments(body, 0, 1); // swap V <-> T
5740 }
5741
5742 MethodHandle[]
5743 iterVar = { startIter, null, hasNext, retv },
5744 bodyClause = { init, filterArgument(step, 0, nextVal) };
5745 return loop(iterVar, bodyClause);
5746 }
5747
5748 private static Class<?> iteratedLoopChecks(MethodHandle iterator, MethodHandle init, MethodHandle body) {
5749 Objects.requireNonNull(body);
5750 MethodType bodyType = body.type();
5751 Class<?> returnType = bodyType.returnType();
5752 List<Class<?>> internalParamList = bodyType.parameterList();
5753 // strip leading V value if present
5754 int vsize = (returnType == void.class ? 0 : 1);
5755 if (vsize != 0 && (internalParamList.size() == 0 || internalParamList.get(0) != returnType)) {
5756 // argument list has no "V" => error
5757 MethodType expected = bodyType.insertParameterTypes(0, returnType);
5758 throw misMatchedTypes("body function", bodyType, expected);
5759 } else if (internalParamList.size() <= vsize) {
5760 // missing T type => error
5761 MethodType expected = bodyType.insertParameterTypes(vsize, Object.class);
5762 throw misMatchedTypes("body function", bodyType, expected);
5763 }
5764 List<Class<?>> externalParamList = internalParamList.subList(vsize + 1, internalParamList.size());
5765 Class<?> iterableType = null;
5766 if (iterator != null) {
5767 // special case; if the body handle only declares V and T then
5768 // the external parameter list is obtained from iterator handle
5769 if (externalParamList.isEmpty()) {
5770 externalParamList = iterator.type().parameterList();
5771 }
5772 MethodType itype = iterator.type();
5773 if (!Iterator.class.isAssignableFrom(itype.returnType())) {
5774 throw newIllegalArgumentException("iteratedLoop first argument must have Iterator return type");
5775 }
5776 if (!itype.effectivelyIdenticalParameters(0, externalParamList)) {
5777 MethodType expected = methodType(itype.returnType(), externalParamList);
5778 throw misMatchedTypes("iterator parameters", itype, expected);
5779 }
5780 } else {
5781 if (externalParamList.isEmpty()) {
5782 // special case; if the iterator handle is null and the body handle
5783 // only declares V and T then the external parameter list consists
5784 // of Iterable
5785 externalParamList = Arrays.asList(Iterable.class);
5786 iterableType = Iterable.class;
5787 } else {
5788 // special case; if the iterator handle is null and the external
5789 // parameter list is not empty then the first parameter must be
5790 // assignable to Iterable
5791 iterableType = externalParamList.get(0);
5792 if (!Iterable.class.isAssignableFrom(iterableType)) {
5793 throw newIllegalArgumentException(
5794 "inferred first loop argument must inherit from Iterable: " + iterableType);
5795 }
5796 }
5797 }
5798 if (init != null) {
5799 MethodType initType = init.type();
5800 if (initType.returnType() != returnType ||
5801 !initType.effectivelyIdenticalParameters(0, externalParamList)) {
5802 throw misMatchedTypes("loop initializer", initType, methodType(returnType, externalParamList));
5803 }
5804 }
5805 return iterableType; // help the caller a bit
5806 }
5807
5808 /*non-public*/ static MethodHandle swapArguments(MethodHandle mh, int i, int j) {
5809 // there should be a better way to uncross my wires
5810 int arity = mh.type().parameterCount();
5811 int[] order = new int[arity];
5812 for (int k = 0; k < arity; k++) order[k] = k;
5813 order[i] = j; order[j] = i;
5814 Class<?>[] types = mh.type().parameterArray();
5815 Class<?> ti = types[i]; types[i] = types[j]; types[j] = ti;
5816 MethodType swapType = methodType(mh.type().returnType(), types);
5817 return permuteArguments(mh, swapType, order);
5818 }
5819
5820 /**
5821 * Makes a method handle that adapts a {@code target} method handle by wrapping it in a {@code try-finally} block.
5822 * Another method handle, {@code cleanup}, represents the functionality of the {@code finally} block. Any exception
5823 * thrown during the execution of the {@code target} handle will be passed to the {@code cleanup} handle. The
5824 * exception will be rethrown, unless {@code cleanup} handle throws an exception first. The
5825 * value returned from the {@code cleanup} handle's execution will be the result of the execution of the
5826 * {@code try-finally} handle.
5827 * <p>
5828 * The {@code cleanup} handle will be passed one or two additional leading arguments.
5829 * The first is the exception thrown during the
5830 * execution of the {@code target} handle, or {@code null} if no exception was thrown.
5831 * The second is the result of the execution of the {@code target} handle, or, if it throws an exception,
5832 * a {@code null}, zero, or {@code false} value of the required type is supplied as a placeholder.
5833 * The second argument is not present if the {@code target} handle has a {@code void} return type.
5834 * (Note that, except for argument type conversions, combinators represent {@code void} values in parameter lists
5835 * by omitting the corresponding paradoxical arguments, not by inserting {@code null} or zero values.)
5836 * <p>
5837 * The {@code target} and {@code cleanup} handles must have the same corresponding argument and return types, except
5838 * that the {@code cleanup} handle may omit trailing arguments. Also, the {@code cleanup} handle must have one or
5839 * two extra leading parameters:<ul>
5840 * <li>a {@code Throwable}, which will carry the exception thrown by the {@code target} handle (if any); and
5841 * <li>a parameter of the same type as the return type of both {@code target} and {@code cleanup}, which will carry
5842 * the result from the execution of the {@code target} handle.
5843 * This parameter is not present if the {@code target} returns {@code void}.
5844 * </ul>
5845 * <p>
5846 * The pseudocode for the resulting adapter looks as follows. In the code, {@code V} represents the result type of
5847 * the {@code try/finally} construct; {@code A}/{@code a}, the types and values of arguments to the resulting
5848 * handle consumed by the cleanup; and {@code B}/{@code b}, those of arguments to the resulting handle discarded by
5849 * the cleanup.
5850 * <blockquote><pre>{@code
5851 * V target(A..., B...);
5852 * V cleanup(Throwable, V, A...);
5853 * V adapter(A... a, B... b) {
5854 * V result = (zero value for V);
5855 * Throwable throwable = null;
5856 * try {
5857 * result = target(a..., b...);
5858 * } catch (Throwable t) {
5859 * throwable = t;
5860 * throw t;
5861 * } finally {
5862 * result = cleanup(throwable, result, a...);
5863 * }
5864 * return result;
5865 * }
5866 * }</pre></blockquote>
5867 * <p>
5868 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
5869 * be modified by execution of the target, and so are passed unchanged
5870 * from the caller to the cleanup, if it is invoked.
5871 * <p>
5872 * The target and cleanup must return the same type, even if the cleanup
5873 * always throws.
5874 * To create such a throwing cleanup, compose the cleanup logic
5875 * with {@link #throwException throwException},
5876 * in order to create a method handle of the correct return type.
5877 * <p>
5878 * Note that {@code tryFinally} never converts exceptions into normal returns.
5879 * In rare cases where exceptions must be converted in that way, first wrap
5880 * the target with {@link #catchException(MethodHandle, Class, MethodHandle)}
5881 * to capture an outgoing exception, and then wrap with {@code tryFinally}.
5882 *
5883 * @param target the handle whose execution is to be wrapped in a {@code try} block.
5884 * @param cleanup the handle that is invoked in the finally block.
5885 *
5886 * @return a method handle embodying the {@code try-finally} block composed of the two arguments.
5887 * @throws NullPointerException if any argument is null
5888 * @throws IllegalArgumentException if {@code cleanup} does not accept
5889 * the required leading arguments, or if the method handle types do
5890 * not match in their return types and their
5891 * corresponding trailing parameters
5892 *
5893 * @see MethodHandles#catchException(MethodHandle, Class, MethodHandle)
5894 * @since 9
5895 */
5896 public static MethodHandle tryFinally(MethodHandle target, MethodHandle cleanup) {
5897 List<Class<?>> targetParamTypes = target.type().parameterList();
5898 List<Class<?>> cleanupParamTypes = cleanup.type().parameterList();
5899 Class<?> rtype = target.type().returnType();
5900
5901 tryFinallyChecks(target, cleanup);
5902
5903 // Match parameter lists: if the cleanup has a shorter parameter list than the target, add ignored arguments.
5904 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
5905 // target parameter list.
5906 cleanup = dropArgumentsToMatch(cleanup, (rtype == void.class ? 1 : 2), targetParamTypes, 0);
5907
5908 // Use asFixedArity() to avoid unnecessary boxing of last argument for VarargsCollector case.
5909 return MethodHandleImpl.makeTryFinally(target.asFixedArity(), cleanup.asFixedArity(), rtype, targetParamTypes);
5910 }
5911
5912 private static void tryFinallyChecks(MethodHandle target, MethodHandle cleanup) {
5913 Class<?> rtype = target.type().returnType();
5914 if (rtype != cleanup.type().returnType()) {
5915 throw misMatchedTypes("target and return types", cleanup.type().returnType(), rtype);
5916 }
5917 MethodType cleanupType = cleanup.type();
5918 if (!Throwable.class.isAssignableFrom(cleanupType.parameterType(0))) {
5919 throw misMatchedTypes("cleanup first argument and Throwable", cleanup.type(), Throwable.class);
5920 }
5921 if (rtype != void.class && cleanupType.parameterType(1) != rtype) {
5922 throw misMatchedTypes("cleanup second argument and target return type", cleanup.type(), rtype);
5923 }
5924 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
5925 // target parameter list.
5926 int cleanupArgIndex = rtype == void.class ? 1 : 2;
5927 if (!cleanupType.effectivelyIdenticalParameters(cleanupArgIndex, target.type().parameterList())) {
5928 throw misMatchedTypes("cleanup parameters after (Throwable,result) and target parameter list prefix",
5929 cleanup.type(), target.type());
5930 }
5931 }
5932
5933 }
--- EOF ---