1 /*
2 * Copyright (c) 2008, 2017, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package java.lang.invoke;
27
28 import jdk.internal.org.objectweb.asm.ClassWriter;
29 import jdk.internal.org.objectweb.asm.Opcodes;
30 import jdk.internal.reflect.CallerSensitive;
31 import jdk.internal.reflect.Reflection;
32 import jdk.internal.vm.annotation.ForceInline;
33 import sun.invoke.util.ValueConversions;
34 import sun.invoke.util.VerifyAccess;
35 import sun.invoke.util.Wrapper;
36 import sun.reflect.misc.ReflectUtil;
37 import sun.security.util.SecurityConstants;
38
39 import java.lang.invoke.LambdaForm.BasicType;
40 import java.lang.reflect.Constructor;
41 import java.lang.reflect.Field;
42 import java.lang.reflect.Member;
43 import java.lang.reflect.Method;
44 import java.lang.reflect.Modifier;
45 import java.lang.reflect.Module;
46 import java.lang.reflect.ReflectPermission;
47 import java.nio.ByteOrder;
48 import java.util.ArrayList;
49 import java.util.Arrays;
50 import java.util.BitSet;
51 import java.util.Iterator;
52 import java.util.List;
53 import java.util.Objects;
54 import java.util.concurrent.ConcurrentHashMap;
55 import java.util.stream.Collectors;
56 import java.util.stream.Stream;
57
58 import static java.lang.invoke.MethodHandleImpl.Intrinsic;
59 import static java.lang.invoke.MethodHandleNatives.Constants.*;
60 import static java.lang.invoke.MethodHandleStatics.newIllegalArgumentException;
61 import static java.lang.invoke.MethodType.methodType;
62
63 /**
64 * This class consists exclusively of static methods that operate on or return
65 * method handles. They fall into several categories:
66 * <ul>
67 * <li>Lookup methods which help create method handles for methods and fields.
68 * <li>Combinator methods, which combine or transform pre-existing method handles into new ones.
69 * <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns.
70 * </ul>
71 *
72 * @author John Rose, JSR 292 EG
73 * @since 1.7
74 */
75 public class MethodHandles {
76
77 private MethodHandles() { } // do not instantiate
78
79 static final MemberName.Factory IMPL_NAMES = MemberName.getFactory();
80
81 // See IMPL_LOOKUP below.
82
83 //// Method handle creation from ordinary methods.
84
85 /**
86 * Returns a {@link Lookup lookup object} with
87 * full capabilities to emulate all supported bytecode behaviors of the caller.
88 * These capabilities include <a href="MethodHandles.Lookup.html#privacc">private access</a> to the caller.
89 * Factory methods on the lookup object can create
90 * <a href="MethodHandleInfo.html#directmh">direct method handles</a>
91 * for any member that the caller has access to via bytecodes,
92 * including protected and private fields and methods.
93 * This lookup object is a <em>capability</em> which may be delegated to trusted agents.
94 * Do not store it in place where untrusted code can access it.
95 * <p>
96 * This method is caller sensitive, which means that it may return different
97 * values to different callers.
98 * <p>
99 * For any given caller class {@code C}, the lookup object returned by this call
100 * has equivalent capabilities to any lookup object
101 * supplied by the JVM to the bootstrap method of an
102 * <a href="package-summary.html#indyinsn">invokedynamic instruction</a>
103 * executing in the same caller class {@code C}.
104 * @return a lookup object for the caller of this method, with private access
105 */
106 @CallerSensitive
107 @ForceInline // to ensure Reflection.getCallerClass optimization
108 public static Lookup lookup() {
109 return new Lookup(Reflection.getCallerClass());
110 }
111
112 /**
113 * Returns a {@link Lookup lookup object} which is trusted minimally.
114 * It can only be used to create method handles to public members in
115 * public classes in packages that are exported unconditionally.
116 * <p>
117 * For now, the {@linkplain Lookup#lookupClass lookup class} of this lookup
118 * object is in an unnamed module.
119 * Consequently, the lookup context of this lookup object will be the bootstrap
120 * class loader, which means it cannot find user classes.
121 *
122 * <p style="font-size:smaller;">
123 * <em>Discussion:</em>
124 * The lookup class can be changed to any other class {@code C} using an expression of the form
125 * {@link Lookup#in publicLookup().in(C.class)}.
126 * but may change the lookup context by virtue of changing the class loader.
127 * A public lookup object is always subject to
128 * <a href="MethodHandles.Lookup.html#secmgr">security manager checks</a>.
129 * Also, it cannot access
130 * <a href="MethodHandles.Lookup.html#callsens">caller sensitive methods</a>.
131 * @return a lookup object which is trusted minimally
132 */
133 public static Lookup publicLookup() {
134 // During VM startup then only classes in the java.base module can be
135 // loaded and linked. This is because java.base exports aren't setup until
136 // the module system is initialized, hence types in the unnamed module
137 // (or any named module) can't link to java/lang/Object.
138 if (!jdk.internal.misc.VM.isModuleSystemInited()) {
139 return new Lookup(Object.class, Lookup.PUBLIC);
140 } else {
141 return LookupHelper.PUBLIC_LOOKUP;
142 }
143 }
144
145 /**
146 * Returns a {@link Lookup lookup object} with full capabilities to emulate all
147 * supported bytecode behaviors, including <a href="MethodHandles.Lookup.html#privacc">
148 * private access</a>, on a target class.
149 * This method checks that a caller, specified as a {@code Lookup} object, is allowed to
150 * do <em>deep reflection</em> on the target class. If {@code m1} is the module containing
151 * the {@link Lookup#lookupClass() lookup class}, and {@code m2} is the module containing
152 * the target class, then this check ensures that
153 * <ul>
154 * <li>{@code m1} {@link Module#canRead reads} {@code m2}.</li>
155 * <li>{@code m2} {@link Module#isOpen(String,Module) opens} the package containing
156 * the target class to at least {@code m1}.</li>
157 * <li>The lookup has the {@link Lookup#MODULE MODULE} lookup mode.</li>
158 * </ul>
159 * <p>
160 * If there is a security manager, its {@code checkPermission} method is called to
161 * check {@code ReflectPermission("suppressAccessChecks")}.
162 * @apiNote The {@code MODULE} lookup mode serves to authenticate that the lookup object
163 * was created by code in the caller module (or derived from a lookup object originally
164 * created by the caller). A lookup object with the {@code MODULE} lookup mode can be
165 * shared with trusted parties without giving away {@code PRIVATE} and {@code PACKAGE}
166 * access to the caller.
167 * @param targetClass the target class
168 * @param lookup the caller lookup object
169 * @return a lookup object for the target class, with private access
170 * @throws IllegalArgumentException if {@code targetClass} is a primitve type or array class
171 * @throws NullPointerException if {@code targetClass} or {@code caller} is {@code null}
172 * @throws IllegalAccessException if the access check specified above fails
173 * @throws SecurityException if denied by the security manager
174 * @since 9
175 * @see Lookup#dropLookupMode
176 */
177 public static Lookup privateLookupIn(Class<?> targetClass, Lookup lookup) throws IllegalAccessException {
178 SecurityManager sm = System.getSecurityManager();
179 if (sm != null) sm.checkPermission(ACCESS_PERMISSION);
180 if (targetClass.isPrimitive())
181 throw new IllegalArgumentException(targetClass + " is a primitive class");
182 if (targetClass.isArray())
183 throw new IllegalArgumentException(targetClass + " is an array class");
184 Module targetModule = targetClass.getModule();
185 Module callerModule = lookup.lookupClass().getModule();
186 if (callerModule != targetModule && targetModule.isNamed()) {
187 if (!callerModule.canRead(targetModule))
188 throw new IllegalAccessException(callerModule + " does not read " + targetModule);
189 String pn = targetClass.getPackageName();
190 assert pn != null && pn.length() > 0 : "unnamed package cannot be in named module";
191 if (!targetModule.isOpen(pn, callerModule))
192 throw new IllegalAccessException(targetModule + " does not open " + pn + " to " + callerModule);
193 }
194 if ((lookup.lookupModes() & Lookup.MODULE) == 0)
195 throw new IllegalAccessException("lookup does not have MODULE lookup mode");
196 return new Lookup(targetClass);
197 }
198
199 /**
200 * Performs an unchecked "crack" of a
201 * <a href="MethodHandleInfo.html#directmh">direct method handle</a>.
202 * The result is as if the user had obtained a lookup object capable enough
203 * to crack the target method handle, called
204 * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect}
205 * on the target to obtain its symbolic reference, and then called
206 * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs}
207 * to resolve the symbolic reference to a member.
208 * <p>
209 * If there is a security manager, its {@code checkPermission} method
210 * is called with a {@code ReflectPermission("suppressAccessChecks")} permission.
211 * @param <T> the desired type of the result, either {@link Member} or a subtype
212 * @param target a direct method handle to crack into symbolic reference components
213 * @param expected a class object representing the desired result type {@code T}
214 * @return a reference to the method, constructor, or field object
215 * @exception SecurityException if the caller is not privileged to call {@code setAccessible}
216 * @exception NullPointerException if either argument is {@code null}
217 * @exception IllegalArgumentException if the target is not a direct method handle
218 * @exception ClassCastException if the member is not of the expected type
219 * @since 1.8
220 */
221 public static <T extends Member> T
222 reflectAs(Class<T> expected, MethodHandle target) {
223 SecurityManager smgr = System.getSecurityManager();
224 if (smgr != null) smgr.checkPermission(ACCESS_PERMISSION);
225 Lookup lookup = Lookup.IMPL_LOOKUP; // use maximally privileged lookup
226 return lookup.revealDirect(target).reflectAs(expected, lookup);
227 }
228 // Copied from AccessibleObject, as used by Method.setAccessible, etc.:
229 private static final java.security.Permission ACCESS_PERMISSION =
230 new ReflectPermission("suppressAccessChecks");
231
232 /**
233 * A <em>lookup object</em> is a factory for creating method handles,
234 * when the creation requires access checking.
235 * Method handles do not perform
236 * access checks when they are called, but rather when they are created.
237 * Therefore, method handle access
238 * restrictions must be enforced when a method handle is created.
239 * The caller class against which those restrictions are enforced
240 * is known as the {@linkplain #lookupClass lookup class}.
241 * <p>
242 * A lookup class which needs to create method handles will call
243 * {@link MethodHandles#lookup MethodHandles.lookup} to create a factory for itself.
244 * When the {@code Lookup} factory object is created, the identity of the lookup class is
245 * determined, and securely stored in the {@code Lookup} object.
246 * The lookup class (or its delegates) may then use factory methods
247 * on the {@code Lookup} object to create method handles for access-checked members.
248 * This includes all methods, constructors, and fields which are allowed to the lookup class,
249 * even private ones.
250 *
251 * <h1><a name="lookups"></a>Lookup Factory Methods</h1>
252 * The factory methods on a {@code Lookup} object correspond to all major
253 * use cases for methods, constructors, and fields.
254 * Each method handle created by a factory method is the functional
255 * equivalent of a particular <em>bytecode behavior</em>.
256 * (Bytecode behaviors are described in section 5.4.3.5 of the Java Virtual Machine Specification.)
257 * Here is a summary of the correspondence between these factory methods and
258 * the behavior of the resulting method handles:
259 * <table border=1 cellpadding=5 summary="lookup method behaviors">
260 * <tr>
261 * <th><a name="equiv"></a>lookup expression</th>
262 * <th>member</th>
263 * <th>bytecode behavior</th>
264 * </tr>
265 * <tr>
266 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</td>
267 * <td>{@code FT f;}</td><td>{@code (T) this.f;}</td>
268 * </tr>
269 * <tr>
270 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</td>
271 * <td>{@code static}<br>{@code FT f;}</td><td>{@code (T) C.f;}</td>
272 * </tr>
273 * <tr>
274 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</td>
275 * <td>{@code FT f;}</td><td>{@code this.f = x;}</td>
276 * </tr>
277 * <tr>
278 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</td>
279 * <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td>
280 * </tr>
281 * <tr>
282 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</td>
283 * <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>
284 * </tr>
285 * <tr>
286 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</td>
287 * <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td>
288 * </tr>
289 * <tr>
290 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</td>
291 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
292 * </tr>
293 * <tr>
294 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</td>
295 * <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td>
296 * </tr>
297 * <tr>
298 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</td>
299 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td>
300 * </tr>
301 * <tr>
302 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</td>
303 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, arg);}</td>
304 * </tr>
305 * <tr>
306 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</td>
307 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
308 * </tr>
309 * <tr>
310 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</td>
311 * <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td>
312 * </tr>
313 * <tr>
314 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</td>
315 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
316 * </tr>
317 * <tr>
318 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findClass lookup.findClass("C")}</td>
319 * <td>{@code class C { ... }}</td><td>{@code C.class;}</td>
320 * </tr>
321 * </table>
322 *
323 * Here, the type {@code C} is the class or interface being searched for a member,
324 * documented as a parameter named {@code refc} in the lookup methods.
325 * The method type {@code MT} is composed from the return type {@code T}
326 * and the sequence of argument types {@code A*}.
327 * The constructor also has a sequence of argument types {@code A*} and
328 * is deemed to return the newly-created object of type {@code C}.
329 * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}.
330 * The formal parameter {@code this} stands for the self-reference of type {@code C};
331 * if it is present, it is always the leading argument to the method handle invocation.
332 * (In the case of some {@code protected} members, {@code this} may be
333 * restricted in type to the lookup class; see below.)
334 * The name {@code arg} stands for all the other method handle arguments.
335 * In the code examples for the Core Reflection API, the name {@code thisOrNull}
336 * stands for a null reference if the accessed method or field is static,
337 * and {@code this} otherwise.
338 * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand
339 * for reflective objects corresponding to the given members.
340 * <p>
341 * The bytecode behavior for a {@code findClass} operation is a load of a constant class,
342 * as if by {@code ldc CONSTANT_Class}.
343 * The behavior is represented, not as a method handle, but directly as a {@code Class} constant.
344 * <p>
345 * In cases where the given member is of variable arity (i.e., a method or constructor)
346 * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}.
347 * In all other cases, the returned method handle will be of fixed arity.
348 * <p style="font-size:smaller;">
349 * <em>Discussion:</em>
350 * The equivalence between looked-up method handles and underlying
351 * class members and bytecode behaviors
352 * can break down in a few ways:
353 * <ul style="font-size:smaller;">
354 * <li>If {@code C} is not symbolically accessible from the lookup class's loader,
355 * the lookup can still succeed, even when there is no equivalent
356 * Java expression or bytecoded constant.
357 * <li>Likewise, if {@code T} or {@code MT}
358 * is not symbolically accessible from the lookup class's loader,
359 * the lookup can still succeed.
360 * For example, lookups for {@code MethodHandle.invokeExact} and
361 * {@code MethodHandle.invoke} will always succeed, regardless of requested type.
362 * <li>If there is a security manager installed, it can forbid the lookup
363 * on various grounds (<a href="MethodHandles.Lookup.html#secmgr">see below</a>).
364 * By contrast, the {@code ldc} instruction on a {@code CONSTANT_MethodHandle}
365 * constant is not subject to security manager checks.
366 * <li>If the looked-up method has a
367 * <a href="MethodHandle.html#maxarity">very large arity</a>,
368 * the method handle creation may fail, due to the method handle
369 * type having too many parameters.
370 * </ul>
371 *
372 * <h1><a name="access"></a>Access checking</h1>
373 * Access checks are applied in the factory methods of {@code Lookup},
374 * when a method handle is created.
375 * This is a key difference from the Core Reflection API, since
376 * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
377 * performs access checking against every caller, on every call.
378 * <p>
379 * All access checks start from a {@code Lookup} object, which
380 * compares its recorded lookup class against all requests to
381 * create method handles.
382 * A single {@code Lookup} object can be used to create any number
383 * of access-checked method handles, all checked against a single
384 * lookup class.
385 * <p>
386 * A {@code Lookup} object can be shared with other trusted code,
387 * such as a metaobject protocol.
388 * A shared {@code Lookup} object delegates the capability
389 * to create method handles on private members of the lookup class.
390 * Even if privileged code uses the {@code Lookup} object,
391 * the access checking is confined to the privileges of the
392 * original lookup class.
393 * <p>
394 * A lookup can fail, because
395 * the containing class is not accessible to the lookup class, or
396 * because the desired class member is missing, or because the
397 * desired class member is not accessible to the lookup class, or
398 * because the lookup object is not trusted enough to access the member.
399 * In any of these cases, a {@code ReflectiveOperationException} will be
400 * thrown from the attempted lookup. The exact class will be one of
401 * the following:
402 * <ul>
403 * <li>NoSuchMethodException — if a method is requested but does not exist
404 * <li>NoSuchFieldException — if a field is requested but does not exist
405 * <li>IllegalAccessException — if the member exists but an access check fails
406 * </ul>
407 * <p>
408 * In general, the conditions under which a method handle may be
409 * looked up for a method {@code M} are no more restrictive than the conditions
410 * under which the lookup class could have compiled, verified, and resolved a call to {@code M}.
411 * Where the JVM would raise exceptions like {@code NoSuchMethodError},
412 * a method handle lookup will generally raise a corresponding
413 * checked exception, such as {@code NoSuchMethodException}.
414 * And the effect of invoking the method handle resulting from the lookup
415 * is <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a>
416 * to executing the compiled, verified, and resolved call to {@code M}.
417 * The same point is true of fields and constructors.
418 * <p style="font-size:smaller;">
419 * <em>Discussion:</em>
420 * Access checks only apply to named and reflected methods,
421 * constructors, and fields.
422 * Other method handle creation methods, such as
423 * {@link MethodHandle#asType MethodHandle.asType},
424 * do not require any access checks, and are used
425 * independently of any {@code Lookup} object.
426 * <p>
427 * If the desired member is {@code protected}, the usual JVM rules apply,
428 * including the requirement that the lookup class must be either be in the
429 * same package as the desired member, or must inherit that member.
430 * (See the Java Virtual Machine Specification, sections 4.9.2, 5.4.3.5, and 6.4.)
431 * In addition, if the desired member is a non-static field or method
432 * in a different package, the resulting method handle may only be applied
433 * to objects of the lookup class or one of its subclasses.
434 * This requirement is enforced by narrowing the type of the leading
435 * {@code this} parameter from {@code C}
436 * (which will necessarily be a superclass of the lookup class)
437 * to the lookup class itself.
438 * <p>
439 * The JVM imposes a similar requirement on {@code invokespecial} instruction,
440 * that the receiver argument must match both the resolved method <em>and</em>
441 * the current class. Again, this requirement is enforced by narrowing the
442 * type of the leading parameter to the resulting method handle.
443 * (See the Java Virtual Machine Specification, section 4.10.1.9.)
444 * <p>
445 * The JVM represents constructors and static initializer blocks as internal methods
446 * with special names ({@code "<init>"} and {@code "<clinit>"}).
447 * The internal syntax of invocation instructions allows them to refer to such internal
448 * methods as if they were normal methods, but the JVM bytecode verifier rejects them.
449 * A lookup of such an internal method will produce a {@code NoSuchMethodException}.
450 * <p>
451 * In some cases, access between nested classes is obtained by the Java compiler by creating
452 * an wrapper method to access a private method of another class
453 * in the same top-level declaration.
454 * For example, a nested class {@code C.D}
455 * can access private members within other related classes such as
456 * {@code C}, {@code C.D.E}, or {@code C.B},
457 * but the Java compiler may need to generate wrapper methods in
458 * those related classes. In such cases, a {@code Lookup} object on
459 * {@code C.E} would be unable to those private members.
460 * A workaround for this limitation is the {@link Lookup#in Lookup.in} method,
461 * which can transform a lookup on {@code C.E} into one on any of those other
462 * classes, without special elevation of privilege.
463 * <p>
464 * The accesses permitted to a given lookup object may be limited,
465 * according to its set of {@link #lookupModes lookupModes},
466 * to a subset of members normally accessible to the lookup class.
467 * For example, the {@link MethodHandles#publicLookup publicLookup}
468 * method produces a lookup object which is only allowed to access
469 * public members in public classes of exported packages.
470 * The caller sensitive method {@link MethodHandles#lookup lookup}
471 * produces a lookup object with full capabilities relative to
472 * its caller class, to emulate all supported bytecode behaviors.
473 * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object
474 * with fewer access modes than the original lookup object.
475 *
476 * <p style="font-size:smaller;">
477 * <a name="privacc"></a>
478 * <em>Discussion of private access:</em>
479 * We say that a lookup has <em>private access</em>
480 * if its {@linkplain #lookupModes lookup modes}
481 * include the possibility of accessing {@code private} members.
482 * As documented in the relevant methods elsewhere,
483 * only lookups with private access possess the following capabilities:
484 * <ul style="font-size:smaller;">
485 * <li>access private fields, methods, and constructors of the lookup class
486 * <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> methods,
487 * such as {@code Class.forName}
488 * <li>create method handles which {@link Lookup#findSpecial emulate invokespecial} instructions
489 * <li>avoid <a href="MethodHandles.Lookup.html#secmgr">package access checks</a>
490 * for classes accessible to the lookup class
491 * <li>create {@link Lookup#in delegated lookup objects} which have private access to other classes
492 * within the same package member
493 * </ul>
494 * <p style="font-size:smaller;">
495 * Each of these permissions is a consequence of the fact that a lookup object
496 * with private access can be securely traced back to an originating class,
497 * whose <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> and Java language access permissions
498 * can be reliably determined and emulated by method handles.
499 *
500 * <h1><a name="secmgr"></a>Security manager interactions</h1>
501 * Although bytecode instructions can only refer to classes in
502 * a related class loader, this API can search for methods in any
503 * class, as long as a reference to its {@code Class} object is
504 * available. Such cross-loader references are also possible with the
505 * Core Reflection API, and are impossible to bytecode instructions
506 * such as {@code invokestatic} or {@code getfield}.
507 * There is a {@linkplain java.lang.SecurityManager security manager API}
508 * to allow applications to check such cross-loader references.
509 * These checks apply to both the {@code MethodHandles.Lookup} API
510 * and the Core Reflection API
511 * (as found on {@link java.lang.Class Class}).
512 * <p>
513 * If a security manager is present, member and class lookups are subject to
514 * additional checks.
515 * From one to three calls are made to the security manager.
516 * Any of these calls can refuse access by throwing a
517 * {@link java.lang.SecurityException SecurityException}.
518 * Define {@code smgr} as the security manager,
519 * {@code lookc} as the lookup class of the current lookup object,
520 * {@code refc} as the containing class in which the member
521 * is being sought, and {@code defc} as the class in which the
522 * member is actually defined.
523 * (If a class or other type is being accessed,
524 * the {@code refc} and {@code defc} values are the class itself.)
525 * The value {@code lookc} is defined as <em>not present</em>
526 * if the current lookup object does not have
527 * <a href="MethodHandles.Lookup.html#privacc">private access</a>.
528 * The calls are made according to the following rules:
529 * <ul>
530 * <li><b>Step 1:</b>
531 * If {@code lookc} is not present, or if its class loader is not
532 * the same as or an ancestor of the class loader of {@code refc},
533 * then {@link SecurityManager#checkPackageAccess
534 * smgr.checkPackageAccess(refcPkg)} is called,
535 * where {@code refcPkg} is the package of {@code refc}.
536 * <li><b>Step 2a:</b>
537 * If the retrieved member is not public and
538 * {@code lookc} is not present, then
539 * {@link SecurityManager#checkPermission smgr.checkPermission}
540 * with {@code RuntimePermission("accessDeclaredMembers")} is called.
541 * <li><b>Step 2b:</b>
542 * If the retrieved class has a {@code null} class loader,
543 * and {@code lookc} is not present, then
544 * {@link SecurityManager#checkPermission smgr.checkPermission}
545 * with {@code RuntimePermission("getClassLoader")} is called.
546 * <li><b>Step 3:</b>
547 * If the retrieved member is not public,
548 * and if {@code lookc} is not present,
549 * and if {@code defc} and {@code refc} are different,
550 * then {@link SecurityManager#checkPackageAccess
551 * smgr.checkPackageAccess(defcPkg)} is called,
552 * where {@code defcPkg} is the package of {@code defc}.
553 * </ul>
554 * Security checks are performed after other access checks have passed.
555 * Therefore, the above rules presuppose a member or class that is public,
556 * or else that is being accessed from a lookup class that has
557 * rights to access the member or class.
558 *
559 * <h1><a name="callsens"></a>Caller sensitive methods</h1>
560 * A small number of Java methods have a special property called caller sensitivity.
561 * A <em>caller-sensitive</em> method can behave differently depending on the
562 * identity of its immediate caller.
563 * <p>
564 * If a method handle for a caller-sensitive method is requested,
565 * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> apply,
566 * but they take account of the lookup class in a special way.
567 * The resulting method handle behaves as if it were called
568 * from an instruction contained in the lookup class,
569 * so that the caller-sensitive method detects the lookup class.
570 * (By contrast, the invoker of the method handle is disregarded.)
571 * Thus, in the case of caller-sensitive methods,
572 * different lookup classes may give rise to
573 * differently behaving method handles.
574 * <p>
575 * In cases where the lookup object is
576 * {@link MethodHandles#publicLookup() publicLookup()},
577 * or some other lookup object without
578 * <a href="MethodHandles.Lookup.html#privacc">private access</a>,
579 * the lookup class is disregarded.
580 * In such cases, no caller-sensitive method handle can be created,
581 * access is forbidden, and the lookup fails with an
582 * {@code IllegalAccessException}.
583 * <p style="font-size:smaller;">
584 * <em>Discussion:</em>
585 * For example, the caller-sensitive method
586 * {@link java.lang.Class#forName(String) Class.forName(x)}
587 * can return varying classes or throw varying exceptions,
588 * depending on the class loader of the class that calls it.
589 * A public lookup of {@code Class.forName} will fail, because
590 * there is no reasonable way to determine its bytecode behavior.
591 * <p style="font-size:smaller;">
592 * If an application caches method handles for broad sharing,
593 * it should use {@code publicLookup()} to create them.
594 * If there is a lookup of {@code Class.forName}, it will fail,
595 * and the application must take appropriate action in that case.
596 * It may be that a later lookup, perhaps during the invocation of a
597 * bootstrap method, can incorporate the specific identity
598 * of the caller, making the method accessible.
599 * <p style="font-size:smaller;">
600 * The function {@code MethodHandles.lookup} is caller sensitive
601 * so that there can be a secure foundation for lookups.
602 * Nearly all other methods in the JSR 292 API rely on lookup
603 * objects to check access requests.
604 */
605 public static final
606 class Lookup {
607 /** The class on behalf of whom the lookup is being performed. */
608 private final Class<?> lookupClass;
609
610 /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */
611 private final int allowedModes;
612
613 /** A single-bit mask representing {@code public} access,
614 * which may contribute to the result of {@link #lookupModes lookupModes}.
615 * The value, {@code 0x01}, happens to be the same as the value of the
616 * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.
617 */
618 public static final int PUBLIC = Modifier.PUBLIC;
619
620 /** A single-bit mask representing {@code private} access,
621 * which may contribute to the result of {@link #lookupModes lookupModes}.
622 * The value, {@code 0x02}, happens to be the same as the value of the
623 * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.
624 */
625 public static final int PRIVATE = Modifier.PRIVATE;
626
627 /** A single-bit mask representing {@code protected} access,
628 * which may contribute to the result of {@link #lookupModes lookupModes}.
629 * The value, {@code 0x04}, happens to be the same as the value of the
630 * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.
631 */
632 public static final int PROTECTED = Modifier.PROTECTED;
633
634 /** A single-bit mask representing {@code package} access (default access),
635 * which may contribute to the result of {@link #lookupModes lookupModes}.
636 * The value is {@code 0x08}, which does not correspond meaningfully to
637 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
638 */
639 public static final int PACKAGE = Modifier.STATIC;
640
641 /** A single-bit mask representing {@code module} access (default access),
642 * which may contribute to the result of {@link #lookupModes lookupModes}.
643 * The value is {@code 0x10}, which does not correspond meaningfully to
644 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
645 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup}
646 * with this lookup mode can access all public types in the module of the
647 * lookup class and public types in packages exported by other modules
648 * to the module of the lookup class.
649 * @since 9
650 */
651 public static final int MODULE = PACKAGE << 1;
652
653 private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE | MODULE);
654 private static final int TRUSTED = -1;
655
656 private static int fixmods(int mods) {
657 mods &= (ALL_MODES - PACKAGE - MODULE);
658 return (mods != 0) ? mods : (PACKAGE | MODULE);
659 }
660
661 /** Tells which class is performing the lookup. It is this class against
662 * which checks are performed for visibility and access permissions.
663 * <p>
664 * The class implies a maximum level of access permission,
665 * but the permissions may be additionally limited by the bitmask
666 * {@link #lookupModes lookupModes}, which controls whether non-public members
667 * can be accessed.
668 * @return the lookup class, on behalf of which this lookup object finds members
669 */
670 public Class<?> lookupClass() {
671 return lookupClass;
672 }
673
674 // This is just for calling out to MethodHandleImpl.
675 private Class<?> lookupClassOrNull() {
676 return (allowedModes == TRUSTED) ? null : lookupClass;
677 }
678
679 /** Tells which access-protection classes of members this lookup object can produce.
680 * The result is a bit-mask of the bits
681 * {@linkplain #PUBLIC PUBLIC (0x01)},
682 * {@linkplain #PRIVATE PRIVATE (0x02)},
683 * {@linkplain #PROTECTED PROTECTED (0x04)},
684 * {@linkplain #PACKAGE PACKAGE (0x08)},
685 * and {@linkplain #MODULE MODULE (0x10)}.
686 * <p>
687 * A freshly-created lookup object
688 * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class}
689 * has all possible bits set, since the caller class can access all its own members,
690 * all public types in the caller's module, and all public types in packages exported
691 * by other modules to the caller's module.
692 * A lookup object on a new lookup class
693 * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object}
694 * may have some mode bits set to zero.
695 * Mode bits can also be
696 * {@linkplain java.lang.invoke.MethodHandles.Lookup#dropLookupMode directly cleared}.
697 * Once cleared, mode bits cannot be restored from the downgraded lookup object.
698 * The purpose of this is to restrict access via the new lookup object,
699 * so that it can access only names which can be reached by the original
700 * lookup object, and also by the new lookup class.
701 * @return the lookup modes, which limit the kinds of access performed by this lookup object
702 * @see #in
703 * @see #dropLookupMode
704 */
705 public int lookupModes() {
706 return allowedModes & ALL_MODES;
707 }
708
709 /** Embody the current class (the lookupClass) as a lookup class
710 * for method handle creation.
711 * Must be called by from a method in this package,
712 * which in turn is called by a method not in this package.
713 */
714 Lookup(Class<?> lookupClass) {
715 this(lookupClass, ALL_MODES);
716 // make sure we haven't accidentally picked up a privileged class:
717 checkUnprivilegedlookupClass(lookupClass, ALL_MODES);
718 }
719
720 private Lookup(Class<?> lookupClass, int allowedModes) {
721 this.lookupClass = lookupClass;
722 this.allowedModes = allowedModes;
723 }
724
725 /**
726 * Creates a lookup on the specified new lookup class.
727 * The resulting object will report the specified
728 * class as its own {@link #lookupClass lookupClass}.
729 * <p>
730 * However, the resulting {@code Lookup} object is guaranteed
731 * to have no more access capabilities than the original.
732 * In particular, access capabilities can be lost as follows:<ul>
733 * <li>If the lookup class for this {@code Lookup} is not in a named module,
734 * and the new lookup class is in a named module {@code M}, then no members in
735 * {@code M}'s non-exported packages will be accessible.
736 * <li>If the lookup for this {@code Lookup} is in a named module, and the
737 * new lookup class is in a different module {@code M}, then no members, not even
738 * public members in {@code M}'s exported packages, will be accessible.
739 * <li>If the new lookup class differs from the old one,
740 * protected members will not be accessible by virtue of inheritance.
741 * (Protected members may continue to be accessible because of package sharing.)
742 * <li>If the new lookup class is in a different package
743 * than the old one, protected and default (package) members will not be accessible.
744 * <li>If the new lookup class is not within the same package member
745 * as the old one, private members will not be accessible.
746 * <li>If the new lookup class is not accessible to the old lookup class,
747 * then no members, not even public members, will be accessible.
748 * (In all other cases, public members will continue to be accessible.)
749 * </ul>
750 * <p>
751 * The resulting lookup's capabilities for loading classes
752 * (used during {@link #findClass} invocations)
753 * are determined by the lookup class' loader,
754 * which may change due to this operation.
755 *
756 * @param requestedLookupClass the desired lookup class for the new lookup object
757 * @return a lookup object which reports the desired lookup class, or the same object
758 * if there is no change
759 * @throws NullPointerException if the argument is null
760 */
761 public Lookup in(Class<?> requestedLookupClass) {
762 Objects.requireNonNull(requestedLookupClass);
763 if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all
764 return new Lookup(requestedLookupClass, ALL_MODES);
765 if (requestedLookupClass == this.lookupClass)
766 return this; // keep same capabilities
767
768 int newModes = (allowedModes & (ALL_MODES & ~PROTECTED));
769 if (!VerifyAccess.isSameModule(this.lookupClass, requestedLookupClass)) {
770 // Allowed to teleport from an unnamed to a named module but resulting
771 // Lookup has no access to module private members
772 if (this.lookupClass.getModule().isNamed()) {
773 newModes = 0;
774 } else {
775 newModes &= ~MODULE;
776 }
777 }
778 if ((newModes & PACKAGE) != 0
779 && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {
780 newModes &= ~(PACKAGE|PRIVATE);
781 }
782 // Allow nestmate lookups to be created without special privilege:
783 if ((newModes & PRIVATE) != 0
784 && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {
785 newModes &= ~PRIVATE;
786 }
787 if ((newModes & PUBLIC) != 0
788 && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, allowedModes)) {
789 // The requested class it not accessible from the lookup class.
790 // No permissions.
791 newModes = 0;
792 }
793
794 checkUnprivilegedlookupClass(requestedLookupClass, newModes);
795 return new Lookup(requestedLookupClass, newModes);
796 }
797
798
799 /**
800 * Creates a lookup on the same lookup class which this lookup object
801 * finds members, but with a lookup mode that has lost the given lookup mode.
802 * The lookup mode to drop is one of {@link #PUBLIC PUBLIC}, {@link #MODULE
803 * MODULE}, {@link #PACKAGE PACKAGE}, {@link #PROTECTED PROTECTED} or {@link #PRIVATE PRIVATE}.
804 * {@link #PROTECTED PROTECTED} is always dropped and so the resulting lookup
805 * mode will never have this access capability. When dropping {@code PACKAGE}
806 * then the resulting lookup will not have {@code PACKAGE} or {@code PRIVATE}
807 * access. When dropping {@code MODULE} then the resulting lookup will not
808 * have {@code MODULE}, {@code PACKAGE}, or {@code PRIVATE} access. If {@code
809 * PUBLIC} is dropped then the resulting lookup has no access.
810 * @param modeToDrop the lookup mode to drop
811 * @return a lookup object which lacks the indicated mode, or the same object if there is no change
812 * @throws IllegalArgumentException if {@code modeToDrop} is not one of {@code PUBLIC},
813 * {@code MODULE}, {@code PACKAGE}, {@code PROTECTED} or {@code PRIVATE}
814 * @since 9
815 * @see MethodHandles#privateLookupIn
816 */
817 public Lookup dropLookupMode(int modeToDrop) {
818 int oldModes = lookupModes();
819 int newModes = oldModes & ~(modeToDrop | PROTECTED);
820 switch (modeToDrop) {
821 case PUBLIC: newModes &= ~(ALL_MODES); break;
822 case MODULE: newModes &= ~(PACKAGE | PRIVATE); break;
823 case PACKAGE: newModes &= ~(PRIVATE); break;
824 case PROTECTED:
825 case PRIVATE: break;
826 default: throw new IllegalArgumentException(modeToDrop + " is not a valid mode to drop");
827 }
828 if (newModes == oldModes) return this; // return self if no change
829 return new Lookup(lookupClass(), newModes);
830 }
831
832 // Make sure outer class is initialized first.
833 static { IMPL_NAMES.getClass(); }
834
835 /** Package-private version of lookup which is trusted. */
836 static final Lookup IMPL_LOOKUP = new Lookup(Object.class, TRUSTED);
837
838 private static void checkUnprivilegedlookupClass(Class<?> lookupClass, int allowedModes) {
839 String name = lookupClass.getName();
840 if (name.startsWith("java.lang.invoke."))
841 throw newIllegalArgumentException("illegal lookupClass: "+lookupClass);
842
843 // For caller-sensitive MethodHandles.lookup() disallow lookup from
844 // restricted packages. This a fragile and blunt approach.
845 // TODO replace with a more formal and less fragile mechanism
846 // that does not bluntly restrict classes under packages within
847 // java.base from looking up MethodHandles or VarHandles.
848 if (allowedModes == ALL_MODES && lookupClass.getClassLoader() == null) {
849 if ((name.startsWith("java.") &&
850 !name.equals("java.lang.Thread") &&
851 !name.startsWith("java.util.concurrent.")) ||
852 (name.startsWith("sun.") &&
853 !name.startsWith("sun.invoke."))) {
854 throw newIllegalArgumentException("illegal lookupClass: " + lookupClass);
855 }
856 }
857 }
858
859 /**
860 * Displays the name of the class from which lookups are to be made.
861 * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)
862 * If there are restrictions on the access permitted to this lookup,
863 * this is indicated by adding a suffix to the class name, consisting
864 * of a slash and a keyword. The keyword represents the strongest
865 * allowed access, and is chosen as follows:
866 * <ul>
867 * <li>If no access is allowed, the suffix is "/noaccess".
868 * <li>If only public access to types in exported packages is allowed, the suffix is "/public".
869 * <li>If only public and module access are allowed, the suffix is "/module".
870 * <li>If only public, module and package access are allowed, the suffix is "/package".
871 * <li>If only public, module, package, and private access are allowed, the suffix is "/private".
872 * </ul>
873 * If none of the above cases apply, it is the case that full
874 * access (public, module, package, private, and protected) is allowed.
875 * In this case, no suffix is added.
876 * This is true only of an object obtained originally from
877 * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
878 * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
879 * always have restricted access, and will display a suffix.
880 * <p>
881 * (It may seem strange that protected access should be
882 * stronger than private access. Viewed independently from
883 * package access, protected access is the first to be lost,
884 * because it requires a direct subclass relationship between
885 * caller and callee.)
886 * @see #in
887 */
888 @Override
889 public String toString() {
890 String cname = lookupClass.getName();
891 switch (allowedModes) {
892 case 0: // no privileges
893 return cname + "/noaccess";
894 case PUBLIC:
895 return cname + "/public";
896 case PUBLIC|MODULE:
897 return cname + "/module";
898 case PUBLIC|MODULE|PACKAGE:
899 return cname + "/package";
900 case ALL_MODES & ~PROTECTED:
901 return cname + "/private";
902 case ALL_MODES:
903 return cname;
904 case TRUSTED:
905 return "/trusted"; // internal only; not exported
906 default: // Should not happen, but it's a bitfield...
907 cname = cname + "/" + Integer.toHexString(allowedModes);
908 assert(false) : cname;
909 return cname;
910 }
911 }
912
913 /**
914 * Produces a method handle for a static method.
915 * The type of the method handle will be that of the method.
916 * (Since static methods do not take receivers, there is no
917 * additional receiver argument inserted into the method handle type,
918 * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)
919 * The method and all its argument types must be accessible to the lookup object.
920 * <p>
921 * The returned method handle will have
922 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
923 * the method's variable arity modifier bit ({@code 0x0080}) is set.
924 * <p>
925 * If the returned method handle is invoked, the method's class will
926 * be initialized, if it has not already been initialized.
927 * <p><b>Example:</b>
928 * <blockquote><pre>{@code
929 import static java.lang.invoke.MethodHandles.*;
930 import static java.lang.invoke.MethodType.*;
931 ...
932 MethodHandle MH_asList = publicLookup().findStatic(Arrays.class,
933 "asList", methodType(List.class, Object[].class));
934 assertEquals("[x, y]", MH_asList.invoke("x", "y").toString());
935 * }</pre></blockquote>
936 * @param refc the class from which the method is accessed
937 * @param name the name of the method
938 * @param type the type of the method
939 * @return the desired method handle
940 * @throws NoSuchMethodException if the method does not exist
941 * @throws IllegalAccessException if access checking fails,
942 * or if the method is not {@code static},
943 * or if the method's variable arity modifier bit
944 * is set and {@code asVarargsCollector} fails
945 * @exception SecurityException if a security manager is present and it
946 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
947 * @throws NullPointerException if any argument is null
948 */
949 public
950 MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
951 MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type);
952 return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerClass(method));
953 }
954
955 /**
956 * Produces a method handle for a virtual method.
957 * The type of the method handle will be that of the method,
958 * with the receiver type (usually {@code refc}) prepended.
959 * The method and all its argument types must be accessible to the lookup object.
960 * <p>
961 * When called, the handle will treat the first argument as a receiver
962 * and dispatch on the receiver's type to determine which method
963 * implementation to enter.
964 * (The dispatching action is identical with that performed by an
965 * {@code invokevirtual} or {@code invokeinterface} instruction.)
966 * <p>
967 * The first argument will be of type {@code refc} if the lookup
968 * class has full privileges to access the member. Otherwise
969 * the member must be {@code protected} and the first argument
970 * will be restricted in type to the lookup class.
971 * <p>
972 * The returned method handle will have
973 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
974 * the method's variable arity modifier bit ({@code 0x0080}) is set.
975 * <p>
976 * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual}
977 * instructions and method handles produced by {@code findVirtual},
978 * if the class is {@code MethodHandle} and the name string is
979 * {@code invokeExact} or {@code invoke}, the resulting
980 * method handle is equivalent to one produced by
981 * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or
982 * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}
983 * with the same {@code type} argument.
984 * <p>
985 * If the class is {@code VarHandle} and the name string corresponds to
986 * the name of a signature-polymorphic access mode method, the resulting
987 * method handle is equivalent to one produced by
988 * {@link java.lang.invoke.MethodHandles#varHandleInvoker} with
989 * the access mode corresponding to the name string and with the same
990 * {@code type} arguments.
991 * <p>
992 * <b>Example:</b>
993 * <blockquote><pre>{@code
994 import static java.lang.invoke.MethodHandles.*;
995 import static java.lang.invoke.MethodType.*;
996 ...
997 MethodHandle MH_concat = publicLookup().findVirtual(String.class,
998 "concat", methodType(String.class, String.class));
999 MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class,
1000 "hashCode", methodType(int.class));
1001 MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class,
1002 "hashCode", methodType(int.class));
1003 assertEquals("xy", (String) MH_concat.invokeExact("x", "y"));
1004 assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy"));
1005 assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy"));
1006 // interface method:
1007 MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class,
1008 "subSequence", methodType(CharSequence.class, int.class, int.class));
1009 assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString());
1010 // constructor "internal method" must be accessed differently:
1011 MethodType MT_newString = methodType(void.class); //()V for new String()
1012 try { assertEquals("impossible", lookup()
1013 .findVirtual(String.class, "<init>", MT_newString));
1014 } catch (NoSuchMethodException ex) { } // OK
1015 MethodHandle MH_newString = publicLookup()
1016 .findConstructor(String.class, MT_newString);
1017 assertEquals("", (String) MH_newString.invokeExact());
1018 * }</pre></blockquote>
1019 *
1020 * @param refc the class or interface from which the method is accessed
1021 * @param name the name of the method
1022 * @param type the type of the method, with the receiver argument omitted
1023 * @return the desired method handle
1024 * @throws NoSuchMethodException if the method does not exist
1025 * @throws IllegalAccessException if access checking fails,
1026 * or if the method is {@code static},
1027 * or if the method is {@code private} method of interface,
1028 * or if the method's variable arity modifier bit
1029 * is set and {@code asVarargsCollector} fails
1030 * @exception SecurityException if a security manager is present and it
1031 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1032 * @throws NullPointerException if any argument is null
1033 */
1034 public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1035 if (refc == MethodHandle.class) {
1036 MethodHandle mh = findVirtualForMH(name, type);
1037 if (mh != null) return mh;
1038 } else if (refc == VarHandle.class) {
1039 MethodHandle mh = findVirtualForVH(name, type);
1040 if (mh != null) return mh;
1041 }
1042 byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual);
1043 MemberName method = resolveOrFail(refKind, refc, name, type);
1044 return getDirectMethod(refKind, refc, method, findBoundCallerClass(method));
1045 }
1046 private MethodHandle findVirtualForMH(String name, MethodType type) {
1047 // these names require special lookups because of the implicit MethodType argument
1048 if ("invoke".equals(name))
1049 return invoker(type);
1050 if ("invokeExact".equals(name))
1051 return exactInvoker(type);
1052 assert(!MemberName.isMethodHandleInvokeName(name));
1053 return null;
1054 }
1055 private MethodHandle findVirtualForVH(String name, MethodType type) {
1056 try {
1057 return varHandleInvoker(VarHandle.AccessMode.valueFromMethodName(name), type);
1058 } catch (IllegalArgumentException e) {
1059 return null;
1060 }
1061 }
1062
1063 /**
1064 * Produces a method handle which creates an object and initializes it, using
1065 * the constructor of the specified type.
1066 * The parameter types of the method handle will be those of the constructor,
1067 * while the return type will be a reference to the constructor's class.
1068 * The constructor and all its argument types must be accessible to the lookup object.
1069 * <p>
1070 * The requested type must have a return type of {@code void}.
1071 * (This is consistent with the JVM's treatment of constructor type descriptors.)
1072 * <p>
1073 * The returned method handle will have
1074 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1075 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
1076 * <p>
1077 * If the returned method handle is invoked, the constructor's class will
1078 * be initialized, if it has not already been initialized.
1079 * <p><b>Example:</b>
1080 * <blockquote><pre>{@code
1081 import static java.lang.invoke.MethodHandles.*;
1082 import static java.lang.invoke.MethodType.*;
1083 ...
1084 MethodHandle MH_newArrayList = publicLookup().findConstructor(
1085 ArrayList.class, methodType(void.class, Collection.class));
1086 Collection orig = Arrays.asList("x", "y");
1087 Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig);
1088 assert(orig != copy);
1089 assertEquals(orig, copy);
1090 // a variable-arity constructor:
1091 MethodHandle MH_newProcessBuilder = publicLookup().findConstructor(
1092 ProcessBuilder.class, methodType(void.class, String[].class));
1093 ProcessBuilder pb = (ProcessBuilder)
1094 MH_newProcessBuilder.invoke("x", "y", "z");
1095 assertEquals("[x, y, z]", pb.command().toString());
1096 * }</pre></blockquote>
1097 * @param refc the class or interface from which the method is accessed
1098 * @param type the type of the method, with the receiver argument omitted, and a void return type
1099 * @return the desired method handle
1100 * @throws NoSuchMethodException if the constructor does not exist
1101 * @throws IllegalAccessException if access checking fails
1102 * or if the method's variable arity modifier bit
1103 * is set and {@code asVarargsCollector} fails
1104 * @exception SecurityException if a security manager is present and it
1105 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1106 * @throws NullPointerException if any argument is null
1107 */
1108 public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1109 if (refc.isArray()) {
1110 throw new NoSuchMethodException("no constructor for array class: " + refc.getName());
1111 }
1112 String name = "<init>";
1113 MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type);
1114 return getDirectConstructor(refc, ctor);
1115 }
1116
1117 /**
1118 * Looks up a class by name from the lookup context defined by this {@code Lookup} object. The static
1119 * initializer of the class is not run.
1120 * <p>
1121 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class}, its class
1122 * loader, and the {@linkplain #lookupModes() lookup modes}. In particular, the method first attempts to
1123 * load the requested class, and then determines whether the class is accessible to this lookup object.
1124 *
1125 * @param targetName the fully qualified name of the class to be looked up.
1126 * @return the requested class.
1127 * @exception SecurityException if a security manager is present and it
1128 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1129 * @throws LinkageError if the linkage fails
1130 * @throws ClassNotFoundException if the class cannot be loaded by the lookup class' loader.
1131 * @throws IllegalAccessException if the class is not accessible, using the allowed access
1132 * modes.
1133 * @exception SecurityException if a security manager is present and it
1134 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1135 * @since 9
1136 */
1137 public Class<?> findClass(String targetName) throws ClassNotFoundException, IllegalAccessException {
1138 Class<?> targetClass = Class.forName(targetName, false, lookupClass.getClassLoader());
1139 return accessClass(targetClass);
1140 }
1141
1142 /**
1143 * Determines if a class can be accessed from the lookup context defined by this {@code Lookup} object. The
1144 * static initializer of the class is not run.
1145 * <p>
1146 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class} and the
1147 * {@linkplain #lookupModes() lookup modes}.
1148 *
1149 * @param targetClass the class to be access-checked
1150 *
1151 * @return the class that has been access-checked
1152 *
1153 * @throws IllegalAccessException if the class is not accessible from the lookup class, using the allowed access
1154 * modes.
1155 * @exception SecurityException if a security manager is present and it
1156 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1157 * @since 9
1158 */
1159 public Class<?> accessClass(Class<?> targetClass) throws IllegalAccessException {
1160 if (!VerifyAccess.isClassAccessible(targetClass, lookupClass, allowedModes)) {
1161 throw new MemberName(targetClass).makeAccessException("access violation", this);
1162 }
1163 checkSecurityManager(targetClass, null);
1164 return targetClass;
1165 }
1166
1167 /**
1168 * Produces an early-bound method handle for a virtual method.
1169 * It will bypass checks for overriding methods on the receiver,
1170 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
1171 * instruction from within the explicitly specified {@code specialCaller}.
1172 * The type of the method handle will be that of the method,
1173 * with a suitably restricted receiver type prepended.
1174 * (The receiver type will be {@code specialCaller} or a subtype.)
1175 * The method and all its argument types must be accessible
1176 * to the lookup object.
1177 * <p>
1178 * Before method resolution,
1179 * if the explicitly specified caller class is not identical with the
1180 * lookup class, or if this lookup object does not have
1181 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
1182 * privileges, the access fails.
1183 * <p>
1184 * The returned method handle will have
1185 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1186 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1187 * <p style="font-size:smaller;">
1188 * <em>(Note: JVM internal methods named {@code "<init>"} are not visible to this API,
1189 * even though the {@code invokespecial} instruction can refer to them
1190 * in special circumstances. Use {@link #findConstructor findConstructor}
1191 * to access instance initialization methods in a safe manner.)</em>
1192 * <p><b>Example:</b>
1193 * <blockquote><pre>{@code
1194 import static java.lang.invoke.MethodHandles.*;
1195 import static java.lang.invoke.MethodType.*;
1196 ...
1197 static class Listie extends ArrayList {
1198 public String toString() { return "[wee Listie]"; }
1199 static Lookup lookup() { return MethodHandles.lookup(); }
1200 }
1201 ...
1202 // no access to constructor via invokeSpecial:
1203 MethodHandle MH_newListie = Listie.lookup()
1204 .findConstructor(Listie.class, methodType(void.class));
1205 Listie l = (Listie) MH_newListie.invokeExact();
1206 try { assertEquals("impossible", Listie.lookup().findSpecial(
1207 Listie.class, "<init>", methodType(void.class), Listie.class));
1208 } catch (NoSuchMethodException ex) { } // OK
1209 // access to super and self methods via invokeSpecial:
1210 MethodHandle MH_super = Listie.lookup().findSpecial(
1211 ArrayList.class, "toString" , methodType(String.class), Listie.class);
1212 MethodHandle MH_this = Listie.lookup().findSpecial(
1213 Listie.class, "toString" , methodType(String.class), Listie.class);
1214 MethodHandle MH_duper = Listie.lookup().findSpecial(
1215 Object.class, "toString" , methodType(String.class), Listie.class);
1216 assertEquals("[]", (String) MH_super.invokeExact(l));
1217 assertEquals(""+l, (String) MH_this.invokeExact(l));
1218 assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method
1219 try { assertEquals("inaccessible", Listie.lookup().findSpecial(
1220 String.class, "toString", methodType(String.class), Listie.class));
1221 } catch (IllegalAccessException ex) { } // OK
1222 Listie subl = new Listie() { public String toString() { return "[subclass]"; } };
1223 assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method
1224 * }</pre></blockquote>
1225 *
1226 * @param refc the class or interface from which the method is accessed
1227 * @param name the name of the method (which must not be "<init>")
1228 * @param type the type of the method, with the receiver argument omitted
1229 * @param specialCaller the proposed calling class to perform the {@code invokespecial}
1230 * @return the desired method handle
1231 * @throws NoSuchMethodException if the method does not exist
1232 * @throws IllegalAccessException if access checking fails,
1233 * or if the method is {@code static},
1234 * or if the method's variable arity modifier bit
1235 * is set and {@code asVarargsCollector} fails
1236 * @exception SecurityException if a security manager is present and it
1237 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1238 * @throws NullPointerException if any argument is null
1239 */
1240 public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,
1241 Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
1242 checkSpecialCaller(specialCaller, refc);
1243 Lookup specialLookup = this.in(specialCaller);
1244 MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type);
1245 return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerClass(method));
1246 }
1247
1248 /**
1249 * Produces a method handle giving read access to a non-static field.
1250 * The type of the method handle will have a return type of the field's
1251 * value type.
1252 * The method handle's single argument will be the instance containing
1253 * the field.
1254 * Access checking is performed immediately on behalf of the lookup class.
1255 * @param refc the class or interface from which the method is accessed
1256 * @param name the field's name
1257 * @param type the field's type
1258 * @return a method handle which can load values from the field
1259 * @throws NoSuchFieldException if the field does not exist
1260 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1261 * @exception SecurityException if a security manager is present and it
1262 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1263 * @throws NullPointerException if any argument is null
1264 * @see #findVarHandle(Class, String, Class)
1265 */
1266 public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1267 MemberName field = resolveOrFail(REF_getField, refc, name, type);
1268 return getDirectField(REF_getField, refc, field);
1269 }
1270
1271 /**
1272 * Produces a method handle giving write access to a non-static field.
1273 * The type of the method handle will have a void return type.
1274 * The method handle will take two arguments, the instance containing
1275 * the field, and the value to be stored.
1276 * The second argument will be of the field's value type.
1277 * Access checking is performed immediately on behalf of the lookup class.
1278 * @param refc the class or interface from which the method is accessed
1279 * @param name the field's name
1280 * @param type the field's type
1281 * @return a method handle which can store values into the field
1282 * @throws NoSuchFieldException if the field does not exist
1283 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1284 * @exception SecurityException if a security manager is present and it
1285 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1286 * @throws NullPointerException if any argument is null
1287 * @see #findVarHandle(Class, String, Class)
1288 */
1289 public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1290 MemberName field = resolveOrFail(REF_putField, refc, name, type);
1291 return getDirectField(REF_putField, refc, field);
1292 }
1293
1294 /**
1295 * Produces a VarHandle giving access to non-static fields of type
1296 * {@code T} declared by a receiver class of type {@code R}, supporting
1297 * shape {@code (R : T)}.
1298 * <p>
1299 * Access checking is performed immediately on behalf of the lookup
1300 * class.
1301 * <p>
1302 * Certain access modes of the returned VarHandle are unsupported under
1303 * the following conditions:
1304 * <ul>
1305 * <li>if the field is declared {@code final}, then the write, atomic
1306 * update, numeric atomic update, and bitwise atomic update access
1307 * modes are unsupported.
1308 * <li>if the field type is anything other than {@code byte},
1309 * {@code short}, {@code char}, {@code int}, {@code long},
1310 * {@code float}, or {@code double} then numeric atomic update
1311 * access modes are unsupported.
1312 * <li>if the field type is anything other than {@code boolean},
1313 * {@code byte}, {@code short}, {@code char}, {@code int} or
1314 * {@code long} then bitwise atomic update access modes are
1315 * unsupported.
1316 * </ul>
1317 * <p>
1318 * If the field is declared {@code volatile} then the returned VarHandle
1319 * will override access to the field (effectively ignore the
1320 * {@code volatile} declaration) in accordance to it's specified
1321 * access modes.
1322 * <p>
1323 * If the field type is {@code float} or {@code double} then numeric
1324 * and atomic update access modes compare values using their bitwise
1325 * representation (see {@link Float#floatToRawIntBits} and
1326 * {@link Double#doubleToRawLongBits}, respectively).
1327 * @apiNote
1328 * Bitwise comparison of {@code float} values or {@code double} values,
1329 * as performed by the numeric and atomic update access modes, differ
1330 * from the primitive {@code ==} operator and the {@link Float#equals}
1331 * and {@link Double#equals} methods, specifically with respect to
1332 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
1333 * Care should be taken when performing a compare and set or a compare
1334 * and exchange operation with such values since the operation may
1335 * unexpectedly fail.
1336 * There are many possible NaN values that are considered to be
1337 * {@code NaN} in Java, although no IEEE 754 floating-point operation
1338 * provided by Java can distinguish between them. Operation failure can
1339 * occur if the expected or witness value is a NaN value and it is
1340 * transformed (perhaps in a platform specific manner) into another NaN
1341 * value, and thus has a different bitwise representation (see
1342 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
1343 * details).
1344 * The values {@code -0.0} and {@code +0.0} have different bitwise
1345 * representations but are considered equal when using the primitive
1346 * {@code ==} operator. Operation failure can occur if, for example, a
1347 * numeric algorithm computes an expected value to be say {@code -0.0}
1348 * and previously computed the witness value to be say {@code +0.0}.
1349 * @param recv the receiver class, of type {@code R}, that declares the
1350 * non-static field
1351 * @param name the field's name
1352 * @param type the field's type, of type {@code T}
1353 * @return a VarHandle giving access to non-static fields.
1354 * @throws NoSuchFieldException if the field does not exist
1355 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1356 * @exception SecurityException if a security manager is present and it
1357 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1358 * @throws NullPointerException if any argument is null
1359 * @since 9
1360 */
1361 public VarHandle findVarHandle(Class<?> recv, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1362 MemberName getField = resolveOrFail(REF_getField, recv, name, type);
1363 MemberName putField = resolveOrFail(REF_putField, recv, name, type);
1364 return getFieldVarHandle(REF_getField, REF_putField, recv, getField, putField);
1365 }
1366
1367 /**
1368 * Produces a method handle giving read access to a static field.
1369 * The type of the method handle will have a return type of the field's
1370 * value type.
1371 * The method handle will take no arguments.
1372 * Access checking is performed immediately on behalf of the lookup class.
1373 * <p>
1374 * If the returned method handle is invoked, the field's class will
1375 * be initialized, if it has not already been initialized.
1376 * @param refc the class or interface from which the method is accessed
1377 * @param name the field's name
1378 * @param type the field's type
1379 * @return a method handle which can load values from the field
1380 * @throws NoSuchFieldException if the field does not exist
1381 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1382 * @exception SecurityException if a security manager is present and it
1383 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1384 * @throws NullPointerException if any argument is null
1385 */
1386 public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1387 MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
1388 return getDirectField(REF_getStatic, refc, field);
1389 }
1390
1391 /**
1392 * Produces a method handle giving write access to a static field.
1393 * The type of the method handle will have a void return type.
1394 * The method handle will take a single
1395 * argument, of the field's value type, the value to be stored.
1396 * Access checking is performed immediately on behalf of the lookup class.
1397 * <p>
1398 * If the returned method handle is invoked, the field's class will
1399 * be initialized, if it has not already been initialized.
1400 * @param refc the class or interface from which the method is accessed
1401 * @param name the field's name
1402 * @param type the field's type
1403 * @return a method handle which can store values into the field
1404 * @throws NoSuchFieldException if the field does not exist
1405 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1406 * @exception SecurityException if a security manager is present and it
1407 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1408 * @throws NullPointerException if any argument is null
1409 */
1410 public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1411 MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
1412 return getDirectField(REF_putStatic, refc, field);
1413 }
1414
1415 /**
1416 * Produces a VarHandle giving access to a static field of type
1417 * {@code T} declared by a given declaring class, supporting shape
1418 * {@code ((empty) : T)}.
1419 * <p>
1420 * Access checking is performed immediately on behalf of the lookup
1421 * class.
1422 * <p>
1423 * If the returned VarHandle is operated on, the declaring class will be
1424 * initialized, if it has not already been initialized.
1425 * <p>
1426 * Certain access modes of the returned VarHandle are unsupported under
1427 * the following conditions:
1428 * <ul>
1429 * <li>if the field is declared {@code final}, then the write, atomic
1430 * update, numeric atomic update, and bitwise atomic update access
1431 * modes are unsupported.
1432 * <li>if the field type is anything other than {@code byte},
1433 * {@code short}, {@code char}, {@code int}, {@code long},
1434 * {@code float}, or {@code double}, then numeric atomic update
1435 * access modes are unsupported.
1436 * <li>if the field type is anything other than {@code boolean},
1437 * {@code byte}, {@code short}, {@code char}, {@code int} or
1438 * {@code long} then bitwise atomic update access modes are
1439 * unsupported.
1440 * </ul>
1441 * <p>
1442 * If the field is declared {@code volatile} then the returned VarHandle
1443 * will override access to the field (effectively ignore the
1444 * {@code volatile} declaration) in accordance to it's specified
1445 * access modes.
1446 * <p>
1447 * If the field type is {@code float} or {@code double} then numeric
1448 * and atomic update access modes compare values using their bitwise
1449 * representation (see {@link Float#floatToRawIntBits} and
1450 * {@link Double#doubleToRawLongBits}, respectively).
1451 * @apiNote
1452 * Bitwise comparison of {@code float} values or {@code double} values,
1453 * as performed by the numeric and atomic update access modes, differ
1454 * from the primitive {@code ==} operator and the {@link Float#equals}
1455 * and {@link Double#equals} methods, specifically with respect to
1456 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
1457 * Care should be taken when performing a compare and set or a compare
1458 * and exchange operation with such values since the operation may
1459 * unexpectedly fail.
1460 * There are many possible NaN values that are considered to be
1461 * {@code NaN} in Java, although no IEEE 754 floating-point operation
1462 * provided by Java can distinguish between them. Operation failure can
1463 * occur if the expected or witness value is a NaN value and it is
1464 * transformed (perhaps in a platform specific manner) into another NaN
1465 * value, and thus has a different bitwise representation (see
1466 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
1467 * details).
1468 * The values {@code -0.0} and {@code +0.0} have different bitwise
1469 * representations but are considered equal when using the primitive
1470 * {@code ==} operator. Operation failure can occur if, for example, a
1471 * numeric algorithm computes an expected value to be say {@code -0.0}
1472 * and previously computed the witness value to be say {@code +0.0}.
1473 * @param decl the class that declares the static field
1474 * @param name the field's name
1475 * @param type the field's type, of type {@code T}
1476 * @return a VarHandle giving access to a static field
1477 * @throws NoSuchFieldException if the field does not exist
1478 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1479 * @exception SecurityException if a security manager is present and it
1480 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1481 * @throws NullPointerException if any argument is null
1482 * @since 9
1483 */
1484 public VarHandle findStaticVarHandle(Class<?> decl, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1485 MemberName getField = resolveOrFail(REF_getStatic, decl, name, type);
1486 MemberName putField = resolveOrFail(REF_putStatic, decl, name, type);
1487 return getFieldVarHandle(REF_getStatic, REF_putStatic, decl, getField, putField);
1488 }
1489
1490 /**
1491 * Produces an early-bound method handle for a non-static method.
1492 * The receiver must have a supertype {@code defc} in which a method
1493 * of the given name and type is accessible to the lookup class.
1494 * The method and all its argument types must be accessible to the lookup object.
1495 * The type of the method handle will be that of the method,
1496 * without any insertion of an additional receiver parameter.
1497 * The given receiver will be bound into the method handle,
1498 * so that every call to the method handle will invoke the
1499 * requested method on the given receiver.
1500 * <p>
1501 * The returned method handle will have
1502 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1503 * the method's variable arity modifier bit ({@code 0x0080}) is set
1504 * <em>and</em> the trailing array argument is not the only argument.
1505 * (If the trailing array argument is the only argument,
1506 * the given receiver value will be bound to it.)
1507 * <p>
1508 * This is equivalent to the following code:
1509 * <blockquote><pre>{@code
1510 import static java.lang.invoke.MethodHandles.*;
1511 import static java.lang.invoke.MethodType.*;
1512 ...
1513 MethodHandle mh0 = lookup().findVirtual(defc, name, type);
1514 MethodHandle mh1 = mh0.bindTo(receiver);
1515 mh1 = mh1.withVarargs(mh0.isVarargsCollector());
1516 return mh1;
1517 * }</pre></blockquote>
1518 * where {@code defc} is either {@code receiver.getClass()} or a super
1519 * type of that class, in which the requested method is accessible
1520 * to the lookup class.
1521 * (Note that {@code bindTo} does not preserve variable arity.)
1522 * @param receiver the object from which the method is accessed
1523 * @param name the name of the method
1524 * @param type the type of the method, with the receiver argument omitted
1525 * @return the desired method handle
1526 * @throws NoSuchMethodException if the method does not exist
1527 * @throws IllegalAccessException if access checking fails
1528 * or if the method's variable arity modifier bit
1529 * is set and {@code asVarargsCollector} fails
1530 * @exception SecurityException if a security manager is present and it
1531 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1532 * @throws NullPointerException if any argument is null
1533 * @see MethodHandle#bindTo
1534 * @see #findVirtual
1535 */
1536 public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1537 Class<? extends Object> refc = receiver.getClass(); // may get NPE
1538 MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
1539 MethodHandle mh = getDirectMethodNoRestrict(REF_invokeSpecial, refc, method, findBoundCallerClass(method));
1540 return mh.bindArgumentL(0, receiver).setVarargs(method);
1541 }
1542
1543 /**
1544 * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
1545 * to <i>m</i>, if the lookup class has permission.
1546 * If <i>m</i> is non-static, the receiver argument is treated as an initial argument.
1547 * If <i>m</i> is virtual, overriding is respected on every call.
1548 * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped.
1549 * The type of the method handle will be that of the method,
1550 * with the receiver type prepended (but only if it is non-static).
1551 * If the method's {@code accessible} flag is not set,
1552 * access checking is performed immediately on behalf of the lookup class.
1553 * If <i>m</i> is not public, do not share the resulting handle with untrusted parties.
1554 * <p>
1555 * The returned method handle will have
1556 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1557 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1558 * <p>
1559 * If <i>m</i> is static, and
1560 * if the returned method handle is invoked, the method's class will
1561 * be initialized, if it has not already been initialized.
1562 * @param m the reflected method
1563 * @return a method handle which can invoke the reflected method
1564 * @throws IllegalAccessException if access checking fails
1565 * or if the method's variable arity modifier bit
1566 * is set and {@code asVarargsCollector} fails
1567 * @throws NullPointerException if the argument is null
1568 */
1569 public MethodHandle unreflect(Method m) throws IllegalAccessException {
1570 if (m.getDeclaringClass() == MethodHandle.class) {
1571 MethodHandle mh = unreflectForMH(m);
1572 if (mh != null) return mh;
1573 }
1574 if (m.getDeclaringClass() == VarHandle.class) {
1575 MethodHandle mh = unreflectForVH(m);
1576 if (mh != null) return mh;
1577 }
1578 MemberName method = new MemberName(m);
1579 byte refKind = method.getReferenceKind();
1580 if (refKind == REF_invokeSpecial)
1581 refKind = REF_invokeVirtual;
1582 assert(method.isMethod());
1583 Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
1584 return lookup.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method, findBoundCallerClass(method));
1585 }
1586 private MethodHandle unreflectForMH(Method m) {
1587 // these names require special lookups because they throw UnsupportedOperationException
1588 if (MemberName.isMethodHandleInvokeName(m.getName()))
1589 return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m));
1590 return null;
1591 }
1592 private MethodHandle unreflectForVH(Method m) {
1593 // these names require special lookups because they throw UnsupportedOperationException
1594 if (MemberName.isVarHandleMethodInvokeName(m.getName()))
1595 return MethodHandleImpl.fakeVarHandleInvoke(new MemberName(m));
1596 return null;
1597 }
1598
1599 /**
1600 * Produces a method handle for a reflected method.
1601 * It will bypass checks for overriding methods on the receiver,
1602 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
1603 * instruction from within the explicitly specified {@code specialCaller}.
1604 * The type of the method handle will be that of the method,
1605 * with a suitably restricted receiver type prepended.
1606 * (The receiver type will be {@code specialCaller} or a subtype.)
1607 * If the method's {@code accessible} flag is not set,
1608 * access checking is performed immediately on behalf of the lookup class,
1609 * as if {@code invokespecial} instruction were being linked.
1610 * <p>
1611 * Before method resolution,
1612 * if the explicitly specified caller class is not identical with the
1613 * lookup class, or if this lookup object does not have
1614 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
1615 * privileges, the access fails.
1616 * <p>
1617 * The returned method handle will have
1618 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1619 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1620 * @param m the reflected method
1621 * @param specialCaller the class nominally calling the method
1622 * @return a method handle which can invoke the reflected method
1623 * @throws IllegalAccessException if access checking fails,
1624 * or if the method is {@code static},
1625 * or if the method's variable arity modifier bit
1626 * is set and {@code asVarargsCollector} fails
1627 * @throws NullPointerException if any argument is null
1628 */
1629 public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException {
1630 checkSpecialCaller(specialCaller, null);
1631 Lookup specialLookup = this.in(specialCaller);
1632 MemberName method = new MemberName(m, true);
1633 assert(method.isMethod());
1634 // ignore m.isAccessible: this is a new kind of access
1635 return specialLookup.getDirectMethodNoSecurityManager(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerClass(method));
1636 }
1637
1638 /**
1639 * Produces a method handle for a reflected constructor.
1640 * The type of the method handle will be that of the constructor,
1641 * with the return type changed to the declaring class.
1642 * The method handle will perform a {@code newInstance} operation,
1643 * creating a new instance of the constructor's class on the
1644 * arguments passed to the method handle.
1645 * <p>
1646 * If the constructor's {@code accessible} flag is not set,
1647 * access checking is performed immediately on behalf of the lookup class.
1648 * <p>
1649 * The returned method handle will have
1650 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1651 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
1652 * <p>
1653 * If the returned method handle is invoked, the constructor's class will
1654 * be initialized, if it has not already been initialized.
1655 * @param c the reflected constructor
1656 * @return a method handle which can invoke the reflected constructor
1657 * @throws IllegalAccessException if access checking fails
1658 * or if the method's variable arity modifier bit
1659 * is set and {@code asVarargsCollector} fails
1660 * @throws NullPointerException if the argument is null
1661 */
1662 public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException {
1663 MemberName ctor = new MemberName(c);
1664 assert(ctor.isConstructor());
1665 Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
1666 return lookup.getDirectConstructorNoSecurityManager(ctor.getDeclaringClass(), ctor);
1667 }
1668
1669 /**
1670 * Produces a method handle giving read access to a reflected field.
1671 * The type of the method handle will have a return type of the field's
1672 * value type.
1673 * If the field is static, the method handle will take no arguments.
1674 * Otherwise, its single argument will be the instance containing
1675 * the field.
1676 * If the field's {@code accessible} flag is not set,
1677 * access checking is performed immediately on behalf of the lookup class.
1678 * <p>
1679 * If the field is static, and
1680 * if the returned method handle is invoked, the field's class will
1681 * be initialized, if it has not already been initialized.
1682 * @param f the reflected field
1683 * @return a method handle which can load values from the reflected field
1684 * @throws IllegalAccessException if access checking fails
1685 * @throws NullPointerException if the argument is null
1686 */
1687 public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
1688 return unreflectField(f, false);
1689 }
1690 private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
1691 MemberName field = new MemberName(f, isSetter);
1692 assert(isSetter
1693 ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
1694 : MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
1695 Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
1696 return lookup.getDirectFieldNoSecurityManager(field.getReferenceKind(), f.getDeclaringClass(), field);
1697 }
1698
1699 /**
1700 * Produces a method handle giving write access to a reflected field.
1701 * The type of the method handle will have a void return type.
1702 * If the field is static, the method handle will take a single
1703 * argument, of the field's value type, the value to be stored.
1704 * Otherwise, the two arguments will be the instance containing
1705 * the field, and the value to be stored.
1706 * If the field's {@code accessible} flag is not set,
1707 * access checking is performed immediately on behalf of the lookup class.
1708 * <p>
1709 * If the field is static, and
1710 * if the returned method handle is invoked, the field's class will
1711 * be initialized, if it has not already been initialized.
1712 * @param f the reflected field
1713 * @return a method handle which can store values into the reflected field
1714 * @throws IllegalAccessException if access checking fails
1715 * @throws NullPointerException if the argument is null
1716 */
1717 public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
1718 return unreflectField(f, true);
1719 }
1720
1721 /**
1722 * Produces a VarHandle that accesses fields of type {@code T} declared
1723 * by a class of type {@code R}, as described by the given reflected
1724 * field.
1725 * If the field is non-static the VarHandle supports a shape of
1726 * {@code (R : T)}, otherwise supports a shape of {@code ((empty) : T)}.
1727 * <p>
1728 * Access checking is performed immediately on behalf of the lookup
1729 * class, regardless of the value of the field's {@code accessible}
1730 * flag.
1731 * <p>
1732 * If the field is static, and if the returned VarHandle is operated
1733 * on, the field's declaring class will be initialized, if it has not
1734 * already been initialized.
1735 * <p>
1736 * Certain access modes of the returned VarHandle are unsupported under
1737 * the following conditions:
1738 * <ul>
1739 * <li>if the field is declared {@code final}, then the write, atomic
1740 * update, numeric atomic update, and bitwise atomic update access
1741 * modes are unsupported.
1742 * <li>if the field type is anything other than {@code byte},
1743 * {@code short}, {@code char}, {@code int}, {@code long},
1744 * {@code float}, or {@code double} then numeric atomic update
1745 * access modes are unsupported.
1746 * <li>if the field type is anything other than {@code boolean},
1747 * {@code byte}, {@code short}, {@code char}, {@code int} or
1748 * {@code long} then bitwise atomic update access modes are
1749 * unsupported.
1750 * </ul>
1751 * <p>
1752 * If the field is declared {@code volatile} then the returned VarHandle
1753 * will override access to the field (effectively ignore the
1754 * {@code volatile} declaration) in accordance to it's specified
1755 * access modes.
1756 * <p>
1757 * If the field type is {@code float} or {@code double} then numeric
1758 * and atomic update access modes compare values using their bitwise
1759 * representation (see {@link Float#floatToRawIntBits} and
1760 * {@link Double#doubleToRawLongBits}, respectively).
1761 * @apiNote
1762 * Bitwise comparison of {@code float} values or {@code double} values,
1763 * as performed by the numeric and atomic update access modes, differ
1764 * from the primitive {@code ==} operator and the {@link Float#equals}
1765 * and {@link Double#equals} methods, specifically with respect to
1766 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
1767 * Care should be taken when performing a compare and set or a compare
1768 * and exchange operation with such values since the operation may
1769 * unexpectedly fail.
1770 * There are many possible NaN values that are considered to be
1771 * {@code NaN} in Java, although no IEEE 754 floating-point operation
1772 * provided by Java can distinguish between them. Operation failure can
1773 * occur if the expected or witness value is a NaN value and it is
1774 * transformed (perhaps in a platform specific manner) into another NaN
1775 * value, and thus has a different bitwise representation (see
1776 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
1777 * details).
1778 * The values {@code -0.0} and {@code +0.0} have different bitwise
1779 * representations but are considered equal when using the primitive
1780 * {@code ==} operator. Operation failure can occur if, for example, a
1781 * numeric algorithm computes an expected value to be say {@code -0.0}
1782 * and previously computed the witness value to be say {@code +0.0}.
1783 * @param f the reflected field, with a field of type {@code T}, and
1784 * a declaring class of type {@code R}
1785 * @return a VarHandle giving access to non-static fields or a static
1786 * field
1787 * @throws IllegalAccessException if access checking fails
1788 * @throws NullPointerException if the argument is null
1789 * @since 9
1790 */
1791 public VarHandle unreflectVarHandle(Field f) throws IllegalAccessException {
1792 MemberName getField = new MemberName(f, false);
1793 MemberName putField = new MemberName(f, true);
1794 return getFieldVarHandleNoSecurityManager(getField.getReferenceKind(), putField.getReferenceKind(),
1795 f.getDeclaringClass(), getField, putField);
1796 }
1797
1798 /**
1799 * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
1800 * created by this lookup object or a similar one.
1801 * Security and access checks are performed to ensure that this lookup object
1802 * is capable of reproducing the target method handle.
1803 * This means that the cracking may fail if target is a direct method handle
1804 * but was created by an unrelated lookup object.
1805 * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a>
1806 * and was created by a lookup object for a different class.
1807 * @param target a direct method handle to crack into symbolic reference components
1808 * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object
1809 * @exception SecurityException if a security manager is present and it
1810 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1811 * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails
1812 * @exception NullPointerException if the target is {@code null}
1813 * @see MethodHandleInfo
1814 * @since 1.8
1815 */
1816 public MethodHandleInfo revealDirect(MethodHandle target) {
1817 MemberName member = target.internalMemberName();
1818 if (member == null || (!member.isResolved() &&
1819 !member.isMethodHandleInvoke() &&
1820 !member.isVarHandleMethodInvoke()))
1821 throw newIllegalArgumentException("not a direct method handle");
1822 Class<?> defc = member.getDeclaringClass();
1823 byte refKind = member.getReferenceKind();
1824 assert(MethodHandleNatives.refKindIsValid(refKind));
1825 if (refKind == REF_invokeSpecial && !target.isInvokeSpecial())
1826 // Devirtualized method invocation is usually formally virtual.
1827 // To avoid creating extra MemberName objects for this common case,
1828 // we encode this extra degree of freedom using MH.isInvokeSpecial.
1829 refKind = REF_invokeVirtual;
1830 if (refKind == REF_invokeVirtual && defc.isInterface())
1831 // Symbolic reference is through interface but resolves to Object method (toString, etc.)
1832 refKind = REF_invokeInterface;
1833 // Check SM permissions and member access before cracking.
1834 try {
1835 checkAccess(refKind, defc, member);
1836 checkSecurityManager(defc, member);
1837 } catch (IllegalAccessException ex) {
1838 throw new IllegalArgumentException(ex);
1839 }
1840 if (allowedModes != TRUSTED && member.isCallerSensitive()) {
1841 Class<?> callerClass = target.internalCallerClass();
1842 if (!hasPrivateAccess() || callerClass != lookupClass())
1843 throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass);
1844 }
1845 // Produce the handle to the results.
1846 return new InfoFromMemberName(this, member, refKind);
1847 }
1848
1849 /// Helper methods, all package-private.
1850
1851 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1852 checkSymbolicClass(refc); // do this before attempting to resolve
1853 Objects.requireNonNull(name);
1854 Objects.requireNonNull(type);
1855 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
1856 NoSuchFieldException.class);
1857 }
1858
1859 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1860 checkSymbolicClass(refc); // do this before attempting to resolve
1861 Objects.requireNonNull(name);
1862 Objects.requireNonNull(type);
1863 checkMethodName(refKind, name); // NPE check on name
1864 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
1865 NoSuchMethodException.class);
1866 }
1867
1868 MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException {
1869 checkSymbolicClass(member.getDeclaringClass()); // do this before attempting to resolve
1870 Objects.requireNonNull(member.getName());
1871 Objects.requireNonNull(member.getType());
1872 return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(),
1873 ReflectiveOperationException.class);
1874 }
1875
1876 void checkSymbolicClass(Class<?> refc) throws IllegalAccessException {
1877 Objects.requireNonNull(refc);
1878 Class<?> caller = lookupClassOrNull();
1879 if (caller != null && !VerifyAccess.isClassAccessible(refc, caller, allowedModes))
1880 throw new MemberName(refc).makeAccessException("symbolic reference class is not accessible", this);
1881 }
1882
1883 /** Check name for an illegal leading "<" character. */
1884 void checkMethodName(byte refKind, String name) throws NoSuchMethodException {
1885 if (name.startsWith("<") && refKind != REF_newInvokeSpecial)
1886 throw new NoSuchMethodException("illegal method name: "+name);
1887 }
1888
1889
1890 /**
1891 * Find my trustable caller class if m is a caller sensitive method.
1892 * If this lookup object has private access, then the caller class is the lookupClass.
1893 * Otherwise, if m is caller-sensitive, throw IllegalAccessException.
1894 */
1895 Class<?> findBoundCallerClass(MemberName m) throws IllegalAccessException {
1896 Class<?> callerClass = null;
1897 if (MethodHandleNatives.isCallerSensitive(m)) {
1898 // Only lookups with private access are allowed to resolve caller-sensitive methods
1899 if (hasPrivateAccess()) {
1900 callerClass = lookupClass;
1901 } else {
1902 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
1903 }
1904 }
1905 return callerClass;
1906 }
1907
1908 /**
1909 * Returns {@code true} if this lookup has {@code PRIVATE} access.
1910 * @return {@code true} if this lookup has {@code PRIVATE} acesss.
1911 * @since 9
1912 */
1913 public boolean hasPrivateAccess() {
1914 return (allowedModes & PRIVATE) != 0;
1915 }
1916
1917 /**
1918 * Perform necessary <a href="MethodHandles.Lookup.html#secmgr">access checks</a>.
1919 * Determines a trustable caller class to compare with refc, the symbolic reference class.
1920 * If this lookup object has private access, then the caller class is the lookupClass.
1921 */
1922 void checkSecurityManager(Class<?> refc, MemberName m) {
1923 SecurityManager smgr = System.getSecurityManager();
1924 if (smgr == null) return;
1925 if (allowedModes == TRUSTED) return;
1926
1927 // Step 1:
1928 boolean fullPowerLookup = hasPrivateAccess();
1929 if (!fullPowerLookup ||
1930 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
1931 ReflectUtil.checkPackageAccess(refc);
1932 }
1933
1934 if (m == null) { // findClass or accessClass
1935 // Step 2b:
1936 if (!fullPowerLookup) {
1937 smgr.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
1938 }
1939 return;
1940 }
1941
1942 // Step 2a:
1943 if (m.isPublic()) return;
1944 if (!fullPowerLookup) {
1945 smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION);
1946 }
1947
1948 // Step 3:
1949 Class<?> defc = m.getDeclaringClass();
1950 if (!fullPowerLookup && defc != refc) {
1951 ReflectUtil.checkPackageAccess(defc);
1952 }
1953 }
1954
1955 void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
1956 boolean wantStatic = (refKind == REF_invokeStatic);
1957 String message;
1958 if (m.isConstructor())
1959 message = "expected a method, not a constructor";
1960 else if (!m.isMethod())
1961 message = "expected a method";
1962 else if (wantStatic != m.isStatic())
1963 message = wantStatic ? "expected a static method" : "expected a non-static method";
1964 else
1965 { checkAccess(refKind, refc, m); return; }
1966 throw m.makeAccessException(message, this);
1967 }
1968
1969 void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
1970 boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
1971 String message;
1972 if (wantStatic != m.isStatic())
1973 message = wantStatic ? "expected a static field" : "expected a non-static field";
1974 else
1975 { checkAccess(refKind, refc, m); return; }
1976 throw m.makeAccessException(message, this);
1977 }
1978
1979 /** Check public/protected/private bits on the symbolic reference class and its member. */
1980 void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
1981 assert(m.referenceKindIsConsistentWith(refKind) &&
1982 MethodHandleNatives.refKindIsValid(refKind) &&
1983 (MethodHandleNatives.refKindIsField(refKind) == m.isField()));
1984 int allowedModes = this.allowedModes;
1985 if (allowedModes == TRUSTED) return;
1986 int mods = m.getModifiers();
1987 if (Modifier.isProtected(mods) &&
1988 refKind == REF_invokeVirtual &&
1989 m.getDeclaringClass() == Object.class &&
1990 m.getName().equals("clone") &&
1991 refc.isArray()) {
1992 // The JVM does this hack also.
1993 // (See ClassVerifier::verify_invoke_instructions
1994 // and LinkResolver::check_method_accessability.)
1995 // Because the JVM does not allow separate methods on array types,
1996 // there is no separate method for int[].clone.
1997 // All arrays simply inherit Object.clone.
1998 // But for access checking logic, we make Object.clone
1999 // (normally protected) appear to be public.
2000 // Later on, when the DirectMethodHandle is created,
2001 // its leading argument will be restricted to the
2002 // requested array type.
2003 // N.B. The return type is not adjusted, because
2004 // that is *not* the bytecode behavior.
2005 mods ^= Modifier.PROTECTED | Modifier.PUBLIC;
2006 }
2007 if (Modifier.isProtected(mods) && refKind == REF_newInvokeSpecial) {
2008 // cannot "new" a protected ctor in a different package
2009 mods ^= Modifier.PROTECTED;
2010 }
2011 if (Modifier.isFinal(mods) &&
2012 MethodHandleNatives.refKindIsSetter(refKind))
2013 throw m.makeAccessException("unexpected set of a final field", this);
2014 int requestedModes = fixmods(mods); // adjust 0 => PACKAGE
2015 if ((requestedModes & allowedModes) != 0) {
2016 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
2017 mods, lookupClass(), allowedModes))
2018 return;
2019 } else {
2020 // Protected members can also be checked as if they were package-private.
2021 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
2022 && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
2023 return;
2024 }
2025 throw m.makeAccessException(accessFailedMessage(refc, m), this);
2026 }
2027
2028 String accessFailedMessage(Class<?> refc, MemberName m) {
2029 Class<?> defc = m.getDeclaringClass();
2030 int mods = m.getModifiers();
2031 // check the class first:
2032 boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
2033 (defc == refc ||
2034 Modifier.isPublic(refc.getModifiers())));
2035 if (!classOK && (allowedModes & PACKAGE) != 0) {
2036 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), ALL_MODES) &&
2037 (defc == refc ||
2038 VerifyAccess.isClassAccessible(refc, lookupClass(), ALL_MODES)));
2039 }
2040 if (!classOK)
2041 return "class is not public";
2042 if (Modifier.isPublic(mods))
2043 return "access to public member failed"; // (how?, module not readable?)
2044 if (Modifier.isPrivate(mods))
2045 return "member is private";
2046 if (Modifier.isProtected(mods))
2047 return "member is protected";
2048 return "member is private to package";
2049 }
2050
2051 private static final boolean ALLOW_NESTMATE_ACCESS = false;
2052
2053 private void checkSpecialCaller(Class<?> specialCaller, Class<?> refc) throws IllegalAccessException {
2054 int allowedModes = this.allowedModes;
2055 if (allowedModes == TRUSTED) return;
2056 if (!hasPrivateAccess()
2057 || (specialCaller != lookupClass()
2058 // ensure non-abstract methods in superinterfaces can be special-invoked
2059 && !(refc != null && refc.isInterface() && refc.isAssignableFrom(specialCaller))
2060 && !(ALLOW_NESTMATE_ACCESS &&
2061 VerifyAccess.isSamePackageMember(specialCaller, lookupClass()))))
2062 throw new MemberName(specialCaller).
2063 makeAccessException("no private access for invokespecial", this);
2064 }
2065
2066 private boolean restrictProtectedReceiver(MemberName method) {
2067 // The accessing class only has the right to use a protected member
2068 // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc.
2069 if (!method.isProtected() || method.isStatic()
2070 || allowedModes == TRUSTED
2071 || method.getDeclaringClass() == lookupClass()
2072 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass())
2073 || (ALLOW_NESTMATE_ACCESS &&
2074 VerifyAccess.isSamePackageMember(method.getDeclaringClass(), lookupClass())))
2075 return false;
2076 return true;
2077 }
2078 private MethodHandle restrictReceiver(MemberName method, DirectMethodHandle mh, Class<?> caller) throws IllegalAccessException {
2079 assert(!method.isStatic());
2080 // receiver type of mh is too wide; narrow to caller
2081 if (!method.getDeclaringClass().isAssignableFrom(caller)) {
2082 throw method.makeAccessException("caller class must be a subclass below the method", caller);
2083 }
2084 MethodType rawType = mh.type();
2085 if (rawType.parameterType(0) == caller) return mh;
2086 MethodType narrowType = rawType.changeParameterType(0, caller);
2087 assert(!mh.isVarargsCollector()); // viewAsType will lose varargs-ness
2088 assert(mh.viewAsTypeChecks(narrowType, true));
2089 return mh.copyWith(narrowType, mh.form);
2090 }
2091
2092 /** Check access and get the requested method. */
2093 private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
2094 final boolean doRestrict = true;
2095 final boolean checkSecurity = true;
2096 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
2097 }
2098 /** Check access and get the requested method, eliding receiver narrowing rules. */
2099 private MethodHandle getDirectMethodNoRestrict(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
2100 final boolean doRestrict = false;
2101 final boolean checkSecurity = true;
2102 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
2103 }
2104 /** Check access and get the requested method, eliding security manager checks. */
2105 private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
2106 final boolean doRestrict = true;
2107 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
2108 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
2109 }
2110 /** Common code for all methods; do not call directly except from immediately above. */
2111 private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method,
2112 boolean checkSecurity,
2113 boolean doRestrict, Class<?> callerClass) throws IllegalAccessException {
2114 checkMethod(refKind, refc, method);
2115 // Optionally check with the security manager; this isn't needed for unreflect* calls.
2116 if (checkSecurity)
2117 checkSecurityManager(refc, method);
2118 assert(!method.isMethodHandleInvoke());
2119
2120 if (refKind == REF_invokeSpecial &&
2121 refc != lookupClass() &&
2122 !refc.isInterface() &&
2123 refc != lookupClass().getSuperclass() &&
2124 refc.isAssignableFrom(lookupClass())) {
2125 assert(!method.getName().equals("<init>")); // not this code path
2126 // Per JVMS 6.5, desc. of invokespecial instruction:
2127 // If the method is in a superclass of the LC,
2128 // and if our original search was above LC.super,
2129 // repeat the search (symbolic lookup) from LC.super
2130 // and continue with the direct superclass of that class,
2131 // and so forth, until a match is found or no further superclasses exist.
2132 // FIXME: MemberName.resolve should handle this instead.
2133 Class<?> refcAsSuper = lookupClass();
2134 MemberName m2;
2135 do {
2136 refcAsSuper = refcAsSuper.getSuperclass();
2137 m2 = new MemberName(refcAsSuper,
2138 method.getName(),
2139 method.getMethodType(),
2140 REF_invokeSpecial);
2141 m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull());
2142 } while (m2 == null && // no method is found yet
2143 refc != refcAsSuper); // search up to refc
2144 if (m2 == null) throw new InternalError(method.toString());
2145 method = m2;
2146 refc = refcAsSuper;
2147 // redo basic checks
2148 checkMethod(refKind, refc, method);
2149 }
2150
2151 DirectMethodHandle dmh = DirectMethodHandle.make(refKind, refc, method);
2152 MethodHandle mh = dmh;
2153 // Optionally narrow the receiver argument to refc using restrictReceiver.
2154 if (doRestrict &&
2155 (refKind == REF_invokeSpecial ||
2156 (MethodHandleNatives.refKindHasReceiver(refKind) &&
2157 restrictProtectedReceiver(method)))) {
2158 mh = restrictReceiver(method, dmh, lookupClass());
2159 }
2160 mh = maybeBindCaller(method, mh, callerClass);
2161 mh = mh.setVarargs(method);
2162 return mh;
2163 }
2164 private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh,
2165 Class<?> callerClass)
2166 throws IllegalAccessException {
2167 if (allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method))
2168 return mh;
2169 Class<?> hostClass = lookupClass;
2170 if (!hasPrivateAccess()) // caller must have private access
2171 hostClass = callerClass; // callerClass came from a security manager style stack walk
2172 MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, hostClass);
2173 // Note: caller will apply varargs after this step happens.
2174 return cbmh;
2175 }
2176 /** Check access and get the requested field. */
2177 private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
2178 final boolean checkSecurity = true;
2179 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
2180 }
2181 /** Check access and get the requested field, eliding security manager checks. */
2182 private MethodHandle getDirectFieldNoSecurityManager(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
2183 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
2184 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
2185 }
2186 /** Common code for all fields; do not call directly except from immediately above. */
2187 private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field,
2188 boolean checkSecurity) throws IllegalAccessException {
2189 checkField(refKind, refc, field);
2190 // Optionally check with the security manager; this isn't needed for unreflect* calls.
2191 if (checkSecurity)
2192 checkSecurityManager(refc, field);
2193 DirectMethodHandle dmh = DirectMethodHandle.make(refc, field);
2194 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) &&
2195 restrictProtectedReceiver(field));
2196 if (doRestrict)
2197 return restrictReceiver(field, dmh, lookupClass());
2198 return dmh;
2199 }
2200 private VarHandle getFieldVarHandle(byte getRefKind, byte putRefKind,
2201 Class<?> refc, MemberName getField, MemberName putField)
2202 throws IllegalAccessException {
2203 final boolean checkSecurity = true;
2204 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
2205 }
2206 private VarHandle getFieldVarHandleNoSecurityManager(byte getRefKind, byte putRefKind,
2207 Class<?> refc, MemberName getField, MemberName putField)
2208 throws IllegalAccessException {
2209 final boolean checkSecurity = false;
2210 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
2211 }
2212 private VarHandle getFieldVarHandleCommon(byte getRefKind, byte putRefKind,
2213 Class<?> refc, MemberName getField, MemberName putField,
2214 boolean checkSecurity) throws IllegalAccessException {
2215 assert getField.isStatic() == putField.isStatic();
2216 assert getField.isGetter() && putField.isSetter();
2217 assert MethodHandleNatives.refKindIsStatic(getRefKind) == MethodHandleNatives.refKindIsStatic(putRefKind);
2218 assert MethodHandleNatives.refKindIsGetter(getRefKind) && MethodHandleNatives.refKindIsSetter(putRefKind);
2219
2220 checkField(getRefKind, refc, getField);
2221 if (checkSecurity)
2222 checkSecurityManager(refc, getField);
2223
2224 if (!putField.isFinal()) {
2225 // A VarHandle does not support updates to final fields, any
2226 // such VarHandle to a final field will be read-only and
2227 // therefore the following write-based accessibility checks are
2228 // only required for non-final fields
2229 checkField(putRefKind, refc, putField);
2230 if (checkSecurity)
2231 checkSecurityManager(refc, putField);
2232 }
2233
2234 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(getRefKind) &&
2235 restrictProtectedReceiver(getField));
2236 if (doRestrict) {
2237 assert !getField.isStatic();
2238 // receiver type of VarHandle is too wide; narrow to caller
2239 if (!getField.getDeclaringClass().isAssignableFrom(lookupClass())) {
2240 throw getField.makeAccessException("caller class must be a subclass below the method", lookupClass());
2241 }
2242 refc = lookupClass();
2243 }
2244 return VarHandles.makeFieldHandle(getField, refc, getField.getFieldType(), this.allowedModes == TRUSTED);
2245 }
2246 /** Check access and get the requested constructor. */
2247 private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException {
2248 final boolean checkSecurity = true;
2249 return getDirectConstructorCommon(refc, ctor, checkSecurity);
2250 }
2251 /** Check access and get the requested constructor, eliding security manager checks. */
2252 private MethodHandle getDirectConstructorNoSecurityManager(Class<?> refc, MemberName ctor) throws IllegalAccessException {
2253 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
2254 return getDirectConstructorCommon(refc, ctor, checkSecurity);
2255 }
2256 /** Common code for all constructors; do not call directly except from immediately above. */
2257 private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor,
2258 boolean checkSecurity) throws IllegalAccessException {
2259 assert(ctor.isConstructor());
2260 checkAccess(REF_newInvokeSpecial, refc, ctor);
2261 // Optionally check with the security manager; this isn't needed for unreflect* calls.
2262 if (checkSecurity)
2263 checkSecurityManager(refc, ctor);
2264 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
2265 return DirectMethodHandle.make(ctor).setVarargs(ctor);
2266 }
2267
2268 /** Hook called from the JVM (via MethodHandleNatives) to link MH constants:
2269 */
2270 /*non-public*/
2271 MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type) throws ReflectiveOperationException {
2272 if (!(type instanceof Class || type instanceof MethodType))
2273 throw new InternalError("unresolved MemberName");
2274 MemberName member = new MemberName(refKind, defc, name, type);
2275 MethodHandle mh = LOOKASIDE_TABLE.get(member);
2276 if (mh != null) {
2277 checkSymbolicClass(defc);
2278 return mh;
2279 }
2280 // Treat MethodHandle.invoke and invokeExact specially.
2281 if (defc == MethodHandle.class && refKind == REF_invokeVirtual) {
2282 mh = findVirtualForMH(member.getName(), member.getMethodType());
2283 if (mh != null) {
2284 return mh;
2285 }
2286 }
2287 MemberName resolved = resolveOrFail(refKind, member);
2288 mh = getDirectMethodForConstant(refKind, defc, resolved);
2289 if (mh instanceof DirectMethodHandle
2290 && canBeCached(refKind, defc, resolved)) {
2291 MemberName key = mh.internalMemberName();
2292 if (key != null) {
2293 key = key.asNormalOriginal();
2294 }
2295 if (member.equals(key)) { // better safe than sorry
2296 LOOKASIDE_TABLE.put(key, (DirectMethodHandle) mh);
2297 }
2298 }
2299 return mh;
2300 }
2301 private
2302 boolean canBeCached(byte refKind, Class<?> defc, MemberName member) {
2303 if (refKind == REF_invokeSpecial) {
2304 return false;
2305 }
2306 if (!Modifier.isPublic(defc.getModifiers()) ||
2307 !Modifier.isPublic(member.getDeclaringClass().getModifiers()) ||
2308 !member.isPublic() ||
2309 member.isCallerSensitive()) {
2310 return false;
2311 }
2312 ClassLoader loader = defc.getClassLoader();
2313 if (!jdk.internal.misc.VM.isSystemDomainLoader(loader)) {
2314 ClassLoader sysl = ClassLoader.getSystemClassLoader();
2315 boolean found = false;
2316 while (sysl != null) {
2317 if (loader == sysl) { found = true; break; }
2318 sysl = sysl.getParent();
2319 }
2320 if (!found) {
2321 return false;
2322 }
2323 }
2324 try {
2325 MemberName resolved2 = publicLookup().resolveOrFail(refKind,
2326 new MemberName(refKind, defc, member.getName(), member.getType()));
2327 checkSecurityManager(defc, resolved2);
2328 } catch (ReflectiveOperationException | SecurityException ex) {
2329 return false;
2330 }
2331 return true;
2332 }
2333 private
2334 MethodHandle getDirectMethodForConstant(byte refKind, Class<?> defc, MemberName member)
2335 throws ReflectiveOperationException {
2336 if (MethodHandleNatives.refKindIsField(refKind)) {
2337 return getDirectFieldNoSecurityManager(refKind, defc, member);
2338 } else if (MethodHandleNatives.refKindIsMethod(refKind)) {
2339 return getDirectMethodNoSecurityManager(refKind, defc, member, lookupClass);
2340 } else if (refKind == REF_newInvokeSpecial) {
2341 return getDirectConstructorNoSecurityManager(defc, member);
2342 }
2343 // oops
2344 throw newIllegalArgumentException("bad MethodHandle constant #"+member);
2345 }
2346
2347 static ConcurrentHashMap<MemberName, DirectMethodHandle> LOOKASIDE_TABLE = new ConcurrentHashMap<>();
2348 }
2349
2350 /**
2351 * Helper class used to lazily create PUBLIC_LOOKUP with a lookup class
2352 * in an <em>unnamed module</em>.
2353 *
2354 * @see Lookup#publicLookup
2355 */
2356 private static class LookupHelper {
2357 private static final String UNNAMED = "Unnamed";
2358 private static final String OBJECT = "java/lang/Object";
2359
2360 private static Class<?> createClass() {
2361 try {
2362 ClassWriter cw = new ClassWriter(0);
2363 cw.visit(Opcodes.V1_8,
2364 Opcodes.ACC_FINAL + Opcodes.ACC_SUPER,
2365 UNNAMED,
2366 null,
2367 OBJECT,
2368 null);
2369 cw.visitSource(UNNAMED, null);
2370 cw.visitEnd();
2371 byte[] bytes = cw.toByteArray();
2372 ClassLoader loader = new ClassLoader(null) {
2373 @Override
2374 protected Class<?> findClass(String cn) throws ClassNotFoundException {
2375 if (cn.equals(UNNAMED))
2376 return super.defineClass(UNNAMED, bytes, 0, bytes.length);
2377 throw new ClassNotFoundException(cn);
2378 }
2379 };
2380 return loader.loadClass(UNNAMED);
2381 } catch (Exception e) {
2382 throw new InternalError(e);
2383 }
2384 }
2385
2386 private static final Class<?> PUBLIC_LOOKUP_CLASS = createClass();
2387
2388 /**
2389 * Lookup that is trusted minimally. It can only be used to create
2390 * method handles to publicly accessible members in exported packages.
2391 *
2392 * @see MethodHandles#publicLookup
2393 */
2394 static final Lookup PUBLIC_LOOKUP = new Lookup(PUBLIC_LOOKUP_CLASS, Lookup.PUBLIC);
2395 }
2396
2397 /**
2398 * Produces a method handle constructing arrays of a desired type.
2399 * The return type of the method handle will be the array type.
2400 * The type of its sole argument will be {@code int}, which specifies the size of the array.
2401 * @param arrayClass an array type
2402 * @return a method handle which can create arrays of the given type
2403 * @throws NullPointerException if the argument is {@code null}
2404 * @throws IllegalArgumentException if {@code arrayClass} is not an array type
2405 * @see java.lang.reflect.Array#newInstance(Class, int)
2406 * @since 9
2407 */
2408 public static
2409 MethodHandle arrayConstructor(Class<?> arrayClass) throws IllegalArgumentException {
2410 if (!arrayClass.isArray()) {
2411 throw newIllegalArgumentException("not an array class: " + arrayClass.getName());
2412 }
2413 MethodHandle ani = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_Array_newInstance).
2414 bindTo(arrayClass.getComponentType());
2415 return ani.asType(ani.type().changeReturnType(arrayClass));
2416 }
2417
2418 /**
2419 * Produces a method handle returning the length of an array.
2420 * The type of the method handle will have {@code int} as return type,
2421 * and its sole argument will be the array type.
2422 * @param arrayClass an array type
2423 * @return a method handle which can retrieve the length of an array of the given array type
2424 * @throws NullPointerException if the argument is {@code null}
2425 * @throws IllegalArgumentException if arrayClass is not an array type
2426 * @since 9
2427 */
2428 public static
2429 MethodHandle arrayLength(Class<?> arrayClass) throws IllegalArgumentException {
2430 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.LENGTH);
2431 }
2432
2433 /**
2434 * Produces a method handle giving read access to elements of an array.
2435 * The type of the method handle will have a return type of the array's
2436 * element type. Its first argument will be the array type,
2437 * and the second will be {@code int}.
2438 * @param arrayClass an array type
2439 * @return a method handle which can load values from the given array type
2440 * @throws NullPointerException if the argument is null
2441 * @throws IllegalArgumentException if arrayClass is not an array type
2442 */
2443 public static
2444 MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException {
2445 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.GET);
2446 }
2447
2448 /**
2449 * Produces a method handle giving write access to elements of an array.
2450 * The type of the method handle will have a void return type.
2451 * Its last argument will be the array's element type.
2452 * The first and second arguments will be the array type and int.
2453 * @param arrayClass the class of an array
2454 * @return a method handle which can store values into the array type
2455 * @throws NullPointerException if the argument is null
2456 * @throws IllegalArgumentException if arrayClass is not an array type
2457 */
2458 public static
2459 MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException {
2460 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.SET);
2461 }
2462
2463 /**
2464 *
2465 * Produces a VarHandle giving access to elements of an array type
2466 * {@code T[]}, supporting shape {@code (T[], int : T)}.
2467 * <p>
2468 * Certain access modes of the returned VarHandle are unsupported under
2469 * the following conditions:
2470 * <ul>
2471 * <li>if the component type is anything other than {@code byte},
2472 * {@code short}, {@code char}, {@code int}, {@code long},
2473 * {@code float}, or {@code double} then numeric atomic update access
2474 * modes are unsupported.
2475 * <li>if the field type is anything other than {@code boolean},
2476 * {@code byte}, {@code short}, {@code char}, {@code int} or
2477 * {@code long} then bitwise atomic update access modes are
2478 * unsupported.
2479 * </ul>
2480 * <p>
2481 * If the component type is {@code float} or {@code double} then numeric
2482 * and atomic update access modes compare values using their bitwise
2483 * representation (see {@link Float#floatToRawIntBits} and
2484 * {@link Double#doubleToRawLongBits}, respectively).
2485 * @apiNote
2486 * Bitwise comparison of {@code float} values or {@code double} values,
2487 * as performed by the numeric and atomic update access modes, differ
2488 * from the primitive {@code ==} operator and the {@link Float#equals}
2489 * and {@link Double#equals} methods, specifically with respect to
2490 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
2491 * Care should be taken when performing a compare and set or a compare
2492 * and exchange operation with such values since the operation may
2493 * unexpectedly fail.
2494 * There are many possible NaN values that are considered to be
2495 * {@code NaN} in Java, although no IEEE 754 floating-point operation
2496 * provided by Java can distinguish between them. Operation failure can
2497 * occur if the expected or witness value is a NaN value and it is
2498 * transformed (perhaps in a platform specific manner) into another NaN
2499 * value, and thus has a different bitwise representation (see
2500 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
2501 * details).
2502 * The values {@code -0.0} and {@code +0.0} have different bitwise
2503 * representations but are considered equal when using the primitive
2504 * {@code ==} operator. Operation failure can occur if, for example, a
2505 * numeric algorithm computes an expected value to be say {@code -0.0}
2506 * and previously computed the witness value to be say {@code +0.0}.
2507 * @param arrayClass the class of an array, of type {@code T[]}
2508 * @return a VarHandle giving access to elements of an array
2509 * @throws NullPointerException if the arrayClass is null
2510 * @throws IllegalArgumentException if arrayClass is not an array type
2511 * @since 9
2512 */
2513 public static
2514 VarHandle arrayElementVarHandle(Class<?> arrayClass) throws IllegalArgumentException {
2515 return VarHandles.makeArrayElementHandle(arrayClass);
2516 }
2517
2518 /**
2519 * Produces a VarHandle giving access to elements of a {@code byte[]} array
2520 * viewed as if it were a different primitive array type, such as
2521 * {@code int[]} or {@code long[]}. The shape of the resulting VarHandle is
2522 * {@code (byte[], int : T)}, where the {@code int} coordinate type
2523 * corresponds to an argument that is an index in a {@code byte[]} array,
2524 * and {@code T} is the component type of the given view array class. The
2525 * returned VarHandle accesses bytes at an index in a {@code byte[]} array,
2526 * composing bytes to or from a value of {@code T} according to the given
2527 * endianness.
2528 * <p>
2529 * The supported component types (variables types) are {@code short},
2530 * {@code char}, {@code int}, {@code long}, {@code float} and
2531 * {@code double}.
2532 * <p>
2533 * Access of bytes at a given index will result in an
2534 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
2535 * or greater than the {@code byte[]} array length minus the size (in bytes)
2536 * of {@code T}.
2537 * <p>
2538 * Access of bytes at an index may be aligned or misaligned for {@code T},
2539 * with respect to the underlying memory address, {@code A} say, associated
2540 * with the array and index.
2541 * If access is misaligned then access for anything other than the
2542 * {@code get} and {@code set} access modes will result in an
2543 * {@code IllegalStateException}. In such cases atomic access is only
2544 * guaranteed with respect to the largest power of two that divides the GCD
2545 * of {@code A} and the size (in bytes) of {@code T}.
2546 * If access is aligned then following access modes are supported and are
2547 * guaranteed to support atomic access:
2548 * <ul>
2549 * <li>read write access modes for all {@code T}, with the exception of
2550 * access modes {@code get} and {@code set} for {@code long} and
2551 * {@code double} on 32-bit platforms.
2552 * <li>atomic update access modes for {@code int}, {@code long},
2553 * {@code float} or {@code double}.
2554 * (Future major platform releases of the JDK may support additional
2555 * types for certain currently unsupported access modes.)
2556 * <li>numeric atomic update access modes for {@code int} and {@code long}.
2557 * (Future major platform releases of the JDK may support additional
2558 * numeric types for certain currently unsupported access modes.)
2559 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
2560 * (Future major platform releases of the JDK may support additional
2561 * numeric types for certain currently unsupported access modes.)
2562 * </ul>
2563 * <p>
2564 * Misaligned access, and therefore atomicity guarantees, may be determined
2565 * for {@code byte[]} arrays without operating on a specific array. Given
2566 * an {@code index}, {@code T} and it's corresponding boxed type,
2567 * {@code T_BOX}, misalignment may be determined as follows:
2568 * <pre>{@code
2569 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
2570 * int misalignedAtZeroIndex = ByteBuffer.wrap(new byte[0]).
2571 * alignmentOffset(0, sizeOfT);
2572 * int misalignedAtIndex = (misalignedAtZeroIndex + index) % sizeOfT;
2573 * boolean isMisaligned = misalignedAtIndex != 0;
2574 * }</pre>
2575 * <p>
2576 * If the variable type is {@code float} or {@code double} then atomic
2577 * update access modes compare values using their bitwise representation
2578 * (see {@link Float#floatToRawIntBits} and
2579 * {@link Double#doubleToRawLongBits}, respectively).
2580 * @param viewArrayClass the view array class, with a component type of
2581 * type {@code T}
2582 * @param byteOrder the endianness of the view array elements, as
2583 * stored in the underlying {@code byte} array
2584 * @return a VarHandle giving access to elements of a {@code byte[]} array
2585 * viewed as if elements corresponding to the components type of the view
2586 * array class
2587 * @throws NullPointerException if viewArrayClass or byteOrder is null
2588 * @throws IllegalArgumentException if viewArrayClass is not an array type
2589 * @throws UnsupportedOperationException if the component type of
2590 * viewArrayClass is not supported as a variable type
2591 * @since 9
2592 */
2593 public static
2594 VarHandle byteArrayViewVarHandle(Class<?> viewArrayClass,
2595 ByteOrder byteOrder) throws IllegalArgumentException {
2596 Objects.requireNonNull(byteOrder);
2597 return VarHandles.byteArrayViewHandle(viewArrayClass,
2598 byteOrder == ByteOrder.BIG_ENDIAN);
2599 }
2600
2601 /**
2602 * Produces a VarHandle giving access to elements of a {@code ByteBuffer}
2603 * viewed as if it were an array of elements of a different primitive
2604 * component type to that of {@code byte}, such as {@code int[]} or
2605 * {@code long[]}. The shape of the resulting VarHandle is
2606 * {@code (ByteBuffer, int : T)}, where the {@code int} coordinate type
2607 * corresponds to an argument that is an index in a {@code ByteBuffer}, and
2608 * {@code T} is the component type of the given view array class. The
2609 * returned VarHandle accesses bytes at an index in a {@code ByteBuffer},
2610 * composing bytes to or from a value of {@code T} according to the given
2611 * endianness.
2612 * <p>
2613 * The supported component types (variables types) are {@code short},
2614 * {@code char}, {@code int}, {@code long}, {@code float} and
2615 * {@code double}.
2616 * <p>
2617 * Access will result in a {@code ReadOnlyBufferException} for anything
2618 * other than the read access modes if the {@code ByteBuffer} is read-only.
2619 * <p>
2620 * Access of bytes at a given index will result in an
2621 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
2622 * or greater than the {@code ByteBuffer} limit minus the size (in bytes) of
2623 * {@code T}.
2624 * <p>
2625 * Access of bytes at an index may be aligned or misaligned for {@code T},
2626 * with respect to the underlying memory address, {@code A} say, associated
2627 * with the {@code ByteBuffer} and index.
2628 * If access is misaligned then access for anything other than the
2629 * {@code get} and {@code set} access modes will result in an
2630 * {@code IllegalStateException}. In such cases atomic access is only
2631 * guaranteed with respect to the largest power of two that divides the GCD
2632 * of {@code A} and the size (in bytes) of {@code T}.
2633 * If access is aligned then following access modes are supported and are
2634 * guaranteed to support atomic access:
2635 * <ul>
2636 * <li>read write access modes for all {@code T}, with the exception of
2637 * access modes {@code get} and {@code set} for {@code long} and
2638 * {@code double} on 32-bit platforms.
2639 * <li>atomic update access modes for {@code int}, {@code long},
2640 * {@code float} or {@code double}.
2641 * (Future major platform releases of the JDK may support additional
2642 * types for certain currently unsupported access modes.)
2643 * <li>numeric atomic update access modes for {@code int} and {@code long}.
2644 * (Future major platform releases of the JDK may support additional
2645 * numeric types for certain currently unsupported access modes.)
2646 * <li>bitwise atomic update access modes for {@code int} and {@code long}.
2647 * (Future major platform releases of the JDK may support additional
2648 * numeric types for certain currently unsupported access modes.)
2649 * </ul>
2650 * <p>
2651 * Misaligned access, and therefore atomicity guarantees, may be determined
2652 * for a {@code ByteBuffer}, {@code bb} (direct or otherwise), an
2653 * {@code index}, {@code T} and it's corresponding boxed type,
2654 * {@code T_BOX}, as follows:
2655 * <pre>{@code
2656 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
2657 * ByteBuffer bb = ...
2658 * int misalignedAtIndex = bb.alignmentOffset(index, sizeOfT);
2659 * boolean isMisaligned = misalignedAtIndex != 0;
2660 * }</pre>
2661 * <p>
2662 * If the variable type is {@code float} or {@code double} then atomic
2663 * update access modes compare values using their bitwise representation
2664 * (see {@link Float#floatToRawIntBits} and
2665 * {@link Double#doubleToRawLongBits}, respectively).
2666 * @param viewArrayClass the view array class, with a component type of
2667 * type {@code T}
2668 * @param byteOrder the endianness of the view array elements, as
2669 * stored in the underlying {@code ByteBuffer} (Note this overrides the
2670 * endianness of a {@code ByteBuffer})
2671 * @return a VarHandle giving access to elements of a {@code ByteBuffer}
2672 * viewed as if elements corresponding to the components type of the view
2673 * array class
2674 * @throws NullPointerException if viewArrayClass or byteOrder is null
2675 * @throws IllegalArgumentException if viewArrayClass is not an array type
2676 * @throws UnsupportedOperationException if the component type of
2677 * viewArrayClass is not supported as a variable type
2678 * @since 9
2679 */
2680 public static
2681 VarHandle byteBufferViewVarHandle(Class<?> viewArrayClass,
2682 ByteOrder byteOrder) throws IllegalArgumentException {
2683 Objects.requireNonNull(byteOrder);
2684 return VarHandles.makeByteBufferViewHandle(viewArrayClass,
2685 byteOrder == ByteOrder.BIG_ENDIAN);
2686 }
2687
2688
2689 /// method handle invocation (reflective style)
2690
2691 /**
2692 * Produces a method handle which will invoke any method handle of the
2693 * given {@code type}, with a given number of trailing arguments replaced by
2694 * a single trailing {@code Object[]} array.
2695 * The resulting invoker will be a method handle with the following
2696 * arguments:
2697 * <ul>
2698 * <li>a single {@code MethodHandle} target
2699 * <li>zero or more leading values (counted by {@code leadingArgCount})
2700 * <li>an {@code Object[]} array containing trailing arguments
2701 * </ul>
2702 * <p>
2703 * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
2704 * the indicated {@code type}.
2705 * That is, if the target is exactly of the given {@code type}, it will behave
2706 * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
2707 * is used to convert the target to the required {@code type}.
2708 * <p>
2709 * The type of the returned invoker will not be the given {@code type}, but rather
2710 * will have all parameters except the first {@code leadingArgCount}
2711 * replaced by a single array of type {@code Object[]}, which will be
2712 * the final parameter.
2713 * <p>
2714 * Before invoking its target, the invoker will spread the final array, apply
2715 * reference casts as necessary, and unbox and widen primitive arguments.
2716 * If, when the invoker is called, the supplied array argument does
2717 * not have the correct number of elements, the invoker will throw
2718 * an {@link IllegalArgumentException} instead of invoking the target.
2719 * <p>
2720 * This method is equivalent to the following code (though it may be more efficient):
2721 * <blockquote><pre>{@code
2722 MethodHandle invoker = MethodHandles.invoker(type);
2723 int spreadArgCount = type.parameterCount() - leadingArgCount;
2724 invoker = invoker.asSpreader(Object[].class, spreadArgCount);
2725 return invoker;
2726 * }</pre></blockquote>
2727 * This method throws no reflective or security exceptions.
2728 * @param type the desired target type
2729 * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
2730 * @return a method handle suitable for invoking any method handle of the given type
2731 * @throws NullPointerException if {@code type} is null
2732 * @throws IllegalArgumentException if {@code leadingArgCount} is not in
2733 * the range from 0 to {@code type.parameterCount()} inclusive,
2734 * or if the resulting method handle's type would have
2735 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2736 */
2737 public static
2738 MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
2739 if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
2740 throw newIllegalArgumentException("bad argument count", leadingArgCount);
2741 type = type.asSpreaderType(Object[].class, leadingArgCount, type.parameterCount() - leadingArgCount);
2742 return type.invokers().spreadInvoker(leadingArgCount);
2743 }
2744
2745 /**
2746 * Produces a special <em>invoker method handle</em> which can be used to
2747 * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
2748 * The resulting invoker will have a type which is
2749 * exactly equal to the desired type, except that it will accept
2750 * an additional leading argument of type {@code MethodHandle}.
2751 * <p>
2752 * This method is equivalent to the following code (though it may be more efficient):
2753 * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)}
2754 *
2755 * <p style="font-size:smaller;">
2756 * <em>Discussion:</em>
2757 * Invoker method handles can be useful when working with variable method handles
2758 * of unknown types.
2759 * For example, to emulate an {@code invokeExact} call to a variable method
2760 * handle {@code M}, extract its type {@code T},
2761 * look up the invoker method {@code X} for {@code T},
2762 * and call the invoker method, as {@code X.invoke(T, A...)}.
2763 * (It would not work to call {@code X.invokeExact}, since the type {@code T}
2764 * is unknown.)
2765 * If spreading, collecting, or other argument transformations are required,
2766 * they can be applied once to the invoker {@code X} and reused on many {@code M}
2767 * method handle values, as long as they are compatible with the type of {@code X}.
2768 * <p style="font-size:smaller;">
2769 * <em>(Note: The invoker method is not available via the Core Reflection API.
2770 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
2771 * on the declared {@code invokeExact} or {@code invoke} method will raise an
2772 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
2773 * <p>
2774 * This method throws no reflective or security exceptions.
2775 * @param type the desired target type
2776 * @return a method handle suitable for invoking any method handle of the given type
2777 * @throws IllegalArgumentException if the resulting method handle's type would have
2778 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2779 */
2780 public static
2781 MethodHandle exactInvoker(MethodType type) {
2782 return type.invokers().exactInvoker();
2783 }
2784
2785 /**
2786 * Produces a special <em>invoker method handle</em> which can be used to
2787 * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
2788 * The resulting invoker will have a type which is
2789 * exactly equal to the desired type, except that it will accept
2790 * an additional leading argument of type {@code MethodHandle}.
2791 * <p>
2792 * Before invoking its target, if the target differs from the expected type,
2793 * the invoker will apply reference casts as
2794 * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
2795 * Similarly, the return value will be converted as necessary.
2796 * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
2797 * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
2798 * <p>
2799 * This method is equivalent to the following code (though it may be more efficient):
2800 * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)}
2801 * <p style="font-size:smaller;">
2802 * <em>Discussion:</em>
2803 * A {@linkplain MethodType#genericMethodType general method type} is one which
2804 * mentions only {@code Object} arguments and return values.
2805 * An invoker for such a type is capable of calling any method handle
2806 * of the same arity as the general type.
2807 * <p style="font-size:smaller;">
2808 * <em>(Note: The invoker method is not available via the Core Reflection API.
2809 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
2810 * on the declared {@code invokeExact} or {@code invoke} method will raise an
2811 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
2812 * <p>
2813 * This method throws no reflective or security exceptions.
2814 * @param type the desired target type
2815 * @return a method handle suitable for invoking any method handle convertible to the given type
2816 * @throws IllegalArgumentException if the resulting method handle's type would have
2817 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2818 */
2819 public static
2820 MethodHandle invoker(MethodType type) {
2821 return type.invokers().genericInvoker();
2822 }
2823
2824 /**
2825 * Produces a special <em>invoker method handle</em> which can be used to
2826 * invoke a signature-polymorphic access mode method on any VarHandle whose
2827 * associated access mode type is compatible with the given type.
2828 * The resulting invoker will have a type which is exactly equal to the
2829 * desired given type, except that it will accept an additional leading
2830 * argument of type {@code VarHandle}.
2831 *
2832 * @param accessMode the VarHandle access mode
2833 * @param type the desired target type
2834 * @return a method handle suitable for invoking an access mode method of
2835 * any VarHandle whose access mode type is of the given type.
2836 * @since 9
2837 */
2838 static public
2839 MethodHandle varHandleExactInvoker(VarHandle.AccessMode accessMode, MethodType type) {
2840 return type.invokers().varHandleMethodExactInvoker(accessMode);
2841 }
2842
2843 /**
2844 * Produces a special <em>invoker method handle</em> which can be used to
2845 * invoke a signature-polymorphic access mode method on any VarHandle whose
2846 * associated access mode type is compatible with the given type.
2847 * The resulting invoker will have a type which is exactly equal to the
2848 * desired given type, except that it will accept an additional leading
2849 * argument of type {@code VarHandle}.
2850 * <p>
2851 * Before invoking its target, if the access mode type differs from the
2852 * desired given type, the invoker will apply reference casts as necessary
2853 * and box, unbox, or widen primitive values, as if by
2854 * {@link MethodHandle#asType asType}. Similarly, the return value will be
2855 * converted as necessary.
2856 * <p>
2857 * This method is equivalent to the following code (though it may be more
2858 * efficient): {@code publicLookup().findVirtual(VarHandle.class, accessMode.name(), type)}
2859 *
2860 * @param accessMode the VarHandle access mode
2861 * @param type the desired target type
2862 * @return a method handle suitable for invoking an access mode method of
2863 * any VarHandle whose access mode type is convertible to the given
2864 * type.
2865 * @since 9
2866 */
2867 static public
2868 MethodHandle varHandleInvoker(VarHandle.AccessMode accessMode, MethodType type) {
2869 return type.invokers().varHandleMethodInvoker(accessMode);
2870 }
2871
2872 static /*non-public*/
2873 MethodHandle basicInvoker(MethodType type) {
2874 return type.invokers().basicInvoker();
2875 }
2876
2877 /// method handle modification (creation from other method handles)
2878
2879 /**
2880 * Produces a method handle which adapts the type of the
2881 * given method handle to a new type by pairwise argument and return type conversion.
2882 * The original type and new type must have the same number of arguments.
2883 * The resulting method handle is guaranteed to report a type
2884 * which is equal to the desired new type.
2885 * <p>
2886 * If the original type and new type are equal, returns target.
2887 * <p>
2888 * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
2889 * and some additional conversions are also applied if those conversions fail.
2890 * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied
2891 * if possible, before or instead of any conversions done by {@code asType}:
2892 * <ul>
2893 * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type,
2894 * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast.
2895 * (This treatment of interfaces follows the usage of the bytecode verifier.)
2896 * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive,
2897 * the boolean is converted to a byte value, 1 for true, 0 for false.
2898 * (This treatment follows the usage of the bytecode verifier.)
2899 * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive,
2900 * <em>T0</em> is converted to byte via Java casting conversion (JLS 5.5),
2901 * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}.
2902 * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean,
2903 * then a Java casting conversion (JLS 5.5) is applied.
2904 * (Specifically, <em>T0</em> will convert to <em>T1</em> by
2905 * widening and/or narrowing.)
2906 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
2907 * conversion will be applied at runtime, possibly followed
2908 * by a Java casting conversion (JLS 5.5) on the primitive value,
2909 * possibly followed by a conversion from byte to boolean by testing
2910 * the low-order bit.
2911 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive,
2912 * and if the reference is null at runtime, a zero value is introduced.
2913 * </ul>
2914 * @param target the method handle to invoke after arguments are retyped
2915 * @param newType the expected type of the new method handle
2916 * @return a method handle which delegates to the target after performing
2917 * any necessary argument conversions, and arranges for any
2918 * necessary return value conversions
2919 * @throws NullPointerException if either argument is null
2920 * @throws WrongMethodTypeException if the conversion cannot be made
2921 * @see MethodHandle#asType
2922 */
2923 public static
2924 MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
2925 explicitCastArgumentsChecks(target, newType);
2926 // use the asTypeCache when possible:
2927 MethodType oldType = target.type();
2928 if (oldType == newType) return target;
2929 if (oldType.explicitCastEquivalentToAsType(newType)) {
2930 return target.asFixedArity().asType(newType);
2931 }
2932 return MethodHandleImpl.makePairwiseConvert(target, newType, false);
2933 }
2934
2935 private static void explicitCastArgumentsChecks(MethodHandle target, MethodType newType) {
2936 if (target.type().parameterCount() != newType.parameterCount()) {
2937 throw new WrongMethodTypeException("cannot explicitly cast " + target + " to " + newType);
2938 }
2939 }
2940
2941 /**
2942 * Produces a method handle which adapts the calling sequence of the
2943 * given method handle to a new type, by reordering the arguments.
2944 * The resulting method handle is guaranteed to report a type
2945 * which is equal to the desired new type.
2946 * <p>
2947 * The given array controls the reordering.
2948 * Call {@code #I} the number of incoming parameters (the value
2949 * {@code newType.parameterCount()}, and call {@code #O} the number
2950 * of outgoing parameters (the value {@code target.type().parameterCount()}).
2951 * Then the length of the reordering array must be {@code #O},
2952 * and each element must be a non-negative number less than {@code #I}.
2953 * For every {@code N} less than {@code #O}, the {@code N}-th
2954 * outgoing argument will be taken from the {@code I}-th incoming
2955 * argument, where {@code I} is {@code reorder[N]}.
2956 * <p>
2957 * No argument or return value conversions are applied.
2958 * The type of each incoming argument, as determined by {@code newType},
2959 * must be identical to the type of the corresponding outgoing parameter
2960 * or parameters in the target method handle.
2961 * The return type of {@code newType} must be identical to the return
2962 * type of the original target.
2963 * <p>
2964 * The reordering array need not specify an actual permutation.
2965 * An incoming argument will be duplicated if its index appears
2966 * more than once in the array, and an incoming argument will be dropped
2967 * if its index does not appear in the array.
2968 * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
2969 * incoming arguments which are not mentioned in the reordering array
2970 * may be of any type, as determined only by {@code newType}.
2971 * <blockquote><pre>{@code
2972 import static java.lang.invoke.MethodHandles.*;
2973 import static java.lang.invoke.MethodType.*;
2974 ...
2975 MethodType intfn1 = methodType(int.class, int.class);
2976 MethodType intfn2 = methodType(int.class, int.class, int.class);
2977 MethodHandle sub = ... (int x, int y) -> (x-y) ...;
2978 assert(sub.type().equals(intfn2));
2979 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
2980 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
2981 assert((int)rsub.invokeExact(1, 100) == 99);
2982 MethodHandle add = ... (int x, int y) -> (x+y) ...;
2983 assert(add.type().equals(intfn2));
2984 MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
2985 assert(twice.type().equals(intfn1));
2986 assert((int)twice.invokeExact(21) == 42);
2987 * }</pre></blockquote>
2988 * <p>
2989 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
2990 * variable-arity method handle}, even if the original target method handle was.
2991 * @param target the method handle to invoke after arguments are reordered
2992 * @param newType the expected type of the new method handle
2993 * @param reorder an index array which controls the reordering
2994 * @return a method handle which delegates to the target after it
2995 * drops unused arguments and moves and/or duplicates the other arguments
2996 * @throws NullPointerException if any argument is null
2997 * @throws IllegalArgumentException if the index array length is not equal to
2998 * the arity of the target, or if any index array element
2999 * not a valid index for a parameter of {@code newType},
3000 * or if two corresponding parameter types in
3001 * {@code target.type()} and {@code newType} are not identical,
3002 */
3003 public static
3004 MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
3005 reorder = reorder.clone(); // get a private copy
3006 MethodType oldType = target.type();
3007 permuteArgumentChecks(reorder, newType, oldType);
3008 // first detect dropped arguments and handle them separately
3009 int[] originalReorder = reorder;
3010 BoundMethodHandle result = target.rebind();
3011 LambdaForm form = result.form;
3012 int newArity = newType.parameterCount();
3013 // Normalize the reordering into a real permutation,
3014 // by removing duplicates and adding dropped elements.
3015 // This somewhat improves lambda form caching, as well
3016 // as simplifying the transform by breaking it up into steps.
3017 for (int ddIdx; (ddIdx = findFirstDupOrDrop(reorder, newArity)) != 0; ) {
3018 if (ddIdx > 0) {
3019 // We found a duplicated entry at reorder[ddIdx].
3020 // Example: (x,y,z)->asList(x,y,z)
3021 // permuted by [1*,0,1] => (a0,a1)=>asList(a1,a0,a1)
3022 // permuted by [0,1,0*] => (a0,a1)=>asList(a0,a1,a0)
3023 // The starred element corresponds to the argument
3024 // deleted by the dupArgumentForm transform.
3025 int srcPos = ddIdx, dstPos = srcPos, dupVal = reorder[srcPos];
3026 boolean killFirst = false;
3027 for (int val; (val = reorder[--dstPos]) != dupVal; ) {
3028 // Set killFirst if the dup is larger than an intervening position.
3029 // This will remove at least one inversion from the permutation.
3030 if (dupVal > val) killFirst = true;
3031 }
3032 if (!killFirst) {
3033 srcPos = dstPos;
3034 dstPos = ddIdx;
3035 }
3036 form = form.editor().dupArgumentForm(1 + srcPos, 1 + dstPos);
3037 assert (reorder[srcPos] == reorder[dstPos]);
3038 oldType = oldType.dropParameterTypes(dstPos, dstPos + 1);
3039 // contract the reordering by removing the element at dstPos
3040 int tailPos = dstPos + 1;
3041 System.arraycopy(reorder, tailPos, reorder, dstPos, reorder.length - tailPos);
3042 reorder = Arrays.copyOf(reorder, reorder.length - 1);
3043 } else {
3044 int dropVal = ~ddIdx, insPos = 0;
3045 while (insPos < reorder.length && reorder[insPos] < dropVal) {
3046 // Find first element of reorder larger than dropVal.
3047 // This is where we will insert the dropVal.
3048 insPos += 1;
3049 }
3050 Class<?> ptype = newType.parameterType(dropVal);
3051 form = form.editor().addArgumentForm(1 + insPos, BasicType.basicType(ptype));
3052 oldType = oldType.insertParameterTypes(insPos, ptype);
3053 // expand the reordering by inserting an element at insPos
3054 int tailPos = insPos + 1;
3055 reorder = Arrays.copyOf(reorder, reorder.length + 1);
3056 System.arraycopy(reorder, insPos, reorder, tailPos, reorder.length - tailPos);
3057 reorder[insPos] = dropVal;
3058 }
3059 assert (permuteArgumentChecks(reorder, newType, oldType));
3060 }
3061 assert (reorder.length == newArity); // a perfect permutation
3062 // Note: This may cache too many distinct LFs. Consider backing off to varargs code.
3063 form = form.editor().permuteArgumentsForm(1, reorder);
3064 if (newType == result.type() && form == result.internalForm())
3065 return result;
3066 return result.copyWith(newType, form);
3067 }
3068
3069 /**
3070 * Return an indication of any duplicate or omission in reorder.
3071 * If the reorder contains a duplicate entry, return the index of the second occurrence.
3072 * Otherwise, return ~(n), for the first n in [0..newArity-1] that is not present in reorder.
3073 * Otherwise, return zero.
3074 * If an element not in [0..newArity-1] is encountered, return reorder.length.
3075 */
3076 private static int findFirstDupOrDrop(int[] reorder, int newArity) {
3077 final int BIT_LIMIT = 63; // max number of bits in bit mask
3078 if (newArity < BIT_LIMIT) {
3079 long mask = 0;
3080 for (int i = 0; i < reorder.length; i++) {
3081 int arg = reorder[i];
3082 if (arg >= newArity) {
3083 return reorder.length;
3084 }
3085 long bit = 1L << arg;
3086 if ((mask & bit) != 0) {
3087 return i; // >0 indicates a dup
3088 }
3089 mask |= bit;
3090 }
3091 if (mask == (1L << newArity) - 1) {
3092 assert(Long.numberOfTrailingZeros(Long.lowestOneBit(~mask)) == newArity);
3093 return 0;
3094 }
3095 // find first zero
3096 long zeroBit = Long.lowestOneBit(~mask);
3097 int zeroPos = Long.numberOfTrailingZeros(zeroBit);
3098 assert(zeroPos <= newArity);
3099 if (zeroPos == newArity) {
3100 return 0;
3101 }
3102 return ~zeroPos;
3103 } else {
3104 // same algorithm, different bit set
3105 BitSet mask = new BitSet(newArity);
3106 for (int i = 0; i < reorder.length; i++) {
3107 int arg = reorder[i];
3108 if (arg >= newArity) {
3109 return reorder.length;
3110 }
3111 if (mask.get(arg)) {
3112 return i; // >0 indicates a dup
3113 }
3114 mask.set(arg);
3115 }
3116 int zeroPos = mask.nextClearBit(0);
3117 assert(zeroPos <= newArity);
3118 if (zeroPos == newArity) {
3119 return 0;
3120 }
3121 return ~zeroPos;
3122 }
3123 }
3124
3125 private static boolean permuteArgumentChecks(int[] reorder, MethodType newType, MethodType oldType) {
3126 if (newType.returnType() != oldType.returnType())
3127 throw newIllegalArgumentException("return types do not match",
3128 oldType, newType);
3129 if (reorder.length == oldType.parameterCount()) {
3130 int limit = newType.parameterCount();
3131 boolean bad = false;
3132 for (int j = 0; j < reorder.length; j++) {
3133 int i = reorder[j];
3134 if (i < 0 || i >= limit) {
3135 bad = true; break;
3136 }
3137 Class<?> src = newType.parameterType(i);
3138 Class<?> dst = oldType.parameterType(j);
3139 if (src != dst)
3140 throw newIllegalArgumentException("parameter types do not match after reorder",
3141 oldType, newType);
3142 }
3143 if (!bad) return true;
3144 }
3145 throw newIllegalArgumentException("bad reorder array: "+Arrays.toString(reorder));
3146 }
3147
3148 /**
3149 * Produces a method handle of the requested return type which returns the given
3150 * constant value every time it is invoked.
3151 * <p>
3152 * Before the method handle is returned, the passed-in value is converted to the requested type.
3153 * If the requested type is primitive, widening primitive conversions are attempted,
3154 * else reference conversions are attempted.
3155 * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
3156 * @param type the return type of the desired method handle
3157 * @param value the value to return
3158 * @return a method handle of the given return type and no arguments, which always returns the given value
3159 * @throws NullPointerException if the {@code type} argument is null
3160 * @throws ClassCastException if the value cannot be converted to the required return type
3161 * @throws IllegalArgumentException if the given type is {@code void.class}
3162 */
3163 public static
3164 MethodHandle constant(Class<?> type, Object value) {
3165 if (type.isPrimitive()) {
3166 if (type == void.class)
3167 throw newIllegalArgumentException("void type");
3168 Wrapper w = Wrapper.forPrimitiveType(type);
3169 value = w.convert(value, type);
3170 if (w.zero().equals(value))
3171 return zero(w, type);
3172 return insertArguments(identity(type), 0, value);
3173 } else {
3174 if (value == null)
3175 return zero(Wrapper.OBJECT, type);
3176 return identity(type).bindTo(value);
3177 }
3178 }
3179
3180 /**
3181 * Produces a method handle which returns its sole argument when invoked.
3182 * @param type the type of the sole parameter and return value of the desired method handle
3183 * @return a unary method handle which accepts and returns the given type
3184 * @throws NullPointerException if the argument is null
3185 * @throws IllegalArgumentException if the given type is {@code void.class}
3186 */
3187 public static
3188 MethodHandle identity(Class<?> type) {
3189 Wrapper btw = (type.isPrimitive() ? Wrapper.forPrimitiveType(type) : Wrapper.OBJECT);
3190 int pos = btw.ordinal();
3191 MethodHandle ident = IDENTITY_MHS[pos];
3192 if (ident == null) {
3193 ident = setCachedMethodHandle(IDENTITY_MHS, pos, makeIdentity(btw.primitiveType()));
3194 }
3195 if (ident.type().returnType() == type)
3196 return ident;
3197 // something like identity(Foo.class); do not bother to intern these
3198 assert (btw == Wrapper.OBJECT);
3199 return makeIdentity(type);
3200 }
3201
3202 /**
3203 * Produces a constant method handle of the requested return type which
3204 * returns the default value for that type every time it is invoked.
3205 * The resulting constant method handle will have no side effects.
3206 * <p>The returned method handle is equivalent to {@code empty(methodType(type))}.
3207 * It is also equivalent to {@code explicitCastArguments(constant(Object.class, null), methodType(type))},
3208 * since {@code explicitCastArguments} converts {@code null} to default values.
3209 * @param type the expected return type of the desired method handle
3210 * @return a constant method handle that takes no arguments
3211 * and returns the default value of the given type (or void, if the type is void)
3212 * @throws NullPointerException if the argument is null
3213 * @see MethodHandles#constant
3214 * @see MethodHandles#empty
3215 * @see MethodHandles#explicitCastArguments
3216 * @since 9
3217 */
3218 public static MethodHandle zero(Class<?> type) {
3219 Objects.requireNonNull(type);
3220 return type.isPrimitive() ? zero(Wrapper.forPrimitiveType(type), type) : zero(Wrapper.OBJECT, type);
3221 }
3222
3223 private static MethodHandle identityOrVoid(Class<?> type) {
3224 return type == void.class ? zero(type) : identity(type);
3225 }
3226
3227 /**
3228 * Produces a method handle of the requested type which ignores any arguments, does nothing,
3229 * and returns a suitable default depending on the return type.
3230 * That is, it returns a zero primitive value, a {@code null}, or {@code void}.
3231 * <p>The returned method handle is equivalent to
3232 * {@code dropArguments(zero(type.returnType()), 0, type.parameterList())}.
3233 * <p>
3234 * @apiNote Given a predicate and target, a useful "if-then" construct can be produced as
3235 * {@code guardWithTest(pred, target, empty(target.type())}.
3236 * @param type the type of the desired method handle
3237 * @return a constant method handle of the given type, which returns a default value of the given return type
3238 * @throws NullPointerException if the argument is null
3239 * @see MethodHandles#zero
3240 * @see MethodHandles#constant
3241 * @since 9
3242 */
3243 public static MethodHandle empty(MethodType type) {
3244 Objects.requireNonNull(type);
3245 return dropArguments(zero(type.returnType()), 0, type.parameterList());
3246 }
3247
3248 private static final MethodHandle[] IDENTITY_MHS = new MethodHandle[Wrapper.COUNT];
3249 private static MethodHandle makeIdentity(Class<?> ptype) {
3250 MethodType mtype = methodType(ptype, ptype);
3251 LambdaForm lform = LambdaForm.identityForm(BasicType.basicType(ptype));
3252 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.IDENTITY);
3253 }
3254
3255 private static MethodHandle zero(Wrapper btw, Class<?> rtype) {
3256 int pos = btw.ordinal();
3257 MethodHandle zero = ZERO_MHS[pos];
3258 if (zero == null) {
3259 zero = setCachedMethodHandle(ZERO_MHS, pos, makeZero(btw.primitiveType()));
3260 }
3261 if (zero.type().returnType() == rtype)
3262 return zero;
3263 assert(btw == Wrapper.OBJECT);
3264 return makeZero(rtype);
3265 }
3266 private static final MethodHandle[] ZERO_MHS = new MethodHandle[Wrapper.COUNT];
3267 private static MethodHandle makeZero(Class<?> rtype) {
3268 MethodType mtype = methodType(rtype);
3269 LambdaForm lform = LambdaForm.zeroForm(BasicType.basicType(rtype));
3270 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.ZERO);
3271 }
3272
3273 private static synchronized MethodHandle setCachedMethodHandle(MethodHandle[] cache, int pos, MethodHandle value) {
3274 // Simulate a CAS, to avoid racy duplication of results.
3275 MethodHandle prev = cache[pos];
3276 if (prev != null) return prev;
3277 return cache[pos] = value;
3278 }
3279
3280 /**
3281 * Provides a target method handle with one or more <em>bound arguments</em>
3282 * in advance of the method handle's invocation.
3283 * The formal parameters to the target corresponding to the bound
3284 * arguments are called <em>bound parameters</em>.
3285 * Returns a new method handle which saves away the bound arguments.
3286 * When it is invoked, it receives arguments for any non-bound parameters,
3287 * binds the saved arguments to their corresponding parameters,
3288 * and calls the original target.
3289 * <p>
3290 * The type of the new method handle will drop the types for the bound
3291 * parameters from the original target type, since the new method handle
3292 * will no longer require those arguments to be supplied by its callers.
3293 * <p>
3294 * Each given argument object must match the corresponding bound parameter type.
3295 * If a bound parameter type is a primitive, the argument object
3296 * must be a wrapper, and will be unboxed to produce the primitive value.
3297 * <p>
3298 * The {@code pos} argument selects which parameters are to be bound.
3299 * It may range between zero and <i>N-L</i> (inclusively),
3300 * where <i>N</i> is the arity of the target method handle
3301 * and <i>L</i> is the length of the values array.
3302 * <p>
3303 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3304 * variable-arity method handle}, even if the original target method handle was.
3305 * @param target the method handle to invoke after the argument is inserted
3306 * @param pos where to insert the argument (zero for the first)
3307 * @param values the series of arguments to insert
3308 * @return a method handle which inserts an additional argument,
3309 * before calling the original method handle
3310 * @throws NullPointerException if the target or the {@code values} array is null
3311 * @see MethodHandle#bindTo
3312 */
3313 public static
3314 MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
3315 int insCount = values.length;
3316 Class<?>[] ptypes = insertArgumentsChecks(target, insCount, pos);
3317 if (insCount == 0) return target;
3318 BoundMethodHandle result = target.rebind();
3319 for (int i = 0; i < insCount; i++) {
3320 Object value = values[i];
3321 Class<?> ptype = ptypes[pos+i];
3322 if (ptype.isPrimitive()) {
3323 result = insertArgumentPrimitive(result, pos, ptype, value);
3324 } else {
3325 value = ptype.cast(value); // throw CCE if needed
3326 result = result.bindArgumentL(pos, value);
3327 }
3328 }
3329 return result;
3330 }
3331
3332 private static BoundMethodHandle insertArgumentPrimitive(BoundMethodHandle result, int pos,
3333 Class<?> ptype, Object value) {
3334 Wrapper w = Wrapper.forPrimitiveType(ptype);
3335 // perform unboxing and/or primitive conversion
3336 value = w.convert(value, ptype);
3337 switch (w) {
3338 case INT: return result.bindArgumentI(pos, (int)value);
3339 case LONG: return result.bindArgumentJ(pos, (long)value);
3340 case FLOAT: return result.bindArgumentF(pos, (float)value);
3341 case DOUBLE: return result.bindArgumentD(pos, (double)value);
3342 default: return result.bindArgumentI(pos, ValueConversions.widenSubword(value));
3343 }
3344 }
3345
3346 private static Class<?>[] insertArgumentsChecks(MethodHandle target, int insCount, int pos) throws RuntimeException {
3347 MethodType oldType = target.type();
3348 int outargs = oldType.parameterCount();
3349 int inargs = outargs - insCount;
3350 if (inargs < 0)
3351 throw newIllegalArgumentException("too many values to insert");
3352 if (pos < 0 || pos > inargs)
3353 throw newIllegalArgumentException("no argument type to append");
3354 return oldType.ptypes();
3355 }
3356
3357 /**
3358 * Produces a method handle which will discard some dummy arguments
3359 * before calling some other specified <i>target</i> method handle.
3360 * The type of the new method handle will be the same as the target's type,
3361 * except it will also include the dummy argument types,
3362 * at some given position.
3363 * <p>
3364 * The {@code pos} argument may range between zero and <i>N</i>,
3365 * where <i>N</i> is the arity of the target.
3366 * If {@code pos} is zero, the dummy arguments will precede
3367 * the target's real arguments; if {@code pos} is <i>N</i>
3368 * they will come after.
3369 * <p>
3370 * <b>Example:</b>
3371 * <blockquote><pre>{@code
3372 import static java.lang.invoke.MethodHandles.*;
3373 import static java.lang.invoke.MethodType.*;
3374 ...
3375 MethodHandle cat = lookup().findVirtual(String.class,
3376 "concat", methodType(String.class, String.class));
3377 assertEquals("xy", (String) cat.invokeExact("x", "y"));
3378 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
3379 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
3380 assertEquals(bigType, d0.type());
3381 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
3382 * }</pre></blockquote>
3383 * <p>
3384 * This method is also equivalent to the following code:
3385 * <blockquote><pre>
3386 * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))}
3387 * </pre></blockquote>
3388 * @param target the method handle to invoke after the arguments are dropped
3389 * @param valueTypes the type(s) of the argument(s) to drop
3390 * @param pos position of first argument to drop (zero for the leftmost)
3391 * @return a method handle which drops arguments of the given types,
3392 * before calling the original method handle
3393 * @throws NullPointerException if the target is null,
3394 * or if the {@code valueTypes} list or any of its elements is null
3395 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
3396 * or if {@code pos} is negative or greater than the arity of the target,
3397 * or if the new method handle's type would have too many parameters
3398 */
3399 public static
3400 MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) {
3401 return dropArguments0(target, pos, copyTypes(valueTypes.toArray()));
3402 }
3403
3404 private static List<Class<?>> copyTypes(Object[] array) {
3405 return Arrays.asList(Arrays.copyOf(array, array.length, Class[].class));
3406 }
3407
3408 private static
3409 MethodHandle dropArguments0(MethodHandle target, int pos, List<Class<?>> valueTypes) {
3410 MethodType oldType = target.type(); // get NPE
3411 int dropped = dropArgumentChecks(oldType, pos, valueTypes);
3412 MethodType newType = oldType.insertParameterTypes(pos, valueTypes);
3413 if (dropped == 0) return target;
3414 BoundMethodHandle result = target.rebind();
3415 LambdaForm lform = result.form;
3416 int insertFormArg = 1 + pos;
3417 for (Class<?> ptype : valueTypes) {
3418 lform = lform.editor().addArgumentForm(insertFormArg++, BasicType.basicType(ptype));
3419 }
3420 result = result.copyWith(newType, lform);
3421 return result;
3422 }
3423
3424 private static int dropArgumentChecks(MethodType oldType, int pos, List<Class<?>> valueTypes) {
3425 int dropped = valueTypes.size();
3426 MethodType.checkSlotCount(dropped);
3427 int outargs = oldType.parameterCount();
3428 int inargs = outargs + dropped;
3429 if (pos < 0 || pos > outargs)
3430 throw newIllegalArgumentException("no argument type to remove"
3431 + Arrays.asList(oldType, pos, valueTypes, inargs, outargs)
3432 );
3433 return dropped;
3434 }
3435
3436 /**
3437 * Produces a method handle which will discard some dummy arguments
3438 * before calling some other specified <i>target</i> method handle.
3439 * The type of the new method handle will be the same as the target's type,
3440 * except it will also include the dummy argument types,
3441 * at some given position.
3442 * <p>
3443 * The {@code pos} argument may range between zero and <i>N</i>,
3444 * where <i>N</i> is the arity of the target.
3445 * If {@code pos} is zero, the dummy arguments will precede
3446 * the target's real arguments; if {@code pos} is <i>N</i>
3447 * they will come after.
3448 * @apiNote
3449 * <blockquote><pre>{@code
3450 import static java.lang.invoke.MethodHandles.*;
3451 import static java.lang.invoke.MethodType.*;
3452 ...
3453 MethodHandle cat = lookup().findVirtual(String.class,
3454 "concat", methodType(String.class, String.class));
3455 assertEquals("xy", (String) cat.invokeExact("x", "y"));
3456 MethodHandle d0 = dropArguments(cat, 0, String.class);
3457 assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
3458 MethodHandle d1 = dropArguments(cat, 1, String.class);
3459 assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
3460 MethodHandle d2 = dropArguments(cat, 2, String.class);
3461 assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
3462 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
3463 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
3464 * }</pre></blockquote>
3465 * <p>
3466 * This method is also equivalent to the following code:
3467 * <blockquote><pre>
3468 * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))}
3469 * </pre></blockquote>
3470 * @param target the method handle to invoke after the arguments are dropped
3471 * @param valueTypes the type(s) of the argument(s) to drop
3472 * @param pos position of first argument to drop (zero for the leftmost)
3473 * @return a method handle which drops arguments of the given types,
3474 * before calling the original method handle
3475 * @throws NullPointerException if the target is null,
3476 * or if the {@code valueTypes} array or any of its elements is null
3477 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
3478 * or if {@code pos} is negative or greater than the arity of the target,
3479 * or if the new method handle's type would have
3480 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3481 */
3482 public static
3483 MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
3484 return dropArguments0(target, pos, copyTypes(valueTypes));
3485 }
3486
3487 // private version which allows caller some freedom with error handling
3488 private static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos,
3489 boolean nullOnFailure) {
3490 newTypes = copyTypes(newTypes.toArray());
3491 List<Class<?>> oldTypes = target.type().parameterList();
3492 int match = oldTypes.size();
3493 if (skip != 0) {
3494 if (skip < 0 || skip > match) {
3495 throw newIllegalArgumentException("illegal skip", skip, target);
3496 }
3497 oldTypes = oldTypes.subList(skip, match);
3498 match -= skip;
3499 }
3500 List<Class<?>> addTypes = newTypes;
3501 int add = addTypes.size();
3502 if (pos != 0) {
3503 if (pos < 0 || pos > add) {
3504 throw newIllegalArgumentException("illegal pos", pos, newTypes);
3505 }
3506 addTypes = addTypes.subList(pos, add);
3507 add -= pos;
3508 assert(addTypes.size() == add);
3509 }
3510 // Do not add types which already match the existing arguments.
3511 if (match > add || !oldTypes.equals(addTypes.subList(0, match))) {
3512 if (nullOnFailure) {
3513 return null;
3514 }
3515 throw newIllegalArgumentException("argument lists do not match", oldTypes, newTypes);
3516 }
3517 addTypes = addTypes.subList(match, add);
3518 add -= match;
3519 assert(addTypes.size() == add);
3520 // newTypes: ( P*[pos], M*[match], A*[add] )
3521 // target: ( S*[skip], M*[match] )
3522 MethodHandle adapter = target;
3523 if (add > 0) {
3524 adapter = dropArguments0(adapter, skip+ match, addTypes);
3525 }
3526 // adapter: (S*[skip], M*[match], A*[add] )
3527 if (pos > 0) {
3528 adapter = dropArguments0(adapter, skip, newTypes.subList(0, pos));
3529 }
3530 // adapter: (S*[skip], P*[pos], M*[match], A*[add] )
3531 return adapter;
3532 }
3533
3534 /**
3535 * Adapts a target method handle to match the given parameter type list. If necessary, adds dummy arguments. Some
3536 * leading parameters can be skipped before matching begins. The remaining types in the {@code target}'s parameter
3537 * type list must be a sub-list of the {@code newTypes} type list at the starting position {@code pos}. The
3538 * resulting handle will have the target handle's parameter type list, with any non-matching parameter types (before
3539 * or after the matching sub-list) inserted in corresponding positions of the target's original parameters, as if by
3540 * {@link #dropArguments(MethodHandle, int, Class[])}.
3541 * <p>
3542 * The resulting handle will have the same return type as the target handle.
3543 * <p>
3544 * In more formal terms, assume these two type lists:<ul>
3545 * <li>The target handle has the parameter type list {@code S..., M...}, with as many types in {@code S} as
3546 * indicated by {@code skip}. The {@code M} types are those that are supposed to match part of the given type list,
3547 * {@code newTypes}.
3548 * <li>The {@code newTypes} list contains types {@code P..., M..., A...}, with as many types in {@code P} as
3549 * indicated by {@code pos}. The {@code M} types are precisely those that the {@code M} types in the target handle's
3550 * parameter type list are supposed to match. The types in {@code A} are additional types found after the matching
3551 * sub-list.
3552 * </ul>
3553 * Given these assumptions, the result of an invocation of {@code dropArgumentsToMatch} will have the parameter type
3554 * list {@code S..., P..., M..., A...}, with the {@code P} and {@code A} types inserted as if by
3555 * {@link #dropArguments(MethodHandle, int, Class[])}.
3556 * <p>
3557 * @apiNote
3558 * Two method handles whose argument lists are "effectively identical" (i.e., identical in a common prefix) may be
3559 * mutually converted to a common type by two calls to {@code dropArgumentsToMatch}, as follows:
3560 * <blockquote><pre>{@code
3561 import static java.lang.invoke.MethodHandles.*;
3562 import static java.lang.invoke.MethodType.*;
3563 ...
3564 ...
3565 MethodHandle h0 = constant(boolean.class, true);
3566 MethodHandle h1 = lookup().findVirtual(String.class, "concat", methodType(String.class, String.class));
3567 MethodType bigType = h1.type().insertParameterTypes(1, String.class, int.class);
3568 MethodHandle h2 = dropArguments(h1, 0, bigType.parameterList());
3569 if (h1.type().parameterCount() < h2.type().parameterCount())
3570 h1 = dropArgumentsToMatch(h1, 0, h2.type().parameterList(), 0); // lengthen h1
3571 else
3572 h2 = dropArgumentsToMatch(h2, 0, h1.type().parameterList(), 0); // lengthen h2
3573 MethodHandle h3 = guardWithTest(h0, h1, h2);
3574 assertEquals("xy", h3.invoke("x", "y", 1, "a", "b", "c"));
3575 * }</pre></blockquote>
3576 * @param target the method handle to adapt
3577 * @param skip number of targets parameters to disregard (they will be unchanged)
3578 * @param newTypes the list of types to match {@code target}'s parameter type list to
3579 * @param pos place in {@code newTypes} where the non-skipped target parameters must occur
3580 * @return a possibly adapted method handle
3581 * @throws NullPointerException if either argument is null
3582 * @throws IllegalArgumentException if any element of {@code newTypes} is {@code void.class},
3583 * or if {@code skip} is negative or greater than the arity of the target,
3584 * or if {@code pos} is negative or greater than the newTypes list size,
3585 * or if {@code newTypes} does not contain the {@code target}'s non-skipped parameter types at position
3586 * {@code pos}.
3587 * @since 9
3588 */
3589 public static
3590 MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos) {
3591 Objects.requireNonNull(target);
3592 Objects.requireNonNull(newTypes);
3593 return dropArgumentsToMatch(target, skip, newTypes, pos, false);
3594 }
3595
3596 /**
3597 * Adapts a target method handle by pre-processing
3598 * one or more of its arguments, each with its own unary filter function,
3599 * and then calling the target with each pre-processed argument
3600 * replaced by the result of its corresponding filter function.
3601 * <p>
3602 * The pre-processing is performed by one or more method handles,
3603 * specified in the elements of the {@code filters} array.
3604 * The first element of the filter array corresponds to the {@code pos}
3605 * argument of the target, and so on in sequence.
3606 * <p>
3607 * Null arguments in the array are treated as identity functions,
3608 * and the corresponding arguments left unchanged.
3609 * (If there are no non-null elements in the array, the original target is returned.)
3610 * Each filter is applied to the corresponding argument of the adapter.
3611 * <p>
3612 * If a filter {@code F} applies to the {@code N}th argument of
3613 * the target, then {@code F} must be a method handle which
3614 * takes exactly one argument. The type of {@code F}'s sole argument
3615 * replaces the corresponding argument type of the target
3616 * in the resulting adapted method handle.
3617 * The return type of {@code F} must be identical to the corresponding
3618 * parameter type of the target.
3619 * <p>
3620 * It is an error if there are elements of {@code filters}
3621 * (null or not)
3622 * which do not correspond to argument positions in the target.
3623 * <p><b>Example:</b>
3624 * <blockquote><pre>{@code
3625 import static java.lang.invoke.MethodHandles.*;
3626 import static java.lang.invoke.MethodType.*;
3627 ...
3628 MethodHandle cat = lookup().findVirtual(String.class,
3629 "concat", methodType(String.class, String.class));
3630 MethodHandle upcase = lookup().findVirtual(String.class,
3631 "toUpperCase", methodType(String.class));
3632 assertEquals("xy", (String) cat.invokeExact("x", "y"));
3633 MethodHandle f0 = filterArguments(cat, 0, upcase);
3634 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
3635 MethodHandle f1 = filterArguments(cat, 1, upcase);
3636 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
3637 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
3638 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
3639 * }</pre></blockquote>
3640 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
3641 * denotes the return type of both the {@code target} and resulting adapter.
3642 * {@code P}/{@code p} and {@code B}/{@code b} represent the types and values
3643 * of the parameters and arguments that precede and follow the filter position
3644 * {@code pos}, respectively. {@code A[i]}/{@code a[i]} stand for the types and
3645 * values of the filtered parameters and arguments; they also represent the
3646 * return types of the {@code filter[i]} handles. The latter accept arguments
3647 * {@code v[i]} of type {@code V[i]}, which also appear in the signature of
3648 * the resulting adapter.
3649 * <blockquote><pre>{@code
3650 * T target(P... p, A[i]... a[i], B... b);
3651 * A[i] filter[i](V[i]);
3652 * T adapter(P... p, V[i]... v[i], B... b) {
3653 * return target(p..., filter[i](v[i])..., b...);
3654 * }
3655 * }</pre></blockquote>
3656 * <p>
3657 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3658 * variable-arity method handle}, even if the original target method handle was.
3659 *
3660 * @param target the method handle to invoke after arguments are filtered
3661 * @param pos the position of the first argument to filter
3662 * @param filters method handles to call initially on filtered arguments
3663 * @return method handle which incorporates the specified argument filtering logic
3664 * @throws NullPointerException if the target is null
3665 * or if the {@code filters} array is null
3666 * @throws IllegalArgumentException if a non-null element of {@code filters}
3667 * does not match a corresponding argument type of target as described above,
3668 * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()},
3669 * or if the resulting method handle's type would have
3670 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3671 */
3672 public static
3673 MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
3674 filterArgumentsCheckArity(target, pos, filters);
3675 MethodHandle adapter = target;
3676 int curPos = pos-1; // pre-incremented
3677 for (MethodHandle filter : filters) {
3678 curPos += 1;
3679 if (filter == null) continue; // ignore null elements of filters
3680 adapter = filterArgument(adapter, curPos, filter);
3681 }
3682 return adapter;
3683 }
3684
3685 /*non-public*/ static
3686 MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
3687 filterArgumentChecks(target, pos, filter);
3688 MethodType targetType = target.type();
3689 MethodType filterType = filter.type();
3690 BoundMethodHandle result = target.rebind();
3691 Class<?> newParamType = filterType.parameterType(0);
3692 LambdaForm lform = result.editor().filterArgumentForm(1 + pos, BasicType.basicType(newParamType));
3693 MethodType newType = targetType.changeParameterType(pos, newParamType);
3694 result = result.copyWithExtendL(newType, lform, filter);
3695 return result;
3696 }
3697
3698 private static void filterArgumentsCheckArity(MethodHandle target, int pos, MethodHandle[] filters) {
3699 MethodType targetType = target.type();
3700 int maxPos = targetType.parameterCount();
3701 if (pos + filters.length > maxPos)
3702 throw newIllegalArgumentException("too many filters");
3703 }
3704
3705 private static void filterArgumentChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
3706 MethodType targetType = target.type();
3707 MethodType filterType = filter.type();
3708 if (filterType.parameterCount() != 1
3709 || filterType.returnType() != targetType.parameterType(pos))
3710 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
3711 }
3712
3713 /**
3714 * Adapts a target method handle by pre-processing
3715 * a sub-sequence of its arguments with a filter (another method handle).
3716 * The pre-processed arguments are replaced by the result (if any) of the
3717 * filter function.
3718 * The target is then called on the modified (usually shortened) argument list.
3719 * <p>
3720 * If the filter returns a value, the target must accept that value as
3721 * its argument in position {@code pos}, preceded and/or followed by
3722 * any arguments not passed to the filter.
3723 * If the filter returns void, the target must accept all arguments
3724 * not passed to the filter.
3725 * No arguments are reordered, and a result returned from the filter
3726 * replaces (in order) the whole subsequence of arguments originally
3727 * passed to the adapter.
3728 * <p>
3729 * The argument types (if any) of the filter
3730 * replace zero or one argument types of the target, at position {@code pos},
3731 * in the resulting adapted method handle.
3732 * The return type of the filter (if any) must be identical to the
3733 * argument type of the target at position {@code pos}, and that target argument
3734 * is supplied by the return value of the filter.
3735 * <p>
3736 * In all cases, {@code pos} must be greater than or equal to zero, and
3737 * {@code pos} must also be less than or equal to the target's arity.
3738 * <p><b>Example:</b>
3739 * <blockquote><pre>{@code
3740 import static java.lang.invoke.MethodHandles.*;
3741 import static java.lang.invoke.MethodType.*;
3742 ...
3743 MethodHandle deepToString = publicLookup()
3744 .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
3745
3746 MethodHandle ts1 = deepToString.asCollector(String[].class, 1);
3747 assertEquals("[strange]", (String) ts1.invokeExact("strange"));
3748
3749 MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
3750 assertEquals("[up, down]", (String) ts2.invokeExact("up", "down"));
3751
3752 MethodHandle ts3 = deepToString.asCollector(String[].class, 3);
3753 MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2);
3754 assertEquals("[top, [up, down], strange]",
3755 (String) ts3_ts2.invokeExact("top", "up", "down", "strange"));
3756
3757 MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1);
3758 assertEquals("[top, [up, down], [strange]]",
3759 (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange"));
3760
3761 MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3);
3762 assertEquals("[top, [[up, down, strange], charm], bottom]",
3763 (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom"));
3764 * }</pre></blockquote>
3765 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
3766 * represents the return type of the {@code target} and resulting adapter.
3767 * {@code V}/{@code v} stand for the return type and value of the
3768 * {@code filter}, which are also found in the signature and arguments of
3769 * the {@code target}, respectively, unless {@code V} is {@code void}.
3770 * {@code A}/{@code a} and {@code C}/{@code c} represent the parameter types
3771 * and values preceding and following the collection position, {@code pos},
3772 * in the {@code target}'s signature. They also turn up in the resulting
3773 * adapter's signature and arguments, where they surround
3774 * {@code B}/{@code b}, which represent the parameter types and arguments
3775 * to the {@code filter} (if any).
3776 * <blockquote><pre>{@code
3777 * T target(A...,V,C...);
3778 * V filter(B...);
3779 * T adapter(A... a,B... b,C... c) {
3780 * V v = filter(b...);
3781 * return target(a...,v,c...);
3782 * }
3783 * // and if the filter has no arguments:
3784 * T target2(A...,V,C...);
3785 * V filter2();
3786 * T adapter2(A... a,C... c) {
3787 * V v = filter2();
3788 * return target2(a...,v,c...);
3789 * }
3790 * // and if the filter has a void return:
3791 * T target3(A...,C...);
3792 * void filter3(B...);
3793 * T adapter3(A... a,B... b,C... c) {
3794 * filter3(b...);
3795 * return target3(a...,c...);
3796 * }
3797 * }</pre></blockquote>
3798 * <p>
3799 * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to
3800 * one which first "folds" the affected arguments, and then drops them, in separate
3801 * steps as follows:
3802 * <blockquote><pre>{@code
3803 * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2
3804 * mh = MethodHandles.foldArguments(mh, coll); //step 1
3805 * }</pre></blockquote>
3806 * If the target method handle consumes no arguments besides than the result
3807 * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)}
3808 * is equivalent to {@code filterReturnValue(coll, mh)}.
3809 * If the filter method handle {@code coll} consumes one argument and produces
3810 * a non-void result, then {@code collectArguments(mh, N, coll)}
3811 * is equivalent to {@code filterArguments(mh, N, coll)}.
3812 * Other equivalences are possible but would require argument permutation.
3813 * <p>
3814 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3815 * variable-arity method handle}, even if the original target method handle was.
3816 *
3817 * @param target the method handle to invoke after filtering the subsequence of arguments
3818 * @param pos the position of the first adapter argument to pass to the filter,
3819 * and/or the target argument which receives the result of the filter
3820 * @param filter method handle to call on the subsequence of arguments
3821 * @return method handle which incorporates the specified argument subsequence filtering logic
3822 * @throws NullPointerException if either argument is null
3823 * @throws IllegalArgumentException if the return type of {@code filter}
3824 * is non-void and is not the same as the {@code pos} argument of the target,
3825 * or if {@code pos} is not between 0 and the target's arity, inclusive,
3826 * or if the resulting method handle's type would have
3827 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3828 * @see MethodHandles#foldArguments
3829 * @see MethodHandles#filterArguments
3830 * @see MethodHandles#filterReturnValue
3831 */
3832 public static
3833 MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) {
3834 MethodType newType = collectArgumentsChecks(target, pos, filter);
3835 MethodType collectorType = filter.type();
3836 BoundMethodHandle result = target.rebind();
3837 LambdaForm lform;
3838 if (collectorType.returnType().isArray() && filter.intrinsicName() == Intrinsic.NEW_ARRAY) {
3839 lform = result.editor().collectArgumentArrayForm(1 + pos, filter);
3840 if (lform != null) {
3841 return result.copyWith(newType, lform);
3842 }
3843 }
3844 lform = result.editor().collectArgumentsForm(1 + pos, collectorType.basicType());
3845 return result.copyWithExtendL(newType, lform, filter);
3846 }
3847
3848 private static MethodType collectArgumentsChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
3849 MethodType targetType = target.type();
3850 MethodType filterType = filter.type();
3851 Class<?> rtype = filterType.returnType();
3852 List<Class<?>> filterArgs = filterType.parameterList();
3853 if (rtype == void.class) {
3854 return targetType.insertParameterTypes(pos, filterArgs);
3855 }
3856 if (rtype != targetType.parameterType(pos)) {
3857 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
3858 }
3859 return targetType.dropParameterTypes(pos, pos+1).insertParameterTypes(pos, filterArgs);
3860 }
3861
3862 /**
3863 * Adapts a target method handle by post-processing
3864 * its return value (if any) with a filter (another method handle).
3865 * The result of the filter is returned from the adapter.
3866 * <p>
3867 * If the target returns a value, the filter must accept that value as
3868 * its only argument.
3869 * If the target returns void, the filter must accept no arguments.
3870 * <p>
3871 * The return type of the filter
3872 * replaces the return type of the target
3873 * in the resulting adapted method handle.
3874 * The argument type of the filter (if any) must be identical to the
3875 * return type of the target.
3876 * <p><b>Example:</b>
3877 * <blockquote><pre>{@code
3878 import static java.lang.invoke.MethodHandles.*;
3879 import static java.lang.invoke.MethodType.*;
3880 ...
3881 MethodHandle cat = lookup().findVirtual(String.class,
3882 "concat", methodType(String.class, String.class));
3883 MethodHandle length = lookup().findVirtual(String.class,
3884 "length", methodType(int.class));
3885 System.out.println((String) cat.invokeExact("x", "y")); // xy
3886 MethodHandle f0 = filterReturnValue(cat, length);
3887 System.out.println((int) f0.invokeExact("x", "y")); // 2
3888 * }</pre></blockquote>
3889 * <p>Here is pseudocode for the resulting adapter. In the code,
3890 * {@code T}/{@code t} represent the result type and value of the
3891 * {@code target}; {@code V}, the result type of the {@code filter}; and
3892 * {@code A}/{@code a}, the types and values of the parameters and arguments
3893 * of the {@code target} as well as the resulting adapter.
3894 * <blockquote><pre>{@code
3895 * T target(A...);
3896 * V filter(T);
3897 * V adapter(A... a) {
3898 * T t = target(a...);
3899 * return filter(t);
3900 * }
3901 * // and if the target has a void return:
3902 * void target2(A...);
3903 * V filter2();
3904 * V adapter2(A... a) {
3905 * target2(a...);
3906 * return filter2();
3907 * }
3908 * // and if the filter has a void return:
3909 * T target3(A...);
3910 * void filter3(V);
3911 * void adapter3(A... a) {
3912 * T t = target3(a...);
3913 * filter3(t);
3914 * }
3915 * }</pre></blockquote>
3916 * <p>
3917 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3918 * variable-arity method handle}, even if the original target method handle was.
3919 * @param target the method handle to invoke before filtering the return value
3920 * @param filter method handle to call on the return value
3921 * @return method handle which incorporates the specified return value filtering logic
3922 * @throws NullPointerException if either argument is null
3923 * @throws IllegalArgumentException if the argument list of {@code filter}
3924 * does not match the return type of target as described above
3925 */
3926 public static
3927 MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
3928 MethodType targetType = target.type();
3929 MethodType filterType = filter.type();
3930 filterReturnValueChecks(targetType, filterType);
3931 BoundMethodHandle result = target.rebind();
3932 BasicType rtype = BasicType.basicType(filterType.returnType());
3933 LambdaForm lform = result.editor().filterReturnForm(rtype, false);
3934 MethodType newType = targetType.changeReturnType(filterType.returnType());
3935 result = result.copyWithExtendL(newType, lform, filter);
3936 return result;
3937 }
3938
3939 private static void filterReturnValueChecks(MethodType targetType, MethodType filterType) throws RuntimeException {
3940 Class<?> rtype = targetType.returnType();
3941 int filterValues = filterType.parameterCount();
3942 if (filterValues == 0
3943 ? (rtype != void.class)
3944 : (rtype != filterType.parameterType(0) || filterValues != 1))
3945 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
3946 }
3947
3948 /**
3949 * Adapts a target method handle by pre-processing
3950 * some of its arguments, and then calling the target with
3951 * the result of the pre-processing, inserted into the original
3952 * sequence of arguments.
3953 * <p>
3954 * The pre-processing is performed by {@code combiner}, a second method handle.
3955 * Of the arguments passed to the adapter, the first {@code N} arguments
3956 * are copied to the combiner, which is then called.
3957 * (Here, {@code N} is defined as the parameter count of the combiner.)
3958 * After this, control passes to the target, with any result
3959 * from the combiner inserted before the original {@code N} incoming
3960 * arguments.
3961 * <p>
3962 * If the combiner returns a value, the first parameter type of the target
3963 * must be identical with the return type of the combiner, and the next
3964 * {@code N} parameter types of the target must exactly match the parameters
3965 * of the combiner.
3966 * <p>
3967 * If the combiner has a void return, no result will be inserted,
3968 * and the first {@code N} parameter types of the target
3969 * must exactly match the parameters of the combiner.
3970 * <p>
3971 * The resulting adapter is the same type as the target, except that the
3972 * first parameter type is dropped,
3973 * if it corresponds to the result of the combiner.
3974 * <p>
3975 * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
3976 * that either the combiner or the target does not wish to receive.
3977 * If some of the incoming arguments are destined only for the combiner,
3978 * consider using {@link MethodHandle#asCollector asCollector} instead, since those
3979 * arguments will not need to be live on the stack on entry to the
3980 * target.)
3981 * <p><b>Example:</b>
3982 * <blockquote><pre>{@code
3983 import static java.lang.invoke.MethodHandles.*;
3984 import static java.lang.invoke.MethodType.*;
3985 ...
3986 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
3987 "println", methodType(void.class, String.class))
3988 .bindTo(System.out);
3989 MethodHandle cat = lookup().findVirtual(String.class,
3990 "concat", methodType(String.class, String.class));
3991 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
3992 MethodHandle catTrace = foldArguments(cat, trace);
3993 // also prints "boo":
3994 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
3995 * }</pre></blockquote>
3996 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
3997 * represents the result type of the {@code target} and resulting adapter.
3998 * {@code V}/{@code v} represent the type and value of the parameter and argument
3999 * of {@code target} that precedes the folding position; {@code V} also is
4000 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
4001 * types and values of the {@code N} parameters and arguments at the folding
4002 * position. {@code B}/{@code b} represent the types and values of the
4003 * {@code target} parameters and arguments that follow the folded parameters
4004 * and arguments.
4005 * <blockquote><pre>{@code
4006 * // there are N arguments in A...
4007 * T target(V, A[N]..., B...);
4008 * V combiner(A...);
4009 * T adapter(A... a, B... b) {
4010 * V v = combiner(a...);
4011 * return target(v, a..., b...);
4012 * }
4013 * // and if the combiner has a void return:
4014 * T target2(A[N]..., B...);
4015 * void combiner2(A...);
4016 * T adapter2(A... a, B... b) {
4017 * combiner2(a...);
4018 * return target2(a..., b...);
4019 * }
4020 * }</pre></blockquote>
4021 * <p>
4022 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4023 * variable-arity method handle}, even if the original target method handle was.
4024 * @param target the method handle to invoke after arguments are combined
4025 * @param combiner method handle to call initially on the incoming arguments
4026 * @return method handle which incorporates the specified argument folding logic
4027 * @throws NullPointerException if either argument is null
4028 * @throws IllegalArgumentException if {@code combiner}'s return type
4029 * is non-void and not the same as the first argument type of
4030 * the target, or if the initial {@code N} argument types
4031 * of the target
4032 * (skipping one matching the {@code combiner}'s return type)
4033 * are not identical with the argument types of {@code combiner}
4034 */
4035 public static
4036 MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
4037 return foldArguments(target, 0, combiner);
4038 }
4039
4040 /**
4041 * Adapts a target method handle by pre-processing some of its arguments, starting at a given position, and then
4042 * calling the target with the result of the pre-processing, inserted into the original sequence of arguments just
4043 * before the folded arguments.
4044 * <p>
4045 * This method is closely related to {@link #foldArguments(MethodHandle, MethodHandle)}, but allows to control the
4046 * position in the parameter list at which folding takes place. The argument controlling this, {@code pos}, is a
4047 * zero-based index. The aforementioned method {@link #foldArguments(MethodHandle, MethodHandle)} assumes position
4048 * 0.
4049 * <p>
4050 * @apiNote Example:
4051 * <blockquote><pre>{@code
4052 import static java.lang.invoke.MethodHandles.*;
4053 import static java.lang.invoke.MethodType.*;
4054 ...
4055 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
4056 "println", methodType(void.class, String.class))
4057 .bindTo(System.out);
4058 MethodHandle cat = lookup().findVirtual(String.class,
4059 "concat", methodType(String.class, String.class));
4060 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
4061 MethodHandle catTrace = foldArguments(cat, 1, trace);
4062 // also prints "jum":
4063 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
4064 * }</pre></blockquote>
4065 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
4066 * represents the result type of the {@code target} and resulting adapter.
4067 * {@code V}/{@code v} represent the type and value of the parameter and argument
4068 * of {@code target} that precedes the folding position; {@code V} also is
4069 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
4070 * types and values of the {@code N} parameters and arguments at the folding
4071 * position. {@code Z}/{@code z} and {@code B}/{@code b} represent the types
4072 * and values of the {@code target} parameters and arguments that precede and
4073 * follow the folded parameters and arguments starting at {@code pos},
4074 * respectively.
4075 * <blockquote><pre>{@code
4076 * // there are N arguments in A...
4077 * T target(Z..., V, A[N]..., B...);
4078 * V combiner(A...);
4079 * T adapter(Z... z, A... a, B... b) {
4080 * V v = combiner(a...);
4081 * return target(z..., v, a..., b...);
4082 * }
4083 * // and if the combiner has a void return:
4084 * T target2(Z..., A[N]..., B...);
4085 * void combiner2(A...);
4086 * T adapter2(Z... z, A... a, B... b) {
4087 * combiner2(a...);
4088 * return target2(z..., a..., b...);
4089 * }
4090 * }</pre></blockquote>
4091 * <p>
4092 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4093 * variable-arity method handle}, even if the original target method handle was.
4094 *
4095 * @param target the method handle to invoke after arguments are combined
4096 * @param pos the position at which to start folding and at which to insert the folding result; if this is {@code
4097 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
4098 * @param combiner method handle to call initially on the incoming arguments
4099 * @return method handle which incorporates the specified argument folding logic
4100 * @throws NullPointerException if either argument is null
4101 * @throws IllegalArgumentException if either of the following two conditions holds:
4102 * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
4103 * {@code pos} of the target signature;
4104 * (2) the {@code N} argument types at position {@code pos} of the target signature (skipping one matching
4105 * the {@code combiner}'s return type) are not identical with the argument types of {@code combiner}.
4106 *
4107 * @see #foldArguments(MethodHandle, MethodHandle)
4108 * @since 9
4109 */
4110 public static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner) {
4111 MethodType targetType = target.type();
4112 MethodType combinerType = combiner.type();
4113 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType);
4114 BoundMethodHandle result = target.rebind();
4115 boolean dropResult = rtype == void.class;
4116 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType());
4117 MethodType newType = targetType;
4118 if (!dropResult) {
4119 newType = newType.dropParameterTypes(pos, pos + 1);
4120 }
4121 result = result.copyWithExtendL(newType, lform, combiner);
4122 return result;
4123 }
4124
4125 /**
4126 * As {@see foldArguments(MethodHandle, int, MethodHandle)}, but with the
4127 * added capability of selecting the arguments from the targets parameters
4128 * to call the combiner with. This allows us to avoid some simple cases of
4129 * permutations and padding the combiner with dropArguments to select the
4130 * right argument, which may ultimately produce fewer intermediaries.
4131 */
4132 static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner, int ... argPositions) {
4133 MethodType targetType = target.type();
4134 MethodType combinerType = combiner.type();
4135 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType, argPositions);
4136 BoundMethodHandle result = target.rebind();
4137 boolean dropResult = rtype == void.class;
4138 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType(), argPositions);
4139 MethodType newType = targetType;
4140 if (!dropResult) {
4141 newType = newType.dropParameterTypes(pos, pos + 1);
4142 }
4143 result = result.copyWithExtendL(newType, lform, combiner);
4144 return result;
4145 }
4146
4147 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType) {
4148 int foldArgs = combinerType.parameterCount();
4149 Class<?> rtype = combinerType.returnType();
4150 int foldVals = rtype == void.class ? 0 : 1;
4151 int afterInsertPos = foldPos + foldVals;
4152 boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
4153 if (ok) {
4154 for (int i = 0; i < foldArgs; i++) {
4155 if (combinerType.parameterType(i) != targetType.parameterType(i + afterInsertPos)) {
4156 ok = false;
4157 break;
4158 }
4159 }
4160 }
4161 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos))
4162 ok = false;
4163 if (!ok)
4164 throw misMatchedTypes("target and combiner types", targetType, combinerType);
4165 return rtype;
4166 }
4167
4168 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType, int ... argPos) {
4169 int foldArgs = combinerType.parameterCount();
4170 if (argPos.length != foldArgs) {
4171 throw newIllegalArgumentException("combiner and argument map must be equal size", combinerType, argPos.length);
4172 }
4173 Class<?> rtype = combinerType.returnType();
4174 int foldVals = rtype == void.class ? 0 : 1;
4175 boolean ok = true;
4176 for (int i = 0; i < foldArgs; i++) {
4177 int arg = argPos[i];
4178 if (arg < 0 || arg > targetType.parameterCount()) {
4179 throw newIllegalArgumentException("arg outside of target parameterRange", targetType, arg);
4180 }
4181 if (combinerType.parameterType(i) != targetType.parameterType(arg)) {
4182 throw newIllegalArgumentException("target argument type at position " + arg
4183 + " must match combiner argument type at index " + i + ": " + targetType
4184 + " -> " + combinerType + ", map: " + Arrays.toString(argPos));
4185 }
4186 }
4187 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos)) {
4188 ok = false;
4189 }
4190 if (!ok)
4191 throw misMatchedTypes("target and combiner types", targetType, combinerType);
4192 return rtype;
4193 }
4194
4195 /**
4196 * Makes a method handle which adapts a target method handle,
4197 * by guarding it with a test, a boolean-valued method handle.
4198 * If the guard fails, a fallback handle is called instead.
4199 * All three method handles must have the same corresponding
4200 * argument and return types, except that the return type
4201 * of the test must be boolean, and the test is allowed
4202 * to have fewer arguments than the other two method handles.
4203 * <p>
4204 * Here is pseudocode for the resulting adapter. In the code, {@code T}
4205 * represents the uniform result type of the three involved handles;
4206 * {@code A}/{@code a}, the types and values of the {@code target}
4207 * parameters and arguments that are consumed by the {@code test}; and
4208 * {@code B}/{@code b}, those types and values of the {@code target}
4209 * parameters and arguments that are not consumed by the {@code test}.
4210 * <blockquote><pre>{@code
4211 * boolean test(A...);
4212 * T target(A...,B...);
4213 * T fallback(A...,B...);
4214 * T adapter(A... a,B... b) {
4215 * if (test(a...))
4216 * return target(a..., b...);
4217 * else
4218 * return fallback(a..., b...);
4219 * }
4220 * }</pre></blockquote>
4221 * Note that the test arguments ({@code a...} in the pseudocode) cannot
4222 * be modified by execution of the test, and so are passed unchanged
4223 * from the caller to the target or fallback as appropriate.
4224 * @param test method handle used for test, must return boolean
4225 * @param target method handle to call if test passes
4226 * @param fallback method handle to call if test fails
4227 * @return method handle which incorporates the specified if/then/else logic
4228 * @throws NullPointerException if any argument is null
4229 * @throws IllegalArgumentException if {@code test} does not return boolean,
4230 * or if all three method types do not match (with the return
4231 * type of {@code test} changed to match that of the target).
4232 */
4233 public static
4234 MethodHandle guardWithTest(MethodHandle test,
4235 MethodHandle target,
4236 MethodHandle fallback) {
4237 MethodType gtype = test.type();
4238 MethodType ttype = target.type();
4239 MethodType ftype = fallback.type();
4240 if (!ttype.equals(ftype))
4241 throw misMatchedTypes("target and fallback types", ttype, ftype);
4242 if (gtype.returnType() != boolean.class)
4243 throw newIllegalArgumentException("guard type is not a predicate "+gtype);
4244 List<Class<?>> targs = ttype.parameterList();
4245 test = dropArgumentsToMatch(test, 0, targs, 0, true);
4246 if (test == null) {
4247 throw misMatchedTypes("target and test types", ttype, gtype);
4248 }
4249 return MethodHandleImpl.makeGuardWithTest(test, target, fallback);
4250 }
4251
4252 static <T> RuntimeException misMatchedTypes(String what, T t1, T t2) {
4253 return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
4254 }
4255
4256 /**
4257 * Makes a method handle which adapts a target method handle,
4258 * by running it inside an exception handler.
4259 * If the target returns normally, the adapter returns that value.
4260 * If an exception matching the specified type is thrown, the fallback
4261 * handle is called instead on the exception, plus the original arguments.
4262 * <p>
4263 * The target and handler must have the same corresponding
4264 * argument and return types, except that handler may omit trailing arguments
4265 * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
4266 * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
4267 * <p>
4268 * Here is pseudocode for the resulting adapter. In the code, {@code T}
4269 * represents the return type of the {@code target} and {@code handler},
4270 * and correspondingly that of the resulting adapter; {@code A}/{@code a},
4271 * the types and values of arguments to the resulting handle consumed by
4272 * {@code handler}; and {@code B}/{@code b}, those of arguments to the
4273 * resulting handle discarded by {@code handler}.
4274 * <blockquote><pre>{@code
4275 * T target(A..., B...);
4276 * T handler(ExType, A...);
4277 * T adapter(A... a, B... b) {
4278 * try {
4279 * return target(a..., b...);
4280 * } catch (ExType ex) {
4281 * return handler(ex, a...);
4282 * }
4283 * }
4284 * }</pre></blockquote>
4285 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
4286 * be modified by execution of the target, and so are passed unchanged
4287 * from the caller to the handler, if the handler is invoked.
4288 * <p>
4289 * The target and handler must return the same type, even if the handler
4290 * always throws. (This might happen, for instance, because the handler
4291 * is simulating a {@code finally} clause).
4292 * To create such a throwing handler, compose the handler creation logic
4293 * with {@link #throwException throwException},
4294 * in order to create a method handle of the correct return type.
4295 * @param target method handle to call
4296 * @param exType the type of exception which the handler will catch
4297 * @param handler method handle to call if a matching exception is thrown
4298 * @return method handle which incorporates the specified try/catch logic
4299 * @throws NullPointerException if any argument is null
4300 * @throws IllegalArgumentException if {@code handler} does not accept
4301 * the given exception type, or if the method handle types do
4302 * not match in their return types and their
4303 * corresponding parameters
4304 * @see MethodHandles#tryFinally(MethodHandle, MethodHandle)
4305 */
4306 public static
4307 MethodHandle catchException(MethodHandle target,
4308 Class<? extends Throwable> exType,
4309 MethodHandle handler) {
4310 MethodType ttype = target.type();
4311 MethodType htype = handler.type();
4312 if (!Throwable.class.isAssignableFrom(exType))
4313 throw new ClassCastException(exType.getName());
4314 if (htype.parameterCount() < 1 ||
4315 !htype.parameterType(0).isAssignableFrom(exType))
4316 throw newIllegalArgumentException("handler does not accept exception type "+exType);
4317 if (htype.returnType() != ttype.returnType())
4318 throw misMatchedTypes("target and handler return types", ttype, htype);
4319 handler = dropArgumentsToMatch(handler, 1, ttype.parameterList(), 0, true);
4320 if (handler == null) {
4321 throw misMatchedTypes("target and handler types", ttype, htype);
4322 }
4323 return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
4324 }
4325
4326 /**
4327 * Produces a method handle which will throw exceptions of the given {@code exType}.
4328 * The method handle will accept a single argument of {@code exType},
4329 * and immediately throw it as an exception.
4330 * The method type will nominally specify a return of {@code returnType}.
4331 * The return type may be anything convenient: It doesn't matter to the
4332 * method handle's behavior, since it will never return normally.
4333 * @param returnType the return type of the desired method handle
4334 * @param exType the parameter type of the desired method handle
4335 * @return method handle which can throw the given exceptions
4336 * @throws NullPointerException if either argument is null
4337 */
4338 public static
4339 MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) {
4340 if (!Throwable.class.isAssignableFrom(exType))
4341 throw new ClassCastException(exType.getName());
4342 return MethodHandleImpl.throwException(methodType(returnType, exType));
4343 }
4344
4345 /**
4346 * Constructs a method handle representing a loop with several loop variables that are updated and checked upon each
4347 * iteration. Upon termination of the loop due to one of the predicates, a corresponding finalizer is run and
4348 * delivers the loop's result, which is the return value of the resulting handle.
4349 * <p>
4350 * Intuitively, every loop is formed by one or more "clauses", each specifying a local <em>iteration variable</em> and/or a loop
4351 * exit. Each iteration of the loop executes each clause in order. A clause can optionally update its iteration
4352 * variable; it can also optionally perform a test and conditional loop exit. In order to express this logic in
4353 * terms of method handles, each clause will specify up to four independent actions:<ul>
4354 * <li><em>init:</em> Before the loop executes, the initialization of an iteration variable {@code v} of type {@code V}.
4355 * <li><em>step:</em> When a clause executes, an update step for the iteration variable {@code v}.
4356 * <li><em>pred:</em> When a clause executes, a predicate execution to test for loop exit.
4357 * <li><em>fini:</em> If a clause causes a loop exit, a finalizer execution to compute the loop's return value.
4358 * </ul>
4359 * The full sequence of all iteration variable types, in clause order, will be notated as {@code (V...)}.
4360 * The values themselves will be {@code (v...)}. When we speak of "parameter lists", we will usually
4361 * be referring to types, but in some contexts (describing execution) the lists will be of actual values.
4362 * <p>
4363 * Some of these clause parts may be omitted according to certain rules, and useful default behavior is provided in
4364 * this case. See below for a detailed description.
4365 * <p>
4366 * <em>Parameters optional everywhere:</em>
4367 * Each clause function is allowed but not required to accept a parameter for each iteration variable {@code v}.
4368 * As an exception, the init functions cannot take any {@code v} parameters,
4369 * because those values are not yet computed when the init functions are executed.
4370 * Any clause function may neglect to take any trailing subsequence of parameters it is entitled to take.
4371 * In fact, any clause function may take no arguments at all.
4372 * <p>
4373 * <em>Loop parameters:</em>
4374 * A clause function may take all the iteration variable values it is entitled to, in which case
4375 * it may also take more trailing parameters. Such extra values are called <em>loop parameters</em>,
4376 * with their types and values notated as {@code (A...)} and {@code (a...)}.
4377 * These become the parameters of the resulting loop handle, to be supplied whenever the loop is executed.
4378 * (Since init functions do not accept iteration variables {@code v}, any parameter to an
4379 * init function is automatically a loop parameter {@code a}.)
4380 * As with iteration variables, clause functions are allowed but not required to accept loop parameters.
4381 * These loop parameters act as loop-invariant values visible across the whole loop.
4382 * <p>
4383 * <em>Parameters visible everywhere:</em>
4384 * Each non-init clause function is permitted to observe the entire loop state, because it can be passed the full
4385 * list {@code (v... a...)} of current iteration variable values and incoming loop parameters.
4386 * The init functions can observe initial pre-loop state, in the form {@code (a...)}.
4387 * Most clause functions will not need all of this information, but they will be formally connected to it
4388 * as if by {@link #dropArguments}.
4389 * <a name="astar"></a>
4390 * More specifically, we shall use the notation {@code (V*)} to express an arbitrary prefix of a full
4391 * sequence {@code (V...)} (and likewise for {@code (v*)}, {@code (A*)}, {@code (a*)}).
4392 * In that notation, the general form of an init function parameter list
4393 * is {@code (A*)}, and the general form of a non-init function parameter list is {@code (V*)} or {@code (V... A*)}.
4394 * <p>
4395 * <em>Checking clause structure:</em>
4396 * Given a set of clauses, there is a number of checks and adjustments performed to connect all the parts of the
4397 * loop. They are spelled out in detail in the steps below. In these steps, every occurrence of the word "must"
4398 * corresponds to a place where {@link IllegalArgumentException} will be thrown if the required constraint is not
4399 * met by the inputs to the loop combinator.
4400 * <p>
4401 * <em>Effectively identical sequences:</em>
4402 * <a name="effid"></a>
4403 * A parameter list {@code A} is defined to be <em>effectively identical</em> to another parameter list {@code B}
4404 * if {@code A} and {@code B} are identical, or if {@code A} is shorter and is identical with a proper prefix of {@code B}.
4405 * When speaking of an unordered set of parameter lists, we say they the set is "effectively identical"
4406 * as a whole if the set contains a longest list, and all members of the set are effectively identical to
4407 * that longest list.
4408 * For example, any set of type sequences of the form {@code (V*)} is effectively identical,
4409 * and the same is true if more sequences of the form {@code (V... A*)} are added.
4410 * <p>
4411 * <em>Step 0: Determine clause structure.</em><ol type="a">
4412 * <li>The clause array (of type {@code MethodHandle[][]}) must be non-{@code null} and contain at least one element.
4413 * <li>The clause array may not contain {@code null}s or sub-arrays longer than four elements.
4414 * <li>Clauses shorter than four elements are treated as if they were padded by {@code null} elements to length
4415 * four. Padding takes place by appending elements to the array.
4416 * <li>Clauses with all {@code null}s are disregarded.
4417 * <li>Each clause is treated as a four-tuple of functions, called "init", "step", "pred", and "fini".
4418 * </ol>
4419 * <p>
4420 * <em>Step 1A: Determine iteration variable types {@code (V...)}.</em><ol type="a">
4421 * <li>The iteration variable type for each clause is determined using the clause's init and step return types.
4422 * <li>If both functions are omitted, there is no iteration variable for the corresponding clause ({@code void} is
4423 * used as the type to indicate that). If one of them is omitted, the other's return type defines the clause's
4424 * iteration variable type. If both are given, the common return type (they must be identical) defines the clause's
4425 * iteration variable type.
4426 * <li>Form the list of return types (in clause order), omitting all occurrences of {@code void}.
4427 * <li>This list of types is called the "iteration variable types" ({@code (V...)}).
4428 * </ol>
4429 * <p>
4430 * <em>Step 1B: Determine loop parameters {@code (A...)}.</em><ul>
4431 * <li>Examine and collect init function parameter lists (which are of the form {@code (A*)}).
4432 * <li>Examine and collect the suffixes of the step, pred, and fini parameter lists, after removing the iteration variable types.
4433 * (They must have the form {@code (V... A*)}; collect the {@code (A*)} parts only.)
4434 * <li>Do not collect suffixes from step, pred, and fini parameter lists that do not begin with all the iteration variable types.
4435 * (These types will checked in step 2, along with all the clause function types.)
4436 * <li>Omitted clause functions are ignored. (Equivalently, they are deemed to have empty parameter lists.)
4437 * <li>All of the collected parameter lists must be effectively identical.
4438 * <li>The longest parameter list (which is necessarily unique) is called the "external parameter list" ({@code (A...)}).
4439 * <li>If there is no such parameter list, the external parameter list is taken to be the empty sequence.
4440 * <li>The combined list consisting of iteration variable types followed by the external parameter types is called
4441 * the "internal parameter list".
4442 * </ul>
4443 * <p>
4444 * <em>Step 1C: Determine loop return type.</em><ol type="a">
4445 * <li>Examine fini function return types, disregarding omitted fini functions.
4446 * <li>If there are no fini functions, the loop return type is {@code void}.
4447 * <li>Otherwise, the common return type {@code R} of the fini functions (their return types must be identical) defines the loop return
4448 * type.
4449 * </ol>
4450 * <p>
4451 * <em>Step 1D: Check other types.</em><ol type="a">
4452 * <li>There must be at least one non-omitted pred function.
4453 * <li>Every non-omitted pred function must have a {@code boolean} return type.
4454 * </ol>
4455 * <p>
4456 * <em>Step 2: Determine parameter lists.</em><ol type="a">
4457 * <li>The parameter list for the resulting loop handle will be the external parameter list {@code (A...)}.
4458 * <li>The parameter list for init functions will be adjusted to the external parameter list.
4459 * (Note that their parameter lists are already effectively identical to this list.)
4460 * <li>The parameter list for every non-omitted, non-init (step, pred, and fini) function must be
4461 * effectively identical to the internal parameter list {@code (V... A...)}.
4462 * </ol>
4463 * <p>
4464 * <em>Step 3: Fill in omitted functions.</em><ol type="a">
4465 * <li>If an init function is omitted, use a {@linkplain #empty default value} for the clause's iteration variable
4466 * type.
4467 * <li>If a step function is omitted, use an {@linkplain #identity identity function} of the clause's iteration
4468 * variable type; insert dropped argument parameters before the identity function parameter for the non-{@code void}
4469 * iteration variables of preceding clauses. (This will turn the loop variable into a local loop invariant.)
4470 * <li>If a pred function is omitted, use a constant {@code true} function. (This will keep the loop going, as far
4471 * as this clause is concerned. Note that in such cases the corresponding fini function is unreachable.)
4472 * <li>If a fini function is omitted, use a {@linkplain #empty default value} for the
4473 * loop return type.
4474 * </ol>
4475 * <p>
4476 * <em>Step 4: Fill in missing parameter types.</em><ol type="a">
4477 * <li>At this point, every init function parameter list is effectively identical to the external parameter list {@code (A...)},
4478 * but some lists may be shorter. For every init function with a short parameter list, pad out the end of the list.
4479 * <li>At this point, every non-init function parameter list is effectively identical to the internal parameter
4480 * list {@code (V... A...)}, but some lists may be shorter. For every non-init function with a short parameter list,
4481 * pad out the end of the list.
4482 * <li>Argument lists are padded out by {@linkplain #dropArgumentsToMatch dropping unused trailing arguments}.
4483 * </ol>
4484 * <p>
4485 * <em>Final observations.</em><ol type="a">
4486 * <li>After these steps, all clauses have been adjusted by supplying omitted functions and arguments.
4487 * <li>All init functions have a common parameter type list {@code (A...)}, which the final loop handle will also have.
4488 * <li>All fini functions have a common return type {@code R}, which the final loop handle will also have.
4489 * <li>All non-init functions have a common parameter type list {@code (V... A...)}, of
4490 * (non-{@code void}) iteration variables {@code V} followed by loop parameters.
4491 * <li>Each pair of init and step functions agrees in their return type {@code V}.
4492 * <li>Each non-init function will be able to observe the current values {@code (v...)} of all iteration variables.
4493 * <li>Every function will be able to observe the incoming values {@code (a...)} of all loop parameters.
4494 * </ol>
4495 * <p>
4496 * <em>Example.</em> As a consequence of step 1A above, the {@code loop} combinator has the following property:
4497 * <ul>
4498 * <li>Given {@code N} clauses {@code Cn = {null, Sn, Pn}} with {@code n = 1..N}.
4499 * <li>Suppose predicate handles {@code Pn} are either {@code null} or have no parameters.
4500 * (Only one {@code Pn} has to be non-{@code null}.)
4501 * <li>Suppose step handles {@code Sn} have signatures {@code (B1..BX)Rn}, for some constant {@code X>=N}.
4502 * <li>Suppose {@code Q} is the count of non-void types {@code Rn}, and {@code (V1...VQ)} is the sequence of those types.
4503 * <li>It must be that {@code Vn == Bn} for {@code n = 1..min(X,Q)}.
4504 * <li>The parameter types {@code Vn} will be interpreted as loop-local state elements {@code (V...)}.
4505 * <li>Any remaining types {@code BQ+1..BX} (if {@code Q<X}) will determine
4506 * the resulting loop handle's parameter types {@code (A...)}.
4507 * </ul>
4508 * In this example, the loop handle parameters {@code (A...)} were derived from the step functions,
4509 * which is natural if most of the loop computation happens in the steps. For some loops,
4510 * the burden of computation might be heaviest in the pred functions, and so the pred functions
4511 * might need to accept the loop parameter values. For loops with complex exit logic, the fini
4512 * functions might need to accept loop parameters, and likewise for loops with complex entry logic,
4513 * where the init functions will need the extra parameters. For such reasons, the rules for
4514 * determining these parameters are as symmetric as possible, across all clause parts.
4515 * In general, the loop parameters function as common invariant values across the whole
4516 * loop, while the iteration variables function as common variant values, or (if there is
4517 * no step function) as internal loop invariant temporaries.
4518 * <p>
4519 * <em>Loop execution.</em><ol type="a">
4520 * <li>When the loop is called, the loop input values are saved in locals, to be passed to
4521 * every clause function. These locals are loop invariant.
4522 * <li>Each init function is executed in clause order (passing the external arguments {@code (a...)})
4523 * and the non-{@code void} values are saved (as the iteration variables {@code (v...)}) into locals.
4524 * These locals will be loop varying (unless their steps behave as identity functions, as noted above).
4525 * <li>All function executions (except init functions) will be passed the internal parameter list, consisting of
4526 * the non-{@code void} iteration values {@code (v...)} (in clause order) and then the loop inputs {@code (a...)}
4527 * (in argument order).
4528 * <li>The step and pred functions are then executed, in clause order (step before pred), until a pred function
4529 * returns {@code false}.
4530 * <li>The non-{@code void} result from a step function call is used to update the corresponding value in the
4531 * sequence {@code (v...)} of loop variables.
4532 * The updated value is immediately visible to all subsequent function calls.
4533 * <li>If a pred function returns {@code false}, the corresponding fini function is called, and the resulting value
4534 * (of type {@code R}) is returned from the loop as a whole.
4535 * <li>If all the pred functions always return true, no fini function is ever invoked, and the loop cannot exit
4536 * except by throwing an exception.
4537 * </ol>
4538 * <p>
4539 * <em>Usage tips.</em>
4540 * <ul>
4541 * <li>Although each step function will receive the current values of <em>all</em> the loop variables,
4542 * sometimes a step function only needs to observe the current value of its own variable.
4543 * In that case, the step function may need to explicitly {@linkplain #dropArguments drop all preceding loop variables}.
4544 * This will require mentioning their types, in an expression like {@code dropArguments(step, 0, V0.class, ...)}.
4545 * <li>Loop variables are not required to vary; they can be loop invariant. A clause can create
4546 * a loop invariant by a suitable init function with no step, pred, or fini function. This may be
4547 * useful to "wire" an incoming loop argument into the step or pred function of an adjacent loop variable.
4548 * <li>If some of the clause functions are virtual methods on an instance, the instance
4549 * itself can be conveniently placed in an initial invariant loop "variable", using an initial clause
4550 * like {@code new MethodHandle[]{identity(ObjType.class)}}. In that case, the instance reference
4551 * will be the first iteration variable value, and it will be easy to use virtual
4552 * methods as clause parts, since all of them will take a leading instance reference matching that value.
4553 * </ul>
4554 * <p>
4555 * Here is pseudocode for the resulting loop handle. As above, {@code V} and {@code v} represent the types
4556 * and values of loop variables; {@code A} and {@code a} represent arguments passed to the whole loop;
4557 * and {@code R} is the common result type of all finalizers as well as of the resulting loop.
4558 * <blockquote><pre>{@code
4559 * V... init...(A...);
4560 * boolean pred...(V..., A...);
4561 * V... step...(V..., A...);
4562 * R fini...(V..., A...);
4563 * R loop(A... a) {
4564 * V... v... = init...(a...);
4565 * for (;;) {
4566 * for ((v, p, s, f) in (v..., pred..., step..., fini...)) {
4567 * v = s(v..., a...);
4568 * if (!p(v..., a...)) {
4569 * return f(v..., a...);
4570 * }
4571 * }
4572 * }
4573 * }
4574 * }</pre></blockquote>
4575 * Note that the parameter type lists {@code (V...)} and {@code (A...)} have been expanded
4576 * to their full length, even though individual clause functions may neglect to take them all.
4577 * As noted above, missing parameters are filled in as if by {@link #dropArgumentsToMatch}.
4578 * <p>
4579 * @apiNote Example:
4580 * <blockquote><pre>{@code
4581 * // iterative implementation of the factorial function as a loop handle
4582 * static int one(int k) { return 1; }
4583 * static int inc(int i, int acc, int k) { return i + 1; }
4584 * static int mult(int i, int acc, int k) { return i * acc; }
4585 * static boolean pred(int i, int acc, int k) { return i < k; }
4586 * static int fin(int i, int acc, int k) { return acc; }
4587 * // assume MH_one, MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
4588 * // null initializer for counter, should initialize to 0
4589 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
4590 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
4591 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
4592 * assertEquals(120, loop.invoke(5));
4593 * }</pre></blockquote>
4594 * The same example, dropping arguments and using combinators:
4595 * <blockquote><pre>{@code
4596 * // simplified implementation of the factorial function as a loop handle
4597 * static int inc(int i) { return i + 1; } // drop acc, k
4598 * static int mult(int i, int acc) { return i * acc; } //drop k
4599 * static boolean cmp(int i, int k) { return i < k; }
4600 * // assume MH_inc, MH_mult, and MH_cmp are handles to the above methods
4601 * // null initializer for counter, should initialize to 0
4602 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
4603 * MethodHandle MH_pred = MethodHandles.dropArguments(MH_cmp, 1, int.class); // drop acc
4604 * MethodHandle MH_fin = MethodHandles.dropArguments(MethodHandles.identity(int.class), 0, int.class); // drop i
4605 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
4606 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
4607 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
4608 * assertEquals(720, loop.invoke(6));
4609 * }</pre></blockquote>
4610 * A similar example, using a helper object to hold a loop parameter:
4611 * <blockquote><pre>{@code
4612 * // instance-based implementation of the factorial function as a loop handle
4613 * static class FacLoop {
4614 * final int k;
4615 * FacLoop(int k) { this.k = k; }
4616 * int inc(int i) { return i + 1; }
4617 * int mult(int i, int acc) { return i * acc; }
4618 * boolean pred(int i) { return i < k; }
4619 * int fin(int i, int acc) { return acc; }
4620 * }
4621 * // assume MH_FacLoop is a handle to the constructor
4622 * // assume MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
4623 * // null initializer for counter, should initialize to 0
4624 * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
4625 * MethodHandle[] instanceClause = new MethodHandle[]{MH_FacLoop};
4626 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
4627 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
4628 * MethodHandle loop = MethodHandles.loop(instanceClause, counterClause, accumulatorClause);
4629 * assertEquals(5040, loop.invoke(7));
4630 * }</pre></blockquote>
4631 *
4632 * @param clauses an array of arrays (4-tuples) of {@link MethodHandle}s adhering to the rules described above.
4633 *
4634 * @return a method handle embodying the looping behavior as defined by the arguments.
4635 *
4636 * @throws IllegalArgumentException in case any of the constraints described above is violated.
4637 *
4638 * @see MethodHandles#whileLoop(MethodHandle, MethodHandle, MethodHandle)
4639 * @see MethodHandles#doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
4640 * @see MethodHandles#countedLoop(MethodHandle, MethodHandle, MethodHandle)
4641 * @see MethodHandles#iteratedLoop(MethodHandle, MethodHandle, MethodHandle)
4642 * @since 9
4643 */
4644 public static MethodHandle loop(MethodHandle[]... clauses) {
4645 // Step 0: determine clause structure.
4646 loopChecks0(clauses);
4647
4648 List<MethodHandle> init = new ArrayList<>();
4649 List<MethodHandle> step = new ArrayList<>();
4650 List<MethodHandle> pred = new ArrayList<>();
4651 List<MethodHandle> fini = new ArrayList<>();
4652
4653 Stream.of(clauses).filter(c -> Stream.of(c).anyMatch(Objects::nonNull)).forEach(clause -> {
4654 init.add(clause[0]); // all clauses have at least length 1
4655 step.add(clause.length <= 1 ? null : clause[1]);
4656 pred.add(clause.length <= 2 ? null : clause[2]);
4657 fini.add(clause.length <= 3 ? null : clause[3]);
4658 });
4659
4660 assert Stream.of(init, step, pred, fini).map(List::size).distinct().count() == 1;
4661 final int nclauses = init.size();
4662
4663 // Step 1A: determine iteration variables (V...).
4664 final List<Class<?>> iterationVariableTypes = new ArrayList<>();
4665 for (int i = 0; i < nclauses; ++i) {
4666 MethodHandle in = init.get(i);
4667 MethodHandle st = step.get(i);
4668 if (in == null && st == null) {
4669 iterationVariableTypes.add(void.class);
4670 } else if (in != null && st != null) {
4671 loopChecks1a(i, in, st);
4672 iterationVariableTypes.add(in.type().returnType());
4673 } else {
4674 iterationVariableTypes.add(in == null ? st.type().returnType() : in.type().returnType());
4675 }
4676 }
4677 final List<Class<?>> commonPrefix = iterationVariableTypes.stream().filter(t -> t != void.class).
4678 collect(Collectors.toList());
4679
4680 // Step 1B: determine loop parameters (A...).
4681 final List<Class<?>> commonSuffix = buildCommonSuffix(init, step, pred, fini, commonPrefix.size());
4682 loopChecks1b(init, commonSuffix);
4683
4684 // Step 1C: determine loop return type.
4685 // Step 1D: check other types.
4686 final Class<?> loopReturnType = fini.stream().filter(Objects::nonNull).map(MethodHandle::type).
4687 map(MethodType::returnType).findFirst().orElse(void.class);
4688 loopChecks1cd(pred, fini, loopReturnType);
4689
4690 // Step 2: determine parameter lists.
4691 final List<Class<?>> commonParameterSequence = new ArrayList<>(commonPrefix);
4692 commonParameterSequence.addAll(commonSuffix);
4693 loopChecks2(step, pred, fini, commonParameterSequence);
4694
4695 // Step 3: fill in omitted functions.
4696 for (int i = 0; i < nclauses; ++i) {
4697 Class<?> t = iterationVariableTypes.get(i);
4698 if (init.get(i) == null) {
4699 init.set(i, empty(methodType(t, commonSuffix)));
4700 }
4701 if (step.get(i) == null) {
4702 step.set(i, dropArgumentsToMatch(identityOrVoid(t), 0, commonParameterSequence, i));
4703 }
4704 if (pred.get(i) == null) {
4705 pred.set(i, dropArguments0(constant(boolean.class, true), 0, commonParameterSequence));
4706 }
4707 if (fini.get(i) == null) {
4708 fini.set(i, empty(methodType(t, commonParameterSequence)));
4709 }
4710 }
4711
4712 // Step 4: fill in missing parameter types.
4713 // Also convert all handles to fixed-arity handles.
4714 List<MethodHandle> finit = fixArities(fillParameterTypes(init, commonSuffix));
4715 List<MethodHandle> fstep = fixArities(fillParameterTypes(step, commonParameterSequence));
4716 List<MethodHandle> fpred = fixArities(fillParameterTypes(pred, commonParameterSequence));
4717 List<MethodHandle> ffini = fixArities(fillParameterTypes(fini, commonParameterSequence));
4718
4719 assert finit.stream().map(MethodHandle::type).map(MethodType::parameterList).
4720 allMatch(pl -> pl.equals(commonSuffix));
4721 assert Stream.of(fstep, fpred, ffini).flatMap(List::stream).map(MethodHandle::type).map(MethodType::parameterList).
4722 allMatch(pl -> pl.equals(commonParameterSequence));
4723
4724 return MethodHandleImpl.makeLoop(loopReturnType, commonSuffix, finit, fstep, fpred, ffini);
4725 }
4726
4727 private static void loopChecks0(MethodHandle[][] clauses) {
4728 if (clauses == null || clauses.length == 0) {
4729 throw newIllegalArgumentException("null or no clauses passed");
4730 }
4731 if (Stream.of(clauses).anyMatch(Objects::isNull)) {
4732 throw newIllegalArgumentException("null clauses are not allowed");
4733 }
4734 if (Stream.of(clauses).anyMatch(c -> c.length > 4)) {
4735 throw newIllegalArgumentException("All loop clauses must be represented as MethodHandle arrays with at most 4 elements.");
4736 }
4737 }
4738
4739 private static void loopChecks1a(int i, MethodHandle in, MethodHandle st) {
4740 if (in.type().returnType() != st.type().returnType()) {
4741 throw misMatchedTypes("clause " + i + ": init and step return types", in.type().returnType(),
4742 st.type().returnType());
4743 }
4744 }
4745
4746 private static List<Class<?>> longestParameterList(Stream<MethodHandle> mhs, int skipSize) {
4747 final List<Class<?>> empty = List.of();
4748 final List<Class<?>> longest = mhs.filter(Objects::nonNull).
4749 // take only those that can contribute to a common suffix because they are longer than the prefix
4750 map(MethodHandle::type).
4751 filter(t -> t.parameterCount() > skipSize).
4752 map(MethodType::parameterList).
4753 reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
4754 return longest.size() == 0 ? empty : longest.subList(skipSize, longest.size());
4755 }
4756
4757 private static List<Class<?>> longestParameterList(List<List<Class<?>>> lists) {
4758 final List<Class<?>> empty = List.of();
4759 return lists.stream().reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
4760 }
4761
4762 private static List<Class<?>> buildCommonSuffix(List<MethodHandle> init, List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, int cpSize) {
4763 final List<Class<?>> longest1 = longestParameterList(Stream.of(step, pred, fini).flatMap(List::stream), cpSize);
4764 final List<Class<?>> longest2 = longestParameterList(init.stream(), 0);
4765 return longestParameterList(Arrays.asList(longest1, longest2));
4766 }
4767
4768 private static void loopChecks1b(List<MethodHandle> init, List<Class<?>> commonSuffix) {
4769 if (init.stream().filter(Objects::nonNull).map(MethodHandle::type).
4770 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonSuffix))) {
4771 throw newIllegalArgumentException("found non-effectively identical init parameter type lists: " + init +
4772 " (common suffix: " + commonSuffix + ")");
4773 }
4774 }
4775
4776 private static void loopChecks1cd(List<MethodHandle> pred, List<MethodHandle> fini, Class<?> loopReturnType) {
4777 if (fini.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
4778 anyMatch(t -> t != loopReturnType)) {
4779 throw newIllegalArgumentException("found non-identical finalizer return types: " + fini + " (return type: " +
4780 loopReturnType + ")");
4781 }
4782
4783 if (!pred.stream().filter(Objects::nonNull).findFirst().isPresent()) {
4784 throw newIllegalArgumentException("no predicate found", pred);
4785 }
4786 if (pred.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
4787 anyMatch(t -> t != boolean.class)) {
4788 throw newIllegalArgumentException("predicates must have boolean return type", pred);
4789 }
4790 }
4791
4792 private static void loopChecks2(List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, List<Class<?>> commonParameterSequence) {
4793 if (Stream.of(step, pred, fini).flatMap(List::stream).filter(Objects::nonNull).map(MethodHandle::type).
4794 anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonParameterSequence))) {
4795 throw newIllegalArgumentException("found non-effectively identical parameter type lists:\nstep: " + step +
4796 "\npred: " + pred + "\nfini: " + fini + " (common parameter sequence: " + commonParameterSequence + ")");
4797 }
4798 }
4799
4800 private static List<MethodHandle> fillParameterTypes(List<MethodHandle> hs, final List<Class<?>> targetParams) {
4801 return hs.stream().map(h -> {
4802 int pc = h.type().parameterCount();
4803 int tpsize = targetParams.size();
4804 return pc < tpsize ? dropArguments0(h, pc, targetParams.subList(pc, tpsize)) : h;
4805 }).collect(Collectors.toList());
4806 }
4807
4808 private static List<MethodHandle> fixArities(List<MethodHandle> hs) {
4809 return hs.stream().map(MethodHandle::asFixedArity).collect(Collectors.toList());
4810 }
4811
4812 /**
4813 * Constructs a {@code while} loop from an initializer, a body, and a predicate.
4814 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
4815 * <p>
4816 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
4817 * method will, in each iteration, first evaluate the predicate and then execute its body (if the predicate
4818 * evaluates to {@code true}).
4819 * The loop will terminate once the predicate evaluates to {@code false} (the body will not be executed in this case).
4820 * <p>
4821 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
4822 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
4823 * and updated with the value returned from its invocation. The result of loop execution will be
4824 * the final value of the additional loop-local variable (if present).
4825 * <p>
4826 * The following rules hold for these argument handles:<ul>
4827 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
4828 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
4829 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
4830 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
4831 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
4832 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
4833 * It will constrain the parameter lists of the other loop parts.
4834 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
4835 * list {@code (A...)} is called the <em>external parameter list</em>.
4836 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
4837 * additional state variable of the loop.
4838 * The body must both accept and return a value of this type {@code V}.
4839 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
4840 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
4841 * <a href="MethodHandles.html#effid">effectively identical</a>
4842 * to the external parameter list {@code (A...)}.
4843 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
4844 * {@linkplain #empty default value}.
4845 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
4846 * Its parameter list (either empty or of the form {@code (V A*)}) must be
4847 * effectively identical to the internal parameter list.
4848 * </ul>
4849 * <p>
4850 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
4851 * <li>The loop handle's result type is the result type {@code V} of the body.
4852 * <li>The loop handle's parameter types are the types {@code (A...)},
4853 * from the external parameter list.
4854 * </ul>
4855 * <p>
4856 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
4857 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
4858 * passed to the loop.
4859 * <blockquote><pre>{@code
4860 * V init(A...);
4861 * boolean pred(V, A...);
4862 * V body(V, A...);
4863 * V whileLoop(A... a...) {
4864 * V v = init(a...);
4865 * while (pred(v, a...)) {
4866 * v = body(v, a...);
4867 * }
4868 * return v;
4869 * }
4870 * }</pre></blockquote>
4871 * <p>
4872 * @apiNote Example:
4873 * <blockquote><pre>{@code
4874 * // implement the zip function for lists as a loop handle
4875 * static List<String> initZip(Iterator<String> a, Iterator<String> b) { return new ArrayList<>(); }
4876 * static boolean zipPred(List<String> zip, Iterator<String> a, Iterator<String> b) { return a.hasNext() && b.hasNext(); }
4877 * static List<String> zipStep(List<String> zip, Iterator<String> a, Iterator<String> b) {
4878 * zip.add(a.next());
4879 * zip.add(b.next());
4880 * return zip;
4881 * }
4882 * // assume MH_initZip, MH_zipPred, and MH_zipStep are handles to the above methods
4883 * MethodHandle loop = MethodHandles.whileLoop(MH_initZip, MH_zipPred, MH_zipStep);
4884 * List<String> a = Arrays.asList("a", "b", "c", "d");
4885 * List<String> b = Arrays.asList("e", "f", "g", "h");
4886 * List<String> zipped = Arrays.asList("a", "e", "b", "f", "c", "g", "d", "h");
4887 * assertEquals(zipped, (List<String>) loop.invoke(a.iterator(), b.iterator()));
4888 * }</pre></blockquote>
4889 *
4890 * <p>
4891 * @apiNote The implementation of this method can be expressed as follows:
4892 * <blockquote><pre>{@code
4893 * MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
4894 * MethodHandle fini = (body.type().returnType() == void.class
4895 * ? null : identity(body.type().returnType()));
4896 * MethodHandle[]
4897 * checkExit = { null, null, pred, fini },
4898 * varBody = { init, body };
4899 * return loop(checkExit, varBody);
4900 * }
4901 * }</pre></blockquote>
4902 *
4903 * @param init optional initializer, providing the initial value of the loop variable.
4904 * May be {@code null}, implying a default initial value. See above for other constraints.
4905 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
4906 * above for other constraints.
4907 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
4908 * See above for other constraints.
4909 *
4910 * @return a method handle implementing the {@code while} loop as described by the arguments.
4911 * @throws IllegalArgumentException if the rules for the arguments are violated.
4912 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
4913 *
4914 * @see #loop(MethodHandle[][])
4915 * @see #doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
4916 * @since 9
4917 */
4918 public static MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
4919 whileLoopChecks(init, pred, body);
4920 MethodHandle fini = identityOrVoid(body.type().returnType());
4921 MethodHandle[] checkExit = { null, null, pred, fini };
4922 MethodHandle[] varBody = { init, body };
4923 return loop(checkExit, varBody);
4924 }
4925
4926 /**
4927 * Constructs a {@code do-while} loop from an initializer, a body, and a predicate.
4928 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
4929 * <p>
4930 * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
4931 * method will, in each iteration, first execute its body and then evaluate the predicate.
4932 * The loop will terminate once the predicate evaluates to {@code false} after an execution of the body.
4933 * <p>
4934 * The {@code init} handle describes the initial value of an additional optional loop-local variable.
4935 * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
4936 * and updated with the value returned from its invocation. The result of loop execution will be
4937 * the final value of the additional loop-local variable (if present).
4938 * <p>
4939 * The following rules hold for these argument handles:<ul>
4940 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
4941 * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
4942 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
4943 * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
4944 * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
4945 * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
4946 * It will constrain the parameter lists of the other loop parts.
4947 * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
4948 * list {@code (A...)} is called the <em>external parameter list</em>.
4949 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
4950 * additional state variable of the loop.
4951 * The body must both accept and return a value of this type {@code V}.
4952 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
4953 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
4954 * <a href="MethodHandles.html#effid">effectively identical</a>
4955 * to the external parameter list {@code (A...)}.
4956 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
4957 * {@linkplain #empty default value}.
4958 * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
4959 * Its parameter list (either empty or of the form {@code (V A*)}) must be
4960 * effectively identical to the internal parameter list.
4961 * </ul>
4962 * <p>
4963 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
4964 * <li>The loop handle's result type is the result type {@code V} of the body.
4965 * <li>The loop handle's parameter types are the types {@code (A...)},
4966 * from the external parameter list.
4967 * </ul>
4968 * <p>
4969 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
4970 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
4971 * passed to the loop.
4972 * <blockquote><pre>{@code
4973 * V init(A...);
4974 * boolean pred(V, A...);
4975 * V body(V, A...);
4976 * V doWhileLoop(A... a...) {
4977 * V v = init(a...);
4978 * do {
4979 * v = body(v, a...);
4980 * } while (pred(v, a...));
4981 * return v;
4982 * }
4983 * }</pre></blockquote>
4984 * <p>
4985 * @apiNote Example:
4986 * <blockquote><pre>{@code
4987 * // int i = 0; while (i < limit) { ++i; } return i; => limit
4988 * static int zero(int limit) { return 0; }
4989 * static int step(int i, int limit) { return i + 1; }
4990 * static boolean pred(int i, int limit) { return i < limit; }
4991 * // assume MH_zero, MH_step, and MH_pred are handles to the above methods
4992 * MethodHandle loop = MethodHandles.doWhileLoop(MH_zero, MH_step, MH_pred);
4993 * assertEquals(23, loop.invoke(23));
4994 * }</pre></blockquote>
4995 *
4996 * <p>
4997 * @apiNote The implementation of this method can be expressed as follows:
4998 * <blockquote><pre>{@code
4999 * MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
5000 * MethodHandle fini = (body.type().returnType() == void.class
5001 * ? null : identity(body.type().returnType()));
5002 * MethodHandle[] clause = { init, body, pred, fini };
5003 * return loop(clause);
5004 * }
5005 * }</pre></blockquote>
5006 *
5007 * @param init optional initializer, providing the initial value of the loop variable.
5008 * May be {@code null}, implying a default initial value. See above for other constraints.
5009 * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
5010 * See above for other constraints.
5011 * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
5012 * above for other constraints.
5013 *
5014 * @return a method handle implementing the {@code while} loop as described by the arguments.
5015 * @throws IllegalArgumentException if the rules for the arguments are violated.
5016 * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
5017 *
5018 * @see #loop(MethodHandle[][])
5019 * @see #whileLoop(MethodHandle, MethodHandle, MethodHandle)
5020 * @since 9
5021 */
5022 public static MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
5023 whileLoopChecks(init, pred, body);
5024 MethodHandle fini = identityOrVoid(body.type().returnType());
5025 MethodHandle[] clause = {init, body, pred, fini };
5026 return loop(clause);
5027 }
5028
5029 private static void whileLoopChecks(MethodHandle init, MethodHandle pred, MethodHandle body) {
5030 Objects.requireNonNull(pred);
5031 Objects.requireNonNull(body);
5032 MethodType bodyType = body.type();
5033 Class<?> returnType = bodyType.returnType();
5034 List<Class<?>> innerList = bodyType.parameterList();
5035 List<Class<?>> outerList = innerList;
5036 if (returnType == void.class) {
5037 // OK
5038 } else if (innerList.size() == 0 || innerList.get(0) != returnType) {
5039 // leading V argument missing => error
5040 MethodType expected = bodyType.insertParameterTypes(0, returnType);
5041 throw misMatchedTypes("body function", bodyType, expected);
5042 } else {
5043 outerList = innerList.subList(1, innerList.size());
5044 }
5045 MethodType predType = pred.type();
5046 if (predType.returnType() != boolean.class ||
5047 !predType.effectivelyIdenticalParameters(0, innerList)) {
5048 throw misMatchedTypes("loop predicate", predType, methodType(boolean.class, innerList));
5049 }
5050 if (init != null) {
5051 MethodType initType = init.type();
5052 if (initType.returnType() != returnType ||
5053 !initType.effectivelyIdenticalParameters(0, outerList)) {
5054 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
5055 }
5056 }
5057 }
5058
5059 /**
5060 * Constructs a loop that runs a given number of iterations.
5061 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5062 * <p>
5063 * The number of iterations is determined by the {@code iterations} handle evaluation result.
5064 * The loop counter {@code i} is an extra loop iteration variable of type {@code int}.
5065 * It will be initialized to 0 and incremented by 1 in each iteration.
5066 * <p>
5067 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
5068 * of that type is also present. This variable is initialized using the optional {@code init} handle,
5069 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
5070 * <p>
5071 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
5072 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
5073 * iteration variable.
5074 * The result of the loop handle execution will be the final {@code V} value of that variable
5075 * (or {@code void} if there is no {@code V} variable).
5076 * <p>
5077 * The following rules hold for the argument handles:<ul>
5078 * <li>The {@code iterations} handle must not be {@code null}, and must return
5079 * the type {@code int}, referred to here as {@code I} in parameter type lists.
5080 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5081 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
5082 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5083 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
5084 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
5085 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
5086 * of types called the <em>internal parameter list</em>.
5087 * It will constrain the parameter lists of the other loop parts.
5088 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
5089 * with no additional {@code A} types, then the internal parameter list is extended by
5090 * the argument types {@code A...} of the {@code iterations} handle.
5091 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
5092 * list {@code (A...)} is called the <em>external parameter list</em>.
5093 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5094 * additional state variable of the loop.
5095 * The body must both accept a leading parameter and return a value of this type {@code V}.
5096 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5097 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5098 * <a href="MethodHandles.html#effid">effectively identical</a>
5099 * to the external parameter list {@code (A...)}.
5100 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5101 * {@linkplain #empty default value}.
5102 * <li>The parameter list of {@code iterations} (of some form {@code (A*)}) must be
5103 * effectively identical to the external parameter list {@code (A...)}.
5104 * </ul>
5105 * <p>
5106 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5107 * <li>The loop handle's result type is the result type {@code V} of the body.
5108 * <li>The loop handle's parameter types are the types {@code (A...)},
5109 * from the external parameter list.
5110 * </ul>
5111 * <p>
5112 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5113 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
5114 * arguments passed to the loop.
5115 * <blockquote><pre>{@code
5116 * int iterations(A...);
5117 * V init(A...);
5118 * V body(V, int, A...);
5119 * V countedLoop(A... a...) {
5120 * int end = iterations(a...);
5121 * V v = init(a...);
5122 * for (int i = 0; i < end; ++i) {
5123 * v = body(v, i, a...);
5124 * }
5125 * return v;
5126 * }
5127 * }</pre></blockquote>
5128 * <p>
5129 * @apiNote Example with a fully conformant body method:
5130 * <blockquote><pre>{@code
5131 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
5132 * // => a variation on a well known theme
5133 * static String step(String v, int counter, String init) { return "na " + v; }
5134 * // assume MH_step is a handle to the method above
5135 * MethodHandle fit13 = MethodHandles.constant(int.class, 13);
5136 * MethodHandle start = MethodHandles.identity(String.class);
5137 * MethodHandle loop = MethodHandles.countedLoop(fit13, start, MH_step);
5138 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("Lambdaman!"));
5139 * }</pre></blockquote>
5140 * <p>
5141 * @apiNote Example with the simplest possible body method type,
5142 * and passing the number of iterations to the loop invocation:
5143 * <blockquote><pre>{@code
5144 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
5145 * // => a variation on a well known theme
5146 * static String step(String v, int counter ) { return "na " + v; }
5147 * // assume MH_step is a handle to the method above
5148 * MethodHandle count = MethodHandles.dropArguments(MethodHandles.identity(int.class), 1, String.class);
5149 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class);
5150 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i) -> "na " + v
5151 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "Lambdaman!"));
5152 * }</pre></blockquote>
5153 * <p>
5154 * @apiNote Example that treats the number of iterations, string to append to, and string to append
5155 * as loop parameters:
5156 * <blockquote><pre>{@code
5157 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
5158 * // => a variation on a well known theme
5159 * static String step(String v, int counter, int iterations_, String pre, String start_) { return pre + " " + v; }
5160 * // assume MH_step is a handle to the method above
5161 * MethodHandle count = MethodHandles.identity(int.class);
5162 * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class, String.class);
5163 * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i, _, pre, _) -> pre + " " + v
5164 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "na", "Lambdaman!"));
5165 * }</pre></blockquote>
5166 * <p>
5167 * @apiNote Example that illustrates the usage of {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}
5168 * to enforce a loop type:
5169 * <blockquote><pre>{@code
5170 * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
5171 * // => a variation on a well known theme
5172 * static String step(String v, int counter, String pre) { return pre + " " + v; }
5173 * // assume MH_step is a handle to the method above
5174 * MethodType loopType = methodType(String.class, String.class, int.class, String.class);
5175 * MethodHandle count = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(int.class), 0, loopType.parameterList(), 1);
5176 * MethodHandle start = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(String.class), 0, loopType.parameterList(), 2);
5177 * MethodHandle body = MethodHandles.dropArgumentsToMatch(MH_step, 2, loopType.parameterList(), 0);
5178 * MethodHandle loop = MethodHandles.countedLoop(count, start, body); // (v, i, pre, _, _) -> pre + " " + v
5179 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("na", 13, "Lambdaman!"));
5180 * }</pre></blockquote>
5181 * <p>
5182 * @apiNote The implementation of this method can be expressed as follows:
5183 * <blockquote><pre>{@code
5184 * MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
5185 * return countedLoop(empty(iterations.type()), iterations, init, body);
5186 * }
5187 * }</pre></blockquote>
5188 *
5189 * @param iterations a non-{@code null} handle to return the number of iterations this loop should run. The handle's
5190 * result type must be {@code int}. See above for other constraints.
5191 * @param init optional initializer, providing the initial value of the loop variable.
5192 * May be {@code null}, implying a default initial value. See above for other constraints.
5193 * @param body body of the loop, which may not be {@code null}.
5194 * It controls the loop parameters and result type in the standard case (see above for details).
5195 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
5196 * and may accept any number of additional types.
5197 * See above for other constraints.
5198 *
5199 * @return a method handle representing the loop.
5200 * @throws NullPointerException if either of the {@code iterations} or {@code body} handles is {@code null}.
5201 * @throws IllegalArgumentException if any argument violates the rules formulated above.
5202 *
5203 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle, MethodHandle)
5204 * @since 9
5205 */
5206 public static MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
5207 return countedLoop(empty(iterations.type()), iterations, init, body);
5208 }
5209
5210 /**
5211 * Constructs a loop that counts over a range of numbers.
5212 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5213 * <p>
5214 * The loop counter {@code i} is a loop iteration variable of type {@code int}.
5215 * The {@code start} and {@code end} handles determine the start (inclusive) and end (exclusive)
5216 * values of the loop counter.
5217 * The loop counter will be initialized to the {@code int} value returned from the evaluation of the
5218 * {@code start} handle and run to the value returned from {@code end} (exclusively) with a step width of 1.
5219 * <p>
5220 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
5221 * of that type is also present. This variable is initialized using the optional {@code init} handle,
5222 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
5223 * <p>
5224 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
5225 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
5226 * iteration variable.
5227 * The result of the loop handle execution will be the final {@code V} value of that variable
5228 * (or {@code void} if there is no {@code V} variable).
5229 * <p>
5230 * The following rules hold for the argument handles:<ul>
5231 * <li>The {@code start} and {@code end} handles must not be {@code null}, and must both return
5232 * the common type {@code int}, referred to here as {@code I} in parameter type lists.
5233 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5234 * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
5235 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5236 * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
5237 * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
5238 * <li>The parameter list {@code (V I A...)} of the body contributes to a list
5239 * of types called the <em>internal parameter list</em>.
5240 * It will constrain the parameter lists of the other loop parts.
5241 * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
5242 * with no additional {@code A} types, then the internal parameter list is extended by
5243 * the argument types {@code A...} of the {@code end} handle.
5244 * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
5245 * list {@code (A...)} is called the <em>external parameter list</em>.
5246 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5247 * additional state variable of the loop.
5248 * The body must both accept a leading parameter and return a value of this type {@code V}.
5249 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5250 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5251 * <a href="MethodHandles.html#effid">effectively identical</a>
5252 * to the external parameter list {@code (A...)}.
5253 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5254 * {@linkplain #empty default value}.
5255 * <li>The parameter list of {@code start} (of some form {@code (A*)}) must be
5256 * effectively identical to the external parameter list {@code (A...)}.
5257 * <li>Likewise, the parameter list of {@code end} must be effectively identical
5258 * to the external parameter list.
5259 * </ul>
5260 * <p>
5261 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5262 * <li>The loop handle's result type is the result type {@code V} of the body.
5263 * <li>The loop handle's parameter types are the types {@code (A...)},
5264 * from the external parameter list.
5265 * </ul>
5266 * <p>
5267 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5268 * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
5269 * arguments passed to the loop.
5270 * <blockquote><pre>{@code
5271 * int start(A...);
5272 * int end(A...);
5273 * V init(A...);
5274 * V body(V, int, A...);
5275 * V countedLoop(A... a...) {
5276 * int e = end(a...);
5277 * int s = start(a...);
5278 * V v = init(a...);
5279 * for (int i = s; i < e; ++i) {
5280 * v = body(v, i, a...);
5281 * }
5282 * return v;
5283 * }
5284 * }</pre></blockquote>
5285 *
5286 * <p>
5287 * @apiNote The implementation of this method can be expressed as follows:
5288 * <blockquote><pre>{@code
5289 * MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
5290 * MethodHandle returnVar = dropArguments(identity(init.type().returnType()), 0, int.class, int.class);
5291 * // assume MH_increment and MH_predicate are handles to implementation-internal methods with
5292 * // the following semantics:
5293 * // MH_increment: (int limit, int counter) -> counter + 1
5294 * // MH_predicate: (int limit, int counter) -> counter < limit
5295 * Class<?> counterType = start.type().returnType(); // int
5296 * Class<?> returnType = body.type().returnType();
5297 * MethodHandle incr = MH_increment, pred = MH_predicate, retv = null;
5298 * if (returnType != void.class) { // ignore the V variable
5299 * incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
5300 * pred = dropArguments(pred, 1, returnType); // ditto
5301 * retv = dropArguments(identity(returnType), 0, counterType); // ignore limit
5302 * }
5303 * body = dropArguments(body, 0, counterType); // ignore the limit variable
5304 * MethodHandle[]
5305 * loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
5306 * bodyClause = { init, body }, // v = init(); v = body(v, i)
5307 * indexVar = { start, incr }; // i = start(); i = i + 1
5308 * return loop(loopLimit, bodyClause, indexVar);
5309 * }
5310 * }</pre></blockquote>
5311 *
5312 * @param start a non-{@code null} handle to return the start value of the loop counter, which must be {@code int}.
5313 * See above for other constraints.
5314 * @param end a non-{@code null} handle to return the end value of the loop counter (the loop will run to
5315 * {@code end-1}). The result type must be {@code int}. See above for other constraints.
5316 * @param init optional initializer, providing the initial value of the loop variable.
5317 * May be {@code null}, implying a default initial value. See above for other constraints.
5318 * @param body body of the loop, which may not be {@code null}.
5319 * It controls the loop parameters and result type in the standard case (see above for details).
5320 * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
5321 * and may accept any number of additional types.
5322 * See above for other constraints.
5323 *
5324 * @return a method handle representing the loop.
5325 * @throws NullPointerException if any of the {@code start}, {@code end}, or {@code body} handles is {@code null}.
5326 * @throws IllegalArgumentException if any argument violates the rules formulated above.
5327 *
5328 * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle)
5329 * @since 9
5330 */
5331 public static MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
5332 countedLoopChecks(start, end, init, body);
5333 Class<?> counterType = start.type().returnType(); // int, but who's counting?
5334 Class<?> limitType = end.type().returnType(); // yes, int again
5335 Class<?> returnType = body.type().returnType();
5336 MethodHandle incr = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopStep);
5337 MethodHandle pred = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopPred);
5338 MethodHandle retv = null;
5339 if (returnType != void.class) {
5340 incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
5341 pred = dropArguments(pred, 1, returnType); // ditto
5342 retv = dropArguments(identity(returnType), 0, counterType);
5343 }
5344 body = dropArguments(body, 0, counterType); // ignore the limit variable
5345 MethodHandle[]
5346 loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
5347 bodyClause = { init, body }, // v = init(); v = body(v, i)
5348 indexVar = { start, incr }; // i = start(); i = i + 1
5349 return loop(loopLimit, bodyClause, indexVar);
5350 }
5351
5352 private static void countedLoopChecks(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
5353 Objects.requireNonNull(start);
5354 Objects.requireNonNull(end);
5355 Objects.requireNonNull(body);
5356 Class<?> counterType = start.type().returnType();
5357 if (counterType != int.class) {
5358 MethodType expected = start.type().changeReturnType(int.class);
5359 throw misMatchedTypes("start function", start.type(), expected);
5360 } else if (end.type().returnType() != counterType) {
5361 MethodType expected = end.type().changeReturnType(counterType);
5362 throw misMatchedTypes("end function", end.type(), expected);
5363 }
5364 MethodType bodyType = body.type();
5365 Class<?> returnType = bodyType.returnType();
5366 List<Class<?>> innerList = bodyType.parameterList();
5367 // strip leading V value if present
5368 int vsize = (returnType == void.class ? 0 : 1);
5369 if (vsize != 0 && (innerList.size() == 0 || innerList.get(0) != returnType)) {
5370 // argument list has no "V" => error
5371 MethodType expected = bodyType.insertParameterTypes(0, returnType);
5372 throw misMatchedTypes("body function", bodyType, expected);
5373 } else if (innerList.size() <= vsize || innerList.get(vsize) != counterType) {
5374 // missing I type => error
5375 MethodType expected = bodyType.insertParameterTypes(vsize, counterType);
5376 throw misMatchedTypes("body function", bodyType, expected);
5377 }
5378 List<Class<?>> outerList = innerList.subList(vsize + 1, innerList.size());
5379 if (outerList.isEmpty()) {
5380 // special case; take lists from end handle
5381 outerList = end.type().parameterList();
5382 innerList = bodyType.insertParameterTypes(vsize + 1, outerList).parameterList();
5383 }
5384 MethodType expected = methodType(counterType, outerList);
5385 if (!start.type().effectivelyIdenticalParameters(0, outerList)) {
5386 throw misMatchedTypes("start parameter types", start.type(), expected);
5387 }
5388 if (end.type() != start.type() &&
5389 !end.type().effectivelyIdenticalParameters(0, outerList)) {
5390 throw misMatchedTypes("end parameter types", end.type(), expected);
5391 }
5392 if (init != null) {
5393 MethodType initType = init.type();
5394 if (initType.returnType() != returnType ||
5395 !initType.effectivelyIdenticalParameters(0, outerList)) {
5396 throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
5397 }
5398 }
5399 }
5400
5401 /**
5402 * Constructs a loop that ranges over the values produced by an {@code Iterator<T>}.
5403 * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
5404 * <p>
5405 * The iterator itself will be determined by the evaluation of the {@code iterator} handle.
5406 * Each value it produces will be stored in a loop iteration variable of type {@code T}.
5407 * <p>
5408 * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
5409 * of that type is also present. This variable is initialized using the optional {@code init} handle,
5410 * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
5411 * <p>
5412 * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
5413 * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
5414 * iteration variable.
5415 * The result of the loop handle execution will be the final {@code V} value of that variable
5416 * (or {@code void} if there is no {@code V} variable).
5417 * <p>
5418 * The following rules hold for the argument handles:<ul>
5419 * <li>The {@code body} handle must not be {@code null}; its type must be of the form
5420 * {@code (V T A...)V}, where {@code V} is non-{@code void}, or else {@code (T A...)void}.
5421 * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
5422 * and we will write {@code (V T A...)V} with the understanding that a {@code void} type {@code V}
5423 * is quietly dropped from the parameter list, leaving {@code (T A...)V}.)
5424 * <li>The parameter list {@code (V T A...)} of the body contributes to a list
5425 * of types called the <em>internal parameter list</em>.
5426 * It will constrain the parameter lists of the other loop parts.
5427 * <li>As a special case, if the body contributes only {@code V} and {@code T} types,
5428 * with no additional {@code A} types, then the internal parameter list is extended by
5429 * the argument types {@code A...} of the {@code iterator} handle; if it is {@code null} the
5430 * single type {@code Iterable} is added and constitutes the {@code A...} list.
5431 * <li>If the iteration variable types {@code (V T)} are dropped from the internal parameter list, the resulting shorter
5432 * list {@code (A...)} is called the <em>external parameter list</em>.
5433 * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
5434 * additional state variable of the loop.
5435 * The body must both accept a leading parameter and return a value of this type {@code V}.
5436 * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
5437 * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
5438 * <a href="MethodHandles.html#effid">effectively identical</a>
5439 * to the external parameter list {@code (A...)}.
5440 * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
5441 * {@linkplain #empty default value}.
5442 * <li>If the {@code iterator} handle is non-{@code null}, it must have the return
5443 * type {@code java.util.Iterator} or a subtype thereof.
5444 * The iterator it produces when the loop is executed will be assumed
5445 * to yield values which can be converted to type {@code T}.
5446 * <li>The parameter list of an {@code iterator} that is non-{@code null} (of some form {@code (A*)}) must be
5447 * effectively identical to the external parameter list {@code (A...)}.
5448 * <li>If {@code iterator} is {@code null} it defaults to a method handle which behaves
5449 * like {@link java.lang.Iterable#iterator()}. In that case, the internal parameter list
5450 * {@code (V T A...)} must have at least one {@code A} type, and the default iterator
5451 * handle parameter is adjusted to accept the leading {@code A} type, as if by
5452 * the {@link MethodHandle#asType asType} conversion method.
5453 * The leading {@code A} type must be {@code Iterable} or a subtype thereof.
5454 * This conversion step, done at loop construction time, must not throw a {@code WrongMethodTypeException}.
5455 * </ul>
5456 * <p>
5457 * The type {@code T} may be either a primitive or reference.
5458 * Since type {@code Iterator<T>} is erased in the method handle representation to the raw type {@code Iterator},
5459 * the {@code iteratedLoop} combinator adjusts the leading argument type for {@code body} to {@code Object}
5460 * as if by the {@link MethodHandle#asType asType} conversion method.
5461 * Therefore, if an iterator of the wrong type appears as the loop is executed, runtime exceptions may occur
5462 * as the result of dynamic conversions performed by {@link MethodHandle#asType(MethodType)}.
5463 * <p>
5464 * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
5465 * <li>The loop handle's result type is the result type {@code V} of the body.
5466 * <li>The loop handle's parameter types are the types {@code (A...)},
5467 * from the external parameter list.
5468 * </ul>
5469 * <p>
5470 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
5471 * the loop variable as well as the result type of the loop; {@code T}/{@code t}, that of the elements of the
5472 * structure the loop iterates over, and {@code A...}/{@code a...} represent arguments passed to the loop.
5473 * <blockquote><pre>{@code
5474 * Iterator<T> iterator(A...); // defaults to Iterable::iterator
5475 * V init(A...);
5476 * V body(V,T,A...);
5477 * V iteratedLoop(A... a...) {
5478 * Iterator<T> it = iterator(a...);
5479 * V v = init(a...);
5480 * while (it.hasNext()) {
5481 * T t = it.next();
5482 * v = body(v, t, a...);
5483 * }
5484 * return v;
5485 * }
5486 * }</pre></blockquote>
5487 * <p>
5488 * @apiNote Example:
5489 * <blockquote><pre>{@code
5490 * // get an iterator from a list
5491 * static List<String> reverseStep(List<String> r, String e) {
5492 * r.add(0, e);
5493 * return r;
5494 * }
5495 * static List<String> newArrayList() { return new ArrayList<>(); }
5496 * // assume MH_reverseStep and MH_newArrayList are handles to the above methods
5497 * MethodHandle loop = MethodHandles.iteratedLoop(null, MH_newArrayList, MH_reverseStep);
5498 * List<String> list = Arrays.asList("a", "b", "c", "d", "e");
5499 * List<String> reversedList = Arrays.asList("e", "d", "c", "b", "a");
5500 * assertEquals(reversedList, (List<String>) loop.invoke(list));
5501 * }</pre></blockquote>
5502 * <p>
5503 * @apiNote The implementation of this method can be expressed approximately as follows:
5504 * <blockquote><pre>{@code
5505 * MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
5506 * // assume MH_next, MH_hasNext, MH_startIter are handles to methods of Iterator/Iterable
5507 * Class<?> returnType = body.type().returnType();
5508 * Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
5509 * MethodHandle nextVal = MH_next.asType(MH_next.type().changeReturnType(ttype));
5510 * MethodHandle retv = null, step = body, startIter = iterator;
5511 * if (returnType != void.class) {
5512 * // the simple thing first: in (I V A...), drop the I to get V
5513 * retv = dropArguments(identity(returnType), 0, Iterator.class);
5514 * // body type signature (V T A...), internal loop types (I V A...)
5515 * step = swapArguments(body, 0, 1); // swap V <-> T
5516 * }
5517 * if (startIter == null) startIter = MH_getIter;
5518 * MethodHandle[]
5519 * iterVar = { startIter, null, MH_hasNext, retv }, // it = iterator; while (it.hasNext())
5520 * bodyClause = { init, filterArguments(step, 0, nextVal) }; // v = body(v, t, a)
5521 * return loop(iterVar, bodyClause);
5522 * }
5523 * }</pre></blockquote>
5524 *
5525 * @param iterator an optional handle to return the iterator to start the loop.
5526 * If non-{@code null}, the handle must return {@link java.util.Iterator} or a subtype.
5527 * See above for other constraints.
5528 * @param init optional initializer, providing the initial value of the loop variable.
5529 * May be {@code null}, implying a default initial value. See above for other constraints.
5530 * @param body body of the loop, which may not be {@code null}.
5531 * It controls the loop parameters and result type in the standard case (see above for details).
5532 * It must accept its own return type (if non-void) plus a {@code T} parameter (for the iterated values),
5533 * and may accept any number of additional types.
5534 * See above for other constraints.
5535 *
5536 * @return a method handle embodying the iteration loop functionality.
5537 * @throws NullPointerException if the {@code body} handle is {@code null}.
5538 * @throws IllegalArgumentException if any argument violates the above requirements.
5539 *
5540 * @since 9
5541 */
5542 public static MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
5543 Class<?> iterableType = iteratedLoopChecks(iterator, init, body);
5544 Class<?> returnType = body.type().returnType();
5545 MethodHandle hasNext = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iteratePred);
5546 MethodHandle nextRaw = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iterateNext);
5547 MethodHandle startIter;
5548 MethodHandle nextVal;
5549 {
5550 MethodType iteratorType;
5551 if (iterator == null) {
5552 // derive argument type from body, if available, else use Iterable
5553 startIter = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_initIterator);
5554 iteratorType = startIter.type().changeParameterType(0, iterableType);
5555 } else {
5556 // force return type to the internal iterator class
5557 iteratorType = iterator.type().changeReturnType(Iterator.class);
5558 startIter = iterator;
5559 }
5560 Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
5561 MethodType nextValType = nextRaw.type().changeReturnType(ttype);
5562
5563 // perform the asType transforms under an exception transformer, as per spec.:
5564 try {
5565 startIter = startIter.asType(iteratorType);
5566 nextVal = nextRaw.asType(nextValType);
5567 } catch (WrongMethodTypeException ex) {
5568 throw new IllegalArgumentException(ex);
5569 }
5570 }
5571
5572 MethodHandle retv = null, step = body;
5573 if (returnType != void.class) {
5574 // the simple thing first: in (I V A...), drop the I to get V
5575 retv = dropArguments(identity(returnType), 0, Iterator.class);
5576 // body type signature (V T A...), internal loop types (I V A...)
5577 step = swapArguments(body, 0, 1); // swap V <-> T
5578 }
5579
5580 MethodHandle[]
5581 iterVar = { startIter, null, hasNext, retv },
5582 bodyClause = { init, filterArgument(step, 0, nextVal) };
5583 return loop(iterVar, bodyClause);
5584 }
5585
5586 private static Class<?> iteratedLoopChecks(MethodHandle iterator, MethodHandle init, MethodHandle body) {
5587 Objects.requireNonNull(body);
5588 MethodType bodyType = body.type();
5589 Class<?> returnType = bodyType.returnType();
5590 List<Class<?>> internalParamList = bodyType.parameterList();
5591 // strip leading V value if present
5592 int vsize = (returnType == void.class ? 0 : 1);
5593 if (vsize != 0 && (internalParamList.size() == 0 || internalParamList.get(0) != returnType)) {
5594 // argument list has no "V" => error
5595 MethodType expected = bodyType.insertParameterTypes(0, returnType);
5596 throw misMatchedTypes("body function", bodyType, expected);
5597 } else if (internalParamList.size() <= vsize) {
5598 // missing T type => error
5599 MethodType expected = bodyType.insertParameterTypes(vsize, Object.class);
5600 throw misMatchedTypes("body function", bodyType, expected);
5601 }
5602 List<Class<?>> externalParamList = internalParamList.subList(vsize + 1, internalParamList.size());
5603 Class<?> iterableType = null;
5604 if (iterator != null) {
5605 // special case; if the body handle only declares V and T then
5606 // the external parameter list is obtained from iterator handle
5607 if (externalParamList.isEmpty()) {
5608 externalParamList = iterator.type().parameterList();
5609 }
5610 MethodType itype = iterator.type();
5611 if (!Iterator.class.isAssignableFrom(itype.returnType())) {
5612 throw newIllegalArgumentException("iteratedLoop first argument must have Iterator return type");
5613 }
5614 if (!itype.effectivelyIdenticalParameters(0, externalParamList)) {
5615 MethodType expected = methodType(itype.returnType(), externalParamList);
5616 throw misMatchedTypes("iterator parameters", itype, expected);
5617 }
5618 } else {
5619 if (externalParamList.isEmpty()) {
5620 // special case; if the iterator handle is null and the body handle
5621 // only declares V and T then the external parameter list consists
5622 // of Iterable
5623 externalParamList = Arrays.asList(Iterable.class);
5624 iterableType = Iterable.class;
5625 } else {
5626 // special case; if the iterator handle is null and the external
5627 // parameter list is not empty then the first parameter must be
5628 // assignable to Iterable
5629 iterableType = externalParamList.get(0);
5630 if (!Iterable.class.isAssignableFrom(iterableType)) {
5631 throw newIllegalArgumentException(
5632 "inferred first loop argument must inherit from Iterable: " + iterableType);
5633 }
5634 }
5635 }
5636 if (init != null) {
5637 MethodType initType = init.type();
5638 if (initType.returnType() != returnType ||
5639 !initType.effectivelyIdenticalParameters(0, externalParamList)) {
5640 throw misMatchedTypes("loop initializer", initType, methodType(returnType, externalParamList));
5641 }
5642 }
5643 return iterableType; // help the caller a bit
5644 }
5645
5646 /*non-public*/ static MethodHandle swapArguments(MethodHandle mh, int i, int j) {
5647 // there should be a better way to uncross my wires
5648 int arity = mh.type().parameterCount();
5649 int[] order = new int[arity];
5650 for (int k = 0; k < arity; k++) order[k] = k;
5651 order[i] = j; order[j] = i;
5652 Class<?>[] types = mh.type().parameterArray();
5653 Class<?> ti = types[i]; types[i] = types[j]; types[j] = ti;
5654 MethodType swapType = methodType(mh.type().returnType(), types);
5655 return permuteArguments(mh, swapType, order);
5656 }
5657
5658 /**
5659 * Makes a method handle that adapts a {@code target} method handle by wrapping it in a {@code try-finally} block.
5660 * Another method handle, {@code cleanup}, represents the functionality of the {@code finally} block. Any exception
5661 * thrown during the execution of the {@code target} handle will be passed to the {@code cleanup} handle. The
5662 * exception will be rethrown, unless {@code cleanup} handle throws an exception first. The
5663 * value returned from the {@code cleanup} handle's execution will be the result of the execution of the
5664 * {@code try-finally} handle.
5665 * <p>
5666 * The {@code cleanup} handle will be passed one or two additional leading arguments.
5667 * The first is the exception thrown during the
5668 * execution of the {@code target} handle, or {@code null} if no exception was thrown.
5669 * The second is the result of the execution of the {@code target} handle, or, if it throws an exception,
5670 * a {@code null}, zero, or {@code false} value of the required type is supplied as a placeholder.
5671 * The second argument is not present if the {@code target} handle has a {@code void} return type.
5672 * (Note that, except for argument type conversions, combinators represent {@code void} values in parameter lists
5673 * by omitting the corresponding paradoxical arguments, not by inserting {@code null} or zero values.)
5674 * <p>
5675 * The {@code target} and {@code cleanup} handles must have the same corresponding argument and return types, except
5676 * that the {@code cleanup} handle may omit trailing arguments. Also, the {@code cleanup} handle must have one or
5677 * two extra leading parameters:<ul>
5678 * <li>a {@code Throwable}, which will carry the exception thrown by the {@code target} handle (if any); and
5679 * <li>a parameter of the same type as the return type of both {@code target} and {@code cleanup}, which will carry
5680 * the result from the execution of the {@code target} handle.
5681 * This parameter is not present if the {@code target} returns {@code void}.
5682 * </ul>
5683 * <p>
5684 * The pseudocode for the resulting adapter looks as follows. In the code, {@code V} represents the result type of
5685 * the {@code try/finally} construct; {@code A}/{@code a}, the types and values of arguments to the resulting
5686 * handle consumed by the cleanup; and {@code B}/{@code b}, those of arguments to the resulting handle discarded by
5687 * the cleanup.
5688 * <blockquote><pre>{@code
5689 * V target(A..., B...);
5690 * V cleanup(Throwable, V, A...);
5691 * V adapter(A... a, B... b) {
5692 * V result = (zero value for V);
5693 * Throwable throwable = null;
5694 * try {
5695 * result = target(a..., b...);
5696 * } catch (Throwable t) {
5697 * throwable = t;
5698 * throw t;
5699 * } finally {
5700 * result = cleanup(throwable, result, a...);
5701 * }
5702 * return result;
5703 * }
5704 * }</pre></blockquote>
5705 * <p>
5706 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
5707 * be modified by execution of the target, and so are passed unchanged
5708 * from the caller to the cleanup, if it is invoked.
5709 * <p>
5710 * The target and cleanup must return the same type, even if the cleanup
5711 * always throws.
5712 * To create such a throwing cleanup, compose the cleanup logic
5713 * with {@link #throwException throwException},
5714 * in order to create a method handle of the correct return type.
5715 * <p>
5716 * Note that {@code tryFinally} never converts exceptions into normal returns.
5717 * In rare cases where exceptions must be converted in that way, first wrap
5718 * the target with {@link #catchException(MethodHandle, Class, MethodHandle)}
5719 * to capture an outgoing exception, and then wrap with {@code tryFinally}.
5720 *
5721 * @param target the handle whose execution is to be wrapped in a {@code try} block.
5722 * @param cleanup the handle that is invoked in the finally block.
5723 *
5724 * @return a method handle embodying the {@code try-finally} block composed of the two arguments.
5725 * @throws NullPointerException if any argument is null
5726 * @throws IllegalArgumentException if {@code cleanup} does not accept
5727 * the required leading arguments, or if the method handle types do
5728 * not match in their return types and their
5729 * corresponding trailing parameters
5730 *
5731 * @see MethodHandles#catchException(MethodHandle, Class, MethodHandle)
5732 * @since 9
5733 */
5734 public static MethodHandle tryFinally(MethodHandle target, MethodHandle cleanup) {
5735 List<Class<?>> targetParamTypes = target.type().parameterList();
5736 List<Class<?>> cleanupParamTypes = cleanup.type().parameterList();
5737 Class<?> rtype = target.type().returnType();
5738
5739 tryFinallyChecks(target, cleanup);
5740
5741 // Match parameter lists: if the cleanup has a shorter parameter list than the target, add ignored arguments.
5742 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
5743 // target parameter list.
5744 cleanup = dropArgumentsToMatch(cleanup, (rtype == void.class ? 1 : 2), targetParamTypes, 0);
5745
5746 // Use asFixedArity() to avoid unnecessary boxing of last argument for VarargsCollector case.
5747 return MethodHandleImpl.makeTryFinally(target.asFixedArity(), cleanup.asFixedArity(), rtype, targetParamTypes);
5748 }
5749
5750 private static void tryFinallyChecks(MethodHandle target, MethodHandle cleanup) {
5751 Class<?> rtype = target.type().returnType();
5752 if (rtype != cleanup.type().returnType()) {
5753 throw misMatchedTypes("target and return types", cleanup.type().returnType(), rtype);
5754 }
5755 MethodType cleanupType = cleanup.type();
5756 if (!Throwable.class.isAssignableFrom(cleanupType.parameterType(0))) {
5757 throw misMatchedTypes("cleanup first argument and Throwable", cleanup.type(), Throwable.class);
5758 }
5759 if (rtype != void.class && cleanupType.parameterType(1) != rtype) {
5760 throw misMatchedTypes("cleanup second argument and target return type", cleanup.type(), rtype);
5761 }
5762 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
5763 // target parameter list.
5764 int cleanupArgIndex = rtype == void.class ? 1 : 2;
5765 if (!cleanupType.effectivelyIdenticalParameters(cleanupArgIndex, target.type().parameterList())) {
5766 throw misMatchedTypes("cleanup parameters after (Throwable,result) and target parameter list prefix",
5767 cleanup.type(), target.type());
5768 }
5769 }
5770
5771 }