1 /*
2 * Copyright (c) 2008, 2016, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package java.lang.invoke;
27
28 import jdk.internal.org.objectweb.asm.ClassWriter;
29 import jdk.internal.org.objectweb.asm.Opcodes;
30 import jdk.internal.reflect.CallerSensitive;
31 import jdk.internal.reflect.Reflection;
32 import sun.invoke.util.ValueConversions;
33 import sun.invoke.util.VerifyAccess;
34 import sun.invoke.util.Wrapper;
35 import sun.reflect.misc.ReflectUtil;
36 import sun.security.util.SecurityConstants;
37
38 import java.lang.invoke.LambdaForm.BasicType;
39 import java.lang.reflect.Constructor;
40 import java.lang.reflect.Field;
41 import java.lang.reflect.Member;
42 import java.lang.reflect.Method;
43 import java.lang.reflect.Modifier;
44 import java.lang.reflect.ReflectPermission;
45 import java.nio.ByteOrder;
46 import java.security.AccessController;
47 import java.security.PrivilegedAction;
48 import java.util.ArrayList;
49 import java.util.Arrays;
50 import java.util.BitSet;
51 import java.util.Iterator;
52 import java.util.List;
53 import java.util.Objects;
54 import java.util.concurrent.ConcurrentHashMap;
55 import java.util.stream.Collectors;
56 import java.util.stream.Stream;
57
58 import static java.lang.invoke.MethodHandleImpl.Intrinsic;
59 import static java.lang.invoke.MethodHandleNatives.Constants.*;
60 import static java.lang.invoke.MethodHandleStatics.newIllegalArgumentException;
61 import static java.lang.invoke.MethodType.methodType;
62
63 /**
64 * This class consists exclusively of static methods that operate on or return
65 * method handles. They fall into several categories:
66 * <ul>
67 * <li>Lookup methods which help create method handles for methods and fields.
68 * <li>Combinator methods, which combine or transform pre-existing method handles into new ones.
69 * <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns.
70 * </ul>
71 *
72 * @author John Rose, JSR 292 EG
73 * @since 1.7
74 */
75 public class MethodHandles {
76
77 private MethodHandles() { } // do not instantiate
78
79 private static final MemberName.Factory IMPL_NAMES = MemberName.getFactory();
80
81 // See IMPL_LOOKUP below.
82
83 //// Method handle creation from ordinary methods.
84
85 /**
86 * Returns a {@link Lookup lookup object} with
87 * full capabilities to emulate all supported bytecode behaviors of the caller.
88 * These capabilities include <a href="MethodHandles.Lookup.html#privacc">private access</a> to the caller.
89 * Factory methods on the lookup object can create
90 * <a href="MethodHandleInfo.html#directmh">direct method handles</a>
91 * for any member that the caller has access to via bytecodes,
92 * including protected and private fields and methods.
93 * This lookup object is a <em>capability</em> which may be delegated to trusted agents.
94 * Do not store it in place where untrusted code can access it.
95 * <p>
96 * This method is caller sensitive, which means that it may return different
97 * values to different callers.
98 * <p>
99 * For any given caller class {@code C}, the lookup object returned by this call
100 * has equivalent capabilities to any lookup object
101 * supplied by the JVM to the bootstrap method of an
102 * <a href="package-summary.html#indyinsn">invokedynamic instruction</a>
103 * executing in the same caller class {@code C}.
104 * @return a lookup object for the caller of this method, with private access
105 */
106 @CallerSensitive
107 public static Lookup lookup() {
108 return new Lookup(Reflection.getCallerClass());
109 }
110
111 /**
112 * Returns a {@link Lookup lookup object} which is trusted minimally.
113 * It can only be used to create method handles to public members in
114 * public classes in packages that are exported unconditionally.
115 * <p>
116 * For now, the {@linkplain Lookup#lookupClass lookup class} of this lookup
117 * object is in an unnamed module.
118 * Consequently, the lookup context of this lookup object will be the bootstrap
119 * class loader, which means it cannot find user classes.
120 *
121 * <p style="font-size:smaller;">
122 * <em>Discussion:</em>
123 * The lookup class can be changed to any other class {@code C} using an expression of the form
124 * {@link Lookup#in publicLookup().in(C.class)}.
125 * but may change the lookup context by virtue of changing the class loader.
126 * A public lookup object is always subject to
127 * <a href="MethodHandles.Lookup.html#secmgr">security manager checks</a>.
128 * Also, it cannot access
129 * <a href="MethodHandles.Lookup.html#callsens">caller sensitive methods</a>.
130 * @return a lookup object which is trusted minimally
131 */
132 public static Lookup publicLookup() {
133 // During VM startup then only classes in the java.base module can be
134 // loaded and linked. This is because java.base exports aren't setup until
135 // the module system is initialized, hence types in the unnamed module
136 // (or any named module) can't link to java/lang/Object.
137 if (!jdk.internal.misc.VM.isModuleSystemInited()) {
138 return new Lookup(Object.class, Lookup.PUBLIC);
139 } else {
140 return LookupHelper.PUBLIC_LOOKUP;
141 }
142 }
143
144 /**
145 * Performs an unchecked "crack" of a
146 * <a href="MethodHandleInfo.html#directmh">direct method handle</a>.
147 * The result is as if the user had obtained a lookup object capable enough
148 * to crack the target method handle, called
149 * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect}
150 * on the target to obtain its symbolic reference, and then called
151 * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs}
152 * to resolve the symbolic reference to a member.
153 * <p>
154 * If there is a security manager, its {@code checkPermission} method
155 * is called with a {@code ReflectPermission("suppressAccessChecks")} permission.
156 * @param <T> the desired type of the result, either {@link Member} or a subtype
157 * @param target a direct method handle to crack into symbolic reference components
158 * @param expected a class object representing the desired result type {@code T}
159 * @return a reference to the method, constructor, or field object
160 * @exception SecurityException if the caller is not privileged to call {@code setAccessible}
161 * @exception NullPointerException if either argument is {@code null}
162 * @exception IllegalArgumentException if the target is not a direct method handle
163 * @exception ClassCastException if the member is not of the expected type
164 * @since 1.8
165 */
166 public static <T extends Member> T
167 reflectAs(Class<T> expected, MethodHandle target) {
168 SecurityManager smgr = System.getSecurityManager();
169 if (smgr != null) smgr.checkPermission(ACCESS_PERMISSION);
170 Lookup lookup = Lookup.IMPL_LOOKUP; // use maximally privileged lookup
171 return lookup.revealDirect(target).reflectAs(expected, lookup);
172 }
173 // Copied from AccessibleObject, as used by Method.setAccessible, etc.:
174 private static final java.security.Permission ACCESS_PERMISSION =
175 new ReflectPermission("suppressAccessChecks");
176
177 /**
178 * A <em>lookup object</em> is a factory for creating method handles,
179 * when the creation requires access checking.
180 * Method handles do not perform
181 * access checks when they are called, but rather when they are created.
182 * Therefore, method handle access
183 * restrictions must be enforced when a method handle is created.
184 * The caller class against which those restrictions are enforced
185 * is known as the {@linkplain #lookupClass lookup class}.
186 * <p>
187 * A lookup class which needs to create method handles will call
188 * {@link MethodHandles#lookup MethodHandles.lookup} to create a factory for itself.
189 * When the {@code Lookup} factory object is created, the identity of the lookup class is
190 * determined, and securely stored in the {@code Lookup} object.
191 * The lookup class (or its delegates) may then use factory methods
192 * on the {@code Lookup} object to create method handles for access-checked members.
193 * This includes all methods, constructors, and fields which are allowed to the lookup class,
194 * even private ones.
195 *
196 * <h1><a name="lookups"></a>Lookup Factory Methods</h1>
197 * The factory methods on a {@code Lookup} object correspond to all major
198 * use cases for methods, constructors, and fields.
199 * Each method handle created by a factory method is the functional
200 * equivalent of a particular <em>bytecode behavior</em>.
201 * (Bytecode behaviors are described in section 5.4.3.5 of the Java Virtual Machine Specification.)
202 * Here is a summary of the correspondence between these factory methods and
203 * the behavior of the resulting method handles:
204 * <table border=1 cellpadding=5 summary="lookup method behaviors">
205 * <tr>
206 * <th><a name="equiv"></a>lookup expression</th>
207 * <th>member</th>
208 * <th>bytecode behavior</th>
209 * </tr>
210 * <tr>
211 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</td>
212 * <td>{@code FT f;}</td><td>{@code (T) this.f;}</td>
213 * </tr>
214 * <tr>
215 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</td>
216 * <td>{@code static}<br>{@code FT f;}</td><td>{@code (T) C.f;}</td>
217 * </tr>
218 * <tr>
219 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</td>
220 * <td>{@code FT f;}</td><td>{@code this.f = x;}</td>
221 * </tr>
222 * <tr>
223 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</td>
224 * <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td>
225 * </tr>
226 * <tr>
227 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</td>
228 * <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>
229 * </tr>
230 * <tr>
231 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</td>
232 * <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td>
233 * </tr>
234 * <tr>
235 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</td>
236 * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
237 * </tr>
238 * <tr>
239 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</td>
240 * <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td>
241 * </tr>
242 * <tr>
243 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</td>
244 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td>
245 * </tr>
246 * <tr>
247 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</td>
248 * <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, arg);}</td>
249 * </tr>
250 * <tr>
251 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</td>
252 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
253 * </tr>
254 * <tr>
255 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</td>
256 * <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td>
257 * </tr>
258 * <tr>
259 * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</td>
260 * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
261 * </tr>
262 * <tr>
263 * <td>{@link java.lang.invoke.MethodHandles.Lookup#findClass lookup.findClass("C")}</td>
264 * <td>{@code class C { ... }}</td><td>{@code C.class;}</td>
265 * </tr>
266 * </table>
267 *
268 * Here, the type {@code C} is the class or interface being searched for a member,
269 * documented as a parameter named {@code refc} in the lookup methods.
270 * The method type {@code MT} is composed from the return type {@code T}
271 * and the sequence of argument types {@code A*}.
272 * The constructor also has a sequence of argument types {@code A*} and
273 * is deemed to return the newly-created object of type {@code C}.
274 * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}.
275 * The formal parameter {@code this} stands for the self-reference of type {@code C};
276 * if it is present, it is always the leading argument to the method handle invocation.
277 * (In the case of some {@code protected} members, {@code this} may be
278 * restricted in type to the lookup class; see below.)
279 * The name {@code arg} stands for all the other method handle arguments.
280 * In the code examples for the Core Reflection API, the name {@code thisOrNull}
281 * stands for a null reference if the accessed method or field is static,
282 * and {@code this} otherwise.
283 * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand
284 * for reflective objects corresponding to the given members.
285 * <p>
286 * The bytecode behavior for a {@code findClass} operation is a load of a constant class,
287 * as if by {@code ldc CONSTANT_Class}.
288 * The behavior is represented, not as a method handle, but directly as a {@code Class} constant.
289 * <p>
290 * In cases where the given member is of variable arity (i.e., a method or constructor)
291 * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}.
292 * In all other cases, the returned method handle will be of fixed arity.
293 * <p style="font-size:smaller;">
294 * <em>Discussion:</em>
295 * The equivalence between looked-up method handles and underlying
296 * class members and bytecode behaviors
297 * can break down in a few ways:
298 * <ul style="font-size:smaller;">
299 * <li>If {@code C} is not symbolically accessible from the lookup class's loader,
300 * the lookup can still succeed, even when there is no equivalent
301 * Java expression or bytecoded constant.
302 * <li>Likewise, if {@code T} or {@code MT}
303 * is not symbolically accessible from the lookup class's loader,
304 * the lookup can still succeed.
305 * For example, lookups for {@code MethodHandle.invokeExact} and
306 * {@code MethodHandle.invoke} will always succeed, regardless of requested type.
307 * <li>If there is a security manager installed, it can forbid the lookup
308 * on various grounds (<a href="MethodHandles.Lookup.html#secmgr">see below</a>).
309 * By contrast, the {@code ldc} instruction on a {@code CONSTANT_MethodHandle}
310 * constant is not subject to security manager checks.
311 * <li>If the looked-up method has a
312 * <a href="MethodHandle.html#maxarity">very large arity</a>,
313 * the method handle creation may fail, due to the method handle
314 * type having too many parameters.
315 * </ul>
316 *
317 * <h1><a name="access"></a>Access checking</h1>
318 * Access checks are applied in the factory methods of {@code Lookup},
319 * when a method handle is created.
320 * This is a key difference from the Core Reflection API, since
321 * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
322 * performs access checking against every caller, on every call.
323 * <p>
324 * All access checks start from a {@code Lookup} object, which
325 * compares its recorded lookup class against all requests to
326 * create method handles.
327 * A single {@code Lookup} object can be used to create any number
328 * of access-checked method handles, all checked against a single
329 * lookup class.
330 * <p>
331 * A {@code Lookup} object can be shared with other trusted code,
332 * such as a metaobject protocol.
333 * A shared {@code Lookup} object delegates the capability
334 * to create method handles on private members of the lookup class.
335 * Even if privileged code uses the {@code Lookup} object,
336 * the access checking is confined to the privileges of the
337 * original lookup class.
338 * <p>
339 * A lookup can fail, because
340 * the containing class is not accessible to the lookup class, or
341 * because the desired class member is missing, or because the
342 * desired class member is not accessible to the lookup class, or
343 * because the lookup object is not trusted enough to access the member.
344 * In any of these cases, a {@code ReflectiveOperationException} will be
345 * thrown from the attempted lookup. The exact class will be one of
346 * the following:
347 * <ul>
348 * <li>NoSuchMethodException — if a method is requested but does not exist
349 * <li>NoSuchFieldException — if a field is requested but does not exist
350 * <li>IllegalAccessException — if the member exists but an access check fails
351 * </ul>
352 * <p>
353 * In general, the conditions under which a method handle may be
354 * looked up for a method {@code M} are no more restrictive than the conditions
355 * under which the lookup class could have compiled, verified, and resolved a call to {@code M}.
356 * Where the JVM would raise exceptions like {@code NoSuchMethodError},
357 * a method handle lookup will generally raise a corresponding
358 * checked exception, such as {@code NoSuchMethodException}.
359 * And the effect of invoking the method handle resulting from the lookup
360 * is <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a>
361 * to executing the compiled, verified, and resolved call to {@code M}.
362 * The same point is true of fields and constructors.
363 * <p style="font-size:smaller;">
364 * <em>Discussion:</em>
365 * Access checks only apply to named and reflected methods,
366 * constructors, and fields.
367 * Other method handle creation methods, such as
368 * {@link MethodHandle#asType MethodHandle.asType},
369 * do not require any access checks, and are used
370 * independently of any {@code Lookup} object.
371 * <p>
372 * If the desired member is {@code protected}, the usual JVM rules apply,
373 * including the requirement that the lookup class must be either be in the
374 * same package as the desired member, or must inherit that member.
375 * (See the Java Virtual Machine Specification, sections 4.9.2, 5.4.3.5, and 6.4.)
376 * In addition, if the desired member is a non-static field or method
377 * in a different package, the resulting method handle may only be applied
378 * to objects of the lookup class or one of its subclasses.
379 * This requirement is enforced by narrowing the type of the leading
380 * {@code this} parameter from {@code C}
381 * (which will necessarily be a superclass of the lookup class)
382 * to the lookup class itself.
383 * <p>
384 * The JVM imposes a similar requirement on {@code invokespecial} instruction,
385 * that the receiver argument must match both the resolved method <em>and</em>
386 * the current class. Again, this requirement is enforced by narrowing the
387 * type of the leading parameter to the resulting method handle.
388 * (See the Java Virtual Machine Specification, section 4.10.1.9.)
389 * <p>
390 * The JVM represents constructors and static initializer blocks as internal methods
391 * with special names ({@code "<init>"} and {@code "<clinit>"}).
392 * The internal syntax of invocation instructions allows them to refer to such internal
393 * methods as if they were normal methods, but the JVM bytecode verifier rejects them.
394 * A lookup of such an internal method will produce a {@code NoSuchMethodException}.
395 * <p>
396 * In some cases, access between nested classes is obtained by the Java compiler by creating
397 * an wrapper method to access a private method of another class
398 * in the same top-level declaration.
399 * For example, a nested class {@code C.D}
400 * can access private members within other related classes such as
401 * {@code C}, {@code C.D.E}, or {@code C.B},
402 * but the Java compiler may need to generate wrapper methods in
403 * those related classes. In such cases, a {@code Lookup} object on
404 * {@code C.E} would be unable to those private members.
405 * A workaround for this limitation is the {@link Lookup#in Lookup.in} method,
406 * which can transform a lookup on {@code C.E} into one on any of those other
407 * classes, without special elevation of privilege.
408 * <p>
409 * The accesses permitted to a given lookup object may be limited,
410 * according to its set of {@link #lookupModes lookupModes},
411 * to a subset of members normally accessible to the lookup class.
412 * For example, the {@link MethodHandles#publicLookup publicLookup}
413 * method produces a lookup object which is only allowed to access
414 * public members in public classes of exported packages.
415 * The caller sensitive method {@link MethodHandles#lookup lookup}
416 * produces a lookup object with full capabilities relative to
417 * its caller class, to emulate all supported bytecode behaviors.
418 * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object
419 * with fewer access modes than the original lookup object.
420 *
421 * <p style="font-size:smaller;">
422 * <a name="privacc"></a>
423 * <em>Discussion of private access:</em>
424 * We say that a lookup has <em>private access</em>
425 * if its {@linkplain #lookupModes lookup modes}
426 * include the possibility of accessing {@code private} members.
427 * As documented in the relevant methods elsewhere,
428 * only lookups with private access possess the following capabilities:
429 * <ul style="font-size:smaller;">
430 * <li>access private fields, methods, and constructors of the lookup class
431 * <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> methods,
432 * such as {@code Class.forName}
433 * <li>create method handles which {@link Lookup#findSpecial emulate invokespecial} instructions
434 * <li>avoid <a href="MethodHandles.Lookup.html#secmgr">package access checks</a>
435 * for classes accessible to the lookup class
436 * <li>create {@link Lookup#in delegated lookup objects} which have private access to other classes
437 * within the same package member
438 * </ul>
439 * <p style="font-size:smaller;">
440 * Each of these permissions is a consequence of the fact that a lookup object
441 * with private access can be securely traced back to an originating class,
442 * whose <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> and Java language access permissions
443 * can be reliably determined and emulated by method handles.
444 *
445 * <h1><a name="secmgr"></a>Security manager interactions</h1>
446 * Although bytecode instructions can only refer to classes in
447 * a related class loader, this API can search for methods in any
448 * class, as long as a reference to its {@code Class} object is
449 * available. Such cross-loader references are also possible with the
450 * Core Reflection API, and are impossible to bytecode instructions
451 * such as {@code invokestatic} or {@code getfield}.
452 * There is a {@linkplain java.lang.SecurityManager security manager API}
453 * to allow applications to check such cross-loader references.
454 * These checks apply to both the {@code MethodHandles.Lookup} API
455 * and the Core Reflection API
456 * (as found on {@link java.lang.Class Class}).
457 * <p>
458 * If a security manager is present, member and class lookups are subject to
459 * additional checks.
460 * From one to three calls are made to the security manager.
461 * Any of these calls can refuse access by throwing a
462 * {@link java.lang.SecurityException SecurityException}.
463 * Define {@code smgr} as the security manager,
464 * {@code lookc} as the lookup class of the current lookup object,
465 * {@code refc} as the containing class in which the member
466 * is being sought, and {@code defc} as the class in which the
467 * member is actually defined.
468 * (If a class or other type is being accessed,
469 * the {@code refc} and {@code defc} values are the class itself.)
470 * The value {@code lookc} is defined as <em>not present</em>
471 * if the current lookup object does not have
472 * <a href="MethodHandles.Lookup.html#privacc">private access</a>.
473 * The calls are made according to the following rules:
474 * <ul>
475 * <li><b>Step 1:</b>
476 * If {@code lookc} is not present, or if its class loader is not
477 * the same as or an ancestor of the class loader of {@code refc},
478 * then {@link SecurityManager#checkPackageAccess
479 * smgr.checkPackageAccess(refcPkg)} is called,
480 * where {@code refcPkg} is the package of {@code refc}.
481 * <li><b>Step 2a:</b>
482 * If the retrieved member is not public and
483 * {@code lookc} is not present, then
484 * {@link SecurityManager#checkPermission smgr.checkPermission}
485 * with {@code RuntimePermission("accessDeclaredMembers")} is called.
486 * <li><b>Step 2b:</b>
487 * If the retrieved class has a {@code null} class loader,
488 * and {@code lookc} is not present, then
489 * {@link SecurityManager#checkPermission smgr.checkPermission}
490 * with {@code RuntimePermission("getClassLoader")} is called.
491 * <li><b>Step 3:</b>
492 * If the retrieved member is not public,
493 * and if {@code lookc} is not present,
494 * and if {@code defc} and {@code refc} are different,
495 * then {@link SecurityManager#checkPackageAccess
496 * smgr.checkPackageAccess(defcPkg)} is called,
497 * where {@code defcPkg} is the package of {@code defc}.
498 * </ul>
499 * Security checks are performed after other access checks have passed.
500 * Therefore, the above rules presuppose a member or class that is public,
501 * or else that is being accessed from a lookup class that has
502 * rights to access the member or class.
503 *
504 * <h1><a name="callsens"></a>Caller sensitive methods</h1>
505 * A small number of Java methods have a special property called caller sensitivity.
506 * A <em>caller-sensitive</em> method can behave differently depending on the
507 * identity of its immediate caller.
508 * <p>
509 * If a method handle for a caller-sensitive method is requested,
510 * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> apply,
511 * but they take account of the lookup class in a special way.
512 * The resulting method handle behaves as if it were called
513 * from an instruction contained in the lookup class,
514 * so that the caller-sensitive method detects the lookup class.
515 * (By contrast, the invoker of the method handle is disregarded.)
516 * Thus, in the case of caller-sensitive methods,
517 * different lookup classes may give rise to
518 * differently behaving method handles.
519 * <p>
520 * In cases where the lookup object is
521 * {@link MethodHandles#publicLookup() publicLookup()},
522 * or some other lookup object without
523 * <a href="MethodHandles.Lookup.html#privacc">private access</a>,
524 * the lookup class is disregarded.
525 * In such cases, no caller-sensitive method handle can be created,
526 * access is forbidden, and the lookup fails with an
527 * {@code IllegalAccessException}.
528 * <p style="font-size:smaller;">
529 * <em>Discussion:</em>
530 * For example, the caller-sensitive method
531 * {@link java.lang.Class#forName(String) Class.forName(x)}
532 * can return varying classes or throw varying exceptions,
533 * depending on the class loader of the class that calls it.
534 * A public lookup of {@code Class.forName} will fail, because
535 * there is no reasonable way to determine its bytecode behavior.
536 * <p style="font-size:smaller;">
537 * If an application caches method handles for broad sharing,
538 * it should use {@code publicLookup()} to create them.
539 * If there is a lookup of {@code Class.forName}, it will fail,
540 * and the application must take appropriate action in that case.
541 * It may be that a later lookup, perhaps during the invocation of a
542 * bootstrap method, can incorporate the specific identity
543 * of the caller, making the method accessible.
544 * <p style="font-size:smaller;">
545 * The function {@code MethodHandles.lookup} is caller sensitive
546 * so that there can be a secure foundation for lookups.
547 * Nearly all other methods in the JSR 292 API rely on lookup
548 * objects to check access requests.
549 */
550 public static final
551 class Lookup {
552 /** The class on behalf of whom the lookup is being performed. */
553 private final Class<?> lookupClass;
554
555 /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */
556 private final int allowedModes;
557
558 /** A single-bit mask representing {@code public} access,
559 * which may contribute to the result of {@link #lookupModes lookupModes}.
560 * The value, {@code 0x01}, happens to be the same as the value of the
561 * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.
562 */
563 public static final int PUBLIC = Modifier.PUBLIC;
564
565 /** A single-bit mask representing {@code private} access,
566 * which may contribute to the result of {@link #lookupModes lookupModes}.
567 * The value, {@code 0x02}, happens to be the same as the value of the
568 * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.
569 */
570 public static final int PRIVATE = Modifier.PRIVATE;
571
572 /** A single-bit mask representing {@code protected} access,
573 * which may contribute to the result of {@link #lookupModes lookupModes}.
574 * The value, {@code 0x04}, happens to be the same as the value of the
575 * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.
576 */
577 public static final int PROTECTED = Modifier.PROTECTED;
578
579 /** A single-bit mask representing {@code package} access (default access),
580 * which may contribute to the result of {@link #lookupModes lookupModes}.
581 * The value is {@code 0x08}, which does not correspond meaningfully to
582 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
583 */
584 public static final int PACKAGE = Modifier.STATIC;
585
586 /** A single-bit mask representing {@code module} access (default access),
587 * which may contribute to the result of {@link #lookupModes lookupModes}.
588 * The value is {@code 0x10}, which does not correspond meaningfully to
589 * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
590 * In conjunction with the {@code PUBLIC} modifier bit, a {@code Lookup}
591 * with this lookup mode can access all public types in the module of the
592 * lookup class and public types in packages exported by other modules
593 * to the module of the lookup class.
594 * @since 9
595 */
596 public static final int MODULE = PACKAGE << 1;
597
598 private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE | MODULE);
599 private static final int TRUSTED = -1;
600
601 private static int fixmods(int mods) {
602 mods &= (ALL_MODES - PACKAGE - MODULE);
603 return (mods != 0) ? mods : (PACKAGE | MODULE);
604 }
605
606 /** Tells which class is performing the lookup. It is this class against
607 * which checks are performed for visibility and access permissions.
608 * <p>
609 * The class implies a maximum level of access permission,
610 * but the permissions may be additionally limited by the bitmask
611 * {@link #lookupModes lookupModes}, which controls whether non-public members
612 * can be accessed.
613 * @return the lookup class, on behalf of which this lookup object finds members
614 */
615 public Class<?> lookupClass() {
616 return lookupClass;
617 }
618
619 // This is just for calling out to MethodHandleImpl.
620 private Class<?> lookupClassOrNull() {
621 return (allowedModes == TRUSTED) ? null : lookupClass;
622 }
623
624 /** Tells which access-protection classes of members this lookup object can produce.
625 * The result is a bit-mask of the bits
626 * {@linkplain #PUBLIC PUBLIC (0x01)},
627 * {@linkplain #PRIVATE PRIVATE (0x02)},
628 * {@linkplain #PROTECTED PROTECTED (0x04)},
629 * {@linkplain #PACKAGE PACKAGE (0x08)},
630 * and {@linkplain #MODULE MODULE (0x10)}.
631 * <p>
632 * A freshly-created lookup object
633 * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class}
634 * has all possible bits set, since the caller class can access all its own members,
635 * all public types in the caller's module, and all public types in packages exported
636 * by other modules to the caller's module.
637 * A lookup object on a new lookup class
638 * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object}
639 * may have some mode bits set to zero.
640 * The purpose of this is to restrict access via the new lookup object,
641 * so that it can access only names which can be reached by the original
642 * lookup object, and also by the new lookup class.
643 * @return the lookup modes, which limit the kinds of access performed by this lookup object
644 */
645 public int lookupModes() {
646 return allowedModes & ALL_MODES;
647 }
648
649 /** Embody the current class (the lookupClass) as a lookup class
650 * for method handle creation.
651 * Must be called by from a method in this package,
652 * which in turn is called by a method not in this package.
653 */
654 Lookup(Class<?> lookupClass) {
655 this(lookupClass, ALL_MODES);
656 // make sure we haven't accidentally picked up a privileged class:
657 checkUnprivilegedlookupClass(lookupClass, ALL_MODES);
658 }
659
660 private Lookup(Class<?> lookupClass, int allowedModes) {
661 this.lookupClass = lookupClass;
662 this.allowedModes = allowedModes;
663 }
664
665 /**
666 * Creates a lookup on the specified new lookup class.
667 * The resulting object will report the specified
668 * class as its own {@link #lookupClass lookupClass}.
669 * <p>
670 * However, the resulting {@code Lookup} object is guaranteed
671 * to have no more access capabilities than the original.
672 * In particular, access capabilities can be lost as follows:<ul>
673 * <li>If the lookup class for this {@code Lookup} is not in a named module,
674 * and the new lookup class is in a named module {@code M}, then no members in
675 * {@code M}'s non-exported packages will be accessible.
676 * <li>If the lookup for this {@code Lookup} is in a named module, and the
677 * new lookup class is in a different module {@code M}, then no members, not even
678 * public members in {@code M}'s exported packages, will be accessible.
679 * <li>If the new lookup class differs from the old one,
680 * protected members will not be accessible by virtue of inheritance.
681 * (Protected members may continue to be accessible because of package sharing.)
682 * <li>If the new lookup class is in a different package
683 * than the old one, protected and default (package) members will not be accessible.
684 * <li>If the new lookup class is not within the same package member
685 * as the old one, private members will not be accessible.
686 * <li>If the new lookup class is not accessible to the old lookup class,
687 * then no members, not even public members, will be accessible.
688 * (In all other cases, public members will continue to be accessible.)
689 * </ul>
690 * <p>
691 * The resulting lookup's capabilities for loading classes
692 * (used during {@link #findClass} invocations)
693 * are determined by the lookup class' loader,
694 * which may change due to this operation.
695 *
696 * @param requestedLookupClass the desired lookup class for the new lookup object
697 * @return a lookup object which reports the desired lookup class
698 * @throws NullPointerException if the argument is null
699 */
700 public Lookup in(Class<?> requestedLookupClass) {
701 Objects.requireNonNull(requestedLookupClass);
702 if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all
703 return new Lookup(requestedLookupClass, ALL_MODES);
704 if (requestedLookupClass == this.lookupClass)
705 return this; // keep same capabilities
706
707 int newModes = (allowedModes & (ALL_MODES & ~PROTECTED));
708 if (!VerifyAccess.isSameModule(this.lookupClass, requestedLookupClass)) {
709 // Allowed to teleport from an unnamed to a named module but resulting
710 // Lookup has no access to module private members
711 if (this.lookupClass.getModule().isNamed()) {
712 newModes = 0;
713 } else {
714 newModes &= ~MODULE;
715 }
716 }
717 if ((newModes & PACKAGE) != 0
718 && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {
719 newModes &= ~(PACKAGE|PRIVATE);
720 }
721 // Allow nestmate lookups to be created without special privilege:
722 if ((newModes & PRIVATE) != 0
723 && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {
724 newModes &= ~PRIVATE;
725 }
726 if ((newModes & PUBLIC) != 0
727 && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, allowedModes)) {
728 // The requested class it not accessible from the lookup class.
729 // No permissions.
730 newModes = 0;
731 }
732
733 checkUnprivilegedlookupClass(requestedLookupClass, newModes);
734 return new Lookup(requestedLookupClass, newModes);
735 }
736
737 // Make sure outer class is initialized first.
738 static { IMPL_NAMES.getClass(); }
739
740 /** Package-private version of lookup which is trusted. */
741 static final Lookup IMPL_LOOKUP = new Lookup(Object.class, TRUSTED);
742
743 private static void checkUnprivilegedlookupClass(Class<?> lookupClass, int allowedModes) {
744 String name = lookupClass.getName();
745 if (name.startsWith("java.lang.invoke."))
746 throw newIllegalArgumentException("illegal lookupClass: "+lookupClass);
747
748 // For caller-sensitive MethodHandles.lookup() disallow lookup from
749 // restricted packages. This a fragile and blunt approach.
750 // TODO replace with a more formal and less fragile mechanism
751 // that does not bluntly restrict classes under packages within
752 // java.base from looking up MethodHandles or VarHandles.
753 if (allowedModes == ALL_MODES && lookupClass.getClassLoader() == null) {
754 if ((name.startsWith("java.") && !name.startsWith("java.util.concurrent.")) ||
755 (name.startsWith("sun.") && !name.startsWith("sun.invoke."))) {
756 throw newIllegalArgumentException("illegal lookupClass: " + lookupClass);
757 }
758 }
759 }
760
761 /**
762 * Displays the name of the class from which lookups are to be made.
763 * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)
764 * If there are restrictions on the access permitted to this lookup,
765 * this is indicated by adding a suffix to the class name, consisting
766 * of a slash and a keyword. The keyword represents the strongest
767 * allowed access, and is chosen as follows:
768 * <ul>
769 * <li>If no access is allowed, the suffix is "/noaccess".
770 * <li>If only public access to types in exported packages is allowed, the suffix is "/public".
771 * <li>If only public and module access are allowed, the suffix is "/module".
772 * <li>If only public, module and package access are allowed, the suffix is "/package".
773 * <li>If only public, module, package, and private access are allowed, the suffix is "/private".
774 * </ul>
775 * If none of the above cases apply, it is the case that full
776 * access (public, module, package, private, and protected) is allowed.
777 * In this case, no suffix is added.
778 * This is true only of an object obtained originally from
779 * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
780 * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
781 * always have restricted access, and will display a suffix.
782 * <p>
783 * (It may seem strange that protected access should be
784 * stronger than private access. Viewed independently from
785 * package access, protected access is the first to be lost,
786 * because it requires a direct subclass relationship between
787 * caller and callee.)
788 * @see #in
789 */
790 @Override
791 public String toString() {
792 String cname = lookupClass.getName();
793 switch (allowedModes) {
794 case 0: // no privileges
795 return cname + "/noaccess";
796 case PUBLIC:
797 return cname + "/public";
798 case PUBLIC|MODULE:
799 return cname + "/module";
800 case PUBLIC|MODULE|PACKAGE:
801 return cname + "/package";
802 case ALL_MODES & ~PROTECTED:
803 return cname + "/private";
804 case ALL_MODES:
805 return cname;
806 case TRUSTED:
807 return "/trusted"; // internal only; not exported
808 default: // Should not happen, but it's a bitfield...
809 cname = cname + "/" + Integer.toHexString(allowedModes);
810 assert(false) : cname;
811 return cname;
812 }
813 }
814
815 /**
816 * Produces a method handle for a static method.
817 * The type of the method handle will be that of the method.
818 * (Since static methods do not take receivers, there is no
819 * additional receiver argument inserted into the method handle type,
820 * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)
821 * The method and all its argument types must be accessible to the lookup object.
822 * <p>
823 * The returned method handle will have
824 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
825 * the method's variable arity modifier bit ({@code 0x0080}) is set.
826 * <p>
827 * If the returned method handle is invoked, the method's class will
828 * be initialized, if it has not already been initialized.
829 * <p><b>Example:</b>
830 * <blockquote><pre>{@code
831 import static java.lang.invoke.MethodHandles.*;
832 import static java.lang.invoke.MethodType.*;
833 ...
834 MethodHandle MH_asList = publicLookup().findStatic(Arrays.class,
835 "asList", methodType(List.class, Object[].class));
836 assertEquals("[x, y]", MH_asList.invoke("x", "y").toString());
837 * }</pre></blockquote>
838 * @param refc the class from which the method is accessed
839 * @param name the name of the method
840 * @param type the type of the method
841 * @return the desired method handle
842 * @throws NoSuchMethodException if the method does not exist
843 * @throws IllegalAccessException if access checking fails,
844 * or if the method is not {@code static},
845 * or if the method's variable arity modifier bit
846 * is set and {@code asVarargsCollector} fails
847 * @exception SecurityException if a security manager is present and it
848 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
849 * @throws NullPointerException if any argument is null
850 */
851 public
852 MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
853 MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type);
854 return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerClass(method));
855 }
856
857 /**
858 * Produces a method handle for a virtual method.
859 * The type of the method handle will be that of the method,
860 * with the receiver type (usually {@code refc}) prepended.
861 * The method and all its argument types must be accessible to the lookup object.
862 * <p>
863 * When called, the handle will treat the first argument as a receiver
864 * and dispatch on the receiver's type to determine which method
865 * implementation to enter.
866 * (The dispatching action is identical with that performed by an
867 * {@code invokevirtual} or {@code invokeinterface} instruction.)
868 * <p>
869 * The first argument will be of type {@code refc} if the lookup
870 * class has full privileges to access the member. Otherwise
871 * the member must be {@code protected} and the first argument
872 * will be restricted in type to the lookup class.
873 * <p>
874 * The returned method handle will have
875 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
876 * the method's variable arity modifier bit ({@code 0x0080}) is set.
877 * <p>
878 * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual}
879 * instructions and method handles produced by {@code findVirtual},
880 * if the class is {@code MethodHandle} and the name string is
881 * {@code invokeExact} or {@code invoke}, the resulting
882 * method handle is equivalent to one produced by
883 * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or
884 * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}
885 * with the same {@code type} argument.
886 * <p>
887 * If the class is {@code VarHandle} and the name string corresponds to
888 * the name of a signature-polymorphic access mode method, the resulting
889 * method handle is equivalent to one produced by
890 * {@link java.lang.invoke.MethodHandles#varHandleInvoker} with
891 * the access mode corresponding to the name string and with the same
892 * {@code type} arguments.
893 * <p>
894 * <b>Example:</b>
895 * <blockquote><pre>{@code
896 import static java.lang.invoke.MethodHandles.*;
897 import static java.lang.invoke.MethodType.*;
898 ...
899 MethodHandle MH_concat = publicLookup().findVirtual(String.class,
900 "concat", methodType(String.class, String.class));
901 MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class,
902 "hashCode", methodType(int.class));
903 MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class,
904 "hashCode", methodType(int.class));
905 assertEquals("xy", (String) MH_concat.invokeExact("x", "y"));
906 assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy"));
907 assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy"));
908 // interface method:
909 MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class,
910 "subSequence", methodType(CharSequence.class, int.class, int.class));
911 assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString());
912 // constructor "internal method" must be accessed differently:
913 MethodType MT_newString = methodType(void.class); //()V for new String()
914 try { assertEquals("impossible", lookup()
915 .findVirtual(String.class, "<init>", MT_newString));
916 } catch (NoSuchMethodException ex) { } // OK
917 MethodHandle MH_newString = publicLookup()
918 .findConstructor(String.class, MT_newString);
919 assertEquals("", (String) MH_newString.invokeExact());
920 * }</pre></blockquote>
921 *
922 * @param refc the class or interface from which the method is accessed
923 * @param name the name of the method
924 * @param type the type of the method, with the receiver argument omitted
925 * @return the desired method handle
926 * @throws NoSuchMethodException if the method does not exist
927 * @throws IllegalAccessException if access checking fails,
928 * or if the method is {@code static},
929 * or if the method is {@code private} method of interface,
930 * or if the method's variable arity modifier bit
931 * is set and {@code asVarargsCollector} fails
932 * @exception SecurityException if a security manager is present and it
933 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
934 * @throws NullPointerException if any argument is null
935 */
936 public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
937 if (refc == MethodHandle.class) {
938 MethodHandle mh = findVirtualForMH(name, type);
939 if (mh != null) return mh;
940 } else if (refc == VarHandle.class) {
941 MethodHandle mh = findVirtualForVH(name, type);
942 if (mh != null) return mh;
943 }
944 byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual);
945 MemberName method = resolveOrFail(refKind, refc, name, type);
946 return getDirectMethod(refKind, refc, method, findBoundCallerClass(method));
947 }
948 private MethodHandle findVirtualForMH(String name, MethodType type) {
949 // these names require special lookups because of the implicit MethodType argument
950 if ("invoke".equals(name))
951 return invoker(type);
952 if ("invokeExact".equals(name))
953 return exactInvoker(type);
954 if ("invokeBasic".equals(name))
955 return basicInvoker(type);
956 assert(!MemberName.isMethodHandleInvokeName(name));
957 return null;
958 }
959 private MethodHandle findVirtualForVH(String name, MethodType type) {
960 try {
961 return varHandleInvoker(VarHandle.AccessMode.valueFromMethodName(name), type);
962 } catch (IllegalArgumentException e) {
963 return null;
964 }
965 }
966
967 /**
968 * Produces a method handle which creates an object and initializes it, using
969 * the constructor of the specified type.
970 * The parameter types of the method handle will be those of the constructor,
971 * while the return type will be a reference to the constructor's class.
972 * The constructor and all its argument types must be accessible to the lookup object.
973 * <p>
974 * The requested type must have a return type of {@code void}.
975 * (This is consistent with the JVM's treatment of constructor type descriptors.)
976 * <p>
977 * The returned method handle will have
978 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
979 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
980 * <p>
981 * If the returned method handle is invoked, the constructor's class will
982 * be initialized, if it has not already been initialized.
983 * <p><b>Example:</b>
984 * <blockquote><pre>{@code
985 import static java.lang.invoke.MethodHandles.*;
986 import static java.lang.invoke.MethodType.*;
987 ...
988 MethodHandle MH_newArrayList = publicLookup().findConstructor(
989 ArrayList.class, methodType(void.class, Collection.class));
990 Collection orig = Arrays.asList("x", "y");
991 Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig);
992 assert(orig != copy);
993 assertEquals(orig, copy);
994 // a variable-arity constructor:
995 MethodHandle MH_newProcessBuilder = publicLookup().findConstructor(
996 ProcessBuilder.class, methodType(void.class, String[].class));
997 ProcessBuilder pb = (ProcessBuilder)
998 MH_newProcessBuilder.invoke("x", "y", "z");
999 assertEquals("[x, y, z]", pb.command().toString());
1000 * }</pre></blockquote>
1001 * @param refc the class or interface from which the method is accessed
1002 * @param type the type of the method, with the receiver argument omitted, and a void return type
1003 * @return the desired method handle
1004 * @throws NoSuchMethodException if the constructor does not exist
1005 * @throws IllegalAccessException if access checking fails
1006 * or if the method's variable arity modifier bit
1007 * is set and {@code asVarargsCollector} fails
1008 * @exception SecurityException if a security manager is present and it
1009 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1010 * @throws NullPointerException if any argument is null
1011 */
1012 public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1013 if (refc.isArray()) {
1014 throw new NoSuchMethodException("no constructor for array class: " + refc.getName());
1015 }
1016 String name = "<init>";
1017 MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type);
1018 return getDirectConstructor(refc, ctor);
1019 }
1020
1021 /**
1022 * Looks up a class by name from the lookup context defined by this {@code Lookup} object. The static
1023 * initializer of the class is not run.
1024 * <p>
1025 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class}, its class
1026 * loader, and the {@linkplain #lookupModes() lookup modes}. In particular, the method first attempts to
1027 * load the requested class, and then determines whether the class is accessible to this lookup object.
1028 *
1029 * @param targetName the fully qualified name of the class to be looked up.
1030 * @return the requested class.
1031 * @exception SecurityException if a security manager is present and it
1032 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1033 * @throws LinkageError if the linkage fails
1034 * @throws ClassNotFoundException if the class cannot be loaded by the lookup class' loader.
1035 * @throws IllegalAccessException if the class is not accessible, using the allowed access
1036 * modes.
1037 * @exception SecurityException if a security manager is present and it
1038 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1039 * @since 9
1040 */
1041 public Class<?> findClass(String targetName) throws ClassNotFoundException, IllegalAccessException {
1042 Class<?> targetClass = Class.forName(targetName, false, lookupClass.getClassLoader());
1043 return accessClass(targetClass);
1044 }
1045
1046 /**
1047 * Determines if a class can be accessed from the lookup context defined by this {@code Lookup} object. The
1048 * static initializer of the class is not run.
1049 * <p>
1050 * The lookup context here is determined by the {@linkplain #lookupClass() lookup class} and the
1051 * {@linkplain #lookupModes() lookup modes}.
1052 *
1053 * @param targetClass the class to be access-checked
1054 *
1055 * @return the class that has been access-checked
1056 *
1057 * @throws IllegalAccessException if the class is not accessible from the lookup class, using the allowed access
1058 * modes.
1059 * @exception SecurityException if a security manager is present and it
1060 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1061 * @since 9
1062 */
1063 public Class<?> accessClass(Class<?> targetClass) throws IllegalAccessException {
1064 if (!VerifyAccess.isClassAccessible(targetClass, lookupClass, allowedModes)) {
1065 throw new MemberName(targetClass).makeAccessException("access violation", this);
1066 }
1067 checkSecurityManager(targetClass, null);
1068 return targetClass;
1069 }
1070
1071 /**
1072 * Produces an early-bound method handle for a virtual method.
1073 * It will bypass checks for overriding methods on the receiver,
1074 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
1075 * instruction from within the explicitly specified {@code specialCaller}.
1076 * The type of the method handle will be that of the method,
1077 * with a suitably restricted receiver type prepended.
1078 * (The receiver type will be {@code specialCaller} or a subtype.)
1079 * The method and all its argument types must be accessible
1080 * to the lookup object.
1081 * <p>
1082 * Before method resolution,
1083 * if the explicitly specified caller class is not identical with the
1084 * lookup class, or if this lookup object does not have
1085 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
1086 * privileges, the access fails.
1087 * <p>
1088 * The returned method handle will have
1089 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1090 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1091 * <p style="font-size:smaller;">
1092 * <em>(Note: JVM internal methods named {@code "<init>"} are not visible to this API,
1093 * even though the {@code invokespecial} instruction can refer to them
1094 * in special circumstances. Use {@link #findConstructor findConstructor}
1095 * to access instance initialization methods in a safe manner.)</em>
1096 * <p><b>Example:</b>
1097 * <blockquote><pre>{@code
1098 import static java.lang.invoke.MethodHandles.*;
1099 import static java.lang.invoke.MethodType.*;
1100 ...
1101 static class Listie extends ArrayList {
1102 public String toString() { return "[wee Listie]"; }
1103 static Lookup lookup() { return MethodHandles.lookup(); }
1104 }
1105 ...
1106 // no access to constructor via invokeSpecial:
1107 MethodHandle MH_newListie = Listie.lookup()
1108 .findConstructor(Listie.class, methodType(void.class));
1109 Listie l = (Listie) MH_newListie.invokeExact();
1110 try { assertEquals("impossible", Listie.lookup().findSpecial(
1111 Listie.class, "<init>", methodType(void.class), Listie.class));
1112 } catch (NoSuchMethodException ex) { } // OK
1113 // access to super and self methods via invokeSpecial:
1114 MethodHandle MH_super = Listie.lookup().findSpecial(
1115 ArrayList.class, "toString" , methodType(String.class), Listie.class);
1116 MethodHandle MH_this = Listie.lookup().findSpecial(
1117 Listie.class, "toString" , methodType(String.class), Listie.class);
1118 MethodHandle MH_duper = Listie.lookup().findSpecial(
1119 Object.class, "toString" , methodType(String.class), Listie.class);
1120 assertEquals("[]", (String) MH_super.invokeExact(l));
1121 assertEquals(""+l, (String) MH_this.invokeExact(l));
1122 assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method
1123 try { assertEquals("inaccessible", Listie.lookup().findSpecial(
1124 String.class, "toString", methodType(String.class), Listie.class));
1125 } catch (IllegalAccessException ex) { } // OK
1126 Listie subl = new Listie() { public String toString() { return "[subclass]"; } };
1127 assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method
1128 * }</pre></blockquote>
1129 *
1130 * @param refc the class or interface from which the method is accessed
1131 * @param name the name of the method (which must not be "<init>")
1132 * @param type the type of the method, with the receiver argument omitted
1133 * @param specialCaller the proposed calling class to perform the {@code invokespecial}
1134 * @return the desired method handle
1135 * @throws NoSuchMethodException if the method does not exist
1136 * @throws IllegalAccessException if access checking fails,
1137 * or if the method is {@code static},
1138 * or if the method's variable arity modifier bit
1139 * is set and {@code asVarargsCollector} fails
1140 * @exception SecurityException if a security manager is present and it
1141 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1142 * @throws NullPointerException if any argument is null
1143 */
1144 public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,
1145 Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
1146 checkSpecialCaller(specialCaller, refc);
1147 Lookup specialLookup = this.in(specialCaller);
1148 MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type);
1149 return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerClass(method));
1150 }
1151
1152 /**
1153 * Produces a method handle giving read access to a non-static field.
1154 * The type of the method handle will have a return type of the field's
1155 * value type.
1156 * The method handle's single argument will be the instance containing
1157 * the field.
1158 * Access checking is performed immediately on behalf of the lookup class.
1159 * @param refc the class or interface from which the method is accessed
1160 * @param name the field's name
1161 * @param type the field's type
1162 * @return a method handle which can load values from the field
1163 * @throws NoSuchFieldException if the field does not exist
1164 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1165 * @exception SecurityException if a security manager is present and it
1166 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1167 * @throws NullPointerException if any argument is null
1168 * @see #findVarHandle(Class, String, Class)
1169 */
1170 public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1171 MemberName field = resolveOrFail(REF_getField, refc, name, type);
1172 return getDirectField(REF_getField, refc, field);
1173 }
1174
1175 /**
1176 * Produces a method handle giving write access to a non-static field.
1177 * The type of the method handle will have a void return type.
1178 * The method handle will take two arguments, the instance containing
1179 * the field, and the value to be stored.
1180 * The second argument will be of the field's value type.
1181 * Access checking is performed immediately on behalf of the lookup class.
1182 * @param refc the class or interface from which the method is accessed
1183 * @param name the field's name
1184 * @param type the field's type
1185 * @return a method handle which can store values into the field
1186 * @throws NoSuchFieldException if the field does not exist
1187 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1188 * @exception SecurityException if a security manager is present and it
1189 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1190 * @throws NullPointerException if any argument is null
1191 * @see #findVarHandle(Class, String, Class)
1192 */
1193 public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1194 MemberName field = resolveOrFail(REF_putField, refc, name, type);
1195 return getDirectField(REF_putField, refc, field);
1196 }
1197
1198 /**
1199 * Produces a VarHandle giving access to non-static fields of type
1200 * {@code T} declared by a receiver class of type {@code R}, supporting
1201 * shape {@code (R : T)}.
1202 * <p>
1203 * Access checking is performed immediately on behalf of the lookup
1204 * class.
1205 * <p>
1206 * Certain access modes of the returned VarHandle are unsupported under
1207 * the following conditions:
1208 * <ul>
1209 * <li>if the field is declared {@code final}, then the write, atomic
1210 * update, and numeric atomic update access modes are unsupported.
1211 * <li>if the field type is anything other than {@code byte},
1212 * {@code short}, {@code char}, {@code int} or {@code long},
1213 * {@code float}, or {@code double} then numeric atomic update
1214 * access modes are unsupported.
1215 * </ul>
1216 * <p>
1217 * If the field is declared {@code volatile} then the returned VarHandle
1218 * will override access to the field (effectively ignore the
1219 * {@code volatile} declaration) in accordance to it's specified
1220 * access modes.
1221 * <p>
1222 * If the field type is {@code float} or {@code double} then numeric
1223 * and atomic update access modes compare values using their bitwise
1224 * representation (see {@link Float#floatToRawIntBits} and
1225 * {@link Double#doubleToRawLongBits}, respectively).
1226 * @apiNote
1227 * Bitwise comparison of {@code float} values or {@code double} values,
1228 * as performed by the numeric and atomic update access modes, differ
1229 * from the primitive {@code ==} operator and the {@link Float#equals}
1230 * and {@link Double#equals} methods, specifically with respect to
1231 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
1232 * Care should be taken when performing a compare and set or a compare
1233 * and exchange operation with such values since the operation may
1234 * unexpectedly fail.
1235 * There are many possible NaN values that are considered to be
1236 * {@code NaN} in Java, although no IEEE 754 floating-point operation
1237 * provided by Java can distinguish between them. Operation failure can
1238 * occur if the expected or witness value is a NaN value and it is
1239 * transformed (perhaps in a platform specific manner) into another NaN
1240 * value, and thus has a different bitwise representation (see
1241 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
1242 * details).
1243 * The values {@code -0.0} and {@code +0.0} have different bitwise
1244 * representations but are considered equal when using the primitive
1245 * {@code ==} operator. Operation failure can occur if, for example, a
1246 * numeric algorithm computes an expected value to be say {@code -0.0}
1247 * and previously computed the witness value to be say {@code +0.0}.
1248 * @param recv the receiver class, of type {@code R}, that declares the
1249 * non-static field
1250 * @param name the field's name
1251 * @param type the field's type, of type {@code T}
1252 * @return a VarHandle giving access to non-static fields.
1253 * @throws NoSuchFieldException if the field does not exist
1254 * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
1255 * @exception SecurityException if a security manager is present and it
1256 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1257 * @throws NullPointerException if any argument is null
1258 * @since 9
1259 */
1260 public VarHandle findVarHandle(Class<?> recv, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1261 MemberName getField = resolveOrFail(REF_getField, recv, name, type);
1262 MemberName putField = resolveOrFail(REF_putField, recv, name, type);
1263 return getFieldVarHandle(REF_getField, REF_putField, recv, getField, putField);
1264 }
1265
1266 /**
1267 * Produces a method handle giving read access to a static field.
1268 * The type of the method handle will have a return type of the field's
1269 * value type.
1270 * The method handle will take no arguments.
1271 * Access checking is performed immediately on behalf of the lookup class.
1272 * <p>
1273 * If the returned method handle is invoked, the field's class will
1274 * be initialized, if it has not already been initialized.
1275 * @param refc the class or interface from which the method is accessed
1276 * @param name the field's name
1277 * @param type the field's type
1278 * @return a method handle which can load values from the field
1279 * @throws NoSuchFieldException if the field does not exist
1280 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1281 * @exception SecurityException if a security manager is present and it
1282 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1283 * @throws NullPointerException if any argument is null
1284 */
1285 public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1286 MemberName field = resolveOrFail(REF_getStatic, refc, name, type);
1287 return getDirectField(REF_getStatic, refc, field);
1288 }
1289
1290 /**
1291 * Produces a method handle giving write access to a static field.
1292 * The type of the method handle will have a void return type.
1293 * The method handle will take a single
1294 * argument, of the field's value type, the value to be stored.
1295 * Access checking is performed immediately on behalf of the lookup class.
1296 * <p>
1297 * If the returned method handle is invoked, the field's class will
1298 * be initialized, if it has not already been initialized.
1299 * @param refc the class or interface from which the method is accessed
1300 * @param name the field's name
1301 * @param type the field's type
1302 * @return a method handle which can store values into the field
1303 * @throws NoSuchFieldException if the field does not exist
1304 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1305 * @exception SecurityException if a security manager is present and it
1306 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1307 * @throws NullPointerException if any argument is null
1308 */
1309 public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1310 MemberName field = resolveOrFail(REF_putStatic, refc, name, type);
1311 return getDirectField(REF_putStatic, refc, field);
1312 }
1313
1314 /**
1315 * Produces a VarHandle giving access to a static field of type
1316 * {@code T} declared by a given declaring class, supporting shape
1317 * {@code ((empty) : T)}.
1318 * <p>
1319 * Access checking is performed immediately on behalf of the lookup
1320 * class.
1321 * <p>
1322 * If the returned VarHandle is operated on, the declaring class will be
1323 * initialized, if it has not already been initialized.
1324 * <p>
1325 * Certain access modes of the returned VarHandle are unsupported under
1326 * the following conditions:
1327 * <ul>
1328 * <li>if the field is declared {@code final}, then the write, atomic
1329 * update, and numeric atomic update access modes are unsupported.
1330 * <li>if the field type is anything other than {@code byte},
1331 * {@code short}, {@code char}, {@code int} or {@code long},
1332 * {@code float}, or {@code double}, then numeric atomic update
1333 * access modes are unsupported.
1334 * </ul>
1335 * <p>
1336 * If the field is declared {@code volatile} then the returned VarHandle
1337 * will override access to the field (effectively ignore the
1338 * {@code volatile} declaration) in accordance to it's specified
1339 * access modes.
1340 * <p>
1341 * If the field type is {@code float} or {@code double} then numeric
1342 * and atomic update access modes compare values using their bitwise
1343 * representation (see {@link Float#floatToRawIntBits} and
1344 * {@link Double#doubleToRawLongBits}, respectively).
1345 * @apiNote
1346 * Bitwise comparison of {@code float} values or {@code double} values,
1347 * as performed by the numeric and atomic update access modes, differ
1348 * from the primitive {@code ==} operator and the {@link Float#equals}
1349 * and {@link Double#equals} methods, specifically with respect to
1350 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
1351 * Care should be taken when performing a compare and set or a compare
1352 * and exchange operation with such values since the operation may
1353 * unexpectedly fail.
1354 * There are many possible NaN values that are considered to be
1355 * {@code NaN} in Java, although no IEEE 754 floating-point operation
1356 * provided by Java can distinguish between them. Operation failure can
1357 * occur if the expected or witness value is a NaN value and it is
1358 * transformed (perhaps in a platform specific manner) into another NaN
1359 * value, and thus has a different bitwise representation (see
1360 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
1361 * details).
1362 * The values {@code -0.0} and {@code +0.0} have different bitwise
1363 * representations but are considered equal when using the primitive
1364 * {@code ==} operator. Operation failure can occur if, for example, a
1365 * numeric algorithm computes an expected value to be say {@code -0.0}
1366 * and previously computed the witness value to be say {@code +0.0}.
1367 * @param decl the class that declares the static field
1368 * @param name the field's name
1369 * @param type the field's type, of type {@code T}
1370 * @return a VarHandle giving access to a static field
1371 * @throws NoSuchFieldException if the field does not exist
1372 * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
1373 * @exception SecurityException if a security manager is present and it
1374 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1375 * @throws NullPointerException if any argument is null
1376 * @since 9
1377 */
1378 public VarHandle findStaticVarHandle(Class<?> decl, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1379 MemberName getField = resolveOrFail(REF_getStatic, decl, name, type);
1380 MemberName putField = resolveOrFail(REF_putStatic, decl, name, type);
1381 return getFieldVarHandle(REF_getStatic, REF_putStatic, decl, getField, putField);
1382 }
1383
1384 /**
1385 * Produces an early-bound method handle for a non-static method.
1386 * The receiver must have a supertype {@code defc} in which a method
1387 * of the given name and type is accessible to the lookup class.
1388 * The method and all its argument types must be accessible to the lookup object.
1389 * The type of the method handle will be that of the method,
1390 * without any insertion of an additional receiver parameter.
1391 * The given receiver will be bound into the method handle,
1392 * so that every call to the method handle will invoke the
1393 * requested method on the given receiver.
1394 * <p>
1395 * The returned method handle will have
1396 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1397 * the method's variable arity modifier bit ({@code 0x0080}) is set
1398 * <em>and</em> the trailing array argument is not the only argument.
1399 * (If the trailing array argument is the only argument,
1400 * the given receiver value will be bound to it.)
1401 * <p>
1402 * This is equivalent to the following code:
1403 * <blockquote><pre>{@code
1404 import static java.lang.invoke.MethodHandles.*;
1405 import static java.lang.invoke.MethodType.*;
1406 ...
1407 MethodHandle mh0 = lookup().findVirtual(defc, name, type);
1408 MethodHandle mh1 = mh0.bindTo(receiver);
1409 mh1 = mh1.withVarargs(mh0.isVarargsCollector());
1410 return mh1;
1411 * }</pre></blockquote>
1412 * where {@code defc} is either {@code receiver.getClass()} or a super
1413 * type of that class, in which the requested method is accessible
1414 * to the lookup class.
1415 * (Note that {@code bindTo} does not preserve variable arity.)
1416 * @param receiver the object from which the method is accessed
1417 * @param name the name of the method
1418 * @param type the type of the method, with the receiver argument omitted
1419 * @return the desired method handle
1420 * @throws NoSuchMethodException if the method does not exist
1421 * @throws IllegalAccessException if access checking fails
1422 * or if the method's variable arity modifier bit
1423 * is set and {@code asVarargsCollector} fails
1424 * @exception SecurityException if a security manager is present and it
1425 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1426 * @throws NullPointerException if any argument is null
1427 * @see MethodHandle#bindTo
1428 * @see #findVirtual
1429 */
1430 public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1431 Class<? extends Object> refc = receiver.getClass(); // may get NPE
1432 MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type);
1433 MethodHandle mh = getDirectMethodNoRestrict(REF_invokeSpecial, refc, method, findBoundCallerClass(method));
1434 return mh.bindArgumentL(0, receiver).setVarargs(method);
1435 }
1436
1437 /**
1438 * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
1439 * to <i>m</i>, if the lookup class has permission.
1440 * If <i>m</i> is non-static, the receiver argument is treated as an initial argument.
1441 * If <i>m</i> is virtual, overriding is respected on every call.
1442 * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped.
1443 * The type of the method handle will be that of the method,
1444 * with the receiver type prepended (but only if it is non-static).
1445 * If the method's {@code accessible} flag is not set,
1446 * access checking is performed immediately on behalf of the lookup class.
1447 * If <i>m</i> is not public, do not share the resulting handle with untrusted parties.
1448 * <p>
1449 * The returned method handle will have
1450 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1451 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1452 * <p>
1453 * If <i>m</i> is static, and
1454 * if the returned method handle is invoked, the method's class will
1455 * be initialized, if it has not already been initialized.
1456 * @param m the reflected method
1457 * @return a method handle which can invoke the reflected method
1458 * @throws IllegalAccessException if access checking fails
1459 * or if the method's variable arity modifier bit
1460 * is set and {@code asVarargsCollector} fails
1461 * @throws NullPointerException if the argument is null
1462 */
1463 public MethodHandle unreflect(Method m) throws IllegalAccessException {
1464 if (m.getDeclaringClass() == MethodHandle.class) {
1465 MethodHandle mh = unreflectForMH(m);
1466 if (mh != null) return mh;
1467 }
1468 if (m.getDeclaringClass() == VarHandle.class) {
1469 MethodHandle mh = unreflectForVH(m);
1470 if (mh != null) return mh;
1471 }
1472 MemberName method = new MemberName(m);
1473 byte refKind = method.getReferenceKind();
1474 if (refKind == REF_invokeSpecial)
1475 refKind = REF_invokeVirtual;
1476 assert(method.isMethod());
1477 Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this;
1478 return lookup.getDirectMethodNoSecurityManager(refKind, method.getDeclaringClass(), method, findBoundCallerClass(method));
1479 }
1480 private MethodHandle unreflectForMH(Method m) {
1481 // these names require special lookups because they throw UnsupportedOperationException
1482 if (MemberName.isMethodHandleInvokeName(m.getName()))
1483 return MethodHandleImpl.fakeMethodHandleInvoke(new MemberName(m));
1484 return null;
1485 }
1486 private MethodHandle unreflectForVH(Method m) {
1487 // these names require special lookups because they throw UnsupportedOperationException
1488 if (MemberName.isVarHandleMethodInvokeName(m.getName()))
1489 return MethodHandleImpl.fakeVarHandleInvoke(new MemberName(m));
1490 return null;
1491 }
1492
1493 /**
1494 * Produces a method handle for a reflected method.
1495 * It will bypass checks for overriding methods on the receiver,
1496 * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
1497 * instruction from within the explicitly specified {@code specialCaller}.
1498 * The type of the method handle will be that of the method,
1499 * with a suitably restricted receiver type prepended.
1500 * (The receiver type will be {@code specialCaller} or a subtype.)
1501 * If the method's {@code accessible} flag is not set,
1502 * access checking is performed immediately on behalf of the lookup class,
1503 * as if {@code invokespecial} instruction were being linked.
1504 * <p>
1505 * Before method resolution,
1506 * if the explicitly specified caller class is not identical with the
1507 * lookup class, or if this lookup object does not have
1508 * <a href="MethodHandles.Lookup.html#privacc">private access</a>
1509 * privileges, the access fails.
1510 * <p>
1511 * The returned method handle will have
1512 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1513 * the method's variable arity modifier bit ({@code 0x0080}) is set.
1514 * @param m the reflected method
1515 * @param specialCaller the class nominally calling the method
1516 * @return a method handle which can invoke the reflected method
1517 * @throws IllegalAccessException if access checking fails,
1518 * or if the method is {@code static},
1519 * or if the method's variable arity modifier bit
1520 * is set and {@code asVarargsCollector} fails
1521 * @throws NullPointerException if any argument is null
1522 */
1523 public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException {
1524 checkSpecialCaller(specialCaller, null);
1525 Lookup specialLookup = this.in(specialCaller);
1526 MemberName method = new MemberName(m, true);
1527 assert(method.isMethod());
1528 // ignore m.isAccessible: this is a new kind of access
1529 return specialLookup.getDirectMethodNoSecurityManager(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerClass(method));
1530 }
1531
1532 /**
1533 * Produces a method handle for a reflected constructor.
1534 * The type of the method handle will be that of the constructor,
1535 * with the return type changed to the declaring class.
1536 * The method handle will perform a {@code newInstance} operation,
1537 * creating a new instance of the constructor's class on the
1538 * arguments passed to the method handle.
1539 * <p>
1540 * If the constructor's {@code accessible} flag is not set,
1541 * access checking is performed immediately on behalf of the lookup class.
1542 * <p>
1543 * The returned method handle will have
1544 * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
1545 * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
1546 * <p>
1547 * If the returned method handle is invoked, the constructor's class will
1548 * be initialized, if it has not already been initialized.
1549 * @param c the reflected constructor
1550 * @return a method handle which can invoke the reflected constructor
1551 * @throws IllegalAccessException if access checking fails
1552 * or if the method's variable arity modifier bit
1553 * is set and {@code asVarargsCollector} fails
1554 * @throws NullPointerException if the argument is null
1555 */
1556 public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException {
1557 MemberName ctor = new MemberName(c);
1558 assert(ctor.isConstructor());
1559 Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this;
1560 return lookup.getDirectConstructorNoSecurityManager(ctor.getDeclaringClass(), ctor);
1561 }
1562
1563 /**
1564 * Produces a method handle giving read access to a reflected field.
1565 * The type of the method handle will have a return type of the field's
1566 * value type.
1567 * If the field is static, the method handle will take no arguments.
1568 * Otherwise, its single argument will be the instance containing
1569 * the field.
1570 * If the field's {@code accessible} flag is not set,
1571 * access checking is performed immediately on behalf of the lookup class.
1572 * <p>
1573 * If the field is static, and
1574 * if the returned method handle is invoked, the field's class will
1575 * be initialized, if it has not already been initialized.
1576 * @param f the reflected field
1577 * @return a method handle which can load values from the reflected field
1578 * @throws IllegalAccessException if access checking fails
1579 * @throws NullPointerException if the argument is null
1580 */
1581 public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
1582 return unreflectField(f, false);
1583 }
1584 private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException {
1585 MemberName field = new MemberName(f, isSetter);
1586 assert(isSetter
1587 ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind())
1588 : MethodHandleNatives.refKindIsGetter(field.getReferenceKind()));
1589 Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this;
1590 return lookup.getDirectFieldNoSecurityManager(field.getReferenceKind(), f.getDeclaringClass(), field);
1591 }
1592
1593 /**
1594 * Produces a method handle giving write access to a reflected field.
1595 * The type of the method handle will have a void return type.
1596 * If the field is static, the method handle will take a single
1597 * argument, of the field's value type, the value to be stored.
1598 * Otherwise, the two arguments will be the instance containing
1599 * the field, and the value to be stored.
1600 * If the field's {@code accessible} flag is not set,
1601 * access checking is performed immediately on behalf of the lookup class.
1602 * <p>
1603 * If the field is static, and
1604 * if the returned method handle is invoked, the field's class will
1605 * be initialized, if it has not already been initialized.
1606 * @param f the reflected field
1607 * @return a method handle which can store values into the reflected field
1608 * @throws IllegalAccessException if access checking fails
1609 * @throws NullPointerException if the argument is null
1610 */
1611 public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
1612 return unreflectField(f, true);
1613 }
1614
1615 /**
1616 * Produces a VarHandle that accesses fields of type {@code T} declared
1617 * by a class of type {@code R}, as described by the given reflected
1618 * field.
1619 * If the field is non-static the VarHandle supports a shape of
1620 * {@code (R : T)}, otherwise supports a shape of {@code ((empty) : T)}.
1621 * <p>
1622 * Access checking is performed immediately on behalf of the lookup
1623 * class, regardless of the value of the field's {@code accessible}
1624 * flag.
1625 * <p>
1626 * If the field is static, and if the returned VarHandle is operated
1627 * on, the field's declaring class will be initialized, if it has not
1628 * already been initialized.
1629 * <p>
1630 * Certain access modes of the returned VarHandle are unsupported under
1631 * the following conditions:
1632 * <ul>
1633 * <li>if the field is declared {@code final}, then the write, atomic
1634 * update, and numeric atomic update access modes are unsupported.
1635 * <li>if the field type is anything other than {@code byte},
1636 * {@code short}, {@code char}, {@code int} or {@code long},
1637 * {@code float}, or {@code double} then numeric atomic update
1638 * access modes are unsupported.
1639 * </ul>
1640 * <p>
1641 * If the field is declared {@code volatile} then the returned VarHandle
1642 * will override access to the field (effectively ignore the
1643 * {@code volatile} declaration) in accordance to it's specified
1644 * access modes.
1645 * <p>
1646 * If the field type is {@code float} or {@code double} then numeric
1647 * and atomic update access modes compare values using their bitwise
1648 * representation (see {@link Float#floatToRawIntBits} and
1649 * {@link Double#doubleToRawLongBits}, respectively).
1650 * @apiNote
1651 * Bitwise comparison of {@code float} values or {@code double} values,
1652 * as performed by the numeric and atomic update access modes, differ
1653 * from the primitive {@code ==} operator and the {@link Float#equals}
1654 * and {@link Double#equals} methods, specifically with respect to
1655 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
1656 * Care should be taken when performing a compare and set or a compare
1657 * and exchange operation with such values since the operation may
1658 * unexpectedly fail.
1659 * There are many possible NaN values that are considered to be
1660 * {@code NaN} in Java, although no IEEE 754 floating-point operation
1661 * provided by Java can distinguish between them. Operation failure can
1662 * occur if the expected or witness value is a NaN value and it is
1663 * transformed (perhaps in a platform specific manner) into another NaN
1664 * value, and thus has a different bitwise representation (see
1665 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
1666 * details).
1667 * The values {@code -0.0} and {@code +0.0} have different bitwise
1668 * representations but are considered equal when using the primitive
1669 * {@code ==} operator. Operation failure can occur if, for example, a
1670 * numeric algorithm computes an expected value to be say {@code -0.0}
1671 * and previously computed the witness value to be say {@code +0.0}.
1672 * @param f the reflected field, with a field of type {@code T}, and
1673 * a declaring class of type {@code R}
1674 * @return a VarHandle giving access to non-static fields or a static
1675 * field
1676 * @throws IllegalAccessException if access checking fails
1677 * @throws NullPointerException if the argument is null
1678 * @since 9
1679 */
1680 public VarHandle unreflectVarHandle(Field f) throws IllegalAccessException {
1681 MemberName getField = new MemberName(f, false);
1682 MemberName putField = new MemberName(f, true);
1683 return getFieldVarHandleNoSecurityManager(getField.getReferenceKind(), putField.getReferenceKind(),
1684 f.getDeclaringClass(), getField, putField);
1685 }
1686
1687 /**
1688 * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
1689 * created by this lookup object or a similar one.
1690 * Security and access checks are performed to ensure that this lookup object
1691 * is capable of reproducing the target method handle.
1692 * This means that the cracking may fail if target is a direct method handle
1693 * but was created by an unrelated lookup object.
1694 * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a>
1695 * and was created by a lookup object for a different class.
1696 * @param target a direct method handle to crack into symbolic reference components
1697 * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object
1698 * @exception SecurityException if a security manager is present and it
1699 * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
1700 * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails
1701 * @exception NullPointerException if the target is {@code null}
1702 * @see MethodHandleInfo
1703 * @since 1.8
1704 */
1705 public MethodHandleInfo revealDirect(MethodHandle target) {
1706 MemberName member = target.internalMemberName();
1707 if (member == null || (!member.isResolved() &&
1708 !member.isMethodHandleInvoke() &&
1709 !member.isVarHandleMethodInvoke()))
1710 throw newIllegalArgumentException("not a direct method handle");
1711 Class<?> defc = member.getDeclaringClass();
1712 byte refKind = member.getReferenceKind();
1713 assert(MethodHandleNatives.refKindIsValid(refKind));
1714 if (refKind == REF_invokeSpecial && !target.isInvokeSpecial())
1715 // Devirtualized method invocation is usually formally virtual.
1716 // To avoid creating extra MemberName objects for this common case,
1717 // we encode this extra degree of freedom using MH.isInvokeSpecial.
1718 refKind = REF_invokeVirtual;
1719 if (refKind == REF_invokeVirtual && defc.isInterface())
1720 // Symbolic reference is through interface but resolves to Object method (toString, etc.)
1721 refKind = REF_invokeInterface;
1722 // Check SM permissions and member access before cracking.
1723 try {
1724 checkAccess(refKind, defc, member);
1725 checkSecurityManager(defc, member);
1726 } catch (IllegalAccessException ex) {
1727 throw new IllegalArgumentException(ex);
1728 }
1729 if (allowedModes != TRUSTED && member.isCallerSensitive()) {
1730 Class<?> callerClass = target.internalCallerClass();
1731 if (!hasPrivateAccess() || callerClass != lookupClass())
1732 throw new IllegalArgumentException("method handle is caller sensitive: "+callerClass);
1733 }
1734 // Produce the handle to the results.
1735 return new InfoFromMemberName(this, member, refKind);
1736 }
1737
1738 /// Helper methods, all package-private.
1739
1740 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
1741 checkSymbolicClass(refc); // do this before attempting to resolve
1742 Objects.requireNonNull(name);
1743 Objects.requireNonNull(type);
1744 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
1745 NoSuchFieldException.class);
1746 }
1747
1748 MemberName resolveOrFail(byte refKind, Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
1749 checkSymbolicClass(refc); // do this before attempting to resolve
1750 Objects.requireNonNull(name);
1751 Objects.requireNonNull(type);
1752 checkMethodName(refKind, name); // NPE check on name
1753 return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(),
1754 NoSuchMethodException.class);
1755 }
1756
1757 MemberName resolveOrFail(byte refKind, MemberName member) throws ReflectiveOperationException {
1758 checkSymbolicClass(member.getDeclaringClass()); // do this before attempting to resolve
1759 Objects.requireNonNull(member.getName());
1760 Objects.requireNonNull(member.getType());
1761 return IMPL_NAMES.resolveOrFail(refKind, member, lookupClassOrNull(),
1762 ReflectiveOperationException.class);
1763 }
1764
1765 void checkSymbolicClass(Class<?> refc) throws IllegalAccessException {
1766 Objects.requireNonNull(refc);
1767 Class<?> caller = lookupClassOrNull();
1768 if (caller != null && !VerifyAccess.isClassAccessible(refc, caller, allowedModes))
1769 throw new MemberName(refc).makeAccessException("symbolic reference class is not accessible", this);
1770 }
1771
1772 /** Check name for an illegal leading "<" character. */
1773 void checkMethodName(byte refKind, String name) throws NoSuchMethodException {
1774 if (name.startsWith("<") && refKind != REF_newInvokeSpecial)
1775 throw new NoSuchMethodException("illegal method name: "+name);
1776 }
1777
1778
1779 /**
1780 * Find my trustable caller class if m is a caller sensitive method.
1781 * If this lookup object has private access, then the caller class is the lookupClass.
1782 * Otherwise, if m is caller-sensitive, throw IllegalAccessException.
1783 */
1784 Class<?> findBoundCallerClass(MemberName m) throws IllegalAccessException {
1785 Class<?> callerClass = null;
1786 if (MethodHandleNatives.isCallerSensitive(m)) {
1787 // Only lookups with private access are allowed to resolve caller-sensitive methods
1788 if (hasPrivateAccess()) {
1789 callerClass = lookupClass;
1790 } else {
1791 throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object");
1792 }
1793 }
1794 return callerClass;
1795 }
1796
1797 private boolean hasPrivateAccess() {
1798 return (allowedModes & PRIVATE) != 0;
1799 }
1800
1801 /**
1802 * Perform necessary <a href="MethodHandles.Lookup.html#secmgr">access checks</a>.
1803 * Determines a trustable caller class to compare with refc, the symbolic reference class.
1804 * If this lookup object has private access, then the caller class is the lookupClass.
1805 */
1806 void checkSecurityManager(Class<?> refc, MemberName m) {
1807 SecurityManager smgr = System.getSecurityManager();
1808 if (smgr == null) return;
1809 if (allowedModes == TRUSTED) return;
1810
1811 // Step 1:
1812 boolean fullPowerLookup = hasPrivateAccess();
1813 if (!fullPowerLookup ||
1814 !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) {
1815 ReflectUtil.checkPackageAccess(refc);
1816 }
1817
1818 if (m == null) { // findClass or accessClass
1819 // Step 2b:
1820 if (!fullPowerLookup) {
1821 smgr.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
1822 }
1823 return;
1824 }
1825
1826 // Step 2a:
1827 if (m.isPublic()) return;
1828 if (!fullPowerLookup) {
1829 smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION);
1830 }
1831
1832 // Step 3:
1833 Class<?> defc = m.getDeclaringClass();
1834 if (!fullPowerLookup && defc != refc) {
1835 ReflectUtil.checkPackageAccess(defc);
1836 }
1837 }
1838
1839 void checkMethod(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
1840 boolean wantStatic = (refKind == REF_invokeStatic);
1841 String message;
1842 if (m.isConstructor())
1843 message = "expected a method, not a constructor";
1844 else if (!m.isMethod())
1845 message = "expected a method";
1846 else if (wantStatic != m.isStatic())
1847 message = wantStatic ? "expected a static method" : "expected a non-static method";
1848 else
1849 { checkAccess(refKind, refc, m); return; }
1850 throw m.makeAccessException(message, this);
1851 }
1852
1853 void checkField(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
1854 boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind);
1855 String message;
1856 if (wantStatic != m.isStatic())
1857 message = wantStatic ? "expected a static field" : "expected a non-static field";
1858 else
1859 { checkAccess(refKind, refc, m); return; }
1860 throw m.makeAccessException(message, this);
1861 }
1862
1863 /** Check public/protected/private bits on the symbolic reference class and its member. */
1864 void checkAccess(byte refKind, Class<?> refc, MemberName m) throws IllegalAccessException {
1865 assert(m.referenceKindIsConsistentWith(refKind) &&
1866 MethodHandleNatives.refKindIsValid(refKind) &&
1867 (MethodHandleNatives.refKindIsField(refKind) == m.isField()));
1868 int allowedModes = this.allowedModes;
1869 if (allowedModes == TRUSTED) return;
1870 int mods = m.getModifiers();
1871 if (Modifier.isProtected(mods) &&
1872 refKind == REF_invokeVirtual &&
1873 m.getDeclaringClass() == Object.class &&
1874 m.getName().equals("clone") &&
1875 refc.isArray()) {
1876 // The JVM does this hack also.
1877 // (See ClassVerifier::verify_invoke_instructions
1878 // and LinkResolver::check_method_accessability.)
1879 // Because the JVM does not allow separate methods on array types,
1880 // there is no separate method for int[].clone.
1881 // All arrays simply inherit Object.clone.
1882 // But for access checking logic, we make Object.clone
1883 // (normally protected) appear to be public.
1884 // Later on, when the DirectMethodHandle is created,
1885 // its leading argument will be restricted to the
1886 // requested array type.
1887 // N.B. The return type is not adjusted, because
1888 // that is *not* the bytecode behavior.
1889 mods ^= Modifier.PROTECTED | Modifier.PUBLIC;
1890 }
1891 if (Modifier.isProtected(mods) && refKind == REF_newInvokeSpecial) {
1892 // cannot "new" a protected ctor in a different package
1893 mods ^= Modifier.PROTECTED;
1894 }
1895 if (Modifier.isFinal(mods) &&
1896 MethodHandleNatives.refKindIsSetter(refKind))
1897 throw m.makeAccessException("unexpected set of a final field", this);
1898 int requestedModes = fixmods(mods); // adjust 0 => PACKAGE
1899 if ((requestedModes & allowedModes) != 0) {
1900 if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
1901 mods, lookupClass(), allowedModes))
1902 return;
1903 } else {
1904 // Protected members can also be checked as if they were package-private.
1905 if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
1906 && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
1907 return;
1908 }
1909 throw m.makeAccessException(accessFailedMessage(refc, m), this);
1910 }
1911
1912 String accessFailedMessage(Class<?> refc, MemberName m) {
1913 Class<?> defc = m.getDeclaringClass();
1914 int mods = m.getModifiers();
1915 // check the class first:
1916 boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
1917 (defc == refc ||
1918 Modifier.isPublic(refc.getModifiers())));
1919 if (!classOK && (allowedModes & PACKAGE) != 0) {
1920 classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), ALL_MODES) &&
1921 (defc == refc ||
1922 VerifyAccess.isClassAccessible(refc, lookupClass(), ALL_MODES)));
1923 }
1924 if (!classOK)
1925 return "class is not public";
1926 if (Modifier.isPublic(mods))
1927 return "access to public member failed"; // (how?, module not readable?)
1928 if (Modifier.isPrivate(mods))
1929 return "member is private";
1930 if (Modifier.isProtected(mods))
1931 return "member is protected";
1932 return "member is private to package";
1933 }
1934
1935 private static final boolean ALLOW_NESTMATE_ACCESS = false;
1936
1937 private void checkSpecialCaller(Class<?> specialCaller, Class<?> refc) throws IllegalAccessException {
1938 int allowedModes = this.allowedModes;
1939 if (allowedModes == TRUSTED) return;
1940 if (!hasPrivateAccess()
1941 || (specialCaller != lookupClass()
1942 // ensure non-abstract methods in superinterfaces can be special-invoked
1943 && !(refc != null && refc.isInterface() && refc.isAssignableFrom(specialCaller))
1944 && !(ALLOW_NESTMATE_ACCESS &&
1945 VerifyAccess.isSamePackageMember(specialCaller, lookupClass()))))
1946 throw new MemberName(specialCaller).
1947 makeAccessException("no private access for invokespecial", this);
1948 }
1949
1950 private boolean restrictProtectedReceiver(MemberName method) {
1951 // The accessing class only has the right to use a protected member
1952 // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc.
1953 if (!method.isProtected() || method.isStatic()
1954 || allowedModes == TRUSTED
1955 || method.getDeclaringClass() == lookupClass()
1956 || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass())
1957 || (ALLOW_NESTMATE_ACCESS &&
1958 VerifyAccess.isSamePackageMember(method.getDeclaringClass(), lookupClass())))
1959 return false;
1960 return true;
1961 }
1962 private MethodHandle restrictReceiver(MemberName method, DirectMethodHandle mh, Class<?> caller) throws IllegalAccessException {
1963 assert(!method.isStatic());
1964 // receiver type of mh is too wide; narrow to caller
1965 if (!method.getDeclaringClass().isAssignableFrom(caller)) {
1966 throw method.makeAccessException("caller class must be a subclass below the method", caller);
1967 }
1968 MethodType rawType = mh.type();
1969 if (rawType.parameterType(0) == caller) return mh;
1970 MethodType narrowType = rawType.changeParameterType(0, caller);
1971 assert(!mh.isVarargsCollector()); // viewAsType will lose varargs-ness
1972 assert(mh.viewAsTypeChecks(narrowType, true));
1973 return mh.copyWith(narrowType, mh.form);
1974 }
1975
1976 /** Check access and get the requested method. */
1977 private MethodHandle getDirectMethod(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
1978 final boolean doRestrict = true;
1979 final boolean checkSecurity = true;
1980 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
1981 }
1982 /** Check access and get the requested method, eliding receiver narrowing rules. */
1983 private MethodHandle getDirectMethodNoRestrict(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
1984 final boolean doRestrict = false;
1985 final boolean checkSecurity = true;
1986 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
1987 }
1988 /** Check access and get the requested method, eliding security manager checks. */
1989 private MethodHandle getDirectMethodNoSecurityManager(byte refKind, Class<?> refc, MemberName method, Class<?> callerClass) throws IllegalAccessException {
1990 final boolean doRestrict = true;
1991 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
1992 return getDirectMethodCommon(refKind, refc, method, checkSecurity, doRestrict, callerClass);
1993 }
1994 /** Common code for all methods; do not call directly except from immediately above. */
1995 private MethodHandle getDirectMethodCommon(byte refKind, Class<?> refc, MemberName method,
1996 boolean checkSecurity,
1997 boolean doRestrict, Class<?> callerClass) throws IllegalAccessException {
1998 checkMethod(refKind, refc, method);
1999 // Optionally check with the security manager; this isn't needed for unreflect* calls.
2000 if (checkSecurity)
2001 checkSecurityManager(refc, method);
2002 assert(!method.isMethodHandleInvoke());
2003
2004 if (refKind == REF_invokeSpecial &&
2005 refc != lookupClass() &&
2006 !refc.isInterface() &&
2007 refc != lookupClass().getSuperclass() &&
2008 refc.isAssignableFrom(lookupClass())) {
2009 assert(!method.getName().equals("<init>")); // not this code path
2010 // Per JVMS 6.5, desc. of invokespecial instruction:
2011 // If the method is in a superclass of the LC,
2012 // and if our original search was above LC.super,
2013 // repeat the search (symbolic lookup) from LC.super
2014 // and continue with the direct superclass of that class,
2015 // and so forth, until a match is found or no further superclasses exist.
2016 // FIXME: MemberName.resolve should handle this instead.
2017 Class<?> refcAsSuper = lookupClass();
2018 MemberName m2;
2019 do {
2020 refcAsSuper = refcAsSuper.getSuperclass();
2021 m2 = new MemberName(refcAsSuper,
2022 method.getName(),
2023 method.getMethodType(),
2024 REF_invokeSpecial);
2025 m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull());
2026 } while (m2 == null && // no method is found yet
2027 refc != refcAsSuper); // search up to refc
2028 if (m2 == null) throw new InternalError(method.toString());
2029 method = m2;
2030 refc = refcAsSuper;
2031 // redo basic checks
2032 checkMethod(refKind, refc, method);
2033 }
2034
2035 DirectMethodHandle dmh = DirectMethodHandle.make(refKind, refc, method);
2036 MethodHandle mh = dmh;
2037 // Optionally narrow the receiver argument to refc using restrictReceiver.
2038 if (doRestrict &&
2039 (refKind == REF_invokeSpecial ||
2040 (MethodHandleNatives.refKindHasReceiver(refKind) &&
2041 restrictProtectedReceiver(method)))) {
2042 mh = restrictReceiver(method, dmh, lookupClass());
2043 }
2044 mh = maybeBindCaller(method, mh, callerClass);
2045 mh = mh.setVarargs(method);
2046 return mh;
2047 }
2048 private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh,
2049 Class<?> callerClass)
2050 throws IllegalAccessException {
2051 if (allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method))
2052 return mh;
2053 Class<?> hostClass = lookupClass;
2054 if (!hasPrivateAccess()) // caller must have private access
2055 hostClass = callerClass; // callerClass came from a security manager style stack walk
2056 MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, hostClass);
2057 // Note: caller will apply varargs after this step happens.
2058 return cbmh;
2059 }
2060 /** Check access and get the requested field. */
2061 private MethodHandle getDirectField(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
2062 final boolean checkSecurity = true;
2063 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
2064 }
2065 /** Check access and get the requested field, eliding security manager checks. */
2066 private MethodHandle getDirectFieldNoSecurityManager(byte refKind, Class<?> refc, MemberName field) throws IllegalAccessException {
2067 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
2068 return getDirectFieldCommon(refKind, refc, field, checkSecurity);
2069 }
2070 /** Common code for all fields; do not call directly except from immediately above. */
2071 private MethodHandle getDirectFieldCommon(byte refKind, Class<?> refc, MemberName field,
2072 boolean checkSecurity) throws IllegalAccessException {
2073 checkField(refKind, refc, field);
2074 // Optionally check with the security manager; this isn't needed for unreflect* calls.
2075 if (checkSecurity)
2076 checkSecurityManager(refc, field);
2077 DirectMethodHandle dmh = DirectMethodHandle.make(refc, field);
2078 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) &&
2079 restrictProtectedReceiver(field));
2080 if (doRestrict)
2081 return restrictReceiver(field, dmh, lookupClass());
2082 return dmh;
2083 }
2084 private VarHandle getFieldVarHandle(byte getRefKind, byte putRefKind,
2085 Class<?> refc, MemberName getField, MemberName putField)
2086 throws IllegalAccessException {
2087 final boolean checkSecurity = true;
2088 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
2089 }
2090 private VarHandle getFieldVarHandleNoSecurityManager(byte getRefKind, byte putRefKind,
2091 Class<?> refc, MemberName getField, MemberName putField)
2092 throws IllegalAccessException {
2093 final boolean checkSecurity = false;
2094 return getFieldVarHandleCommon(getRefKind, putRefKind, refc, getField, putField, checkSecurity);
2095 }
2096 private VarHandle getFieldVarHandleCommon(byte getRefKind, byte putRefKind,
2097 Class<?> refc, MemberName getField, MemberName putField,
2098 boolean checkSecurity) throws IllegalAccessException {
2099 assert getField.isStatic() == putField.isStatic();
2100 assert getField.isGetter() && putField.isSetter();
2101 assert MethodHandleNatives.refKindIsStatic(getRefKind) == MethodHandleNatives.refKindIsStatic(putRefKind);
2102 assert MethodHandleNatives.refKindIsGetter(getRefKind) && MethodHandleNatives.refKindIsSetter(putRefKind);
2103
2104 checkField(getRefKind, refc, getField);
2105 if (checkSecurity)
2106 checkSecurityManager(refc, getField);
2107
2108 if (!putField.isFinal()) {
2109 // A VarHandle does not support updates to final fields, any
2110 // such VarHandle to a final field will be read-only and
2111 // therefore the following write-based accessibility checks are
2112 // only required for non-final fields
2113 checkField(putRefKind, refc, putField);
2114 if (checkSecurity)
2115 checkSecurityManager(refc, putField);
2116 }
2117
2118 boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(getRefKind) &&
2119 restrictProtectedReceiver(getField));
2120 if (doRestrict) {
2121 assert !getField.isStatic();
2122 // receiver type of VarHandle is too wide; narrow to caller
2123 if (!getField.getDeclaringClass().isAssignableFrom(lookupClass())) {
2124 throw getField.makeAccessException("caller class must be a subclass below the method", lookupClass());
2125 }
2126 refc = lookupClass();
2127 }
2128 return VarHandles.makeFieldHandle(getField, refc, getField.getFieldType(), this.allowedModes == TRUSTED);
2129 }
2130 /** Check access and get the requested constructor. */
2131 private MethodHandle getDirectConstructor(Class<?> refc, MemberName ctor) throws IllegalAccessException {
2132 final boolean checkSecurity = true;
2133 return getDirectConstructorCommon(refc, ctor, checkSecurity);
2134 }
2135 /** Check access and get the requested constructor, eliding security manager checks. */
2136 private MethodHandle getDirectConstructorNoSecurityManager(Class<?> refc, MemberName ctor) throws IllegalAccessException {
2137 final boolean checkSecurity = false; // not needed for reflection or for linking CONSTANT_MH constants
2138 return getDirectConstructorCommon(refc, ctor, checkSecurity);
2139 }
2140 /** Common code for all constructors; do not call directly except from immediately above. */
2141 private MethodHandle getDirectConstructorCommon(Class<?> refc, MemberName ctor,
2142 boolean checkSecurity) throws IllegalAccessException {
2143 assert(ctor.isConstructor());
2144 checkAccess(REF_newInvokeSpecial, refc, ctor);
2145 // Optionally check with the security manager; this isn't needed for unreflect* calls.
2146 if (checkSecurity)
2147 checkSecurityManager(refc, ctor);
2148 assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here
2149 return DirectMethodHandle.make(ctor).setVarargs(ctor);
2150 }
2151
2152 /** Hook called from the JVM (via MethodHandleNatives) to link MH constants:
2153 */
2154 /*non-public*/
2155 MethodHandle linkMethodHandleConstant(byte refKind, Class<?> defc, String name, Object type) throws ReflectiveOperationException {
2156 if (!(type instanceof Class || type instanceof MethodType))
2157 throw new InternalError("unresolved MemberName");
2158 MemberName member = new MemberName(refKind, defc, name, type);
2159 MethodHandle mh = LOOKASIDE_TABLE.get(member);
2160 if (mh != null) {
2161 checkSymbolicClass(defc);
2162 return mh;
2163 }
2164 // Treat MethodHandle.invoke and invokeExact specially.
2165 if (defc == MethodHandle.class && refKind == REF_invokeVirtual) {
2166 mh = findVirtualForMH(member.getName(), member.getMethodType());
2167 if (mh != null) {
2168 return mh;
2169 }
2170 }
2171 MemberName resolved = resolveOrFail(refKind, member);
2172 mh = getDirectMethodForConstant(refKind, defc, resolved);
2173 if (mh instanceof DirectMethodHandle
2174 && canBeCached(refKind, defc, resolved)) {
2175 MemberName key = mh.internalMemberName();
2176 if (key != null) {
2177 key = key.asNormalOriginal();
2178 }
2179 if (member.equals(key)) { // better safe than sorry
2180 LOOKASIDE_TABLE.put(key, (DirectMethodHandle) mh);
2181 }
2182 }
2183 return mh;
2184 }
2185 private
2186 boolean canBeCached(byte refKind, Class<?> defc, MemberName member) {
2187 if (refKind == REF_invokeSpecial) {
2188 return false;
2189 }
2190 if (!Modifier.isPublic(defc.getModifiers()) ||
2191 !Modifier.isPublic(member.getDeclaringClass().getModifiers()) ||
2192 !member.isPublic() ||
2193 member.isCallerSensitive()) {
2194 return false;
2195 }
2196 ClassLoader loader = defc.getClassLoader();
2197 if (!jdk.internal.misc.VM.isSystemDomainLoader(loader)) {
2198 ClassLoader sysl = ClassLoader.getSystemClassLoader();
2199 boolean found = false;
2200 while (sysl != null) {
2201 if (loader == sysl) { found = true; break; }
2202 sysl = sysl.getParent();
2203 }
2204 if (!found) {
2205 return false;
2206 }
2207 }
2208 try {
2209 MemberName resolved2 = publicLookup().resolveOrFail(refKind,
2210 new MemberName(refKind, defc, member.getName(), member.getType()));
2211 checkSecurityManager(defc, resolved2);
2212 } catch (ReflectiveOperationException | SecurityException ex) {
2213 return false;
2214 }
2215 return true;
2216 }
2217 private
2218 MethodHandle getDirectMethodForConstant(byte refKind, Class<?> defc, MemberName member)
2219 throws ReflectiveOperationException {
2220 if (MethodHandleNatives.refKindIsField(refKind)) {
2221 return getDirectFieldNoSecurityManager(refKind, defc, member);
2222 } else if (MethodHandleNatives.refKindIsMethod(refKind)) {
2223 return getDirectMethodNoSecurityManager(refKind, defc, member, lookupClass);
2224 } else if (refKind == REF_newInvokeSpecial) {
2225 return getDirectConstructorNoSecurityManager(defc, member);
2226 }
2227 // oops
2228 throw newIllegalArgumentException("bad MethodHandle constant #"+member);
2229 }
2230
2231 static ConcurrentHashMap<MemberName, DirectMethodHandle> LOOKASIDE_TABLE = new ConcurrentHashMap<>();
2232 }
2233
2234 /**
2235 * Helper class used to lazily create PUBLIC_LOOKUP with a lookup class
2236 * in an <em>unnamed module</em>.
2237 *
2238 * @see Lookup#publicLookup
2239 */
2240 private static class LookupHelper {
2241 private static final String UNNAMED = "Unnamed";
2242 private static final String OBJECT = "java/lang/Object";
2243
2244 private static Class<?> createClass() {
2245 try {
2246 ClassWriter cw = new ClassWriter(0);
2247 cw.visit(Opcodes.V1_8,
2248 Opcodes.ACC_FINAL + Opcodes.ACC_SUPER,
2249 UNNAMED,
2250 null,
2251 OBJECT,
2252 null);
2253 cw.visitSource(UNNAMED, null);
2254 cw.visitEnd();
2255 byte[] bytes = cw.toByteArray();
2256 ClassLoader loader = new ClassLoader(null) {
2257 @Override
2258 protected Class<?> findClass(String cn) throws ClassNotFoundException {
2259 if (cn.equals(UNNAMED))
2260 return super.defineClass(UNNAMED, bytes, 0, bytes.length);
2261 throw new ClassNotFoundException(cn);
2262 }
2263 };
2264 return loader.loadClass(UNNAMED);
2265 } catch (Exception e) {
2266 throw new InternalError(e);
2267 }
2268 }
2269
2270 private static final Class<?> PUBLIC_LOOKUP_CLASS = createClass();
2271
2272 /**
2273 * Lookup that is trusted minimally. It can only be used to create
2274 * method handles to publicly accessible members in exported packages.
2275 *
2276 * @see MethodHandles#publicLookup
2277 */
2278 static final Lookup PUBLIC_LOOKUP = new Lookup(PUBLIC_LOOKUP_CLASS, Lookup.PUBLIC);
2279 }
2280
2281 /**
2282 * Produces a method handle constructing arrays of a desired type.
2283 * The return type of the method handle will be the array type.
2284 * The type of its sole argument will be {@code int}, which specifies the size of the array.
2285 * @param arrayClass an array type
2286 * @return a method handle which can create arrays of the given type
2287 * @throws NullPointerException if the argument is {@code null}
2288 * @throws IllegalArgumentException if {@code arrayClass} is not an array type
2289 * @see java.lang.reflect.Array#newInstance(Class, int)
2290 * @since 9
2291 */
2292 public static
2293 MethodHandle arrayConstructor(Class<?> arrayClass) throws IllegalArgumentException {
2294 if (!arrayClass.isArray()) {
2295 throw newIllegalArgumentException("not an array class: " + arrayClass.getName());
2296 }
2297 MethodHandle ani = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_Array_newInstance).
2298 bindTo(arrayClass.getComponentType());
2299 return ani.asType(ani.type().changeReturnType(arrayClass));
2300 }
2301
2302 /**
2303 * Produces a method handle returning the length of an array.
2304 * The type of the method handle will have {@code int} as return type,
2305 * and its sole argument will be the array type.
2306 * @param arrayClass an array type
2307 * @return a method handle which can retrieve the length of an array of the given array type
2308 * @throws NullPointerException if the argument is {@code null}
2309 * @throws IllegalArgumentException if arrayClass is not an array type
2310 * @since 9
2311 */
2312 public static
2313 MethodHandle arrayLength(Class<?> arrayClass) throws IllegalArgumentException {
2314 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.LENGTH);
2315 }
2316
2317 /**
2318 * Produces a method handle giving read access to elements of an array.
2319 * The type of the method handle will have a return type of the array's
2320 * element type. Its first argument will be the array type,
2321 * and the second will be {@code int}.
2322 * @param arrayClass an array type
2323 * @return a method handle which can load values from the given array type
2324 * @throws NullPointerException if the argument is null
2325 * @throws IllegalArgumentException if arrayClass is not an array type
2326 */
2327 public static
2328 MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException {
2329 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.GET);
2330 }
2331
2332 /**
2333 * Produces a method handle giving write access to elements of an array.
2334 * The type of the method handle will have a void return type.
2335 * Its last argument will be the array's element type.
2336 * The first and second arguments will be the array type and int.
2337 * @param arrayClass the class of an array
2338 * @return a method handle which can store values into the array type
2339 * @throws NullPointerException if the argument is null
2340 * @throws IllegalArgumentException if arrayClass is not an array type
2341 */
2342 public static
2343 MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException {
2344 return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.SET);
2345 }
2346
2347 /**
2348 *
2349 * Produces a VarHandle giving access to elements of an array type
2350 * {@code T[]}, supporting shape {@code (T[], int : T)}.
2351 * <p>
2352 * Certain access modes of the returned VarHandle are unsupported under
2353 * the following conditions:
2354 * <ul>
2355 * <li>if the component type is anything other than {@code byte},
2356 * {@code short}, {@code char}, {@code int} or {@code long},
2357 * {@code float}, or {@code double} then numeric atomic update access
2358 * modes are unsupported.
2359 * </ul>
2360 * <p>
2361 * If the component type is {@code float} or {@code double} then numeric
2362 * and atomic update access modes compare values using their bitwise
2363 * representation (see {@link Float#floatToRawIntBits} and
2364 * {@link Double#doubleToRawLongBits}, respectively).
2365 * @apiNote
2366 * Bitwise comparison of {@code float} values or {@code double} values,
2367 * as performed by the numeric and atomic update access modes, differ
2368 * from the primitive {@code ==} operator and the {@link Float#equals}
2369 * and {@link Double#equals} methods, specifically with respect to
2370 * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
2371 * Care should be taken when performing a compare and set or a compare
2372 * and exchange operation with such values since the operation may
2373 * unexpectedly fail.
2374 * There are many possible NaN values that are considered to be
2375 * {@code NaN} in Java, although no IEEE 754 floating-point operation
2376 * provided by Java can distinguish between them. Operation failure can
2377 * occur if the expected or witness value is a NaN value and it is
2378 * transformed (perhaps in a platform specific manner) into another NaN
2379 * value, and thus has a different bitwise representation (see
2380 * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
2381 * details).
2382 * The values {@code -0.0} and {@code +0.0} have different bitwise
2383 * representations but are considered equal when using the primitive
2384 * {@code ==} operator. Operation failure can occur if, for example, a
2385 * numeric algorithm computes an expected value to be say {@code -0.0}
2386 * and previously computed the witness value to be say {@code +0.0}.
2387 * @param arrayClass the class of an array, of type {@code T[]}
2388 * @return a VarHandle giving access to elements of an array
2389 * @throws NullPointerException if the arrayClass is null
2390 * @throws IllegalArgumentException if arrayClass is not an array type
2391 * @since 9
2392 */
2393 public static
2394 VarHandle arrayElementVarHandle(Class<?> arrayClass) throws IllegalArgumentException {
2395 return VarHandles.makeArrayElementHandle(arrayClass);
2396 }
2397
2398 /**
2399 * Produces a VarHandle giving access to elements of a {@code byte[]} array
2400 * viewed as if it were a different primitive array type, such as
2401 * {@code int[]} or {@code long[]}. The shape of the resulting VarHandle is
2402 * {@code (byte[], int : T)}, where the {@code int} coordinate type
2403 * corresponds to an argument that is an index in a {@code byte[]} array,
2404 * and {@code T} is the component type of the given view array class. The
2405 * returned VarHandle accesses bytes at an index in a {@code byte[]} array,
2406 * composing bytes to or from a value of {@code T} according to the given
2407 * endianness.
2408 * <p>
2409 * The supported component types (variables types) are {@code short},
2410 * {@code char}, {@code int}, {@code long}, {@code float} and
2411 * {@code double}.
2412 * <p>
2413 * Access of bytes at a given index will result in an
2414 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
2415 * or greater than the {@code byte[]} array length minus the size (in bytes)
2416 * of {@code T}.
2417 * <p>
2418 * Access of bytes at an index may be aligned or misaligned for {@code T},
2419 * with respect to the underlying memory address, {@code A} say, associated
2420 * with the array and index.
2421 * If access is misaligned then access for anything other than the
2422 * {@code get} and {@code set} access modes will result in an
2423 * {@code IllegalStateException}. In such cases atomic access is only
2424 * guaranteed with respect to the largest power of two that divides the GCD
2425 * of {@code A} and the size (in bytes) of {@code T}.
2426 * If access is aligned then following access modes are supported and are
2427 * guaranteed to support atomic access:
2428 * <ul>
2429 * <li>read write access modes for all {@code T};
2430 * <li>atomic update access modes for {@code int}, {@code long},
2431 * {@code float} or {@code double}.
2432 * (Future major platform releases of the JDK may support additional
2433 * types for certain currently unsupported access modes.)
2434 * <li>numeric atomic update access modes for {@code int} and {@code long}.
2435 * (Future major platform releases of the JDK may support additional
2436 * numeric types for certain currently unsupported access modes.)
2437 * </ul>
2438 * <p>
2439 * Misaligned access, and therefore atomicity guarantees, may be determined
2440 * for {@code byte[]} arrays without operating on a specific array. Given
2441 * an {@code index}, {@code T} and it's corresponding boxed type,
2442 * {@code T_BOX}, misalignment may be determined as follows:
2443 * <pre>{@code
2444 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
2445 * int misalignedAtZeroIndex = ByteBuffer.wrap(new byte[0]).
2446 * alignmentOffset(0, sizeOfT);
2447 * int misalignedAtIndex = (misalignedAtZeroIndex + index) % sizeOfT;
2448 * boolean isMisaligned = misalignedAtIndex != 0;
2449 * }</pre>
2450 * <p>
2451 * If the variable type is {@code float} or {@code double} then atomic
2452 * update access modes compare values using their bitwise representation
2453 * (see {@link Float#floatToRawIntBits} and
2454 * {@link Double#doubleToRawLongBits}, respectively).
2455 * @param viewArrayClass the view array class, with a component type of
2456 * type {@code T}
2457 * @param byteOrder the endianness of the view array elements, as
2458 * stored in the underlying {@code byte} array
2459 * @return a VarHandle giving access to elements of a {@code byte[]} array
2460 * viewed as if elements corresponding to the components type of the view
2461 * array class
2462 * @throws NullPointerException if viewArrayClass or byteOrder is null
2463 * @throws IllegalArgumentException if viewArrayClass is not an array type
2464 * @throws UnsupportedOperationException if the component type of
2465 * viewArrayClass is not supported as a variable type
2466 * @since 9
2467 */
2468 public static
2469 VarHandle byteArrayViewVarHandle(Class<?> viewArrayClass,
2470 ByteOrder byteOrder) throws IllegalArgumentException {
2471 Objects.requireNonNull(byteOrder);
2472 return VarHandles.byteArrayViewHandle(viewArrayClass,
2473 byteOrder == ByteOrder.BIG_ENDIAN);
2474 }
2475
2476 /**
2477 * Produces a VarHandle giving access to elements of a {@code ByteBuffer}
2478 * viewed as if it were an array of elements of a different primitive
2479 * component type to that of {@code byte}, such as {@code int[]} or
2480 * {@code long[]}. The shape of the resulting VarHandle is
2481 * {@code (ByteBuffer, int : T)}, where the {@code int} coordinate type
2482 * corresponds to an argument that is an index in a {@code ByteBuffer}, and
2483 * {@code T} is the component type of the given view array class. The
2484 * returned VarHandle accesses bytes at an index in a {@code ByteBuffer},
2485 * composing bytes to or from a value of {@code T} according to the given
2486 * endianness.
2487 * <p>
2488 * The supported component types (variables types) are {@code short},
2489 * {@code char}, {@code int}, {@code long}, {@code float} and
2490 * {@code double}.
2491 * <p>
2492 * Access will result in a {@code ReadOnlyBufferException} for anything
2493 * other than the read access modes if the {@code ByteBuffer} is read-only.
2494 * <p>
2495 * Access of bytes at a given index will result in an
2496 * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
2497 * or greater than the {@code ByteBuffer} limit minus the size (in bytes) of
2498 * {@code T}.
2499 * <p>
2500 * Access of bytes at an index may be aligned or misaligned for {@code T},
2501 * with respect to the underlying memory address, {@code A} say, associated
2502 * with the {@code ByteBuffer} and index.
2503 * If access is misaligned then access for anything other than the
2504 * {@code get} and {@code set} access modes will result in an
2505 * {@code IllegalStateException}. In such cases atomic access is only
2506 * guaranteed with respect to the largest power of two that divides the GCD
2507 * of {@code A} and the size (in bytes) of {@code T}.
2508 * If access is aligned then following access modes are supported and are
2509 * guaranteed to support atomic access:
2510 * <ul>
2511 * <li>read write access modes for all {@code T};
2512 * <li>atomic update access modes for {@code int}, {@code long},
2513 * {@code float} or {@code double}.
2514 * (Future major platform releases of the JDK may support additional
2515 * types for certain currently unsupported access modes.)
2516 * <li>numeric atomic update access modes for {@code int} and {@code long}.
2517 * (Future major platform releases of the JDK may support additional
2518 * numeric types for certain currently unsupported access modes.)
2519 * </ul>
2520 * <p>
2521 * Misaligned access, and therefore atomicity guarantees, may be determined
2522 * for a {@code ByteBuffer}, {@code bb} (direct or otherwise), an
2523 * {@code index}, {@code T} and it's corresponding boxed type,
2524 * {@code T_BOX}, as follows:
2525 * <pre>{@code
2526 * int sizeOfT = T_BOX.BYTES; // size in bytes of T
2527 * ByteBuffer bb = ...
2528 * int misalignedAtIndex = bb.alignmentOffset(index, sizeOfT);
2529 * boolean isMisaligned = misalignedAtIndex != 0;
2530 * }</pre>
2531 * <p>
2532 * If the variable type is {@code float} or {@code double} then atomic
2533 * update access modes compare values using their bitwise representation
2534 * (see {@link Float#floatToRawIntBits} and
2535 * {@link Double#doubleToRawLongBits}, respectively).
2536 * @param viewArrayClass the view array class, with a component type of
2537 * type {@code T}
2538 * @param byteOrder the endianness of the view array elements, as
2539 * stored in the underlying {@code ByteBuffer} (Note this overrides the
2540 * endianness of a {@code ByteBuffer})
2541 * @return a VarHandle giving access to elements of a {@code ByteBuffer}
2542 * viewed as if elements corresponding to the components type of the view
2543 * array class
2544 * @throws NullPointerException if viewArrayClass or byteOrder is null
2545 * @throws IllegalArgumentException if viewArrayClass is not an array type
2546 * @throws UnsupportedOperationException if the component type of
2547 * viewArrayClass is not supported as a variable type
2548 * @since 9
2549 */
2550 public static
2551 VarHandle byteBufferViewVarHandle(Class<?> viewArrayClass,
2552 ByteOrder byteOrder) throws IllegalArgumentException {
2553 Objects.requireNonNull(byteOrder);
2554 return VarHandles.makeByteBufferViewHandle(viewArrayClass,
2555 byteOrder == ByteOrder.BIG_ENDIAN);
2556 }
2557
2558
2559 /// method handle invocation (reflective style)
2560
2561 /**
2562 * Produces a method handle which will invoke any method handle of the
2563 * given {@code type}, with a given number of trailing arguments replaced by
2564 * a single trailing {@code Object[]} array.
2565 * The resulting invoker will be a method handle with the following
2566 * arguments:
2567 * <ul>
2568 * <li>a single {@code MethodHandle} target
2569 * <li>zero or more leading values (counted by {@code leadingArgCount})
2570 * <li>an {@code Object[]} array containing trailing arguments
2571 * </ul>
2572 * <p>
2573 * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
2574 * the indicated {@code type}.
2575 * That is, if the target is exactly of the given {@code type}, it will behave
2576 * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
2577 * is used to convert the target to the required {@code type}.
2578 * <p>
2579 * The type of the returned invoker will not be the given {@code type}, but rather
2580 * will have all parameters except the first {@code leadingArgCount}
2581 * replaced by a single array of type {@code Object[]}, which will be
2582 * the final parameter.
2583 * <p>
2584 * Before invoking its target, the invoker will spread the final array, apply
2585 * reference casts as necessary, and unbox and widen primitive arguments.
2586 * If, when the invoker is called, the supplied array argument does
2587 * not have the correct number of elements, the invoker will throw
2588 * an {@link IllegalArgumentException} instead of invoking the target.
2589 * <p>
2590 * This method is equivalent to the following code (though it may be more efficient):
2591 * <blockquote><pre>{@code
2592 MethodHandle invoker = MethodHandles.invoker(type);
2593 int spreadArgCount = type.parameterCount() - leadingArgCount;
2594 invoker = invoker.asSpreader(Object[].class, spreadArgCount);
2595 return invoker;
2596 * }</pre></blockquote>
2597 * This method throws no reflective or security exceptions.
2598 * @param type the desired target type
2599 * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
2600 * @return a method handle suitable for invoking any method handle of the given type
2601 * @throws NullPointerException if {@code type} is null
2602 * @throws IllegalArgumentException if {@code leadingArgCount} is not in
2603 * the range from 0 to {@code type.parameterCount()} inclusive,
2604 * or if the resulting method handle's type would have
2605 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2606 */
2607 public static
2608 MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
2609 if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
2610 throw newIllegalArgumentException("bad argument count", leadingArgCount);
2611 type = type.asSpreaderType(Object[].class, leadingArgCount, type.parameterCount() - leadingArgCount);
2612 return type.invokers().spreadInvoker(leadingArgCount);
2613 }
2614
2615 /**
2616 * Produces a special <em>invoker method handle</em> which can be used to
2617 * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
2618 * The resulting invoker will have a type which is
2619 * exactly equal to the desired type, except that it will accept
2620 * an additional leading argument of type {@code MethodHandle}.
2621 * <p>
2622 * This method is equivalent to the following code (though it may be more efficient):
2623 * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)}
2624 *
2625 * <p style="font-size:smaller;">
2626 * <em>Discussion:</em>
2627 * Invoker method handles can be useful when working with variable method handles
2628 * of unknown types.
2629 * For example, to emulate an {@code invokeExact} call to a variable method
2630 * handle {@code M}, extract its type {@code T},
2631 * look up the invoker method {@code X} for {@code T},
2632 * and call the invoker method, as {@code X.invoke(T, A...)}.
2633 * (It would not work to call {@code X.invokeExact}, since the type {@code T}
2634 * is unknown.)
2635 * If spreading, collecting, or other argument transformations are required,
2636 * they can be applied once to the invoker {@code X} and reused on many {@code M}
2637 * method handle values, as long as they are compatible with the type of {@code X}.
2638 * <p style="font-size:smaller;">
2639 * <em>(Note: The invoker method is not available via the Core Reflection API.
2640 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
2641 * on the declared {@code invokeExact} or {@code invoke} method will raise an
2642 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
2643 * <p>
2644 * This method throws no reflective or security exceptions.
2645 * @param type the desired target type
2646 * @return a method handle suitable for invoking any method handle of the given type
2647 * @throws IllegalArgumentException if the resulting method handle's type would have
2648 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2649 */
2650 public static
2651 MethodHandle exactInvoker(MethodType type) {
2652 return type.invokers().exactInvoker();
2653 }
2654
2655 /**
2656 * Produces a special <em>invoker method handle</em> which can be used to
2657 * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
2658 * The resulting invoker will have a type which is
2659 * exactly equal to the desired type, except that it will accept
2660 * an additional leading argument of type {@code MethodHandle}.
2661 * <p>
2662 * Before invoking its target, if the target differs from the expected type,
2663 * the invoker will apply reference casts as
2664 * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
2665 * Similarly, the return value will be converted as necessary.
2666 * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
2667 * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
2668 * <p>
2669 * This method is equivalent to the following code (though it may be more efficient):
2670 * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)}
2671 * <p style="font-size:smaller;">
2672 * <em>Discussion:</em>
2673 * A {@linkplain MethodType#genericMethodType general method type} is one which
2674 * mentions only {@code Object} arguments and return values.
2675 * An invoker for such a type is capable of calling any method handle
2676 * of the same arity as the general type.
2677 * <p style="font-size:smaller;">
2678 * <em>(Note: The invoker method is not available via the Core Reflection API.
2679 * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
2680 * on the declared {@code invokeExact} or {@code invoke} method will raise an
2681 * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
2682 * <p>
2683 * This method throws no reflective or security exceptions.
2684 * @param type the desired target type
2685 * @return a method handle suitable for invoking any method handle convertible to the given type
2686 * @throws IllegalArgumentException if the resulting method handle's type would have
2687 * <a href="MethodHandle.html#maxarity">too many parameters</a>
2688 */
2689 public static
2690 MethodHandle invoker(MethodType type) {
2691 return type.invokers().genericInvoker();
2692 }
2693
2694 /**
2695 * Produces a special <em>invoker method handle</em> which can be used to
2696 * invoke a signature-polymorphic access mode method on any VarHandle whose
2697 * associated access mode type is compatible with the given type.
2698 * The resulting invoker will have a type which is exactly equal to the
2699 * desired given type, except that it will accept an additional leading
2700 * argument of type {@code VarHandle}.
2701 *
2702 * @param accessMode the VarHandle access mode
2703 * @param type the desired target type
2704 * @return a method handle suitable for invoking an access mode method of
2705 * any VarHandle whose access mode type is of the given type.
2706 * @since 9
2707 */
2708 static public
2709 MethodHandle varHandleExactInvoker(VarHandle.AccessMode accessMode, MethodType type) {
2710 return type.invokers().varHandleMethodExactInvoker(accessMode);
2711 }
2712
2713 /**
2714 * Produces a special <em>invoker method handle</em> which can be used to
2715 * invoke a signature-polymorphic access mode method on any VarHandle whose
2716 * associated access mode type is compatible with the given type.
2717 * The resulting invoker will have a type which is exactly equal to the
2718 * desired given type, except that it will accept an additional leading
2719 * argument of type {@code VarHandle}.
2720 * <p>
2721 * Before invoking its target, if the access mode type differs from the
2722 * desired given type, the invoker will apply reference casts as necessary
2723 * and box, unbox, or widen primitive values, as if by
2724 * {@link MethodHandle#asType asType}. Similarly, the return value will be
2725 * converted as necessary.
2726 * <p>
2727 * This method is equivalent to the following code (though it may be more
2728 * efficient): {@code publicLookup().findVirtual(VarHandle.class, accessMode.name(), type)}
2729 *
2730 * @param accessMode the VarHandle access mode
2731 * @param type the desired target type
2732 * @return a method handle suitable for invoking an access mode method of
2733 * any VarHandle whose access mode type is convertible to the given
2734 * type.
2735 * @since 9
2736 */
2737 static public
2738 MethodHandle varHandleInvoker(VarHandle.AccessMode accessMode, MethodType type) {
2739 return type.invokers().varHandleMethodInvoker(accessMode);
2740 }
2741
2742 static /*non-public*/
2743 MethodHandle basicInvoker(MethodType type) {
2744 return type.invokers().basicInvoker();
2745 }
2746
2747 /// method handle modification (creation from other method handles)
2748
2749 /**
2750 * Produces a method handle which adapts the type of the
2751 * given method handle to a new type by pairwise argument and return type conversion.
2752 * The original type and new type must have the same number of arguments.
2753 * The resulting method handle is guaranteed to report a type
2754 * which is equal to the desired new type.
2755 * <p>
2756 * If the original type and new type are equal, returns target.
2757 * <p>
2758 * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
2759 * and some additional conversions are also applied if those conversions fail.
2760 * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied
2761 * if possible, before or instead of any conversions done by {@code asType}:
2762 * <ul>
2763 * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type,
2764 * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast.
2765 * (This treatment of interfaces follows the usage of the bytecode verifier.)
2766 * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive,
2767 * the boolean is converted to a byte value, 1 for true, 0 for false.
2768 * (This treatment follows the usage of the bytecode verifier.)
2769 * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive,
2770 * <em>T0</em> is converted to byte via Java casting conversion (JLS 5.5),
2771 * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}.
2772 * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean,
2773 * then a Java casting conversion (JLS 5.5) is applied.
2774 * (Specifically, <em>T0</em> will convert to <em>T1</em> by
2775 * widening and/or narrowing.)
2776 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
2777 * conversion will be applied at runtime, possibly followed
2778 * by a Java casting conversion (JLS 5.5) on the primitive value,
2779 * possibly followed by a conversion from byte to boolean by testing
2780 * the low-order bit.
2781 * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive,
2782 * and if the reference is null at runtime, a zero value is introduced.
2783 * </ul>
2784 * @param target the method handle to invoke after arguments are retyped
2785 * @param newType the expected type of the new method handle
2786 * @return a method handle which delegates to the target after performing
2787 * any necessary argument conversions, and arranges for any
2788 * necessary return value conversions
2789 * @throws NullPointerException if either argument is null
2790 * @throws WrongMethodTypeException if the conversion cannot be made
2791 * @see MethodHandle#asType
2792 */
2793 public static
2794 MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
2795 explicitCastArgumentsChecks(target, newType);
2796 // use the asTypeCache when possible:
2797 MethodType oldType = target.type();
2798 if (oldType == newType) return target;
2799 if (oldType.explicitCastEquivalentToAsType(newType)) {
2800 return target.asFixedArity().asType(newType);
2801 }
2802 return MethodHandleImpl.makePairwiseConvert(target, newType, false);
2803 }
2804
2805 private static void explicitCastArgumentsChecks(MethodHandle target, MethodType newType) {
2806 if (target.type().parameterCount() != newType.parameterCount()) {
2807 throw new WrongMethodTypeException("cannot explicitly cast " + target + " to " + newType);
2808 }
2809 }
2810
2811 /**
2812 * Produces a method handle which adapts the calling sequence of the
2813 * given method handle to a new type, by reordering the arguments.
2814 * The resulting method handle is guaranteed to report a type
2815 * which is equal to the desired new type.
2816 * <p>
2817 * The given array controls the reordering.
2818 * Call {@code #I} the number of incoming parameters (the value
2819 * {@code newType.parameterCount()}, and call {@code #O} the number
2820 * of outgoing parameters (the value {@code target.type().parameterCount()}).
2821 * Then the length of the reordering array must be {@code #O},
2822 * and each element must be a non-negative number less than {@code #I}.
2823 * For every {@code N} less than {@code #O}, the {@code N}-th
2824 * outgoing argument will be taken from the {@code I}-th incoming
2825 * argument, where {@code I} is {@code reorder[N]}.
2826 * <p>
2827 * No argument or return value conversions are applied.
2828 * The type of each incoming argument, as determined by {@code newType},
2829 * must be identical to the type of the corresponding outgoing parameter
2830 * or parameters in the target method handle.
2831 * The return type of {@code newType} must be identical to the return
2832 * type of the original target.
2833 * <p>
2834 * The reordering array need not specify an actual permutation.
2835 * An incoming argument will be duplicated if its index appears
2836 * more than once in the array, and an incoming argument will be dropped
2837 * if its index does not appear in the array.
2838 * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
2839 * incoming arguments which are not mentioned in the reordering array
2840 * may be of any type, as determined only by {@code newType}.
2841 * <blockquote><pre>{@code
2842 import static java.lang.invoke.MethodHandles.*;
2843 import static java.lang.invoke.MethodType.*;
2844 ...
2845 MethodType intfn1 = methodType(int.class, int.class);
2846 MethodType intfn2 = methodType(int.class, int.class, int.class);
2847 MethodHandle sub = ... (int x, int y) -> (x-y) ...;
2848 assert(sub.type().equals(intfn2));
2849 MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
2850 MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
2851 assert((int)rsub.invokeExact(1, 100) == 99);
2852 MethodHandle add = ... (int x, int y) -> (x+y) ...;
2853 assert(add.type().equals(intfn2));
2854 MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
2855 assert(twice.type().equals(intfn1));
2856 assert((int)twice.invokeExact(21) == 42);
2857 * }</pre></blockquote>
2858 * <p>
2859 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
2860 * variable-arity method handle}, even if the original target method handle was.
2861 * @param target the method handle to invoke after arguments are reordered
2862 * @param newType the expected type of the new method handle
2863 * @param reorder an index array which controls the reordering
2864 * @return a method handle which delegates to the target after it
2865 * drops unused arguments and moves and/or duplicates the other arguments
2866 * @throws NullPointerException if any argument is null
2867 * @throws IllegalArgumentException if the index array length is not equal to
2868 * the arity of the target, or if any index array element
2869 * not a valid index for a parameter of {@code newType},
2870 * or if two corresponding parameter types in
2871 * {@code target.type()} and {@code newType} are not identical,
2872 */
2873 public static
2874 MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
2875 reorder = reorder.clone(); // get a private copy
2876 MethodType oldType = target.type();
2877 permuteArgumentChecks(reorder, newType, oldType);
2878 // first detect dropped arguments and handle them separately
2879 int[] originalReorder = reorder;
2880 BoundMethodHandle result = target.rebind();
2881 LambdaForm form = result.form;
2882 int newArity = newType.parameterCount();
2883 // Normalize the reordering into a real permutation,
2884 // by removing duplicates and adding dropped elements.
2885 // This somewhat improves lambda form caching, as well
2886 // as simplifying the transform by breaking it up into steps.
2887 for (int ddIdx; (ddIdx = findFirstDupOrDrop(reorder, newArity)) != 0; ) {
2888 if (ddIdx > 0) {
2889 // We found a duplicated entry at reorder[ddIdx].
2890 // Example: (x,y,z)->asList(x,y,z)
2891 // permuted by [1*,0,1] => (a0,a1)=>asList(a1,a0,a1)
2892 // permuted by [0,1,0*] => (a0,a1)=>asList(a0,a1,a0)
2893 // The starred element corresponds to the argument
2894 // deleted by the dupArgumentForm transform.
2895 int srcPos = ddIdx, dstPos = srcPos, dupVal = reorder[srcPos];
2896 boolean killFirst = false;
2897 for (int val; (val = reorder[--dstPos]) != dupVal; ) {
2898 // Set killFirst if the dup is larger than an intervening position.
2899 // This will remove at least one inversion from the permutation.
2900 if (dupVal > val) killFirst = true;
2901 }
2902 if (!killFirst) {
2903 srcPos = dstPos;
2904 dstPos = ddIdx;
2905 }
2906 form = form.editor().dupArgumentForm(1 + srcPos, 1 + dstPos);
2907 assert (reorder[srcPos] == reorder[dstPos]);
2908 oldType = oldType.dropParameterTypes(dstPos, dstPos + 1);
2909 // contract the reordering by removing the element at dstPos
2910 int tailPos = dstPos + 1;
2911 System.arraycopy(reorder, tailPos, reorder, dstPos, reorder.length - tailPos);
2912 reorder = Arrays.copyOf(reorder, reorder.length - 1);
2913 } else {
2914 int dropVal = ~ddIdx, insPos = 0;
2915 while (insPos < reorder.length && reorder[insPos] < dropVal) {
2916 // Find first element of reorder larger than dropVal.
2917 // This is where we will insert the dropVal.
2918 insPos += 1;
2919 }
2920 Class<?> ptype = newType.parameterType(dropVal);
2921 form = form.editor().addArgumentForm(1 + insPos, BasicType.basicType(ptype));
2922 oldType = oldType.insertParameterTypes(insPos, ptype);
2923 // expand the reordering by inserting an element at insPos
2924 int tailPos = insPos + 1;
2925 reorder = Arrays.copyOf(reorder, reorder.length + 1);
2926 System.arraycopy(reorder, insPos, reorder, tailPos, reorder.length - tailPos);
2927 reorder[insPos] = dropVal;
2928 }
2929 assert (permuteArgumentChecks(reorder, newType, oldType));
2930 }
2931 assert (reorder.length == newArity); // a perfect permutation
2932 // Note: This may cache too many distinct LFs. Consider backing off to varargs code.
2933 form = form.editor().permuteArgumentsForm(1, reorder);
2934 if (newType == result.type() && form == result.internalForm())
2935 return result;
2936 return result.copyWith(newType, form);
2937 }
2938
2939 /**
2940 * Return an indication of any duplicate or omission in reorder.
2941 * If the reorder contains a duplicate entry, return the index of the second occurrence.
2942 * Otherwise, return ~(n), for the first n in [0..newArity-1] that is not present in reorder.
2943 * Otherwise, return zero.
2944 * If an element not in [0..newArity-1] is encountered, return reorder.length.
2945 */
2946 private static int findFirstDupOrDrop(int[] reorder, int newArity) {
2947 final int BIT_LIMIT = 63; // max number of bits in bit mask
2948 if (newArity < BIT_LIMIT) {
2949 long mask = 0;
2950 for (int i = 0; i < reorder.length; i++) {
2951 int arg = reorder[i];
2952 if (arg >= newArity) {
2953 return reorder.length;
2954 }
2955 long bit = 1L << arg;
2956 if ((mask & bit) != 0) {
2957 return i; // >0 indicates a dup
2958 }
2959 mask |= bit;
2960 }
2961 if (mask == (1L << newArity) - 1) {
2962 assert(Long.numberOfTrailingZeros(Long.lowestOneBit(~mask)) == newArity);
2963 return 0;
2964 }
2965 // find first zero
2966 long zeroBit = Long.lowestOneBit(~mask);
2967 int zeroPos = Long.numberOfTrailingZeros(zeroBit);
2968 assert(zeroPos <= newArity);
2969 if (zeroPos == newArity) {
2970 return 0;
2971 }
2972 return ~zeroPos;
2973 } else {
2974 // same algorithm, different bit set
2975 BitSet mask = new BitSet(newArity);
2976 for (int i = 0; i < reorder.length; i++) {
2977 int arg = reorder[i];
2978 if (arg >= newArity) {
2979 return reorder.length;
2980 }
2981 if (mask.get(arg)) {
2982 return i; // >0 indicates a dup
2983 }
2984 mask.set(arg);
2985 }
2986 int zeroPos = mask.nextClearBit(0);
2987 assert(zeroPos <= newArity);
2988 if (zeroPos == newArity) {
2989 return 0;
2990 }
2991 return ~zeroPos;
2992 }
2993 }
2994
2995 private static boolean permuteArgumentChecks(int[] reorder, MethodType newType, MethodType oldType) {
2996 if (newType.returnType() != oldType.returnType())
2997 throw newIllegalArgumentException("return types do not match",
2998 oldType, newType);
2999 if (reorder.length == oldType.parameterCount()) {
3000 int limit = newType.parameterCount();
3001 boolean bad = false;
3002 for (int j = 0; j < reorder.length; j++) {
3003 int i = reorder[j];
3004 if (i < 0 || i >= limit) {
3005 bad = true; break;
3006 }
3007 Class<?> src = newType.parameterType(i);
3008 Class<?> dst = oldType.parameterType(j);
3009 if (src != dst)
3010 throw newIllegalArgumentException("parameter types do not match after reorder",
3011 oldType, newType);
3012 }
3013 if (!bad) return true;
3014 }
3015 throw newIllegalArgumentException("bad reorder array: "+Arrays.toString(reorder));
3016 }
3017
3018 /**
3019 * Produces a method handle of the requested return type which returns the given
3020 * constant value every time it is invoked.
3021 * <p>
3022 * Before the method handle is returned, the passed-in value is converted to the requested type.
3023 * If the requested type is primitive, widening primitive conversions are attempted,
3024 * else reference conversions are attempted.
3025 * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
3026 * @param type the return type of the desired method handle
3027 * @param value the value to return
3028 * @return a method handle of the given return type and no arguments, which always returns the given value
3029 * @throws NullPointerException if the {@code type} argument is null
3030 * @throws ClassCastException if the value cannot be converted to the required return type
3031 * @throws IllegalArgumentException if the given type is {@code void.class}
3032 */
3033 public static
3034 MethodHandle constant(Class<?> type, Object value) {
3035 if (type.isPrimitive()) {
3036 if (type == void.class)
3037 throw newIllegalArgumentException("void type");
3038 Wrapper w = Wrapper.forPrimitiveType(type);
3039 value = w.convert(value, type);
3040 if (w.zero().equals(value))
3041 return zero(w, type);
3042 return insertArguments(identity(type), 0, value);
3043 } else {
3044 if (value == null)
3045 return zero(Wrapper.OBJECT, type);
3046 return identity(type).bindTo(value);
3047 }
3048 }
3049
3050 /**
3051 * Produces a method handle which returns its sole argument when invoked.
3052 * @param type the type of the sole parameter and return value of the desired method handle
3053 * @return a unary method handle which accepts and returns the given type
3054 * @throws NullPointerException if the argument is null
3055 * @throws IllegalArgumentException if the given type is {@code void.class}
3056 */
3057 public static
3058 MethodHandle identity(Class<?> type) {
3059 Wrapper btw = (type.isPrimitive() ? Wrapper.forPrimitiveType(type) : Wrapper.OBJECT);
3060 int pos = btw.ordinal();
3061 MethodHandle ident = IDENTITY_MHS[pos];
3062 if (ident == null) {
3063 ident = setCachedMethodHandle(IDENTITY_MHS, pos, makeIdentity(btw.primitiveType()));
3064 }
3065 if (ident.type().returnType() == type)
3066 return ident;
3067 // something like identity(Foo.class); do not bother to intern these
3068 assert (btw == Wrapper.OBJECT);
3069 return makeIdentity(type);
3070 }
3071
3072 /**
3073 * Produces a constant method handle of the requested return type which
3074 * returns the default value for that type every time it is invoked.
3075 * The resulting constant method handle will have no side effects.
3076 * <p>The returned method handle is equivalent to {@code empty(methodType(type))}.
3077 * It is also equivalent to {@code explicitCastArguments(constant(Object.class, null), methodType(type))},
3078 * since {@code explicitCastArguments} converts {@code null} to default values.
3079 * @param type the expected return type of the desired method handle
3080 * @return a constant method handle that takes no arguments
3081 * and returns the default value of the given type (or void, if the type is void)
3082 * @throws NullPointerException if the argument is null
3083 * @see MethodHandles#constant
3084 * @see MethodHandles#empty
3085 * @see MethodHandles#explicitCastArguments
3086 * @since 9
3087 */
3088 public static MethodHandle zero(Class<?> type) {
3089 Objects.requireNonNull(type);
3090 return type.isPrimitive() ? zero(Wrapper.forPrimitiveType(type), type) : zero(Wrapper.OBJECT, type);
3091 }
3092
3093 private static MethodHandle identityOrVoid(Class<?> type) {
3094 return type == void.class ? zero(type) : identity(type);
3095 }
3096
3097 /**
3098 * Produces a method handle of the requested type which ignores any arguments, does nothing,
3099 * and returns a suitable default depending on the return type.
3100 * That is, it returns a zero primitive value, a {@code null}, or {@code void}.
3101 * <p>The returned method handle is equivalent to
3102 * {@code dropArguments(zero(type.returnType()), 0, type.parameterList())}.
3103 * <p>
3104 * @apiNote Given a predicate and target, a useful "if-then" construct can be produced as
3105 * {@code guardWithTest(pred, target, empty(target.type())}.
3106 * @param type the type of the desired method handle
3107 * @return a constant method handle of the given type, which returns a default value of the given return type
3108 * @throws NullPointerException if the argument is null
3109 * @see MethodHandles#zero
3110 * @see MethodHandles#constant
3111 * @since 9
3112 */
3113 public static MethodHandle empty(MethodType type) {
3114 Objects.requireNonNull(type);
3115 return dropArguments(zero(type.returnType()), 0, type.parameterList());
3116 }
3117
3118 private static final MethodHandle[] IDENTITY_MHS = new MethodHandle[Wrapper.values().length];
3119 private static MethodHandle makeIdentity(Class<?> ptype) {
3120 MethodType mtype = methodType(ptype, ptype);
3121 LambdaForm lform = LambdaForm.identityForm(BasicType.basicType(ptype));
3122 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.IDENTITY);
3123 }
3124
3125 private static MethodHandle zero(Wrapper btw, Class<?> rtype) {
3126 int pos = btw.ordinal();
3127 MethodHandle zero = ZERO_MHS[pos];
3128 if (zero == null) {
3129 zero = setCachedMethodHandle(ZERO_MHS, pos, makeZero(btw.primitiveType()));
3130 }
3131 if (zero.type().returnType() == rtype)
3132 return zero;
3133 assert(btw == Wrapper.OBJECT);
3134 return makeZero(rtype);
3135 }
3136 private static final MethodHandle[] ZERO_MHS = new MethodHandle[Wrapper.values().length];
3137 private static MethodHandle makeZero(Class<?> rtype) {
3138 MethodType mtype = methodType(rtype);
3139 LambdaForm lform = LambdaForm.zeroForm(BasicType.basicType(rtype));
3140 return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.ZERO);
3141 }
3142
3143 private static synchronized MethodHandle setCachedMethodHandle(MethodHandle[] cache, int pos, MethodHandle value) {
3144 // Simulate a CAS, to avoid racy duplication of results.
3145 MethodHandle prev = cache[pos];
3146 if (prev != null) return prev;
3147 return cache[pos] = value;
3148 }
3149
3150 /**
3151 * Provides a target method handle with one or more <em>bound arguments</em>
3152 * in advance of the method handle's invocation.
3153 * The formal parameters to the target corresponding to the bound
3154 * arguments are called <em>bound parameters</em>.
3155 * Returns a new method handle which saves away the bound arguments.
3156 * When it is invoked, it receives arguments for any non-bound parameters,
3157 * binds the saved arguments to their corresponding parameters,
3158 * and calls the original target.
3159 * <p>
3160 * The type of the new method handle will drop the types for the bound
3161 * parameters from the original target type, since the new method handle
3162 * will no longer require those arguments to be supplied by its callers.
3163 * <p>
3164 * Each given argument object must match the corresponding bound parameter type.
3165 * If a bound parameter type is a primitive, the argument object
3166 * must be a wrapper, and will be unboxed to produce the primitive value.
3167 * <p>
3168 * The {@code pos} argument selects which parameters are to be bound.
3169 * It may range between zero and <i>N-L</i> (inclusively),
3170 * where <i>N</i> is the arity of the target method handle
3171 * and <i>L</i> is the length of the values array.
3172 * <p>
3173 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3174 * variable-arity method handle}, even if the original target method handle was.
3175 * @param target the method handle to invoke after the argument is inserted
3176 * @param pos where to insert the argument (zero for the first)
3177 * @param values the series of arguments to insert
3178 * @return a method handle which inserts an additional argument,
3179 * before calling the original method handle
3180 * @throws NullPointerException if the target or the {@code values} array is null
3181 * @see MethodHandle#bindTo
3182 */
3183 public static
3184 MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
3185 int insCount = values.length;
3186 Class<?>[] ptypes = insertArgumentsChecks(target, insCount, pos);
3187 if (insCount == 0) return target;
3188 BoundMethodHandle result = target.rebind();
3189 for (int i = 0; i < insCount; i++) {
3190 Object value = values[i];
3191 Class<?> ptype = ptypes[pos+i];
3192 if (ptype.isPrimitive()) {
3193 result = insertArgumentPrimitive(result, pos, ptype, value);
3194 } else {
3195 value = ptype.cast(value); // throw CCE if needed
3196 result = result.bindArgumentL(pos, value);
3197 }
3198 }
3199 return result;
3200 }
3201
3202 private static BoundMethodHandle insertArgumentPrimitive(BoundMethodHandle result, int pos,
3203 Class<?> ptype, Object value) {
3204 Wrapper w = Wrapper.forPrimitiveType(ptype);
3205 // perform unboxing and/or primitive conversion
3206 value = w.convert(value, ptype);
3207 switch (w) {
3208 case INT: return result.bindArgumentI(pos, (int)value);
3209 case LONG: return result.bindArgumentJ(pos, (long)value);
3210 case FLOAT: return result.bindArgumentF(pos, (float)value);
3211 case DOUBLE: return result.bindArgumentD(pos, (double)value);
3212 default: return result.bindArgumentI(pos, ValueConversions.widenSubword(value));
3213 }
3214 }
3215
3216 private static Class<?>[] insertArgumentsChecks(MethodHandle target, int insCount, int pos) throws RuntimeException {
3217 MethodType oldType = target.type();
3218 int outargs = oldType.parameterCount();
3219 int inargs = outargs - insCount;
3220 if (inargs < 0)
3221 throw newIllegalArgumentException("too many values to insert");
3222 if (pos < 0 || pos > inargs)
3223 throw newIllegalArgumentException("no argument type to append");
3224 return oldType.ptypes();
3225 }
3226
3227 /**
3228 * Produces a method handle which will discard some dummy arguments
3229 * before calling some other specified <i>target</i> method handle.
3230 * The type of the new method handle will be the same as the target's type,
3231 * except it will also include the dummy argument types,
3232 * at some given position.
3233 * <p>
3234 * The {@code pos} argument may range between zero and <i>N</i>,
3235 * where <i>N</i> is the arity of the target.
3236 * If {@code pos} is zero, the dummy arguments will precede
3237 * the target's real arguments; if {@code pos} is <i>N</i>
3238 * they will come after.
3239 * <p>
3240 * <b>Example:</b>
3241 * <blockquote><pre>{@code
3242 import static java.lang.invoke.MethodHandles.*;
3243 import static java.lang.invoke.MethodType.*;
3244 ...
3245 MethodHandle cat = lookup().findVirtual(String.class,
3246 "concat", methodType(String.class, String.class));
3247 assertEquals("xy", (String) cat.invokeExact("x", "y"));
3248 MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
3249 MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
3250 assertEquals(bigType, d0.type());
3251 assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
3252 * }</pre></blockquote>
3253 * <p>
3254 * This method is also equivalent to the following code:
3255 * <blockquote><pre>
3256 * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))}
3257 * </pre></blockquote>
3258 * @param target the method handle to invoke after the arguments are dropped
3259 * @param valueTypes the type(s) of the argument(s) to drop
3260 * @param pos position of first argument to drop (zero for the leftmost)
3261 * @return a method handle which drops arguments of the given types,
3262 * before calling the original method handle
3263 * @throws NullPointerException if the target is null,
3264 * or if the {@code valueTypes} list or any of its elements is null
3265 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
3266 * or if {@code pos} is negative or greater than the arity of the target,
3267 * or if the new method handle's type would have too many parameters
3268 */
3269 public static
3270 MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) {
3271 MethodType oldType = target.type(); // get NPE
3272 int dropped = dropArgumentChecks(oldType, pos, valueTypes);
3273 MethodType newType = oldType.insertParameterTypes(pos, valueTypes);
3274 if (dropped == 0) return target;
3275 BoundMethodHandle result = target.rebind();
3276 LambdaForm lform = result.form;
3277 int insertFormArg = 1 + pos;
3278 for (Class<?> ptype : valueTypes) {
3279 lform = lform.editor().addArgumentForm(insertFormArg++, BasicType.basicType(ptype));
3280 }
3281 result = result.copyWith(newType, lform);
3282 return result;
3283 }
3284
3285 private static int dropArgumentChecks(MethodType oldType, int pos, List<Class<?>> valueTypes) {
3286 int dropped = valueTypes.size();
3287 MethodType.checkSlotCount(dropped);
3288 int outargs = oldType.parameterCount();
3289 int inargs = outargs + dropped;
3290 if (pos < 0 || pos > outargs)
3291 throw newIllegalArgumentException("no argument type to remove"
3292 + Arrays.asList(oldType, pos, valueTypes, inargs, outargs)
3293 );
3294 return dropped;
3295 }
3296
3297 /**
3298 * Produces a method handle which will discard some dummy arguments
3299 * before calling some other specified <i>target</i> method handle.
3300 * The type of the new method handle will be the same as the target's type,
3301 * except it will also include the dummy argument types,
3302 * at some given position.
3303 * <p>
3304 * The {@code pos} argument may range between zero and <i>N</i>,
3305 * where <i>N</i> is the arity of the target.
3306 * If {@code pos} is zero, the dummy arguments will precede
3307 * the target's real arguments; if {@code pos} is <i>N</i>
3308 * they will come after.
3309 * @apiNote
3310 * <blockquote><pre>{@code
3311 import static java.lang.invoke.MethodHandles.*;
3312 import static java.lang.invoke.MethodType.*;
3313 ...
3314 MethodHandle cat = lookup().findVirtual(String.class,
3315 "concat", methodType(String.class, String.class));
3316 assertEquals("xy", (String) cat.invokeExact("x", "y"));
3317 MethodHandle d0 = dropArguments(cat, 0, String.class);
3318 assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
3319 MethodHandle d1 = dropArguments(cat, 1, String.class);
3320 assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
3321 MethodHandle d2 = dropArguments(cat, 2, String.class);
3322 assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
3323 MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
3324 assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
3325 * }</pre></blockquote>
3326 * <p>
3327 * This method is also equivalent to the following code:
3328 * <blockquote><pre>
3329 * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))}
3330 * </pre></blockquote>
3331 * @param target the method handle to invoke after the arguments are dropped
3332 * @param valueTypes the type(s) of the argument(s) to drop
3333 * @param pos position of first argument to drop (zero for the leftmost)
3334 * @return a method handle which drops arguments of the given types,
3335 * before calling the original method handle
3336 * @throws NullPointerException if the target is null,
3337 * or if the {@code valueTypes} array or any of its elements is null
3338 * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
3339 * or if {@code pos} is negative or greater than the arity of the target,
3340 * or if the new method handle's type would have
3341 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3342 */
3343 public static
3344 MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
3345 return dropArguments(target, pos, Arrays.asList(valueTypes));
3346 }
3347
3348 // private version which allows caller some freedom with error handling
3349 private static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos,
3350 boolean nullOnFailure) {
3351 List<Class<?>> oldTypes = target.type().parameterList();
3352 int match = oldTypes.size();
3353 if (skip != 0) {
3354 if (skip < 0 || skip > match) {
3355 throw newIllegalArgumentException("illegal skip", skip, target);
3356 }
3357 oldTypes = oldTypes.subList(skip, match);
3358 match -= skip;
3359 }
3360 List<Class<?>> addTypes = newTypes;
3361 int add = addTypes.size();
3362 if (pos != 0) {
3363 if (pos < 0 || pos > add) {
3364 throw newIllegalArgumentException("illegal pos", pos, newTypes);
3365 }
3366 addTypes = addTypes.subList(pos, add);
3367 add -= pos; assert(addTypes.size() == add);
3368 }
3369 // Do not add types which already match the existing arguments.
3370 if (match > add || !oldTypes.equals(addTypes.subList(0, match))) {
3371 if (nullOnFailure) {
3372 return null;
3373 }
3374 throw newIllegalArgumentException("argument lists do not match", oldTypes, newTypes);
3375 }
3376 addTypes = addTypes.subList(match, add);
3377 add -= match; assert(addTypes.size() == add);
3378 // newTypes: ( P*[pos], M*[match], A*[add] )
3379 // target: ( S*[skip], M*[match] )
3380 MethodHandle adapter = target;
3381 if (add > 0) {
3382 adapter = dropArguments(adapter, skip+ match, addTypes);
3383 }
3384 // adapter: (S*[skip], M*[match], A*[add] )
3385 if (pos > 0) {
3386 adapter = dropArguments(adapter, skip, newTypes.subList(0, pos));
3387 }
3388 // adapter: (S*[skip], P*[pos], M*[match], A*[add] )
3389 return adapter;
3390 }
3391
3392 /**
3393 * Adapts a target method handle to match the given parameter type list, if necessary, by adding dummy arguments.
3394 * Some leading parameters are first skipped; they will be left unchanged and are otherwise ignored.
3395 * The remaining types in the target's parameter type list must be contained as a sub-list of the given type list,
3396 * at the given position.
3397 * Any non-matching parameter types (before or after the matching sub-list) are inserted in corresponding
3398 * positions of the target method handle's parameters, as if by {@link #dropArguments}.
3399 * (More precisely, elements in the new list before {@code pos} are inserted into the target list at {@code skip},
3400 * while elements in the new list after the match beginning at {@code pos} are inserted at the end of the
3401 * target list.)
3402 * The target's return type will be unchanged.
3403 * @apiNote
3404 * Two method handles whose argument lists are "effectively identical" (i.e., identical
3405 * in a common prefix) may be mutually converted to a common type
3406 * by two calls to {@code dropArgumentsToMatch}, as follows:
3407 * <blockquote><pre>{@code
3408 import static java.lang.invoke.MethodHandles.*;
3409 import static java.lang.invoke.MethodType.*;
3410 ...
3411 ...
3412 MethodHandle h0 = constant(boolean.class, true);
3413 MethodHandle h1 = lookup().findVirtual(String.class, "concat", methodType(String.class, String.class));
3414 MethodType bigType = h1.type().insertParameterTypes(1, String.class, int.class);
3415 MethodHandle h2 = dropArguments(h1, 0, bigType.parameterList());
3416 if (h1.type().parameterCount() < h2.type().parameterCount())
3417 h1 = dropArgumentsToMatch(h1, 0, h2.type().parameterList(), 0); // lengthen h1
3418 else
3419 h2 = dropArgumentsToMatch(h2, 0, h1.type().parameterList(), 0); // lengthen h2
3420 MethodHandle h3 = guardWithTest(h0, h1, h2);
3421 assertEquals("xy", h3.invoke("x", "y", 1, "a", "b", "c"));
3422 * }</pre></blockquote>
3423 * @param target the method handle to adapt
3424 * @param skip number of targets parameters to disregard (they will be unchanged)
3425 * @param newTypes the desired argument list of the method handle
3426 * @param pos place in {@code newTypes} where the non-skipped target parameters must occur
3427 * @return a possibly adapted method handle
3428 * @throws NullPointerException if either argument is null
3429 * @throws IllegalArgumentException if any element of {@code newTypes} is {@code void.class},
3430 * or if {@code skip} is negative or greater than the arity of the target,
3431 * or if {@code pos} is negative or greater than the newTypes list size,
3432 * or if the non-skipped target parameter types match the new types at {@code pos}
3433 * @since 9
3434 */
3435 public static
3436 MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos) {
3437 Objects.requireNonNull(target);
3438 Objects.requireNonNull(newTypes);
3439 return dropArgumentsToMatch(target, skip, newTypes, pos, false);
3440 }
3441
3442 /**
3443 * Adapts a target method handle by pre-processing
3444 * one or more of its arguments, each with its own unary filter function,
3445 * and then calling the target with each pre-processed argument
3446 * replaced by the result of its corresponding filter function.
3447 * <p>
3448 * The pre-processing is performed by one or more method handles,
3449 * specified in the elements of the {@code filters} array.
3450 * The first element of the filter array corresponds to the {@code pos}
3451 * argument of the target, and so on in sequence.
3452 * <p>
3453 * Null arguments in the array are treated as identity functions,
3454 * and the corresponding arguments left unchanged.
3455 * (If there are no non-null elements in the array, the original target is returned.)
3456 * Each filter is applied to the corresponding argument of the adapter.
3457 * <p>
3458 * If a filter {@code F} applies to the {@code N}th argument of
3459 * the target, then {@code F} must be a method handle which
3460 * takes exactly one argument. The type of {@code F}'s sole argument
3461 * replaces the corresponding argument type of the target
3462 * in the resulting adapted method handle.
3463 * The return type of {@code F} must be identical to the corresponding
3464 * parameter type of the target.
3465 * <p>
3466 * It is an error if there are elements of {@code filters}
3467 * (null or not)
3468 * which do not correspond to argument positions in the target.
3469 * <p><b>Example:</b>
3470 * <blockquote><pre>{@code
3471 import static java.lang.invoke.MethodHandles.*;
3472 import static java.lang.invoke.MethodType.*;
3473 ...
3474 MethodHandle cat = lookup().findVirtual(String.class,
3475 "concat", methodType(String.class, String.class));
3476 MethodHandle upcase = lookup().findVirtual(String.class,
3477 "toUpperCase", methodType(String.class));
3478 assertEquals("xy", (String) cat.invokeExact("x", "y"));
3479 MethodHandle f0 = filterArguments(cat, 0, upcase);
3480 assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
3481 MethodHandle f1 = filterArguments(cat, 1, upcase);
3482 assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
3483 MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
3484 assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
3485 * }</pre></blockquote>
3486 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
3487 * denotes the return type of both the {@code target} and resulting adapter.
3488 * {@code P}/{@code p} and {@code B}/{@code b} represent the types and values
3489 * of the parameters and arguments that precede and follow the filter position
3490 * {@code pos}, respectively. {@code A[i]}/{@code a[i]} stand for the types and
3491 * values of the filtered parameters and arguments; they also represent the
3492 * return types of the {@code filter[i]} handles. The latter accept arguments
3493 * {@code v[i]} of type {@code V[i]}, which also appear in the signature of
3494 * the resulting adapter.
3495 * <blockquote><pre>{@code
3496 * T target(P... p, A[i]... a[i], B... b);
3497 * A[i] filter[i](V[i]);
3498 * T adapter(P... p, V[i]... v[i], B... b) {
3499 * return target(p..., filter[i](v[i])..., b...);
3500 * }
3501 * }</pre></blockquote>
3502 * <p>
3503 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3504 * variable-arity method handle}, even if the original target method handle was.
3505 *
3506 * @param target the method handle to invoke after arguments are filtered
3507 * @param pos the position of the first argument to filter
3508 * @param filters method handles to call initially on filtered arguments
3509 * @return method handle which incorporates the specified argument filtering logic
3510 * @throws NullPointerException if the target is null
3511 * or if the {@code filters} array is null
3512 * @throws IllegalArgumentException if a non-null element of {@code filters}
3513 * does not match a corresponding argument type of target as described above,
3514 * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()},
3515 * or if the resulting method handle's type would have
3516 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3517 */
3518 public static
3519 MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
3520 filterArgumentsCheckArity(target, pos, filters);
3521 MethodHandle adapter = target;
3522 int curPos = pos-1; // pre-incremented
3523 for (MethodHandle filter : filters) {
3524 curPos += 1;
3525 if (filter == null) continue; // ignore null elements of filters
3526 adapter = filterArgument(adapter, curPos, filter);
3527 }
3528 return adapter;
3529 }
3530
3531 /*non-public*/ static
3532 MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
3533 filterArgumentChecks(target, pos, filter);
3534 MethodType targetType = target.type();
3535 MethodType filterType = filter.type();
3536 BoundMethodHandle result = target.rebind();
3537 Class<?> newParamType = filterType.parameterType(0);
3538 LambdaForm lform = result.editor().filterArgumentForm(1 + pos, BasicType.basicType(newParamType));
3539 MethodType newType = targetType.changeParameterType(pos, newParamType);
3540 result = result.copyWithExtendL(newType, lform, filter);
3541 return result;
3542 }
3543
3544 private static void filterArgumentsCheckArity(MethodHandle target, int pos, MethodHandle[] filters) {
3545 MethodType targetType = target.type();
3546 int maxPos = targetType.parameterCount();
3547 if (pos + filters.length > maxPos)
3548 throw newIllegalArgumentException("too many filters");
3549 }
3550
3551 private static void filterArgumentChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
3552 MethodType targetType = target.type();
3553 MethodType filterType = filter.type();
3554 if (filterType.parameterCount() != 1
3555 || filterType.returnType() != targetType.parameterType(pos))
3556 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
3557 }
3558
3559 /**
3560 * Adapts a target method handle by pre-processing
3561 * a sub-sequence of its arguments with a filter (another method handle).
3562 * The pre-processed arguments are replaced by the result (if any) of the
3563 * filter function.
3564 * The target is then called on the modified (usually shortened) argument list.
3565 * <p>
3566 * If the filter returns a value, the target must accept that value as
3567 * its argument in position {@code pos}, preceded and/or followed by
3568 * any arguments not passed to the filter.
3569 * If the filter returns void, the target must accept all arguments
3570 * not passed to the filter.
3571 * No arguments are reordered, and a result returned from the filter
3572 * replaces (in order) the whole subsequence of arguments originally
3573 * passed to the adapter.
3574 * <p>
3575 * The argument types (if any) of the filter
3576 * replace zero or one argument types of the target, at position {@code pos},
3577 * in the resulting adapted method handle.
3578 * The return type of the filter (if any) must be identical to the
3579 * argument type of the target at position {@code pos}, and that target argument
3580 * is supplied by the return value of the filter.
3581 * <p>
3582 * In all cases, {@code pos} must be greater than or equal to zero, and
3583 * {@code pos} must also be less than or equal to the target's arity.
3584 * <p><b>Example:</b>
3585 * <blockquote><pre>{@code
3586 import static java.lang.invoke.MethodHandles.*;
3587 import static java.lang.invoke.MethodType.*;
3588 ...
3589 MethodHandle deepToString = publicLookup()
3590 .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
3591
3592 MethodHandle ts1 = deepToString.asCollector(String[].class, 1);
3593 assertEquals("[strange]", (String) ts1.invokeExact("strange"));
3594
3595 MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
3596 assertEquals("[up, down]", (String) ts2.invokeExact("up", "down"));
3597
3598 MethodHandle ts3 = deepToString.asCollector(String[].class, 3);
3599 MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2);
3600 assertEquals("[top, [up, down], strange]",
3601 (String) ts3_ts2.invokeExact("top", "up", "down", "strange"));
3602
3603 MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1);
3604 assertEquals("[top, [up, down], [strange]]",
3605 (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange"));
3606
3607 MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3);
3608 assertEquals("[top, [[up, down, strange], charm], bottom]",
3609 (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom"));
3610 * }</pre></blockquote>
3611 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
3612 * represents the return type of the {@code target} and resulting adapter.
3613 * {@code V}/{@code v} stand for the return type and value of the
3614 * {@code filter}, which are also found in the signature and arguments of
3615 * the {@code target}, respectively, unless {@code V} is {@code void}.
3616 * {@code A}/{@code a} and {@code C}/{@code c} represent the parameter types
3617 * and values preceding and following the collection position, {@code pos},
3618 * in the {@code target}'s signature. They also turn up in the resulting
3619 * adapter's signature and arguments, where they surround
3620 * {@code B}/{@code b}, which represent the parameter types and arguments
3621 * to the {@code filter} (if any).
3622 * <blockquote><pre>{@code
3623 * T target(A...,V,C...);
3624 * V filter(B...);
3625 * T adapter(A... a,B... b,C... c) {
3626 * V v = filter(b...);
3627 * return target(a...,v,c...);
3628 * }
3629 * // and if the filter has no arguments:
3630 * T target2(A...,V,C...);
3631 * V filter2();
3632 * T adapter2(A... a,C... c) {
3633 * V v = filter2();
3634 * return target2(a...,v,c...);
3635 * }
3636 * // and if the filter has a void return:
3637 * T target3(A...,C...);
3638 * void filter3(B...);
3639 * T adapter3(A... a,B... b,C... c) {
3640 * filter3(b...);
3641 * return target3(a...,c...);
3642 * }
3643 * }</pre></blockquote>
3644 * <p>
3645 * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to
3646 * one which first "folds" the affected arguments, and then drops them, in separate
3647 * steps as follows:
3648 * <blockquote><pre>{@code
3649 * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2
3650 * mh = MethodHandles.foldArguments(mh, coll); //step 1
3651 * }</pre></blockquote>
3652 * If the target method handle consumes no arguments besides than the result
3653 * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)}
3654 * is equivalent to {@code filterReturnValue(coll, mh)}.
3655 * If the filter method handle {@code coll} consumes one argument and produces
3656 * a non-void result, then {@code collectArguments(mh, N, coll)}
3657 * is equivalent to {@code filterArguments(mh, N, coll)}.
3658 * Other equivalences are possible but would require argument permutation.
3659 * <p>
3660 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3661 * variable-arity method handle}, even if the original target method handle was.
3662 *
3663 * @param target the method handle to invoke after filtering the subsequence of arguments
3664 * @param pos the position of the first adapter argument to pass to the filter,
3665 * and/or the target argument which receives the result of the filter
3666 * @param filter method handle to call on the subsequence of arguments
3667 * @return method handle which incorporates the specified argument subsequence filtering logic
3668 * @throws NullPointerException if either argument is null
3669 * @throws IllegalArgumentException if the return type of {@code filter}
3670 * is non-void and is not the same as the {@code pos} argument of the target,
3671 * or if {@code pos} is not between 0 and the target's arity, inclusive,
3672 * or if the resulting method handle's type would have
3673 * <a href="MethodHandle.html#maxarity">too many parameters</a>
3674 * @see MethodHandles#foldArguments
3675 * @see MethodHandles#filterArguments
3676 * @see MethodHandles#filterReturnValue
3677 */
3678 public static
3679 MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) {
3680 MethodType newType = collectArgumentsChecks(target, pos, filter);
3681 MethodType collectorType = filter.type();
3682 BoundMethodHandle result = target.rebind();
3683 LambdaForm lform;
3684 if (collectorType.returnType().isArray() && filter.intrinsicName() == Intrinsic.NEW_ARRAY) {
3685 lform = result.editor().collectArgumentArrayForm(1 + pos, filter);
3686 if (lform != null) {
3687 return result.copyWith(newType, lform);
3688 }
3689 }
3690 lform = result.editor().collectArgumentsForm(1 + pos, collectorType.basicType());
3691 return result.copyWithExtendL(newType, lform, filter);
3692 }
3693
3694 private static MethodType collectArgumentsChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
3695 MethodType targetType = target.type();
3696 MethodType filterType = filter.type();
3697 Class<?> rtype = filterType.returnType();
3698 List<Class<?>> filterArgs = filterType.parameterList();
3699 if (rtype == void.class) {
3700 return targetType.insertParameterTypes(pos, filterArgs);
3701 }
3702 if (rtype != targetType.parameterType(pos)) {
3703 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
3704 }
3705 return targetType.dropParameterTypes(pos, pos+1).insertParameterTypes(pos, filterArgs);
3706 }
3707
3708 /**
3709 * Adapts a target method handle by post-processing
3710 * its return value (if any) with a filter (another method handle).
3711 * The result of the filter is returned from the adapter.
3712 * <p>
3713 * If the target returns a value, the filter must accept that value as
3714 * its only argument.
3715 * If the target returns void, the filter must accept no arguments.
3716 * <p>
3717 * The return type of the filter
3718 * replaces the return type of the target
3719 * in the resulting adapted method handle.
3720 * The argument type of the filter (if any) must be identical to the
3721 * return type of the target.
3722 * <p><b>Example:</b>
3723 * <blockquote><pre>{@code
3724 import static java.lang.invoke.MethodHandles.*;
3725 import static java.lang.invoke.MethodType.*;
3726 ...
3727 MethodHandle cat = lookup().findVirtual(String.class,
3728 "concat", methodType(String.class, String.class));
3729 MethodHandle length = lookup().findVirtual(String.class,
3730 "length", methodType(int.class));
3731 System.out.println((String) cat.invokeExact("x", "y")); // xy
3732 MethodHandle f0 = filterReturnValue(cat, length);
3733 System.out.println((int) f0.invokeExact("x", "y")); // 2
3734 * }</pre></blockquote>
3735 * <p>Here is pseudocode for the resulting adapter. In the code,
3736 * {@code T}/{@code t} represent the result type and value of the
3737 * {@code target}; {@code V}, the result type of the {@code filter}; and
3738 * {@code A}/{@code a}, the types and values of the parameters and arguments
3739 * of the {@code target} as well as the resulting adapter.
3740 * <blockquote><pre>{@code
3741 * T target(A...);
3742 * V filter(T);
3743 * V adapter(A... a) {
3744 * T t = target(a...);
3745 * return filter(t);
3746 * }
3747 * // and if the target has a void return:
3748 * void target2(A...);
3749 * V filter2();
3750 * V adapter2(A... a) {
3751 * target2(a...);
3752 * return filter2();
3753 * }
3754 * // and if the filter has a void return:
3755 * T target3(A...);
3756 * void filter3(V);
3757 * void adapter3(A... a) {
3758 * T t = target3(a...);
3759 * filter3(t);
3760 * }
3761 * }</pre></blockquote>
3762 * <p>
3763 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3764 * variable-arity method handle}, even if the original target method handle was.
3765 * @param target the method handle to invoke before filtering the return value
3766 * @param filter method handle to call on the return value
3767 * @return method handle which incorporates the specified return value filtering logic
3768 * @throws NullPointerException if either argument is null
3769 * @throws IllegalArgumentException if the argument list of {@code filter}
3770 * does not match the return type of target as described above
3771 */
3772 public static
3773 MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
3774 MethodType targetType = target.type();
3775 MethodType filterType = filter.type();
3776 filterReturnValueChecks(targetType, filterType);
3777 BoundMethodHandle result = target.rebind();
3778 BasicType rtype = BasicType.basicType(filterType.returnType());
3779 LambdaForm lform = result.editor().filterReturnForm(rtype, false);
3780 MethodType newType = targetType.changeReturnType(filterType.returnType());
3781 result = result.copyWithExtendL(newType, lform, filter);
3782 return result;
3783 }
3784
3785 private static void filterReturnValueChecks(MethodType targetType, MethodType filterType) throws RuntimeException {
3786 Class<?> rtype = targetType.returnType();
3787 int filterValues = filterType.parameterCount();
3788 if (filterValues == 0
3789 ? (rtype != void.class)
3790 : (rtype != filterType.parameterType(0)))
3791 throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
3792 }
3793
3794 /**
3795 * Adapts a target method handle by pre-processing
3796 * some of its arguments, and then calling the target with
3797 * the result of the pre-processing, inserted into the original
3798 * sequence of arguments.
3799 * <p>
3800 * The pre-processing is performed by {@code combiner}, a second method handle.
3801 * Of the arguments passed to the adapter, the first {@code N} arguments
3802 * are copied to the combiner, which is then called.
3803 * (Here, {@code N} is defined as the parameter count of the combiner.)
3804 * After this, control passes to the target, with any result
3805 * from the combiner inserted before the original {@code N} incoming
3806 * arguments.
3807 * <p>
3808 * If the combiner returns a value, the first parameter type of the target
3809 * must be identical with the return type of the combiner, and the next
3810 * {@code N} parameter types of the target must exactly match the parameters
3811 * of the combiner.
3812 * <p>
3813 * If the combiner has a void return, no result will be inserted,
3814 * and the first {@code N} parameter types of the target
3815 * must exactly match the parameters of the combiner.
3816 * <p>
3817 * The resulting adapter is the same type as the target, except that the
3818 * first parameter type is dropped,
3819 * if it corresponds to the result of the combiner.
3820 * <p>
3821 * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
3822 * that either the combiner or the target does not wish to receive.
3823 * If some of the incoming arguments are destined only for the combiner,
3824 * consider using {@link MethodHandle#asCollector asCollector} instead, since those
3825 * arguments will not need to be live on the stack on entry to the
3826 * target.)
3827 * <p><b>Example:</b>
3828 * <blockquote><pre>{@code
3829 import static java.lang.invoke.MethodHandles.*;
3830 import static java.lang.invoke.MethodType.*;
3831 ...
3832 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
3833 "println", methodType(void.class, String.class))
3834 .bindTo(System.out);
3835 MethodHandle cat = lookup().findVirtual(String.class,
3836 "concat", methodType(String.class, String.class));
3837 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
3838 MethodHandle catTrace = foldArguments(cat, trace);
3839 // also prints "boo":
3840 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
3841 * }</pre></blockquote>
3842 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
3843 * represents the result type of the {@code target} and resulting adapter.
3844 * {@code V}/{@code v} represent the type and value of the parameter and argument
3845 * of {@code target} that precedes the folding position; {@code V} also is
3846 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
3847 * types and values of the {@code N} parameters and arguments at the folding
3848 * position. {@code B}/{@code b} represent the types and values of the
3849 * {@code target} parameters and arguments that follow the folded parameters
3850 * and arguments.
3851 * <blockquote><pre>{@code
3852 * // there are N arguments in A...
3853 * T target(V, A[N]..., B...);
3854 * V combiner(A...);
3855 * T adapter(A... a, B... b) {
3856 * V v = combiner(a...);
3857 * return target(v, a..., b...);
3858 * }
3859 * // and if the combiner has a void return:
3860 * T target2(A[N]..., B...);
3861 * void combiner2(A...);
3862 * T adapter2(A... a, B... b) {
3863 * combiner2(a...);
3864 * return target2(a..., b...);
3865 * }
3866 * }</pre></blockquote>
3867 * <p>
3868 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
3869 * variable-arity method handle}, even if the original target method handle was.
3870 * @param target the method handle to invoke after arguments are combined
3871 * @param combiner method handle to call initially on the incoming arguments
3872 * @return method handle which incorporates the specified argument folding logic
3873 * @throws NullPointerException if either argument is null
3874 * @throws IllegalArgumentException if {@code combiner}'s return type
3875 * is non-void and not the same as the first argument type of
3876 * the target, or if the initial {@code N} argument types
3877 * of the target
3878 * (skipping one matching the {@code combiner}'s return type)
3879 * are not identical with the argument types of {@code combiner}
3880 */
3881 public static
3882 MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
3883 return foldArguments(target, 0, combiner);
3884 }
3885
3886 private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType) {
3887 int foldArgs = combinerType.parameterCount();
3888 Class<?> rtype = combinerType.returnType();
3889 int foldVals = rtype == void.class ? 0 : 1;
3890 int afterInsertPos = foldPos + foldVals;
3891 boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
3892 if (ok && !(combinerType.parameterList()
3893 .equals(targetType.parameterList().subList(afterInsertPos,
3894 afterInsertPos + foldArgs))))
3895 ok = false;
3896 if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos))
3897 ok = false;
3898 if (!ok)
3899 throw misMatchedTypes("target and combiner types", targetType, combinerType);
3900 return rtype;
3901 }
3902
3903 /**
3904 * Makes a method handle which adapts a target method handle,
3905 * by guarding it with a test, a boolean-valued method handle.
3906 * If the guard fails, a fallback handle is called instead.
3907 * All three method handles must have the same corresponding
3908 * argument and return types, except that the return type
3909 * of the test must be boolean, and the test is allowed
3910 * to have fewer arguments than the other two method handles.
3911 * <p>
3912 * Here is pseudocode for the resulting adapter. In the code, {@code T}
3913 * represents the uniform result type of the three involved handles;
3914 * {@code A}/{@code a}, the types and values of the {@code target}
3915 * parameters and arguments that are consumed by the {@code test}; and
3916 * {@code B}/{@code b}, those types and values of the {@code target}
3917 * parameters and arguments that are not consumed by the {@code test}.
3918 * <blockquote><pre>{@code
3919 * boolean test(A...);
3920 * T target(A...,B...);
3921 * T fallback(A...,B...);
3922 * T adapter(A... a,B... b) {
3923 * if (test(a...))
3924 * return target(a..., b...);
3925 * else
3926 * return fallback(a..., b...);
3927 * }
3928 * }</pre></blockquote>
3929 * Note that the test arguments ({@code a...} in the pseudocode) cannot
3930 * be modified by execution of the test, and so are passed unchanged
3931 * from the caller to the target or fallback as appropriate.
3932 * @param test method handle used for test, must return boolean
3933 * @param target method handle to call if test passes
3934 * @param fallback method handle to call if test fails
3935 * @return method handle which incorporates the specified if/then/else logic
3936 * @throws NullPointerException if any argument is null
3937 * @throws IllegalArgumentException if {@code test} does not return boolean,
3938 * or if all three method types do not match (with the return
3939 * type of {@code test} changed to match that of the target).
3940 */
3941 public static
3942 MethodHandle guardWithTest(MethodHandle test,
3943 MethodHandle target,
3944 MethodHandle fallback) {
3945 MethodType gtype = test.type();
3946 MethodType ttype = target.type();
3947 MethodType ftype = fallback.type();
3948 if (!ttype.equals(ftype))
3949 throw misMatchedTypes("target and fallback types", ttype, ftype);
3950 if (gtype.returnType() != boolean.class)
3951 throw newIllegalArgumentException("guard type is not a predicate "+gtype);
3952 List<Class<?>> targs = ttype.parameterList();
3953 test = dropArgumentsToMatch(test, 0, targs, 0, true);
3954 if (test == null) {
3955 throw misMatchedTypes("target and test types", ttype, gtype);
3956 }
3957 return MethodHandleImpl.makeGuardWithTest(test, target, fallback);
3958 }
3959
3960 static <T> RuntimeException misMatchedTypes(String what, T t1, T t2) {
3961 return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
3962 }
3963
3964 /**
3965 * Makes a method handle which adapts a target method handle,
3966 * by running it inside an exception handler.
3967 * If the target returns normally, the adapter returns that value.
3968 * If an exception matching the specified type is thrown, the fallback
3969 * handle is called instead on the exception, plus the original arguments.
3970 * <p>
3971 * The target and handler must have the same corresponding
3972 * argument and return types, except that handler may omit trailing arguments
3973 * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
3974 * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
3975 * <p>
3976 * Here is pseudocode for the resulting adapter. In the code, {@code T}
3977 * represents the return type of the {@code target} and {@code handler},
3978 * and correspondingly that of the resulting adapter; {@code A}/{@code a},
3979 * the types and values of arguments to the resulting handle consumed by
3980 * {@code handler}; and {@code B}/{@code b}, those of arguments to the
3981 * resulting handle discarded by {@code handler}.
3982 * <blockquote><pre>{@code
3983 * T target(A..., B...);
3984 * T handler(ExType, A...);
3985 * T adapter(A... a, B... b) {
3986 * try {
3987 * return target(a..., b...);
3988 * } catch (ExType ex) {
3989 * return handler(ex, a...);
3990 * }
3991 * }
3992 * }</pre></blockquote>
3993 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
3994 * be modified by execution of the target, and so are passed unchanged
3995 * from the caller to the handler, if the handler is invoked.
3996 * <p>
3997 * The target and handler must return the same type, even if the handler
3998 * always throws. (This might happen, for instance, because the handler
3999 * is simulating a {@code finally} clause).
4000 * To create such a throwing handler, compose the handler creation logic
4001 * with {@link #throwException throwException},
4002 * in order to create a method handle of the correct return type.
4003 * @param target method handle to call
4004 * @param exType the type of exception which the handler will catch
4005 * @param handler method handle to call if a matching exception is thrown
4006 * @return method handle which incorporates the specified try/catch logic
4007 * @throws NullPointerException if any argument is null
4008 * @throws IllegalArgumentException if {@code handler} does not accept
4009 * the given exception type, or if the method handle types do
4010 * not match in their return types and their
4011 * corresponding parameters
4012 * @see MethodHandles#tryFinally(MethodHandle, MethodHandle)
4013 */
4014 public static
4015 MethodHandle catchException(MethodHandle target,
4016 Class<? extends Throwable> exType,
4017 MethodHandle handler) {
4018 MethodType ttype = target.type();
4019 MethodType htype = handler.type();
4020 if (!Throwable.class.isAssignableFrom(exType))
4021 throw new ClassCastException(exType.getName());
4022 if (htype.parameterCount() < 1 ||
4023 !htype.parameterType(0).isAssignableFrom(exType))
4024 throw newIllegalArgumentException("handler does not accept exception type "+exType);
4025 if (htype.returnType() != ttype.returnType())
4026 throw misMatchedTypes("target and handler return types", ttype, htype);
4027 handler = dropArgumentsToMatch(handler, 1, ttype.parameterList(), 0, true);
4028 if (handler == null) {
4029 throw misMatchedTypes("target and handler types", ttype, htype);
4030 }
4031 return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
4032 }
4033
4034 /**
4035 * Produces a method handle which will throw exceptions of the given {@code exType}.
4036 * The method handle will accept a single argument of {@code exType},
4037 * and immediately throw it as an exception.
4038 * The method type will nominally specify a return of {@code returnType}.
4039 * The return type may be anything convenient: It doesn't matter to the
4040 * method handle's behavior, since it will never return normally.
4041 * @param returnType the return type of the desired method handle
4042 * @param exType the parameter type of the desired method handle
4043 * @return method handle which can throw the given exceptions
4044 * @throws NullPointerException if either argument is null
4045 */
4046 public static
4047 MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) {
4048 if (!Throwable.class.isAssignableFrom(exType))
4049 throw new ClassCastException(exType.getName());
4050 return MethodHandleImpl.throwException(methodType(returnType, exType));
4051 }
4052
4053 /**
4054 * Constructs a method handle representing a loop with several loop variables that are updated and checked upon each
4055 * iteration. Upon termination of the loop due to one of the predicates, a corresponding finalizer is run and
4056 * delivers the loop's result, which is the return value of the resulting handle.
4057 * <p>
4058 * Intuitively, every loop is formed by one or more "clauses", each specifying a local iteration value and/or a loop
4059 * exit. Each iteration of the loop executes each clause in order. A clause can optionally update its iteration
4060 * variable; it can also optionally perform a test and conditional loop exit. In order to express this logic in
4061 * terms of method handles, each clause will determine four actions:<ul>
4062 * <li>Before the loop executes, the initialization of an iteration variable or loop invariant local.
4063 * <li>When a clause executes, an update step for the iteration variable.
4064 * <li>When a clause executes, a predicate execution to test for loop exit.
4065 * <li>If a clause causes a loop exit, a finalizer execution to compute the loop's return value.
4066 * </ul>
4067 * <p>
4068 * Some of these clause parts may be omitted according to certain rules, and useful default behavior is provided in
4069 * this case. See below for a detailed description.
4070 * <p>
4071 * Each clause function, with the exception of clause initializers, is able to observe the entire loop state,
4072 * because it will be passed <em>all</em> current iteration variable values, as well as all incoming loop
4073 * parameters. Most clause functions will not need all of this information, but they will be formally connected as
4074 * if by {@link #dropArguments}.
4075 * <p>
4076 * Given a set of clauses, there is a number of checks and adjustments performed to connect all the parts of the
4077 * loop. They are spelled out in detail in the steps below. In these steps, every occurrence of the word "must"
4078 * corresponds to a place where {@link IllegalArgumentException} may be thrown if the required constraint is not met
4079 * by the inputs to the loop combinator. The term "effectively identical", applied to parameter type lists, means
4080 * that they must be identical, or else one list must be a proper prefix of the other.
4081 * <p>
4082 * <em>Step 0: Determine clause structure.</em><ol type="a">
4083 * <li>The clause array (of type {@code MethodHandle[][]} must be non-{@code null} and contain at least one element.
4084 * <li>The clause array may not contain {@code null}s or sub-arrays longer than four elements.
4085 * <li>Clauses shorter than four elements are treated as if they were padded by {@code null} elements to length
4086 * four. Padding takes place by appending elements to the array.
4087 * <li>Clauses with all {@code null}s are disregarded.
4088 * <li>Each clause is treated as a four-tuple of functions, called "init", "step", "pred", and "fini".
4089 * </ol>
4090 * <p>
4091 * <em>Step 1A: Determine iteration variables.</em><ol type="a">
4092 * <li>Examine init and step function return types, pairwise, to determine each clause's iteration variable type.
4093 * <li>If both functions are omitted, use {@code void}; else if one is omitted, use the other's return type; else
4094 * use the common return type (they must be identical).
4095 * <li>Form the list of return types (in clause order), omitting all occurrences of {@code void}.
4096 * <li>This list of types is called the "common prefix".
4097 * </ol>
4098 * <p>
4099 * <em>Step 1B: Determine loop parameters.</em><ul>
4100 * <li><b>If at least one init function is given,</b><ol type="a">
4101 * <li>Examine init function parameter lists.
4102 * <li>Omitted init functions are deemed to have {@code null} parameter lists.
4103 * <li>All init function parameter lists must be effectively identical.
4104 * <li>The longest parameter list (which is necessarily unique) is called the "common suffix".
4105 * </ol>
4106 * <li><b>If no init function is given,</b><ol type="a">
4107 * <li>Examine the suffixes of the step, pred, and fini parameter lists, after removing the "common prefix".
4108 * <li>The longest of these suffixes is taken as the "common suffix".
4109 * </ol></ul>
4110 * <p>
4111 * <em>Step 1C: Determine loop return type.</em><ol type="a">
4112 * <li>Examine fini function return types, disregarding omitted fini functions.
4113 * <li>If there are no fini functions, use {@code void} as the loop return type.
4114 * <li>Otherwise, use the common return type of the fini functions; they must all be identical.
4115 * </ol>
4116 * <p>
4117 * <em>Step 1D: Check other types.</em><ol type="a">
4118 * <li>There must be at least one non-omitted pred function.
4119 * <li>Every non-omitted pred function must have a {@code boolean} return type.
4120 * </ol>
4121 * <p>
4122 * <em>Step 2: Determine parameter lists.</em><ol type="a">
4123 * <li>The parameter list for the resulting loop handle will be the "common suffix".
4124 * <li>The parameter list for init functions will be adjusted to the "common suffix". (Note that their parameter
4125 * lists are already effectively identical to the common suffix.)
4126 * <li>The parameter list for non-init (step, pred, and fini) functions will be adjusted to the common prefix
4127 * followed by the common suffix, called the "common parameter sequence".
4128 * <li>Every non-init, non-omitted function parameter list must be effectively identical to the common parameter
4129 * sequence.
4130 * </ol>
4131 * <p>
4132 * <em>Step 3: Fill in omitted functions.</em><ol type="a">
4133 * <li>If an init function is omitted, use a {@linkplain #constant constant function} of the appropriate
4134 * {@code null}/zero/{@code false}/{@code void} type. (For this purpose, a constant {@code void} is simply a
4135 * function which does nothing and returns {@code void}; it can be obtained from another constant function by
4136 * {@linkplain MethodHandle#asType type conversion}.)
4137 * <li>If a step function is omitted, use an {@linkplain #identity identity function} of the clause's iteration
4138 * variable type; insert dropped argument parameters before the identity function parameter for the non-{@code void}
4139 * iteration variables of preceding clauses. (This will turn the loop variable into a local loop invariant.)
4140 * <li>If a pred function is omitted, the corresponding fini function must also be omitted.
4141 * <li>If a pred function is omitted, use a constant {@code true} function. (This will keep the loop going, as far
4142 * as this clause is concerned.)
4143 * <li>If a fini function is omitted, use a constant {@code null}/zero/{@code false}/{@code void} function of the
4144 * loop return type.
4145 * </ol>
4146 * <p>
4147 * <em>Step 4: Fill in missing parameter types.</em><ol type="a">
4148 * <li>At this point, every init function parameter list is effectively identical to the common suffix, but some
4149 * lists may be shorter. For every init function with a short parameter list, pad out the end of the list by
4150 * {@linkplain #dropArguments dropping arguments}.
4151 * <li>At this point, every non-init function parameter list is effectively identical to the common parameter
4152 * sequence, but some lists may be shorter. For every non-init function with a short parameter list, pad out the end
4153 * of the list by {@linkplain #dropArguments dropping arguments}.
4154 * </ol>
4155 * <p>
4156 * <em>Final observations.</em><ol type="a">
4157 * <li>After these steps, all clauses have been adjusted by supplying omitted functions and arguments.
4158 * <li>All init functions have a common parameter type list, which the final loop handle will also have.
4159 * <li>All fini functions have a common return type, which the final loop handle will also have.
4160 * <li>All non-init functions have a common parameter type list, which is the common parameter sequence, of
4161 * (non-{@code void}) iteration variables followed by loop parameters.
4162 * <li>Each pair of init and step functions agrees in their return types.
4163 * <li>Each non-init function will be able to observe the current values of all iteration variables, by means of the
4164 * common prefix.
4165 * </ol>
4166 * <p>
4167 * <em>Loop execution.</em><ol type="a">
4168 * <li>When the loop is called, the loop input values are saved in locals, to be passed (as the common suffix) to
4169 * every clause function. These locals are loop invariant.
4170 * <li>Each init function is executed in clause order (passing the common suffix) and the non-{@code void} values
4171 * are saved (as the common prefix) into locals. These locals are loop varying (unless their steps are identity
4172 * functions, as noted above).
4173 * <li>All function executions (except init functions) will be passed the common parameter sequence, consisting of
4174 * the non-{@code void} iteration values (in clause order) and then the loop inputs (in argument order).
4175 * <li>The step and pred functions are then executed, in clause order (step before pred), until a pred function
4176 * returns {@code false}.
4177 * <li>The non-{@code void} result from a step function call is used to update the corresponding loop variable. The
4178 * updated value is immediately visible to all subsequent function calls.
4179 * <li>If a pred function returns {@code false}, the corresponding fini function is called, and the resulting value
4180 * is returned from the loop as a whole.
4181 * </ol>
4182 * <p>
4183 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the types / values
4184 * of loop variables; {@code A}/{@code a}, those of arguments passed to the resulting loop; and {@code R}, the
4185 * result types of finalizers as well as of the resulting loop.
4186 * <blockquote><pre>{@code
4187 * V... init...(A...);
4188 * boolean pred...(V..., A...);
4189 * V... step...(V..., A...);
4190 * R fini...(V..., A...);
4191 * R loop(A... a) {
4192 * V... v... = init...(a...);
4193 * for (;;) {
4194 * for ((v, p, s, f) in (v..., pred..., step..., fini...)) {
4195 * v = s(v..., a...);
4196 * if (!p(v..., a...)) {
4197 * return f(v..., a...);
4198 * }
4199 * }
4200 * }
4201 * }
4202 * }</pre></blockquote>
4203 * <p>
4204 * @apiNote Example:
4205 * <blockquote><pre>{@code
4206 * // iterative implementation of the factorial function as a loop handle
4207 * static int one(int k) { return 1; }
4208 * static int inc(int i, int acc, int k) { return i + 1; }
4209 * static int mult(int i, int acc, int k) { return i * acc; }
4210 * static boolean pred(int i, int acc, int k) { return i < k; }
4211 * static int fin(int i, int acc, int k) { return acc; }
4212 * // assume MH_one, MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
4213 * // null initializer for counter, should initialize to 0
4214 * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
4215 * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
4216 * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
4217 * assertEquals(120, loop.invoke(5));
4218 * }</pre></blockquote>
4219 *
4220 * @param clauses an array of arrays (4-tuples) of {@link MethodHandle}s adhering to the rules described above.
4221 *
4222 * @return a method handle embodying the looping behavior as defined by the arguments.
4223 *
4224 * @throws IllegalArgumentException in case any of the constraints described above is violated.
4225 *
4226 * @see MethodHandles#whileLoop(MethodHandle, MethodHandle, MethodHandle)
4227 * @see MethodHandles#doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
4228 * @see MethodHandles#countedLoop(MethodHandle, MethodHandle, MethodHandle)
4229 * @see MethodHandles#iteratedLoop(MethodHandle, MethodHandle, MethodHandle)
4230 * @since 9
4231 */
4232 public static MethodHandle loop(MethodHandle[]... clauses) {
4233 // Step 0: determine clause structure.
4234 checkLoop0(clauses);
4235
4236 List<MethodHandle> init = new ArrayList<>();
4237 List<MethodHandle> step = new ArrayList<>();
4238 List<MethodHandle> pred = new ArrayList<>();
4239 List<MethodHandle> fini = new ArrayList<>();
4240
4241 Stream.of(clauses).filter(c -> Stream.of(c).anyMatch(Objects::nonNull)).forEach(clause -> {
4242 init.add(clause[0]); // all clauses have at least length 1
4243 step.add(clause.length <= 1 ? null : clause[1]);
4244 pred.add(clause.length <= 2 ? null : clause[2]);
4245 fini.add(clause.length <= 3 ? null : clause[3]);
4246 });
4247
4248 assert Stream.of(init, step, pred, fini).map(List::size).distinct().count() == 1;
4249 final int nclauses = init.size();
4250
4251 // Step 1A: determine iteration variables.
4252 final List<Class<?>> iterationVariableTypes = new ArrayList<>();
4253 for (int i = 0; i < nclauses; ++i) {
4254 MethodHandle in = init.get(i);
4255 MethodHandle st = step.get(i);
4256 if (in == null && st == null) {
4257 iterationVariableTypes.add(void.class);
4258 } else if (in != null && st != null) {
4259 checkLoop1a(i, in, st);
4260 iterationVariableTypes.add(in.type().returnType());
4261 } else {
4262 iterationVariableTypes.add(in == null ? st.type().returnType() : in.type().returnType());
4263 }
4264 }
4265 final List<Class<?>> commonPrefix = iterationVariableTypes.stream().filter(t -> t != void.class).
4266 collect(Collectors.toList());
4267
4268 // Step 1B: determine loop parameters.
4269 final List<Class<?>> commonSuffix = buildCommonSuffix(init, step, pred, fini, commonPrefix.size());
4270 checkLoop1b(init, commonSuffix);
4271
4272 // Step 1C: determine loop return type.
4273 // Step 1D: check other types.
4274 final Class<?> loopReturnType = fini.stream().filter(Objects::nonNull).map(MethodHandle::type).
4275 map(MethodType::returnType).findFirst().orElse(void.class);
4276 checkLoop1cd(pred, fini, loopReturnType);
4277
4278 // Step 2: determine parameter lists.
4279 final List<Class<?>> commonParameterSequence = new ArrayList<>(commonPrefix);
4280 commonParameterSequence.addAll(commonSuffix);
4281 checkLoop2(step, pred, fini, commonParameterSequence);
4282
4283 // Step 3: fill in omitted functions.
4284 for (int i = 0; i < nclauses; ++i) {
4285 Class<?> t = iterationVariableTypes.get(i);
4286 if (init.get(i) == null) {
4287 init.set(i, empty(methodType(t, commonSuffix)));
4288 }
4289 if (step.get(i) == null) {
4290 step.set(i, dropArgumentsToMatch(identityOrVoid(t), 0, commonParameterSequence, i));
4291 }
4292 if (pred.get(i) == null) {
4293 pred.set(i, dropArguments(constant(boolean.class, true), 0, commonParameterSequence));
4294 }
4295 if (fini.get(i) == null) {
4296 fini.set(i, empty(methodType(t, commonParameterSequence)));
4297 }
4298 }
4299
4300 // Step 4: fill in missing parameter types.
4301 List<MethodHandle> finit = fillParameterTypes(init, commonSuffix);
4302 List<MethodHandle> fstep = fillParameterTypes(step, commonParameterSequence);
4303 List<MethodHandle> fpred = fillParameterTypes(pred, commonParameterSequence);
4304 List<MethodHandle> ffini = fillParameterTypes(fini, commonParameterSequence);
4305
4306 assert finit.stream().map(MethodHandle::type).map(MethodType::parameterList).
4307 allMatch(pl -> pl.equals(commonSuffix));
4308 assert Stream.of(fstep, fpred, ffini).flatMap(List::stream).map(MethodHandle::type).map(MethodType::parameterList).
4309 allMatch(pl -> pl.equals(commonParameterSequence));
4310
4311 return MethodHandleImpl.makeLoop(loopReturnType, commonSuffix, finit, fstep, fpred, ffini);
4312 }
4313
4314 private static List<MethodHandle> fillParameterTypes(List<MethodHandle> hs, final List<Class<?>> targetParams) {
4315 return hs.stream().map(h -> {
4316 int pc = h.type().parameterCount();
4317 int tpsize = targetParams.size();
4318 return pc < tpsize ? dropArguments(h, pc, targetParams.subList(pc, tpsize)) : h;
4319 }).collect(Collectors.toList());
4320 }
4321
4322 /**
4323 * Constructs a {@code while} loop from an initializer, a body, and a predicate. This is a convenience wrapper for
4324 * the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
4325 * <p>
4326 * The loop handle's result type is the same as the sole loop variable's, i.e., the result type of {@code init}.
4327 * The parameter type list of {@code init} also determines that of the resulting handle. The {@code pred} handle
4328 * must have an additional leading parameter of the same type as {@code init}'s result, and so must the {@code
4329 * body}. These constraints follow directly from those described for the {@linkplain MethodHandles#loop(MethodHandle[][])
4330 * generic loop combinator}.
4331 * <p>
4332 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
4333 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
4334 * passed to the loop.
4335 * <blockquote><pre>{@code
4336 * V init(A);
4337 * boolean pred(V, A);
4338 * V body(V, A);
4339 * V whileLoop(A a) {
4340 * V v = init(a);
4341 * while (pred(v, a)) {
4342 * v = body(v, a);
4343 * }
4344 * return v;
4345 * }
4346 * }</pre></blockquote>
4347 * <p>
4348 * @apiNote Example:
4349 * <blockquote><pre>{@code
4350 * // implement the zip function for lists as a loop handle
4351 * static List<String> initZip(Iterator<String> a, Iterator<String> b) { return new ArrayList<>(); }
4352 * static boolean zipPred(List<String> zip, Iterator<String> a, Iterator<String> b) { return a.hasNext() && b.hasNext(); }
4353 * static List<String> zipStep(List<String> zip, Iterator<String> a, Iterator<String> b) {
4354 * zip.add(a.next());
4355 * zip.add(b.next());
4356 * return zip;
4357 * }
4358 * // assume MH_initZip, MH_zipPred, and MH_zipStep are handles to the above methods
4359 * MethodHandle loop = MethodHandles.whileLoop(MH_initZip, MH_zipPred, MH_zipStep);
4360 * List<String> a = Arrays.asList("a", "b", "c", "d");
4361 * List<String> b = Arrays.asList("e", "f", "g", "h");
4362 * List<String> zipped = Arrays.asList("a", "e", "b", "f", "c", "g", "d", "h");
4363 * assertEquals(zipped, (List<String>) loop.invoke(a.iterator(), b.iterator()));
4364 * }</pre></blockquote>
4365 *
4366 * <p>
4367 * @implSpec The implementation of this method is equivalent to:
4368 * <blockquote><pre>{@code
4369 * MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
4370 * MethodHandle[]
4371 * checkExit = {null, null, pred, identity(init.type().returnType())},
4372 * varBody = {init, body};
4373 * return loop(checkExit, varBody);
4374 * }
4375 * }</pre></blockquote>
4376 *
4377 * @param init initializer: it should provide the initial value of the loop variable. This controls the loop's
4378 * result type. Passing {@code null} or a {@code void} init function will make the loop's result type
4379 * {@code void}.
4380 * @param pred condition for the loop, which may not be {@code null}.
4381 * @param body body of the loop, which may not be {@code null}.
4382 *
4383 * @return the value of the loop variable as the loop terminates.
4384 * @throws IllegalArgumentException if any argument has a type inconsistent with the loop structure
4385 *
4386 * @see MethodHandles#loop(MethodHandle[][])
4387 * @since 9
4388 */
4389 public static MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
4390 MethodHandle fin = init == null || init.type().returnType() == void.class ? zero(void.class) :
4391 identity(init.type().returnType());
4392 MethodHandle[] checkExit = {null, null, pred, fin};
4393 MethodHandle[] varBody = {init, body};
4394 return loop(checkExit, varBody);
4395 }
4396
4397 /**
4398 * Constructs a {@code do-while} loop from an initializer, a body, and a predicate. This is a convenience wrapper
4399 * for the {@linkplain MethodHandles#loop(MethodHandle[][]) generic loop combinator}.
4400 * <p>
4401 * The loop handle's result type is the same as the sole loop variable's, i.e., the result type of {@code init}.
4402 * The parameter type list of {@code init} also determines that of the resulting handle. The {@code pred} handle
4403 * must have an additional leading parameter of the same type as {@code init}'s result, and so must the {@code
4404 * body}. These constraints follow directly from those described for the {@linkplain MethodHandles#loop(MethodHandle[][])
4405 * generic loop combinator}.
4406 * <p>
4407 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
4408 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
4409 * passed to the loop.
4410 * <blockquote><pre>{@code
4411 * V init(A);
4412 * boolean pred(V, A);
4413 * V body(V, A);
4414 * V doWhileLoop(A a) {
4415 * V v = init(a);
4416 * do {
4417 * v = body(v, a);
4418 * } while (pred(v, a));
4419 * return v;
4420 * }
4421 * }</pre></blockquote>
4422 * <p>
4423 * @apiNote Example:
4424 * <blockquote><pre>{@code
4425 * // int i = 0; while (i < limit) { ++i; } return i; => limit
4426 * static int zero(int limit) { return 0; }
4427 * static int step(int i, int limit) { return i + 1; }
4428 * static boolean pred(int i, int limit) { return i < limit; }
4429 * // assume MH_zero, MH_step, and MH_pred are handles to the above methods
4430 * MethodHandle loop = MethodHandles.doWhileLoop(MH_zero, MH_step, MH_pred);
4431 * assertEquals(23, loop.invoke(23));
4432 * }</pre></blockquote>
4433 *
4434 * <p>
4435 * @implSpec The implementation of this method is equivalent to:
4436 * <blockquote><pre>{@code
4437 * MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
4438 * MethodHandle[] clause = { init, body, pred, identity(init.type().returnType()) };
4439 * return loop(clause);
4440 * }
4441 * }</pre></blockquote>
4442 *
4443 *
4444 * @param init initializer: it should provide the initial value of the loop variable. This controls the loop's
4445 * result type. Passing {@code null} or a {@code void} init function will make the loop's result type
4446 * {@code void}.
4447 * @param pred condition for the loop, which may not be {@code null}.
4448 * @param body body of the loop, which may not be {@code null}.
4449 *
4450 * @return the value of the loop variable as the loop terminates.
4451 * @throws IllegalArgumentException if any argument has a type inconsistent with the loop structure
4452 *
4453 * @see MethodHandles#loop(MethodHandle[][])
4454 * @since 9
4455 */
4456 public static MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
4457 MethodHandle fin = init == null || init.type().returnType() == void.class ? zero(void.class) :
4458 identity(init.type().returnType());
4459 MethodHandle[] clause = {init, body, pred, fin};
4460 return loop(clause);
4461 }
4462
4463 /**
4464 * Constructs a loop that runs a given number of iterations. The loop counter is an {@code int} initialized from the
4465 * {@code iterations} handle evaluation result. The counter is passed to the {@code body} function, so that must
4466 * accept an initial {@code int} argument. The result of the loop execution is the final value of the additional
4467 * local state. This is a convenience wrapper for the {@linkplain MethodHandles#loop(MethodHandle[][]) generic loop
4468 * combinator}.
4469 * <p>
4470 * The result type and parameter type list of {@code init} determine those of the resulting handle. The {@code
4471 * iterations} handle must accept the same parameter types as {@code init} but return an {@code int}. The {@code
4472 * body} handle must accept the same parameter types as well, preceded by an {@code int} parameter for the counter,
4473 * and a parameter of the same type as {@code init}'s result. These constraints follow directly from those described
4474 * for the {@linkplain MethodHandles#loop(MethodHandle[][]) generic loop combinator}.
4475 * <p>
4476 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
4477 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
4478 * passed to the loop.
4479 * <blockquote><pre>{@code
4480 * int iterations(A);
4481 * V init(A);
4482 * V body(int, V, A);
4483 * V countedLoop(A a) {
4484 * int end = iterations(a);
4485 * V v = init(a);
4486 * for (int i = 0; i < end; ++i) {
4487 * v = body(i, v, a);
4488 * }
4489 * return v;
4490 * }
4491 * }</pre></blockquote>
4492 * <p>
4493 * @apiNote Example:
4494 * <blockquote><pre>{@code
4495 * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
4496 * // => a variation on a well known theme
4497 * static String start(String arg) { return arg; }
4498 * static String step(int counter, String v, String arg) { return "na " + v; }
4499 * // assume MH_start and MH_step are handles to the two methods above
4500 * MethodHandle fit13 = MethodHandles.constant(int.class, 13);
4501 * MethodHandle loop = MethodHandles.countedLoop(fit13, MH_start, MH_step);
4502 * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("Lambdaman!"));
4503 * }</pre></blockquote>
4504 *
4505 * <p>
4506 * @implSpec The implementation of this method is equivalent to:
4507 * <blockquote><pre>{@code
4508 * MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
4509 * return countedLoop(null, iterations, init, body); // null => constant zero
4510 * }
4511 * }</pre></blockquote>
4512 *
4513 * @param iterations a handle to return the number of iterations this loop should run.
4514 * @param init initializer for additional loop state. This determines the loop's result type.
4515 * Passing {@code null} or a {@code void} init function will make the loop's result type
4516 * {@code void}.
4517 * @param body the body of the loop, which must not be {@code null}.
4518 * It must accept an initial {@code int} parameter (for the counter), and then any
4519 * additional loop-local variable plus loop parameters.
4520 *
4521 * @return a method handle representing the loop.
4522 * @throws IllegalArgumentException if any argument has a type inconsistent with the loop structure
4523 *
4524 * @since 9
4525 */
4526 public static MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
4527 return countedLoop(null, iterations, init, body);
4528 }
4529
4530 /**
4531 * Constructs a loop that counts over a range of numbers. The loop counter is an {@code int} that will be
4532 * initialized to the {@code int} value returned from the evaluation of the {@code start} handle and run to the
4533 * value returned from {@code end} (exclusively) with a step width of 1. The counter value is passed to the {@code
4534 * body} function in each iteration; it has to accept an initial {@code int} parameter
4535 * for that. The result of the loop execution is the final value of the additional local state
4536 * obtained by running {@code init}.
4537 * This is a
4538 * convenience wrapper for the {@linkplain MethodHandles#loop(MethodHandle[][]) generic loop combinator}.
4539 * <p>
4540 * The constraints for the {@code init} and {@code body} handles are the same as for {@link
4541 * #countedLoop(MethodHandle, MethodHandle, MethodHandle)}. Additionally, the {@code start} and {@code end} handles
4542 * must return an {@code int} and accept the same parameters as {@code init}.
4543 * <p>
4544 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
4545 * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
4546 * passed to the loop.
4547 * <blockquote><pre>{@code
4548 * int start(A);
4549 * int end(A);
4550 * V init(A);
4551 * V body(int, V, A);
4552 * V countedLoop(A a) {
4553 * int s = start(a);
4554 * int e = end(a);
4555 * V v = init(a);
4556 * for (int i = s; i < e; ++i) {
4557 * v = body(i, v, a);
4558 * }
4559 * return v;
4560 * }
4561 * }</pre></blockquote>
4562 *
4563 * <p>
4564 * @implSpec The implementation of this method is equivalent to:
4565 * <blockquote><pre>{@code
4566 * MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
4567 * MethodHandle returnVar = dropArguments(identity(init.type().returnType()), 0, int.class, int.class);
4568 * // assume MH_increment and MH_lessThan are handles to x+1 and x<y of type int,
4569 * // assume MH_decrement is a handle to x-1 of type int
4570 * MethodHandle[]
4571 * indexVar = {start, MH_increment}, // i = start; i = i+1
4572 * loopLimit = {end, null, MH_lessThan, returnVar }, // i<end
4573 * bodyClause = {init,
4574 * filterArgument(dropArguments(body, 1, int.class), 0, MH_decrement}; // v = body(i-1, v)
4575 * return loop(indexVar, loopLimit, bodyClause);
4576 * }
4577 * }</pre></blockquote>
4578 *
4579 * @param start a handle to return the start value of the loop counter.
4580 * If it is {@code null}, a constant zero is assumed.
4581 * @param end a non-{@code null} handle to return the end value of the loop counter (the loop will run to {@code end-1}).
4582 * @param init initializer for additional loop state. This determines the loop's result type.
4583 * Passing {@code null} or a {@code void} init function will make the loop's result type
4584 * {@code void}.
4585 * @param body the body of the loop, which must not be {@code null}.
4586 * It must accept an initial {@code int} parameter (for the counter), and then any
4587 * additional loop-local variable plus loop parameters.
4588 *
4589 * @return a method handle representing the loop.
4590 * @throws IllegalArgumentException if any argument has a type inconsistent with the loop structure
4591 *
4592 * @since 9
4593 */
4594 public static MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
4595 Class<?> resultType;
4596 MethodHandle actualInit;
4597 if (init == null) {
4598 resultType = body == null ? void.class : body.type().returnType();
4599 actualInit = empty(methodType(resultType));
4600 } else {
4601 resultType = init.type().returnType();
4602 actualInit = init;
4603 }
4604 MethodHandle defaultResultHandle = resultType == void.class ? zero(void.class) : identity(resultType);
4605 MethodHandle actualBody = body == null ? dropArguments(defaultResultHandle, 0, int.class) : body;
4606 MethodHandle returnVar = dropArguments(defaultResultHandle, 0, int.class, int.class);
4607 MethodHandle actualEnd = end == null ? constant(int.class, 0) : end;
4608 MethodHandle[] indexVar = {start, MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopStep)};
4609 MethodHandle[] loopLimit = {actualEnd, null,
4610 MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopPred), returnVar};
4611 MethodHandle[] bodyClause = {actualInit,
4612 filterArgument(dropArguments(actualBody, 1, int.class), 0,
4613 MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_decrementCounter))};
4614 return loop(indexVar, loopLimit, bodyClause);
4615 }
4616
4617 /**
4618 * Constructs a loop that ranges over the elements produced by an {@code Iterator<T>}.
4619 * The iterator will be produced by the evaluation of the {@code iterator} handle.
4620 * This handle must have {@link java.util.Iterator} as its return type.
4621 * If this handle is passed as {@code null} the method {@link Iterable#iterator} will be used instead,
4622 * and will be applied to a leading argument of the loop handle.
4623 * Each value produced by the iterator is passed to the {@code body}, which must accept an initial {@code T} parameter.
4624 * The result of the loop execution is the final value of the additional local state
4625 * obtained by running {@code init}.
4626 * <p>
4627 * This is a convenience wrapper for the
4628 * {@linkplain MethodHandles#loop(MethodHandle[][]) generic loop combinator}, and the constraints imposed on the {@code body}
4629 * handle follow directly from those described for the latter.
4630 * <p>
4631 * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
4632 * the loop variable as well as the result type of the loop; {@code T}/{@code t}, that of the elements of the
4633 * structure the loop iterates over, and {@code A}/{@code a}, that of the argument passed to the loop.
4634 * <blockquote><pre>{@code
4635 * Iterator<T> iterator(A); // defaults to Iterable::iterator
4636 * V init(A);
4637 * V body(T,V,A);
4638 * V iteratedLoop(A a) {
4639 * Iterator<T> it = iterator(a);
4640 * V v = init(a);
4641 * for (T t : it) {
4642 * v = body(t, v, a);
4643 * }
4644 * return v;
4645 * }
4646 * }</pre></blockquote>
4647 * <p>
4648 * The type {@code T} may be either a primitive or reference.
4649 * Since type {@code Iterator<T>} is erased in the method handle representation to the raw type
4650 * {@code Iterator}, the {@code iteratedLoop} combinator adjusts the leading argument type for {@code body}
4651 * to {@code Object} as if by the {@link MethodHandle#asType asType} conversion method.
4652 * Therefore, if an iterator of the wrong type appears as the loop is executed,
4653 * runtime exceptions may occur as the result of dynamic conversions performed by {@code asType}.
4654 * <p>
4655 * @apiNote Example:
4656 * <blockquote><pre>{@code
4657 * // reverse a list
4658 * static List<String> reverseStep(String e, List<String> r, List<String> l) {
4659 * r.add(0, e);
4660 * return r;
4661 * }
4662 * static List<String> newArrayList(List<String> l) { return new ArrayList<>(); }
4663 * // assume MH_reverseStep, MH_newArrayList are handles to the above methods
4664 * MethodHandle loop = MethodHandles.iteratedLoop(null, MH_newArrayList, MH_reverseStep);
4665 * List<String> list = Arrays.asList("a", "b", "c", "d", "e");
4666 * List<String> reversedList = Arrays.asList("e", "d", "c", "b", "a");
4667 * assertEquals(reversedList, (List<String>) loop.invoke(list));
4668 * }</pre></blockquote>
4669 * <p>
4670 * @implSpec The implementation of this method is equivalent to (excluding error handling):
4671 * <blockquote><pre>{@code
4672 * MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
4673 * // assume MH_next and MH_hasNext are handles to methods of Iterator
4674 * Class<?> itype = iterator.type().returnType();
4675 * Class<?> ttype = body.type().parameterType(0);
4676 * MethodHandle returnVar = dropArguments(identity(init.type().returnType()), 0, itype);
4677 * MethodHandle nextVal = MH_next.asType(MH_next.type().changeReturnType(ttype));
4678 * MethodHandle[]
4679 * iterVar = {iterator, null, MH_hasNext, returnVar}, // it = iterator(); while (it.hasNext)
4680 * bodyClause = {init, filterArgument(body, 0, nextVal)}; // v = body(t, v, a);
4681 * return loop(iterVar, bodyClause);
4682 * }
4683 * }</pre></blockquote>
4684 *
4685 * @param iterator a handle to return the iterator to start the loop.
4686 * The handle must have {@link java.util.Iterator} as its return type.
4687 * Passing {@code null} will make the loop call {@link Iterable#iterator()} on the first
4688 * incoming value.
4689 * @param init initializer for additional loop state. This determines the loop's result type.
4690 * Passing {@code null} or a {@code void} init function will make the loop's result type
4691 * {@code void}.
4692 * @param body the body of the loop, which must not be {@code null}.
4693 * It must accept an initial {@code T} parameter (for the iterated values), and then any
4694 * additional loop-local variable plus loop parameters.
4695 *
4696 * @return a method handle embodying the iteration loop functionality.
4697 * @throws IllegalArgumentException if any argument has a type inconsistent with the loop structure
4698 *
4699 * @since 9
4700 */
4701 public static MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
4702 checkIteratedLoop(iterator, body);
4703 Class<?> resultType = init == null ?
4704 body == null ? void.class : body.type().returnType() :
4705 init.type().returnType();
4706 boolean voidResult = resultType == void.class;
4707
4708 MethodHandle initIterator;
4709 if (iterator == null) {
4710 MethodHandle initit = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_initIterator);
4711 initIterator = initit.asType(initit.type().changeParameterType(0,
4712 body.type().parameterType(voidResult ? 1 : 2)));
4713 } else {
4714 initIterator = iterator.asType(iterator.type().changeReturnType(Iterator.class));
4715 }
4716
4717 Class<?> ttype = body.type().parameterType(0);
4718
4719 MethodHandle returnVar =
4720 dropArguments(voidResult ? zero(void.class) : identity(resultType), 0, Iterator.class);
4721 MethodHandle initnx = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iterateNext);
4722 MethodHandle nextVal = initnx.asType(initnx.type().changeReturnType(ttype));
4723
4724 MethodHandle[] iterVar = {initIterator, null, MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iteratePred),
4725 returnVar};
4726 MethodHandle[] bodyClause = {init, filterArgument(body, 0, nextVal)};
4727
4728 return loop(iterVar, bodyClause);
4729 }
4730
4731 /**
4732 * Makes a method handle that adapts a {@code target} method handle by wrapping it in a {@code try-finally} block.
4733 * Another method handle, {@code cleanup}, represents the functionality of the {@code finally} block. Any exception
4734 * thrown during the execution of the {@code target} handle will be passed to the {@code cleanup} handle. The
4735 * exception will be rethrown, unless {@code cleanup} handle throws an exception first. The
4736 * value returned from the {@code cleanup} handle's execution will be the result of the execution of the
4737 * {@code try-finally} handle.
4738 * <p>
4739 * The {@code cleanup} handle will be passed one or two additional leading arguments.
4740 * The first is the exception thrown during the
4741 * execution of the {@code target} handle, or {@code null} if no exception was thrown.
4742 * The second is the result of the execution of the {@code target} handle, or, if it throws an exception,
4743 * a {@code null}, zero, or {@code false} value of the required type is supplied as a placeholder.
4744 * The second argument is not present if the {@code target} handle has a {@code void} return type.
4745 * (Note that, except for argument type conversions, combinators represent {@code void} values in parameter lists
4746 * by omitting the corresponding paradoxical arguments, not by inserting {@code null} or zero values.)
4747 * <p>
4748 * The {@code target} and {@code cleanup} handles must have the same corresponding argument and return types, except
4749 * that the {@code cleanup} handle may omit trailing arguments. Also, the {@code cleanup} handle must have one or
4750 * two extra leading parameters:<ul>
4751 * <li>a {@code Throwable}, which will carry the exception thrown by the {@code target} handle (if any); and
4752 * <li>a parameter of the same type as the return type of both {@code target} and {@code cleanup}, which will carry
4753 * the result from the execution of the {@code target} handle.
4754 * This parameter is not present if the {@code target} returns {@code void}.
4755 * </ul>
4756 * <p>
4757 * The pseudocode for the resulting adapter looks as follows. In the code, {@code V} represents the result type of
4758 * the {@code try/finally} construct; {@code A}/{@code a}, the types and values of arguments to the resulting
4759 * handle consumed by the cleanup; and {@code B}/{@code b}, those of arguments to the resulting handle discarded by
4760 * the cleanup.
4761 * <blockquote><pre>{@code
4762 * V target(A..., B...);
4763 * V cleanup(Throwable, V, A...);
4764 * V adapter(A... a, B... b) {
4765 * V result = (zero value for V);
4766 * Throwable throwable = null;
4767 * try {
4768 * result = target(a..., b...);
4769 * } catch (Throwable t) {
4770 * throwable = t;
4771 * throw t;
4772 * } finally {
4773 * result = cleanup(throwable, result, a...);
4774 * }
4775 * return result;
4776 * }
4777 * }</pre></blockquote>
4778 * <p>
4779 * Note that the saved arguments ({@code a...} in the pseudocode) cannot
4780 * be modified by execution of the target, and so are passed unchanged
4781 * from the caller to the cleanup, if it is invoked.
4782 * <p>
4783 * The target and cleanup must return the same type, even if the cleanup
4784 * always throws.
4785 * To create such a throwing cleanup, compose the cleanup logic
4786 * with {@link #throwException throwException},
4787 * in order to create a method handle of the correct return type.
4788 * <p>
4789 * Note that {@code tryFinally} never converts exceptions into normal returns.
4790 * In rare cases where exceptions must be converted in that way, first wrap
4791 * the target with {@link #catchException(MethodHandle, Class, MethodHandle)}
4792 * to capture an outgoing exception, and then wrap with {@code tryFinally}.
4793 *
4794 * @param target the handle whose execution is to be wrapped in a {@code try} block.
4795 * @param cleanup the handle that is invoked in the finally block.
4796 *
4797 * @return a method handle embodying the {@code try-finally} block composed of the two arguments.
4798 * @throws NullPointerException if any argument is null
4799 * @throws IllegalArgumentException if {@code cleanup} does not accept
4800 * the required leading arguments, or if the method handle types do
4801 * not match in their return types and their
4802 * corresponding trailing parameters
4803 *
4804 * @see MethodHandles#catchException(MethodHandle, Class, MethodHandle)
4805 * @since 9
4806 */
4807 public static MethodHandle tryFinally(MethodHandle target, MethodHandle cleanup) {
4808 List<Class<?>> targetParamTypes = target.type().parameterList();
4809 List<Class<?>> cleanupParamTypes = cleanup.type().parameterList();
4810 Class<?> rtype = target.type().returnType();
4811
4812 checkTryFinally(target, cleanup);
4813
4814 // Match parameter lists: if the cleanup has a shorter parameter list than the target, add ignored arguments.
4815 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
4816 // target parameter list.
4817 cleanup = dropArgumentsToMatch(cleanup, (rtype == void.class ? 1 : 2), targetParamTypes, 0);
4818
4819 return MethodHandleImpl.makeTryFinally(target, cleanup, rtype, targetParamTypes);
4820 }
4821
4822 /**
4823 * Adapts a target method handle by pre-processing some of its arguments, starting at a given position, and then
4824 * calling the target with the result of the pre-processing, inserted into the original sequence of arguments just
4825 * before the folded arguments.
4826 * <p>
4827 * This method is closely related to {@link #foldArguments(MethodHandle, MethodHandle)}, but allows to control the
4828 * position in the parameter list at which folding takes place. The argument controlling this, {@code pos}, is a
4829 * zero-based index. The aforementioned method {@link #foldArguments(MethodHandle, MethodHandle)} assumes position
4830 * 0.
4831 * <p>
4832 * @apiNote Example:
4833 * <blockquote><pre>{@code
4834 import static java.lang.invoke.MethodHandles.*;
4835 import static java.lang.invoke.MethodType.*;
4836 ...
4837 MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
4838 "println", methodType(void.class, String.class))
4839 .bindTo(System.out);
4840 MethodHandle cat = lookup().findVirtual(String.class,
4841 "concat", methodType(String.class, String.class));
4842 assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
4843 MethodHandle catTrace = foldArguments(cat, 1, trace);
4844 // also prints "jum":
4845 assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
4846 * }</pre></blockquote>
4847 * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
4848 * represents the result type of the {@code target} and resulting adapter.
4849 * {@code V}/{@code v} represent the type and value of the parameter and argument
4850 * of {@code target} that precedes the folding position; {@code V} also is
4851 * the result type of the {@code combiner}. {@code A}/{@code a} denote the
4852 * types and values of the {@code N} parameters and arguments at the folding
4853 * position. {@code Z}/{@code z} and {@code B}/{@code b} represent the types
4854 * and values of the {@code target} parameters and arguments that precede and
4855 * follow the folded parameters and arguments starting at {@code pos},
4856 * respectively.
4857 * <blockquote><pre>{@code
4858 * // there are N arguments in A...
4859 * T target(Z..., V, A[N]..., B...);
4860 * V combiner(A...);
4861 * T adapter(Z... z, A... a, B... b) {
4862 * V v = combiner(a...);
4863 * return target(z..., v, a..., b...);
4864 * }
4865 * // and if the combiner has a void return:
4866 * T target2(Z..., A[N]..., B...);
4867 * void combiner2(A...);
4868 * T adapter2(Z... z, A... a, B... b) {
4869 * combiner2(a...);
4870 * return target2(z..., a..., b...);
4871 * }
4872 * }</pre></blockquote>
4873 * <p>
4874 * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
4875 * variable-arity method handle}, even if the original target method handle was.
4876 *
4877 * @param target the method handle to invoke after arguments are combined
4878 * @param pos the position at which to start folding and at which to insert the folding result; if this is {@code
4879 * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
4880 * @param combiner method handle to call initially on the incoming arguments
4881 * @return method handle which incorporates the specified argument folding logic
4882 * @throws NullPointerException if either argument is null
4883 * @throws IllegalArgumentException if {@code combiner}'s return type
4884 * is non-void and not the same as the argument type at position {@code pos} of
4885 * the target signature, or if the {@code N} argument types at position {@code pos}
4886 * of the target signature
4887 * (skipping one matching the {@code combiner}'s return type)
4888 * are not identical with the argument types of {@code combiner}
4889 *
4890 * @see #foldArguments(MethodHandle, MethodHandle)
4891 * @since 9
4892 */
4893 public static MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner) {
4894 MethodType targetType = target.type();
4895 MethodType combinerType = combiner.type();
4896 Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType);
4897 BoundMethodHandle result = target.rebind();
4898 boolean dropResult = rtype == void.class;
4899 LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType());
4900 MethodType newType = targetType;
4901 if (!dropResult) {
4902 newType = newType.dropParameterTypes(pos, pos + 1);
4903 }
4904 result = result.copyWithExtendL(newType, lform, combiner);
4905 return result;
4906 }
4907
4908
4909 private static void checkLoop0(MethodHandle[][] clauses) {
4910 if (clauses == null || clauses.length == 0) {
4911 throw newIllegalArgumentException("null or no clauses passed");
4912 }
4913 if (Stream.of(clauses).anyMatch(Objects::isNull)) {
4914 throw newIllegalArgumentException("null clauses are not allowed");
4915 }
4916 if (Stream.of(clauses).anyMatch(c -> c.length > 4)) {
4917 throw newIllegalArgumentException("All loop clauses must be represented as MethodHandle arrays with at most 4 elements.");
4918 }
4919 }
4920
4921 private static void checkLoop1a(int i, MethodHandle in, MethodHandle st) {
4922 if (in.type().returnType() != st.type().returnType()) {
4923 throw misMatchedTypes("clause " + i + ": init and step return types", in.type().returnType(),
4924 st.type().returnType());
4925 }
4926 }
4927
4928 private static List<Class<?>> buildCommonSuffix(List<MethodHandle> init, List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, int cpSize) {
4929 final List<Class<?>> empty = List.of();
4930 final List<MethodHandle> nonNullInits = init.stream().filter(Objects::nonNull).collect(Collectors.toList());
4931 if (nonNullInits.isEmpty()) {
4932 final List<Class<?>> longest = Stream.of(step, pred, fini).flatMap(List::stream).filter(Objects::nonNull).
4933 // take only those that can contribute to a common suffix because they are longer than the prefix
4934 map(MethodHandle::type).filter(t -> t.parameterCount() > cpSize).map(MethodType::parameterList).
4935 reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
4936 return longest.size() == 0 ? empty : longest.subList(cpSize, longest.size());
4937 } else {
4938 return nonNullInits.stream().map(MethodHandle::type).map(MethodType::parameterList).
4939 reduce((p, q) -> p.size() >= q.size() ? p : q).get();
4940 }
4941 }
4942
4943 private static void checkLoop1b(List<MethodHandle> init, List<Class<?>> commonSuffix) {
4944 if (init.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::parameterList).
4945 anyMatch(pl -> !pl.equals(commonSuffix.subList(0, pl.size())))) {
4946 throw newIllegalArgumentException("found non-effectively identical init parameter type lists: " + init +
4947 " (common suffix: " + commonSuffix + ")");
4948 }
4949 }
4950
4951 private static void checkLoop1cd(List<MethodHandle> pred, List<MethodHandle> fini, Class<?> loopReturnType) {
4952 if (fini.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
4953 anyMatch(t -> t != loopReturnType)) {
4954 throw newIllegalArgumentException("found non-identical finalizer return types: " + fini + " (return type: " +
4955 loopReturnType + ")");
4956 }
4957
4958 if (!pred.stream().filter(Objects::nonNull).findFirst().isPresent()) {
4959 throw newIllegalArgumentException("no predicate found", pred);
4960 }
4961 if (pred.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
4962 anyMatch(t -> t != boolean.class)) {
4963 throw newIllegalArgumentException("predicates must have boolean return type", pred);
4964 }
4965 }
4966
4967 private static void checkLoop2(List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, List<Class<?>> commonParameterSequence) {
4968 final int cpSize = commonParameterSequence.size();
4969 if (Stream.of(step, pred, fini).flatMap(List::stream).filter(Objects::nonNull).map(MethodHandle::type).
4970 map(MethodType::parameterList).
4971 anyMatch(pl -> pl.size() > cpSize || !pl.equals(commonParameterSequence.subList(0, pl.size())))) {
4972 throw newIllegalArgumentException("found non-effectively identical parameter type lists:\nstep: " + step +
4973 "\npred: " + pred + "\nfini: " + fini + " (common parameter sequence: " + commonParameterSequence + ")");
4974 }
4975 }
4976
4977 private static void checkIteratedLoop(MethodHandle iterator, MethodHandle body) {
4978 if (null != iterator && !Iterator.class.isAssignableFrom(iterator.type().returnType())) {
4979 throw newIllegalArgumentException("iteratedLoop first argument must have Iterator return type");
4980 }
4981 if (null == body) {
4982 throw newIllegalArgumentException("iterated loop body must not be null");
4983 }
4984 }
4985
4986 private static void checkTryFinally(MethodHandle target, MethodHandle cleanup) {
4987 Class<?> rtype = target.type().returnType();
4988 if (rtype != cleanup.type().returnType()) {
4989 throw misMatchedTypes("target and return types", cleanup.type().returnType(), rtype);
4990 }
4991 List<Class<?>> cleanupParamTypes = cleanup.type().parameterList();
4992 if (!Throwable.class.isAssignableFrom(cleanupParamTypes.get(0))) {
4993 throw misMatchedTypes("cleanup first argument and Throwable", cleanup.type(), Throwable.class);
4994 }
4995 if (rtype != void.class && cleanupParamTypes.get(1) != rtype) {
4996 throw misMatchedTypes("cleanup second argument and target return type", cleanup.type(), rtype);
4997 }
4998 // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
4999 // target parameter list.
5000 int cleanupArgIndex = rtype == void.class ? 1 : 2;
5001 List<Class<?>> cleanupArgSuffix = cleanupParamTypes.subList(cleanupArgIndex, cleanupParamTypes.size());
5002 List<Class<?>> targetParamTypes = target.type().parameterList();
5003 if (targetParamTypes.size() < cleanupArgSuffix.size() ||
5004 !cleanupArgSuffix.equals(targetParamTypes.subList(0, cleanupParamTypes.size() - cleanupArgIndex))) {
5005 throw misMatchedTypes("cleanup parameters after (Throwable,result) and target parameter list prefix",
5006 cleanup.type(), target.type());
5007 }
5008 }
5009
5010 }