--- a/jdk/src/share/classes/java/dyn/MethodHandle.java Fri Mar 18 00:03:24 2011 -0700
+++ /dev/null Thu Jan 01 00:00:00 1970 +0000
@@ -1,1006 +0,0 @@
-/*
- * Copyright (c) 2008, 2011, Oracle and/or its affiliates. All rights reserved.
- * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
- *
- * This code is free software; you can redistribute it and/or modify it
- * under the terms of the GNU General Public License version 2 only, as
- * published by the Free Software Foundation. Oracle designates this
- * particular file as subject to the "Classpath" exception as provided
- * by Oracle in the LICENSE file that accompanied this code.
- *
- * This code is distributed in the hope that it will be useful, but WITHOUT
- * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
- * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
- * version 2 for more details (a copy is included in the LICENSE file that
- * accompanied this code).
- *
- * You should have received a copy of the GNU General Public License version
- * 2 along with this work; if not, write to the Free Software Foundation,
- * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
- *
- * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
- * or visit www.oracle.com if you need additional information or have any
- * questions.
- */
-
-package java.dyn;
-
-
-import static java.dyn.MethodHandleStatics.*;
-
-/**
- * A method handle is a typed, directly executable reference to an underlying method,
- * constructor, field, or similar low-level operation, with optional
- * transformations of arguments or return values.
- * These transformations are quite general, and include such patterns as
- * {@linkplain #asType conversion},
- * {@linkplain #bindTo insertion},
- * {@linkplain java.dyn.MethodHandles#dropArguments deletion},
- * and {@linkplain java.dyn.MethodHandles#filterArguments substitution}.
- * <p>
- * <em>Note: The super-class of MethodHandle is Object.
- * Any other super-class visible in the Reference Implementation
- * will be removed before the Proposed Final Draft.
- * Also, the final version will not include any public or
- * protected constructors.</em>
- *
- * <h3>Method handle contents</h3>
- * Method handles are dynamically and strongly typed according to type descriptor.
- * They are not distinguished by the name or defining class of their underlying methods.
- * A method handle must be invoked using type descriptor which matches
- * the method handle's own {@linkplain #type method type}.
- * <p>
- * Every method handle reports its type via the {@link #type type} accessor.
- * This type descriptor is a {@link java.dyn.MethodType MethodType} object,
- * whose structure is a series of classes, one of which is
- * the return type of the method (or {@code void.class} if none).
- * <p>
- * A method handle's type controls the types of invocations it accepts,
- * and the kinds of transformations that apply to it.
- * <p>
- * A method handle contains a pair of special invoker methods
- * called {@link #invokeExact invokeExact} and {@link #invokeGeneric invokeGeneric}.
- * Both invoker methods provide direct access to the method handle's
- * underlying method, constructor, field, or other operation,
- * as modified by transformations of arguments and return values.
- * Both invokers accept calls which exactly match the method handle's own type.
- * The {@code invokeGeneric} invoker also accepts a range of other call types.
- * <p>
- * Method handles are immutable and have no visible state.
- * Of course, they can be bound to underlying methods or data which exhibit state.
- * With respect to the Java Memory Model, any method handle will behave
- * as if all of its (internal) fields are final variables. This means that any method
- * handle made visible to the application will always be fully formed.
- * This is true even if the method handle is published through a shared
- * variable in a data race.
- * <p>
- * Method handles cannot be subclassed by the user.
- * Implementations may (or may not) create internal subclasses of {@code MethodHandle}
- * which may be visible via the {@link java.lang.Object#getClass Object.getClass}
- * operation. The programmer should not draw conclusions about a method handle
- * from its specific class, as the method handle class hierarchy (if any)
- * may change from time to time or across implementations from different vendors.
- *
- * <h3>Method handle compilation</h3>
- * A Java method call expression naming {@code invokeExact} or {@code invokeGeneric}
- * can invoke a method handle from Java source code.
- * From the viewpoint of source code, these methods can take any arguments
- * and their result can be cast to any return type.
- * Formally this is accomplished by giving the invoker methods
- * {@code Object} return types and variable-arity {@code Object} arguments,
- * but they have an additional quality called <em>signature polymorphism</em>
- * which connects this freedom of invocation directly to the JVM execution stack.
- * <p>
- * As is usual with virtual methods, source-level calls to {@code invokeExact}
- * and {@code invokeGeneric} compile to an {@code invokevirtual} instruction.
- * More unusually, the compiler must record the actual argument types,
- * and may not perform method invocation conversions on the arguments.
- * Instead, it must push them on the stack according to their own unconverted types.
- * The method handle object itself is pushed on the stack before the arguments.
- * The compiler then calls the method handle with a type descriptor which
- * describes the argument and return types.
- * <p>
- * To issue a complete type descriptor, the compiler must also determine
- * the return type. This is based on a cast on the method invocation expression,
- * if there is one, or else {@code Object} if the invocation is an expression
- * or else {@code void} if the invocation is a statement.
- * The cast may be to a primitive type (but not {@code void}).
- * <p>
- * As a corner case, an uncasted {@code null} argument is given
- * a type descriptor of {@code java.lang.Void}.
- * The ambiguity with the type {@code Void} is harmless, since there are no references of type
- * {@code Void} except the null reference.
- *
- * <h3>Method handle invocation</h3>
- * The first time a {@code invokevirtual} instruction is executed
- * it is linked, by symbolically resolving the names in the instruction
- * and verifying that the method call is statically legal.
- * This is true of calls to {@code invokeExact} and {@code invokeGeneric}.
- * In this case, the type descriptor emitted by the compiler is checked for
- * correct syntax and names it contains are resolved.
- * Thus, an {@code invokevirtual} instruction which invokes
- * a method handle will always link, as long
- * as the type descriptor is syntactically well-formed
- * and the types exist.
- * <p>
- * When the {@code invokevirtual} is executed after linking,
- * the receiving method handle's type is first checked by the JVM
- * to ensure that it matches the descriptor.
- * If the type match fails, it means that the method which the
- * caller is invoking is not present on the individual
- * method handle being invoked.
- * <p>
- * In the case of {@code invokeExact}, the type descriptor of the invocation
- * (after resolving symbolic type names) must exactly match the method type
- * of the receiving method handle.
- * In the case of {@code invokeGeneric}, the resolved type descriptor
- * must be a valid argument to the receiver's {@link #asType asType} method.
- * Thus, {@code invokeGeneric} is more permissive than {@code invokeExact}.
- * <p>
- * After type matching, a call to {@code invokeExact} directly
- * and immediately invoke the method handle's underlying method
- * (or other behavior, as the case may be).
- * <p>
- * A call to {@code invokeGeneric} works the same as a call to
- * {@code invokeExact}, if the type descriptor specified by the caller
- * exactly matches the method handle's own type.
- * If there is a type mismatch, {@code invokeGeneric} attempts
- * to adjust the type of the receiving method handle,
- * as if by a call to {@link #asType asType},
- * to obtain an exactly invokable method handle {@code M2}.
- * This allows a more powerful negotiation of method type
- * between caller and callee.
- * <p>
- * (Note: The adjusted method handle {@code M2} is not directly observable,
- * and implementations are therefore not required to materialize it.)
- *
- * <h3>Invocation checking</h3>
- * In typical programs, method handle type matching will usually succeed.
- * But if a match fails, the JVM will throw a {@link WrongMethodTypeException},
- * either directly (in the case of {@code invokeExact}) or indirectly as if
- * by a failed call to {@code asType} (in the case of {@code invokeGeneric}).
- * <p>
- * Thus, a method type mismatch which might show up as a linkage error
- * in a statically typed program can show up as
- * a dynamic {@code WrongMethodTypeException}
- * in a program which uses method handles.
- * <p>
- * Because method types contain "live" {@code Class} objects,
- * method type matching takes into account both types names and class loaders.
- * Thus, even if a method handle {@code M} is created in one
- * class loader {@code L1} and used in another {@code L2},
- * method handle calls are type-safe, because the caller's type
- * descriptor, as resolved in {@code L2},
- * is matched against the original callee method's type descriptor,
- * as resolved in {@code L1}.
- * The resolution in {@code L1} happens when {@code M} is created
- * and its type is assigned, while the resolution in {@code L2} happens
- * when the {@code invokevirtual} instruction is linked.
- * <p>
- * Apart from the checking of type descriptors,
- * a method handle's capability to call its underlying method is unrestricted.
- * If a method handle is formed on a non-public method by a class
- * that has access to that method, the resulting handle can be used
- * in any place by any caller who receives a reference to it.
- * <p>
- * Unlike with the Core Reflection API, where access is checked every time
- * a reflective method is invoked,
- * method handle access checking is performed
- * <a href="MethodHandles.Lookup.html#access">when the method handle is created</a>.
- * In the case of {@code ldc} (see below), access checking is performed as part of linking
- * the constant pool entry underlying the constant method handle.
- * <p>
- * Thus, handles to non-public methods, or to methods in non-public classes,
- * should generally be kept secret.
- * They should not be passed to untrusted code unless their use from
- * the untrusted code would be harmless.
- *
- * <h3>Method handle creation</h3>
- * Java code can create a method handle that directly accesses
- * any method, constructor, or field that is accessible to that code.
- * This is done via a reflective, capability-based API called
- * {@link java.dyn.MethodHandles.Lookup MethodHandles.Lookup}
- * For example, a static method handle can be obtained
- * from {@link java.dyn.MethodHandles.Lookup#findStatic Lookup.findStatic}.
- * There are also conversion methods from Core Reflection API objects,
- * such as {@link java.dyn.MethodHandles.Lookup#unreflect Lookup.unreflect}.
- * <p>
- * Like classes and strings, method handles that correspond to accessible
- * fields, methods, and constructors can also be represented directly
- * in a class file's constant pool as constants to be loaded by {@code ldc} bytecodes.
- * A new type of constant pool entry, {@code CONSTANT_MethodHandle},
- * refers directly to an associated {@code CONSTANT_Methodref},
- * {@code CONSTANT_InterfaceMethodref}, or {@code CONSTANT_Fieldref}
- * constant pool entry.
- * (For more details on method handle constants,
- * see the <a href="package-summary.html#mhcon">package summary</a>.)
- * <p>
- * Method handles produced by lookups or constant loads from methods or
- * constructors with the variable arity modifier bit ({@code 0x0080})
- * have a corresponding variable arity, as if they were defined with
- * the help of {@link #asVarargsCollector asVarargsCollector}.
- * <p>
- * A method reference may refer either to a static or non-static method.
- * In the non-static case, the method handle type includes an explicit
- * receiver argument, prepended before any other arguments.
- * In the method handle's type, the initial receiver argument is typed
- * according to the class under which the method was initially requested.
- * (E.g., if a non-static method handle is obtained via {@code ldc},
- * the type of the receiver is the class named in the constant pool entry.)
- * <p>
- * When a method handle to a virtual method is invoked, the method is
- * always looked up in the receiver (that is, the first argument).
- * <p>
- * A non-virtual method handle to a specific virtual method implementation
- * can also be created. These do not perform virtual lookup based on
- * receiver type. Such a method handle simulates the effect of
- * an {@code invokespecial} instruction to the same method.
- *
- * <h3>Usage examples</h3>
- * Here are some examples of usage:
- * <p><blockquote><pre>
-Object x, y; String s; int i;
-MethodType mt; MethodHandle mh;
-MethodHandles.Lookup lookup = MethodHandles.lookup();
-// mt is (char,char)String
-mt = MethodType.methodType(String.class, char.class, char.class);
-mh = lookup.findVirtual(String.class, "replace", mt);
-s = (String) mh.invokeExact("daddy",'d','n');
-// invokeExact(Ljava/lang/String;CC)Ljava/lang/String;
-assert(s.equals("nanny"));
-// weakly typed invocation (using MHs.invoke)
-s = (String) mh.invokeWithArguments("sappy", 'p', 'v');
-assert(s.equals("savvy"));
-// mt is (Object[])List
-mt = MethodType.methodType(java.util.List.class, Object[].class);
-mh = lookup.findStatic(java.util.Arrays.class, "asList", mt);
-assert(mh.isVarargsCollector());
-x = mh.invokeGeneric("one", "two");
-// invokeGeneric(Ljava/lang/String;Ljava/lang/String;)Ljava/lang/Object;
-assert(x.equals(java.util.Arrays.asList("one","two")));
-// mt is (Object,Object,Object)Object
-mt = MethodType.genericMethodType(3);
-mh = mh.asType(mt);
-x = mh.invokeExact((Object)1, (Object)2, (Object)3);
-// invokeExact(Ljava/lang/Object;Ljava/lang/Object;Ljava/lang/Object;)Ljava/lang/Object;
-assert(x.equals(java.util.Arrays.asList(1,2,3)));
-// mt is { => int}
-mt = MethodType.methodType(int.class);
-mh = lookup.findVirtual(java.util.List.class, "size", mt);
-i = (int) mh.invokeExact(java.util.Arrays.asList(1,2,3));
-// invokeExact(Ljava/util/List;)I
-assert(i == 3);
-mt = MethodType.methodType(void.class, String.class);
-mh = lookup.findVirtual(java.io.PrintStream.class, "println", mt);
-mh.invokeExact(System.out, "Hello, world.");
-// invokeExact(Ljava/io/PrintStream;Ljava/lang/String;)V
- * </pre></blockquote>
- * Each of the above calls to {@code invokeExact} or {@code invokeGeneric}
- * generates a single invokevirtual instruction with
- * the type descriptor indicated in the following comment.
- *
- * <h3>Exceptions</h3>
- * The methods {@code invokeExact} and {@code invokeGeneric} are declared
- * to throw {@link java.lang.Throwable Throwable},
- * which is to say that there is no static restriction on what a method handle
- * can throw. Since the JVM does not distinguish between checked
- * and unchecked exceptions (other than by their class, of course),
- * there is no particular effect on bytecode shape from ascribing
- * checked exceptions to method handle invocations. But in Java source
- * code, methods which perform method handle calls must either explicitly
- * throw {@code java.lang.Throwable Throwable}, or else must catch all
- * throwables locally, rethrowing only those which are legal in the context,
- * and wrapping ones which are illegal.
- *
- * <h3><a name="sigpoly"></a>Signature polymorphism</h3>
- * The unusual compilation and linkage behavior of
- * {@code invokeExact} and {@code invokeGeneric}
- * is referenced by the term <em>signature polymorphism</em>.
- * A signature polymorphic method is one which can operate with
- * any of a wide range of call signatures and return types.
- * In order to make this work, both the Java compiler and the JVM must
- * give special treatment to signature polymorphic methods.
- * <p>
- * In source code, a call to a signature polymorphic method will
- * compile, regardless of the requested type descriptor.
- * As usual, the Java compiler emits an {@code invokevirtual}
- * instruction with the given type descriptor against the named method.
- * The unusual part is that the type descriptor is derived from
- * the actual argument and return types, not from the method declaration.
- * <p>
- * When the JVM processes bytecode containing signature polymorphic calls,
- * it will successfully link any such call, regardless of its type descriptor.
- * (In order to retain type safety, the JVM will guard such calls with suitable
- * dynamic type checks, as described elsewhere.)
- * <p>
- * Bytecode generators, including the compiler back end, are required to emit
- * untransformed type descriptors for these methods.
- * Tools which determine symbolic linkage are required to accept such
- * untransformed descriptors, without reporting linkage errors.
- * <p>
- * For the sake of tools (but not as a programming API), the signature polymorphic
- * methods are marked with a private yet standard annotation,
- * {@code @java.dyn.MethodHandle.PolymorphicSignature}.
- * The annotation's retention is {@code RUNTIME}, so that all tools can see it.
- *
- * <h3>Formal rules for processing signature polymorphic methods</h3>
- * <p>
- * The following methods (and no others) are signature polymorphic:
- * <ul>
- * <li>{@link java.dyn.MethodHandle#invokeExact MethodHandle.invokeExact}
- * <li>{@link java.dyn.MethodHandle#invokeGeneric MethodHandle.invokeGeneric}
- * </ul>
- * <p>
- * A signature polymorphic method will be declared with the following properties:
- * <ul>
- * <li>It must be native.
- * <li>It must take a single varargs parameter of the form {@code Object...}.
- * <li>It must produce a return value of type {@code Object}.
- * <li>It must be contained within the {@code java.dyn} package.
- * </ul>
- * Because of these requirements, a signature polymorphic method is able to accept
- * any number and type of actual arguments, and can, with a cast, produce a value of any type.
- * However, the JVM will treat these declaration features as a documentation convention,
- * rather than a description of the actual structure of the methods as executed.
- * <p>
- * When a call to a signature polymorphic method is compiled, the associated linkage information for
- * its arguments is not array of {@code Object} (as for other similar varargs methods)
- * but rather the erasure of the static types of all the arguments.
- * <p>
- * In an argument position of a method invocation on a signature polymorphic method,
- * a null literal has type {@code java.lang.Void}, unless cast to a reference type.
- * (Note: This typing rule allows the null type to have its own encoding in linkage information
- * distinct from other types.
- * <p>
- * The linkage information for the return type is derived from a context-dependent target typing convention.
- * The return type for a signature polymorphic method invocation is determined as follows:
- * <ul>
- * <li>If the method invocation expression is an expression statement, the method is {@code void}.
- * <li>Otherwise, if the method invocation expression is the immediate operand of a cast,
- * the return type is the erasure of the cast type.
- * <li>Otherwise, the return type is the method's nominal return type, {@code Object}.
- * </ul>
- * (Programmers are encouraged to use explicit casts unless it is clear that a signature polymorphic
- * call will be used as a plain {@code Object} expression.)
- * <p>
- * The linkage information for argument and return types is stored in the descriptor for the
- * compiled (bytecode) call site. As for any invocation instruction, the arguments and return value
- * will be passed directly on the JVM stack, in accordance with the descriptor,
- * and without implicit boxing or unboxing.
- *
- * <h3>Interoperation between method handles and the Core Reflection API</h3>
- * Using factory methods in the {@link java.dyn.MethodHandles.Lookup Lookup} API,
- * any class member represented by a Core Reflection API object
- * can be converted to a behaviorally equivalent method handle.
- * For example, a reflective {@link java.lang.reflect.Method Method} can
- * be converted to a method handle using
- * {@link java.dyn.MethodHandles.Lookup#unreflect Lookup.unreflect}.
- * The resulting method handles generally provide more direct and efficient
- * access to the underlying class members.
- * <p>
- * As a special case,
- * when the Core Reflection API is used to view the signature polymorphic
- * methods {@code invokeExact} or {@code invokeGeneric} in this class,
- * they appear as single, non-polymorphic native methods.
- * Calls to these native methods do not result in method handle invocations.
- * Since {@code invokevirtual} instructions can natively
- * invoke method handles under any type descriptor, this reflective view conflicts
- * with the normal presentation via bytecodes.
- * Thus, these two native methods, as viewed by
- * {@link java.lang.Class#getDeclaredMethod Class.getDeclaredMethod},
- * are placeholders only.
- * If invoked via {@link java.lang.reflect.Method#invoke Method.invoke},
- * they will throw {@code UnsupportedOperationException}.
- * <p>
- * In order to obtain an invoker method for a particular type descriptor,
- * use {@link java.dyn.MethodHandles#exactInvoker MethodHandles.exactInvoker},
- * or {@link java.dyn.MethodHandles#genericInvoker MethodHandles.genericInvoker}.
- * The {@link java.dyn.MethodHandles.Lookup#findVirtual Lookup.findVirtual}
- * API is also able to return a method handle
- * to call {@code invokeExact} or {@code invokeGeneric},
- * for any specified type descriptor .
- *
- * <h3>Interoperation between method handles and Java generics</h3>
- * A method handle can be obtained on a method, constructor, or field
- * which is declared with Java generic types.
- * As with the Core Reflection API, the type of the method handle
- * will constructed from the erasure of the source-level type.
- * When a method handle is invoked, the types of its arguments
- * or the return value cast type may be generic types or type instances.
- * If this occurs, the compiler will replace those
- * types by their erasures when when it constructs the type descriptor
- * for the {@code invokevirtual} instruction.
- * <p>
- * Method handles do not represent
- * their function-like types in terms of Java parameterized (generic) types,
- * because there are three mismatches between function-like types and parameterized
- * Java types.
- * <ul>
- * <li>Method types range over all possible arities,
- * from no arguments to up to 255 of arguments (a limit imposed by the JVM).
- * Generics are not variadic, and so cannot represent this.</li>
- * <li>Method types can specify arguments of primitive types,
- * which Java generic types cannot range over.</li>
- * <li>Higher order functions over method handles (combinators) are
- * often generic across a wide range of function types, including
- * those of multiple arities. It is impossible to represent such
- * genericity with a Java type parameter.</li>
- * </ul>
- *
- * @see MethodType
- * @see MethodHandles
- * @author John Rose, JSR 292 EG
- */
-public abstract class MethodHandle {
- // { JVM internals:
-
- private byte vmentry; // adapter stub or method entry point
- //private int vmslots; // optionally, hoist type.form.vmslots
- /*non-public*/ Object vmtarget; // VM-specific, class-specific target value
-
- // TO DO: vmtarget should be invisible to Java, since the JVM puts internal
- // managed pointers into it. Making it visible exposes it to debuggers,
- // which can cause errors when they treat the pointer as an Object.
-
- // These two dummy fields are present to force 'I' and 'J' signatures
- // into this class's constant pool, so they can be transferred
- // to vmentry when this class is loaded.
- static final int INT_FIELD = 0;
- static final long LONG_FIELD = 0;
-
- // vmentry (a void* field) is used *only* by the JVM.
- // The JVM adjusts its type to int or long depending on system wordsize.
- // Since it is statically typed as neither int nor long, it is impossible
- // to use this field from Java bytecode. (Please don't try to, either.)
-
- // The vmentry is an assembly-language stub which is jumped to
- // immediately after the method type is verified.
- // For a direct MH, this stub loads the vmtarget's entry point
- // and jumps to it.
-
- // } End of JVM internals.
-
- static { MethodHandleImpl.initStatics(); }
-
- // interface MethodHandle<R throws X extends Exception,A...>
- // { MethodType<R throws X,A...> type(); public R invokeExact(A...) throws X; }
-
- /**
- * Internal marker interface which distinguishes (to the Java compiler)
- * those methods which are <a href="MethodHandle.html#sigpoly">signature polymorphic</a>.
- */
- @java.lang.annotation.Target({java.lang.annotation.ElementType.METHOD})
- @java.lang.annotation.Retention(java.lang.annotation.RetentionPolicy.RUNTIME)
- @interface PolymorphicSignature { }
-
- private MethodType type;
-
- /**
- * Report the type of this method handle.
- * Every invocation of this method handle via {@code invokeExact} must exactly match this type.
- * @return the method handle type
- */
- public MethodType type() {
- return type;
- }
-
- /**
- * Package-private constructor for the method handle implementation hierarchy.
- * Method handle inheritance will be contained completely within
- * the {@code java.dyn} package.
- */
- // @param type type (permanently assigned) of the new method handle
- /*non-public*/ MethodHandle(MethodType type) {
- type.getClass(); // elicit NPE
- this.type = type;
- }
-
- /**
- * Invoke the method handle, allowing any caller type descriptor, but requiring an exact type match.
- * The type descriptor at the call site of {@code invokeExact} must
- * exactly match this method handle's {@link #type type}.
- * No conversions are allowed on arguments or return values.
- * <p>
- * When this method is observed via the Core Reflection API,
- * it will appear as a single native method, taking an object array and returning an object.
- * If this native method is invoked directly via
- * {@link java.lang.reflect.Method#invoke Method.invoke}, via JNI,
- * or indirectly via {@link java.dyn.MethodHandles.Lookup#unreflect Lookup.unreflect},
- * it will throw an {@code UnsupportedOperationException}.
- * @throws WrongMethodTypeException if the target's type is not identical with the caller's type descriptor
- * @throws Throwable anything thrown by the underlying method propagates unchanged through the method handle call
- */
- public final native @PolymorphicSignature Object invokeExact(Object... args) throws Throwable;
-
- /**
- * Invoke the method handle, allowing any caller type descriptor,
- * and optionally performing conversions on arguments and return values.
- * <p>
- * If the call site type descriptor exactly matches this method handle's {@link #type type},
- * the call proceeds as if by {@link #invokeExact invokeExact}.
- * <p>
- * Otherwise, the call proceeds as if this method handle were first
- * adjusted by calling {@link #asType asType} to adjust this method handle
- * to the required type, and then the call proceeds as if by
- * {@link #invokeExact invokeExact} on the adjusted method handle.
- * <p>
- * There is no guarantee that the {@code asType} call is actually made.
- * If the JVM can predict the results of making the call, it may perform
- * adaptations directly on the caller's arguments,
- * and call the target method handle according to its own exact type.
- * <p>
- * The type descriptor at the call site of {@code invokeGeneric} must
- * be a valid argument to the receivers {@code asType} method.
- * In particular, the caller must specify the same argument arity
- * as the callee's type,
- * if the callee is not a {@linkplain #asVarargsCollector variable arity collector}.
- * <p>
- * When this method is observed via the Core Reflection API,
- * it will appear as a single native method, taking an object array and returning an object.
- * If this native method is invoked directly via
- * {@link java.lang.reflect.Method#invoke Method.invoke}, via JNI,
- * or indirectly via {@link java.dyn.MethodHandles.Lookup#unreflect Lookup.unreflect},
- * it will throw an {@code UnsupportedOperationException}.
- * @throws WrongMethodTypeException if the target's type cannot be adjusted to the caller's type descriptor
- * @throws ClassCastException if the target's type can be adjusted to the caller, but a reference cast fails
- * @throws Throwable anything thrown by the underlying method propagates unchanged through the method handle call
- */
- public final native @PolymorphicSignature Object invokeGeneric(Object... args) throws Throwable;
-
- /**
- * Perform a varargs invocation, passing the arguments in the given array
- * to the method handle, as if via {@link #invokeGeneric invokeGeneric} from a call site
- * which mentions only the type {@code Object}, and whose arity is the length
- * of the argument array.
- * <p>
- * Specifically, execution proceeds as if by the following steps,
- * although the methods are not guaranteed to be called if the JVM
- * can predict their effects.
- * <ul>
- * <li>Determine the length of the argument array as {@code N}.
- * For a null reference, {@code N=0}. </li>
- * <li>Determine the generic type {@code TN} of {@code N} arguments as
- * as {@code TN=MethodType.genericMethodType(N)}.</li>
- * <li>Force the original target method handle {@code MH0} to the
- * required type, as {@code MH1 = MH0.asType(TN)}. </li>
- * <li>Spread the array into {@code N} separate arguments {@code A0, ...}. </li>
- * <li>Invoke the type-adjusted method handle on the unpacked arguments:
- * MH1.invokeExact(A0, ...). </li>
- * <li>Take the return value as an {@code Object} reference. </li>
- * </ul>
- * <p>
- * Because of the action of the {@code asType} step, the following argument
- * conversions are applied as necessary:
- * <ul>
- * <li>reference casting
- * <li>unboxing
- * <li>widening primitive conversions
- * </ul>
- * <p>
- * The result returned by the call is boxed if it is a primitive,
- * or forced to null if the return type is void.
- * <p>
- * This call is equivalent to the following code:
- * <p><blockquote><pre>
- * MethodHandle invoker = MethodHandles.spreadInvoker(this.type(), 0);
- * Object result = invoker.invokeExact(this, arguments);
- * </pre></blockquote>
- * <p>
- * Unlike the signature polymorphic methods {@code invokeExact} and {@code invokeGeneric},
- * {@code invokeWithArguments} can be accessed normally via the Core Reflection API and JNI.
- * It can therefore be used as a bridge between native or reflective code and method handles.
- *
- * @param arguments the arguments to pass to the target
- * @return the result returned by the target
- * @throws ClassCastException if an argument cannot be converted by reference casting
- * @throws WrongMethodTypeException if the target's type cannot be adjusted to take the given number of {@code Object} arguments
- * @throws Throwable anything thrown by the target method invocation
- * @see MethodHandles#spreadInvoker
- */
- public Object invokeWithArguments(Object... arguments) throws Throwable {
- int argc = arguments == null ? 0 : arguments.length;
- MethodType type = type();
- if (type.parameterCount() != argc) {
- // simulate invokeGeneric
- return asType(MethodType.genericMethodType(argc)).invokeWithArguments(arguments);
- }
- if (argc <= 10) {
- MethodHandle invoker = type.invokers().genericInvoker();
- switch (argc) {
- case 0: return invoker.invokeExact(this);
- case 1: return invoker.invokeExact(this,
- arguments[0]);
- case 2: return invoker.invokeExact(this,
- arguments[0], arguments[1]);
- case 3: return invoker.invokeExact(this,
- arguments[0], arguments[1], arguments[2]);
- case 4: return invoker.invokeExact(this,
- arguments[0], arguments[1], arguments[2],
- arguments[3]);
- case 5: return invoker.invokeExact(this,
- arguments[0], arguments[1], arguments[2],
- arguments[3], arguments[4]);
- case 6: return invoker.invokeExact(this,
- arguments[0], arguments[1], arguments[2],
- arguments[3], arguments[4], arguments[5]);
- case 7: return invoker.invokeExact(this,
- arguments[0], arguments[1], arguments[2],
- arguments[3], arguments[4], arguments[5],
- arguments[6]);
- case 8: return invoker.invokeExact(this,
- arguments[0], arguments[1], arguments[2],
- arguments[3], arguments[4], arguments[5],
- arguments[6], arguments[7]);
- case 9: return invoker.invokeExact(this,
- arguments[0], arguments[1], arguments[2],
- arguments[3], arguments[4], arguments[5],
- arguments[6], arguments[7], arguments[8]);
- case 10: return invoker.invokeExact(this,
- arguments[0], arguments[1], arguments[2],
- arguments[3], arguments[4], arguments[5],
- arguments[6], arguments[7], arguments[8],
- arguments[9]);
- }
- }
-
- // more than ten arguments get boxed in a varargs list:
- MethodHandle invoker = type.invokers().spreadInvoker(0);
- return invoker.invokeExact(this, arguments);
- }
- /** Equivalent to {@code invokeWithArguments(arguments.toArray())}. */
- public Object invokeWithArguments(java.util.List<?> arguments) throws Throwable {
- return invokeWithArguments(arguments.toArray());
- }
-
- /**
- * Produce an adapter method handle which adapts the type of the
- * current method handle to a new type
- * The resulting method handle is guaranteed to report a type
- * which is equal to the desired new type.
- * <p>
- * If the original type and new type are equal, returns {@code this}.
- * <p>
- * This method provides the crucial behavioral difference between
- * {@link #invokeExact invokeExact} and {@link #invokeGeneric invokeGeneric}. The two methods
- * perform the same steps when the caller's type descriptor is identical
- * with the callee's, but when the types differ, {@link #invokeGeneric invokeGeneric}
- * also calls {@code asType} (or some internal equivalent) in order
- * to match up the caller's and callee's types.
- * <p>
- * This method is equivalent to {@link MethodHandles#convertArguments convertArguments},
- * except for variable arity method handles produced by {@link #asVarargsCollector asVarargsCollector}.
- *
- * @param newType the expected type of the new method handle
- * @return a method handle which delegates to {@code this} after performing
- * any necessary argument conversions, and arranges for any
- * necessary return value conversions
- * @throws WrongMethodTypeException if the conversion cannot be made
- * @see MethodHandles#convertArguments
- */
- public MethodHandle asType(MethodType newType) {
- return MethodHandles.convertArguments(this, newType);
- }
-
- /**
- * Make an adapter which accepts a trailing array argument
- * and spreads its elements as positional arguments.
- * The new method handle adapts, as its <i>target</i>,
- * the current method handle. The type of the adapter will be
- * the same as the type of the target, except that the final
- * {@code arrayLength} parameters of the target's type are replaced
- * by a single array parameter of type {@code arrayType}.
- * <p>
- * If the array element type differs from any of the corresponding
- * argument types on the original target,
- * the original target is adapted to take the array elements directly,
- * as if by a call to {@link #asType asType}.
- * <p>
- * When called, the adapter replaces a trailing array argument
- * by the array's elements, each as its own argument to the target.
- * (The order of the arguments is preserved.)
- * They are converted pairwise by casting and/or unboxing
- * to the types of the trailing parameters of the target.
- * Finally the target is called.
- * What the target eventually returns is returned unchanged by the adapter.
- * <p>
- * Before calling the target, the adapter verifies that the array
- * contains exactly enough elements to provide a correct argument count
- * to the target method handle.
- * (The array may also be null when zero elements are required.)
- * @param arrayType usually {@code Object[]}, the type of the array argument from which to extract the spread arguments
- * @param arrayLength the number of arguments to spread from an incoming array argument
- * @return a new method handle which spreads its final array argument,
- * before calling the original method handle
- * @throws IllegalArgumentException if {@code arrayType} is not an array type
- * @throws IllegalArgumentException if target does not have at least
- * {@code arrayLength} parameter types
- * @throws WrongMethodTypeException if the implied {@code asType} call fails
- * @see #asCollector
- */
- public MethodHandle asSpreader(Class<?> arrayType, int arrayLength) {
- Class<?> arrayElement = arrayType.getComponentType();
- if (arrayElement == null) throw newIllegalArgumentException("not an array type");
- MethodType oldType = type();
- int nargs = oldType.parameterCount();
- if (nargs < arrayLength) throw newIllegalArgumentException("bad spread array length");
- int keepPosArgs = nargs - arrayLength;
- MethodType newType = oldType.dropParameterTypes(keepPosArgs, nargs);
- newType = newType.insertParameterTypes(keepPosArgs, arrayType);
- return MethodHandles.spreadArguments(this, newType);
- }
-
- /**
- * Make an adapter which accepts a given number of trailing
- * positional arguments and collects them into an array argument.
- * The new method handle adapts, as its <i>target</i>,
- * the current method handle. The type of the adapter will be
- * the same as the type of the target, except that a single trailing
- * parameter (usually of type {@code arrayType}) is replaced by
- * {@code arrayLength} parameters whose type is element type of {@code arrayType}.
- * <p>
- * If the array type differs from the final argument type on the original target,
- * the original target is adapted to take the array type directly,
- * as if by a call to {@link #asType asType}.
- * <p>
- * When called, the adapter replaces its trailing {@code arrayLength}
- * arguments by a single new array of type {@code arrayType}, whose elements
- * comprise (in order) the replaced arguments.
- * Finally the target is called.
- * What the target eventually returns is returned unchanged by the adapter.
- * <p>
- * (The array may also be a shared constant when {@code arrayLength} is zero.)
- * <p>
- * (<em>Note:</em> The {@code arrayType} is often identical to the last
- * parameter type of the original target.
- * It is an explicit argument for symmetry with {@code asSpreader}, and also
- * to allow the target to use a simple {@code Object} as its last parameter type.)
- * <p>
- * In order to create a collecting adapter which is not restricted to a particular
- * number of collected arguments, use {@link #asVarargsCollector asVarargsCollector} instead.
- * @param arrayType often {@code Object[]}, the type of the array argument which will collect the arguments
- * @param arrayLength the number of arguments to collect into a new array argument
- * @return a new method handle which collects some trailing argument
- * into an array, before calling the original method handle
- * @throws IllegalArgumentException if {@code arrayType} is not an array type
- * or {@code arrayType} is not assignable to this method handle's trailing parameter type,
- * or {@code arrayLength} is not a legal array size
- * @throws WrongMethodTypeException if the implied {@code asType} call fails
- * @see #asSpreader
- * @see #asVarargsCollector
- */
- public MethodHandle asCollector(Class<?> arrayType, int arrayLength) {
- Class<?> arrayElement = arrayType.getComponentType();
- if (arrayElement == null) throw newIllegalArgumentException("not an array type");
- MethodType oldType = type();
- int nargs = oldType.parameterCount();
- if (nargs == 0) throw newIllegalArgumentException("no trailing argument");
- MethodType newType = oldType.dropParameterTypes(nargs-1, nargs);
- newType = newType.insertParameterTypes(nargs-1,
- java.util.Collections.<Class<?>>nCopies(arrayLength, arrayElement));
- return MethodHandles.collectArguments(this, newType);
- }
-
- /**
- * Make a <em>variable arity</em> adapter which is able to accept
- * any number of trailing positional arguments and collect them
- * into an array argument.
- * <p>
- * The type and behavior of the adapter will be the same as
- * the type and behavior of the target, except that certain
- * {@code invokeGeneric} and {@code asType} requests can lead to
- * trailing positional arguments being collected into target's
- * trailing parameter.
- * Also, the last parameter type of the adapter will be
- * {@code arrayType}, even if the target has a different
- * last parameter type.
- * <p>
- * When called with {@link #invokeExact invokeExact}, the adapter invokes
- * the target with no argument changes.
- * (<em>Note:</em> This behavior is different from a
- * {@linkplain #asCollector fixed arity collector},
- * since it accepts a whole array of indeterminate length,
- * rather than a fixed number of arguments.)
- * <p>
- * When called with {@link #invokeGeneric invokeGeneric}, if the caller
- * type is the same as the adapter, the adapter invokes the target as with
- * {@code invokeExact}.
- * (This is the normal behavior for {@code invokeGeneric} when types match.)
- * <p>
- * Otherwise, if the caller and adapter arity are the same, and the
- * trailing parameter type of the caller is a reference type identical to
- * or assignable to the trailing parameter type of the adapter,
- * the arguments and return values are converted pairwise,
- * as if by {@link MethodHandles#convertArguments convertArguments}.
- * (This is also normal behavior for {@code invokeGeneric} in such a case.)
- * <p>
- * Otherwise, the arities differ, or the adapter's trailing parameter
- * type is not assignable from the corresponding caller type.
- * In this case, the adapter replaces all trailing arguments from
- * the original trailing argument position onward, by
- * a new array of type {@code arrayType}, whose elements
- * comprise (in order) the replaced arguments.
- * <p>
- * The caller type must provides as least enough arguments,
- * and of the correct type, to satisfy the target's requirement for
- * positional arguments before the trailing array argument.
- * Thus, the caller must supply, at a minimum, {@code N-1} arguments,
- * where {@code N} is the arity of the target.
- * Also, there must exist conversions from the incoming arguments
- * to the target's arguments.
- * As with other uses of {@code invokeGeneric}, if these basic
- * requirements are not fulfilled, a {@code WrongMethodTypeException}
- * may be thrown.
- * <p>
- * In all cases, what the target eventually returns is returned unchanged by the adapter.
- * <p>
- * In the final case, it is exactly as if the target method handle were
- * temporarily adapted with a {@linkplain #asCollector fixed arity collector}
- * to the arity required by the caller type.
- * (As with {@code asCollector}, if the array length is zero,
- * a shared constant may be used instead of a new array.
- * If the implied call to {@code asCollector} would throw
- * an {@code IllegalArgumentException} or {@code WrongMethodTypeException},
- * the call to the variable arity adapter must throw
- * {@code WrongMethodTypeException}.)
- * <p>
- * The behavior of {@link #asType asType} is also specialized for
- * variable arity adapters, to maintain the invariant that
- * {@code invokeGeneric} is always equivalent to an {@code asType}
- * call to adjust the target type, followed by {@code invokeExact}.
- * Therefore, a variable arity adapter responds
- * to an {@code asType} request by building a fixed arity collector,
- * if and only if the adapter and requested type differ either
- * in arity or trailing argument type.
- * The resulting fixed arity collector has its type further adjusted
- * (if necessary) to the requested type by pairwise conversion,
- * as if by another application of {@code asType}.
- * <p>
- * When a method handle is obtained by executing an {@code ldc} instruction
- * of a {@code CONSTANT_MethodHandle} constant, and the target method is marked
- * as a variable arity method (with the modifier bit {@code 0x0080}),
- * the method handle will accept multiple arities, as if the method handle
- * constant were created by means of a call to {@code asVarargsCollector}.
- * <p>
- * In order to create a collecting adapter which collects a predetermined
- * number of arguments, and whose type reflects this predetermined number,
- * use {@link #asCollector asCollector} instead.
- * <p>
- * No method handle transformations produce new method handles with
- * variable arity, unless they are documented as doing so.
- * Therefore, besides {@code asVarargsCollector},
- * all methods in {@code MethodHandle} and {@code MethodHandles}
- * will return a method handle with fixed arity,
- * except in the cases where they are specified to return their original
- * operand (e.g., {@code asType} of the method handle's own type).
- * <p>
- * Calling {@code asVarargsCollector} on a method handle which is already
- * of variable arity will produce a method handle with the same type and behavior.
- * It may (or may not) return the original variable arity method handle.
- * <p>
- * Here is an example, of a list-making variable arity method handle:
- * <blockquote><pre>
-MethodHandle asList = publicLookup()
- .findStatic(Arrays.class, "asList", methodType(List.class, Object[].class))
- .asVarargsCollector(Object[].class);
-assertEquals("[]", asList.invokeGeneric().toString());
-assertEquals("[1]", asList.invokeGeneric(1).toString());
-assertEquals("[two, too]", asList.invokeGeneric("two", "too").toString());
-Object[] argv = { "three", "thee", "tee" };
-assertEquals("[three, thee, tee]", asList.invokeGeneric(argv).toString());
-List ls = (List) asList.invokeGeneric((Object)argv);
-assertEquals(1, ls.size());
-assertEquals("[three, thee, tee]", Arrays.toString((Object[])ls.get(0)));
- * </pre></blockquote>
- * <p style="font-size:smaller;">
- * <em>Discussion:</em>
- * These rules are designed as a dynamically-typed variation
- * of the Java rules for variable arity methods.
- * In both cases, callers to a variable arity method or method handle
- * can either pass zero or more positional arguments, or else pass
- * pre-collected arrays of any length. Users should be aware of the
- * special role of the final argument, and of the effect of a
- * type match on that final argument, which determines whether
- * or not a single trailing argument is interpreted as a whole
- * array or a single element of an array to be collected.
- * Note that the dynamic type of the trailing argument has no
- * effect on this decision, only a comparison between the static
- * type descriptor of the call site and the type of the method handle.)
- * <p style="font-size:smaller;">
- * As a result of the previously stated rules, the variable arity behavior
- * of a method handle may be suppressed, by binding it to the exact invoker
- * of its own type, as follows:
- * <blockquote><pre>
-MethodHandle vamh = publicLookup()
- .findStatic(Arrays.class, "asList", methodType(List.class, Object[].class))
- .asVarargsCollector(Object[].class);
-MethodHandle mh = MethodHandles.exactInvoker(vamh.type()).bindTo(vamh);
-assert(vamh.type().equals(mh.type()));
-assertEquals("[1, 2, 3]", vamh.invokeGeneric(1,2,3).toString());
-boolean failed = false;
-try { mh.invokeGeneric(1,2,3); }
-catch (WrongMethodTypeException ex) { failed = true; }
-assert(failed);
- * </pre></blockquote>
- * This transformation has no behavioral effect if the method handle is
- * not of variable arity.
- *
- * @param arrayType often {@code Object[]}, the type of the array argument which will collect the arguments
- * @return a new method handle which can collect any number of trailing arguments
- * into an array, before calling the original method handle
- * @throws IllegalArgumentException if {@code arrayType} is not an array type
- * or {@code arrayType} is not assignable to this method handle's trailing parameter type
- * @see #asCollector
- * @see #isVarargsCollector
- */
- public MethodHandle asVarargsCollector(Class<?> arrayType) {
- Class<?> arrayElement = arrayType.getComponentType();
- if (arrayElement == null) throw newIllegalArgumentException("not an array type");
- return MethodHandles.asVarargsCollector(this, arrayType);
- }
-
- /**
- * Determine if this method handle
- * supports {@linkplain #asVarargsCollector variable arity} calls.
- * Such method handles arise from the following sources:
- * <ul>
- * <li>a call to {@linkplain #asVarargsCollector asVarargsCollector}
- * <li>a call to a {@linkplain java.dyn.MethodHandles.Lookup lookup method}
- * which resolves to a variable arity Java method or constructor
- * <li>an {@code ldc} instruction of a {@code CONSTANT_MethodHandle}
- * which resolves to a variable arity Java method or constructor
- * </ul>
- * @return true if this method handle accepts more than one arity of {@code invokeGeneric} calls
- * @see #asVarargsCollector
- */
- public boolean isVarargsCollector() {
- return false;
- }
-
- /**
- * Bind a value {@code x} to the first argument of a method handle, without invoking it.
- * The new method handle adapts, as its <i>target</i>,
- * to the current method handle.
- * The type of the bound handle will be
- * the same as the type of the target, except that a single leading
- * reference parameter will be omitted.
- * <p>
- * When called, the bound handle inserts the given value {@code x}
- * as a new leading argument to the target. The other arguments are
- * also passed unchanged.
- * What the target eventually returns is returned unchanged by the bound handle.
- * <p>
- * The reference {@code x} must be convertible to the first parameter
- * type of the target.
- * @param x the value to bind to the first argument of the target
- * @return a new method handle which collects some trailing argument
- * into an array, before calling the original method handle
- * @throws IllegalArgumentException if the target does not have a
- * leading parameter type that is a reference type
- * @throws ClassCastException if {@code x} cannot be converted
- * to the leading parameter type of the target
- * @see MethodHandles#insertArguments
- */
- public MethodHandle bindTo(Object x) {
- return MethodHandles.insertArguments(this, 0, x);
- }
-
- /**
- * Returns a string representation of the method handle,
- * starting with the string {@code "MethodHandle"} and
- * ending with the string representation of the method handle's type.
- * In other words, this method returns a string equal to the value of:
- * <blockquote><pre>
- * "MethodHandle" + type().toString()
- * </pre></blockquote>
- * <p>
- * Note: Future releases of this API may add further information
- * to the string representation.
- * Therefore, the present syntax should not be parsed by applications.
- *
- * @return a string representation of the method handle
- */
- @Override
- public String toString() {
- return getNameString(this);
- }
-}