| /* |
| * Copyright (c) 2008, 2013, 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.lang.invoke; |
| |
| |
| import java.util.*; |
| import java.lang.invoke.LambdaForm.BasicType; |
| import sun.invoke.util.*; |
| import sun.misc.Unsafe; |
| |
| import static java.lang.invoke.MethodHandleStatics.*; |
| import static java.lang.invoke.LambdaForm.BasicType.*; |
| |
| /** |
| * 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.lang.invoke.MethodHandles#dropArguments deletion}, |
| * and {@linkplain java.lang.invoke.MethodHandles#filterArguments substitution}. |
| * |
| * <h1>Method handle contents</h1> |
| * Method handles are dynamically and strongly typed according to their parameter and return types. |
| * They are not distinguished by the name or the defining class of their underlying methods. |
| * A method handle must be invoked using a symbolic type descriptor which matches |
| * the method handle's own {@linkplain #type type descriptor}. |
| * <p> |
| * Every method handle reports its type descriptor via the {@link #type type} accessor. |
| * This type descriptor is a {@link java.lang.invoke.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 #invoke invoke}. |
| * 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 plain, inexact 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. |
| * |
| * <h1>Method handle compilation</h1> |
| * A Java method call expression naming {@code invokeExact} or {@code invoke} |
| * 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 invoke} 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 symbolic type descriptor which |
| * describes the argument and return types. |
| * <p> |
| * To issue a complete symbolic 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 symbolic 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. |
| * |
| * <h1>Method handle invocation</h1> |
| * 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 invoke}. |
| * In this case, the symbolic 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 symbolic 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 symbolic type 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 plain, inexact {@code invoke}, the resolved type descriptor |
| * must be a valid argument to the receiver's {@link #asType asType} method. |
| * Thus, plain {@code invoke} 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 plain {@code invoke} works the same as a call to |
| * {@code invokeExact}, if the symbolic type descriptor specified by the caller |
| * exactly matches the method handle's own type. |
| * If there is a type mismatch, {@code invoke} 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> |
| * (<em>Note:</em> The adjusted method handle {@code M2} is not directly observable, |
| * and implementations are therefore not required to materialize it.) |
| * |
| * <h1>Invocation checking</h1> |
| * 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 invoke}). |
| * <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 symbolic type |
| * descriptor, as resolved in {@code L2}, |
| * is matched against the original callee method's symbolic 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. |
| * |
| * <h1>Method handle creation</h1> |
| * 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.lang.invoke.MethodHandles.Lookup MethodHandles.Lookup} |
| * For example, a static method handle can be obtained |
| * from {@link java.lang.invoke.MethodHandles.Lookup#findStatic Lookup.findStatic}. |
| * There are also conversion methods from Core Reflection API objects, |
| * such as {@link java.lang.invoke.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 full details on method handle constants, |
| * see sections 4.4.8 and 5.4.3.5 of the Java Virtual Machine Specification.) |
| * <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> |
| * Method handle constants are subject to the same link-time access checks |
| * their corresponding bytecode instructions, and the {@code ldc} instruction |
| * will throw corresponding linkage errors if the bytecode behaviors would |
| * throw such errors. |
| * <p> |
| * As a corollary of this, access to protected members is restricted |
| * to receivers only of the accessing class, or one of its subclasses, |
| * and the accessing class must in turn be a subclass (or package sibling) |
| * of the protected member's defining class. |
| * If a method reference refers to a protected non-static method or field |
| * of a class outside the current package, the receiver argument will |
| * be narrowed to the type of the accessing class. |
| * <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. |
| * |
| * <h1>Usage examples</h1> |
| * Here are some examples of usage: |
| * <blockquote><pre>{@code |
| 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; |
| assertEquals(s, "nanny"); |
| // weakly typed invocation (using MHs.invoke) |
| s = (String) mh.invokeWithArguments("sappy", 'p', 'v'); |
| assertEquals(s, "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.invoke("one", "two"); |
| // invoke(Ljava/lang/String;Ljava/lang/String;)Ljava/lang/Object; |
| assertEquals(x, 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; |
| assertEquals(x, 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 plain {@code invoke} |
| * generates a single invokevirtual instruction with |
| * the symbolic type descriptor indicated in the following comment. |
| * In these examples, the helper method {@code assertEquals} is assumed to |
| * be a method which calls {@link java.util.Objects#equals(Object,Object) Objects.equals} |
| * on its arguments, and asserts that the result is true. |
| * |
| * <h1>Exceptions</h1> |
| * The methods {@code invokeExact} and {@code invoke} 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 Throwable}, or else must catch all |
| * throwables locally, rethrowing only those which are legal in the context, |
| * and wrapping ones which are illegal. |
| * |
| * <h1><a name="sigpoly"></a>Signature polymorphism</h1> |
| * The unusual compilation and linkage behavior of |
| * {@code invokeExact} and plain {@code invoke} |
| * is referenced by the term <em>signature polymorphism</em>. |
| * As defined in the Java Language Specification, |
| * a signature polymorphic method is one which can operate with |
| * any of a wide range of call signatures and return types. |
| * <p> |
| * In source code, a call to a signature polymorphic method will |
| * compile, regardless of the requested symbolic type descriptor. |
| * As usual, the Java compiler emits an {@code invokevirtual} |
| * instruction with the given symbolic type descriptor against the named method. |
| * The unusual part is that the symbolic 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 symbolic 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 symbolic type descriptors for these methods. |
| * Tools which determine symbolic linkage are required to accept such |
| * untransformed descriptors, without reporting linkage errors. |
| * |
| * <h1>Interoperation between method handles and the Core Reflection API</h1> |
| * Using factory methods in the {@link java.lang.invoke.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.lang.invoke.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 plain {@code invoke} in this class, |
| * they appear as ordinary non-polymorphic methods. |
| * Their reflective appearance, as viewed by |
| * {@link java.lang.Class#getDeclaredMethod Class.getDeclaredMethod}, |
| * is unaffected by their special status in this API. |
| * For example, {@link java.lang.reflect.Method#getModifiers Method.getModifiers} |
| * will report exactly those modifier bits required for any similarly |
| * declared method, including in this case {@code native} and {@code varargs} bits. |
| * <p> |
| * As with any reflected method, these methods (when reflected) may be |
| * invoked via {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}. |
| * However, such reflective calls do not result in method handle invocations. |
| * Such a call, if passed the required argument |
| * (a single one, of type {@code Object[]}), will ignore the argument and |
| * will throw an {@code UnsupportedOperationException}. |
| * <p> |
| * Since {@code invokevirtual} instructions can natively |
| * invoke method handles under any symbolic type descriptor, this reflective view conflicts |
| * with the normal presentation of these methods via bytecodes. |
| * Thus, these two native methods, when reflectively viewed by |
| * {@code Class.getDeclaredMethod}, may be regarded as placeholders only. |
| * <p> |
| * In order to obtain an invoker method for a particular type descriptor, |
| * use {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker}, |
| * or {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}. |
| * The {@link java.lang.invoke.MethodHandles.Lookup#findVirtual Lookup.findVirtual} |
| * API is also able to return a method handle |
| * to call {@code invokeExact} or plain {@code invoke}, |
| * for any specified type descriptor . |
| * |
| * <h1>Interoperation between method handles and Java generics</h1> |
| * 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 it constructs the symbolic 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 the <a href="MethodHandle.html#maxarity">maximum number</a> of allowed arguments. |
| * 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> |
| * |
| * <h1><a name="maxarity"></a>Arity limits</h1> |
| * The JVM imposes on all methods and constructors of any kind an absolute |
| * limit of 255 stacked arguments. This limit can appear more restrictive |
| * in certain cases: |
| * <ul> |
| * <li>A {@code long} or {@code double} argument counts (for purposes of arity limits) as two argument slots. |
| * <li>A non-static method consumes an extra argument for the object on which the method is called. |
| * <li>A constructor consumes an extra argument for the object which is being constructed. |
| * <li>Since a method handle’s {@code invoke} method (or other signature-polymorphic method) is non-virtual, |
| * it consumes an extra argument for the method handle itself, in addition to any non-virtual receiver object. |
| * </ul> |
| * These limits imply that certain method handles cannot be created, solely because of the JVM limit on stacked arguments. |
| * For example, if a static JVM method accepts exactly 255 arguments, a method handle cannot be created for it. |
| * Attempts to create method handles with impossible method types lead to an {@link IllegalArgumentException}. |
| * In particular, a method handle’s type must not have an arity of the exact maximum 255. |
| * |
| * @see MethodType |
| * @see MethodHandles |
| * @author John Rose, JSR 292 EG |
| */ |
| public abstract class MethodHandle { |
| static { MethodHandleImpl.initStatics(); } |
| |
| /** |
| * 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 final MethodType type; |
| /*private*/ final LambdaForm form; |
| // form is not private so that invokers can easily fetch it |
| /*private*/ MethodHandle asTypeCache; |
| // asTypeCache is not private so that invokers can easily fetch it |
| |
| /** |
| * Reports 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.lang.invoke} package. |
| */ |
| // @param type type (permanently assigned) of the new method handle |
| /*non-public*/ MethodHandle(MethodType type, LambdaForm form) { |
| type.getClass(); // explicit NPE |
| form.getClass(); // explicit NPE |
| this.type = type; |
| this.form = form; |
| |
| form.prepare(); // TO DO: Try to delay this step until just before invocation. |
| } |
| |
| /** |
| * Invokes the method handle, allowing any caller type descriptor, but requiring an exact type match. |
| * The symbolic 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 java.lang.reflect.Method.invoke}, via JNI, |
| * or indirectly via {@link java.lang.invoke.MethodHandles.Lookup#unreflect Lookup.unreflect}, |
| * it will throw an {@code UnsupportedOperationException}. |
| * @param args the signature-polymorphic parameter list, statically represented using varargs |
| * @return the signature-polymorphic result, statically represented using {@code Object} |
| * @throws WrongMethodTypeException if the target's type is not identical with the caller's symbolic 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; |
| |
| /** |
| * Invokes the method handle, allowing any caller type descriptor, |
| * and optionally performing conversions on arguments and return values. |
| * <p> |
| * If the call site's symbolic 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 resolved type descriptor at the call site of {@code invoke} 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 java.lang.reflect.Method.invoke}, via JNI, |
| * or indirectly via {@link java.lang.invoke.MethodHandles.Lookup#unreflect Lookup.unreflect}, |
| * it will throw an {@code UnsupportedOperationException}. |
| * @param args the signature-polymorphic parameter list, statically represented using varargs |
| * @return the signature-polymorphic result, statically represented using {@code Object} |
| * @throws WrongMethodTypeException if the target's type cannot be adjusted to the caller's symbolic 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 invoke(Object... args) throws Throwable; |
| |
| /** |
| * Private method for trusted invocation of a method handle respecting simplified signatures. |
| * Type mismatches will not throw {@code WrongMethodTypeException}, but could crash the JVM. |
| * <p> |
| * The caller signature is restricted to the following basic types: |
| * Object, int, long, float, double, and void return. |
| * <p> |
| * The caller is responsible for maintaining type correctness by ensuring |
| * that the each outgoing argument value is a member of the range of the corresponding |
| * callee argument type. |
| * (The caller should therefore issue appropriate casts and integer narrowing |
| * operations on outgoing argument values.) |
| * The caller can assume that the incoming result value is part of the range |
| * of the callee's return type. |
| * @param args the signature-polymorphic parameter list, statically represented using varargs |
| * @return the signature-polymorphic result, statically represented using {@code Object} |
| */ |
| /*non-public*/ final native @PolymorphicSignature Object invokeBasic(Object... args) throws Throwable; |
| |
| /** |
| * Private method for trusted invocation of a MemberName of kind {@code REF_invokeVirtual}. |
| * The caller signature is restricted to basic types as with {@code invokeBasic}. |
| * The trailing (not leading) argument must be a MemberName. |
| * @param args the signature-polymorphic parameter list, statically represented using varargs |
| * @return the signature-polymorphic result, statically represented using {@code Object} |
| */ |
| /*non-public*/ static native @PolymorphicSignature Object linkToVirtual(Object... args) throws Throwable; |
| |
| /** |
| * Private method for trusted invocation of a MemberName of kind {@code REF_invokeStatic}. |
| * The caller signature is restricted to basic types as with {@code invokeBasic}. |
| * The trailing (not leading) argument must be a MemberName. |
| * @param args the signature-polymorphic parameter list, statically represented using varargs |
| * @return the signature-polymorphic result, statically represented using {@code Object} |
| */ |
| /*non-public*/ static native @PolymorphicSignature Object linkToStatic(Object... args) throws Throwable; |
| |
| /** |
| * Private method for trusted invocation of a MemberName of kind {@code REF_invokeSpecial}. |
| * The caller signature is restricted to basic types as with {@code invokeBasic}. |
| * The trailing (not leading) argument must be a MemberName. |
| * @param args the signature-polymorphic parameter list, statically represented using varargs |
| * @return the signature-polymorphic result, statically represented using {@code Object} |
| */ |
| /*non-public*/ static native @PolymorphicSignature Object linkToSpecial(Object... args) throws Throwable; |
| |
| /** |
| * Private method for trusted invocation of a MemberName of kind {@code REF_invokeInterface}. |
| * The caller signature is restricted to basic types as with {@code invokeBasic}. |
| * The trailing (not leading) argument must be a MemberName. |
| * @param args the signature-polymorphic parameter list, statically represented using varargs |
| * @return the signature-polymorphic result, statically represented using {@code Object} |
| */ |
| /*non-public*/ static native @PolymorphicSignature Object linkToInterface(Object... args) throws Throwable; |
| |
| /** |
| * Performs a variable arity invocation, passing the arguments in the given list |
| * to the method handle, as if via an inexact {@link #invoke invoke} from a call site |
| * which mentions only the type {@code Object}, and whose arity is the length |
| * of the argument list. |
| * <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 general 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: |
| * <blockquote><pre>{@code |
| * 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 invoke}, |
| * {@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; |
| @SuppressWarnings("LocalVariableHidesMemberVariable") |
| MethodType type = type(); |
| if (type.parameterCount() != argc || isVarargsCollector()) { |
| // simulate invoke |
| return asType(MethodType.genericMethodType(argc)).invokeWithArguments(arguments); |
| } |
| MethodHandle invoker = type.invokers().varargsInvoker(); |
| return invoker.invokeExact(this, arguments); |
| } |
| |
| /** |
| * Performs a variable arity invocation, passing the arguments in the given array |
| * to the method handle, as if via an inexact {@link #invoke invoke} from a call site |
| * which mentions only the type {@code Object}, and whose arity is the length |
| * of the argument array. |
| * <p> |
| * This method is also equivalent to the following code: |
| * <blockquote><pre>{@code |
| * invokeWithArguments(arguments.toArray() |
| * }</pre></blockquote> |
| * |
| * @param arguments the arguments to pass to the target |
| * @return the result returned by the target |
| * @throws NullPointerException if {@code arguments} is a null reference |
| * @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 |
| */ |
| public Object invokeWithArguments(java.util.List<?> arguments) throws Throwable { |
| return invokeWithArguments(arguments.toArray()); |
| } |
| |
| /** |
| * Produces 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> |
| * The new method handle, when invoked, will perform the following |
| * steps: |
| * <ul> |
| * <li>Convert the incoming argument list to match the original |
| * method handle's argument list. |
| * <li>Invoke the original method handle on the converted argument list. |
| * <li>Convert any result returned by the original method handle |
| * to the return type of new method handle. |
| * </ul> |
| * <p> |
| * This method provides the crucial behavioral difference between |
| * {@link #invokeExact invokeExact} and plain, inexact {@link #invoke invoke}. |
| * The two methods |
| * perform the same steps when the caller's type descriptor exactly matches |
| * the callee's, but when the types differ, plain {@link #invoke invoke} |
| * also calls {@code asType} (or some internal equivalent) in order |
| * to match up the caller's and callee's types. |
| * <p> |
| * If the current method is a variable arity method handle |
| * argument list conversion may involve the conversion and collection |
| * of several arguments into an array, as |
| * {@linkplain #asVarargsCollector described elsewhere}. |
| * In every other case, all conversions are applied <em>pairwise</em>, |
| * which means that each argument or return value is converted to |
| * exactly one argument or return value (or no return value). |
| * The applied conversions are defined by consulting the |
| * the corresponding component types of the old and new |
| * method handle types. |
| * <p> |
| * Let <em>T0</em> and <em>T1</em> be corresponding new and old parameter types, |
| * or old and new return types. Specifically, for some valid index {@code i}, let |
| * <em>T0</em>{@code =newType.parameterType(i)} and <em>T1</em>{@code =this.type().parameterType(i)}. |
| * Or else, going the other way for return values, let |
| * <em>T0</em>{@code =this.type().returnType()} and <em>T1</em>{@code =newType.returnType()}. |
| * If the types are the same, the new method handle makes no change |
| * to the corresponding argument or return value (if any). |
| * Otherwise, one of the following conversions is applied |
| * if possible: |
| * <ul> |
| * <li>If <em>T0</em> and <em>T1</em> are references, then a cast to <em>T1</em> is applied. |
| * (The types do not need to be related in any particular way. |
| * This is because a dynamic value of null can convert to any reference type.) |
| * <li>If <em>T0</em> and <em>T1</em> are primitives, then a Java method invocation |
| * conversion (JLS 5.3) is applied, if one exists. |
| * (Specifically, <em>T0</em> must convert to <em>T1</em> by a widening primitive conversion.) |
| * <li>If <em>T0</em> is a primitive and <em>T1</em> a reference, |
| * a Java casting conversion (JLS 5.5) is applied if one exists. |
| * (Specifically, the value is boxed from <em>T0</em> to its wrapper class, |
| * which is then widened as needed to <em>T1</em>.) |
| * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing |
| * conversion will be applied at runtime, possibly followed |
| * by a Java method invocation conversion (JLS 5.3) |
| * on the primitive value. (These are the primitive widening conversions.) |
| * <em>T0</em> must be a wrapper class or a supertype of one. |
| * (In the case where <em>T0</em> is Object, these are the conversions |
| * allowed by {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}.) |
| * The unboxing conversion must have a possibility of success, which means that |
| * if <em>T0</em> is not itself a wrapper class, there must exist at least one |
| * wrapper class <em>TW</em> which is a subtype of <em>T0</em> and whose unboxed |
| * primitive value can be widened to <em>T1</em>. |
| * <li>If the return type <em>T1</em> is marked as void, any returned value is discarded |
| * <li>If the return type <em>T0</em> is void and <em>T1</em> a reference, a null value is introduced. |
| * <li>If the return type <em>T0</em> is void and <em>T1</em> a primitive, |
| * a zero value is introduced. |
| * </ul> |
| * (<em>Note:</em> Both <em>T0</em> and <em>T1</em> may be regarded as static types, |
| * because neither corresponds specifically to the <em>dynamic type</em> of any |
| * actual argument or return value.) |
| * <p> |
| * The method handle conversion cannot be made if any one of the required |
| * pairwise conversions cannot be made. |
| * <p> |
| * At runtime, the conversions applied to reference arguments |
| * or return values may require additional runtime checks which can fail. |
| * An unboxing operation may fail because the original reference is null, |
| * causing a {@link java.lang.NullPointerException NullPointerException}. |
| * An unboxing operation or a reference cast may also fail on a reference |
| * to an object of the wrong type, |
| * causing a {@link java.lang.ClassCastException ClassCastException}. |
| * Although an unboxing operation may accept several kinds of wrappers, |
| * if none are available, a {@code ClassCastException} will be thrown. |
| * |
| * @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 NullPointerException if {@code newType} is a null reference |
| * @throws WrongMethodTypeException if the conversion cannot be made |
| * @see MethodHandles#explicitCastArguments |
| */ |
| public MethodHandle asType(MethodType newType) { |
| // Fast path alternative to a heavyweight {@code asType} call. |
| // Return 'this' if the conversion will be a no-op. |
| if (newType == type) { |
| return this; |
| } |
| // Return 'this.asTypeCache' if the conversion is already memoized. |
| MethodHandle atc = asTypeCache; |
| if (atc != null && newType == atc.type) { |
| return atc; |
| } |
| return asTypeUncached(newType); |
| } |
| |
| /** Override this to change asType behavior. */ |
| /*non-public*/ MethodHandle asTypeUncached(MethodType newType) { |
| if (!type.isConvertibleTo(newType)) |
| throw new WrongMethodTypeException("cannot convert "+this+" to "+newType); |
| return asTypeCache = convertArguments(newType); |
| } |
| |
| /** |
| * Makes an <em>array-spreading</em> method handle, 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.) |
| * <p> |
| * If, when the adapter is called, the supplied array argument does |
| * not have the correct number of elements, the adapter will throw |
| * an {@link IllegalArgumentException} instead of invoking the target. |
| * <p> |
| * Here are some simple examples of array-spreading method handles: |
| * <blockquote><pre>{@code |
| MethodHandle equals = publicLookup() |
| .findVirtual(String.class, "equals", methodType(boolean.class, Object.class)); |
| assert( (boolean) equals.invokeExact("me", (Object)"me")); |
| assert(!(boolean) equals.invokeExact("me", (Object)"thee")); |
| // spread both arguments from a 2-array: |
| MethodHandle eq2 = equals.asSpreader(Object[].class, 2); |
| assert( (boolean) eq2.invokeExact(new Object[]{ "me", "me" })); |
| assert(!(boolean) eq2.invokeExact(new Object[]{ "me", "thee" })); |
| // try to spread from anything but a 2-array: |
| for (int n = 0; n <= 10; n++) { |
| Object[] badArityArgs = (n == 2 ? null : new Object[n]); |
| try { assert((boolean) eq2.invokeExact(badArityArgs) && false); } |
| catch (IllegalArgumentException ex) { } // OK |
| } |
| // spread both arguments from a String array: |
| MethodHandle eq2s = equals.asSpreader(String[].class, 2); |
| assert( (boolean) eq2s.invokeExact(new String[]{ "me", "me" })); |
| assert(!(boolean) eq2s.invokeExact(new String[]{ "me", "thee" })); |
| // spread second arguments from a 1-array: |
| MethodHandle eq1 = equals.asSpreader(Object[].class, 1); |
| assert( (boolean) eq1.invokeExact("me", new Object[]{ "me" })); |
| assert(!(boolean) eq1.invokeExact("me", new Object[]{ "thee" })); |
| // spread no arguments from a 0-array or null: |
| MethodHandle eq0 = equals.asSpreader(Object[].class, 0); |
| assert( (boolean) eq0.invokeExact("me", (Object)"me", new Object[0])); |
| assert(!(boolean) eq0.invokeExact("me", (Object)"thee", (Object[])null)); |
| // asSpreader and asCollector are approximate inverses: |
| for (int n = 0; n <= 2; n++) { |
| for (Class<?> a : new Class<?>[]{Object[].class, String[].class, CharSequence[].class}) { |
| MethodHandle equals2 = equals.asSpreader(a, n).asCollector(a, n); |
| assert( (boolean) equals2.invokeWithArguments("me", "me")); |
| assert(!(boolean) equals2.invokeWithArguments("me", "thee")); |
| } |
| } |
| MethodHandle caToString = publicLookup() |
| .findStatic(Arrays.class, "toString", methodType(String.class, char[].class)); |
| assertEquals("[A, B, C]", (String) caToString.invokeExact("ABC".toCharArray())); |
| MethodHandle caString3 = caToString.asCollector(char[].class, 3); |
| assertEquals("[A, B, C]", (String) caString3.invokeExact('A', 'B', 'C')); |
| MethodHandle caToString2 = caString3.asSpreader(char[].class, 2); |
| assertEquals("[A, B, C]", (String) caToString2.invokeExact('A', "BC".toCharArray())); |
| * }</pre></blockquote> |
| * @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 NullPointerException if {@code arrayType} is a null reference |
| * @throws IllegalArgumentException if {@code arrayType} is not an array type, |
| * or if target does not have at least |
| * {@code arrayLength} parameter types, |
| * or if {@code arrayLength} is negative, |
| * or if the resulting method handle's type would have |
| * <a href="MethodHandle.html#maxarity">too many parameters</a> |
| * @throws WrongMethodTypeException if the implied {@code asType} call fails |
| * @see #asCollector |
| */ |
| public MethodHandle asSpreader(Class<?> arrayType, int arrayLength) { |
| asSpreaderChecks(arrayType, arrayLength); |
| int spreadArgPos = type.parameterCount() - arrayLength; |
| return MethodHandleImpl.makeSpreadArguments(this, arrayType, spreadArgPos, arrayLength); |
| } |
| |
| private void asSpreaderChecks(Class<?> arrayType, int arrayLength) { |
| spreadArrayChecks(arrayType, arrayLength); |
| int nargs = type().parameterCount(); |
| if (nargs < arrayLength || arrayLength < 0) |
| throw newIllegalArgumentException("bad spread array length"); |
| if (arrayType != Object[].class && arrayLength != 0) { |
| boolean sawProblem = false; |
| Class<?> arrayElement = arrayType.getComponentType(); |
| for (int i = nargs - arrayLength; i < nargs; i++) { |
| if (!MethodType.canConvert(arrayElement, type().parameterType(i))) { |
| sawProblem = true; |
| break; |
| } |
| } |
| if (sawProblem) { |
| ArrayList<Class<?>> ptypes = new ArrayList<>(type().parameterList()); |
| for (int i = nargs - arrayLength; i < nargs; i++) { |
| ptypes.set(i, arrayElement); |
| } |
| // elicit an error: |
| this.asType(MethodType.methodType(type().returnType(), ptypes)); |
| } |
| } |
| } |
| |
| private void spreadArrayChecks(Class<?> arrayType, int arrayLength) { |
| Class<?> arrayElement = arrayType.getComponentType(); |
| if (arrayElement == null) |
| throw newIllegalArgumentException("not an array type", arrayType); |
| if ((arrayLength & 0x7F) != arrayLength) { |
| if ((arrayLength & 0xFF) != arrayLength) |
| throw newIllegalArgumentException("array length is not legal", arrayLength); |
| assert(arrayLength >= 128); |
| if (arrayElement == long.class || |
| arrayElement == double.class) |
| throw newIllegalArgumentException("array length is not legal for long[] or double[]", arrayLength); |
| } |
| } |
| |
| /** |
| * Makes an <em>array-collecting</em> method handle, 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. |
| * <p> |
| * Here are some examples of array-collecting method handles: |
| * <blockquote><pre>{@code |
| MethodHandle deepToString = publicLookup() |
| .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class)); |
| assertEquals("[won]", (String) deepToString.invokeExact(new Object[]{"won"})); |
| MethodHandle ts1 = deepToString.asCollector(Object[].class, 1); |
| assertEquals(methodType(String.class, Object.class), ts1.type()); |
| //assertEquals("[won]", (String) ts1.invokeExact( new Object[]{"won"})); //FAIL |
| assertEquals("[[won]]", (String) ts1.invokeExact((Object) new Object[]{"won"})); |
| // arrayType can be a subtype of Object[] |
| MethodHandle ts2 = deepToString.asCollector(String[].class, 2); |
| assertEquals(methodType(String.class, String.class, String.class), ts2.type()); |
| assertEquals("[two, too]", (String) ts2.invokeExact("two", "too")); |
| MethodHandle ts0 = deepToString.asCollector(Object[].class, 0); |
| assertEquals("[]", (String) ts0.invokeExact()); |
| // collectors can be nested, Lisp-style |
| MethodHandle ts22 = deepToString.asCollector(Object[].class, 3).asCollector(String[].class, 2); |
| assertEquals("[A, B, [C, D]]", ((String) ts22.invokeExact((Object)'A', (Object)"B", "C", "D"))); |
| // arrayType can be any primitive array type |
| MethodHandle bytesToString = publicLookup() |
| .findStatic(Arrays.class, "toString", methodType(String.class, byte[].class)) |
| .asCollector(byte[].class, 3); |
| assertEquals("[1, 2, 3]", (String) bytesToString.invokeExact((byte)1, (byte)2, (byte)3)); |
| MethodHandle longsToString = publicLookup() |
| .findStatic(Arrays.class, "toString", methodType(String.class, long[].class)) |
| .asCollector(long[].class, 1); |
| assertEquals("[123]", (String) longsToString.invokeExact((long)123)); |
| * }</pre></blockquote> |
| * @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 NullPointerException if {@code arrayType} is a null reference |
| * @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, |
| * or the resulting method handle's type would have |
| * <a href="MethodHandle.html#maxarity">too many parameters</a> |
| * @throws WrongMethodTypeException if the implied {@code asType} call fails |
| * @see #asSpreader |
| * @see #asVarargsCollector |
| */ |
| public MethodHandle asCollector(Class<?> arrayType, int arrayLength) { |
| asCollectorChecks(arrayType, arrayLength); |
| int collectArgPos = type().parameterCount()-1; |
| MethodHandle target = this; |
| if (arrayType != type().parameterType(collectArgPos)) |
| target = convertArguments(type().changeParameterType(collectArgPos, arrayType)); |
| MethodHandle collector = ValueConversions.varargsArray(arrayType, arrayLength); |
| return MethodHandles.collectArguments(target, collectArgPos, collector); |
| } |
| |
| // private API: return true if last param exactly matches arrayType |
| private boolean asCollectorChecks(Class<?> arrayType, int arrayLength) { |
| spreadArrayChecks(arrayType, arrayLength); |
| int nargs = type().parameterCount(); |
| if (nargs != 0) { |
| Class<?> lastParam = type().parameterType(nargs-1); |
| if (lastParam == arrayType) return true; |
| if (lastParam.isAssignableFrom(arrayType)) return false; |
| } |
| throw newIllegalArgumentException("array type not assignable to trailing argument", this, arrayType); |
| } |
| |
| /** |
| * Makes 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 invoke} 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> |
| * This transformation may return {@code this} if the method handle is |
| * already of variable arity and its trailing parameter type |
| * is identical to {@code arrayType}. |
| * <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 plain, inexact {@link #invoke invoke}, 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 invoke} 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 #asType asType} on a fixed arity |
| * method handle. |
| * <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 plain {@code invoke}, 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 |
| * plain, inexact {@code invoke} 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>{@code |
| MethodHandle deepToString = publicLookup() |
| .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class)); |
| MethodHandle ts1 = deepToString.asVarargsCollector(Object[].class); |
| assertEquals("[won]", (String) ts1.invokeExact( new Object[]{"won"})); |
| assertEquals("[won]", (String) ts1.invoke( new Object[]{"won"})); |
| assertEquals("[won]", (String) ts1.invoke( "won" )); |
| assertEquals("[[won]]", (String) ts1.invoke((Object) new Object[]{"won"})); |
| // findStatic of Arrays.asList(...) produces a variable arity method handle: |
| MethodHandle asList = publicLookup() |
| .findStatic(Arrays.class, "asList", methodType(List.class, Object[].class)); |
| assertEquals(methodType(List.class, Object[].class), asList.type()); |
| assert(asList.isVarargsCollector()); |
| assertEquals("[]", asList.invoke().toString()); |
| assertEquals("[1]", asList.invoke(1).toString()); |
| assertEquals("[two, too]", asList.invoke("two", "too").toString()); |
| String[] argv = { "three", "thee", "tee" }; |
| assertEquals("[three, thee, tee]", asList.invoke(argv).toString()); |
| assertEquals("[three, thee, tee]", asList.invoke((Object[])argv).toString()); |
| List ls = (List) asList.invoke((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 symbolic |
| * type descriptor of the call site and the type descriptor of the method handle.) |
| * |
| * @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 NullPointerException if {@code arrayType} is a null reference |
| * @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 |
| * @see #asFixedArity |
| */ |
| public MethodHandle asVarargsCollector(Class<?> arrayType) { |
| Class<?> arrayElement = arrayType.getComponentType(); |
| boolean lastMatch = asCollectorChecks(arrayType, 0); |
| if (isVarargsCollector() && lastMatch) |
| return this; |
| return MethodHandleImpl.makeVarargsCollector(this, arrayType); |
| } |
| |
| /** |
| * Determines 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.lang.invoke.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 plain, inexact {@code invoke} calls |
| * @see #asVarargsCollector |
| * @see #asFixedArity |
| */ |
| public boolean isVarargsCollector() { |
| return false; |
| } |
| |
| /** |
| * Makes a <em>fixed arity</em> method handle which is otherwise |
| * equivalent to the current method handle. |
| * <p> |
| * If the current method handle is not of |
| * {@linkplain #asVarargsCollector variable arity}, |
| * the current method handle is returned. |
| * This is true even if the current method handle |
| * could not be a valid input to {@code asVarargsCollector}. |
| * <p> |
| * Otherwise, the resulting fixed-arity method handle has the same |
| * type and behavior of the current method handle, |
| * except that {@link #isVarargsCollector isVarargsCollector} |
| * will be false. |
| * The fixed-arity method handle may (or may not) be the |
| * a previous argument to {@code asVarargsCollector}. |
| * <p> |
| * Here is an example, of a list-making variable arity method handle: |
| * <blockquote><pre>{@code |
| MethodHandle asListVar = publicLookup() |
| .findStatic(Arrays.class, "asList", methodType(List.class, Object[].class)) |
| .asVarargsCollector(Object[].class); |
| MethodHandle asListFix = asListVar.asFixedArity(); |
| assertEquals("[1]", asListVar.invoke(1).toString()); |
| Exception caught = null; |
| try { asListFix.invoke((Object)1); } |
| catch (Exception ex) { caught = ex; } |
| assert(caught instanceof ClassCastException); |
| assertEquals("[two, too]", asListVar.invoke("two", "too").toString()); |
| try { asListFix.invoke("two", "too"); } |
| catch (Exception ex) { caught = ex; } |
| assert(caught instanceof WrongMethodTypeException); |
| Object[] argv = { "three", "thee", "tee" }; |
| assertEquals("[three, thee, tee]", asListVar.invoke(argv).toString()); |
| assertEquals("[three, thee, tee]", asListFix.invoke(argv).toString()); |
| assertEquals(1, ((List) asListVar.invoke((Object)argv)).size()); |
| assertEquals("[three, thee, tee]", asListFix.invoke((Object)argv).toString()); |
| * }</pre></blockquote> |
| * |
| * @return a new method handle which accepts only a fixed number of arguments |
| * @see #asVarargsCollector |
| * @see #isVarargsCollector |
| */ |
| public MethodHandle asFixedArity() { |
| assert(!isVarargsCollector()); |
| return this; |
| } |
| |
| /** |
| * Binds 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>, |
| * the current method handle by binding it to the given argument. |
| * 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. |
| * <p> |
| * (<em>Note:</em> Because method handles are immutable, the target method handle |
| * retains its original type and behavior.) |
| * @param x the value to bind to the first argument of the target |
| * @return a new method handle which prepends the given value to the incoming |
| * argument list, 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) { |
| Class<?> ptype; |
| @SuppressWarnings("LocalVariableHidesMemberVariable") |
| MethodType type = type(); |
| if (type.parameterCount() == 0 || |
| (ptype = type.parameterType(0)).isPrimitive()) |
| throw newIllegalArgumentException("no leading reference parameter", x); |
| x = ptype.cast(x); // throw CCE if needed |
| return bindReceiver(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>{@code |
| * "MethodHandle" + type().toString() |
| * }</pre></blockquote> |
| * <p> |
| * (<em>Note:</em> 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() { |
| if (DEBUG_METHOD_HANDLE_NAMES) return debugString(); |
| return standardString(); |
| } |
| String standardString() { |
| return "MethodHandle"+type; |
| } |
| String debugString() { |
| return standardString()+"/LF="+internalForm()+internalProperties(); |
| } |
| |
| //// Implementation methods. |
| //// Sub-classes can override these default implementations. |
| //// All these methods assume arguments are already validated. |
| |
| // Other transforms to do: convert, explicitCast, permute, drop, filter, fold, GWT, catch |
| |
| /*non-public*/ |
| MethodHandle setVarargs(MemberName member) throws IllegalAccessException { |
| if (!member.isVarargs()) return this; |
| int argc = type().parameterCount(); |
| if (argc != 0) { |
| Class<?> arrayType = type().parameterType(argc-1); |
| if (arrayType.isArray()) { |
| return MethodHandleImpl.makeVarargsCollector(this, arrayType); |
| } |
| } |
| throw member.makeAccessException("cannot make variable arity", null); |
| } |
| /*non-public*/ |
| MethodHandle viewAsType(MethodType newType) { |
| // No actual conversions, just a new view of the same method. |
| return MethodHandleImpl.makePairwiseConvert(this, newType, 0); |
| } |
| |
| // Decoding |
| |
| /*non-public*/ |
| LambdaForm internalForm() { |
| return form; |
| } |
| |
| /*non-public*/ |
| MemberName internalMemberName() { |
| return null; // DMH returns DMH.member |
| } |
| |
| /*non-public*/ |
| Class<?> internalCallerClass() { |
| return null; // caller-bound MH for @CallerSensitive method returns caller |
| } |
| |
| /*non-public*/ |
| MethodHandle withInternalMemberName(MemberName member) { |
| if (member != null) { |
| return MethodHandleImpl.makeWrappedMember(this, member); |
| } else if (internalMemberName() == null) { |
| // The required internaMemberName is null, and this MH (like most) doesn't have one. |
| return this; |
| } else { |
| // The following case is rare. Mask the internalMemberName by wrapping the MH in a BMH. |
| MethodHandle result = rebind(); |
| assert (result.internalMemberName() == null); |
| return result; |
| } |
| } |
| |
| /*non-public*/ |
| boolean isInvokeSpecial() { |
| return false; // DMH.Special returns true |
| } |
| |
| /*non-public*/ |
| Object internalValues() { |
| return null; |
| } |
| |
| /*non-public*/ |
| Object internalProperties() { |
| // Override to something like "/FOO=bar" |
| return ""; |
| } |
| |
| //// Method handle implementation methods. |
| //// Sub-classes can override these default implementations. |
| //// All these methods assume arguments are already validated. |
| |
| /*non-public*/ MethodHandle convertArguments(MethodType newType) { |
| // Override this if it can be improved. |
| return MethodHandleImpl.makePairwiseConvert(this, newType, 1); |
| } |
| |
| /*non-public*/ |
| MethodHandle bindArgument(int pos, BasicType basicType, Object value) { |
| // Override this if it can be improved. |
| return rebind().bindArgument(pos, basicType, value); |
| } |
| |
| /*non-public*/ |
| MethodHandle bindReceiver(Object receiver) { |
| // Override this if it can be improved. |
| return bindArgument(0, L_TYPE, receiver); |
| } |
| |
| /*non-public*/ |
| MethodHandle dropArguments(MethodType srcType, int pos, int drops) { |
| // Override this if it can be improved. |
| return rebind().dropArguments(srcType, pos, drops); |
| } |
| |
| /*non-public*/ |
| MethodHandle permuteArguments(MethodType newType, int[] reorder) { |
| // Override this if it can be improved. |
| return rebind().permuteArguments(newType, reorder); |
| } |
| |
| /*non-public*/ |
| MethodHandle rebind() { |
| // Bind 'this' into a new invoker, of the known class BMH. |
| MethodType type2 = type(); |
| LambdaForm form2 = reinvokerForm(this); |
| // form2 = lambda (bmh, arg*) { thismh = bmh[0]; invokeBasic(thismh, arg*) } |
| return BoundMethodHandle.bindSingle(type2, form2, this); |
| } |
| |
| /*non-public*/ |
| MethodHandle reinvokerTarget() { |
| throw new InternalError("not a reinvoker MH: "+this.getClass().getName()+": "+this); |
| } |
| |
| /** Create a LF which simply reinvokes a target of the given basic type. |
| * The target MH must override {@link #reinvokerTarget} to provide the target. |
| */ |
| static LambdaForm reinvokerForm(MethodHandle target) { |
| MethodType mtype = target.type().basicType(); |
| LambdaForm reinvoker = mtype.form().cachedLambdaForm(MethodTypeForm.LF_REINVOKE); |
| if (reinvoker != null) return reinvoker; |
| if (mtype.parameterSlotCount() >= MethodType.MAX_MH_ARITY) |
| return makeReinvokerForm(target.type(), target); // cannot cache this |
| reinvoker = makeReinvokerForm(mtype, null); |
| return mtype.form().setCachedLambdaForm(MethodTypeForm.LF_REINVOKE, reinvoker); |
| } |
| private static LambdaForm makeReinvokerForm(MethodType mtype, MethodHandle customTargetOrNull) { |
| boolean customized = (customTargetOrNull != null); |
| MethodHandle MH_invokeBasic = customized ? null : MethodHandles.basicInvoker(mtype); |
| final int THIS_BMH = 0; |
| final int ARG_BASE = 1; |
| final int ARG_LIMIT = ARG_BASE + mtype.parameterCount(); |
| int nameCursor = ARG_LIMIT; |
| final int NEXT_MH = customized ? -1 : nameCursor++; |
| final int REINVOKE = nameCursor++; |
| LambdaForm.Name[] names = LambdaForm.arguments(nameCursor - ARG_LIMIT, mtype.invokerType()); |
| Object[] targetArgs; |
| MethodHandle targetMH; |
| if (customized) { |
| targetArgs = Arrays.copyOfRange(names, ARG_BASE, ARG_LIMIT, Object[].class); |
| targetMH = customTargetOrNull; |
| } else { |
| names[NEXT_MH] = new LambdaForm.Name(NF_reinvokerTarget, names[THIS_BMH]); |
| targetArgs = Arrays.copyOfRange(names, THIS_BMH, ARG_LIMIT, Object[].class); |
| targetArgs[0] = names[NEXT_MH]; // overwrite this MH with next MH |
| targetMH = MethodHandles.basicInvoker(mtype); |
| } |
| names[REINVOKE] = new LambdaForm.Name(targetMH, targetArgs); |
| return new LambdaForm("BMH.reinvoke", ARG_LIMIT, names); |
| } |
| |
| private static final LambdaForm.NamedFunction NF_reinvokerTarget; |
| static { |
| try { |
| NF_reinvokerTarget = new LambdaForm.NamedFunction(MethodHandle.class |
| .getDeclaredMethod("reinvokerTarget")); |
| } catch (ReflectiveOperationException ex) { |
| throw newInternalError(ex); |
| } |
| } |
| |
| /** |
| * Replace the old lambda form of this method handle with a new one. |
| * The new one must be functionally equivalent to the old one. |
| * Threads may continue running the old form indefinitely, |
| * but it is likely that the new one will be preferred for new executions. |
| * Use with discretion. |
| */ |
| /*non-public*/ |
| void updateForm(LambdaForm newForm) { |
| if (form == newForm) return; |
| // ISSUE: Should we have a memory fence here? |
| UNSAFE.putObject(this, FORM_OFFSET, newForm); |
| this.form.prepare(); // as in MethodHandle.<init> |
| } |
| |
| private static final long FORM_OFFSET; |
| static { |
| try { |
| FORM_OFFSET = UNSAFE.objectFieldOffset(MethodHandle.class.getDeclaredField("form")); |
| } catch (ReflectiveOperationException ex) { |
| throw newInternalError(ex); |
| } |
| } |
| } |