--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/src/java.base/share/classes/java/lang/invoke/MethodHandle.java Tue Sep 12 19:03:39 2017 +0200
@@ -0,0 +1,1592 @@
+/*
+ * Copyright (c) 2008, 2017, 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 jdk.internal.HotSpotIntrinsicCandidate;
+
+import java.util.Arrays;
+import java.util.Objects;
+
+import static java.lang.invoke.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.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 generate instructions that 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 generates an {@code invokevirtual} instruction that invokes
+ * 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 an {@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 also holds for 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 type 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 type descriptor checks,
+ * 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}
+ * or {@link #withVarargs withVarargs}.
+ * <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 id="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 id="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
+ * @since 1.7
+ */
+public abstract class MethodHandle {
+
+ /**
+ * 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
+ /*non-public*/ byte customizationCount;
+ // customizationCount should be accessible from invokers
+
+ /**
+ * 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) {
+ this.type = Objects.requireNonNull(type);
+ this.form = Objects.requireNonNull(form).uncustomize();
+
+ this.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
+ */
+ @HotSpotIntrinsicCandidate
+ 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
+ */
+ @HotSpotIntrinsicCandidate
+ 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}
+ */
+ @HotSpotIntrinsicCandidate
+ /*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}
+ */
+ @HotSpotIntrinsicCandidate
+ /*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}
+ */
+ @HotSpotIntrinsicCandidate
+ /*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}
+ */
+ @HotSpotIntrinsicCandidate
+ /*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}
+ */
+ @HotSpotIntrinsicCandidate
+ /*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 {
+ MethodType invocationType = MethodType.genericMethodType(arguments == null ? 0 : arguments.length);
+ return invocationType.invokers().spreadInvoker(0).invokeExact(asType(invocationType), 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 = asTypeCached(newType);
+ if (atc != null) {
+ return atc;
+ }
+ return asTypeUncached(newType);
+ }
+
+ private MethodHandle asTypeCached(MethodType newType) {
+ MethodHandle atc = asTypeCache;
+ if (atc != null && newType == atc.type) {
+ return atc;
+ }
+ return null;
+ }
+
+ /** 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 = MethodHandleImpl.makePairwiseConvert(this, newType, true);
+ }
+
+ /**
+ * 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) {
+ return asSpreader(type().parameterCount() - arrayLength, arrayType, arrayLength);
+ }
+
+ /**
+ * Makes an <em>array-spreading</em> method handle, which accepts an array argument at a given position and spreads
+ * its elements as positional arguments in place of the array. 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
+ * {@code arrayLength} parameters of the target's type, starting at the zero-based position {@code spreadArgPos},
+ * are replaced by a single array parameter of type {@code arrayType}.
+ * <p>
+ * This method behaves very much like {@link #asSpreader(Class, int)}, but accepts an additional {@code spreadArgPos}
+ * argument to indicate at which position in the parameter list the spreading should take place.
+ *
+ * @apiNote Example:
+ * <blockquote><pre>{@code
+ MethodHandle compare = LOOKUP.findStatic(Objects.class, "compare", methodType(int.class, Object.class, Object.class, Comparator.class));
+ MethodHandle compare2FromArray = compare.asSpreader(0, Object[].class, 2);
+ Object[] ints = new Object[]{3, 9, 7, 7};
+ Comparator<Integer> cmp = (a, b) -> a - b;
+ assertTrue((int) compare2FromArray.invoke(Arrays.copyOfRange(ints, 0, 2), cmp) < 0);
+ assertTrue((int) compare2FromArray.invoke(Arrays.copyOfRange(ints, 1, 3), cmp) > 0);
+ assertTrue((int) compare2FromArray.invoke(Arrays.copyOfRange(ints, 2, 4), cmp) == 0);
+ * }</pre></blockquote>
+ * @param spreadArgPos the position (zero-based index) in the argument list at which spreading should start.
+ * @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 an array argument at a given position,
+ * 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 {@code spreadArgPos} has an illegal value (negative, or together with arrayLength exceeding the
+ * number of arguments),
+ * 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 #asSpreader(Class, int)
+ * @since 9
+ */
+ public MethodHandle asSpreader(int spreadArgPos, Class<?> arrayType, int arrayLength) {
+ MethodType postSpreadType = asSpreaderChecks(arrayType, spreadArgPos, arrayLength);
+ MethodHandle afterSpread = this.asType(postSpreadType);
+ BoundMethodHandle mh = afterSpread.rebind();
+ LambdaForm lform = mh.editor().spreadArgumentsForm(1 + spreadArgPos, arrayType, arrayLength);
+ MethodType preSpreadType = postSpreadType.replaceParameterTypes(spreadArgPos, spreadArgPos + arrayLength, arrayType);
+ return mh.copyWith(preSpreadType, lform);
+ }
+
+ /**
+ * See if {@code asSpreader} can be validly called with the given arguments.
+ * Return the type of the method handle call after spreading but before conversions.
+ */
+ private MethodType asSpreaderChecks(Class<?> arrayType, int pos, int arrayLength) {
+ spreadArrayChecks(arrayType, arrayLength);
+ int nargs = type().parameterCount();
+ if (nargs < arrayLength || arrayLength < 0)
+ throw newIllegalArgumentException("bad spread array length");
+ if (pos < 0 || pos + arrayLength > nargs) {
+ throw newIllegalArgumentException("bad spread position");
+ }
+ Class<?> arrayElement = arrayType.getComponentType();
+ MethodType mtype = type();
+ boolean match = true, fail = false;
+ for (int i = pos; i < pos + arrayLength; i++) {
+ Class<?> ptype = mtype.parameterType(i);
+ if (ptype != arrayElement) {
+ match = false;
+ if (!MethodType.canConvert(arrayElement, ptype)) {
+ fail = true;
+ break;
+ }
+ }
+ }
+ if (match) return mtype;
+ MethodType needType = mtype.asSpreaderType(arrayType, pos, arrayLength);
+ if (!fail) return needType;
+ // elicit an error:
+ this.asType(needType);
+ throw newInternalError("should not return");
+ }
+
+ 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);
+ }
+ }
+ /**
+ * Adapts this method handle to be {@linkplain #asVarargsCollector variable arity}
+ * if the boolean flag is true, else {@linkplain #asFixedArity fixed arity}.
+ * If the method handle is already of the proper arity mode, it is returned
+ * unchanged.
+ * @apiNote
+ * <p>This method is sometimes useful when adapting a method handle that
+ * may be variable arity, to ensure that the resulting adapter is also
+ * variable arity if and only if the original handle was. For example,
+ * this code changes the first argument of a handle {@code mh} to {@code int} without
+ * disturbing its variable arity property:
+ * {@code mh.asType(mh.type().changeParameterType(0,int.class))
+ * .withVarargs(mh.isVarargsCollector())}
+ * @param makeVarargs true if the return method handle should have variable arity behavior
+ * @return a method handle of the same type, with possibly adjusted variable arity behavior
+ * @throws IllegalArgumentException if {@code makeVarargs} is true and
+ * this method handle does not have a trailing array parameter
+ * @since 9
+ * @see #asVarargsCollector
+ * @see #asFixedArity
+ */
+ public MethodHandle withVarargs(boolean makeVarargs) {
+ if (!makeVarargs) {
+ return asFixedArity();
+ } else if (!isVarargsCollector()) {
+ return asVarargsCollector(type().lastParameterType());
+ } else {
+ return this;
+ }
+ }
+
+ /**
+ * 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}
+ * or {@link #withVarargs withVarargs} 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>
+ * <p>
+ * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
+ * variable-arity method handle}, even if the original target method handle was.
+ * @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) {
+ return asCollector(type().parameterCount() - 1, arrayType, arrayLength);
+ }
+
+ /**
+ * Makes an <em>array-collecting</em> method handle, which accepts a given number of positional arguments starting
+ * at a given position, 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 the parameter at the position indicated by {@code collectArgPos} (usually of type {@code arrayType})
+ * is replaced by {@code arrayLength} parameters whose type is element type of {@code arrayType}.
+ * <p>
+ * This method behaves very much like {@link #asCollector(Class, int)}, but differs in that its {@code
+ * collectArgPos} argument indicates at which position in the parameter list arguments should be collected. This
+ * index is zero-based.
+ *
+ * @apiNote Examples:
+ * <blockquote><pre>{@code
+ StringWriter swr = new StringWriter();
+ MethodHandle swWrite = LOOKUP.findVirtual(StringWriter.class, "write", methodType(void.class, char[].class, int.class, int.class)).bindTo(swr);
+ MethodHandle swWrite4 = swWrite.asCollector(0, char[].class, 4);
+ swWrite4.invoke('A', 'B', 'C', 'D', 1, 2);
+ assertEquals("BC", swr.toString());
+ swWrite4.invoke('P', 'Q', 'R', 'S', 0, 4);
+ assertEquals("BCPQRS", swr.toString());
+ swWrite4.invoke('W', 'X', 'Y', 'Z', 3, 1);
+ assertEquals("BCPQRSZ", swr.toString());
+ * }</pre></blockquote>
+ * <p>
+ * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
+ * variable-arity method handle}, even if the original target method handle was.
+ * @param collectArgPos the zero-based position in the parameter list at which to start collecting.
+ * @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 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 array parameter type,
+ * or {@code arrayLength} is not a legal array size,
+ * or {@code collectArgPos} has an illegal value (negative, or greater than the number of arguments),
+ * 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 #asCollector(Class, int)
+ * @since 9
+ */
+ public MethodHandle asCollector(int collectArgPos, Class<?> arrayType, int arrayLength) {
+ asCollectorChecks(arrayType, collectArgPos, arrayLength);
+ BoundMethodHandle mh = rebind();
+ MethodType resultType = type().asCollectorType(arrayType, collectArgPos, arrayLength);
+ MethodHandle newArray = MethodHandleImpl.varargsArray(arrayType, arrayLength);
+ LambdaForm lform = mh.editor().collectArgumentArrayForm(1 + collectArgPos, newArray);
+ if (lform != null) {
+ return mh.copyWith(resultType, lform);
+ }
+ lform = mh.editor().collectArgumentsForm(1 + collectArgPos, newArray.type().basicType());
+ return mh.copyWithExtendL(resultType, lform, newArray);
+ }
+
+ /**
+ * See if {@code asCollector} can be validly called with the given arguments.
+ * Return false if the last parameter is not an exact match to arrayType.
+ */
+ /*non-public*/ boolean asCollectorChecks(Class<?> arrayType, int pos, int arrayLength) {
+ spreadArrayChecks(arrayType, arrayLength);
+ int nargs = type().parameterCount();
+ if (pos < 0 || pos >= nargs) {
+ throw newIllegalArgumentException("bad collect position");
+ }
+ if (nargs != 0) {
+ Class<?> param = type().parameterType(pos);
+ if (param == arrayType) return true;
+ if (param.isAssignableFrom(arrayType)) return false;
+ }
+ throw newIllegalArgumentException("array type not assignable to 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} and {@code withVarargs},
+ * 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 #withVarargs
+ * @see #asFixedArity
+ */
+ public MethodHandle asVarargsCollector(Class<?> arrayType) {
+ Objects.requireNonNull(arrayType);
+ boolean lastMatch = asCollectorChecks(arrayType, type().parameterCount() - 1, 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
+ * @see #withVarargs
+ */
+ 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.
+ * <p>
+ * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
+ * variable-arity method handle}, even if the original target method handle was.
+ * @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) {
+ x = type.leadingReferenceParameter().cast(x); // throw CCE if needed
+ return bindArgumentL(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>{@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 "MethodHandle"+debugString();
+ return standardString();
+ }
+ String standardString() {
+ return "MethodHandle"+type;
+ }
+ /** Return a string with a several lines describing the method handle structure.
+ * This string would be suitable for display in an IDE debugger.
+ */
+ String debugString() {
+ return type+" : "+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
+
+ BoundMethodHandle bindArgumentL(int pos, Object value) {
+ return rebind().bindArgumentL(pos, value);
+ }
+
+ /*non-public*/
+ MethodHandle setVarargs(MemberName member) throws IllegalAccessException {
+ if (!member.isVarargs()) return this;
+ try {
+ return this.withVarargs(true);
+ } catch (IllegalArgumentException ex) {
+ throw member.makeAccessException("cannot make variable arity", null);
+ }
+ }
+
+ /*non-public*/
+ MethodHandle viewAsType(MethodType newType, boolean strict) {
+ // No actual conversions, just a new view of the same method.
+ // Note that this operation must not produce a DirectMethodHandle,
+ // because retyped DMHs, like any transformed MHs,
+ // cannot be cracked into MethodHandleInfo.
+ assert viewAsTypeChecks(newType, strict);
+ BoundMethodHandle mh = rebind();
+ return mh.copyWith(newType, mh.form);
+ }
+
+ /*non-public*/
+ boolean viewAsTypeChecks(MethodType newType, boolean strict) {
+ if (strict) {
+ assert(type().isViewableAs(newType, true))
+ : Arrays.asList(this, newType);
+ } else {
+ assert(type().basicType().isViewableAs(newType.basicType(), true))
+ : Arrays.asList(this, newType);
+ }
+ return true;
+ }
+
+ // 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*/
+ MethodHandleImpl.Intrinsic intrinsicName() {
+ // no special intrinsic meaning to most MHs
+ return MethodHandleImpl.Intrinsic.NONE;
+ }
+
+ /*non-public*/
+ MethodHandle withInternalMemberName(MemberName member, boolean isInvokeSpecial) {
+ if (member != null) {
+ return MethodHandleImpl.makeWrappedMember(this, member, isInvokeSpecial);
+ } 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 to follow this.form, like "\n& FOO=bar"
+ return "";
+ }
+
+ //// Method handle implementation methods.
+ //// Sub-classes can override these default implementations.
+ //// All these methods assume arguments are already validated.
+
+ /*non-public*/
+ abstract MethodHandle copyWith(MethodType mt, LambdaForm lf);
+
+ /** Require this method handle to be a BMH, or else replace it with a "wrapper" BMH.
+ * Many transforms are implemented only for BMHs.
+ * @return a behaviorally equivalent BMH
+ */
+ abstract BoundMethodHandle rebind();
+
+ /**
+ * 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) {
+ assert(newForm.customized == null || newForm.customized == this);
+ if (form == newForm) return;
+ newForm.prepare(); // as in MethodHandle.<init>
+ UNSAFE.putObject(this, FORM_OFFSET, newForm);
+ UNSAFE.fullFence();
+ }
+
+ /** Craft a LambdaForm customized for this particular MethodHandle */
+ /*non-public*/
+ void customize() {
+ if (form.customized == null) {
+ LambdaForm newForm = form.customize(this);
+ updateForm(newForm);
+ } else {
+ assert(form.customized == this);
+ }
+ }
+
+ private static final long FORM_OFFSET
+ = UNSAFE.objectFieldOffset(MethodHandle.class, "form");
+}