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Diffstat (limited to 'java/lang/invoke/MethodHandle.java')
| -rw-r--r-- | java/lang/invoke/MethodHandle.java | 1347 |
1 files changed, 11 insertions, 1336 deletions
diff --git a/java/lang/invoke/MethodHandle.java b/java/lang/invoke/MethodHandle.java index af3db103..159f9dd7 100644 --- a/java/lang/invoke/MethodHandle.java +++ b/java/lang/invoke/MethodHandle.java @@ -25,1353 +25,28 @@ package java.lang.invoke; - -import dalvik.system.EmulatedStackFrame; - -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 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 { - // Android-changed: - // - // static { MethodHandleImpl.initStatics(); } - // - // LambdaForm and customizationCount are currently unused in our implementation - // and will be substituted with appropriate implementation / delegate classes. - // - // /*private*/ final LambdaForm form; - // form is not private so that invokers can easily fetch it - // /*non-public*/ byte customizationCount; - // customizationCount should be accessible from invokers - - - /** - * Internal marker interface which distinguishes (to the Java compiler) - * those methods which are <a href="MethodHandle.html#sigpoly">signature polymorphic</a>. - * - * @hide - */ - @java.lang.annotation.Target({java.lang.annotation.ElementType.METHOD}) - @java.lang.annotation.Retention(java.lang.annotation.RetentionPolicy.RUNTIME) - public @interface PolymorphicSignature { } - - /** - * The type of this method handle, this corresponds to the exact type of the method - * being invoked. - */ - private final MethodType type; - - /** - * The nominal type of this method handle, will be non-null if a method handle declares - * a different type from its "real" type, which is either the type of the method being invoked - * or the type of the emulated stackframe expected by an underyling adapter. - */ - private MethodType nominalType; - - /** - * The spread invoker associated with this type with zero trailing arguments. - * This is used to speed up invokeWithArguments. - */ - private MethodHandle cachedSpreadInvoker; - - /** - * The INVOKE* constants and SGET/SPUT and IGET/IPUT constants specify the behaviour of this - * method handle with respect to the ArtField* or the ArtMethod* that it operates on. These - * behaviours are equivalent to the dex bytecode behaviour on the respective method_id or - * field_id in the equivalent instruction. - * - * INVOKE_TRANSFORM is a special type of handle which doesn't encode any dex bytecode behaviour, - * instead it transforms the list of input arguments or performs other higher order operations - * before (optionally) delegating to another method handle. - * - * INVOKE_CALLSITE_TRANSFORM is a variation on INVOKE_TRANSFORM where the method type of - * a MethodHandle dynamically varies based on the callsite. This is used by - * the VarargsCollector implementation which places any number of trailing arguments - * into an array before invoking an arity method. The "any number of trailing arguments" means - * it would otherwise generate WrongMethodTypeExceptions as the callsite method type and - * VarargsCollector method type appear incompatible. - */ - - /** @hide */ public static final int INVOKE_VIRTUAL = 0; - /** @hide */ public static final int INVOKE_SUPER = 1; - /** @hide */ public static final int INVOKE_DIRECT = 2; - /** @hide */ public static final int INVOKE_STATIC = 3; - /** @hide */ public static final int INVOKE_INTERFACE = 4; - /** @hide */ public static final int INVOKE_TRANSFORM = 5; - /** @hide */ public static final int INVOKE_CALLSITE_TRANSFORM = 6; - /** @hide */ public static final int IGET = 7; - /** @hide */ public static final int IPUT = 8; - /** @hide */ public static final int SGET = 9; - /** @hide */ public static final int SPUT = 10; - - // The kind of this method handle (used by the runtime). This is one of the INVOKE_* - // constants or SGET/SPUT, IGET/IPUT. - /** @hide */ protected final int handleKind; - - // The ArtMethod* or ArtField* associated with this method handle (used by the runtime). - /** @hide */ protected final long artFieldOrMethod; - - /** @hide */ - protected MethodHandle(long artFieldOrMethod, int handleKind, MethodType type) { - this.artFieldOrMethod = artFieldOrMethod; - this.handleKind = handleKind; - this.type = type; - } - - /** - * 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() { - if (nominalType != null) { - return nominalType; - } - - return type; - } - - /** - * 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; - - // Android-changed: Removed implementation details. - // - // /*non-public*/ final native @PolymorphicSignature Object invokeBasic(Object... args) - // /*non-public*/ static native @PolymorphicSignature Object linkToVirtual(Object... args) - // /*non-public*/ static native @PolymorphicSignature Object linkToStatic(Object... args) - // /*non-public*/ static native @PolymorphicSignature Object linkToSpecial(Object... args) - // /*non-public*/ static native @PolymorphicSignature Object linkToInterface(Object... args) - - /** - * 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 { - MethodHandle invoker = null; - synchronized (this) { - if (cachedSpreadInvoker == null) { - cachedSpreadInvoker = MethodHandles.spreadInvoker(this.type(), 0); - } - - invoker = cachedSpreadInvoker; - } - - return invoker.invoke(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 m atches - * 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; - } - - if (!type.isConvertibleTo(newType)) { - throw new WrongMethodTypeException("cannot convert " + this + " to " + newType); - } - - MethodHandle mh = duplicate(); - mh.nominalType = newType; - return mh; - } - - /** - * 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) { - MethodType postSpreadType = asSpreaderChecks(arrayType, arrayLength); - - final int targetParamCount = postSpreadType.parameterCount(); - MethodType dropArrayArgs = postSpreadType.dropParameterTypes( - (targetParamCount - arrayLength), targetParamCount); - MethodType adapterType = dropArrayArgs.appendParameterTypes(arrayType); - - return new Transformers.Spreader(this, adapterType, arrayLength); - } - - /** - * 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 arrayLength) { - spreadArrayChecks(arrayType, arrayLength); - int nargs = type().parameterCount(); - if (nargs < arrayLength || arrayLength < 0) - throw newIllegalArgumentException("bad spread array length"); - Class<?> arrayElement = arrayType.getComponentType(); - MethodType mtype = type(); - boolean match = true, fail = false; - for (int i = nargs - arrayLength; i < nargs; 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, arrayLength); - if (!fail) return needType; - // elicit an error: - this.asType(needType); - throw newInternalError("should not return", null); - } - - 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); - - return new Transformers.Collector(this, arrayType, arrayLength); - } - - /** - * 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 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) { - arrayType.getClass(); // explicit NPE - boolean lastMatch = asCollectorChecks(arrayType, 0); - if (isVarargsCollector() && lastMatch) - return this; - return new Transformers.VarargsCollector(this); - } + public MethodType type() { return null; } - /** - * 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; - } + public final Object invokeExact(Object... args) throws Throwable { return null; } - /** - * 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() { - // Android-changed: implementation specific. - MethodHandle mh = this; - if (mh.isVarargsCollector()) { - mh = ((Transformers.VarargsCollector) mh).asFixedArity(); - } - assert(!mh.isVarargsCollector()); - return mh; - } + public final Object invoke(Object... args) throws Throwable { return null; } - /** - * 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) { - x = type.leadingReferenceParameter().cast(x); // throw CCE if needed + public Object invokeWithArguments(Object... arguments) throws Throwable { return null; } - return new Transformers.BindTo(this, x); - } + public Object invokeWithArguments(java.util.List<?> arguments) throws Throwable { return null; } - /** - * 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() { - // Android-changed: Removed debugging support. - return "MethodHandle"+type; - } + public MethodHandle asType(MethodType newType) { return null; } - /** @hide */ - public int getHandleKind() { - return handleKind; - } + public MethodHandle asCollector(Class<?> arrayType, int arrayLength) { return null; } - /** @hide */ - protected void transform(EmulatedStackFrame arguments) throws Throwable { - throw new AssertionError("MethodHandle.transform should never be called."); - } + public MethodHandle asVarargsCollector(Class<?> arrayType) { return null; } - /** - * Creates a copy of this method handle, copying all relevant data. - * - * @hide - */ - protected MethodHandle duplicate() { - try { - return (MethodHandle) this.clone(); - } catch (CloneNotSupportedException cnse) { - throw new AssertionError("Subclass of Transformer is not cloneable"); - } - } + public boolean isVarargsCollector() { return false; } + public MethodHandle asFixedArity() { return null; } - /** - * This is the entry point for all transform calls, and dispatches to the protected - * transform method. This layer of indirection exists purely for convenience, because - * we can invoke-direct on a fixed ArtMethod for all transform variants. - * - * NOTE: If this extra layer of indirection proves to be a problem, we can get rid - * of this layer of indirection at the cost of some additional ugliness. - */ - private void transformInternal(EmulatedStackFrame arguments) throws Throwable { - transform(arguments); - } + public MethodHandle bindTo(Object x) { return null; } - // Android-changed: Removed implementation details : - // - // String standardString(); - // String debugString(); - // - //// 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); - // /*non-public*/ MethodHandle setVarargs(MemberName member); - // /*non-public*/ MethodHandle viewAsType(MethodType newType, boolean strict); - // /*non-public*/ boolean viewAsTypeChecks(MethodType newType, boolean strict); - // - // Decoding - // - // /*non-public*/ LambdaForm internalForm(); - // /*non-public*/ MemberName internalMemberName(); - // /*non-public*/ Class<?> internalCallerClass(); - // /*non-public*/ MethodHandleImpl.Intrinsic intrinsicName(); - // /*non-public*/ MethodHandle withInternalMemberName(MemberName member, boolean isInvokeSpecial); - // /*non-public*/ boolean isInvokeSpecial(); - // /*non-public*/ Object internalValues(); - // /*non-public*/ Object internalProperties(); - // - //// 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); - // abstract BoundMethodHandle rebind(); - // /*non-public*/ void updateForm(LambdaForm newForm); - // /*non-public*/ void customize(); - // private static final long FORM_OFFSET; } |