- * 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). - *
- * A method handle's type controls the types of invocations it accepts, - * and the kinds of transformations that apply to it. - *
- * 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. - *
- * 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. - *
- * 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. - * - *
- * 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. - *
- * 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}). - *
- * 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. - * - *
- * 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. - *
- * 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}. - *
- * 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). - *
- * 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. - *
- * (Note: The adjusted method handle {@code M2} is not directly observable, - * and implementations are therefore not required to materialize it.) - * - *
- * 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. - *
- * 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. - *
- * 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. - *
- * Unlike with the Core Reflection API, where access is checked every time - * a reflective method is invoked, - * method handle access checking is performed - * when the method handle is created. - * 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. - *
- * 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. - * - *
- * 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.) - *
- * 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}. - *
- * 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.) - *
- * 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. - *
- * 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. - *
- * When a method handle to a virtual method is invoked, the method is - * always looked up in the receiver (that is, the first argument). - *
- * 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. - * - *
{@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
- * }- * 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. - *
- * 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.) - *
- * 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. - * - *
- * 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. - *
- * 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}. - *
- * 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. - *
- * 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 . - * - *
- * 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. - *
- * 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. - *
- * 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}. - *
- * 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. - *
- * 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. - *
- * 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}. - *
- * When this method is observed via the Core Reflection API, - * it will appear as a single native method, taking an object array and returning an object. - * If this native method is invoked directly via - * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}, via JNI, - * or indirectly via {@link java.lang.invoke.MethodHandles.Lookup#unreflect Lookup.unreflect}, - * it will throw an {@code UnsupportedOperationException}. - * @param args the signature-polymorphic parameter list, statically represented using varargs - * @return the signature-polymorphic result, statically represented using {@code Object} - * @throws WrongMethodTypeException if the target's type cannot be adjusted to the caller's symbolic type descriptor - * @throws ClassCastException if the target's type can be adjusted to the caller, but a reference cast fails - * @throws Throwable anything thrown by the underlying method propagates unchanged through the method handle call - */ - public final native @PolymorphicSignature Object invoke(Object... args) throws Throwable; - - /** - * Private method for trusted invocation of a method handle respecting simplified signatures. - * Type mismatches will not throw {@code WrongMethodTypeException}, but could crash the JVM. - *
- * The caller signature is restricted to the following basic types: - * Object, int, long, float, double, and void return. - *
- * The caller is responsible for maintaining type correctness by ensuring - * that the each outgoing argument value is a member of the range of the corresponding - * callee argument type. - * (The caller should therefore issue appropriate casts and integer narrowing - * operations on outgoing argument values.) - * The caller can assume that the incoming result value is part of the range - * of the callee's return type. - * @param args the signature-polymorphic parameter list, statically represented using varargs - * @return the signature-polymorphic result, statically represented using {@code Object} - */ - /*non-public*/ final native @PolymorphicSignature Object invokeBasic(Object... args) throws Throwable; - - /** - * Private method for trusted invocation of a MemberName of kind {@code REF_invokeVirtual}. - * The caller signature is restricted to basic types as with {@code invokeBasic}. - * The trailing (not leading) argument must be a MemberName. - * @param args the signature-polymorphic parameter list, statically represented using varargs - * @return the signature-polymorphic result, statically represented using {@code Object} - */ - /*non-public*/ static native @PolymorphicSignature Object linkToVirtual(Object... args) throws Throwable; - - /** - * Private method for trusted invocation of a MemberName of kind {@code REF_invokeStatic}. - * The caller signature is restricted to basic types as with {@code invokeBasic}. - * The trailing (not leading) argument must be a MemberName. - * @param args the signature-polymorphic parameter list, statically represented using varargs - * @return the signature-polymorphic result, statically represented using {@code Object} - */ - /*non-public*/ static native @PolymorphicSignature Object linkToStatic(Object... args) throws Throwable; - - /** - * Private method for trusted invocation of a MemberName of kind {@code REF_invokeSpecial}. - * The caller signature is restricted to basic types as with {@code invokeBasic}. - * The trailing (not leading) argument must be a MemberName. - * @param args the signature-polymorphic parameter list, statically represented using varargs - * @return the signature-polymorphic result, statically represented using {@code Object} - */ - /*non-public*/ static native @PolymorphicSignature Object linkToSpecial(Object... args) throws Throwable; - - /** - * Private method for trusted invocation of a MemberName of kind {@code REF_invokeInterface}. - * The caller signature is restricted to basic types as with {@code invokeBasic}. - * The trailing (not leading) argument must be a MemberName. - * @param args the signature-polymorphic parameter list, statically represented using varargs - * @return the signature-polymorphic result, statically represented using {@code Object} - */ - /*non-public*/ static native @PolymorphicSignature Object linkToInterface(Object... args) throws Throwable; - - /** - * Performs a variable arity invocation, passing the arguments in the given list - * to the method handle, as if via an inexact {@link #invoke invoke} from a call site - * which mentions only the type {@code Object}, and whose arity is the length - * of the argument list. - *
- * 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. - *
- * Because of the action of the {@code asType} step, the following argument - * conversions are applied as necessary: - *
- * The result returned by the call is boxed if it is a primitive, - * or forced to null if the return type is void. - *
- * This call is equivalent to the following code: - *
{@code
- * MethodHandle invoker = MethodHandles.spreadInvoker(this.type(), 0);
- * Object result = invoker.invokeExact(this, arguments);
- * }- * Unlike the signature polymorphic methods {@code invokeExact} and {@code invoke}, - * {@code invokeWithArguments} can be accessed normally via the Core Reflection API and JNI. - * It can therefore be used as a bridge between native or reflective code and method handles. - * - * @param arguments the arguments to pass to the target - * @return the result returned by the target - * @throws ClassCastException if an argument cannot be converted by reference casting - * @throws WrongMethodTypeException if the target's type cannot be adjusted to take the given number of {@code Object} arguments - * @throws Throwable anything thrown by the target method invocation - * @see MethodHandles#spreadInvoker - */ - public Object invokeWithArguments(Object... arguments) throws Throwable { - int argc = arguments == null ? 0 : arguments.length; - @SuppressWarnings("LocalVariableHidesMemberVariable") - MethodType type = type(); - if (type.parameterCount() != argc || isVarargsCollector()) { - // simulate invoke - return asType(MethodType.genericMethodType(argc)).invokeWithArguments(arguments); - } - MethodHandle invoker = type.invokers().varargsInvoker(); - return invoker.invokeExact(this, arguments); - } - - /** - * Performs a variable arity invocation, passing the arguments in the given array - * to the method handle, as if via an inexact {@link #invoke invoke} from a call site - * which mentions only the type {@code Object}, and whose arity is the length - * of the argument array. - *
- * This method is also equivalent to the following code: - *
{@code
- * invokeWithArguments(arguments.toArray()
- * }- * If the original type and new type are equal, returns {@code this}. - *
- * The new method handle, when invoked, will perform the following - * steps: - *
- * 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. - *
- * 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 pairwise, - * 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. - *
- * Let T0 and T1 be corresponding new and old parameter types, - * or old and new return types. Specifically, for some valid index {@code i}, let - * T0{@code =newType.parameterType(i)} and T1{@code =this.type().parameterType(i)}. - * Or else, going the other way for return values, let - * T0{@code =this.type().returnType()} and T1{@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: - *
- * The method handle conversion cannot be made if any one of the required - * pairwise conversions cannot be made. - *
- * At runtime, the conversions applied to reference arguments - * or return values may require additional runtime checks which can fail. - * An unboxing operation may fail because the original reference is null, - * causing a {@link java.lang.NullPointerException NullPointerException}. - * An unboxing operation or a reference cast may also fail on a reference - * to an object of the wrong type, - * causing a {@link java.lang.ClassCastException ClassCastException}. - * Although an unboxing operation may accept several kinds of wrappers, - * if none are available, a {@code ClassCastException} will be thrown. - * - * @param newType the expected type of the new method handle - * @return a method handle which delegates to {@code this} after performing - * any necessary argument conversions, and arranges for any - * necessary return value conversions - * @throws NullPointerException if {@code newType} is a null reference - * @throws WrongMethodTypeException if the conversion cannot be made - * @see MethodHandles#explicitCastArguments - */ - public MethodHandle asType(MethodType newType) { - // Fast path alternative to a heavyweight {@code asType} call. - // Return 'this' if the conversion will be a no-op. - if (newType == type) { - return this; - } - // Return 'this.asTypeCache' if the conversion is already memoized. - MethodHandle atc = asTypeCache; - if (atc != null && newType == atc.type) { - return atc; - } - return asTypeUncached(newType); - } - - /** Override this to change asType behavior. */ - /*non-public*/ MethodHandle asTypeUncached(MethodType newType) { - if (!type.isConvertibleTo(newType)) - throw new WrongMethodTypeException("cannot convert "+this+" to "+newType); - return asTypeCache = convertArguments(newType); - } - - /** - * Makes an array-spreading method handle, which accepts a trailing array argument - * and spreads its elements as positional arguments. - * The new method handle adapts, as its target, - * 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}. - *
- * 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}. - *
- * 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. - *
- * 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.) - *
- * 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. - *
- * Here are some simple examples of array-spreading method handles: - *
{@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()));
- * }- * 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}. - *
- * 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. - *
- * (The array may also be a shared constant when {@code arrayLength} is zero.) - *
- * (Note: 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.) - *
- * In order to create a collecting adapter which is not restricted to a particular - * number of collected arguments, use {@link #asVarargsCollector asVarargsCollector} instead. - *
- * Here are some examples of array-collecting method handles: - *
{@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));
- * }- * 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. - *
- * 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}. - *
- * When called with {@link #invokeExact invokeExact}, the adapter invokes - * the target with no argument changes. - * (Note: 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.) - *
- * 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.) - *
- * 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. - *
- * 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. - *
- * 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. - *
- * In all cases, what the target eventually returns is returned unchanged by the adapter. - *
- * 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}.) - *
- * 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}. - *
- * 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}. - *
- * 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. - *
- * 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). - *
- * 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. - *
- * Here is an example, of a list-making variable arity method handle: - *
{@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)));
- * }- * Discussion: - * These rules are designed as a dynamically-typed variation - * of the Java rules for variable arity methods. - * In both cases, callers to a variable arity method or method handle - * can either pass zero or more positional arguments, or else pass - * pre-collected arrays of any length. Users should be aware of the - * special role of the final argument, and of the effect of a - * type match on that final argument, which determines whether - * or not a single trailing argument is interpreted as a whole - * array or a single element of an array to be collected. - * Note that the dynamic type of the trailing argument has no - * effect on this decision, only a comparison between the symbolic - * type descriptor of the call site and the type descriptor of the method handle.) - * - * @param arrayType often {@code Object[]}, the type of the array argument which will collect the arguments - * @return a new method handle which can collect any number of trailing arguments - * into an array, before calling the original method handle - * @throws NullPointerException if {@code arrayType} is a null reference - * @throws IllegalArgumentException if {@code arrayType} is not an array type - * or {@code arrayType} is not assignable to this method handle's trailing parameter type - * @see #asCollector - * @see #isVarargsCollector - * @see #asFixedArity - */ - public MethodHandle asVarargsCollector(Class arrayType) { - Class arrayElement = arrayType.getComponentType(); - boolean lastMatch = asCollectorChecks(arrayType, 0); - if (isVarargsCollector() && lastMatch) - return this; - return MethodHandleImpl.makeVarargsCollector(this, arrayType); - } - - /** - * Determines if this method handle - * supports {@linkplain #asVarargsCollector variable arity} calls. - * Such method handles arise from the following sources: - *
- * 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}. - *
- * 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}. - *
- * Here is an example, of a list-making variable arity method handle: - *
{@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());
- * }- * 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. - *
- * The reference {@code x} must be convertible to the first parameter - * type of the target. - *
- * (Note: Because method handles are immutable, the target method handle - * retains its original type and behavior.) - * @param x the value to bind to the first argument of the target - * @return a new method handle which prepends the given value to the incoming - * argument list, before calling the original method handle - * @throws IllegalArgumentException if the target does not have a - * leading parameter type that is a reference type - * @throws ClassCastException if {@code x} cannot be converted - * to the leading parameter type of the target - * @see MethodHandles#insertArguments - */ - public MethodHandle bindTo(Object x) { - Class ptype; - @SuppressWarnings("LocalVariableHidesMemberVariable") - MethodType type = type(); - if (type.parameterCount() == 0 || - (ptype = type.parameterType(0)).isPrimitive()) - throw newIllegalArgumentException("no leading reference parameter", x); - x = ptype.cast(x); // throw CCE if needed - return bindReceiver(x); - } - - /** - * Returns a string representation of the method handle, - * starting with the string {@code "MethodHandle"} and - * ending with the string representation of the method handle's type. - * In other words, this method returns a string equal to the value of: - *
{@code
- * "MethodHandle" + type().toString()
- * }
- * (Note: Future releases of this API may add further information
- * to the string representation.
- * Therefore, the present syntax should not be parsed by applications.)
- *
- * @return a string representation of the method handle
- */
- @Override
- public String toString() {
- if (DEBUG_METHOD_HANDLE_NAMES) return debugString();
- return standardString();
- }
- String standardString() {
- return "MethodHandle"+type;
- }
- String debugString() {
- return standardString()+"/LF="+internalForm()+internalProperties();
- }
-
- //// Implementation methods.
- //// Sub-classes can override these default implementations.
- //// All these methods assume arguments are already validated.
-
- // Other transforms to do: convert, explicitCast, permute, drop, filter, fold, GWT, catch
-
- /*non-public*/
- MethodHandle setVarargs(MemberName member) throws IllegalAccessException {
- if (!member.isVarargs()) return this;
- int argc = type().parameterCount();
- if (argc != 0) {
- Class arrayType = type().parameterType(argc-1);
- if (arrayType.isArray()) {
- return MethodHandleImpl.makeVarargsCollector(this, arrayType);
- }
- }
- throw member.makeAccessException("cannot make variable arity", null);
- }
- /*non-public*/
- MethodHandle viewAsType(MethodType newType) {
- // No actual conversions, just a new view of the same method.
- return MethodHandleImpl.makePairwiseConvert(this, newType, 0);
- }
-
- // Decoding
-
- /*non-public*/
- LambdaForm internalForm() {
- return form;
- }
-
- /*non-public*/
- MemberName internalMemberName() {
- return null; // DMH returns DMH.member
- }
-
- /*non-public*/
- Class internalCallerClass() {
- return null; // caller-bound MH for @CallerSensitive method returns caller
- }
-
- /*non-public*/
- MethodHandle withInternalMemberName(MemberName member) {
- if (member != null) {
- return MethodHandleImpl.makeWrappedMember(this, member);
- } else if (internalMemberName() == null) {
- // The required internaMemberName is null, and this MH (like most) doesn't have one.
- return this;
- } else {
- // The following case is rare. Mask the internalMemberName by wrapping the MH in a BMH.
- MethodHandle result = rebind();
- assert (result.internalMemberName() == null);
- return result;
- }
- }
-
- /*non-public*/
- boolean isInvokeSpecial() {
- return false; // DMH.Special returns true
- }
-
- /*non-public*/
- Object internalValues() {
- return null;
- }
-
- /*non-public*/
- Object internalProperties() {
- // Override to something like "/FOO=bar"
- return "";
- }
-
- //// Method handle implementation methods.
- //// Sub-classes can override these default implementations.
- //// All these methods assume arguments are already validated.
-
- /*non-public*/ MethodHandle convertArguments(MethodType newType) {
- // Override this if it can be improved.
- return MethodHandleImpl.makePairwiseConvert(this, newType, 1);
- }
-
- /*non-public*/
- MethodHandle bindArgument(int pos, char basicType, Object value) {
- // Override this if it can be improved.
- return rebind().bindArgument(pos, basicType, value);
- }
-
- /*non-public*/
- MethodHandle bindReceiver(Object receiver) {
- // Override this if it can be improved.
- return bindArgument(0, 'L', receiver);
- }
-
- /*non-public*/
- MethodHandle bindImmediate(int pos, char basicType, Object value) {
- // Bind an immediate value to a position in the arguments.
- // This means, elide the respective argument,
- // and replace all references to it in NamedFunction args with the specified value.
-
- // CURRENT RESTRICTIONS
- // * only for pos 0 and UNSAFE (position is adjusted in MHImpl to make API usable for others)
-// assert pos == 0 && basicType == 'L' && value instanceof Unsafe;
- MethodType type2 = type.dropParameterTypes(pos, pos + 1); // adjustment: ignore receiver!
- LambdaForm form2 = form.bindImmediate(pos + 1, basicType, value); // adjust pos to form-relative pos
- return copyWith(type2, form2);
- }
-
- /*non-public*/
- MethodHandle copyWith(MethodType mt, LambdaForm lf) {
- throw new InternalError("copyWith: " + this.getClass());
- }
-
- /*non-public*/
- MethodHandle dropArguments(MethodType srcType, int pos, int drops) {
- // Override this if it can be improved.
- return rebind().dropArguments(srcType, pos, drops);
- }
-
- /*non-public*/
- MethodHandle permuteArguments(MethodType newType, int[] reorder) {
- // Override this if it can be improved.
- return rebind().permuteArguments(newType, reorder);
- }
-
- /*non-public*/
- MethodHandle rebind() {
- // Bind 'this' into a new invoker, of the known class BMH.
- MethodType type2 = type();
- LambdaForm form2 = reinvokerForm(this);
- // form2 = lambda (bmh, arg*) { thismh = bmh[0]; invokeBasic(thismh, arg*) }
- return BoundMethodHandle.bindSingle(type2, form2, this);
- }
-
- /*non-public*/
- MethodHandle reinvokerTarget() {
- throw new InternalError("not a reinvoker MH: "+this.getClass().getName()+": "+this);
- }
-
- /** Create a LF which simply reinvokes a target of the given basic type.
- * The target MH must override {@link #reinvokerTarget} to provide the target.
- */
- static LambdaForm reinvokerForm(MethodHandle target) {
- MethodType mtype = target.type().basicType();
- LambdaForm reinvoker = mtype.form().cachedLambdaForm(MethodTypeForm.LF_REINVOKE);
- if (reinvoker != null) return reinvoker;
- if (mtype.parameterSlotCount() >= MethodType.MAX_MH_ARITY)
- return makeReinvokerForm(target.type(), target); // cannot cache this
- reinvoker = makeReinvokerForm(mtype, null);
- return mtype.form().setCachedLambdaForm(MethodTypeForm.LF_REINVOKE, reinvoker);
- }
- private static LambdaForm makeReinvokerForm(MethodType mtype, MethodHandle customTargetOrNull) {
- boolean customized = (customTargetOrNull != null);
- MethodHandle MH_invokeBasic = customized ? null : MethodHandles.basicInvoker(mtype);
- final int THIS_BMH = 0;
- final int ARG_BASE = 1;
- final int ARG_LIMIT = ARG_BASE + mtype.parameterCount();
- int nameCursor = ARG_LIMIT;
- final int NEXT_MH = customized ? -1 : nameCursor++;
- final int REINVOKE = nameCursor++;
- LambdaForm.Name[] names = LambdaForm.arguments(nameCursor - ARG_LIMIT, mtype.invokerType());
- Object[] targetArgs;
- MethodHandle targetMH;
- if (customized) {
- targetArgs = Arrays.copyOfRange(names, ARG_BASE, ARG_LIMIT, Object[].class);
- targetMH = customTargetOrNull;
- } else {
- names[NEXT_MH] = new LambdaForm.Name(NF_reinvokerTarget, names[THIS_BMH]);
- targetArgs = Arrays.copyOfRange(names, THIS_BMH, ARG_LIMIT, Object[].class);
- targetArgs[0] = names[NEXT_MH]; // overwrite this MH with next MH
- targetMH = MethodHandles.basicInvoker(mtype);
- }
- names[REINVOKE] = new LambdaForm.Name(targetMH, targetArgs);
- return new LambdaForm("BMH.reinvoke", ARG_LIMIT, names);
- }
-
- private static final LambdaForm.NamedFunction NF_reinvokerTarget;
- static {
- try {
- NF_reinvokerTarget = new LambdaForm.NamedFunction(MethodHandle.class
- .getDeclaredMethod("reinvokerTarget"));
- } catch (ReflectiveOperationException ex) {
- throw newInternalError(ex);
- }
- }
-
- /**
- * Replace the old lambda form of this method handle with a new one.
- * The new one must be functionally equivalent to the old one.
- * Threads may continue running the old form indefinitely,
- * but it is likely that the new one will be preferred for new executions.
- * Use with discretion.
- */
- /*non-public*/
- void updateForm(LambdaForm newForm) {
- if (form == newForm) return;
- this.form = newForm;
- this.form.prepare(); // as in MethodHandle.