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 package java.lang.invoke;

 import java.util.*;

 import sun.invoke.util.*;

 import sun.misc.Unsafe;

 import static java.lang.invoke.MethodHandleStatics.*;

 import java.util.logging.Level;

 import java.util.logging.Logger;

 /**

  * 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&rsquo;s {@code invoke} method (or other signature-polymorphic method) is non-virtual,

  *     it consumes an extra argument for the method handle itself, in addition to any non-virtual receiver object.

  * </ul>

  * These limits imply that certain method handles cannot be created, solely because of the JVM limit on stacked arguments.

  * For example, if a static JVM method accepts exactly 255 arguments, a method handle cannot be created for it.

  * Attempts to create method handles with impossible method types lead to an {@link IllegalArgumentException}.

  * In particular, a method handle’s type must not have an arity of the exact maximum 255.

  *

  * @see MethodType

  * @see MethodHandles

  * @author John Rose, JSR 292 EG

  */

 public abstract class MethodHandle {

     static { MethodHandleImpl.initStatics(); }

     /**

      * Internal marker interface which distinguishes (to the Java compiler)

      * those methods which are <a href="MethodHandle.html#sigpoly">signature polymorphic</a>.

      */

     @java.lang.annotation.Target({java.lang.annotation.ElementType.METHOD})

     @java.lang.annotation.Retention(java.lang.annotation.RetentionPolicy.RUNTIME)

     @interface PolymorphicSignature { }

     private final MethodType type;

     /*private*/ final LambdaForm form;

     // form is not private so that invokers can easily fetch it

     /*private*/ MethodHandle asTypeCache;

     // asTypeCache is not private so that invokers can easily fetch it

     /**

      * Reports the type of this method handle.

      * Every invocation of this method handle via {@code invokeExact} must exactly match this type.

      * @return the method handle type

      */

     public MethodType type() {

         return type;

     }

     /**

      * Package-private constructor for the method handle implementation hierarchy.

      * Method handle inheritance will be contained completely within

      * the {@code java.lang.invoke} package.

      */

     // @param type type (permanently assigned) of the new method handle

     /*non-public*/ MethodHandle(MethodType type, LambdaForm form) {

         type.getClass();  // explicit NPE

         form.getClass();  // explicit NPE

         this.type = type;

         this.form = form;

         form.prepare();  // TO DO:  Try to delay this step until just before invocation.

     }

     /**

      * Invokes the method handle, allowing any caller type descriptor, but requiring an exact type match.

      * The symbolic type descriptor at the call site of {@code invokeExact} must

      * exactly match this method handle's {@link #type type}.

      * No conversions are allowed on arguments or return values.

      * <p>

      * When this method is observed via the Core Reflection API,

      * it will appear as a single native method, taking an object array and returning an object.

      * If this native method is invoked directly via

      * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}, via JNI,

      * or indirectly via {@link java.lang.invoke.MethodHandles.Lookup#unreflect Lookup.unreflect},

      * it will throw an {@code UnsupportedOperationException}.

      * @param args the signature-polymorphic parameter list, statically represented using varargs

      * @return the signature-polymorphic result, statically represented using {@code Object}

      * @throws WrongMethodTypeException if the target's type is not identical with the caller's symbolic type descriptor

      * @throws Throwable anything thrown by the underlying method propagates unchanged through the method handle call

      */

     public final native @PolymorphicSignature Object invokeExact(Object... args) throws Throwable;

     /**

      * Invokes the method handle, allowing any caller type descriptor,

      * and optionally performing conversions on arguments and return values.

      * <p>

      * If the call site's symbolic type descriptor exactly matches this method handle's {@link #type type},

      * the call proceeds as if by {@link #invokeExact invokeExact}.

      * <p>

      * Otherwise, the call proceeds as if this method handle were first

      * adjusted by calling {@link #asType asType} to adjust this method handle

      * to the required type, and then the call proceeds as if by

      * {@link #invokeExact invokeExact} on the adjusted method handle.

      * <p>

      * There is no guarantee that the {@code asType} call is actually made.

      * If the JVM can predict the results of making the call, it may perform

      * adaptations directly on the caller's arguments,

      * and call the target method handle according to its own exact type.

      * <p>

      * The resolved type descriptor at the call site of {@code invoke} must

      * be a valid argument to the receivers {@code asType} method.

      * In particular, the caller must specify the same argument arity

      * as the callee's type,

      * if the callee is not a {@linkplain #asVarargsCollector variable arity collector}.

      * <p>

      * When this method is observed via the Core Reflection API,

      * it will appear as a single native method, taking an object array and returning an object.

      * If this native method is invoked directly via

      * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}, via JNI,

      * or indirectly via {@link java.lang.invoke.MethodHandles.Lookup#unreflect Lookup.unreflect},

      * it will throw an {@code UnsupportedOperationException}.

      * @param args the signature-polymorphic parameter list, statically represented using varargs

      * @return the signature-polymorphic result, statically represented using {@code Object}

      * @throws WrongMethodTypeException if the target's type cannot be adjusted to the caller's symbolic type descriptor

      * @throws ClassCastException if the target's type can be adjusted to the caller, but a reference cast fails

      * @throws Throwable anything thrown by the underlying method propagates unchanged through the method handle call

      */

     public final native @PolymorphicSignature Object invoke(Object... args) throws Throwable;

     /**

      * Private method for trusted invocation of a method handle respecting simplified signatures.

      * Type mismatches will not throw {@code WrongMethodTypeException}, but could crash the JVM.

      * <p>

      * The caller signature is restricted to the following basic types:

      * Object, int, long, float, double, and void return.

      * <p>

      * The caller is responsible for maintaining type correctness by ensuring

      * that the each outgoing argument value is a member of the range of the corresponding

      * callee argument type.

      * (The caller should therefore issue appropriate casts and integer narrowing

      * operations on outgoing argument values.)

      * The caller can assume that the incoming result value is part of the range

      * of the callee's return type.

      * @param args the signature-polymorphic parameter list, statically represented using varargs

      * @return the signature-polymorphic result, statically represented using {@code Object}

      */

     /*non-public*/ final native @PolymorphicSignature Object invokeBasic(Object... args) throws Throwable;

     /**

      * Private method for trusted invocation of a MemberName of kind {@code REF_invokeVirtual}.

      * The caller signature is restricted to basic types as with {@code invokeBasic}.

      * The trailing (not leading) argument must be a MemberName.

      * @param args the signature-polymorphic parameter list, statically represented using varargs

      * @return the signature-polymorphic result, statically represented using {@code Object}

      */

     /*non-public*/ static native @PolymorphicSignature Object linkToVirtual(Object... args) throws Throwable;

     /**

      * Private method for trusted invocation of a MemberName of kind {@code REF_invokeStatic}.

      * The caller signature is restricted to basic types as with {@code invokeBasic}.

      * The trailing (not leading) argument must be a MemberName.

      * @param args the signature-polymorphic parameter list, statically represented using varargs

      * @return the signature-polymorphic result, statically represented using {@code Object}

      */

     /*non-public*/ static native @PolymorphicSignature Object linkToStatic(Object... args) throws Throwable;

     /**

      * Private method for trusted invocation of a MemberName of kind {@code REF_invokeSpecial}.

      * The caller signature is restricted to basic types as with {@code invokeBasic}.

      * The trailing (not leading) argument must be a MemberName.

      * @param args the signature-polymorphic parameter list, statically represented using varargs

      * @return the signature-polymorphic result, statically represented using {@code Object}

      */

     /*non-public*/ static native @PolymorphicSignature Object linkToSpecial(Object... args) throws Throwable;

     /**

      * Private method for trusted invocation of a MemberName of kind {@code REF_invokeInterface}.

      * The caller signature is restricted to basic types as with {@code invokeBasic}.

      * The trailing (not leading) argument must be a MemberName.

      * @param args the signature-polymorphic parameter list, statically represented using varargs

      * @return the signature-polymorphic result, statically represented using {@code Object}

      */

     /*non-public*/ static native @PolymorphicSignature Object linkToInterface(Object... args) throws Throwable;

     /**

      * Performs a variable arity invocation, passing the arguments in the given list

      * to the method handle, as if via an inexact {@link #invoke invoke} from a call site

      * which mentions only the type {@code Object}, and whose arity is the length

      * of the argument list.

      * <p>

      * Specifically, execution proceeds as if by the following steps,

      * although the methods are not guaranteed to be called if the JVM

      * can predict their effects.

      * <ul>

      * <li>Determine the length of the argument array as {@code N}.

      *     For a null reference, {@code N=0}. </li>

      * <li>Determine the general type {@code TN} of {@code N} arguments as

      *     as {@code TN=MethodType.genericMethodType(N)}.</li>

      * <li>Force the original target method handle {@code MH0} to the

      *     required type, as {@code MH1 = MH0.asType(TN)}. </li>

      * <li>Spread the array into {@code N} separate arguments {@code A0, ...}. </li>

      * <li>Invoke the type-adjusted method handle on the unpacked arguments:

      *     MH1.invokeExact(A0, ...). </li>

      * <li>Take the return value as an {@code Object} reference. </li>

      * </ul>

      * <p>

      * Because of the action of the {@code asType} step, the following argument

      * conversions are applied as necessary:

      * <ul>

      * <li>reference casting

      * <li>unboxing

      * <li>widening primitive conversions

      * </ul>

      * <p>

      * The result returned by the call is boxed if it is a primitive,

      * or forced to null if the return type is void.

      * <p>

      * This call is equivalent to the following code:

      * <blockquote><pre>{@code

      * MethodHandle invoker = MethodHandles.spreadInvoker(this.type(), 0);

      * Object result = invoker.invokeExact(this, arguments);

      * }</pre></blockquote>

      * <p>

      * Unlike the signature polymorphic methods {@code invokeExact} and {@code invoke},

      * {@code invokeWithArguments} can be accessed normally via the Core Reflection API and JNI.

      * It can therefore be used as a bridge between native or reflective code and method handles.

      *

      * @param arguments the arguments to pass to the target

      * @return the result returned by the target

      * @throws ClassCastException if an argument cannot be converted by reference casting

      * @throws WrongMethodTypeException if the target's type cannot be adjusted to take the given number of {@code Object} arguments

      * @throws Throwable anything thrown by the target method invocation

      * @see MethodHandles#spreadInvoker

      */

     public Object invokeWithArguments(Object... arguments) throws Throwable {

         int argc = arguments == null ? 0 : arguments.length;

         @SuppressWarnings("LocalVariableHidesMemberVariable")

         MethodType type = type();

         if (type.parameterCount() != argc || isVarargsCollector()) {

             // simulate invoke

             return asType(MethodType.genericMethodType(argc)).invokeWithArguments(arguments);

         }

         MethodHandle invoker = type.invokers().varargsInvoker();

         return invoker.invokeExact(this, arguments);

     }

     /**

      * Performs a variable arity invocation, passing the arguments in the given array

      * to the method handle, as if via an inexact {@link #invoke invoke} from a call site

      * which mentions only the type {@code Object}, and whose arity is the length

      * of the argument array.

      * <p>

      * This method is also equivalent to the following code:

      * <blockquote><pre>{@code

      *   invokeWithArguments(arguments.toArray()

      * }</pre></blockquote>

      *

      * @param arguments the arguments to pass to the target

      * @return the result returned by the target

      * @throws NullPointerException if {@code arguments} is a null reference

      * @throws ClassCastException if an argument cannot be converted by reference casting

      * @throws WrongMethodTypeException if the target's type cannot be adjusted to take the given number of {@code Object} arguments

      * @throws Throwable anything thrown by the target method invocation

      */

     public Object invokeWithArguments(java.util.List<?> arguments) throws Throwable {

         return invokeWithArguments(arguments.toArray());

     }

     /**

      * Produces an adapter method handle which adapts the type of the

      * current method handle to a new type.

      * The resulting method handle is guaranteed to report a type

      * which is equal to the desired new type.

      * <p>

      * If the original type and new type are equal, returns {@code this}.

      * <p>

      * The new method handle, when invoked, will perform the following

      * steps:

      * <ul>

      * <li>Convert the incoming argument list to match the original

      *     method handle's argument list.

      * <li>Invoke the original method handle on the converted argument list.

      * <li>Convert any result returned by the original method handle

      *     to the return type of new method handle.

      * </ul>

      * <p>

      * This method provides the crucial behavioral difference between

      * {@link #invokeExact invokeExact} and plain, inexact {@link #invoke invoke}.

      * The two methods

      * perform the same steps when the caller's type descriptor exactly 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;

         }

         // Return 'this.asTypeCache' if the conversion is already memoized.

         MethodHandle atc = asTypeCache;

         if (atc != null && newType == atc.type) {

             return atc;

         }

         return asTypeUncached(newType);

     }

     /** Override this to change asType behavior. */

     /*non-public*/ MethodHandle asTypeUncached(MethodType newType) {

         if (!type.isConvertibleTo(newType))

             throw new WrongMethodTypeException("cannot convert "+this+" to "+newType);

         return asTypeCache = convertArguments(newType);

     }

     /**

      * Makes an <em>array-spreading</em> method handle, which accepts a trailing array argument

      * and spreads its elements as positional arguments.

      * The new method handle adapts, as its <i>target</i>,

      * the current method handle.  The type of the adapter will be

      * the same as the type of the target, except that the final

      * {@code arrayLength} parameters of the target's type are replaced

      * by a single array parameter of type {@code arrayType}.

      * <p>

      * If the array element type differs from any of the corresponding

      * argument types on the original target,

      * the original target is adapted to take the array elements directly,

      * as if by a call to {@link #asType asType}.

      * <p>

      * When called, the adapter replaces a trailing array argument

      * by the array's elements, each as its own argument to the target.

      * (The order of the arguments is preserved.)

      * They are converted pairwise by casting and/or unboxing

      * to the types of the trailing parameters of the target.

      * Finally the target is called.

      * What the target eventually returns is returned unchanged by the adapter.

      * <p>

      * Before calling the target, the adapter verifies that the array

      * contains exactly enough elements to provide a correct argument count

      * to the target method handle.

      * (The array may also be null when zero elements are required.)

      * <p>

      * If, when the adapter is called, the supplied array argument does

      * not have the correct number of elements, the adapter will throw

      * an {@link IllegalArgumentException} instead of invoking the target.

      * <p>

      * Here are some simple examples of array-spreading method handles:

      * <blockquote><pre>{@code

 MethodHandle equals = publicLookup()

   .findVirtual(String.class, "equals", methodType(boolean.class, Object.class));

 assert( (boolean) equals.invokeExact("me", (Object)"me"));

 assert(!(boolean) equals.invokeExact("me", (Object)"thee"));

 // spread both arguments from a 2-array:

 MethodHandle eq2 = equals.asSpreader(Object[].class, 2);

 assert( (boolean) eq2.invokeExact(new Object[]{ "me", "me" }));

 assert(!(boolean) eq2.invokeExact(new Object[]{ "me", "thee" }));

 // try to spread from anything but a 2-array:

 for (int n = 0; n <= 10; n++) {

   Object[] badArityArgs = (n == 2 ? null : new Object[n]);

   try { assert((boolean) eq2.invokeExact(badArityArgs) && false); }

   catch (IllegalArgumentException ex) { } // OK

 }

 // spread both arguments from a String array:

 MethodHandle eq2s = equals.asSpreader(String[].class, 2);

 assert( (boolean) eq2s.invokeExact(new String[]{ "me", "me" }));

 assert(!(boolean) eq2s.invokeExact(new String[]{ "me", "thee" }));

 // spread second arguments from a 1-array:

 MethodHandle eq1 = equals.asSpreader(Object[].class, 1);

 assert( (boolean) eq1.invokeExact("me", new Object[]{ "me" }));

 assert(!(boolean) eq1.invokeExact("me", new Object[]{ "thee" }));

 // spread no arguments from a 0-array or null:

 MethodHandle eq0 = equals.asSpreader(Object[].class, 0);

 assert( (boolean) eq0.invokeExact("me", (Object)"me", new Object[0]));

 assert(!(boolean) eq0.invokeExact("me", (Object)"thee", (Object[])null));

 // asSpreader and asCollector are approximate inverses:

 for (int n = 0; n <= 2; n++) {

     for (Class<?> a : new Class<?>[]{Object[].class, String[].class, CharSequence[].class}) {

         MethodHandle equals2 = equals.asSpreader(a, n).asCollector(a, n);

         assert( (boolean) equals2.invokeWithArguments("me", "me"));

         assert(!(boolean) equals2.invokeWithArguments("me", "thee"));

     }

 }

 MethodHandle caToString = publicLookup()

   .findStatic(Arrays.class, "toString", methodType(String.class, char[].class));

 assertEquals("[A, B, C]", (String) caToString.invokeExact("ABC".toCharArray()));

 MethodHandle caString3 = caToString.asCollector(char[].class, 3);

 assertEquals("[A, B, C]", (String) caString3.invokeExact('A', 'B', 'C'));

 MethodHandle caToString2 = caString3.asSpreader(char[].class, 2);

 assertEquals("[A, B, C]", (String) caToString2.invokeExact('A', "BC".toCharArray()));

      * }</pre></blockquote>

      * @param arrayType usually {@code Object[]}, the type of the array argument from which to extract the spread arguments

      * @param arrayLength the number of arguments to spread from an incoming array argument

      * @return a new method handle which spreads its final array argument,

      *         before calling the original method handle

      * @throws NullPointerException if {@code arrayType} is a null reference

      * @throws IllegalArgumentException if {@code arrayType} is not an array type,

      *         or if target does not have at least

      *         {@code arrayLength} parameter types,

      *         or if {@code arrayLength} is negative,

      *         or if the resulting method handle's type would have

      *         <a href="MethodHandle.html#maxarity">too many parameters</a>

      * @throws WrongMethodTypeException if the implied {@code asType} call fails

      * @see #asCollector

      */

     public MethodHandle asSpreader(Class<?> arrayType, int arrayLength) {

         asSpreaderChecks(arrayType, arrayLength);

         int spreadArgPos = type.parameterCount() - arrayLength;

         return MethodHandleImpl.makeSpreadArguments(this, arrayType, spreadArgPos, arrayLength);

     }

     private void asSpreaderChecks(Class<?> arrayType, int arrayLength) {

         spreadArrayChecks(arrayType, arrayLength);

         int nargs = type().parameterCount();

         if (nargs < arrayLength || arrayLength < 0)

             throw newIllegalArgumentException("bad spread array length");

         if (arrayType != Object[].class && arrayLength != 0) {

             boolean sawProblem = false;

             Class<?> arrayElement = arrayType.getComponentType();

             for (int i = nargs - arrayLength; i < nargs; i++) {

                 if (!MethodType.canConvert(arrayElement, type().parameterType(i))) {

                     sawProblem = true;

                     break;

                 }

             }

             if (sawProblem) {

                 ArrayList<Class<?>> ptypes = new ArrayList<>(type().parameterList());

                 for (int i = nargs - arrayLength; i < nargs; i++) {

                     ptypes.set(i, arrayElement);

                 }

                 // elicit an error:

                 this.asType(MethodType.methodType(type().returnType(), ptypes));

             }

         }

     }

     private void spreadArrayChecks(Class<?> arrayType, int arrayLength) {

         Class<?> arrayElement = arrayType.getComponentType();

         if (arrayElement == null)

             throw newIllegalArgumentException("not an array type", arrayType);

         if ((arrayLength & 0x7F) != arrayLength) {

             if ((arrayLength & 0xFF) != arrayLength)

                 throw newIllegalArgumentException("array length is not legal", arrayLength);

             assert(arrayLength >= 128);

             if (arrayElement == long.class ||

                 arrayElement == double.class)

                 throw newIllegalArgumentException("array length is not legal for long[] or double[]", arrayLength);

         }

     }

     /**

      * Makes an <em>array-collecting</em> method handle, which accepts a given number of trailing

      * positional arguments and collects them into an array argument.

      * The new method handle adapts, as its <i>target</i>,

      * the current method handle.  The type of the adapter will be

      * the same as the type of the target, except that a single trailing

      * parameter (usually of type {@code arrayType}) is replaced by

      * {@code arrayLength} parameters whose type is element type of {@code arrayType}.

      * <p>

      * If the array type differs from the final argument type on the original target,

      * the original target is adapted to take the array type directly,

      * as if by a call to {@link #asType asType}.

      * <p>

      * When called, the adapter replaces its trailing {@code arrayLength}

      * arguments by a single new array of type {@code arrayType}, whose elements

      * comprise (in order) the replaced arguments.

      * Finally the target is called.

      * What the target eventually returns is returned unchanged by the adapter.

      * <p>

      * (The array may also be a shared constant when {@code arrayLength} is zero.)

      * <p>

      * (<em>Note:</em> The {@code arrayType} is often identical to the last

      * parameter type of the original target.

      * It is an explicit argument for symmetry with {@code asSpreader}, and also

      * to allow the target to use a simple {@code Object} as its last parameter type.)

      * <p>

      * In order to create a collecting adapter which is not restricted to a particular

      * number of collected arguments, use {@link #asVarargsCollector asVarargsCollector} instead.

      * <p>

      * Here are some examples of array-collecting method handles:

      * <blockquote><pre>{@code

 MethodHandle deepToString = publicLookup()

   .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));

 assertEquals("[won]",   (String) deepToString.invokeExact(new Object[]{"won"}));

 MethodHandle ts1 = deepToString.asCollector(Object[].class, 1);

 assertEquals(methodType(String.class, Object.class), ts1.type());

 //assertEquals("[won]", (String) ts1.invokeExact(         new Object[]{"won"})); //FAIL

 assertEquals("[[won]]", (String) ts1.invokeExact((Object) new Object[]{"won"}));

 // arrayType can be a subtype of Object[]

 MethodHandle ts2 = deepToString.asCollector(String[].class, 2);

 assertEquals(methodType(String.class, String.class, String.class), ts2.type());

 assertEquals("[two, too]", (String) ts2.invokeExact("two", "too"));

 MethodHandle ts0 = deepToString.asCollector(Object[].class, 0);

 assertEquals("[]", (String) ts0.invokeExact());

 // collectors can be nested, Lisp-style

 MethodHandle ts22 = deepToString.asCollector(Object[].class, 3).asCollector(String[].class, 2);

 assertEquals("[A, B, [C, D]]", ((String) ts22.invokeExact((Object)'A', (Object)"B", "C", "D")));

 // arrayType can be any primitive array type

 MethodHandle bytesToString = publicLookup()

   .findStatic(Arrays.class, "toString", methodType(String.class, byte[].class))

   .asCollector(byte[].class, 3);

 assertEquals("[1, 2, 3]", (String) bytesToString.invokeExact((byte)1, (byte)2, (byte)3));

 MethodHandle longsToString = publicLookup()

   .findStatic(Arrays.class, "toString", methodType(String.class, long[].class))

   .asCollector(long[].class, 1);

 assertEquals("[123]", (String) longsToString.invokeExact((long)123));

      * }</pre></blockquote>

      * @param arrayType often {@code Object[]}, the type of the array argument which will collect the arguments

      * @param arrayLength the number of arguments to collect into a new array argument

      * @return a new method handle which collects some trailing argument

      *         into an array, before calling the original method handle

      * @throws NullPointerException if {@code arrayType} is a null reference

      * @throws IllegalArgumentException if {@code arrayType} is not an array type

      *         or {@code arrayType} is not assignable to this method handle's trailing parameter type,

      *         or {@code arrayLength} is not a legal array size,

      *         or the resulting method handle's type would have

      *         <a href="MethodHandle.html#maxarity">too many parameters</a>

      * @throws WrongMethodTypeException if the implied {@code asType} call fails

      * @see #asSpreader

      * @see #asVarargsCollector

      */

     public MethodHandle asCollector(Class<?> arrayType, int arrayLength) {

         asCollectorChecks(arrayType, arrayLength);

         int collectArgPos = type().parameterCount()-1;

         MethodHandle target = this;

         if (arrayType != type().parameterType(collectArgPos))

             target = convertArguments(type().changeParameterType(collectArgPos, arrayType));

         MethodHandle collector = ValueConversions.varargsArray(arrayType, arrayLength);

         return MethodHandles.collectArguments(target, collectArgPos, collector);

     }

     // private API: return true if last param exactly matches arrayType

     private boolean asCollectorChecks(Class<?> arrayType, int arrayLength) {

         spreadArrayChecks(arrayType, arrayLength);

         int nargs = type().parameterCount();

         if (nargs != 0) {

             Class<?> lastParam = type().parameterType(nargs-1);

             if (lastParam == arrayType)  return true;

             if (lastParam.isAssignableFrom(arrayType))  return false;

         }

         throw newIllegalArgumentException("array type not assignable to trailing argument", this, arrayType);

     }

     /**

      * Makes a <em>variable arity</em> adapter which is able to accept

      * any number of trailing positional arguments and collect them

      * into an array argument.

      * <p>

      * The type and behavior of the adapter will be the same as

      * the type and behavior of the target, except that certain

      * {@code invoke} and {@code asType} requests can lead to

      * trailing positional arguments being collected into target's

      * trailing parameter.

      * Also, the last parameter type of the adapter will be

      * {@code arrayType}, even if the target has a different

      * last parameter type.

      * <p>

      * This transformation may return {@code this} if the method handle is

      * already of variable arity and its trailing parameter type

      * is identical to {@code arrayType}.

      * <p>

      * When called with {@link #invokeExact invokeExact}, the adapter invokes

      * the target with no argument changes.

      * (<em>Note:</em> This behavior is different from a

      * {@linkplain #asCollector fixed arity collector},

      * since it accepts a whole array of indeterminate length,

      * rather than a fixed number of arguments.)

      * <p>

      * When called with plain, inexact {@link #invoke invoke}, if the caller

      * type is the same as the adapter, the adapter invokes the target as with

      * {@code invokeExact}.

      * (This is the normal behavior for {@code invoke} when types match.)

      * <p>

      * Otherwise, if the caller and adapter arity are the same, and the

      * trailing parameter type of the caller is a reference type identical to

      * or assignable to the trailing parameter type of the adapter,

      * the arguments and return values are converted pairwise,

      * as if by {@link #asType asType} on a fixed arity

      * method handle.

      * <p>

      * Otherwise, the arities differ, or the adapter's trailing parameter

      * type is not assignable from the corresponding caller type.

      * In this case, the adapter replaces all trailing arguments from

      * the original trailing argument position onward, by

      * a new array of type {@code arrayType}, whose elements

      * comprise (in order) the replaced arguments.

      * <p>

      * The caller type must provides as least enough arguments,

      * and of the correct type, to satisfy the target's requirement for

      * positional arguments before the trailing array argument.

      * Thus, the caller must supply, at a minimum, {@code N-1} arguments,

      * where {@code N} is the arity of the target.

      * Also, there must exist conversions from the incoming arguments

      * to the target's arguments.

      * As with other uses of plain {@code invoke}, if these basic

      * requirements are not fulfilled, a {@code WrongMethodTypeException}

      * may be thrown.

      * <p>

      * In all cases, what the target eventually returns is returned unchanged by the adapter.

      * <p>

      * In the final case, it is exactly as if the target method handle were

      * temporarily adapted with a {@linkplain #asCollector fixed arity collector}

      * to the arity required by the caller type.

      * (As with {@code asCollector}, if the array length is zero,

      * a shared constant may be used instead of a new array.

      * If the implied call to {@code asCollector} would throw

      * an {@code IllegalArgumentException} or {@code WrongMethodTypeException},

      * the call to the variable arity adapter must throw

      * {@code WrongMethodTypeException}.)

      * <p>

      * The behavior of {@link #asType asType} is also specialized for

      * variable arity adapters, to maintain the invariant that

      * plain, inexact {@code invoke} is always equivalent to an {@code asType}

      * call to adjust the target type, followed by {@code invokeExact}.

      * Therefore, a variable arity adapter responds

      * to an {@code asType} request by building a fixed arity collector,

      * if and only if the adapter and requested type differ either

      * in arity or trailing argument type.

      * The resulting fixed arity collector has its type further adjusted

      * (if necessary) to the requested type by pairwise conversion,

      * as if by another application of {@code asType}.

      * <p>

      * When a method handle is obtained by executing an {@code ldc} instruction

      * of a {@code CONSTANT_MethodHandle} constant, and the target method is marked

      * as a variable arity method (with the modifier bit {@code 0x0080}),

      * the method handle will accept multiple arities, as if the method handle

      * constant were created by means of a call to {@code asVarargsCollector}.

      * <p>

      * In order to create a collecting adapter which collects a predetermined

      * number of arguments, and whose type reflects this predetermined number,

      * use {@link #asCollector asCollector} instead.

      * <p>

      * No method handle transformations produce new method handles with

      * variable arity, unless they are documented as doing so.

      * Therefore, besides {@code asVarargsCollector},

      * all methods in {@code MethodHandle} and {@code MethodHandles}

      * will return a method handle with fixed arity,

      * except in the cases where they are specified to return their original

      * operand (e.g., {@code asType} of the method handle's own type).

      * <p>

      * Calling {@code asVarargsCollector} on a method handle which is already

      * of variable arity will produce a method handle with the same type and behavior.

      * It may (or may not) return the original variable arity method handle.

      * <p>

      * Here is an example, of a list-making variable arity method handle:

      * <blockquote><pre>{@code

 MethodHandle deepToString = publicLookup()

   .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));

 MethodHandle ts1 = deepToString.asVarargsCollector(Object[].class);

 assertEquals("[won]",   (String) ts1.invokeExact(    new Object[]{"won"}));

 assertEquals("[won]",   (String) ts1.invoke(         new Object[]{"won"}));

 assertEquals("[won]",   (String) ts1.invoke(                      "won" ));

 assertEquals("[[won]]", (String) ts1.invoke((Object) new Object[]{"won"}));

 // findStatic of Arrays.asList(...) produces a variable arity method handle:

 MethodHandle asList = publicLookup()

   .findStatic(Arrays.class, "asList", methodType(List.class, Object[].class));

 assertEquals(methodType(List.class, Object[].class), asList.type());

 assert(asList.isVarargsCollector());

 assertEquals("[]", asList.invoke().toString());

 assertEquals("[1]", asList.invoke(1).toString());

 assertEquals("[two, too]", asList.invoke("two", "too").toString());

 String[] argv = { "three", "thee", "tee" };

 assertEquals("[three, thee, tee]", asList.invoke(argv).toString());

 assertEquals("[three, thee, tee]", asList.invoke((Object[])argv).toString());

 List ls = (List) asList.invoke((Object)argv);

 assertEquals(1, ls.size());

 assertEquals("[three, thee, tee]", Arrays.toString((Object[])ls.get(0)));

      * }</pre></blockquote>

      * <p style="font-size:smaller;">

      * <em>Discussion:</em>

      * These rules are designed as a dynamically-typed variation

      * of the Java rules for variable arity methods.

      * In both cases, callers to a variable arity method or method handle

      * can either pass zero or more positional arguments, or else pass

      * pre-collected arrays of any length.  Users should be aware of the

      * special role of the final argument, and of the effect of a

      * type match on that final argument, which determines whether

      * or not a single trailing argument is interpreted as a whole

      * array or a single element of an array to be collected.

      * Note that the dynamic type of the trailing argument has no

      * effect on this decision, only a comparison between the symbolic

      * type descriptor of the call site and the type descriptor of the method handle.)

      *

      * @param arrayType often {@code Object[]}, the type of the array argument which will collect the arguments

      * @return a new method handle which can collect any number of trailing arguments

      *         into an array, before calling the original method handle

      * @throws NullPointerException if {@code arrayType} is a null reference

      * @throws IllegalArgumentException if {@code arrayType} is not an array type

      *         or {@code arrayType} is not assignable to this method handle's trailing parameter type

      * @see #asCollector

      * @see #isVarargsCollector

      * @see #asFixedArity

      */

     public MethodHandle asVarargsCollector(Class<?> arrayType) {

         Class<?> arrayElement = arrayType.getComponentType();

         boolean lastMatch = asCollectorChecks(arrayType, 0);

         if (isVarargsCollector() && lastMatch)

             return this;

         return MethodHandleImpl.makeVarargsCollector(this, arrayType);

     }

     /**

      * Determines if this method handle

      * supports {@linkplain #asVarargsCollector variable arity} calls.

      * Such method handles arise from the following sources:

      * <ul>

      * <li>a call to {@linkplain #asVarargsCollector asVarargsCollector}

      * <li>a call to a {@linkplain java.lang.invoke.MethodHandles.Lookup lookup method}

      *     which resolves to a variable arity Java method or constructor

      * <li>an {@code ldc} instruction of a {@code CONSTANT_MethodHandle}

      *     which resolves to a variable arity Java method or constructor

      * </ul>

      * @return true if this method handle accepts more than one arity of plain, inexact {@code invoke} calls

      * @see #asVarargsCollector

      * @see #asFixedArity

      */

     public boolean isVarargsCollector() {

         return false;

     }

     /**

      * Makes a <em>fixed arity</em> method handle which is otherwise

      * equivalent to the current method handle.

      * <p>

      * If the current method handle is not of

      * {@linkplain #asVarargsCollector variable arity},

      * the current method handle is returned.

      * This is true even if the current method handle

      * could not be a valid input to {@code asVarargsCollector}.

      * <p>

      * Otherwise, the resulting fixed-arity method handle has the same

      * type and behavior of the current method handle,

      * except that {@link #isVarargsCollector isVarargsCollector}

      * will be false.

      * The fixed-arity method handle may (or may not) be the

      * a previous argument to {@code asVarargsCollector}.

      * <p>

      * Here is an example, of a list-making variable arity method handle:

      * <blockquote><pre>{@code

 MethodHandle asListVar = publicLookup()

   .findStatic(Arrays.class, "asList", methodType(List.class, Object[].class))

   .asVarargsCollector(Object[].class);

 MethodHandle asListFix = asListVar.asFixedArity();

 assertEquals("[1]", asListVar.invoke(1).toString());

 Exception caught = null;

 try { asListFix.invoke((Object)1); }

 catch (Exception ex) { caught = ex; }

 assert(caught instanceof ClassCastException);

 assertEquals("[two, too]", asListVar.invoke("two", "too").toString());

 try { asListFix.invoke("two", "too"); }

 catch (Exception ex) { caught = ex; }

 assert(caught instanceof WrongMethodTypeException);

 Object[] argv = { "three", "thee", "tee" };

 assertEquals("[three, thee, tee]", asListVar.invoke(argv).toString());

 assertEquals("[three, thee, tee]", asListFix.invoke(argv).toString());

 assertEquals(1, ((List) asListVar.invoke((Object)argv)).size());

 assertEquals("[three, thee, tee]", asListFix.invoke((Object)argv).toString());

      * }</pre></blockquote>

      *

      * @return a new method handle which accepts only a fixed number of arguments

      * @see #asVarargsCollector

      * @see #isVarargsCollector

      */

     public MethodHandle asFixedArity() {

         assert(!isVarargsCollector());

         return this;

     }

     /**

      * Binds a value {@code x} to the first argument of a method handle, without invoking it.

      * The new method handle adapts, as its <i>target</i>,

      * the current method handle by binding it to the given argument.

      * The type of the bound handle will be

      * the same as the type of the target, except that a single leading

      * reference parameter will be omitted.

      * <p>

      * When called, the bound handle inserts the given value {@code x}

      * as a new leading argument to the target.  The other arguments are

      * also passed unchanged.

      * What the target eventually returns is returned unchanged by the bound handle.

      * <p>

      * The reference {@code x} must be convertible to the first parameter

      * type of the target.

      * <p>

      * (<em>Note:</em>  Because method handles are immutable, the target method handle

      * retains its original type and behavior.)

      * @param x  the value to bind to the first argument of the target

      * @return a new method handle which prepends the given value to the incoming

      *         argument list, before calling the original method handle

      * @throws IllegalArgumentException if the target does not have a

      *         leading parameter type that is a reference type

      * @throws ClassCastException if {@code x} cannot be converted

      *         to the leading parameter type of the target

      * @see MethodHandles#insertArguments

      */

     public MethodHandle bindTo(Object x) {

         Class<?> ptype;

         @SuppressWarnings("LocalVariableHidesMemberVariable")

         MethodType type = type();

         if (type.parameterCount() == 0 ||

             (ptype = type.parameterType(0)).isPrimitive())

             throw newIllegalArgumentException("no leading reference parameter", x);

         x = ptype.cast(x);  // throw CCE if needed

         return bindReceiver(x);

     }

     /**

      * Returns a string representation of the method handle,

      * starting with the string {@code "MethodHandle"} and

      * ending with the string representation of the method handle's type.

      * In other words, this method returns a string equal to the value of:

      * <blockquote><pre>{@code

      * "MethodHandle" + type().toString()

      * }</pre></blockquote>

      * <p>

      * (<em>Note:</em>  Future releases of this API may add further information

      * to the string representation.

      * Therefore, the present syntax should not be parsed by applications.)

      *

      * @return a string representation of the method handle

      */

     @Override

     public String toString() {

         if (DEBUG_METHOD_HANDLE_NAMES)  return debugString();

         return standardString();

     }

     String standardString() {

         return "MethodHandle"+type;

     }

     String debugString() {

         return standardString()+"/LF="+internalForm()+internalProperties();

     }

     //// Implementation methods.

     //// Sub-classes can override these default implementations.

     //// All these methods assume arguments are already validated.

     // Other transforms to do:  convert, explicitCast, permute, drop, filter, fold, GWT, catch

     /*non-public*/

     MethodHandle setVarargs(MemberName member) throws IllegalAccessException {

         if (!member.isVarargs())  return this;

         int argc = type().parameterCount();

         if (argc != 0) {

             Class<?> arrayType = type().parameterType(argc-1);

             if (arrayType.isArray()) {

                 return MethodHandleImpl.makeVarargsCollector(this, arrayType);

             }

         }

         throw member.makeAccessException("cannot make variable arity", null);

     }

     /*non-public*/

     MethodHandle viewAsType(MethodType newType) {

         // No actual conversions, just a new view of the same method.

         return MethodHandleImpl.makePairwiseConvert(this, newType, 0);

     }

     // Decoding

     /*non-public*/

     LambdaForm internalForm() {

         return form;

     }

     /*non-public*/

     MemberName internalMemberName() {

         return null;  // DMH returns DMH.member

     }

     /*non-public*/

     Class<?> internalCallerClass() {

         return null;  // caller-bound MH for @CallerSensitive method returns caller

     }

     /*non-public*/

     MethodHandle withInternalMemberName(MemberName member) {

         if (member != null) {

             return MethodHandleImpl.makeWrappedMember(this, member);

         } else if (internalMemberName() == null) {

             // The required internaMemberName is null, and this MH (like most) doesn't have one.

             return this;

         } else {

             // The following case is rare. Mask the internalMemberName by wrapping the MH in a BMH.

             MethodHandle result = rebind();

             assert (result.internalMemberName() == null);

             return result;

         }

     }

     /*non-public*/

     boolean isInvokeSpecial() {

         return false;  // DMH.Special returns true

     }

     /*non-public*/

     Object internalValues() {

         return null;

     }

     /*non-public*/

     Object internalProperties() {

         // Override to something like "/FOO=bar"

         return "";

     }

     //// Method handle implementation methods.

     //// Sub-classes can override these default implementations.

     //// All these methods assume arguments are already validated.

     /*non-public*/ MethodHandle convertArguments(MethodType newType) {

         // Override this if it can be improved.

         return MethodHandleImpl.makePairwiseConvert(this, newType, 1);

     }

     /*non-public*/

     MethodHandle bindArgument(int pos, 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;

         // ISSUE: Should we have a memory fence here?

         UNSAFE.putObject(this, FORM_OFFSET, newForm);

         this.form.prepare();  // as in MethodHandle.<init>

     }

     private static final long FORM_OFFSET;

     static {

         try {

             FORM_OFFSET = UNSAFE.objectFieldOffset(MethodHandle.class.getDeclaredField("form"));

         } catch (ReflectiveOperationException ex) {

             throw newInternalError(ex);

         }

     }

 }