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 package java.lang.invoke;

 import java.io.Serializable;

 import java.util.Arrays;

 /**

  * <p>Methods to facilitate the creation of simple "function objects" that

  * implement one or more interfaces by delegation to a provided {@link MethodHandle},

  * possibly after type adaptation and partial evaluation of arguments.  These

  * methods are typically used as <em>bootstrap methods</em> for {@code invokedynamic}

  * call sites, to support the <em>lambda expression</em> and <em>method

  * reference expression</em> features of the Java Programming Language.

  *

  * <p>Indirect access to the behavior specified by the provided {@code MethodHandle}

  * proceeds in order through three phases:

  * <ul>

  *     <li><em>Linkage</em> occurs when the methods in this class are invoked.

  *     They take as arguments an interface to be implemented (typically a

  *     <em>functional interface</em>, one with a single abstract method), a

  *     name and signature of a method from that interface to be implemented, a

  *     method handle describing the desired implementation behavior

  *     for that method, and possibly other additional metadata, and produce a

  *     {@link CallSite} whose target can be used to create suitable function

  *     objects.  Linkage may involve dynamically loading a new class that

  *     implements the target interface. The {@code CallSite} can be considered a

  *     "factory" for function objects and so these linkage methods are referred

  *     to as "metafactories".</li>

  *

  *     <li><em>Capture</em> occurs when the {@code CallSite}'s target is

  *     invoked, typically through an {@code invokedynamic} call site,

  *     producing a function object.  This may occur many times for

  *     a single factory {@code CallSite}.  Capture may involve allocation of a

  *     new function object, or may return an existing function object.  The

  *     behavior {@code MethodHandle} may have additional parameters beyond those

  *     of the specified interface method; these are referred to as <em>captured

  *     parameters</em>, which must be provided as arguments to the

  *     {@code CallSite} target, and which may be early-bound to the behavior

  *     {@code MethodHandle}.  The number of captured parameters and their types

  *     are determined during linkage.</li>

  *

  *     <li><em>Invocation</em> occurs when an implemented interface method

  *     is invoked on a function object.  This may occur many times for a single

  *     function object.  The method referenced by the behavior {@code MethodHandle}

  *     is invoked with the captured arguments and any additional arguments

  *     provided on invocation, as if by {@link MethodHandle#invoke(Object...)}.</li>

  * </ul>

  *

  * <p>It is sometimes useful to restrict the set of inputs or results permitted

  * at invocation.  For example, when the generic interface {@code Predicate<T>}

  * is parameterized as {@code Predicate<String>}, the input must be a

  * {@code String}, even though the method to implement allows any {@code Object}.

  * At linkage time, an additional {@link MethodType} parameter describes the

  * "instantiated" method type; on invocation, the arguments and eventual result

  * are checked against this {@code MethodType}.

  *

  * <p>This class provides two forms of linkage methods: a standard version

  * ({@link #metafactory(MethodHandles.Lookup, String, MethodType, MethodType, MethodHandle, MethodType)})

  * using an optimized protocol, and an alternate version

  * {@link #altMetafactory(MethodHandles.Lookup, String, MethodType, Object...)}).

  * The alternate version is a generalization of the standard version, providing

  * additional control over the behavior of the generated function objects via

  * flags and additional arguments.  The alternate version adds the ability to

  * manage the following attributes of function objects:

  *

  * <ul>

  *     <li><em>Bridging.</em>  It is sometimes useful to implement multiple

  *     variations of the method signature, involving argument or return type

  *     adaptation.  This occurs when multiple distinct VM signatures for a method

  *     are logically considered to be the same method by the language.  The

  *     flag {@code FLAG_BRIDGES} indicates that a list of additional

  *     {@code MethodType}s will be provided, each of which will be implemented

  *     by the resulting function object.  These methods will share the same

  *     name and instantiated type.</li>

  *

  *     <li><em>Multiple interfaces.</em>  If needed, more than one interface

  *     can be implemented by the function object.  (These additional interfaces

  *     are typically marker interfaces with no methods.)  The flag {@code FLAG_MARKERS}

  *     indicates that a list of additional interfaces will be provided, each of

  *     which should be implemented by the resulting function object.</li>

  *

  *     <li><em>Serializability.</em>  The generated function objects do not

  *     generally support serialization.  If desired, {@code FLAG_SERIALIZABLE}

  *     can be used to indicate that the function objects should be serializable.

  *     Serializable function objects will use, as their serialized form,

  *     instances of the class {@code SerializedLambda}, which requires additional

  *     assistance from the capturing class (the class described by the

  *     {@link MethodHandles.Lookup} parameter {@code caller}); see

  *     {@link SerializedLambda} for details.</li>

  * </ul>

  *

  * <p>Assume the linkage arguments are as follows:

  * <ul>

  *      <li>{@code invokedType} (describing the {@code CallSite} signature) has

  *      K parameters of types (D1..Dk) and return type Rd;</li>

  *      <li>{@code samMethodType} (describing the implemented method type) has N

  *      parameters, of types (U1..Un) and return type Ru;</li>

  *      <li>{@code implMethod} (the {@code MethodHandle} providing the

  *      implementation has M parameters, of types (A1..Am) and return type Ra

  *      (if the method describes an instance method, the method type of this

  *      method handle already includes an extra first argument corresponding to

  *      the receiver);</li>

  *      <li>{@code instantiatedMethodType} (allowing restrictions on invocation)

  *      has N parameters, of types (T1..Tn) and return type Rt.</li>

  * </ul>

  *

  * <p>Then the following linkage invariants must hold:

  * <ul>

  *     <li>Rd is an interface</li>

  *     <li>{@code implMethod} is a <em>direct method handle</em></li>

  *     <li>{@code samMethodType} and {@code instantiatedMethodType} have the same

  *     arity N, and for i=1..N, Ti and Ui are the same type, or Ti and Ui are

  *     both reference types and Ti is a subtype of Ui</li>

  *     <li>Either Rt and Ru are the same type, or both are reference types and

  *     Rt is a subtype of Ru</li>

  *     <li>K + N = M</li>

  *     <li>For i=1..K, Di = Ai</li>

  *     <li>For i=1..N, Ti is adaptable to Aj, where j=i+k</li>

  *     <li>The return type Rt is void, or the return type Ra is not void and is

  *     adaptable to Rt</li>

  * </ul>

  *

  * <p>Further, at capture time, if {@code implMethod} corresponds to an instance

  * method, and there are any capture arguments ({@code K > 0}), then the first

  * capture argument (corresponding to the receiver) must be non-null.

  *

  * <p>A type Q is considered adaptable to S as follows:

  * <table summary="adaptable types">

  *     <tr><th>Q</th><th>S</th><th>Link-time checks</th><th>Invocation-time checks</th></tr>

  *     <tr>

  *         <td>Primitive</td><td>Primitive</td>

  *         <td>Q can be converted to S via a primitive widening conversion</td>

  *         <td>None</td>

  *     </tr>

  *     <tr>

  *         <td>Primitive</td><td>Reference</td>

  *         <td>S is a supertype of the Wrapper(Q)</td>

  *         <td>Cast from Wrapper(Q) to S</td>

  *     </tr>

  *     <tr>

  *         <td>Reference</td><td>Primitive</td>

  *         <td>for parameter types: Q is a primitive wrapper and Primitive(Q)

  *         can be widened to S

  *         <br>for return types: If Q is a primitive wrapper, check that

  *         Primitive(Q) can be widened to S</td>

  *         <td>If Q is not a primitive wrapper, cast Q to the base Wrapper(S);

  *         for example Number for numeric types</td>

  *     </tr>

  *     <tr>

  *         <td>Reference</td><td>Reference</td>

  *         <td>for parameter types: S is a supertype of Q

  *         <br>for return types: none</td>

  *         <td>Cast from Q to S</td>

  *     </tr>

  * </table>

  *

  * @apiNote These linkage methods are designed to support the evaluation

  * of <em>lambda expressions</em> and <em>method references</em> in the Java

  * Language.  For every lambda expressions or method reference in the source code,

  * there is a target type which is a functional interface.  Evaluating a lambda

  * expression produces an object of its target type. The recommended mechanism

  * for evaluating lambda expressions is to desugar the lambda body to a method,

  * invoke an invokedynamic call site whose static argument list describes the

  * sole method of the functional interface and the desugared implementation

  * method, and returns an object (the lambda object) that implements the target

  * type. (For method references, the implementation method is simply the

  * referenced method; no desugaring is needed.)

  *

  * <p>The argument list of the implementation method and the argument list of

  * the interface method(s) may differ in several ways.  The implementation

  * methods may have additional arguments to accommodate arguments captured by

  * the lambda expression; there may also be differences resulting from permitted

  * adaptations of arguments, such as casting, boxing, unboxing, and primitive

  * widening. (Varargs adaptations are not handled by the metafactories; these are

  * expected to be handled by the caller.)

  *

  * <p>Invokedynamic call sites have two argument lists: a static argument list

  * and a dynamic argument list.  The static argument list is stored in the

  * constant pool; the dynamic argument is pushed on the operand stack at capture

  * time.  The bootstrap method has access to the entire static argument list

  * (which in this case, includes information describing the implementation method,

  * the target interface, and the target interface method(s)), as well as a

  * method signature describing the number and static types (but not the values)

  * of the dynamic arguments and the static return type of the invokedynamic site.

  *

  * @implNote The implementation method is described with a method handle. In

  * theory, any method handle could be used. Currently supported are direct method

  * handles representing invocation of virtual, interface, constructor and static

  * methods.

  */

 public class LambdaMetafactory {

     /** Flag for alternate metafactories indicating the lambda object

      * must be serializable */

     public static final int FLAG_SERIALIZABLE = 1 << 0;

     /**

      * Flag for alternate metafactories indicating the lambda object implements

      * other marker interfaces

      * besides Serializable

      */

     public static final int FLAG_MARKERS = 1 << 1;

     /**

      * Flag for alternate metafactories indicating the lambda object requires

      * additional bridge methods

      */

     public static final int FLAG_BRIDGES = 1 << 2;

     private static final Class<?>[] EMPTY_CLASS_ARRAY = new Class<?>[0];

     private static final MethodType[] EMPTY_MT_ARRAY = new MethodType[0];

     /**

      * Facilitates the creation of simple "function objects" that implement one

      * or more interfaces by delegation to a provided {@link MethodHandle},

      * after appropriate type adaptation and partial evaluation of arguments.

      * Typically used as a <em>bootstrap method</em> for {@code invokedynamic}

      * call sites, to support the <em>lambda expression</em> and <em>method

      * reference expression</em> features of the Java Programming Language.

      *

      * <p>This is the standard, streamlined metafactory; additional flexibility

      * is provided by {@link #altMetafactory(MethodHandles.Lookup, String, MethodType, Object...)}.

      * A general description of the behavior of this method is provided

      * {@link LambdaMetafactory above}.

      *

      * <p>When the target of the {@code CallSite} returned from this method is

      * invoked, the resulting function objects are instances of a class which

      * implements the interface named by the return type of {@code invokedType},

      * declares a method with the name given by {@code invokedName} and the

      * signature given by {@code samMethodType}.  It may also override additional

      * methods from {@code Object}.

      *

      * @param caller Represents a lookup context with the accessibility

      *               privileges of the caller.  When used with {@code invokedynamic},

      *               this is stacked automatically by the VM.

      * @param invokedName The name of the method to implement.  When used with

      *                    {@code invokedynamic}, this is provided by the

      *                    {@code NameAndType} of the {@code InvokeDynamic}

      *                    structure and is stacked automatically by the VM.

      * @param invokedType The expected signature of the {@code CallSite}.  The

      *                    parameter types represent the types of capture variables;

      *                    the return type is the interface to implement.   When

      *                    used with {@code invokedynamic}, this is provided by

      *                    the {@code NameAndType} of the {@code InvokeDynamic}

      *                    structure and is stacked automatically by the VM.

      *                    In the event that the implementation method is an

      *                    instance method and this signature has any parameters,

      *                    the first parameter in the invocation signature must

      *                    correspond to the receiver.

      * @param samMethodType Signature and return type of method to be implemented

      *                      by the function object.

      * @param implMethod A direct method handle describing the implementation

      *                   method which should be called (with suitable adaptation

      *                   of argument types, return types, and with captured

      *                   arguments prepended to the invocation arguments) at

      *                   invocation time.

      * @param instantiatedMethodType The signature and return type that should

      *                               be enforced dynamically at invocation time.

      *                               This may be the same as {@code samMethodType},

      *                               or may be a specialization of it.

      * @return a CallSite whose target can be used to perform capture, generating

      *         instances of the interface named by {@code invokedType}

      * @throws LambdaConversionException If any of the linkage invariants

      *                                   described {@link LambdaMetafactory above}

      *                                   are violated

      */

     public static CallSite metafactory(MethodHandles.Lookup caller,

                                        String invokedName,

                                        MethodType invokedType,

                                        MethodType samMethodType,

                                        MethodHandle implMethod,

                                        MethodType instantiatedMethodType)

      {

         throw new IllegalStateException();

     }

     /**

      * Facilitates the creation of simple "function objects" that implement one

      * or more interfaces by delegation to a provided {@link MethodHandle},

      * after appropriate type adaptation and partial evaluation of arguments.

      * Typically used as a <em>bootstrap method</em> for {@code invokedynamic}

      * call sites, to support the <em>lambda expression</em> and <em>method

      * reference expression</em> features of the Java Programming Language.

      *

      * <p>This is the general, more flexible metafactory; a streamlined version

      * is provided by {@link #altMetafactory(MethodHandles.Lookup, String, MethodType, Object...)}.

      * A general description of the behavior of this method is provided

      * {@link LambdaMetafactory above}.

      *

      * <p>The argument list for this method includes three fixed parameters,

      * corresponding to the parameters automatically stacked by the VM for the

      * bootstrap method in an {@code invokedynamic} invocation, and an {@code Object[]}

      * parameter that contains additional parameters.  The declared argument

      * list for this method is:

      *

      * <pre>{@code

      *  CallSite altMetafactory(MethodHandles.Lookup caller,

      *                          String invokedName,

      *                          MethodType invokedType,

      *                          Object... args)

      * }</pre>

      *

      * <p>but it behaves as if the argument list is as follows:

      *

      * <pre>{@code

      *  CallSite altMetafactory(MethodHandles.Lookup caller,

      *                          String invokedName,

      *                          MethodType invokedType,

      *                          MethodType samMethodType,

      *                          MethodHandle implMethod,

      *                          MethodType instantiatedMethodType,

      *                          int flags,

      *                          int markerInterfaceCount,  // IF flags has MARKERS set

      *                          Class... markerInterfaces, // IF flags has MARKERS set

      *                          int bridgeCount,           // IF flags has BRIDGES set

      *                          MethodType... bridges      // IF flags has BRIDGES set

      *                          )

      * }</pre>

      *

      * <p>Arguments that appear in the argument list for

      * {@link #metafactory(MethodHandles.Lookup, String, MethodType, MethodType, MethodHandle, MethodType)}

      * have the same specification as in that method.  The additional arguments

      * are interpreted as follows:

      * <ul>

      *     <li>{@code flags} indicates additional options; this is a bitwise

      *     OR of desired flags.  Defined flags are {@link #FLAG_BRIDGES},

      *     {@link #FLAG_MARKERS}, and {@link #FLAG_SERIALIZABLE}.</li>

      *     <li>{@code markerInterfaceCount} is the number of additional interfaces

      *     the function object should implement, and is present if and only if the

      *     {@code FLAG_MARKERS} flag is set.</li>

      *     <li>{@code markerInterfaces} is a variable-length list of additional

      *     interfaces to implement, whose length equals {@code markerInterfaceCount},

      *     and is present if and only if the {@code FLAG_MARKERS} flag is set.</li>

      *     <li>{@code bridgeCount} is the number of additional method signatures

      *     the function object should implement, and is present if and only if

      *     the {@code FLAG_BRIDGES} flag is set.</li>

      *     <li>{@code bridges} is a variable-length list of additional

      *     methods signatures to implement, whose length equals {@code bridgeCount},

      *     and is present if and only if the {@code FLAG_BRIDGES} flag is set.</li>

      * </ul>

      *

      * <p>Each class named by {@code markerInterfaces} is subject to the same

      * restrictions as {@code Rd}, the return type of {@code invokedType},

      * as described {@link LambdaMetafactory above}.  Each {@code MethodType}

      * named by {@code bridges} is subject to the same restrictions as

      * {@code samMethodType}, as described {@link LambdaMetafactory above}.

      *

      * <p>When FLAG_SERIALIZABLE is set in {@code flags}, the function objects

      * will implement {@code Serializable}, and will have a {@code writeReplace}

      * method that returns an appropriate {@link SerializedLambda}.  The

      * {@code caller} class must have an appropriate {@code $deserializeLambda$}

      * method, as described in {@link SerializedLambda}.

      *

      * <p>When the target of the {@code CallSite} returned from this method is

      * invoked, the resulting function objects are instances of a class with

      * the following properties:

      * <ul>

      *     <li>The class implements the interface named by the return type

      *     of {@code invokedType} and any interfaces named by {@code markerInterfaces}</li>

      *     <li>The class declares methods with the name given by {@code invokedName},

      *     and the signature given by {@code samMethodType} and additional signatures

      *     given by {@code bridges}</li>

      *     <li>The class may override methods from {@code Object}, and may

      *     implement methods related to serialization.</li>

      * </ul>

      *

      * @param caller Represents a lookup context with the accessibility

      *               privileges of the caller.  When used with {@code invokedynamic},

      *               this is stacked automatically by the VM.

      * @param invokedName The name of the method to implement.  When used with

      *                    {@code invokedynamic}, this is provided by the

      *                    {@code NameAndType} of the {@code InvokeDynamic}

      *                    structure and is stacked automatically by the VM.

      * @param invokedType The expected signature of the {@code CallSite}.  The

      *                    parameter types represent the types of capture variables;

      *                    the return type is the interface to implement.   When

      *                    used with {@code invokedynamic}, this is provided by

      *                    the {@code NameAndType} of the {@code InvokeDynamic}

      *                    structure and is stacked automatically by the VM.

      *                    In the event that the implementation method is an

      *                    instance method and this signature has any parameters,

      *                    the first parameter in the invocation signature must

      *                    correspond to the receiver.

      * @param  args       An {@code Object[]} array containing the required

      *                    arguments {@code samMethodType}, {@code implMethod},

      *                    {@code instantiatedMethodType}, {@code flags}, and any

      *                    optional arguments, as described

      *                    {@link #altMetafactory(MethodHandles.Lookup, String, MethodType, Object...)} above}

      * @return a CallSite whose target can be used to perform capture, generating

      *         instances of the interface named by {@code invokedType}

      * @throws LambdaConversionException If any of the linkage invariants

      *                                   described {@link LambdaMetafactory above}

      *                                   are violated

      */

     public static CallSite altMetafactory(MethodHandles.Lookup caller,

                                           String invokedName,

                                           MethodType invokedType,

                                           Object... args)

     {

         throw new IllegalStateException();

     }

 }