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  *

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 package java.lang.reflect;

 /**

  * {@code Proxy} provides static methods for creating dynamic proxy

  * classes and instances, and it is also the superclass of all

  * dynamic proxy classes created by those methods.

  *

  * <p>To create a proxy for some interface {@code Foo}:

  * <pre>

  *     InvocationHandler handler = new MyInvocationHandler(...);

  *     Class proxyClass = Proxy.getProxyClass(

  *         Foo.class.getClassLoader(), new Class[] { Foo.class });

  *     Foo f = (Foo) proxyClass.

  *         getConstructor(new Class[] { InvocationHandler.class }).

  *         newInstance(new Object[] { handler });

  * </pre>

  * or more simply:

  * <pre>

  *     Foo f = (Foo) Proxy.newProxyInstance(Foo.class.getClassLoader(),

  *                                          new Class[] { Foo.class },

  *                                          handler);

  * </pre>

  *

  * <p>A <i>dynamic proxy class</i> (simply referred to as a <i>proxy

  * class</i> below) is a class that implements a list of interfaces

  * specified at runtime when the class is created, with behavior as

  * described below.

  *

  * A <i>proxy interface</i> is such an interface that is implemented

  * by a proxy class.

  *

  * A <i>proxy instance</i> is an instance of a proxy class.

  *

  * Each proxy instance has an associated <i>invocation handler</i>

  * object, which implements the interface {@link InvocationHandler}.

  * A method invocation on a proxy instance through one of its proxy

  * interfaces will be dispatched to the {@link InvocationHandler#invoke

  * invoke} method of the instance's invocation handler, passing the proxy

  * instance, a {@code java.lang.reflect.Method} object identifying

  * the method that was invoked, and an array of type {@code Object}

  * containing the arguments.  The invocation handler processes the

  * encoded method invocation as appropriate and the result that it

  * returns will be returned as the result of the method invocation on

  * the proxy instance.

  *

  * <p>A proxy class has the following properties:

  *

  * <ul>

  * <li>Proxy classes are public, final, and not abstract.

  *

  * <li>The unqualified name of a proxy class is unspecified.  The space

  * of class names that begin with the string {@code "$Proxy"}

  * should be, however, reserved for proxy classes.

  *

  * <li>A proxy class extends {@code java.lang.reflect.Proxy}.

  *

  * <li>A proxy class implements exactly the interfaces specified at its

  * creation, in the same order.

  *

  * <li>If a proxy class implements a non-public interface, then it will

  * be defined in the same package as that interface.  Otherwise, the

  * package of a proxy class is also unspecified.  Note that package

  * sealing will not prevent a proxy class from being successfully defined

  * in a particular package at runtime, and neither will classes already

  * defined by the same class loader and the same package with particular

  * signers.

  *

  * <li>Since a proxy class implements all of the interfaces specified at

  * its creation, invoking {@code getInterfaces} on its

  * {@code Class} object will return an array containing the same

  * list of interfaces (in the order specified at its creation), invoking

  * {@code getMethods} on its {@code Class} object will return

  * an array of {@code Method} objects that include all of the

  * methods in those interfaces, and invoking {@code getMethod} will

  * find methods in the proxy interfaces as would be expected.

  *

  * <li>The {@link Proxy#isProxyClass Proxy.isProxyClass} method will

  * return true if it is passed a proxy class-- a class returned by

  * {@code Proxy.getProxyClass} or the class of an object returned by

  * {@code Proxy.newProxyInstance}-- and false otherwise.

  *

  * <li>The {@code java.security.ProtectionDomain} of a proxy class

  * is the same as that of system classes loaded by the bootstrap class

  * loader, such as {@code java.lang.Object}, because the code for a

  * proxy class is generated by trusted system code.  This protection

  * domain will typically be granted

  * {@code java.security.AllPermission}.

  *

  * <li>Each proxy class has one public constructor that takes one argument,

  * an implementation of the interface {@link InvocationHandler}, to set

  * the invocation handler for a proxy instance.  Rather than having to use

  * the reflection API to access the public constructor, a proxy instance

  * can be also be created by calling the {@link Proxy#newProxyInstance

  * Proxy.newProxyInstance} method, which combines the actions of calling

  * {@link Proxy#getProxyClass Proxy.getProxyClass} with invoking the

  * constructor with an invocation handler.

  * </ul>

  *

  * <p>A proxy instance has the following properties:

  *

  * <ul>

  * <li>Given a proxy instance {@code proxy} and one of the

  * interfaces implemented by its proxy class {@code Foo}, the

  * following expression will return true:

  * <pre>

  *     {@code proxy instanceof Foo}

  * </pre>

  * and the following cast operation will succeed (rather than throwing

  * a {@code ClassCastException}):

  * <pre>

  *     {@code (Foo) proxy}

  * </pre>

  *

  * <li>Each proxy instance has an associated invocation handler, the one

  * that was passed to its constructor.  The static

  * {@link Proxy#getInvocationHandler Proxy.getInvocationHandler} method

  * will return the invocation handler associated with the proxy instance

  * passed as its argument.

  *

  * <li>An interface method invocation on a proxy instance will be

  * encoded and dispatched to the invocation handler's {@link

  * InvocationHandler#invoke invoke} method as described in the

  * documentation for that method.

  *

  * <li>An invocation of the {@code hashCode},

  * {@code equals}, or {@code toString} methods declared in

  * {@code java.lang.Object} on a proxy instance will be encoded and

  * dispatched to the invocation handler's {@code invoke} method in

  * the same manner as interface method invocations are encoded and

  * dispatched, as described above.  The declaring class of the

  * {@code Method} object passed to {@code invoke} will be

  * {@code java.lang.Object}.  Other public methods of a proxy

  * instance inherited from {@code java.lang.Object} are not

  * overridden by a proxy class, so invocations of those methods behave

  * like they do for instances of {@code java.lang.Object}.

  * </ul>

  *

  * <h3>Methods Duplicated in Multiple Proxy Interfaces</h3>

  *

  * <p>When two or more interfaces of a proxy class contain a method with

  * the same name and parameter signature, the order of the proxy class's

  * interfaces becomes significant.  When such a <i>duplicate method</i>

  * is invoked on a proxy instance, the {@code Method} object passed

  * to the invocation handler will not necessarily be the one whose

  * declaring class is assignable from the reference type of the interface

  * that the proxy's method was invoked through.  This limitation exists

  * because the corresponding method implementation in the generated proxy

  * class cannot determine which interface it was invoked through.

  * Therefore, when a duplicate method is invoked on a proxy instance,

  * the {@code Method} object for the method in the foremost interface

  * that contains the method (either directly or inherited through a

  * superinterface) in the proxy class's list of interfaces is passed to

  * the invocation handler's {@code invoke} method, regardless of the

  * reference type through which the method invocation occurred.

  *

  * <p>If a proxy interface contains a method with the same name and

  * parameter signature as the {@code hashCode}, {@code equals},

  * or {@code toString} methods of {@code java.lang.Object},

  * when such a method is invoked on a proxy instance, the

  * {@code Method} object passed to the invocation handler will have

  * {@code java.lang.Object} as its declaring class.  In other words,

  * the public, non-final methods of {@code java.lang.Object}

  * logically precede all of the proxy interfaces for the determination of

  * which {@code Method} object to pass to the invocation handler.

  *

  * <p>Note also that when a duplicate method is dispatched to an

  * invocation handler, the {@code invoke} method may only throw

  * checked exception types that are assignable to one of the exception

  * types in the {@code throws} clause of the method in <i>all</i> of

  * the proxy interfaces that it can be invoked through.  If the

  * {@code invoke} method throws a checked exception that is not

  * assignable to any of the exception types declared by the method in one

  * of the proxy interfaces that it can be invoked through, then an

  * unchecked {@code UndeclaredThrowableException} will be thrown by

  * the invocation on the proxy instance.  This restriction means that not

  * all of the exception types returned by invoking

  * {@code getExceptionTypes} on the {@code Method} object

  * passed to the {@code invoke} method can necessarily be thrown

  * successfully by the {@code invoke} method.

  *

  * @author      Peter Jones

  * @see         InvocationHandler

  * @since       1.3

  */

 public class Proxy implements java.io.Serializable {

     private static final long serialVersionUID = -2222568056686623797L;

     /**

      * the invocation handler for this proxy instance.

      * @serial

      */

     protected InvocationHandler h;

     /**

      * Prohibits instantiation.

      */

     private Proxy() {

     }

     /**

      * Constructs a new {@code Proxy} instance from a subclass

      * (typically, a dynamic proxy class) with the specified value

      * for its invocation handler.

      *

      * @param   h the invocation handler for this proxy instance

      */

     protected Proxy(InvocationHandler h) {

         this.h = h;

     }

     /**

      * Returns the {@code java.lang.Class} object for a proxy class

      * given a class loader and an array of interfaces.  The proxy class

      * will be defined by the specified class loader and will implement

      * all of the supplied interfaces.  If a proxy class for the same

      * permutation of interfaces has already been defined by the class

      * loader, then the existing proxy class will be returned; otherwise,

      * a proxy class for those interfaces will be generated dynamically

      * and defined by the class loader.

      *

      * <p>There are several restrictions on the parameters that may be

      * passed to {@code Proxy.getProxyClass}:

      *

      * <ul>

      * <li>All of the {@code Class} objects in the

      * {@code interfaces} array must represent interfaces, not

      * classes or primitive types.

      *

      * <li>No two elements in the {@code interfaces} array may

      * refer to identical {@code Class} objects.

      *

      * <li>All of the interface types must be visible by name through the

      * specified class loader.  In other words, for class loader

      * {@code cl} and every interface {@code i}, the following

      * expression must be true:

      * <pre>

      *     Class.forName(i.getName(), false, cl) == i

      * </pre>

      *

      * <li>All non-public interfaces must be in the same package;

      * otherwise, it would not be possible for the proxy class to

      * implement all of the interfaces, regardless of what package it is

      * defined in.

      *

      * <li>For any set of member methods of the specified interfaces

      * that have the same signature:

      * <ul>

      * <li>If the return type of any of the methods is a primitive

      * type or void, then all of the methods must have that same

      * return type.

      * <li>Otherwise, one of the methods must have a return type that

      * is assignable to all of the return types of the rest of the

      * methods.

      * </ul>

      *

      * <li>The resulting proxy class must not exceed any limits imposed

      * on classes by the virtual machine.  For example, the VM may limit

      * the number of interfaces that a class may implement to 65535; in

      * that case, the size of the {@code interfaces} array must not

      * exceed 65535.

      * </ul>

      *

      * <p>If any of these restrictions are violated,

      * {@code Proxy.getProxyClass} will throw an

      * {@code IllegalArgumentException}.  If the {@code interfaces}

      * array argument or any of its elements are {@code null}, a

      * {@code NullPointerException} will be thrown.

      *

      * <p>Note that the order of the specified proxy interfaces is

      * significant: two requests for a proxy class with the same combination

      * of interfaces but in a different order will result in two distinct

      * proxy classes.

      *

      * @param   loader the class loader to define the proxy class

      * @param   interfaces the list of interfaces for the proxy class

      *          to implement

      * @return  a proxy class that is defined in the specified class loader

      *          and that implements the specified interfaces

      * @throws  IllegalArgumentException if any of the restrictions on the

      *          parameters that may be passed to {@code getProxyClass}

      *          are violated

      * @throws  NullPointerException if the {@code interfaces} array

      *          argument or any of its elements are {@code null}

      */

     public static Class<?> getProxyClass(ClassLoader loader,

                                          Class<?>... interfaces)

         throws IllegalArgumentException

     {

         throw new IllegalArgumentException();

     }

     /**

      * Returns an instance of a proxy class for the specified interfaces

      * that dispatches method invocations to the specified invocation

      * handler.  This method is equivalent to:

      * <pre>

      *     Proxy.getProxyClass(loader, interfaces).

      *         getConstructor(new Class[] { InvocationHandler.class }).

      *         newInstance(new Object[] { handler });

      * </pre>

      *

      * <p>{@code Proxy.newProxyInstance} throws

      * {@code IllegalArgumentException} for the same reasons that

      * {@code Proxy.getProxyClass} does.

      *

      * @param   loader the class loader to define the proxy class

      * @param   interfaces the list of interfaces for the proxy class

      *          to implement

      * @param   h the invocation handler to dispatch method invocations to

      * @return  a proxy instance with the specified invocation handler of a

      *          proxy class that is defined by the specified class loader

      *          and that implements the specified interfaces

      * @throws  IllegalArgumentException if any of the restrictions on the

      *          parameters that may be passed to {@code getProxyClass}

      *          are violated

      * @throws  NullPointerException if the {@code interfaces} array

      *          argument or any of its elements are {@code null}, or

      *          if the invocation handler, {@code h}, is

      *          {@code null}

      */

     public static Object newProxyInstance(ClassLoader loader,

                                           Class<?>[] interfaces,

                                           InvocationHandler h)

         throws IllegalArgumentException

     {

         if (h == null) {

             throw new NullPointerException();

         }

         throw new IllegalArgumentException();

     }

     /**

      * Returns true if and only if the specified class was dynamically

      * generated to be a proxy class using the {@code getProxyClass}

      * method or the {@code newProxyInstance} method.

      *

      * <p>The reliability of this method is important for the ability

      * to use it to make security decisions, so its implementation should

      * not just test if the class in question extends {@code Proxy}.

      *

      * @param   cl the class to test

      * @return  {@code true} if the class is a proxy class and

      *          {@code false} otherwise

      * @throws  NullPointerException if {@code cl} is {@code null}

      */

     public static boolean isProxyClass(Class<?> cl) {

         if (cl == null) {

             throw new NullPointerException();

         }

         return false;

     }

     /**

      * Returns the invocation handler for the specified proxy instance.

      *

      * @param   proxy the proxy instance to return the invocation handler for

      * @return  the invocation handler for the proxy instance

      * @throws  IllegalArgumentException if the argument is not a

      *          proxy instance

      */

     public static InvocationHandler getInvocationHandler(Object proxy)

         throws IllegalArgumentException

     {

         /*

          * Verify that the object is actually a proxy instance.

          */

         if (!isProxyClass(proxy.getClass())) {

             throw new IllegalArgumentException("not a proxy instance");

         }

         Proxy p = (Proxy) proxy;

         return p.h;

     }

     private static native Class defineClass0(ClassLoader loader, String name,

                                              byte[] b, int off, int len);

 }