Java example source code file (NotExtending.java)

This example Java source code file (NotExtending.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

notextending, object, outofmemoryerror, passing, remote, remoteexception, rmi, runtimeexception

The NotExtending.java Java example source code

/*
 * Copyright (c) 1998, 2012, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

/* @test
 * @bug 4099660 4102938
 * @summary Remote classes not extending RemoteObject should be able to
 *          implement hashCode() and equals() methods so that instances
 *          can be successfully compared to RemoteObject instances
 *          (specifically: stubs) that contain the instance's RemoteRef.
 * @author Peter Jones
 *
 * @build NotExtending_Stub NotExtending_Skel
 * @run main/othervm/timeout=240 NotExtending
 */


import java.rmi.*;
import java.rmi.server.*;

public class NotExtending implements Remote {

    /** remote stub for this server instance */
    private Remote stub;
    /** value of stub's hash code */
    private int hashValue;
    /** true if the hashValue field has been initialized */
    private boolean hashValueInitialized = false;

    public NotExtending() throws RemoteException {
        stub = UnicastRemoteObject.exportObject(this);
        setHashValue(stub.hashCode());
    }

    private void setHashValue(int value) {
        hashValue = value;
        hashValueInitialized = true;
    }

    public int hashCode() {
        /*
         * Test fails with a RuntimeException if the hashCode() method is
         * called (during the export procedure) before the correct hash
         * value has been initialized.
         */
        if (!hashValueInitialized) {
            throw new RuntimeException(
                "hashCode() invoked before hashValue initialized");
        }
        return hashValue;
    }

    public boolean equals(Object obj) {
        return stub.equals(obj);
    }

    public static void main(String[] args) throws Exception {
        /*
         * The following line is required with the JDK 1.2 VM so that the
         * VM can exit gracefully when this test completes.  Otherwise, the
         * conservative garbage collector will find a handle to the server
         * object on the native stack and not clear the weak reference to
         * it in the RMI runtime's object table.
         */
        Object dummy = new Object();

        NotExtending server;
        try {
            /*
             * Verify that hashCode() is not invoked before it is
             * initialized.  Tests bugid 4102938.
             */
            server = new NotExtending();
            System.err.println("Server exported without invoking hashCode().");

            /*
             * Verify that passing stub to server's equals() method
             * returns true.
             */
            if (server.equals(server.stub)) {
                System.err.println(
                    "Passing stub to server's equals() method succeeded.");
            } else {
                throw new RuntimeException(
                    "passing stub to server's equals() method failed");
            }

            /*
             * Verify that passing server to stub's equals() method
             * returns true.  Tests bugid 4099660.
             */
            if (server.stub.equals(server)) {
                System.err.println(
                    "Passing server to stub's equals() method succeeded.");
            } else {
                throw new RuntimeException(
                    "passing server to stub's equals() method failed");
            }

        } finally {
            server = null;
            flushCachedRefs();
        }
    }

    /**
     * Force desparate garbage collection so that all sun.misc.Ref instances
     * will be cleared.
     *
     * This method is required with the JDK 1.1.x RMI runtime so that the
     * VM can exit gracefully when this test completes.  See bugid 4006356.
     */
    public static void flushCachedRefs() {
        java.util.Vector chain = new java.util.Vector();
        try {
            while (true) {
                int[] hungry = new int[65536];
                chain.addElement(hungry);
            }
        } catch (OutOfMemoryError e) {
        }
    }
}