Java example source code file (VMID.java)

This example Java source code file (VMID.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

deprecated, securerandom, security, stringbuffer, uid, vmid

The VMID.java Java example source code

/*
 * Copyright (c) 1996, 2013, 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.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * 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.
 */

package java.rmi.dgc;

import java.rmi.server.UID;
import java.security.SecureRandom;

/**
 * A VMID is a identifier that is unique across all Java virtual
 * machines.  VMIDs are used by the distributed garbage collector
 * to identify client VMs.
 *
 * @author      Ann Wollrath
 * @author      Peter Jones
 */
public final class VMID implements java.io.Serializable {
    /** Array of bytes uniquely identifying this host */
    private static final byte[] randomBytes;

    /**
     * @serial array of bytes uniquely identifying host created on
     */
    private byte[] addr;

    /**
     * @serial unique identifier with respect to host created on
     */
    private UID uid;

    /** indicate compatibility with JDK 1.1.x version of class */
    private static final long serialVersionUID = -538642295484486218L;

    static {
        // Generate 8 bytes of random data.
        SecureRandom secureRandom = new SecureRandom();
        byte bytes[] = new byte[8];
        secureRandom.nextBytes(bytes);
        randomBytes = bytes;
    }

    /**
     * Create a new VMID.  Each new VMID returned from this constructor
     * is unique for all Java virtual machines under the following
     * conditions: a) the conditions for uniqueness for objects of
     * the class <code>java.rmi.server.UID are satisfied, and b) an
     * address can be obtained for this host that is unique and constant
     * for the lifetime of this object.
     */
    public VMID() {
        addr = randomBytes;
        uid = new UID();
    }

    /**
     * Return true if an accurate address can be determined for this
     * host.  If false, reliable VMID cannot be generated from this host
     * @return true if host address can be determined, false otherwise
     * @deprecated
     */
    @Deprecated
    public static boolean isUnique() {
        return true;
    }

    /**
     * Compute hash code for this VMID.
     */
    public int hashCode() {
        return uid.hashCode();
    }

    /**
     * Compare this VMID to another, and return true if they are the
     * same identifier.
     */
    public boolean equals(Object obj) {
        if (obj instanceof VMID) {
            VMID vmid = (VMID) obj;
            if (!uid.equals(vmid.uid))
                return false;
            if ((addr == null) ^ (vmid.addr == null))
                return false;
            if (addr != null) {
                if (addr.length != vmid.addr.length)
                    return false;
                for (int i = 0; i < addr.length; ++ i)
                    if (addr[i] != vmid.addr[i])
                        return false;
            }
            return true;
        } else {
            return false;
        }
    }

    /**
     * Return string representation of this VMID.
     */
    public String toString() {
        StringBuffer result = new StringBuffer();
        if (addr != null)
            for (int i = 0; i < addr.length; ++ i) {
                int x = addr[i] & 0xFF;
                result.append((x < 0x10 ? "0" : "") +
                              Integer.toString(x, 16));
            }
        result.append(':');
        result.append(uid.toString());
        return result.toString();
    }
}