root/trunk/LogicMail/src/org/logicprobe/LogicMail/util/UniqueIdGenerator.java

/*-
 * Copyright (c) 2007, Derek Konigsberg
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer. 
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution. 
 * 3. Neither the name of the project nor the names of its
 *    contributors may be used to endorse or promote products derived
 *    from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
 * OF THE POSSIBILITY OF SUCH DAMAGE.
 */


package org.logicprobe.LogicMail.util;

import java.util.Random;
import org.logicprobe.LogicMail.AppInfo;

/**
 * This class provides a simple unique ID generator.
 */
public class UniqueIdGenerator {
    private static UniqueIdGenerator instance;
    private long base;
    private long offset;
    
    private UniqueIdGenerator() {
        base = AppInfo.GUID + (new Random()).nextLong();
        offset = 0;
    }
    
    /**
     * Gets the unique ID generator instance.
     * @return Instance
     */
    public static synchronized UniqueIdGenerator getInstance() {
        if(instance == null) {
            instance = new UniqueIdGenerator();
        }
        return instance;
    }
    
    public long getUniqueId() {
        return base + offset++;
    }
}