linkedlistnode.java

Jive 是一个系统工程

/**
 * $RCSfile: LinkedListNode.java,v $
 * $Revision: 1.2 $
 * $Date: 2000/12/21 17:47:20 $
 *
 * Copyright (C) 2000 CoolServlets.com. All rights reserved.
 *
 * ===================================================================
 * The Apache Software License, Version 1.1
 *
 * 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. The end-user documentation included with the redistribution,
 *    if any, must include the following acknowledgment:
 *       "This product includes software developed by
 *        CoolServlets.com (http://www.coolservlets.com)."
 *    Alternately, this acknowledgment may appear in the software itself,
 *    if and wherever such third-party acknowledgments normally appear.
 *
 * 4. The names "Jive" and "CoolServlets.com" must not be used to
 *    endorse or promote products derived from this software without
 *    prior written permission. For written permission, please
 *    contact [e-mail].
 *
 * 5. Products derived from this software may not be called "Jive",
 *    nor may "Jive" appear in their name, without prior written
 *    permission of CoolServlets.com.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED 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 COOLSERVLETS.COM OR
 * ITS 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.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of CoolServlets.com. For more information
 * on CoolServlets.com, please see <http://www.coolservlets.com>.
 */

package com.coolservlets.util;

/**
 * Doubly linked node in a LinkedList. Most LinkedList implementations keep the
 * equivalent of this class private. We make it public so that references
 * to each node in the list can be maintained externally.
 *
 * Exposing this class lets us make remove operations very fast. Remove is
 * built into this class and only requires to reference reassignments. If
 * remove was built into the main LinkedList class, a linear scan would have to
 * be performed to find the correct node to delete.
 *
 * The linked list implementation was specifically written for the CoolServlets
 * cache system. While it can be used as a general purpose linked list, for
 * most applications, it is more suitable to use the linked list that is part
 * of the Java Collections package.
 *
 * @see LinkedList
 */
public class LinkedListNode {

    public LinkedListNode previous;
    public LinkedListNode next;
    public Object object;

    /**
     * This class is further customized for the CoolServlets cache system. It
     * maintains a timestamp of when a Cacheable object was first added to
     * cache. Timestamps are stored as long values and represent the number
     * of milleseconds passed since January 1, 1970 00:00:00.000 GMT.<p>
     *
     * The creation timestamp is used in the case that the cache has a
     * maximum lifetime set. In that case, when
     * [current time] - [creation time] > [max lifetime], the object will be
     * deleted from cache.
     */
    public long timestamp;

    /**
     * Constructs a new linked list node.
     *
     * @param object the Object that the node represents.
     * @param next a reference to the next LinkedListNode in the list.
     * @param previous a reference to the previous LinkedListNode in the list.
     */
    public LinkedListNode(Object object, LinkedListNode next,
            LinkedListNode previous)
    {
        this.object = object;
        this.next = next;
        this.previous = previous;
    }

    /**
     * Removes this node from the linked list that it is a part of.
     */
    public void remove() {
        previous.next = next;
        next.previous = previous;
    }
    /**
     * Returns a String representation of the linked list node by calling the
     * toString method of the node's object.
     *
     * @return a String representation of the LinkedListNode.
     */
    public String toString() {
        return object.toString();
    }
}