dxlistdeque.java

用Java写的面相对象的数据库管理系统

// You can redistribute this software and/or modify it under the terms of
// the Ozone Library License version 1 published by ozone-db.org.
//
// The original code and portions created by SMB are
// Copyright (C) 1997-2000 by SMB GmbH. All rights reserved.
//
// $Id: DxListDeque.java,v 1.6 2000/10/28 16:55:14 daniela Exp $

package org.ozoneDB.DxLib;

/**
 * 
 * 
 * @author <a href="http://www.softwarebuero.de/">SMB</a>
 * @version $Revision: 1.6 $Date: 2000/10/28 16:55:14 $
 */
public class DxListDeque extends DxListBag implements DxDeque {
    
    final static long serialVersionUID = 1L;
    
    
    /**
     */
    public DxListDeque() {
    }
    
    
    /**
     */
    public Object peek() {
        return peekBottom();
    } 
    
    
    /**
     */
    public Object peekTop() {
        //if the deque is empty, this return null
        return top.prev().data();
    } 
    
    
    /**
     */
    public Object peekBottom() {
        //if the deque is empty, this return null
        return start.next().data();
    } 
    
    
    /**
     */
    public synchronized void push( Object obj ) {
        pushBottom( obj );
    } 
    
    
    /**
     */
    public synchronized void pushTop( Object obj ) {
        top.storeInfront( new DxListNode( obj ) );
        itemCount++;
    } 
    
    
    /**
     */
    public synchronized void pushBottom( Object obj ) {
        start.storeBehind( new DxListNode( obj ) );
        itemCount++;
    } 
    
    
    /**
     */
    public Object pop() {
        return popBottom();
    } 
    
    
    /**
     */
    public Object popTop() {
        Object answer = top.prev().data();
        if (answer != null) {
            top.prev().remove();
            itemCount--;
        } 
        return answer;
    } 
    
    
    /**
     */
    public Object popBottom() {
        Object answer = start.next().data();
        if (answer != null) {
            start.next().remove();
            itemCount--;
        } 
        return answer;
    } 
}