valuestack 根对象CompoundRoot 源码

/*
 * Copyright 2002-2006,2009 The Apache Software Foundation.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.opensymphony.xwork2.util;

import java.util.ArrayList;
import java.util.List;

/**
 * A Stack that is implemented using a List.
 *
 * @author plightbo
 * @version $Revision: 894090 $
 */
public class CompoundRoot extends ArrayList {

    public CompoundRoot() {
    }

    public CompoundRoot(List list) {
        super(list);
    }

    public CompoundRoot cutStack(int index) {
        return new CompoundRoot(subList(index, size()));
    }

    public Object peek() {
        return get(0);
    }

//出栈
    public Object pop() {
        return remove(0);
    }

//进栈
    public void push(Object o) {
        add(0, o);
    }
}