001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.collections;
018
019import java.util.ArrayList;
020import java.util.EmptyStackException;
021
022/**
023 * An implementation of the {@link java.util.Stack} API that is based on an
024 * <code>ArrayList</code> instead of a <code>Vector</code>, so it is not
025 * synchronized to protect against multi-threaded access.  The implementation
026 * is therefore operates faster in environments where you do not need to
027 * worry about multiple thread contention.
028 * <p>
029 * The removal order of an <code>ArrayStack</code> is based on insertion 
030 * order: The most recently added element is removed first.  The iteration
031 * order is <i>not</i> the same as the removal order.  The iterator returns
032 * elements from the bottom up, whereas the {@link #remove()} method removes
033 * them from the top down.
034 * <p>
035 * Unlike <code>Stack</code>, <code>ArrayStack</code> accepts null entries.
036 * <p>
037 * <strong>Note:</strong> this class should be bytecode-identical to the 
038 * version in commons collections. This is required to allow backwards 
039 * compability with both previous versions of BeanUtils and also allow 
040 * coexistance with both collections 2.1 and 3.0.
041 *
042 * @see java.util.Stack
043 * @since Commons Collections 1.0
044 * @version $Revision: 555824 $ $Date: 2007-07-13 01:27:15 +0100 (Fri, 13 Jul 2007) $
045 * 
046 * @author Craig R. McClanahan
047 * @author Paul Jack
048 * @author Stephen Colebourne
049 */
050public class ArrayStack extends ArrayList implements Buffer {
051
052    /** Ensure serialization compatibility */    
053    private static final long serialVersionUID = 2130079159931574599L;
054
055    /**
056     * Constructs a new empty <code>ArrayStack</code>. The initial size
057     * is controlled by <code>ArrayList</code> and is currently 10.
058     */
059    public ArrayStack() {
060        super();
061    }
062
063    /**
064     * Constructs a new empty <code>ArrayStack</code> with an initial size.
065     * 
066     * @param initialSize  the initial size to use
067     * @throws IllegalArgumentException  if the specified initial size
068     *  is negative
069     */
070    public ArrayStack(int initialSize) {
071        super(initialSize);
072    }
073
074    /**
075     * Return <code>true</code> if this stack is currently empty.
076     * <p>
077     * This method exists for compatibility with <code>java.util.Stack</code>.
078     * New users of this class should use <code>isEmpty</code> instead.
079     * 
080     * @return true if the stack is currently empty
081     */
082    public boolean empty() {
083        return isEmpty();
084    }
085
086    /**
087     * Returns the top item off of this stack without removing it.
088     *
089     * @return the top item on the stack
090     * @throws EmptyStackException  if the stack is empty
091     */
092    public Object peek() throws EmptyStackException {
093        int n = size();
094        if (n <= 0) {
095            throw new EmptyStackException();
096        } else {
097            return get(n - 1);
098        }
099    }
100
101    /**
102     * Returns the n'th item down (zero-relative) from the top of this
103     * stack without removing it.
104     *
105     * @param n  the number of items down to go
106     * @return the n'th item on the stack, zero relative
107     * @throws EmptyStackException  if there are not enough items on the
108     *  stack to satisfy this request
109     */
110    public Object peek(int n) throws EmptyStackException {
111        int m = (size() - n) - 1;
112        if (m < 0) {
113            throw new EmptyStackException();
114        } else {
115            return get(m);
116        }
117    }
118
119    /**
120     * Pops the top item off of this stack and return it.
121     *
122     * @return the top item on the stack
123     * @throws EmptyStackException  if the stack is empty
124     */
125    public Object pop() throws EmptyStackException {
126        int n = size();
127        if (n <= 0) {
128            throw new EmptyStackException();
129        } else {
130            return remove(n - 1);
131        }
132    }
133
134    /**
135     * Pushes a new item onto the top of this stack. The pushed item is also
136     * returned. This is equivalent to calling <code>add</code>.
137     *
138     * @param item  the item to be added
139     * @return the item just pushed
140     */
141    public Object push(Object item) {
142        add(item);
143        return item;
144    }
145
146    /**
147     * Returns the one-based position of the distance from the top that the
148     * specified object exists on this stack, where the top-most element is
149     * considered to be at distance <code>1</code>.  If the object is not
150     * present on the stack, return <code>-1</code> instead.  The
151     * <code>equals()</code> method is used to compare to the items
152     * in this stack.
153     *
154     * @param object  the object to be searched for
155     * @return the 1-based depth into the stack of the object, or -1 if not found
156     */
157    public int search(Object object) {
158        int i = size() - 1;        // Current index
159        int n = 1;                 // Current distance
160        while (i >= 0) {
161            Object current = get(i);
162            if ((object == null && current == null) ||
163                (object != null && object.equals(current))) {
164                return n;
165            }
166            i--;
167            n++;
168        }
169        return -1;
170    }
171
172    /**
173     * Returns the element on the top of the stack.
174     *
175     * @return the element on the top of the stack
176     * @throws BufferUnderflowException  if the stack is empty
177     */
178    public Object get() {
179        int size = size();
180        if (size == 0) {
181            throw new BufferUnderflowException();
182        }
183        return get(size - 1);
184    }
185
186    /**
187     * Removes the element on the top of the stack.
188     *
189     * @return the removed element 
190     * @throws BufferUnderflowException  if the stack is empty
191     */
192    public Object remove() {
193        int size = size();
194        if (size == 0) {
195            throw new BufferUnderflowException();
196        }
197        return remove(size - 1);
198    }
199
200}