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1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one or more
3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * The ASF licenses this file to You under the Apache License, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License.  You may obtain a copy of the License at
8    *
9    *      http://www.apache.org/licenses/LICENSE-2.0
10   *
11   * Unless required by applicable law or agreed to in writing, software
12   * distributed under the License is distributed on an "AS IS" BASIS,
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   * See the License for the specific language governing permissions and
15   * limitations under the License.
16   */
17  package org.apache.commons.collections;
18  
19  import java.util.ArrayList;
20  import java.util.EmptyStackException;
21  
22  /***
23   * An implementation of the {@link java.util.Stack} API that is based on an
24   * <code>ArrayList</code> instead of a <code>Vector</code>, so it is not
25   * synchronized to protect against multi-threaded access.  The implementation
26   * is therefore operates faster in environments where you do not need to
27   * worry about multiple thread contention.
28   * <p>
29   * The removal order of an <code>ArrayStack</code> is based on insertion 
30   * order: The most recently added element is removed first.  The iteration
31   * order is <i>not</i> the same as the removal order.  The iterator returns
32   * elements from the bottom up, whereas the {@link #remove()} method removes
33   * them from the top down.
34   * <p>
35   * Unlike <code>Stack</code>, <code>ArrayStack</code> accepts null entries.
36   * <p>
37   * <strong>Note:</strong> this class should be bytecode-identical to the 
38   * version in commons collections. This is required to allow backwards 
39   * compability with both previous versions of BeanUtils and also allow 
40   * coexistance with both collections 2.1 and 3.0.
41   *
42   * @see java.util.Stack
43   * @since Commons Collections 1.0
44   * @version $Revision: 555824 $ $Date: 2007-07-13 01:27:15 +0100 (Fri, 13 Jul 2007) $
45   * 
46   * @author Craig R. McClanahan
47   * @author Paul Jack
48   * @author Stephen Colebourne
49   */
50  public class ArrayStack extends ArrayList implements Buffer {
51  
52      /*** Ensure serialization compatibility */    
53      private static final long serialVersionUID = 2130079159931574599L;
54  
55      /***
56       * Constructs a new empty <code>ArrayStack</code>. The initial size
57       * is controlled by <code>ArrayList</code> and is currently 10.
58       */
59      public ArrayStack() {
60          super();
61      }
62  
63      /***
64       * Constructs a new empty <code>ArrayStack</code> with an initial size.
65       * 
66       * @param initialSize  the initial size to use
67       * @throws IllegalArgumentException  if the specified initial size
68       *  is negative
69       */
70      public ArrayStack(int initialSize) {
71          super(initialSize);
72      }
73  
74      /***
75       * Return <code>true</code> if this stack is currently empty.
76       * <p>
77       * This method exists for compatibility with <code>java.util.Stack</code>.
78       * New users of this class should use <code>isEmpty</code> instead.
79       * 
80       * @return true if the stack is currently empty
81       */
82      public boolean empty() {
83          return isEmpty();
84      }
85  
86      /***
87       * Returns the top item off of this stack without removing it.
88       *
89       * @return the top item on the stack
90       * @throws EmptyStackException  if the stack is empty
91       */
92      public Object peek() throws EmptyStackException {
93          int n = size();
94          if (n <= 0) {
95              throw new EmptyStackException();
96          } else {
97              return get(n - 1);
98          }
99      }
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 }