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Java > Open Source Codes > org > apache > commons > collections > ArrayStack


1 /*
2  * Copyright 2001-2004 The Apache Software Foundation
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  * http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 package org.apache.commons.collections;
17
18 import java.util.ArrayList JavaDoc;
19 import java.util.EmptyStackException JavaDoc;
20
21 /**
22  * An implementation of the {@link java.util.Stack} API that is based on an
23  * <code>ArrayList</code> instead of a <code>Vector</code>, so it is not
24  * synchronized to protect against multi-threaded access. The implementation
25  * is therefore operates faster in environments where you do not need to
26  * worry about multiple thread contention.
27  * <p>
28  * The removal order of an <code>ArrayStack</code> is based on insertion
29  * order: The most recently added element is removed first. The iteration
30  * order is <i>not</i> the same as the removal order. The iterator returns
31  * elements from the bottom up, whereas the {@link #remove()} method removes
32  * them from the top down.
33  * <p>
34  * Unlike <code>Stack</code>, <code>ArrayStack</code> accepts null entries.
35  *
36  * @see java.util.Stack
37  * @since Commons Collections 1.0
38  * @version $Revision: 1.17 $ $Date: 2004/02/18 01:15:42 $
39  *
40  * @author Craig R. McClanahan
41  * @author Paul Jack
42  * @author Stephen Colebourne
43  */
44 public class ArrayStack extends ArrayList JavaDoc implements Buffer {
45
46     /** Ensure serialization compatibility */
47     private static final long serialVersionUID = 2130079159931574599L;
48
49     /**
50      * Constructs a new empty <code>ArrayStack</code>. The initial size
51      * is controlled by <code>ArrayList</code> and is currently 10.
52      */
53     public ArrayStack() {
54         super();
55     }
56
57     /**
58      * Constructs a new empty <code>ArrayStack</code> with an initial size.
59      *
60      * @param initialSize the initial size to use
61      * @throws IllegalArgumentException if the specified initial size
62      * is negative
63      */
64     public ArrayStack(int initialSize) {
65         super(initialSize);
66     }
67
68     /**
69      * Return <code>true</code> if this stack is currently empty.
70      * <p>
71      * This method exists for compatibility with <code>java.util.Stack</code>.
72      * New users of this class should use <code>isEmpty</code> instead.
73      *
74      * @return true if the stack is currently empty
75      */
76     public boolean empty() {
77         return isEmpty();
78     }
79
80     /**
81      * Returns the top item off of this stack without removing it.
82      *
83      * @return the top item on the stack
84      * @throws EmptyStackException if the stack is empty
85      */
86     public Object JavaDoc peek() throws EmptyStackException JavaDoc {
87         int n = size();
88         if (n <= 0) {
89             throw new EmptyStackException JavaDoc();
90         } else {
91             return get(n - 1);
92         }
93     }
94
95     /**
96      * Returns the n'th item down (zero-relative) from the top of this
97      * stack without removing it.
98      *
99      * @param n the number of items down to go
100      * @return the n'th item on the stack, zero relative
101      * @throws EmptyStackException if there are not enough items on the
102      * stack to satisfy this request
103      */
104     public Object JavaDoc peek(int n) throws EmptyStackException JavaDoc {
105         int m = (size() - n) - 1;
106         if (m < 0) {
107             throw new EmptyStackException JavaDoc();
108         } else {
109             return get(m);
110         }
111     }
112
113     /**
114      * Pops the top item off of this stack and return it.
115      *
116      * @return the top item on the stack
117      * @throws EmptyStackException if the stack is empty
118      */
119     public Object JavaDoc pop() throws EmptyStackException JavaDoc {
120         int n = size();
121         if (n <= 0) {
122             throw new EmptyStackException JavaDoc();
123         } else {
124             return remove(n - 1);
125         }
126     }
127
128     /**
129      * Pushes a new item onto the top of this stack. The pushed item is also
130      * returned. This is equivalent to calling <code>add</code>.
131      *
132      * @param item the item to be added
133      * @return the item just pushed
134      */
135     public Object JavaDoc push(Object JavaDoc item) {
136         add(item);
137         return item;
138     }
139
140     /**
141      * Returns the one-based position of the distance from the top that the
142      * specified object exists on this stack, where the top-most element is
143      * considered to be at distance <code>1</code>. If the object is not
144      * present on the stack, return <code>-1</code> instead. The
145      * <code>equals()</code> method is used to compare to the items
146      * in this stack.
147      *
148      * @param object the object to be searched for
149      * @return the 1-based depth into the stack of the object, or -1 if not found
150      */
151     public int search(Object JavaDoc object) {
152         int i = size() - 1; // Current index
153 int n = 1; // Current distance
154 while (i >= 0) {
155             Object JavaDoc current = get(i);
156             if ((object == null && current == null) ||
157                 (object != null && object.equals(current))) {
158                 return n;
159             }
160             i--;
161             n++;
162         }
163         return -1;
164     }
165
166     /**
167      * Returns the element on the top of the stack.
168      *
169      * @return the element on the top of the stack
170      * @throws BufferUnderflowException if the stack is empty
171      */
172     public Object JavaDoc get() {
173         int size = size();
174         if (size == 0) {
175             throw new BufferUnderflowException();
176         }
177         return get(size - 1);
178     }
179
180     /**
181      * Removes the element on the top of the stack.
182      *
183      * @return the removed element
184      * @throws BufferUnderflowException if the stack is empty
185      */
186     public Object JavaDoc remove() {
187         int size = size();
188         if (size == 0) {
189             throw new BufferUnderflowException();
190         }
191         return remove(size - 1);
192     }
193
194 }
195
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