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Java > Open Source Codes > org > apache > mina > util > Stack


1 /*
2  * Licensed to the Apache Software Foundation (ASF) under one
3  * or more contributor license agreements. See the NOTICE file
4  * distributed with this work for additional information
5  * regarding copyright ownership. The ASF licenses this file
6  * to you under the Apache License, Version 2.0 (the
7  * "License"); you may not use this file except in compliance
8  * with the License. You may obtain a copy of the License at
9  *
10  * http://www.apache.org/licenses/LICENSE-2.0
11  *
12  * Unless required by applicable law or agreed to in writing,
13  * software distributed under the License is distributed on an
14  * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
15  * KIND, either express or implied. See the License for the
16  * specific language governing permissions and limitations
17  * under the License.
18  *
19  */
20 package org.apache.mina.util;
21
22 import java.io.Serializable JavaDoc;
23 import java.util.Arrays JavaDoc;
24
25 /**
26  * A unbounded stack.
27  *
28  * @author The Apache Directory Project (mina-dev@directory.apache.org)
29  * @version $Rev: 555855 $, $Date: 2007-07-13 12:19:00 +0900 (금, 13 7월 2007) $
30  */
31 public class Stack implements Serializable JavaDoc {
32     private static final long serialVersionUID = 3546919169401434168L;
33
34     private static final int DEFAULT_CAPACITY = 4;
35
36     private Object JavaDoc[] items;
37
38     private int size = 0;
39
40     /**
41      * Construct a new, empty stack.
42      */
43     public Stack() {
44         items = new Object JavaDoc[DEFAULT_CAPACITY];
45     }
46
47     /**
48      * Clears this stack.
49      */
50     public void clear() {
51         Arrays.fill(items, null);
52         size = 0;
53     }
54
55     /**
56      * Pops from this stack.
57      *
58      * @return <code>null</code>, if this stack is empty or the element is
59      * really <code>null</code>.
60      */
61     public Object JavaDoc pop() {
62         if (size == 0) {
63             return null;
64         }
65
66         int pos = size - 1;
67         Object JavaDoc ret = items[pos];
68         items[pos] = null;
69         size--;
70
71         return ret;
72     }
73
74     /**
75      * Push into this stack.
76      */
77     public void push(Object JavaDoc obj) {
78         if (size == items.length) {
79             // expand queue
80 final int oldLen = items.length;
81             Object JavaDoc[] tmp = new Object JavaDoc[oldLen * 2];
82             System.arraycopy(items, 0, tmp, 0, size);
83             items = tmp;
84         }
85
86         items[size] = obj;
87         size++;
88     }
89
90     public void remove(Object JavaDoc o) {
91         for (int i = size - 1; i >= 0; i--) {
92             if (items[i] == o) {
93                 System.arraycopy(items, i + 1, items, i, size - i - 1);
94                 items[size - 1] = null;
95                 size--;
96                 break;
97             }
98         }
99     }
100
101     /**
102      * Returns the first element of the stack.
103      *
104      * @return <code>null</code>, if the stack is empty, or the element is
105      * really <code>null</code>.
106      */
107     public Object JavaDoc first() {
108         if (size == 0) {
109             return null;
110         }
111
112         return items[size - 1];
113     }
114
115     public Object JavaDoc last() {
116         if (size == 0) {
117             return null;
118         }
119
120         return items[0];
121     }
122
123     /**
124      * Returns <code>true</code> if the stack is empty.
125      */
126     public boolean isEmpty() {
127         return (size == 0);
128     }
129
130     /**
131      * Returns the number of elements in the stack.
132      */
133     public int size() {
134         return size;
135     }
136 }
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