ExpiringStack


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  ;
23  import java.util.Arrays  ;
24  
25  /**
26   * A unbounded stack with expiration.
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 ExpiringStack implements Serializable   {
32      private static final long serialVersionUID = 3546919169401434168L;
33  
34      private static final int DEFAULT_CAPACITY = 4;
35  
36      private Object  [] items;
37  
38      private long[] timestamps;
39  
40      private int size = 0;
41  
42      /**
43       * Construct a new, empty stack.
44       */
45      public ExpiringStack() {
46          items = new Object  [DEFAULT_CAPACITY];
47          timestamps = new long[DEFAULT_CAPACITY];
48      }
49  
50      /**
51       * Clears this stack.
52       */
53      public void clear() {
54          Arrays.fill(items, null);
55          size = 0;
56      }
57  
58      /**
59       * Pops from this stack.
60       * 
61       * @return <code>null</code>, if this stack is empty or the element is
62       *         really <code>null</code>.
63       */
64      public Object   pop() {
65          if (size == 0) {
66              return null;
67          }
68  
69          int pos = size - 1;
70          Object   ret = items[pos];
71          items[pos] = null;
72          size--;
73  
74          return ret;
75      }
76  
77      /**
78       * Push into this stack.
79       */
80      public void push(Object   obj) {
81          if (size == items.length) {
82              // expand queue
83              final int oldLen = items.length;
84              Object  [] tmpItems = new Object  [oldLen * 2];
85              System.arraycopy(items, 0, tmpItems, 0, size);
86              long[] tmpTimestamps = new long[oldLen * 2];
87              System.arraycopy(timestamps, 0, tmpTimestamps, 0, size);
88              items = tmpItems;
89              timestamps = tmpTimestamps;
90          }
91  
92          items[size] = obj;
93          timestamps[size] = System.currentTimeMillis();
94          size++;
95      }
96  
97      public void remove(Object   o) {
98          for (int i = size - 1; i >= 0; i--) {
99              if (items[i] == o) {
100                 System.arraycopy(items, i + 1, items, i, size - i - 1);
101                 System
102                         .arraycopy(timestamps, i + 1, timestamps, i, size - i
103                                 - 1);
104                 items[size - 1] = null;
105                 size--;
106                 break;
107             }
108         }
109     }
110 
111     public void expireBefore(long time) {
112         int i;
113         for (i = 0; i < size; i++) {
114             if (timestamps[i] >= time) {
115                 break;
116             }
117         }
118 
119         if (i > 0) {
120             size -= i;
121             System.arraycopy(items, i, items, 0, size);
122             System.arraycopy(timestamps, i, timestamps, 0, size);
123             Arrays.fill(items, size, items.length, null);
124         }
125     }
126 
127     /**
128      * Returns the first element of the stack.
129      * 
130      * @return <code>null</code>, if the stack is empty, or the element is
131      *         really <code>null</code>.
132      */
133     public Object   first() {
134         if (size == 0) {
135             return null;
136         }
137 
138         return items[size - 1];
139     }
140 
141     public Object   last() {
142         if (size == 0) {
143             return null;
144         }
145 
146         return items[0];
147     }
148 
149     /**
150      * Returns <code>true</code> if the stack is empty.
151      */
152     public boolean isEmpty() {
153         return (size == 0);
154     }
155 
156     /**
157      * Returns the number of elements in the stack.
158      */
159     public int size() {
160         return size;
161     }
162 }
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