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Java > Open Source Codes > org > apache > oro > util > CacheRandom


1 package org.apache.oro.util;
2
3 /* ====================================================================
4  * The Apache Software License, Version 1.1
5  *
6  * Copyright (c) 2000 The Apache Software Foundation. All rights
7  * reserved.
8  *
9  * Redistribution and use in source and binary forms, with or without
10  * modification, are permitted provided that the following conditions
11  * are met:
12  *
13  * 1. Redistributions of source code must retain the above copyright
14  * notice, this list of conditions and the following disclaimer.
15  *
16  * 2. Redistributions in binary form must reproduce the above copyright
17  * notice, this list of conditions and the following disclaimer in
18  * the documentation and/or other materials provided with the
19  * distribution.
20  *
21  * 3. The end-user documentation included with the redistribution,
22  * if any, must include the following acknowledgment:
23  * "This product includes software developed by the
24  * Apache Software Foundation (http://www.apache.org/)."
25  * Alternately, this acknowledgment may appear in the software itself,
26  * if and wherever such third-party acknowledgments normally appear.
27  *
28  * 4. The names "Apache" and "Apache Software Foundation", "Jakarta-Oro"
29  * must not be used to endorse or promote products derived from this
30  * software without prior written permission. For written
31  * permission, please contact apache@apache.org.
32  *
33  * 5. Products derived from this software may not be called "Apache"
34  * or "Jakarta-Oro", nor may "Apache" or "Jakarta-Oro" appear in their
35  * name, without prior written permission of the Apache Software Foundation.
36  *
37  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
38  * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
39  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
40  * DISCLAIMED. IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
41  * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
42  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
43  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
44  * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
45  * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
46  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
47  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
48  * SUCH DAMAGE.
49  * ====================================================================
50  *
51  * This software consists of voluntary contributions made by many
52  * individuals on behalf of the Apache Software Foundation. For more
53  * information on the Apache Software Foundation, please see
54  * <http://www.apache.org/>.
55  *
56  * Portions of this software are based upon software originally written
57  * by Daniel F. Savarese. We appreciate his contributions.
58  */
59
60 import java.util.*;
61
62 /**
63  * This class is a GenericCache subclass implementing a random
64  * cache replacement policy. In other words,
65  * values are added to the cache until it becomes full. Once the
66  * cache is full, when a new value is added to the cache, it replaces
67  * a randomly selected value in the cache.
68
69  @author <a HREF="dfs@savarese.org">Daniel F. Savarese</a>
70  @version $Id: CacheRandom.java,v 1.1.1.1 2000/07/23 23:08:54 jon Exp $
71
72  * @see GenericCache
73  */
74 public final class CacheRandom extends GenericCache {
75   private Random __random;
76
77   /**
78    * Creates a CacheRandom instance with a given cache capacity.
79    * <p>
80    * @param capacity The capacity of the cache.
81    */
82   public CacheRandom(int capacity) {
83     super(capacity);
84     __random = new Random(System.currentTimeMillis());
85   }
86
87   /**
88    * Same as:
89    * <blockquote><pre>
90    * CacheRandom(GenericCache.DEFAULT_CAPACITY);
91    * </pre></blockquote>
92    */
93   public CacheRandom(){
94     this(GenericCache.DEFAULT_CAPACITY);
95   }
96
97   /**
98    * Adds a value to the cache. If the cache is full, when a new value
99    * is added to the cache, it replaces the first of the current values
100    * in the cache to have been added (i.e., Random).
101    * <p>
102    * @param key The key referencing the value added to the cache.
103    * @param value The value to add to the cache.
104    */
105   public final synchronized void addElement(Object JavaDoc key, Object JavaDoc value) {
106
107     int index;
108     Object JavaDoc obj;
109
110     obj = _table.get(key);
111
112     if(obj != null) {
113       GenericCacheEntry entry;
114
115       // Just replace the value.
116 entry = (GenericCacheEntry)obj;
117       entry._value = value;
118       entry._key = key;
119
120       return;
121     }
122
123     // Expression is not in cache.
124
125     // If we haven't filled the cache yet, put it at the end.
126 if(!isFull()) {
127       index = _numEntries;
128       ++_numEntries;
129     } else {
130       // Otherwise, replace a random entry.
131 index = (int)(_cache.length*__random.nextFloat());
132       _table.remove(_cache[index]._key);
133     }
134
135     _cache[index]._value = value;
136     _cache[index]._key = key;
137     _table.put(key, _cache[index]);
138   }
139 }
140
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