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


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 is the base class for all cache implementations provided in the
64  * org.apache.oro.util package. To derive a subclass from GenericCache
65  * only the ... methods
66  * need be overridden.
67  * Although 4 subclasses of GenericCache are provided with this
68  * package, users may not derive subclasses from this class.
69  * Rather, users should create their own implmentations of the
70  * {@link Cache} interface.
71
72  @author <a HREF="dfs@savarese.org">Daniel F. Savarese</a>
73  @version $Id: GenericCache.java,v 1.1.1.1 2000/07/23 23:08:54 jon Exp $
74
75  * @see Cache
76  * @see CacheLRU
77  * @see CacheFIFO
78  * @see CacheFIFO2
79  * @see CacheRandom
80  */
81 public abstract class GenericCache implements Cache, java.io.Serializable JavaDoc {
82   /**
83    * The default capacity to be used by the GenericCache subclasses
84    * provided with this package. Its value is 20.
85    */
86   public static final int DEFAULT_CAPACITY = 20;
87
88   int _numEntries;
89   GenericCacheEntry[] _cache;
90   Hashtable _table;
91
92   /**
93    * The primary constructor for GenericCache. It has default
94    * access so it will only be used within the package. It initializes
95    * _table to a Hashtable of capacity equal to the capacity argument,
96    * _cache to an array of size equal to the capacity argument, and
97    * _numEntries to 0.
98    * <p>
99    * @param capacity The maximum capacity of the cache.
100    */
101   GenericCache(int capacity) {
102     _numEntries = 0;
103     _table = new Hashtable(capacity);
104     _cache = new GenericCacheEntry[capacity];
105
106     while(--capacity >= 0)
107       _cache[capacity] = new GenericCacheEntry(capacity);
108   }
109
110   public abstract void addElement(Object JavaDoc key, Object JavaDoc value);
111
112   public synchronized Object JavaDoc getElement(Object JavaDoc key) {
113     Object JavaDoc obj;
114
115     obj = _table.get(key);
116
117     if(obj != null)
118       return ((GenericCacheEntry)obj)._value;
119
120     return null;
121   }
122
123   public final Enumeration keys() { return _table.keys(); }
124
125   /**
126    * Returns the number of elements in the cache, not to be confused with
127    * the {@link #capacity()} which returns the number
128    * of elements that can be held in the cache at one time.
129    * <p>
130    * @return The current size of the cache (i.e., the number of elements
131    * currently cached).
132    */
133   public final int size() { return _numEntries; }
134
135   /**
136    * Returns the maximum number of elements that can be cached at one time.
137    * <p>
138    * @return The maximum number of elements that can be cached at one time.
139    */
140   public final int capacity() { return _cache.length; }
141
142   public final boolean isFull() { return (_numEntries >= _cache.length); }
143 }
144
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