001: /*
002: * $Id: CacheFIFO.java,v 1.7 2003/11/07 20:16:25 dfs Exp $
003: *
004: * ====================================================================
005: * The Apache Software License, Version 1.1
006: *
007: * Copyright (c) 2000 The Apache Software Foundation. All rights
008: * reserved.
009: *
010: * Redistribution and use in source and binary forms, with or without
011: * modification, are permitted provided that the following conditions
012: * are met:
013: *
014: * 1. Redistributions of source code must retain the above copyright
015: * notice, this list of conditions and the following disclaimer.
016: *
017: * 2. Redistributions in binary form must reproduce the above copyright
018: * notice, this list of conditions and the following disclaimer in
019: * the documentation and/or other materials provided with the
020: * distribution.
021: *
022: * 3. The end-user documentation included with the redistribution,
023: * if any, must include the following acknowledgment:
024: * "This product includes software developed by the
025: * Apache Software Foundation (http://www.apache.org/)."
026: * Alternately, this acknowledgment may appear in the software itself,
027: * if and wherever such third-party acknowledgments normally appear.
028: *
029: * 4. The names "Apache" and "Apache Software Foundation", "Jakarta-Oro"
030: * must not be used to endorse or promote products derived from this
031: * software without prior written permission. For written
032: * permission, please contact apache@apache.org.
033: *
034: * 5. Products derived from this software may not be called "Apache"
035: * or "Jakarta-Oro", nor may "Apache" or "Jakarta-Oro" appear in their
036: * name, without prior written permission of the Apache Software Foundation.
037: *
038: * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
039: * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
040: * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
041: * DISCLAIMED. IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
042: * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
043: * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
044: * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
045: * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
046: * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
047: * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
048: * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
049: * SUCH DAMAGE.
050: * ====================================================================
051: *
052: * This software consists of voluntary contributions made by many
053: * individuals on behalf of the Apache Software Foundation. For more
054: * information on the Apache Software Foundation, please see
055: * <http://www.apache.org/>.
056: */
057:
058: package org.apache.oro.util;
059:
060: import java.util.*;
061:
062: /**
063: * This class is a GenericCache subclass implementing a FIFO (First
064: * In First Out) cache replacement policy. In other words, values are
065: * added to the cache until the cache becomes full. Once the cache is full,
066: * if a new pattern is added to the cache, it replaces the first of
067: * the current patterns in the cache to have been added.
068: *
069: * @version @version@
070: * @since 1.0
071: * @see GenericCache
072: */
073:
074: public final class CacheFIFO extends GenericCache {
075: private int __curent = 0;
076:
077: /**
078: * Creates a CacheFIFO instance with a given cache capacity.
079: * <p>
080: * @param capacity The capacity of the cache.
081: */
082: public CacheFIFO(int capacity) {
083: super (capacity);
084: }
085:
086: /**
087: * Same as:
088: * <blockquote><pre>
089: * CacheFIFO(GenericCache.DEFAULT_CAPACITY);
090: * </pre></blockquote>
091: */
092: public CacheFIFO() {
093: this (GenericCache.DEFAULT_CAPACITY);
094: }
095:
096: /**
097: * Adds a value to the cache. If the cache is full, when a new value
098: * is added to the cache, it replaces the first of the current values
099: * in the cache to have been added (i.e., FIFO).
100: * <p>
101: * @param key The key referencing the value added to the cache.
102: * @param value The value to add to the cache.
103: */
104: public final synchronized void addElement(Object key, Object value) {
105: int index;
106: Object obj;
107:
108: obj = _table.get(key);
109:
110: if (obj != null) {
111: GenericCacheEntry entry;
112:
113: // Just replace the value. Technically this upsets the FIFO ordering,
114: // but it's expedient.
115: entry = (GenericCacheEntry) obj;
116: entry._value = value;
117: entry._key = key;
118:
119: return;
120: }
121:
122: // If we haven't filled the cache yet, put it at the end.
123: if (!isFull()) {
124: index = _numEntries;
125: ++_numEntries;
126: } else {
127: // Otherwise, replace the current pointer, which takes care of
128: // FIFO in a circular fashion.
129: index = __curent;
130:
131: if (++__curent >= _cache.length)
132: __curent = 0;
133:
134: _table.remove(_cache[index]._key);
135: }
136:
137: _cache[index]._value = value;
138: _cache[index]._key = key;
139: _table.put(key, _cache[index]);
140: }
141:
142: }
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