FIFO First In First Out cache replacement policy

    



import java.util.*;

/**
 * This class is a GenericCache subclass implementing a second
 * chance FIFO (First In First Out) cache replacement policy.  In other
 * words, values are added to the cache until the cache becomes full.
 * Once the cache is full, when a new value is added to the cache, it 
 * replaces the first of the current values in the cache to have been
 * added, unless that value has been used recently (generally
 * between the last cache replacement and now).
 * If the value to be replaced has been used, it is given
 * a second chance, and the next value in the cache is tested for
 * replacement in the same manner.  If all the values are given a
 * second chance, then the original pattern selected for replacement is
 * replaced.
 *
 * @version @version@
 * @since 1.0
 * @see GenericCache
 */
public final class CacheFIFO2 extends GenericCache {
  private int __current = 0;
  private boolean[] __tryAgain;

  /**
   * Creates a CacheFIFO2 instance with a given cache capacity.
   * <p>
   * @param capacity  The capacity of the cache.
   */
  public CacheFIFO2(int capacity) { 
    super(capacity);

    __tryAgain = new boolean[_cache.length];
  }


  /**
   * Same as:
   * <blockquote><pre>
   * CacheFIFO2(GenericCache.DEFAULT_CAPACITY);
   * </pre></blockquote>
   */
  public CacheFIFO2(){
    this(GenericCache.DEFAULT_CAPACITY);
  }


  public synchronized Object getElement(Object key) { 
    Object obj;

    obj = _table.get(key);

    if(obj != null) {
      GenericCacheEntry entry;

      entry = (GenericCacheEntry)obj;

      __tryAgain[entry._index] = true;
      return entry._value;
    }

    return null;
  }


  /**
   * Adds a value to the cache.  If the cache is full, when a new value
   * is added to the cache, it replaces the first of the current values
   * in the cache to have been added (i.e., FIFO2).
   * <p>
   * @param key   The key referencing the value added to the cache.
   * @param value The value to add to the cache.
   */
  public final synchronized void addElement(Object key, Object value) {
    int index;
    Object obj;

    obj = _table.get(key);

    if(obj != null) {
      GenericCacheEntry entry;

      // Just replace the value.  Technically this upsets the FIFO2 ordering,
      // but it's expedient.
      entry = (GenericCacheEntry)obj;
      entry._value = value;
      entry._key   = key;

      // Set the try again value to compensate.
      __tryAgain[entry._index] = true;

      return;
    }

    // If we haven't filled the cache yet, put it at the end.
    if(!isFull()) {
      index = _numEntries;
      ++_numEntries;
    } else {
      // Otherwise, find the next slot that doesn't have a second chance.
      index = __current;
      
      while(__tryAgain[index]) {
  __tryAgain[index] = false;
  if(++index >= __tryAgain.length)
    index = 0;
      }

      __current = index + 1;
      if(__current >= _cache.length)
  __current = 0;

      _table.remove(_cache[index]._key);
    }

    _cache[index]._value = value;
    _cache[index]._key   = key;
    _table.put(key, _cache[index]);
  }

}

/*
 * $Id: GenericCache.java,v 1.8 2003/11/07 20:16:25 dfs Exp $
 *
 * 
 * The Apache Software License, Version 1.1
 *
 * Copyright (c) 2000 The Apache Software Foundation.  All rights
 * reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. The end-user documentation included with the redistribution,
 *    if any, must include the following acknowledgment:
 *       "This product includes software developed by the
 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowledgment may appear in the software itself,
 *    if and wherever such third-party acknowledgments normally appear.
 *
 * 4. The names "Apache" and "Apache Software Foundation", "Jakarta-Oro" 
 *    must not be used to endorse or promote products derived from this
 *    software without prior written permission. For written
 *    permission, please contact apache@apache.org.
 *
 * 5. Products derived from this software may not be called "Apache" 
 *    or "Jakarta-Oro", nor may "Apache" or "Jakarta-Oro" appear in their 
 *    name, without prior written permission of the Apache Software Foundation.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED.  IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * 
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 */


/**
 * This is the base class for all cache implementations provided in the
 * org.apache.oro.util package.  To derive a subclass from GenericCache
 * only the ... methods
 * need be overridden.
 * Although 4 subclasses of GenericCache are provided with this
 * package, users may not derive subclasses from this class.
 * Rather, users should create their own implmentations of the
 * {@link Cache} interface.
 *
 * @version @version@
 * @since 1.0
 * @see Cache
 * @see CacheLRU
 * @see CacheFIFO
 * @see CacheFIFO2
 * @see CacheRandom
 */
 abstract class GenericCache implements Cache, java.io.Serializable {
  /**
   * The default capacity to be used by the GenericCache subclasses
   * provided with this package.  Its value is 20.
   */
  public static final int DEFAULT_CAPACITY = 20;

  int _numEntries;
  GenericCacheEntry[] _cache;
  HashMap _table;

  /**
   * The primary constructor for GenericCache.  It has default
   * access so it will only be used within the package.  It initializes
   * _table to a Hashtable of capacity equal to the capacity argument,
   * _cache to an array of size equal to the capacity argument, and
   * _numEntries to 0.
   * <p>
   * @param capacity The maximum capacity of the cache.
   */
  GenericCache(int capacity) {
    _numEntries = 0;
    _table    = new HashMap(capacity);
    _cache    = new GenericCacheEntry[capacity];

    while(--capacity >= 0)
      _cache[capacity] = new GenericCacheEntry(capacity);
  }

  public abstract void addElement(Object key, Object value);

  public synchronized Object getElement(Object key) { 
    Object obj;

    obj = _table.get(key);

    if(obj != null)
      return ((GenericCacheEntry)obj)._value;

    return null;
  }

  public final Iterator keys() {
    return _table.keySet().iterator();
  }

  /**
   * Returns the number of elements in the cache, not to be confused with
   * the {@link #capacity()} which returns the number
   * of elements that can be held in the cache at one time.
   * <p>
   * @return  The current size of the cache (i.e., the number of elements
   *          currently cached).
   */
  public final int size() { return _numEntries; }

  /**
   * Returns the maximum number of elements that can be cached at one time.
   * <p>
   * @return The maximum number of elements that can be cached at one time.
   */
  public final int capacity() { return _cache.length; }

  public final boolean isFull() { return (_numEntries >= _cache.length); }
}


/*
 * $Id: Cache.java,v 1.7 2003/11/07 20:16:25 dfs Exp $
 *
 * 
 * The Apache Software License, Version 1.1
 *
 * Copyright (c) 2000 The Apache Software Foundation.  All rights
 * reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. The end-user documentation included with the redistribution,
 *    if any, must include the following acknowledgment:
 *       "This product includes software developed by the
 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowledgment may appear in the software itself,
 *    if and wherever such third-party acknowledgments normally appear.
 *
 * 4. The names "Apache" and "Apache Software Foundation", "Jakarta-Oro" 
 *    must not be used to endorse or promote products derived from this
 *    software without prior written permission. For written
 *    permission, please contact apache@apache.org.
 *
 * 5. Products derived from this software may not be called "Apache" 
 *    or "Jakarta-Oro", nor may "Apache" or "Jakarta-Oro" appear in their 
 *    name, without prior written permission of the Apache Software Foundation.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED.  IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * 
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 */



/**
 * An interface defining the basic functions of a cache.
 *
 * @version @version@
 * @since 1.0
 */
 interface Cache {

  public void addElement(Object key, Object value);

  public Object getElement(Object key);

  /**
   * Returns the number of elements in the cache, not to be confused with
   * the {@link #capacity()} which returns the number
   * of elements that can be held in the cache at one time.
   * <p>
   * @return  The current size of the cache (i.e., the number of elements
   *          currently cached).
   */
  public int size();


  /**
   * Returns the maximum number of elements that can be cached at one time.
   * <p>
   * @return The maximum number of elements that can be cached at one time.
   */
  public int capacity();

}

 /*
  * $Id: GenericCacheEntry.java,v 1.7 2003/11/07 20:16:25 dfs Exp $
  *
  * 
  * The Apache Software License, Version 1.1
  *
  * Copyright (c) 2000 The Apache Software Foundation.  All rights
  * reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  *
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in
  *    the documentation and/or other materials provided with the
  *    distribution.
  *
  * 3. The end-user documentation included with the redistribution,
  *    if any, must include the following acknowledgment:
  *       "This product includes software developed by the
  *        Apache Software Foundation (http://www.apache.org/)."
  *    Alternately, this acknowledgment may appear in the software itself,
  *    if and wherever such third-party acknowledgments normally appear.
  *
  * 4. The names "Apache" and "Apache Software Foundation", "Jakarta-Oro" 
  *    must not be used to endorse or promote products derived from this
  *    software without prior written permission. For written
  *    permission, please contact apache@apache.org.
  *
  * 5. Products derived from this software may not be called "Apache" 
  *    or "Jakarta-Oro", nor may "Apache" or "Jakarta-Oro" appear in their 
  *    name, without prior written permission of the Apache Software Foundation.
  *
  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
  * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
  * DISCLAIMED.  IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
  * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
  * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
  * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  * 
  *
  * This software consists of voluntary contributions made by many
  * individuals on behalf of the Apache Software Foundation.  For more
  * information on the Apache Software Foundation, please see
  * <http://www.apache.org/>.
  */




 /**
  * A structure used to store values in a GenericCache.  It
  * is declared with default access to limit it to use only within the
  * package.
  *
  * @version @version@
  * @since 1.0
  */
 final class GenericCacheEntry implements java.io.Serializable {
   /** The cache array index of the entry. */
   int _index;
   /** The value stored at this entry. */
   Object _value;
   /** The key used to store the value. */
   Object _key;

   GenericCacheEntry(int index) {
     _index = index;
     _value = null;
     _key   = null;
   }
 }
Related examples in the same category

1.	A LRU (Least Recently Used) cache replacement policy
2.	A Map that is size-limited using an LRU algorithm
3.	A random cache replacement policy
4.	A second chance FIFO (First In First Out) cache replacement policy
5.	An LRU (Least Recently Used) cache replacement policy
6.	Async LRU List
7.	Implementation of a Least Recently Used cache policy
8.	Generic LRU Cache
9.	LRU Cache
10.	A Least Recently Used Cache
11.	The class that implements a simple LRU cache
12.	Map implementation for cache usage
13.	Weak Cache Map
14.	Provider for the application cache directories.
15.	Fixed length cache with a LRU replacement policy.
16.	A small LRU object cache.
17.	A least recently used (LRU) cache.
18.	LRU Cache 2
19.	A cache that purges values according to their frequency and recency of use and other qualitative values.
20.	A thread-safe cache that keeps its values as java.lang.ref.SoftReference so that the cache is, in effect, managed by the JVM and kept as small as is required
21.	Cache LRU
22.	A FastCache is a map implemented with soft references, optimistic copy-on-write updates, and approximate count-based pruning.
23.	A HardFastCache is a map implemented with hard references, optimistic copy-on-write updates, and approximate count-based pruning.
FIFO First In First Out cache replacement policy : Cache « Development Class « Java

Related examples in the same category
