cacherandom.java

jakarta-oro-2.0.8 正则表达式 引擎 源代码

/*
 * $Id: CacheRandom.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 [e-mail].
 *
 * 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
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 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
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 * 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/>.
 */


package org.apache.oro.util;

import java.util.*;

/**
 * This class is a GenericCache subclass implementing a random
 * cache replacement policy.  In other words,
 * values are added to the cache until it becomes full.  Once the
 * cache is full, when a new value is added to the cache, it replaces
 * a randomly selected value in the cache.
 *
 * @version @version@
 * @since 1.0
 * @see GenericCache
 */
public final class CacheRandom extends GenericCache {
  private Random __random;

  /**
   * Creates a CacheRandom instance with a given cache capacity.
   * <p>
   * @param capacity  The capacity of the cache.
   */
  public CacheRandom(int capacity) { 
    super(capacity);
    __random = new Random(System.currentTimeMillis());
  }

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

  /**
   * 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., Random).
   * <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.
      entry = (GenericCacheEntry)obj;
      entry._value = value;
      entry._key   = key;

      return;
    }

    // Expression is not in cache.

    // If we haven't filled the cache yet, put it at the end.
    if(!isFull()) {
      index = _numEntries;
      ++_numEntries;
    } else {
      // Otherwise, replace a random entry.
      index = (int)(_cache.length*__random.nextFloat());
      _table.remove(_cache[index]._key);
    }

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