Soft HashMap : Soft Map « Collections Data Structure « Java

1. Java
2. Collections Data Structure
3. Soft Map

Soft HashMap

 


/*
 * dbXML - Native XML Database
 * Copyright (C) 1999-2004  The dbXML Group, L.L.C.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
 *
 * $Id: SoftHashMap.java,v 1.2 2004/02/12 00:17:58 bradford Exp $
 */

import java.lang.ref.ReferenceQueue;
import java.lang.ref.SoftReference;
import java.util.AbstractMap;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;

/**
 * SoftHashMap
 */

public final class SoftHashMap extends AbstractMap {
   private Map hash = new HashMap();
   private final ReferenceQueue queue = new ReferenceQueue();

   public SoftHashMap() {
   }

   public Object get(Object key) {
      Object res = null;
      SoftReference sr = (SoftReference)hash.get(key);
      if ( sr != null ) {
         res = sr.get();
         if ( res == null )
            hash.remove(key);
      }
      return res;
   }

   private void processQueue() {
      for ( ;; ) {
         SoftValue sv = (SoftValue)queue.poll();
         if ( sv != null )
            hash.remove(sv.key);
         else
            return;
      }
   }

   public Object put(Object key, Object value) {
      processQueue();
      return hash.put(key, new SoftValue(value, key, queue));
   }

   public Object remove(Object key) {
      processQueue();
      return hash.remove(key);
   }

   public void clear() {
      processQueue();
      hash.clear();
   }

   public int size() {
      processQueue();
      return hash.size();
   }

   public Set entrySet() {
      /** @todo Figure this out */
      throw new UnsupportedOperationException();
   }


   /**
    * SoftValue
    */

   private static class SoftValue extends SoftReference {
      private final Object key;

      private SoftValue(Object k, Object key, ReferenceQueue q) {
         super(k, q);
         this.key = key;
      }
   }
}

   
  

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