001/*
002 *                    BioJava development code
003 *
004 * This code may be freely distributed and modified under the
005 * terms of the GNU Lesser General Public Licence.  This should
006 * be distributed with the code.  If you do not have a copy,
007 * see:
008 *
009 *      http://www.gnu.org/copyleft/lesser.html
010 *
011 * Copyright for this code is held jointly by the individual
012 * authors.  These should be listed in @author doc comments.
013 *
014 * For more information on the BioJava project and its aims,
015 * or to join the biojava-l mailing list, visit the home page
016 * at:
017 *
018 *      http://www.biojava.org/
019 *
020 */
021
022package org.biojava.utils.cache;
023
024import java.lang.ref.Reference;
025import java.lang.ref.SoftReference;
026
027/**
028 * Cache which is cleared according to memory pressure.  This
029 * is simply a wrapper around java.lang.ref.SoftReference, and
030 * the performance will depend on the behaviour of SoftReference
031 * on your platform.
032 *
033 * @author Thomas Down
034 * @since 1.1
035 */
036
037public class SoftReferenceCache implements Cache {
038    public CacheReference makeReference(Object o) {
039            return new ReferenceReference(new SoftReference(o));
040    }
041
042    private static class ReferenceReference implements CacheReference {
043      private Reference ref;
044      
045      ReferenceReference(Reference r) {
046        ref = r;
047      }
048      
049      public Object get() {
050        if (ref != null)
051          return ref.get();
052        return null;
053      }
054      
055      public void clear() {
056        ref = null;
057      }
058    }
059}