Mega Code Archive
Soft HashMap
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/*
* 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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