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package com.c2kernel.utils;
import java.lang.ref.Reference;
import java.util.AbstractMap;
import java.util.AbstractSet;
import java.util.Hashtable;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
/**************************************************************************
* TransientCache - Uses transient references to allow unused entries to be
* reaped by the java garbage collector.
*
* $Revision: 1.1 $
* $Date: 2004/04/20 09:37:02 $
*
* Copyright (C) 2003 CERN - European Organization for Nuclear Research
* All rights reserved.
**************************************************************************/
public abstract class TransientCache<K, V> extends AbstractMap<K, V> {
private Map<K, Reference<V>> map = new Hashtable<K, Reference<V>>();
@Override
public synchronized Set<Entry<K, V>> entrySet() {
Map<K, V> newMap = new Hashtable<K,V>();
Iterator<Entry<K, Reference<V>>> iter = map.entrySet().iterator();
while (iter.hasNext()) {
Entry<K, Reference<V>> me = iter.next();
Reference<V> ref = me.getValue();
V o = ref.get();
if (o == null) {
// Delete cleared reference
iter.remove();
} else {
// Copy out interior object
newMap.put(me.getKey(), o);
}
}
// Return set of interior objects
return newMap.entrySet();
}
@Override
public synchronized V put(K key, V value) {
Reference<V> ref = makeReference(value);
ref = map.put(key, ref);
if (ref != null)
return (ref.get());
return null;
}
public abstract Reference<V> makeReference(Object value);
@Override
public V remove(Object key) {
Iterator<Entry<K, Reference<V>>> i = map.entrySet().iterator();
Entry<K, Reference<V>> correctEntry = null;
if (key == null) {
while (correctEntry == null && i.hasNext()) {
Entry<K, Reference<V>> e = i.next();
if (e.getKey() == null)
correctEntry = e;
}
} else {
while (correctEntry == null && i.hasNext()) {
Entry<K, Reference<V>> e = i.next();
if (key.equals(e.getKey()))
correctEntry = e;
}
}
V oldValue = null;
if (correctEntry != null) {
Reference<V> correctReference = correctEntry.getValue();
oldValue = correctReference.get();
i.remove();
}
return oldValue;
}
/**
*
*/
@Override
public void clear() {
map.entrySet().clear();
}
private transient Set<K> keySet = null;
@Override
public Set<K> keySet() {
if (keySet == null) {
keySet = new AbstractSet<K>() {
@Override
public Iterator<K> iterator() {
return new Iterator<K>() {
private Iterator<Entry<K, Reference<V>>> i = map.entrySet().iterator();
@Override
public boolean hasNext() {
return i.hasNext();
}
@Override
public K next() {
return i.next().getKey();
}
@Override
public void remove() {
i.remove();
}
};
}
@Override
public int size() {
return TransientCache.this.size();
}
@Override
public boolean contains(Object k) {
return TransientCache.this.containsKey(k);
}
};
}
return keySet;
}
}
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